INTRODUCTION

ESDUpac A9615 provides a computer program for the selection of
bearing materials suitable for dry rubbing conditions. The program
can also be used to analyse the performance of a dry rubbing
bearing of known material. Use of the program for both selection
and analysis is described in this Data Item.

The dry rubbing bearings dealt with by the program comprise a
"self lubricating" material rubbing against a metallic or ceramic
counterface. Wear of the bearing material is inevitable and the
friction will usually be higher than with alternative types of
bearings. Dry rubbing bearings are, however, often the first choice
for applications where the operating conditions do not allow a
liquid lubricant film to be maintained (e.g. high loads
and low speeds). Typical operating regimes for various bearing
types are shown in Sketch 2a of ESDU 87007. Dry rubbing bearings
are also used when the ambient conditions are unsuitable for a
conventional lubricant (e.g. high temperatures, vacuum,
radiation or presence of solvents) or when contamination of the
surroundings by the lubricant must be avoided (e.g. food
handling). Sometimes, even when a liquid lubricant is present, a
bearing material suitable for dry rubbing is used as a safeguard in
case the fluid film breaks down or the lubricant supply fails.

The ESDUpac program described in this Data Item implements the
analysis and selection methods of the previously issued Item, ESDU
87007, entitled "Design and material selection for dry rubbing
bearings". In order to use the program effectively, that Data Item
should be referred to for the theoretical limitations of the
methods and for discussion of practical considerations. The methods
apply for both journal and thrust bearings with either continuous
rotation or oscillatory motion. Other dry rubbing bearings, such as
might be used for reciprocating motion, can also be analysed.
Corrections for intermittent operation, in which the bearing is
periodically stationary, can be applied. The computer program
allows flexibility in the specification of bearing geometry as
explained later in this Data Item.

Dry rubbing bearing materials are often based on a polymer
matrix incorporating various fillers intended to modify both the
mechanical and tribological properties. Bearing materials based on
bulk carbon/graphites and on metals with solid lubricant additions
are also available. ESDUpac A9615 includes a database that covers
all these basic types of materials. The database incorporates the
results of tests on polymer based bearing materials carried out at
the National Centre of Tribology's own laboratories. These results
consist of a set of friction and wear data based on more than six
years' work representing over 150u000 test hours (Derivation 3).
Inevitably, some of the materials tested by NCT will no longer be
available and also new materials will have subsequently become
available. However, the program can be run with alternative
databases the preparation of which is explained in this Data
Item.