Oil seal basic concept:
1. Type of oil seal structure Oil seal is a mechanical component for sealing oil, also known as rotary shaft lip seal. This product is widely used in automotive, metallurgy, shipbuilding, machinery and other industries, and can be used in various hydraulic and pneumatic systems and components. There are 6 kinds of basic forms of sealing according to GB13871-92: in-frame skeleton type (B type), exposed skeleton type (W type), assembly type (Z type), with sub-lip inner package skeleton type (FB type), with accessory lip Exposed skeleton type (FW type), assembly type with sub-lip (FZ type).
2. There are generally three types of materials that make up the oil seal:
2.1. An elastic sealing element composed of a rubber elastomer (also commonly referred to as a lip material);
2.2. Metal frame assembly and supporting embedded components (often called skeleton materials);
2.3. Spring. As the loading element, there are one, two or even three skeletons; the springs can also be different structures.
For the sealing principle of oil seals, there are more theoretical explanations. However, the theory of fluid dynamic sealing is now recognized by foreign seal researchers. According to the theory of hydrodynamic sealing, under dynamic conditions, a liquid film has a fluid flow characteristic on the narrow contact zone of the oil seal and the shaft. These characteristics include a reduction in the friction between the shaft and the seal, which is subjected to a tangential force in the circumferential direction due to the tangential force in the circumferential direction of the frictional force and tangential deformation, which improves the dynamic lubrication from the surface. The liquid film has a certain thickness and shape. Many microscopic ridges and depressions on the sealing surface, corresponding to the tiny sliding bearing plate under dynamic conditions, dynamically bring the viscous liquid into the wedge-shaped gap to form a hydrodynamic liquid film, thereby lubricating and sealing. This theory is constantly enriched and developed, but the actual working condition of the seal is very complicated. It is generally believed that when the oil seal is in contact with the shaft during actual work, there are three cases of dry friction, boundary lubrication and fluid lubrication on the contact surface, which alternately change, so even if the oil seal has good performance, there are still problems of wear and slight leakage.
Fluid power oil seal
Fluid dynamic oil seals are commonly referred to as "return oil seals", which are characterized by reflow, and are mainly used in situations where the working environment is relatively harsh, for example, when the radial runout of the shaft is relatively large. One-way return oil seal: The main feature is that it has a recirculating effect. The interference of the lip is smaller than that of the ordinary oil seal, the radial force is reduced, the friction heat generation is reduced, and the service life is improved. Since the main lip line is in contact with the shaft, there is no oil leakage during parking or short-time low-speed reversal (speed when the car is retreating). In general, unidirectional return oil seals are suitable for use in high speed operation in the same direction. There are several thread ribs on the lip working face of the unidirectional return oil seal, both counterclockwise and clockwise. The threaded rib intersects the static lip at the tip of the lip. As the shaft rotates, the portion of the thread in contact with the shaft creates a pressure that opposes the leakage, causing the fluid to be leaked out to return to the tank. This oil seal has been widely used in the automotive industry. Two-way reflow seal: The bidirectional return oil seal is characterized by a plurality of ribs that are inclined at a certain angle to the lip on the air side of the seal lip, and the ribs are parallel to each other. After trimming the lip to the desired inner diameter size, a portion of the rib is severed and intersects the lip to form two or more pairs of oil return cavities. In this way, the left and right halves of the lip form a symmetrical number of ribs in opposite directions, and intersect the lip at an acute angle. These intersecting ribs form an acute angular contact area when the oil package is fitted to the shaft. When rotating clockwise (or counterclockwise), the oil particles leaking through the lip can be collected into the acute angular contact area of the left semicircle (right semicircle). As the oil increases, the internal pressure increases, and an automatic direction is generated. The thrust in the back makes the leaked oil return to the original cavity, thus sealing and leakproof.
Main features of two-way reflow seal
1) No matter whether the shaft rotates in any direction, it will return to prevent leakage.
2) There is always oil movement inside and outside in the lip contact area, which acts as a lubrication and wear reduction.
Standard for rubber materials
Chemical Industry Standards HG/T2811-1996 "Rubbers for Rotary Shaft Lip Seals" stipulates the classification, requirements, sampling, test methods and marking, labeling, packaging and storage of rubber materials for rotary shaft lip seals.
