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.

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. 

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.

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.

Type Designations for Specific Applications

Viscosity or grade designations may be used by other groups or organizations. AGMA are  the  best  example of  such a group, but  the  American Society of  Refrigeration Engineers have set up  viscosity standards and  other  organizations are  contemplating  such  action.

The  manufacturer  of  machinery  often  finds it  necessary  to  provide a  designation of a  lubricant which  has been  found  satisfactory for a specific mechanism. At times  such a  designation may  include  the name  of the  device as  is  the case  with  automatic  transmission fluid, known as ATF. Other  such  types  of  lubricants may be  evident  when  specific  applications  are  considered.  

Turbine Oils

In many turbine installations the oil must  serve  not only the bearings  but  also  the  reduction  gearing and  perhaps the  thrust  elements. Therefore, consideration of this type of lubricant is necessary. The viscosity of the oil used in geared turbines is generally a compromise since the bearings would require a lower viscosity than the gearing. The base oil should be in the range of 300 to 500 SUS at 100 degree F. This oil should be  well refined  so that  it  will  have  long  life  and  so that  any naturally  occurring  compounds which might  contribute  to  emulsions are  removed. All of these points to solvent refined oils.

Alkyl  phenols, such as 2, 6-ditertbutyl – 4 – methyl phenol, or “Ionol” in a  proportion of 0.1 to 1 per cent are  satisfactory  oxidation  inhibitors for  most  turbine  oil formulations.

Rust  inhibitors should  be  of a nature  which  will not  contribute  to  emulsions nor  be  removed  from the oil by water. Or this reason “Lubrizol 850” or “Alox 1832” can be used. The former is effective in concentrations o 0.05 to 0.10 per cent and the latter in amount up to 2.5 per cent.

An  antifoaming  agent,  such  as a dimethyl  silicon polymer, in  a  concentration of about 0.001  per cent, should  be  present  in turbine  oils.

According to Landis et al. the emulsive tendencies of antirust turbine oils can be reduced by the addition of small amounts of aryl sulfonic acids or their salts. A typical composition  consists of : a solvent  refined  oil having  a viscosity  of 350 to 600 SUS  at  100 degree F  and  containing  0.25  per cent  by  weight  of  2, 6 – ditertbutyl -4 – methylphenol; 0.1 per cent  of  phenyl  alpha  naphthylamine; 0.1 per cent  of an  antitrust  agent obtained   by  reacting  oleic  acid  with  triethylenetetramine, in a molar ratio of 1.3  to 1, to  produce an  intermediate  product  which  is  then  reacted  with  triisobutenyl  succinic  acid  anhydride in a molar  ratio of 2.3 to 1; and  0.02 per cent  of sodium  petroleum  sulfonate. As  a  substitute  for  the  last  ingredient, 0.02 per cent  of either barium  or zinc  petroleum  sulfonate  or  0.05 per cent  of  ammonium  petroleum sulfonate, can  be used. The proportion of such demulsifies is critical and an excess defeats the purpose.

Overrunning clutch lubricants

 The  freewheeling  clutch is  probably  a  thing  of  the  past  in  automotive  vehicles but  still  finds  some  use  in industry. Therefore, mention will be made of the characteristics of oils   required for this service. Such  a  clutch  will  be  a  part  of the  driving  mechanism  and  consequently  will  logically  be  lubricated  with  the  gear  oil  in the  case.

However, there  is a limit  on  the  viscosity  and pour  point of a  satisfactory  overrunning  clutch  lubricant  as  recognized  by  Roos  and James  who  stated:

“ If  excessive thick  lubricant is used  the  roller clutch will not operate  in cold   weather  until the car  has been  driven for  one  or two  blocks  with the  transmission in  positive  engagement.

                                                                                   

Influence of Additives on Viscosity Tests

Erratic viscosity results can be obtained in some cases with oils containing additives. If the gear oil contains diluents, some of this fraction might escape before a test is completed, particularly if the determination is conducted at 210 degree F.

Some  additives  which  are sensitive  to  heat  may change  under similar  conditions  or two agents  may  react and thus change  the final viscosity. Also, in case  the  lubricant contains a polymers, such as “Paratac”, heat  may tend  to  reduce its  effectiveness  and  in turn  the  viscosity of the  mixture.

