222   Pin-On-Disc Testing   To address the concern of cross -contamination damage due to potential inter -mixing of Pennzane and  Braycote, Pin- On-Disc testing was conducted with a 50/50 by mass mixture of Braycote 600EF and  Rheolube 2000. The test was conducted at a 0.77 m/s rate in one rotational direction, with a pin pressure  of 500 MPa. The result is shown in Figure 14. An increase in the coefficient of friction (CoF) was seen at  the test onset, which settled relativel y quickly after about 200 m, staying constant until around 3.5 km. After  this, the measurement noise and the CoF both increased and fluctuated slightly until the test was completed  after 7.5 km of pin travel through the lubricant mixture. The test demonstr ated that there would be no  significant detriment to performance with a potential long- term mixing of the Rheolube and the Braycote.  

A Final Lubrication with an Unexpected Twist   The results of the Pennzane accelerated test, cold testing, and Pin- On Disc testing all gave the green light  to reattempt the Endurance Test with the new lubricant configuration. A final spare, un- used and undesignated HD remained, and was selected to be the first to receive the new treatment. The unit was  cleaned first with the vapor degreaser and Vertrel XF to remove the Braycote 601EF, then reprocessed  using a 10/90 by mass Rheolube 2000/Heptane grease plate, followed by a 40/60 by mass Nye Synthetic  Oil 2001/Rheolube 2000 slurry fill process. When the HD was installed into the Drive Output Subassembly,  a small piece of debris was found in the Wave Generator bearing lubricant, accompanied by a crunchy  feeling upon bearing rotation. The unit was re- cleaned, re- inspected, and received an additional abrasive  touch- up to remove some newly found corrosion. New lubricant was applied, and a similar result occurred  with a mysterious grease discoloration discovered upon higher -level assembly of the HD, accompanied by  more bearing crunch.  

Figure 14.  Pin-On-Disc Results for 50/50 by Mass Braycote 600EF/Rheolube 2000 L ubricant on 440C  (58-62 HRC) S ubstrate in a Uni-Directional Test Configuration with a P in Pressure of 500 MPa and R ate  of 0.77 m/s.  

Thus the time had come to completely disassemble the Wave Generator subassemblies, down to the  individual ball level, for inspection. Each bearing was pressed off of the Wave Generator, preserving  serialization between the two sets of bearing components. T his revealed a significant amount of corrosion,  on the bearing balls and races, and along ball paths. The source of the crunchiness was confirmed. The  corroded surfaces were abraded as much as possible, the components were cleaned with boiling deionized  water followed by Heptane, reassembled into bearings, which were re- bonded onto the Wave Generators.  The Wave Generator assemblies were then re- grease plated and filled, as before.  

The coppery appearance of the bearing sample had been due to high levels of  iron oxide, according to the  Raman spectroscopy results. It was highly likely that similar high levels of corrosion hiding in the corners  of the Wave Generator bearings in the previously failed Endurance Test helped accelerate the PFPE  degradation, readil y able to help produce the high Lewis acid fluoride contents seen in Table 1.