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.

Load carrying Capacity SAE Test Apparatus

As previously mentioned, this machine is a device in which two Timken test cups, no. T-48651, are rotated  in line  contact  with  each  other  and  in  opposite  directions, with  provision  for  controlling  the  speed  of rotation, the  slipping  velocity  and  the  rate  of  applying  pressure  at the  line  contact  between  the  rotating  cylinders  or  cups. To obtain reproducible  result, it is  essential  that  the  surface  finish  of the  cups  used  be  uniform  and  that  the  shafts  on  which these  test  pieces  are  carried be in  perfect  alignment. Both points are covered in details of the test methods. The  total  variation  in surface  finish  shall  not  exceed 10  micro inches and  the  inside  and  outside  surfaces  of the  test  cups  shall be  concentric  within  0.0005 inch.

With the  lubricant  tester  in good  mechanical  condition, test  shafts  true, and  the  alignment properly  adjusted, the  test  cups of  specified  surface  finish  and  concentrically  are  placed  on the upper and lower  shafts. With the oil box overflowing, an initial load of 15 to 20 pounds is applied. The  machine  is  then  started and  at the  end of a  30 second  period   the  automatic  loading  device, at  the desired  rate  of loading , is  started. The test cups are then observed for signs of scoring. This  is most  readily  detected  by  observing  the  lower  test  cup  on the  trailing  side  at a  position  approximately ½  inch  from  the  contact  line. When  signs of  scoring  are  detected, the  drive  motors  are  stopped  and the load  removed. After  thorough  cleaning  and  with  new  test  pieces and  fresh  oil  the test  can  be  repeated.

The suggested conditions of test are a main shaft speed of 1000 rpm and a rubbing ratio of 14:6:1. The  load should  not exceed 450 pounds and  if no  scoring  occurs  at this point  the test  is stopped to  prevent  over heating  of the  shafts, etc.

This test  has been  primarily  used for evaluation of automotive  gear  lubricants  but has not  replaced  tests  with gears.