Inboard Marine Engines and Transmissions gear lubrication

Where  inboard  engines,  either  gasoline  or diesel, are  used to  drive pleasure  craft  or  small  commercial  boats, there  will  be  a wide  variance in the  lubricants used in the  transmissions. This is due to design differences. Therefore, the  lubricating fluid recommended  may  be an  EP gear  oil  or a  straight  mineral  oil  falling within the SAE  90, 140 or 250 viscosity  range, a motor oil, or an  automatic transmission fluid. The  lubricant for the  reduction gears may be  supplied  under  pressure  from the engine oil  system or an independent  oil  system  for the  gears  alone  may be provided. The  lubricant then  will  no  doubt  be an  SAE 50  oil  for summer  and an  SAE 30  or 40 for  winter operation. With separate  lubricating  system  for the  gears, the  corresponding oils may be an  SAE  140  or  SAE  90.

The  fluid  used  in a  hydraulically  shifted transmission must serve as a  hydraulic  medium  for a  complex  control  system and also  act as a  lubricant and heat  transfer medium. This, then points to the use  of ATF. In addition to the transmission, which provides for reversing, neutral, and forward speed, in large boats, a further reduction gear unit may be found. It may even be that the former gears may be lubricated from the engine and the latter require the heavy gear oil.

Due to the variations in drives and methods of lubrication, the supplier of the engine is in the best position to recommend the proper lubricant for gear trains.  

Electromagnetic Transmissions

This type of transmission seems to have little connection with gear oils but since this is a method of transmitting energy in automotive drives, it will be mentioned. It is said that such a coupling, incorporated in an automatic transmission, is being offered as optional equipment in Hillman Minx cars. Magnetized iron particles bind two plates of a clutch to transmit power.

Allied to the above may be what Biryukov describes as an electromagnetic lubricant. This lubricant used to transmit mechanical  energy  by  friction, consists  of 30 per cent of a  medium  viscosity  oil, 4  per cent  of  rosin, 5 per cent of Paratone  and 61 per cent of iron carbonyl . The iron carbonyl should have a particle size of 8 to 13 microns. 

Diesel Locomotives –tractions Gear-Lubrication

Most traction gears on diesel locomotives are lubricated with high viscosity, adhesive gear oils. Residuum  type products  with  viscosities    as  high  as 500 Furol  at  210 degree F    have  been  used, but  in most  cases  a viscosity  of  2000 SUS at 210 degree F is  satisfactory. About  fifteen  pounds is  required  for an  initial  fill  and  since there  is  some  leakage,  the  gear  case  should  be  checked and refilled at  least  every  month. U.S. specification MIL-L-13914 (ORD) provides for two  grades of such oil, one  with  a viscosity  of 170 to 240  Say bolt  Furol  at 210 degree F and  the other  with a similar  viscosity of  480 to 580. A lubricating  greases is  recommended for the  purpose by  Morway  and  Ball^38  in which  the  thickener  is a  complex  sodium  soap  and the fluid is a mixture of  14.93 parts of a  low  cold  test oil  having  a  viscosity of 55  SUS at  210 degree F  and 75 parts of a  resin  from a Pennsylvania  oil  having a  viscosity  of  14,000 SUS at  210 degree F. When  such a  lubricant was used  in a  locomotive  in  freight  service  it did  not  leak  from  the gear  case, and  after  one  year  of  service there  was  only  slight  wear  on the  pinion  and driving  gear  teeth. 

Carbonated Beverages and Gears

In preparing   beverages, gears are often used on meters to synchronize delivery of syrup and water to carbo coolers. Also on automatic   bottle cleaners, gears are used to rotate brushes both on the inside and outside of the bottle. These latter gears are often flooded with the detergent   solution used in washing and other lubrication is not permitted.

Conveyors, in such  establishments, when  driven  by  reduction gears,  can be  serviced  by  an  oil  of about  500  viscosity SUS at 100 degree F, if enclosed, or a residual  type  of about  2000 SUS at 210 degree F, if of the open  type.

