CONTENTS

The 80th Anniversary of the E.O. Paton Electric Welding

Institute of the NAS of Ukraine ................................................ 2

SCIENTIFIC AND TECHNICALPaton B.E., Lobanov L.M., Lysak V.L., Knysh V.V.,Pavlovsky V.I., Prilutsky V.P., Timoshenko A.N.,Goncharov P.V. and Guan Qiao. Deformation-free

welding of stringer panels of titanium alloy VT20 ...................... 6

Krikent I.V., Krivtsun I.V. and Demchenko V.F.

Simulation of electric arc with refractory cathode and

evaporating anode .................................................................. 17

Lankin Yu.N., Ryabtsev I.A., Soloviov V.G., ChernyakYa.P. and Zhdanov V.A. Effect of electric parameters of

arc surfacing using flux-cored wire on process stability

and base metal penetration ..................................................... 25

INDUSTRIALYushchenko K.A., Kozulin S.M., Lychko I.I. and KozulinM.G. Joining of thick metal by multipass electroslag

welding .................................................................................. 30

Korotynsky A.E., Drachenko N.P. and Shapka V.A.

Peculiarities of application of supercapacitors in

devices for pulse welding technologies .................................... 34

Lebedev V.A., Maksimov S.Yu., Pichak V.G. and

Zajnulin D.I. Automatic machine for wet underwater

welding in confined spaces ..................................................... 39

Levchenko O.G., Kuleshov V.A. and Arlamov A.Yu.

Sanitary-hygienic evaluation of noise in manual arc

welding with covered electrodes .............................................. 45

INFORMATIONThe 55th Anniversary of the Experimental Design

Technological Bureau of the E.O. Paton Electric

Welding Institute ..................................................................... 49

Paton Turbine Technologies – new name of a

well-known company .............................................................. 51

English translation of the monthly «Avtomaticheskaya Svarka» (Automatic Welding) journal published in Russian since 1948

Editor-in-Chief B.E.Paton

EDITORIAL BOARDYu.S. Borisov,

B.V. Khitrovskaya (exec. secretary),V.F. Khorunov, V.V. Knysh, I.V. Krivtsun,S.I. Kuchuk-Yatsenko (vice-chief editor),

Yu.N. Lankin, V.N. Lipodaev (vice-chief editor),L.M. Lobanov, A.A. Mazur,

O.K. Nazarenko, I.K. Pokhodnya,V.D. Poznyakov, I.A. Ryabtsev,

K.A. Yushchenko,A.T. Zelnichenko (exec. director)

(Editorial Board Includes PWI Scientists)

INTERNATIONAL EDITORIALCOUNCIL

N.P. AlyoshinN.E. Bauman MSTU, Moscow, Russia

V.G. FartushnyWelding Society of Ukraine, Kiev, Ukraine

Guan QiaoBeijing Aeronautical Institute, China

V.I. LysakVolgograd State Technical University, Russia

B.E. PatonPWI, Kiev, Ukraine

Ya. PilarczykWeiding Institute, Gliwice, Poland

U. ReisgenWelding and Joining Institute, Aachen, Germany

O.I. SteklovWelding Society, Moscow, Russia

G.A. TurichinSt.-Petersburg State Polytechn. Univ., Russia

M. ZinigradCollege of Judea & Samaria, Ariel, Israel

A.S. ZubchenkoOKB «Gidropress», Podolsk, Russia

FoundersE.O. Paton Electric Welding Institute

of the NAS of Ukraine,International Association «Welding»

PublisherInternational Association «Welding»

TranslatorsA.A. Fomin, O.S. Kurochko,

I.N. KutianovaEditor

N.A. DmitrievaElectron galley

D.I. Sereda, T.Yu. Snegiryova

AddressE.O. Paton Electric Welding Institute,International Association «Welding»

11, Bozhenko Str., 03680, Kyiv, UkraineTel.: (38044) 200 60 16, 200 82 77Fax: (38044) 200 82 77, 200 81 45

E-mail: journal@paton.kiev.uawww.patonpublishinghouse.com

State Registration CertificateKV 4790 of 09.01.2001

ISSN 0957-798X

Subscriptions$348, 12 issues per year,

air postage and packaging included.Back issues available.

All rights reserved.This publication and each of the articles contained

herein are protected by copyright.Permission to reproduce material contained in this

journal must be obtained in writing from thePublisher.

September 2014No.9

Published since 2000

E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine

International Scientific-Technical and Production Journal

© PWI, International Association «Welding», 2014

THE 80th ANNIVERSARYOF THE E.O. PATON ELECTRIC WELDING INSTITUTE

OF THE NAS OF UKRAINE

The Institute of ElectricWelding was founded as amember of the All-Ukrain-ian Academy of Sciences byacademician Evgeny O. Pa-ton in 1934 on the facilityof electric welding labora-tory at the Chair of Engi-neering Constructions ofthe AUAS and ElectricWelding Committee. For-mation and all the furtheractivity of the ElectricWelding Institute are asso-ciated with the name of the

outstanding engineer and scientist. He definedthe main scientific trends of the Institute in thefield of welding technology and welded struc-tures, which are also urgent nowadays.

E.O. Paton could predict the great progressin the development of technology of electricwelding of metals. The convinced confirmationof this scientific prediction is the indisputablefact that welding today is the leading techno-logical process of permanent joining of metallicand non-metallic materials. This was due to thegreat contribution of the Institute staff during80 years of its activity.

At the first stage the specialists of the Instituteproved the feasibility of manufacture of weldedstructures, being not inferior to riveted ones as totheir strength and reliability and by some charac-teristics even significantly surpassing them. Thisserved a basis for the further mass application ofwelding. In the 1930s the conception of arc weldingas a metallurgical process was scientificallygrounded at the Institute and investigations for itsautomation were carried out under supervision ofE.O. Paton. By 1940 the development of high-ef-ficient process of submerged arc welding was fi-nalized and implementation at plants of the countrywas started. During the World War II the auto-matic submerged arc welding conquered the deci-sive importance. Directly in the tank plant shopsin the Urals the Institute specialists developed andimplemented the technology of automatic weldingof armored steel, which made it possible to createthe production line for manufacture of welded bod-ies of tanks T-34 and to mechanize the welding ofother military machinery.

Pre-war and war stagesin the Institute activitywere the period of estab-lishment of scientificschool, the convincedauthority of which was con-firmed by awarding the In-stitute with name ofEvgeny O. Paton in 1945.

The solution of mainproblem, i.e. improvementof efficiency and level ofmechanization of weldingjobs, required the continu-ous widening of research works at the Institutefor searching new methods and techniques ofmechanized welding, naturally, without mini-mizing of works on increasing the rational fieldsof application of submerged arc welding. Searchfor feasibility of submerged arc welding of weldslocated in various spatial positions was finalizedby the development under supervision of E.O.Paton of forced formation of weld to start themechanization of arc welding of welds in verticalplane.

On August 12, 1953 E.O. Paton, the man addeda vivid page to the history of national science andtechnology, died at the 84th year of his life. Since1953 until now academician Boris E. Paton, hisson, is the Director of the Institute.

One of the most significant achievements ofthe Institute at the beginning of the 1950s becamethe development of new technology of fusionmelting of thick metal, namely an electroslagwelding, which changed radically the technologyof manufacture of heavy frameworks, boilers, hy-draulic units and other unique rolled-welded andcast-welded structures. Its application allowedproducing the high-quality welded joints withinthe wide range of thicknesses.

Later, the CO2 welding method with thin wirewas developed, finding the wide spreading inindustry and providing the significant growth inlevel of mechanization of welding jobs. The fur-ther development of gas electric consumable elec-trode welding became the development of processand equipment for pulsed-arc welding, weldingin mixtures of active and inert gases.

AcademicianE.O. Paton

AcademicianB.E. Paton

2 9/2014

At the end of the 1950s the investigations inthe field of electron beam welding activelystarted at the Institute. The efforts of scientistswere directed to investigation of physical-metal-lurgical processes under the action of powerful(up to 100 kW) sharply-focused beam of elec-trons to thick-sheet (150—200 mm) structural ma-terials. The problem of a particular importanceand successfully solved by the Institute con-cerned the development of technology of closingthe circular welds to prevent the root defects inthe form of cavities, pores and discontinuities.Over the recent 10 years more than 60 sets ofdifferent types of equipment for EBW, includingthe installations with a volume of vacuum cham-bers of up to 100 m3, were put into industrialoperation.

The next stage in development of the beamtechnology was its application for welding andcutting by a laser. The systematic investigationsare carried out in the field of pulsed and continuouslaser welding. During recent years the specialistsof the Institute have developed the hybrid laser—arcand laser—plasma sources of heating.

Investigations were progressing on all themain trends of pressure welding, such as flash-butt welding and resistance welding, spot weld-ing, friction and diffusion welding.

Physical and technological peculiarities ofnew technological processes of flash-butt weldingwere studied, the systems of automatic controland diagnostics of quality of joints were devel-oped. On the basis of new technologies the manu-facture of several generations of specialized anduniversal machines for flash-butt welding of alarge assortment of parts of cross-section area ofup to 200,000 mm2 of low-alloy and high-strengthsteels, as well as of aluminium, titanium, chro-mium and copper alloys, was organized and mas-tered. Machines for welding of rails of variouscategories under field and stationary conditions,

serially manufactured at Kakhovka Plant of Elec-tric Welding Equipment, machines for weldingof pipes of diameter from 150 up to 1420 mm inconstruction of main pipelines, installations forwelding of elements of aerospace engineeringstructures found the widest spreading. Equip-ment for flash-butt welding of rails is exportedto many countries of the world.

Over many years the Institute carries out in-vestigations on space welding. In 1969, V. Kuba-sov, the pilot-cosmonaut, performed the first inthe world unique experiment on the board ofspaceship «Soyuz-6» for welding by electronbeam, plasma and consumable electrode in theunit «Vulkan», designed and manufactured atthe PWI. Thus, the beginning of the space tech-nology was started, having the great importancein the program of space exploration. In 1984 theextremely important experiment, prepared by thePWI, was carried out on the board of orbitalstation in open space. Cosmonauts S. Savitskayaand V. Dzhanibekov performed for the first timewelding, brazing, cutting and spraying in openspace by using the hand electron beam tool.

In parallel, such a complex problem wassolved at the Institute as mechanization of under-water arc welding, which acquired a great impor-tance in exploration of the World ocean shelf. Spe-cialists of the Institute designed the equipment formechanized arc welding and cutting by a specialflux-cored wire at depths of up to 200 m.

The intensive growth of the advanced engi-neering is accompanied by a continuous wideningof assortment of structural metals and alloys forwelded structures. During investigations forstudy of processes proceeding in the weld thenew welding consumables were developed: elec-trodes, metal and flux-cored wires, fluxes andgas mixtures.

Investigations and research works in the fieldof strength of welded joints and structures are

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the traditional directions in the Institute researcharea, started by E.O. Paton. Today, these inves-tigations are of an integrated nature, making itpossible to develop the new effective methods ofimprovement of reliability of critical engineeringstructures at static and cyclic loading. The prob-lem of manufacture of reliable welded structurescovers also the problems of selection of materials,rational design solutions, technologies of manu-facture and erection, reduction of metal inten-sity, which are solved successfully by the Insti-tute in collaboration with many industrial or-ganizations and enterprises. During recently, theintensive works are carried out for improvementof reliability, durability and service life of weldedstructures, as well as development of effectivemethods of their diagnostics.

At the present time the systems of continuousmonitoring, developed at the Institute, are suc-cessfully operated at a number of petrochemicalenterprises with use of Internet system of com-munication. This allows developing the monitor-ing and controlling systems, which give the op-portunity to observe the state of structure froma common specialized diagnostic center inde-pendently of its location site.

Since the 1950s by the initiative of academi-cian Boris E. Paton the searching investigationsand experimental developments were started forrevealing the feasibility of applying the weldingsources of heating for producing metals and alloysof ultra-high quality and reliability, on the basisof which one more basic scientific direction inthe Institute activity was formed – a specialelectrometallurgy. Efforts and successes of theInstitute team in this new field provided the no-ticeable progress in the development of the ad-vanced quality metallurgy.

The new electrometallurgical processes in-clude, first of all, the electroslag remelting ofconsumable electrode into a water-cooled mould.Fundamental studies of the electroslag process,its physical-chemical, metallurgical and electro-technical features provided the advanced posi-tions of the Institute in the development andapplication of electroslag technology, includingremelting, surfacing, casting, hot topping, etc.

During recent years, a complex of researchworks was carried out at the Institute, serving asa base for the development of new generation ofelectroslag technologies, based on producing ingotsand billets directly from molten metal without re-melting of consumable electrodes. These technolo-gies are patented in Ukraine and abroad and real-ized in industry. In particular, a unique complexfor production of bimetal mill rolls was manufac-

tured at Novo-Kramatorsk Machine-BuildingWorks on the basis of these technologies.

Two more electrometallurgical technologieswere developed at the Institute: plasma-arc andelectron beam. Development of technique andtechnology of these remelting processes was car-ried out in parallel with fundamental investiga-tions of physical-metallurgical peculiarities of re-fining in controllable atmosphere or vacuum andprocesses of crystallization of steels, complexly-alloyed alloys, non-ferrous and refractory metals.

Due to systematic investigations of high-tem-perature gas-metal systems the plasma-arc re-melting opened up the wide opportunities forproduction of the new class of structural mate-rials, namely the high-nitrogen steels. Design ofpowerful plasmatrons for metallurgy allowed theInstitute «to enter» the great metallurgy: newdesigns of units of ladle—furnace type of up to100 t capacity were developed. The quality ofmetal, produced in these units, is not inferior toelectroslag one.

Using the joint efforts of the Institute scien-tists, industry research institutes and manufac-turers the advanced electron beam equipment wasdesigned, and the technology of electron beamremelting in vacuum became indispensible proc-ess for producing the ultra-quality materials inmetallurgy and machine building. The works inthis direction are concentrated at the RE Center«Titan», established at the Institute.

Investigations of process of evaporation in vac-uum of metallic and non-metallic materials andtheir subsequent condensation as a basis for vapor-phase metallurgy opened up the feasibility of pro-ducing coatings of different materials, includingheat-resistant, refractory and composite ones withregulation of composition, structure and propertiesof deposited layers. Thickness of deposited layersis regulated, depending on purpose, from tens ofmicrometers up to several millimeters.

At the beginning of the 1980s the new scien-tific direction was formed at the Institute, deal-ing with the development of new processes andimprovement of existing processes of thermalspraying of protective and wear-resistant coat-ings. At present, the Institute is developing al-most all the advanced processes of spraying ofprotective and strengthening coatings. Technol-ogy and equipment have been developed forplasma-arc spraying of wear-resistant coatings,as well as installations for detonation spraying,which can operate with applying different work-ing gases (acetylene, propane, hydrogen).

Result of investigations and developments inthe field of building welded structures, made by

4 9/2014

the PWI scientists, became the building of fa-mous constructions, among them, first of all, theunique all-welded bridge, named after E.O. Pa-ton, across the Dnieper river. Principles, ap-proaches and design-technological solutions,used in its designing and construction, gave theway to a wide application of welding in bridgeconstruction. This bridge was recognized by theAmerican Welding Society as the outstandingwelded structure of the XX century. The expe-rience in construction of E.O. Paton bridge wasused in construction of bridges across the Dnieperriver in Kiev (Yuzhny, Moskovsky, Gavansky,Podolsko-Voskresensky, road and railwaybridges) and bridges in Dnepropetrovsk andZaporozhie, as well as bridge across the Smotrichriver in Kamenetsk-Podolsk. In collaborationwith Research Institute «Ukrproektstalkon-struktsiya» the projects and technologies of con-struction have been worked out, which were re-alized successfully in construction of unique TVtowers in Kiev, St.-Petersburg, Erevan, Tbilisi,Vitebsk, Kharkov. Technologies of welding, de-veloped at the PWI, were applied successfullyin construction of huge monument «Mother-land», as well as in construction of objects ofEuro-2012 in Kiev.

Over the recent years the great attention ispaid to the realization of achievements of ad-vanced science and technology in practical medi-cine. In the 1990s B.E. Paton gave an idea toapply welding for joining of live tissues and or-ganized a creative team of scientists of the PWI,A.A. Shalimov Institute of Surgery and Trans-plantation, Central Hospital of Security Servicesof Ukraine and other medical institutions. Thiscooperation allowed developing the new methodof joining (welding) of soft live tissues. At thePWI the advanced equipment of several genera-tions for welding of live tissues has been designedand manufactured already in industry. Method ofelectric welding of live tissues is applied in morethan 50 clinics of Ukraine. Since 2001 more than100,000 surgical operations of different profileswere made and more than 130 new surgical proce-dures have been developed and used in practice.

Owing to the combination of purposeful fun-damental theoretical investigations with engi-neering-applied developments, close creative re-lations with industrial enterprises in realizationof technological innovations the Institute trans-formed for the past 80 years of its activity intothe largest center in the field welding and relatedtechnologies in the country and world.

Today, the PWI staff is 1560 persons. Thescientific potential of the Institute is 440 scien-tists, among which 8 academicians and 4 corre-sponding members of the NAS of Ukraine, 72Dr. of Techn, Sci. and more than 200 Candidatesof Techn. Sci.

Results of works of the Institute are confirmedby licensees and received patents, more than 150licensees have been sold to the USA, Germany,Japan, Russia, Sweden, France, China, etc.About 2600 patents of Ukraine and near and farforeign countries, as well as more than 6500Author’s Certificates were received.

For the years of the PWI activity more than60 most outstanding developments, fulfilled andimplemented in national economy by the Insti-tute specialists in collaboration with industrialteams, were awarded by the Lenin and StatePrizes, and also by various Prizes of Ukraine.

The Institute supports international relationswith leading welding centers in Europe, USA,Asia and is the member of the International In-stitute of Welding and European Federation ofWelding.

Results of investigations of scientists of theInstitute are published in journals «Avto-maticheskaya Svarka», «Tekhnicheskaya Diag-nostika i Nerazrushayushchy Kontrol», «Sovre-mennaya Elektrometallurgiya», «The PatonWelding Journal», which have a wide readingaudience. Monographs, subject collections, pro-ceedings of the conferences, handbooks and otherbook products are also published at the Institute.Specialized councils are working at the PWI fordefending the theses for degrees of Dr. or Can-didate of Techn. Sci. The associates of the Insti-tute defended more than 139 theses for Dr. ofTechn. Sci. and about 720 theses for Candidateof Techn. Sci. The Institute organizes differentconferences, seminars, exhibitions and takes partin the national and international exhibitions.

Due to implementation of the PWI develop-ments in industry, the production of welding con-sumables and equipment has been created inUkraine, that allows recognizing the welding asone of the few branches of economy having astable positive foreign trade balance.

Over 80 years the Institute team has passed aglorious path. Today, this is a team of confederates,increasing the achievements of the Paton scientificschool, which has the world recognition. All theactivity is directed for the further progress of weld-ing and related processes, as well for the solutionof basic problems of industrial production.

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DEFORMATION-FREE WELDING OF STRINGER PANELSOF TITANIUM ALLOY VT20

B.E. PATON1, L.M. LOBANOV1, V.L. LYSAK1, V.V. KNYSH1, V.I. PAVLOVSKY1,V.P. PRILUTSKY1, A.N. TIMOSHENKO1, P.V. GONCHAROV1 and GUAN QIAO2

1E.O. Paton Electric Welding Institute, NASU11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

2BAMTRI. Beijing, China. E-mail: guang@cae.cn

Presented are the results of complex of carried out investigations on development of technology for weldingby penetration welds of stringer panels of titanium alloy VT20 providing minimum residual stresses anddeformations and also high values of their life at cyclic loads. On the full-scale specimens, simulatingstringer panels, the penetration welds of T-joints were produced using three methods: electron beam,automatic argon-arc nonconsumable-electrode welding over the layer of activating flux, and automaticargon-arc nonconsumable-electrode welding with immersed arc. To prevent the residual welding stressesand deformations, preliminary elastic deformation of elements being welded was applied. The fatigue testsof all the types of specimens at longitudinal cyclic tension were carried out. The effect of heat treatment,impact mechanical treatment and repair-welding technologies on their fatigue life was also determined.Basing on the results of investigations of full-scale specimens the batches of stringer panels of 1200 mmlength were manufactured and tested. The penetration welds, made by argon arc non-consumable electrodewelding over the layer of activating flux using preliminary elastic deformation and high-frequency mechanicalpeening of welds, provide the higher values of fatigue life of welded stringer panels of high-strength titaniumalloy VT20 as compared to electron beam welding and argon arc non-consumable electrode welding withimmersed arc. The developed technology can be accepted for industrial production of welded stringer panelsof high-strength titanium alloys. 14 Ref., 1 Table, 13 Figures.

Keywo r d s : thin-sheet welded structures, stringerstiffened panels, T-joints, penetration weld, residualstresses and deformations, preliminary elastic deformation,fatigue strength, high-frequency mechanical peening

Stringer panels of light alloys find ever widerapplication in aircraft, aerospace engineering,shipbuilding and other fields of industry. Theleading aircraft companies pay increased atten-tion to designing of new and updating of existingtechnologies for manufacture of load-carryingthin-walled panels of high-strength titanium al-loys. The characteristic example is application ofstringer panels of titanium alloy VT20 of 2.5 mmthickness and up to 2000 mm length with argon-arc welded-on stiffeners of up to 25 mm heightin the fighters of the Company «Sukhoy». Afterwelding, the panels in a jig of stainless steel aresubjected to thermal annealing in electric vac-uum furnace for relieving the residual stressesand deformations [1].

