Oil seals, also known as sealing rings, are original components or parts used in industrial equipment to prevent lubricating oil leakage and foreign object intrusion. They are diverse in type and classification, commonly categorized by cross-sectional shape, material, and working condition.
1. Classification by Cross-sectional Shape:
O-rings: This is the most common type of sealing ring, with a circular cross-section. It features simple structure, easy installation, and good sealing performance, making it suitable for various static and low-speed dynamic sealing applications, such as pipe connections, valves, and pumps. O-rings are made from a wide variety of materials, allowing selection based on different working environments and media.
Y-rings: These have a cross-sectional shape resembling the letter "Y." The sealing lip of this type of ring has good mobility and adaptability, compensating for larger tolerances and angular deviations. It prevents internal grease or oil leakage and also prevents external splashes of water or dust intrusion. Y-rings are widely used in reciprocating motion sealing devices in hydraulic, mechanical, and pneumatic industries.
V-ring: An axially acting elastic rubber seal with good elasticity and sealing performance, suitable for pressureless sealing of rotating shafts. V-rings can compensate for larger tolerances and angular deviations, making them suitable for applications with high sealing requirements and complex operating conditions.
U-ring: With a "U"-shaped cross-section, U-rings are commonly used in reciprocating seals in hydraulic systems, widely applied in hydraulic cylinder seals in engineering machinery. U-rings offer good sealing performance and can withstand certain pressure and wear, but attention must be paid to orientation and position during installation.
X-ring: With a "X"-shaped cross-section, X-rings offer good sealing and wear resistance, suitable for applications with high sealing performance requirements. However, due to their relatively complex structure and difficulty in manufacturing and installation, their application range is relatively narrow.
L-ring: Generally used for sealing right angles or corners. Their shape adapts to corner structures, providing a good seal. For example, L-rings are used at corners of mechanical equipment and bends in pipelines.
**Star-shaped Seal Rings:** Also known as star-shaped rings, these are specially shaped seal rings composed of multiple sealing lips, resembling a star. They offer excellent sealing performance and elasticity, adapting to varying working pressures and temperatures. They are commonly used for sealing hydraulic cylinders, pneumatic cylinders, and other equipment.
**Hollow Tube Seal Rings:** These seal rings have a hollow internal structure, reducing material usage and cost while maintaining sealing performance. They are frequently used in applications with weight and space constraints, such as aerospace and medical devices.
**Irregularly Shaped Seal Rings:** These are non-standard shaped seal rings designed to meet specific sealing requirements of equipment or components. For example, irregularly shaped containers and pipe joints require irregularly shaped seal rings for sealing.
2. Classification by Material
**Natural Rubber Seal Rings:** These possess good wear resistance, elasticity, tensile strength, and elongation. However, they are prone to aging in air, become sticky when heated, and easily swell and dissolve in mineral oil or gasoline. They are alkali-resistant but not resistant to strong acids. Suitable for applications with low sealing requirements and relatively mild operating environments, such as general mechanical equipment and door/window sealing.
Nitrile rubber seals: These are currently the most widely used and lowest-cost rubber seals, suitable for use with petroleum-based hydraulic oils, glycol-based hydraulic oils, diester-based lubricating oils, gasoline, water, silicone greases, and silicone oils. However, they are not suitable for use in polar solvents such as ketones, ozone, nitro hydrocarbons, MEK, and chloroform. The general operating temperature range is -40℃ to 120℃.
Hydrogenated nitrile rubber seals: These have excellent corrosion resistance, tear resistance, and compression set resistance. They also have good ozone resistance, sunlight resistance, and weather resistance, and better wear resistance than nitrile rubber. Suitable for washing machines, automotive engine systems, and refrigeration systems using the new environmentally friendly refrigerant R134a. Not recommended for use in alcohol, ester, or aromatic solutions. The general operating temperature range is -40℃ to 150℃.
Silicone rubber sealing rings: These possess excellent heat resistance, cold resistance, ozone resistance, and atmospheric aging resistance, and have good insulation properties. However, their tensile strength is lower than that of ordinary rubber, and they lack oil resistance. They are suitable for household appliances such as electric water heaters, electric irons, and microwave ovens, as well as various items that come into contact with the human body, such as kettles and water dispensers. They are not recommended for use in most concentrated solvents, oils, concentrated acids, and sodium hydroxide. The general operating temperature range is -55℃ to 250℃.
Metal-rubber sealing rings: Made of stainless steel wire, these contain no rubber components and have strong performance characteristics, maintaining normal operation in environments such as high vacuum, high and low temperatures, strong radiation, and various corrosive conditions. The sealing ring skin is made of different materials depending on the application, such as stainless steel, copper, and polytetrafluoroethylene (PTFE). The encased metal-rubber component serves as the lining core, offering advantages such as high sealing strength, good performance, and reusability.
3. Classification by working state:
Static seals: The sealing part is stationary, such as pipe flanges, threaded connections, and seals between pressure vessels and covers. Static seals commonly use O-rings and rectangular sealing rings. Static seals require high performance in terms of compression and elasticity of the sealing ring to effectively prevent media leakage when stationary.
Gasket Materials
(1) Non-metallic materials: such as paper, hemp, leather, asbestos products, plastics, and rubber.
(2) Metallic materials: Generally, metallic materials have high strength and strong temperature resistance. Commonly used materials include brass, copper, aluminum, low-carbon steel, stainless steel, Monel alloy, silver, and nickel.
(3) Composite materials: such as metal-clad (internal asbestos) gaskets, combined corrugated gaskets, and spiral wound gaskets.
Common gaskets include: rubber flat gaskets, rubber O-rings, plastic flat gaskets, PTFE-clad gaskets, asbestos rubber gaskets, metal flat gaskets, shaped metal gaskets, metal-clad gaskets, corrugated gaskets, and spiral wound gaskets.
Dynamic seals: These seals involve relative movement between the sealing parts and can be divided into rotary seals and reciprocating seals. Rotary seals are commonly used for sealing rotating shafts, such as mechanical seals and oil seals; reciprocating seals are used for sealing reciprocating moving parts such as pistons and piston rods, such as Y-rings and U-rings. Dynamic seals require high performance in terms of wear resistance and fatigue resistance of the sealing rings to ensure good sealing performance during operation.
