Evaluation of non-ozone-depleting-chemical cleaning methods for space mechanisms using a vacuum spiral orbit rolling contact tribometer

Because CFC 113, an ozone depleting chemical (ODC), can no longer be produc ed, alternative bearing cleaning methods must be studied. The objective of this work was to study the effect of the new cleaning methods on lubricant lifetime using a vacuum bearing simulator, the Spiral Orbit Tribometer (SOT ). In addition to baselines tests using CFC 113, four alternative cleaning methods were studied. They were ultra-violet (UV) ozone, aqueous levigated alumina slurry (ALAS), super critical fluid (SCF) CO2, and aqueous Brulin ( TM) 815GD. Test conditions were the following: a vacuum of at least 1.3 x 1 0(-6) Pa, 440C steel components, a rotational speed of 10 RPM, a lubricant charge of between 60-75 micrograms, a perfluoropolyalkylether (PFPAE) lubri cant (Z-25), and a load of 200N (a mean Hertzian stress of 1.5 GPa). Normal ized lubricant lifetime was determined by dividing the total number of ball orbits by the amount of lubricant. The failure condition was a friction co efficient of 0.38. Post-test XPS analysis showed a greater amount of carbon on the surfaces cleaned with Brulin (TM) 815GD and SCF CO2 than with the o ther techniques, which may represent residual hydrocarbons. Statistical analysis of the resultant data was conducted and it was determi ned that the data sets were most directly comparable when subjected to a na tural log transformation. The natural log life (NL-Life) data for each clea ning method were reasonably normally (statistically) distributed and yielde d standard deviations that were not significantly different among the five cleaning methods investigated. This made comparison of their NL-Life means very straightforward using a Bonferroni multiple comparison of means proced ure. This procedure showed that the ALAS. UV-ozone and CFC 113 methods were not statistically significantly different from one another with respect to mean NL-Life. It also found that the SCF CO2 method yielded a significantl y higher mean NL-Life than the mean NL-lives of the three previously mentio ned methods. It also determined that the aqueous Brulin (TM) 815GD method y ielded a mean NL-Life that was statistically significantly higher than the mean NL-lives of each of the other four methods. Baseline tests using CFC 113 cleaned parts yielded a mean NL-Life 3.6 orbit s/mug. ALAS and UV-ozone yielded similar mean NL-Life of 3.3 orbits/mug and 3.3 orbits/mug respectively. Finally, SCF CO2 gave a mean NL-Life of 4.1 o rbits/mug, while aqueous Brulin (TM) 815GD data yielded the longest mean NL -Life (4.7 orbits/mug).