A theoretical algorithm for the analysis of bidirectional interaction of combined journal and thrust bearings is presented. While many theoretical and experimental investigations on the operating behavior of single journal and thrust bearings can be found only few results for combined bearings are available. However, combined bearings interact by exchanging lubricant and heat which can affect significant changes of boundary conditions compared to a single bearing application. Therefore, a novel procedure is developed to combine two separate codes for journal and thrust bearings in order to iteratively determine the coupling boundary conditions due to the special design of the entire bearing unit. The degree of interaction strongly depends on the type of lubrication. In a first step predictions are verified by measurement data for a combined bearing with a fixed-pad offset-halves journal bearing and a directed lubricated tilting-pad thrust bearing. Experiments were conducted on a high speed test rig up to sliding speeds of 107 m/s at the mean radius of the thrust bearing. As expected the interaction of the two oil films is comparably low in the investigated speed and load range for this bearing design because of the active lubrication of both bearings and the low hydraulic resistance of the thrust bearing. In order to theoretically investigate interaction of thrust and journal bearings in more details a combined bearing with fixed-pad thrust parts lubricated exclusively by the side flow of the journal bearing is studied. A variation of modeling level, pocket design of the journal part, thrust load and rotating frequency provides the following results: (i) hydraulic and energetic interaction have to be modelled in details, (ii) the axial flow resistance of the pockets strongly influences flow rates and the pressure level at the interfaces (iii) the level of interface pressure rises with increasing thrust loads and decreasing rotor speed, (iv) the axial bearing clearance is rather of minor importance for the investigated bearing. Finally, improvements in order to predict operating conditions more precisely are comprehensively discussed.

Despite their superior tribological properties, thick-layer bearing coatings based on Polyetheretherketone (PEEK) have up to now not been applied in a very high number of plain bearings for industrial applications. This can at least partly be credited to the high costs and low flexibility associated with the coating process for these materials. At the same time, while thick-layer PTFE coatings have been successfully applied in industrial plain bearings for around 50 years, thin-layer PTFE coatings today constitute the vast majority of applications of PTFE in plain bearings. It is therefore reasonable to assume a similar approach for thin-layer PEEK coatings. This paper reports the performance of a thin-layer PEEK coating directly applied on a mild steel substrate, with results ranging from first sample test through component tests to application in an actual machine and behavior during realistic operating conditions and induced bearing failure.

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