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Four common failure conditions of FAG imported bearings
Source: Bearing network time: 2013-05-27
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According to FAG imported bearing operation, the formation mechanism of the grinding layer is affected; the primary factor affecting the grinding and enthalpy layer is the effect of grinding heat and grinding force. The following is a professional professor of bearing trading network for us to analyze the cause of FAG imported bearing failure. .
1. The grinding heat of FAG imported bearings is in the grinding process of FAG imported bearings; the grinding wheel and the workpiece touch area; it consumes a lot of energy; many grinding heat occurs; part of the instantaneous high temperature that constitutes the grinding zone. The linear motion heat source is used. The theoretical formula of heat transfer is deduced, accounted, or measured by the infrared method and the thermocouple method. The instantaneous temperature in the grinding zone can be as high as 1000 to 1500 °C. Instantaneous high temperature; high temperature oxidation of the outer surface of the work surface to a certain depth; 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 extremely thin (20-30 nm). It is worth noting that the thickness of the oxide layer and the surface of the entangled layer are The 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 to 100 nm). Under the condition that the austenitizing temperature is not reached; The improvement of the heating temperature; the appearance of the layer will be changed according to 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 (Ac1); then the austenitizing of the layer is arranged in the subsequent cooling process; Quenching into martensite arrangement. However, any workpiece with secondary quenching burn; under the secondary quenching layer must be a very high temperature tempering layer.
(5) Grinding cracks Secondary quenching burns will change the stress on 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. FAG imported bearings due to the grinding force of the transformation layer in the grinding process; the outer surface of the workpiece will be affected by the cutting force, tightening force and friction of the grinding wheel. Especially the effect of the latter two; make the outer surface of the workpiece constitute the direction Very strong plastic deformation layer and work hardening layer. The professional professor of the bearing trading network emphasizes: "These metamorphic layers must affect the changes of the 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; even the degree of elasticity is not reached. At this moment, the outer surface of the work is under grinding force. Especially under the effect of tightening force and friction; the resulting free expansion; bound 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 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 subsequent processing; the residual surface of the workpiece will also constitute the surface softening and transformation; promote the early failure of FAG imported bearings.
3. Cracking failure FAG imported bearing cracking failure is the primary cause of shortcomings and overload. When the applied load exceeds the data strength limit, the component cracking is called overload cracking. The overload is caused by the host's sudden fault or improper installation. FAG imported bearing parts The shortcomings of microcracks, shrinkage cavities, air bubbles, large foreign objects, overheating arrangements and partial burns will also cause cracking in the shortcomings during impact overload or severe oscillation; called fault cracking. The professional professor of the bearing trading network also pointed out; FAG imported bearings are in the process of production; in the re-inspection of the original materials, the quality control of casting and heat treatment, and the processing of the processing process, the above-mentioned shortcomings can be correctly analyzed through the instrument; in the future, the control must be strengthened. However, in general; Generally, FAG imported bearing cracking failure is mostly overload failure.
4. FAG imported bearings are in operation; FAG imported bearings are in operation; because of the influence of external or intrinsic elements; the original cooperation gap is changed; the accuracy is reduced; even the “bite death†is called the clearance modification failure. The external factors such as excessive interference are too large. The device is not in place; the large amount of expansion caused by temperature rise, instantaneous overload, etc.; connotation elements such as residual austenite and residual stress are unstable, which are the primary reasons for the failure of the play change.
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