Guide to use different types of sealing gaskets

Selection of Sealing Gaskets (1) Natural rubber sealed sheets are ideal for water, seawater, air, inert gases, alkalis, salts, and aqueous solutions, but they are not resistant to mineral oils or non-polar solvents. They can be used up to a maximum temperature of 90°C, and offer excellent low-temperature performance, working effectively down to -60°C. Nitrile rubber is suited for petroleum products like oil, lubricants, and fuel. It can operate continuously at 120°C, and can handle temperatures up to 150°C in hot oil environments, with a lower temperature limit of around -10 to -20°C. Neoprene is suitable for seawater, weak acids, weak bases, and salt solutions. It has good resistance to oxygen and ozone degradation, performing better than general rubbers but slightly worse than nitrile rubber. Its long-term use temperature is below 90°C, with a maximum operating temperature of 130°C, and a low-temperature range of -30 to -50°C. Fluorocarbon elastomers, available in many variations, are resistant to acids, oxidants, oils, and solvents. They work well in nearly all acidic media and some oils and solvents, with a continuous operating temperature of up to 200°C. As flange gaskets, rubber sheets are commonly used in frequently dismantled pipe or manhole/hand hole connections, with pressures not exceeding 1.568 MPa. Rubber gaskets are soft and provide good conformity, enabling effective sealing with minimal preload force. However, they can be easily extruded due to their thickness or low hardness. When exposed to organic solvents like benzene, ketones, and ethers, rubber sheets tend to swell, increase in weight, soften, and become sticky, leading to seal failure. Swelling over 30% is generally unacceptable. For low-pressure (below 0.6 MPa) and vacuum conditions, rubber gaskets are more appropriate. They offer good density and low permeability. Fluorocarbon elastomers, for instance, are suitable for sealing vacuum containers up to a vacuum degree of 1.3 × 10⁻⁷ Pa. At ultra-high vacuum levels (10⁻¹ to 10⁻⁷ Pa), rubber gaskets need to be baked and degassed before use. Asbestos rubber sheets are economical and user-friendly but have limitations. Despite adding rubber and fillers, they cannot fully seal micro-pores, leading to minor leaks. This makes them unsuitable for highly polluting media, even at moderate pressures and temperatures. In high-temperature oil applications, the rubber and fillers may carbonize over time, reducing strength and causing leaks and smoke. Additionally, asbestos rubber sheets can bond to flange surfaces at high temperatures, complicating gasket replacement. (2) Synthetic fiber rubber sheets are eco-friendly, heat-resistant, and pressure-resistant, offering broad media compatibility. Bode synthetic fiberboards can withstand pressures up to 120 bar and temperatures ranging from -200°C to 800°C. Sealing performance can be tailored based on specific conditions, making them a popular choice in the sealing industry. (3) Polytetrafluoroethylene (PTFE) tends to deform under high pressure and temperature due to cold flow and creep. Thus, it’s typically used in low-pressure, medium-temperature environments with strong corrosives or where contamination must be avoided, such as strong acids, bases, halogens, and pharmaceuticals. Its safe operating temperature is 150°C with a pressure limit below 1 MPa. Filled PTFE has higher strength, but its operating temperature does not exceed 200°C, and its corrosion resistance diminishes. The maximum pressure for PTFE gaskets rarely exceeds 2 MPa. (4) Asbestos resin sheets and non-asbestos impregnated gaskets are widely used in pipelines, pumps, valves, and flanges handling various acidic media. These gaskets are suitable for temperatures up to 80°C and pressures below 0.6 MPa. (5) Metal-clad asbestos gaskets involve coating an asbestos board or rubber sheet with a thin metal layer, preventing direct contact with the medium. This enhances strength and prevents leakage, expanding the use of asbestos rubber sheets. Metal-clad asbestos gaskets can operate at temperatures up to 450°C (some up to 600–700°C, e.g., in flue gases under normal pressure ~0.16 MPa) and pressures up to 4 MPa, with a maximum of 6 MPa. However, higher pressures risk cross-flow and core material extrusion. Since these gaskets require significant bolt tightening forces, flanges below pg 25 kg cannot be used at pressures less than 2.45 MPa. Insufficient flange and bolt stiffness could lead to deformation and sealing failure. Replacing the core material with elastic synthetic rubber reduces tightening requirements, but this is ineffective since the force is absorbed by the core, damaging the gasket. Moreover, in chloride-rich and acidic media, the overlap between stainless steel and iron pads can cause crevice corrosion. (6) Metal flat gaskets, corrugated gaskets, and toothed gaskets are typically used on medium-to-high-pressure valves, pipes, and small-diameter equipment flanges. Pressure depends on temperature: flat gaskets range from 1.568 to 31.36 MPa, while corrugated gaskets range from 1.568 to 3.92 MPa. Material selection depends on the medium and temperature. (7) Octagonal and elliptical gaskets excel in trapezoidal groove flanges and elliptical groove flanges (commonly called “oil rings” in the refining industry). Octagonal gaskets achieve surface contact, while elliptical gaskets create line contact. Elliptical gaskets seal well under low tightening forces but require two passes, whereas octagonal gaskets usually seal after one tightening. Both require high bolt tightening forces. In low-pressure, high-temperature conditions, the flange must be rated at pg25 kg or higher. In conclusion, selecting the right gasket involves balancing material compatibility, temperature, pressure, and environmental factors.

Aluminum External Door

External aluminium sliding door,aluminum glass door,aluminium and glass sliding door

SMIRO DOORS AND WINDOWS CO., LTD , https://www.smirowindows.com