45920321 defects in hot rolled products1

8/12/2019 45920321 Defects in Hot Rolled Products1

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1. Defects in Hot Rolled Products

Rolled in Scale (RIS)

Sliver / Seams

Blister

Edge Cracks

Spongy Edge

Rolled in Extraneous Material

Roll Marks

Indentation Mark

Scratch Mark

olds

!amination

Cam"er

latness

#vality

BC!

$CC

%ig %ag &rapping

Bulging

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2. Rolled in Scale (RIS)

Different types of RIS

'rimary Scales due to 'oor escaling

'rimary Scales due to igh $emperature

Secondary Scales due to 'oor escaling

Secondary Scales ( rag / Comet type) *rom Coil Box+

$ertiary Scales due to Roll Roughness ( Salt , 'epper /Banded type)+

Silicon / Red Scales ($iger Scale)

Steps to control RIS

Cleaning o** loose scales *rom sla" sur*ace -voiding overheating o* sla" sur*ace

rop out temp+Edging

escaling impression test.se o* scale master no le , use o* optimum height "et0eenthe strip and the no le tip+Coil "ox "y1pass#xidi ing atmosphere

escaling pressureRoll cooling and roll "ite lu"rication'roper scheduling o* sur*ace critical grades+

amage o* sur*ace *rom apron plate+.se o* interstand descaler

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Primary Scales due to Poor Descaling

Scale (Iron #xides) generated at various ot rolling Stages get rolledinto the Strip Sur*ace due to di**erent reasons+

Prone Grades 2 -ny grade

Location 2 Scattered

ppearance 2 Black13rey

#rigin / Root Cause

Improper descaling / *ailure o* 'rimary descaler+ 4o le clogging o* 'rimary descaler+ Sticky Scale (lo0 #56 igh $emperature , igh Retention

$ime)+

Remedy / 'rocess Control

Maintain high escaler 'ressure ( 789: Bar)+

$ake Impression / Correction o* 4o le Impression+ Maintain #xidi ing atmosphere (75;)6 lo0 temperature

(85:: hrs+)+

Primary Scales due to Hig! "emperature

Prone grades 2 3rades processed 0ith high RME$1I S

Location 2 Scattered6 in portions 0here high temp 0asexperienced "y sla"

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ppearance 2 ?M@ shaped

#rigin $ Root %ause

igh urnace / Roughing Mill Exit $emperature

Remedy $ Process %ontrol

!o0 Roughing Mill Exit $emperature (A8:9:


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#rigin $ Root %ause

#vality o* Coil in Coil Box+ .n1*latness o* $r+ Bar+ &orn out rolls in Coil Box+


Maintain Roughing Mill Exit $emperature+ Coil ($r+ Bar) $ightness+ .se o* leveler+ re uent check / Replacement o* &orn out Rolls+

"ertiary Scales due to Roll Roug!ness( Salt Pepper $ &anded type).

Prone grades 2 $hinner sections/high strength

Location 2 Banded6 throughout 0idth

ppearance 2 Small6 spotted type

#rigin $ Root %ause

igh $emperature due to high Mill pacing+ Roll Cooling &ater Duantity+ -mount o* RB!+ Rolling !oads due to -dverse ' D S+ Scheduling Rules (&ear M)+


#ptimi ation o* Roll Cooling &ater+ #ptimi ation o* RB!+

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Right product mix+ Schedule !ength 0+r+t+ &ear M

Silicon $ Red Scales ("iger Scale)Prone grades 3rades having Silicon (7F:+5:;)6 Cu 6 Cr (7F:+ :;)

Location Scattered6 "oth sur*aces

ppearance Elongated6 patchy nature

#rigin $ Root %ause

'resence o* Si6 Cu6 Cr type Elements leading to Stickiness+ Soaking $emperature+ Retention $ime+


Increase escaling 'ressure (789: Bar)+ -ll 'ass escaling in Roughing Mill+ .se o* IS in inishing Mill+

*. Sli+er $ Seams

Defect Description

Irregular *laky overlapping material 0ith non1metallic inclusions orscales under it+ It is *ound along the rolling direction and can appearon "oth sur*aces+ Sometime also called seams6 shell+

Possi,le causes

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Slag or nonmetallic material entrapment during casting orrolling+

$ransverse crack in sla"+

"ypes of Sli+er

Body Sliver / Seams

Edge !ine Slivers

Body !ine Slivers

&ody Sli+er $ Seams

Su" Sur*ace e*ects in Sla"s6 !ike 4on1metallic Inclusions6 Mould

'o0der entrapment6 3aseous inclusions etc+ 0hich open up insu"se uent ot Rolling / Cold Rolling Stage+