It is mainly used to manufacture seals for rotary motion in petroleum-based hydraulic oils and lubricants. 1. Classification and marking are divided into four types: A, B, C, and D: Class A is three materials based on nitrile rubber; Class B is a material based on acrylate rubber; Class C is silicon. Rubber-based material; Class D is two materials based on fluororubber; Marking: XA xxxx HG/T2811-1996 Standard number Compressive permanent deformation Maximum elongation at break Minimum tensile strength Minimum hardness Value rotary shaft lip seal.
Oil seal size series
GB13871-92 is equivalent to the international standard ISO6194/1-1982 "Rotating shaft lip seals - Part 6: Basic dimensions and tolerances". This standard specifies the basic dimensions and tolerances of oil seals with shaft diameters from 6 to 400 mm and corresponding hole diameters from 6 to 440 mm. It is suitable for seals with working pressures equal to or less than 0.05 MPa. It is not suitable for higher work. pressure.
Oil seal failure
Main reasons: 1. Working conditions: good or bad working conditions; 2. Improper selection: the sealing type is not compatible with the working conditions, the product characteristics are not consistent with the required functions; 3. Sealing material: and working conditions Suitable; 4, groove structure: the structure should be reasonable or match the product structure; 5, improper assembly: improper assembly caused by product deformation or even damage; 6, system failure: such as hydraulic system pressure is too high, containing impurities, lubrication Poor system, dry friction, impurities, etc.; 7, storage factors: storage period is too long, improper preservation methods (products are subject to extrusion deformation, sunshine, exposure to chemical reactants, etc.); 8, normal damage: product use to its failure 9. Other reasons: poor installation, unreasonable lip structure, unreasonable spring size, etc. caused the spring to fall off; assembly reversed; the size is too poor, the cavity hole chamfer design is not standardized, the installation method is not suitable, etc. The circle is damaged.
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 storage, packaging, maintenance and installation of rotary shaft lip seals. This standard applies to the storage, maintenance, installation, and various hazards and prevention methods of the rotating shaft lip seal.
1. Check the sealing ring before installation to ensure that the sealing ring is clean and intact;
2. The seal should be coated with a suitable clean lubricant before installation. The seal for dustproof should be coated with suitable grease.
3. Under normal circumstances, the front surface of the sealing lip of the sealing ring should face the liquid to be sealed;
4. The end of the shaft and the opening in the cavity shall have a lead-in chamfer in accordance with GB13871;
5. Mounting perpendicularity is a characteristic factor of the sealing ring. The verticality is achieved by pressing the sealing ring into the end face of the hole in the cavity or against the end face of the hole in the cavity;
6. The installation tool for pressing the sealing ring into the installation position is shown in Figure 1;
7. The sealing ring can be installed in the same manner as the front end surface of the hole in the cavity, or close to the bottom end surface of the hole in the cavity. However, in both cases, the positioning reference surface should be a machined surface, and the unprocessed reference surface. Cannot be used to avoid biasing the seal;
8. The installation method for inserting the seal into the cavity in the reverse direction is shown in Figure 4 to Figure 7:
9. During installation, any surface that the seal lip slides should be smooth and undamaged. If the seal is to slide over a shaft with splines, keyways or holes, the special installation tool shown below should be used. This special tool should not be made of soft metal (such as aluminum) or notched installation tools.
10. If the mating part (shaft) must be forced through the working face of the seal, the diameter of the sliding portion of the shaft can be reduced by 0.2 mm. Seals designed for the original shaft can still be used without affecting their sealing performance. See below:
11. When installing the inner package skeleton seal, a thin layer of suitable lubricant should be applied to the outer edge of the seal to fit the seal into the cavity. Uniform speed and pressure should be used during assembly to prevent springs from falling out.
12. If the seal must be installed at low temperatures, place the seal for 10-15 minutes in a clean liquid below 50 °C that is the same as its sealing medium to restore the elasticity of the seal lip.
13. When replacing a failed seal with a new seal, the seal lip of the new seal should not match the previous rotation path, but the new seal lip should be closer to the side of the liquid being sealed, which can be installed by The gasket, the conversion bushing and the slip ring, and the method of changing the depth of the press-in cavity are realized.