Additives for Straight Mineral Oil Gear Lubricants

All gear oils should contain a foam inhibitor, probably in the range of 5 to 10 parts per million. In order to arrive at approximately the correct proportion of such an additive, it is best to use a concentrate. This may be a ten per cent dispersion of a dimethy1 silicone in either kerosene or carbon tetrachloride.

Suppliers of silicone polymers offer antifoam additives, most often as concentrates and will suggest proportions to add to gear lubricants. Other compounds or  dispersions of the  same  are also  available  from  additive  suppliers who  furnish  instructions  for use.

While  most  industrial gear oils  are  not subjected  to  elevated  temperatures, the  presence  of a small  proportion of  oxidation  inhibitor is an assurance  of long life  and little deterioration of the oils. Additives such as 2, 6 – ditertiary – buty1 -4 – methyl  phenols or phenyl  alpha or  beta  naphthylamine , used  in  proportions  of 0.1 to 1.0 per cent, should be  found satisfactory for  most  straight  mineral gear  oils. The first compound or one quite similar is supplied by several concerns, often under a trade name. Other  antioxidants  will  be  noted in  various formulations to  follow and  will also  be  found in  Boner where the  source  is also shown.

For special applications other types of additives may also be found necessary in what can be classed as straight mineral oils. Thus, Watson  and Tierney  Formulated oils to be used under wet  conditions on paper  making  machines where a circulating  oil would  serve both bearings  and  gears. Since, in  this  operation, the  oil passing through the  system is  quickly  contaminated  with  water which  settles out, retention of  the rust   preventive additive  is quite important. A  suitable  formulation, which  retained the  major portion of the  additives after over a 1000 hours of  service, consists of : a  base  oil  blended from a paraffin  distillate  and a  paraffin residual  and having a  viscosity SUS at 100 degree F of 653, a pour  point of -10 degree F, and  a V.I. of  85; 2.0 per cent  by  weight  of a 50  per cent concentrate of  barium  dinonylnaphthalene   sulfonate in a light oil; 0.75 per cent of Zinc  dimethylisobutyl  carbinyl  dithiophosphate ; 0,10 per cent  of a  chlorinated  paraffin  wax naphthalene  condensation product; and 150  ppm of a 10 per cent  solution of  dimethyl  silicone  polymer in  kerosine.

Designation and recommendation of gear lubricants

While  industrial  gear  lubricants  are  often  marketed  under  trade  names, information  is  always  available  as  to  how  these  products  conform  to  AGMA  numbers . Therefore, little   difficulty occurs   with the designation of this time of gear oils.

However, in  the  case  of automotive  transmission  and  axle  types  of  oils the  marketing  designation  has  not  always  been  clear  and is, in fact, sometimes  misleading. The SAE  Handbook, in  about  1924, started  to  include SAE  viscosity  numbers  for  such  lubricants, and when , in 1951, API approved  definitions  for ‘Regular-Type Gear  Lubricant,’’ ‘Mild  Type  EP  Gear  Lubricant,’’ and  ‘Multipurpose Type  Gear  Lubricant’’ these  terms  were  suggested  for  use  by  SAE. With the  availability  of   improved  EP  gear  oils, as  mentioned  above,  the  API   Lubricating  Committee, in 1957,agreed  that  such  products  should  be  known  as  ‘Multipurpose  Type  Gear  Lubricants (API  Service  GL 4).” Such oils were described as follows:

“This  term  designates  Lubricants  which  have  adequate  load  carrying  ability  and  other   required  properties  to protect  hypoid  gears  in  sustained  high   speed  and /or  high  torque  service  in  modern  high  powered  passenger  cars  and  trucks.  Also  suitable   for  use  in  spiral   bevel  gears, many  transmissions, and  worm  gears  in  some  types  of  service.  Such Lubricants are identified as meeting ‘A.P.I. Service GL4’.’’

The  consumer   of  gear  lubricants  should  bear  in  mind  that   such  products  are  like  other  commodities, in  that , while  a  conscious  organization  may  set  tolerances  for  material   to  be  supplied  under  a  given  designation, some  products  offered  will  barely  meet  the  required  specifications. Therefore, the  purchaser  or  user  of  gear  oils  should   deal  only  with  reputable  firms.