In recent years, China has been moving towards becoming a manufacturing powerhouse, and reducers are developing towards high speed, noise reduction, high stability, and miniaturization. The reducer gears have different processing techniques according to their application scenarios, and different processing techniques have different impacts on the later use of gears. During the operation of the reducer gear, there are often phenomena such as tooth surface pitting, tooth surface wear, tooth surface adhesion, and tooth fracture. ZHY Gear mainly takes cylindrical gear reducers as an example to explore how to extend the service life of the reducer gear.
1. Understand the failure modes of reducer teeth
1.1 Tooth breakage
When the reducer is in operation, the root of the reducer gear teeth is subjected to significant alternating stress, and there is a considerable stress concentration at the root of the reducer gear teeth. After cyclic loading, when the stress value on the mechanical structure exceeds the strength limit, fatigue cracks will occur, and the cracks will continue to expand, ultimately causing the reducer gear teeth to break.
1.2 Tooth surface pitting
When the contact stress of the reducer gear is repeatedly applied, cracks will appear on the surface of the reducer gear. When lubricating oil is squeezed in during operation, the cracks gradually increase, causing the metal particles on the tooth surface to peel off, forming small pits, causing vibration, noise, and unstable transmission, resulting in a decrease in bearing capacity.
1.3 Tooth surface bonding
When the reducer operates at low speed and heavy load, the pressure between the meshing reducer gear teeth increases, the local temperature on the tooth surface is too high, the oil film ruptures, and the tooth surfaces come into direct contact. The metal between the tooth surfaces will adhere to each other. The wear of the tooth surface causes friction and wear between the tooth surfaces during meshing of the reducer gear. Wear on the tooth surface causes damage to the tooth profile of the reducer gear, resulting in reduced transmission accuracy, increased noise, increased impact force, thinning of the teeth, and susceptibility to fracture.
1.4 Tooth surface wear
During the meshing transmission process, the tooth surfaces of the reducer gears will slide against each other, and the dust and hard debris particles between the tooth surfaces will cause wear. When this kind of wear reaches a certain degree, the gap between the tooth sides will increase, resulting in greater impact and noise, and may even lead to tooth breakage.
1.5 Plastic deformation of tooth surface
During the operation of the reducer, due to factors such as excessive stress, frequent starting, and overload, the teeth of the reducer gear may undergo plastic deformation. This deformation is caused by the yielding of the gear teeth, resulting in greater noise and vibration during meshing of the reducer gear components.
2. Strengthen the installation and maintenance of reducer gears
2.1 Understand the structure of the reducer gear and install it correctly
Professional technical personnel can predict the service life of the reducer gears based on the working environment and usage load of the reducer, supervise the assembly of the reducer, select appropriate reducer gear materials and heat treatment processes, etc. When installing the reducer gear on the equipment, it should be installed according to the type of reducer gear. During installation, strictly follow the installation process and steps, and use tools for installation. After installation, debugging and inspection should also be carried out to ensure the installation accuracy of the reducer gear, improve the contact accuracy of the reducer gear, and thus reduce pitting corrosion. If there are any abnormalities, they should be rectified in a timely manner.
2.2 Strengthen the maintenance and upkeep of reducer gears
Firstly, regularly inspect the bearings and seals of the reducer gears to maintain their good working condition. If necessary, replace damaged or aged bearings and seals in a timely manner. Carefully inspect the oil seal of the reducer gear and its surrounding components. The oil seal is a very fragile part, and special care should be taken during inspection and disassembly. Do not apply excessive force to avoid damaging the reducer gear. Even if the oil seal does not produce any defects temporarily, it should be replaced regularly because poor oil seal can affect the service life of the reducer gear and cause equipment shutdown. Regularly use cleaning agents or compressed air to clean the reducer gears and remove oil, dust, and other dirt from the surface of the reducer gears.
Secondly, ensure that the reducer gears are in good working condition. Choose the appropriate lubricating oil or grease, and the selection of lubricating oil or grease needs to consider factors such as the material, operating environment, load, and speed of the reducer gear. Generally speaking, lubricating oil is suitable for high-speed reducer gears, while lubricating grease is suitable for low-speed reducer gears. At the same time, it is also necessary to consider parameters such as viscosity and temperature range of lubricating oil or grease. When the oil temperature is too high, the viscosity of lubricating oil will significantly decrease, affecting the formation of oil film between the gear teeth of the reducer. When the lubricating film on the meshing surface of the reducer gear becomes thinner, the load-bearing and anti-wear capacity of the tooth surface decreases, and it is easy to cause pitting corrosion on the tooth surface.
In the parts where lubricating grease cannot be used, solid lubricant can be sprayed onto the surface of the gear teeth of the reducer. After the surface of the gear teeth is dry, a film can be formed. The film thickness can be calculated using an elastohydrodynamic lubrication model. The thicker the film thickness, the better the lubrication conditions of the reducer gear, which can effectively prevent micro motion corrosion during the running in stage of the reducer gear. At the same time, regularly replace lubricating oil or grease to maintain good lubrication of the reducer gears. The replacement time of lubricating oil and grease needs to be determined based on specific situations, and it is generally recommended to replace lubricating oil or grease at least once a year. In addition, it is necessary to check the quantity and quality of the lubricating oil. If the quality does not meet the specified requirements, it should be replaced. When the quantity is small, it should be added in a timely manner.
