Water lubricated bearing bush thermal properties as a key parameter for durable operation

Michał Wodtke² , Agnieszka Barszczewska¹, Wojciech Litwin¹

¹  Faculty of Ocean Engineering and Ship Technology, ² Faculty Mechanical Engineering , Gdansk University of Technology, Poland

INTRODUCTION: Polymer journal bearings are frequently used as water-lubricated bearings in propeller shafts of small marine units. The choice of these bearings is based on their simple construction, sea water lubrication capability in open and closed loops, as well as relatively low purchase and maintenance costs. In addition, properly designed and installed water lubricated bearings may well last for over a decade.

Despite these facts, in practice, there are cases of rapid wear or failure in these bearings. Some of these failures may be caused by lack of lubricant or its limited flow through the bearing e.g. due to inlet chocking by ocean debris. This leads to overheating especially in the bush material¹.

Recently, some experimental tests for real scale bearings were conducted, where a steel sleeve with polymer bearing bush located inside was filled with boiling water. The temperature changes in time were measured. It was proven that bearing bush heat conductivity had significant influence on process of increasing temperature in friction zone ²³.

The idea behind the recent work was to focus on bearing bush’s thermal properties as a key parameter in conditions of no lubricant flow when the overheating process often appears.

METHODS: Commercial software was used for CFD simulations.

Geometry of the tested bearing was the same as that of an actual, real size bearing used during experimental work. Details of the bush geometry, meshing method and calculated temperature points are presented below (Fig. 1 and Fig.2).

Figure 1 – Calculations model; a) Typical cartilage deformations during highlighted parts of the experiment.  b) FEM mesh

Figure 2 – Calculated temperature points

RESULTS: The calculation and measurement results are presented in the diagram below (Fig. 3). One may notice that after this very simple experiment – filling bush with boiling water – the difference in water temperature inside as a function of time is significant.

Figure 3 – Calculations and measurement results for selected bearing bushes

CONCLUSIONS: Bush thermal conductivity plays a significant role for bearing operation under critical conditions of lubricant flow absence. The conducted FEM calculation help to understand the impact of bush geometry on the problem of bearing overheating.

ACKNOWLEDGEMENTS: 

This work was a part of a research grant no. 2016/23/B/ST8/03104 entitled “Research on water lubricated sliding couples in conditions of improper lubrication conditions” financed by the Polish National Science Centre.

REFERENCES:

1.          Litwin, W. & Dymarski, C. Experimental research on water-lubricated marine stern tube bearings in conditions of improper lubrication and cooling causing rapid bush wear. Tribol. Int. (2016). doi:10.1016/j.triboint.2015.12.005

2.          Litwin, W. Influence of bush wear in water lubricated marine stern tube bearings with shaft misalignment. in 5th World Tribology Congress, WTC 2013 4, (2013).

3.          Barszczewska, A., Sadowski, J. & Litwin, W. Research on water lubricated main shaft bearings in conditions of improper lubrication and cooling conducted on high torque real-life scale bush test rig. in World Tribology Congress , Beijing, China, September 17 – 22, 2017 (2017).