Development and application of PTFE oil seal for driving gear

Descriptor: Active gear oil seal Zhang Qing: 1% 5 years old, female, Yuejin Automobile Group, the quality department of the company, senior engineer.
1 Overview With the rapid development of the automotive industry, the reliability requirements for the engine, chassis and other assemblies are getting higher and higher, and the oil seals used, especially the rotating shaft oil seals, are becoming more and more demanding. The seal and the reliability of the oil seal are particularly important.
In the automotive field, rubber seals have been used. The most widely used are nitrile rubber seals and fluororubber seals. The former is cheap and low-cost, but the temperature and seal are poor, and the leakage is more serious. Temperature resistance and sealing have been significantly improved, but the cost is high, and still have some common commonalities of ordinary rubber materials, such as being particularly sensitive to the eccentric reaction of the shaft, and the leakage phenomenon is still relatively common.
In the early 1980s, companies such as Mather and National in the United States successively developed a filled polytetrafluoroethylene (PTFE) oil seal instead of a lip rubber skeleton oil seal, which successfully solved the engine leakage and oil problems, and greatly improved the technical performance of the engine and even the automobile. .
Yuejin Group Company N1043 series chassis rear axle drive gear oil seal used before the Ningqing rubber material, the leakage is more serious, the company has to bear several hundred thousand yuan of "three guarantees" claims each year, and affect the image of the r vehicle. Under this circumstance, the company has organized relevant units to carry out technical research and used oil seals of materials such as fluororubbers. The effect is still not satisfactory.
To this end, the relevant departments of Yuejin Group Co., Ltd. specialize in working with Nanjing Sanfu Industrial Co., Ltd. (Nanjing Glass Fiber Research and Design Institute) to develop a PTFE active gear oil seal. After more than half a year of hard work, it passed strict material performance testing and assembly. The bench test and the loading road test were finally successfully developed, which solved the oil leakage problem of the rear axle drive gear.
2 Material characteristics Polytetrafluoroethylene, also known as Teflon or plastic king, is a copolymer of tetrafluoroethylene monomer, which has the following characteristics: (1) high chemical stability: good chemical inertness, strong acid, strong Alkali or strong oxidizing agents and organic solvents do not work for it.
Good thermal stability: The cracking temperature is above 400C, so it can work normally in a temperature range of 200C300C. Good friction reduction: the friction coefficient between PTFE materials is 1.2, the dry friction coefficient between metal and metal is 1.3, and in the case of liquid lubrication is 0.02004, the dynamic and static friction coefficient is relatively small, and the beginning The dynamic friction coefficient is almost the same as the dynamic friction coefficient. (3) Excellent self-lubricity: The surface of the PTFE material has outstanding surface S lubricity, and almost all viscous substances cannot adhere to its surface.
Since the polytetraethylene acetonitrile material has the above characteristics, if it is appropriately improved, it is preferable to use it as an automobile rotary shaft oil seal material.
3 oil seal development and its structural type and sealing mechanism We developed the oil seal structure as shown.
1 main sealing lip 2 - dusting secondary lip) 3 - spiral groove diagram iPTFE oil seal structure The main sealing lip has a spiral groove (reflow groove), its function is to "catch" the lubricating medium that is trying to leak out Inside the cavity. The interference is large, and the radial force is mainly guaranteed by the interference of the lip, which belongs to the surface contact. The dust lip (sub-lip) is mainly used to prevent external impurities (sand, dust, water, etc.) from entering the sealed medium, and also to prevent external impurities from entering between the main sealing lip and the rotating shaft, so as not to cause the oil seal lip or Wear of the rotating shaft.
Compared with rubber, PTFE is two distinct materials, so it has its own characteristics in design and structure. 1. PTFE oil seals generally use uniform thin-walled sealing elements. The aspect is to compensate for the poly E E. The high flexural modulus of the olefinic material satisfies the application under conditions of large dynamic eccentricity. On the other hand, the thin wall surface can also reduce the thermal expansion and compression creep value to reduce the change of the contact state.
2. The contact between the sealing lip and the shaft is in surface contact so that a sufficient amount of oil can be maintained.
