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. 

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 Steering Gear Fluids

As a base for such a fluids, a solvent refined oil of about 250 viscosity SUS at 100 degree F may be used. While , as Johnson and Mortensen state, the major requirements are shear  stability  and high  V.I., the oil should  also  be  resistant  to oxidation and  have no  adverse effects on both metals  and  seal and  hose  materials. Likewise the blended oil should have a low pour point. All of the above point to a solvent refined oil which will have the desired high V.I. and aniline number.

Chrysler MS 3590 “Hydraulic Steering Fluid with Rust Preventive”, summarizes the composition requirements as follows:

“Well refined oil with admixture of proper rust preventive additives. Small amounts of oxidation inhibitor and pour depressant may also be used to meet the details requirements. The use of   detergents and V.I. improvers is prohibited. The additives small be selected to have a minimum effect on the seal and hose materials”.

Therefore, additives may  include up to 0.5 per cent  of an  oxidation inhibitor, such as  can be  recommended  by  an  additive supplier, or  may  be  phenyl  alpha napththylamine , 2,6-ditertbutyl – 4- methyl  phenol, mixtures  of these  two  types, or  an oil-soluble  organic thiophosphate salt of certain  metals, such  as zinc  methylphenyl  dithiophosphate.

If the pour point of the oil is above -20 degree F, from 0.2 to 1 per cent of a pour depressant, such as “Acryloid  150”, “Paraflow”, or “ Santopour C”, can be added.

Suitable rust inhibitors, used in concentrations of 0.5 to 2 per cent, include petroleum or synthetic sulfonates, such as “Petronate” or barium dinonyl naphthalene sulfonate. A combination oxidation and rust inhibitor, which is usually used in a concentration of 1 per cent or less, is “Vanlube 76”. 

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. 

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.

Oxidation stability of gear lubricants

Once a proper gear lubricant is selected for a given application it should suffer a minimum chemical and physical change during use. One of the changes most likely to occur is oxidation  of  the oil  which ultimately  will  lead  to the formation of undesirable  products  and  changes in the characteristics  of the oil. Such changes may result in the formation of acidic  products which  may corrode  the metal  surfaces, in an increase  in viscosity  of  the  oil, or in production  of  insoluble  materials. Oxidation  of  lubricants  is  accelerated  by  high  temperatures or  by  the  presence of  certain catalysts, particularly  soluble  metals. The  immediate  effects  of  oxidation  may appear  beneficial  in  that  petroleum  acids formed  function  as  oiliness  agents, perhaps by  the formation  of  monolayers  of metallic  soaps. Ultimately, as oxidation of oil proceeds, the harmful effects become evident. The degradation of the oil by oxidation may result in not only the formation of acidic products but also asphaltenes, resins, or other polymers. Changes in the lubricant will  probably  be  accompanied  by  increase  in  viscosity , darkening  in  color, and  the  formation  of  sludge. Cases have been noted where gear oils became almost solid due to oxidation.

However, oxidation of gear lubricants can be retarded by addition of antioxidants or oxidation inhibitors. The use of such agents in most gear oils is wise since the environment for the lubricants is favorable for oxidation in that both air and heat are present and thin films of the oil are in contact with the air.

The mechanism of the action of antioxidants is generally considered to be that of chain breaking as the additive reacts with a “hot” molecule, thus being itself oxidized. In this process the oxidant molecule is destroyed, but with dissipation of the energy possessed by the “hot” molecule, so that the chain reaction is broken. Thus, the oxidation of hundreds or perhaps thousands of molecules of hydrocarbons is prevented, since the energy would be passed on from one molecule to the next in the normal chain reaction.

The suggestion was made by Larsen and Diamond^35 that antioxidants may be either inhibitors or retardants, the former acting to break reaction chains and the latter being converted into an inhibitor during the oxidation process. Three possibilities were given by Murphy et al.^42  for the possible disposition of such inhibitors after they had reacted: (a) the inhibitor is oxidized to a compound which is incapable of further antioxidant action; (b) the inhibitor is oxidized to a compound which still exhibits antioxidant action, but generally to a reduced extent; (c)  the inhibitor is capable of regeneration. The latter type of additive is the most desirable, provided the rate and degree of regeneration are high.

Specific compounds suitable as antioxidants will be suggested in a later section, but most of these agents fall in the following bellows: (a) various types of phenols, (b) certain sulfur bearing compounds, (c) numerous organic phosphites, and (d) certain of the amines. A number of additives function as dual purpose agents and thus, in some cases, a specific antioxidant may not be required.