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Gear Gas Nitriding Common Problems And Countermeasures

1.Compared with plasmanitriding, gas nitriding has the advantages of simple operatplasma, high process repeatability, simple equipment structure and nitriding principle, and can realize automatic control of the process. The most prominent feature is the nitriding temperature and atmosphere. Uniformity is better. For gear nitriding, especially for small module gears, the difference between the depth of the nitriding layer between the tooth root and the pitch circle is smaller than that of plasmanitriding.

In recent years, gas nitriding processes have developed rapidly, such as pre-oxidative gas nitriding processes and various gas nitriding catalysis, etc. These new processes have shortened the productplasma cycle between plasma nitriding and gas nitriding to varying degrees. difference. However, the following problems should also be paid attentplasma to in the process of gear controlled atmosphere gas nitriding.

2.Cleaning before gas nitriding

The gears should be cleaned before gas nitriding and furnace installation, and there should be no moisture and impurities remaining, otherwise the appearance of the gears after nitriding will not be uniform, and dark spots will appear. Although there is no obvious difference in the depth of nitriding layer, nitriding hardness and metallographic structure between the piebald and the normal area, the piebald will seriously affect the appearance quality of the gear. Macroscopic topography analysis was performed by super-depth-of-field stereo microscopy on the irregular mottled area.

The abnormal mottled area has a higher content of O element than the normal area. In addition to high O element, it also contains a small amount of elements such as Na, S, Cl, K, Ca, Mg and Al. These elements are mainly derived from residues of water, cleaning agents and shaving oils. From the above analysis, it can be seen that the appearance of gas nitriding mottle is caused by the unclean cleaning before nitriding. Therefore, special attention should be paid to the following points in the cleaning of gas nitriding gears.

1) When using water-based cleaning agent for cleaning, the water temperature of the final rinse should not be too high. When the rinsing water temperature is too high, the water will be directly dried on the surface of the workpiece, so it is better to appropriately reduce the rinsing temperature and use a high-pressure air gun to dry.

2) Use acetone, gasoline and other substances for cleaning, but these substances have low flash points, and attention should be paid to the ventilation and fire safety of the cleaning environment.

3) The workpiece should be dehydrated before cleaning with a hydrocarbon cleaning machine.

4) Pay attention to the quality of the water used in the cleaning process, and use pure water as much as possible.

3.Control of gear gas nitriding distortion

Gear nitriding distortion is related to gear shape, machining residual stress, gear material, nitriding tooling, nitriding process and the cooling rate of the gear after nitriding. In daily production, people often pay attention to the first few factors, but ignore the cooling rate of the gear after nitriding, especially the distortion of the inner hole of the thin-walled gear is more sensitive to the cooling rate after nitriding.

The size of the inner hole before nitriding is φ52-0.02-0.035mm. It can be seen from the test results that the distortion trend of the inner hole of the gear with different cooling rates is the same. When the cooling rate after nitriding is slow, the distortion of the inner hole is larger, and when the cooling rate after nitriding is faster, the distortion of the inner hole is smaller. In order to stabilize the distortion of the inner hole of the gear and improve the pass rate of the inner hole after nitriding of the gear, the cooling rate of the gear gas after nitriding must be strictly controlled.

4.Remedy for Oxidation Caused by Gas Leakage in Gas Nitriding Furnace

When the gas nitriding furnace leaks due to problems such as sealing, it will cause oxidation on the surface of the workpiece. This oxidation has no effect on the intrinsic quality of the workpiece, but does not meet the requirements of appearance quality. In this state, the repair process can be used to restore.

When carrying out appearance reduction, it must be noted that the nitriding temperature during reduction cannot exceed the temperature of the first nitriding, and usually the nitriding temperature during reduction should be lower than the previous nitriding temperature by about 20°C. Depending on the severity of oxidation, the process time can be appropriately extended.

5.Conclusion

From the above three problems and solutions, we can see that when there is a problem in the heat treatment process, we should pay attention to every detail in the process, and grasp the key to solve the problem.