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2013年7月4日星期四

Metal gasket types and selection

Including metallic flat gasket metal gasket, wave washer and toothed washers. Metal flat pad and metal pad is generally used in high-voltage waveform valves smaller diameter pipes and equipment Metal Jacketed Gasketsflange. The use of pressure, the former is 1.568 a 31. 36MPa, which is 1.568 a 3. 92MPa, gasket material based on medium and temperature selection.

Metal toothed flange gasket sealing surface in easily after leaving indentations, it is generally used for removing small parts. Use a pressure of 1.96 MPa-19.6MPa. In some of the removable large pressure vessel manholes, upholstered cushion layer of paste on both sides, such as high pressure asbestos rubber sheet, flexible graphite gaskets, aluminum, copper, etc., not only protects the flange sealing performance has improved markedly . The reason is that this combination depends mainly on the cushion pad tooth preload generated when the plastic deformation after compression flange contact with one side is flat, the other side is the tooth shape. Crimping part of the tooth tip thickness only 0.1 a 0.25rnm, plastic flow of the gap is very small, with sharp teeth to bite, flat pad is difficult to produce plastic flow, to maintain a high sealing pressure. Toothed washer in addition to increasing the elasticity of combination pad, but also serve to strengthen the role for upholstered pieces, resulting in lower strength of such asbestos rubber gasket material can withstand high pressure.

Octagonal oval metal gaskets and Reinforced Graphite Gasketmetal gaskets. Trapezoidal groove flange for octagonal pad (octagonal cross-section of the sealing ring) and metal oval gasket sealing ring [oval cross-section, the refining industry known as "soil Rims") are better sealing performance of the trench mouth cone, octagonal and oval gasket surface contact pads is line contact. Thus, in a small oval pads fit under the tightening force is good, but need a second fastening, and octagonal gasket once tightened, they are less prone to leaks inadequacies as requiring transfer large bolt tightening force.

In accordance with the selection criteria gaskets, steel mats are used at temperatures above 450'C, pressure 6.27 a 15. 88MPa occasions. However, recently it is used extensively for the refining industry to shift higher than 350 ℃, the low-pressure sealing parts.Spiral Wound Gaskets A unit conducted a survey, at atmospheric pressure 2.35 21MPa, temperature of 350 a 400Z ℃ oils medium, 83 a nominal diameter of 150 500mm flange gasket, steel mats (56.6%). Because this type of gasket than a predetermined temperature, low pressure range the case a "use, so good sealing performance, only the individual event of leakage, but such use is not entirely rational. Firstly, the choice often brings flange and rim Bolt upgrades as the original open trapezoidal groove on the flange, the flange stiffness reduction, flange and bolt deformation and stress concentration; Second, steel pad itself and the flange surface machining situation and smoothness requirements more high in the case of large diameter, quality assurance is not easy in the right machines, pumps, equipment flange machining trapezoidal slot, once the casting defects, it may cause the entire device scrapped; Third, compared with interchangeable rims pad poor, after fastening flange inevitably leave indentations. installation, if allowed, causing a leak off the bit, eliminating the indentation larger workload.

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