Study of progeny particle size distribution in an impact hammer mill

Abstract

Optimized crushing can lead to much savings in the total energy requirement for the comminution circuit. Impact hammer mill is an attractive secondary/tertiary crushing unit due to the high reduction ratio achievable and the uniformity of the product size distribution. However, due to higher wear of the hammers and the inner shell it is generally not used for harder materials. In this work, a systematic study on the comminution of a soft (coal) and a hard (iron ore) material is carried out to investigate the product size distribution under various operating conditions. The effect of the feed rate, the grate opening and the rotational speed on the product size distribution is investigated. Also, the breakage pattern is observed in the absence of a grate under various conditions. The quantity of fines was observed to reflect the degree of attrition in the mill. The open discharge condition with a high rotor speed and a high feed rate was observed to generate much less fines with substantial comminution of the large particles. At low rpm the comminution was not adequate under open discharge condition. The product size distribution was found to be quite uniform under all conditions when a grate is used. High reduction ratios were obtained under most conditions. The employment of impact hammer mill in the secondary crushing circuit may eliminate the need for tertiary crushing. The product size distribution data from the hammer mill suggests that the load on the grinding circuit may be reduced significantly by using this comminution unit. Size reduction was found to be adequate even with the harder material at higher rotational speeds. In order to exploit the advantages of high reduction ratio and uniform product size distribution obtained in the hammer mill suggestions were made for the employment of this unit for relatively harder materials too.