leakage:
Leakage is one of the common malfunctions in mechanical equipment. The main reasons for leakage are twofold: firstly, due to the results of mechanical processing, there are inevitably various defects and shape and size deviations on the surface of mechanical products. Therefore, gaps are inevitably generated at the joints of mechanical parts; Secondly, there is a pressure difference on both sides of the seal, and the working medium will leak through the gap.

Reducing or eliminating gaps is the main way to prevent leaks. The function of sealing is to seal the gap between the joint surfaces, isolate or cut off the leakage channel, increase the resistance in the leakage channel, or add small power components in the channel to create pressure on the leakage material, partially offset or completely balance the pressure difference that causes the leakage, in order to prevent leakage.

For the sealing of vacuum systems, in addition to the direct leakage of the sealing medium through the sealing surface mentioned above, the following two leakage forms should also be considered:

Leakage. The leakage of the sealed medium through the capillary tube of the sealing material under the pressure difference is called leakage;

Spread. Under the effect of concentration difference, the substance generated by the sealed medium through the sealing gap or the capillary of the sealing material is transferred into diffusion.

Classification of Seals:
Sealing can be divided into two categories: static sealing between relatively stationary mating surfaces and dynamic sealing between relatively moving mating surfaces. Static sealing mainly includes three categories: sealing, adhesive sealing, and contact sealing. According to working pressure, static seals can be divided into medium and low pressure static seals and high pressure static seals. Medium and low pressure static seals are commonly sealed with softer materials and wider gaskets, while high pressure static seals use harder materials and narrower contact widths with metal gaskets. Dynamic seals can be divided into two basic types: rotary seals and reciprocating seals. Seals can be divided into contact seals and non-contact seals based on whether they are in contact with the moving parts they act on. Generally speaking, contact seals have good sealing performance, but are limited by friction and wear, making them suitable for situations with lower linear speeds on the sealing surface. Non contact sealing has poor sealing performance and is suitable for situations with higher speeds.

Selection of seals:
The basic requirements for sealing are good sealing performance, safety and reliability, long service life, and should strive for compact structure, simple system, convenient manufacturing and maintenance, and low cost. Most seals are vulnerable parts and should ensure interchangeability, achieve standardization, and serialization.

Sealing material:
The sealing material should meet the requirements of sealing function. Due to the different media being sealed and the different working conditions of the equipment, it is required that the sealing material has different adaptability. The general requirements for sealing materials are:

1) The material has good density and is not easy to leak the medium;

2) Having appropriate mechanical strength and hardness;

3) Good compressibility and resilience, with small permanent deformation;

4) Not softening or decomposing at high temperatures, not hardening or brittle cracking at low temperatures;

5) Good corrosion resistance, able to work for a long time in acidic, alkaline, oil and other media, with small changes in volume and hardness, and not adhering to metal surfaces;

6) Low friction coefficient and good wear resistance;

7) Has flexibility that combines with the sealing surface;

8) Good aging resistance and durability;

9) Convenient processing and manufacturing, affordable price, and easy material selection.


Rubber is the most commonly used sealing material. In addition to rubber, graphite, polytetrafluoroethylene, and various sealants are also suitable as sealing materials.

1.4.2 General rubber sealing product materials

Universal rubber sealing products are increasingly widely used in defense, chemical, coal, petroleum, metallurgy, transportation, and machinery manufacturing industries, and have become basic components and accessories in various industries.


The commonly used materials for rubber sealing products are as follows:

1.4.2.1 Nitrile rubber


Nitrile rubber has excellent resistance to fuel oil and aromatic solvents, but is not resistant to media such as ketones, esters, and hydrogen chloride. Therefore, oil resistant sealing products and nitrile rubber are mainly used.

1.4.2.2 Neoprene rubber

Neoprene rubber has good oil and solvent resistance properties. It has good resistance to gear oil and transformer oil, but is not resistant to aromatic oils. Neoprene rubber also has excellent weather resistance and ozone aging performance. The crosslinking fracture temperature of chloroprene rubber is above 200 ℃, and chloroprene rubber is usually used to make door and window sealing strips. Neoprene rubber also has good corrosion resistance to inorganic acids. In addition, due to its good flexibility and non breathability, chloroprene rubber can be used to make sealing products for membranes and vacuum applications.

1.4.2.3 Natural rubber


Compared with most synthetic rubbers, natural rubber has good comprehensive mechanical properties, cold resistance, higher rebound and wear resistance. Natural rubber is not resistant to mineral oils, but is more stable in vegetable oils and alcohols. In the hydraulic brake system composed of a mixture of n-butanol and refined castor oil, the rubber bowl used as the sealing element is made of natural rubber, and the sealing ring is also commonly made of natural rubber.

1.4.2.4 Fluorine rubber


Fluorine rubber has outstanding heat resistance (200-250 ℃) and oil resistance, and can be used to manufacture cylinder liner seals, rubber bowls, and rotating lip seals, significantly improving service life.

1.4.2.5 Silicone rubber

Silicone rubber has outstanding resistance to high and low temperatures, ozone, and weather aging. It can maintain its unique elasticity, ozone resistance, and weather resistance within the working temperature range of -70 to 260 ℃. It is suitable for making sealing gaskets required in thermal mechanisms, such as sealing rings for strong light source lampshades, valve gaskets, etc. Due to the lack of oil resistance of silicone rubber,