Stress Relaxation of Expressed Cake

Abstract

When expression is stopped before a material reaches its equilibrium compression state, the cake stress will decrease as the material relaxes. In this paper, the change of cake stress with time was measured after an interruption of a constant-pressure or constant-rate expression operation of a semisolid material. This relaxation process is analyzed by considering the elastic deformation of the material and its irreversibility and non-linearity. It is found by numerical calculation that local expansion appears near the drainage surface while local consolidation appears near the center of the cake. The calculated stress in a transient stage falls faster than the empirical stress. The theoretical values of the equilibrium cake stress, however, agree well with the empirical ones. It is found that the equilibrium cake stress does not depend on the mode of expression (constant-pressure or constant-rate expression) but is uniquely determined by the average consolidation ratio when the expression is interrupted.