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Grinding heat of FAG bearings during processing

wallpapers Tech 2020-06-17
In the grinding process of FAG bearings, a large amount of energy is consumed in the contact area between the grinding wheel and the workpiece. A large amount of grinding heat is generated, causing a local instantaneous high temperature in the grinding zone. The immediate temperature under the experimental conditions is deduced, calculated, or measured by the infrared ray method and the thermocouple method using the linear motion heat source heat transfer theoretical formula. It can be found that the instantaneous temperature in the grinding zone can be as high as 1000-1500 ℃ in 0.1-0.001ms. Such instantaneous high temperature is enough to cause high-temperature oxidation of the surface layer at a certain depth on the working surface, amorphous structure, high-temperature tempering, secondary quenching, and even burn cracking and other changes.
1. Surface oxide layer
The steel surface under the action of instantaneous high temperature interacts with the oxygen in the air to form a skinny (20 ~ 30nm) thin layer of iron oxide. It is worth noting that the oxide layer thickness corresponds to the test result of the total width of the surface-modified metamorphic layer. This shows that the oxide layer's thickness is directly related to the grinding process and is an essential symbol of the abrasive quality.
2. Amorphous structure layer
When the instantaneous high temperature in the grinding zone brings the surface of the workpiece to a molten state, the molten metal molecule flow is evenly coated on the working surface. It is cooled by the base metal at a rapid rate, forming a skinny layer of amorphous state Organization layer. It has high hardness and toughness, but it is only about 10nm, it is easy to be removed in precision grinding processing.
3. High-temperature tempering layer
The instantaneous high temperature in the grinding zone can make the surface heated to a temperature higher than the workpiece tempering heating within a specified depth (10 ~ 100nm). When the austenitizing temperature is not reached, as the temperature to be heated increases, the surface of the surface layer by layer will produce a tempering or high-temperature tempering transformation corresponding to the heating temperature, and the hardness will also decrease. The higher the heating temperature, the more the hardness decreases.
4. Two-layer quenching layer
When the instantaneous high temperature in the grinding zone heats the surface layer of the workpiece above the austenitizing temperature (Ac1), the austenitized structure of this layer is re-quenched into a martensite structure during the subsequent cooling process. The high-temperature tempering layer with extremely low hardness must be below the secondary quenching layer for any workpiece with secondary quenching burn.
5. Grinding cracks
The secondary quenching burn will change the stress of the surface layer of the workpiece. The secondary quenching zone is under compression, and the material in the high-temperature tempering zone below it has the highest tensile stress. This is where the crack core is most likely to occur. Cracks are most likely to propagate along the original austenite grain boundaries. Severe burns can cause cracks (mostly cracks) on the entire grinding surface and cause the workpiece to be scrapped.

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Tag: FAG   Bearings