Deposit Forming Tendencies of Aircraft Turbine Lubricants

This test method describes  a procedure for  determining the  deposit  and  sludge  forming  tendencies  of  aircraft gas  turbine  lubricants when  a sample  of the  oil is circulated  under  controlled conditions for a  prescribed  period of time  through an  aerated test  chamber  containing  an  aluminum  tube  held at a constant  temperature.

The coking tube is held at 590 degree F while oil  heated  to  300 degree F  is circulated by  a pump  from  the  chamber through  a  cooler and a line  filter and  back  into  the chamber. The oil flow is regulated to 300 ml per minute while air flow is the same amount.

At  the  end  of the test, the  weight of solid  decomposition  products  on  the  heated tube  and  in the  line after  are  determined. Also,  changes  in the  viscosity and  neutralization  number  of the oil can be  determined  if  desired.

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.

Chlorine in lubricating oils

In the first  methods the  sample  is oxidized  by  combustion  in a  bomb  containing  oxygen  under  pressure. The  chlorine  compounds thus  liberated  are  absorbed  in a  sodium carbonate  solution and  the amount  of  chlorine  present is determined gravimetrically  by  precipitation  as  silver  chloride.

With the second method, the sample, dissolved in a low boiling hydrocarbon mixture, is boiled under reflux with metallic sodium and n-butyl   alcohol. Under  these  conditions the  chlorine  is converted  to sodium  chloride which  is then  extracted  with  water. The  chloride in  the  extract is  determined  volumetrically  by  titration  with silver in the  presence of  thiocyanate.

  

Chemical Analysis for Metals in Lubricating oils

These methods of chemical analysis are intended  for the  determination of barium, tin, silica, zinc, aluminum, calcium, magnesium, sodium and potassium in  new  and used  lubricating  oils. Other metallic elements, sulfur, phosphorus and  chlorine in  amounts  commonly  found  in lubricating  oils  do not  interfere in this  method.

Essentially,  the  method  consists  of  igniting  the sample, dissolving  the  residue  in  mineral acid and  then  separating  the various  metals by  conventional  methods.  

Sulfur in Gear Oils

In this method  the sample is vaporized  and  burned in a  stream of air, and  the  oxidation completed  by passing  over  quartz particles  maintained  at a temperature  of 950 to 1000 degree C. The combustion  products are then  passed  through hydrogen  peroxide  which  absorbs  the  sulfur  as sulfuric  acid  and  the  chlorine  as hydrochloric  acid. The  absorbent  is then  analyzed  for total  acidity  and  for chloride ion. The  procedure for  the  determination  of  chlorine  is  included  only  for  correcting   the  sulfur  content  and  the  method is not  recommended  for the  determination  of chlorine  alone. 

Pentane and Benzene Insolubles in Used Lubricating Oils

Normals  pentane insolubles are the  insoluble  matter  which can be separated from a solution of oil  in n-pentane and  in addition  to benzene  insolubles, may  include  insoluble resinous  bitumens produced from the  oxidation of oil. While  this  test  was  designed  primarily  for  use with used  engine oils, it does  have  some  value   in determining that  a breakdown has  occurred  in gear  oils. Any  appreciable  amount  of pentane  insolubles  in used  gear  lubricants indicates that  the  gear  box  has been  quite hot, usually  above 300 degree F.

Benzene  insolubles  are  that  portion of n-pentane  insolubles  not  soluble  in benzene and  may  include  insoluble  matter  produced by  oxidation and  thermal  decomposition  of the  oil  and  oil  additives. Any  suspended  particles  from  metal  wear  or from  external  contamination  will  also be  present  in the  benzene insoluble  fraction.

Aniline Point of Petroleum Products

Aniline point is the minimum equilibrium  solution temperature, generally given  in F although C is also used, for  equal  volumes  of  aniline  and  oil. Aromatic  compounds in oils  contribute to a low  aniline point  which  in  turn  indicates that  such  an  oil will  soften or  swell  both  natural  and  most  synthetic  rubbers. Therefore  to  insure  minimum  action  on rubber  gaskets, seals, etc., oils  with high  aniline  points  should  be  selected. Solvent refined oils  as a  rule  satisfy  such  requirements. 

Missile and Space Vehicles Gear Mechanisms and their Lubrication

While details of space vehicles are not publicized, it can be expected that gears may enter, even if only for small instruments. These will no doubt be of a nature which will not require fluid lubrication. However, Hartman^24 mentions that there may be a gear drive between the turbine and the shaft on certain liquid rocket engines. Where kerosene is the fuel used, this also provides lubrication for the gears. However, kerosene alone allowed scoring of gears and consequently additives were included. Use of 2 per cent by volume of zinc dialkyldithiophosphate  in the fuel, decreased gear wear. This combination also improved the rust resistance of gears. Such a kerosene additive mixture is suggested as a break in lubricant no matter what type of lubricant may be used in service. In this connection, an article by Watson^51 entitled “Materials and Ratings for Dry Running Gears” should be of interest. After  experimenting  with  various  materials for  gears, it  was  found  that  under  light  loads, spur  gears, made of case  hardened  En  steel, Phosphate  prior  to  coating  the  flanks with  molybdenum  disulfide, would run  continuously  in a dry state  without measurable wear.

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.

Flour Milling and Gear Lubrication

Up to time grain enters the mills, conveyors are used for handling. These  may  take the  form  of screw,  bucket, ribbon or belt and  any  one of these  types can be  driven  by gear  reducers. A  turbine type of oil  having  a viscosity of 500 SUS  at 100 degree F,  that  is AGMA  No. 3 grade, can  be  used  throughout  these  gear  reducers. In  the  northern  states  this  oil  should  have  a pour point  of zero or lower. An  oil of this  viscosity  will not cause excessive  power   loss and  yet  it  will  protect the  moving  gear  teeth.

Gear motors may be used for some conveyors and blowers. The  same  type  and viscosity of oil  should  be  satisfactory  for the  bath  lubrication  of such  gears, especially  if bearings are  serviced from the same  source. Where the drives in gear motors run quite warm, an oil of about 750 viscosity SUS at 100 degree F or an AGMA No. 4, may be desired. If such motors have a plate showing the recommended viscosity of oil, this suggestion should be abided by.

