Self Repairing Surfaces on Gears

Some thought has been given to addition of material to lubricants which would aid in providing a more uniform surface on gear faces as  they operated. Thus,  a report was  made of the use  of molybdenum disulfide particles, mixed with the lubricant, which were  presumed to pack in  irregularities of the teeth  on a large gear. Where other solids are  used in  gear  lubricants, they may  act as mild abrasives and, thus, produce a  polished surface after  running. Where gear  faces are  smoothed out  during operation, the  action  is  probably  due  to  attrition. Therefore, any  self healing  procedure  for such  surfaces  remains  to be  devised.

SAE Extreme Pressure Lubricant Testing Machine

Since  investigators  often  refer  to wear  tests using  the SAE EP Lubricants  Tester, this  apparatus  deserves  mention at  this point. The machine  was  constructed  under  the  sponsorship  of SAE  by  the  Bureau  of Standards. The  action  is  presumed  to  imitate  the  rubbing  of  gear  teeth  by  rotating  two  Tim ken  test  cups (T-48651)  in line  contact  with  each  other  and  in  opposite  directions, under  controlled  speed, slipping  velocity,  temperature  and operating  pressure.

The  conditions selected by  Calish  for wear  tests  on an SAE  machine  were: 500 rpm; 3:4:1  roll ratio; 180 lb  load; 225 degree F; 500 ml /min  flow  rate; and  4  hours  test  duration. This author makes the following comment relative to this test:

“ Experience  in the  laboratory  and  from  service  indicates  that  it  is  desirable  to  hold  the wear to less  than  30 mg  in the  test  consistent  with  other  desired  oil  properties.”     

The Timken test cups can be weighed before and after a run and thus the weight loss in mg determined. For  wear tests on an  SAE    EP Tester  the  conditions  should  be  modified over  those  used  to  determine EP values. Such conditions are speed, rubbing ratio,     pressure and perhaps temperature.