Page 198 - Rollingbearings

B.8 Sealing, mounting and dismounting
Non-contact seals Fig. 5 Fig. 6
External gap-type seal External gap-type seal with concentric
The simplest seal used outside a bearing is grooves
the gap-type seal, which creates a small gap
between the shaft and housing cover (ig. 5)
This type of seal is mainly used for grease
lubricated applications that operate in dry,
dust-free environments To enhance the
effectiveness of this seal, one or more con-
centric grooves can be machined in the
housing cover bore at the shaft end (ig. 6)
The grease emerging through the gap ills
the grooves and helps to prevent entry of
contaminants
With oil lubrication and horizontal shafts,
helical grooves can be machined into the Fig. 7 Fig. 8
shaft or housing bore, either right-handed External gap-type seal with helical External labyrinth seal, passages
or left-handed, depending on the direction grooves arranged axially
of shaft rotation (ig. 7) These grooves are
designed to return emerging oil to the bear-
ing; therefore, it is essential that the shaft
rotates in one direction only
Sealing, mounting and dismounting as disruptors/lingers Additional shaft collars External labyrinth seal, passages Fig. 9 External labyrinth seal, with inclined Fig. 10
Other shapes can be machined into the
shaft Non-helical grooves may be used on
the shaft and in the housing; these function

can prevent oil leakage, whatever the direc-
tion of rotation
Single or multi-stage labyrinth seals, typ-
ically used with grease lubrication, are con-
siderably more effective than simple gap-
type seals, but are also more expensive
arranged radially
Their effectiveness can be further improved
passages
the labyrinth passages The passages of the
labyrinth seal can be arranged axially (ig. 8)
B.8 by periodically applying grease, via a duct, to
or radially (ig. 9), depending on the housing
type (split or non-split), mounting proced-
ures, available space, etc The radial gaps of
the labyrinth (ig. 8) remain unchanged when
axial displacement of the shaft occurs in oper-
ation; therefore, the gaps can be very narrow
Where angular misalignment of the shaft
relative to the housing can occur, labyrinths
with inclined passages can be used (ig. 10)
Effective and inexpensive labyrinth seals Fig. 11 Fig. 12
can be made using SKF sealing washers Labyrinth seal consisting of multiple SKF Rotating disc acting as a shield
(ig. 11) Sealing effectiveness increases with sealing washers
the number of washer sets and can be fur-
ther improved by incorporating locked
washers For additional information on these
sealing washers, refer to Power transmission
seals, (skf com/seals)
Rotating discs (ig. 12) are often itted to
the shaft to act as a shield Flingers, grooves
or discs are also used with oil lubrication
The oil from the linger is collected in a chan-
nel in the housing and returned to the hous-
ing sump through suitable ducts (ig. 13)

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