Oil seal is the customary title of general seals, which is simply the sealing of lubricating oil. It is a mechanical component used to seal grease (oil is the most common liquid substance in the transmission system, also generally refers to the meaning of general liquid substance). It isolates the parts that need lubrication in the transmission parts from the output parts, so as not to let the lubricating oil leak. The seals used for static seal and dynamic seal (generally reciprocating motion) are called oil seals.

The representative form of oil seal is TC oil seal, which is a double lip oil seal with self tightening spring completely covered by rubber. Generally speaking, oil seal often refers to this TC skeleton oil seal.

Chinese name oil seal foreign name oil seal function oil seal defines the representative form of mechanical components of oil seal TC oil seal shape ring national standard gb13871-1992

Oil seals are generally divided into single type and assembly type. The assembly type is that the framework and lip materials can be freely combined, which is generally used for special oil seals.

From the sealing function, characteristics, structural type, working state and sealing mechanism of the oil seal, it can be divided into various forms and different names, but it is customary to call the lip seal ring of the rotating shaft oil seal, and the seals for static seal and dynamic seal (generally reciprocating motion) are called seals.

The representative form of oil seal is TC oil seal, which is a double lip oil seal with self tightening spring completely covered by rubber. Generally speaking, oil seal often refers to this TC skeleton oil seal. See the figure for the schematic diagram of skeleton oil seal.

Material Science

The common materials of oil seal are: nitrile rubber, fluororubber, silicone rubber, acrylate rubber, polyurethane, PTFE, etc.

Nitrile rubber (NBR)

It has good heat resistance and wear resistance, and is resistant to various lubricating oils, greases, oil-gas mixtures, etc. the applicable temperature is - 30 ~ 120 ℃, but it can no longer be used in phosphate ester hydraulic oil and gear oil containing extreme pressure additives. It has stable performance in gasoline and low aniline point mineral oil.

Polyacrylate rubber (ACM)

Superior oil resistance and heat resistance, wear resistance, ozone resistance and ultraviolet radiation resistance, especially lubricating oil, gear oil, motor oil, engine oil and petroleum hydraulic oil containing extreme pressure fluid agent. It is suitable for working in the range of - 30 ~ 150 ℃.

Fluororubber

It is aging resistant, heat-resistant and oil resistant. It is applicable to almost all lubricating oils, fuel oils and gasoline. It is not easy to harden in the oil containing extreme pressure additives, but it has poor cold resistance, high temperature wear resistance and large permanent compression deformation. It is applicable to the temperature of - 20 ~ 250 ℃.

silicon rubber

It can be used under ultra-high temperature without long-term change; It can be used continuously for 10000 hours under 200, and can maintain its unique flexibility, ozone resistance, weather resistance and other advantages in the working temperature range of - 70 ~ 260.

teflon

It has outstanding chemical stability, thermal stability, antifriction and self lubrication, and its cracking temperature is above 400. Therefore, it can work normally in the temperature range of - 200 ~ 300 ℃. In addition to free fluorine and alkali metals, it has excellent corrosion resistance to chemicals, solvents, oxyhydrogen compounds and acids [2].

Nitrile rubber and fluororubber materials are widely used oil seals. The former has low cost, but the temperature resistance and sealing performance have been significantly improved, but the cost is high, and still has some bad commonalities of ordinary rubber materials, such as poor wear resistance, short service life, especially sensitive to shaft eccentricity, etc. The leakage phenomenon is still common. PTFE oil seal is a product with high technical content, which is the development direction of oil seal in the future [2].

When selecting the material of the oil seal, the compatibility of the material with the working medium, the adaptability to the working temperature range and the following ability of the lip to the high-speed rotation of the rotating shaft must be considered. Generally, when the oil seal works, the temperature of its lip is 20 ~ 50 ℃ higher than the temperature of the working medium. Attention should be paid to the selection of oil seal materials. The working range of oil seal is related to the material used for oil seal: when the material is nitrile rubber (NBR), it is - 40 ~ 120 ℃, Alec rubber (ACM) - 30 ~ 180 ℃, and fluororubber (FPM) - 25 ~ 300 ℃.

Function

Engine: crankshaft - front and rear oil seals of crankshaft - valve - valve oil seal (O-ring of engine repair kit) (distributor oil seal, water pump oil seal, balance shaft oil seal, oil pump oil seal...); Camshaft - camshaft oil seal; Transmission: transmission - transmission front and rear oil seals, shift lever oil seals (transmission repair kit O-ring) (transfer case - transfer case front and rear oil seals); Rear axle: half axle -- rear half axle oil seal differential -- (front) rear angle sagittal oil seal rear wheel oil seal front wheel oil seal steering gear oil seal (steering gear repair kit O-ring) steering booster oil seal (front half axle oil seal).

