Industrial Gaskets

There are many types of gasket, such as Industrial Rubber Sheet, Asbestos Rubber Sheet, PTFE Gasket,  Spiral Wound Gasket and so on.

Industrial Rubber Sheet

Natural Rubber

Natural rubber is suitable for water, seawater, air, inert gas, alkali type, salt water solution and other media, but not resistant to mineral oil and non-polar solvents. The working temperature is no more than 90 ℃ for long-term usage. Low temperature application can reach above -60 ℃.

NBR

NBR applies to petroleum products, such as oil, lubricants, fuel oil, etc.. Working temperature for long-term use is 120 ℃. But in hot oil it can withstand 150 ℃. Low working temperature is -10~-20℃.

Neoprene

Neoprene is suitable for seawater, weak acid, weak alkali, salt solution. It has excellent oxygen-resistance and ozone aging performance. The oil-resistance is secondary to nitrite rubber but better than other general-purpose rubbers. Working temperature for long-term use is less than 90 ℃, the maximum working temperature of not more than 130 ℃, lower working temperature is -30~-50℃.

Fluorine Rubber

Fluorine rubber has a number of varieties. They have good acid resistance, oxidation resistance, oil resistance,and solvent resistance. They may suit for all acid media and some oil or solvents media, working temperature for long-term use is less than 200 ℃.

Rubber Sheet

As a flange gasket, the rubber sheet is used for the pipe or the manhole, hand hole, and the pressure is no more than 1.568MPa. Among various gaskets, the rubber gasket is the softest, has good laminating performance. Under small pre-tension, it can play the sealing role. But when it is subjected to internal pressure, it is easily extruded because the gasket is too thick and has low hardness. Rubber sheet appears swelling, weight gain, soft, sticky in organic solvents like benzene, ketone, and ether, which can lead to sealing failure. General speaking, it should be replaced when the swelling degree is more than 30%.

Conclusion

Rubber cushion is more suitable in the low pressure (especially under 0.6MPa), and vacuum condition. The rubber material has good compactness and low permeability. For example, fluorine rubber, the most suitable gasket for vacuum container sealing, the highest degree of vacuum can reach 1.3×10-7pa. The rubber cushion is used in the 10-1~10-7PA vacuum range and is processed by baking and gas extraction.

 

Asbestos Rubber Sheet

Polluting Medium

It is the most cheaper gasket and is convenience. The biggest problem of this gasket is its materials. Although it contains rubber and some fillers, it still can not fully fill the small pores of the collusion, then leads to the traces of infiltration. Therefore, with a highly polluting medium, even if the pressure, temperature is not high it can not be used.

High-Temperature Oil Medium

In some high-temperature oil medium, the rubber and filler will be carbonizationin late period, so strength becomes less and material becomes loose, then in the interface and gasket internal will find infiltration, coking and smoke phenomenon happens. In addition, asbestos rubber board is easily bonded to the flange sealing surface at high temperature, causing a lot of troubles to replace the gasket.

Heating Condition

Under the condition of heating, the pressure of the gasket in different mediums depends on the strength retention rate of the gasket material.

Crystalline water and adsorbed water exist in the asbestos fiber.

• At 110 ° C, 2/3 adsorbed water precipitated. Fiber tensile strength is about 10%.
• At 368℃, adsorbed water all precipitated. Fiber tensile strength reduces about 20%.
• More than 500 ℃, crystalline water began to precipitate. The intensity is lower.

Dielectric

The dielectric also has a great influence on the strength of the asbestos rubber sheet.

For example, applied NO. 400 oil-resistant asbestos rubber sheet to aviation lubricants and aviation fuels, the horizontal difference of tensile strength is 80%. This is due to the plate rubber is easier swelling in aviation fuel.

Taking into account the above factors, the recommended safe usage range of domestic asbestos rubber sheet XB450 is

• Temperature 250℃~300℃,
• Pressure 3~3.5mpa;
• Working temperature of 400 oil-resistant asbestos rubber plate should beside 350 ℃.

Oil Medium

Asbestos rubber sheet containing chloride ions and sulfides, easily absorbs and rusts with metal flanges after water absorption. Especially the oil-resistant asbestos rubber plate has several times the sulfur content of the ordinary asbestos rubber plate, is not suitable for the Non-oil medium application. Swelling will occur in oil and solvent medium, but it has no impact on sealing performance.