A tight  housing  is  essential  in any  of the gear cases in flour mills, more  from  the  standpoint  of prevention of contamination  from dust  than  from  leakage. Since  the oil  level  in gear  cases  should  be  inspected  every  month  or  sixty days, care  should  be  exercised that  dust  does  not enter  when  the  filling  plug or cap is removed.

Open  gears  are not  used too  often  around  flour mills; but if  these  are  encountered, it  is wiser to use  a  light  oil  as the  lubricant  rather  than  a  residual type. This can be the same oil as suggested for use in conveyor gear reducers, that 500 viscosity SUS at 100 degree F. As  such an oil  becomes  mixed  with dust, the paste formed will  slump off rather  than pack  in  the  bottom  of gears; thus, misalignment should  not be a  problem.  

Flour mills  may  be  self contained, in that cleaning, tempering, grinding and  sifting may  all take  place  in one  enclosure, or the latter operation  may be  separated. Such machinery will vary, but often the rolls are driven by gears. Here again the turbine oil type 500 viscosity SUS at 100 degree F can be used. Machinery handling middlings or bran will be much the same as previously mentioned and if gearing is used, the same recommendation will hold.  

In the manufacture of corn meal or animal feeds the same type of processing and machinery will be found. Thus, conveyors  and screens  will have  similar  drives but the  crushing or milling  can be  by  rolls  or  discs. In any event the gear oil used can be the same type and grade as recommended for flour mills.

It will  be noted that  a simplified  lubrication  application for  reduction  gears  is suggested  in grain mills, that is, a  single  oil  throughout with one  exception. This  is in  gear motors and even here  the  sanction  of the motor manufacturer  might  be  obtained for use  of the  500 viscosity  oil.

Construction Equipment in General and Gear Lubrication

While one should  not go contrary  to the  recommendations of the  supplier of construction equipment, practically all enclosed gears  on such  machinery  can  no  doubt  be  serviced with SAE 80  or SAE 90  EP or  MP gear oil. An  exception  are  worm  drives which should be  lubricated with a  compounded  oil  of SAE  140  grade. The use of certain mild EP oils is permissible for the lubrication of worm drives provided the oil supplier so advises. Air and oil filters require the same attention as in the case of tractors. Also drain periods on any construction equipment should be established at a maximum of 1000 hours. It is best to drain immediately after operating and while the gear boxes are warm. If the discarded lubricant is very dirty, flushing of the gear compartments before adding fresh oil is desirable. Open gears will be found on many pieces of construction equipment. For example, large shovels, cranes, drag lines, concrete mixers, etc. The  recommended lubricant for  such  gears is a residual  type  having  a  viscosity of 1000 SUS  at  210 degree F for cold  weather  and 2000 for  warm  weather. If the machinery  is to be used  under wet  conditions, the lubricant should  contain additive which  will  insure that  the oil  adhere to gear  surfaces  when  water is present. Better  still  these  open  gear lubricants  should contain both  EP  and  rust  inhibiting additives. Exposed gears are lubricated as required, often on each eight hour shift. If  railroad  equipment  is used  in  construction, the  tractor  motor gears  can be lubricated  with  the heavier  grade of open  gear oil. 

Lubrication of Gear Sets on Agricultural Equipment

While some open gears are still encountered on farm machinery, modern equipment, for the most part, has precision cut gear sets operating in enclosed gear cases. Therefore, most gearing on farm machinery can be satisfactorily lubricated with two types of gear oils.

First , for  open gears  a  residual  type  of  adhesive  gear lubricant, which can  also  be used on  wire ropes  and  some  chains, is  recommended. Such  a  lubricant is available as a material  which will  hardly  pour at ordinary temperatures  and  must  sometimes be  heated in  order to apply. Much more convenient is a cut back from of such lubricants which can be applied by pouring or dipping. Likewise, aerosol containers of the same type of material permit spray application.

The enclosed gearing on farm equipment is bath lubricated so that the partially submerged gears, when in operation, pick up the gear oil and where necessary, transfer a portion to bearings. While  it is  not  possible  to  list every  variation  in the  mechanisms of  gearing  on  agricultural  machinery, the  rules for  lubrication of such expensive  and  often  intricate  equipment follow  general  pattern. That is, the use of the proper gear lubricant in the proper amount and the regular replacement of such oils as required.

While the  recommendations  of  the  manufacturer  are a  guide  as to the proper  gear  oil to use  in each  piece of  equipment, there  is a  tendency  to  simplify the  number of  lubricants  required  on a farm. With this in mind, multipurpose gear oil will serve most enclosed gear sets. This  can be  a  mild  or  regular EP  type with  the  use of an SAE  140  grade for   hot weather  and  an SAE 90 grade  for  winter. In very cold weather an SAE 75 grade of gear oil can be used.  The  matter  of  reduction in the number  of  lubricants  necessary  for  farm  equipment  will have  further mention in  the next section. It  will  then be  evident that  manufacturers   of  such  machinery also  have  this  in  mind.     

Chemical Changes in steel surfaces During Extreme Pressure Lubrication

Analysis may aid in explaining the mechanisms by which gear lubricants, particularly EP oils, function. Which  it is  generally  accepted  that  iron sulfides, chlorides and  phosphates are  possible reaction products  of  EP additives  under extreme operating conditions, this  may not  be the  complete explanation. Godfrey^5 considered that there was a lack of understanding of the above actions. Consequently, EP films and  fragments  were  obtained  and  analyzed  by : electron  diffraction, X-ray diffraction, emission  spectrograph, proton  scattering, chemical spot tests, and  volumetric  analysis. For one wishing to study the chemical mechanisms of extreme pressure lubrication this article should provide suggestions as to analysis. Suggestions have also been made that changes in EP additives while in service may be measured by infra-red spectroscopic technique.