As mentioned above, a spiral groove is engraved on the U portion of the main lip of the oil seal, and the shape of the enlarged seal is as shown in the cabinet 2, and the assembled Teflon oil seal is deformed by itself after a few revolutions. The lip portion is well fitted to the shaft diameter. During the working process, the lubricating oil film entering the oil sealing portion and the journal engaging portion rotates together with the rotating shaft, and when the oil film hits the oil sealing spiral groove, It will be subjected to the action of the spiral bevel to create a force to seal the medium inside the machine. This force will press the liquid medium to be discharged back to the oil storage end (that is, the oil seal spiral groove has the function of pumping). The sealing can be achieved when the force is greater than the oil pressure from the oil reservoir end received by the oil seal itself.
The above pressure can be calculated by the following formula: P'-the axial reaction force generated by the spiral groove; the gap between the C-rotation axis and the oil seal lip; the contact width between the L-lip and the shaft; the dynamic viscosity of the liquid medium P- It can be seen from the above formula that when the tli bridge condition is certain (M, v, C is basically unchanged) and the design conditions (ie, L is constant), FU, S) is an important reason that affects the above partial pressure, that is, The geometry, direction, hardness of the sealing material and its elasticity of the oil seal spiral groove will directly affect the partial pressure of the oil seal and the sealing performance of the oil seal.
Oil film stress analysis chart 1SFYn formula material physical property number physical property unit performance index 1 density g/cm22. 02.12 hardness (Shore D) degree 50 583 tensile strength Mpa16 184 fracture length ratio %2603005 wear scar width mm4. Standard requirements measured condition test oil SAE15W/40 oil shaft jump Mm0.0750.2 hole eccentric Mm0. 202 maximum speed r/min380038004000 test oil temperature C ambient temperature + 6090100 fuel amount oil level and shaft center line flush oil level and shaft center line Level of sample sample 62 Test period H350350 Result part number Item performance test results After the test, the maximum allowable leakage of 6 seals 01 is 12g for life test, and the maximum allowable leakage of single seal is 3 from the test device. If there is no leakage, no cracks and wear. 02 Oil seal lips should not have cracks and obvious wear.
4 Test and application research In order to ensure the performance of the drive gear PTFE oil seal, a number of tests were carried out according to the technical conditions.
Carbon fiber reinforced polytetrafluoroethylene (CFRP) is an emerging sealing material with higher wear resistance, temperature resistance, strength and elastic mold than other filled polytetrafluoroethylene. It has excellent self-lubricating properties. It has developed rapidly at home and abroad, and the oil seal we developed is made of this material.
In the material research process, five formulas of SFYI, SFYI, SFYM, SFYIV and SFYV were designed by orthogonal design method. After the test performance comparison, the SFYn formula was selected to better adapt to the light truck company's rear axle drive gear sealing condition. The physical properties are shown in Table 1. The situation is shown in Table 2. The test results of the 02050B drive gear oil seal performance are shown in Table 3. Table 3 24A1-02050B drive gear oil seal test - 100A rotary oil seal test bench. The test bench is stepless speed change, automatic time recording, automatic temperature control, and six oil seals can be used for simulation test at the same time. The four types of drive gear oil seals developed by the ―02050B drive gear oil seal test all meet the technical standards. In order to increase the credibility and repeatability of the test results, a third-party authority was also commissioned to conduct a bench test on the oil seal and all passed.
Twenty N103 vehicles equipped with Teflon drive gear seals passed the 30,000 km road test and met the technical requirements for leak-free.
After a lot of experimental research work, the developed PTFE active gear oil seal has been put into use in large quantities. So far, tens of thousands of cars have been loaded, and the results have been good, with satisfactory results.
4 Conclusions PTFE is the best self-lubricating oil material with good self-lubricating performance and low friction coefficient. It is 0(2) PTFE oil seal resistant to high and low temperature in liquid lubrication, and the temperature range is not sensitive to the eccentricity of a pair of shafts. It can still work normally under the condition of radial runout of 04mm.
The PTFE oil seal is suitable for sealing various conditions such as engine, drive gear and gearbox.
The four types of drive gear oil seals developed have met the requirements of national standard indicators, which solved the oil leakage problem of the rear axle drive gear oil seals well and produced great economic and social benefits.
Filled PTFE oil seal is a kind of high technical content, which is the direction of oil seal development in the future.
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