Nonferrous Metal Rolling Gear Lubrication

Metals such  as aluminum, brass, copper etc., are  rolled  into  sheets or  other  shapes in  continuous rolling  mills designed  somewhat like those  found in steel  mills. Modern mills use circulating oils to lubricate the gear drives, pinion stands, and journal bearings. Either mild EP or MP gear oils of a noncorrosive nature can   be employed in such service. The  grade  of  oil  will depend  upon the speeds  of the gears  and  may  vary  from an  SAE  80  to an SAE  140. In  screw down  equipment  either of the above  type  of oils  or a straight  mineral  oil  can  be  used. Where  any  of the above  drives  are  through open gears, a residual  type  of gear  oil  containing  a  rust  inhibitor  and having  a viscosity  of 1000 to  2000 SUS at 210  degree F  should  prove  satisfactory. The  best  practice  is to  apply  such a lubricant automatically so as  to  insure a coating on  the  gears  at all  times. 

Corrosion prevention by gear lubricants

Ellis et al.^22 consider that staining, tarnishing, and rusting are all  indications of corrosion. The thought is that light stain or tarnish represents the early stages of corrosion since, unfortunately these  changes do not proceed very far before pitting starts. Unreactive gear oils, which have not been subjected to excessive high temperature oxidation, have no tendency  to corrode  metals but, under moist or humid conditions or in the presence of  most salts or acids, do not offer proper protection against  rusting of ferrous  metal  surfaces such as gears. However, additives can be included in gear compounds which will provide rust prevention. Where conditions of incipient rusting prevail, the gears and other metal parts even to the inside of the gear case may require protection, particularly when idle. In such cases not only will the presence of a rust inhibitor but also the viscosity of the base oil be factors. Thus, the higher the viscosity of the gear lubricant, the slower this will drain from the metal surfaces and consequently the greater the rust prevention. Rusting may occur in different environments and various theories are offered as to the mechanisms of corrosion, but normally moisture and oxygen are the offenders

Most rust preventives are polar substances, such as long chain fatty acids, fatty amines, metal sulfonates, certain esters, oxidized petroleum fractions, etc. Such materials wet a metal surface preferentially and displace any water which may come in contact with the steel. The coating of polar substance then acts as a barrier against water reaching the metal surface.

As previously mentioned, controlled  corrosion due  to  EP  additives  is generally beneficial in  that  it  corrodes  away high  spots   on the gear  teeth after  which corrosion may decrease. With the proper selection of the chemical agents, these are not activated except under extreme conditions of load and /or temperature. Further, most of the EP additives which are  used  in  gear  lubricants will have little effect  upon  other  metals such  as bronze, copper, etc; at the bulk oil temperatures maintained  in normal  gear operation .