Finally, it is necessary to regularly and meticulously inspect the operating condition of the reducer gears, including their wear, deformation, cracks, and other conditions. These inspections can be completed by disassembling the reducer gear or using specific inspection tools. If serious wear problems are found in the reducer gears, they must be replaced immediately to prevent further damage. During the operation of the reducer gear, the operation of the reducer gear set will be directly affected by the wear of the reducer gear. Therefore, once signs of wear on the reducer gears are detected, they must be replaced immediately to ensure the normal operation of the system.
3. Improve the surface hardness of the reducer gears
3.1 Surface heat treatment
Surface heat treatment is a commonly used method to improve the hardness of reducer gears. Common surface heat treatment methods include carburization, nitriding, quenching, etc. Among them, carburization and nitriding are suitable for large-scale production of reducer gears, while quenching is suitable for small-scale production or individual reducer gears. During the surface heat treatment process, a hard alloy layer is formed on the surface of the reducer gear to improve its wear resistance and hardness.
3.1.1 Carburization
Carburization is a surface heat treatment method that infiltrates carbon elements into the surface of reducer gears. Through this method, a layer of high carbon alloy layer can be formed on the surface of reducer gears, improving their hardness and wear resistance. The carburization method is suitable for reducer gears made of materials such as low-carbon steel, alloy steel, cast iron, etc. Among them, gas carburization is a carburizing method that places the workpiece in a sealed gas carburizing furnace, heats it to austenitize, and then drips carburizing agent into the furnace or directly introduces carburizing atmosphere to allow carbon atoms to penetrate the surface of the workpiece, thereby increasing the carbon content of the surface of the workpiece.
3.1.2 Nitridation
Nitriding is a surface heat treatment method that infiltrates nitrogen elements into the surface of reducer gears. Through this method, a layer of high nitrogen alloy layer can be formed on the surface of reducer gears, improving their hardness and wear resistance. The nitriding method is suitable for reducer gears made of materials such as steel and cast iron.
3.1.3 Quenching
Quenching is a surface heat treatment method that heats the surface of a reducer gear to a critical temperature and then rapidly cools it. Through this method, a layer of high hardness metal structure can be formed on the surface of the reducer gear, improving its hardness and wear resistance. The quenching method is suitable for small batch production or individual gearbox gears.
3.1.4 Shot peening strengthening
The shot peening strengthening process uses high-speed steel shots to strike the bending part of the reducer gear root, generating significant compressive stress on the surface of the reducer gear. This can damage the residual tensile stress inside the workpiece, thereby improving the bending fatigue strength of the reducer gear root, and thus extending the service life of the reducer gear. The rapid development of shot peening strengthening technology and its application scope will be increasingly wide. Among them, WPC precision shot peening is a treatment method that compresses gas and mixes it with suitable material particles, and then uses high-speed spraying to spray it onto the surface of the reducer gear. This treatment method uses particle media to spray the reducer gear at high speed, which can improve the fatigue strength of the reducer gear but does not change the bending strength of the metal.
Due to the fast spraying speed of this process, the medium is rapidly sprayed onto the reducer gear, causing an instantaneous increase in the surface temperature of the gear teeth, resulting in the melting of the crystalline state on the surface of the gear teeth. Subsequently, through rapid cooling, a fine and tough microstructure is formed on the surface of the reducer gear. With the continuous progress of science and technology and the continuous upgrading of precision automation control systems, the flexibility of shot peening strengthening systems has been significantly enhanced, thereby achieving more ideal part strengthening effects.
3.2 Reasonable Material Selection
A reducer is a mechanical device that can increase torque and reduce speed, widely used in various mechanical equipment to meet various operational requirements. The reducer gear is its main load-bearing component, mainly affected by two forces: the transmission power of the reducer gear and the axial force. Among them, the power transmission of the reducer gear includes tangential force and radial force, which directly affect the service life of the reducer gear. The force direction of the reducer gear is not fixed and unchanged, but varies periodically, which means that the reducer gear is subjected to alternating loads. Different types of reducers also have different forces on their gears, so when selecting materials, it is necessary to make reasonable choices based on different situations. The general principle of material selection is to choose materials with good hardness, strength, toughness, and wear resistance to process the gears of the reducer, such as hard alloy, high-speed steel, special alloy steel, etc.
3.3 Improving the machining accuracy of reducer gears
The machining accuracy of reducer gears directly affects their service life, while improving the machining accuracy of reducer gears can indirectly enhance their hardness. The machining accuracy of the reducer gear is relatively low, and the surface quality of the reducer gear will also be affected, resulting in a decrease in its surface hardness. Therefore, improving the machining accuracy of the reducer gear can extend the service life of the reducer gear.
