Filtering properties of porous materials from nonspherical powders

Abstract

1. The results are presented of a study of sintered filters from nonspherical powders. It is shown that the optimum combination of permeability and stopping power is attained with high-porosity filters produced from powders with fine particles, the actual choice of a powder fraction being governed by the necessary stopping power. 2. It was established that the permeability coefficient of sintered filters pressed from nonspherical powder substantially increases with increasing filter thickness, which is due to the presence of a densified surface layer. The dependence of the permeability coefficient on filter thickness is more pronounced in the case of filters pressed from powders of lower apparent density. 3. It is shown that the stopping power of filters is independent of specimen thickness (over the 2–8-mm range investigated). An exception are filters of 55% porosity produced from a 0.28–0.36-mm powder fraction, whose stopping power becomes greater with increasing thickness. 4. Studies of the sludge-holding capacity of filters from nonspherical powders demonstrated that, depending on whether filtration is controlled by a volume of surface mechanism, different laws govern the increase in the resistance of filters operating in a contaminated fluid. The rate of rise in the resistance of operating filters increases with decreasing specimen thickness and porosity. 5. Assessment of regeneration power on the basis of the extent to which the starting sludge-holding capacity of filters is restored is clearly more appropriate than other techniques. Ultrasonic cleaning restores 90% or more of the starting sludge-holding capacity of filters from nonspherical powders.