Advantages and applications of metal-coated asbestos pads?
The asbestos sheet or asbestos rubber sheet is covered by the metal sheet, so that it does not directly contact with the medium, avoiding the decrease of the strength of the asbestos fiber, and overcoming the leakage phenomenon, thereby expanding the scope of use of the asbestos rubber sheet.
The general metal-clad asbestos mats use temperature is 450 ℃ (individually up to 600 ~ 700 ℃, such as in flue gas at normal pressure ~ 0.16MPa), the operating pressure is 4MPa, up to 6MPa. If the pressure is increased again, the gasket is prone to cross flow, and the core material is extruded from the overlap.
Since metal-clad asbestos pads require a larger bolt tightening force, even when the operating pressure is lower than 2.45MPa, flanges below pg25 kg cannot be used. Otherwise, the rigidity of the flanges and bolts will be insufficient, and the deformation will cause the seal to fail. Some people think that if the core material is changed to synthetic rubber with better elasticity, its tightening force will decrease.
In fact, it is not true, because after the core material is changed to soft, the fastening force is absorbed by the core material, and the fastening force required for the metal plate to fit on the flange surface cannot be provided, and the packing is easily damaged. In addition, in media containing more chloride ions and acidic media, crevice corrosion is likely to occur at the overlap of stainless steel pads and iron pads.
If the temperature is higher than 450 ℃, ceramic fiber or carbon fiber can be used for the core material. A steel plant uses metal-clad ceramic fiber gaskets for high temperatures of 1100 ° C and has not been damaged for two years. Flexible graphite is the most suitable core material. At present, domestic production of metal-coated flexible graphite mats has been mass-produced. Its use effect is better than the metal asbestos pad.
The metal packing can be made into various shapes, and is widely used in various heat exchangers, large cover of reactor, loading and unloading hole, manhole flange, etc. I have produced iron-clad pads with a diameter of 2m in China, which are in good use.
A layer of flexible graphite sheet is affixed to the surface of the metal cladding. Compared with similar metal claddings which are not coated on the surface, this type of gasket has a lower preloading ratio and better sealing performance.