MEASUREMENT OF PAPER STRAIN IN THE NIP OF AN EXPERIMENTAL CALENDER

In-nip paper thickness was measured using a new laboratory-scale calen dar reproducing all industrial operating conditions except width: nip load ranged from 10-210 kN/m, sheet speed from 90-950 m/min, and roll radius from 202-355 mm. Sheet width was 70 mm. In-nip strains imposed on a 100% TMP newsprint were computed and related to the operating con ditions by means of an in-nip calendering equation. A new empirical re lationship between in-nip and permanent strains was developed which al lows on-line computation of in-nip strain given the permanent strain a nd the operating conditions. Paper thickness was measured at two point s shortly after the nip. The data were used to calculate a time consta nt defining paper thickness recovery after the nip, and to estimate th e amount of elastic recovery immediately after the nip.