Spanwise spreading of gypsum slurry during deposition on the belt under a roller

Abstract

An experimental setup was designed and built to explore the spreading of a slurry layer during deposition on a moving belt before a rotating roller. The case of the water-to-stucco ratio of 75 was studied. The roller could be at rest (no rotation) or in co-rotation and counter-rotation compared to the directional motion of the spreading plastic belt (parchment paper). The widening of the slurry layer was measured and compared with the predictions of the theory developed previously by the present group, and the predicted maximum width reasonably agreed with the experimental observations. Particle image velocimetry was used to measure the velocity field at the surface of the slurry layer in top and side views. A flow pattern was observed before the slurry bypassed under the roller, in the domain where variations in entrainment led to different surface profiles. Depending on the roller's rotating direction and speed, the slurry was either more effectively drawn under the roller, forming a mild ridge, or less effectively entrained, resulting in a pronounced ridge.