During web formation, the difference between the speed of the pulp suspension and that of the wire gives rise to a smear force that orients fibres preferentially along the machine direction . This has been known for a long time. It is less clear, however, haw the distribution of fibre orientations is fly related to the conditions of web formation and to the properties of papermaking fibres. We have studied this question using simple theoretical models and experimental data inc1-tiding irk-We analysis results.
We find that fibre-to-fibre interactions determinehow much individual fibres are rotated by the oriented shear field. In this way the fibre orientation distribution obtained for a given speed cliff an the pulp properties. On the other hand, the turbulence of the pulp flow seems to be the mechanism through. which the conditions of web formation affect fibre orientation. In particular, we suggest that the on set of hear-induced turbulence in the suspension flow determine the maximum fibre orientation anisotropy that can be achieved.
The model calculations show that the distribution of fibre orientations cannot be represented in terns of a simple functional form with only one adjustable parameter. The shape of the distribution depends an the fibre p and especially the wet fibre flexibility. In paper the orientation distribution of curly fibres is quite different from that of straight fibres. On the other hand, no diff in the distribution is observed if long and short fibre are examined separately.