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Several factors affecting the performance and life of oil seals
2022-04-28
1. Structural selection of oil seals for excavator accessories
The structure of the oil seal is various. In use, oil seals such as single-lip type, double-lip type, pressure-resistant type, anti-eccentric type, one-way return type, two-way return type, etc. are often used. Therefore, the correct selection of the structural form is related to the different conditions and uses during use. The performance and life of the oil seal.
If it is used in dusty conditions, the performance of the oil seal will be reduced, and the oil seal with dust-proof structure design should be selected.
2. Selection of oil seal material
At present, the commonly used oil seal materials for excavator parts in China are still mainly nitrile rubber, acrylate rubber, polyurethane rubber and other materials. From the perspective of material formula, hardness, compression set, aging resistance, expansion, wear resistance, high and low temperature resistance Performance is the main item of material requirements.
For example, for the high and low temperature resistance of the material, nitrile rubber and polyurethane rubber can be used when the operating temperature at low speed is in the range of -20 to 80 °C; Sulfonated polyethylene and silicone rubber and other materials; when the operating temperature at high speed is in the range of -20 to 180 °C, silicone rubber, silicone fluorine rubber or fluorine rubber can be used because acrylate rubber has better heat resistance. Acrylate rubber can also be used.
Therefore, it is very important to choose different material formulations under different use media, temperature and pressure conditions. Another example is that the hardness of the oil seal of the excavator accessories is related to the elastic modulus of the rubber. The hardness change of the oil seal will affect the contact pressure, contact width, and friction characteristics between the oil seal lip and the rotating shaft.
The oil seal lip should have a certain resilience to reduce friction with the shaft and frictional heat. Appropriate hardness can improve the service life of the oil seal. In the use of the oil seal, the hardness of the oil seal material changes. For example, if the hardness of the oil seal material is too high, the temperature of the hot lip part due to friction with the shaft is fast, and it is easy to accelerate the aging and hardening. The service life of the oil seal is shortened.
If the hardness of the oil seal material is too low, when the oil pressure of the sealing medium is too large during use, the oil seal will deform at the waist and leak oil. When the medium pressure of the oil seal is high, the material hardness can be slightly higher. In most cases, the oil seal for automobiles is used under low pressure conditions. The hardness of the general oil seal compound can be 70±5HA or 60±5HA.
3. Interference and eccentricity between the oil seal lip and the rotating shaft
The interference between the oil seal lip and the rotating shaft is mainly to make the sealing lip have the ability to follow the shaft center and the radial runout of the shaft to compensate for the wear of the sealing lip during use and to give the rotating shaft an appropriate radial force.
Under normal circumstances, it is unavoidable that there is a certain eccentricity after the oil seal of the excavator parts is installed and the radial runout after the shaft is processed. At this time, it is necessary to have a certain amount of interference between the oil seal lip and the surface of the rotating shaft.
The interference to the lip should be as small as possible, but when the interference of the oil seal lip to the surface of the rotating shaft is too small, when the lip cannot follow or compensate for the eccentricity of the shaft, a gap will occur and cause leakage. When the oil seal lip is opposite to the rotating shaft If the interference of the surface is too large, the radial pressure of the lip on the shaft surface will also increase.
The friction between the oil seal lip and the shaft surface increases, so that the temperature of the oil seal lip rises. As the friction time increases, the lip temperature rises, and the aging of the oil seal lip becomes brittle, the wear of the oil seal lip increases, and the performance of the oil seal increases. decline and reduced service life.
At present, the oil seal lip interference varies with the diameter of the shaft, and the recommended oil seal lip interference is in the range of 0.15 to 0.9 mm.
4. The eccentricity and runout of the shaft and the surface roughness of the shaft
The eccentricity and runout of the shaft are a major factor affecting the service life and leakage of the oil seal. It is unavoidable that the oil seal has a certain amount of eccentricity during installation and use. The shaft has two cases of assembly eccentricity and shaft radial runout. Generally, the deviation between the center line of the oil seal and the center line of the rotating shaft is mainly due to the processing of the oil seal installation slot hole, the machining accuracy of the oil seal mold, the production process of the oil seal, and the improper installation of the oil seal. Caused.
The eccentricity of the shaft and the runout of the shaft are mainly caused by the roundness deviation of the shaft during machining. There are many reasons for radial runout. When the radial runout of the shaft is large, the peripheral part of the lip cannot keep up with the gap generated by the radial runout of the shaft. This runout and eccentricity make the oil film on the surface of the lip and the rotating shaft disordered, resulting in the oil seal. Oil spill.
