Overview of the Physics of Forming

Abstract

In this overview forming covers all processes from the dilution of thick stock into a mix, using recirculated white water in the short circulation, to the dewatering in the wire section. Grammage non uniformity in the paper web is to a predominant degree generated by the forming process, and especially the small scale variations summarized in the term formation. The term mass formation is recommended when only grammage is considered and not the optical impressions there of. The forming process also generates the main part of the large scale variations, that is the MD-,CD-and residual grammage variance. Mass formation has traditionally been evaluated using beta radiography, combined with micro densitometry or image analysis. A new technique involving the direct recording of electron beam transmission is underdevelopment, with promises off aster processing, perhaps even on-line, and high geometrical resolution.Characterization techniques based on the co-occurrence matrix, applicable to image analysis, can be a useful complement to the traditional power spectra techniques. It has recently been conclusively demonstrated that in flowing fibre suspensions, flocs are kept together by the bending forces of interlocked fibres. To study the dynamic behaviour off lowing fibre suspensions, modern video techniques, high speed movie pictures and image analysis are applied.