Three solutions to unqualified bearing rings
Date:2022-07-16 Editor:Oukai Bearing

Three solutions to unqualified bearing rings

1. Center offset method

1. Rescue the inner and outer diameters of bearing rings

First, accurately measure the size of each defect (asymmetric type) existing in the part, calculate the small grinding amount (the amount of grinding when the size of the finished product deviates) M, and then offset the center of the part during grinding ( Offset in the direction of increasing the grinding amount at the defect), the maximum offset is M/2, that is, the grinding amount is relatively increased for the defect, and the focus is on grinding.

2. Rescue the inner and outer raceways of the ferrule

The design basis for 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. For example, the inner race is taken as an example. If there is asymmetrical defect in the inner raceway, it is necessary to accurately measure the The inner diameter of the part is calculated, and the maximum wear amount M and the maximum wear amount M1 at the defect of the inner raceway are calculated. When M1 < M, the center of the inner ring needs to be offset when grinding the inner diameter, and the maximum offset is M1/2, that is, when machining the inner diameter, first increase the amount of grinding at the defect of the inner raceway, and then grind the inner ring. When the raceway is used, its defects will be ground with emphasis, and the scrap can be saved. When M1≥M, it cannot be removed by normal grinding. According to the situation, the method described in Section 1.1 can be used to save it.

Grinding by the center offset method is carried out on the premise of ensuring the hardness of the parts 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. The repeated process of grinding - measuring - adjusting the offset - retry grinding is completed. After the defects are ground, re-align and normal grinding to correct the ovality. This method is less efficient and requires operators to have a higher technical level, but in single-machine and single-piece production, this method has a higher success rate and does not delay the production schedule. After several years of practice verification, the effect is good.

2. Heat treatment expansion method

The quenched structure of bearing steel is composed of quenched martensite, a small amount of undissolved secondary carbide and about 12% to 14% of retained austenite. Quenched martensite and retained austenite are unstable structures. The decomposition of martensite in the tempering process shrinks the volume of the steel, while the decomposition of retained austenite expands the volume of the steel. With the increase of tempering temperature, the transformation and decomposition of retained austenite increases. Under the condition of ensuring the hardness required by the process, the tempering temperature should be appropriately increased to decompose the retained austenite and transform it into martensite with a larger specific volume. The structure of the workpiece can increase the volume of the workpiece accordingly, that is, the amount of grinding of the outer diameter is increased. Using this method, the defective parts of the bearing ring can be saved under normal grinding conditions and become waste products.

This method is more effective for thick and heavy workpieces (especially for spherical roller bearings) with high retained austenite content. In 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 structure transformation can be fully transformed, resulting in larger swelling, correspondingly increasing the amount of grinding, and saving waste products. .

3. Chemical deposition method

For bearing parts whose dimensional tolerances exceed design standards, chemical deposition methods 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 the chemical reaction 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, but does not change the shape tolerance of the part. Therefore, chemical deposition is an effective rescue method for parts with out-of-tolerance dimensional tolerances. At present, the thickness of unilateral deposition can reach about 0.1mm.

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