Biting condition & Roll bite friction coefficient 
Roll bite friction coefficient = tangential or frictional force/normal force
Biting
In the roll gap are two forces :
1. Friction FR : tries to pull through the stock
2. Pressure of rolls FN : tries to push back the stock
Biting condition
Biting condition : friction angle bigger than roll angle
Biting condition (example):
too large stock - large roll angle
- small friction angle
* resulting force pushes backwards
* no biting
Influences on roll bite friction coefficient
Influences on roll angle
1. If friction coefficient is fix, biting conditions can be improved by decreasing roll angle.
2. For fix height reduction :
by bigger roll diameter and / or smaller initial billet size
3. For fix roll diameter : by smaller height reduction
Law of continuity
Cross section • stock speed = constant
A0 = Cross section of entrance
A1 = Cross section of exit
v0 = Entrance speed of stock
v1 = Exit speed of stock
Law of constancy of volume
Distribution of the velocity in the roll gap and constitution of the roll Neutral point
Neutral point :
point where roll (at circumference) and working piece have the same speed
*Zone of backward slip : here the main deformation is done
speed of roll > speed of working piece
*Zone of forward slip :determines real exit speed.
number of revolutions of following stands
control of flying shears
speed of coilers
*The slip,i.e.the difference of speed of rolls and working piece before and after the neutral point,is the main reason for wear of rolls.
Rolling speeds
Law of volume constancy and law of continuity.
v1 : Rolling speed in the first stand
A1 : Material cross-sectional area in the first stand
v2 : Rolling speed in the second stand
A2 : Material cross-sectional area in the second stand
Rolling torque
In general,torque = force • lever arm
Rolling power
