Calcium in Lubricating Oil

While the ASTM Methods and Fed. Test Method use the same sample  for  determination  of  several  metals, the IP  Methods  is  specifically concerned with  calcium  analysis. This calls  for ashing  followed  by determination  of the  calcium  either  as oxide  or oxalate.

Boron Compounds as EP Agents

Boron compounds have been  recommended as EP agents and also for other  purposes in fluid lubricants; hence, they may have a place in gear oils. Thus, organic borates  for  use in mineral oils to  prevent  excessive oxidation is  claimed. The use  of  compounds  such as  chlorophenylboric  acid  dibutyl  ester, as well as  organic fatty  materials reacted  with  boron trifluoride, have been  mentioned as EP  agents, finally boric  acid has been used for the purpose.

Identification of Gear oil Additives

Verification of the presence of  various additives  in gear oils is often of  interest and different methods have been  suggested for the purpose. To identify dialkyldithiophosphate additives in lubricating oils, lewkowitsch  isolated  the  compounds in the form of copper salts. Paper  chromatography  was applied to the  identification of certain  anti-oxidants by Delves. Among the compounds  distinguished  were  diphenylamine, phenothiazine, and  phenyl alpha and  phenyl  beta  naphthylamines.

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.  

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.

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. 

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.

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.

Industry Trends As They Affect Transmission Lubrication

Every industry  is alert to  equipment  and  processing  changes whereby  improvements can  be  made in quality and  quantity of their  products. It is  only  by  such  changes  that  this  nation or  any  country  can continue  to  provide  what  have  come  to be  considered the  necessary  elements of  our  mode  of life. Practically any specific   industry could be singled out to indicate this trend. Everyone is familiar with the steps being taken by the steel industry in this regard, but perhaps a better illustration concerns the miracle of modern agriculture. Fewer farmers than  formerly are cultivating less land but producing an over abundance of food and fiber. The change has taken place in one generation. Thus, in 1920 the product of one  farmer  would  feed eight  persons, whereas  in 1963 one farmer  can produce   enough  food  for  twenty   eight people. Most of the above increase has occurred since 1950   during which period the output per man on a farm has doubled. One factor making this change possible is the availability and use of expensive machinery. Proper gear and transmission lubricants assure that this machinery operates satisfactorily and with a minimum of difficulty.

The lubrication industry can take pride  in the fact  that  the  lubricants  it  supplies are  a very  essential part  of the  miracle of modern agriculture  and also  of the  miracles  taking  place in other industries. As  a corollary,  it might be kept  in mind that  further  improvements  in  production and in  services which are  accepted as a part  of our  living will only be possible  if the  proper gear and  transmission lubricants are  available.

Food processing Industries and Gear lubrication

A variety of industries are grouped together so that prevention of contamination by gear or transmission lubricants can be stressed. While such possibility is remote, Government Inspectors are becoming more particular in this regard. Also, both  manufacturers  of food processing  machinery  and operators of plants are  aware  of the  importance of cleanliness  and lack  of contamination. Proper seals, well maintained, should prevent leakage from gear cases. As an aid in this direction, over lubrication should be avoided and when and if lubricating grease is applied, this should be at very low pressure. As a general rule, straight petroleum oils can be used in gear lubrication of the subjected equipment. Some operators of machinery handling foodstuffs prefer light colored lubricants. White oils are available in viscosities up to 300 or perhaps 500 SUS at 100 degree F. The  same  oils can  be  thickened  to  a  semi fluid or non  flowing  nature  by the  use of fine silica  or non toxic  soaps, such  as  aluminum  or calcium. Light  colored  fillers, such  as  magnesium  oxide  or zinc oxide, can be added to  lubricating greases, although fillers have little  if any  place  in gear  lubrication.

Caution  should  be  used  in supplying  gear  lubricants containing additives  to  food  processing  plants. Oils  containing  EP agents should  only  be  used  if the gear  cases  containing such  oils are  sufficiently  removed  from  the food  products so that  leakage  will  cause no  contamination. Foam inhibitors are permissible because the concentration is quite low. Stable oils are recommended because they will require a minimum of oxidation inhibitors. Such additives, as well as  rust  inhibitors, which  will  be  desirable  under  wet  conditions, should only  be used  with assurance  that  the compounds are not  harmful to  animals  or humans.

