Types of Seals
- Axial Seal: A seal that operates along the axis of a shaft, preventing leakage by being compressed between components in a longitudinal direction. These seals are used when there is no relative movement between the sealed components.
- Radial Seal: A seal that functions perpendicular to the shaft, designed to contain fluids in applications with rotating or reciprocating shafts, such as pumps and motors.
- O-Ring: A ring-shaped seal that provides a simple, versatile sealing solution for both static and dynamic applications. O-rings are known for their ability to withstand high pressure when seated properly in a groove.
- Shaft Seal: A radial seal designed specifically for rotating shafts to prevent leakage of fluid along the shaft. Common types include rotary shaft seals and mechanical seals.
- Lip Seal: A seal that features one or more flexible lips that press against the sealing surface, typically used in dynamic applications like rotating shafts to prevent contamination and fluid leakage.
Materials Used in Seals
- NBR (Nitrile Butadiene Rubber): A widely used elastomer known for its excellent resistance to oils, fuels, and other chemicals. It performs well in temperatures between -40°C and +100°C, making it suitable for automotive and industrial applications.
- HNBR (Hydrogenated Nitrile Butadiene Rubber): A hydrogenated version of NBR, providing greater resistance to heat, ozone, and chemical degradation. HNBR operates in a broader temperature range (-40°C to +150°C) and is used in high-performance applications like automotive seals.
- EPDM (Ethylene Propylene Diene Monomer): A synthetic rubber with outstanding resistance to weathering, ozone, and water. It is widely used in seals for water-based applications, as well as in the automotive and construction industries due to its high heat resistance.
- VMQ (Silicone Rubber): Known for its excellent flexibility at low temperatures and thermal stability at high temperatures, silicone rubber is used in food, pharmaceutical, and medical seals. It performs well in extreme temperatures ranging from -60°C to +200°C.
- FFKM (Perfluoroelastomer): A high-performance elastomer with excellent resistance to heat, chemicals, and solvents. FFKM can operate in environments up to 327°C and is used in the chemical and semiconductor industries.
- PTFE (Polytetrafluoroethylene): A non-elastomeric material known for its low friction and chemical resistance. PTFE is often used in environments where other materials would degrade, such as in aggressive chemical applications or extreme temperatures.
- FPM/FKM (Fluoroelastomer): A highly durable elastomer, often referred to by the brand name Viton, known for its exceptional resistance to heat, oils, fuels, and chemicals. It is commonly used in automotive and aerospace applications where both chemical and temperature resistance are critical.
Seal Properties and Performance
- Compression Set: The percentage of a seal’s deformation that remains after a compressive load is removed. A low compression set is desirable for long-term sealing performance, as it indicates the material’s ability to recover its original shape.
- Abrasion Resistance: The ability of a material to withstand wear due to friction or contact with moving surfaces. Seals in dynamic applications, such as rotary shaft seals, require high abrasion resistance.
- Modulus of Elasticity: A measure of a material’s stiffness, which indicates how much it will deform under stress. Materials with higher modulus values are stiffer and less likely to deform under load.
- Gas Permeability: A measure of how easily gases can pass through a sealing material. For applications where gas leakage must be minimized, materials with low gas permeability, such as FKM or PTFE, are preferred.
- Chemical Resistance: The ability of a sealing material to resist degradation from exposure to aggressive chemicals or solvents. This property is crucial in seals used in chemical processing, oil and gas, or pharmaceutical industries.
- Rebound: The ability of a material to return to its original shape after compression. High rebound is important for maintaining a seal over a long period of use.
Seal Applications and Installation
- Breakaway Torque: The torque required to initiate movement in a sealed system, such as rotating a shaft. This is influenced by the friction between the seal and the surface it contacts.
- Surface Roughness (Ra): A measure of the texture of a surface; in sealing applications, smoother surfaces generally result in better sealing performance by reducing the potential for leakage paths.
- Clearance: The free space between the seal and the surface it is sealing against. Adequate clearance is necessary to avoid excessive wear while maintaining a proper seal.
- Seal Cross-Section: The profile or diameter of the seal’s body, which influences the amount of sealing force it can apply and the type of sealing application it is suitable for.
- Installation Space: The physical space available for the installation of the seal. The size and type of seal must be carefully selected based on the available installation space to ensure proper function.
Food Industry Regulations and Standards
- FDA 21 CFR 177.2600: A U.S. Food and Drug Administration (FDA) regulation that specifies which elastomers and rubber materials can be used in food-contact applications. This regulation outlines testing for extraction of chemical substances that could migrate into food.
- NSF 51: A standard that defines the safety and sanitation requirements for materials used in the construction of commercial food equipment. It ensures that materials do not impart harmful contaminants to food during processing.
- BFR XXI/Category IV: A German standard issued by the Bundesinstitut für Risikobewertung (BfR) that defines the safety requirements for rubber and silicone materials in contact with food. It ensures compliance with EU safety regulations.
- EU 1935/2004: A European regulation that sets safety standards for all materials intended to come into contact with food. It ensures that materials do not transfer harmful substances to food, impact the organoleptic properties of food, or otherwise compromise food safety.
- GMP (Good Manufacturing Practices): A system for ensuring that products are consistently produced and controlled according to quality standards. In the food industry, GMP ensures that manufacturing processes are safe and hygienic.
- 3-A Sanitary Standards: A standard in the U.S. that defines hygienic design for food processing equipment. It ensures that equipment is easy to clean and prevents contamination, particularly in dairy and other liquid processing industries.
Seal Types for Specific Environments
- High-Temperature Seal: Seals that are designed to withstand extreme temperatures, often made from materials such as FFKM, silicone, or graphite. These seals are used in environments like engines, turbines, and ovens.
- Labyrinth Seal: A non-contact seal that uses a series of interlocking passages to restrict fluid flow. This design is ideal for high-speed rotating equipment where minimal friction and wear are important.
- Spring-Energized Seal: A seal that uses an internal spring to maintain contact with
