Abstract
An investigation was conducted to determine the effect of the ball diameter sizes on milling operation. A laboratory size ball mill was used with ball media of sizes 10 mm, 20 mm and 30 mm respectively. Quartz was the material used to perform the experiment and was arranged into 3 mono-sizes namely -8 mm +5.6 mm, -4 mm +2.8 mm and-2 mm +1.4 mm for the experiment. A mill run having a mixture of the 3 ball diameter sizes was also conducted. It was determined that the 30 mm diameter balls were most effective of the three sizes during the grinding of the 3 monosize feed material samples. The 10 mm diameter balls were the least effective as minimum particle breakage was observed whereas the 20 mm diameter balls were relatively effective to some extent. The selection function of the 30mm balls was also much greater as it had a higher maximum point and a very low small abnormal region. The mill run conducted using a mixture of ball sizes however was slightly better than that of the 30 mm diameter balls. The primary breakage function was observed as to be non-related to the ball diameter but rather to the 3 mono-sizes of the feed material. In terms of the power draw, there seemed to be no link between it and the ball diameter size.
Highlights
Milling is the third and final stage of comminution after crushing which involves the reduction of solid particle sizes to micron size level
The size of the steel balls used during the milling process are related to the size of the mill charge material whereby small diameter balls are used for feed material of small sizes while larger diameter balls are used for larger sized feed material [4]
To further support the statement made by Katubilwa et al which stated that larger feed material size would require larger ball diameters during milling, Figure 3 below shows the cumulative 5 passing curve for a feed material of size -2 mm +1.4 mm when milled under the same conditions
Summary
Milling is the third and final stage of comminution after crushing which involves the reduction of solid particle sizes to micron size level. Only about 20% of the energy generated by the mill is utilized for actual grinding of the ore [2] This inefficiency is a result of various factors such mill load, rotation speed, type of milling (wet or dry) as well as the size of the steel balls [3]. Mills are one of the largest energy consumers in processing plants which can be estimated to about 50% of the total energy utilized in minerals processing This indicates that it is very vital that mills operate under optimum conditions [2,3]. These different energies are relative to the optimum ball diameter, which differs according to the size of the mill as well as the desired size reduction of the feed material [3,4]
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