Abstract
Today, several important parameters in sheet forming on the paper machine are changing considerably.
The twin wire concept is about to become the standard for new installations. Here, the drainage zone is drastically reduced compared to the fourdrinier, with corresponding reduction in drainage time. Besides, there is a general increase in paper machine speed. The drainage elements are changed, reducing the degree of pulsed drainage.
Also the papermaking furnish is changing.
New fibre raw materials are introduced by a change from mature to juvenile trees on the one hand and the increasing use of tropical hardwoods on the other. This implies a significant change in the fibre compositions of the furnishes.
This tendency is enhanced by another technical trend, partly caused by scarce wood supplies, towards pulps of higher yields. The trend is significant both within the conventional chemical pulping processes, and for the development of new processes like the thermomechanical pulping methods.
The change in paper forming speed, and in the fibre composition may cause problems for the production process. It therefore seems useful to try to produce new information on the influence of fibre form on the pulp drainage characteristics.
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