(1) Reduce the casting error of reducer gear blank. The error of the gear blank of the reducer has a fundamental impact on the machining accuracy of the reducer gear, especially when machining high-precision reducer gears, the accuracy of the gear blank plays a crucial role. The machining of reducer gears mostly uses their inner holes and end faces as positioning benchmarks, which affects the subsequent machining, installation, and positioning accuracy of reducer gears. During the gear hobbing process of the reducer, if the installation gap of the reducer gear blank is large, it may cause eccentricity in the machining of the blank, resulting in a large deviation of the gear ring runout, affecting the subsequent machining of the reducer gear, and even causing the machining failure of the reducer gear. Therefore, it is necessary to strictly control the machining quality of the reducer gear blank, ensuring that the accuracy of the reducer gear hole, the outer diameter of the blank, the outer diameter accuracy of the shaft type reducer gear blank, and the outer circle runout all meet the relevant technical requirements.
(2) Before machining the reducer gear, the machine tool parts should be carefully inspected. The machining machine tool for reducer gears has a direct impact on the machining accuracy of reducer gears, and the reason for the low machining accuracy of most reducer gears is that the machining accuracy of the machine tool does not meet the requirements. Therefore, it is necessary to select cutting tools reasonably based on the material of the reducer gear blank and the accuracy of the reducer gear to meet the machining requirements. The clamping error of the reducer gear can also affect the machining accuracy of the reducer gear. The manufacturing and installation accuracy of the gear hobbing fixture is not high, which can cause radial runout of the gear ring and tooth alignment error. The installation accuracy of the gear blank mainly depends on the manufacturing and installation accuracy of the fixture. Therefore, reducing the clamping error of the reducer gear can also improve the machining accuracy of the reducer gear.
In summary, there are many factors that affect the machining accuracy of reducer gears. The machining environment of reducer gears has an impact on the machining accuracy of reducer gears, and various factors in the machining process of reducer gears can also affect the machining accuracy of reducer gears. Therefore, in order to improve the machining accuracy of reducer gears, the first step is to enhance the quality awareness of the machining personnel. Starting from each link of reducer gear machining, including the machining machine tool, fixture, tool and other production processes, strict quality control of each link is required to ensure the scientificity and standardization of the reducer gear machining process, thereby ensuring the improvement of reducer gear accuracy.
4. Comprehensive optimization of the machining process for reducer gears
Firstly, by optimizing the shape, size, number of teeth, and other structural designs of the reducer gear tooth surface, sliding friction and thermal stress between tooth surfaces can be reduced, thereby reducing tooth surface wear. At the same time, surface carburization and hardening processes can be added to improve the surface hardness and wear resistance of reducer gears, thereby extending their service life.
Secondly, the machining accuracy of the reducer gear will affect the wear of the tooth surface. Therefore, by improving the machining process and enhancing the machining accuracy of the reducer gear, the sliding friction between the tooth surfaces can be reduced, and the wear of the tooth surface can be reduced. At the same time, high-quality raw materials and advanced heat treatment processes can also be used to improve the material hardness and wear resistance of the reducer gears.
Once again, before determining the values of the main parameters such as the gear ratio of the reducer, it is necessary to conduct a detailed analysis based on the motion as the transmission chain. For the establishment of the gear transmission ratio of the reducer, the relationship between modulus and number of teeth should be considered. Appropriately increasing the modulus can reduce the number of teeth, making the structure of the reducer gear more sturdy and able to withstand greater load forces, in order to avoid situations such as tooth breakage and tooth surface wear. However, increasing the modulus can also lead to an increase in the size and weight of the reducer gears, causing certain inconvenience to transportation and installation. On the contrary, reducing the modulus helps to reduce the contact stress of the reducer gear, prolong the service life of the reducer gear, and at the same time, reduce the noise and vibration of the reducer gear, improving the smoothness of the transmission. When determining the modulus of the reducer gear, it is necessary to make a reasonable selection based on the actual situation.
Finally, when using the generation method to machine the reducer gear, the rack tool rolls purely along the indexing circle of the reducer gear. According to the principle of minimum number of teeth without root cutting, the reasonable number of teeth for the small gear can be determined. Usually, the minimum number of teeth that do not produce root cutting is 17. In addition, the circumferential force acting on the gear teeth should also be calculated based on the torque acting on the small gear.
5. Conclusion
In recent years, the types and processes of reducers in China have been constantly updated, but it is crucial to extend the service life of reducers in order to meet the requirements of minimizing costs. Starting from the failure forms of reducer gears, this article comprehensively analyzes various ways such as installation and maintenance of reducer gears, improving the surface hardness of reducer gears, and improving processing technology, in order to effectively extend the service life of reducer gears and continuously promote China’s development towards a strong mechanized country. In the actual production process of the reducer, designers should conduct a comprehensive analysis based on the working requirements of the reducer gear and the basic principles of machining the reducer gear, design the reducer gear reasonably, and fully extend the service life of the reducer gear.