The extremely small leakage requires the hydraulic seal to have a very small leakage and a good sealing effect.
The performance of hydraulic seals
As the pressure of the hydraulic oil increases, its sealing effect is automatically improved. Even under the harsh working environment of high pressure and high temperature, the leakage of the hydraulic seals has not increased significantly.
Good compatibility Because hydraulic seals are immersed in hydraulic oil for a long time, they are easy to swell, dissolve or become brittle and hard, etc., making them lose their sealing effect. Therefore, hydraulic seals are required to have good compatibility with hydraulic oil.
Low friction resistance In order to avoid or reduce the adverse phenomena such as low-pressure crawling produced by hydraulic equipment, hydraulic seals are required to have low static friction resistance and dynamic friction resistance, and the friction coefficient should be very stable.
Long service life Hydraulic seals should have good elasticity, heat resistance, cold resistance, pressure resistance, wear resistance, and certain physical and mechanical strength, and have a long service life.
Low-cost hydraulic seals should be easy to manufacture and install, and their corresponding sealing grooves are easy to process and manufacture, and the requirements for the machining accuracy of the sealing surface are low, and they are inexpensive and inexpensive.
Structure of hydraulic seal
Commonly used self-sealing compression hydraulic seals are mainly ○-shaped sealing rings, round sealing rings and square sealing rings. They have the advantages of simple structure, easy manufacturing, low cost, etc., so they are widely used in hydraulic transmission systems Dynamic sealing element and static sealing element. They are usually installed in the sealing groove to produce 10-25% of the radial compression deformation, and produce a higher initial contact stress on the sealing surface, thereby preventing the leakage of non-pressure liquid.
When the hydraulic cylinder is working, the pressure liquid squeezes the self-sealing compact hydraulic seal to further deform it, and generates a large pressure with the pressure liquid on the sealing surface, which should be strictly speaking the pressure. The increased and increased additional contact stress, together with the initial contact stress, prevents pressure fluid leakage. However, when the working pressure is greater than 10Mpa, in order to prevent a part of the synthetic rubber self-sealing compression hydraulic seal from being squeezed into the sealing gap and being cut off during the reciprocating movement of the hydraulic cylinder to cause leakage, the synthetic rubber self-sealing pressure The pressure-sensitive side of the tight hydraulic seal is provided with a synthetic resin retaining ring, such as a nylon retaining ring, a polyacetal retaining ring and a filled polytetrafluoroethylene retaining ring.
Because the synthetic rubber self-sealing compression hydraulic seal has a large compression deformation during operation, its static friction resistance is particularly large, usually more than twice its dynamic friction resistance. Such a large static friction resistance is bound to cause undesirable phenomena such as low-pressure crawling and difficult operation in some low-pressure hydraulic transmission systems. This is why self-sealing compact hydraulic seals are very small and used as dynamic seals alone.
Classification of hydraulic seals
Lip seals The commonly used hydraulic combination seals of hydraulic machinery and hydraulic cylinders in ceramic factories are mainly composed of ○-shaped seals and square seals, U-shaped seals, Y-shaped seals, YX-shaped seals and other special-shaped hydraulic seals. The superposition of circles is composed of
V-shaped sealing ring has good sealing performance. The number of sealing rings can be determined according to the working pressure. Usually, the gland adjustment must be used to compensate for the wear of the sealing ring. The fatal weakness is the structure It is complicated and usually consists of three parts: support ring, seal ring and pressure ring. Its friction resistance is large and increases with the increase of working pressure and the number of seal rings. Therefore, the V-shaped sealing ring is only suitable for hydraulic cylinders with low moving speed and high working pressure.
U-shaped sealing ring The U-shaped sealing ring has good sealing performance, but it is very easy to roll when used alone, so it needs to be used with a tin bronze support ring. Its friction resistance is large and increases with the increase of working pressure. Therefore, the U-shaped sealing ring is only suitable for hydraulic cylinders with lower working pressure or lower moving speed.
