Eliminating early fatigue pitting of low speed and heavy load gear with soft tooth surface

As the cement mill, mine hoist and other soft tooth surface reducer gear, the main problem is to eliminate early fatigue pitting, the following measures can be taken.

1.Due to the soft tooth surface reducer gears such as cement mill and mine hoist, the main problem is to eliminate the early fatigue pitting. The following measures can be taken. The gear spare parts imported from abroad in the early 1960s, the tooth surface finish is only ▽ 4, the reducer can run the tooth surface into a mirror shape in a few days, so as to achieve full tooth contact and prevent early fatigue pitting.

2.Select the material and metallographic structure that is beneficial to the running in of the tooth surface. Due to the low yield ratio and the precipitation of massive ferrite during heat treatment, it is easy to cause local micro plastic deformation on the tooth surface. Within a very short number of cycles, the stress on the local surface exceeds the yield strength of the tooth surface (mainly in the area of ferrite precipitation), resulting in micro plastic extrusion deformation and forming a mirror shape. However, the number of cycles is very small, which is not enough to form a mirror shape As the tooth surface gradually runs in due to extrusion, the load on the tooth surface is uniform. Even if the number of cycles increases, the load per unit area has decreased to below the allowable stress, and there is no longer fatigue candle.

The addition of some ferrite strengthening elements, such as Si, can increase the fatigue strength of the precipitated massive ferrite by 15-30%, which is beneficial to the micro plastic deformation of the tooth surface and the fatigue resistance.

According to the investigation materials and our bench test, the low stress (allowable stress ≤ 5000kgf / cm2) SIMN steel is used to normalize the big gear, and the small gear is equipped with quenching and tempering. Compared with the big gear and the small gear, the low alloy steel is used for quenching and tempering (the hardness of the big gear is hb30-50 higher than that of the normalized gear), which can more effectively prevent the early fatigue pitting.