Candy Manufacture and Gears

The method  of mixing  batches  of candy  will  vary  depending  upon  both  the  size  of the lots  and the  stiffness. Cake mixers may be used in some cases. In other instances, rollers, gear driven, will be used. Thus, either enclosed or open gears may be encountered. In  the  former case, the  gear  oil  can be  of about  500 viscosity  SUS  at 100 degree F, and in the  latter case  about  2000 SUS at 210 degree F.

Alcohol and Brewing Industries and Gear Lubrication

The raw material for either alcohol or beer is to a large extent, grain with lesser amounts of molasses or sugar. The use of speed reduction gears starts with the handling of the grain. This  may be  by  conveyors  of  various  types  which, if not  chain  driven, will  be driven  by gear  reducers. Often the grain will be screened before going into storage bins. The screens, which may be of the reel or shaker type, can be driven by gear reducers. A suitable  gear  oil  for  the  above  operations is one  of about  500 viscosity SUS at 100 degree F, equivalent  to  AGMA lubricant No.3.

In a  brewery  might be  found barley sieves  driven  with  open  gears, grading  screens  with similar drives, melting drums  likewise  driven  with  open  helical  gears, malt  grinders with  gear  driven  rolls, spent  grain presses  with  open  gearing, hop  extruding  machines  having  enclosed  gears,  beer  centrifuges  with  enclosed gears, etc. The  open  gearing  in the  above  applications  should be  lubricated  with  a  residual  oil  having a  viscosity of  about  2000 SUS at 210 degree F. This  should  be  applied sparingly  and if there is the  least possibility  of contamination  of  the  material  being  processed, a  shield  might  be installed  to  prevent  this. Enclosed gears can be  lubricated with well  refined oils of 200 to  500 SUS at 100  degree F. Centrifuges  should  use  the lower  viscosity  grade or  an  equivalent  to  AGMA  lubricant  No. 1 or 2.

Truck Transmission and Differential Lubricants

Truck gears, in the main, require higher viscosity oils than do the gears in passenger cars. However, it is difficult to generalize since any one manufacturer of trucks may employ a variety of methods of speed reduction as well as perhaps more than one type of differential. However, lubrication charts are kept up to date and such charts, as well as the recommendations of the truck manufacturer should be consulted as to the proper grade and type of gear lubricant to use. Lubricating charts should be read with care because blanket recommendations are not made for all trucks of a given make. Also footnotes  are  frequently used  to  provide additional  or  more  detailed  information about  truck gear  oils.

A number of truck manufacturers depend upon specialty companies to provide them with transmissions or axles. In this case the parts manufacturer may suggest the most satisfactory gear lubricant. These firms often issue. Field maintenance Manuals devoted to each type of speed reduction unit or each type of axle. Such manuals generally contain sections on lubrication.

Almost all truck distributors suggest some variation in the viscosity of gear oils used as the temperatures change. A blanket statement cannot be made, but sometimes above 32 degree F an  SAE 140  grade of  lubricant  will be  recommended and  below this  an SAE 90.

While it has  been pointed out that lubrication would be  simplified by the use of a common  lubricant  for  transmission and  axles of  trucks,  there is not  an  agreement on this. Thus, Nelson and  Valentine^40 mention that a rear axle  lubricant must be  capable  of  absorbing  greater  torque  or providing  better  load  carrying  qualities  than  a  transmission, particularly  in  the  first  three gears.

Fletcher^19  notes that  many fleets have  standardized on the use of  engine oils in transmissions and  cites  a large  bus line which has used  SAE 30  and  modified SAE 10 engine  oils in  transmissions  for  many  years. The 30  grade is used  in straight mechanical boxes  and  the 10  grade  when mechanical  transmissions are  combined with  a  converter or coupling  and  a common  oil  supply  is  required for  the  two  units. This author objects to the oxidation and sludging of EP oils compared to straight mineral oils. His suggestion is the use of SAE 50 oil for transmissions. Another argument in  favor of  the  engine oils  is that  in  corrosion tests, using bronze specimens, such oils showed  little corrosion whereas  both  HP and  MP  oils  showed excessive corrosion.

