Different from small bearings, super large bearings are processed by single machine, single person and single piece, with strong randomness, which is very easy to cause out of tolerance of dimension or shape, such as small grinding amount after machining, out of tolerance of heat treatment deformation, excessive shrinkage and uneven shrinkage, carburizing pad damage, handling collision and jamming, etc.
If processed according to the normal process, these parts will become nonconforming products. After Salvage Measures analysis, some nonconforming products can be saved by taking measures.
1 center offset method
1.1 repair of inner and outer diameter of bearing ring
Firstly, the size of each defect (asymmetric type) of the part is accurately measured, and the small grinding amount (the grinding amount when the size deviation of the finished product) m is calculated. Then, during grinding, the center of the part is offset (offset in the direction of increasing the grinding amount at the defect), and the large offset is m / 2, that is, the grinding amount is relatively increased at the defect, focusing on grinding,.
1.2 rescue of inner and outer raceways of ferrule
The grinding design basis of bearing ring is inner diameter or outer diameter, that is, grinding the inner (outer) diameter first and then the raceway. Taking the inner race as an example, if the inner raceway has asymmetric defects, it is necessary to accurately measure the inner diameter of the part, and calculate the large grinding amount m and the large grinding amount M1 at the defects of the inner raceway.
When M1 ＜ m, the inner ring center offset is required when grinding the inner diameter, and the large offset is M1 / 2, that is, when machining the Salvage Measures inner diameter, the grinding amount is relatively increased in advance for the defect of the inner raceway, and then when grinding the inner raceway,
the defect will be mainly ground and the waste products will be saved. Salvage Measures When M1 ≥ m, it cannot be removed by normal grinding, and the method described in Section 1.1 can be adopted according to the situation.
The center offset grinding is carried out on the premise of ensuring the hardness of parts and the depth of carburized layer. The total offset Salvage Measures cannot be completed in one offset grinding. It is generally divided into several grinding, that is, it is completed through the repeated process of offset trial grinding –
Measurement – adjustment of offset – re grinding. After the defects are ground off, it is re aligned and the ovality is corrected by normal grinding. The efficiency of this method is low, and the operator is required to have a high technical level. However, this method has a high success rate in single machine and single piece production and does not delay the production progress. After several years of practice, the effect is good.
The bearing parts whose dimensional tolerance exceeds the design Salvage Measures standard can be saved by chemical deposition method. The principle of chemical deposition is to evenly 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 coating is the same as the original hardness and mechanical properties of the part through additional tempering. Chemical deposition only increases the size of parts and does not change the shape tolerance of parts. Therefore, for parts with out of tolerance, chemical deposition is an effective saving method. At present, the thickness of large single side deposition can reach about 0.1mm.
3 heat treatment bulging method
The quenched structure of bearing steel consists of quenched martensite, a small amount of insoluble secondary carbides and about 12% ~ 14% residual austenite. Quenched martensite and retained austenite belong to unstable structure. During tempering, the decomposition of martensite shrinks the volume of steel, while the decomposition of retained austenite expands the volume of steel.
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, appropriately increase the tempering temperature to decompose the residual austenite and transform it into martensite structure with large specific volume, which can correspondingly increase the volume of the workpiece,
that is, relatively increase the external diameter grinding amount, Using this method, the parts with bearing ring defects that become waste under Salvage Measures normal grinding conditions can be saved.
This method is effective for thick and heavy workpieces with large residual austenite content (especially for self-aligning roller bearings). In the actual production, different tempering Salvage Measures processes are formulated for parts with different specifications, sizes and thicknesses.
On the premise of ensuring hardness and deformation, the microstructure Salvage Measures is fully transformed, resulting in large bulging, correspondingly increasing the grinding amount and saving the waste products.