Zinc by paper Chromatography

The above methods are concerned primarily with unused lubricants and consequently a report by Goodwin and Begeman^6 are of interest. This  article  describes a methods  of  tracing  Zinc dialkyldithiophosphate  decomposition  in axle lubricants by  paper  chromatography. For  the  purpose, a  sample  of the oil  was  allowed to  soak  into  a sheet  of filter paper after  which  the  paper  was suspended  in  a  chromatogram   above  a  developing  solvent. About 1/8 inch of the lower edge of the paper was immersed in the solution until the solvent front had traveled to within 1 ½ inches from the top.  Following this treatment, the paper was dried. Since  the  zinc  compounds  in the developed chromatograms  are  colorless, a colored  zinc  derivative  was formed  by spraying  the paper with a 0.05  per cent  solution of  diphenylthiocarbozone  (dithiozone)  in  chloroform. This formed a purplish red zinc dithioozonate. Any  excess  dithiozone  was  removed  by  immersing  in a weak  ammonium  hydroxide  solution and then  washing  with water. The  red  color  fades over  a period of days  but may be  photographed  with  color  films to give  a permanent record. The intensity of the color indicates the relative amount of zinc present. Thus, the intensity of colors in tests decreased considerably in the interval of road mileage from 2,006 to 5,144.

Radioactive Tests for Metals in Oils

Tests in which the radioactivity of metals or their compounds is used as a means of determining their presence or concentration are largely confined to experimental investigations. This  is true  because, first  activated metals or  compounds must  be present  and  this is not true of  commercial  lubricants and second, the life  of some of the  isotopes  used  is short so that  after  prolonged service the activity would  almost  disappear.

Clay processing Plants and gear Lubrication

Clays are the basis for a number of products, but the equipment necessary for processing the clay is much the same in each instance; consequently, lubrication problems have much in common. Clay based industries include brick manufacture, ceramics and tile. The earth may either be prepared at the point of consumption or crushed and ground at the mine for shipment. Normally, clay come from the mines or quarries as hard lumps which may be fed to a jaw or single roll crusher. The nature of the clay determines the method of crushing or grinding. Soft, friable earths require only crushing; while others have the particles partially cemented together and must be ground. Most of the drives for either purpose are by motors and reduction gears. These gears may be enclosed or open. The enclosed gears throughout the plants may be lubricated with oil 300 to 500 SUS at 100 degree F. This can be either a straight mineral oil or one containing a mild EP additive. Dust is almost certain to work into gear cases and, therefore, with large installations, circulating oil which can be filtered is desirable. Where this is not practical, the gear boxes should be drained every two to six months, flushed out and refilled. Open gears may be lubricated with a residuum of about 2000 viscosity SUS at 210 degree F which can be warmed for application. Frequent use will help flush off dust which becomes mixed with the lubricant. Following crushing or grinding, the clay is screened and the entire process may be repeated to obtain the desired fineness. Most clay is next mixed with water in pug mills and then are extruded or formed into desired articles. From such operations most clay based products are handled on conveyors unless placed on carts or cars for drying and burning or vitrifying. Even then, if the kilns are of the tunnel variety, further conveyor chains may move the carts through the kiln. Much of this equipment is driven by reduction gears, often enclosed. Therefore the same type and grade of lubricants as were mentioned earlier can be used throughout the plant. Gears should not be present in kilns and, therefore, are not subjected to any great heat. Other types of equipment, if present, can receive similar lubrication. These might include drives for elevators, augers, cutting machines and fans.     

Nuclear Power plants Gear Lubrication

Present indications are that the principal gearing in nuclear power plants will be in connection with turbines. Such  reduction units should be  far  enough removed  from the area of high  radiation that no degradation  of the oil  from such  a source  will occur.

Cox et al.^14 who have considered this matter state: “Irradiation tests of turbine oils show that maximum expected radiation doses in  current and projected power plants over a twenty year period  does not change the  physical  properties of the oil. Oxidation stability and other properties are, therefore, still of most importance in turbine oil selection”.

Also  Okrent^43  in treating  design considerations of nuclear powered  surface vessels concludes that the  reduction gearing  in connection with  the  turbine presents no problems  from a radiation standpoint. In spite of the  above thoughts, Watson^51  mentions  that in  nuclear  power  generating  stations, a  number of applications  will be found where  gears  should  be run  without  lubrication. Experiments were, therefore, made with various materials, run in a dry state, with latter wear. As a  result, it is suggested that if loads are not heavy, spur gears, made of  case hardened  En steel, phosphate prior to coating  the flanks with  molybdenum  disulfide, can  be run  continuously, in a dry state, without  measurable  wear. Also  a worm wheel , made  from  woven  asbestos base  with  a case  hardened  steel worm, is promising for  operation in a dry  state.

No doubt, when and if gear oils with radiation resistance are necessary, suitable fluids will have been developed. Thus, polybenzenoid   compounds containing short alkyd groups show promise in such applications.

One  interested  in this subject might  avail himself  of a series of  eight  papers devoted to “Non-conventional  Lubricants  and Bearing  Materials such  as Are Used  in Nuclear  Engineering”. These were presented at the Manchester college of Science and Technology on April 12, 1962 by the lubrication and Wear Group of The Institute of Mechanical Engineers (British).   

Mixers and Gear Lubrication

Mixers include a wide variety of speeds, size and types of equipment; consequently, the lubrication of gear drives will be equally varied. Also, both enclosed and open gears will be encountered in such machines. Lacking  recommendations by the equipment manufacturer, one should  rely upon  the fact  that  high speeds in the  gears  demand low  viscosity oils and  low speeds  require high  viscosity lubricants. If the service is severe, use EP oils.

Malfunctioning of Other Mechanical Elements

Misalignment may be due to wear of bearings and in extreme cases of failures it may be difficult to determine whether a bearing or a gear failed first. In case of bearing failures, when lubrication was at fault, either oil did not get to the bearing. Or the proper oil was not used. Where  a common  oil is used for bearings and gearing, the  viscosity of the oil is  generally  a compromise  since  the bearings operate best with  a lower  viscosity oil than  is dictated for the gear sets. Therefore, when bearing trouble is encountered, thought might be given to use of a somewhat lower viscosity lubricant.

Malfunctioning of flexible couplings may also contribute to trouble with gear sets. Such couplings are often used to connect reduction gears with a different piece of apparatus. These  couplings may not only  break but  also  become  jammed, so that  they  are no longer flexible; thus the  gear  shaft will  be thrown out of line. Another possible source of trouble might be a break in a gear case or supports which would permit a shaft carrying gears to be misaligned.

