Influence of geometric design variables on the efficiency of the high energy horizontal chromite type ball milling process

Abstract

Elemental chromium (Cr) does not occur in nature, but Cr exists in chromite ores as FeOCr2O3. There are some processes to obtain Cr from chromite. For all processes milling process is essential. In milling process of chromite, ball mills are generally used, because follow-up processes need fine particle size. Due to the fact that chromites with a high iron content are hard, mill components like liner and grinding media wear faster than many mines which is a significant problem in chromite grinding. This paper presents an experimental investigation of the influence of liner profile design and speed on chromite ball milling process. For evaluation of the experiments, power consumption, particle size and wear rate datas are calculated. In this experimental study, five liner profiles were designed and worked with three speeds (60, 70 and 80 % critical speed). By this combination, this study contains fifteen experiments. The ball milling process efficiency is related with shape of grinding media, kind of grinding media and product filling degree, ball size distrubition, etc., all other factors are kept constant. It was investigated the effects of liner profiles-milling speed variations on milling efficiency. 70 % critical speed was the optimum speed for all liner types. Best particle size result was meausured in the 10th experiment as 95 μm which has the highest liner. Also, the steepest liner profile has the second-best result at a critical speed of 70 %. Energy saving is important for selecting liner profile. Besides, shallowest design with 80 % critical speed has the worst particle size result. Although highest liner profile Type 5 has the best result for particle size, the difference of wear rates is nearly two times (160 g versus 90 g) compared to Type 3 which has a particle size result of 100 μm. This means nearly half life time difference between two liners. By considering three parameters, power consumption, particle size and wear rate, the best results occurred with the steepest and medium liner profile, and these may even be further improved.