Question

A steel plate 50 mm thick is to be rolled to 42 mm in a four high mill having roll diameter 340 mm. The yield stress is 200 MPa. The coefficient of friction, if the given reduction is the maximum reduction possible, is

• A. 0.158
• B. 0.217
• C. 0.312
• D. 0.425

Answer 1

The correct option is B 0.217

Rolling (four high mill)
$H_o$ = 50mm
$H_1$ = 42 mm
$△$$H=H_o-H_1=50-42=8mm$
$D_R$= 340 mm,
R = 170 mm,
${\sigma }_y$ = 200 MPa
We know,
Maximum reduction $(△H_{max}{)}_{pass}$$={\mu }^2\times R8mm={\mu }^2\times 170$
$\mu =0.2169$