METHOD OF QUICK-OPENING A SET OF ROLLS IN A CALENDER, IN PARTICULAR IN A SUPERCALENDER, AND A HYDRAULIC SYSTEM FOR A SET OF ROLLS IN A CALENDER, IN PARTICULAR A SUPERCALENDER

摘要

The invention relates to a method of quick-opening a set of rolls in a calender, in particular a supercalender, in a calender (10) in which a paper or board web (W) to be calendered is passed through calendering nips (N1-N9) formed by a variable-crown top roll (13), a variable-crown bottom roll (14) and by two or more intermediate rolls (15-22) fitted between the top and bottom rolls (13, 14). The rolls (13-22) are arranged to form a substantially vertical stack of rolls (12), and the intermediate rolls (15-22) are supported by means of hydraulic relief cylinders (155-225) so as to relieve the nip load produced by the masses of bearing housings (151-221) of said intermediate rolls (15-22) and of auxiliary devices (154-224) associated therewith. During the quick-opening of the set of rolls, the bottom roll (14) of the set of rolls is lowered and the relief pressures in the hydraulic relief cylinders (155-225) are discharged so as to open the calendering nips (N1-N9). The hydraulic oil flowing out from the relief cylinders (155-225) is controlled by means of valves connected to the relief cylinders (155-225) of each intermediate roll (15-22) so that, during quick-opening of the set of rolls, the roll nips (N1-N9) may be opened in a controlled way in a desired order. The invention also relates to a hydraulic system for the set of rolls.