Natural rubber can withstand media including freshwater, saltwater, air, inert gas, alkalis, and salt solutions; nevertheless, mineral oil and non-polar solvents will damage it. It performs exceptionally well at low temperatures and has a long-term use temperature of no more than 90°C. It is functional at -60 °C. Use the example above.
Petroleum compounds including fuel oil, lubricating oil, and petroleum are acceptable for nitrile rubber. The temperature range for long-term use is 120°C, 150°C in hot oil, and -10°C to -20°C at low temperatures.
Seawater, weak acids, weak alkalis, salt solutions, excellent oxygen and ozone aging resistance, oil resistance that is inferior to nitrile rubber but better than other general rubber, long-term use temperatures that are lower than 90 °C, maximum use temperatures that are not higher than 130 °C, and low temperatures that are between -30 and 50 °C are all suitable for chloroprene rubber.
Fluorine rubber comes in a variety of forms, all of which have good acid, oxidation, oil, and solvent resistance. The long-term use temperature is lower than 200°C, and it can be used with practically all acid media as well as some oils and solvents.
The rubber sheet is mostly used as a flange gasket for pipelines or often demolished manholes and hand holes, and the pressure is not greater than 1.568MPa. Rubber gaskets are the softest and best at bonding among all types of gaskets, and they can produce a sealing effect with just a little pre-tightening force. Because of its thickness or poor hardness, the gasket is therefore easily squeezed out when under internal pressure.
Rubber sheets are employed in organic solvents like benzene, ketone, ether, etc. that might cause seal failure due to swelling, weight growth, softening, and stickiness. In general, it cannot be used if the swelling level is greater than 30%.
Rubber pads are preferable in vacuum and low pressure situations (particularly below 0.6MPa). The rubber substance is dense and air permeable to a little extent. For vacuum containers, for instance, fluorine rubber works best as a sealing gasket since the vacuum level can go as high as 1.310-7Pa. The rubber pad must be baked and pumped before use in the vacuum range of 10-1 to 10-7Pa.
Although rubber and various fillers have been added to the gasket material, the major issue is that it still cannot entirely seal the tiny pores that are there, and there is a little degree of penetration even though the price is less than other gaskets and it is simple to use. Therefore, even if the pressure and temperature are not excessive, it cannot be used in highly contaminating media. Due to the carbonization of rubber and fillers when used in some high-temperature oil medium, usually near the end of usage, the strength is diminished, the material becomes loose, and penetration occurs at the interface and inside the gasket, leading to coking and smoke.Additionally, at high temperatures, the asbestos rubber sheet readily adheres to the flange sealing surface, which complicates the process of replacing the gasket.
The strength retention of the gasket material determines the pressure of the gasket in various media in a heated condition. Materials containing asbestos fibers contain both crystallization water and adsorption water. Over 500°C, the water of crystallization starts to precipitate, and the strength is lower. At 110°C, two-thirds of the adsorbed water between the fibers has precipitated, and the fiber’s tensile strength has decreased by about 10%. At 368°C, all of the adsorbed water has precipitated, and the fiber’s tensile strength has decreased by about 20%.
The strength of asbestos rubber sheet is significantly influenced by the medium as well. For instance, the transverse tensile strength of No. 400 oil-resistant asbestos rubber sheet varies between aviation lubricating oil and aviation fuel by 80%, which is because the swelling of the rubber in the sheet by aviation gasoline is more severe than that of aircraft lubricating oil. In light of the aforementioned considerations, the safe operating temperature and pressure ranges for domestic asbestos rubber sheet XB450 are 250 °C to 300 °C and 3 3.5 MPa; the maximum temperature for No. 400 oil-resistant asbestos rubber sheet is 350 °C.
Chloride and sulfur ions are present in asbestos rubber sheet. Metal flanges can quickly build a corrosion battery after absorbing water. Particularly, oil-resistant asbestos rubber sheet has a sulfur content that is several times higher than regular asbestos rubber sheet, making it unsuitable for usage in non-oily media. In oil and solvent media, the gasket will swell, but up to a point, it essentially has no impact on the sealing ability. For instance, a 24-hour immersion test in aviation fuel at room temperature is performed on No. 400 oil-resistant asbestos rubber sheet, and it is mandated that the weight increase caused by oil absorption should not be greater than 15%.
Post time: Apr-20-2023
