Experimental investigation of the particle size distribution and the influence of operating parameters in limestone drilling

The feature of rock drilling particles is closely related to the improvement of drilling efficiency. The characteristics of drilling particle size distribution (PSD) and its relationship between the operating parameters in limestone drilling are experimentally investigated. Experimental results show that drilling particles are mainly distributed in a range of 0.1-1000 mu m and show a bimodal distribution. The PSDs are systematically analyzed by characterization parameters. PSD width defines the distribution scope and uniformity, and large width shows at medium rotation rates or high penetration rates. Compactness reflects the particles packing condition in the drill hole, based on the gradation analysis and Fuller theory, which is less influenced by higher rotation rates while tends to decrease at higher penetration rates. The bimodal feature is described by bimodal span and bimodal amplitude ratio, which characterize the fine and coarse fractions and influence the structure of particulate system, and both of them show a concave function of rotation rate. An overall parameter, average particle size, shows a concave curve under increasing rotation rates and different monotonic curves under increasing penetration rates. Moreover, the agglomeration of fine particles appears at higher rotation rates in the grinding and comminution process, which reduces the breakage of coarse particles and causes an increase of average particle size.