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Analysis of the main factors affecting the grinding layer of SKF bearing
Source: China Bearing Network Time: 2017-10-02
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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 6206 bearing during 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 workpiece is subjected to a kneading effect (ploughing effect); the surface of the workpiece is left with a significant plastic deformation layer. The degree of deformation of the deformation layer will increase with the degree of grinding of the grinding wheel and the increase of the grinding feed. Big.
(2) Thermoplastic deformation (or high temperature deformation) The instantaneous temperature of the layer grinding heat on the outside of the work; the 6206-2RS1 bearing makes the elastic limit of the outer surface of the workpiece at a certain depth sharply decrease; even the degree of elasticity is not visible. Under the effect of grinding force; especially the effect of tightening force and friction; the spontaneous expansion caused by the base metal; the outer surface is tightened (more plough); the plastic deformation is formed on the outer surface. The high temperature plastic deformation is in the grinding process. In the case of constant; increase with the increase of the external temperature of the workpiece.
(3) The work hardening 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, SKF bearing calculation or the instantaneous temperature under the conditions of the infrared method and the thermocouple method; the instantaneous temperature in the grinding zone can be as high as 1000-1500 ° C in the range of 0.1 to 0. 001 ms. High-temperature oxidation of the outer surface of the work surface with a certain depth of appearance; amorphous arrangement, high temperature tempering, secondary quenching; and even burn cracking and other changes.
(1) The effect of the outer surface of the SKF bearing on the surface of the steel and the oxygen in the air; the thin layer of iron oxide which is extremely thin (20-30 nm). It is worth noting that the thickness of the oxide layer and the surface grinding 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) The amorphous state arranges the instantaneous high temperature of the grinding zone to make the workpiece surface 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 speed; 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 temperature of the workpiece at a certain depth (10 ~ 100nm). In the case of not reaching the austenitizing temperature; The improvement of the heating temperature; the appearance of the layer will be re-tempered or high-temperature tempering corresponding to the heating temperature; the hardness of the 6206-2RS1 bearing will also decrease. The higher the heating temperature, the more fierce the hardness is.
(4) Two-layer quenching layer of SKF bearing 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 .6206 bearing crack is most simply conveyed along the original austenite grain boundary. Severe burns will cause the entire grinding surface to appear cracks (more cracks) to form the workpiece.
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