Page 40 - The Tribology Handbook

LUBRICATION
FELT
As a general recommendation, the oil in the pores should
be replenished every 1000 hours of use or every year,
whichever is the sooner. However, the data in Fig. 6.5
porosity bearings should be replenished more frequently. *---+
should be used to modify this general recommendation. Low
Bearings running submerged or receiving oil-splash will
not require replenishment. See the notes in Table 6.1 about
compositions which are more tolerant to oil starvation.
Figure 6.6 gives details of some typical assemblies with pro-
vision for supplementary lubrication. OIL PACKED INTO CORED RECESS

)AKED FELT WICK
n

10 lo2 10’ lo4
HOURS OF SHAFT ROTATION
Fig. 6.5. The need to replenish the oil in the pores
arises because of oil loss (which increases with TYPICAL METHODS OF SUPPLEMENTING AND REPLENISHING
shaft velocity) and oil deterioration (which THE OIL IN THE PORES OF A FORCE FITTED BEARING
increases with running temperature). The above
curves relate to the preferred standard bearing materials in
Table 6.1

Selection of lubricant
Figure 6.7 gives general guidance on the choice of oil
viscosity according to load and temperature.
Lubricants must have high oxidation resistance.
Unless otherwise specified, most standard porous metal
bearings axe impregnated with a highly refined and SIMPLE LUBRICATION ARRANGEMENT WHICH CAN BE
oxidation-inhibited oil with an SAE 20130 viscosity. EMPLOYED WITH A PAIR OF FORCE FITTED POROUS METAL
BEARINGS
Do not select oils which are not miscible with common
mineral oils unless replenishment by the user with the Fig, 6.6. Some typical assemblies showing altern-
wrong oil can be safeguarded. ative means of providing suppjementary lubrica-
Do not use grease, except to fill a blind cavity of a tion facilities
sealed assembly (see Fig. 6.6).
Avoid suspensions of solid lubricants unless experience
in special applications indicates otherwise.
For methods of re-impregnation-consult the manu- 4 6 810 SHAFT VELOCITY, fl/rnin
20
40 60 100 200 400 600
facturers. 1000
V
600
SELF ALIGNING
END CAP MAY BE FILLED
n POROUS METAL n WITH GREASE z 400 4 400
w
v, 200
0
a
s 100
W
V
- 60
5
’” 20 20
>
I I I I I It11 10
.01 .02 .04 .06 0.1 0.2 0.4 0.6 1 2 4
SHAFT VELOCITY, m/s
blL SOAKED FELT PAD’
ASSEMBLIES OF SELF-ALIGNING POROUS METAL Fig. 6.7. General guide to the selection of oil
BEARINGS WITH PROVISION FOR ADDITIONAL LUBRICATION viscosity expressed in centipoises at 60’C
A6.5