A Training Report On

EXTRUSION PROCESS

Bachelor of Technology

In

MECHANICAL ENGINEERING

Under the Supervision of:- Submitted By:-

Mr. S.K.Arora Aditya Singh

(Asst. Manager) B.Tech. 4th year

Mechanical Eng.

1116440010

ACKNOWLEDGEMENT

I have a great pleasure in expressing my deep sense of gratitude

indebtedness to my training supervisor and co-ordinator,Mr. S.K. Arora for hisinspiring guidance, invaluable discussions for giving the utmost freedom andflexibility throughout progress of this Training work.

I have a gratification in expressing my sincere thanks to Dean and ,Headof the Department of Mechanical Engineering Dr. NitinSrivastava, , PranveerSingh Institute of Technology, Kanpur, for providing opportunity to go forindustrial training. However I have strided hard to gain knowledge during thetraining and present a good report.

Above all, I am forever thankful to my parents for their love and encouragement.

Date: - 1stJuly 2014 Aditya Singh

List of Contents

Contents Page No.

Introduction 01

Classification of extrusion processes 02

on basis of direction

(i)Direct extrusion 03

(ii)Indirect extrusion 04

on basis of operating temperature

(i)Hot extrusion 06

(ii)Cold extrusion 07

on basis of equipment

(i)Vertical extrusion 08

(ii)Horizontal extrusion 09

Extrusion equipments 10

Extrusion dies

Extrusion tools

Lubrication 13

Defects in extrusion 15

Extrusion products 17

INTRODUCTION

Extrusion is a process used to create objects ofa fixed cross-sectional profile. Amaterial ispushed or drawn through a die of the desiredcross-section. The two mainadvantages of thisprocess over other manufacturing processes areits ability to create verycomplex cross-sections,and to work materials that are brittle, becausethe material onlyencounters compressive andshear stresses. It also forms parts with an excellent surface finish.Extrusion may be continuous (theoreticallyproducing indefinitely long material) or semi-continuous (producing many pieces). Theextrusion process can be done with the materialhotor cold.

Commonly extruded materials include metals,polymers , ceramics, concrete, playdough, andfoodstuffs. The products of extrusion aregenerally called "extrudates".Hollowcavities within extruded material cannotbe produced using a simple flat extrusion die,becausethere would be no way to support thecenter barrier of the die. Instead, the dieassumes theshape of a block with depth,beginning first with a shape profile thatsupports the centersection. The die shape theninternally changes along its length into the finalshape, with thesuspended center piecessupported from the back of the die.

ExtrusionProcess of a round blank through adie.The process begins by heating thestockmaterial (for hot or warm extrusion). It is thenloaded into the container in the press. Adummyblock is placed behind it where the ram thenpresses on the material to push it out ofthedie. Afterward the extrusion is stretched inorder to straighten it. If better propertiesarerequired then it may be heat treated or cold worked .The extrusion ratio is defined as thestartingcross-sectional area divided by the cross-sectional area of the final extrusion. One ofthemain advantages of the extrusion process is thatthis ratio can be very large while stillproducingquality parts.

CLASSIFICATION OF EXTRUSION PROCESS

On Basis of Direction

(i)Direct extrusion

Plot of forces required by various extrusionprocesses.Direct extrusion, also known asforwardextrusion, is the most common extrusion process.It works by placing the billet in aheavy walledcontainer. The billet is pushed through the dieby a ram or screw. There is areusable dummyblock between the ram and the billet to keepthem separated. The majordisadvantage of thisprocess is that the force required to extrudethe billet is greater than thatneeded in theindirect extrusion process because of thefrictional forces introduced by the needfor thebillet to travel the entire length of thecontainer. Because of this the greatestforcerequired is at the beginning of process andslowly decreases as the billet is used up. Attheend of the billet the force greatly increasesbecause the billet is thin and the materialmustflow radially to exit the die. The end of thebillet (called the butt end) is not used forthisreason.

Fig: Schemtic view of direct extrusion

(ii)Indirect extrusion

In indirect extrusion, also known as backwardsextrusion, the billet and container movetogether while the die is stationary. The die isheld in place by a "stem" which has to be longerthan the container length. The maximum lengthof the extrusion is ultimately dictated by thecolumn strength of the stem. Because the billetmoves with the container the frictional

forcesare eliminated.

