Low friction gear sets for fluid pressure devices

摘要

Device comprises: internally toothed gear comprising compacted powdered ferrous metal ring with inner peripheral wall and equally circumferentially spaced recess in ring and opening to peripheral wall; and externally toothed gear located within ring and arranged to mesh with internally toothed gear. At least one of meshing surfaces has a thin coating of electroless nickel on it, giving a low friction, longer wear life surface. Preferably, coating has Rockwell C hardness 45-50, thickness 0.0005-0.002 inch, is Ni containing 5-10% P, and is on ring having hardness 85 Rockwell B and tensile strength 50000 p.s.i. Strength of ring-coating bond is 30000-60000 p.s.i. Advantages: for motor-pump hydraulic devices, makes it possible to use non-heat treated sintered powdered metal compacts in the stator assembly. Coating characteristics provide the gear set with improvements in wear life and low friction operating characteristics, without requiring heat-treatment or expensive machining.