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1 Center shift method 1.1 Rescue the inner and outer di […]
1 Center shift method
1.1 Rescue the inner and outer diameter of the bearing ring
First, accurately measure the size of each defect (asymmetric) of the part, calculate the minimum amount of wear (the amount of wear to the finished size deviation) M, and then perform the center offset of the part during grinding ( Offset to the direction that increases the amount of grinding at the defect), the maximum offset is M/2, that is, to increase the amount of grinding at the defect, and focus on grinding.
1.2 Rescue of the inner and outer raceways of the ring
The design basis for the grinding of bearing rings is the inner diameter or outer diameter, that is, the inner (outer) diameter is ground first, and then the raceway is ground. Take the inner ring as an example. If the inner raceway has an asymmetric defect, it needs to be accurately measured. The inner diameter size of the part, and calculate the maximum amount of wear M and the maximum amount of wear M1 at the defect of the inner raceway. When M1＜M, the inner ring center is required to be offset when grinding the inner diameter. The maximum offset is M1/2, that is, when the inner diameter is processed, the inner raceway defect is relatively increased in advance, and then the inner ring is ground. In the raceway, the defects will be sharpened and the waste can be saved. When M1≥M, the normal grinding cannot be removed, and the method described in section 1.1 can be used to save it according to the situation.
Grinding using the center offset method is performed under the premise of ensuring the hardness of the part and the depth of the carburized layer. The total offset cannot be completed in one offset grinding. Generally, it is divided into several grindings, that is, through the offset test Grinding-measuring-adjusting the offset-retrying the repeated process of grinding to complete, after the defect is worn away, re-alignment, normal grinding to correct the ovality. The efficiency of this method is low, and the operator is required to have a higher technical level. However, the use of this method in single-machine and single-piece production has a higher rescue success rate and does not delay the production schedule. After years of practice, the effect is good
2 Chemical deposition
For bearing parts whose dimensional tolerance exceeds the design standard, chemical deposition can be used to save. The principle of chemical deposition is to uniformly produce a certain thickness of metal coating on the surface of the part through the chemical reaction between a variety of chemical raw materials, and ensure that the metal layer is the same as the original hardness and mechanical properties of the part through additional tempering. Chemical deposition only increases the size of the part without changing the shape tolerance of the part. Therefore, for parts with out-of-tolerance tolerance, chemical deposition is an effective rescue method. At present, the maximum single-sided deposition thickness can reach about 0.1mm.
3 Heat treatment expansion method
The quenched structure of bearing steel consists of quenched martensite, a small amount of undissolved secondary carbides and approximately 12% to 14% of retained austenite. Quenched martensite and retained austenite are unstable structures. The decomposition of martensite during tempering causes the volume of steel to shrink, while the decomposition of retained austenite causes the volume of steel to expand.
With the increase of tempering temperature, the amount of transformation and decomposition of retained austenite will increase. Under the condition of ensuring the required hardness of the process, the tempering temperature should be appropriately increased to decompose the retained austenite and transform into martensite with a larger specific volume. The organization can increase the volume of the workpiece correspondingly, that is, increase the amount of outer diameter grinding. This method can save the parts of the bearing ring that become waste under normal grinding conditions.
This method is more effective for thick and heavy workpieces (especially for spherical roller bearings) with large retained austenite content. In actual production, different tempering processes have been formulated for parts of different specifications, different sizes, and different thicknesses. Under the premise of ensuring hardness and deformation, the structure can be fully transformed, resulting in larger swelling, and the amount of grinding should be increased accordingly to save the waste. .