Crown and crown correction
From a mechanical standpoint, a calender
roll is a rotating beam. Beams, we
know, deflect under load. Vary the load,
the deflection varies with it.
To compensate for the deflection, we
can change the shape of the beam so
that when it deflects under load, it presents
a flat surface. With rolls, the shape
takes the form of a very skinny barrel,
and we say that such a roll is “crowned”
or has a crown of such and such. (Crown
is measured on the diameter; the amount
of crown necessary to correct for the deflection
of the roll is twice the amount of
the deflection.)
Because loads are not always the
same, two basic techniques have evolved
for making gap between two adjacent
rolls appear to be straight or “flat” under
a range of load conditions