NTN - Plummer Blocks


Bearing Seals

(3) S grease seal (Fig. 6.3)

The S grease seal (synthetic rubber seal with spring)

excels in sealing performance and is well suited for

grease or oil lubrication. Custom specification variants

can be used in a plummer block.

Its recommended peripheral speed falls within a range

of 10 to 12 m/s. The surface roughness and hardness of

the shaft in contact with this sealing material necessitates

special attention.

Fig. 6.5 Special labyrinth seal

Shaft design specification for the area in contact with the seal

The quality of a shaft section in contact with the seal lip

greatly affects the sealing performance of the seal.

Therefore, strictly adhere to the design standard for

shafts in Table 6.2.

Table 6.2 Shaft design standard

Fig. 6.4 Labyrinth seal

6.2 Non-contact seals

(1) Labyrinth seal (Fig. 6.4)

The labyrinth seal used in the bore of plummer blocks --

SD31TS and SD32TS series-- comprise a labyrinth

ring that is fitted into the bore of the plummer block. A

labyrinth seal is used in clearance fit to a shaft (h9)

together with an O-ring so that it can be readily installed

and can follow expansion/compression of the shaft.

This seal type excels in sealing performance, and can

be used for grease or oil lubrication.






at end face

Design standard


0.8Ra or smaller

The end face to which a

seal is fitted must be

tapered and the sharp

corner must be rounded.


The finish surface should

be finish-ground without


6.3 Combination seals

The combination seals used for the SBG series are

unique seals that comprise both of an oil seal and

labyrinth seal and are installed in the bore of a plummer

block. They are used in environments where heavy dust

and contaminants are present.

For better sealing effect, the labyrinth seal is often filled

with grease.

Fig. 6.4 Labyrinth seal

(2) Special labyrinth seal (Fig. 6.5)

The special labyrinth seals such as those in Fig. 6.5 are

very useful for applications where heavy soil and dust are


The plummer blocks used in conjunction with this seal

type are manufactured per custom specifications. For

further information, contact NTN Engineering.

Fig. 6.6 Combination seal

With a continuous or intermittent lubrication

scheme, lubricant can tend to leak. Use a seal

that positively offers reliable sealing.


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