Dispersion of Silicone Antifoam Agents

Most often  the  additives  employed  in   compounding  gear  oils  are  readily  soluble  in the  base  oil; therefore , simple  mixing, as described  above, is  sufficient  to obtain a  satisfactory  blend. On the other hand,  since  silicone fluids which are  frequently  used  as  antifoam  agents have  limited  solubility in oils, they  must  be  thoroughly  dispersed, or they  will settle  out. In view  of this  Beerbower  and  Barnum  made  a study  of  dispersions  of  silicone  defoamers  in oils  using  radioactive tracers  to  determine  dispersion  and  separation of these  additives. They  concluded  that  to  form  stable  dispersions  of  silicones  in oil  the  droplet  size  of the  additive  should  be  in the  10  micron  range. This  could  be arrived at by  heat  and the use  of  high  intensity  mixing  approaching colloid  milling. In laboratory mixers, a speed of 4800 rpm and a temperature of 200 degree F “gave blends in which the silicone was uniformly dispersed after 70 days of storage”.

Lubrication of Special steels

If special alloys are used in one or both members of a gear set, special consideration may be necessary in choosing a lubricant.  The supplier of the equipment will no doubt have the answer since, as Forbes et al. ^20 states:

“The choice  of  metals  that will operate together in a particular type of  reduction  gear is based on practical  data  that have been secured by trial  and error methods  over a period of years.”

It is known that some steels are more difficult to lubricate than others. Stainless steel is very important in this time. Some alloys will not react readily with certain EP elements. Chromium  is  practically  inert  to  sulfur  compounds  but will react  with most chlorine  compounds. Therefore, with high nickel-chrome-molybdenum alloy steels it is important that an EP lubricant contain chlorine additives as well as sulfur compounds.