PhD. Transactions of Machine Elements Division. Lund 1992

Abstract:

The gas-lubricant flat spiral groove thrust bearing has been the subject of this study. A finite element program for the calculation of the true pressure distribution in the bearing was developed. The finite element method has been found to be very suitable for the analysis of the bearing in question, as it was for the liquid-lubricated bearing dealt with in a prior work (1).

Because of the non-linearity of the governing differential equation for the pressure build-up in gas lubricants, the linear finite element formulation from (1) had to be combined with an iterative solution of the result in system of equations. The well-known Newton iteration method was used with great success.

The new groove design proposed for the liquid-lubricated bearing is not recommended for the gas-lubricated bearing, primarily because it is unnecessary, as cavitation is no problem for the gas-lubricated bearing. The minimum pressure in the bearing was found to be only slightly below the ambient pressure.

At a small number of grooves the optimum values of the other bearing parameters differ considerably from the values obtained from the often used theory assuming an infinite number of grooves. At high compressibility numbers this difference becomes even more significant. However, when the number of grooves increases, the influence of compressibility decreases. For an infinite number of grooves there is no difference between the incompressible and the compressible solution.

The theory assuming an infinite number of grooves was also shown to give load over estimations above 100 % for small numbers of grooves and high compressibility numbers. On the other hand, by using the optimum values related to the true number of groove and compressibility number, presented in chapter 7 in this work, the load capacity becomes to the load capacity for an infinite number of grooves.

The relative power loss of the flat spiral groove thrust bearing has been found to be very low compared to, for example, the sector-shaped tilting pad thrust bearing. This holds for both the liquid- and gas-lubricated bearing The flat spiral groove thrust bearing must be considered an attractive alternative to tilting pad thrust bearing, and also to hydrostatic thrust bearings, since no external high pressure supply is required as is the case for the hydrostatic bearing.

An experimental investigation has been carried out. The agreement between the experimental and the theoretical results is good.