In the Langley Research Center (NASA) formanufacture of such structures the method ofbraze-welding was developed. Using thismethod, at first Z-shaped stiffeners of titaniumalloy are welded-on to the titanium sheet by spotsthrough the interlayer of aluminium brazing al-loy, and then the as-assembled structure of the

panel is placed to the vacuum chamber wherebrazing process takes place [1].

The structures of fighter F-14 of titanium alloyare manufactured using EBW providing highproperties of a joint and process efficiency [2].

In any case, notwithstanding whether it refersto structures of titanium or other alloys, in thriv-ing of aircraft builders to replace the riveted ormilled thin-sheet stiffened structures by thestructures with welded-on stiffeners, the tech-nologists encounter the necessity to minimize theinfluence of such negative factors as residualstresses and deformations, which are present dur-ing welding process and greatly decrease the serv-ice characteristics of a product, first of all, ac-curacy and life [3].

To solve the problems of increasing the accu-racy and fatigue characteristics of welded thin-sheet structures, such methods were developedat the E.O. Paton Electric Welding Institute aspreliminary elastic deforming (PED) [4—7] andhigh-frequency mechanical peening (HFMP)[8], which are nowadays successfully applied forshipbuilding structures of aluminium alloys andsteels [9]. It should be noted that unlike othermethods of surface plastic deformation, for ex-ample, using shot blast treatment, HFMP is dis-

© B.E. PATON, L.M. LOBANOV, V.L. LYSAK, V.V. KNYSH, V.I. PAVLOVSKY, V.P. PRILUTSKY, A.N. TIMOSHENKO, P.V. GONCHAROV and GUAN QIAO, 2014

6 9/2014

tinguished by its influence on a narrow fusionzone of 4—7 mm width. It forms compressive re-sidual stresses in the surface layer of fusion zoneand decreases concentration of stresses due tosmoothing of transition from weld to base metal.

In work [9] the efficiency of PED applicationto control residual stresses and strains in weldingof thin-sheet structures of titanium alloys wasexperimentally confirmed.

As a rule, in thin-sheet structures the joiningof sheet with stiffeners is performed using fusionwelding on the side of stiffener. Here, in mostcases two-sided fillet welds are used, made by auto-matic argon-arc welding with tungsten electrode(TIG), EBW or laser welding. The technology ofproducing penetration welds in the structures,when T-joint is made by one pass only on the sideof sheet by its penetration across the thickness andpartial penetration of stiffener, is challenging andat the same time more complicated.

However, in arc welding the processes of weldpool formation, heating of near-weld zone andpenetration of metal depend greatly on heattransfer and, respectively, heat conductivity ofmetal. Therefore, in the conventional arc weldingthe problems of producing the quality penetra-tion welds of relatively large depth, narrow zonesof residual tensile stresses and minimum distor-tions are obvious.

The processes of formation of penetration weldas compared to the butt weld are considerablydifferent. This problem is essentially complicatedin use of titanium alloys due to their thermalphysical and physical-mechanical properties.

It is known that the main type of metallurgicaldefects of welded joints of titanium alloys, madeboth by arc as well as by beam welding methods,are pores. The pore formation in weld metal canbe essentially decreased by a careful pre-weldingpreparation of surfaces of metal in the weldingzone. According to the statistic data on defectsin welded T-joints of titanium alloy VT20, themost frequent problem occurs with pores of asmall size (0.1—0.4 mm).

The presence of pores in welds scarcely influ-ences the behavior of welded joints at staticloads, but considerably decreases life of their op-eration under the conditions of cyclic loads,sharply decreasing the fatigue strength. In cyclictensile loads the sources of fracture of titaniumalloys mostly arise from the inner weld defects.The longest life is observed in welds with care-fully treated smooth transitions from reinforce-ment to base metal.

It is known that the process of deformationat cyclic loads causes the directed diffusion of

hydrogen into the zone, adjacent to pore, withincreased stress. The origin of cracks can occurnot only from the inner surface of pore but alsoin the nearest zone. Moreover, the growth ofconcentration of hydrogen at the surface of de-veloping crack near the pore is by one orderhigher than at some distance from the pore.

The life of welds is mainly influenced not sosignificantly by the size of pores, but by theirlocation zone. The pores far from the stress con-centrators decrease the life by 2—3 times, whereaspores in the zone of stress concentration decreasethe life by one order [10].

It was noted that application of surface coldworking arrests the development of fatigue frac-ture sources from the defects close to the surfaceand increases the life of welded joint.

The successful application of welding technol-ogy with penetration welds in the panel struc-tures is impossible without development of specialmeasures, which could provide necessary strengthand fatigue characteristics of welded joints andstructures, low residual welding deformations andstresses, high accuracy of product manufacturealongside with high quality of welds.

The aim of this investigation was the devel-opment of technology for manufacture of weldedstringer panels of titanium alloy VT20 providingtheir high accuracy and fatigue characteristics.

Titanium alloy VT20 relates to a pseudo-α′-alloys with the following content of alloying ele-ments, %: 5.5—7.0 Al, 1.5—2.5 Zr, 0.5—2.0 Mo,0.8—2.5 V. The coefficient of stability of β-phasein this alloy in annealed state depending on thecontent of alloying elements amounts to 5—7 %.

Phase transformations in the alloy duringcooling in the process of welding are proceedingaccording to the martensite kinetics, β→α trans-formation is observed. The increase in cooling rateresults in refining of α′-phase formed in weld metaland HAZ, however this does not considerably in-fluence the properties of joints at static tests.

The formed α′-structure is slightly alloyed byβ-stabilizers, therefore, it is close by its propertiesto the common α′-structure with the correspond-ing alloying. The structure is not changed alsoin the process of long low-temperature heating.Therefore, annealing for the purposes of stabiliz-ing of structure and hardening postweld heattreatment are not efficient. It is rationally toconduct annealing for relieving residual weldingstresses, decreasing concentrations in the site oftransition from the base metal to weld.

It should be noted that at the present time atthe enterprises producing welded structures oftitanium alloys, annealing remains the main

9/2014 7

method used for prevention of residual stressesand deformations. Here, the main disadvantagesof this technological process are great energylosses, restricted application due to the sizes of thetreated parts and also high material capacity of therigging, applied for fastening of annealed struc-tures. In this connection, in the present investiga-tions the additional aim was followed, i.e. a searchof the alternative for the annealing operation.

The strength properties of weld metal in weld-ing of alloy VT20 are close to the properties ofbase metal, and slight decrease in ductility isconnected with the peculiarity of formation ofcast structure. The size of grains in weld metaldepends on the energy input introduced in weld-ing. During slow cooling of joint after weldingthe ductility of cast metal decreases as a resultof increase in grains size. At the same time, thehigh rates of cooling result in decrease of ductilitybecause of formation of fine-acicular β-structurewhere α′-phase is absent [11].

The development of technology of deforma-tion-free welding of stringer panels of alloy VT20was carried out in two stages. At the first stage,on the experimented T-welded specimens the pos-sible methods of welding-on of stiffener to thesheet by penetration weld in combination withdifferent technological procedures, directed toimprovement of accuracy of producing T-joints,were investigated. At the second stage, on thebase of mastered technological variants the batchof stiffened panels was manufactured, whichwere subjected to tests at cyclic tension to con-firm the possibility of producing large-size air-

craft panels, meeting the operation requirementswithout heat treatment application.

Welded T-joint specimens and stiffened panelsfor investigations had geometric parameters cor-responding to the parameters of structures ap-plied in the aircraft construction. During per-formance of tasks of the first stage the weldingof T-specimens with one stiffener (Figure 1, a)was performed, of which specimens of blade typewere cut out (Figure 1, b) for fatigue tests.

The design of stiffened panel for the secondstage of investigations with four welded-onstringers, and specimen of blade type of it forfatigue tests, are given in Figure 2.

The load-carrying assembly rigging (Fi-gure 3) of the first stage of works is designed formanufacture of T-specimens and provides a pos-sibility of preliminary elastic tension of sheet andstiffeners being welded and also simultaneoussheet bending in the transverse direction. It wascomposed of three functional units: tension ofsheet, tension of stiffener, and berth. The unitof tension of T-specimen sheet (see Figure 3, b)was designed according to the principle of abreaking lever, the length of which exceeds thedistance between the edges of opposite clampsfor the value of required tension of sheet.

The application of the breaking lever in theload-carrying rigging design allowed providingits minimum sizes and weight, due to which itwas easily mated without additional resettingwith welding equipment for different weldingmethods. Moreover, the rigging allowed perform-ing nondestructive testing of quality of weld and

Figure 1. Welded T-specimen of VT20 alloy for the first stage of investigations: a – sketch of specimen; b – sketchof specimen of blade type; c – specimen for fatigue tests clamped in the machine

8 9/2014

its simultaneous repair at detection of defect di-rectly after welding without disassembly and intensile state.

In the unit of tension of T-specimen stiffener(see Figure 3, c) the stiffener under tension islocated between two traverses, receiving theload, and the tension of specimen is created bya screw jack and transmitted to the stiffenerthrough its clamps.

The unit of berth (Figure 3, d) is manufac-tured in the form a rigid basement with raisinglodgement, which serves as a support for unitsof tension and has a shape of reverse bending ofsheet in the transverse direction, and its longi-tudinal guides are rectilinear.

In the position for welding the sheet wastightly pressed to the lodgement, and stiffener –to the sheet. Moreover, copper water-cooledbackings were pressed to sheet and stiffener,which served for formation of fillets of weld rootand its gas protection.

Load-carrying welding rigging of the secondstage of works, designed for manufacture ofstringer panels, is similar and composed of thesame units as the rigging for specimens, but withthe only difference that there are four units fortension of stiffeners in its composition, which aresimultaneously installed below the panel sheet.

The laboratory equipment for argon-arc weld-ing using penetration welds of stiffened speci-mens and panels under the conditions of PED(Figure 4) was also applied. In welding instal-lation the power source Fronius Magic Ware 3300

was used and also welding head with improvedgas protection of arc and cooling weld area, whichwas moved by a three-coordinate manipulator.The control of welding installation was per-formed by a programmable controller. The in-stallation included also water cooling and gascylinder equipment.

At the first stage of investigations, three meth-ods of welding were selected: automatic argon-arc nonconsumable-electrode welding over thelayer of flux (TIG-F), automatic argon-arc non-consumable-electrode welding with immersed arc(TIG-I), and EBW. The selection of these meth-ods was determined considering the experienceof the PWI works on welding of titanium alloysand need in providing the complete penetrationof the sheet, its reliable fusion with the stiffener,uniform formation of fillet transitions on the sideof stiffener and also producing the weld rein-forcement on the face side without undercuts.

In connection with some physical propertiesof titanium, certain difficulties in welding occurconnected with providing quality formation ofpenetration weld root on both sides of stiffenerwith smooth mating of surfaces of stiffener andsheet. It is predetermined, on the one hand, bya high coefficient of surface tension of moltentitanium (1.5 times higher than that of alu-minium), which hinders a free sagging and for-mation of solidifying metal on the backing. Onthe other hand, a low viscosity of molten titaniumfacilitates the intensification of hydraulic pro-cesses in weld pool, that can not only influence

Figure 2. Welded stiffened panel of alloy VT20 for the second stage of investigations: a – general view; b – sketchof panel; c – sketch of specimen of blade type; d – appearance of specimen for fatigue tests

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the structure of weld and formation of pores init, but also influence the arc penetrability.

Therefore, in TIG welding of titanium by thesurface arc a low coefficient of heat conductivityof titanium and low heat power factor predeter-mine producing of wide welds with undesirablysmall coefficient of weld shape (relation of pene-

tration width to weld depth). To produce therequired complete penetration of joint using thismethod, the considerable increase in welding cur-rent and high heat input are required.

The TIG-I welding method is intended to in-crease the depth of penetration and differs fromthe method with surface arc by a peculiarity thatthe arc and also the electrode tip are submergedinto the pool lower than the surface of sheet,which considerably complicates the welded jointformation. The conditions of burning of the arcitself and movement of metal in the pool areprincipally differed from the welding by surfacearc. Actually, the whole arc is burning in a coni-cal depression, the walls of which are washed bymolten metal flows. It is transferred mostly fromthe front part of pool to its rear part, where itscooling takes place. In welding by immersed arcthe molten metal of weld pool is not sufficientlyinvolved to the total stirring, thus influencingthe processes of shape and pores formation.

Using immersion the maximum efficiency ofwelding arc heat is attained, hydrodynamic proc-esses and heat exchange in weld pool are inten-sified, however, heat and current loads on theelectrode tip are abruptly increased. At decreasedvalues of current or increased speeds the process

Figure 4. Laboratory equipment for argon-arc welding ofstiffened panels under the conditions of PED: 1 – gentrywith carriage for movement of welding head; 2 – controlunit; 3 – welding head; 4 – power source; 5 – load-car-rying assembly stand for PED of parts being welded; 6 –welded panel

Figure 3. Load-carrying assembly rigging for welding of T-specimens under the conditions of PED: a – general viewof rigging with specimen after welding; b – unit of sheet tension; c – unit of stiffener tension; d – unit of birth; 1,2 – clamping of stiffener and sheet, respectively; 3 – sheet of T-specimen; 4 – breaking lever; 5 – clamps; 6 – jackrod; 7 – jack nut; 8 – copper water-cooled backing; 9 – angle of transverse bending of sheet

10 9/2014

of welding is characterized by frequent short-pe-riod short circuits and, respectively, sharp cur-rent fluctuations. They cause changes in the shapeof electrode due to current erosion of its tip. Dueto this the unpredicted jumps of welding processparameters and non-quality formations of weldedT-joint occur. The width of weld and depth ofpenetration are changed. As the arc moves forward,the frequency of short circuits grows and totalvoltage drops. During this method there is a highprobability of getting the unstable result at thesame conditions of assembly and welding conditionparameters. The process is very sensitive to thetemporary welding deformations and it is used tostop because of common short circuiting, arc ex-tinction and «freezing» of electrode at negligibledeplanations of sheet, as a rule. Due to that theuse of TIG-I welding in manufacture of structureswith long welds is restricted.

The EBW method is characterized by com-paratively high concentration of energy and, asa rule, is applied for joining of large thicknesses.While producing penetrated T-joints electronbeam cuts through the sheet metal quite easilyunlike the arc, providing the guaranteed meltingof stiffener, which is under the sheet [12]. Atthe same time, the necessity in formation of radiiof fillets (up to 2 mm) from below the sheet onboth sides of stiffener imposes quite severe re-strictions for selection of modes, as this leads towidening the pool on the joint face side. It isdifficult to maintain in balance the wide pool onsheet and, as a result, the flaky surface of weldis formed with undercuts. The tendency to burn-outs and pores is also high near the root weld.To eliminate the defects in this case the additionalsmoothing of weld by repeated pass of unfocusedbeam is necessary.

The analysis of results of selection of EBWmode parameters for T-joints of VT20 alloy withpenetration welds shows the following. The bet-ter conditions for formation of smooth fillets onthe weld bottom are achieved during the modeswith deep penetration of beam to the stiffenerand high heat inputs, which are close to the proc-ess of sheet cutting. However, the better forma-tion of weld surface on the face side is achievedat modes close to the process of smoothing. The

selection of optimal mode consists in finding thegrounded compromise between these processes.

The method of TIG-F welding is designed forproducing welds on titanium alloys of 0.8—6.0 mm thickness [13]. Before welding a layerof flux is deposited on the surface of parts beingwelded. The welding is performed in one passwithout preparation of edges both with filler wireand also without it. The adding of halogenidefluxes into the welding zone causes constrictionof arc, predetermined by physical processes,which occur in the arc column. Here the condi-tions of welded joint formation are changed inprinciple and technological capabilities of TIG-Fwelding are widened as compared to welding us-ing surface arc.

The main advantages of TIG-F welding areincrease of penetration depth at negligible de-crease of input energy, decrease in width of weldand HAZ, prevention of porosity. Thus, inputenergy is 1.5—2 times decreased, width of weldsis characterized by the small coefficient of weldshape. Metallurgical treatment of metal of weldpool by a liquid slag almost completely preventsthe formation of pores in joint in welding ofdifferent titanium alloys. It is connected withthe fact that as a result of metallurgical reactionsoccurred in a weld pool between flux and tita-nium the chemical binding of hydrogen occurs.Hydrogen, dissolved in weld pool molten metal,is bonded by fluorine to hydride-fluorides re-maining in weld metal as microscopic slag inclu-sions. As the mechanical properties of weld metalare determined by the state of α′- and β-phasesand not by interphase interlayers, then TIG-Fwelding provides sufficiently high level of prop-erties of joints.

Besides, during this method the welding cur-rent is increased by 20—25 % above the optimumone, thus leading to the growth of width of re-verse formation (by 30—50 %) at negligible in-crease (by 7—12 %) of weld width. This featureallows efficiently using this method to produceT-welded joints by through penetration of sheetwith simultaneous melting of the stiffener.

Carrying out the first stage of investigationson the T-joint specimens with penetration weldsthe optimal modes of welding process were prac-ticed. The mentioned modes for each of three meth-ods of welding of alloy VT20 are given in the Table.

Method ofwelding

Weldingspeed,m/h

Fillerdiameter,

mmProtection

Beamcurrent,

mA

Acceleratingvoltage,

kV

Focusingcurrent,

mA

Scanningamplitude,

mm

Scanningfrequency,

Hz

Weldingcurrent, A

Arc voltage,V

EBW 14 1 Vacuum (10—5) 70 28 80 8 380 — —

TIG-F 18 1 Argon — — — — — 195 14.0—14.5

TIG-I 17 1 Same — — — — — 250 11.2—11.5

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Microstructures of welded joints produced us-ing mentioned methods are quite of the sametype. As is seen from Figure 5, microcracks andpores in weld and HAZ metal are absent. Itshould be noted that the length of HAZ is variedin the ranges of 2.5—3 mm, the weld widthamounts to 6—7 mm. In the weld from the fusionzone to the center of welded joint the non-uniaxial grains are solidified, mostly columnarcrystallites, elongated to the direction of heatremoval. In the central part of joint the crystal-lites are formed, close to uniaxial shape, whichgrow together along the axis of weld at the anglesof about 60—90°. The grains in weld are uniformby their size.

To strengthen the weld, filler wire VT1-00(commercial titanium) of 1.0 mm diameter wasused. In the experiments of the first stage theinfluence of adding of this filler wire to weldpool for decrease of content of alloyed elementsin welded joint was investigated. The quantita-

tive evaluation of change in level of weld metalalloying was carried out using X-ray spectralanalysis. The content of alloying elements, de-termined in the single spots, changed in the fol-lowing ranges, %: 5.91—6.33 Al; 1.65—1.84 Zr;0.77—1.24 Mo; 1.06—1.17 V, that corresponds tothe content of alloying elements in alloy VT20.

To decrease welding stresses and deformationsthe PED of elements to be welded was applied.The sheet and stiffener were subjected to longi-tudinal tension at a preset level of stresses. Be-sides, the sheet was subjected to bending in thetransverse direction as regards to angular weldingdeformations.

To set the optimal parameters of PED, theexperiments on determination of dependence ofresidual stress-strain state of the specimen on thepreliminary stresses of tension of sheet and stiff-ener were determined. It is seen from Figure 6that residual welding stresses are considerablydecreased with increase of preliminary tensilestresses to 0.5σ0.2. The residual welding defor-mations of shape changing in welded T-joints arealso decreased during increase of initial tensilestresses. Reaching the level of initial stresses(0.30—0.35)σ0.2 the residual welding distortionsalmost correspond to the values of deformationsof initial sheets.

The reverse transverse bending of sheet is ap-plied to eliminate completely the angular residualdeformations. The reverse bending, determinedexperimentally, amounted to 0.75 of the valueof residual angular deformations produced inwelding of specimen in a free state.

In T-welded specimens (Figure 7), producedusing EBW without application of PED at op-timal parameters, the significant torsional defor-mations are seen and also those of longitudinaland transverse bending, while on the specimensapplying PED the mentioned deformations areabsent. In welding of specimens using TIG-I and

Figure 5. Macrosection (a) and appearance (b) of the faceside of VT20 welded T-joint of 2.5 mm thickness of elements(TIG-F welding, flux ANT-25A)

Figure 6. Diagrams of distribution of longitudinal residual stresses in the transverse section of EB-welded T-specimensof alloy VT20 with penetration weld in plate (a) and stiffener (b): 1 – welding of specimen in the rigging withouttension; 2 – welding of specimen under the conditions of PED at σsh = 220 and σst = 250 MPa; 3 – welding of specimenunder the conditions of PED at σsh = σst = 450 MPa

12 9/2014

TIG-F methods under PED conditions and with-out it, the similar results were obtained.

Five specimens, produced applying threewelding technologies, were subjected to PWHT.According to the recommendations accepted dur-ing manufacture of elements of welded aircraftstructures of titanium alloys, PWHT was carriedout in electric furnace in vacuum with automaticcontrol of temperature (Figure 8). To preventdistortions of specimens during treatment the fix-ing rigging of stainless steel was applied. Theapplied mode was the following: heating to650 °C in vacuum 1.33⋅10—1 MPa for 2 h, furnacecooling in vacuum. Then all the specimens weretreated by HFMP to increase the fatigue resis-tance (Figure 9). HFMP of specimens consistedin peening of fusion zones of welded joint bothalong the sheet as well as along the stiffenerusing ultrasonic impact tool, where hard-alloystrikers with radius rounding at the ends wereused as the working part.