On the other hand, Calish^8 cites evidence of the practicality of the use of a common transmission and axle lubricant in heavy equipment. A specific additive oil composition was used in some 1420 vehicles representing sixteen makes of trucks. The inference is that such a uniform transmission and axle lubricant proved satisfactory to the thirty-four accounts operating the above trucks over a period of several years.

When transfer cases are used to drive various devices, the same grade and type of oil as is  used  in the  transmission case will be satisfactory. Transfer  case  is a term applied to gear assemblies which transfer  power from  the  main  drive  line to  auxiliary equipment such  as  front wheel  drives, pulleys, hydraulic pumps, windlasses, and other mechanisms. For example,  many heavy  duty utility  vehicles carry winches for  erecting  heavy poles, devices for  boring holes  in  the  earth, and  other tools which  must  be  driven from  the  same  power source.

Where trucks  are  equipped  with  automatic  transmissions, ATF is  satisfactory  for use  and is so  listed in most  lubrication charts. However,  as a  matter  of  economy, General Motors  suggests the  use  of a  Hydraulic transmission Fluid, type C for  certain heavy duty trucks, buses, and  earth- moving  vehicles. Type C does not  have all  the  characteristics of  ATF  but  does  have  to  pass a  Powerglide Transmission Test, have  low  varnish and  sludge  deposits, and  must have  a  minimum effect  on rubber  seals. This Type C should never be substituted for ATF where the latter is specified.

Truck  Axle Lubricants. There seems to be little question as to the necessity of EP gear oils in axles of heavy duty trucks. However, there is not  common agreement as to  the  proper  grade  or  viscosity  of  lubricant  for  such  applications. Johnson^27, who considered these subjects, states:

“ Our  field experience is quite  conclusive to  the  effect  that  an SAE-140  viscosity lubricant is  far  superior to an SAE-90 in  its  ability  to  prevent gear wear  and  related  problems. On  numerous occasions  we have been  able  to  overcome  gear  wear  problems by  merely  effecting  a change  from  an SAE-90 to an SAE-140 viscosity”.

Also, it was found  that, with the heavier gear oil, temperatures in the  gear  case  did not  increase  but actually were  5 to  10 degree F lower than when  operating  with  the  lower  viscosity oil. The use of SAE 250  gear  oil  was  investigated but  it  was  found  that  this did run hotter  than  the SAE 140 grade.

A  further  advantage  of  the  use  of the higher  viscosity oil was found  by  this  investigator^27 when  the two  grades of hypoid lubricants were tested  on  eighteen driven units in the laboratory, using hypoid gears with a  61/6 ratio. The results obtained were:

“At 3000 rpm, the SAE-140 lubricant supported a torque load 21% greater than the SAE-90. At 2500 rpm, the advantage was 23%, and at 2000 rpm, it was 20%”.

Another factor, indicating the desirability of higher viscosity oils in axles of trucks, is that pointed out by Blok^3. It  was  mentioned that,  under  conditions of  impact  load  on  gears, viscosity is of  prime importance and  that  this  property of the oil  cannot  be  replaced by  antiwelding  activity  if wear  is to be  prevented.

Gears in  heavy duty trucks are  subjected to  low  speeds  and  high  torque conditions during much  of  their operation. For example, Nelson and  Valentine^40 determined that  in  highway operation a truck having  a 5-speed transmission used first speed about 2 per cent of the time, second  speed about 3 per cent, and  third speed  about 10 per cent , or a total of  15 per cent. The resulting comment was: “It is in this interval that gear destruction is prevalent, if the lubricant does not have proper EP qualities”. Further, mention is  made  that  in  off -high way  service, such trucks  operate approximately 50 per cent of the  time  in  the  first  three transmission gears.

Not all EP gear oils will provide satisfactory protection to axle gears operating at low speeds, and high torque, as do those in trucks. Therefore,  assurance  should be  obtained that  lubricants satisfactory for  such service  are  used  for  truck  axles. Lead soap active sulfur EP lubricants have been favored by some for such application. Since the  prevalent operation of  passenger cars is  under  high  speed  and  low  torque conditions, it is  desirable that a single  type  gear  oil  satisfy these conditions as well as  those  of  operating trucks. With this in mind, what is considered by some as a truly multipurpose gear lubricant has been provided? Such oils are those  conforming  to  specification MIL-L-2105B  which  is accepted  for  the  requirements of  all  vehicles operated by  the  U.S Military and by  many  other  users.

