If dust and water get inside a bearing, this leads to premature failure. Therefore choosing the right protective seals is important for the working life of a bearing. The centrifugal seal (CS) is designed for harsh conditions where there is a risk of contamination. And if you want extra protection in a dusty, abrasive environment, you can choose the DS type.
Centrifugal seals (CS) and Double seals (DS)
Why choose a centrifugal seal?
Dusty, abrasive environments are one of the most difficult for bearings. When handling powders or in processes generating dust, the protection of bearings against contamination by fine particles requires special consideration. Radial oil seals, such as the AS and SA seals made of nitrile rubber, are selected mainly for ordinary conditions, but they are generally unsatisfactory in harsh or dusty conditions. Over time, the nitrile rubber is attacked by dirt, water, sand and various other contaminants. Small particles get into the soft material of the rubber and the lip can cause fretting of the shaft (causing a groove under the lip). Tiny particles of moisture on the shaft can be drawn past the lip and a jet of water sprayed at high pressure directly at the lip seal penetrates past the seal and into the bearing.
Extreme Bearing has developed the centrifugal seal to solve these problems! Many Extreme Bearing housings feature centrifugal seals specially developed to repel dirt and contaminants using centrifugal force generated by the shaft. The CS seal works for speeds up to 5 m/s and for temperatures from -25°C up to 95°C.
Triple barrier sealing
CS seals are superior against sand, dirt and detergents
- Double lip centrifugal seal
- Grease-filled housing
- 2-RS bearing sea
Firstly, the centrifugal seal made of rubber attached to the shaft provides a primary barrier. It repels dirt and contaminants using the centrifugal force generated by the shaft. Secondly, the bearing housing is filled with grease to prevent contaminants from entering and damaging the bearing. Finally, there is a type of bearing seal called 2-RS to protect the bearing.
The rubber of the CS-seal clamps around the shaft and is turning with the shaft vertically against the stator ring. Because the lips are positioned vertically against the stator ring, the dirt will be repelled by the centrifugal force from the sealing lips. The rotor ring can be moved eccentrically in relation to the stator ring. In this way, the centrifugal seal is able to absorb any misalignment of the shaft without creating wear on the rubber lips.
The grease passes the retaining edge through the lubrication channels under the stator ring and between the two sealing lips and stator ring. This makes sure that any dirt is flushed away. The clamping of the rubber rotor ring around the shaft means that the bearing can be assembled even on a shaft which has suffered light surface damage such as a groove.
The gaps between the lips of the centrifugal seal and the stator must be sealed to keep out dust and water. To improve bearing life for centrifugal shaft seals, it is recommended to use an automatic lubricator or to lubricate regularly. Only a small quantity of grease is necessary when slowly flushed into the bearing cavity to force dust and moisture away from the working parts.
Examples of grease diagrams using CS seals
If the contamination is only on one side of the bearing unit, a seal combination such as those shown in the diagrams can be chosen. By refilling the grease on this side, it will flow and be released from the bearing housing and the contamination along with the grease will flow away from the sealing lips.
When applying the CS seal, it must be taken into account that it is not flush with the surface of the housing and expands the dimensions of the housing slightly, as shown in the table.
DS Double seal
The DS (double seal) is a combination of a CS(centrifugal seal) together with a CC PTFE sealand has been developed for bearings used inabrasive environments.
The DS seal combines the advantages of two seals in a single seal set. The CS seal means that the underlying CC seal has extra protection against abrasive particles.
Because the DS seal has a larger size, a spacer ring is needed on the cover side to provide extra space. To ensure that the grease does not choose the path of least resistance, the spacer ring is also equipped with a grease nipple. This ensures that grease flushes away and with it, the dirt is washed away and the seal remains in operation.