How do you fix a broken gear?
The repair methods of gears mainly include: commutation method, surfacing method, hot forging method, insert method and so on.
(1) Repair method for surface damage of gear teeth
① The end face reversal method repairs the tooth surface. For gears with partial (such as one end) wear on the tooth surface or wear on a single working surface (one-way rotation), if the worn gear is symmetrical in the axial center plane, it is economical to use the end face reversing (axial turning) method to repair it. with suitable. For example, some gearbox gears, due to frequent shifting and shifting, often have impact wear at one end of the gear teeth. For example, the gears are axially symmetrical, and the head can be adjusted to improve the impact degree. Some gears have been designed to take into account the special requirements for easy replacement and repair after their local parts (on one side) and single working surface are worn.
②The surfacing method repairs the tooth surface. When the gears are severely worn and have severe pitting or spalling, the surfacing method can be considered for repair. Usually, the surfacing method can obtain greater economic benefits for the damage of large and important gears, and it can also resume production as soon as possible. The process of gear surfacing is: annealing before welding → cleaning → welding → machining → heat treatment → finishing.
③The tooth surface is repaired by hot forging. When the working surface of the gear teeth is seriously worn and the tooth thickness is seriously reduced, the metal of the tooth top part can be extruded onto the working tooth surface by hot forging to obtain the tooth thickness including the machining allowance for tooth shape repair, and then only Weld overlay on top of gear teeth. Compared with the tooth surface surfacing method, this method is easy to operate, the metal fusion state is better, and the quality is easy to ensure, but it needs hot forging process and corresponding complex equipment support, and the cost is also high.
(2) Repair method for broken gear teeth
①The tooth insert method is used to repair the broken tooth. For individual broken teeth, the other gear teeth on the gear are intact (especially the adjacent teeth of the broken teeth should be paid attention to); at the same time, if the precision of the gear is not very high and the working speed is low, it can be repaired by the insert method .
②Splicing method to repair broken teeth. When the large ring gear is broken, or when part of the teeth of the larger gear is damaged, it can be repaired by splicing. Use gas welding or saw (or toothless saw) to cut off the damaged part of the gear, and then use special tools to restore the deformed gear to its original shape, as shown in Figure 9-30. Then remove the required part from the same gear that cannot be repaired, or make a part of the ring gear with the same or similar material as the original gear according to the size and shape of the notch, and weld it to the notch.
Before welding, a 45° groove should be ground at the welding place as a weld with a width of 8-10mm, and mechanical processing should be carried out after welding. In order to ensure the uniform pitch between the spliced part and the original gear, the common normal length W should be measured repeatedly during the whole process of splicing.
③The surfacing method repairs broken teeth. When using the surfacing method to repair individual broken teeth, the broken tooth mode must be carefully judged before welding.
Cracks, especially fatigue cracks, must be cleared to the crack front before welding. In order to avoid the thermal influence of the welding process, the gear can be immersed in water, only the welding part is exposed to the water surface, and the surface adjacent to the surfacing welding area is covered with asbestos cloth.
(3) Repair of gear cracks
① Repair of gear fatigue cracks. For the initial fatigue micro-cracks on gear teeth or rims and webs, drilling (passivation holes) at the front of the crack propagation can prevent it from continuing to expand to prolong its service life. In fact, for more serious gear tooth fatigue cracks, the propagation front is not clear, and it is difficult to locate and quantify even with non-destructive testing. It can be considered to saw off the residual teeth along the crack propagation direction, and then repair them according to the broken teeth.
② Repair of cracks in gear technology. For surface (or subsurface) cracks that are still growing steadily, they can be eliminated by grinding or filing to prolong their service life. When removing cracks, the deformation layer at the crack tip should be removed as well.
③ Repair of internal cracks in gear materials. After localization and quantification by non-destructive testing, fracture mechanics are used to evaluate the residual life, and then appropriate disposal; limited use, or scrapped and replaced.
(4) Repair of permanent deformation of gears
① Repair of slight plastic deformation of gears. Less serious damage, such as burrs, small indentations, ridges, etc., can be trimmed by filing and trimming the plastically deformed convex parts. If the tooth material is too soft, surface strengthening (or local hardening treatment), such as shot peening, can be given. If the lubrication is poor, the lubrication can be improved. For example, for gears with ridge damage, a high-viscosity lubricating oil containing extreme pressure additives can be used to improve the lubrication conditions.
② Repair of serious plastic deformation of gears. For serious damage such as end face impact plastic deformation, under the condition of axially adjustable head, the end face reversing method is used for this damaged gear. Or when it is valuable (such as a large batch) and hot forging is available, it can be repaired by hot forging. For gears with severe plastic deformation damage, in addition to taking the above measures to repair, the specific load or (and) environment and other factors that cause damage should also be excluded.
③ Repair of serious bending plastic deformation of gear shaft. When the gear shaft has bending plastic deformation, it can be repaired by means of pressure (with a press) straightening and cooling straightening. In order to overcome the influence of elastic failure, for gear shafts with a diameter (maximum effective diameter) less than 50mm, it can be heated to 400 ~ 500 ℃ and kept for 0.5 ~ 1h; for gear shafts with larger diameter and (or) larger deformation, Then the heating temperature should be appropriately increased (500-600°C), because straightening under such hot conditions can ensure the stability of straightening recovery.
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