Seal

 

The seal in bearings prevents from entering additional materials into the bearing and lubricantpermeates. For choosing a proper seal should consider some parameters such as lubricant type (oil or grease), rotational speed, shaft condition (vertical or horizontal) and possibility of non-alignment, available space, and friction of seal and its resulted heating and workplace. The seal may be integrated with bearing or in separate is out of the bearing.

Types of Seal

The seal divides in two groups of Rubbing seals and non-Rubbing seals.

-         Non-Rubbing seals:

There is a distance between these seals and bearing or shaft. Their operation depends on said gap (distance) which is in the vertical-horizontal form or horizontal-vertical form. On the other hand, this gapcause’s failure to produce friction and heat, but its sealing features is not as same as rubbing one in which this feature can be improved through filling the gap (distance) by grease. The high speed in bearing with this seal is another benefit.

-         Rubbing seals

The operation of these seals depends on pressure amount in contact place with bearing. Their advantages are the full sealing against extra material penetration and impossibility of the grease leaking. Some of their disadvantages are friction and heat which can be adjusted by betterment of contact surface. These seals are vulnerable against impact which can solved this problem by putting a non-rubbing seal nearby them.

Seal selection

The type of seal has a great influence on bearing operation. In this case, determining the environmental conditions is necessary to choose a proper seal.

Integral seals

Some of bearings are produced by rubber or steel seals in one side or both sides. These bearings are filled by proper grease at montage time so there is no need to re-injecting grease. When it is impossible to use external seals for outside of the bearing for some reason such as lack of space, then use from bearing with seal. The steel sealed used when the pollutions and moisture is in low level and speed is high; because these are non-rubbing seals. If there is a high pollution or moisture, the rubbing seal can be used.

External seals

The simplest type of these seals located in little space from shaft exit of bearing that provides a proper sealing. In non-rubbing seals seal, the gaps may be vertical – horizontal or horizontal-vertical. There is multi-layer seal which is more effective than the first type. The sealing washers are as same as labyrinth seals which are non-robbing, effective and cheap. By increasing the number of washers in front of bearing, its sealing feature also will be increased. The felt seals which used in lubricating by grease have a simple structure and in some cases it used when the speed is till 4 m/s and temperature is till 100° cg. Spring washers are another type of seals and their simple structure and using a little space made an effective sealing during grease lubricating. Radial lip seals are rubbing type and used in lubricating with oil that has highest level of using. Generally, the seals are rubber that reinforced by using a steel ring or locating in a steel shaft. The edge of seal made of synthetic rubber which pressed on the shaft by a spring which located inside it.