Life of Scanner Bearings w ith Four Space Liquid Lubricants 

Dean G. Bazi net*, Mark A. Espino sa*, Stuart H. Loe wenthal*,  Lois G schwender**, William R. Jones, Jr.+ and Roam er E. Predmo re++ 

Abstract 

The results o f a life te st program to  evaluate bearing life with dif ferent space lubricants and cleaning  solvent s is presented. Thirty pairs of flight-like scan ner bea rings were tested over a period of seve n  years. Lub ricants included two well kno wn perfl uorinate d spa ce oil s (Brayco 81 5Z™  and Kryto x  143AB™), a  more re cent synthetic hydro carbon oil (Pennzane 2001 ™), and  one yet to be in spa ce  servi ce (sila hydrocarbon oi l). Bearin gs lubricated with Penn zane 2001 oil were found to hav e the longe st  lives. Life improveme nts up  to 18X relative to perfluor inated oil s and 3X relative to the silahyd rocarbon oi l  were me asured. No statist ically si gnificant life impro vement wa s found with TiC-coate d balls relative to  stand ard plain steel ball s for Penzan ne 200 1 bea rings. Bearin g life was generally long er when the   beari ngs were cl eaned with o zone-safe aque ous or hydrofluo rocarbon (HFC) so lvents as alternate s to th e  discontin ued CFC-1 13. 

Introduc tion 

Bearin gs for spa ce appli cation s have  histori cally been cl eaned with a chl orofluo rocarbon CF C-113  (Freon ) solve nt until the early 1990’ s when the prod uction of this oz one-depleting solvent wa s bann ed.  The n eed arose  to qu alify alternate  cleane rs since bea ring l ubricant life was considered to be ve ry  sensitive to surface chemi stry. A full-scale bearing lif e test  program was initiated for NASA in April 1996 to  evaluate three environme ntal-frie ndly clea ning solv ents.  The so lvents in cluded in thi s study we re an  aque ous-based clea ner (Brulin 815 GD), a perfluorinated  hyd rocarbon  (morpholin e) solvent (3M PF - 5052 ), and a n HFC solve nt (DuPo nt Vertrel XF). Interm ediate test re sults p reviou sly rep orted [1, 2]   showed bea ring lives with these alte rnate clea ners were at lea st as lo ng a s those cleaned with th e  traditional  CFC solvent. Th is was not consistent with  earlie r tests using a tran sient ela stohydrodyn amic  appa ratus in air, whi ch indicated that  beari ng lifet imes mi ght be comp romised by som e of the ne w  cleaning te chnique s [3]. Later a ccelerated tests using a Spiral Orbit Tri bometer in va cuum, howeve r,  yielded no d etrimental effe cts on lu bricant lifetime [4]. 

An equally i mporta nt obj ective of the  tests was to evaluate pot ential life im provem ents attended with  improve d space va cuum lubricants. Although exten ded mi ssion lifetimes of many ne w space sy stem s  have d riven the n eed to e valuate n ew flight lub ricant s, thei r acceptance  is contingent on est ablishing  an  adeq uate life test datab ase. The lub ricants incl uded in this stu dy were tradition al perfluorinate d oils, which  were co mpared with a rela tively new mu ltiply-alkylat ed cyclo penta ne oil (Pen nzane 20 01). At the time the  interme diate test results were re ported, the Pennz ane 2001 be aring lives we re much long er than those   with the baseline pe rfluorinated oil s and six of the eight Penn zane-lubri cated bearing s were still runni ng.  The present i nvestigatio n report s the final life test re sults, with the addition of a new silahyd rocarbon oil  which has a good va por pre ssure an d goo d low tempe rature v iscosity p roperties [5, 6]. The u se of  titanium ca rbide (Ti C) coated ball s as a mean s to increa se b earing life over that of sta ndard 44 0C  stainle ss stee l balls was al so evalu ated with Penn zane 2001. 

Thirty pai rs of flight-like scanne r ball bearing s were tested i n a 10-6 Torr va cuum at ambie nt temperature   in this current  study. Periodic bear ing health torque checks were perf ormed, consi sting of  oscillations and                                                    * Lockhee d Martin Spa ce Systems, Sunn yvale, CA  ** Air Force Rese arch La boratory, Wright -Patterson A FB, Dayton, OH  + SEST, Inc ., Middleburg Heights , OH  ++ Swal es Aerospace, Beltsville, MD 

Procee dings of the 37th Aeros pace Mec hanisms Sy mpos ium, Joh nson S pace Ce nter, May 19-2 1, 200 4  333