Corrosion fog cabinet

A number of test  methods, of which  this is one, make  use  of  bench  tests to  indicate  how  well  a lubricant will  protect steel  from rusting. These  methods  are  most  often  used  for  comparatively  low viscosity oils,  such  as  turbine or  aircraft oils.

Cold - rolled sheet steel panels 2 x 4 x 1/8 inch, surface ground to a finish of approximately 20 micro –inches as measured by  a  Brush analyzer, are  used  as  specimens. These are  coated with  the  oil by  dipping  after  which  they  are  held  in a  rotating  table in a  cabinet  into  which  water  is  atomized. The  cabinet  is capable  of  regulation  from  110  to 160  degree F, but  most  tests are  run  at the lower  temperature  for a given  number  of days  or  hours.

The  specimens  are  observed  through  a window  at the  end of the  first  24  hours  and  each  subsequent  24  hours  increment of  exposure. The  time  of  failure  of a  specimen  is  recorded  as  the  day  on which  at least  3 rust  sports 1 millimeter  in  diameter  forms  on the  front  surface  of  the  specimen  in the  central  area  which  excludes  ¼ -inch zones  adjacent  to  the  top  and  sides  and a ½ - inch zone  at the  bottom. Three specimens are coated with particular oil. At  least  two  of  these  must  last  the  specified time  without  failure.

Flour Milling and Gear Lubrication

Up to time grain enters the mills, conveyors are used for handling. These  may  take the  form  of screw,  bucket, ribbon or belt and  any  one of these  types can be  driven  by gear  reducers. A  turbine type of oil  having  a viscosity of 500 SUS  at 100 degree F,  that  is AGMA  No. 3 grade, can  be  used  throughout  these  gear  reducers. In  the  northern  states  this  oil  should  have  a pour point  of zero or lower. An  oil of this  viscosity  will not cause excessive  power   loss and  yet  it  will  protect the  moving  gear  teeth.

Gear motors may be used for some conveyors and blowers. The  same  type  and viscosity of oil  should  be  satisfactory  for the  bath  lubrication  of such  gears, especially  if bearings are  serviced from the same  source. Where the drives in gear motors run quite warm, an oil of about 750 viscosity SUS at 100 degree F or an AGMA No. 4, may be desired. If such motors have a plate showing the recommended viscosity of oil, this suggestion should be abided by.

A tight  housing  is  essential  in any  of the gear cases in flour mills, more  from  the  standpoint  of prevention of contamination  from dust  than  from  leakage. Since  the oil  level  in gear  cases  should  be  inspected  every  month  or  sixty days, care  should  be  exercised that  dust  does  not enter  when  the  filling  plug or cap is removed.

Open  gears  are not  used too  often  around  flour mills; but if  these  are  encountered, it  is wiser to use  a  light  oil  as the  lubricant  rather  than  a  residual type. This can be the same oil as suggested for use in conveyor gear reducers, that 500 viscosity SUS at 100 degree F. As  such an oil  becomes  mixed  with dust, the paste formed will  slump off rather  than pack  in  the  bottom  of gears; thus, misalignment should  not be a  problem.  

Flour mills  may  be  self contained, in that cleaning, tempering, grinding and  sifting may  all take  place  in one  enclosure, or the latter operation  may be  separated. Such machinery will vary, but often the rolls are driven by gears. Here again the turbine oil type 500 viscosity SUS at 100 degree F can be used. Machinery handling middlings or bran will be much the same as previously mentioned and if gearing is used, the same recommendation will hold.  

In the manufacture of corn meal or animal feeds the same type of processing and machinery will be found. Thus, conveyors  and screens  will have  similar  drives but the  crushing or milling  can be  by  rolls  or  discs. In any event the gear oil used can be the same type and grade as recommended for flour mills.

It will  be noted that  a simplified  lubrication  application for  reduction  gears  is suggested  in grain mills, that is, a  single  oil  throughout with one  exception. This  is in  gear motors and even here  the  sanction  of the motor manufacturer  might  be  obtained for use  of the  500 viscosity  oil.

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.

Turbine oils for Automotive Vehicles

Since  gas  turbine  engines  for  automobiles  have  a  potential  which  no  doubt will  soon  be  realized,  mention will  be  made  of the  lubricant  requirements  for  the  drives. The oil will be used to lubricate both bearings and gearing. The  bulk oil  temperature will  probably  be at least  300 degree F during  operation, but  the oil will  not  be  subjected   to hot combustion gases  and thus should remain    comparatively   clean.

Whether   the oils  used will preferably  be  petroleum or  synthetic or  blends  of  the  two  is a  question. Whatever type, they will   no doubt contain various additives, such as   antifoam    agents, oxidation inhibitors, metal deactivators, and antiwear agents.

Speculation as  to  consumption  and  renewal  of  such  oils   indicates that  the oil  reservoir  will  have  a capacity  of about  3 quarts  and that  the   consumption will be  almost  nil  but  that  an  oil  change  yearly  can be  expected.

Lubricants for Automotive Turbine Engines

This is still a speculative subject but within the next few years no doubt the requirements for vehicle turbine engine lubricants will be material. Since  the bulk  oil  temperature  of the oils in service may well  be 300 degree F  or  higher  and a long  life is expected , a  relatively  high  unit  price  can be  expected  for  the  lubricant. This points to the use of synthetic fluids, probably diesters.

As a basis for formulation it is suggested that those of aircraft turbine lubricants, which are described later, be considered. A starting basis might be the formulation for MIL-L-7808. Specifications for  such  lubricants, issued  by  automotive  manufacturers, should be  available  as soon  as  vehicle turbine  engines  and  drives  pass the  experimental stage. Suppliers of diester and additives can be relied upon for suggestions for formulations to meet the required lubricants.

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. 

Aircraft Gear lubricating problems

The oils used  to  lubricate  aircraft  turbine  gears  are  almost  without  exception ones  which  conform  to  specifications of military  agencies  of  various nations or  those  issued  by  engine manufacturers. Even though  the oils  have been  approved for use, this  does not necessarily  eliminate  the  chance  for lubricating  problems but  does  reduce the  possibility. If the lubricant is actually at fault, in case of trouble with aircraft gears, the first correction is to use oil from another lot. The oil in question may have oxidized, lost its load carrying ability, or become contaminated. Contamination may arise from unexpected sources. Thus, failure of aircraft engine pinion sets is cited in Lubrication^32 where: “At one engine overhaul shop, engine pinion gear set failure began to occur during green runs”. Finally, the trouble was traced to abrasive material used to clean parts by blasting. Such abrasives were being “built into” the engines at overhaul. Later these abrasives were picked up by the circulating oil on test stands.

The steps by which this problem was solved illustrate the investigation sometimes necessary before the reasons for gear trouble can be pinpointed. To  determine if the  failures were  due  to  overhaul  practice   or  to test stand  operation, pinion  gear  set  which had  operated  satisfactorily  in flight  service for  1,400 hours was  installed in a  freshly overhauled  engine. On the test stand this gear set promptly failed. Abrasive scoring was found on both the gear and the bushings. Therefore, the deposit from the oil screen was examined under a microscope followed by photomicrographs and emission spectrographic analysis. All  of this  pointed  to  alpha aluminum  oxide  as  the  primary  offender, this being  the  material  used to  clean  parts  by  blasting.