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Gasket Medium Pressure System Or Require A Higher Occasion
Aug 09, 2017

Gasket is the most critical link that affects the sealing performance of the joint. Flanges and bolts are designed to ensure that the gasket is operated in the most suitable condition. Therefore, the sealing performance of the flange joint should be considered first.

For a long time, China has not quantified the leakage rate as a major factor affecting the safety of pressure vessels and pipelines, and the selection of gasket material has not been paid attention to. Some devices in the selection of gasket also have many errors:

⑴ asbestos rubber sheet as a universal gasket, do not consider the use of conditions and widely used. In fact, the asbestos rubber sheet is made of asbestos fiber and other rubber and other adhesives after mixing, is a porous non-metallic materials, and with the composition of the variety and ratio is different, its performance is very big.

China's asbestos rubber sheet standard has two, that is GB3985-2008 "asbestos rubber sheet" and GB539-2008 "oil asbestos rubber sheet", for a long time we mistakenly believe that asbestos rubber sheet can be used to 450 ℃, 6MPa (XB450), regardless Steam systems, hydrogen systems, oil systems can be used universally. In fact, the use of asbestos rubber sheet in foreign countries have strict restrictions, such as the United States DuPont regulations flammable media shall not use asbestos rubber sheet, because in the event of fire, the use of asbestos rubber sheet flange joints is difficult to ensure that no secondary leakage The Japan "asbestos rubber sheet for petroleum industry" standard provides flammable and toxic gas asbestos rubber sheet conditions for the 0 ~ 260 ℃, ≤ 1.0MPa, water, air, water vapor is -50 ~ 260 ℃, ≤ 3.0MPa. Moreover, the foreign standards of asbestos rubber sheet performance requirements than the domestic similar products to be high.

    ⑵ thick gasket better than thin pads. In fact, the asbestos rubber sheet is a porous material, the thicker the gasket, the higher its permeability, in order to ensure a higher seal, you must apply a greater pressure than the thin pad, in order to its core Leakage rate is reduced, so the thick gasket is greater than the required tightening force for the pad. For the macromolecule liquid such as water, the leakage rate through the pad core is small and the thickness has little effect. Usually the thick gasket is only a larger flange diameter, consider the use of sealing surface wave or scoop. Generally its thickness in turn using 0.81,0.6,3.2 mm.

The width of the gasket is not the wider the better, on the contrary, the appropriate narrow can improve its seal than the pressure. But non-metallic gasket to ensure a certain width is necessary, one can control the internal leakage, the second is not to make the compression force is too large, the gasket crushed.

⑶ metal wound pad is now often used in a semi-metal pad. It is usually from about 0.2mm V-shaped metal belt and non-metallic band (such as tetrafluoroethane, graphite, etc.) wound, non-metallic belt generally outcropping a few millimeters to form a non-metallic sealing layer on both sides of the surface. Metal wound pad is characterized by high strength, good elasticity, anti-leakage, high temperature. So the winding pad for medium pressure system or require a higher occasion. But in use, there will be no inner and outer ring of the gasket for the plane of the situation, because the inner and outer ring positioning, reinforcement (under the action of the compression force will not collapse), control the compression force Role, when the flange sealing surface is flat, such as the use of the winding pad without the inner and outer ring, easy to make the gasket crush, so that sealing failure.

  The gasket is installed in the middle of the bushing and bushing of the sealing tape (or stationery tape), and there is no stationery gasket or sealing gasket. The inner diameter has a protruding position and is mounted on the take- So that the speed of the gasket is synchronized with the speed of the take-up reel, and the tape after the cutting is smoothly and neatly wound around the paper tube (or plastic core) on the take-up shaft.

The gasket is mounted in the middle of the bushing and bushing of the take-up shaft, not only to prevent the stiffening of the bushing on the bushing, but also to match the speed of the bushing with the take-up shaft to achieve the slit Wrap on the liner of the bushing.