Fig: Schemtic view of indirect extrusion

On Basis of Operating Temperature

(i)Hot extrusion

Hot extrusion is a hot working process, whichmeans it is done above thematerial'srecrystallization temperature to keep thematerial from work hardening and to makeiteasier to push the material through the die.Most hot extrusions are done onhorizontalhydraulic presses that range from 230 to 11,000metric tons (250 to 12,130 shorttons).Pressures range from 30 to 700 MPa (4,400 to101,500 psi), therefore lubrication isrequired,which can be oil or graphite for lowertemperature extrusions, or glass powderforhigher temperature extrusions. The biggestdisadvantage of this process is its costformachinery and its upkeep.

The extrusion process is generally economicalwhen producing between severalkilograms(pounds) and many tons, depending on thematerial being extruded. There is acrossoverpoint where roll forming becomes moreeconomical. For instance, some steelsbecomemore economical to roll if producing more than20,000 kg (50,000 lb).

Fig:Hot Extrusion

Aluminium hot extrusion die Front side of a four family die. Forreference, the die is 228 mm(9.0 in) indiameter.Close up of the shape cut into the die. Noticethat the walls are drafted andthat the backwall thickness varies.Back side of die. The wall thickness of theextrusion is 3mm (0.12 in).

(ii)Cold extrusion

Cold extrusion is done at room temperature ornear room temperature. The advantagesof thisover hot extrusion are the lack of oxidation,higher strength due to cold working ,closertolerances, good surface finish, and fastextrusion speeds if the material is subject tohotshortness .

Materials that are commonly cold extrudedinclude: lead , tin, aluminum, copper ,zirconium,titanium , molybdenum, beryllium , vanadium,niobium, and steel .Examples ofproducts produced by this processare: collapsible tubes, fire extinguisher cases,shockabsorber cylinders and gear blanks.

.

Fig: Cold extrusion

On Basis of Equipment

(i)Vertical extrusion

Vertical extrusion generally used in the production of thin-wall tubing.uniform deformation, due to uniform cooling of the billet in the container. Need considerable headroom to make extrusions of appreciable length. A floor pit is necessary

Advantages: Easier alignment between the press ram and tools. Higher rate of production. Require less floor space than horizontal presses.

Horizontal extrusion

Horizontal extrusion take place in impact extrusion of spindle by hydrollicaction.In horizontal extrusion load carrying capacity is high (from 15-35to 140MN)

Advantages Used for most commercial extrusion of bars and shapes.

deformation is non-uniform due to different temperatures between topandbottom parts of the billet.

EXTRUSION EQUIPMENTS

Extrusion of thermoplastics is a process in which the material is melted by external heatfrictional heat and conveyed forward by a screw to the opening of the die, which givestheshape of the required product. Extrusion process is a continuous process by whichmanyproducts like Films, Raffia tapes, Pipes, Sheets, Mono filaments, Fiber andFilaments can bemanufactured

ExtrudersExtruders comprise of Hopper, Barrel/Screw and Dies. Figure 1 shows the

componentsof a modern extruder.

HopperAll the extruders have an opening in the barrel wall at the driven end, through which

theplastic granules enter the extruder. The hopper, a simple sheet - metal enclosure,ismounted above that opening and holds about an hour's capacity material. Hopper isprovidedwith heating system, if the material has to be preheated before entering theextruder.

ScrewThis is the heart of the extruder. Screw conveys the molten polymer to the opening of

the die after properly homogenizing the molten polymer.

Mixing HeadsThe metering section of a standard screw is not a good mixer. Smooth laminar

flowpatterns are established in the channel which do not mix dissimilar elements in themelt.Mixing devices are frequently installed in screws to disrupt these flow patternsandimprove melt homogenization.

Breaker Plate / Screen Pack

Breaker plate with screen packs (Fig. 9) inserted are kept in the adapter which is ajointbetween the end of the extruder and the beginning of the die. This assembly hasseveralfunctionsArrest the rotational flow of the melt and convert into axial flowImproves melt homogeneity by splitting and recombining the flowImproves mixing by increasing back pressureRemoves any contaminants and unmelt

DiesVarious types of dies are used for processing PVC and PE/PP. They can be

eitherAnnular dies or Flat dies (T-Die or Coat hanger dies). Details of various dies are giveninAnneure – 1.

LUBRICATION

Lubrication is the most efficient method in order to reduce the negative effects offriction. Lubrication provides a uniform material flow thus decreases the extrusion forcerequired for the process and increases the tool life. However a lubricant which is suitable tothe properties of extrusion material and the extrusion temperature should be selected and ahomogeneous lubrication should be applied. Otherwise various extrusion faults can occurduring process.

The effect of friction on the material flow and the extrusion load can be reduced partlyor completely by applying a suitable and homogeneous lubrication.There are two ways toreduce the friction force and to lubricate the parts in extrusion processes.

