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Analysis of the main factors affecting the grinding layer of FAG bearing
Source: China Bearing Network Time: 2018-01-29
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1. Grinding force is in the grinding process; the outer surface of the workpiece will be affected by the cutting force, tightening force and friction force of the grinding wheel. Especially the effect of the latter two; the outer surface of the workpiece constitutes a strong directional plastic deformation Layer and work hardening layer. These metamorphic layers must affect the change of residual stress in the outer layer.
.1) The cold plastic deformation layer is in the grinding process; each moment the abrasive grain is equivalent to a cutting edge. However, in many cases, the rake angle of the cutting edge is negative; the abrasive grain is in addition to the cutting effect; The appearance of the kneading effect (ploughing effect); leaving a significant plastic deformation layer on the surface of the workpiece. The degree of deformation of this deformation layer will increase with the degree of grinding wheel blunt and the increase of grinding feed.
.2) Thermoplastic deformation (or high temperature deformation) The instantaneous temperature at which the layer grinding heat is formed on the outside of the work; the elastic limit of the outer surface of the workpiece at a certain depth is drastically reduced; and the degree of elasticity is not reached. At this moment, the outer surface of the work is under grinding force. In particular, the effect of tightening force and friction; the free expansion caused by the base; the constraint of the base metal; the outer surface is tightened (more plowed); the plastic deformation is formed on the outer surface. The high temperature plastic deformation does not change during the grinding process. Lower; as the workpiece surface temperature increases.
.3) The work hardened layer can sometimes be found by microhardness method and metallographic method; the hardness of the outer layer is increased due to processing deformation.
2, grinding heat in the grinding process; grinding wheel and workpiece touch area; cost a lot of energy; a lot of grinding heat occurs; part of the instantaneous high temperature forming the grinding zone. Using linear motion heat source heat transfer theory formula derivation, Calculate or use the infrared method and the thermocouple method to measure the instantaneous temperature under the test conditions; the instantaneous temperature in the grinding zone can be as high as 1000-1500 ° C. The instantaneous high temperature is enough to make the operation The surface of the outer surface must have high temperature oxidation; amorphous arrangement, high temperature tempering, secondary quenching; and even burn cracking and other changes.
.1) The outer surface of the fag bearing oxide layer under the effect of instantaneous high temperature on the surface of the steel and the oxygen effect in the air; the thin layer of iron oxide which is raised to the pole of 20 to 30 nm. It is worth noting that the thickness of the oxide layer and the surface of the enthalpy layer are ground. The total thickness test results are in a corresponding relationship. This indicates that the thickness of the oxide layer is directly related to the grinding process; it is an important mark of the grinding quality.
.2) Amorphous arrangement of the instantaneous high temperature of the grinding zone causes the workpiece to reach the molten state; the molten metal molecular flow is uniformly applied to the work surface; and is cooled by the base metal at a very fast rate; Very thin layer of amorphous arrangement. It has high hardness and resistance; but it only needs about 10nm; it is very simple to be removed in fine grinding.
.3) The instantaneous high temperature in the grinding zone of the high temperature tempering layer can be heated to a temperature higher than the tempering heating of the workpiece at a certain depth (10 to 100 nm). In the case where the austenitizing temperature is not reached; The improvement of the heating temperature; the appearance of layer-by-layer will occur with the re-tempering or high-temperature tempering corresponding to the heating temperature; the hardness will also decrease. The higher the heating temperature, the more fierce the hardness is.
.4) Fag bearing two-layer quenching layer When the instantaneous high temperature of the grinding zone heats the outer surface of the workpiece to above the austenitizing temperature (Ac1); the austenitizing of the layer is arranged in the subsequent cooling process; It is quenched from the head into a martensite arrangement. However, any workpiece with secondary quenching burns must have a very high hardness tempering layer under the secondary quenching layer.
.5) Grinding cracks Secondary quenching burns will change the stress of the outer surface of the workpiece. The secondary quenching zone is under pressure; the maximum tensile stress exists in the high temperature tempering zone below; here is the most likely crack center The local crack is most simply conveyed along the original austenite grain boundary. Severe burns will cause the entire surface of the grinding to show cracks (more cracks) to form the workpiece.
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