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.”

Self Repairing Surfaces on Gears

Some thought has been given to addition of material to lubricants which would aid in providing a more uniform surface on gear faces as  they operated. Thus,  a report was  made of the use  of molybdenum disulfide particles, mixed with the lubricant, which were  presumed to pack in  irregularities of the teeth  on a large gear. Where other solids are  used in  gear  lubricants, they may  act as mild abrasives and, thus, produce a  polished surface after  running. Where gear  faces are  smoothed out  during operation, the  action  is  probably  due  to  attrition. Therefore, any  self healing  procedure  for such  surfaces  remains  to be  devised.

Corrosion fog cabinet

A number of test  methods, of which  this is one, make  use  of  bench  tests to  indicate  how  well  a lubricant will  protect steel  from rusting. These  methods  are  most  often  used  for  comparatively  low viscosity oils,  such  as  turbine or  aircraft oils.

Cold - rolled sheet steel panels 2 x 4 x 1/8 inch, surface ground to a finish of approximately 20 micro –inches as measured by  a  Brush analyzer, are  used  as  specimens. These are  coated with  the  oil by  dipping  after  which  they  are  held  in a  rotating  table in a  cabinet  into  which  water  is  atomized. The  cabinet  is capable  of  regulation  from  110  to 160  degree F, but  most  tests are  run  at the lower  temperature  for a given  number  of days  or  hours.

The  specimens  are  observed  through  a window  at the  end of the  first  24  hours  and  each  subsequent  24  hours  increment of  exposure. The  time  of  failure  of a  specimen  is  recorded  as  the  day  on which  at least  3 rust  sports 1 millimeter  in  diameter  forms  on the  front  surface  of  the  specimen  in the  central  area  which  excludes  ¼ -inch zones  adjacent  to  the  top  and  sides  and a ½ - inch zone  at the  bottom. Three specimens are coated with particular oil. At  least  two  of  these  must  last  the  specified time  without  failure.

Meat Packing and Gear Lubrication

Most of the machinery in meat packing plants is subjected to moisture and thus the conditions are such that rusting occurs. For this  reason  gear  cases  should  be  tight  to  prevent  entry of water. Even so, the gear oils used should contain a rust inhibitor. Another  factor  to  consider  is that  the  temperatures  to  which  the  lubricant  is  exposed  will  be  below  normal. Therefore, low cold test oils should be employed. Gear reduction units found in most packing plants may consist of spur or worm gears. A number  of these  will be on  conveyors and in  general  an oil  of 300 to 500  viscosity  SUS  at 100 degree F  and  containing  both  oxidation and rust  inhibitors  should  be  used. For the worm drives a compounded oil of 125 to 150 SUS at 210 degree F is best. When making frankfurters or sausages, grinders and mixers are used. The grinder will probably be driven by a motor coupled to a herringbone gear. The  mixer may  consist  of a hopper  with  paddle  agitators which  are  driven  through a reduction  gear. In either case the 300 to 500 oil noted above may be used on the enclosed gears. A reservation should  be made  that if gear  reducers operate in a cold  room  where  the temperature  is near  or below  zero, it  will be best  to use  a low  pour  point oil  of 150 to 200 viscosity SUS  at 100 degree  F. Occasionally open  gears  will be  found  in packing  plants. If this is true, residual type oil having a viscosity of 500 to 1000 SUS at 210 degree F and containing a rust inhibitor should be used as needed.

Turbine oils for Automotive Vehicles

Since  gas  turbine  engines  for  automobiles  have  a  potential  which  no  doubt will  soon  be  realized,  mention will  be  made  of the  lubricant  requirements  for  the  drives. The oil will be used to lubricate both bearings and gearing. The  bulk oil  temperature will  probably  be at least  300 degree F during  operation, but  the oil will  not  be  subjected   to hot combustion gases  and thus should remain    comparatively   clean.

Whether   the oils  used will preferably  be  petroleum or  synthetic or  blends  of  the  two  is a  question. Whatever type, they will   no doubt contain various additives, such as   antifoam    agents, oxidation inhibitors, metal deactivators, and antiwear agents.

Speculation as  to  consumption  and  renewal  of  such  oils   indicates that  the oil  reservoir  will  have  a capacity  of about  3 quarts  and that  the   consumption will be  almost  nil  but  that  an  oil  change  yearly  can be  expected.

Reserve Lubrication on Gear Teeth

The problem of providing reserve lubricant on gear teeth has been considered. A method suggested  for  ball  bearing  assemblies, to pack compositions containing  solid  lubricants  in depressions of  retainers, inner rings, etc., so that  reserve  lubricant  would  be available, seems out of  place in gears. The solids used were graphite or molybdenum disulfide or mixtures of the two. While solution of a problem of this nature is desirable, immediate results are not apparent.

                                                                  

                                                                       

Potato chip Production and gear lubrication

The production of  potato  chips illustrates  food  handling  where  the gears  concerned are so  located that  little  contamination from the  lubricant  is possible. Numerous conveyors will be found for the potatoes, the slices, or the packages. Most of the gear reducers  for  conveyors will  be  subjected  to  only  moderate   temperatures  and not too  much  stress. Hence, either  straight  mineral  oil  or  MP  lubricant  of SAE  80  grade  can be used  for  the gears.

