Custom Universal Worm Gearboxes Manufacturers

How to set the assembly clearance of a universal worm gear reducer? What temperature rise and wear factors need to be considered?

1. Setting the assembly clearance of a universal worm gear speed reducer
During the assembly process of a universal worm gear reducer, clearance setting is a key link to ensure its normal operation and performance. Reasonable assembly clearance can ensure the smoothness, accuracy and efficiency of the transmission, while extending the service life of the equipment.
(I) Types and functions of assembly clearance
The assembly clearance of a universal worm gearbox mainly includes the meshing clearance between the worm wheel and the worm, as well as the matching clearance between the bearing and the shaft, and between the bearing and the bearing seat. Among them, the meshing clearance of the worm gear is one of the core factors affecting the transmission performance. Appropriate meshing clearance can store lubricating oil, form an oil film, play a role in lubrication and cooling, and reduce tooth surface wear; at the same time, it can also compensate for deformation caused by factors such as temperature changes, manufacturing errors and installation errors during the transmission process, and avoid tooth surface jamming. The bearing matching clearance affects the rotation accuracy of the shaft and the service life of the bearing. The appropriate clearance can ensure the normal operation of the bearing and reduce friction, heat generation and vibration.
(II) Principles and methods for setting assembly clearance
Principle
According to transmission requirements: Different application scenarios have different requirements for the transmission accuracy, load-bearing capacity and transmission efficiency of the reducer. For example, in high-precision transmission occasions, such as precision machine tools, instruments and meters, a smaller meshing clearance is required to ensure the accuracy of transmission; while in heavy loads and large impact loads, such as mining machinery, lifting machinery, etc., a larger meshing clearance is required to buffer the impact and prevent damage to the tooth surface.
Consider material properties: The materials of the worm wheel and the worm are different, and their thermal expansion coefficients are also different. When setting the clearance, it is necessary to consider the expansion and contraction of the material at the working temperature to avoid excessive or too small clearance due to temperature changes. For example, when the worm is made of steel and the worm wheel is made of copper alloy, due to the large thermal expansion coefficient of copper alloy, the expansion of the worm wheel may be greater than that of the worm in a high temperature environment, resulting in a reduction in the meshing clearance. Therefore, a larger clearance needs to be reserved during normal temperature assembly.
Combined with manufacturing and installation accuracy: Manufacturing and installation accuracy directly affect the actual size of the assembly clearance. If the machining accuracy of the parts is high and the installation error is small, then a smaller assembly clearance can be set; otherwise, the clearance needs to be appropriately increased to compensate for the error.
Method
Measurement method: During the assembly process, the meshing clearance of the worm gear and the bearing fit clearance are directly measured by using professional measuring tools such as dial gauges and feeler gauges. For example, use a feeler gauge to measure the clearance between the tooth surfaces of the worm gear, insert the feeler gauge between the tooth surfaces, and the thickness of the feeler gauge that can be easily inserted is the meshing clearance value. For the bearing fit clearance, a dial gauge can be used to measure the axial and radial movement of the shaft in the bearing to determine whether the clearance meets the requirements.
Calculation method: According to the design parameters and material properties of the reducer, the assembly clearance is determined by theoretical calculation. For example, for the meshing clearance of the worm gear, the clearance calculation formula of the gear transmission can be used to calculate it according to the module, number of teeth, center distance and other parameters. At the same time, it is also necessary to consider the impact of temperature changes on the clearance, and adjust the clearance value by calculating the thermal expansion of the material.
Experience method: For some common general worm gear reducer models, the clearance can be set by referring to previous assembly experience and industry standards. For example, for worm gears with smaller modules (such as modules less than 3), the meshing clearance is usually set to 0.05-0.15mm; for worm gears with larger modules (such as modules greater than 5), the meshing clearance can be appropriately increased to 0.15-0.3mm. Of course, the specific clearance value needs to be adjusted according to the actual situation.
(III) Assembly clearance adjustment method
During the assembly process, if the assembly clearance is found to be not in line with the requirements, it needs to be adjusted. Common adjustment methods include the following:
Shim adjustment method: By adding or reducing the thickness of the shim between the bearing seat and the bearing or the axial position of the worm gear, the bearing fit clearance and the meshing clearance of the worm gear are adjusted. For example, when adjusting the axial position of the worm gear, a shim can be added between the worm gear hub and the shaft, and the meshing depth of the worm gear and the worm gear can be adjusted by changing the thickness of the shim, thereby changing the meshing clearance.