The challenging task in manufacture of thin-sheet structures of light alloys is the developmentof repair-welding technologies and evaluation oftheir influence on strength and life of weldedjoints. For T-joints, made with penetration weld,two types of defects are peculiar: absence of smoothtransition (fillets) from sheet to stiffener, and alsothe presence of inner weld defects (pores, inclu-sions, microcracks). In this connection the evalu-ation of efficiency of two repair technologies wascarried out. To eliminate the first type of defects,smoothing of the fillet using argon-arc nonconsu-mable-electrode welding was performed, and toeliminate the second one the defects were drilled

out, at first, on the face part of weld, and thenthey were filled by argon-arc welding using fillerwire VT20 of 2.0 mm diameter. The repair weld-ing was performed in special rigging providingfixation of the specimen and gas protection ofsurfaces of sheet and stiffener. After the repairHFMP of welded joints was performed.

For fatigue tests the specimens were fixed inclamps of testing machine URS-20 along the flatareas near the edges (without clamping of stiff-ener) (see Figure 1, a) and loaded by longitudinaltensile cyclic load with asymmetry of cycle Rσ == 0.1 at frequency of 7 Hz. The preset tensile

Figure 8. Heat treatment of welded specimens of alloy VT20 in electric vacuum furnace: 1 – T-specimens; 2 – riggingfor annealing in furnace

Figure 7. Appearance of T-specimens manufactured usingEBW without (a) and with (b) PED of sheet at σsh = 220and σst = 250 MPa

9/2014 13

force was selected so that the calculation levelof maximum stresses of the cycle in specimensheet part (not considering the stiffener)amounted to 0.5σ0.2 for alloy VT20. However, atthe given scheme of loading the welded-on stiffenerwas subjected to the certain part of applied loading.As a result, the maximum cycle stresses in T-jointnet-section were lower than calculated ones. Todetermine the real stresses, the strain gauges wereused. The measurements performed by themshowed that maximum stresses in the middle sec-tion of sheet amounted to 350 MPa.

The fatigue tests of specimens were carriedout until their complete fracture, and correspond-ing amount of stresses was taken as a criterionfor evaluation of investigated variant of weldingtechnology and treatment.

In the summarized diagram in Figure 10 thetest results for T-specimens, used in the experi-ments of the first type, are given. During teststhe specimens were mainly fractured in the work-ing sections 60 mm width. Here the fatigue crackwas initiated in the sheet in the transition zonefrom weld to base metal and further was propa-gated to both directions until the complete frac-ture. The microfractographic examinations of thesurface of fatigue fractures showed that the char-acter of fracture in the zone of penetration weldwas mostly tough-brittle and tough-quasi-brittle.

As the base variants, T-joints produced usingone of three welding methods (specimens TIG-I-1,TIG-F-1, EBW-1) without PED were fatiguetested (see Figure 10). As is seen, weldingmethod influences the level of life of tested speci-mens. The shortest life is observed in EBW andit is increased in TIG-I and TIG-F welding.

PED results in increase of cyclic life of weldedspecimens (TIG-I-2, TIG-F-2, EBW-2) up totwice as compared to the base variants.

Smoothing of weld legs decreases cyclic lifeof welded specimens, produced under the condi-tions of PED, at all the welding methods (speci-mens TIG-I-3, TIG-F-3, EBW-3).

HFMP by ultrasonic impact tool of welds pro-duced using PED, greatly increases their load-carrying capacity, especially in TIG-F welding(specimens TIG-I-4, TIG-F-4, EBW-4).

The fatigue properties of welded specimens(TIG-I-5, TIG-F-5, EBW-5) sharply decrease asa result of repair of defect by surface arc on theside of sheet.

The heat-treated specimens (TIG-I-6, TIG-F-6,EBW-6) showed a considerable increase in cycliclife in case of welding over the activating flux.However it should be noted that PWHT is lessefficient as compared to mechanical peening ofwelds using ultrasonic impact tool.

Thus, the fatigue tests of specimens showedthat the highest load-carrying capacity of T-welded joints with penetration weld can be ob-tained in TIG-F and TIG-I welding applyingPED and HFMP.

At the second stage the welding of groups ofpanels was performed using two methods: TIG-Iand TIG-F (Figure 11). Technological modes ofwelding of panels corresponded to the modes ofwelding of T-specimens. The welding of panelswas performed applying PED of sheet and stiff-eners at the level σsh = σst = 220 MPa and reversebend with the arrow of bend of 14 mm. Weldedjoints of all the panels were treated by HFMPusing the tool and technology, which were mas-tered at the first stage of investigations.

It should be noted that as a result of applica-tion of PED of sheet and stiffeners the residualshape changes of panels after welding were lessthan initial bends of sheet plates.

The quality control of welded joints was per-formed using the method developed at the PWIbased on the application of electron shearography[14], which allows operative determination ofdefect areas of welds without disassembly of load-carrying rigging and, if necessary, starting therepair immediately. Thus, welding and repair werejoined in one technological process, that facilitatedthe improvement of the quality of panels.

According to the results of quality control ontwo panels manufactured using TIG-I welding,the defects as a chain of pores of 2 mm diameterwere corrected applying mechanical preparationof the weld. On two panels corresponding toTIG-F welding the repair smoothing of leg areawas performed.

To carry out the fatigue tests of welded panelsthe large-size specimens of blade type with test

Figure 9. HFMP of specimen of VT20 alloy T-welded jointby hand impact tool: 1 – specimen; 2 – backing; 3 –working head of impact tool

14 9/2014

part of 450 × 350 × 2.5 mm and grinded edgeswere manufactured (see Figure 2, c). The testswere carried out in the modernized universal ser-vohydraulic testing machine HydroPuls-Schenkwith maximum tensile force of 100 t, the controlwas performed by 4-channel digital controllerMTC Flex Test GT.

For evaluation of the real level of stresses inthe test section of the specimen and check up ofits correct disposition in the clamps of testingmachine the set-up tensometry was carried outfor each specimen. For this purpose, strain gaugesKF 5 P1-200 connected to tensomeasuring systemSIIT-2 were glued in the test part of sheet andstiffeners of specimen in three sections along thelength (Figure 12).

In the process of set-up tensometry the panelspecimen was loaded stepwise with a pitch of

50 kN up to maximum tensile loading. At eachstep of loading the level of stresses was measuredaccording to the strain gauges. Uniformity andmaximum stresses on strain gauges were evalu-ated and, when necessary, maximum test loadwas corrected to approximate the test conditionsof each panel. As a result, maximum test loadwas set individually for each panel in the limitsfrom 300 to 320 kN.

At the fatigue tests the loading of specimenswas performed by cyclic loading at the frequencyof 0.5 Hz and the coefficient of cycle asymmetryRσ = 0.1.

The test results of panels manufactured at thesecond stage of works are presented in Figure 13.As is seen from the diagram, fatigue life of speci-mens, where the repair of defects of welds is carried

Figure 10. Results of fatigue tests at cyclic longitudinal tension of T-welded specimens of alloy VT20 (indicated usingmethod of welding: 1 – specimens rigidly clamped in the rigging without tension in welding; 2 – produced applyingPED; 3 – with smoothing of weld leg; 4 – treated using ultrasonic impact tool; 5 – with repair of defect atop (orrepair simulation); 6 – after heat treatment)

Figure 11. TIG-F- (a) and TIG-I- (b) welded stringer panels of alloy VT20 after fatigue tests

9/2014 15

out, drops sharply. The higher fatigue life be-longs to panels, manufactured applying technol-ogy of welding over the layer of activating flux.

The results of the second stage of investiga-tions showed that the technology of argon-arcwelding by penetration welds over the layer ofactivating flux applying PED of the elements beingwelded and further HFMP of welds can serve asa basis for industrial production of stringer panelsof high-strength titanium alloy VT20.

Conclusions

1. It was established that producing of penetra-tion welds using argon-arc welding by non-con-sumable electrode over the layer of activatingflux, PED and HFMP of welds provides highervalues of fatigue life of welded stringer panelsof high-strength titanium alloy VT20 as com-pared to EBW and argon-arc nonconsumable-electrode welding with immersion arc.

2. The application of PED at the level lowerthan 0.25σ0.2 in welding of large-size stringerpanels of alloy VT20 gives a possibility to elimi-nate welding distortions and improve the condi-tions of welding process in automatic mode.

3. The postweld HFMP of welds noticeably in-creases the fatigue life of structure of titanium alloys.

4. The technology of manufacture of weldedstringer panels of alloy VT20 without PWHTwas offered.

1. Matvienko, S.V., Astafiev, A.R., Karasyov, I.G.(2003) Welding and related technologies in aircraftconstruction. Tendencies of development. Svarka vSibiri, 2, 36—40.

2. Robert, W., Messler, J.R. (2007) The greatest storynever told: EB welding on the F-14. Welding J.,May, 41—47.

3. Bratukhin, A.G., Dmitriev, O.N., Kovalkov, Yu.A.(1997) Stamping, welding, brazing and heat treat-ment of titanium and its alloys in aircraft construc-tion. Moscow: Mashinostroenie.

4. Paton, B.E. (1992) Advanced trends in improvementof welded structures. In: Welding and Surf. Rev.,Vol. 2., 1—8. Amsterdam: Harwood Acad. Publ.

5. Paton, B.E., Utkin, V.F., Lobanov, L.M. et al.(1989) Fabrication of welded large-sized panels fromhigh-strength aluminium alloys. Avtomatich. Svarka,10, 37—45.

6. Lobanov, L.M., Pavlovsky, V.I., Lysak, V.V. (1987)Elastische Vorspannung beim Schweissen vonDuennblechen aus Aluminiumlegierungen. Schweis-stechnik, 10, 443, 447—449.

7. Lobanov, L.M., Pavlovsky, V.I., Pivtorak, V.A.(1992) Optical methods of studying and means ofcontrolling welding strains and stresses. In: Weldingand Surf. Rev. Amsterdam: Harwood Acad. Publ.

8. Lobanov, L.M., Kirian, V.I., Knysh, V.V. et al. (2006)Improvement of fatigue resistance of welded joints inmetal structures by high-frequency mechanical peening(Review). The Paton Welding J., 9, 2—8.

9. Stanhope, F., Hasellhurs, R.H. (1972) Welding air-frame structures in titanium alloys using tensile load-ing as a means of overcoming distortion. In: Proc. ofInt. Conf. on Welding and Fabrication of Non-Fer-rous Metals (Eastbourne, 1972), Vol. 1, 72—82.

10. Muraviov, V.I. (1986) Specifics of fabrication andquality evaluation of large-sized thin welded struc-tures of VT20 alloy. Avtomatich. Svarka, 8, 15—18.

11. Zamkov, V.N., Prilutsky, V.P., Petrichenko, I.I. etal. (2001) Effect of the method of fusion welding onproperties of welded joints in alloy Ti—6Al—4V. ThePaton Welding J., 4, 2—6.

12. Savitsky, V.A., Shevelev, A.D., Zamkov, V.N. et al.(1989) Electron beam welding of stiffened panel ele-ments in VT20 titanium alloy. Avtomatich. Svarka,4, 55—57.

13. Paton, B.E., Zamkov, V.N., Prilutsky, V.P. et al.(2000) Contraction of the welding arc caused by theflux in tungsten-electrode argon-arc welding. The Pa-ton Welding J., 1, 5—11.

14. Lobanov, L.M., Pivtorak, V.A., Savitskaya, E.M. etal. (2011) In-process quality control of welded panelsof alloy VT20 using method of electron shearography.Ibid., 11, 22—27.

Received 03.12.2013

Figure 12. Panel with glued strain gauges installed in theclamps of machine for fatigue tests

Figure 13. Results of fatigue tests at cyclic longitudinaltension of alloy VT20 welded panels (designated usingmethod of welding: TIG-I-5, TIG-F-3 – panels with repairof weld defect, respectively, with preparation of its faceside and smoothing of leg from the weld back side)

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SIMULATION OF ELECTRIC ARCWITH REFRACTORY CATHODE

AND EVAPORATING ANODE

I.V. KRIKENT1, I.V. KRIVTSUN2 and V.F. DEMCHENKO2

1Dneprodzerzhinsk State Technical University2 Dneprostroevskaya Str., 51918, Dneprodzerzhinsk, Ukraine. E-mail: science@dstu.dp.ua

2E.O. Paton Electric Welding Institute, NASU11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

Equation of convective diffusion of ionized metal vapour in arc plasma, allowing for the difference incoefficients of diffusion of atoms, single- and double-charged metal ions, presence of thermodiffusion flowsof metal particles, as well as ion drift in the electric field, was proposed to more precisely define the earlierdeveloped complex model of the processes of energy, mass and charge transfer in the column and anoderegion of electric arc with refractory cathode and evaporating anode, running in inert gas. Based on thethus precised complex mathematical model, numerical analysis of the influence of diffusion-induced evapo-ration of anode material (Fe) on heat, gas-dynamic and electromagnetic characteristics of multicomponentplasma of the column and anode region of stationary electric arc with refractory cathode (W) at its runningin inert gas (Ar) was performed. An essential influence of metal surface temperature distribution in theregion of anode binding of the arc on distribution of temperature and electric current density in near-anodeplasma, as well as on distributed and integral characteristics of its thermal impact on evaporating anodesurface, is shown. 18 Ref., 12 Figures.

Keywo r d s : electric arc, refractory cathode, evapo-rating anode, arc column, anode region, multicomponentplasma, metal vapour, diffusion, mathematical simula-tion

Electric arc plasma in inert-gas nonconsumable-electrode welding, as a rule, is multicomponent,as alongside shielding gas particles, it containsatoms and ions of metal vapour coming to thearc gap due to evaporation of anode metal fromweld pool surface. Presence of an even smallamount of metal component in inert gas arcplasma has an essential influence on its ionizationcomposition, thermodynamic, transport and op-tical properties. It leads to a significant differenceof heat, electromagnetic and gas-dynamic char-acteristics of plasma in near-anode zone of arccolumn in nonconsumable-electrode weldingfrom respective characteristics of arc dischargewith refractory cathode and nonevaporating, forinstance, water-cooled anode. Characteristics ofwelding arc anode region, determining the con-ditions of thermal and electromagnetic interac-tion of the arc with metal being welded and,consequently, nature of its penetration, are alsodifferent [1].

In the first publications, devoted to mathe-matical simulation of the processes of heat, massand charge transfer in refractory cathode arcs[2—10], arc plasma was assumed to be single-com-

ponent, i.e. containing atoms and ions of just theshielding gas. Such idealization did not incorpo-rate any conditions of running of real weldingarcs, and required further improvement of mathe-matical models of the arc, in order to allow fora number of additional physical factors, relatedto multicomponent nature of arc plasma. Publi-cations devoted to allowing for evaporation ofanode material in simulation of nonconsumable-electrode welding arc, appeared in the world sci-entific literature comparatively recently [11—13].When describing diffusion of ionized metal va-pour in arc plasma, however, these works do notdifferentiate between vapour atoms and ions,having diffusion coefficients, differing signifi-cantly by their magnitude [1]. The integratedmathematical model of nonconsumable-electrodewelding arc proposed in [14] is an attempt toallow for the difference in the above coefficients.However, when writing the equation of convec-tive diffusion of evaporated anode metal in arccolumn plasma, thermodiffusion of atoms andions of metal vapour, as well as metal drift inthe electric field, were not allowed for. There-fore, the objective of this work is improvementof the model of convective diffusion of metalvapour in arc plasma and applying the precisedintegrated mathematical model [14] for numeri-cal analysis of characteristics of multicomponentplasma of the column and anode region of sta-

© I.V. KRIKENT, I.V. KRIVTSUN and V.F. DEMCHENKO, 2014

9/2014 17

tionary electric arc with refractory (W) cathodeand evaporating (Fe) anode at its running ininert gas (Ar).

Equation of metal vapour transfer in arcplasma. A specific feature of metal vapour dif-fusion in arc plasma is that metal atoms evapo-rated from molten anode surface, may ionize,forming single- and double-charged ions, whosecoefficients of diffusion differ significantly fromthe respective coefficients for neutral particles.More over, processes of ionization and recombi-nation of particles in arc plasma column proceedmuch faster than those of transfer of substanceand thermal energy [15, 16]. Therefore, we willassume that concentrations of all the particles ofmulticomponent plasma of the considered arc col-umn (electrons, atoms and single-charged ionsof argon, atoms, single- and double-charged ionsof iron) differ only slightly from equilibrium val-ues determined by the principle of detailed equi-librium. We will also assume that arc columnplasma is in the state of local thermodynamicequilibrium at electron temperature equal to thatof heavy particles (single-temperature model).

In the general case the equation of diffusionfor atoms, single- and double-charged metal ionsin inert gar plasma can be expressed as follows:

∂nm0

∂t = —div (nm0w

→m0) — n

.m0; (1)

∂nm1

∂t = —div (nm1w

→m1) — n

.m1 + n

.m0; (2)

∂nm2

∂t = —div (nm2w

→m2) + n

.m1, (3)

where nm0, nm1, nm2 are the concentrations ofatoms, single- and double-charged metal ions;w→m0, w

→m1, w

→m2 are the rates of their directed

motion; n.mZ (Z = 0, 1) are the reaction rates of

first and second ionization, respectively.Let us represent the rate w→m0 of metal atom

motion in the form of a sum of mean velocityw→C of plasma particle motion and diffusion rateof neutral metal particles w→D0:

w→m0 = w→

C + w→D0. (4)

If atomic masses of all the plasma componentsare the same, then average velocity of particlemotion coincides with average mass (gas dy-namic) velocity of plasma motion W

→. Otherwise,

w→C value can be determined from the followingbalance relationship:

ρW→

= ρw→C + MmY→

m0 + M___

m0Y→

m0___, (5)

where ρ is the plasma velocity; Mm is the massof metal atoms; Y

→m0 is the density of diffusion

flow of metal atoms; Y→

m0___, M

___m0 is the density of

diffusion flow and average statistical mass of par-ticles, substituting metal atoms.

As diffusion processes do not have any essen-tial influence on pressure distribution in arcplasma, we can assume that it is determined,mainly, by gas-dynamic factors. For the consid-ered here stationary free-running arc the pressurein its column differs only slightly from the at-mospheric one [17]. Therefore, metal vapour dif-fusion in such an arc can with a high degree ofaccuracy be considered as a process running atconstant (atmospheric) pressure. In this case, theresult of diffusion is plasma-forming particles ex-changing their places. It follows from here thatspecific diffusion flows Y

→m0 and Y

__m0___ compensate

each other, i.e. condition Y→

m0 = —Y→

m0 is fulfilled.Then, equation (5) yields the following expres-sion for determination of mean velocity of parti-cle motion:

w→C = W→

— Mm — M

___

m0ρ Y

→m0. (6)

Average statistical weight of particles substi-tuting metal atoms, can be approximately calcu-lated by the following formula:

M___

m0 = ρ — Mmnm0

n0 — nm0.

Here n0 = p0/kT is the total concentration ofparticles in arc column plasma assumed to beisothermal; p0 is the atmospheric pressure; T isthe plasma temperature; k is the Boltzmann con-stant. In terms of the above approach, the sumof specific mass flows of atoms of metal and otherparticles, forming the plasma, is equal to totaldensity of plasma mass flow. This is indicativeof consistent description of gas-dynamic and dif-fusion processes.

Diffusion rate w→D0 of metal atoms is connectedwith their concentration nm0 and diffusion flowdensity Y

→m0 as follows:

w→D0 = Ym0

nn0,

where Y→

m0 value in the simplest case can be de-termined from the following relationship [1]:

Y→

m0 = — D0

T grad (nm0T), (7)

where D0 is the coefficient of metal atom diffu-sion in plasma.

18 9/2014

Substituting (4), (6), (7) into equation (1),we obtain

dnm0

dt = div [G0 grad (nm0T)] — nm0 div W

→ — n

.m0, (8)

where dnm0/dt is the substantial derivative;

G0 = D0

T ⎛⎜⎝1 — nm0

Mm — M___

m0ρ

⎞⎟⎠.

We will perform similar transformations withequations (2), (3) and will additionally allowfor drift of charged metal particles (single- anddouble-charged ions) in the electric field. As aresult we will have

dnm1

dt = div [G1 grad (nm1T) +

+ b1mm1 grad ϕ] — nm1 div W→

— n.m1 + n

.m0,

(9)

dnm2

dt = div [G2 grad (nm2T) +

+ b2mm2 grad ϕ] — nm2 div W→

+ n.m1.

(10)

Here, GZ = DZ

T ⎛⎜⎝1 — nmZ

Mm — M___

mZρ

⎞⎟⎠; DZ are

the coefficients of diffusion of metal ions withcharge number Z (Z = 1, 2);

M___

mZ = ρ — MmnmZ

n0 — nmZ;

bZ = eZk

GZ are the mobilities of metal ions in

the electric field; e is the electron charge; ϕ isthe scalar potential of electric field in the arccolumn.

Summing up equations (8)—(10), we obtainthe equation of metal particle transfer in arcplasma

dnm

dt = div [G0 grad (nmT) +

+ (G1 — G0) grad (nm1T) ++ (G2 — G0) grad (nm2T) +

+ (b1nm1 + b2nm2) grad ϕ] — nm div W→

,

(11)

where nm = nm0 + nm1 + nm2 is the total concen-tration of heavy particles of metal vapour.

