âž” fig ).A distinction is made between the
1
Product information Table for the end of servicelife is reached. The life is expressed
either in operating hours or in the num-
ber of oscillating movements (
2
Recommendations
3
Product data Page ................4 Basic rating life Page ..............57
Basic rating life
basic rating lifeand the service life ac-
tually achieved. The basic rating lifeis a guidelinevalue which will be attained or ex-
ceeded by the majority of a large num-
ber of apparently identical bearings
under the same test conditions.The service life achieved by identi-cal bearings has been found to differ,
as the service life depends on the ac-tual operating conditions. These inclu-de not only the magnitude and type of
load but also other factors such as
contamination, corrosion, load and
movement cycles of high frequency,
and shock loads. These factors are
difficult or even impossible to quantify. Spherical plain bearings belong to thecategory “dry sliding bearings”. In con-
trast to, say, hydrodynamic plain bear-
ings, no lubricant film can form to fully
separate the sliding surfaces. There-
fore, under dynamic loads wear is nat-
urally produced which enlarges the
internal clearance. The service life of a spherical plainbearing or rod end represents the op-
erating period under test conditions
which is ended when one of the criteria
listed in
2
Calculation of basic rating life By using the SKF Interactive Engin-
eering Catalogue it is possible to per-
form all the necessary calculations for
spherical plain bearing selection at the
click of a mouse using the programs
incorporated in the catalogue. The
product data necessary for the calcu-
lations is automatically put in by select-
ing a spherical plain bearing or rod endfrom the product tables. It is then only
necessary to fill in the fields for the
operating data.The SKF Interactive EngineeringCatalogue is available on CD-ROM or
online at www.skf.com.
1 3 Criteria for end of service life Table 1 Sliding contact surface combinationIncrease Coefficient in bearingof frictionclearance µ –mm– Steel-on-steel > 0,004 d
k 0,20 Steel-on-bronze > 0,004 d
k 0,25 Steel/sinter bronze composite constant direction load0,20,20alternating direction load 0,40,20 Steel/PTFE fabric constant direction load 0,30,20alternating direction load 0,60,20 Steel/PTFE composite design and0,25size dependent
17