All parts with liquid lubricating oil in the running body box and connected with the outside need oil seal. Some are rubber, some are metal, and most are steel reinforced rubber, such as crankshaft rear oil seal, gearbox front and rear oil seal, left and right axle oil seal, main reducer front oil seal, air compressor crankshaft oil seal, etc. [2].

Type and purpose
 

Ordinary single lip B (SC)

It is generally used to seal mineral oil, water and other media for high and low speed rotating shafts and reciprocating motion.

Ordinary oil seal is used when there is less dust and impurities. When the medium pressure is less than 0.05Mpa, the highest line speed is 15m / s and the reciprocating speed is less than 0.1m/s [3].

Ordinary double lip FB (TC)

In addition to the use characteristics of the above S-type oil seal, it can also prevent dust.

Ordinary oil seal with dust-proof lip can prevent dust. It is resistant to medium pressure < 0.05Mpa, and the linear speed is ≤ 15m / s.

Springless BV

Single lip type rubber oil seal without spring and with frame inside.

It is generally applicable to low-speed working conditions, and the sealing medium is lubricating ester. Linear speed ≤ 6m / s.

Outer skeleton single lip w

Single lip exposed skeleton rubber oil seal with spring, thin waist, good follow-up and good rigidity.

Ordinary oil seal is used under the condition of less dust and impurities, and is resistant to medium pressure < 0.05Mpa. When the rotation axis speed is ≤ 15m / s.

Outer skeleton double lip FW

The double lip exposed skeleton rubber oil seal with auxiliary lip has thin waist, good follow-up, high stiffness and good coaxiality.

Ordinary oil seal, with dust-proof lip, can be dust-proof and resistant to medium pressure < 0.05Mpa. Speed ≤ 15m / s.

Assembled single lip FZ

The outer frame oil seal is assembled and rolled by the inner and outer frame, and has the characteristics of high installation accuracy, fast heat dissipation and heavy load.

It is applicable to heavy load working conditions under high temperature and high speed conditions, with medium pressure ≤ 0.05Mpa and maximum speed ≤ 15m / s.

Unidirectional reflux right-handed Sr and left-handed DL

The inclined rib with angle is measured in the lip air, which produces one-way pumping effect and reflux effect by using the principle of hydrodynamics.

It is related to the rotation direction of the shaft. Due to the reflux effect, the radial force is smaller than that of the ordinary oil seal, which reduces wear and heat generation and improves the service life. It is suitable for occasions with medium pressure < 0.05Mpa and rotating speed ≤ 20m / s [3].

Pressure resistant NY

With short lips and thick waist, it has the function of pressure resistance, and the working pressure is ≤ 3Mpa.

It is applicable to occasions with medium pressure ≤ 3Mpa and shaft end oil seal of high-pressure pump. Generally, PV value ≤ 8. Rotation axis speed ≤ 15m / s .

matters attention

1. Preparations and precautions before startup

a. Comprehensively check whether the mechanical seal and the installation of auxiliary devices and pipelines are complete and meet the technical requirements.

b. Before starting the mechanical seal, conduct static pressure test to check whether the mechanical seal has leakage. If there are many leaks, find out the causes and try to eliminate them. If it is still invalid, it shall be disassembled, inspected and reinstalled. The general static pressure test pressure is 2 ~ 3kg / cm2.

c. Rotate the turning gear according to the pump and check whether it is light and uniform. If the turning gear is hard or stationary, check whether the assembly size is wrong and whether the installation is reasonable.

2. Installation and shutdown

a. Keep the sealing cavity filled with liquid before starting. When transporting solidified medium, steam shall be used to heat the sealing cavity to melt the medium. Turning must be carried out before starting to prevent the soft ring from breaking due to sudden starting.

b. For the mechanical seal using the oil sealing system outside the pump, the oil sealing system should be started first. Stop the oil sealing system after shutdown.

c. After the hot oil pump is shut down, the cooling water of the oil sealing chamber and the end face seal cannot be stopped immediately. The cooling water can be stopped only when the oil temperature at the end face seal drops below 80 degrees, so as to avoid damaging the sealing parts.