Let us express the concentrations of metal ionsnmZ (Z = 1, 2) through total concentration ofmetal particles in the plasma: nmZ = KZnm, wherecoefficients KZ correspond to first (Z = 1) andsecond (Z = 2) ionization of metal atoms. Con-sidering the assumption of local thermodynamicequilibrium of arc column plasma, coefficients

KZ can be determined for equilibrium plasma ofspecified composition and temperature.

Introducing G__

1 = G1 — G0; G__

2 = G2 — G0designations, we will rewrite equation (11) fortotal concentration of metal particles in theplasma:

dnm

dt + nm div W

→ = div [G0 grad (nmT) +

+ G__

1 grad (K1nmT) + G__

2 grad (K2nmT)] +

+ div [b1K1 + b2K2)nm grad ϕ].

(12)

Equation (12) describes the following kindsof transfer of heavy particles of metal vapour inarc plasma: convective transfer, concentrationdiffusion, thermodiffusion, as well as vapour iondrift in the electric field. Knowing the solutionof this equation, nm and considering the takenassumption of local thermodynamic equilibriumof arc column plasma, its ionization compositioncan be determined through application of therespective system of Saha’s equations, law of par-tial pressures and condition of plasma quasineu-trality [14]. The thus calculated concentrationsof particles of multicomponent arc columnplasma can be used for calculation of its thermo-dynamic and transport properties [18], includedinto complex model equations [14].

We will define boundary conditions for dif-fusion equation (12). Assuming that the arc col-umn is characterized by axial symmetry, we willintroduce the cylindrical system of coordinates(r, z) and consider design region Ω = {0 < r << R, 0 < z < L}, shown in Figure 1.

Considering the direction of movement ofshielding gas and plasma in near-cathode zone ofarc column [17], we will assume that particlesof evaporated anode metal do not reach plane

Figure 1. Schematic for mathematical description of arcplasma: 1 – refractory cathode; 2 – shielding gas, 3 –arc column plasma; 4 – molten (evaporating) metal; 5 –anode

9/2014 19

z = 0 (see Figure 1), i.e. on upper limit of designregion we will set

nm⎪⎪z = 0

= 0. (13)

On the arc axis (at r = 0) we will assume thefollowing conditions of symmetry:

∂nm

∂r⎪⎪r = 0

= 0. (14)

On the outer limit of design region (at r = R)we will assign «soft» boundary conditions

nm|r = R = 0 at Wr(R, z) ≤ 0;

dnm

dt⎪⎪r = R

= 0 at Wr(R, z) > 0,(15)

where Wr(r, z) is the radial component of thevector of average mass velocity of plasma.

On the boundary of multicomponent plasmawith anode layer (at z = L) we can write theboundary condition in the following form:

nm|z = L = nm0L (r) + nm1

L (r) + nm2L (r), (16)

where nmZL (r) = nmZ(r, L) are the respective dis-

tributions of concentration of metal vapour par-ticles, being in charge state Z, which can be de-termined according to model of anode region ofthe arc with evaporating anode [14], dependingon local values of near-anode plasma temperatureand anode surface temperature, its evaporationmode, as well as kind of shielding gas. Limitingfurther consideration to diffusion evaporationmode, it can be assumed with sufficient accuracythat local values of partial pressure of atoms andions of metal component of plasma pm on theabove boundary are equal to pressure of saturatedvapour of anode metal at the respective value oftemperature on its surface Ta:

pm|z = L = p0 exp ⎧

⎨

⎩

⎪

⎪

λv

k ⎡⎢⎣

1TB

— 1

Ta(r)

⎤⎥⎦

⎫

⎬

⎭

⎪

⎪, (17)

where λv is the energy consumed for transitionof one metal particle from the liquid into thevapour phase; TB is the boiling temperature ofanode metal.

Model of convective diffusion of ionized metalvapour (12)—(17) is a component part of complexmodel of processes of energy, pulse, mass andcharge transfer in multicomponent plasma of thecolumn and anode region of electric arc in inert-gas nonconsumable-electrode welding [14]. Fornumerical simulation of heat, gas-dynamic andelectromagnetic processes in such plasma we willuse equations of single-temperature model [17].When allowing for evaporation of anode metal

on the boundary of condensed phase with arcplasma, there exists a diffusion flow of metalvapour, as a result of which the axial componentof plasma velocity vector on this boundary is notequal to zero (unlike the condition of «sticking»,used in [17] for the case of water-cooled anode).Considering the fact that atoms and ions ofshielding gas, which is inert, cannot accumulateon the anode surface, the resulting flow of heavyparticles of gas near the anode surface can beconsidered to be equal to zero. Then, allowingfor diffusion and convective mechanisms of metalvapour particle transfer, the boundary conditionfor axial component of vector of average massvelocity of plasma on the boundary of arc columnwith the anode region (at z = L) can be writtenin the following form:

Wz|z = L = Mm[Ym0Z

L (r) + Ym1Z

L (r) + Ym2Z

L (r)]

ρ(r, L) — Mm[nm0L (r) + nm1

L (r) + nm2L (r)]

. (18)

Here YmZZ

L (r) are the respective distributions of

axial components of densities of diffusion flowsof metal atoms and ions, which are in chargedstate Z.

Simulation results and their discussion. Fornumerical analysis of the influence of diffusionevaporation of anode metal on processes of en-ergy, mass and charge transfer in anode regionand column of the considered arc we will assignanode surface temperature distribution by nor-mal-circular law Ta(r) = (Ta0 — T∞) exp (—a2r2) ++ T∞, where Ta0 is the temperature on the axisof the region of arc anode binding; T∞ is thetemperature of metal surface at a distance fromthe above region. We will select coefficient ofconcentration a so that diameter of molten zoneon anode surface was 5 mm. Characteristic pro-files of Ta(r) distribution at T∞ = 500 K are shownin Figure 2.

Numerical simulation of characteristics ofmulticomponent plasma of the column and anoderegion of electric arc with tungsten cathode andevaporating anode from low-carbon steel wasconducted at the following parameters: arclength L = 2.9 mm; arc current I = 200 A; shield-ing gas is argon, and evaporating element is iron.Initial distributions of arc column plasma char-acteristics, required to solve the non-stationaryproblem [17], together with equation (12), wereassigned as specified in [17]; initial concentrationof metal vapour in the arc gap was also taken tobe zero. Calculations were performed right up toestablishment of steady state of arc plasma.

We will introduce γ = nm/(ng + nm) designa-tion, where ng = ng0 + ng1 is the total concentra-

20 9/2014

tion of heavy particles (atoms and ions) of shield-ing gas, and will consider the distribution of thefraction of heavy metal particles γ in arc columnplasma for two variants of distribution of evapo-rating anode surface temperature, which corre-spond to Ta0 = 2600 K (Figure 3, a) and Ta0 == 3065 K (Figure 3, b). At 2500—2600 K tem-perature of molten anode metal, evaporated met-al particles appear above its surface, their contentreaching 10 % (see Figure 3, a). At increase oftemperature in the center of the region of arcanode binding above 3000 K, mass flow of vapourfrom anode surface into arc column increases,that results in formation of a region of arc plasmawith high (up to 80 %) content of metal vapour(Figure 3, b).

Field of concentration of evaporated metalparticles nm in near-anode plasma forms as a re-sult of interaction of the following four factors:diffusion and convective transfer of metal parti-cles from anode surface into arc column; arcplasma flow with low content of metal vapour,moving over the anode; transfer of metal vapourparticles towards the anode due to thermodiffu-sion; drift of charged metal particles (single- anddouble-charged ions) in the electric field. Distri-bution of the fraction of heavy iron particles inthe considered arc plasma, presented in Figure3, is the result of competing interaction of theabove-mentioned four transfer mechanisms. Twocharacteristic features of evaporated metal par-ticle distribution in near-anode plasma can besingled out. On the one hand, convective flowof plasma from near-cathode region of the col-umn, containing practically no metal vapour, istrying to oust metal vapours from evaporationzone in the radial direction. As a result, widthof near-surface plasma layer, containing a notice-able quantity of metal vapour (γ > 3 %), turnsout to be 1.5—2 times greater than the radius ofmolten zone on anode surface, and thickness of

this layer is 0.3—0.5 mm. As thickness of theregion taken up by vapour is small compared toarc length, influence of evaporated metal in theconsidered case is limited to just near-anode re-gion of the arc and practically does not affectthe processes of heat, mass and charge transferin it is column. At the same time, region of near-anode plasma, the most enriched in iron vapours,turns out to be «cut off» from the anode surface.This effect can be explained as follows. Ionizationcomposition of metal vapour, which comes tonear-anode region of arc column and is furtheron transported into the region with higher plasmatemperature, undergoes changes due to intensiveionization of metal atoms. On the other hand,because of low diffusion mobility of metal ions,they accumulate in the above region, that is ex-actly what causes formation of a zone of maxi-mum content of metal vapour, localized at a cer-tain distance from anode surface.

Diffusion evaporation of anode metal has thegreatest influence on such characteristics of ano-de region of the considered arc as fraction of iron

Figure 2. Temperature distribution of anode surface in theregion of arc anode binding (here and in Figures 4—7: 1 –Ta0 = 2400 K; 2 – 2700; 3 – 3000; 4 – 3065; 5 – water-cooled (nonevaporating) anode)

Figure 3. Distribution of fraction of heavy iron particles in near-anode region of arc plasma column: a – Ta0 = 2600 K;b – 3065

9/2014 21

particles in near-anode plasma γa(r) = γ(r, L)and its temperature Tpa(r) = T(r, L), electriccurrent density ja(r) and heat flow density qa(r)on anode surface. Let us consider the influenceof temperature on evaporating anode surface ondistribution of the above characteristics in theregion of anode binding of the arc. Figures 4—7give the results of calculations of γa, Tpa, ja andqa for different thermal states of anode surface.

Maximum content of metal vapour is reachedon the axis of near-anode plasma layer, increasingwith temperature rise on anode surface in thecenter of the region of arc anode binding (seeFigure 4). Here, maximum value of average massvelocity of vapour motion |Wz(0, L)| near anodesurface also rises at increase of the above tem-perature. So, for instance, at Ta0 = 3065 K thisvelocity can reach more than 10 m/s. Such in-tensive flow of relatively cold vapour, movingfrom anode surface into arc column, causes localfreezing of near-anode plasma. This effect is mani-fested in that part of anode region, which is lo-

cated above the most heated zone of molten anodemetal surface, and the more so, the higher thesurface temperature in this zone (see Figure 5).

Despite the fact that increase of concentrationof easily ionized (compared to argon) metal va-pour in multicomponent plasma with Ta0 riseshould lead to increase of its electric conductivityσ, the above-noted effect of local freezing of near-anode plasma by vapour flow has a more signifi-cant role, leading to lowering of σ and of electriccurrent density in near-axis zone of the region ofarc anode binding, respectively (see Figure 6).

Density of heat flow, applied by the arc toevaporating anode, behaves in a similar fashion(see Figure 7). Considerable lowering of qa valueat high values of anode metal surface temperatureis related to reduction of convective energy flowfrom arc column, as a result of respective vari-ation of gas-dynamic and electromagnetic situ-ation in near-anode region of arc plasma, as wellas reduction of heat flow transported to the anode

Figure 4. Radial distribution of fraction of heavy iron par-ticles in multicomponent near-anode plasma Figure 6. Radial distributions of electric current density on

anode surface

Figure 5. Radial distribution of arc column plasma tem-perature on the interface with anode region

Figure 7. Radial distributions of density of heat flow appliedby the arc to the anode

22 9/2014

by charged particles, at the expense of respectivereduction of ja (see Figure 6).

Now let us analyze dependencies of axial val-ues of the considered characteristics on anodesurface temperature in the center of the regionof arc anode binding. Variation of Tpa0 = T(0,L), ja0 = ja(0, L) and qa0 = qa(0, L) with Ta0rise is shown in Figures 8—10. Range of variationof maximum surface temperature of molten anodemetal studied in this work can be conditionallydivided into two intervals: Ta0 < 2400 K – cor-responds to nonevaporating anode; 2400 K << Ta0 < 3100 K – corresponds to diffusion modeof anode metal evaporation. In the first tempera-ture range all the characteristics of arc anoderegion weakly depend on Ta0, whereas in thesecond range an essential lowering of Tpa0 takesplace. As regards ja0 and qa0, they behave non-monotonically (see Figures 9 and 10). Initiallyobserved reduction of electric current density anddensity of heat flow entering the anode on theaxis of the region of arc anode binding is replacedby their certain increase, so that at Ta0 ≈ 2800 Kthese values reach their local maximums. Theirfurther lowering proceeds the faster, the moreintensive is anode metal evaporation. The notedpeculiarity is the most pronounced in the behav-iour of such an integral characteristic of thermalinteraction of arc plasma with anode metal as

complete heat power P applied by the arc (Fi-gure 11).

Dependence of density of heat losses of anodemetal for evaporation in near-axis zone of theregion of the arc anode binding qv0 on its surfacetemperature in this zone is shown in Figure 12.As follows from calculation data given in thisFigure, at Ta0 rise up to 3000 K, the above valuecan be equal to about 25 % of the respective valueof heat flow applied by arc plasma to evaporatinganode (compare Figures 10 and 12), and it shouldbe taken into account at determination of energybalance of its surface.

Figure 8. Dependence of axial value of arc plasma tempera-ture on anode region interface on anode surface temperaturein the center of the region of arc anode binding

Figure 10. Dependence of axial value of density of heatflow to the anode on its surface temperature in the centerof the region of arc anode binding

Figure 9. Dependence of axial value of density of electriccurrent on the anode on its surface temperature in the centerof the region of arc anode binding

Figure 11. Dependence of heat power applied by the arc tothe anode on anode surface temperature in the center of theregion of arc anode binding

Figure 12. Dependence of axial value of density of energylosses for anode metal evaporation on its surface temperaturein the center of the region of arc anode binding

9/2014 23

On the whole, numerical analysis of the in-fluence of diffusion evaporation of anode metalon characteristics of the column and anode regionof the arc with refractory cathode, running ininert gas, which was conducted in this work,leads to the following conclusions:

1. In the case of inert-gas nonconsumable-elec-trode arc welding the influence of evaporatedanode material on characteristics of arc columnplasma is manifested only in thin (just up to0.5 mm) layer adjacent to anode region. As re-gards arc plasma characteristics in the rest of arccolumn, they practically do not change, com-pared to the arc running to water-cooled (noneva-porating) anode.

2. Evaporation of metal being welded leadsto an essential restructuring of spatial distribu-tions of plasma characteristics of anode region ofwelding arc with nonconsumable electrode, aswell as characteristics of its thermal and electro-magnetic interaction with weld pool surface. Inparticular, with increase of melt surface tempera-ture in the center of the region of arc anode bind-ing, density of heat flow applied by the arc tothe item being welded and density of electriccurrent on its surface decrease. Alongside lossesof molten metal energy for evaporation, this leadsto lowering of effectiveness of arc heating of themetal being welded.

1. Murphy, Ant.B. (2010) The effects of metal vapourin arc welding. J. Phys. D: Appl. Phys., 43.

2. Hsu, K.C., Etemadi, K., Pfender, E. (1983) Study ofthe free-burning high-intensity argon arc. J. Appl.Phys., 54(3), 1293—1301.

3. Hsu, K.C., Pfender, E. (1983) Two-temperaturemodeling of the free-burning high-intensity arc.Ibid., 54(8), 4359—4366.

4. Engelsht, V.S., Gurovich, V.Ts., Desyatkov, G.A. etal. (1990) Low-temperature plasma. Vol. 1: Theoryof electric arc column. Novosibirsk: Nauka.

5. Zhu, P., Lowke, J.J., Morrow, R. et al. (1995) Pre-diction of anode temperatures of free burning arcs. J.Phys. D: Appl. Phys., 28, 1369—1376.

6. Jenista, J., Heberlein, J.V.R., Pfender, E. (1997)Numerical model of the anode region of high-currentelectric arcs. IEEE Transact. on Plasma Science,25(5), 883—890.

7. Lowke, J.J., Morrow, R., Haidar, J. (1997) A sim-plified unified theory of arcs and their electrodes. J.Phys. D: Appl. Phys., 30, 2033—2042.

8. Haidar, J. (1999) Non-equilibrium modeling of trans-ferred arcs. Ibid., 32, 263—272.

9. Sansonnets, L., Haidar, J., Lowke, J.J. (2000) Pre-diction of properties of free burning arcs including ef-fects of ambipolar diffusion. Ibid., 33, 148—157.

10. Nishiyama, H., Sawada, T., Takana, H. et al. (2006)Computational simulation of arc melting process withcomplex interactions. ISIJ Int., 46(5), 705—711.

11. Lago, F., Gonzalez, J.J., Freton, P. et al. (2004) Anumerical modeling of an electric arc and its interac-tion with the anode. Pt 1: The two-dimensionalmodel. Ibid., 37, 883—897.

12. Tanaka, M., Yamamoto, K., Tashiro, S. et al. (2008)Metal vapour behaviour in gas tungsten arc thermalplasma during welding. Welding in the World,52(11/12), 82—88.

13. Mougenot, J., Gonzalez, J.J., Freton, P. et al.(2013) Plasma—weld pool interaction in tungsten in-ert-gas configuration. J. Phys. D: Appl. Phys., 46,135—206.

14. Krivtsun, I.V., Demchenko, V.F., Krikent, I.V.(2010) Model of the processes of heat-, mass- andcharge transfer in the anode region and column of thewelding arc with refractory cathode. The PatonWelding J., 6, 2—9.

15. Almeida, R.M.S., Benilov, M.S., Naidis, G.V. (2000)Simulation of the layer of non-equilibrium ionization ina high-pressure argon plasma with multiply-chargedions. J. Phys. D: Appl. Phys., 33, 960—967.

16. Krivtsun, I.V., Krikent, I.V., Demchenko, V.F.(2013) Modelling of dynamic characteristics of apulsed arc with refractory cathode. The Paton Weld-ing J., 7, 13—23.

17. Krikent, I.V., Krivtsun, I.V., Demchenko, V.F.(2012) Modelling of processes of heat-, mass- andelectric transfer in column and anode region of arcwith refractory cathode. Ibid., 3, 2—6.

18. Krivtsun, I.V., Porytsky, P., Demchenko, V. et al.(2010) On the application of the theory ofLorentzian plasma to calculation of transport proper-ties of multicomponent arc plasmas. Europ. Phys. J.D, 57, 77—85.

Received 17.04.2014

24 9/2014

EFFECT OF ELECTRIC PARAMETERSOF ARC SURFACING USING FLUX-CORED WIRE

ON PROCESS STABILITYAND BASE METAL PENETRATION

Yu.N. LANKIN, I.A. RYABTSEV, V.G. SOLOVIOV, Ya.P. CHERNYAK and V.A. ZHDANOVE.O. Paton Electric Welding Institute, NASU

11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

Effect of electric parameters of arc surfacing using self-shielding flux-cored wires on process stability andbase metal penetration was investigated. The experiments were carried out with computer registration ofelectric parameters of surfacing. The results of oscillogram processing were used for plotting of Iw and Uwdiagrams with outlined areas of stable process of surfacing, short circuits and arc extinctions. Coefficientof process instability γ was derived from received real parameters of arc surfacing using flux-cored wire. Itis determined that voltage has the largest effect on stability indices and its rise improves process stability.Effect of modes of surfacing on penetration and portion of base metal in the deposited metal was investigated.3D chart was plotted on estimation results. An area of optimum modes, providing sufficient stability ofthe process at minimum penetration and good formation of deposited beads, is outlined. 4 Ref., 2 Tables,7 Figures.

Keywo r d s : arc surfacing, flux-cored wire, stabilityof surfacing process, instability coefficient, base metalpenetration, portion of base metal

Necessary composition of the deposited metal inmultilayer arc surfacing can be obtained only inthe third or fourth layer [1] due to its mixingwith the base metal. Five layers as minimumshould be surfaced, if machining of part is nec-essary after surfacing. The problem becomes morecomplicated due to the fact that rise of thicknessof the deposited layer promotes for growth ofresidual shearing stresses and, simultaneously,increases the possibility of appearance in the de-posited layer of different type defects, which re-duce its service properties, including fatigue lifeunder cyclic loading [2, 3]. Thus, one of the mostimportant characteristics for surfacing is a por-tion of base metal (PBM) in the deposited metalproportional to base metal penetration otherthings equal. Reduction of the base metal pene-tration not only decreases consumption of expen-sive consumables, but improves quality and serv-ice properties of the parts to be surfaced.

Aim of the present work is a study of effectof electric parameters of flux-cored arc surfacing,in particular, stability of these indices on char-acteristics of the base metal penetration.

Consumables and equipment. Self-shieldingflux-cored wire PP-AN130 was used for investi-gations. It provides for production of surfacedmetal of tool steel 25Kh5FMS type. Gas-slag-

forming system of the flux-cored wire, whichwould provide the best welding-technologicalproperties, was preliminary selected. Four self-shielding flux-cored wires PP-AN130 of 2 mmdiameter having different systems of gas-slag-forming components, namely СаO + TiO2 +MgO + CaF2 + Al2O3 (wire with reference des-ignation PP-AN130-1); СаO + MgO + CaF2 +Al2O3 (PP-AN130-2); СаO + CaF2 + Al2O3 (PP-AN130-3); СаO + CaF2 + Al2O3 + starch (PP-AN130-4), were manufactured for this purpose.

