The common faults of gear boxes are gear damage, bearing damage, tooth surface fatigue, cementation, shaft breakage and leakage, high oil temperature.
There are many factors affecting gear damage in gear boxes, including material selection, design and calculation, processing, heat treatment, installation and debugging, lubrication and maintenance. There are two types of gear damage: tooth face damage and gear breakage.
(1) Gear breakage (broken tooth)
Gear boxes broken teeth are often gradually expanded by tiny cracks. According to the crack propagation and the cause of tooth fracture, the broken teeth can be divided into overload fracture (including impact fracture), fatigue fracture and random fracture.
Overload fracture is always caused by the stress acting on the gear teeth exceeding its limit stress, leading to rapid crack propagation. The common causes of gear box are sudden impact overload, bearing damage, shaft bending or large hard objects into the meshing area. The fracture surface of gear box has a radial pattern of crack propagation zone, and sometimes there is flat plastic deformation at the fracture surface, and the fracture pair can often be assembled. Careful inspection can see the material defects of the gear box, tooth surface accuracy is too poor, the root of the gear tooth has not been carefully treated and so on. The necessary measures should be taken in the design to fully consider the overload prevention factors. When installing, prevent gearbox body deformation, prevent hard foreign objects from entering the box body, etc.
The fundamental reason of fatigue fracture is that the fatigue crack of the gear box teeth, which originates from the fatigue source of the dangerous section (such as the root) under the repeated action of excessive alternating stress, expands continuously, so that the stress on the residual section of the gear tooth exceeds its ultimate stress, resulting in instantaneous fracture. The origin of fatigue fracture is the starting point of the shell pattern expansion and radiates outward. The reasons are the inadequate design load estimation, improper material selection, low gear accuracy, heat treatment cracks, grinding burns, root stress concentration and so on. Therefore, the dynamic load spectrum of transmission, the optimization of gear parameters, the correct selection of materials and gear accuracy, the machining accuracy to eliminate stress concentration factors and so on should be fully considered in the design of gearbox.
The random fracture of gearbox is usually caused by material defects, excessive local stress caused by pitting, spalling or other stress concentration, or large hard foreign bodies falling into the meshing zone.
(2) Tooth surface fatigue
Tooth surface fatigue of gearbox is a kind of damage caused by fatigue cracks on the surface or under the surface of gearbox under the action of excessive contact shear stress and stress cycling times. Its manifestations are early pitting corrosion, destructive pitting corrosion, tooth surface spalling, and surface crushing. Special gear box is a destructive pitting corrosion, often occurs in the meshing line of the gear, and continues to expand, so that serious damage to the tooth surface, increased wear, and ultimately lead to tooth failure. Correct design of gear strength, selection of material, guarantee of heat treatment quality, selection of appropriate precision matching, improvement of installation accuracy and lubrication conditions are the fundamental measures to solve tooth surface fatigue.
Gluing is the phenomenon that the boundary film of the meshing tooth surface is destroyed at the meshing point, which causes the metal on the contact tooth surface to be torn off by melting and welding. It may be caused by bad lubrication condition or interference. Properly improving lubrication condition and eliminating interference cause in time, adjusting the parameters of transmission parts and eliminating local load concentration can be used. Reduce or eliminate the glue phenomenon.
2. Bearing damage
Bearing is the most important part of gear boxes, and its failure often causes catastrophic damage to gearbox. During the operation of the bearing, the ring and the surface of the rolling element are subjected to alternating loads. Due to installation, lubrication, maintenance and other reasons, pitting corrosion, cracks, surface peeling and other defects occur, which make the bearing invalid and cause damage to the gear pair and the box. According to statistics, among the many factors affecting bearing failure, 16% belong to installation, 16% belong to pollution, and 34% belong to lubrication and fatigue. More than 70% of the bearings in use can not meet the predetermined life expectancy. Therefore, it is very necessary to pay attention to the design and selection of bearings, to ensure the lubrication conditions, to install and debug according to the specifications, and to strengthen the monitoring of bearing operation. Usually set up a bearing temperature alarm point on the gearbox to monitor the abnormal high temperature phenomenon of bearings, the temperature difference between different bearings on the same box is generally not more than 15_C, to check the change of lubricating oil at any time and anywhere, found abnormal immediately stop processing.
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