Machines operating in dusty environments, such as mining and civil works, are prone to premature failure, leading to production losses. To address this problem, this research project examines the interaction between solid contaminants and the bearing micro-geometry, in lubricated surface contacts. In particular, it seeks to identify anti-wear additives that are effective in reducing wear under abrasive conditions, making machine elements more dirt tolerant.
In general, the influence of antiwear additive is so small that it is difficult to isolate it. Manufactures often make claims about their antiwear products, which are difficult to verify. Hence, there is a need to characterising the antiwear additives available with a well-defined parameter, making it easier for consumers to compare the efficacy of various additives, and be able to select the most suitable additive for a given environment.
Effect of micro-geometry parameters such as radial clearance, out-of-roughness and surface roughness was examined and a Film Shape Factor (FSF) – also termed gamma ratio – has been proposed for ensuring adequate separation of journal bearings operating in hydrodynamic lubrication regime, where the out-of-roundness values are higher than the surface roughness values.
In this research, an experimental study has been conducted on journal bearings, to examine the influence of five antiwear additives on the bearing wear and micro-geometry. The test additives were provided by the industry partner without revealing their chemical identity or composition; however, these included some of the most commonly used antiwear additives. The tests were performed under three conditions: pure base oil, base oil containing contaminants, and base oil containing contaminants treated with five different additives.
The experiments were aimed at choosing one wear measuring technique that evaluates the performance of an individual additive reliably, and based on this technique the additives were characterised. To achieve these objectives, a multi-wear parameter approach (MWPA) was developed, which employed three main wear measurement methodologies, i.e. weight loss, micro-geometry and particle counts –to examine the effect of the antiwear additives. Minimum oil film thickness was also measured to study the lubrication status in the bearing contacts. The MWPA helped in comparing different wear measuring methods, and in selecting the most reliable one. This approach also helped in developing short duration wear tests, thereby saving time, while still getting reliable results without repeating these.
Wear experiments were performed on seven sets of bronze bearings and steel sleeve shafts. The test contaminant was 16 micron Aluminium oxide Al2O3 powder mixed in oil with 4% concentration by weight. These solid contaminants were treated with five different antiwear additives to study their influence on the bearings. Bearings were operated such that the minimum oil film thickness in the bearing was equal to the size of the contaminants. These tests were run for a constant sliding distance of 7536m.
The results showed that most of the wear measuring techniques do not suit heavily contaminated test conditions. However, the out-of-roundness technique proved to be the most reliable and practical. Based on this technique a methodology was developed which gave a wear characteristic number (N). A unique value of N can be derived for each additive, thereby ranking the additives for their efficacy.
The finding of this research provides a better understanding of the methodologies used for measuring wear in journal bearings subjected to dusty environments, and examines the efficacy of each one of these. The wear characteristic number (N) can be used by manufacturers with support from international standards organisations, so that the users can confidently choose the most appropriate antiwear additive for their application.
Machines operating in a dusty environment, such as mining industry and civil works are prone to premature failure with subsequent production losses. In response to this problem, this research project examines the interaction between solid contaminant particles and the lubricant film micro-geometry in lubricated surface contacts. In particular, it seeks to identify lubricant anti-wear additives, which are effective in reducing wear under abrasive conditions and thus making machine elements more dirt tolerant.
| Identifer | oai:union.ndltd.org:ADTP/265775 |
| Date | January 2008 |
| Creators | Sharma, Subhash Chandra |
| Publisher | Queensland University of Technology |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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