#rigin $ Root %ause

Severe mould oscillations+ lushing #peration+

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Speed Gariation+ Mould level *luctuation+


Control over a"ove 'arameters

-dge Line Sli+ers

$ransverse cracks on the sla" edges lead to these de*ect during otRolling+

#rigin $ Root %ause

Duenching e**ect o* the sla" edges in sec+ one+ 'oor ductility+ eep oscillation marks at the edges


Reduce 0ater in secondary cooling one+ Control mould level *luctuation+

&ody Line Sli+ers

Star / longitudinal cracks on sla"s ("ody) leading to Sliver on ot RollStrips+

#rigin $ Root %ause

Garying mould *lux ( eat extraction)+

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Mould po0der uality (viscosity)+ igh casting speed+


Control o* mould 0ater+ .se o* high viscosity mould po0der+ Slo0er casting speeds+

. &lister

Su" Sur*ace "lo0 holes o* varying si e and shape located closely6mainly due to argon entrapment during casting6 leading to Blisters in

R / CR a*ter rolling+

#rigin $ Root %ause

Excess argon purging+ Mould level *luctuation Rapid solidi*ication near the mold 0all causes gas entrapment+


Control a"ove parameters+

/. -dge %rac0

$here are cracks o"served on the edges o* R coil due to excessuenching e**ect+

#rigin $ Root %ause

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Excess 0ater in M / R#$ / C cooling the strip edges / "ody .n1*latness leading to 0ater carryover+


-void cooling 0ater in M6 R#$ (cross spray) and 'inch roll0ater in C+

Roll *lat strip / remove 0ater on R#$

. Spongy -dge

$here are cracks / pin holes on the edges due to improper ductility

#rigin $ Root %ause

'in holes on sla" edges+ eep oscillation marks+ 'oor Mn / S ratio+


-void pin holes / deep oscillation marks+ Maintain Mn / S 785

. Rolled in -'traneous material

Bolt6 Mould po0der6 etc+6 get rolled in the strip+

#rigin $ Root %ause

Bolts *alling on the sla" / $r+ Bar+ Mould po0der on the sla"+ Roll material a*ter spalling+ Burrs on the sla"s+

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'roper maintenance practices+ 'roper casting parameters / sla" uality+ Better roll uality , 'ro*ile+ Maintain operational practices+

3. Roll 4ar0s

"ype of roll mar0s

!ump

Sticker

G1Shape

ire1Crack

%e"ra 'attern Mark

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Lump

Roll Spalling or portion o* roll sur*ace chipping out giving rise to !umpmarks at regular interval+$his interval is depending on roll diameter+

#rigin $ Root %ause

Material o* roll clipping o** due to tail che0ing+ Extraneous material denting the rolls+


-void $ail Che0ing+

'roper sla" Duality 0+r+t+ Burrs+ Su**icient cropping o* $r+ Bar+ ollo0 up remedies as suggest *or Rolled in extraneous

material+

Stic0er

$his de*ect is o"served 0hen small pieces o* scrap sticks on the rollsur*ace generating dent marks (replica o* the scrap) at regularinterval depending on the roll diameter+

#rigin $ Root %ause

Sticking o* extraneous material (Burrs) on rolls

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-void $ail Che0ing+ 'roper sla" Duality 0+r+t+ Burrs+ Su**icient cropping o* $r+ Bar+ ollo0 up remedies as suggested *or Rolled in extraneous

material+

56S!ape

Cold head mark o* the $r+ Bar on the roll sur*ace+

#rigin $ Root %ause

Cold head end o* $r+ Bar+


Su**icient cropping+ Maintain high temperature at head end+

7ire6%rac0

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$hese are the trans*er marks *rom the cracks generated on the*inishing roll sur*ace due to thermal shocks+ -ppears on the regularintervals+

#rigin $ Root %ause

$hermal Shock on the rolls due to the strip remaining in contact0ith the roll "ite *or sometime particularly during co""les+


-void co""les in M+ 'roper dressing o* rolls+

8e,ra Pattern 4ar0

$his is a mark 0hich is generated on the strip sur*ace due to

undulation o* roll sur*ace+

#rigin $ Root %ause

Improper grinding o* the rolls+

Remedy $ Process %ontrol Skill o* the grinder+ 'roper *inish o* the roll sur*ace+

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Indentation 4ar0s

$his is a ent mark 0hich is o"served at the ead End o* the stripapprox+ 5:1>: meters+

