Apparatus for controlling the heating and cooling of a roll

DETAILED DESCRIPTION Accordingly, one of the problems to which the invention is concerned is the problem of shortening the heating-up and cooling-down time periods of rolls of the type under discussion, without endangering the structural integrity of the hollow rolls.
According to the invention, the problem is solved by provision of a temperature controllable roll for treating webs of material that includes an inner surface disposed within the roll and an outer working surface disposed at an outer circumference of the roll.
An inner temperature adjusting device is disposed inside the roll for adjusting the temperature of the inner surface and an outer temperature adjusting device is disposed outside the roll for adjusting the temperature of the outer working surface.
A thermostatic control and regulating device is coupled to at least one of the inner temperature adjusting device and the outer temperature adjusting device for maintaining the temperature of the inner surface and the temperature of the outer working surface at the same level during a first temperature adjustment phase in which the inner and outer temperature adjusting devices change the temperatures of the inner surface and outer surface, respectively, from a first predetermined value to a second predetermined value.
Since the temperature is the same at the outer and inner surfaces of the hollow roll, the generation of high temperature gradients in a direction radial to the hollow roll is prevented.
While there can be a temperature gradient between the inner and outer circumferential surfaces of the hollow roll and its interior, such a temperature gradient is limited because of the relatively small heat capacity, along with the great thermal conductivity, of the hollow roll.
No temperature differential between the inside and outside of the hollow roll occurs that results in thermal stress which, together with the internal stress, can have harmful consequences.
No heat is exchanged though the roll body because a temperature differential between the inside and outside of the roll is not present