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The failure modes of rolling bearings are external contact fatigue, abrasive wear, adhesive wear and corrosion wear; they always occur in the outer and outer layers of the bearing operation; the quality of the outer surface of the work is critical to the reliability and service life of the bearing. important. /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
The surface quality of rolling bearing operation includes: external description, external material and external enthalpy layer analysis, external stress analysis, external wear and corrosion analysis.
Because of the influence of cold and hot processing conditions and smooth media, the microscopic arrangement, physical, chemical and mechanical properties of the bearing operation are often very different from those of the heart. The microscopic layout and physics of the bearing appearance. The outer surface layer whose chemical and mechanical properties have changed is called the outer surface enthalpy change layer. If the outer surface enthalpy change layer is caused by the grinding process, it is called grinding surface enthalpy change layer. The rolling bearing operation external surface enthalpy layer analysis is the primary analysis of bearing external surface quality analysis. Component; of course, one of the important components of bearing failure analysis.
The mechanism of grinding the enthalpy layer according to the bearing work surface; the primary factor affecting the grinding enthalpy layer is the effect of grinding heat and grinding force.
1. Grinding heat in the grinding process; grinding wheel and workpiece touch area; cost a lot of energy; many grinding heat occurs; part of the instantaneous high temperature that constitutes the grinding zone. Use the linear motion heat source heat transfer theory formula to derive, account or The infrared temperature method and the thermocouple method are used to measure the instantaneous temperature under the test conditions; 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. Such instantaneous high temperature is sufficient for the operation appearance to be certain High-temperature oxidation of the outer surface layer; amorphous arrangement, high temperature tempering, secondary quenching; and even burn cracking and other changes.
(1) The effect of the outer surface of the oxide layer on the appearance of oxygen in the steel and the oxygen 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 total thickness of the entangled layer of the surface are ground. The 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 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) 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 (Ac 1 ); the austenitizing of the layer is arranged in the subsequent cooling process; From the head quenching into a martensite arrangement. However, any workpiece with secondary quenching burns; under the secondary quenching layer must be a very high hardness tempering 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 cracks (greater cracks) in the entire grinding surface to form the workpiece.
2. The moiré layer formed by the grinding force is in the grinding process; the outer surface of the workpiece will be affected by the cutting force, the tightening force and the friction force of the grinding wheel. Especially the effect of the latter two; the outer surface of the workpiece is very 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 of the layer grinding heat on the surface of the work; the elastic limit of the outer surface of the workpiece at a certain depth is sharply reduced; and the degree of elasticity is not reached. At the moment, the outer surface of the work is under grinding force. Especially under 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 plough); the plastic deformation is formed on the outer surface. The high temperature plastic deformation is unchanged in the grinding process. Lower; as the workpiece surface temperature increases.
(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.
In addition to the grinding process; the outer decarburization layer formed by casting and heat treatment heating; if it is not completely gone in the future processing; the residual on the surface of the workpiece will also constitute the surface softening and transformation; promote the early failure of the bearing.
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Bearing appearance and outer skin quality
Source: China Bearing Network Time: 2014-02-14