Industrial rubber
Natural rubber is suitable for water, seawater, air, inert gases, alkalis, salts, aqueous solutions and other media, but not resistant to mineral oil and non-polar solvents, long-term use temperature does not exceed 90 ℃, low temperature performance is excellent, can be used above -60 ℃.
NBR is suitable for petroleum products, such as petroleum, lubricating oil, fuel oil, etc., long-term use temperature of 120 ℃, such as in hot oil can be resistant to 150 ℃, low temperature of -10 ~ -20 ℃.
Chloroprene rubber is suitable for seawater, weak acid, weak alkali, salt solution, excellent resistance to oxygen and ozone aging performance, oil resistance is second to nitrile rubber and better than other general-purpose rubber, long-term use temperature is lower than 90 ℃, the maximum use temperature does not exceed 130 ℃, low temperature of -30 ~ -50 ℃.
There are several varieties of fluoroelastomers, which have good acid resistance, oxidation resistance and oil and solvent resistance. It can be used in almost all acid media as well as some oils and solvents, and the long-term use temperature is lower than 200℃.
Rubber sheet as a flange gasket, mostly used in pipelines or frequently dismantled manhole, handhole, pressure does not exceed 1.568 MPa. Because in all types of gaskets, rubber gasket is the softest, good fitting performance, in the smaller preload can play a sealing effect. Because of this, when subjected to internal pressure, the gasket is easily extruded due to its thickness or low hardness.
Rubber sheet used in benzene, ketone, ether and other organic solvents, easy to dissolve, weight, soften, sticky phenomenon, resulting in sealing failure. Generally swelling degree more than 30% can not be used.
In low pressure (especially below 0.6MPa), vacuum, the use of rubber gasket is more appropriate. Rubber materials are dense, low permeability. For example, fluoroelastomer is the most suitable gasket for vacuum containers, and the vacuum degree can be up to 1.3×10-7 Pa. When the rubber gasket is used in the vacuum degree range of 10-1~10-7 Pa, it needs to be baked and pumped.
Asbestos Rubber Sheet
The price is lower than other gaskets, easy to use; the biggest problem is: gasket material, although adding rubber and some fillers, still can not fill those stringing tiny pores completely, there is a trace of infiltration. Therefore, in the highly polluting medium, even if the pressure, temperature is not high can not be used. When used in some high-temperature oil media, usually in the late use, due to the rubber and filler carbonisation, strength reduction, material becomes loose, then in the interface and the gasket inside the infiltration, coking and fuming phenomenon. In addition, asbestos rubber sheet is easy to bond on the flange sealing surface at high temperature, which brings a lot of trouble to the replacement of gaskets.
In the heated state, the gasket in a variety of media in the use of pressure depends on the strength of the gasket material retention rate. Asbestos fibre material in the presence of crystalline water and adsorbed water. 110 ℃, between the fibres of adsorbed water has been 2 / 3 precipitation, the tensile strength of the fibre is reduced by about 10%; 368 ℃, all the adsorbed water precipitation, the tensile strength of the fibre is reduced by about 20%; more than 500 ℃, the crystalline water began to precipitate, the strength is even lower.
The medium also has a great influence on the strength of asbestos rubber sheet. For example, in aviation lubricant and aviation fuel oil, 400 oil-resistant asbestos rubber sheet lateral tensile strength difference of 80%, which is due to aviation fuel oil on the rubber in the sheet of the swelling than the aviation lubricant is serious. Considering the above factors, the recommended safe use range of domestic asbestos rubber sheet XB450: temperature 250℃~300℃, pressure 3~3.5MPa; the use temperature of No.400 oil-resistant asbestos rubber sheet should not exceed 350℃.
Asbestos rubber sheet contains chlorine ions and sulphide, it is easy to form corrosive primary battery with metal flange after absorbing water, especially the sulphur content in oil-resistant asbestos rubber sheet is several times higher than that of ordinary asbestos rubber sheet, so it is not suitable to be used in non-oil medium. Gasket in oil and solvent media will occur in the swelling phenomenon, but within a certain range, the sealing performance is basically no effect. For example, No. 400 oil-resistant asbestos rubber sheet in room temperature aviation fuel for 24 hours immersion test, the requirements due to oil absorption weight increase shall not exceed 15%.
Domestic asbestos rubber sheet compared with foreign brand-name products still have a certain gap. A unit of statistics show that more than 350 ℃ in the oil medium, where the use of asbestos rubber sheets do not leak most of the imported products. Japan's petroleum industry standard JPI-7S-71 "petroleum industry asbestos rubber sheet use standard", the use of the period of about one year.
