Silicone rubber sealing materials for forged steel valve
Mar 27, 2019
Silicone rubber (Si or VMQ) is a linear polymer with a silicon-oxygen bond unit (-si-o-si) as the main chain and an organic group as a side group.
Due to the development of cutting-edge industries such as aviation and aerospace, there is an urgent need for rubber sealing materials that are resistant to high temperatures and low temperatures. The natural rubbers such as natural cyanide and chloroprene used in the early days have not been able to meet the needs of industrial development. Therefore, in the early 1940s, two companies in the United States began to produce dimethyl silicone rubber, which was the earliest silicone rubber. China also succeeded in research and put it into production in the early 1960s. After decades of development, the variety, performance and output of silica gel have been greatly developed.
The main characteristics of silica gel:
1) Heat resistance. The high temperature stability of silica gel is good. It can be used at 150 °C for a long time, and the performance will not change significantly; it can work continuously for more than 10,000 hours at 200 °C, and can even be used for a short time at 350 °C.
2) Cold resistance. Low phenyl silica gel and medium phenyl silica gel have good low temperature elasticity at -60 ° C and -70 ° C when the cold resistance coefficient is above 0.65. In general, the use temperature of silica gel is -50 °C.
3) Oil and chemical resistance. Silica gel has good resistance to polar solvents such as ethanol and acetone, and food oils. It only causes little expansion and mechanical properties are basically not reduced. Silica gel is also resistant to low concentrations of acid, alkali and salt. If it is placed in 10% sulfuric acid solution for 7 days, the volume change rate is less than 1%, and the mechanical properties are basically unchanged. However, silica gel is not resistant to non-polar solvents such as concentrated sulfuric acid, concentrated alkali, carbon tetrachloride and toluene.
4) Strong aging resistance. Silica gel has obvious ozone resistance and radiation resistance, which is unmatched by ordinary rubber.
5) Dielectric properties. Silica gel has a high volume resistivity (1014 to 1016 Ω•cm) and its resistance value is stable over a wide range. Silicone is suitable as an insulating material under high pressure conditions.
6) Flame retardant properties. Silica gel does not burn immediately in case of fire, and its combustion produces less toxic gases. The products after combustion will form insulating ceramics. Therefore, silica gel is also an excellent flame retardant material.
Based on the above characteristics, silica gel is widely used in seals or rubber parts used in the household appliance industry, such as electric heating pots, electric irons, rubber parts in microwave ovens; seals or rubber parts in the electronics industry, such as mobile phone buttons, DVDs Shock absorbers, seals in cable joints, etc.; seals on various types of articles that come into contact with the human body, such as water bottles, water dispensers, etc.
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