Thickeners for gear oils

The use of thickeners in gear lubricants is not common:  hence, little space need be devoted to the subject. Where lubricating  greases  are  used  in gear sets,  soap  is  normally  the thickener  and  hence will  be  present. In  gear  housings  which  are not  tight, grease will  stay  in  place better  than  will  oil. Later  some  specific  applications  will be  mentioned  where  lubricating  greases are  employed, and  in  such  cases  the  type  of thickener   present will  be  evident.

Resins, both natural and synthetic, are occasionally recommended as thickeners in gear lubricants. Thus, resins separated from Pennsylvania residua are so used. Likewise, certain  grades of  polyethylene  are  thought  to  have not  only  thickening  power  but  also  to  contribute  film  strength  to  lubricants.

Inorganic solids, which  were  previously  mentioned as  being  used  in  gear oils  because of their EP  characteristics, have some  thickening  power  but  are  normally  used  in such  low  proportions that  bodying  is  not  evident. However, fine  silica  is a  component  of  some  semi fluid lubricating  greases  used  in   gear  cases  which  are not  tight and thus would  show  abnormal  leakage  with  fluids. 

Diesel Locomotives –tractions Gear-Lubrication

Most traction gears on diesel locomotives are lubricated with high viscosity, adhesive gear oils. Residuum  type products  with  viscosities    as  high  as 500 Furol  at  210 degree F    have  been  used, but  in most  cases  a viscosity  of  2000 SUS at 210 degree F is  satisfactory. About  fifteen  pounds is  required  for an  initial  fill  and  since there  is  some  leakage,  the  gear  case  should  be  checked and refilled at  least  every  month. U.S. specification MIL-L-13914 (ORD) provides for two  grades of such oil, one  with  a viscosity  of 170 to 240  Say bolt  Furol  at 210 degree F and  the other  with a similar  viscosity of  480 to 580. A lubricating  greases is  recommended for the  purpose by  Morway  and  Ball^38  in which  the  thickener  is a  complex  sodium  soap  and the fluid is a mixture of  14.93 parts of a  low  cold  test oil  having  a  viscosity of 55  SUS at  210 degree F  and 75 parts of a  resin  from a Pennsylvania  oil  having a  viscosity  of  14,000 SUS at  210 degree F. When  such a  lubricant was used  in a  locomotive  in  freight  service  it did  not  leak  from  the gear  case, and  after  one  year  of  service there  was  only  slight  wear  on the  pinion  and driving  gear  teeth.