Page 16 - The Tribology Handbook

Selection of bearing type and form AI

Bearings alllow relative movement between the com- The form of bearing which can be used is determined
ponents of ma.chines, while providing some type of location by the nature of the relative movement required and the
between them. type of constraints which have to be applied to it.

Rektive movement between machine components and the constraints applied

Conrtraznt applied to Continuow movement Oscillating mouement
the movement

About a point The movement will be a rotation, and the arrange- If only an oscillatory movement is required, some
ment can therefore make repeated use of accurate additional arrangements can be used in which the
surfaces geometric layout prevents continuous rotation

About a line The movement will be a rotation, and the arrange- If only an oscillatory movement is required, some
ment can therefore make repeated use of accurate additional arrangements can be used in which the
surfaces geometric layout prevents continuous rotation

Along a line The movement will be a translation. Therefore one If the translational movement is a reciprocation,
surface must be long and continuous, and to be the arrangement can make repeated use of accurate
economically attractive must be fairly cheap. surfaces and more mechanisms become economic-
The shorter, moving component must usually be ally attractive
supported on a fluid film or rolling contact for an
acceptable wear rate

In a plane If the movement is a rotation, the arrangement can If the movement is rotational and oscillatory, some
make repeated use of accurate surfaces additional arrangements can be used in which the
V
geometric layout prevents continuous rotation

If the imovement is a translation one surface must If the movement is translational and oscillatory, the
be large and continuous and to be economically arrangement can make repeated use of accurate
attractive must be fairly cheap. The smaller surfaces and more mechanisms become economic-
moving component must usually be supported on a ally attractive
fluid film or rolling contact for an acceptable wear
rate

For both continuous and oscillating movement, there The following tables give examples of both these forms
will be forms aif bearing which allow movement only within of bearing, and in the case of those allowing additional
a required constraint, and also forms of bearing which movement, describe the effect which this can have on a
allow this movement among others. machine design.

Al.l