Study On Failure Mechanism Of Rock Cutting By Concial Picks Of Mining Machinery

The study on unmanned excavation equipment in deep hazardous coal seam is the forefront of the current international coal field and an unsolved worldwide problem for a long time.An important challenge is the adaptive conflict between efficient excavation operations and complex coal and rock conditions.This is related to the unclear fracture mechanism of coal and rock cut by picks of mining machinery and insufficient cutting theory of guiding the practice.In view of the existing imperfect cutting theory,change rules of cutting force of concial picks and failure mode of coal and rock under various cutting conditions and cutting parameters are studied through theoretical analysis,physical test and numerical simulation.The main research results are as follows:(1)Based on cutting model by Evans and limit equilibrium analysis method,a new theoretical formula for calculating peak cutting force is put forward under conditions of plane cutting and symmetrical cutting slot.Compared with other existing theoretical formulas,in addition to taking into account the influence of half cone angle of picks,tensile strength of coal and rock and friction coefficient between rock and teeth,a new parameter named brittleness index of coal and rock is introduced,and more consistent with the test results.(2)Influence of half cone angle of picks and brittleness index of coal and rock on breakup angle of coal and rock?contact radius and friction coefficient between rock and teeth are analyzed.Theoretical determination method of the scaling factor in the modified formula by Roxborough and the theoretical formula satisfying plane cutting and symmetrical cutting slot conditions are presented.(3)By equivalent method for contact radius and peak cutting force based on conditions of dissymmetrical cutting slot and symmetrical cutting slot,the equivalent cutting thickness under symmetry of cutting slot is converted.By simplified peak cutting force formula under conditions of symmetrical cutting slot,peak cutting force under conditions of dissymmetric cutting slot is deduced.(4)Combined with stress solution of elastic body with circular hole subjected to vertical and horizontal ground stress,force balance of the mass that is about to crack is analyzed and peak cutting force considering horizontal ground stress under conditions of plane cutting and symmetrical cutting slot is derived.The influence of horizontal stress on failure mode of coal and rock and cutting force is also analyzed.Linear relationship exists between peak cutting force and ratio of ground stress to tensile strength of coal and rock.(5)Peak cutting force considering nonzero attack angle of picks under conditions of plane cutting and symmetrical cutting slot is deduced.Comparison with previous theoretical and experimental results,the results show that the calculation accuracy is higher.Attack angle has little effect on the breakup angle of coal and rock.Peak cutting force increases nonlinearly with increase of attack angle.(6)A static penetration test platform for picks is designed and reformed by oneself.And combined with another dynamic cutting test platform,tests of edge chipping of samples and cutting test of different cutting thicknesses,different cutting spaces,different penetrating angle or cutting angle and different pick specifications are implemented.Influence of different cutting parameters on failure modes of coal and rock and load of picks are analyzed.Influence of brittleness index and boundary condition on failure modes of coal and rock is numerically analyzed by finite element software RFPA.Based on elastic solution of stress distribution by penetrating of picks into coal and rock,causes of dense nucleation formation and tensile fracture of coal and rock are analyzed.