Common forms of flange sealing surfaces
The sealing surface of the flange is a smooth plane, and sometimes there are two concentric circular grooves (commonly known as water lines) with a triangular interface on the sealing surface. As shown in Figure 3-1 (a).
Sealing surface of flat flange
The gaskets for flat flanges are available in a variety of non-metallic flat washers, wraps, metal wraps, and wrap-around gaskets (with either inner or outer rings or inner and outer rings). The utility model has the advantages of simple structure, convenient processing and convenient construction of the anticorrosive lining, so it can be used when the nominal pressure p < 2.45 MPa. It is especially suitable in places with low temperature below 0.588MPa, but the contact area between the sealing surface and the gasket is large (especially for wide flanges for pipelines). The required pressing force is large, and the gasket should not be positioned during installation. . After preloading, the gasket is easy to stretch or move to both sides. Therefore, if the friction coefficient is small, such as PTFE, it is not suitable to use this kind of sealing surface. In addition, if a wound gasket is used, in order to reuse the gasket, the triangular groove is not formed on the sealing surface.
2. Concave surface flange
The flange sealing surface is composed of a concave surface and a convex surface, and the gasket is placed in the concave surface. The gaskets suitable for use as shown in Figure 3-1(b) are: various non-metallic flat pads, covering pads , metal pad, wound gasket (basic or with inner ring), metal wave pad, metal flat pad, metal toothed pad.
Compared with the flat flange, the gasket in the concave-convex surface flange is not easy to be extruded, and it is easy to center during assembly. The working pressure range is wider than that of the flat flange, and it is used for the occasion where the sealing requirements are strict. However, for equipment with a high operating temperature and a large sealing diameter, when the sealing surface is used, the gasket may still be extruded. For example, a heat exchanger, a pressure of 2.45 MPa, a temperature of 250 ° C, using a pure aluminum flat gasket. According to the data provided in Table 2-2, the maximum use temperature of pure aluminum is 425 ° C, and the seal should be reliable. In fact, the heat exchanger leaks shortly after it is put into operation, and it only lasts for a while after the second tightening. After parking inspection, it was found that the inner diameter of the gasket was significantly deformed. The reason is that the plasticity of pure aluminum is good, the yield strength at 250 ° C is about 15% at normal temperature, and the elongation is as high as 4 to 5 times, which means that the aluminum pad is calendered at a high temperature, and the creep phenomenon is serious. Therefore, the required sealing pressure cannot be maintained between the gasket and the flange surface, so the gasket material must be replaced or a grooved flange and a concave-convex flange with two stops (such as a high-pressure seal, metal) The flange face of the flat pad is solved).
3. Grooved surface flange
The flange sealing surface is composed of a groove surface and a groove surface, and the gasket is placed in the groove, as shown in Figure 3-1(c). The gasket is: metal and non-metal flat pad, metal pad , winding mat (basic type) and so on. Like the concave-convex flange, the groove surface flange is not extruded in the groove, and the pressing area is the smallest (only 52 to 68% of the flat flange and the concave-surface flange), and the gasket is evenly stressed. Since the gasket is not in direct contact with the medium, the influence of the corrosion of the medium and the penetration of the pressure mechanism is minimal, and it can be used in places where the sealing requirements such as high pressure, flammability, explosiveness, and toxic medium are strict. The sealing surface gasket is good for neutral installation, and the sealing surface processing and gasket replacement are difficult.
4. Other sealing surface type flange
In addition to the above three sealing surface types, there are also trapezoidal groove sealing faces, and the special sealing surface type with ø-ring and lens pad is shown in Figure 3-2.
Figure 3-2 (a) shows the form of a sealing surface using a rubber o-ring and a metal hollow o-ring.
Figure 3-2 (b) is a trapezoidal groove sealing surface, which can be equipped with a metal octagonal pad and an elliptical pad.
Figure 3-2(c) shows the lens pad seal structure for the connection of high pressure pipes.