Deposit Forming Tendencies of Aircraft Turbine Lubricants

This test method describes  a procedure for  determining the  deposit  and  sludge  forming  tendencies  of  aircraft gas  turbine  lubricants when  a sample  of the  oil is circulated  under  controlled conditions for a  prescribed  period of time  through an  aerated test  chamber  containing  an  aluminum  tube  held at a constant  temperature.

The coking tube is held at 590 degree F while oil  heated  to  300 degree F  is circulated by  a pump  from  the  chamber through  a  cooler and a line  filter and  back  into  the chamber. The oil flow is regulated to 300 ml per minute while air flow is the same amount.

At  the  end  of the test, the  weight of solid  decomposition  products  on  the  heated tube  and  in the  line after  are  determined. Also,  changes  in the  viscosity and  neutralization  number  of the oil can be  determined  if  desired.

Color stabilizers for gear and transmission lubricants

While there is little likelihood of the necessity for the use of color stabilizers in gear transmission lubricants, information should be available if desired. In a sense, oxidation inhibitors are color stabilizers for lubricating oils because oxidized oils often  turn  dark  or black. However, what  is in mind  here  are  compounds  which may  stop or  change  chemical   reactions which  tend  to  form color  bodies.

For  the  purpose , Bart Maas^7  recommend  the  addition of 0.0001 to 0.01 per cent of an oil soluble  sodium hydrocarbyl  phenate to  lubricating oils. Kalil^47 lists as color stabilizers: Certain  hydroquinones, dithiocarbamates, aliphatic amines and dicyclohexylamines.

Introduction

Almost  all  modern  machinery  makes  some  use  of  gears  as  a  medium  for  transmitting  power. Such use  may  be  for  the  purpose  of  either  changing  the  speed  of  a  driven  member  or  changing  the  direction  of  movement. In  either  case  the  gears  act as a lever  so  that , in  most  cases, the  force  transmitted  is  multiplied  and  in  so  doing  speed  will  be  reduced. When  variations  in  the  torque  or  speed  transmitted  are  desired, a  series  of  gear  ratios  can  be  provided  in  the  same  mechanism.

Most  gear  sets  are  lubricated  with  fluid  products  or  gear  oils, and  consequently, such  compounds  will  receive  major  consideration . Since  plastic  or  semi-fluid  products, such  as  lubricating  greases, as  well  as  solids  are  sometimes  used  as  gear  lubricants, they  will  also  receive  mention.

It  is  also  the  purpose  to  describe  fluids  employed  in  certain  fluid  drives, particularly  automatic  transmissions  in  automotive  vehicles. Here  the  oils  in  question  serve  a  number  of  functions, and  it  is  necessary  that  a  single  fluid  satisfy  not  only  lubrication  of  different  mechanisms, but  also  act  as  a  torque  converter  and  hydraulic  agent.

This  is  simply  an  extension  of  the  functions  which  gear  oils  fill  in  many  case. Thus, gear lubricants   also take care of bearing lubrication in many   applications. It will  be  presumed  that  most  readers  are familiar  with  the  mechanisms  to  be  lubricated, such  as  automatic  transmissions, hypoid  gears, worm  gears, etc. Therefore, little description of mechanical details will be attempted.

The  primary  interest  will  be  in  lubricants  for  metal  gears, although  mention  will  be  made  of  the  requirements  for  gears  made  from  other  materials. An  attempt  will  be  made  to  thoroughly   explain  how  lubricants  for  gears  function, what  they  contain, how  they   are  compounded, and  the  limitations  of  their  use. In  all  of  this  it  should  be  kept   in  mind  that  to  be  most  effective   any  lubricant  should  be  applied  in  the  right  amount  at  the  right  place  and  the  right  time.

Fundamentally  the   types   of  motion  in  operating  gear  sets  are  those  occurring  in  other  machine  elements , namely, rolling  and  sliding  motion. The two types of movement   may occur simultaneously as in meshing   hypoid gears. This  is  pointed  out  so  that  it  will  be  realized  that, even  though  the  configuration  of  gears  differ   from  bearings, the  lubricating  problems  are similar  for  both  mechanisms. Another  point  to  keep  in  mind  is  that  while  the  title  of  the  mentions  both  gear  and  transmission  lubrication, the latter  mechanism  is  most  often  one  or   more  gear  sets  serving  a specific  purpose. Therefore, except  in  the  case  of  fluid  drives, the  problem  is  one  of  gear  lubrication. Finally , some of  the  possibilities  of  future  trends  and  developments  in  gear  lubricants  and  torque  fluids  will  be  mentioned.