Deodorizing Gear Lubricants

Straight mineral oils should have no offensive odor. Lubricants containing EP agents will  often  have odors which  are not  too pleasant. However, when in an  enclosed gear case  this will  not  be  particularly  noticeable  unless the  operating  temperature is high. If a problem of this  nature is encountered, the  first  step will be to  see if addition of another  odoriferous substance will cover up the first  scent. Thus, pine oil might serve for this purpose. Addition of chemicals which might  change  the  odor of EP lubricants  should  be made  with  caution because  they  might  interfere  with  the EP value  of the  composition.

Pentane and Benzene Insolubles in Used Lubricating Oils

Normals  pentane insolubles are the  insoluble  matter  which can be separated from a solution of oil  in n-pentane and  in addition  to benzene  insolubles, may  include  insoluble resinous  bitumens produced from the  oxidation of oil. While  this  test  was  designed  primarily  for  use with used  engine oils, it does  have  some  value   in determining that  a breakdown has  occurred  in gear  oils. Any  appreciable  amount  of pentane  insolubles  in used  gear  lubricants indicates that  the  gear  box  has been  quite hot, usually  above 300 degree F.

Benzene  insolubles  are  that  portion of n-pentane  insolubles  not  soluble  in benzene and  may  include  insoluble  matter  produced by  oxidation and  thermal  decomposition  of the  oil  and  oil  additives. Any  suspended  particles  from  metal  wear  or from  external  contamination  will  also be  present  in the  benzene insoluble  fraction.

Viscosity Index Improvers

While  the change in viscosity  of lubrication oils with  change  in temperature  can  be  reduced  by  the  addition  of  certain  long  chain  polymers, such  use  in gear  oils  is not  common. Such  polymers when  subjected  to   the  shearing  action of  gear  sets  degrade  and  form  shorter  chain  compounds  which are  less effective  than  the  original  additives. These agents may also function as pour depressants. The  reason  the  polymers in  question  are  effective  is that  at  low temperatures  they  are  coiled  up  and  only  colloidally  dispersed. As  the  temperature  increases  the  polymers  uncoil and  go  into  solution  to  increase  the  viscosity  of the mixture.

Pour Point Depressants

Certain  polymers when  added to wax containing lubricating oils in  proportions of 0.1 to 5 per  cent, will  alter  the  crystal  structure  of the  wax  and  thus  permit  movement  of the  oil  at a much  lower  temperature  than  before  the addition. Some  agents  used  for  other  purposes, for  example V.I. improvers, may  have a similar  influence on  pour  points.

Most  industrial  gear  oils do not  require  this  type  of  additive but  pour  depressants are  often  included in  automotive  gear  lubricants. The agents  normally  used  include  “Acryloids”  which  are  methacrylate  polymers,  and  “Paraflow”  or “ Santopour”  which  are  wax condensation  products with either  naphthalene or  phenol.