Simplification  of gear  lubrication  should  be  kept  in mind and  if  possible, only  one type  and grade  of gear  oil be used in a  specific  plant. Thus, in spite of the  recommendations above for the  use of such oils  with  very  judicious  inclusion  of  additives, the suggestion  has been made^31  that  a  premium  grade  rust  and oxidation  inhibited turbine and  hydraulic  oil  be  used in all  gear reducers  in dairies. Therefore, similar oils will also be recommended for other foodstuff handling equipment. Open gearing will be found in some food handling machinery or plants.  It  is  presumed  that such  gears  will  be so located  that  drips from  the  same  will  not  contaminate food. Therefore, a  general  recommendation  is to  apply  a  residual  type  of  gear  lubricant  very  sparingly. The viscosity will be dictated by the service but will probably be one of 1000 to 2000 SUS at 210 degree F.

In the  group  to  follow, equipment  used  to process some medicinal  items, alcohol  products etc., will be  included since  they  are  restricted   to the  same  limitations as far as contamination is  concerned. By  mentioning  some  of the unit  operations  which may be  encountered   in food  processing, the  variety  of machinery  involved and therefore,  the  possibility of the  use  of  gear  drives will   be  evident. Thus, cleaning,  coating, conveying, decorating,  disintegrating, drying, evaporating, forming, heating, mixing, packaging, pumping and  separating are a few  such  operations. 

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. 

Compressors and Gear Lubrication

Gearing in connection with compressors, whether for air, gas or refrigeration, is almost entirely confined to auxiliary functions. Some  air  conditioning units  have  gear  pumps to provide  forced  feed  lubrication  for  the  equipment. Also, some portable air compressors have gear driven rotary oil pumps. In either case lubrication of the gears may be by the crank case oil.

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.

Prevention of Contamination of Gear Lubricants

Gear sets operate under such varied conditions that it is difficult to give general suggestions for prevention of contamination of the gear lubricant. The two contaminants most often encountered are water and dust. In the latter are included large particles such as scale in steel mills. Less trouble is encountered where a circulating  system  provides  the  lubricant  rather  than  a  splash system, since the former  can  be  supplied  with settling  tanks  or filters. Even here regular inspection is necessary and accumulated water should be drawn off whenever noted. Such accumulations may  be quite  large  in the case of  gear  oils  for  ship  propellers or in oils servicing  paper  mill  machinery  or steel  mill  gears.

Where  gear cases  are  vented, the location  of the vent or a pipe  connection to the  same  should  be so  located  that  the least  dirt  possible  can enter. One automobile  manufacturer reduced  contamination in  differential cases by  extending  a  line  from  the  vent  and  securing  it  forward  under  the  car  frame  with  the  opening  toward  the  side  of  the  vehicle.

Prevention of contamination of lubricants by chemicals must have individual consideration. In  extreme  cases it  may  be  necessary  to  provide  pressure  on  gear  cases to  prevent  entry  of contaminants.

Nonferrous Gears and Their Lubrication

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

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

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

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

Reasonable Costs of Gear and Transmission Lubricants

Cost is a quality just as are physical characteristics, and by discussing it immediately following characteristics, the reader will have in mind all of the requirements of gear oils and can thus visualize the fact that considerable effort and precise compounding goes into the manufacture of a satisfactory lubricant.

At one time gear oils consisted, in the main, of black oils which were not too well refined. While some residual products are now sold for the purpose, most gear lubricants are on par with motor oils in quality and price. As further demands are made on gear lubricants for specific applications, more expensive additives and even synthetic fluids will be required in some cases. Thus, the trend of cost of such products can be expected to increase to some extent. In return, the consumer will obtain a better product and in many cases a longer service life.

It is appropriate, when considering the cost of a lubricant, to also keep in mind the cost of the equipment to be serviced. The proper lubricant, applied as needed in the right amount, will protect and prolong the life of machinery many years.