301 Efficacy  of Lead  Naphthenate  for Wear  Protection  in High  Vacuum    Space  Mechanisms  

Jason T. Galary* 

Abstract  

The purpose of this research is to investigate the efficacy of lead naphthenate as a wear additive in a multi - alkylated cyclopentane (MAC) fluid for use in high vacuum space mechanism applications. The use of lead  naphthenate in MAC lubricants has a spacef light history of over thirty years. However,  despite the history  of use for this additive in a variety of rolling and sliding applications, little is known or  understood about the  tribochemical process by which these additives  function.  

This research looks at the performance of this additive in simulated contact tests using SRV (Sliding in  Atmospheric and Vacuum Conditions ), as well as a scuffing test performed in a mixed rolling/sliding contact.  In addition, application simulation tests are being performed including high vacuum spiral orbit tribometry  (SOT) and vacuum angular contact ball bearing testing. This test program evaluates the additive in both a  mixed film and boundary lubrication contact under vacuum and atmospheric conditions to better understand  how the additive functions on a metal surface. This report  of the test programs  current progress will include  high vacuum bearing life testing, boundary/mixed lubrication scuffing wear, outgassing, and SOT.  

The results of this work will help the design engineer understand how materials, including lubricants, play  a critical role in  the performance and life of space mechanisms in demanding high vacuum environments.  A greater understanding of the relationship between lead content and tribological performance will be  developed along with further understanding of the tribochemical degra dation process. Data gathered from  wear testing and application simulation work will provide mechanism design engineers with a better  understanding of the tribological performance of this lubricant additive .   

Introduction and Background  

Lead naphthenate has been used heavily as an anti -wear and extreme pressure additive in multi alkylated  cyclopentane lubricants for high vacuum space mechanisms. The additive consists of a centralized lead  ion that is bonded with the oxygen atoms of two carboxylate groups  each attached to naphthenate aromatic  rings . The naphthenate aromatic hydrocarbon rings provide solubility of the lead naphthenate in different  hydrocarbon oils , but the way the additive reacts with steel and protects against wear in various lubrication  regimes is still not fully understood.  

The historical use of lead naphthenate originates from industrial gears and bearings where it was used an  extreme pressure additive over fifty years ago. Over the last thirty years, it has gained a lot of spaceflight  history although there are still many questions regarding its efficacy , primarily how does it function in various  lubrication regimes, the effects of different metallurgy, and how environmental pressure effect its  performance.  

With the increasing number of space mechanisms being developed and launched as well as the increasing  length of mission time required, it is critical to have a robust design with high reli ability. To improve the  reliability, it is necessary  to have long lives  for all of the components in the design. This will require  that the  lubricants used for space  mechanisms  must also improve. The use of lead naphthenate additive in multi  alkylated cycl opentane fluids  is a proven additive package with spaceflight history but in order to develop 

* Nye Lubricants, Inc., Fairhaven, MA  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center, 2020