Expert estimation (5 examiners) of the weld-ing-technological properties of all four wire types(nature of metal transfer, slag coating of thedeposited beads, presence of pores) was carriedout. The following system of the expert estima-tions was used for that. The transfer was markedby the following digits, namely 1 – fine-drop;2 – globular; 3 – mixed; level of slag coatingwas estimated in percents; porosity – using two-point system: pores are present (yes) or absent(no). The preference was given to fine-drop trans-fer, 100 % slag coating of the deposited beadsand absence of pores in the deposited metal.

Surfacing of the specimens was carried outusing 230—250 A current and 20 m/h rate. Volt-age has the key effect on pore formation in flux-cored wire surfacing [4], therefore it was variedfrom 24 V and higher up to pore formation inthe deposited metal for each type of flux-coredwire (Table 1).

© Yu.N. LANKIN, I.A. RYABTSEV, V.G. SOLOVIOV, Ya.P. CHERNYAK and V.A. ZHDANOV, 2014

9/2014 25

According to expert estimation flux-coredwire PP-AN130-1 has the best welding-techno-logical properties and it was selected for furtherexperiments.

AD-231 automatic surfacing machine withVDU 506 rectifier was used for surfacing experi-ments. Surfacing was made on sheets from steelSt.3 of 15 mm thickness. Surfacing current andvoltage were registered with the help of computerdata measurement system. Instrument shunt75ShS-450-05 was used as a primary measuringwelding current converter, and resistor devider10:1 was applied for voltage determination.Measuring voltage converter L-Card E14-440with imbedded 14-row 16-channel AD converterhaving conversion frequency up to 440 kHz wasused for digitization and enter of data of primaryconverters in the computer. Registration of theparameters in our experiments was performed at20 kHz frequency, which is sufficient enough foraccurate study of high-rate processes in the arc,

for example, arc gap short-circuiting. Figure 1and Table 2 provide for current and voltage os-cillograms of surfacing at different modes usingself-shielding flux-cored wire PP-AN130-1.

Data processing was carried out using spe-cially-designed software in Visual Studio.NET,PowerGraph3.3 and MATLAB 7 media. Currentcondition of process being studied (arc ignition,arc extinction, short circuiting of arc gap, periodof arcing) is automatically identified on data en-tered in the computer, and parameters of currentand voltage for corresponding condition of sur-facing process are calculated.

Results. A full-factorial experiment was car-ried out in order to determine the effect of sur-facing current and voltage on process instabilityand PBM in the deposited metal. Current andvoltage (factors) were varied at three levels, thatgive the possibility to construct a second-ordermodel, providing more adequate description ofthe process being studied. The currents were setat 200, 250 and 300 A levels, voltage – at 22,24 and 26 V. Surfacing rate in all cases was con-stant and made 20 m/h. Table 2 gives measuredand calculated process parameters.

3D diagrams of distribution of Uw and Iw jointprobability density only for surfacing processwithout period of initial arc ignition are shownin Figure 2. Probability p of appearance of spe-cific combination of current and voltage in cor-responding section of (Iw—Uw) plane is plottedalong the vertical axis. The areas of arcing andshort circuiting are outlined on the diagrams.Since arc extinctions in surfacing are rare andtheir duration is short, the probability density isalso very small and being indistinguishable onthe diagrams.

Figure 2 and Table 2 show that rise of arcvoltage promotes for process stabilizing, i.e. num-ber and duration of short circuits and arc extinc-tions is reduced. Short circuits and arc extinc-tions are virtually absent at 26 V voltage. How-ever, appearance of pores in the deposited metalis shown with rise of voltage and, respectively,

Figure 1. Oscillograms of current and voltage in surfacing using PP-AN130-1 flux-cored wire at different modes: a—c –experiments 2, 5 and 8, respectively, according to Table 2

Table 1. Results of estimation of welding-technological proper-ties of flux-cored wires of PP-AN130 type

Designation offlux-cored wire

Voltage, VSlag

coating, %Presenceof pores

Characterof

transfer,point

PP-AN130-1 24 100 No 3

28 100 Same 3

32 100 Yes 2

PP-AN130-2 24 100 No 3

28 80 Yes 3

32 60 Same 2

PP-AN130-3 24 100 No 3

28 100 Same 3

32 80 Yes 2

PP-AN130-4 24 90 No 1

28 90 Same 3

32 90 » 3

34 90 » 3

36 90 Yes 3

26 9/2014

arc length in self-shielding flux-cored wire sur-facing.

Coefficient of instability γ was used for esti-mation of instability of process of flux-cored arcsurfacing:

γ = [V(Ua) + V(Ia)]ta +[V(Ush.c) + V(Ish.c)]tsh.c + texNex.

(1)

It is the sum of coefficients of variation ofarcing current and voltage, coefficients of vari-ations of current and voltage of arc gap shortcircuiting, number of arc extinctions multipliedby weight coefficients. Specific durations of arc-ing, arc gap short circuiting and arc extinctions

were taken as weight coefficients (for designa-tions see Table 2).

Dependence of instability coefficient of sur-facing process on current and voltage was re-ceived on formula (1) and data from Table 2 ina form of regression second-order model. Figure 3shows geometric representation of this model (re-sponse surface). Lines of constant value of insta-bility coefficient (lines of equi-response) are alsoshown in (Iw—Uw) plane. The minimum numberof arc extinctions and short circuits is observedat 25 V voltage. The coefficient of instability γlies in the ranges from 0.50 to 0.32 and arcing ismore stable at this current and voltage, changing

Table 2. Parameters of process of arc surfacing using self-shielding flux-cored wire PP-AN130-1

ParameterNumber of experiment

1 2 3 4 5 6 7 8 9

Uw, V 22.4 21.8 20.8 23.7 24.8 23.5 25.3 24.4 26

V(Uw) 0.50 0.32 0.68 0.22 0.31 0.19 0.17 0.18 0.11

Iw, A 188 256.7 293.7 181.9 243.5 288.1 193.5 241.2 277.9

V(Iw) 0.54 0.45 0.69 0.39 0.35 0.31 0.29 0.27 0.22

Ia, A 174.5 239.4 235.3 175.4 241.1 280.7 190.4 237.8 277.2

V(Ia) 0.41 0.37 0.48 0.32 0.30 0.26 0.25 0.25 0.22

Ua, V 23.6 23.3 23.7 24.6 24.9 24.1 25.7 24.8 26.1

V(Ua) 0.17 0.15 0.21 0.12 0.15 0.12 0.11 0.13 0.10

Ish.c, A 369.5 433.5 528.8 325 493.4 485.3 328.5 385.6 435.4

V(Ish.c) 0.39 0.33 0.27 0.37 0.34 0.28 0.36 0.32 0.29

Ush.c, V 6.6 6.2 9.2 4.6 7.9 6.7 5.5 6.1 7.3

V(Ush.c) 0.61 0.44 0.40 0.41 0.49 0.37 0.69 0.38 0.33

ta, % 90.76 90.81 77.23 95.62 97.59 96.40 97.70 97.65 99.57

tsh.c, % 6.60 8.94 19.57 4.38 1 3.60 2.30 2.28 0.43

tex, % 2.60 0.25 3.20 0 1.41 0 0 0.07 0

Fsh.c, Hz 13.29 19.25 13.75 14.58 2.49 8.21 9.91 8.38 1.99

Tig, s 0 0 0.45 0 0.83 0 0 0 0

Tw, s 42.33 41.12 43.85 39.98 41.41 41.51 40.13 39.99 42.03

Nex 10 3 21 0 6 0 0 1 0

Nsh.c.ig 1 1 5 1 7 1 1 1 1

γ, rel. un. 1.03 0.607 1.78 0.47 0.59 0.41 0.38 0.39 0.32

g0, % 34.75 24.10 20.60 39.10 30.20 330 42.35 29.10 33.10

Note. Uw, Iw – average values of voltage and current during surfacing; V(Uw), V(Iw) – coefficients of variation of voltage and currentduring surfacing, where coefficient of variation is the relationship of root-mean-square value of parameter to its average value; Ia, Ua, V(Ia),V(Ua) – average values of current, voltage, coefficient of current and voltage variation during arcing (without periods of initial arc excita-tion); Ish.c, Ush.c, V(Ish.c), V(Ush.c) – average values of current, voltage, coefficient of current and voltage variation during arc gap shortcircuiting (without periods of initial arc excitation); ta – specific duration of arcing, equal total duration of periods of arcing and totaltime of welding without period of arc ignition; tsh.c – specific duration of short circuits, equal total duration of periods of short circuits andtotal time of welding without arc ignition period; tex – specific duration of arc extinctions, equal relationship of total duration of periodsof arc extinction to total duration of surfacing; Fsh.c – frequency of arc gap short circuiting without period of arc ignition; Tig, Tw – dura-tion of time of initial arc excitation and total duration of surfacing; Nsh.s.ig – quantity of short circuits during the period of initial arc exci-tation; Nex – number of extinctions during Tw; γ – coefficient of process instability; g0 – PBM in deposited metal.

9/2014 27

in the ranges from 200—300 A. The coefficient ofinstability rises up to 0.9—1.0 in voltage reductionto 22 V and at the same currents.

Specimens deposited using the modes givenabove were also used for investigation of effectof surfacing modes on penetration and PBM inthe deposited metal. As an example, Figure 4shows the appearance of beads, deposited usingdifferent currents at 22 V and 20 m/h, and Fi-gure 5 represents transverse macrosections ofthese beads.

Cutting of all specimens across the depositedbeads was carried out after surfacing. Eightmacrosections were manufactured from eachspecimen. They were used for determination ofaverage from eight measurements of PMB in thedeposited metal g0 (see Table 2).

The calculation was carried out on expression

g0 = F0

F0 + Fd 100 %, (2)

where F0 is the cross-section of molten base met-al; Fd is the cross-section of deposited metal.

Regression equitation of g0 dependence on cur-rent and voltage was received as for instabilitycoefficient. Figure 6 shows respective response

Figure 4. Appearance of beads deposited by flux-cored wirePP-AN130-1 at 200 (a), 250 (b) and 300 (c) A, 22 V and20 m/h

Figure 2. Distribution of joint probability density of sur-facing current and arc voltage calculated for oscillogramsin Figure 1

Figure 3. Dependence of coefficient of instability of arcprocess on surfacing current and arc voltage in surfacingusing self-shielding flux-cored wire PP-AN130-1

Figure 5. Macrosections of beads deposited using flux-coredwire PP-AN130-1 at different voltages, 250 A (a), and dif-ferent currents, 24 V (b)

28 9/2014

surface. Tendency to PBM decrease is observedin rise of surfacing current. It is related with thefact that the increase of surfacing current is di-rectly connected with the rise of wire feed rate.This increases quantity of the deposited metalper unit of weld length at constant rate of sur-facing. Rise of voltage from 22 to 24 V resultsin some increase of g0 index at all values of sur-facing current. However, this index does notchange at further increase of voltage up to 26 V.

Relationship between quality of depositedbead formation, PBM in the deposited metal andindices of stability of surfacing process were alsoestimated. Figure 7 gives the combined 2D sec-tions of the response surface for instability coef-ficient and PBM in the deposited metal. Area ofoptimum modes, providing sufficient process sta-bility at minimum penetration and good forma-tion of the deposited beads, is outlined by greycolor. This area includes such modes of surfacingof specific part, selecting of which to the utmostfulfill conditions of its operation, structure ofpart and requirements to the deposited metal. Inparticular, if structure of the part requires sur-facing of layers of large thickness in severalpasses, then more intensive mode of surfacingwith sufficiently large penetration in the firstpass can be selected. Surfacing of thin layer re-quires using the modes from area of surfacingprocess minimum stability with large bridging ofthe neighbor beads.

Conclusions

1. It is determined that wire having СаO + TiO2 +MgO + CaF2 + Al2O3 gas-slag-forming systemhas the best welding-technological propertiesamong the experimental self-shielding flux-corewires of PP-AN130-1 type.

2. Instability of arcing depends, first of all,on voltage and reduces with its rise. Coefficientof instability reaches the minimum at 25 V inthe carried experiments with use of self-shieldingflux-cored wire of 2 mm diameter. Current hassignificantly smaller effect on arcing instability.The minimum instability coefficient for indicatedwire is observed at 250—260 A.

3. Area of optimum surfacing modes, provid-ing sufficient stability of the process (γ = 0.32—0.80) at satisfactory penetration (g0 = 23—30 %),lies in 230—270 A current and 22—24 V voltagechange range.

1. Frumin, I.I. (1961) Automatic electric arc surfacing.Kharkov: Metallurgizdat.

2. Ryabtsev, I.A., Kondratiev, I.A., Babinets, A.A. etal. (2012) Effect of high-temperature thermal cyclingon deposited metal of the type of heat-resistant diesteels. The Paton Welding J., 2, 22—24.

3. Senchenkov, I.K., Chervinko, O.P., Ryabtsev, I.A.et al. (2013) Determination of service resource of sur-faced parts under cyclic, thermal and mechanic loads.Svarochn. Proizvodstvo, 1, 8—3.

4. Yuzvenko, Yu.A., Kirilyuk, G.A. (1973) Surfacingwith flux-cored wire. Moscow: Mashinostroenie.

Received 06.03.2014

Figure 6. Dependence of PBM in the deposited metal oncurrent and arc voltage

Figure 7. Contour curves of instability coefficient of arcingand PBM in the deposited metal

9/2014 29

JOINING OF THICK METALBY MULTIPASS ELECTROSLAG WELDING

K.A. YUSHCHENKO1, S.M. KOZULIN1, I.I. LYCHKO1 and M.G. KOZULIN2

1E.O. Paton Electric Welding Institute, NASU11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

2Toliatti State University14 Belorusskaya Str., Toliatti, RF. E-mail: office@tetsu.ru

Nonstandard schemes of ESW (multi-layer, well-like etc.) are mostly used for reconstruction repair oflarge-sized parts of heavy machine building. Through-thickness cracks are the most often type of fractureand they take place mainly in heavy-loaded machine parts being operated under alternating load. Suchdefects differ by large branching and twisting of the cracks as well as impressive sizes of fracture sections(2.5—6.8)⋅105 mm2. A method of muptipass consumable nozzle electroslag welding (MCNESW) is the mostappropriate for performance of repair works. Science-based combination of developed technical and tech-nological approaches in MCNESW realizing provides for weld metal with high ductility, homogeneousstructure and hardness, absence of hardening structures in HAZ and defects in fusion zone. The method ofrepair of large through-thickness cracks in large-sized parts directly at operation site is successfully imple-mented at six enterprises. Technical scheme, workup level and versatile of technological process of MCNESWperformance allows also recommending it for joining of thick metal during production of new welded metalstructures. 16 Ref., 4 Figures.

Keywo r d s : multipass electroslag welding, consum-able nozzle, repair, large-sized parts, through-thicknesscracks

Single-pass electroslag welding (ESW) is mostlycarried out by three main means, i.e. wire elec-trodes, consumable nozzle and large-section elec-trodes. These means can be used for productionof virtually all existing types of butt, fillet andtee-welded joints, obtaining at that longitudinaland circumferential welds as well as welds ofcomplex profile [1]. Elements of the weldedjoints are classified on shape of weld longitudinalsection according to GOST 15164—95 and DSTU3490—96. Surfaces of edges being welded, form-ing an assembly gap, are produced by machining,flame and plasma cutting as well as after rolling.Efficiency of application of single-pass ESW inmanufacture of new large-sized metal structuresis provided by correct selection of welding equip-ment and complex solving of issues of techniqueand technology of weld performance.

Refining of structure of the welded joint metaland reduction of the level of residual stressesrequire application of a postweld expensive high-temperature treatment (HTT). Therefore, anydecision on rejection or, at least, decrease of vol-umes of its application, is always a priority [2].

One of the ways of approaching of full-strength joint to base metal without HTT is per-formance of ESW using the schemes differing

from traditional ones, for example, by means ofjoining of thick metal with the help of multilayerwelds [3—5]. Efficiency of ESW application injoining of bi-metal billets rises, if the joint iswelded by two welds in sequence [6].

Nonstandard schemes of ESW are mostly usedfor reconstruction repair of the large-sized partsof heavy-machine building, including, directlyat operation site. Work [7] generalizes accumu-lated scientific-production experience of organ-izing and performance of such works and tech-nological recommendations, used by correspond-ing engineering services of many enterprises andorganizations, are proposed.

Mineral resource industry, metallurgy, powerengineering and other branches have a variety ofdifferent large-sized parts in the units, fracturedduring operation. This requires realizing of indi-vidual approach in organizing of repair work foreach specific case. It can be caused, first of all,by geometry parameters and spatial position ofa fracture place as well as technical supply ofworking place and conditions of repair.

This work is dedicated to generalization of theresults of testing, development and implementa-tion of effective techniques of ESW repair of thethrough-thickness cracks, appearing mainly inheavy-loaded machine parts. The typical exampleof such objects are the solid rectangular and pro-filed cross-section bearing bands of rotary kilns,

© K.A. YUSHCHENKO, S.M. KOZULIN, I.I. LYCHKO and M.G. KOZULIN, 2014

30 9/2014

which often fracture in operation due to through-thickness cracks [8]. Most of the bands, cross-section sizes of which make (355—500) × (900—1350) mm, are manufactured from medium-carb-on steels of 35L type using traditional casting insand molds or electroslag casting (steel 34L-ESh). Peculiarity of repair of such defects is re-lated to significant extent with large branchingand twisting of the cracks as well as impressivesize of fracture sections (Figure 1), area of whichcan make (2.5—6.8)⋅105 mm2. At that, the widegaps, 2—5 times exciding standard ones, are in-evitably formed after welding edge preparationand volume of the removed defective metal canmake 0.3—0.4 m3. Rough oxidized surface of theedges (after removal of damaged metal by oxygencutting) creates new difficulties for providing ofquality fusion during ESW.

Methods of repair of through-thickness cracksin the bands at operation site using electric-arcmethods of welding differ by extremely low ef-ficiency and do not always provide the qualitywelded joints as well as required occupationalhygiene conditions [8]. Application of ESW tra-ditional methods is also ineffective due to largeexpenditure of time for delivery of large-sizedwelding equipment, complexity of assembly andoperation of multielectrode machines at greatheight (more than 20 m), and impossibility toreceive guaranteed fusion of base metal edgeswith the weld in the beginning of welding, etc.

Application of some untraditional ESW me-thods [8—10] is complicated, mainly, due to im-possibility of complete removal of the defect,having branching (spatial) character, providingof guaranteed fusion of edges being welded andlow hot crack formation resistance of the welds.

Development of repair method to the maxi-mum free of indicated disadvantages was neces-sary for solving of the issues of organizing of

on-line repair of equipment with the through-thickness fractures at operation site.

In the best way these requirements are ful-filled by the method of muptipass consumablenozzle electroslag welding (MCNESW) (Fi-gure 2) [11].

Metallurgical, energy and technical issues, re-lated with specifics of reconstruction works, wereinvestigated for development of MCNESW prin-ciple technology.

The following was determined as the results:• mechanisms of defect-free formation of

welded joint in a wide gap;• conditions of guaranteed fusion and quality

formation of weld;• energy peculiarities of process from point of

view of its stability and absence of defects inwelded joints;

• conditions for prevention hot cracks inwelds;

• effect of process thermal cycle on structureand mechanical properties of welded joint metal.

Figure 1. Scheme of typical positioning of crack in fracturedband of rotary kiln

Figure 2. Scheme of the method of multipass ESW of big parts with large cross-section of elements being joined: 1 –part being welded; 2 – forming inserts; 3 – electrode wire; 4 – consumable nozzle; 5 – water-cooled device; 6 –hopper; 7 – welds; 8 – slag pool; 9 – metal pool; 10 – deposited metal; S – thickness of metal being welded; B –welding gap

9/2014 31

Required depth of base metal penetration andwidth of melting of forming insert for real gapsof 60—150 mm, formed in area of occurrence ofthe through-thickness crack after removal of de-fective metal, are provided at values of weldingprocess specific energy in the range of 220—340 kJ/cm2.

Technological strength of welded joint metalis provided by set of measures, preventing hotcrack formation [12, 13, 14], namely:

• reduction of weld metal shrinkage due toperformance of multisection permanent joint byseparate welds;

• positioning of weld plane in direction beingin close agreement with tensile stress vector;

• reduction of level of tensile stresses in theperiod of solidification of metal pool due to flexi-bility of assembly separating inserts;

• selection of parameters of welding mode foreach pass with weld shape coefficient in 5—8range;

• distribution of stress field density by meansof symmetric welding-up of separate sections ofthe assembly.

This process is characterized by such a typeof welding thermal cycle, at which cooling ratesof HAZ metal are very low (0.2—0.8 °C/s), andtime of staying of cooling metal in the range ofthe lowest stability of austenite is so long thatconditions for HAZ structure formation can beconsidered closed to equilibrium [15].

Combination of welding wires of general des-ignation with increased manganese content (forexample, Sv-08G2 and Sv-10G2) and fused fluxesof SiO2—MnO—CaF2 system (AN-8M and AN-9U)during MCNESW of cast carbon steels of 35Ltype provides for required mechanical propertiesunder conditions that material of assembly form-ing inserts will contain not less than 1 % Mn atlow content of carbon and make 28—38 wt.% fromthe deposited weld metal (Figure 3).

Sufficient strength of reconstructed metal ofthe welded joints in heavily-loaded assemblies ofthe structures from medium-carbon cast steels of35L type under conditions of static and impactloading as well as high long-term strength atalternating load are provided [15] due to highductility of weld metal, homogeniety of its struc-ture and hardness, absence of hardening struc-tures in HAZ and defects in the fusion zone (Fi-gure 4).

