Specialized reducer for non-ferrous metals

In the metallurgical industry, reducers are considered as general equipment, with a long manufacturing cycle and high value. When purchasing non-durable parts, manufacturing enterprises have multiple standards. This has led to the occurrence of tooth-breaking accidents in special reducers for non-ferrous metals becoming a topic of great concern for current maintenance personnel. A certain steel company experienced a problem where the gear shaft of the reducer broke, causing the large gear to have tooth damage. To solve this issue, the maintenance personnel adopted targeted techniques such as gear repair and shaft replacement, and promptly resumed production without having spare parts, thus ensuring the economic benefits of the enterprise.

1. Shaft Breakage Repair Procedure 

1.1 Analysis of the Causes of Shaft Failure 

First, the selection of materials is convenient. The material of the high-speed shaft has a loose structure and contains many impurities inside. During the operation of the gear shaft, it is very likely to crack due to insufficient toughness, and under the action of alternating stress, the cracks will continuously extend and expand, eventually causing the bearing to break. To address this, when the bearing mainly transmits power, the material should be selected as a quenched and tempered steel with high hardenability. Second, in terms of structural design, after the shoulder of the shaft is welded and repaired, there is no transitional rounded corner. At this time, under the concentrated bending force, it is very likely to appear fatigue cracks, thereby causing the shaft to break. Third, in terms of heat treatment, before welding and repairing the gear shaft, if there is no sufficient preheating, it will cause uneven heating in the welding area, thereby generating internal stress. Under the action of this force, it is very likely to cause shaft breakage. After the repair of the welding, if there is no good heat treatment work, the residual force of the welding will increase, reducing the shaft's resistance to alternating stress. When the bearing vibrates, it is very likely to appear cracks, leading to a breakage problem. Fourth, in terms of processing technology, analysis and measurement have found that the processing size at the shaft neck is relatively small, which is very likely to cause excessive bearing clearance problems, and the shaft wear will further aggravate the breakage. Fifth, in terms of assembly technology, the main source of shaft vibration is the incorrect assembly process at the input end of the high-speed shaft. This will reduce the fatigue strength of the high-speed shaft and further aggravate the wear, leading to a breakage problem. 

1.2 Shaft Breakage Repair Technology 

The cross-sectional shape of the gear shaft is irregular. After grinding the broken section, its length will decrease. The bending strength after welding is relatively low at this time. At this point, the re-making work of the small end of the broken shaft should be done properly. The specific manufacturing process is as follows: First, select the quenched and tempered adhesive rod of 42CrMo as the manufacturing material, and one end is made according to the original size. The other end is processed into a long shaft and the processing holes are also fabricated in coordination. Second, the bevels of the two mating surfaces are welded. Third, the gear surface is processed by the machine for grinding and polishing. 

II. Gear Repair Technology 

2.1 Technical Preparation 

When formulating the repair technical plan, the staff should combine the gear parameters, usage conditions, and material characteristics, select reasonable and scientific welding techniques, and conduct strengthening repairs during the welding process, using multiple welding materials. First, for the base layer welding, in order to ensure the toughness and strength of the material, high-alloy welding materials should be effectively used as the base layer welding material to obtain a welding structure with good mechanical properties. Second, for the filling layer welding, in order to obtain better strength and toughness and improve mechanical properties, high-strength welding materials should be used when welding the filling layer to fully ensure the impact resistance of the gear after welding and avoid brittle fracture problems in the future. Third, for the strengthening wear-resistant welding, in order to ensure the wear resistance of the tooth surface and the design requirements, the staff should rough-grind the filling layer after welding and reserve a 1mm thickness, and apply a wear-resistant strengthening layer on the welding surface. During the welding repair process, imported high-alloy welding materials should be used, and local heat treatment technology and stress relief technology should be comprehensively adopted to effectively prevent the transformation of welding internal stress, enhance the material's impact resistance, and prevent the generation of cracks, ensuring reasonable tooth surface hardness indicators. Fourth, fine grinding and polishing, the staff should complete the fine grinding and polishing work according to the actual situation on site and data information. Fifth, make tooling, the staff should make special heat treatment tooling according to the construction situation on site, and perform local heat treatment to repair the gears. 

2.2 Key Construction Techniques 

First, cleaning: The staff should thoroughly clean the gears and use non-destructive testing technology to inspect the tooth surface cracks. Second, comprehensive inspection: Based on this, determine the condition of the gears and judge whether there are other defects besides wear. Third, remove the fatigue layer: Remove the fatigue layer of the welded gears and conduct another inspection to ensure that there are no other defect issues before welding. Fourth, control the welding process: Use low heat input welding technology during welding, control the temperature of the tooth surface, and reduce the generation of welding stress. The base layer should use short arc and short weld passes. After welding, hammer the weld seam until obvious deformation occurs. At the same time, during the welding process, strictly control the thickness of the weld layer and the length of the weld pass, use semi-automatic gas protection welding to repair the filler layer, control the deformation of the tooth shape, and leave sufficient size space for subsequent welding. After welding, the filler layer should be ground, and the wear-resistant layer should be welded using hydrogen arc welding. Through precise arc termination, the performance of the transition area can be determined. It should be noted that the staff should dynamically detect the deformation parameters and welding stress data of the gears to clearly identify the welding position, and adjust the welding amount on the basis of strictly controlling the welding deformation range. During the welding process, vibration methods should be used to reduce welding stress, and the material layer quantity ratio should be strictly controlled to ensure that the expansion coefficient of the weld seam material is consistent with the parent material. Fifth, pay attention to the restoration of size accuracy and post-weld treatment work. When adjusting and stabilizing the performance of the weld seam, use local heat treatment technology to ensure that the heat resistance of the weld seam reaches the best state. After the post-weld treatment work is completed, relevant staff should finely grind the repair parts of the sample and the inter-teeth alignment template, simulate the running-in of the driving gear, ensure that the meshing rate can be higher than 70%, and in case of necessity, perform disc rotation and grinding to ensure the overall accuracy. 

III. Practical Application Results 

First, after repairing the gear shaft and the gears, the reducer operated for 4 months. The vibration data met the requirements for production line operation, providing sufficient time for the purchase of new equipment. After the repair, there was obvious vibration during the gear meshing, with a high frequency. Second, the gear shaft and the gears could be repaired and put back into use shortly after damage, reducing maintenance time and costs, and avoiding the problem of spare parts replacement. 

After analyzing the reasons for the high-speed breakage of the reducer, the staff should adopt targeted repair techniques to solve the problem of breakage and ensure the smooth operation of the reducer. Practice has shown that analyzing the reasons for the tooth breakage of the gear shaft and the corresponding countermeasures are reliable and practical, and are worthy of further promotion and application in subsequent industrial production.