Sintered sprocket for silent chain and production method therefor

Abstract

A sintered sprocket for a silent chain is obtained from a material with few addition elements by a simple densifying method. The sintered sprocket is made of an ferrous material having an ovarall composition containing Cu at 1 to 2%, C at 0.5 to 0.8%, Mn as an inevitable impurity at 0.10% or less, and balance of Fe and other inevitable impurities by mass and has a density of 7.1 Mg/m 3 or higher, 65 HRA or higher as a hardness in the gear teeth, and a martensite, sorbite, bainite, or their mixed structure as a cross-sectional microscopic structure in at least the gear teeth and the peripheral area of the gear teeth.

1 . A sintered sprocket for a silent chain, comprising Cu at 1 to 2%, C at 0.5 to 0.8%, Mn as an inevitable impurity at 0.10% or less, and the balance of Fe and other inevitable impurities by mass, having a density of at least 7.1 Mg/m 3 , a surface hardness in gear teeth of 65 HRA or higher, and a structure of a martensite, sorbite, bainite, or their mixed structure as a cross-sectional microscopic structure in at least the gear teeth and the peripheral area of the gear teeth.  
     
     
         2 . The sintered sprocket for a silent chain according to  claim 1 , wherein a density of the gear teeth and the peripheral parts of the gear teeth are 7.1 Mg/m 3  or higher and a density of other parts is lower than that of the gear teeth and the peripheral parts and is 6.6 Mg/m 3  or higher.  
     
     
         3 . A production method for a sintered sprocket for a silent chain, comprising steps of 
 preparing a mixed powder containing a Cu powder at 1 to 2% by mass, a graphite powder at 0.6 to 1.0% by mass, a lubricant powder at 1% or less by mass, and an atomized iron powder as balance, in the entire composition,    compacting the mixed powder to form into a sprocket shape having a density of 7.1 Mg/m 3  or higher at least in a gear teeth and a peripheral parts of the gear teeth, thereby obtaining a green compact,    sintering the green compact in a non-oxidizing gas atmosphere, thereby obtaining a sintered body, and    quenching and tempering at least the gear teeth of the sintered body.    
     
     
         4 . The production method for a sintered sprocket for a silent chain, according to  claim 3 , wherein a green density is 7.05 Mg/m 3  or higher when a zinc stearate powder of 0.75% by mass is mixed with the atomized iron powder, thereby obtaining a mixed powder, and the powder is compacted by a pressure of 490.3 MPa to form the green compact.  
     
     
         5 . The production method for a sintered sprocket for a silent chain, according to  claim 3 , wherein the atomized iron powder contains Mn at 0.10% or less by mass and 0 (oxygen) at 0.10% or less by mass in inevitable impurities.