Three solutions to unqualified bearing rings

1、 Center offset method

1. Salvage of the inner and outer diameters of bearing rings

Firstly, accurately measure the size of each defect (asymmetric type) in the part, calculate the small grinding amount (to the finished product size deviation) M, and then offset the center of the part during grinding (towards the direction that increases the grinding amount at the defect), with a large deviation of M/2, that is, increase the grinding amount at the defect relatively, and focus on grinding,.

2. Saving the inner and outer raceways of the ferrule

The grinding design basis for bearing rings is the inner diameter or outer diameter, which means grinding the inner (outer) diameter first and then grinding the raceway. Taking the inner race as an example, if there are asymmetric defects in the inner raceway, it is necessary to accurately measure the inner diameter size of the part and calculate the maximum grinding amount M and the large grinding amount M1 at the defect of the inner raceway. When M1<M, the center of the inner ring needs to be offset when grinding the inner diameter, with a large offset of M1/2. That is, when machining the inner diameter, a relative increase in grinding amount is given to the defect area of the inner raceway in advance. Then, when grinding the inner raceway, the defect area will be heavily ground, and the waste will be saved. When M1 ≥ M, normal grinding cannot remove it. According to the situation, the methods described in section 1.1 can be used to save it.

The use of the center offset method for grinding is carried out on the premise of ensuring the hardness and depth of the carburized layer of the parts. The total offset cannot be completed in one offset grinding, and is generally divided into several grinding processes, that is, through the repeated process of offset trial grinding, measurement, adjustment of offset, and trial grinding. After the defects are removed, they are re aligned and the ellipticity is corrected through normal grinding. This method has low efficiency and requires the operator to have a high level of technical proficiency. However, in single machine and single piece production, this method has a high success rate in rescuing and does not delay the production progress. After several years of practical verification, the effect is good.

2、 Heat treatment expansion method

The quenching structure of bearing steel consists of quenched Martensite, a small amount of insoluble secondary carbide and about 12%~14% residual austenite. Quenched Martensite and residual austenite belong to unstable structure. Decomposition of Martensite during tempering makes the volume of steel shrink, while decomposition of residual austenite makes the volume of steel expand. With the increase of tempering temperature, the transformation and decomposition amount of residual austenite increases. Under the condition of ensuring the hardness required by the process, properly increase the tempering temperature to decompose the residual austenite and transform it into Martensite structure with large specific volume, which can increase the volume of the workpiece accordingly, that is, relatively increase the external diameter grinding amount. Using this method, the bearing ring defects can be saved as scrap parts under normal grinding conditions.

This method has a significant effect on thick and heavy workpieces with high residual austenite content, especially for self-aligning roller bearings. In actual production, different tempering processes have been developed for parts of different specifications, sizes, and thicknesses. While ensuring hardness and deformation, the microstructure is fully transformed, resulting in significant expansion and corresponding increase in grinding volume to save waste products.

3、 Chemical deposition method

For bearing parts with dimensional tolerances exceeding design standards, chemical deposition method can be used to rescue them. The principle of chemical deposition is to uniformly produce a certain thickness of metal coating on the surface of the part through chemical reactions between various chemical raw materials, and to ensure that the metal layer has the same hardness and mechanical properties as the original part through additional tempering. Chemical deposition only increases the size of the part and does not change the shape tolerance of the part. Therefore, for parts with dimensional tolerance exceeding the tolerance, chemical deposition is an effective rescue method. Currently, the thickness of unilateral deposition can reach about 0.1mm.