Vertical pin stirred mills are used for fine grinding in the minerals industry. They achieve size reduction through attrition between the particles and the grinding media. This process results in significant wear to the mill parts and the grinding media.
This study investigated the effect of stirred mill design on wear. The following mill variables were investigated: Grinding media type (natural and manufactured) and vessel design (baffles and no baffles). The wear of stirrer was monitored in terms of relative mass loss as well as the wear pattern. Graphical visualization of the results would be used in the analysis.
The standard wear test was conducted at 420 RPM with the vessel filled with grinding media and one liter of water. The impeller was fitted with one aluminium pin and one steel pin for both the top and bottom row. The testes ran for two hours with stoppage intervals at 30 min, 60 min and 120 min. The initial pin weight and pin length was measured for each pin as was the weight loss and change in length. The change in pin diameter was measured at intervals of 0 mm, 2 mm, 5 mm and 10 mm on both sides of the pin along the vertical and horizontal axis of the pin.
The rate of pin wear was determined to be directly related to the hardness of the pin material and the physical characteristics of the grinding material. The rate of wear was also determined to be proportional to the power input. The rate of wear is also dependent on the coarseness of the grinding material as the coarse Colorado sand produced a greater rate of wear than the smooth steel shot. For the same grinding media type the wear rate is dependent on the size of the grinding media. Colorado sand produces a much greater wear rate than the finer beach sand.
The wear profiles generated from the test work indicate that the wear shape of the profile is independent of the grinding media and the pin material. The different wear shape generated in the test with the vessel with baffles indicates that the wear profile may be largely dependent on the vessel geometry.
The similarity between the shape of wear on the test pins and the industrial impellers at Century Zinc and the result that the wear shape is largely dependent on the mill geometry indicates that the testing apparatus could be successfully used to model and scale up the wear profiles of industrial mills.