 If  a batch  peeler is used,  this may consist of  a  vertical  cylinder with  a rotating  abrasive  disc in the  bottom  which  will  be  driven  by  gears. Also, in washing potato slices, a gear driven drum will probably be used. The gear oil mentioned above will also serve these latter applications.  

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.

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.

Forced Feed Application of Gear Oils

Forced feed application of gear oils may take the form of circulating systems which deliver the lubricant as a stream running over the gearing or to jets or sprays of some type. Such methods not only provide lubrication but also utilize the gear oil as a cooling medium. Brewer^5 mentions three types of circulating systems, namely:

(1)    Wet sump, in which the oil is pumped under pressure directly from the sump to the lubricating points. Failure of the pump on such a system will cause almost immediate starved condition of lubrication.             

(2)    Dry sump, where a scavenging pump draws the excess oil from a sump and delivers it to a reservoir located above the gearing. A circulating pump then draws oil from this reservoir and delivers it to the point requiring lubrication. Since the scavenging pump has greater capacity than the circulating pump, the sump remains practically dry. A  pump failure  on  such a system  does not result  in as star rapid vation as in the  wet system  since some oil can feed by  gravity  from the reservoir  through  an idle pump.

(3)    Gravity  feed  which the sump  pump delivers  the oil, dripping  from the gearing, to a reservoir  set  high enough to give the desired  pressure. From this tank which may be thirty feet above the gear sets, gravity feed through regulating valves and perhaps sight glasses provides the lubrication.

Any of the above systems may also include oil filters, coolers, and even alarm devices to warm against malfunction of pumps. Gear oils used in paper mills, steel mills, and other locations are frequently contaminated with water, mill scale etc. Such lubricants may have to be reclaimed by settling, filtering and centrifuging before reuse. The oils used in forced feed applications are generally those which are quite fluid at ambient temperature and not of the residual type. However, if warmed, the latter type of lubricant can be handled in circulating systems.

                            Barring a pump or line failure, circulating oil systems provide a reliable flow of clean oil to gears. If necessary, this oil can serve additional functions, such as a hydraulic fluid in addition to lubricating practically any mechanism necessary. Such methods flush contaminants continually out of the lubricating areas and in most cases sufficient oil is in the system so that a portion can be withdrawn for a purification step during the cycle. Most of the heat  absorbed by  the oil  passing  through the  operating  area  is released  in the storage  or by coolers before  the return  cycle.

The lower the viscosity of a gear oil, the more satisfactory it will be for removal of heat from gear sets. In circulating systems, Dudley^16 considers that about a gallon of oil per minute will remove the heat developed when 400 hp are transmitted through a gear set. With larger installations considerably less than this ratio circulating oil to power is required.

Air-Oil Devices for Lubricating Gears

By injecting or pumping oil drop-by drop into an air stream the air will carry the lubricant to the points of application, such as gears. A similar mixture can be obtained by the aspiratory action of compressed air. With such systems, provision can be made to start the oil flow with the start of the machine and stop it when the gears stop. The delivery is positive and there is little chance for contamination because the gear box is under some pressure which prevents entry of dust. Also,rate of oil feed can be regulated.

On the negative side, it is necessary to provide compressed air and a considerable flow of air escapes through the vent of the gear case. While this air will have some cooling value, it may carry some oil mist. The oil is used on a once through basis and provision has to be made to drain the sump of the gear case at times.

Hand application of Gear Lubricants

Hand  application of gear lubricants, while often used on slow speed  exposed gearing, should  be discouraged because  there is  always  a certain  amount of hazard to  such a procedure, the amount  of lubricant used is indeterminate, and  the operation is wasteful of both time and lubricant. However, primarily because of the lower initial cost, open gears have considerable use. Also, both location of the gears and immediate economy, dictate hand application of lubricants to such gears. Consequently, some of the methods of hand application follow:

(1)    By paddle, when the lubricant is a heavy residual type or consists of a solid or stiff grease. Usually more of the lubricant than is necessary is applied and consequently the excess either   drops off or is thrown off into the surrounding area. This is not only wasteful but also contributes to poor housekeeping.

(2)    By hand in case the residual type is heavy enough. Such a product can be formed into a ball by hand and then dropped into the gear mesh where in time it is distributed.

(3)    By bags, made of plastic, most often polyethylene, which is filled with the gear lubricant. A filled bag is dropped between the gear teeth where eventually it is chewed to pieces by the gears and the lubricant is released. This makes a somewhat cleaner operation than the previous methods and the hands are not soiled while applying the lubricant. If a large opening is provided in a gear case, this method of application can sometimes be used for enclosed gears.

(4)    By pouring from a can, bucket, or any spouted container. Such applications are made at intervals and in case of gear oil is very heavy, it may require heating to reduce the consistency before applying. The lubricant is then poured in a fine stream into the teeth as the gears slowly revolve toward each  other. If the oil is applied relatively frequently in small amounts rather than at longer intervals in large amounts, there will be less chance of its being thrown off.

(5)    By hand spray at intervals, most often from “ AerosoI” containers. Such a package, which ordinarily holds up to a pound of a diluted gear compound, makes for ease of application and cleanliness because an excess of the lubricant is not applied. The gear compound is diluted with a non-inflammable solvent which evaporates rapidly after release from the container and leaves a viscous coating on the gear teeth. While the diluents present may be toxic, the amount released at one application is normally so small that it dissipates without harmful effects.