Crown tolerance, as determined by shell deflection and roll position, is set to ensure that pressure will not
vary too much across the face length of the nip. During the Valmet grinding process, crown is measured
continuously along the roll shell, and there is a limit on how much the crown can vary from station to
station.
It is also very important to follow temperature
variations on the roll face when measuring shape
tolerances. A 750 mm diameter calender roll for
example, ground perfectly, will go out of shape
tolerance if the temperature exceeds a variance of 1.2 ºC
in the cross direction. This is called thermal crowning.