3. Run

a. If there is slight leakage after the pump is started, observe it for a period of time. If the leakage does not decrease after continuous operation for 4 hours, stop the pump for inspection.

b. The operating pressure of the pump shall be stable, and the pressure fluctuation shall not be greater than 1kg / cm2.

c. During the operation of the pump, evacuation shall be avoided to avoid dry friction and seal damage on the sealing surface.

d. The sealing condition should be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil shall not be more than 5 drops / min and the light oil shall not be more than 10 drops / min. if there is still no improvement trend within 2-3 days, stop the pump and check the sealing device.

Problem cause editing and broadcasting

Main factors causing oil leakage of oil seal

The loose sealing of oil seal is the main factor causing oil leakage. When the shaft is worn to form a groove, and the seal cannot be sealed even if a new oil seal is replaced, it is because the contact pressure between the oil seal lip and the shaft decreases, resulting in too small interference between the oil seal lip diameter and the shaft diameter after installation.

Taking the crankshaft oil seal of S195 diesel engine as an example, the main reasons for its lax sealing are analyzed as follows:

① Poor manufacturing quality of oil seal;

② Poor quality of shaft or bearing;

③ Improper use and maintenance;

④ Improper installation;

⑤ Improper storage and adverse effects caused by environmental pollution.

Countermeasures for oil leakage due to loose oil seal

1. Master and identify the basic knowledge of fake and shoddy products, and buy high-quality and standard oil seals.

2. During installation, if the outer surface roughness of the shaft diameter is low or there are rust spots, rust, burrs and other defects, it shall be polished with fine abrasive cloth or oilstone; Apply clean engine oil or lubricating grease on the lip of oil seal or the corresponding position of shaft diameter. The outer ring of the oil seal shall be coated with sealant, and the keyway on the shaft shall be wrapped with hard paper to avoid scratching the lip of the oil seal. The oil seal shall be rotated and pressed inward with a special tool. Do not hit the hard punch hard to prevent the oil seal from deforming or breaking the spring and becoming invalid; In case of lip flanging, spring falling off and oil seal deflection, it must be removed and reinstalled. It should be noted that when the shaft diameter is not worn and the spring force of the oil seal is sufficient, do not tighten the inner spring [4] without authorization.

3. Oil seals used in machinery generally have poor working conditions, large environmental temperature difference, much dust and frequent vibration of machines and tools. When the stress condition of parts changes constantly, they should be inspected, maintained and maintained frequently.

4. If the shaft diameter and bearing are seriously worn; In case of aging of oil seal rubber or failure of spring, repair and replace corresponding parts in time.

5. The abnormal heating parts or assemblies shall be eliminated in time; Avoid mechanical overspeed and overload operation to prevent oil seal lip temperature rise, rubber aging, early wear of lip, etc.

6. Check the oil level frequently. If there are too many impurities in the oil and there are alloy powder and metal iron filings, completely replace the new oil. The brand and quality of the changed oil shall meet the requirements of the season. It is suggested to add maitrey super sealant lubricant to the engine oil. It is an excellent gearbox additive, which can form an inert material film on the parts. It can slow down the leakage of oil seal, prolong the service life of oil seal gear, and reduce the noise of gearbox. The use of maitrey super sealing lubricant will not pollute or deteriorate the oil.

Instructions for use:

① When the lubricating oil volume of reducer is ≤ 7L, the amount of lubricating oil added per liter is 20 ‐ 30ml;

② When 7-15l, add 15-20ml per liter of lubricating oil;

③ When > 15L, add 10ml per liter of lubricating oil;

7. The temporarily unused oil seal shall be properly kept to prevent oil stain, dust or sun exposure.

8. When the oil seal is in contact with the "V-shaped" oil seal, it can not make up for the wear of the shaft when the oil seal is in contact with the "V-shaped" oil seal.

advantage

1. The oil seal structure is simple and easy to manufacture. The simple oil seal can be molded at one time. Even for the most complex oil seal, the manufacturing process is not complicated. The metal skeleton oil seal can form the required oil seal with metal and rubber only through stamping, bonding, inlay, molding and other processes.

2. The oil seal has light weight and less consumables. Each oil seal is a combination of thin-walled metal parts and rubber parts, and its material consumption is very low, so the weight of each oil seal is very light.

3. The installation position of oil seal is small, the axial size is small, it is easy to process, and makes the machine compact.

4. The oil seal has good sealing function and long service life. It has certain adaptability to the vibration of the machine and the eccentricity of the main shaft.

5. The oil seal is easy to disassemble and inspect.

6. Oil seals are cheap.