Y-shaped seal ring Y-shaped seal ring relies on its opened lip to close to the sealing surface to maintain the seal, usually can be used alone, its sealing performance is better, less friction resistance, good pressure resistance performance, working stability Good and long service life. Therefore, the Y-shaped sealing ring is suitable for hydraulic cylinders with high-speed variable pressure, large cylinder diameter and large stroke.
YX-shaped seal ring YX-shaped seal ring is a Y-shaped seal ring with a ratio of section height to width greater than 2 and unequal height of working lip to non-working lip. It is divided into YX-shaped seal ring for hole and YX-shaped seal ring for shaft. The sealing performance is the same. In addition to all the advantages of the Y-shaped seal ring, the YX-shaped seal ring never rolls when used alone, further improving its pressure resistance and working stability. Therefore, the YX-shaped sealing ring is particularly suitable for high-pressure, high-speed variable pressure and fast-moving hydraulic cylinders.
Self-sealing compact hydraulic seals: Lip seals, like self-sealing compact hydraulic seals, produce a higher initial contact stress on the sealing surface according to their own deformation, preventing leakage of non-pressure liquid. When the hydraulic cylinder is working, the pressure liquid squeezes and expands its sealing lip, making it close to the sealing surface to produce a higher additional contact stress that increases with the pressure of the pressure liquid, and together with the initial contact stress to prevent the pressure Liquid leakage.
Combined seals The commonly used combined seals of hydraulic cylinders are mainly bud ring, grid ring and ster seal.
1: bud circle
The bud ring is usually composed of the superimposed use of a synthetic rubber ○-shaped sealing ring and a cloth-rubber-shaped Y-shaped sealing ring, and is combined with a self-sealing compression hydraulic seal and a self-sealing compact hydraulic sealing ring, lip type Like the seals, it generates a higher initial contact stress on the sealing surface according to its own deformation, preventing leakage of non-pressure liquid. When the hydraulic cylinder is working, the pressure liquid always squeezes and stretches the sealing lip of the Y-shaped seal ring through the elastic deformation of the ○-shaped seal ring, so that it is close to the sealing surface and produces a higher pressure that increases with the pressure of the pressure liquid. The additional contact stress, together with the initial contact stress, prevents leakage of pressure fluid.
2: Grid Circle
The grid ring is usually composed of the superimposed use of a synthetic rubber ○-shaped sealing ring and a PTFE-filled square sealing ring. It can be divided into a grid ring for holes and a grid ring for shafts, but its seal The effect is the same, according to its own deformation to produce a higher initial contact stress on the sealing surface to prevent the leakage of non-pressure liquid. When the hydraulic cylinder is working, the pressure liquid will squeeze the square seal ring to the maximum extent through the elastic deformation of the ○-shaped seal ring to make it close to the sealing surface to generate a higher additional contact stress that increases with the pressure of the pressure liquid. Together with the initial contact stress, it prevents pressure fluid leakage.
Sterling seal is usually composed of a synthetic rubber ○-shaped sealing ring and a special shape rectangle filled with polytetrafluoroethylene-trapezoidal sealing ring, which can be divided into a hole sealing and shaft like the Glai ring With the Sterling seal, its sealing function and sealing mechanism are the same as those of the Gele ring, but it only has a one-way sealing effect.
Self-sealing compact hydraulic sealing ring: lip-shaped sealing ring, the contact area of the lip that closely fits the sealing surface is small, can produce greater compression deformation, and obtain a better sealing effect. But it is easy to wear, and its sealing effect is significantly reduced after wear. If a ○-shaped sealing ring is used in superposition with it, that is, when the seal is combined, even after the lip is worn, because the synthetic rubber ○-shaped sealing ring has greater elasticity, it It will force the lips of the lip-shaped sealing ring to be close to the sealing surface, and generate sufficient surface contact stress to achieve the sealing effect, and the friction resistance is small, the work is stable, and it is easy to assemble and maintain. Therefore, the hydraulic seals widely used in fully automatic hydraulic brick presses, daily ceramic products, discs, dishes and other static pressure forming machines and medium pressure grouting and high pressure grouting sanitary ceramic forming machines are almost all combined seals, such as Glai circle and Stir circle etc.