I. Basic Concepts of Oil Seals:

　　1. Oil Seal Structure Types: Oil seals are mechanical components used for sealing oil, also known as rotary shaft lip seals. These products are widely used in the automotive, metallurgical, shipping, and machinery industries and can be used in various hydraulic and pneumatic systems and components. According to GB13871-92, there are six basic forms of sealing: internal skeleton type (B type), external skeleton type (W type), assembly type (Z type), internal skeleton type with secondary lip (FB type), external skeleton type with secondary lip (FW type), and assembly type with secondary lip (FZ type).

　　2. The materials that make up oil seals generally include three types:

　　　2.1. Elastic sealing components made of rubber elastomers (usually called lip materials);

　　　2.2. Embedded components for metal skeleton assembly and support (usually called skeleton materials);

　　　2.3. Springs. As loading components, there may be one, two, or even three skeletons; springs can also have different structures.

　　II. Sealing Principle

　　There are many theories to explain the sealing principle of oil seals. However, the fluid dynamic sealing theory is currently recognized by foreign seal researchers. The fluid dynamic sealing theory suggests that under dynamic conditions, a layer of fluid film with fluid flow characteristics exists on the narrow contact area between the oil seal and the shaft. These characteristics include reducing the friction between the shaft and the seal. Due to the tangential force acting on the contact surface of the seal, tangential deformation occurs, improving lubrication under dynamic conditions. This fluid film has a certain thickness and shape. Many microscopic bumps and depressions on the sealing surface act as miniature sliding bearings under dynamic conditions, bringing viscous liquid into the wedge-shaped gap to form a hydrodynamic fluid film, thus achieving lubrication and sealing. This theory is constantly being enriched and developed, but the actual working conditions of seals are very complex. It is generally believed that when the oil seal contacts the shaft in actual work, three situations occur: dry friction, boundary lubrication, and fluid lubrication, which alternate continuously. Therefore, even high-performance oil seals still have problems such as wear and slight leakage.

　　III. Hydrodynamic Oil Seals

　　Hydrodynamic oil seals, commonly known as "return flow oil seals," are characterized by their return flow function and are mainly used in harsh working environments, such as when the radial runout of the shaft is relatively large. One-way return flow oil seals: The main feature is the return flow function. The interference fit of the lip is smaller than that of ordinary oil seals, reducing radial force, friction heat, and improving service life. Because the main lip is in contact with the shaft, there will be no oil leakage during parking or short-term low-speed reverse rotation (speed when the car is reversing). Generally speaking, one-way return flow oil seals are suitable for high-speed operation in one direction. Several threaded protrusions are designed on the working surface of the lip of the one-way return flow oil seal, with counterclockwise and clockwise types. The threaded protrusions intersect with the static lip at the lip tip. When the shaft rotates, a pressure opposite to the leakage is generated in the part where the thread contacts the shaft, causing the fluid about to leak to return to the oil tank. This oil seal has been widely used in the automotive industry. Two-way return flow oil seals: The characteristic of two-way return flow oil seals is that several protrusions at a certain angle to the lip are molded on the air side of the sealing lip, and the protrusions are parallel to each other. After the lip is machined to the required inner diameter, some protrusions are cut off and intersect with the lip, forming two or more return oil chambers. In this way, symmetrical numbers of protrusions with opposite directions are formed in the left and right halves of the lip, and they intersect with the lip at an acute angle. When the oil seal is assembled onto the shaft, these intersecting protrusions form an acute contact area. When rotating clockwise (or counterclockwise), the oil particles leaking past the lip can be collected into the acute contact area of the left semicircle (right semicircle). As the oil gradually increases, the internal pressure increases, producing an automatic inward thrust, causing the leaked oil to return to the original cavity, thus achieving sealing and leak prevention.

　　IV. Main Characteristics of Two-Way Return Flow Oil Seals

　　1) The return flow and leak prevention function works regardless of the direction of shaft rotation.

　　2) There is always oil movement inside and outside the lip contact area, providing lubrication and reducing wear.

　　V. Rubber Material Standards

　　The chemical industry standard HG/T2811-1996 "Rubber materials for rotary shaft lip seals" specifies the classification, requirements, sampling, testing methods, marking, labeling, packaging, and storage of rubber materials for rotary shaft lip seals.

