Experimental and numerical studies of the reelspool and the parent roll interaction under gravity forces

Abstract

In wide paper machines, gravity forces may cause excessive stresses to the paperlayers of the parent roll due to bending of the reel spool. Experimental and numerical studies of these effects will be described in this paper. Experiments done by strain gage measurements and numerical techniques involved will be described in the first part of the paper. In the second part, the same phenomena are studied by using FE modelling.

First, measurement techniques of reel spool bending strains is described. Measurements are done in static loading situations using several differently reeled parent rolls. Then, a method to estimate the contact pressure distribution between the parent roll and the reel spool from the measured bending strains is presented. Calculated experimental results are compared qualitatively and quantitatively to the FE modelling of the same situation. The unknown elastic orthotropic coefficients of the parent paper roll are estimated so that the finite element calculations give practically the same results as the experiments. Finally, FE model is used for further numerical studies of different reeling recipes etc.

The most essential result of the measurements and numerical studies is that the reel spool carries the parent paper roll almost entirely at the edges of the spool causing large stresses to the paper layers in this area. The well known fact is that most printing roll defects are found from roll sets, which are made from edge and inside part of the parent roll.

Research results have changed the design philosophy of the reel spool for various paper grades, as machines are made for heavier and heavier reels. Experimental work is much more laborious and time-consuming than numerical studies, and therefore even a bit vaguely calibrated FE model is very effective design tool for new concepts.