How to improve the processing technology of steel balls

- Sep 23, 2020-

With the rapid development of the aviation industry, higher requirements are put forward for the quality of aviation bearings. As a key part of the bearing, the improvement of the quality of the steel ball has become one of the key technologies to be solved urgently by the manufacturer. In order to solve this problem, the domestic and foreign processing technology of 19/32" aero-engine special bearing steel ball was compared, and on this basis, the improved steel ball processing technology was determined. This article mainly discusses the improved steel ball processing Process and corresponding measures taken.

1. Process formulation and corresponding measures

1.1 Improve tool design and reduce steel ball processing reserve

Under the premise of ensuring accuracy, reducing the amount of steel balls left in each process can reduce the grinding time, and at the same time reduce the degeneration layer caused by excessive grinding, and reduce the chance of grinding quality problems. According to the original characteristics of the aviation bearing materials, the hardness alloy stamping dies and auxiliary tools were developed by themselves, and repeated pressure ball verification was carried out. The results showed that: the use of cemented carbide blades and cutting tires improves the cutting quality and reduces the pressure. Folding; Adopting cemented carbide pressed spherical tires, insisting that the mold is basically not deformed during the stamping process, and improving the precision of the ball blank. At the same time, the selected material diameter and cutting length ensure that the compression ratio (cutting length/material diameter) is between 2.02.2, so that the material section is in the best deformation state during the molding process. As a result, the size of the processed ball blanks is basically the same, and the ring belt is small and thin, so that the total allowance for steel ball processing is reduced from 1.2mm to 0.8mm

1.2 Use deep pickling and non-destructive inspection instead of hot pickling inspection

The hot pickling process not only consumes the overall size of the steel ball, but also because of the high stress of the ring and the poles, the corrosion rate is high, the corrosion layer depth is 0.18mm, and the intergranular corrosion occurs seriously. This not only needs to increase the total reserve of steel balls, but also prone to fatigue during processing. For this reason, deep pickling and eddy current testing are used instead of hot pickling, and a reasonable acid ratio is used to control the size consumption of steel ball deep pickling to 0.040.05mm. To verify its reliability, 500 grains are used for deep pickling and The eddy current flaw detection steel ball was subjected to hot pickling inspection, and no problem was found. It can be seen that it is feasible to replace hot pickling inspection with deep pickling and eddy current testing

1.3 Reduce fatigue during steel ball processing

According to the characteristics of steel ball processing, the process of replacing the light with grinding is adopted. The soft grinding process is updated and transformed the grinder, equipped with an automatic grinding wheel dressing system and 80#120# grinding wheel instead of the light ball process. It can eliminate the excessive stress concentration generated in the process of photosphere processing. In the lapping process, by controlling the processing conditions, the water-based grinding is used instead of the oil-based grinding to shorten the lapping time and reduce the fatigue generated during the grinding process. By testing the auxiliary tools, emulsified lapping liquid and surface active agent lapping liquid of the lapping machine tool, the abrasive ratio and operating procedures of the rough lapping, lapping 1 and lapping 2 water agent lapping of steel balls can be determined. The steel ball grinding (coarse grinding and fine grinding) time is shortened from the original 48h to within 36h. The precision (spherical deviation, ball diameter change) of the processed steel ball after ultra-finishing reaches 0.2μm and the surface roughness Ra≤0.02μm

1.4 Improve the state of soft and fine grinding process and improve the processing quality

Update soft and fine grinding processing equipment. The new machine tool has the automatic dressing function of the grinding wheel, so that the steel ball is always in the best processing state. The actual verification of the steel ball grinding efficiency can increase the output by 10% 15%, and the burn of the steel ball fine grinding process is effectively controlled.

1.5 Improve the uniformity of the surface hardness of the steel ball

Use maintenance atmosphere quenching instead of air furnace heating and quenching, and improve the temperature control accuracy of the equipment, and the uniformity of the surface hardness of the steel ball is effectively improved. The single hardness difference of the scrap steel ball is ≤0.5HRC, and the batch hardness difference is ≤1HRC

2. Conclusion

The improved steel ball processing technology reduces the total retention from the original 1.2mm to 0.8mm, which reduces the chance of a degeneration layer due to excessive grinding, and uses deep pickling and non-destructive testing instead of hot pickling to reduce crystals. Inter-corrosion, the use of grinding instead of light technology to eliminate the excessive stress concentration generated during the photosphere processing. Practice has proved that the improved steel ball processing technology is effective and feasible, achieves the expected effect, and can be applied to production.