Missile and Space Vehicles Gear Mechanisms and their Lubrication

While details of space vehicles are not publicized, it can be expected that gears may enter, even if only for small instruments. These will no doubt be of a nature which will not require fluid lubrication. However, Hartman^24 mentions that there may be a gear drive between the turbine and the shaft on certain liquid rocket engines. Where kerosene is the fuel used, this also provides lubrication for the gears. However, kerosene alone allowed scoring of gears and consequently additives were included. Use of 2 per cent by volume of zinc dialkyldithiophosphate  in the fuel, decreased gear wear. This combination also improved the rust resistance of gears. Such a kerosene additive mixture is suggested as a break in lubricant no matter what type of lubricant may be used in service. In this connection, an article by Watson^51 entitled “Materials and Ratings for Dry Running Gears” should be of interest. After  experimenting  with  various  materials for  gears, it  was  found  that  under  light  loads, spur  gears, made of case  hardened  En  steel, Phosphate  prior  to  coating  the  flanks with  molybdenum  disulfide, would run  continuously  in a dry state  without measurable wear.

Wear Prevention Agents

A number of investigators have distinguished between wear prevention and EP agents in lubricants. The  former are  effective  by  a  chemical  polishing action, which  takes  place  at a  lower  temperature  than  does  the  formation of antiweld  films by EP agents. A very  extensive  investigation  of  wear  prevention  agents,  which are  effective  in  lubricants for  two  steel  surfaces was  reported by  Beeck, et  al^9. Calhoun and  Murphy^18, who  reported  on both  anti wear  and EP  additives  for  lubricants found that it  was  possible to  blend  two  or  more  types  of  additives  and  attain both  properties in  the same  composition.

Typical  of  anti wear  additives  are  tricresyl  phosphate  and  Zinc  dialkyl  dithiophosphate.  Such  agents  are  seldom  used  in  industrial  gear  oils  but  are  valuable  in  lubricants  such  as  those  for  jet  turbines  where  the  oil  serves  several  mechanisms  including  gearing.