Element analysis: gear fracture is divided into fatigue fracture and overload fracture.During the working of the gear transmission, the gear teeth are subjected to alternating loads for many times, and the bending fatigue stress acts on the risk section of the tooth root, and fatigue cracks occur at the tooth root. Under the action of the alternating bending fatigue stress, the fatigue cracks gradually Widening, after all, causes the teeth to bend, fatigue and break; when the gear transmission is working, the gears are overloaded for a short time, or impact load, or the teeth are severely worn and thinned, and the overload and breakage will occur.
Treatment method: increase the transition fillet radius of the tooth root, and reduce the value of the surface roughness to be processed as much as possible, which can reduce the influence of stress convergence, increase the stiffness of the shaft and support, and ease the load on the tooth surface; make the gear teeth The core has sufficient toughness; proper strengthening treatment at the tooth root can improve the fracture resistance of the gear teeth.
2 Gear pitting and dropout
Analysis of the factors: The pitting corrosion and falling off of the gear surface are mainly caused by the lack of contact fatigue strength of the gear.The difference between this kind of pitting and falling off is that the metal is not worn away in the form of particles, but falls off in the form of blocks, forming pits on the tooth surface, which seriously damages the correctness of the tooth profile. sex.The damage process is as follows: first, small cracks occur on the tooth surface, and the lubricating oil enters the fatigue cracks, and then through repeated meshing actions, the cracks are continuously widened and extended, and the lubricating oil continues to fill the deep part of the cracks as the cracks widen and extend. Until a small piece of metal falls off the tooth surface.This phenomenon damages the normal meshing function of the gears.The primary factors for pitting corrosion on the tooth surface are:
a. Material, hardness and defects.The material of the gear does not meet the requirements; the main factor affecting the contact fatigue strength of the gear is the low hardness after heat treatment, which cannot guarantee the proper contact fatigue strength of the gear.In addition, there are defects on the surface or inside of the tooth, which is also one of the indispensable factors for contact fatigue strength.
b. Gear accuracy is poor.The gear processing and equipment accuracy do not meet the requirements, such as poor meshing accuracy and movement accuracy.There is also the fact that the base distance of the housing of the arc gear is too large.
c. The lubricating oil does not meet the requirements.The brand of lubricating oil used is wrong, the viscosity of the oil is low, and the lubrication performance is poor.
d. The oil level is too high.If the oil level is too high, the oil temperature rises higher, which reduces the viscosity of the lubricating oil, damages the lubricating function, and reduces the working thickness of the oil film.
Solution: increase the hardness of the tooth surface, reduce the value of the tooth surface roughness, use a large variation coefficient as much as possible, increase the viscosity of the lubricating oil and reduce the dynamic load, which can help prevent fatigue pitting on the tooth surface.
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