rolling

Question 1

what is rolling

Answer 1

process in which thickness is reduced by compressive forces from two opposing rolls. rolls rotate to draw work into gap, and squeeze

Question 2

three shapes that can be rolled

Answer 2

blooms (square x sections then for I beams and rails)
slabs (rectangle x section then rolled to sheets and strips)
billets (square x sections then rolled into bars and rods)

Question 3

microstructural changes from rolling?

Answer 3

grains flattened.
hot rolling - recrystallisation happens and new grains form
cold/warm rolling - grains star flattened. often anneal at diff temp to cause change of microstructure

Question 4

describe recrystallisation for treating cold worked material

Answer 4

when cold worked material heated above certain temp, rapid recovery eliminates residual stresses, produces polygonised dislocation structure. new small grains nucleate @ grain boundaries.
recrystallised material has low strength but high ductility

Question 5

types of rolling mills

Answer 5

two-high (basic opposing rolls. for hot rolling)
three high (3 rolls in column. hot rolling)
four high (2 small that contact work, two backing behind. cold rolling)
cluster (2 small plus number of large backing rolls. for cold working)

Question 6

effect of roll diameter on length of contact

Answer 6

small working rolls, less length of contact so lower force to produce given change. but small rolls not stiff enough, need large backing rolls to support them