A Little Knowledge About Rubber Gaskets

Rubber gaskets are mostly used for pipes or manholes and hand holes that are often dismantled, and the pressure does not exceed 1.568MPa. Among all kinds of sealing gaskets, rubber gaskets are the softest and have good fitting performance, and can play a sealing effect with a small preload. Because of this, when subjected to internal pressure, the gasket is easy to be squeezed out due to its thick or low hardness.

The use of rubber sheets in organic solvents such as benzene, ketone, and ether is prone to swelling, weight gain, softening, and stickiness, resulting in seal failure. Generally, the swelling degree exceeds 30% and cannot be used.

In the case of low pressure (especially below 0.6MPa) and vacuum, it is more appropriate to use rubber gaskets. The rubber material has good compactness and low air permeability. For example, fluorine rubber is most suitable for sealing gaskets of vacuum containers, and the vacuum degree can reach up to 1.3×10-7Pa. When the rubber gasket is used in the vacuum range of 10-1~10-7Pa, it needs to be baked and exhausted.

The price of asbestos rubber sheet is lower than that of other gaskets, and it is easy to use; the biggest problem is that although rubber and some fillers are added to the sealing gasket material, it is still unable to completely fill the tiny pores that are colluding, and there is a small amount of penetration. Therefore, in a highly polluting medium, it cannot be used even if the pressure and temperature are not high. When used in some high-temperature oil media, usually in the later period of use, due to the carbonization of rubber and fillers, the strength is reduced, and the material becomes loose, which will infiltrate the interface and inside the rubber gasket, resulting in coking and smoking. In addition, the asbestos rubber sheet is easy to bond to the flange sealing surface at high temperature, which brings a lot of trouble to the replacement of the gasket.

In the heated state, the use pressure of the rubber gasket in various media depends on the strength retention rate of the gasket material. Crystalline water and adsorbed water exist in asbestos fiber material. At 110 °C, 2/3 of the adsorbed water between the fibers has been precipitated, and the tensile strength of the fiber is reduced by about 10%; at 368 °C, all the adsorbed water is precipitated, and the tensile strength of the fiber is reduced by about 20%; over 500 °C, Water of crystallization begins to separate out, and the strength is lower.

The medium also has a great influence on the strength of the asbestos rubber sheet. For example, in aviation lubricating oil and aviation fuel, the transverse tensile strength of No. 400 oil-resistant asbestos rubber sheet differs by 80%, which is due to the fact that aviation fuel swells the rubber in the sheet more seriously than aviation lubricating oil. Taking into account the above factors, the recommended safe use range of asbestos rubber sheet XB450: temperature 250 ℃ ~ 300 ℃, pressure 3 ~ 3.5MPa; 400 oil-resistant asbestos rubber sheet using temperature should not exceed 350 ℃.

Asbestos rubber sheets contain chloride ions and sulfides, which are easy to form corrosion 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 it is not suitable for use in non-oily media. Rubber gaskets will swell in oil and solvent media, but within a certain range, they have little effect on sealing performance. For example, the No. 400 oil-resistant asbestos rubber sheet is subjected to a 24-hour immersion test in normal temperature aviation fuel, and it is required that the weight increase due to oil absorption should not exceed 15%.