contin uous rotation patterns. Te st acceleratio n factors included increa sing th e prel oad of each bea ring  pair by roug hly a facto r of three  time s from typical  scanne r bearings, reducing the am ount of the lu bricant  to about one -third, and con tinuou sly cycl ing the bea rings at a small stroke such that compl ete rewetting of  the ball  conta ct does not occur. At th e time of thi s report, all  but one pair of b earings had  been te sted to  failure. 

Test Des cription 

Test Matrix   The o riginal test serie s evaluated th ree different ODC-free bea ring clea ning solv ents against the CFC-11 3  (Freon ) ba seline. The se con sisted of an aque ous-ba sed wash (Bruli n 815G D), a perfluo rinated  hydro carbon solvent (m orpholin e) from  3M (PF-50 52), and a hy drofluo rocarbon solve nt from DuPo nt  (Vertrel XF). A fourth solve nt, heptane, wa s used in preparing the silahydro carbon-lub ricated b earin gs. 

The baseline lubri cant wa s Brayco 815Z ™ oil, a perfluor inated p olyalkylether (PFPE)  linea r fluid, cu rrently  distrib uted by  Castrol Ind ustrial North Ameri ca. Thi s oil has more  flight history  than any ot her class of  space lubricant. The second te st lub ricant was a fo rmulated multi ply-alkylate d cyclo penta ne (MAC) oil,  gene rically re ferred to as Pennzane 2001™ and distributed by Nye  Lubricants. This lubricant contai ned a  triphenyl phosphate anti wear additive along with an antioxidant. The thi rd test lubri cant was a branched   PFPE oil (Krytox 143AB™) manufactu red by DuPont. The fourth and final test lubri cant, a late addition to  the test p rogram, was a silahyd rocarbon oil formul ation. The m olecular fo rmula for thi s unimole cular  silahyd rocarbon ba se oil was CH 3Si(CH 2CH 2Si(C 6H13)3)3, with a molecula r weight of 976 a mu. This oil  was synthe sized a nd form ulated by Nye Lubri cants, wi th the sam e formulatio n as used in the Penn zane  2001. Origi nally develop ed by the Ai r Force fo r high temperature  aircraft b earing applications, it h as low  vapor pre ssure and relativ ely low col d temperature viscosity ma king it a poten tially good candidate fo r  future spa ce appli cation s [5, 6]. Approximately one-t hird the n ormal amou nt of lubri cant (60 to 80 mg of   Brayco  815Z and 30 to 50 mg of the  other test lub ricants) was used in all  test bearin gs, in order to  provide  for accelerated test results. 

With the exception of the  three pai rs of silahyd rocarbon-lubricated bea rings, all of the so lvent – lube   combi nation s were teste d in duplicate to  provide greater confid ence in  the results. All test  bearing s were   processed by the Mi niature Pre cision Bearin g (MPB) di vision of Timken,  in order to represe nt end  user  appli cation, again with the exce ption of those lu bricated with silahy drocarbon oil. The se latter te st  beari ngs were clea ned with heptan e and lubri cated a t the Lockhee d Martin facili ty with oil sup plied by the   Air Force Research La bs. 

Test Bearings  The angular conta ct ball bearin gs used for te st (Figu re 1) were sel ected as representative of the type that  would be use d for a spa ce scanner bea ring ap plication.  The test beari ngs are 39.6-mm (1.56-in) bore by   50.8-mm  (2.0-in) O D conta ining 34 balls of 3.2 -mm (1/8-in) diam eter. Th ey were man ufactu red from AISI   440-C steel a nd hard prel oaded ba ck to back with 200 ± 22 N (45 ± 5 lb), resulting in a peak mean Hertz  stress of 0.75  GPa (1 09 KSI). This p reload p rovide d additi onal test acceleration , in that it is a pproxim ately  three time s greate r than  that normall y specified for this si ze beari ng in a  typical long-lived sca nner  appli cation. T he ball se parators a re alte rnating PTFE  toroids. The races a re fini shed to rms rough ness of  less than 0.0 8 micron s (3 micro-in ch). The test b earings had pla in steel b alls, except for a  limited test   series fo r two  pairs  of Pennza ne-lubricated beari ngs whe re TiC-co ated ball s were teste d. Further bea ring  specification s, includi ng a highlight of differences between typical  flight bea rings and tho se used for life   test are p resented in Table 1. 

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