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Selection and Scope of Eight (8) Types of Flange Gaskets (II)

02 Asbestos Rubber Sheet

The price is lower than other gaskets and it is convenient to use; The biggest problem is that although rubber and some fillers are added to the gasket material, it is still unable to completely fill the tiny pores that are connected, and there is a small amount of penetration. Therefore, it cannot be used in highly polluting media even if the pressure and temperature are not high. When used in some high-temperature oil media, usually in the later stage of use, due to the carbonization of rubber and filler, the strength decreases, and the material becomes loose, which will lead to penetration in the interface and gasket and coking and smoking. In addition, the asbestos rubber plate is easy to adhere to the flange sealing surface under high temperature, which brings a lot of trouble to replace the gasket.

Under heating condition, the service pressure of gasket in various media depends on the strength retention rate of gasket material. Crystalline water and adsorbed water exist in asbestos fiber materials. At 110 ℃, 2/3 of the adsorbed water between the fibers has precipitated, and the tensile strength of the fibers is reduced by about 10%; At 368 ℃, the adsorbed water is completely separated, and the tensile strength of the fiber is reduced by about 20%; Above 500 ℃, crystalline water begins to precipitate, and the strength is lower.

The medium also has a great influence on the strength of asbestos rubber sheets. For example, in aviation lubricating oil and aviation fuel, the transverse tensile strength of 400 # oil-resistant asbestos rubber plate is 80% different, which is because the swelling of aviation fuel on the rubber in the plate is more serious than that of aviation lubricating oil. Considering the above factors, the recommended safe use range of domestic asbestos rubber sheet XB450: temperature 250 ℃~300 ℃, pressure 3~3.5MPa; The service temperature of 400 # oil-resistant asbestos rubber plate should not exceed 350 ℃.

Asbestos rubber sheets contain chloride ions and sulfides, which can easily form corrosive primary cells with metal flanges after absorbing water. Especially, the sulfur content of oil-resistant asbestos rubber sheets is several times higher than that of ordinary asbestos rubber sheets, so they should not be used in non-oil media. The gasket will swell in oil and solvent media, but within a certain range, it has little effect on the sealing performance. For example, the 400 # oil-resistant asbestos rubber plate is subjected to 24-hour immersion test in normal temperature aviation fuel, which requires that the weight increase due to oil absorption should not exceed 15%.

Unfinished (to be continued) ……

Post time: Mar-09-2023