High speeds

The term “high” of course is relative but with pitch line velocities of several thousand feet per minute the lubrication of gears is not simple. Naturally, a low  viscosity oil is  required and the problems are : to have  assurance that a film  of oil  is present when the gear teeth  mesh; to have  an  abundance of oil to remove  heat; and to be  sure that the leaving  oil  will  get out  of the way of fast moving gear teeth. If  a problem is  encountered  as to delivery of oil  to the  mating  surfaces  of high speed gears, the  experience of Dern^20 may  help. This  investigator found  that  when  gears  run at 16,000 to 18,000 feet  per minute, “more satisfactory  results may  be  obtained by   spraying oil radically into  the  teeth  of both gears  at a point as close  as  possible to the mash”. For the purpose, one or two jets of 0.040 to 0.060 inch in diameter, delivering a solid stream of oil, were used. Where the pitch line velocity was 20,000 to 25,000 feet per minute, jets on the leaving side of the gears removed most heat.

Trouble may be encountered with high speed gears churning the gear oil which in turn causes heating. This  is one  reason directional  baffles or  even  a shroud around  the gears  may be necessary in order to keep leaving oil away from the gears  and directed toward a gear case outlet. 

Leakage of Gear Oil onto Brakes

The most common reason for leakage of oil from differential gear cases onto brakes is overfilling of the housing. Under such conditions, the leakage will probably take place no matter how effective packing may be. Use of quite low viscosity gear lubricants, for example, SAE 75 grade in hot weather may also contribute to such leakage. Use of air pressure to help remove oil from the gear box may also cause leakage onto brakes. Failure of packing should also be investigated case there is a problem of gear lubricant on brakes.

Helicopter Gear Lubricating Problems

Since the gearing in question is high speed, reference to a previous section, which deals with problems in lubricating high speed gears, may indicate similar problems. Also an investigation by peck et al.^39 is an aid in this regard. Under high speed conditions, good results were obtained by lubricating with a “jet hitting the center of the gear tooth on the outgoing side of the tooth mesh”. Also baffles were used to prevent swirling of the oil with resulting heating. Likewise, baffles were necessary to direct oil to the suction lines “without being picked up by high velocity airflow's and whirled around”. The characteristics of suitable oil for lubrication of highly loaded helicopter transmission, turbo-prop reduction gears, variable pitch propeller gearing etc., are similar to those required in aircraft turbine oils. Therefore, if lubricating problems occur, they will be similar in both instances.

Limitations on Heating of Lubricants for Application

Heavy bodied lubricants, particularly residual types used on exposed gears, are often heated in order to make application easier. If such lubricants are straight mineral oil products, the amount and intensity of heat should not harm them. However, if additives are included, only a very moderate heat should be used. Otherwise some change in the composition is possible. A supplier of the lubricant can advice the limitations on heating. A similar caution is necessary in case lubricating greases are used as gear lubricants. The thickeners for such products may be soaps which upon the application of considerable or prolonged heat will separate from the oil present. 

Problems in Connection with Flushing of Gear Cases

 Different problems may arise in connection with flushing gear cases. First the used oil should be removed from the case as  completely as  possible so that  contaminants  are also  removed  and none  of the Oxidized  oil  remains to act  as a catalyst  for the  fresh oil. In so doing, if a volatile solvent is used, this should also be removed completely. Very little of a solvent is required to reduce the viscosity of gear oil, and naturally this is undesirable. Further the  gears should not  be left  without  a coating  of oil  for even a short  period because  rusting  will take place  under  such  conditions. Also  the gears should  not  be  operated  without  a coating  of oil,  even though there  is no load. Troubles have been encountered when gear cases were washed out with chlorinated solvents. 

                                                                 

After fresh oil was added, corrosion developed because some of the solvent was trapped in the case. The best correction for this problem is not to use such a solvent. In fact the safest course in flushing gear cases is to use prepared flushing oil. 

Processing Various Foodstuffs with Gear Driven Machinery

While  the listing of processes and  machinery used in handling and  preparing  foodstuffs  is not  complete, the examples  indicate  the gear lubricants which  are  suitable for such applications  and the precautions necessary in their use. However, a few  other  illustrations of such equipment  where gears are  the drives follow : cocoa and cocoa  butter are  handled  in gear  driven  mills; gelatin  is sometimes dried  in rotating  heated drums with connections to gear  reducers; spices  are milled in many  cases with the mill  being  gear  driven; yeast may be  concentrated  by centrifuging  with the rotation being  through  gear reducers; and  fish  flour in some  plants  makes use of  gear drives for both pulverizing and drying.

When to Change Gear Oil

The  ideal method of lubricating  enclosed  gear sets would be to place the  proper  amount  and quality  of gear  lubricant  is a  sealed case and  make  no  renewal  of the oil  during  the life  of the  mechanism. Manufacturers  of  automobiles have  this  in  mind  and  approach  such  a  solution  of gear  lubrication by  recommending  no  drain  periods and prolonged  use of gear oils. Manufacturers of other equipment have the same thought in mind and the trend will no doubt increase. For illustration a side entering mixer description states: “Lubricant is sealed in the gear case at the factory and is designed to last five years.” Naturally, any statement as to the life of gear lubricants should be modified with an expression as to operating condition, environment, etc. However, it is questionable if the present gear oils are everlasting even under the best of conditions. Therefore, from  both a service and economy  standpoint, used gear  oils  should  be removed  from  the gear cases  and replaced with fresh  lubricant either  when the oil  has  deteriorated or become  contaminated  or at stated intervals.

AGMA, which is interested in insuring log and uninterrupted service from gear sets, recommends the following: “The oil in a new unit should be drained at the end of two weeks operation and the case thoroughly flushed with light flushing oil. After this, a change of oil every 2500 hours of operation or every six months, whichever occurs first, is recommended for the units operating under favorable conditions. Where  operating  conditions  are  severe  such  as  rapid rise  or fall  in temperature of the gear  case with  accompanied  sweating  of the inside  walls  resulting  in a formation of  sludge, or where  operation  is in  moist or dusty atmosphere or in the  presence of chemical fumes, it may be  necessary to change the oil at  intervals of one  to three  months.”   