Axial adjustment method: The meshing clearance is changed by adjusting the axial position of the worm gear or the worm gear. For example, for a worm shaft with a tapered roller bearing, the axial position of the worm can be changed by adjusting the axial preload of the bearing, thereby adjusting the meshing clearance.
Parts replacement method: If the assembly clearance cannot be adjusted to meet the requirements due to manufacturing errors or wear of parts, you can consider replacing related parts, such as replacing the worm wheel, worm or bearing, to ensure that the clearance meets the design requirements.
2. Temperature rise factors to be considered when setting the assembly clearance
During the operation of the general worm gear reducer, temperature rise is a factor that cannot be ignored, which will have a significant impact on the assembly clearance. Therefore, when setting the assembly clearance, the temperature rise factor must be fully considered to ensure that the reducer can operate normally at the operating temperature.
(I) The influence mechanism of temperature rise on the assembly clearance
Part thermal expansion: During the operation of the reducer, heat will be generated due to friction, loss, etc., causing the temperature of the parts to rise. The parts will expand after being heated, and the amount of expansion is related to the thermal expansion coefficient of the material, the temperature rise value and the size of the parts. For worm gear transmission, the worm is usually made of steel with a small thermal expansion coefficient; the worm wheel is mostly made of copper alloy or aluminum alloy with a large thermal expansion coefficient. Therefore, under the same temperature rise, the radial expansion of the worm wheel may be greater than that of the worm, resulting in a decrease in the meshing clearance between the worm wheel and the worm. If the meshing clearance set at room temperature is too small, tooth surface extrusion and jamming may occur during high-temperature operation, seriously affecting the transmission performance or even damaging parts.
Changes in lubricant performance: Temperature rise will cause the viscosity of the lubricant to decrease and the lubrication performance to decrease. When the viscosity of the lubricant decreases, the thickness of the oil film formed between the tooth surfaces becomes thinner, the load-bearing capacity is weakened, and it is easy to cause increased wear on the tooth surfaces. At the same time, if the lubricant temperature is too high, oxidation and deterioration may occur, resulting in sedimentation, blocking the lubrication channel, further affecting the lubrication effect, and aggravating temperature rise and wear.
(II) Calculation and evaluation of temperature rise
Temperature rise calculation: In order to evaluate the impact of temperature rise on the assembly clearance, it is necessary to calculate the temperature rise of the reducer during operation. The calculation of temperature rise is usually based on the principle of thermal balance, that is, the heat generated by the reducer is equal to the heat dissipated. The heat generation power of the reducer mainly includes gear meshing loss, bearing friction loss, oil stirring loss, etc.; the heat dissipation power is related to the heat dissipation area, surface heat transfer coefficient, ambient temperature and other factors of the reducer. The stable temperature rise of the reducer can be obtained by calculation, and then the thermal expansion of the parts can be calculated according to the thermal expansion coefficient of the parts, providing a basis for the setting of the assembly clearance.
Temperature rise evaluation standard: Reducers of different types and uses have different limit standards for temperature rise. Generally speaking, the temperature rise limit of general worm gear reducers is usually 60-80℃ (when the ambient temperature is 20℃). In practical applications, it is necessary to evaluate the temperature rise according to the working conditions and requirements of the reducer and refer to relevant standards to ensure that the temperature rise is within the allowable range, so as to avoid excessive changes in assembly clearance and damage to parts due to excessive temperature rise.
(III) Measures to deal with the impact of temperature rise
Reasonable selection of materials: When designing and manufacturing reducers, the materials of worm wheels and worms should be reasonably selected to minimize the difference in thermal expansion coefficients between the two. For example, steel worm and cast iron worm wheel can be used. The thermal expansion coefficient of cast iron is relatively small, and the difference with the thermal expansion coefficient of steel is small, which can reduce the meshing clearance change caused by temperature change to a certain extent.
