Solids as Gear Lubricants

Dry solids, such as graphite or molybdenum disulfide, have had very limited use as lubricants for gears. More often such solids are used in conjunction with fluids for gear lubrication. Such use is not general and data as to their value is meager.                                                     

                                                                                     
A large gear on a radar  installation was  said  to  be  difficult to  move  until  molybdenum  disulfide was  mixed  with  the oil used. Vago^50 cites  gears operating  in excess  of 200 degree (F)  where  both automotive gear oil and  a molybdenum disulfide  fortified  lubricant were tested. After three years, inspection of the gear teeth indicated no advantage of the latter lubricant over “the chemically fortified gear oils”.

If  solids  are  included  in gear oils, the particle size of the additives  is  of  importance and should  preferably  be of  colloidal size. Thus, Kyropoulos^28 in citing  claims  for a 20 per cent increase in efficiency  with  a  worm gear  unit after  adding  colloidal  graphite, also stated  that powdered  graphite was not  effective. While settling of the solid occurred in this case there was said to be no  clogging of oil ducts.

No mention is made of the proportion of solids  desirable, but one  per  cent  of a  colloidal  suspension, which  in turn  contains 10 per cent  of  solids, is a  normal dosage. This holds true for either graphite or molybdenum disulfide. The latter  material  has  been  recommended where  there  is  impact  loading, or  oscillating or  reversing motion.

Application of Lubricating Greases to Gearing

Methods of application of lubricating greases to gearing will vary with the specific mechanism. As a rule, such products are not used on fast moving gears or on those where considerable cooling is necessary. Lubricating  greases  do have a place  when  gears are used  infrequently  and receive scant  attention, as in home  washing  machines, kitchen mixers, etc. Here the lubricant may be applied during assembly.

Thinking  on the application of  lubricating  greases  to gears may  change  if  the   results reported  by  Gesdorf^21 can be  repeated. As, a trial, all points on a steel mill table were lubricated by spraying a lithium base grease once an hour. The points covered were 38 table roll and line shaft bearings and 27 on open gearing. Previous to the test, 40 pounds of gear lubricant and 2 gallons of bearing oil were used on each 8 hour shift. After installation of the new spray system, 1.6 pounds of lubricating grease were used per eight hour operating turn. Further, it was found that bearing life was increased 40 per cent and it was estimated that gear life was increased 75 per cent.

Rather than make general recommendations, suggestions for applying lubricating greases will be given when lubrication of specific equipment is discussed.