Technology for repair of the parts of uniqueequipment without its disassembly and special-ized welding equipment [16] were currently de-veloped using new MCNESW method. The tech-nology was realized in repair of the through-thickness cracks of bands of rotary kilns at sixenterprises. Experience of many years of opera-tion of the reconstructed bands showed that long-term strength of the welded joints, produced byMCNESW under conditions of alternating loads,makes not less than 107 cycles. Application ofthe developed technology in repair of thethrough-thickness cracks in bands of rotary kilnsallowed 3 times reduction of the total time of

Figure 3. Portion of insert metal in composition of weld metal in MCNESW of the first (central) pass (a) and adjacentpasses (b): 1 – base metal; 2 – electrode wires; 3 – metal of inserts; 4 – plate of consumable nozzle; 5 – metal ofadjacent weld

Figure 4. Transverse macrosection (a) and sulphur print(b) of 480 mm thick welded joint produced by newMCNESW method

32 9/2014

repair works in comparison with repair usingautomatic submerged twin-arc welding.

Conclusions

1. MCNESW is the efficient method of repair ofthe through-thickness coarse cracks in large-sizedparts, immediately at operation site, that is in-dicated by results of its successful implementa-tion at six enterprises.

2. Science-based combination of the developedtechnologies and techniques during realizing ofMCNESW provides for high ductility of weldmetal, homogeneity of its structure and hardness,absence of hardening structures in HAZ and de-fects in fusion zone.

3. Versatile of technological process and pro-cedure of MCNESW allows also recommendingit for joining of thick metal in production of newwelded metal structures.

1. (1980) Electroslag welding and surfacing. Ed. byB.E. Paton. Moscow: Mashinostroenie.

2. Paton, B.E. (1971) Some predictions on welding de-velopment. Avtomatich. Svarka, 5.

3. (1959) Electroslag welding. Ed. by B.E. Paton.Moscow; Kiev.

4. Anders, W., Maushake, W. Verfahren zumVerschweissen von Groessen Querschnitten mittelsElektroschlackeschweissung. Veroeff. 06.10.61.

5. Khoruzhik, G.I., Sushchuk-Slyusarenko, I.I., Andri-anov, G.G. et al. Forming device for vertical weld-

ing. USSR author’s cert. 284224. Int. Cl. B 23 K25/00. Fil. 22.01.78. Regist. 21.03.80.

6. Sushchuk-Slyusarenko, I.I., Lychko, I.I., Khrundzhe,V.M. et al. Forming device for vertical welding.USSR author’s cert. 747659. Regist. 23.01.78.

7. Sushchuk-Slyusarenko, I.I., Lychko, I.I., Kozulin,M.G. et al. (1989) Electroslag welding and surfac-ing in repair works. Kiev: Naukova Dumka.

8. Kozulin, S.M., Lychko, I.I., Kozulin, M.G. (2007)Methods of reconditioning rotary kilns (Review).The Paton Welding J., 10, 33—39.

9. Sushchuk-Slyusarenko, I.I. (1977) Electroslag weld-ing and surfacing. Vol. 9. Moskow: Svarka.

10. Filchenkov, D.I., Kozulin, M.G., Sushchuk-Slyusa-renko, I.I. (1982) Repair of defects of cast productsfrom 30GSL steel by multilayer electroslag welding.Svarochn. Proizvodstvo, 9, 19—20.

11. Kozulin, M.G., Kozulin, S.M. (1992) Method ofmultilayer electroslag welding. USSR author’s cert.1756074. Int. Cl. B23K 25/00. 33/00.

12. Kozulin, S.M. (2011) Selection of the groove shapefor repair of through cracks by multilayer electroslagwelding. The Paton Welding J., 3, 32—35.

13. Kozulin, S.M., Lychko, I.I., Kozulin, M.G. (2010)Increase of resistance of welds to formation of crys-talline cracks in repair of bands of kiln furnaces us-ing electroslag welding. Ibid., 1, 32—34.

14. Kozulin, S.M., Lychko, I.I. (2011) Deformations ofwelded joints in multilayer electroslag welding.Ibid., 1, 23—27.

15. Kozulin, S.M., Lychko, I.I., Podyma, G.S. (2013)Structure and properties of steel 35L welded jointsproduced using multilayer electroslag welding. Ibid.,8, 7—12.

16. Yushchenko, K.A., Lychko, I.I., Kozulin, S.M. et al.(2012) Portable apparatus for consumable-nozzleelectroslag welding. Ibid., 8, 45—46.

Received 14.07.2014

9/2014 33

PECULIARITIES OF APPLICATIONOF SUPERCAPACITORS IN DEVICES

FOR PULSE WELDING TECHNOLOGIES

A.E. KOROTYNSKY, N.P. DRACHENKO and V.A. SHAPKAE.O. Paton Electric Welding Institute, NASU

11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

The prospective areas of application of supercapacitors (SC) are resistance spot welding, resistance buttwelding as well as pulse-arc welding, where they can be used as slope controllers. Main technical charac-teristics of SC and bank of SC (BSC), based on series connection of separate SC, are given. Provided arethe main calculation relationships, designed for evaluation of electric parameters of BSC, charge-dischargecharacteristics for developed BSC are experimentally determined. It is shown that the main disadvantageof series connection of SC cells in the bank is a voltage spread, which is proposed to be eliminated inpresent work by means of application of special charging device – equalizer. Different schemes of equalizersare considered, their advantages and disadvantages when using in pulse current generators are described.Relevance of application of energy-saving scheme of equalizer for pulse welding methods is shown. Schemeof such a device is proposed and described and calculation relationships providing analytical descriptionof its operation are presented. A scheme for resistance spot welding, based on equalizer and bank of 6 SCis given as an example and technical characteristics of the proposed device are presented. 7 Ref., 1 Table,6 Figures.

Keywo r d s : pulse welding, pulse current generators,slope controllers, supercapacitor, bank of supercapaci-tors, charge-discharge characteristics, equalizer

Application of electric pulse energy storages isextremely efficient in some welding processes.This, first of all, refers to resistance spot welding[1], resistance butt welding [2], stud welding

[3] as well as gas-shielded pulse-arc welding [4],where they are used as pulse slope controllers.The authors of present work have positive expe-rience of application of capacitor storages in arccutting, where pulse effect, in contrast to air-arccutting, is created by current pulse, that allowssignificant equipment simplification.

Simplicity of switching of bank of capacitorsduring charge and discharge and possibility ofstrict dosing of accumulated energy due to regu-lation of level of charge voltage or duration ofpulse effect are to be referred to significant ad-vantages of the capacitor storages, that expandstheir application in pulse technologies. Capacitorbanks, based on cells with double-electriclayer – supercapacitors (SC) – find more andmore application at present time as capacitor stor-ages. Still, SC cells are connected in the banksfor receiving of necessary electric characteristicsof the storages due to low level of operating volt-age of SC cell (USC ≤ 2.7 V). However, there arespecific difficulties in manufacture of the bankswith series SC (BSC) because of technologicalspread of capacity values of SC in the ranges ofone nominal. Figure 1 shows the examples of per-formance of such BSC for 4 and 6 cells.

Account must be taken of CΣ(n) = Ci/n,UΣ(n) = nUi (where Ci is the capacity of separateSC; Ui is its operating voltage) in calculation ofenergy, accumulated in series BSC. Hence, itfollows according to known formulae that energy

Figure 1. Examples of assembly of series BSC based on 4(a) and 6 (b) cells

© A.E. KOROTYNSKY, N.P. DRACHENKO and V.A. SHAPKA, 2014

34 9/2014

W(n) = CΣ(n)(UΣ(n))

2

2 =

nCiUi2

2 = nWi.

Technical characteristics of applied SC aregiven in the Table.

Voltage is usually non-uniformly distributedin the cell during operation of such banks and itwill be in inverse proportion to the values ofcapacity in circuit of series capacitors: U1C1 == U2C2 = U3C3 = UnCn. Therefore, factor of non-uniform distribution of voltages in the circuit ofseries SC should be taken into account in charg-ing of such a bank and stop charging process afterachievement of maximum voltage UCi = UC maxby any of capacitors. At that total voltage at ca-pacitor bank will be lower than nominal one: Ub ≤≤ nUC max = Ub max or ΔUb max = Ub max — Ub.

Experimental investigations of voltage spreadin BSC cells in the process of test operation werecarried out at test bench, scheme of which isshown in Figure 2. Obtained test results wereused for plotting of histograms of distribution ofvoltage in BSC cells (Figure 3), consisting of 10series SC of VSAR3000 R270 K05 type. Resultsof investigation of SC behavior in mode of long-term storage of electric charge are given in Fi-gure 4. Obtained experimental data showed thatseries connection of power SC provides for prob-lems, related with undercharging of separate ele-ments of BSC, that reduces to significant extentenergy efficiency of pulse generator.

This work is dedicated to elimination of giveneffect and, thus, increase of energy efficiency ofpulse generators, made using SC.

Preliminary selection of SC on values of ca-pacity and assembly of banks from SC cells withsimilar capacity are carried out in order to provideequal voltage at cells and Ub = Ub max in chargeof bank of series SC. However, some charge ofcapacity of SC cells is possible in process of SCoperation, that can result in not always uniformdistribution of voltages in BSC cells (see Fi-gure 3). At present time, the equalizer type de-vices are used for voltage adjustment at BSCcells for the purpose of more efficient applicationof energy properties of SC in the course of the

whole guaranteed period of operation. There aredifferent types of equalizers, i.e. passive dissipa-tive [5], active dissipative [6] and active energy-saving [7].

Designing of systems for SC recharging usingthe active energy-saving equalizers is proposed

Characteristics of SC used for series BSC

BSC typeQuantity of cells

C, FR,

μOhmτ = RC,

sUop, V W, J

BSC-4 4 750 0.96 0.72 10.8 43,740

BSC-6 6 500 1.44 0.72 16.2 65,610

BSC-10* 10 300 2.44 0.72 27 109,350

*BSC-10 is the structure with series BSC-4 and BSC-6.

Figure 3. Histograms of distribution of voltages in cells1—10 of charged (a) and uncharged (b) BSC at differentquantity of charge—discharge operating cycles

Figure 2. Scheme of experimental bench for verification ofBSC: K1, K2 – switching units; C1—C10 – capacitor cells

9/2014 35

for consideration due to modern requirements toecology of energy systems and energy-saving.

Principle of their work is based on applicationof BSC cell energy-exchanging processes, at thatthe cells with increased voltage are used for re-charging of the cells with reduced one. Uniformdistribution of voltages in the circuit, virtuallyfor the whole voltage operating range of thebank, is maintained in BSC as a result of workof such a system in the process of energy exchangebetween the cells. Earlier similar hardware means[6, 7] were used in operation of power lithium-ionbanks in different mobile and aerospace devices.The lithium-ion banks are very similar to BSC

in some characteristics (for example, they arecharacterized by directly proportional depend-ence of voltage in cell on charge level), thereforethe similar approaches to equalizers can be usedfor BSC. The example of such adapted equalizerscheme applicable to SC is shown in Figure 5.

The scheme includes a charging supply unit(CSU), designed for formation of BSC chargecurrent from primary mains, series supercapaci-tors SC1—SCn, where their quantity is deter-mined by the requirements to load supply.Scheme of active equalizer is based on matchingtransformers Tr1—Tr(n + 1) and electronic powerswitches T1—Tn. Diodes D1—Dn are integratedin a structure of crystal of electronic powerswitch. Drivers Dr1—Drn are designed for match-ing of switch drive circuits T1—Tn with regula-tion scheme. Regulation scheme of master oscil-lator (MO) is performed on standard two-phasePWM controller, at that output of the first phaseF1 is connected to uneven, and the second F2 toeven switchers of the scheme. High-frequencyinverter (Inv) is designed for parallel supply ofmatching transformers for adjustment of voltagebetween even and uneven groups of cells. In proc-

ess of device operation the capacitorbank is charged from CSU or dis-charged into load (L). If voltages atall capacitors are equal, voltage UW2 i == USC i/2 — ΔUVT i (where ΔUVT i isthe overbalance voltage) is supplied tosecondary windings W2.1—W2(n ++ 1) of matching transformers Tr1—Tr(n + 1). Voltage at secondary wind-ings of the transformers is determinedfrom UW2 i ≈ UBSC/2n condition,when voltage at the primary windingsUW1 i = UBSC.

If voltage at any of the capacitorsis more or less than average one (USC

av ≠ UBSC/n), then equalizing currentsstart to flow through windings of Tr1—Tr(n + 1) and open switches T1—Tn,resulting in voltage balancing at thecapacitors. Matching inverter operatessynchronously with switching of T1—Tn switches and in turn carries out re-charging of even and uneven groups ofcapacitors, thus balancing voltages be-tween the groups. Operation of thescheme results in balancing of voltagesat SC cells and reduction of values ofequalizing currents to the minimum.Currents in primary windings of thetransformers are reduced to the valuesdetermined by losses of transformer

Figure 4. Self-charging of bank from 10 series SC

Figure 5. Scheme of BSC equalizer (see designations in the text)

36 9/2014

open-circuit. Balancing of voltages at BSC cellsis carried out exactly in such a way.

The peculiarity of this device (see Figure 5),making it different from described in work [7],is application of separate sections of matchingtransformers for each SC cell as well as replace-ment of the diodes for synchronous rectifiers(field-controlled transistor), that providedhigher rate and accuracy of voltage balancing.

Compare energy parameters of BSC in use ofscheme of active equalizer (see Figure 5).

Energy, accumulated in BSC with series ca-pacitor cells, is determined by the expression

EBSC = nC0U0

2

2, (1)

where n is the quantity of cells; C0 is the nominalcapacity; U0 is the nominal voltage.

If BSC has a capacitor cell with reduced ca-pacity

Ci = kC0, (2)

(where k < 1 is the coefficient of underchargingof separate cell), charged to nominal voltageUCi = U0, then voltage at remaining cells withnominal voltage will equal

Ux = kU0(kC0U0 = C0Ux). (3)

It follows from this that sum voltage at sucha bank with series cells

UBSC = U0k(n — 1) + U0 = U0(1 + k(n — 1)). (4)

Energy, accumulated by BSC, including onecapacitor cell with reduced capacity, will equal

EBSC′ =

CBSC′ Uop

′

2 =

= C0

k1 + k(n — 1)

[U0k(n — 1) + U0]2

2 =

= C0U0

2k(1 + k(n — 1))

2.

(5)

Energy accumulated in BSC in use of equal-izer, balancing the voltage at capacitor cells, is

EBSC′′ =

CBSC′′ Uop

′′2

2 =

C0 k

1 + k(n — 1) (nU0)

2

2 =

= C0U0

2

2

kn2

1 + k(n — 1).

(6)

Comparative analysis of energy efficiency ofequalizer application can be carried out with thehelp of given expressions (4)—(6). If coefficientof efficiency of BSC with similar cells is takenfor Kef = 1, then efficiency of BSC with cell,having reduced capacity, will be determined byrelationship

Kef1 = EBSC′EBSC

= kC0U0

2[1 + k(n — 1)]

nC0U02

=

= k2(n —1) + k

n,

(7)

and efficiency of BSC with equalizer and cell,having reduced capacity, is

Kef2 = EBSC′′

EBSC =

kn2

1 + k(n — 1)n

= kn

1 + k(n — 1). (8)

Therefore, fractional increase of BSC effi-ciency with equalizer will be determined by re-lationship

Q = 1 — Kef1

Kef2 = 1 —

⎛⎜⎝k(n — 1) + 1

n

⎞⎟⎠

2

. (9)

Use of given calculation relationship (7)—(9)for estimation of energy efficiency of the equal-izer allows proving that significant effect is notedeven at 10 % deviation of capacity of only onecapacitor from nominal value.

It is necessary to outline that application ofequalizers in different devices for pulse weldingtechnologies allows reaching not only high en-ergy indices, but providing high stability of weld-

Figure 6. Example of application of equalizer in resistance spot welding device

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ing-technological indices due to precision BSCcharging.

Figure 6 as an example shows a scheme ofdevice for resistance spot welding. Its main dif-ference from known devices [1] is presence of theequalizer. Inverter of charging current afterswitching of electric supply provides charging ofcapacitors SC1 and SC6 to a level of voltage,determined by controller, after what the schemeis transformed in a waiting mode. Simultane-ously, the equalizer scheme analyzes balancingof voltages in SC cells and, if necessary, carriesout active balancing of voltages in BSC cells.«Start» command blocks the operation of charg-ing inverter and regulation pulse is supplied todriver of current switch T. As a result, emergenceof pulse of operating current, flowing along cir-cuit: SC1—SC6, T, Lfeed, Rfeed, CS, SC1—SC6, isobserved. Welding device allows dosing of en-ergy, supplied to contact gap by means of pro-gramming of SC1—SC6 voltage and duration ofcurrent pulse, determined by switching unit. Du-ration of current pulse can be varied in the rangesfrom units to several hundred milliseconds. Also,series of pulses with individual parameters foreach pulse in the series is possible. Information,received from current and voltage sensors CS andVS2, is used for control and regulation of energy,supplied to the contact gap of part being welded.High technological indices in given device areachieved due to application of high-speed electroncurrent switching unit, which carries out accuratedosing of energy, supplied to welding zone.

Experimental check of the device for resis-tance spot welding, assembled on given scheme(see Figure 6), provides for the following results:maximum welding current equals 1200 A; con-sumed energy makes 2 VA in open-circuit mode,500 VA in BSC charge mode and 100 VA in weld-ing mode at supply from single-phase mains220 V. Smoothly regulated duration of weldingcurrent pulse is at the level of 0.01÷0.5 s.

In practice the SC cells should be connectedin the banks for receiving of necessary and ac-

ceptable load resistance of the capacitor storage.Quantity of series cells in such a bank determinesits operating voltage, and number of parallelbranches is defined by its maximum operatingcurrent and efficiency, that should be consideredin BSC designing. Due to the fact that SC hassome internal loss resistance R0, energy accumu-lated in it during discharge is released for loadresistance Rl as well as R0. Obviously that thehigher R0 in relation to Rl, the lower is the levelof loss in SC and, as a result, the lower is thelevel of energy-conversion efficiency in load dur-ing its operation. Clearly that it is necessary tobe assumed in BSC use. Moreover, it is desirableto consider not only the effect of bank and itsweight-dimension indices, but environment re-quirements of electrical consumers as well aseconomy criterion, determined among other bycost of electric energy and operation expenses,for designing of current welding equipment andother technological equipment using BSC as en-ergy storage.

1. Paton, B.E., Korotynsky, A.E., Drachenko, N.P. etal. (2009) Application of supercapacitors for increasethe power efficiency of devices for spot resistancewelding. In: Proc. of Int. Sci.-Pract. Conf. onPower- and Resources-Saving in Industry, PowerEngineering and Transport (Kiev, 2009), 54—58.

2. Kuchuk-Yatsenko, S.I., Lebedev, V.K. (1976) Con-tinuous flash-butt welding. Kiev: Naukova Dumka.

3. Paton, B.E., Drachenko, M.P., Kaleko, D.M. et al.Apparatus for stud welding. Pat. 92389 Ukraine.Int. Cl. B 23 K 9/20. Publ. 25.10.2010.

4. Korotynsky, A.E. (2002) State-of-the-art, tendenciesand prospects of development of high-frequencywelding converters (Review). The Paton Welding J.,7, 44—47.

5. Shurygina, V. (2003) Supercapacitors as the helpersor competitors to battery power sources. Electronics:science, technology, business, Vol. 3, 20—24.

6. Cizov, M. (2003) Device for voltage rectification onelements of supercapacitor bank. Sovr. Elektronika,1, 40—43.

7. Eremenko, V., Vorontsov, K., Varlamov, D. (2007)Hardware methods of increase in power efficiency ofhigh-voltage accumularor bank. Elektr. Kompo-nenty – Ukraina, 7/8, 62—66.

Received 21.10.2013

38 9/2014

AUTOMATIC MACHINE FOR WET UNDERWATERWELDING IN CONFINED SPACES*

V.A. LEBEDEV1, S.Yu. MAKSIMOV1, V.G. PICHAK1 and D.I. ZAJNULIN2

1E.O. Paton Electric Welding Institute, NASU11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

2Greenfield Energy Ltd, Great Britain

PWI developed technology and equipment allowing performance of automatic flux-cored wire wet under-water welding of structural elements, reliably insulating the lower part of heat exchanger column. Theunique aspect of the work consists in development of an automatic welding machine, capable of operatingwhen immersed into a pipe of 119 mm inner diameter into liquid heat carrier medium at 200 m depth. Thesemiautomatic machine was designed with application of special torque electric drives for electrode wirefeed and welding displacement mechanisms. A special cable with welding and control wires was developed,capable of operating at a large distance from the arc power sources and control system. Cable uncoilerdesign was also developed, with digital recording of automatic machine position along the pipe length.Approbation results showed that application of special automatic machine allows increasing heat exchangerreliability, reducing time loss during performance of work on its sealing, rational use of site area andreducing financial expenses. 5 Ref., 8 Figures.

Keywo r d s : wet arc welding, geothermal heat ex-changers, sealing, automatic machine, power source, ca-ble uncoiler, control system

Process of mechanized wet arc welding, equip-ment and flux-cored wire for its implementationwere proposed at PWI [1] and are currently beingdeveloped in different spheres. This is repair ofships and vessels, underwater product lines, portunderwater facilities, etc [2, 3].

