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There are many types of gaskets on the market, so how do we choose? In this regard, the Gasket Sheet Manufacturer has analyzed the three major gasket plates for us, telling us which aspects should be selected:
The price is lower than other gaskets, and it is easy to use; the biggest problem is that although the gasket material is added with rubber and some fillers, it still can;t completely fill the tiny pores that collude, and there is a trace of penetration. Therefore, it cannot be used in highly polluting media even if the pressure and temperature are not high.
In the heated state, the pressure of the gasket in various media depends on the strength retention rate of the gasket material. Crystal water and adsorption water exist in asbestos fiber materials. 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%; above 500°C, Crystal water begins to precipitate, and the strength is lower. The medium also has a great influence on the strength of the Asbestos Rubber Sheet. For example, in aviation lubricants and aviation fuels, the transverse tensile strength of No. 400 oil-resistant asbestos rubber sheets differs by 80%. This is because aviation fuel swells the rubber in the sheet more seriously than aviation lubricants. Taking into account the above factors, the recommended safe use range of asbestos rubber sheet distributors: temperature 250 ℃ ~ 300 ℃, pressure 3 ~ 3.5 MPa; 400 oil-resistant asbestos rubber sheet temperature should not exceed 350 ℃.
PTFE is easy to cold flow and creep under pressure and high temperature, so it is generally used in low pressure, medium temperature, strong corrosion and media that does not allow pollution, such as strong acid, strong alkali, halogen, medicine, etc. The safe use temperature is 150℃ and the pressure is below 1MPa. Although filled with PTFE has higher strength, its use temperature does not exceed 200°C, and its corrosion resistance is reduced. The maximum working pressure of PTFE cushion is generally not more than 2MPa.
As the temperature rises, the material creeps, causing the sealing pressure to drop significantly. Even if the temperature is not increased, as time goes by, the compression stress of the sealing surface will decrease, resulting in a stress relaxation phenomenon. This phenomenon occurs in all kinds of gaskets, but the stress relaxation phenomenon of PTFE gaskets is more serious. Should pay attention.
Asbestos Rubber Sheet
The friction coefficient of PTFE is small (the compression stress is greater than 4MPa, and the friction coefficient is 0.035~0.04), and the gasket is easy to slip outward during pre-tightening, so it is better to use concave and convex flange faces. When a flat flange is used, the outer diameter of the gasket can be contacted with the bolt, and the bolt can be used to prevent the gasket from sliding. Since the glass-lined equipment is sprayed with a layer of enamel on the metal surface and then sintered, the glaze layer is very brittle, and the uneven spraying and flow of the glaze layer make the flange surface flatness poor. The use of metal composite gaskets is easy to damage the glaze layer, so it is recommended to use a PTFE gasket with asbestos board and rubber core material. This kind of packing pad is easy to fit with the flange surface and is also corrosion resistant, and the use effect is good.
Many factories use asbestos rubber sheets to wrap raw polytetrafluoroethylene tapes in strong corrosive media with low temperature and pressure, which are used in manholes and pipelines that are often dismantled. It is very popular because of its easy production and use.
Octagonal gaskets and oval gaskets (commonly known as ;earth steel ring; in the oil refining industry) for trapezoidal groove flanges have good sealing performance. On the tapered surface of the groove, the octagonal pad is in surface contact and the oval pad is in line contact. Therefore, the oval pad has a good fit under low tightening force, but it needs to be tightened twice; while the octagonal pad is generally not easy to leak after being tightened once. Their shortcomings are that they require a large bolt tightening force. When used in low pressure and high temperature conditions, the flange level must be above pg25 kg.
If you have any needs in this regard, please feel free to contact our Gasket Sheet Manufacturer.
