Grinding mechanism of grinding wheel
When the grinding wheel surface high temperature, if the cooling measures are not good, it is easy in the workpiece surface (from dozens of um to several hundred um) secondary quenching and high temperature tempering. If the instantaneous temperature of the surface of the grinding wheel surface of the grinding wheel exceeds the AC1 point of the steel, the quench martensite is quenched under the action of the cooling liquid. Under the surface, the temperature gradient is large and the time is short, This creates a tensile stress between the surface and the sub-surface, and the surface is a thin, brittle, second-quenched martensite that produces cracks when it can not withstand it.
1) Residual austenitic grinding wheel grinding residual austenite due to grinding wheel grinding when the heat and pressure generated by the transition, and may be accompanied by surface tempering and grinding wheel grinding cracks. The amount of retained austenite should be controlled within 30%.
2) The concentration of carbon in the carbon layer is too high, and the net carbide or too much free carbide is easily formed in the microstructure. Due to the extremely hard material, local overheating and surface tempering may occur during grinding wheel grinding. Thickness of the layer of carbon is too high, will cause the workpiece surface too much residual austenite. Resulting in burns and cracks. Therefore, the surface carbon concentration increases, then reduce the grinding wheel performance, the general surface carbon concentration should be controlled within the range of 0.75% -0.95%.
3) Carbide distribution and morphology Carbide distribution should be uniform, the average particle size is not greater than lμm; Carbide morphology should be spherical, powder or fine dot along the network distribution, does not allow a mesh or angular carbide.
4) decarburization heat treatment. Surface or environmental protection will produce improper surface oxidation, so that the workpiece will produce a thin layer of decarburization, this layer of soft decarburization layer will cause the wheel overload or overheating, resulting in surface tempering.
5) tempering to ensure the hardness of the premise, the tempering temperature as high as possible, tempering time as long as possible. This increases the plasticity of the carburized hardened surface and allows the residual stress to be balanced or reduced. Improve the distribution of surface stress. This can reduce the chance of occurrence of workpiece cracks, thereby improving the efficiency of grinding wheel grinding the workpiece.
6) deformation should be as much as possible to reduce heat treatment deformation. This can reduce the grinding wheel grinding allowance. If the deformation of the heat treatment is too large, if the grinding wheel grinding operation does not begin grinding of the grinding wheel at the maximum of the radial runout of the workpiece, the grinding wheel clearance at these points will be abnormal for each grinding wheel grinding Burns and cracks.