One of the new objects of effective applicationof wet welding are complexes of Greenfield En-ergy Ltd Company – technology developer andoperator of power efficient GeoscartTM com-plexes, combining such systems for satisfyingproduction needs as closed-loop heating systems,systems of treatment of consumed hot water forproduction purposes, refrigeration units and airconditioning systems.

GeostartTM system was developed to controlheat flows of public and commercial buildingsand enterprises with continuous high-density en-ergy consumption such as modern supermarkets,higher class hotel business enterprises, stationaryhospital complexes, as well as satisfying produc-tion needs of food and pharmacological industry.One of the main functional features of Geos-cartTM system is the ability to store excess ther-mal energy up to the moment of this energy defi-cit. Company uses geothermal heat exchangers

of a special design for fast and efficient transferof excess or deficit of low-grade thermal energy,using high density and heat capacity of forma-tions located much lower the surface soils. Stand-ard depths for the main transaction of heat-ex-change process are the ranges down to 200 mfrom ground surface level.

At construction of heat exchangers, the quan-tity of which can reach several tens, dependingon facility size, principles similar to methods ap-plied in oil and gas well drilling, but with certaindifferences in construction technology, are used.In particular, closed-loop heat exchangers re-quire guaranteed insulation of the lower part ofinsulation column, in order to avoid losses ofexpensive heat-conducting working liquid, pro-duced from a composition of nonpolluting pro-pylene glycols, extracted from the plant mass.Used for these purposes are plugs of a specialdesign, made from organic uncured rubber. Op-eration experience of these heat exchangers, how-ever, showed that natural ageing of plug materialin service results in a change of its dimensions,and leakage of its working fluid. Mounting a newplug requires shutting down the complex. Con-sidering that heat exchangers are usually locatedin the territory of vehicle parking areas near theserviced facility, this operation leads to signifi-cant financial losses, in addition to losses of op-

© V.A. LEBEDEV, S.Yu. MAKSIMOV, V.G. PICHAK and D.I. ZAJNULIN, 2014

*V.K. Zyakhor, I.S. Kuzmin, V.G. Novgorodsky, N.A. Poddubny and I.V. Lendel participated in the work.

9/2014 39

eration effectiveness at lowering of liquid level.As an alternative, PWI proposed a process ofheat exchanger tube sealing by placing and weld-ing-on a cap.

The objective of this work was developmentand introduction of a special automatic weldingmachine and its application technology for weld-ing-on the plug-cap inside the pipe at down to200 m depths, that will allow shortening timelosses, lowering financial expenses, reducing lossof useful area, and improving heat exchanger re-liability.

Pipe neck design and conditions of work per-formance are shown in Figure 1.

Conditions and environment of welding per-formance predetermine the complexity of theproblem being addressed both in terms of equip-ment and technology. Development was basedon PWI experience on designing mechanizedequipment for wet welding with application ofspecial flux-cored electrode wires. However,rather great welding depths, extremely confinedconditions (pipe inner diameter is not more than120 mm), as well as the medium (25 % watersolution of polyethylene glycol) required a largescope of additional research both on individualcomponents of welding equipment, and on weld-ing technology and welding consumables, as ex-perience of equipment design and its applicationin the automatic welding mode for these condi-tions is lacking either at PWI or in the worldpractice.

Development of the automatic machine properfor cap welding-on at great depth is just part ofthe complex, which should include welding cur-rent source of a special design (remoteness ofwelding site with inevitable voltage drop in thecable), special load-carrying cable with powerconductors and control wires, as well as a devicefor automatic machine lowering and lifting. Theentire equipment set and its application condi-tions are shown in Figure 2.

Algorithm of welding performance envisagesthat the cap of a special design to be welded onis placed into the automatic welding machineclamp before immersion, and is disengaged fromit after welding and beginning of automatic ma-chine lifting.

Considering that none of the complex compo-nents without exception could be selected fromcommercially manufactured equipment, featuresof their development and design are of interest.

Let us consider ADSP-200 automatic machinefor wet welding at great depth in a confinedspace. The automatic machine is a tubular metalstructure, combining the following main compo-

Figure 1. Heat exchanger pipe neck and external conditionsof work performance

Figure 2. Complex of equipment for automatic weldinginside the pipe at great depth

40 9/2014

nents: module of electrode wire feed, module ofwelding head rotation (of feed mechanism), mod-ule of contact components. Feed module and ro-tation module are based on gearless computerizedDC electric drives incorporated into commuta-torless electric motors with bevel drive to feedroller. Feed module consists of the device of elec-trode wire pressing down, nozzle with guidechannel and current-conducting tip. Module fur-ther includes nozzle oscillator, as well as the as-sembly of cap fixing with fixation force regulatorfor guaranteed disengagement of the cap fromthe automatic machine after the welding cycle,as well as sliding contact component of weldingvoltage current transfer (return wire «—»). Ad-dition of nozzle oscillator to the module is dueto presence of quite large gaps between the capbeing welded-on and pipe inner surface, on theone hand, and impossibility of essentially increas-ing the welding modes, because of the possibleoverheating of automatic machine componentsand pipe wall burn-through. The guide channel,accommodating the electrode wire stock requiredfor a single welding cycle, is made of plastic witha low coefficient of friction. Channel length is15—18 m. Considering the confined conditions,electrode wire is not wound on the spool, as itis usually done, but is in the straightened state.Two effects are achieved here: space saving forautomatic machine systems, and essential reduc-tion of feeding force. To provide protection fromthe liquid medium, feed mechanism electric mo-tor is placed into a water-tight box filled withinsulating-lubricating fluid and having a com-pensating diaphragm, as well as special sealedconnector for control cable connection.

Main difficulties in development of automaticwelding machine ADSP-200 consisted in selec-tion of layout solutions in an extremely confinedspace, with performance of a large scope of ex-perimental studies, with development of weldingequipment mock-ups and simulation of weldingconditions. This enabled effective solution of theproblem of development of nozzle oscillator ofan ingenious design, where the drive is combinedwith electrode wire feed drive and, as a result,increase of the required moment on drive electricmotor shaft. The impossibility of mounting sen-sors of nozzle position relative to the butt beingwelded determined the search for engineering so-lutions in two directions. Before the automaticmachine lifting the nozzle is oriented by the fu-ture gap relative to the cap fixed in the clamp.The start and end of welding is possible from anypoint and is pre-programmed by controller-basedcontrol system of rotation module, with analysis

of path covered by nozzle, and then the operationof weld closing by automatic machine is per-formed by a similar algorithm.

Figure 3 shows the ADSP-200 automatic weld-ing machine in the position before immersion forwelding.

The complexity of the task of connecting andsealing the welding cables and control wiresshould be noted. The great length predeterminedthe need to develop engineering solutions fortheir fast connection to automatic machine sys-tems and sealing. This also involves special deep-water connectors, and couplings filled with low-melting dielectrics.

Welding current source of VDU 25-506 MPtype. It is obviously impossible to implement thewelding process with the required characteristicsat considerable distance from the object of weld-ing, by using traditional welding current sourceswith flat external volt-ampere characteristics(VAC). This follows from experimental investi-gations and conclusions of [4]. Source VAC inthe arcing zone changes significantly because ofgreat lengths of welding cables of a limited sec-tion (ohmic resistance of outer circuit rises and,hence, voltage drop in the cable becomes higher).Here, compensation of voltage drop in the outercircuit due to voltage rise, does not yield therequired result. Inductance of source—arc systemchanges noticeably, that has a negative effect onthe nature of arcing and electrode metal transfer.In order to solve these problems, specializedVDU 25-506 MP source for mechanized and auto-matic welding at large distance of feed mecha-nism (of automatic machine) from power sourcewas designed and manufactured, in particular, forwet automatic welding at 200 m depth. Figure 4shows the appearance of VDU 25-506 MP source.

To ensure high quality of welding at applica-tion of various kinds of electrode wire, the sourceenables adjustment of dynamic characteristics toestablish the rate of current rise, required for aspecific wire type. Ability to perform such addi-tional adjustments is ensured through application

Figure 3. Automatic machine for welding in confined con-ditions at great depth: 1 – case; 2 – rotation mechanism;3 – guide channel; 4 – feed mechanism with nozzle os-cillator; 5 – nozzle; 6 – fixtures and elements of currenttransfer to the cap; 7 – cap

9/2014 41

of Moller programmable logic controller (Ger-many). Application of the principle of propor-tional plus integral plus derivative control ofwelding contour dynamics to ensure the requiredpower source characteristics at operation withlong welding cables allows guaranteeing its sta-ble performance in the entire adjustment rangeand repeatability of the selected adjustment pa-rameters.

Cable. As shown by results of experiments onpossibilities of transfer of welding current, con-trol and adjustment signals, the only correct en-gineering solution for operation under confinedconditions is combining all the electric circuits

in one cable, which, in addition to that, shouldalso be carrying, i.e. should be able to supportthe automatic machine weight, its own weight,as well as overcome the hydrostatic resistance ofthe environment at immersion and lifting stages.

Industry lacks cables, capable of satisfyingsuch a set of requirements. It turned out to bepossible to solve the above-defined problems atpurposeful development of a cable, which wasgiven the technical name «Cable flexible armoredstrengthened submersible for electric weldingKGBUPES 2×95+(4×2.5)e+(10×2.5)e» [5].

Cable specification

Design weight of 1 km of cable, kg .......................... 3850Cable outer diameter .............................................. 47.5Tensile force, N ................................ not less than 20,000Minimum radius of inner loop of cable bending inouter cable diameters ............................... not less than 8

It should be noted that all the conductors withrational layout of cores and conductors to ensurereliable insulation and flexibility are made ofcopper. Power and control conductors areshielded. Measuring (with one meter spacing)marks are made on the cable for additional con-trol of the length of its unwinding or winding.Figure 5 shows the cross-section of cable of com-plex design KGBUPES 2×95+(4×2.5)e+(10×2.5)e. Cable strength at considerable tensileforce is ensured by additionally incorporatedflexible enclosing steel elements, including flex-ible armour. Additional strengthening was pro-vided by a large number of mylar filaments ofdifferent diameter. Insulation of each conductorand conductor layer was performed with appli-cation of reliable modern insulating materials,such as PET-E film, folsan, etc., with multiple(3—4 times) overlapping.

Cable uncoiler. Cable uncoiler is designed forstorage, transportation, lifting and lowering ofautomatic welding machine into the pipe to200 m depth and its subsequent removal, and isa drum of lattice-rod design, mounted on rotatordrive shaft. On the other end the shaft is addi-tionally supported by roller support adjustableby its position (backrest). Rotary motion of theshaft with drum with adjustable frequency is pro-vided by variable frequency electric drive withasynchronous electric motor, connected to drumshaft through a reduction gear. Drum design en-visages availability of a special cable box for fastconnection of welding and control cables. Theentire structure of the drum, rotator and rollersupport is mounted on a welded bed.

Uncoiler incorporates its own local system ofcontrol and adjustment, allowing control of boththe direction of drum rotation, and its rotation

Figure 4. Source of welding current for working with remoteobjects

Figure 5. Section of cable for underwater automatic welding

42 9/2014

frequency. For convenience of automatic machineimmersion or lifting, the uncoiler has a remotecontrol panel. More over, uncoiler incorporatesguide roller, ensuring stable advance of the cableinto the pipe to the welding area. The roller isfitted with rubber-bonded bush, ensuring rollerengagement with the cable at its uncoiling. Theroller is also connected to incremental encoder(digital converter of cable movement), ensuringcalculation of length of uncoiled cable (loweredto welding area) with result digitizing. Figure 6shows the considered uncoiler in the position ofautomatic machine readiness for immersion.

Main technical characteristics of cable uncoilerMinimum drum diameter, mm ................................... 100Nominal rotation frequency, rpm ............................ 0.267Range of rotation frequency adjustment .................... 1:10Nominal moment, N⋅m .......................................... 40095

System of control and adjustment of automa-tic machine ADSP-200. The system is designedfor adjustment control of direction of rotation ofelectric motors of electrode wire feed and rotationmechanisms, setting the rates of wire feed andwelding displacement (feed mechanism rota-tion). System of control and adjustment is basedon welding cycle control module, several ofwhich can be used and which differ by the methodof arc excitation and weld crater welding up.The model is based on a programmable controller.This system further includes modules of control-lerized control of automatic machine electric mo-tors with the possibility of setting and monitoringtheir shaft rotation frequencies, as well as weld-ing cycle control. Each of the modules is fittedwith its own power stabilizer block. All theabove-mentioned is installed on a special control

Figure 6. Appearance of cable uncoiler Figure 7. Appearance of control panel of ADSP-200 auto-matic machine

Figure 8. Results of welding the cap to pipe inner surface: a – circumferential weld with overlapping; b – actual gapbetween the cap and pipe; c – welded joint shape

9/2014 43

panel with sealing elements (Figure 7). The samepanel separately accommodates matching equip-ment, for instance, decoupling relays for remotecontrol of welding current source. Front controlpanel carries signaling devices, elements for pro-tection from overloads and short-circuit currents,control and adjustment elements, as well as dialmonitoring instruments. Connection with the ob-jects of control is provided through a number ofconnectors.

For testing and adjustment of both individualcomponents of ADSP-200 automatic machine,and the complex as a whole, PWI developed aspecialized facility, where basic technology wasoptimized. Deep-water technological experi-ments were performed in a special pressure cham-ber. Some test results are shown in Figure 8.Note that the welding cycle consists of two stages:cap fixing with application of the arc processpreventing rotation of automatic machine withthe cap relative to the pipe, and welding per-formance around the contour of the fixed capwith weld overlapping.

The complex has passed production trials atGFE facility (London). Obtained results showedthat application of special automatic welding ma-chine allows heat exchanger reliability to be in-creased, time losses for performance of work for

its sealing to be reduced, site area to be rationallyused and financial losses to be reduced.

Conclusions

1. Technology and equipment are proposed, allow-ing performance of flux-cored wire wet automaticarc welding of structural elements, reliably insu-lating the lower part of heat exchanger column.

2. Automatic welding machine has been de-signed, which is capable of operation when im-mersed into a pipe of 119 mm inner diameter intoliquid heat carrier at 200 m depth.

1. Savich, I.M., Smolyarko, V.B., Kamyshev, M.A.(1976) Technology and equipment for semiautomaticunderwater welding of metal structures.Neftepromysl. Stroitelstvo, 1, 10—11.

2. Kononenko, V.Ya., Rybchenkov, A.G. (1994) Expe-rience of wet mechanized welding with self-shieldedflux-cored wires in underwater repair of gas-and-oilpipelines. Avtomatich. Svarka, 9/10, 29—32.

3. Kononenko, V.Ya., Gritsaj, P.M. (1994) Mechanizedwet welding in repair of ship hulls. Morskoj Flot,11/12, 21—22.

4. Lebedev, V.K., Uzilevsky, Yu.A., Savich, I.M. et al.(1980) Analysis of possibility of self-adjustment sys-tem compensating typical disturbances of arc lengthin mechanized underwater welding. In: Underwaterwelding and cutting of metals, 10—23. Kiev: PWI.

5. Martinovich, V.N., Martinovich, N.P., Lebedev,V.A. et al. (2010) High-quality hose packs for under-water welding and cutting. The Paton Welding J.,9, 33—35.

Received 02.04.2014

44 9/2014

SANITARY-HYGIENIC EVALUATION OF NOISEIN MANUAL ARC WELDING

WITH COVERED ELECTRODES

O.G. LEVCHENKO1, V.A. KULESHOV1 and A.Yu. ARLAMOV2

1E.O. Paton Electric Welding Institute, NASU11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua

2NTUU «Kiev Polytechnic Institute»6/2 Dashavskaya Str., 03056, Kiev, Ukraine

Presented are the results of measurements of noise characteristics at working place at the distance of 0.55 mfrom welding arc using covered electrodes designed for welding carbon and low-alloyed steels. It wasestablished that the equivalent level of sound is 83—86 dBA, and the maximum level does not exceed93 dBA. It is shown that in welding with covered electrodes the noise level is linearly increased withincrease of welding current, here the noise at the working place is mainly contributed by welding process,and the noise from current generator and ventilation equipment is in the ranges of measurements error. Thedata are given, which can be used for sanitary-hygienic evaluation of noise level at the working place indefinite processes of arc welding. 13 Ref., 7 Tables, 1 Figure.

Keywo r d s : electric arc welding, steel, electrodesMR-3, UONI-13/55, ANO-4, ANO-12, ANO-36, noiselevel, sanitary-hygienic evaluation

Welding and allied technologies remain thesources of many dangerous and harmful industrialfactors, including an acoustic noise [1, 2]. Fromthe psycho-physiological and social-economicalpoint of view the noise is any kind of sound,harmful for health, interfering the reception ofuseful signals and reducing the labor efficiencyof a human [3]. In the structure of professionaldeceases this kind of «noise decease» as deafnesstogether with deceases of breathing organs, lo-comotor apparatus and with vibration deceasecompose the main group of deceases of industrialworkers [4].

Among the 80 welding technologies in accord-ance with ISO 857-1:1998 [5] the excessive noiseexceeding the limiting allowable level (LAL) [6]is typical of many welding processes. Thus,among methods of fusion welding the gas, laser,plasma and electric arc welding, magnetic-pulsed, percussion, ultrasonic and explosion weld-ing from methods of pressure welding, and resis-tance welding from combined welding are distin-guished. However, in the national publications thequantitative data about acoustic noise in weldingproduction, as a rule, are not given [1].

The aim of the present work was the investi-gation of noise environment at the working placeduring manual arc welding with covered elec-trodes (MR-3, UONI-13/55, ANO-4, ANO-12,

ANO-36), designed for welding carbon and low-alloyed steels.

Methods of investigation. The levels of noisewere determined in the process of manual surfac-ing with 4 mm diameter electrodes, having dif-ferent types of coatings (Table 1), on St.3 steelplate, arranged on welding table at the operatinglocal exhaust ventilation of 1700 m3/h efficiencyand 2 kW power. Welding rectifier VDU-506was used as a power source. Distance from theplace of arcing to the nearest wall was not lessthan 0.5 m. The working place of a welder wasat the distance of 0.55 m from welding arc.

The noise parameters were measured by inte-grating meter of noise level of the first class ofaccuracy (Bruel&Kjaer noise meter of 2230model), the functional and technical charac-teristics of which are in compliance with the re-quirements of the interstate standards (GOST17187—2010) of CIS countries [7]. Noise meterhas a verification certificate and allows deter-mining the noise characteristics of up to 1 dBaccuracy.

Table 1. Characteristics of electrodes applied for determinationof level of noise in manual surfacing

Grade Type of coating Iw, A

MR-3 Rutile 140—220

UONI-13/55 Basic 130—160

ANO-4 Rutile 140—210

ANO-12 Basic 140—210

ANO-36 Rutile-cellulose 130—180

© O.G. LEVCHENKO, V.A. KULESHOV and A.Yu. ARLAMOV, 2014

9/2014 45

The measurements and sanitary-hygienicevaluation of noise at the working place werecarried out in accordance with the requirementsof GOST 12.1.003—83, GOST 12.1.050—86 andDSN 3.3.6.037—99 [8—10]. Duration of measure-ment was equal to duration of electrodes burning(about 60 s). Each measurement was three timesrepeated. As a component of technological noisethe noise generated by the current generator andequipment of air ventilation was taken. Measu-rement of background noise, generated by aux-iliary equipment, was made before the beginningof electric arc surfacing process. At all the meas-urements the noise levels with a frequency cor-rection A (dBA), required for finding the tem-porary nature of noise and carrying out of sani-tary-hygienic evaluation, were recorded [6]: theequivalent level of sound Leq, maximum Lop maxand minimum Lop min levels of sound pressure.

Results of investigations. The measured lev-els of background and technological sound at theworking place of operators are given in Tables 2and 3. Surfacing with each type of electrode wasmade at current almost at the level of maximumallowable welding current (see Table 3).

Let us apply the obtained results for evalu-ation of noise in welding L. The recorded noiseis composed of noise Lw, generated by arc weldingprocess, and background noise Lb, generated byoperation of auxiliary equipment. By using theprinciple of additivity of power flows in the point

of measurement [11], the measuring level of noisecan be determined as

L = Lw + 10 lg (1 + 10Lb — Lw/10). (1)

If Lw — Lb ≥ 10, then L ≈ Lw, as the additionis not more than 0.4 dB and commeasurable withthe error of measurements. It follows from theanalysis of obtained data (see Tables 2 and 3)that this condition is fulfilled for all the meas-urements. Consequently, the contribution ofbackground noise can be neglected and the meas-uring noise as a welding one should be considered.

Let us determine the accuracy of obtained re-sults [12]. The best estimate of measurements Nof the same value L is equal to their averagevalue:

L__

= ∑ i = 1

N

Li/N.

It can be expected that the true meaning ofmeasuring value lies in the ranges of L

__ ± δL

__. The

full error consists of instrumental or systematicerror of noise meter δLinstr = ±1 dBA and randomcomponent of error δL

__r whose source, in the first

turn, is the non-uniformity of the technologicalwelding process. The random error is equal tothe error of mean value:

δL__

r = σL__ =

σL

√⎯⎯N,

where the standard or mean-square deviation ofsingle measurement is equal to

σL = √⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯1N — 1

∑ i = 1

N

(Li — L__)2 .

Then the full error shall be

δL__

= √⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ ⎯(δLinstr )2 + (δL

__

r)2 .

By assuming that L = Leq and L = Lop max weshall find the values of appropriate errors for thedata given in Table 3 (Tables 4 and 5).