For example, soaking the NO. 400 oil-resistant asbestos rubber sheet in aviation fuel at ambient temperature for 24 hours, the oil absorption does not exceed 15% of the weight that requirement. To be honest, there is a gap between domestic asbestos rubber plate and foreign famous brand products. Statistics show that in petroleum media application above 350 °C, the asbestos rubber sheets are mostly imported.

PTFE Gasket

PTFE is prone to occor cold flow and creep under high pressure and high temperature. It is generally common for low pressure, medium temperature and strong corrosion conditions. It is not allowed to contact with contaminated media, such as acid, alkali and drugs.

Safe usage condition is under temperature 150 ℃, pressure 1Mpa. Although the strength of PTFE filler is higher, but the working temperature is no more than 200 ℃.

The Maximum working pressure is generally no more than 2MPa. With increas of temperature, the decline of sealing pressure is obviously. Even if without heating, the compressive stress of sealing surface will decrease with the prolonging of time, resulting in “stress relaxation phenomenon.” This phenomenon is general actually, but PTFE gasket ismore serious and attracts you attention.

PTFE Gasket Application

The friction coefficient of PTFE is small (the compression stress is greater than 4MPa, the friction coefficient is 0.035~0.04). So the gasket is easy to slip when preloading, and the concave flange surface is the best choice.

When the plane flange is adopted, the outside diameter of gasket can be contacted with bolts, in order to prevent the gasket from slipping. Because the glass-lined is sprayed on the surface with a brittle glaze layer, and the spraying may be uneven and the glaze layer will flow, so the surface is irregularity.

Metal composite gaskets would damage the glaze layer, so it is recommended to adopt PTFE gasket with . This kind of cushion is easy to match with the flange surface with corrosion resistance. It is popular because of the easy production and usage.

 

Asbestos Resin Board and Impregnated Asbestos Sheet Gasket

It is used for a variety of acidic media pipelines, pumps, valves, import and export flange, the use of temperature in 80 ℃, pressure under 0.6MPa. The Asbestos preparation gasket is suitable for under the pressure 0.1MPa, the temperature does not surpass 800 ℃ low pressure, the high temperature working condition. And according to the specific requirements of equipment, woven into the width, thickness, diameter of the gasket. or cut the asbestos strip directly to the flange surface. The working fields are large sulfuric acid, nitric acid oxidation furnace and some raw equipment interface, the effect is far more than the original asbestos rope.

Spiral Wound Gasket 

Spiral Wound Gasket skillfully utilizes the heat resistance, resilience and strength of the metal and the softness of non-metallic materials. So it has better sealing performance, and the performance of the stainless steel tape winding Flexible graphite mat is the best.

The metal strip uses 0cr13 more often, while the other media is 1cr18ni9ti.

Gas Medium

In the gas medium it usually uses stainless steel with flexible graphite winding pad, working pressure is 14.7MPa (domestic is up to 19.6MPa).

Liquid Medium

In the liquid, the pressure can be 30Mpa, temperature is -190~ 600 ℃ (available to 1000 ℃ in the case of anaerobic and low-pressure).

Low-Temperature Medium

The low-temperature resistance of PTFE is good. Its yield strength at low temperature is much higher than that at ambient temperature. Therefore, PTFE winding pad suits for low-temperature medium, such as liquid hydrocarbon. At the same time, due to the addition of metal belt to improve the thermal conductivity, PTFE winding pad working temperature is up to 250 ℃. And in the acidic medium it can be 9MPa, 200 ℃. The winding pad is suitable for the heat exchanger, reactor, pipe, and valve for pressure and temperature fluctuation system. For the conditions that more than 300 ℃, it is better use inner ring, outer ring or inner ring. If use concave-convex flange, the winding cushion effect is better with the inner ring.

Good Sealing Effect

It can get a good sealing effect by sticking flexible graphite plate on both sides of flexible graphite winding pad. The key equipment with high temperature and high pressure such as the waste heat boiler of a large chemical fertilizer plant, is better use gasket with flexible graphite winding pad with outer ring. It can prevent leakage when full and reducing load.

 

Octangon Gasket and Elliptical Gasket

The octagonal cushion and ellipse pad (commonly known as “Earth rims”) for trapezoidal groove flanges are well sealed. On the cone of the groove, the octagonal mat is contact with the surface and the ellipse pad is the line contact. Therefore, the ellipse cushion under the low fastening force of good adhesion, but need to carry out two times fastening, and the octagonal pad is generally once fastening, not easy to leak. Their deficiencies are to require a larger bolt tightening force, when use it in low temperature conditions, the flange grade must be above pg25 kg level