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Analysis of the Causes of Failure of NSK Tapered Roller Bearings

Source: China Bearing Network Time: 2018-05-15

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1. The grinding heat of NSK tapered roller bearings is in the grinding process of NSK tapered roller bearings; the grinding wheel and the workpiece touch area; it consumes a lot of energy; a lot of grinding heat occurs; the part of the grinding zone is instantaneously high temperature. Linear heat transfer heat transfer theoretical formula derivation, accounting or the use of infrared and thermocouple method to test the instantaneous temperature; the instantaneous temperature of the grinding zone can be as high as 1000 ~ 1500 Â°C. Such 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 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 enthalpy layer of the external grinding 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) Amorphous arrangement of the instantaneous high temperature of the grinding zone to cause the workpiece to reach the molten state; the molten metal molecular flow is evenly 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) 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 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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