The Navy Gear Wear Tester

The Navy Gear Wear Tester is described in Federal Methods 791, Methods 335. The  equipment  makes  use  of  small  brass and  steel  gears,  but  Ninos  has  also  used  mating  gears  of other metals, such  as  brass on  stainless  steel, Phosphor  Bronze, and  ST Aluminum   on  SAE     4130 steel  and  SAE B-1112  steel  against  stainless  steel.

In  the  test  two  helical  gears  of  dissimilar  metals, each  approximately  one half inch  in  diameter are  rotated  together  as the  driving  motor  delivers a simple  harmonic motion     of 4.0  inches  amplitude  and  40 cycles per minute, through a  crack  to  the  upper  brass gear. This gear  oscillates  approximately  one  revolution while  a torque load of about  three  and  one  half inch pounds  is applied to  the  test  gears by  means  of a seven  pound  weight. The  gears  are  oscillated  for the  desired  number  of  cycles, or until gear  tooth  failure  due  to  excessive  wear  occurs. At the completion of the test, the gears are removed from the fixture, cleaned as before, and reweighed to    determine weight loss. The wear rate in mg for 10,000 cycles is then calculated permitting a comparison of different lubricants. New  test  gears  are  used  for  each  run even  though  there  is  virtually  no wear  of the  steel  gear  as  compared  to the  brass  gear.

Both fluid products and lubricating greases can be tested as gear lubricants on this apparatus. Indications  are  that  with  increase  in viscosity  of  gear  oils  the  gear wear   decreases. No  speculations are  given  as to how  much  of    the  wear  might  be  due  to abrasion which  is due  to particles  from  the gears.

Types of gears to be lubricated

Where   gears  are  on  parallel  axes, either  spur  or  helical  gears  are  generally  employed. Either type can be used as external or internal drives.   The  herringbone  gear  is  similar  to  two  helical   gears  having  reversed   directions   of   spiral, placed  side  by   side  so  that  the  teeth  come  together   to  form  a  chevron   pattern. The rack and pinion, used to convert rotary motion to reciprocating, generally   uses a spur gear.

For   intersecting   axes either straight   bevel    or   spiral   bevel   gears   are used   as a  rule. The   latter type may be used   on angle   drives where   the   shafts    do not    intersect at full   90 degrees. The contact   of the   teeth in such gears gives   a rolling motion. With  non intersecting  and   nonparallel  axes  the  types   of   gears  used  are  crossed   helical, single  enveloping  worm, double  enveloping    worm, or  hypoid. Here the  contact  of  the  teeth  gives  a  sliding  as  well  as  a  rolling   motion. In  most  cases  a  gear  set  will  be  used  to  change  speed, and  in  such  cases  the  smaller   gear  is  designated  as  the pinion. Both  the  number   of  teeth  on a  pinion  and  the  ratio    of  the  teeth  on  the  driving   and  driven   member   may  vary ,   but  with  bevel  gears  there  is  seldom  less  than  12 teeth  to  a  pinion.

While   some  spur  and  straight  bevel  gears  are  still   made  of  cast  iron, the  tendency  in  all   types   of  gearing  is  for  the  use of  steel. Exceptions   will  be found  to  such  practice, for  example,  in the   use  of  bronze  for   one  member   of  worm   gears. Some small gears and even   larger pinions are   made   of plastics, such as ‘Delrin,’’ ‘Nylon.’’ ‘Teflon,’’ etc. Pinions  have been and   may still be  made  of  rawhide, pressed  paper,  etc, but  our  concern  is  primarily   with   lubrication  of  metal  gears.