By Dr. Jody Muelaner
Industrial seals are used to prevent leakage, hold pressure, and deflect contamination at interfaces between components. Industrial seals are used at static and dynamic interfaces. Examples of static interfaces include the entry point of bolts and screws, and the interface between an engine block and cylinder head.
Adhesives and gaskets are used as static seals. Dynamic interfaces are typically linear, such as the seal between pistons and cylinders, or rotary, such as the seal between bearing housings and axles.
Some common types of industrial seal:
- Gasket: Sheet of flexible material, which seals the interface between two static, usually planar, surfaces. Gaskets depend on compression and their ability to conform to imperfections in the two surfaces to create a seal. Bolted connections are often used to provide this compression.
- Labyrinth seal: A non-contact dynamic seal with a series of interlocking grooves or teeth, on each side of the interface. This creates a long narrow pathway through which it is difficult for fluid to escape. Labyrinth seals on rotating shafts do not simply rely on the viscosity of the contained fluid but also utilize centrifugal force and controlled vortices to prevent leakage.
- Lip seal or radial shaft seal: Sprung sealing lip that contacts against a rotating axle, typically to contain oil and exclude contamination.
- O-ring: Torus shaped loop of elastomer, which can be seated in a groove and compressed to form a seal. May be considered a type of gasket.
- Bonded seal: A washer with an outer ring of hard material and an inner ring of thicker and more flexible material that acts as a gasket. Normally used to seal between a bolt head and the part being fastened. This seals the hole through which the bolt is inserted.
- Hose couplings and pipe connections: Many types of seals are available to provide connections between hoses, pipes and associated fittings. Many of these are compression seals that use an axisymmetric gasket.
- Piston Seals: Rings of flexible material that sit in grooves around the radius of a piston and seal against the walls of a cylinder. Multiple split rings may be used to facilitate fitting. Different materials are used depending on the presence of different gasses or liquids in the cylinder, lubrication, temperature and pressure. For example, an O-ring in an air pump, a polyurethane ring in a hydraulic cylinder or a metal ring in an engine.
- Sealant: When adhesives are used primarily to provide a seal they are normally referred to as sealant. Sealants are used in many applications, for example, to ensure that aircraft wings constructed from riveted aluminum panels are able to hold fuel without leakage.
- Caulking: Sealants used with construction, to seal against water ingress and drafts around windows, doors and other fittings
- Welding: Welding is often used to joint pipes and sections of pressure vessels while also sealing these interfaces.
- Glass-to-metal seals: Provide a seal between glass and metallic components, for example in light bulbs and other electrical devices with vacuum chambers. They require no third material to act as a seal, instead they depend on the molten glass wetting the metal component during manufacture.