Manual Lubrication of Press Tools

Manual lubrication methods are primarily used where automatic lubrication is notpossible. They are most often used where automation is not possible due to space, budgetary,or process constraints. In fact, there are certain tools, such as the die ring, container ring, andrelated die components cannot reasonably be lubricated automatically. Manual methods,when compared to automatic alternatives are often slow, inconsistent, and potentially unsafe.For this reason, the trend is now (and will likely continue to be) toward the use of automaticapplicators fordispensing liquids, powders and solid waxes.

Fig: Lubrication internal side of machine

Automatic Lubrication of Press Tools

Automatic press tool lubrication can be used to improve extrusion press efficiency,safety,and repeatability. Specifically, the use of automatic lubrication for butt shear blades,log sheartools, fixed dummy blocks, and billet scalpers, is now in common use; other areassuch as piercing mandrels are under consideration.

Manual and automatic lubrication of press tools is well documented to provideimprovements in cut and quality, while at the same time reducing or eliminating metal hang-up and sticking if performed on a regular basis. The technology is at a point where thecombination of application-specific chemicals, used in combination with the properapplicator system, can be expected to operate continuously and predictably to provide theseresults. As with all forms of automation, automatic spray lubrication requires scheduledmaintenance and adjustment so as to optimize expected results.

EXTRUSION DEFECTS

Inhomogeneous deformation in direct extrusion provides the dead zone along the outersurface of the billet due to the movement of the metal in the center being higher than theperiphery.

After 2/3 of the billet is extruded, the outer surface of the billet (normally withoxidized skin) moves toward the center and extrudes to the through the die, resulting ininternal oxide stringers. - Transverse section can be seen as an annular ring of oxide

.

Fig: Inhomogeneous deformation in tubes

If lubricant film is carried into the interior of the extrusion along the shear bands, this willshow as longitudinal laminations in a similar way as oxide

Surface cracking, ranging from a badly roughened surface to repetitive transverse crackingcalled fir-tree cracking. This is due to longitudinal tensile stresses generated as the extrusionpasses through the die.

Fig: Surface cracking in extrusion dies

Too high extrusion speed, too large a friction too high a temperature may result information of surface cracks. Fir-tree cracks are transverse cracks which often occur in aluminumor magnesium due to hot shortness. Longitudinal tensile stresses may be induced on the outerlayer, causing the cracks. At lower temperatures, stick-slip phenomenon may cause cracksespecially in hydrostatic extrusion where pressures are very high. Sticking may happen due tothick viscous oil film.

Centre burst or chevron cracking, can occur at lowextrusion ratio due to low frictionalconditions on the zone of deformation at the extrusion die

• High friction (at a the tool-billet interface) a sound product.

• Low friction center burst.

Variations in structure and properties within the extrusions•• due to non-uniform deformation for example at the front and the back of theextrusion in both longitudinal and transverse directions.

• Regions of exaggerated grain growth, see Fig, due to high hot working temperature.

EXTRUSION PRODUCTS

Food

Fig: Elbow macaroni is an extruded hollow pasta.

With the advent of industrial manufacturing, extrusion found application in foodprocessing of instant foods and snacks, along with its already known uses in plastics andmetal fabrication. Products such as certain pastas, many breakfast cereals, premade cookiedough, some French fries, certain baby foods, dry or semi-moist pet food and ready-to-eatsnacks are mostly manufactured by extrusion. It is also used to produce modified starch, andto pelletize animal feed.

Drug carriersFor use in pharmaceutical products, extrusion through Nano-porous, polymeric filters

is being used to produce suspensions of lipid vesicles liposomes or transverses with aparticular size of a narrow size distribution. The anti-cancer drug Doxorubicin in liposomedelivery system is formulated by extrusion, for example.

Biomass briquettes

The extrusion production technology of fuel briquettes is the process of extrusionscrew wastes (straw, sunflower husks, buckwheat, etc.) or finely shredded wood waste(sawdust) under high pressure when heated from 160 to 350 °C. The resultingfuel briquettes do not include any of the binders, but one natural – the lignin contained in thecells of plant wastes. The temperature during compression causes melting of the surface ofbricks, making it more solid, which is important for the transportation of briquettes.

Extruded parts:

Fig: Complex cross-section tubes

Commonly use phosphate coatings Extrusion is suited for producing seamless pipeand tubing, especially for metals which are difficult to work. The red-hot billet is rotated anddrawn by rolls over a piercing rod, or mandrel. The action of the rolls causes the metal toflow over and about the mandrel to create a hollow pipe shell.After reheating, the shell ismoved forward over a support bar and is hot-rolled in several reducing/sizing stands to thedesired wall thickness and diameter.