Wear Mechanisms And Mathematical Models Of Steel Balls In Wet Grinding

This dissertation is the main contents of the projects, Wear Mechanisms and Laws of Steel Balls in Ball Mill, [1996] 107 supported by the Developmental Program of Science and Technology of the Ministry of Chemical Industry of China, and the Aiding Grinding-Inhibiting Corrosion Technique in Wet Grinding, [2001 ] 118 by the Specialist Foundation of the Personnel Department of Hubei Province, China. Effects of different grinding conditions, slurry rheological behaviors, electrochemical aspects and chemical additiVes on the wear of steel balls in wet grinding are systematically studied. A new technique of aiding grinding-inhibiting corrosion is developed to reduce the wear rate of steel balls and raise the grinding efficiency. It is applied in industrial test of phosphate ore flotation. A dynamic model and a statistical model of the wear of steel balls are established on the basis of theories and experiments. The models are examined to be satisfactory with trial data.Effects of such grinding conditions as grinding way, grinding atmosphere, pulp volume density and charge volume on the wear rate of steel balls and the grinding efficiency are respectively investigated in this thesis. Test results show that the wear rate of steel balls R is arranged in order: Rorganic>Rwet>Rdry, the net mass fraction of -0.043mm size in grinding products F: Fwet>Forganic>Fdry under different conditions, namely dry, wet and in the presence of an organic liquid. The wear rate increases more rapidly in grinding iron ore than in grinding quartzite or phosphorus ore as the oxygen partial pressure in the mill is increased. It decreases in order of grinding quartzite, iron ore and phosphate ore under nitrogen flushing condition. In the presence of oxygen (oxygen or air flushed into the mill), the corrosive wear of steel balls accelerates in grinding iron ore due to form galvanic coupling between sulfide minerals in iron ore and steel balls. The wear rate increases with either of the pulp volume density and the ball charge, and reaches a maximum at about 25%. The net mass fraction of -0.043mmIVmaterial produced also increases with either of the pulp volume density and the ball charge, but it decreases slightly over pulp volume density of 50% and its growth speed decreases as the charge volume increases.Effects of slurry rheological characteristics on the wear performance of the balls are studied. Test results indicate that slurry rheological behaviors change outstandingly at pulp volume density of approximately 50%. Pulp viscosity increases gradually with pulp volume density under 50%, and does rapidly over 50%. The slurry rheological behaviors can be improved by adding some chemical additives into pulp with high volume density. The wear rate increases with pulp viscosity, and reaches a maximum at a critical viscosity of about 200mPa.s with a shear rate of 22.4Is"'.A law that the thickness of pulp layer coating on the balls varies with pulp volumetric solids content is found. The wear rate of steel balls with small pulp layer thickness is higher. The wear rate decreases and the grinding efficiency increases as the thickness increases, but the grinding efficiency decreases when it is over the best thickness.Electrochemical determining data demonstrate that the galvanic couples form between the pyrite particles and the steel balls when they contact with each other, because the rest potential of the steel ball electrode as an anode is lower and that of pyrite electrode as a cathode is higher. The initial combination potential and the initial galvanic current of a pyrite-steel ball couple in aeration of oxygen are greater than those in aeration of air. The combination potential and the galvanic current decrease more quickly with time in aeration of oxygen than they do in aeration of air. In an experiment of simulating wear differences, between two different balls in wear degree exists a galvanic current, which is smaller than that between pyrite and the ball. Under different grinding time conditions, the equivalent corrosion currents calcula...