　　Mainly used for manufacturing seals for rotary motion in petroleum-based hydraulic oils and lubricating oils. 1. Classification and Marking Divided into four types: A, B, C, and D: Type A is three materials based on nitrile rubber; Type B is one material based on acrylate rubber; Type C is one material based on silicone rubber; Type D is two materials based on fluororubber; Marking: XA xxxx HG/T2811-1996 Standard number Maximum compression set Minimum elongation at break Minimum tensile strength Hardness value Rotary shaft lip seal.

　　 VI. Oil Seal Size Series

　　 GB13871-92 is equivalent to the international standard ISO6194/1-1982 "Rotary shaft lip seals—Part 1: Basic dimensions and tolerances." This standard specifies the basic dimensions and tolerances of oil seals with shaft diameters ranging from 6 to 400 mm and corresponding sealing cavity inner diameters ranging from 6 to 440 mm. It is applicable to seals with working pressures equal to or less than 0.05 MPa and not applicable to higher working pressures.

　　 VII. Oil Seal Failure

　　Main reasons: 1. Operating conditions: The quality of operating conditions; 2. Improper selection: The seal type is not suitable for the operating conditions, and the product characteristics do not match the required functions; 3. Sealing material: Suitable for operating conditions; 4. Groove structure: The structure must be reasonable or match the product structure; 5. Improper assembly: Improper assembly causes product deformation or even damage; 6. System failure: Such as excessive pressure in the hydraulic system, impurities, poor lubrication system, dry friction, impurities, etc.; 7. Storage factors: Excessive storage period, improper storage methods (product compression deformation, sunlight, contact with chemical reactants, etc.); 8. Normal damage: The product has reached its service life; 9. Other reasons: Poor installation, unreasonable lip structure, unreasonable spring size causing spring fall-off; reverse assembly; dimensional deviation, chamfer design and processing of cavity holes are not standardized, and improper installation methods cause damage to the outer circle of the oil seal.

　　 VIII. Storage, Maintenance and Installation of Oil Seals

　　 HG/T2330-92 is equivalent to the international standard ISO6194.3-1988 "Rotary shaft lip seals Part 2: Storage, maintenance, and installation." This standard specifies the requirements and methods for the storage, packaging, maintenance, and installation of rotary shaft lip seals. This standard is applicable to the storage, maintenance, installation, and various hazards and prevention methods of rotary shaft lip seals.

　 　IX. Installation

　　1. Before installation, check the seal ring to ensure that it is clean and undamaged;

　　2. Before installing the seal ring, apply an appropriate amount of clean lubricant to the lip. Dust-proof seal rings should be coated with an appropriate lubricating grease;

　　3. Normally, the front surface of the sealing lip of the seal ring should face the sealed liquid;

　　4. The shaft end and the cavity bore should have a lead chamfer in accordance with GB13871;

　　5. Verticality is a characteristic factor of the seal ring. Verticality is achieved by pressing the seal ring into alignment with the front surface of the cavity bore or against the bottom surface of the cavity bore shoulder;

　　6. The installation tool for pressing the seal ring into the installation position is shown in Figure 1;

　　7. The seal ring can be generally flush with the front surface of the cavity bore, or it can be close to the bottom surface of the cavity bore. However, in both cases, the installation datum surface should be a machined surface. Unmachined datum surfaces cannot be used to avoid misalignment of the seal ring;

　　8. The installation method of installing the seal ring into the cavity in reverse is shown in Figures 4 to 7:

　　9. During installation, any surface over which the lip of the seal ring slides should be smooth and undamaged. If the seal ring needs to slide over a shaft with splines, keyways, or holes, a special installation tool as shown in the figure below should be used. This special tool should not be made of soft metal (such as aluminum), nor should it be used with a notched installation tool.

　　10. If the mating part (shaft) must be forcibly passed through the working surface of the seal ring, the diameter of the sliding part of the shaft can be reduced by 0.2mm. The seal ring designed for the original shaft can still be used, and its sealing performance will not be affected. See the figure below:

　　11. When installing an inner-wrapped skeleton seal ring, apply a thin layer of suitable lubricant to the outer edge of the seal ring to facilitate installation into the cavity. During assembly, use a uniform speed and pressure to prevent the spring from falling off.

　　12. If the seal ring must be installed at low temperatures, the seal ring can be placed in a clean liquid below 50℃ and the same as its sealing medium for 10-15min to restore the elasticity of the lip of the seal ring.

　　13. When replacing a failed seal ring with a new one, the sealing lip of the new seal ring should not coincide with the previous rotation trajectory, but should be closer to the sealed liquid side. This can be achieved by installing gaskets, changing bushings and slip rings, and changing the depth of pressing into the cavity.