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DESIGN OF SHAFTS AND HOUSINGS
For thrust bearings, the squareness and contact area 11.3 Bearing Seals (2) Flinger (Slinger) Type Seals (3) Labyrinth Seals
of the supporting face for the bearing rings must
be adequate. In the case of thrust ball bearings, the To insure the longest possible life of a bearing, it may A flinger is designed to force water and dust away Labyrinth seals are formed by interdigitated segments
housing shoulder diameter Da should be less than be necessary to provide seals to prevent leakage of by means of the centrifugal force acting on any attached to the shaft and housing that are separated
the pitch circle diameter of the balls, and the shaft lubricant and entry of dust, water and other harmful contaminants on the shaft. Sealing mechanisms with by a very small gap. They are particularly suitable for
shoulder diameter da should be greater than the pitch material like metallic particles. The seals must be free flingers inside the housing as shown in Fig. 11.6 (a), preventing oil leakage from the shaft at high speeds.
circle diameter of the balls (Fig. 11.3). from excessive running friction and the probability of (b) are mainly intended to prevent oil leakage, and The type shown in Fig. 11.7 (a) is widely used because
For thrust roller bearings, it is advisable for the seizure. They should also be easy to assemble and are used in environments with relatively little dust. of its ease of assembly, but those shown in Fig. 11.7
full contact length between rollers and rings to be disassemble. It is necessary to select a suitable seal for Dust and moisture are prevented from entering by the (b), (c) have better seal effectiveness.
supported by the shaft and housing shoulder (Fig. each application considering the lubricating method. centrifugal force of flingers shown in Figs 11.6 (c), (d).
11.4).
These diameters da and Da are listed in the bearing 11.3.1 Non-Contact Type Seals Table 11. 4 Gaps between Shafts and Table 11. 5 Labyrinth Seal Gaps
tables. Housings for Units : mm
Various sealing devices that do not contact the Oil-Groove Type Seals
jd a shaft, such as oil grooves, flingers, and labyrinths,
are available. Satisfactory sealing can usually Units : mm
jDa be obtained with such seals because of their close
Fig. 11.3 Face Supporting Diameters running clearance. Centrifugal force may also assist in Labyrinth Gaps
Fig. 11. 3 for Thrust Ball Bearings preventing internal contamination and leakage of the
lubricant. Nominal Shaft Diameter Radial Gap Nominal Shaft Diameter
jda
(1) Oil Groove Seals Radial Gap Axiall Gap
jDa
Fig. 11.4 Face Supporting Diameters The effectiveness of oil groove seals is obtained by Under 50 0.25 to 0.4
Fig. 11.4 for Thrust Roller Bearings means of the small gap between the shaft and housing
bore and by multiple grooves on either or both of the Under 50 0.25 to 0.4 1 to 2
housing bore and shaft surface (Fig. 11.5 (a), (b)).
Since the use of oil grooves alone is not completely 50-200 0.5 to 1.5
effective, except at low speeds, a flinger or labyrinth
type seal is often combined with an oil groove seal 50-200 0.5 to 1.5 2 to 5
(Fig. 11.5 (c)). The entry of dust is impeded by packing
grease with a consistency of about 200 into the
grooves.
The smaller the gap between the shaft and housing,
the greater the sealing effect; however, the shaft and
housing must not come in contact while running. The
recommended gaps are given in Table 11.4.
The recommended groove width is approximately 3 to
5mm, with a depth of about 4 to 5mm. In the case of
sealing methods using grooves only, there should be
three or more grooves.
(a) (b) (c) (d)
Fig. 11.6 Examples of Flinger Configurations
(a) (b) (c)
A 102 Fig. 11.5 Examples of Oil Grooves
(a) Axial Labyrinth (b) Radial Labyrinth (c) Labyrinth for Self-Aligning Shaft
Fig. 11.7 Examples of Labyrinth Designs A 103
