Oil seal is a mechanical element for sealing, also known as rotary shaft lip seal ring. Oil seal is used to prevent the oil from leaking from the machinery to prevent oil entering the friction part of the machinery when the machinery is running. The common type is skeleton oil seal.
1、 Common expression method of oil seal: oil seal type - inner diameter - outer diameter - height - material, for example: TC40 * 62 * 12-NBR indicates: double lip inner framework oil seal, with inner diameter of 40, outer diameter of 62, thickness of 12, and material of nitrile rubber oil seal.
2、 The framework oil seal is made of nitrile rubber (NBR): wear-resistant, oil resistant (cannot be used in medium), temperature resistant: - 40~120 ℃.
Hydrogenated nitrile rubber (HNBR): wear resistance, oil resistance, aging resistance, temperature resistance: - 40~200 ℃ (stronger than NBR temperature resistance).
Fluorocarbon (FKM): acid and alkali resistance, oil resistance (resistance to all oils), temperature resistance: - 20~300 ℃ (oil resistance is better than the above two).
Polyurethane rubber (TPU): wear resistance, aging resistance, temperature resistance: - 20~250 ℃ (good aging resistance).
Silicone rubber (PMQ): heat resistance, cold resistance, small compression deformation, low mechanical strength, temperature resistance: - 60~250 ℃ (excellent temperature resistance).
Polytetrafluoroethylene (PTFE): good chemical stability, acid and alkali resistance, oil and other media, wear resistance and high temperature resistance, high mechanical strength, good self-lubricating performance.
Generally speaking, the materials commonly used for skeleton oil seals are nitrile rubber, fluororubber, silicone rubber, and polytetrafluoroethylene, which have good self-lubricating properties, especially the effect is better after adding bronze. They are all used to make retaining rings, Gere rings, Stefan seals, etc.
3、 Distinguish the skeleton oil seal model C type skeleton oil seal can be divided into five types: SC type, TC type, VC type, KC type and DC type. They are single lip inner skeleton oil seal, double lip inner skeleton oil seal, single lip springless inner skeleton oil seal, double lip springless inner skeleton oil seal and double lip double spring inner skeleton oil seal.
The G type skeleton oil seal is threaded outside, which is the same type as the C type, except that it is technically modified to be threaded outside, which is similar to the function of the O-ring, that is, it plays a role in strengthening the sealing effect, and it can also play a role in fixing the oil seal.
B-type skeleton oil seal is made of rubber inside the skeleton or no rubber inside or outside the skeleton. Without rubber, the heat dissipation performance will be better.
The A-type skeleton oil seal is a fabricated oil seal. Its structure is relatively complex compared with the above three types, and it is characterized by better pressure bearing performance and better performance.
4、 Framework oil seal is divided into three parts: self tightening spring, sealing main body and strengthening framework.
• Sealing principle of skeleton oil seal: because there is an oil film controlled by the oil seal edge between the oil seal and the shaft, this oil film has the characteristics of fluid lubrication.
• Sealing principle analysis: under the action of skeleton oil seal, the rigidity of oil film just makes the contact end of oil film and air form a crescent surface, preventing the leakage of working medium, thus realizing the sealing of rotating shaft. The sealing ability of the oil seal depends on the thickness of the oil film on the sealing surface. If the thickness is too large, the oil seal will leak; If the thickness is too small, dry friction may occur, causing wear of oil seal and shaft; If there is no oil film between the sealing lip and the shaft, it is easy to cause heat and wear. Therefore, during installation, apply some oil on the seal ring, and ensure that the skeleton oil seal is perpendicular to the shaft centerline. If not, the seal lip of the oil seal will drain the lubricating oil from the shaft, which will also lead to excessive wear of the seal lip. During operation, the lubricant in the housing slightly leaks out to form at the sealing surface.
5、 The role of the skeleton oil seal is generally to isolate the parts that need lubrication in the transmission parts from the output parts, so as not to let the lubricating oil leak. It is usually used for the rotating shaft and is a rotating shaft lip seal. The skeleton is like the reinforcement in the concrete component, which plays a role in strengthening and maintaining the shape and tension of the oil seal. According to the framework type, it can be divided into internal framework oil seal, external framework oil seal and exposed framework oil seal. The skeleton oil seal is made of nitrile rubber and steel plate, with stable quality and long service life.
1. Prevent sand, dust, moisture, etc. from invading the bearing from outside; 2. Limit the leakage of lubricating oil from the bearing. The requirement for oil seal is that the size (inner diameter, outer diameter and thickness) should meet the requirements; It is required to have proper elasticity, which can properly clamp the shaft and play a sealing role; Heat resistance, wear resistance, good strength, medium resistance (oil or water, etc.), and long service life.
