Applications of Eight Different Gaskets

2. Asbestos rubber gaskets
Asbestos rubber gaskets can be classified into ordinary asbestos rubber gaskets and oil-resistant asbestos rubber gaskets according to their formulations, processing properties and applications. Asbestos rubber gaskets can be divided into low pressure asbestos rubber gaskets, medium pressure asbestos rubber gaskets and high pressure asbestos rubber gaskets based on operating temperatures and pressure.

The price of the asbestos rubber gasket is lower than other gaskets', and the asbestos rubber gasket is easy to be used. The biggest problem of asbestos rubber gaskets is that although rubber and some fillers are added to asbestos rubber gaskets' materials, tiny holes can not be completely filled, resulting in very tiny amount of penetration. Therefore, asbestos rubber gaskets can not be used for highly polluting media, even if pressure and temperature are not high. Penetration will happen at boundaries and inner parts of asbestos rubber gaskets because of carbonation of rubber and fillers, strength reduction and loose material, resulting in coking and smoking when asbestos rubber gaskets are applied to media such as high temperature oil. Penetration usually happens in the later period when the asbestos rubber gasket is used. In addition, asbestos rubber gaskets will easily bond with sealing surfaces of flanges at high temperatures, which brings a lot of trouble for replacing asbestos rubber gaskets.

In the state of being heated, working pressure of gaskets in the various media is determined by strength retention of gaskets' materials. Asbestos fiber materials contain crystal water and absorbed water. At a temperature of 110℃, two thirds of absorbed water between fibers will precipitate, and tensile strength of fibers will be reduced 10%; at a temperature of 368℃, absorbed water will precipitate completely, and tensile strength of fibers will be reduced 20%; at a temperature of over 500℃, crystal water will precipitate, and the tensile strength will be lower.

The effect of the medium on the strength of the asbestos rubber sheet is also great. Given the factors above, the temperature from 250℃ to 300℃ and pressure from 3 to 3.5MPa are recommended for domestic asbestos rubber sheets XB450, and operating temperatures of 400 oil-resistant asbestos rubber gaskets should be lower than 350℃.

Asbestos rubber sheets contain chloride ion and sulfide, and can easily form corrosion cells with metal flanges after asbestos rubber sheets absorbing water. Sulphur content of oil-resistant asbestos rubber sheets is several times higher than sulphur content of ordinary asbestos rubber sheets; therefore, asbestos rubber sheets should not be used in non oily media. Swellings of gaskets will happen in media such as petroleum products and solvents. However, swellings within a certain range basically don't have influence on sealing performance of asbestos rubber gaskets.