Since the birth of the first O-ring in the mid-19th century, rubber seals have been widely used due to their advantages of simple structure, convenient loading and unloading, reliable sealing, small dynamic friction resistance and no need for periodic adjustment. Rubbers commonly used in vacuum systems include natural latex vulcanized rubber, synthetic rubber (such as butyl, chlorine, nitrile rubber) and silicone rubber, fluorine rubber, etc.

The key of rubber seal lies in the reasonable seal structure design and material selection. The main factors affecting the vacuum seal performance are heat resistance, compression deformation resistance, air leakage rate, air permeability, air output rate and sublimation (weight loss), etc.

01

Heat resistance

Vacuum systems often need to be baked to degas, which requires rubber seals to have a certain degree of heat resistance. Generally, when the vacuum is below 120℃ and 10⁻⁵ Pa, butyl or nitrile rubber is suitable. Fluorine rubber is more suitable for higher baking temperature and working in ultra-high vacuum environment.

02

Resistance to compression and deformation

A large number of vacuum seals work under compression, in order to ensure the reliability and life of the seal, the vacuum sealing rubber should have a small compression deformation value (less than 35% is preferred) and slow compression stress relaxation degree (that is, a large compression stress relaxation coefficient).

03

Air leakage rate

In a particular vacuum system, the rubber leak rate should not be greater than 5.25×10⁻³ Pa · cm³/s to maintain 5×10⁻⁷ Pa vacuum degree when the pump pumping rate was 8000 L/s. The leakage rate of different rubbers is different.

04

Permeability of air

Different rubbers have different air permeability at different temperatures, depending on their internal structure.

Nitrile rubber because of the methyl group gas permeability is low, and the acrylonitrile polar group to non-polar gas permeability is low, the higher the acrylonitrile content is, the lower the permeability is. The increase of temperature will increase the air permeability, and the air permeability of different gases in different rubbers is also different, such as in the same gas, the order of the air permeability is natural rubber > styrene butadiene rubber > nitrile rubber > chloroprene rubber > butyl rubber.

05

Gas out rate

Rubber gas output rate refers to the gas output per unit area per unit time at a certain temperature. Vacuum sealing is generally required to be within 10⁻⁴ ~ 10⁻⁵ Pa · L/s. According to the gas output rate, it is chlorol rubber > vinyl silicone rubber > natural rubber > nitrile rubber > chloroprene rubber > fluorine rubber.

06

Sublimation of rubber (weight loss)

The weight loss of rubber at a certain degree of vacuum and temperature is sublimation. Vacuum sealing requires small sublimation value of sealing material (generally less than 10%), according to the sublimation value of natural rubber > nitrile rubber > neoprene rubber > chlorol rubber > vinyl silicone rubber > fluorine rubber. In the high vacuum system, the main factors affecting the ultimate pressure of rubber sealing elements are the leakage rate and the exhaust rate.