Commonly used gasket performance --- and new materials and new technologies


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Commonly used gasket performance --- and new materials and new technologies
A) Common gasket performance

Use of the valve, often depending on the circumstances, the replacement of the original with washers. Often washer: flat rubber gasket, rubber O-ring, plastic flat washers, PTFE package washers, asbestos rubber gasket, metal flat washer shaped, metal gaskets, metal foreskin washers, wave washers, spiral wound gasket and so on.

(1) rubber flat washers: deformed easily, effortlessly when pressed, but the pressure, temperature capabilities are poor, only for low pressure, high temperature. Natural rubber acid and alkali resistance, the temperature should not exceed 60 C; neoprene and ability to pH, use temperature of 80 C; nitrile rubber oil, can be used to 80 C; good corrosion resistance of Viton, temperature performance than ordinary rubber, can be used in medium 150 .
(2) rubber O-ring gasket: cross sectional shape is a perfect circle, the Self-tightening effect, seal better than the flat washer, the pressing force is smaller.

(3) plastic flat washers: the biggest characteristic of the plastic is corrosion resistance, most of the plastic heat resistant performance is not good. PTFE plastic for the crown, not only excellent corrosion resistance, and relatively wide temperature range, -180 ~ +200 C long-term use.

(4) PTFE package washers: In order to give full play to the advantages of PTFE, and at the same time compensate for the shortcomings of its less flexible, made of PTFE covered with rubber or asbestos rubber gasket. In this way, both with PTFE flat washers, like corrosion resistance and good flexibility, and enhance the sealing effect, reduce the pressing force. Its cross sectional shape shown in Figure 4-20.

(5) Asbestos rubber gasket: cut by asbestos rubber sheet. Its components is 60 to 80 percent asbestos and 10 to 20 percent of the rubber, as well as fillers, curing agents. It has good heat resistance, cold tolerance, chemical stability, and supply abundant and cheap. When used, the pressing force does not have to. Adhesion of metal because of it, so it is best coated with a layer of graphite, in order to avoid the demolition effort.

Asbestos rubber sheet, there are four colors: gray for low voltage (grades XB-200, the pressure of 16 kg / square cm, the temperature of 200 C); red for medium voltage (grades XB-350, the pressure up to 40 kg / square cm, temperature of 350 C); purple for high pressure (grades XB-450 pressure of 100 kg / square cm temperature 450 C); green for oil, the pressure resistance is also very good .

(6) metal flat hot laps: Lead, temperature 100 C; aluminum 430 C; copper 315 C; 550 C low carbon steel; silver 650 C; Nickel 810 C; monel (nickel-copper) alloy 810 C, stainless steel 870 C . Which lead pressure less capable, the aluminum can withstand 64 kg / square cm, and other materials that can withstand high pressure.

(7), metal opposite washers:

Lens gasket: Self-tightening effect, the use of high-pressure valve.
Oval washer: a high-pressure self-tight gasket.
Cone washers: for high-pressure self-tight seal.

In addition, square, diamond, triangular, toothed, dovetail shape B, C-shaped, etc., generally in the high pressure valve.

(8) metal the foreskin washer: metal has good temperature pressure resistance and good flexibility. The foreskin materials are aluminum, copper, mild steel, stainless steel, Monel alloy, etc.. Inside the filler material asbestos, PTFE, glass fiber.

Wave washer (9): a small compaction force, the sealing effect is good. Often used in the form of metal and nonmetal combination.

(10) wound gasket: a thin metal band and non-metallic belt close together, wound into a multi-layered circular section wavy, have a good flexibility and sealing. Metal band available to the production of steel 08, 0Cr13 1Cr13, 2Cr13, 1Cr18Ni9Ti, copper, aluminum, titanium, Monel alloy and so on. Non-metallic belt materials such as asbestos, PTFE.

More about the gasket performance, some relevant figures. Have to say that these figures have a close relationship with the flange forms of media situation and install the repair technology, can sometimes exceed, and sometimes reach, and the pressure and heat resistance, but also transformed into each other, such as high temperature resistance, The pressure capacity is often reduced, these subtle problems can only realize in practice.

B) new materials and new technologies
The gasket described above is far from comprehensive, Moreover, the sealing technology is in rapid development. The following are examples of the introduction of several new materials and new technologies.

Liquid seal (1): With the rapid development of polymer organic synthesis industry, in recent years, liquid sealant, for use in static sealing; this new technology, often called liquid seal. The principle of the liquid seal, liquid sealant adhesion, mobility and single-molecule membrane effect (the thinner the membrane Replies natural tendency of the greater) at the appropriate pressure to make it work like washers. Therefore, the use of sealants, also known as liquid gaskets.

(2) Teflon seal: PTFE is also a high molecular organic compounds, it is sintered into products before, called the raw material, texture soft, monolayers effect. Band called the raw material made of raw material, can be rolled into long-term preservation. Free to use shape, any connector, as long as a pressure, they form a uniform to play a role in sealing the annular membrane. The washer of the valve body and bonnet, in the case without removing the valve or gate, forced open a gap, into the raw material brought on line. Pressing force is small, sticky, non-stick flange surface, very easy to replace. Most suitable for tongue and groove flange. Teflon, can also be made of tubular and rod for sealing.

(3) hollow metal O-ring: good elasticity, the pressing force is small, since the tight role, you can choose a variety of metal materials, which can adapt to low temperature, high temperature and strong corrosive medium.

(4) graphite boards seals: in people's impression, graphite is a brittle material, lack of flexibility and toughness, but specially treated graphite is soft and good elasticity. In this way, heat resistance and chemical stability of the graphite gasket material to be displayed; and this gasket compression force, the sealing effect is very favorable. This graphite can be made with, with the metal band with composition of the performance wound gasket. Graphite plates and graphite seals ---- the metal spiral wound gasket, is a major breakthrough in high-temperature corrosion-resistant seal. This type of washer, foreign mass production and use



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