#rigin $ Root %ause

$ongue shape o* the strip head end+ !o0 temperature o* the tongue+ $ension o* the strip 0hile coiling+ igh temperature o* the strip (excluding tongue)+


ead end un1cooled to keep tongue hot+ Reduce tension (maintaining coil tightness) to avoid excess

pressure+ Reduce C$ to avoid sticking o* 0raps+

9. Scratc!es $ Groo+es

!ine marks on the strip sur*ace 0hich is generated *rom stationaryparts+

#rigin $ Root %ause

Mechanical a"rasion o* strip 0ith stationery part+


Strip should not touch stationery parts+ -ll (ta"le / R#$ etc+) to "e in rotation+

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1:. 7olds

Different "ypes of folds are

-dge 7old

#rigin / Root Cause

Cam"er in strip (mainly E / $E) 0hile coiling+ C side guide pressure


Control 0edge / cam"er at RM+ #ptimi e / maintain side guide pressure+

&ody 7old

#rigin / Root Cause

!oop in strip "e*ore coiling


$ension "et0een H / 'inch roll / do0n coiler to "e maintained+

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11. Lamination

e*ect in sheets and plates6 0hich appear in a local area in layers

and are generally caused due to segregation

#rigin $ Root %ause

Segregation in sla" (mainly centre portion)+


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!o0 ?S@ content (A:+:: )+ !o0 super heat (A>:


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$rans*er Bar &edge+ $rans*er Bar Cam"er+ Servo valve response+


Control &edge in $r+ Bar A:+8 mm+ Control Cam"er A8: mm+ Servo valve nil o**set A85;+

1*. 7latness

"ypes of flatness defects

Edge &avinessCentre Buckle

#rigin $ Root %ause

Improper S0iveling / Bending+ Improper CGC setup+

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Servo value Response+ aulty 'ressure transducer+


Control S0iveling / Bending+ 'rovide un1*latness correction+ Maintain "asic conditions o* e uipments+

1 . #+ality

$he Inner diameter o* coil is not same in all direction and it 0as o* aoval shape and having a minor , maJor axis+ Such a de*ect is kno0n

as ovality+ #rigin $ Root %ause

Sagging o* coils a*ter taking out o* o0n Coilers+ It happensdue to heat dissipations a*ter coiling and on conveyor+

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Control o* *latness+ Control o* C$ to complete trans*ormation on R#$ itsel*+ $ension in C+

1/. &%L

"ype 2

a) !oose Coiling+

a) &rap Shi*ting+#rigin $ Root %ause

!oose 0raps a*ter coiling+ 'rotruding outer 0raps (like $CC) a*ter coiling+

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1 . 8ig 8ag ;raping

#rigin $ Root %ause

Shi*ting o* 0raps on either side (#/S , /S) 0hile coiling+


.se o* correct+ ot K+' valves+ Correct strip tension values+ igher C$+

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'roper 'roduct Section / grade+

13. &ulging

#rigin $ Root %ause

Belly shaped coiling due to Cam"er *rom RM6 lo0 strip tensionin do0n coiler+


Control Cam"er in RM+ Maintains proper tension+ 4o dia *luctuation o* mandrel+

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19. Some Practical -'amples #f HR Products Defect

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Longitudinal line defect.(&S

caused edge crac0ing.

Surface rupture (-6*3)

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-"ove o"servation indicates that the Lrupture marksL 0ere caused "ysome mechanical a"rasion in cold condition as revealed "y grainde*ormation along the de*ect+

%rac0ing t!roug! ?eld @one (


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eed"ack2 IS 5:H5 3rade B6 85mm thick R coil supplied to M/SInternational -uto !td+6 0as cracking at : : "end 0ith a radius o* 8960hile making -ir Bracket *or $E!C#+

3as cut sample *rom -ir Bracket sho0s multiple cracks at the : :

"end+ $he sheared *ace sho0s cracks extending up to mid thickness

one o* the strip+ &hile one large crack occurred exactly on the "end6other cracks appeared slightly a0ay *rom the "end+ Cavity like de*ect0as also o"served on the sheared *ace6 close to mid thickness one+

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H#L-

H#L- DA- "# SLI5-R ("4&P62)

-DG- %R %< (RI4)

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D-PR-SSI#B 4 R< (LPG)

D-PR-SSI#B 4 R< (LPG)

PI""IBG 4 R< $ S%R "%H (LPG)

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%-B"R- LIB- S-

$he de*ect 0as in the*orm o* deep continuousline on the right side o* *iga"ove+ Multiple linede*ects 0ere alsoo"served on the le*t sideo* *ig 8+

Close up o* sur*acede*ect as sho0n on theright side o* ig 8+

Close up o* sur*acede*ect as sho0n on thele*t side o* ig 8+

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45920321 defects in hot rolled products1

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