236 There are three levels for cleanliness in a grease:  

• Unfiltered grease –  Can contain particles larger than 75 µm.   • Filtered or so- called “Clean” grease –  For example MIL- G-81322 Aircraft grease cannot have any  particles greater than 75 µm and there must be fewer than 1,000 particles/cm3 between 24 µm and  74 µm.  • Ultrafiltered or “Ultraclean” grease –  Such as MIL- G-81937 must not contain any particles greater  than 35  µm. In addition to this it cannot have more than 1,000 particles/cm3 between 10  µm and   34 µm in size.  

While these processes will certainly help remove or break up bulk and “hard” contaminants which will lead  to smoother operation, reduced vibration, and lower noise in bearings, ball screws, and o ther motion  applications, it may have little effect on the amount of particles “shed” or generated from a lubricant in a dynamic condition. So th is leaves thoughts about  what effect the lubricant truly has on this phenomenon   and how does the base fluid, th ickener, additive, and manufacturing processes effect this property and  ultimately the application environment around it. The first step to investigate this new area of lubricant properties required the construction of a new test apparatus and creation of an accurate and repeatable  test method [5].  

Objective for Testing  The primary purpose of this study was to use a newly developed test method and apparatus that could be  used to accurately and repeatedly measure the Dynamic Particle Generation of a lubricating grease. This study centered around two different types of lubricants, Perfluoropolyethers (PFPE),  and Multiply -alkylated  cyclopentanes  (MAC). MAC’s are composed of one cyclopentane ring with two to five alkyl groups  substituted  on the ring. The synthesis is performed by reacting dicyclopentadiene with various chain length  alcohols  producing a lubricant  with a various range of  physical properties [7 ]. PFPE’s are produced through  the oxidation of hexafluoropropylene and are fully fluorinated oligomers that contain fluorocarbon links containing oxygen atoms. Two PFPE’s (Braycote ® 601EF and NyeTorr ® 6300) as well as three MAC  lubricants (Rheolube ® 2000, 2000F, and NyeTorr ® 6200) were tested in this study  

Table 1.  Materials tested in study  

 The key factors of this study will be:   1. To study the particle generation tendencies  of different aerospace lubricants  evaluated under  dynamic conditions .   2. To examine the effect that speed plays on the particle generation of a particular system   3. To examine the profile of the particle generation results plot; that is how the system behaves with respect to time and number of particles generated.  

Dynamic Particle Generation B ackground    To compare the D ynamic Particle Generation characteristics of various lubricating greases, a custom test  apparatus was designed and built to detect, analyze, and classify the products  being examined. As this is  a newly created test method and fixture, a Design of Experiments  was put together to investigate  repeatability, variability , and statistical significance  [5].    The core of the test apparatus is a high- precision ball screw assembly meant for  cleanroom and low  outgassing applications . This ball screw design was used due to the fact that when lubricated correctly and  under light load, it experiences virtually zero wear on its components. Since a ball screw assembly utilizes Braycote 601EF NyeTorr 6300 Rheolube 2000 Rheolube 2000F NyeTorr 6200 Base Chemistry PFPE PFPFE MAC MAC MAC Thickener PTFE PTFE Sodium PTFE PTFE