It is also pointed out that gear sets are usually treated by the manufacturer with rust preventive s before shipment. Such materials may have an adverse effect upon the gear lubricant and, therefore, should be removed before gear oil is added. Petroleum solvents are best for this purpose, and such fluids will also help to remove contaminants, such as metal chips. Immediately  upon removal  of such solvents a low viscosity  flushing oil  should  be  sprayed  on the  gears; otherwise, the  metal  surfaces may  rust  in a few  minutes. Also the gears should not be operated, even for a short time, in a dry condition.

In enclosed  gear  cases  which do not  have  a  drain or a  circulating  system, the used gear oil or flushing oil  should  be removed by suction.  Use of pressure to  force  out  such oil may damage seals  and in the case  of  automotive  equipment will probably force oil  onto  the brake  bands. When  considering  oil changes  for reduction  gears, Forbes et al.^20  mention that  the first  month  of  operation is the most  critical in the life  of  gears; therefore, they  suggest  a change or  careful  filtration of the lubricants within two  weeks  after  the unit is put  in service. It is  pointed  out  that  fine metal  particles  resulting  from the run in period act  as catalysts  for oxidation if left  in the gear case. Rather than  setting  an arbitrary  period of change, the  above  authors^20  think  that  periodic oil samples should be taken  to determine if the oil  is in a  usable  condition. Such samples can be checked for presence of dirt, metals and water. Also the acid number, viscosity and interfacial tension can be determined. Certain fleet owners operating heavy trucks have a rule that the oil in transmissions or rear axles must be changed when the viscosity has increased by fifty per cent.

Where gears are lubricated by  circulating  systems, Forbes et al.^20 states: “ the  charge may often  be used for several  years without change,  particularly  when  adequate  filtering  equipment is employed”. However, cleaning such a system when changing oil requires more effort than in splash systems. Flushing  oils  are available  which, due to  either additives  or the  particular solvents used, will  remove most of the  deposits  from  the  oil reservoir and the piping as well as  the gear case. However, a final cleaning with dry rags free from lint may be necessary.

The greatest care should  be  used  in  cleaning  gear  cases and  auxiliary  equipment since  any used  gear  oil left  in a case and mixed with fresh  oil  will  tend to act as  a  catalyst to  promote deterioration of the new  lubricant. With the flushing oil on the gear set an inspection is possible. If this shows rust, the gear manufacturer should be consulted before operating. If the gears appear to be in satisfactory condition, they should be coated with the gear oil as soon as possible. In the  case  of a  circulating system this  can  be  done  without  operating  the gears. If a splash system is employed the gears can be sprayed or wiped with the lubricant before operating.

Where meshing gears are of dissimilar metals as in most worm gear sets, the importance of a change of oil and inspection of the mechanism is very necessary. As the gears seat themselves bronze particles may become attached to the worm. Such  particles  adhere  to the steel  and  cause  a rough  surface which  will  score the gear. Removal of the used lubricant and cleaning of the worm threads after a short period of use will often prevent further wear.

When oils are used on a once through basis flushing may not be possible. In the case of lubrication by oil fog, only fresh oil is supplied, and the tight system is under some pressure so that contaminants should not enter. However, in the case of open gearing, cleaning at intervals is advisable. Not only does the residuum  type  of gear oils pick  up  dirt  which  in turn  may act as abrasives, but  also some of the  heavy material  packs in the  roots  of the gear  teeth. If such build ups continue shafts may be thrown out of line. Such deposits can usually be softened by kerosene or some other solvent provided there is not a fire risk. If drip pans are provided for open gears these should also be cleaned at regular intervals.

Load carrying Capacity SAE Test Apparatus

As previously mentioned, this machine is a device in which two Timken test cups, no. T-48651, are rotated  in line  contact  with  each  other  and  in  opposite  directions, with  provision  for  controlling  the  speed  of rotation, the  slipping  velocity  and  the  rate  of  applying  pressure  at the  line  contact  between  the  rotating  cylinders  or  cups. To obtain reproducible  result, it is  essential  that  the  surface  finish  of the  cups  used  be  uniform  and  that  the  shafts  on  which these  test  pieces  are  carried be in  perfect  alignment. Both points are covered in details of the test methods. The  total  variation  in surface  finish  shall  not  exceed 10  micro inches and  the  inside  and  outside  surfaces  of the  test  cups  shall be  concentric  within  0.0005 inch.

With the  lubricant  tester  in good  mechanical  condition, test  shafts  true, and  the  alignment properly  adjusted, the  test  cups of  specified  surface  finish  and  concentrically  are  placed  on the upper and lower  shafts. With the oil box overflowing, an initial load of 15 to 20 pounds is applied. The  machine  is  then  started and  at the  end of a  30 second  period   the  automatic  loading  device, at  the desired  rate  of loading , is  started. The test cups are then observed for signs of scoring. This  is most  readily  detected  by  observing  the  lower  test  cup  on the  trailing  side  at a  position  approximately ½  inch  from  the  contact  line. When  signs of  scoring  are  detected, the  drive  motors  are  stopped  and the load  removed. After  thorough  cleaning  and  with  new  test  pieces and  fresh  oil  the test  can  be  repeated.

The suggested conditions of test are a main shaft speed of 1000 rpm and a rubbing ratio of 14:6:1. The  load should  not exceed 450 pounds and  if no  scoring  occurs  at this point  the test  is stopped to  prevent  over heating  of the  shafts, etc.

This test  has been  primarily  used for evaluation of automotive  gear  lubricants  but has not  replaced  tests  with gears.    

                                                                                                                                                                                                              

SAE Extreme Pressure Lubricant Testing Machine

Since  investigators  often  refer  to wear  tests using  the SAE EP Lubricants  Tester, this  apparatus  deserves  mention at  this point. The machine  was  constructed  under  the  sponsorship  of SAE  by  the  Bureau  of Standards. The  action  is  presumed  to  imitate  the  rubbing  of  gear  teeth  by  rotating  two  Tim ken  test  cups (T-48651)  in line  contact  with  each  other  and  in  opposite  directions, under  controlled  speed, slipping  velocity,  temperature  and operating  pressure.

