Coolant-containing hollow poppet valve and process for producing the same

Abstract

This invention provides a coolant-containing hollow poppet valve, which, in use, in consideration of a temperature distribution caused in each pert of the valve, causes a lowering in fatigue strength and creep strength in the valve at its site exposed to high temperatures falling within the tolerante of design standard, and, in consideration of required properties at the other valve sites, holds abrasion resistance and strength, and a process for producing the same. An improvement in heat resistance, abrasion resistance and strength depending upon properties required in each site can be realized by conducting a cold drawing step and an intermediate annealing step to bring the Vickers hardnesses of a cylindrical shaft portion ( 12 ) and a fillet-shaped head portion ( 14 ) open in a flare form to the other end of the shaft portion ( 12 ) to approximately not less than 250 Hv and not more than 350 Hv, and approximately not less than 350 Hv, respectively, and conducting cold pressing to bring the Vickers hardness of a seat portion ( 15 ) in the outer periphery of the opening to not less than 380 Hv.

1 . A hollow poppet valve charged with a coolant and having portions of different hardness formed by steps of:
 cold pressing a material into a cup-shaped object having a thick edge at the open end of said cup-shaped object;   intermediate annealing to soften said cup-shaped object;   cold drawing to form a head portion having a flared opening at said open end of said cup-shaped object, a cylindrical hollow shaft portion integral with said head portion, and   a tapered seat portion around the outer periphery of said thick edge, whereby hardening said head portions to Vickers hardness in the range from about 250 HV to 350 HV inclusive.   
   
   
       2 . The hollow poppet valve charged with a coolant according to  claim 1 , wherein the Vickers hardness of said stem portion is not less than about 350 HV. 
   
   
       3 . The hollow poppet valve charged with a coolant according to  claim 1  or  claim 2 , wherein the Vickers hardness of the surface layer of said tapered seat portion is not less than 380 HV. 
   
   
       4 . A method of manufacturing a hollow poppet valve charged with a coolant, said method comprising steps of:
 cold pressing a material into a cup-shaped object having a thick edge at the open end of said cup-shaped object;   intermediate annealing to soften said cup-shaped object;   cold drawing to form a head portion having an flared opening at said open end of said cup-shaped object, a cylindrical hollow shaft portion integral with said head portion, and   a tapered seat portion around the outer periphery of the edge of said thick open end,   said method including at least one intermediate annealing step prior to said steps of cold drawing and arbitrary times of annealing steps during said cold drawing as needed, whereby said head portion is hardened to Vickers hardness in the range from about 250 to 350 HV inclusive.   
   
   
       5 . The method of manufacturing a hollow poppet valve according to  claim 4 , wherein said shaft portion is hardened to Vickers hardness not less than 350 HV in said steps of cold drawing. 
   
   
       6 . The method of manufacturing a hollow poppet valve according to  claim 4  or  claim 5 , wherein said surface layer of said seat portion is hardened to Vickers hardness not less than about 380 HV in said steps of cold forming.