Future Trends

If the business of providing proper lubrication for  gears and transmissions were a  static one, people  would  lose  interest in it, and  there  would  be no  purpose  in this volume. However, as indicated by the just preceding, there are problems in connection with gear lubrication and gear lubricants. While  the immediate reaction  to a complaint  or a  problem  of this  sort  is to  blame  the lubricant, it  should be  again  pointed  out  that  perhaps  only  ten  per cent  of   such  complaints are due to  deficiencies  in either  the lubricant or the  application. In spite of this , the  industry  does  have problems and since they  will not  always solve  themselves, it  is necessary  to give  thought  to the  future  when  solution of  the  immediate  problems will be possible  but new  ones  will be  confronted.

Since a little  adversity is good  for the soul, these  problems stimulate  thought  and are the  cause  of many  improvements  and  advancements  in   all industry. In the lubrication of   gearing, the problems do not always take the form of complaints but often of suggestions. Whatever the form,  such  questions do indicate that  modification of  not  only  present  products  but  also  present  thought may be  necessary if the  lubrication industry  is  to  play  a part  in continually improving  the world.

No matter how  did  wild  dreams about providing  different  or better lubricants for gears may  be,  they  would  come  to naught  if  practical considerations are not  kept  in mind. These  include  the economy  of   the suggestion,  the  availability  of  the  necessary  components of the  composition, the  ease of  application, compatibility  with other  materials, and  acceptance  by  other industries  and  by the public. Any or all of these factors may change with time; hence, it is well to dream.    

Shear Stability of Gear and Transmission Lubricants

While most mechanisms containing gears will tolerate a considerable variation in viscosity of the gear oil used for lubrication, a radical change in viscosity at a stated temperature, while in use is not desirable. Further, if such a change is due to a partial breakdown of an additive the purpose of the agent may be defeated. Such changes may occur due to shear while in service. The components most often affected are polymers such as V.I. improvers.

At present, products used in vehicles are the lubricants most often influenced by shear. Such changes will become increasingly important as a single fluid is used for several purposes such as a hydraulic fluid, for ATF, and perhaps as an axle lubricant. Further, a multirange gear and transmission oil has advantage in cars and trucks. That is, oil which will cover two or three SAE viscosity ranges.

Under present formulations some of the lubricants offered for the above services contain polymers as V.I. improvers. However, the action of gears or even pumps tends to change the polymers by shear. The shearing action causes either a chemical or mechanical breakdown of the large polymer molecules so that their value is largely lost in the oil. In some cases a viscosity decrease in service is temporary and in such instances there may be an alignment of the polymer molecules at high rates of shear. Of course some polymers or additives are more resistant to break down with shear than others but unfortunately those of high molecular weight, which prove the most effective V.I. improvers, are also most susceptible to loss of viscosity with shear.

Where high V.I. is necessary or desirable in gear oils, tests should be made to determine the viscosity after shear tests. This is most often done by using a test where a pump forces the lubricant through a sharp edge orifice for a stated time at a given temperature. A similar breakdown of polymers occurs with sonic shear, and a method using this procedure has also been used to evaluate the shear resistance of V.I. improvers.

Klaus and Fenske^34 tested fluids containing about 7 per cent of polymer for their permanent decrease in viscosity due to shear. After 5000 cycles in a pump at 100 degree (F) and a pressure drop of 800 psi, decreases of 25.5 to 30.5 per cent occurred. At a pressure drop of 1500 psi, the decreases were 38.5 and 40.5 per cent. The time required to stabilize viscosity will vary both with the mechanism and the fluid used. 

Minimum action of gear oils on components of mechanisms

Well refined mineral lubricating oils have little if any action on most metals, particularly ferrous metals. It is only upon prolonged use at elevated temperatures that such oils may from compounds which will act upon metals. Since such oil changes can be retarded or almost completely arrested by the use of oxidation inhibitors and also metal deactivators or pacifiers can be included, there should be little concern about the action of straight mineral oils upon the metal components with which they come in contact.

What we are concerned with here is the action on parts made from other materials, such as paper, plastics, rubber, etc. Seals are likely to be made from rubber, either artificial or natural, and any deterioration of the compositions due to the lubricant should be at a minimum. Many seals consist of compounded materials, such as “neoprene,” and it is found that oils high in aniline points, as are most high V.I. oils, will have little effect on this compound.

Automatic transmission mechanisms may be found to contain paper and “Nylon” parts. In future devices which will require transmission fluids, a greater variety of components may be used. The safest course when supplying oils for contact with unusual materials is to have the fluids pretested to determine their suitability.