Optimize the lubrication system: A good lubrication system can effectively reduce temperature rise and wear. Lubricating oil suitable for working conditions should be selected, such as lubricating oil with suitable viscosity and good anti-oxidation performance, and ensure that the lubrication system is adequately supplied and unobstructed. At the same time, forced lubrication, circulating cooling and other methods can be used to improve the heat dissipation effect and reduce the temperature of the lubricating oil.
Reserve temperature compensation gap: When setting the assembly gap, it is necessary to consider the thermal expansion of parts caused by temperature rise and reserve a certain temperature compensation gap. For example, according to the calculated thermal expansion of the worm wheel and worm at the highest operating temperature, the meshing clearance is set to the sum of the design clearance and the thermal expansion during normal temperature assembly to ensure that the meshing clearance is still within a reasonable range when running at high temperature.
3. Wear factors to be considered when setting the assembly clearance
Wear is an inevitable phenomenon of general worm gear reducer in the long-term operation process. It will cause the size of parts to change and the assembly clearance to increase, thereby affecting the transmission performance and service life of the reducer. Therefore, when setting the assembly clearance, the wear factor must be fully considered to ensure that the reducer can maintain a good operating condition throughout its service life.
(I) Types and causes of wear
Adhesive wear: During the worm gear transmission process, when the lubricating oil film between the tooth surfaces is destroyed and the metal surfaces are in direct contact, adhesive wear will occur. Adhesive wear usually occurs under heavy load, low speed or poor lubrication, and is manifested as scratches, tears or even welding on the tooth surface.
Abrasive wear: Impurities, metal debris and other abrasive particles inside the reducer enter the tooth surface, causing abrasive wear. Abrasive wear will gradually wear and thin the tooth surface, reduce the tooth shape accuracy, and increase the meshing clearance.
Fatigue wear: Under the action of alternating loads, fatigue cracks will occur on the tooth surface. As the cracks expand and connect, the tooth surface material will peel off, forming fatigue wear. Fatigue wear usually occurs in areas where the contact stress on the tooth surface is large, such as the tooth top and tooth root.
Corrosive wear: When the lubricating oil contains acidic substances or water, it will corrode the tooth surface and bearings and other parts, causing corrosive wear. Corrosion and wear will cause rust and spots on the surface of parts, reducing the strength and wear resistance of parts.
(II) The impact of wear on assembly clearance
As wear occurs, the tooth thickness of the worm wheel and worm will gradually decrease, and the raceway and rolling element of the bearing will gradually wear, resulting in an increase in assembly clearance. For example, the meshing clearance of the worm wheel and worm will increase as the tooth surface wears. When the clearance increases to a certain extent, it will lead to a decrease in transmission accuracy, increased noise, increased vibration, and even transmission failure. The increase in bearing clearance will lead to a decrease in the rotation accuracy of the shaft, affecting the overall performance of the reducer.
(III) Measures to deal with the impact of wear
Reasonably select part materials and heat treatment processes: Select materials with good wear resistance to manufacture worm wheels and worms, such as using high-quality alloy steel for the worm and performing surface quenching treatment, and using wear-resistant copper alloy for the worm wheel. Through reasonable heat treatment processes, such as quenching, tempering, carburizing, etc., the hardness and wear resistance of the surface of the parts can be improved, and the occurrence of wear can be reduced.
Optimize gear design parameters: Rationally design the modulus, number of teeth, pressure angle, helix angle and other parameters of the worm gear to reduce the contact stress and sliding speed of the tooth surface and reduce wear. For example, increasing the modulus can improve the load-bearing capacity of the tooth surface and reduce wear; adopting a suitable helix angle can improve the meshing condition of the tooth surface and reduce the sliding friction coefficient.
Strengthen lubrication and cleaning management: Regularly replace the lubricating oil to maintain the cleanliness and performance of the lubricating oil and prevent impurities and moisture from entering the reducer. At the same time, a filter device is set at the entrance of the reducer to filter out the abrasive particles and impurities in the lubricating oil to reduce the occurrence of abrasive wear.
Reserve wear compensation clearance: When setting the assembly clearance, it is necessary to consider the wear amount of the parts during the service life cycle and reserve a certain wear compensation clearance. For example, based on experience or test data, the wear speed and wear amount of the worm gear and bearing under normal working conditions are estimated, and the clearance is set to the sum of the initial design clearance and the expected wear amount during assembly to ensure that the clearance is still within the allowable range after wear.