Wear behavior and mechanism of spheroidal graphite cast iron were studied on a pin-on-disk elevated temperature wear tester.The phase and morphology of worn surfaces were examined by X-ray diffraction and scanning electron microscopy.Results show that with an increase of load,wear rate of spheroidal graphite cast iron gradually increases under low loads,rapidly increases or potentially increases under high loads;wear rate increases with increasing ambient temperature.At 25-200℃,adhesive wear prevails;oxidative wear and adhesive wear coexist at 400℃.As load surpasses 150 Nat 400℃,extrusive wear appears.The elevated-temperature wear of spheroidal graphite cast iron is a physical and chemical process including the following reactions:xFe+y/2O2—Fex Oy,2C+O2—2CO and Fex Oy+yCO—xFe+yCO2.Hence,at 400℃,the amount of graphite and tribo-oxides are substantially reduced because of reductive function of graphite.It can be suggested that wear-reduced effect of graphite and tribo-oxides is impaired.
Floor heave is the most common convergence in gob-side entry retaining.The paper analyzes the form,process and characteristics of gob-side entry retaining with the comprehensive methods of theoretical analysis,numerical simulation and the field trial.Research results present that bending and folding floor heave is the main factor in the stage of the first panel mining;squeezing and fluidity floor heave plays a great role in the stable stage of gob-side entry retaining;the combination of the former two factors affects mainly the stage of the second mining ahead;abutment pressure is a fundamental contribution to the serious floor heave of gob-side entry retaining,and sides corners of solid coal body are key part in the case of floor heave controlling of gob-side entry retaining.Floor heave of gob-side entry retaining can be significantly controlled by reinforcing sides and corners of solid coal body,and influence rules on the floor heave of gob side entry retaining of sides supporting strength and the bottom bolt orientation in solid coal side are obtained.Research results have been successfully applied in gob-side entry retaining of G20-F23070 face haulage roadway in #2 coal mine of Pingmei Group,and the field observation shows that the proposed technique is an effective way in controlling the floor heave of gob-side entry retaining.
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