Some axle manufacturers and truck producers prefer to  either issue specifications for  what  they  know to be  satisfactory  axle lubricants or  to  state the type of EP  gear oil  to  employ. Hence, it is well to abide by the opinion of the truck supplier when choosing lubricants for truck axles.

This is all the more true because the gearing in truck axles may vary. Most  of  such variations, with  the exception of worm  drives, will probably  require  the  same  type  and  grade of  gear  oil as will  straight  hypoid  gears.  Thus, Rockwell  standard for  either  Planetary Axles or Hypoid- Helical  Two- Speed Double-Reduction Drive Units, as  well as  Spiral Bevel Gears,  recommend oils conforming to  their  Standard 0-65, which  is  an  SAE 140  EP  product. Use of Standard 0-65, the SAE 90 grade is optional but is suggested for lower operating temperatures than the 0-65.

Lubrication of Worm Drives on Trucks. In the case of worm drives on trucks, recommendations for the lubricant vary. While some suppliers of EP gear lubricants claim such oils can be used safely in worm drives, Watson^51 states:

“Actually, in practice, an EP lubricant is usually unnecessary for a worm gear. When lubrication failure occurs in a  rear-axle worm gear, only  in  exceptional  circumstances can it be  attributed  to  lack  of load carrying capacity  of the  oil used”.

Certainly  if temperatures  exceed 200 degree F, as they  may  at  times in axles of any  large  vehicle, EP additives may  cause  excessive corrosion of  bronze. Since EP agents and combinations of the same cover such a wide range of chemical compounds, the above statement may require modification. Perhaps the worst offenders are sulfur compounds, even some not considered active at 200 degree F. The possible  explanation may  be  that since  copper has  considerable affinity  for  sulfur, temperatures at  contact  points  of  the  gear  and worm  will  be  high  enough  to  cause  reduction of the  metal and sulfur. That, is the action may be akin to temperature flashes which occur with hypoid gears.

However, substitutions  have been  made for  recommended worm gear  lubricants; and if this  is done, fleet operators  are in a  better position to  observe result  than are  individual vehicle operators. In  certain  busses of  the  London Transport Company  having worm  drives, it  was  reasoned that  a fuel saving would be possible if there was less  drag due  to  the  axle lubricant. An  exceptionally thin oil  gave  satisfactory lubrication, but  when  changing from  first  to second gear  on  a level road, the  lay shaft  spun so  freely  that  the  higher gear  could  not  be  engaged until the  bus  came  to rest. An inhibited castor oil was then tried and proved satisfactory. However, the operation of these  specific  vehicles with  considerable stop  and start does  not  result  in  heating of the axle  lubricant, with  a consequent  possibility of oxidation, as would be the  case  in over-the –road vehicles.

While possible variations in oils for servicing worm gears of trucks have been mentioned, this is for information only. The safest  course  for  the  owner or  user  of  such a truck  is to follow the  recommendations of  the  manufacturer  of the  equipment.

Viscosity Temperature Characteristics of Gear Lubricants

Since gear and transmission oils are subjected to widely varying temperatures, particularly in vehicles, it is desirable that such lubricants have as little change in viscosity with temperature changes as is possible. In other words, high V.I. oils are desirable in many gear oil applications and absolutely necessary in certain cases. An illustration of the latter is automatic transmission fluid. Base oils with V.I. values of 90 to 95 are readily available when needed. Where it is desired to increase the V.I. of oil, additives, known as V.I. improvers, are sometimes used. These agents are generally  polymers  which act by either coiling  up or  becoming less  soluble  at  low temperatures but reverse  this action as temperatures  increase,  so as to  contribute increasing body at higher temperatures. In normal gear  operation the shearing  effect  tends to break  down such polymers  into those  of lower molecular weight  which  are  less  effective  as V.I. improvers. However, these agents do have a place in services such as ATF where they maintain their effectiveness.

Certain  high molecular weight  petroleum resins  have been found to improve  the V.I. of some lubricating  oils  and  not  have  the defect  of  breakdown with  shear.