1 Center offset method
1.1 Saving the inner and outer diameter of the bearing ring
Firstly, the size of each defect (asymmetric type) existing in the part is accurately measured, and the minimum amount of grinding (the amount of grinding to the deviation of the finished product size) M is calculated, and then the center is offset at the time of grinding ( To offset the direction in which the amount of wear is increased at the defect, the maximum offset is M/2, that is, the relative amount of wear at the defect is increased, and the focus is sharpened.
1.2 Rescue of the inner and outer raceways of the ferrule
The design standard of the grinding ring of the bearing ring is the inner diameter or the outer diameter, that is, grinding the inner (outer) diameter and grinding the raceway first. Taking the inner ring as an example, if there is an asymmetrical defect in the inner raceway, it is necessary to accurately measure the The inner diameter of the part is calculated, and the maximum grinding amount M and the maximum grinding amount M1 at the inner raceway defect are calculated. When M1<M, the inner ring center offset is required when grinding the inner diameter, and the maximum offset is M1/2, that is, when the inner diameter is processed, the inner raceway defect is firstly increased in advance, and then the grinding is performed. When the raceway is rolled, the defects will be sharply ground and the waste will be saved. When M1 ≥ M, normal grinding can not be ground, according to the situation can be saved by the method described in section 1.1.
Grinding by center offset method is carried out 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, the offset test. Grinding - Measuring - Adjusting the offset - Repeat the process of re-grinding. After the defect has been worn away, re-align it and normal grinding to correct the ellipticity. This method is less efficient, and requires the operator to have a higher level of technology, but in this single-machine, single-piece production, this method has a higher success rate and does not delay the production schedule. After several years of practice, the effect is good.
2 Chemical deposition method
For bearing parts with dimensional tolerances exceeding the design criteria, chemical deposition can be used for salvage. The principle of chemical deposition is to uniformly produce a certain thickness of metal plating on the surface of the part through chemical reaction between various chemical materials, and to ensure the same hardness and mechanical properties of the metal layer and the part by additional tempering. Chemical deposition only increases the size of the part and does not change the shape tolerance of the part. Therefore, chemical deposition is an effective salvage method for parts with poor dimensional tolerance. At present, the maximum unilateral deposition thickness can reach about 0.1 mm.
3 heat treatment rising method
The quenched structure of the bearing steel consists of quenched martensite, a small amount of undissolved secondary carbide, and approximately 12% to 14% of retained austenite. The quenched martensite and retained austenite are unstable structures. During the tempering process, the decomposition of martensite shrinks the volume of the steel, and the decomposition of the retained austenite causes the volume of the steel to expand.
With the increase of tempering temperature, the amount of residual austenite transformation and decomposition increases. Under the condition of ensuring the hardness of the process, the tempering temperature is appropriately increased to decompose the retained austenite and transform into martensite with larger specific volume. The structure can increase the volume of the workpiece correspondingly, that is, increase the grinding capacity of the outer diameter. With this method, the parts of the bearing ring which are defective under normal grinding conditions can be saved.
This method is more effective for thick and heavy workpieces with a large residual austenite content (especially for spherical roller bearings). In the actual production, different tempering processes are formulated for parts of different specifications, different sizes and different thicknesses. Under the premise of ensuring hardness and deformation, the organization is fully transformed, resulting in a large increase, correspondingly increasing the amount of grinding and saving waste.
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