Defects of gear heat treatment and examples of technical improvement

The problem of spline hole distortion of xf-125 primary transmission gear by China First Tractor internal combustion engine company is studied. Experiments are carried out from the aspects of raw materials, heat treatment process and cold working stress. Many influencing factors of Huajian hole shrinkage are explored and corresponding technical measures are taken to solve this technical key. Research shows:

1. The banded and widmanstatten structure level of raw material tooth blank directly affects the distortion of gear spline hole after carburizing and quenching. The absolute distortion of gear spline hole with banded structure of grade 4 ~ 5 and widmanstatten structure of grade 3 is about 0.08mm. Therefore, among the factors causing distortion, the microstructure level of raw material tooth blank is one of the important factors.

2. Cold working stress is particularly sensitive to distortion after carburizing and quenching of spline hole of primary traditional gear. The gear end face is printed, so that the distortion of the spline hole is doubled, and the absolute distortion is about 0.1mm.

3. Quenching temperature, quenching oil, cooling mode and clamping method all affect the spline distortion of primary transmission gear, but they have less influence than raw materials and cold working stress. Quenching temperatures of 880 ℃ and 910 ℃ have no obvious effect on the distortion of spline hole of primary transmission gear. CMH clamping method based on thermal stress makes the spline hole of primary transmission gear swell; Ch method clamping based on tissue stress can reduce the spline hole of primary transmission gear.

4. The best carburizing and quenching process to reduce or control the distortion of spline hole of primary transmission gear is as follows: carburizing at 910 ℃, isothermal at 820 ℃ and oil quenching at 355 ℃. The tooth blank shall ensure that the banded structure is ≤ grade 1; Widmanstatten tissue grade 0; The absolute distortion of spline hole is about 0.04mm in 355 ℃ oil quenching and about 0.05mm in G oil quenching without additional increase of cold working stress.

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