Why do wet-particles adhere to a high-speed roll in a three-roll mill?

Abstract

A three-roll mill is used in various engineering fields to manufacture high-value-added products. This mill has three horizontally positioned rolls with different rotational velocities. In the mill, viscous materials (or pastes) pass through the narrow gap between the rolls to be mixed, refined, dispersed, and/or homogenized. The viscous materials tend to consist of wet-particles connected by liquid bridges. Although viscous materials always adhere to a faster roll in the three-roll mill, the mechanism has not yet been clarified. Herein, the adhesion mechanism is clarified scientifically by numerical simulation. In the calculations, a Lagrangian method, such as the discrete element method, is used to analyze the specific phenomena in the particle–particle and the particle–wall interaction. A latest liquid bridge force model is used in this study to examine the effect of a wide range of liquid volumes on the adhesion phenomena. In the calculation, a lump of wet-particles is fed into the gap between the two rolls and the roll speed is changed to investigate its influence on the adhesion phenomena. Through numerical examples, it is proven that wet-particles always adhere to a fast roll because the liquid bridge force that acts on the faster roll is larger than that on the slower roll after the compression force is released. This is because the extension of the wet-particles is larger on the faster roll because of the speed difference between the two rolls. Consequently, the adhesion mechanism of the wet-particles in the three-roll mill is proven scientifically to be the force balance due to the liquid bridge force.