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.

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.  

Lubrication of Special steels

If special alloys are used in one or both members of a gear set, special consideration may be necessary in choosing a lubricant.  The supplier of the equipment will no doubt have the answer since, as Forbes et al. ^20 states:

“The choice  of  metals  that will operate together in a particular type of  reduction  gear is based on practical  data  that have been secured by trial  and error methods  over a period of years.”

It is known that some steels are more difficult to lubricate than others. Stainless steel is very important in this time. Some alloys will not react readily with certain EP elements. Chromium  is  practically  inert  to  sulfur  compounds  but will react  with most chlorine  compounds. Therefore, with high nickel-chrome-molybdenum alloy steels it is important that an EP lubricant contain chlorine additives as well as sulfur compounds.

Reduction of wear in gear sets and transmissions

Wear has been defined by a Committee of the Institute  of  Mechanical Engineers as: “Progressive loss  of substance  from the surface of a body  brought  about by mechanical  action ( usually it  reduces the serviceability of  a  body  but  can  be  beneficial  in its  initial  stages  in  running in)”.

It is evident from  this definition  that  what  is desired  in a gear lubricant  is  prevention  of  continuous  wear. With highly loaded moving parts, which include gears, the following types of wear may occur:

                            

                            (a) Abrasive and cutting wear.

                            (b) Corrosive wear           

                            (c) Fatigue wear.