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.

   

Pour Point Depressants

Certain  polymers when  added to wax containing lubricating oils in  proportions of 0.1 to 5 per  cent, will  alter  the  crystal  structure  of the  wax  and  thus  permit  movement  of the  oil  at a much  lower  temperature  than  before  the addition. Some  agents  used  for  other  purposes, for  example V.I. improvers, may  have a similar  influence on  pour  points.

Most  industrial  gear  oils do not  require  this  type  of  additive but  pour  depressants are  often  included in  automotive  gear  lubricants. The agents  normally  used  include  “Acryloids”  which  are  methacrylate  polymers,  and  “Paraflow”  or “ Santopour”  which  are  wax condensation  products with either  naphthalene or  phenol. 

Additives for Straight Mineral Oil Gear Lubricants

All gear oils should contain a foam inhibitor, probably in the range of 5 to 10 parts per million. In order to arrive at approximately the correct proportion of such an additive, it is best to use a concentrate. This may be a ten per cent dispersion of a dimethy1 silicone in either kerosene or carbon tetrachloride.

Suppliers of silicone polymers offer antifoam additives, most often as concentrates and will suggest proportions to add to gear lubricants. Other compounds or  dispersions of the  same  are also  available  from  additive  suppliers who  furnish  instructions  for use.

While  most  industrial gear oils  are  not subjected  to  elevated  temperatures, the  presence  of a small  proportion of  oxidation  inhibitor is an assurance  of long life  and little deterioration of the oils. Additives such as 2, 6 – ditertiary – buty1 -4 – methyl  phenols or phenyl  alpha or  beta  naphthylamine , used  in  proportions  of 0.1 to 1.0 per cent, should be  found satisfactory for  most  straight  mineral gear  oils. The first compound or one quite similar is supplied by several concerns, often under a trade name. Other  antioxidants  will  be  noted in  various formulations to  follow and  will also  be  found in  Boner where the  source  is also shown.

For special applications other types of additives may also be found necessary in what can be classed as straight mineral oils. Thus, Watson  and Tierney  Formulated oils to be used under wet  conditions on paper  making  machines where a circulating  oil would  serve both bearings  and  gears. Since, in  this  operation, the  oil passing through the  system is  quickly  contaminated  with  water which  settles out, retention of  the rust   preventive additive  is quite important. A  suitable  formulation, which  retained the  major portion of the  additives after over a 1000 hours of  service, consists of : a  base  oil  blended from a paraffin  distillate  and a  paraffin residual  and having a  viscosity SUS at 100 degree F of 653, a pour  point of -10 degree F, and  a V.I. of  85; 2.0 per cent  by  weight  of a 50  per cent concentrate of  barium  dinonylnaphthalene   sulfonate in a light oil; 0.75 per cent of Zinc  dimethylisobutyl  carbinyl  dithiophosphate ; 0,10 per cent  of a  chlorinated  paraffin  wax naphthalene  condensation product; and 150  ppm of a 10 per cent  solution of  dimethyl  silicone  polymer in  kerosine.

Venting Gear Housings

While Forbes et al.^20  mention that gear housings should be vented so that oil vapors may escape, such openings  may  tend to permit  entrance of humid air. In fact water has been drawn off from gear cases which could only have arisen from condensation. If such conditions generally prevail, the gear oil should contain a rust preventive additive. Cartridges or filters containing dehydrating agents and attached to the vent of gear cases are not too practical because of the necessity of frequent renewal. Removal of condensed water from circulating systems is simpler than where the gears are bath lubricated. Entrance of contaminants other than water through gear housing vents is possible and often problem. The location and atmosphere surrounding the gear set will determine such possibilities and also what corrective measures need be taken. Thus, gear cases of large tractors, such as are used on road and construction work, have a breather with an air filter which should be renewed at 250 hours operation intervals. One manufacturer reports some trouble with dirt in gear cases probably due to the filter not being changed at the required interval. Farm tractors also have the same problem and a proper air filter and frequent renewal is desirable on vents from gear cases. 

Automobile and truck gear cases are subjected to similar contamination. Thus, a large car manufacturer  mentioned in a service bulletin that two major  contributing factors  to  a considerable number of ring and pinion  failures in axles  was moisture  and  foreign  materials  entering  the axle  and contaminating the lubricant. The corrective action was to install a new vent system. The vent was fitted with a hose and hose clamp. The hose, 19 inches  long , goes  up under  the  frame  and  body of the car  and  is  clamped  so  that  the  open  end  faces  toward  the  side of the  vehicle.

Industrial gear set installations may require similar filters or extensions of gear case vent opening to points where the concentration of contaminants is at a minimum.

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. 

Demulsibility of gear oils

Lubricating oils vary in their tendency to emulsify with water; therefore, if emulsification of gear oils is likely to be a problem, the base oil should be investigated. Any polar compounds remaining in the oil after refining, such as sulfonates, petroleum acids, and even asphaltic bodies, may help to stabilize emulsions. Well refined oils of low viscosity  will  have  the  least  tendency  to  from  permanent  emulsions  with  water.

High interfacial tension will tend to cause emulsions to break. Many oil field emulsions are broken by causing the emulsion to revert from water in oil type to oil in water type. However, the best solution for this type of trouble is to choose oil additive combinations which do not promote emulsification.