A seal is a component or system designed to prevent or control the passage of liquids, gases or contaminants between two surfaces or environments. Seals are widely used in mechanical engineering, hydraulic systems and industrial machinery, where leakage prevention and protection from external contaminants are essential.
In engineering, the word seal can refer both to the sealing element itself, such as an O-ring or gasket, and to the sealing function achieved by a component or assembly.
How Sealing Works
The primary function of a sealing system is to restrict a potential leakage path between regions at different pressures or between an enclosed environment and the surroundings. Depending on the application, it may operate between stationary components or between parts that move relative to one another.
Its effectiveness depends on several factors, including pressure differential, temperature, fluid properties, material compatibility and type of movement. The sealing element must maintain sufficient contact with the mating surfaces while accommodating the conditions of the application.
Main Types
Industrial sealing technology includes a wide variety of components and systems. The following are some of the most common examples, although these categories are not mutually exclusive and may overlap depending on their design and application.
O-Rings
O-rings are circular elastomeric seals with a round cross-section. They are commonly installed in grooves and compressed between mating surfaces generating initial contact pressure that provides sealing.Fluid pressure can further increase the contact pressure and help maintain sealing. They are primarily used in static applications but can also be employed in certain dynamic sealing systems.
Gaskets
Gaskets are sealing elements placed between two stationary mating surfaces, typically flanges or housings. They conform to surface irregularities and maintain sufficient contact pressure to restrict leakage when the assembly is tightened.
Rotary Shaft Seals
Rotary shaft seals, often called oil seals, are used where a rotating shaft passes through a stationary housing. They retain lubricants while helping prevent external contaminants from entering the assembly.
Mechanical Seals
Mechanical seals are precision assemblies typically used in rotating equipment such as pumps and mixers. They generally rely on two closely fitted sealing faces, one rotating and the other stationary, to control leakage.
Unlike conventional radial shaft seals, which typically use a flexible lip in contact with the shaft, mechanical seals generally employ sealing faces arranged perpendicular to the shaft axis.
Hydraulic Seals
Hydraulic seals are designed for hydraulic cylinders and other fluid-power systems. Rod seals and piston seals help maintain pressure and control fluid leakage during reciprocating movement.
Hydraulic sealing systems may also incorporate wipers, which help prevent dirt and other external contaminants from entering the cylinder.
Static vs. Dynamic Applications
One of the main distinctions in sealing technology is between static and dynamic applications.
Static seals are installed between components that do not move relative to each other, such as bolted flanges or fixed housings. They must maintain an effective barrier under the expected operating pressure and temperature.
Dynamic seals operate between moving surfaces, including rotating shafts and reciprocating components. In these applications, sealing performance must be balanced with friction, wear, lubrication and heat generation.
The type of movement, operating speed and pressure are therefore important considerations when selecting a suitable sealing solution.
Common Materials
The choice of sealing material depends on the operating environment and the substances with which the component comes into contact.
Common materials include:
- NBR (nitrile rubber): frequently used for seals exposed to mineral oils and hydraulic fluids.
- FKM (fluoroelastomer): suitable for many applications involving elevated temperatures, oils and chemicals.
- EPDM: commonly used in water, steam and certain chemical applications, depending on the formulation.
- PTFE: valued for its chemical resistance and low-friction properties.
- Polyurethane: widely used in hydraulic seals because of its wear and abrasion resistance.
- Metals, graphite and ceramics: used in certain gaskets and mechanical sealing systems.
No single material is suitable for every application. Temperature, pressure, chemical compatibility and operating conditions must always be considered.
Industrial Applications
Sealing systems are essential in numerous industrial sectors, including construction machinery, agricultural equipment, mining, manufacturing, automotive engineering and fluid-power systems.
In hydraulic cylinders, rod and piston seals help maintain pressure and control fluid leakage during operation. In pumps and rotating equipment, mechanical seals and other sealing solutions control leakage around moving shafts.
In engines, gearboxes and industrial machinery, seals help retain lubricants and protect internal components from external contaminants.
Correct selection and installation can help reduce premature wear, maintenance requirements and unexpected equipment downtime.
Seals, Bushings and Moving Components
Seals and bushings perform different but often complementary functions in mechanical assemblies. While seals control fluid leakage and contamination, bushings support and guide moving components, helping manage friction and wear.
In some applications, a bushing can also provide the counterface on which a sealing lip operates. Instead of allowing the seal to run directly on the main shaft, a precision steel bushing can be fitted onto the shaft, protecting it from wear while providing the seal with a controlled contact surface.
This solution can be used, for example, with rotary shaft seals, where continuous contact between the sealing lip and the rotating surface can progressively cause wear. In these applications, characteristics such as surface roughness, hardness, dimensional accuracy and roundness are particularly important for both the bushing and the sealing system.
Custom Steel Bushings for Sealing Applications
Sibo manufactures custom steel bushings for applications involving rotary shaft seals and other demanding mechanical systems. Dimensions, materials, heat treatments and surface characteristics can be defined according to the specific operating requirements of the application.
In applications where the sealing lip runs directly on the bushing, particular attention can be given to the outer diameter, dimensional tolerances and surface finish in order to provide a suitable and consistent contact surface for the sealing element.
If you need a custom steel bushing for a sealing system or another industrial application, contact us to discuss your technical requirements or request a quotation.
You can also request our bushings catalog using the form below to explore our standard product range and available solutions.
