Commonly used self-sealing compression type hydraulic seals are mainly ○-shaped seals, round seals and square seals, etc. They have the advantages of simple structure, easy manufacturing and low cost, so they are widely used in hydraulic transmission systems as dynamic sealing components and static sealing components. They are installed in the seal groove usually produce 10-25% of the radial compression deformation, and produce a high initial contact stress on the sealing surface, so as to prevent the leakage of non-pressure fluid. When the hydraulic cylinder is in operation, the pressure fluid squeezes the self-sealing compression hydraulic seal, deforming it further and generating a higher pressure on the sealing surface with the pressure fluid, which should be strictly speaking a compressive force. The additional contact stress is increased and together with the initial contact stress, it stops the leakage of the pressure fluid. However, when the working pressure is greater than 10Mpa, in order to avoid a part of the synthetic rubber self-sealing hydraulic seal being squeezed into the sealing gap and cut off in the reciprocating movement of the hydraulic cylinder and causing leakage, a synthetic resin retaining ring, such as nylon retaining ring, polyformaldehyde retaining ring and filled PTFE retaining ring, must be set on each side of the synthetic rubber self-sealing hydraulic seal under pressure. Because of the large compression deformation of the synthetic rubber self-sealing compression hydraulic seals, their static frictional resistance is particularly high, usually more than twice as high as their dynamic frictional resistance. Such high static frictional resistance in some low pressure hydraulic transmission systems is bound to cause undesirable phenomena such as low pressure crawling and difficult operation, which is why self-sealing compression hydraulic seals are rarely used as dynamic seals alone. Lip Type Seals At present, the hydraulic combination seals commonly used in hydraulic cylinders of hydraulic machinery and equipment in ceramic plants are mainly composed of ○-shaped seals and square seals, U-shaped seals, Y-shaped seals, YX-shaped seals and other special shapes of hydraulic seals used in the superposition V-shaped seals The sealing performance of V-shaped seal is better, according to the size of the working pressure to determine the number of seals used, usually with the help of the gland adjustment to compensate for the amount of wear of the seal, its Achilles’ heel is the complex structure, usually by the support ring, seal and pressure ring three parts, its friction resistance and with the working pressure and the number of seals increases. Therefore, V-shaped seal is only suitable for low speed and high pressure hydraulic cylinder. U-shaped seal The sealing performance of U-shaped seal is good, but it is easy to roll over when used alone, so it needs to be used with tin bronze support ring, whose frictional resistance is larger and increases with the increase of working pressure. Therefore, U-shaped seal ring is only suitable for low working pressure or low speed hydraulic cylinder. Y-shaped seal Y-shaped seal relies on its open lip to seal the surface and keep the seal, usually can be used alone, its sealing performance is better, less frictional resistance, good pressure resistance, good work stability, long service life. Therefore, Y-shaped seal is suitable for high-speed variable pressure, large bore, large stroke hydraulic cylinders. YX-shaped seal YX-shaped seal is a Y-shaped seal with the ratio of cross-sectional height to width greater than 2 and the working lip is not as high as the non-working lip, it is divided into YX-shaped seal for hole and YX-shaped seal for shaft, its sealing performance is the same, in addition to all the advantages of Y-shaped seal, YX-shaped seal never rolls over when used alone, further improving its pressure resistance and work stability. Therefore, YX-shaped seal is especially suitable for high pressure, high speed variable pressure and fast moving hydraulic cylinder. Self-sealing tight hydraulic seals: Lip seals, like self-sealing compression hydraulic seals, produce high initial contact stress on the sealing surface by their own deformation, preventing leakage of non-pressure fluids. When the hydraulic cylinder is in operation, the pressure fluid squeezes and holds open the sealing lip, causing a high additional contact stress that increases with the pressure of the pressure fluid and, together with the initial contact stress, prevents leakage of the pressure fluid. Combination Seals The main combination seals commonly used in hydraulic cylinders are lace rings, gripper rings, and stirrups. 1: Lace Ring The lace-shaped ring is usually composed of a synthetic rubber ○-shaped seal and a laminated cloth rubber Y-shaped seal, which are used in combination with self-sealing compression hydraulic seals and self-sealing tight hydraulic seals, and lip seals, which generate high initial contact stress on the sealing surface according to their own deformation to prevent leakage of non-pressure liquid. When the hydraulic cylinder is in operation, the pressure liquid is always squeezed and propped up by the elastic deformation of the ○-shaped seal, so that the sealing lip of the Y-shaped seal is tightly attached to the sealing surface and generates higher additional contact stress with the increased pressure of the pressure liquid, and together with the initial contact stress, prevents the leakage of the pressure liquid. 2：Glare ring Glare ring is usually made of synthetic rubber ○-shaped seal and filled with PTFE square seal superimposed on the use of the composition, it can be divided into hole Glare ring and shaft Glare ring, but its sealing role is the same, according to its own deformation of the sealing surface to produce a higher initial contact stress, to prevent the leakage of non-pressure liquid. When the hydraulic cylinder is working, the pressure liquid through the elastic deformation of the ○-shaped seal starts to squeeze the square seal to the maximum, so that it is close to the sealing surface and produces higher additional contact stress with the pressure of the pressure liquid, and together with the initial contact stress to prevent the leakage of pressure liquid. 3: Stetzel The seal is usually made of synthetic rubber ○-shaped seal and filled with PTFE special shape rectangular – trapezoidal seal, and can be divided into hole seal and shaft seal, its sealing effect and sealing mechanism is the same as the seal, but it only has a one-way sealing effect. Self-sealing tight hydraulic seal: lip-shaped seal, and the sealing surface closely fit the lip contact area is smaller, can produce greater compression deformation, to obtain a better sealing effect. But easy to wear, wear its sealing role significantly reduced, if the use of ○-shaped seal ring and the superposition of the use, that is, the combination of seals, even after the lip wear, due to synthetic rubber ○-shaped seal ring has a large elasticity, it will force the lip of the lip seal ring tightly against the sealing surface, produce a large enough surface contact stress, to achieve the role of sealing, and friction resistance is small, smooth work, and easy to assemble and maintenance, etc. Therefore, the current automatic hydraulic brick press, daily-use ceramic products, discs, plates and other hydrostatic molding machines and medium-pressure grouting, high-pressure grouting sanitary ceramic molding machines are almost all widely used hydraulic seals are combination seals, such as the Glaze ring and Sturt ring.

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