Detailed explanation: skf bearing accuracy error knowledge

In the production of large-volume skf bearings, the process system is generally adjusted by using prototypes, prototypes, blocks and masters; in single-piece small batch production, the scale on the machine tool or the gauge block is usually used for adjustment. The content of the adjustment work also varies depending on the complexity of the workpiece. For simple surfaces (such as inner and outer cylindrical surfaces), only the positional relationship of each forming motion is generally adjusted; for complex surfaces (such as spiral surfaces and involute surfaces), Also adjust the speed relationship of the forming motion. Therefore, adjusting the skf bearing error is caused by a variety of factors.

The skf bearing measurement error should be less than 10% of the tolerance. The general measurement error warfare difference is 10% to 33%, and as the tolerance level increases, the proportion of error is larger, that is, the smaller the tolerance, the higher the proportion of error, and the tolerance of skf imported bearings It is difficult to reach 10% above IT5. Measurement error does not mean that the inspection tolerance can be relaxed by 10%, but a certain safety margin is given to ensure that the user is qualified according to the standard acceptance.

In each process of skf bearing parts processing, in order to obtain the size, shape and positional accuracy of the bearing surface, the machine tool, fixture and tool must be adjusted, and any adjustment work will inevitably bring certain errors. The production batch and machining accuracy of bearing parts in machining are often different, and the adjustment methods used are also different.

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Three solutions for unqualified bearing rings

First, the center offset method

1. Rescue of the inner and outer diameter of the skf 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.

2. Rescue of the inner and outer raceways of the ferrule

The design of the grinding of the skf 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 race, it needs to be accurately measured. The inner diameter of the part is calculated, and the maximum amount of wear M and the maximum amount of wear 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.

Second, heat treatment upsizing method

The quenched structure of the skf 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 skf bearing ring which are defective under normal grinding conditions can be saved.

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