The  conditions selected by  Calish  for wear  tests  on an SAE  machine  were: 500 rpm; 3:4:1  roll ratio; 180 lb  load; 225 degree F; 500 ml /min  flow  rate; and  4  hours  test  duration. This author makes the following comment relative to this test:

“ Experience  in the  laboratory  and  from  service  indicates  that  it  is  desirable  to  hold  the wear to less  than  30 mg  in the  test  consistent  with  other  desired  oil  properties.”     

The Timken test cups can be weighed before and after a run and thus the weight loss in mg determined. For  wear tests on an  SAE    EP Tester  the  conditions  should  be  modified over  those  used  to  determine EP values. Such conditions are speed, rubbing ratio,     pressure and perhaps temperature.                              

The Navy Gear Wear Tester

The Navy Gear Wear Tester is described in Federal Methods 791, Methods 335. The  equipment  makes  use  of  small  brass and  steel  gears,  but  Ninos  has  also  used  mating  gears  of other metals, such  as  brass on  stainless  steel, Phosphor  Bronze, and  ST Aluminum   on  SAE     4130 steel  and  SAE B-1112  steel  against  stainless  steel.

In  the  test  two  helical  gears  of  dissimilar  metals, each  approximately  one half inch  in  diameter are  rotated  together  as the  driving  motor  delivers a simple  harmonic motion     of 4.0  inches  amplitude  and  40 cycles per minute, through a  crack  to  the  upper  brass gear. This gear  oscillates  approximately  one  revolution while  a torque load of about  three  and  one  half inch pounds  is applied to  the  test  gears by  means  of a seven  pound  weight. The  gears  are  oscillated  for the  desired  number  of  cycles, or until gear  tooth  failure  due  to  excessive  wear  occurs. At the completion of the test, the gears are removed from the fixture, cleaned as before, and reweighed to    determine weight loss. The wear rate in mg for 10,000 cycles is then calculated permitting a comparison of different lubricants. New  test  gears  are  used  for  each  run even  though  there  is  virtually  no wear  of the  steel  gear  as  compared  to the  brass  gear.

Both fluid products and lubricating greases can be tested as gear lubricants on this apparatus. Indications  are  that  with  increase  in viscosity  of  gear  oils  the  gear wear   decreases. No  speculations are  given  as to how  much  of    the  wear  might  be  due  to abrasion which  is due  to particles  from  the gears.

Cement Mills Gear Lubrication

The lubrication problems of gearing  in connection with  quarrying  and  handling  rock, shale etc., for  use  in  cement manufacture  will  be  treated under  the  section devoted to  surface  mining and  quarrying. In cement mills proper, grinding or pulverizing. Mixing,  conveying  and  heating  of  ingredients are  required  and  most  of these  operations  employ  gear  drives  which  in  turn  need  lubricants.

Dust  of an  abrasive  nature  is an  ever  present  possibility  in the case  of  any  gear  lubricants  in  cement  plants, even  in  enclosed  gear  cases. In  some  applications  this  threat  to  lubricated   surfaces  is  countered   by  the  use  of  circulating  oil  systems. If this manner of application is used, filtration is possible. This  is true with  some  types  of rock  crushers, such  as  gyratory  crushers or  hydraulic  cone  crushers. The  gear  oil  employed  in either  of  the  above  can  be  a  mild EP  type  having  viscosities  of 300  to  500 SUS  at 100 degree F.

Whether  the  process  used  for  cement  manufacture  is the  dry  or wet  one, agitators, conveyors, elevators, mixers, grinders and  various  other  mechanisms  are  driven  by gear  reducers  from  electric  motors. In  the wet  process  the  listing  may  include  pumps for  handling  slurries, thickeners  which  may  have  worm  drives, as well as  the first  types of  machines. A  general  recommendation, which  simplifies  the  storage  and handling of  gear  lubricants, is  to  use  a mild  EP  oil  having a  viscosity  of 300  to 500  SUS  at 100  degree F. If  the  EP  agent  includes  a  lead   soap, such  an oil  might  be used for worm  drives.

                                                                                 

Open gears are also found in cement plants. One illustration is a ring gear and pinion driving a ball or rod mill. Here  a  residual  type  of  petroleum  product  having  a  viscosity  of  2000 to  3000 SUS  at 210 degree F  can  be  used.  This  lubricant will  pick  up  and carry  with  it rock or  cement dust, and  since  this  will  be  true no  matter  what  the  viscosity of  the  product ,  the  best procedure  is  frequent application. By this means the excess lubricant will be rejected and carry with it some of the abrasive material.

Cement  kilns  are  rotated  by  a  speed  reducer, followed  by a  pinion  and girth  gear. Different methods for lubrication of the exposed pinion and gear have been used. While  dust and  grit  are  present, the main  problem  is heat,  radiated  from  the    hot  shell  of the  kiln  to the  gearing. High  melting  point  lubricating  greases  have been  used to  some  extent,  but  require frequent application  unless they  are  in the  form  of a brick  which  is  pressed  against  the  pinion. This method has led to excess consumption.

A  better  procedure  for lubrication  of  cement  kiln  girth  gears  and  pinions is to  provide  a bath  for the latter. Cylinder stocks or SAE 250 EP gear oils have been used in this bath. In  this case,  the cylinder  stock  used  should  have  a  minimum  flash  point  of 600 degree F. However, perhaps  the  most  common  method of  lubrication of such  a drive  is to use  residuum  having a viscosity of about 5000 SUS at  210 degree F. This can be heated to aid in application. Also this  open  gear  lubricant may contain  three  to  five  per  cent  of  graphite  or  molybdenum  disulfide, which  of course are  no melting  and will  adhere  to the  gear  teeth and act  as a  lubricant.   

Power Take off Tractor Lubrication

Farm  tractors  from  different  sources  employ  various  types  of power  take off  devices. Therefore, a common recommendation cannot be given for lubrication of such equipment. In  order to  regulate  the  speed  of the  PTO  independently  of the  speed  of the  tractor, clutches  or a  different  set  of gears  may be   used. With  gears  alone, the grade  and type  of gear oil used  for the tractor  transmission may  be  encountered  and in this  case  ATF  may  be  used. The best  procedure is not  depend  upon  the  recommendations  of the  supplier  of  the  machine.

Garden Tractors and Gear Lubrication

The gears in most garden tractors can be lubricated with engine oil. This should preferably be at least an SAE 30 in weight. Any classification of automotive oil available will be satisfactory. At the end of the season the gear case should be drained and refilled with fresh oil.

