Liberation properties of middling coking coal under shear force

The relationship between shear force and selective liberation of middling coking coal was investigated by crushing the coal at different shear angles (15°, 30°, 45°, 60°, and 75°). Subsequent analysis of the middling coking coal revealed that as the ash content of coal increased, the shear strength and cohesion increased, while the internal friction angle gradually decreased. Increasing the shear angle caused a gradual increase in the quantity of coarse particles and a decrease in the quantity of fine particles, ultimately leading to a dominant particle size of >10mm at a shear angle of 75°. The cumulative ash and cumulative yield curves showed that the liberation of middling coking coal through crushing was optimum when the shear angle was smaller than the internal friction angle. Lamellar tear fractures observed with low-shear-angle crushing could contribute to the liberation of coal, but the step-like morphology characteristics of medium and high shear angles was not conducive to liberation. Because the liberation of middling coking coal through crushing was optimum when the shear angle was smaller than the internal friction angle, a high ash content or high shear angle may make the release of clean coal more difficult. [Display omitted] •An evaluation index of selective crushing was proposed.•Smaller shear angle is good for middling coal crushing.•High ash content and high shear angle make the release of clean coal more difficult.