Planetary gear reducers are highly used devices in transmission systems. In the industrial and mechanical industries, we often see planetary gear reducers. For such a high-efficiency device, it is inevitable to encounter gear damage problems. In general, gear damage can be divided into three types: broken teeth, gear pitting and peeling, and gear wear.
So, what are the reasons behind these three types of gear damage and how can we solve them?
(1)Broken teeth
Generally speaking, broken teeth in planetary gear reducers are divided into fatigue fracture and overload fracture. When the planetary gear reducer is working, the gear teeth are repeatedly subjected to alternating loads, and bending fatigue stress acts on the dangerous section of the tooth root, causing fatigue cracks at the tooth root. Under the action of alternating bending fatigue stress, the fatigue cracks gradually expand, eventually leading to bending fatigue fracture of the gear teeth; when the planetary gear reducer is working, the gears are subjected to short-term overload, or impact load, or the gear teeth are severely worn and thinned, overload fracture will occur.
How to solve broken teeth?
Increasing the transition fillet radius of the teeth root and minimizing the roughness of the processed surface can reduce the influence of stress concentration, increase the stiffness of the shaft and support, and alleviate the local load on the teeth surface; making the core of the gear teeth have sufficient toughness; and performing appropriate strengthening treatment at the teeth root can improve the gear teeth’s resistance to fracture.
Of course, if the gear breaks during operation, it is necessary to replace it with a new part of the same model.
(2).Gear pitting and spalling
During the long-term operation of the planetary gear reducer, pitting and spalling may occur on the gear surface, which is mainly due to the insufficient contact fatigue strength of the gear. The difference between this pitting and spalling and wear is that the metal is not worn away in the form of particles, but in the form of blocks, causing pits on the tooth surface, which seriously damages the correctness of the teeth shape.
The destruction process is as follows: first, tiny cracks are generated on the teeth surface, lubricating oil enters the fatigue cracks, and then after repeated meshing, the cracks continue to expand and extend. As the cracks expand and extend, the lubricating oil continues to fill the deep cracks until a small piece of metal peels off and leaves the tooth surface. This phenomenon destroys the normal meshing performance of the gear.
The main reasons for pitting on the teeth surface are:
- 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, defects on the surface or inside of the teeth are also one of the reasons for insufficient contact fatigue strength.
- The gear accuracy is poor, and the gear processing and assembly accuracy do not meet the requirements, such as poor meshing accuracy and motion accuracy. In addition, the shell center distance error of the arc gear is too large.
3) The lubricating oil does not meet the requirements, the brand of lubricating oil used is incorrect, the viscosity of the oil is low, and the lubrication performance is poor.
4) The oil level is too high. If the oil level is too high, the oil temperature will rise, which will reduce the viscosity of the lubricating oil, destroy the lubrication performance, and reduce the working thickness of the oil film.
Solutions to solve Gear pitting and spalling:
Improve the hardness of the gear teeth surface, reduce the roughness value of the teeth surface, use a large displacement 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 teeth surface.
(3). Gear wear
Mechanical parts may experience varying degrees of wear during long-term use, and planetary gear reducers are no exception. Gear wear is the most common type of damage in the operation of planetary gear reducers. Possible causes of this wear include: lack of oil, metal scraps mixed in the lubricating oil, which will also cause teeth surface wear; gear materials do not meet the requirements, causing abnormal wear; gears have defects such as sand holes, pores, looseness, and insufficient spheroidal graphitization; heat treatment hardness is not enough or no heat treatment is performed; gear meshing accuracy and motion accuracy do not meet the requirements; arc gears are very sensitive to center distance errors, especially the positive error of center distance, which not only reduces the bending strength of the gear teeth, but also increases sliding wear.
Solutions to solve gear wear:
Improve the hardness of the gear teeth surface, reduce the surface roughness value, keep the transmission device and lubricating oil clean, ensure sufficient lubrication, add suitable anti-wear additives to the lubricating oil, add several magnetic bodies in the oil tank, and use the magnetic effect to absorb metal particles in the lubricating fluid to reduce the metal particle content in the lubricating fluid.
In planetary gear reducers, gears are one of the most core components. The key to planetary gear design lies in the uniformity and high precision of gear meshing. No matter what degree of gear damage occurs, it should be repaired or replaced with a new gear in time, otherwise it will seriously affect the mechanical transmission. (Author: SGR, Angie Zhang)
Related Video Link:
https://www.tiktok.com/@gear.reducer/video/7395154639278116126