Moisture Corrosion Characteristics of Universal Gear Lubricants

A full  scale axle  gear  unit is used  for this test. Before the test , the  parts  are cleaned as follows: immerse   in a 1 per cent solution of Sodium Hydroxide  for  1 hour. Rinse  the  parts with water  until free  of caustic. Dry  the parts  by  rinsing  with  methanol, followed by  air-blowing to  remove  the  methanol. After  the assembly, 28 ml of  distilled  water  is put in the axle housing followed by  filling with  the gear lubricant to the  level plug. The  propeller  shaft is  rotated  at a speed of 2,400 rpm  for  4 hours while  the  oil  is maintained  at a temperature  of 180 degree F. At the  end of the  4 hour period, the  drive is stopped and  the  axle  test  unit  is placed on the  storage  rack  without  draining  the  lubricant. There  it  is allowed to remain for a  10 day period at room  temperature.

At the  end of the 10 day period, the lubricant is  drained and  the  axle  disassembled  for  inspection. The  rating  of the  lubricant shall  be based  upon  visual  inspection for  rusting  of the  gears, the  pinion-gear  bearing,  the  differential-carrier  bearings and  the  differential-gear  thrust surfaces.     

Chemical Activity Toward Copper of Universal Gear Lubricants

This test, which provides for  immersion  of a clean  copper strip in a  sample  of the  lubricant for a  prescribed  time  and  at a given  temperature, rates the  strip at the  end  of the test  as follows: “ At the conclusion  of the  test  the copper  strip  is removed, rinsed with sulfur-free  acetone and  inspected. The  degree  of discoloration of the  strip  is expressed  in one  of the  following  terms:

a.       None

b.      Stained

c.       Light peacock

d.      Dark  peacock

e.      Black.”

Carbon Residue of Oils

These methods provide  some  indication of the  coke forming tendencies  of oils and  hence have  little  application  to gear  lubricants. Also oils  containing ash – forming  ingredients will have  erroneously  high  carbon residue. Values  obtained by  the  two  methods  noted  are not the same. Older  specifications for high  viscosity oils  often  give the Carbon  Residue by the Conradson Method, but the present thought is to  use the  Ramsbottom  Method

For the determination  of this  value a weighed  amount of oil is  subjected to heat so that  evaporation and  pyrolysis  takes  places under  conditions of  restricted  air  supply. In  fact  in the Ramsbottom  Method the  sample  is contained  in  a Coking  Bulb with  a very small  opening. While  the term  Carbon  Residue  is used, it is  recognized  that the  coke  remaining  after  such  tests is not  entirely  composed of carbon.