Table 2. Level of background noise at the working place ofwelder at the distance of 0.55 m from the arc

Parameters of noise, dBA

Leq Lop max Lop min

Number of measurements

1 2 3 1 2 3 1 2 3

69.1 69.1 69.2 78.4 78.7 78.9 66.9 66.8 66.5

Table 3. Level of technological noise at the working place of welder at the distance of 0.55 m from the arc during surfacing usingelectrodes of different grades

Grade ofelectrode

Iw, A

Parameters of noise, dBA

Leq Lop max Lop min

Number of measurements

1 2 3 1 2 3 1 2 3

MR-3 200 83.1 83.4 82.7 89.6 90.1 89.9 68.3 68.4 67.9

UONI-13/55 150 82.4 82.8 82.4 90.5 90.3 91.9 68.7 69.3 69.0

ANO-4 200 86.0 85.9 86.1 89.3 90.0 90.4 70.2 69.8 70.1

ANO-12 200 84.6 84.2 84.7 92.8 92.7 93.0 69.5 69.5 69.4

ANO-36 170 83.5 83.4 83.2 92.1 89.9 91.9 68.0 67.9 68.1

46 9/2014

It follows from Tables 4 and 5 that the meas-urements error is completely determined by valueof instrumental error and, consequently, the fur-ther increase in number of measurements (morethan 3) will not lead to decrease of full error.As the error is equal to ±1 dBA, the noise levelis presented at an accuracy of up to 1 dBA. Thetotal results of analysis of all the obtained dataare summarized in Table 6.

Let us consider the nature of dependence ofnoise level on welding current within the ranges

of its rated values for electrode MR-3, used inthe widest range of welding current values (seeTable 1). Results of noise measurements at thedistance of 1 m from the arc are given in Table 7.

Using the least squares method [12] the fol-lowing linear relationship between the obtaineddata was found (Figure):

Leq = 0.04Iw + 74.056. (2)

The square of linear correlation value R2 == 0.9705 indicates the high degree of validity of

Table 4. Error in measurements of equivalent level of sound, dBA

Grade of electrode

Measured Leq

L__

δLinstr δL__

r δL__

Error of LeqmeasurementNumber of measurements

1 2 3

MR-3 83.1 83.4 82.7 83.1 1 0.2 1 83 ± 1

UONI-13/55 82.4 82.8 82.4 82.5 1 0.1 1 83 ± 1

ANO-4 86.0 85.9 86.1 86.0 1 0.1 1 86 ± 1

ANO-12 84.6 84.2 84.7 84.5 1 0.2 1 85 ± 1

ANO-36 83.5 83.4 83.2 83.4 1 0.1 1 83 ± 1

Table 5. Error in measurements of maximum level of sound, dBA

Grade of electrode

Lop max

L__

δLinstr δL__

r δL__ Error of

Lop maxmeasurement

Number of measurements

1 2 3

MR-3 89.6 90.1 89.9 89.9 1 0.1 1.0 90 ± 1

UONI-13/55 90.5 90.3 91.9 90.9 1 0.5 1.1 91 ± 1

ANO-4 89.3 90.0 90.4 89.9 1 0.3 1.0 90 ± 1

ANO-12 92.8 92.7 93.0 92.8 1 0.1 1.0 93 ± 1

ANO-36 92.1 92.0 89.9 91.3 1 0.5 1.1 91 ± 1

Table 6. Level of noise at the working place of welder at the distance of 0.55 m from the arc during surfacing using electrodes of dif-ferent grades

Grade of electrode Type of coating Iw, A Is, A Leq, dBA Lop max, dBA

MR-3 Rutile 140—220 200 83 ± 1 90 ± 1

UONI-13/55 Basic 130—160 150 83 ± 1 91 ± 1

ANO-4 Rutile 140—210 200 86 ± 1 90 ± 1

ANO-12 Basic 140—210 200 85 ± 1 93 ± 1

ANO-36 Rutile-cellulose 130—180 170 83 ± 1 91 ± 1

Table 7. Level of noise at the distance of 1 m from the arc in welding using electrodes MR-3 at different welding current

Iw, A

Noise parameters, dBA

Leq Lop max Lop min

Number of measurements

1 2 3 1 2 3 1 2 3

150 79.8 80.3 80.2 85.9 88.9 84.9 73.6 76.4 72.1

180 81.3 81.1 81.1 85.1 85.4 85.8 79.0 78.6 78.4

210 82.7 82.4 82.4 86.0 85.9 85.6 80.3 80.3 80.1

Lb, dBA

68.1 68.0 68.3 73.8 74.6 75.1 66.9 67.5 68.0

9/2014 47

the established linear dependence of noise levelon welding current value. However, it is evidentfrom the results of carried out investigations thatquantitative increase in current strength has anegligible effect on noise level. Thus, the currentincrease by 40 % led to growth of noise level onlyby 2.5 %. It is clear that the level of generatednoise in surfacing with electrodes of other typesand at other distances from the source of noisewill also depend linearly on current value, as thephysical principle of occurrence and spreading ofacoustic noise in arc welding at different modesis one and the same, namely: the noise level isdetermined by the arcing stability.

Sanitary-hygienic evaluation of noise. In ac-cordance with the requirements of GOST12.1.003—83 [8] let us determine the temporarynature of noise and appropriate limits for thelevel of acoustic parameters being examined. Asthe change in sound level during all the meas-urements exceeds 5 dBA (see Tables 2 and 3),the noise at electric arc welding should be clas-sified as non-constant. For the non-constant noisethe LAL are accepted for Leq and Lop max. TheLAL depends on kind of activity with accountfor difficulty and labor intensity. In the givenwork the manual arc welding is regarded as aphysical work connected with accuracy, concen-tration or periodical aural control. For this kindof labor the safe Leq level for personnel during8 h working day should not exceed 80 dBA, andthe maximum sound level at the working placeshould not exceed 110 dBA. As it follows fromthe measured values (see Table 6), the lattercondition is fulfilled, while the noise level ex-ceeds the standard LAL. However, it is not rightto state that the LAL was exceeded [13], as thecomparison should be made at a single time baseequal to 8 h. However, we had a single measure-ment, continued only 1 min. In practice, the proc-esses of surfacing and welding are running withintervals. Moreover, the duration of noise epi-sodes can be much lower than 8 h, and the noise

level here is much higher than 80 dBA. The stand-ards admit operation under the conditions of in-creased (more than 80 dBA noise level), but itsduration should be, respectively, decreased ac-cording to the procedure regulated by GOST12.1.050—86 [9].

Conclusions

1. It was found that electric arc process of weld-ing with covered electrodes mainly contributesto the noise at working place and the contributionof noise generating by current generator and ven-tilation equipment is negligibly low and is in theranges of measurements error.

2. The level of generated noise is growing line-arly with increase of welding current value, butchange of level in the range of rated current val-ues is negligible.

3. The equivalent level of sound is in theranges of 83—86 dBA, and the maximum leveldoes not exceed 93 dBA. The levels of recordednoise exceed officially the LAL (80 dBA) regulatedby the standard documents for this kind of laboractivity at 8 h working shift. However, for thecorrect sanitary-hygienic evaluation it is necessaryto carry out comparison at a single time base.

4. The given data can be used for sanitary-hy-gienic evaluation of noise episodes of definiteprocesses of electric arc welding.

1. Levchenko, O.G. (2010) Labor protection in weldingproduction: Manual. Kyiv: Osnova.

2. Encyclopedia of ILO. Welding and flame cutting.http://base.safework.ru/iloenc

3. Yudin, E.Ya., Borisov, L.A., Gorenshtejn, I.V. et al.(1985) Noise control in production: Refer. Book.Moscow: Mashinostroenie.

4. Kononova, I.G. (2010) Occupational disease of work-ers of machine-building enterprises. Ukr. ZhurnalProblem Med. Pratsi, 21(1), 9—14.

5. ISO 857-1:1998: Welding and allied processes – Vo-cabulary. Pt 1: Metal welding processes. Publ.12.01.98.

6. Levchenko, O.G., Kuleshov, V.A. (2013) In-plantnoise. Pt 1. Svarshchik, 2, 36—41.

7. GOST 17187—2010: Noise dosimeter. Pt 1: Specifica-tions. Introd. 01.11.2012.

8. GOST 12.1.003—83: Safety general requirements. In-trod. 01.07.84.

9. GOST 12.1.050—86: Methods of noise measurementon workplace. Introd. 01.01.87.

10. DSN 3.3.6.037—99: Sanitary codes of in-plant noise,ultrasound and infrasound. Introd. 01.12.99.

11. Grinchenko, V.T., Vovk, Sh.V., Matsipura, V.T.(2007) Principles of acoustics. Kiev: NaukovaDumka.

12. Taylor, J. (1985) Introduction to theory of errors.Moscow: Mir.

13. Levchenko, O.G., Kuleshov, V.A. (2013) In-plantnoise. Pt 2. Svarshchik, 3, 44—48.

Received 17.02.2014

Dependence of noise level on welding current in surfacingwith electrodes MR-3

48 9/2014

The 55th Anniversary of the Experimental Design TechnologicalBureau of the E.O. Paton Electric Welding Institute

In May, 1959 the Experimental Design Bureau(currently the State Enterprise «The Experimen-tal Design Technological Bureau of the E.O. Pa-ton Electric Welding Institute» – PWI EDTB)was founded with the purpose of development ofnew welding equipment and technologies, de-sign-technological provision of research worksand acceleration of implementation of scientificand technical developments into the nationaleconomy. EDTB was founded on the basis ofdevelopments of the design department of theInstitute in prewar, further war and postwartimes. The principle «laboratory—design bureau—pilot production» established by Evgeny O. Pa-ton during foundation of the Institute, was fullyrealized. This close relation with practice, pro-duction, readiness to solve any tasks, put forwardby the national economy, allowed EDTB to par-ticipate efficiently in creation of reliable weldedstructures and implementation of mechanized andautomated welding processes.

Within close cooperation with the PWI sci-entists and specialists, branch institutes andother leading enterprises during 55 years EDTBhas been designing equipment for differentmechanized welding methods, testing of equip-ment and technology of welding, implementingthe completed research developments of the In-stitute into industry. The main attention is paidto the complex mechanization of welding pro-duction, creation of highly-efficient machinesand automated production lines.

The welding machines, developed by theEDTB designers and produced in tens of thou-sands by many plants, were used in such branchesas construction, machine and ship building, pro-

duction of pipes for main pipelines, nuclearpower engineering, etc.

In different periods five Doctors and morethan forty Candidates of Techn. Sci. were work-ing at EDTB. Twenty six works, in which to-gether with the scientists of the Institute theEDTB colleagues were participating, wereawarded with two Lenin Prizes, eight USSRState Prizes, nine Prizes of the Council of Min-isters of the USSR and six Prizes of the Councilof Ministers of the Ukrainian SSR. 29 specialistsof EDTB have a title of laureates of these prizes.Many colleagues of the EDTB were also awardedwith other state prizes.

EDTB during its 55 years of activity washeaded by the following members: Dr. P.I. Sev-bo, a team-mate of E.O. Paton; Profs A.I.Chvertko, V.F. Moshkin, as well as S.I. Pritulaand V.S. Romanyuk. During many yearsDr. Vladimir E. Paton talented designer, workedas the chief of the department and later as the

9/2014 49

EDTB Deputy Chief. At the present time EDTBis headed by G.V. Zhuk.

EDTB carries out works on the following maindirections:

• technology and equipment for arc and resis-tance welding;

• materials, technology and equipment formechanized surfacing and thermal spraying ofwear-resistant materials;

• mechanization and automation of assembly-welding works;

• technology and equipment for welding inbuilding and bridge construction;

• development and manufacture of automatedsystems for ultrasonic and eddy-current control;

• working out of design documentation andmanufacture of non-standard equipment forwelding production;

• complex mechanization and auxiliary equip-ment;

• development and manufacture of control sys-tems for welding and surfacing equipment.

Today the welding equipment, created by theEDTB designers and technologists, is operatingin on-land and underground conditions, in spaceand under water. This equipment is used to per-form most of the technologies in welding, sur-facing and spraying of different steels, cast iron,nonferrous metals, which are known to the mod-ern science.

In close cooperation with the PWI researchdepartments and PWI Pilot Plant of WeldingEquipment, the EDTB designers and technolo-gists in the period of 2000—2013 designed, manu-factured and implemented the equipment forwelding and surfacing of wide range of metalsand alloys. These works were performed on theorders of enterprises and organizations of

Ukraine, the countries of near and far abroadand also order of the NAS of Ukraine and «Gos-informnauka».

EDTB during many years has been closelycooperating with many educational establish-ments of Ukraine, including NTTU «Kiev Poly-technic Institute». The EDTB specialists deliverlectures on welding equipment, conduct practicalclasses, supervise industrial and pre-graduationpractice of students, head the State examinationboards on defense of diploma projects.

In most cases in welding equipment, designedby EDTB, the modern design and technologicalsolutions are applied, which allowed authors toreceive hundreds of author certificates, dozens ofpatents and awards for the participation in na-tional and international exhibitions. The EDTBspecialists published the results of their work inhundreds of information letters and articles inthe journal «Avtomaticheskaya Svarka» andother leading technical journals and, finally, thecatalogue-guidebook «Welding equipment» ineleven volumes, created at EDTB, the first vol-ume of which was published in 1968.

From the day of its foundation up to the pre-sent time the EDTB staff has always been feelingand still feels the continuous and active supportof Prof. Boris E. Paton, Director of the Institute,the President of the National Academy of Sci-ences of Ukraine, who made great contributionto the foundation of EDTB, its formation anddevelopment.

Today EDTB is a mobile friendly team, whereimmense experience of veterans gained duringdecades, maturity of high-skilled specialists ofmiddle-aged generation and thirst for knowledgeof talented youth are closely combined.

G.V. Zhuk, PWI EDTB

50 9/2014

Paton Turbine Technologies –new name of a well-known company

History of emergence of Paton Turbine Technolo-gies Company, which before April 2014 operatedunder the name of Pratt&Whitney-Paton, datesback to the beginning of 1993. This is exactlywhen the E.O. Paton Electric Welding Institute(PWI) of the NAS of Ukraine and Pratt&Whit-ney – Division of United Technologies Corpo-ration (UTC), USA, one of the leading worldmanufacturers of aircraft engines, signed anAgreement on establishing in Kiev a joint ven-ture, which has been successfully operating formore than 20 years in the world market.

This resulted in formation of a modern high-technology company, involved both in depositionof protective coatings on blades for aviation andindustrial gas turbines, and manufacturing ofcommercial EB-PVD equipment, evaporationmaterials, as well as repair of blades and otherparts of various purpose turbines.

Intensive activities of the staff, as well as long-term joint work with our US partners allowedthe company reaching world-class level of pro-

duction, which has been evaluated as «Silver»in ACE system of UTC competitiveness assess-ment that is a quite high mark.

With support and very direct involvement ofPratt&Whitney, the JV has been certified to allthe necessary international standards, that al-lowed it to successfully operate in the worldmarkets of aviation and power gas turbine con-struction.

Company customers include such well-knownnames as Pratt&Whitney (USA), Siemens (Swe-den), Honeywell (USA), Rolls Royce (UK),Turbine Overhaul Services (Singapore), Kawa-saki Heavy Industries (Japan), Permsksie Mo-tory (Russia), Mayer Tools (USA), Glen Group(USA) etc., as well as Ukrainian enterprises op-erating in the field of gas turbine construction,aircraft repair and gas transportation.

In March, 2014 United Technologies Corpo-ration, one of the founders, left Pratt&Whitney-Paton JV, in connection with global change ofits business strategy, which was followed by the

Protective coating shop

9/2014 51

Company changing its name to Paton TurbineTechnologies (PTT). Company sphere of activ-ity, standards and management system, includingquality management system, and customers, re-mained the same.

Quality management system (QMS) is basedon the requirements of international general tech-nical standard ISO 9001, as well as internationalaerospace standard AS9100, which is harmonizedwith EN 9100 and JIS Q 9100 standards. TheCompany is certified as overseas repair stationfor compliance with US Federal Aviation Regu-lations CFR FAR145. Availability of such a cer-tificate allows performance of work on mainte-

nance of aviation equipment, registered in theUSA. Starting from 2006 the Company takes partin the US National Program on accreditation andqualification of processes in the defense and aero-space industries – Nadcap. In July 2014, PTTsuccessfully passed the regular audit on this Pro-gram, that once more confirmed the high inter-national technical level of organization of pro-duction in the Company.

Company personnel are highly-qualifiedworkers, engineers, researchers and office work-ers, who continuously improve their skills andperformance through various courses and trainingprograms. Program of personnel training in keep-

Paton Turbine Technologies Certificates ISO 9001:2008 and AS 9100C-JISQ 9100:2009

Designed and manufactured at Pratt&Whitney-Paton EB unit for deposition of protective coatings on aircraft gas turbineblades at customer facility

52 9/2014

ing with the requirements of US Federal AviationAgency has been introduced and is running inthe Company.

PTT now manufactures products and providesservices with optimum price-quality ratio in thefollowing business segments:

• EB deposition of metal and ceramic coatingson blades of various-purpose gas turbines;

• design, manufacture and servicing of EBequipment for coating deposition;

• production of consumable materials (ceramicand metal ingots) for deposition of EB coatings;

• comprehensive reconditioning of gas turbineengine components with application of classical(welding, brazing, microplasma) and original(EB PVD) repair technologies;

• engineering of processes, materials andequipment.

Thermal barrier coatings of up to 200 μmthickness proposed to customers by PTT are ap-plied by EB PVD of ceramic ingots, mainly ofzirconium dioxide. Coatings have columnarstructure with specified thickness distributionover the cross-section, that ensures excellent per-formance of coatings on turbine parts exposed toboth mechanical and temperature cyclic loads.

It should be noted that achieving the specifieddistribution of coating thickness on turbineblades is a complex engineering problem that issuccessfully solved due to many years of experi-ence of our staff.

The Company developed technology of depo-sition of coatings based also on other oxidesthat appears to be promising for protection ofaircraft turbine parts with increased workingtemperatures.

Application of protective ceramic coating re-quires presence of a bond coat on the part surfacethat ensures both adhesion of thermal barrier ce-ramic layer to part surface, and its protectionfrom the impact of turbine aggressive workingenvironment. Technologies developed in theCompany (surface preparation, heat treatment,EB deposition, etc.) allow deposition of bothonly the ceramic coating on parts, which alreadyhave a bond coat, and of two-layer coating (met-al + ceramic). The most wide-spread combina-tions are bond coat from nickel aluminide (orplatinum), as well as nickel, cobalt and chro-mium alloys, doped by aluminium and yttrium(MCrAlY). Deposition of purely metal protec-tive coatings of various composition is also per-formed.

Procedures of deposition of structural coat-ings, for instance from titanium alloys, to restorethe shape of worn fan blades have been mastered.

In this case, EB PVD technology with ionizationof evaporation metal can be applied that allowsan abrupt increase of coating adhesion to the baseof the parts being reconditioned.

Over many years of working in the market,the Company has acquired experience of coatingdeposition on parts of various types of gas tur-bines, including their aircraft, land and navyvariants. Here are some of them: PW4000, JT9D-7Q, JT9D-7R4, PW4090, CF6-80C2, G61,CFM56-5B, CFM56-7B, GTX100, PS90A,PS90GP, V84.3A2, V94.3A2, etc.

PTT Company can rightfully be regarded asone of the reliable producers of world-class com-mercial EB PVD equipment for deposition ofceramic and metal coatings. Our equipment isrunning successfully in the US and Singapore.We provide servicing of our equipment and sup-ply spares and consumables.

As was noted above, PTT produces high-qual-ity ceramic and metal ingots, which are both used

Typical microstructure of thermal barrier coating

Commercial gas turbine blade with thermal barrier coating

9/2014 53

in its own production, and are supplied to cus-tomers as a separate product.

Ceramic ingots are made by special methodsof compacting oxide powders of the required com-position with subsequent high-temperature sin-tering. The most widely accepted type of mate-rials is zirconium dioxide, partially stabilized byyttrium oxide (ZrO2—6—8 % Y2O3). Manufactur-ing technology ensures ingot density on the levelof 3.6—4.2 g/cm3.

Metal ingots are made by vacuum-inductionmelting with double EB remelting that provideshigh quality of billets for subsequent evaporationin vacuum. Ingot manufacturing to customerspecification is possible.

The Company has been developing technologyand performing repair of components of aircraftand land gas turbine engines stating from 2001.Many years of practical experience of operationand high professional level of personnel, appli-cation of high technologies and unique special-ized equipment, high quality standards and effi-cient management system allow the Company tosatisfy customer requirements to the maximumboth in terms of quality, and in terms of economic

efficiency (terms, volume, price). Nowadays cus-tomers are offered a complete range of repairoperations, including those with application ofEB technology of deposition of high-temperatureMeCrAlY and thermal barrier ZrO2—7 % Y2O3coatings.

Availability of an up-to-date laboratory ofmetallographic examination, directly integratedinto the technological process, equipment andinstruments applied for nondestructive and de-structive testing, in addition to highly qualifiedpersonnel, enables PTT maintaining and devel-oping reliable manufacturing with invariablyhigh product quality. Company laboratory hasbeen certified in the LCS system, applied at UTC,and has confirmed its compliance to the require-ments of Nadcap Program.

One can see from the above-said that PatonTurbine Technologies Company is a reliable part-ner, which successfully operates in Ukraine in com-pliance with the best world business practices.

Prof. G.S. Marinsky,Director of PTT Company

www.patontt.com

Ceramic (left) and metal (right) ingots

54 9/2014