Mine hoist reducer gear cracking analysis Mine hoist reducer gear cracking analysis bookmark0 Wang Yulei 1 Kang Xueqin 2bookmark1 1 School of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China 2 School of Materials Science and Engineering, China University of Mining and Technology fcj mine main shaft hoist winch reducer The gear tooth surface crack occurs when the gear is used for less than 2 years, and the equipment should be operated normally for more than 15 years according to the design requirements. The mine hoist winch not only bears the main task of upgrading the coal transportation of the mine, but also bears the transportation work of the personnel. Once the gear of the reducer is cracked, the gear is broken and the hoist is out of control, which will seriously affect the mine production and safety.
Therefore, it is necessary to conduct a comprehensive analysis of the cracked gear to find out the cause of gear cracking to avoid accidents.
1 Cracking gear cracking analysis The overall shape of the bookmark2 cracked gear is as shown. The ring gear material is ZC45, and the hot press is set on the ring gear after processing. One of the meshed pair of gears has a tooth surface crack and another crack is not found. The gear cracking has penetrated the entire gear ring. Under the original interference force, the crack opening maximum is about 5mm. The tooth surface crack has eight B and C, as shown. From the crack size and distribution, the A crack can be determined as the main crack. When the A crack rapidly spreads through the entire tooth surface, the fitting state between the teeth is broken, and the two tooth faces adjacent to the broken teeth are crushed and cracked during the transmission process.
In order to determine the nature of the gear cracking, the cracking gear is opened and the resulting gear cracking surface is as shown. It can be seen that the crack crack source is located at the root of the gear. It can be determined from the macroscopic morphology of crack propagation and belongs to fatigue fracture. The crack fatigue expansion zone is relatively bright and has a semi-elliptical shape, and the fatigue arc formed during the crack propagation process can be vaguely observed. After the crack fatigue expands to a certain size, it rapidly expands under the action of external force, forming an overload fracture pattern. The crack edge formed by the crack propagation at the edge of the fatigue fracture zone is rough and the crack surface is clear and radial.
The tooth surface damage of the entire gear is more serious. There are a lot of pitting on the cracked tooth surface and the non-cracked tooth surface, and some places have formed a peeling pit, see.
3 and show that in the source region of the root fracture, the cracked surface presents a dead wood-like fracture pattern with many massive cracked inclusions and secondary cracks; it is difficult to observe the fatigue streaks formed by the obvious fatigue fracture on the fracture. Only in the local grain, there is a fracture pattern similar to the fatigue streak. In the secondary crack part, more crack-like inclusions are observed in the crack, and the grain on both sides has obvious rubbing marks, and the edge of the section is also obvious. Wear and extrusion, local microporous depth, small orifice 2 metallurgical structure and performance analysis of gear material. In order to further determine the cause of gear fracture, sampling in different parts of the fractured tooth surface, metallographic analysis, typical tissue of each part The form is as shown. It can be seen from the metallographic structure of different parts of the gear teeth that the shape and shape of the tooth surface of the gear are basically the same as those of the core. There are large inclusions and casting defects in the tissue. This is the main factor leading to a reduction in the fatigue strength of the material.
The teeth and adjacent teeth are taken to check the hardness of the gears. The results are shown in Table 1 and Table 2. The gear hardness is low, and the hardness of the tooth surface is only HRC3Q and the hardness of the gear core is not much different. In particular, the hardness of the root is low, only HRC25.
The gear cracking analysis of the mine hoist reducer determines that the fracture of the gear is a fatigue fracture. The root cause of the early breakage of the gear is mainly: the hardness of the surface, especially the root portion. On the one hand, the root of the gear must bear the large bending stress when the gear teeth mesh in the gear operation; the meshing surface produces more serious wear and contact fatigue, forming the peeling pit on the tooth surface, and impact and large vibration occur in the process.
Can withstand such loads, fatigue cracks are formed and expanded from the root of the gear; (2) coarse as-cast microstructures and inclusions and casting defects in the steel increase the rate of crack propagation, leading to rapid expansion of fatigue cracks and accelerated fracture (3) From the gear tooth surface wear and peeling pit morphology and the ratio of the fatigue zone of the broken tooth to the final instantaneous fault zone, it can be seen that the actual running load of the gear is large, providing mechanical conditions for the formation and expansion of the crack. .
A large number of experiments have shown that the surface hardness of parts subjected to alternating loads has a great influence on the fatigue of the parts. In this analysis, the single tooth hardness test result (hv) of the gear table 1 is basically the same as the tooth center hardness, and the hardness of the tooth root is lower than the hardness of the tooth top and the tooth surface. It can be seen that the gear is not processed after processing. In the effective heat treatment, even if the surface is subjected to flame quenching treatment, since the hardened layer is thin, the effect of improving the fatigue strength of the material is not obtained.
The results of the study on the influence of metal structure on fatigue and cold life are complicated and lack the necessary comparative data. However, it is generally believed that defects in steel have a greater impact on fatigue strength, and this effect is greater than the impact on static load strength. Much, the fatigue limit of metals decreases with increasing crystal grains and defects, and the probability of fatigue fracture increases significantly. The metallographic structure of this broken tooth is coarse, with serious casting defects and inclusions, which seriously reduces the fatigue of the gear. The fatigue crack growth rate is linear with the grain size. At the front of the fatigue crack growth, the inclusions are easy to form microcracks and accelerate the fatigue crack growth. The stress concentration is formed at the front of the fatigue crack growth, which increases the actual stress level and promotes crack propagation. Inclusions and casting defects in the steel result in increased brittleness of the material, reduced strength and toughness, resulting in rapid brittle fracture.
(1) The fracture of the gear belongs to the fatigue fracture, and the fatigue crack originates from the root of the tooth. The root of the tooth is subjected to the maximum alternating stress. When the fatigue strength of the material is insufficient to withstand the load force, the fatigue property occurs. (2) The gear material has serious structural defects, casting defects and large-sized inclusions. This reduces the fatigue resistance of the material.
(3) The hardness of the tooth surface is relatively low, which causes the tooth surface to form severe wear during the transmission process. Under the contact stress, the tooth surface forms contact fatigue damage. In particular, the root hardness is low and the fatigue resistance is low, which is insufficient to withstand the bending stress and the vibration and impact load formed by the tooth surface damage.
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