Gear Materials of the Future

The lubricants required in the future  for gear  service  will  probably be  tailored to the  mating  surfaces which are to  be  protected  against wear. Not only will improved ferrous alloys and other metals be used, but also there will be more nonmetallic gears in service. Whether these will be primarily plastic gears or simply improvements on such forms as laminated gears remain to be seen. Probably plastic gear use will increase, particularly in small mechanisms and where loads are light and there is no wide temperature variation.

Investigations are being made  to determine what  combinations of  mating  gears will  show  the  least  wear  when  no  lubricant is provided. This is a fertile field and the supplier of lubricants should keep advised of the advances.

Nonferrous Gears and Their Lubrication

While the tendency is to think only of gears made of ferrous metals, we find in Dudley^16 the statement: “A wide variety of bronzes, aluminum alloys, zinc alloys, and nonmetallic plastics and laminates are used to make gears.”

Fortunately, well refined mineral oils have little action on most of the combinations. We say  combinations  because in  many  cases the nonferrous  gear is driven by a  steel pinion, but when the loads are light and the  gears are small, both members  may be of the nonferrous  material.

Nonreactive oils should be used with nonferrous gears unless specific recommendations state otherwise. This is illustrated in the case of worm gears where the gear is normally made of bronze. The  general  recommendation for  such units is a mineral  oil  containing  tallow, although  often  such  oils  contain  lead  soaps  and  occasionally certain EP agents.

Synthetic fluids, both diesters and “Ucon fluids, have been used as lubricants with nonferrous or ferrous and nonferrous combinations of gears. Where a problem of lubricating  an  unusual combination of  gear  materials is  encountered, the manufacturer of  the gear set should  be  able to  make a safe  recommendation. However, lacking a  suggestion, a well  refined  lubricating  oil  with no reactive additives  present  can  generally be used with safety in the  case of  nonferrous  gear sets.

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.