where L is the roll-strip contact length, 1/U is the width of the strip, and Yavg is the
average true stress (see Section 2.2) of the strip in the roll gap. Equation (13.2) is
for a frictionless situation; however, an estimate of the actual roll force, including
friction, may be made by increasing this calculated force by about 20%.
The torque on the roll is the product of F and a. The power required per roll
can be estimated by assuming that F acts in the middle of the arc of contact; thus, in
Fig. 13.2c, a = L/2. Therefore, the total power (for two rolls), in S.I. units, is