Page 120 - Rollingbearings

B.4 Lubrication
Additional factors and Heavy and very heavy bearing
The low and high temperature limits for reli- loads
able operation, indicated by the green zone considerations when
in diagram 4, page 117, are: selecting a grease
For bearings subjected to a load ratio
• low temperature performance limit (LTPL), Verify the lubrication condition, C/P < 4, the calculated relubrication interval
deined as the temperature at which may be so short that it dictates the use of
grease no longer shows suficient oil bleed consider EP/AW additives continuous relubrication or oil lubrication
as measured in DIN 51817 The LTPL
values for roller bearings are provided in The lubrication condition, κ, is evaluated by Miscibility with other greases
diagram 5, page 117. The LTPL values for using the base oil viscosity as described in
ball bearings are approximately 20 °C Lubrication condition – the viscosity ratio, κ, If it becomes necessary to change from one
(35 °F) lower page 102 In the lubrication condition grease type to another, consider the miscib-
• high temperature performance limit domain deined by κ below 1, EP/AW addi- ility of the greases and their ability to be
(HTPL), determined by the SKF R0F tives are recommended mixed without adverse effects (table 6 and
grease life test EP/AW additives of the sulphur-phospho- table 7) If incompatible greases are mixed,
rus type, which are the most commonly used the consistency of the grease mix can change
Within these two limits, the grease fulils its today, may also have a negative inluence on dramatically such that bearing damage
function reliably and the relubrication interval the fatigue life of the bearings This is because because of severe leakage could result Note
or grease life is predictable Because the in the presence of humidity, which can never that PTFE-thickened greases are not com-
deinition of the temperature performance be completely avoided, sulphur and phos- patible with other grease types
limits is not standardized internationally, phorus acids are produced which induce a
care must be taken when interpreting data more aggressive chemical process at the Miscibility with preservation oils
from grease suppliers other than SKF rolling contact This effect increases with
At temperatures above the high tempera- temperature and, for temperatures above The preservative oils with which SKF bear-
ture performance limit (HTPL), grease 80 °C (175 °F), a lubricant with EP/AW addi- ings are treated are compatible with the
degrades with increasing rapidity Therefore, tives should only be used after careful testing majority of lubricating greases, with the
temperatures in the amber zone, between SKF greases have been tested and can be exception of synthetic luorinated oil based
the high temperature performance limit used above 80 °C (175 °F) until the HTPL is greases using a PTFE thickener, for example,
(HTPL) and the high temperature limit reached SKF LGET 2 grease For PTFE-thickened
(HTL), should only be allowed to occur for greases, the bearing preservatives must be
very short periods Low speeds removed before applying the grease White
An amber zone also exists for low temper-
spirit is recommended as a solvent Make
Lubrication atures, between the low temperature limit Bearings that operate at very low to low sure all remnants of solvent have evaporated
(LTL) and the low temperature performance
and then immediately apply the grease
speeds (table 4, page 116) under heavy
loads should be lubricated with a grease that
limit (LTPL) In this zone, the temperatures
additives The thickener should contribute to
The width of the amber zone depends on the
B.4 are too low to provide suficient oil bleeding has a high viscosity base oil containing EP
the surface separation Suficient oil bleeding Assessing the
grease type and bearing type Serious
damage can result when the bearings are should assure oil replenishment during suitability of non-
operated continuously below the LTPL operation
Short periods in this zone, such as during a Solid additives, such as graphite or molyb- SKF greases
cold start, are generally not harmful because denum disulide (MoS ), should be considered
2
the heat caused by friction brings the bearing for a speed factor nd < 20 000 mm/min Greases from suppliers other than SKF must
m
temperature into the green zone SKF LGEV2 is successfully used up to be approved by the supplier Use diagram 6,
nd = 80 000 page 120, to evaluate the temperature per-
m
formance and grease life prediction Where
relevant, take into account the considerations
speciied for SKF greases

118