UBC Theses and Dissertations
Process optimization of jet mills for metallurgical powder production Ramanathan, Gurupraveen
The jet mill operates on the principle of collisions between particles to grind ultrafine powder material without the introduction of heat or any other external force and is capable of particle size reduction from about 100 microns down to 250 nm. The optimization process depends on parameters such as feed rate, grinding air pressure, physical characteristics of the solids (density, hardness, abrasiveness, or tenacity), physical characteristics of the mill shell liner, as well as feed and product particle size distribution (PSD). This research studied the optimization of the jet mill grinding process of ultrafine metallurgical powders in a small-scale 4” jet mill. The research was aimed to understand the effects of feed rate, compartment pressure, and feed particle size distribution on overall mill efficiency and iron entrainment using a stainless-steel shell. In addition, the effect of a polymer-based shell coating on milling efficiency, shell abrasion rate, and iron contamination reduction was assessed. The main variables affecting grinding such as feed rate, grinding air pressure, and feed size were investigated. Optimal operating conditions for running the lab scale jet mill are at the pressure range of 70 to 80 psi, with a feed rate of 3 to 5 kg/hr. At high grinding air pressures, the jet mill produces a small particle size, but high pressure requires more gaseous fluid which makes the process less efficient by consuming more energy. It is concluded that density and hardness seem to have a significant effect on the product fineness. Hard materials such as TaC, WC, and WTiTaC resulted in a finer product size than soft materials like TiC. High grinding air pressure has a greater effect on harder materials than on softer materials in achieving the fine product size. It is understood that jet milling can be more effective than ball milling if the optimum parameters are followed, as recommended in the study; such as feed rate, pressure, feed size, and the liner used in producing the metallurgical powders TiC, TaC, WC, or a combination of any of these.
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