The gasket is a mechanical seal between two objects, and is often used to prevent pressure, corrosion, and piping from spontaneous expansion and contraction between two objects. As the machined surface can not be perfect, use the gasket to fill the irregularity.
Proper use of gasket is the key to ensuring that equipment is not leaked. For the same conditions, there are generally a number of gaskets to choose from. Must be based on the physical properties of the media, pressure, temperature and equipment size, operating conditions, the length of continuous operation cycle, etc., a reasonable choice of gasket, avoid weaknesses, give full play to the characteristics of various gaskets.
1, the choice of the correct choice of gasket is to ensure that the equipment is no key to leakage. For the same kind of conditions, there are generally a number of mats. When selecting a gasket, the following factors should be taken into account:
(1) have good flexibility and restorability, can adapt to pressure changes and temperature fluctuations;
(2) with appropriate flexibility, with the contact surface is a good fit;
(3) does not pollute the process medium;
(4) have sufficient toughness without causing breakage due to pressure and tightening forces;
(5) do not harden at low temperature, shrinkage is small;
(6) processing performance is good, easy to install, compact;
(7) non-adhesive sealing surface, easy to disassemble;
(8) cheap, long service life.
In the use of gasket, the pressure and temperature are mutually constrained, with the temperature rise, the equipment running for some time, the gasket material softening, creep, stress relaxation phenomenon, mechanical strength will decline, The pressure of the seal is reduced. vice versa. For example, the manual listed high pressure asbestos rubber sheet XB450 in water, steam medium, the use of temperature 450 ℃, pressure <6MPa (the material for the sealing performance test, in the 440 ℃ ~ 450 ℃, 12MPa steam for 30 minutes) The But in the long-term practical use, the temperature reached 450 ℃, can seal the pressure of only 0.3 ~ 0.4MPa. For the strong permeability of the gas medium is only 0.1 ~ 0.2MPa.
The above situation should be taken into account in the selection.
The price is lower than other gaskets, easy to use; the biggest problem is: gasket material, although the addition of rubber and some fillers, still can not be filled with those tiny pores completely filled, there is a trace of penetration. Therefore, in highly polluting medium, even if the pressure, the temperature is not high can not be used. When used in some high-temperature oil medium, usually in the late use, due to rubber and filler carbonation, reduced strength, material becomes loose, then the interface and the gasket inside the penetration, coking and smoke phenomenon. In addition, asbestos rubber sheet at high temperatures easily bonded to the flange sealing surface, to replace the gasket brought a lot of trouble.
In the heated state, the use pressure of the gasket in the various media depends on the strength retention of the gasket material. Asbestos fiber material exists in the crystal water and adsorption of water. 110 ℃, the adsorption of water between the fiber has 2/3 precipitation, the tensile strength of fiber reduced by about 10%; 368 ℃, the adsorption of water all precipitation, fiber tensile strength reduced by about 20%; more than 500 ℃, Crystal water began to precipitate, the intensity is lower. The effect of medium on the strength of asbestos rubber sheet is also great.
All gaskets are sealed and leaked when the gasket is sealed. Ideally, good sealing performance can reduce product loss, improve safety and save costs. If the gasket has been leaked at room temperature, then the situation at high temperatures may be more serious. You can use 0.8mm thick gasket test. The thinner the gasket, the better the sealing capacity, because the media can pass through the less part of the material. Practical applications in the selection of a lot of 1.5mm or 3mm thickness of the gasket, coupled with the impact of temperature, so the leakage rate is higher. If the medium is a gas, then the leakage rate is higher because the molecules of the gas are smaller and easier to pass through the gasket and the gasket.