POA * ONLINE SUBSCRIPTION ONLY

INTRODUCTION

This Data Item describes the use of ESDUpac A9719 which provides a computer program for determining the equilibrium temperatures and heat flow rates in a network of heat conducting and dissipating components. The thermal network analysis implemented by the program is quite general but is most immediately applicable to self-contained bearing assemblies such as dry rubbing bearings, rolling element bearings, fluid film bearings lubricated by oil or grease, and oil-impregnated porous bearings. The program incorporates representations of a number of standard parts, such as shaft and bush parts, that can be combined to model the heat generation, conduction and dissipation (by convection and radiation) in the complete assembly.

The temperatures in a bearing assembly might need to be estimated so that wear rates and load limits can be determined or operating film thickness and power loss be estimated. Also, an estimate of reservoir or sump temperature might allow thermal degradation of lubricants and lubricant life to be assessed. The temperatures at other points in the assembly might also need to be determined. For example, bearing temperatures are usually measured at the bearing back rather than at the friction surface and it may be required to predict this temperature for comparison with test results. Temperatures at external surfaces may also be required for assessment of any safety hazard.

Another important reason for pursuing such an analysis is to identify thermal conditions that could lead to problems or failure in operation. For example, if the predicted temperature for the inner race of a rolling bearing were considerably higher than that of the outer race a loss of diametral clearance, and consequential risk of thermal runaway, would be indicated.

The program implements much of the heat transfer and heat dissipation analysis methods described in a previously issued set of Data Items numbered 78026, 78027, 78028, 78029 and 79002 (see Derivations 6 to 10) and provides a replacement for the manual method of determining the equilibrium conditions in a bearing assembly described in those Data Items. The Items can be referred to for the theoretical basis of some of the analysis and for discussion of practical considerations.