1. Types and Applications of Sealing Materials
Sealing materials must meet the functional requirements of sealing. Due to variations in the media being sealed and the different operating conditions of equipment, sealing materials must possess different adaptabilities. In general, the requirements for sealing materials include:
1. Good material density to prevent leakage of media
2. Adequate mechanical strength and hardness
3. Good compressibility and resilience, with minimal permanent deformation
4. No softening or decomposition at high temperatures, and no hardening or cracking at low temperatures
5. Excellent corrosion resistance—able to work in media like acids, alkalis, and oils over long periods with minimal volume and hardness changes, and without sticking to metal surfaces
6. Low coefficient of friction and good wear resistance
7. Flexibility to conform to sealing surfaces
8. Excellent aging resistance and long service life
9. Ease of processing and manufacturing, cost-effectiveness, and ready availability
Rubber is the most commonly used sealing material. In addition to rubber, other suitable sealing materials include graphite, polytetrafluoroethylene (PTFE), and various sealants.
2. Common Rubber Materials for Sealing Products
General-purpose rubber sealing products are increasingly used across national defense, chemical industry, coal mining, petroleum, metallurgy, transportation, and machinery manufacturing. They have become fundamental components and accessories in various industries. Common rubber materials used for sealing products include:
2.1 Nitrile Rubber (NBR)
Nitrile rubber offers excellent resistance to fuel oils and aromatic solvents, but it is not resistant to ketones, esters, or hydrochloric acid. Therefore, oil-resistant sealing products primarily use nitrile rubber.
2.2 Neoprene Rubber (CR)
Neoprene has good oil and solvent resistance, particularly to gear oils and transformer oils, though it is not resistant to aromatic oils. It also boasts excellent resistance to weathering and ozone aging. Its crosslinking breakdown temperature is above 200°C. Neoprene is commonly used in door and window sealing strips and is resistant to inorganic acids. Its good flexibility and gas impermeability also make it suitable for diaphragms and vacuum sealing products.
2.3 Natural Rubber (NR)
Compared with most synthetic rubbers, natural rubber has excellent overall mechanical properties, good low-temperature resistance, high elasticity, and wear resistance. It is not resistant to mineral oils but is relatively stable in vegetable oils and alcohols. Natural rubber is commonly used in hydraulic braking systems with butanol-castor oil-based brake fluids and is also widely used in general-purpose sealing adhesives.
2.4 Fluororubber (FKM)
Fluororubber is known for its outstanding heat resistance (200–250°C) and oil resistance. It is used for manufacturing cylinder liner seals, diaphragms, and rotary lip seals, significantly improving service life.
2.5 Silicone Rubber (VMQ)
Silicone rubber offers excellent resistance to extreme temperatures, ozone, and weathering. It retains elasticity and other properties within a wide operating temperature range of -70°C to 220°C. It is ideal for heat-resistant sealing applications such as sealing rings for high-intensity lamp housings and valve gaskets. However, it is not oil-resistant, has low mechanical strength, and is expensive—making it unsuitable for oil-resistant applications.
2.6 Ethylene Propylene Diene Monomer Rubber (EPDM)
EPDM features a fully saturated linear main chain structure without double bonds, and diene groups on its side chains allow for sulfur vulcanization. It has excellent aging resistance, ozone resistance, weatherability, heat resistance (usable up to 150°C), and chemical resistance (e.g., to alcohols, acids, strong alkalis, and oxidants). However, it is not resistant to aliphatic or aromatic solvents. EPDM has the lowest density among rubbers and can be highly filled but lacks self-adhesiveness. It also has excellent steam resistance, making it suitable for steam-resistant diaphragms. EPDM is widely used in parts for washing machines, TVs, and door/window seals, as well as in multi-component rubber strip production.
2.7 Polyurethane Rubber (PU)
Polyurethane rubber has excellent wear resistance and good impermeability. Its usable temperature range is typically -20°C to 80°C. It also offers moderate oil, oxygen, and ozone resistance but is not resistant to acids, alkalis, water, steam, or ketones. It is suitable for manufacturing various sealing products such as oil seals, O-rings, and diaphragms.
2.8 Epichlorohydrin Rubber (ECO)
Epichlorohydrin rubber combines the advantages of nitrile, neoprene, and acrylate rubbers. It offers excellent resistance to oil, heat, ozone, flame, alkalis, water, and organic solvents, along with good processing properties. Its low-temperature resistance is relatively poor. When not exposed to extreme cold, ECO is still an excellent material for manufacturing oil seals, sealing rings, gaskets, diaphragms, and dust covers.
2.9 Acrylate Rubber (ACM)
Acrylate rubber is resistant to hot oils (including mineral oil, lubricants, and fuels), especially at high temperatures, typically up to 175°C, and short-term exposure up to 200°C. Its drawback is poor low-temperature resistance. Therefore, it is suitable for high-temperature oil-resistant seals in non-cold environments, but not for applications involving stretching or compressive stress under high temperatures.
