235 The Dynamic Particle Generation of Lubricating Greases for use   in Space Mechanisms 

Jason T. Galary* 

 The purpose of this study is to examine the phenomenon of Dynamic Particle Generation in lubricating  greases that are used in a variety of critical a erospace mechanisms . Particle Gene ration occurs in bearings,  ball screw s, and other mechanical devices where  dynamic conditions are present . This  should not be  confused with outgassi ng as particle generation is un related to the pressure effects on a system. This is a  critical factor in many systems as particle generation can contaminate systems or processes causing them to fail. These failures can lead to excessive costs, production failure, and equipment damage.    In this study, several greases made from Multiplyalkylated Cyclopentane and Perfluoropolyether base fluids were tested to evaluate their particle generation properties. This particle generation phenomenon was studied using a custom test rig utilizing a high- precision cleanroom ball screw  to simulate true application  conditions. The ball screw  was tested at speeds from 200, 1,200, and 2,400 RPM to illustrate the effect of  speed on the particle generation across different appli cations. This paper will show the tendencies of  different lubricant chemistries to generate particles and which ones present advantages of improved durability and environmental cleanliness for critical processes and applications.  

Introduction    Contaminat ion is an element of great concern in regards to mechanisms designed and planned for space  flight. While there are many types of contamination including volatile outgassing, residual ions , airborne  particulates , etc., the route that the contamination enters the system is just as important. Outgassing has  been a well -documented method for contamination in a system and there are many ways to quantify it .  Methods like ASTM E -595 and E -1559 are used to generate control limits. The counterpart to outgassing   or even the more typical volatile evaporation is called Dynamic Particle Generation which can be as  significant of a problem  as outgassing. The term D ynamic Particle Generation describes what happens  when contaminants are created by being forced from a lubricat ed ball screw , bearing, or gear  system into  the operating environment. These contaminants could include base oil constituents, thickener particles, additives, etc. all of which could be volatile or non-volatile.  

The manner in which these contaminants are freed from the lubricant system is through dynamic  mechanical action whether it be rolling, sliding, or a combination of both. This study will begin to investigate and illustrate that factors like mechanical and chemical compatibility, fri ction, speed, etc . all have an effect  on the amount of contamination generated through particle generation. I will also illustrate that physiochemical effects between lubricating fluids and thickeners play a key factor as well.    Aside from the space appli cation environment , materials c an also be contaminated through the   manufacturing process  even if done in a clean room environment . In these environments, the  focus is  typically on the quality of the air in the room and it has long been known  that lubricant s are a source of  contamination in cleanroom and vacuum environments . Historically , in order to alleviate the worries of many  manufacturers , the solution over the last twenty years has been to u ltrafilter 1 the lubricant to reduce the  number of particles in the lubricant and the size of them.  

                                                     * Nye Lubricants, Inc., Fairhaven, MA  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6, 2016