A rolling mill is used to reduce the thickness of a plate from 50
A rolling mill is used to reduce the thickness of a plate from 50 mm to 25 mm. The roll diameter is 700 mm and the coefficient of friction at the roll work interface is 0.1. It is required that the draft in each pass must be the same. Assuming no front and back tensions, the minimum number of passes required in the rolling are:
A. 16
B. 8
C. 4
D. 12
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Right Answer is: B
SOLUTION
Concept:
Draft in rolling (ΔHmax):
It is the maximum possible reduction in thickness in one pass of a rolling operation. It is given by
ΔHmax = μ2R
where
μ = coefficient of friction at the roll work interface
R = radius of roller and
ΔH = H1 – H2 (in one pass of rolling)
Calculation:
Given:
Diameter of roll = 700 mm ⇒ radius R = 350 mm, μ = 0.1,
∵ ΔHmax = μ2R ⇒ (0.1)2 × 350 = 3.5 mm
∴ In one pass of rolling operation 3.5 mm of thickness is reduced.
Total reduction required = Hinitial - Hfinal ⇒ 50 – 25 = 25 mm.
⇒ 8 passes required (rounded off to next integer)