  

Methods of Application of Gear oils to Heavy Duty Gears

Older equipment employing heavy duty gears may make use of bath systems   for application. Many  plants  have  converted  such  systems  to  circulating  application such as  is used  on most  modern  machinery. By  this  means, oil sprays  can  be  directed  to  the line  of  meshing  of the  gear  teeth and  if  necessary the  oil can be supplied  to  other  machine  components, such  as  bearings. By  this  means, when  accompanied with  proper auxiliary equipment, such as coolers, filters, settling tanks etc., the life of the oil is prolonged and contaminants removed.

Industrial Application of Gear Lubricants

While  it  is  impossible  to give  specific  recommendations  for the  choice  and application of gear  lubricants for  every  type  of  mechanism  which  quently  of  lubrication is possible. Designations  of heavy  duty, medium  duty and  light  duty  gear sets  will  serve as a  basis  for  differentiation in  selection and  application  of  lubricants. Later, comments will be made on gear lubrication in certain industries. Unless otherwise mentioned, enclosed gears will be considered. 

  

Dynamic Loading of Automotive Hypoid Gears

While the  tests just described  permit  rating and screening  of  gear  oils  for  various purposes, an illustration of  further tests, their result  and  the  conclusions reached,  indicate  both  the  possibility of  extension of   full  scale and road  tests  and  also  the  extreme conditions to  which  gear  oils  can be subjected. Powell  and  Barton  reported  the  results  of an  investigation  relative  to the   magnitude of  tooth   loading  in  hypoid rear axle  gears  under  normal and  severe operating  conditions. For  the  purpose  they  used  a   6-cylinder  passenger  car  with  a  pre- war  torque drive; a drive   system   duplicating  that  of  this car  on a  “T”   dynamo meter  stand; and  Army  M-37  truck  with  a 4 ton  load  plus  a   1.75  ton  trailed  load; and  an  Army  M-211  truck with  a 12 ton  load  plus  a 4 ton  trailed  load. The conclusions reached were:

      (a)    With  heavily  loaded trucks  the  climbing  of  steep  grades  can  increase  the  ring  gear  torque         as  much  as  13 to  24  times  that  of  level  road  under  steady  speed.

      (b)   The addition of trailed loads causes large increases in gear torque.

      (c)    The  highest  gear  loads  produced   under  normal  operating   conditions  occur as  a  result  of     gear  shifting.

      (d)   Engine  misfiring  resulting  from  spark  plug  fouling  causes   repetitive  gear  loadings  equal  to  the  60 m.p.h. drive  side  shock  in  the  CRC  L-19  test.

      (e)   Changes  in  rate of  throttle  opening  result  in large   differences in  the  drive  side  shock  loading  of  the  gears. The  substitution    of  electric  solenoid  throttle  controls  for  hydraulic  controls in the  CRC L-19  test  nearly  doubled  the  drive  side  shock  torque.

      (f)     Rate  of  throttle  closing  appeared  to  have  little   effect  on  the  coast side  gear  shock  loads.

      (g)    Shocks  imposed  in gear  shifting  of  heavily  loaded  trucks   on  steep  grades  produce  severe  lubrication  requirements  by  imposing  large  stepwise  changes  of loading  on a   contact  point  in one   revolution  of the  pinion.

Load Carrying Ability of Lubricating oils at 400 Degree F

Federal Test Method 6511 describes a procedure for determining load carrying ability of lubricating oils at 400 degree F with respect to gears. Using  a  modified  Ryder  Erdco  Test  Drive  System operating  at 10,000 rpm, the  lubricant  to a  series  of  400 degree F controlled tests  at increasing  gear tooth  loads. The  teeth  of one of the  gears  are   then  examined  to  determine  the  scuffing  area. The load carrying ability of the lubricant is rated in accordance with the per cent of the tooth working area scuffed.

Automatic Transmission Fluid proving Ground Tests

Satisfactory operation of such  fluid is  observed  during  a 2000 mile  schedule  on proving  Ground Automatic   Transmission  Performance Test  Schedule. This requires a new or rebuilt Hydro Matic transmission   in stalled in a car. Characteristics of the fluid, such as viscosity at 200 degree F before and after the test are observed. Tendency to squawk is noted and also smoothness of operation.

Continuous Automatic Bending

Continuous  automatic blending of  gear  oils  is  accomplished  by  synchronizing  a  series  of pumps  and  meters  so that  desired  proportions  of  ingredients are  fed  to a  blender  or  homogenizer  where  the  mixing  is  completed. Such  a  blender  is of  rather  small   cubical  capacity, perhaps  holding  a  barrel  of  fluid; therefore , the  entire  system  contains  a minimum of  fluid at any one time. For this reason changes from one grade to another necessitates very little rejection of oil. Several  equipment  manufacturers  offer  systems  to  accomplish  the above  purpose  and most  compounders  rely  on  such  firms  rather  than  design their  own  blending  equipment. Details of such systems, which include “Bowser Blending Systems”, “Cornell Proportioning Units” or    “Proportioneers Oils Bending Unit”, can be obtained from the distributers.

                                                                                        

One such unit which is used for blending gear oils is shown. In this  instance  the  supply  of oil  comes  from storage tanks  outside  the  building, and  the  pumps at the tanks  are remotely  controlled at the  blending  unit. The oil passes through air eliminators, pressure controlled, and automatic temperature compensating proportioning meters. From  the  three  meters  the  fluid  goes  into  a common  header, through  a  master    meter, and  then  into the  blender from which  it can  go to  storage  or   through a small  surge  tank  to  package. This  unit is installed      over  a  great  which  allows  any  spillage  to  drain to a waste  tank  in the  basement of the  building. With  such  systems  two  to  six  or  eight  different  components can be  blended. While  there  are  variations  in the  different  systems, a typical  one  uses  a series  of  positive  displacement  piston   type  meters in which  a  selector  at the  top  of the  meter  sets a train  of  gears  to  determine   the  delivery. The flow rates of a ¾ in. meter can be varied   from 0.4   to 15 gpm and of a 3 in. size from 10 to 250 gpm. 