This requires that the runout and eccentricity of the oil seal lip of the excavator accessories to the shaft increase with the increase of the rotational speed. The smaller the eccentricity of the follow-up shaft, the better. To solve the eccentricity of the shaft, the oil seal lip can generally be lengthened, the amount of interference is appropriately increased, and the material with moderate hardness and softness is selected. There are also corresponding requirements for the surface roughness of the shaft. certain influence.
If the surface of the shaft is too rough, there are obvious machining tool marks, scratches, burrs and bumps on the surface of the shaft. In actual use, it is required to improve the surface roughness of the shaft, and the Ra is generally 1.6 to 0.4 μm.
5. Friction torque and temperature rise of oil seal lip
The greater the radial force of the oil seal lip on the shaft, the greater the friction torque between the oil seal lip and the shaft surface, resulting in the higher the temperature of the oil seal lip. Generally, the lip temperature is 10-40°C higher than the oil temperature.
The mechanical energy generated by friction between the oil seal lip and the shaft surface is converted into heat energy and accumulates in the contact part, causing the temperature of the lip part to rise, accelerating the aging, hardening and aggravating the wear of the lip part, which affects the performance and life of the oil seal.
Because the friction torque is closely related to the radial force of the oil seal, generally the radial force of the oil seal used for the high-speed excavator parts shaft takes the low value and the low-speed shaft oil seal radial force takes the high value. In order to achieve better sealing performance and service life.
6. Installation and storage of oil seal
Oil seals for excavator accessories should be stored in a dry and clean environment. Oil seals must be packaged and stacked neatly and should not be stacked arbitrarily. Do not use threads or ropes to wear them together to avoid damaging the lip of the oil seal and affecting the service life. In addition, the damage of the oil seal lip due to the improper installation method affects the sealing effect and also easily affects the service life of the oil seal and causes problems such as failure and leakage. To install the oil seal, follow the procedure below.
a. Before installation, carefully check the shaft surface for burrs, machining tool marks, etc. to prevent damage to the oil seal lip.
b. Carefully check the oil seal lip for damage and the appearance of dust and impurities.
c. Apply clean grease on the sealing flange to facilitate installation and prevent scratching of the lip during installation. The oil seal used as a dustproof should be filled with grease.
The structure of the oil seal is various. In use, oil seals such as single-lip type, double-lip type, pressure-resistant type, anti-eccentric type, one-way return type, two-way return type, etc. are often used. Therefore, the correct selection of the structural form is related to the different conditions and uses during use. The performance and life of the oil seal.
If it is used in dusty conditions, the performance of the oil seal will be reduced, and the oil seal with dust-proof structure design should be selected.
2. Selection of oil seal material
At present, the commonly used oil seal materials for excavator parts in China are still mainly nitrile rubber, acrylate rubber, polyurethane rubber and other materials. From the perspective of material formula, hardness, compression set, aging resistance, expansion, wear resistance, high and low temperature resistance Performance is the main item of material requirements.
For example, for the high and low temperature resistance of the material, nitrile rubber and polyurethane rubber can be used when the operating temperature at low speed is in the range of -20 to 80 °C; Sulfonated polyethylene and silicone rubber and other materials; when the operating temperature at high speed is in the range of -20 to 180 °C, silicone rubber, silicone fluorine rubber or fluorine rubber can be used because acrylate rubber has better heat resistance. Acrylate rubber can also be used.
Therefore, it is very important to choose different material formulations under different use media, temperature and pressure conditions. Another example is that the hardness of the oil seal of the excavator accessories is related to the elastic modulus of the rubber. The hardness change of the oil seal will affect the contact pressure, contact width, and friction characteristics between the oil seal lip and the rotating shaft.
The oil seal lip should have a certain resilience to reduce friction with the shaft and frictional heat. Appropriate hardness can improve the service life of the oil seal. In the use of the oil seal, the hardness of the oil seal material changes. For example, if the hardness of the oil seal material is too high, the temperature of the hot lip part due to friction with the shaft is fast, and it is easy to accelerate the aging and hardening. The service life of the oil seal is shortened.
If the hardness of the oil seal material is too low, when the oil pressure of the sealing medium is too large during use, the oil seal will deform at the waist and leak oil. When the medium pressure of the oil seal is high, the material hardness can be slightly higher. In most cases, the oil seal for automobiles is used under low pressure conditions. The hardness of the general oil seal compound can be 70±5HA or 60±5HA.
3. Interference and eccentricity between the oil seal lip and the rotating shaft
The interference between the oil seal lip and the rotating shaft is mainly to make the sealing lip have the ability to follow the shaft center and the radial runout of the shaft to compensate for the wear of the sealing lip during use and to give the rotating shaft an appropriate radial force.
Under normal circumstances, it is unavoidable that there is a certain eccentricity after the oil seal of the excavator parts is installed and the radial runout after the shaft is processed. At this time, it is necessary to have a certain amount of interference between the oil seal lip and the surface of the rotating shaft.
