Update on sealing technologies

Non-contact seals, like these from Centritec Seals, form a reliable seal even when subjected to severe vibration and shaft motion. They do not require tight axial or radial alignment between the inner and outer ring.

In any motion control system, the risk from dirt and other ingress materials is great. Contaminants like these can damage bearings and other rotating equipment, destroy whole machinery systems and cause unwanted downtime and costs. To prevent these catastrophic events, all motion systems require some type of sealing system. In addition to stopping the ingress of contamintants, seals also prevent leakage of necessary lubricants, such as oil, grease or hydraulic fluid.

Molded seals and v-shaped seals are two of the most common seals found in power transmission applications. V-shaped seals, such as wipers, are used most commonly in fluid power systems to prevent contaminants from entering a system while allowing lubricating oils to return to a system on inward stroke of the hydraulic piston.

Molded seals, which are more common in power transmission applications, can be further divided into O-rings, radial lip seals and shaft seals. O-rings are one of the most common types of seals because of their simple and inexpensive construction. They are designed to create a seal between the interfaces of two or more components. They generally consist of an elastomer ring with a circular cross section and are usually placed in a groove. They are used frequently in hydraulic components, particularly on cylinder pistons and rotating pump shafts.

Mechanical face seals, or heavy-duty seals, are used in extreme applications, such as bearings, gearboxes, turbines and machinery used in extremely tough and dirty environments, such as mining and agriculture. They feature two metal seal rings identical in nature that mount separately on a lapped face seal. A flexible, elastomer element centers the metal rings, allowing one half to rotate while the other remains still.

While many seals are designed primarily to prevent debris from entering a machine, radial lip seals are designed to keep lubricants within a machine that has rotating or oscillating parts. These seals are available as one of two types — spring loaded and non-spring loaded. Each is suited to a particular type of lubricant, grease or oil. Non-spring loaded seals are suited for applications that use a highly viscous lubricant and operate at slower shaft speeds. Spring-loaded seals are best paired with lubricants with low viscosity and higher speeds. The spring helps the seal lip maintain its contact with the shaft even as the seal material itself breaks down.

In addition to keeping contaminants out and fluids in, rotary and shaft seals have the extra benefit of providing low friction and resistance to wear, thus extending component life.

To reduce efficiency and power loss, bearing users can turn to non-contact seal designs. These seals eliminate efficiency and frictional power loss, and also reduce maintenance and contamination problems associated with contact or rubber seals. Several different styles of non-contact seals exist, including labyrinth and centrifugal seals. Designed to eliminate the physical contact between a machine’s stationary and rotating elements, they don’t suffer parasitic drag or wear.

Radial shaft seals are used between rotating and stationary machine components or between two components in relative motion. A cylindrical outer covering of sheet steel (case) or an elastomer has the requisite interference fit to seal statically against the housing bore. Additionally, a sealing lip made of an elastomeric or thermoplastic material seals dynamically and statically against the shaft. Image courtesy of SKF.