Modeling Suction Shoes in Twin Wire Blade Forming: Theory, 1998 Engineering Conference Proceedings

Previous papers have described the effect of blade width, blade shape, wire tension, and wire wrap angle on the pressure pulses generated by a single blade in twin wire blade forming. This paper considers the influence of applied suction in the suction shoe on the same pressure pulse generation.

As a result of applied suction, the forming fabric exposed to the suction is pulled down between the forming blades, producing arced shapes rather than the nearly linear fabric profiles that characterize a forming shoe without suction. The suction also causes substantially more dewatering to occur from the suction side (bottom wire) than from the other side (top wire) of the web. This difference in dewatering causes more fibres to adhere to the bottom wire side than to the top wire side, leading to significant two-sidedness of the paper sheet. All of these phenomena are modelled in a new computer code that has been developed to simulate suction shoe dewatering. The computer simulation developed here can also be used to calculate dewatering over the multiple blades comprising a forming shoe, without applied suction.

This paper documents only the development of the computer code. In order to keep this paper to a reasonable length, discussion of the results of the computer simulation and comparison with mill trials will be left to a companion paper.