Where  a  single  additive is    to be  introduced  into    an oil  and  no further  blending  is  desired, a  continuous  system of injection   mixing  can be used. One  of the  most  positive  means for  injection  mixing  is to  use  an  injection   pump  driven  by  a motor  which  is controlled  by  an  interlocking  switch  connected  to that  of the oil  line  pump  motor. The  injection  pumps  are  generally  adjustable  over  a 10  to  1  capacity range and have capacities  varying from 5 cc/min to 40 gpm. No pump is required if the additive is introduced by the pressure of a closed tank. In  this case  a flow  indicator, such  as a “Rotometer ,”  can  be  included in the  additive  line  and  a  calibration point arrived  at  by  checking  the  consumption  of  the  additive  over  a given  period  with  the  gallonage  of oil  pumped.

In  these   automatic  blending  units  provision  is made  to  either  stop  the  flow  or  continuously  recycle  the  mixture  without  delivery  if  the  flow  of  one  or  more  of the  ingredients cease. Also, when  changing  blends  the  mixer  can  be  either  sucked  or blown  dry to  prevent  contamination. Since  continuous  automatic  blending  of gear  oils  decreases  the  labor  and  supervision  of such  operations  and   also  affords  considerable  saving  in space  requirements, such  methods  should  have  consideration   in all  new  installations  of any   magnitude.

   

Wheel Type Tractors and their Gear Lubrication

According to  Caterpillar, transmissions of a  few  models of wheel  type  tractors  require series  3 motor oils in an  SAE  30  grade above 32 degree F  and  in an  SAE  10W   grade  for  lower  starting  atmospheric  temperatures. The  transmission  lubricant  suggested  for  most  models of  wheel  type tractors  is a multipurpose type  gear oil conforming to MIL-L-2105. An  SAE 90  grade  is  recommended for  starting  temperatures above 32 degree F and  an  SAE 80  grade  for lower  temperatures. Below -10 degree F it may be necessary to dilute this latter grade with kerosene.

The  same MIL-L-2105 type of gear oil  and like  grades  are  suggested  for all models of wheel  tractor differential  and final  drive  compartments. It is recommended that transmission oil filters be changed every   250 hours, except in the case of three models where the period is 500 hours. The  suggested  oil  change  period  for both  transmission  and differential  and final drive  compartments  of wheel  type  tractors is 1000 hours.

 Similar tractors of other makes, as well as allied equipment, such as motor grades etc., will probably require similar types and grades of gear lubricants. However, it is better to follow instructions furnished by the equipment manufacturer or supplier.

Wear Prevention Agents

A number of investigators have distinguished between wear prevention and EP agents in lubricants. The  former are  effective  by  a  chemical  polishing action, which  takes  place  at a  lower  temperature  than  does  the  formation of antiweld  films by EP agents. A very  extensive  investigation  of  wear  prevention  agents,  which are  effective  in  lubricants for  two  steel  surfaces was  reported by  Beeck, et  al^9. Calhoun and  Murphy^18, who  reported  on both  anti wear  and EP  additives  for  lubricants found that it  was  possible to  blend  two  or  more  types  of  additives  and  attain both  properties in  the same  composition.

Typical  of  anti wear  additives  are  tricresyl  phosphate  and  Zinc  dialkyl  dithiophosphate.  Such  agents  are  seldom  used  in  industrial  gear  oils  but  are  valuable  in  lubricants  such  as  those  for  jet  turbines  where  the  oil  serves  several  mechanisms  including  gearing.

Water in Petroleum products and other bituminous materials

This  method  is  intended for  use  in the  determination of water in bituminous  products  which  would  include  asphaltic  residua  used as  exposed gear  lubricants. A sample  of  the  product in  question is  diluted  with  a solvent  and  distilled  the  water  being  caught  in a  graduated  trap. Water in gear oils should only be present as a contaminant. A qualitative test  for  moisture  in gear  lubricants  consists of  holding  a  sample  in  a  beaker or  can  on a  hot  plate  and  when  the  temperature  reaches  about  212 degree F, observing  if  foaming  takes place.

Tests  for Other Characteristics of Lubricating Oils. Before  lubricating  oils  are  selected for  use  in  compounding  specific  types  of gear lubricants,  other  characteristics may  need  to  be  considered. For example, compatibility with   the other ingredients of a composition is very important. This and other qualities will be mentioned as need arises.

Viscosity Index Improvers

While  the change in viscosity  of lubrication oils with  change  in temperature  can  be  reduced  by  the  addition  of  certain  long  chain  polymers, such  use  in gear  oils  is not  common. Such  polymers when  subjected  to   the  shearing  action of  gear  sets  degrade  and  form  shorter  chain  compounds  which are  less effective  than  the  original  additives. These agents may also function as pour depressants. The  reason  the  polymers in  question  are  effective  is that  at  low temperatures  they  are  coiled  up  and  only  colloidally  dispersed. As  the  temperature  increases  the  polymers  uncoil and  go  into  solution  to  increase  the  viscosity  of the mixture.

Various Fluids as Gear Lubricants

While a  number of  viscous fluids have no  doubt  been used  as  gear lubricants, most of these, other than the  petroleum or synthetic  oils, are  deficient in  desirable  characteristics. However, glycerol has been   suggested as a lubricant and carrier for molybdenum   disulfide. The  specific  application in this case  was  on  small gear sets of  the  worm  and  hypoid  types. Also, molasses was used as a transmission gear lubricant in France during World War II.

The London Transport Company has experimented with   an inhibited castor oil in the axles of certain buses. The thought behind this use was to reduce the fuel consumption of the vehicles. Low viscosity oils or  synthetic fluids were  previously tried but  with  such  lubricants the  necessary  damping  effect was  absent so that  proper shifting was  not  possible. Caution  is given that  this  application of  castor oil is only  possible  under  the  stop and go  operation of busses and  would not  be possible  in over the  road  vehicles. The axle in this case consists of a worm drive with a bronze worm wheel.

Gear pumps depend upon the fluid being handled as the lubricants, and this is sometimes water. Also, water has been employed as lubricant in the case of some nonmetallic gears but has its limitations. First, the temperature range over which water can be used is limited. Next, it will contribute to rusting of the ferrous parts with which it comes in contact unless inhibitors are present. Further, water affords little protection against wear.