Study of Wear of Pitched Blade Impellers in a Solid-Liquid Suspension

Abstract

A study was made of the erosion wear of the blades of pitched blade impellers in a suspension of silicious sand (C_V= 5 %, d=0.325 mm, degree of hardness "7.5") in water under a turbulent flow regime of agitated charge when complete homogeneity of the suspension was achieved. Two aims of the study were defined: the dependence of the rate of the erosion process of the impeller blades on impeller frequency of revolution and on the size of the mixing equipment. Experiments were carried out on pilot plant mixing equipment of two sizes (geometrically similar) made of stainless steel (diameters of cylindrical vessels T₁ = 200 mm and T₂ = 300 mm, diameters of impellers D₁ = 100 mm and D₂= 66. 7 mm, impeller off bottom clearances h₁ = 100 mm and h₂= 66. 7 mm, respectively) equipped with four radial baffles (width b₁ = 30 mm, b₂ =20 mm, respectively) and an impeller with four inclined plane blades (pitch angle α =30°, 45°, relative blade with W/D = 0.2) made of rolled brass (Brinnel hardness 40-50 BM) always pumping the liquid downwards towards the float vessel bottom. The wear of the impeller was described by an analytical approximation in exponential form with two parameters (the wear rate constant k and the geometrical parameters of the worn blade C) calculated by the least squares method from the experimentally found profile of the worn leading edge of the impeller blades. While the wear rate constant exhibits a monotonous dependence on the pitch angle only, the geometric parameter is dependent both on the pitch angle and in linear form on the impeller tip speed. Thus in the procedure for scaling up the rate of erosion wear of the pitched blade impellers in a suspension of higher solid particle hardness, the decision process parameters are the impeller blade pitch angle and the impeller tip speed.