The interference to the lip should be as small as possible, but when the interference of the oil seal lip to the surface of the rotating shaft is too small, when the lip cannot follow or compensate for the eccentricity of the shaft, a gap will occur and cause leakage. When the oil seal lip is opposite to the rotating shaft If the interference of the surface is too large, the radial pressure of the lip on the shaft surface will also increase.
The friction between the oil seal lip and the shaft surface increases, so that the temperature of the oil seal lip rises. As the friction time increases, the lip temperature rises, and the aging of the oil seal lip becomes brittle, the wear of the oil seal lip increases, and the performance of the oil seal increases. decline and reduced service life.
At present, the oil seal lip interference varies with the diameter of the shaft, and the recommended oil seal lip interference is in the range of 0.15 to 0.9 mm.
4. The eccentricity and runout of the shaft and the surface roughness of the shaft
The eccentricity and runout of the shaft are a major factor affecting the service life and leakage of the oil seal. It is unavoidable that the oil seal has a certain amount of eccentricity during installation and use. The shaft has two cases of assembly eccentricity and shaft radial runout. Generally, the deviation between the center line of the oil seal and the center line of the rotating shaft is mainly due to the processing of the oil seal installation slot hole, the machining accuracy of the oil seal mold, the production process of the oil seal, and the improper installation of the oil seal. Caused.
The eccentricity of the shaft and the runout of the shaft are mainly caused by the roundness deviation of the shaft during machining. There are many reasons for radial runout. When the radial runout of the shaft is large, the peripheral part of the lip cannot keep up with the gap generated by the radial runout of the shaft. This runout and eccentricity make the oil film on the surface of the lip and the rotating shaft disordered, resulting in the oil seal. Oil spill.
This requires that the runout and eccentricity of the oil seal lip of the excavator accessories to the shaft increase with the increase of the rotational speed. The smaller the eccentricity of the follow-up shaft, the better. To solve the eccentricity of the shaft, the oil seal lip can generally be lengthened, the amount of interference is appropriately increased, and the material with moderate hardness and softness is selected. There are also corresponding requirements for the surface roughness of the shaft. certain influence.
If the surface of the shaft is too rough, there are obvious machining tool marks, scratches, burrs and bumps on the surface of the shaft. In actual use, it is required to improve the surface roughness of the shaft, and the Ra is generally 1.6 to 0.4 μm.
5. Friction torque and temperature rise of oil seal lip
The greater the radial force of the oil seal lip on the shaft, the greater the friction torque between the oil seal lip and the shaft surface, resulting in the higher the temperature of the oil seal lip. Generally, the lip temperature is 10-40°C higher than the oil temperature.
The mechanical energy generated by friction between the oil seal lip and the shaft surface is converted into heat energy and accumulates in the contact part, causing the temperature of the lip part to rise, accelerating the aging, hardening and aggravating the wear of the lip part, which affects the performance and life of the oil seal.
Because the friction torque is closely related to the radial force of the oil seal, generally the radial force of the oil seal used for the high-speed excavator parts shaft takes the low value and the low-speed shaft oil seal radial force takes the high value. In order to achieve better sealing performance and service life.
6. Installation and storage of oil seal
Oil seals for excavator accessories should be stored in a dry and clean environment. Oil seals must be packaged and stacked neatly and should not be stacked arbitrarily. Do not use threads or ropes to wear them together to avoid damaging the lip of the oil seal and affecting the service life. In addition, the damage of the oil seal lip due to the improper installation method affects the sealing effect and also easily affects the service life of the oil seal and causes problems such as failure and leakage. To install the oil seal, follow the procedure below.
a. Before installation, carefully check the shaft surface for burrs, machining tool marks, etc. to prevent damage to the oil seal lip.
b. Carefully check the oil seal lip for damage and the appearance of dust and impurities.
c. Apply clean grease on the sealing flange to facilitate installation and prevent scratching of the lip during installation. The oil seal used as a dustproof should be filled with grease.
d. Carefully check the dimensional tolerance of the oil seal spring and install it correctly. e. On the edge of the shaft shoulder, in order to facilitate the installation of the oil seal so that the lip is not damaged, there should be rounded or chamfered corners. When the oil seal is installed along the shaft, the shaft should be slightly rotated to facilitate the installation operation. f. When pressing the oil seal of excavator accessories into the hole seat, the diameter of the axial pressure tool should be uniform and stable, and the diameter of the tool should be smaller than the diameter of the oil seal. damage. g. The oil seal installation should not be interrupted for a long time to avoid the weight of the shaft causing the oil seal to be compressed and deformed, causing damage to the lip. Therefore, in order to obtain good sealing performance and long service life, attention must be paid to the storage and installation of the oil seal.
