1-Hot+Rolling.pdf

Metal Forming Hot Rolling Manufacturing Processes and Systems Mechanical Engineering University of Colorado

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Rolling

Source: http://uk.geocities.com/plinehanuk/management.htm

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Hot Rolling

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Basic Rolling Process • Heated metal is passes between two rolls • The rolls: – Rotate in opposite directions – Rotate with a surface velocity higher than the speed of the incoming metal

• Friction along the contact surface propels the metal forward 4

Ref: W.F. Hosford and R. Caddell “Metal Forming” 3rd Edition

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Friction vs. Position

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Calculating Roll Force

𝒉 = (𝒉𝟎 +𝒉𝒇 )/𝟐 𝝈𝟎 = 𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒇𝒍𝒐𝒘 𝒔𝒕𝒓𝒆𝒔𝒔 𝝁 = 𝒄𝒐𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒕 𝒐𝒇 𝒇𝒓𝒊𝒄𝒕𝒊𝒐𝒏

bt and ft = back tension and front tension, respectively

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Reducing Roll Force with Small Diameter Rolls

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Roll Deflection

Source: http://www.me.gatech.edu/jonathan.colton/me4210/deform.pdf

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Defects From Roll Deflection

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Edge Cracking

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Rolling Defects Defects

Cause

• Wavy Edges or Center Buckle (shape issues)

 Roll Deflections

• Edge Cracks

 Barreling

• Zipper Cracks

 Low Ductility

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Yeah, it does happen…

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Shape Correction • Roll bending and roll shifting

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Roll Defects • Typically marks that repeat at a distance equal to the working roll circumference

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Flow Stress in Hot Working

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Thermomechanical Processing • Controlled Rolling • Accelerated Cooling

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Source: http://www.ipmx.com/html/tour/hotmill.html#lfc

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Al

B

C

Co

Cr

Cu

Fe

H

Mn

X52_vintage

0.002

<0.0001

0.238

0.004

0.014

0.085

98.48

0.96

X52_new

0.017

<0.0001

0.071

0.002

0.033

0.016

98.37

Mo

N

Nb

Ni

P

S

Si

0.000 1 0.000 6 Ti

X52_vintage

0.004

0.003

0.001

0.003

0.011

0.021

0.064

0.002

0.002

X52_new

0.003

0.004

0.026

0.004

0.012

0.004

0.24

0.038

0.004

Steel

σy [MPa ± std. dev.]

σUTS [MPa ± std. dev.]

X52_vintage

325±4

526±4

X52_new

487±5

588±5

1.06

V

Vintage X52 Alloy

New X52 Alloy

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Seamless Tube

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