ELECTROMAGNETIC HEATING SYSTEM FOR CALENDER ROLLS OR THE LIKE

摘要

A calender roll whose shell consists of ferromagnetic material is heated by several groups of electromagnets which are mounted within the shell on a stationary carrier and whose pole shoes are adjacent to the internal surface of the shell. The temperature of the external surface of the shell is monitored at several locations as considered in the axial direction of the roll, and the resulting signals are compared with reference signals denoting the optimum or desired temperatures at such locations. Signals denoting the differences between the actual temperature signals and desired temperature signals are used to regulate the characteristics of electric current which is supplied to the windings of the electromagnets. Each electromagnets of each group can be regulated independently of all other electromagnets. Alternatively, two or more electromagnets of each group or entire groups of electromagnets may be regulated simultaneously. Additional electromagnets are provided to heat the end portions of the shell. Alternatively, such end portions can be heated by the rotors of electric motors which rotate the shell. The characteristics of current which is supplied to the windings of certain electromagnets can be influenced by signals which denote the magnitude of flexural stresses upon selected portions of the shell so that the corresponding electromagnets oppose deformation of adjacent portions of the shell.