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several problems in seal design have to pay attention
Mar 01, 2018

1. Sealing materials

Sealing material should meet the requirements of sealing function. Because the sealed medium is different and the working conditions of the equipment are different, the sealing material is required to have different applicability. The requirements for sealing materials are: ① material compactness is good, not easy to leak medium; ② has appropriate mechanical strength and hardness, ③ compressibility and resilience, permanent deformation is small, ④ at high temperature does not soften, does not decompose, low-temperature, not hardening, not brittle crack, ⑤ corrosion resistance, in acid, alkali, oil and other medium can long-term work, Its volume one hardness changes small, and does not adhere to the metal surface, the ⑥ friction coefficient is small, the abrasion resistance is good, the ⑦ has with the sealing surface pastes the whole softness, the ⑧ anti-aging resistance is good, durable, the ⑨ processing manufacture convenience, the price is cheap, the material is easy. Obviously, it is impossible for any material to fully meet the above requirements, but materials with excellent sealing properties can meet most of the above requirements.

Rubber is the most commonly used sealing materials, in addition to rubber, suitable for sealing materials, as well as graphite belt, PTFE and a variety of sealant, sealing design in several problems.

2. Processing technology

Good processing technology and molding process are the effective means to ensure the size accuracy, surface characteristics and to improve the resistance to the gymnasium and abrasion resistance of the sealing parts. Sealing-related processes include molding, impregnation, spraying, sintering, welding, electroplating and surface heat treatment. The same material, if the processing process is different, its characteristics will be very big difference. In the sealing parts of the most commonly used molding process, if the finished product in the shape, size and other aspects of the error is very large, there are flying edge, burr, for seals are very unfavorable. Take rubber O-ring as an example, it is to rely on a given compression deformation to ensure that the seal, if due to poor dimensional accuracy to ensure that the necessary compression deformation volume, there will be leakage. In addition, as the O-ring is installed in a pre-tensile state of the seal, when the movement friction heat, the O-ring is not expansion, but contraction (the tensile state of rubber heat contraction, called the Joule Effect), which may also reduce the amount of compression deformation at work when the leak occurs. Therefore, the design must strictly control the size accuracy, and should take into account a variety of factors, such as the contact with the seal parts of the size accuracy, surface roughness and texture direction.

3. Friction, wear and lubrication

Friction and wear are the inevitable problems in contact type dynamic seals. Contact-type dynamic seals and sealed parts of contact, due to the relative movement of friction, resulting in heat and parts of the surface wear, which is caused by leakage and sealing the main reason for damage. Therefore, the choice of lubrication hydraulic and lubricants has become a sealed design must carefully consider the problem. Generally choose self-lubricating methods, such as impregnation of various lubricants filler, impregnated graphite and the use of small friction coefficient of poly-ethylene and so on. When the medium is lubricated, it is lubricated with the medium itself.

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