Industrial shaft seals

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Shaft requirements – small diameter seals (SDS)
Table 7. Counterface for small diameter radial shaft seals
SL
e 2
e 1
SL SL′
General
To achieve reliable sealing and sufficiently long
service life, the counterface for small radial
shaft seals on the shaft should meet the
requirements outlined in the following. The
counterface is considered to be the extent of
the surface of a shaft, or sleeve mounted on a
shaft, over which the edge of the sealing lip
can run, taking into account all permissible
deviations and movements – surface SL, see
Table 7, as well as an additional surface SL'
which may be required in the case of repairs or
inspection.
Tolerances
The diameter of the shaft d1 at the
counterface should be machined to the
tolerances given in Table 8 for metric seals
and in Table 9 for inch size seals.
If components which are to be mounted with
an interference fit are to be passed over the
counterface the shaft diameter should be
reduced by 0,2 mm. The seal which was
originally chosen can still be used without its
sealing properties being impaired.
e = SL 4
e 3
Surface roughness
The surface roughness to ISO 4288–1985 of
the counterface for radial shaft seals should be
kept within the following limits:
Seal width Counterface 1)
b e 1 e 2 e 3 e 4
min
min
mm
mm
7–7,938 3,5 6,1 1,5 7,6
8 3,5 6,8 1,5 8,3
9,525–10 4,5 8,5 2 10,5
11,112–12 5 10 2 2
12,7 5 11 2 13
14,288–15 6 12 3 15
20 9 16,5 3 19,5
1) SL'~ washer width
R a 0,2 to 0,63 µm
R z 0,8 to 2,5 µm
R max 6,3 µm
The lower values for R a and R z are minimum
values as otherwise lubricant supply to the
sealing lip will be affected. The temperature
rise caused by inadequate lubrication,
particularly at high circumferential speeds,
would lead to hardening and cracking of the lip
and thus to premature seal failure. If the
surfaces are too rough there will be excessive
seal lip wear and seal life will be shortened. If
the value R max is exceeded leakage may occur.
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