Lubrication of Non-Reactive Surfaces at High Loads

By non-reactive is meant that the  surface will not react with  what  are  customarily  known  as EP elements such as  chlorine, phosphorus, or sulfur compounds. While there is little likelihood of extensive use of  some metal  combinations, it is well  to mention the possibilities. Thus,Antler suggests that 0.03 to 10  per  cent of trimeric  tin  sulfide compounds in  either  oils  or lubricating greases will  increase  the anti wear  qualities of the lubricant on surfaces such as  titanium-on-titanium, stainless steel-on-stainless steel, or gold-on-gold. The same  additives are also  said to be  effective on plastics, such as “nylon”, polyvinyl  chloride, polyethylene, etc.

Chromium is inert to most sulfur compounds but  will  react  with  most  chlorine compounds. Consequently, in  lubricating stainless steel  gears  under  heavy  loads, the  use  of chlorine compounds is  dictated.

Manufacturers  of gears  from  special  metals or  other  materials will no  doubt have  suggestions as to  the  proper  lubricants. Since EP agents are not  effective on  Babbitt, use of such  compounds in lubricants for  certain journal  bearings will  not  increase  the  lubricating  value.

Method of application

The best lubricant in the world will fail to accomplish its purpose if it fails to be present on the moving surfaces when required and in the proper amount. Therefore, it should be kept in mind that method of application is as important as the product used. Lubricants may be applied to gearsets and auxiliary mechanisms either manually or mechanically. Hand application is seldom practiced except in the case of exposed gears. Minor exceptions to this rule  will  be  found  in the case of small mechanisms, couplings, etc; where  most often  lubricating greases are  added  by hand, either upon installation of the equipment or  at  very  infrequent intervals. Mechanical application may take the form of bath, drip, splash, or forced feed. The  latter method  may  simply involve a  stream  of  oil  but  most  often  will  be  in the  form  of  jets  or spray,  fog or mist.

Normally one thinks of gear lubrication in terms  of fluids but an occasional  situation will permit  or  require  either  a  lubricating  grease or  a solid.

The  manufacturer  of equipment will  generally  provide a method for application of gear lubricants, but  sometimes  the  user of a  machine  will  consider  a  change  in lubrication methods.  Therefore, enough detail  of  each  method  of application will  follow  to  permit  selection of the  most  desirable.

The  most  important  factor in a lubricating  system is  reliability  because  failure  to  supply  lubricant will  cause damage  to  machinery . This  then points  to  automatic  gear  lubrication which  is more certain  than  hand  lubrication. Another factor to consider is cost. Circulating oil systems entail a high first cost as they are usually complex. Hand application devices cost little  but  there  is a  possibility  that  use of this method  of  application  may  lead  to higher  maintenance charges than if  the  lubrication were  automatic. Where an  oil is  used  on  a once-through basis, as in hand  application, a less expensive oil  may be used  than  in  bath, splash, or circulating  lubrication. Cleanliness, which  carries with it  less fire  hazard, greater safety, and reduced possibility of damage  to material  being  processed, is  best  obtained  by  enclosed systems  of gear lubrication. While  automatic  methods of gear  lubrication are  the most  efficient and  reliable  of  the systems  mentioned, such  devices  require  some  attention  to  see  that  a  proper  supply  of  uncontaminated oil  is  available  and that  the  feed  is  properly adjusted.

Further, installation of  a particular type of a  lubricating  system does not  necessarily  mean  that  this  will  function as  desired. While some  problems which may  be  encountered will  be mentioned, either  when  different methods  of application  are  described or  in  a  future  chapter devoted  to problems, there  is  often  greater  possibility  that  the  trouble  is  mechanical  rather  than  due  to  the  means  of  application. Therefore, a correction  of a gear  lubrication  problem  may be  a step- by step  process, such  as  that  described by  Gesdorf^21  when  an  automatic spray  system was  developed  for  open  gears. When and  if  unsatisfactory lubrication of gears  occurs  and  an  automatic  system is  involved, the  best  procedure  is to  bring  in  both  the  oil  supplier  and  the   manufacturer of the  lubricating equipment.

Reduction of wear in gear sets and transmissions

Wear has been defined by a Committee of the Institute  of  Mechanical Engineers as: “Progressive loss  of substance  from the surface of a body  brought  about by mechanical  action ( usually it  reduces the serviceability of  a  body  but  can  be  beneficial  in its  initial  stages  in  running in)”.

It is evident from  this definition  that  what  is desired  in a gear lubricant  is  prevention  of  continuous  wear. With highly loaded moving parts, which include gears, the following types of wear may occur:

                            

                            (a) Abrasive and cutting wear.

                            (b) Corrosive wear           

                            (c) Fatigue wear.