discuss the effects of hot and cold rolling on the mechanical properties of a material

7/30/2019 Discuss the Effects of Hot and Cold Rolling on the Mechanical Properties of a Material

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1) Discuss the effects of hot and cold rolling on the mechanical properties of amaterial.

In hot rolling diclocation propogation and softening process with or without

recystallization are occurs together.The dominant mechanism of hot rolling depends on

temperature and grain size.Generally the recrystallized structure becomes finer with

lower deformation temperature and faster cooling rates and material of superior

properties are obtained by controlling the finishing temperature. [4]

Cold rolling process increases hardness. Like the hardness dislocation density increases

too which leads to an increasing in the yield stress. But because of higher dislocation

energy the ductility decreases. [2]

[2]http://my.metalinfo.com/mm_utilities/metalglossary.cfm?action=search&crit=s

2) Give examples of rolling defects (with figures and a brief explanation)

Roll misalignment

Misalignment of the rolls leads either to curvature of the strip to one side as it comes

out of the roll gap, if it is relatively thick, or to a wavy edge on one side if it is thin

strip, Adjust the roll screws to give a parallel roll gap. [4]

Figure 1 - Defects due to misalignment of the rolls [4]
http://my.metalinfo.com/mm_utilities/metalglossary.cfm?action=search&crit=shttp://my.metalinfo.com/mm_utilities/metalglossary.cfm?action=search&crit=shttp://my.metalinfo.com/mm_utilities/metalglossary.cfm?action=search&crit=shttp://my.metalinfo.com/mm_utilities/metalglossary.cfm?action=search&crit=s


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Figure 3 - Using a high mill for minimising

roll bending [4]

Edge cracking

Edge cracking is commonly caused by overworking between anneals. It is important

to trim edges at the time it occurs as further rolling will increase the danger of some

cracks suddenly running into the centre of the strip and turning through right angles,

greatly increasing the amount which has to be scrapped. [1]

Bow defects


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It is curvature of sheet or plate. If it is across the rolling direction, usually caused by a

slight difference between the extension of the center of the sheet or plate and the edge

Figure 5: Bow defects[5]

[4] http://www.thefabricator.com/Articles/Fabricating_Article.cfm?ID=311

[5] http://www.kaisertwd.com/CustomerService/Glossary/C_Glossary.asp

[6]http://wwwold.ajou.ac.kr/~powder/files/processing6-b.pdf

[7]

http://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/Visua

lQu alityCharacteristics.pdf

3) Write down the dimensions of the part and calculate the volume of the part:

Explain the volume change in each step.
http://wwwold.ajou.ac.kr/~powder/files/processing6-b.pdfhttp://wwwold.ajou.ac.kr/~powder/files/processing6-b.pdfhttp://wwwold.ajou.ac.kr/~powder/files/processing6-b.pdfhttp://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/VisualQu%20alityCharacteristics.pdfhttp://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/VisualQu%20alityCharacteristics.pdfhttp://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/VisualQu%20alityCharacteristics.pdfhttp://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/VisualQu%20alityCharacteristics.pdfhttp://www.aluminum.org/Content/NavigationMenu/The_Industry/Sheet,_Plate/VisualQu%20alityCharacteristics.pdfhttp://wwwold.ajou.ac.kr/~powder/files/processing6-b.pdf


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a. At the end of casting d=30mm, l=61.8mm V= r2l = 1.52(6.18)=43.6 cm3 this is the original volume with roughly measured

dimensions

b. At the end of extrusion

Length: 730mm

Width: 20.2mm

Height: 3mm

V = 4.42 cm3 Since only some part of the material is extruded the volume is smaller.

c. At the end of rollingV= 3.54 cm3 since rolling was not done properly some part of it slipped so the final

volume is even smaller.

As can be seen from the results, though the cross sectional area decreases, due to

increase in length, there is no significant change in volume. The little change in the

volume can stem from no-efficient rolling or the low accuracy of measurements.

4) What is isotropy and anisotropy? Explain if the material we processed duringlab section is isotropic or not.

Isotropy: Properties of a material are identical in all directions

anisotropy: Properties of a material depend on the direction

the material we processed during lab section is isotropic


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What is Poissons Ratio?

Poisson's ratio (for aluminum 0.334) is the ratio of transverse

contraction strain to longitudinal extension strain in the

direction of stretching force.

a. For the material we processed in lab, what do you expect the relationbetween the strains in transverse directions due to rolling? Explain thisexpectation in terms of Poissons ratio.

b. By comparing the thickness and width of the part before and afterrolling, calculate the ratio of strains in transverse directions and discuss

your calculation with your expectation. If they do not match. Give the

reasons of this consequence.

NOTE for the question # 5 in Rolling: Check Figure 1.

Assume that we processed the part (applied rolling) in x direction. So; x direction is

the longitudinal direction and y and z directions are the transverse directions.

Figure 1.


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Poisson's Ratio can be expressed as

= - t/ l (1)

where

= Poisson's ratio

t= transverse strain

l= longitudinal or axial strain

Strain can be expressed as

= dl/L(2)

where

dl = change in length

L = initial length

For most common materials the Poisson's ratio is in the range 0 -

0.5.

According to the poisons ratio we expect that strains ratio stay

close to the value of 0.334.

= dl/L = 2/3 = 0.66

= dl/L = 20.2-22/20.2 = 0.089

= - t/ l = 0.135

Since the rolling operation is not done accurately the results are

also not accurate.

discuss the effects of hot and cold rolling on the mechanical properties of a material

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