6、 Selection of oil seal The selection of oil seal shall be based on the sealing medium and working conditions. The sealing medium needs to select the material of oil seal. The working conditions mainly consider the operating pressure, working linear speed and working temperature range.
When selecting the oil seal material, consider the compatibility of the material with the working medium, the adaptability to the operating temperature range, and the ability of the lip to follow the rotating shaft at high speed. Generally, the temperature of the lip of the oil seal is 20~50 ℃ higher than the temperature of the working medium when it is working. Attention should be paid to the selection of oil seal materials.
The service pressure of ordinary oil seal generally does not exceed 0.05MPa. When the working pressure exceeds this value, pressure resistant oil seal shall be selected.
Under the condition of the same diameter, oil seals made of different materials have different ability to adapt to the linear speed of shaft surface rotation. The linear speed range of oil seal is generally less than 15m/s.
The working range of oil seal is related to the material used for oil seal: - 40~120 ℃ for NBR, - 30~180 ℃ for ACM and - 25~300 ℃ for FPM.
7、 The design requirements of the corresponding shaft and cavity: 1. The surface roughness. Because the speed and oil volume of the shaft are different, the roughness of the shaft is too large or too small, which will affect the leakage and wear of the oil seal. The allowable range of shaft surface roughness is Rz1.0~5.0 μ m； Ra0.2～0.8 μ m。 Take 2.5~1.6 oil seal for rotating shaft μ mRz。
2. Hardness: the surface hardness of rotating shaft is generally ≥ 35HRC. When the medium is dirty, there are impurities from outside, or the shaft surface speed is>12m/s, the shaft surface hardness should be above 55HRC, and the depth of the shaft surface quenching layer should be>0.2mm.
3. The recommended chamfer of the shaft is 15 °~30 °, so that the oil seal can be installed without damaging the oil seal lip.
4. Shaft processing, correct shaft processing is the decisive factor to ensure the normal operation of the sealing system. The appropriate oil seal shaft processing method is horizontal feeding fine grinding and emery paper polishing. Unsuitable processing methods are finishing on the lathe, ultra finishing, rolling, emery paper polishing (sandpaper polishing in axial movement).
5. The shaft is mainly made of ordinary carbon structural steel, such as C35 and C45, as well as cast iron, ceramics and resin plastics. However, the shaft of the last three materials has defects in sealing oil seals.
Design of cavity: 1. See the table below for surface roughness and diameter tolerance.
Position diameter tolerance surface roughness/mmRa ≤ Rz ≤ seat hole frameless oil seal H113.212.5 framework oil seal H8 or H71.66.3 rotating shaft h9 or f90.8~0.43.2~1.62, recommended installation chamfer value 15 °~30 °.
3. The cavity is made of steel or cast iron, and rubber or metal oil seals can be used. Generally, light alloy and resin have large thermal expansion coefficient, so it is suitable to use rubber oil seals.
4. Unsuitable cavity structure, such as punching, thread assembly and split cavity.
8、 Installation of oil seal 1. Before installation, the oil seal should be properly coated with lithium ester added with molybdenum disulfide between the lips to prevent dry grinding of the lip when the shaft starts in an instant, which will affect the interference of the lip. It should be assembled as soon as possible. If the oil seal seat of the oil seal is not installed immediately, it is recommended to cover it with cloth to prevent foreign matters from adhering to the oil seal. The hands or tools coated with lithium grease must be clean.
2. The oil seal shall be installed flatly without inclination. It is recommended to use oil pressure equipment or sleeve tools for installation. The pressure should not be too high, and the speed should be even and slow.
3. When installing the oil seal, apply oil or lubricating oil, and round the shaft end and shoulder.
4. When installing the oil seal, make sure that the lip end faces the side of the oil to be sealed, and avoid reverse assembly.
5. When the oil seal is installed into the seat hole, it should be pushed in with a special tool to prevent the position deflection.
6. Various measures shall be taken at the thread, keyway, spline and other places where the oil seal lip passes to prevent lip damage, and special tools shall be used for assembly.
7. Avoid bumping the inner surface of the cavity and the surface of the shaft when removing the oil seal.
8. The used oil seal cannot be used even though its appearance is good. Replace it with a new one.
9. If the shaft surface is bruised or rusted, repair it.
10. When installing the new oil seal, in order to make it leave the old lip contact part, the gasket should be used to avoid the original friction trace.
