Concept of oil seal

Oil seal (English Name: oil seal) is used to seal oil (oil is the most common lubricating medium in the transmission system) mechanical components, it will need to lubricate the parts of the machine and transmission parts isolated, not to let the lubricating oil leakage. From the sealing function, characteristics, structural type, working state and sealing mechanism of oil seal, it can be divided into various forms and different names, but it is customary to call the rotary shaft lip seal ring as oil seal.

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 usually refers to this TC framework oil seal.

Oil seal commonly used materials are: nitrile rubber, fluororubber, silicone rubber, acrylate rubber, polyurethane, polytetrafluoroethylene and so on. When choosing the material of the oil seal, the compatibility of the material to the working medium, the adaptability to the working temperature range and the ability of the lip to follow the rotating shaft at high speed must be considered. In general, the temperature of oil seal lip is 20 ~ 50 ℃ higher than that of working medium, so attention should be paid to the selection of oil seal material. The working range of the oil seal is related to the material used for the oil seal, for example, NBR is - 40 ~ 120 ℃ and FPM is - 25 ~ 300 ℃.

Oil seal is widely used. Take engine as an example, some oil seals are listed. Crankshaft front and rear oil seal; valve oil seal; distributor oil seal; water pump oil seal; balance shaft oil seal; oil pump oil seal; camshaft oil seal; transmission front and rear oil seal; shift lever oil seal; transfer case front and rear oil seal; rear axle shaft oil seal; differential (front) rear angle vector oil seal; wheel oil seal; steering gear oil seal; direction booster oil seal.

In a word, oil seals are needed for all parts of the running body box that have liquid lubricating oil and are connected with the outside. Some are rubber, some are metal, most are steel 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 and other oil seals

Requirements for assembly shaft of oil seal:

1. The surface roughness of the shaft shall be in accordance with the provisions of gb1801. The surface of the shaft in contact with the oil seal shall be ground to a surface roughness of ra0.2-0.63um and Rmax = 0.8-2.5um.

2. The diameter tolerance of the shaft shall not exceed H11 according to gb1801.

3. The chamfering width shall be in accordance with the requirements of gb13871-92.

4. Surface hardness: carbon steel and alloy steel are suitable for the shaft, and the recommended hardness is above hrc45. When the medium is dirty and there are pollutants from outside or the linear speed of the shaft is ≥ 12m / s, the surface hardness of the shaft should be hrc50-60, and the depth of quenching layer should be ≥ 0.3mm.

5. The shaft chamfering shall be 30 degrees (maximum), and there shall be no burr, sharp angle and spiral machining marks on the chamfering surface. The roughness of chamfering surface shall be RA ≤ 3.2um, and the carbonized layer of heat treatment must be polished and removed.

Special attention:

(1) The surface roughness of the shaft is too high, and the oil seal lip is easy to wear and leak oil.

(2) The burr, sharp angle and spiral machining mark at the chamfering are easy to scratch the oil seal lip, resulting in the initial seal failure of the oil seal.

(3) Avoid or reduce the shaft damage, sand hole, installation eccentricity and radial runout and other defects.

Requirements for oil seal mounting seat hole

1. The surface roughness of pore diameter shall be in accordance with the provisions of GB 1301: coating rubber ra3.2 ~ 6.3um, exposed skeleton Ra0.8 ~ 3.2um.

2. The hole diameter tolerance shall not exceed H8 according to the provisions of gb1801

3. The chamfering length shall be in accordance with GB 13871-92. The minimum and maximum chamfering degrees of seat hole shall be 15 degrees and 25 degrees respectively. The roughness of chamfering surface shall be the same as that of shaft diameter.

Special attention:

If the chamfering angle of the hole diameter is greater than 45 degrees or there is no chamfering, it is easy to gnaw or scratch the oil seal, cause the outer diameter of the oil seal, the assembly inclination and the deformation of the oil seal framework, which may cause oil leakage or oil leakage in the early stage of the oil packer.

3. Installation direction requirements

Check the oil seal before installation. If the oil seal is clean and intact, press the oil seal in. When installing the oil seal with unidirectional return line, make sure that the arrow direction marked on the oil seal is consistent with the rotation direction of the shaft. Do not install it in reverse.

Requirements for main lip of four protection oil seals

1. When the oil seal passes through the shaft with spline, keyway or hole, bullet head type protective tooling shall be adopted.

2. The surface roughness Ra max of bullet type tooling shall not exceed 3.2um, and there shall be no scratch or burr.

3. The outer diameter and main lip of oil seal must be coated with a layer of lubricant during assembly.

4. Uniform speed and pressure should be used in oil seal assembly to prevent spring falling off.

5. Installation method

(1) Recommended oil seal installation tooling and method

1. The oil seal can be installed flush with the front end of the housing bore or close to the low section of the housing bore.

2. The datum plane for installation and positioning shall be machined surface, and the unprocessed datum plane shall not be used.

3. The outer diameter of oil seal should be coated with a layer of lubricating oil during assembly.

4. Press the oil seal by hydraulic or pneumatic uniform speed.

Note: the matching surface of the oil package is flush with the reference plane of the shell to ensure the perpendicularity of the installation of the shaft and the shaft center, so that the oil seal lip forms a line contact belt on the shaft surface to achieve good sealing effect.

(2) No oil seal tooling installation

1. The outer diameter of oil seal shall be coated with a suitable layer of lubricating oil during assembly

2. The force of knocking oil seal should be even and not inclined.

3. Check that the oil seal is flush with the reference surface of the housing after being installed.

Check that the oil seal spring should not fall off.

Six wrong assembly methods and improvement measures

Common errors:

a. The hammer hits the oil seal directly.

b. The oil seal is forced to be assembled without reference surface.

c. Unreasonable oil seal tooling.

Consequences:

a. The oil seal is deformed.

b. Oil seal outer diameter and dust lip gnawing and scratch

c. The oil seal is degummed with the framework.

d. The oil seal spring fell off.

e. The main lip of oil seal is deformed.