Process for manufacturing toothed sprockets for rewinding devices of safety belts

Abstract

A process for manufacturing toothed sprockets, comprising the steps of pressure die-casting a molten metal alloy into a runner ( 7 ) communicating with a molding cavity ( 6 ) so as to define at least one toothed sprocket ( 1 ) associated with a respective die-casting sprue; the die-casting sprue is cut off leaving a residual sprue portion ( 8 ) projecting from the sprocket ( 1 ). Subsequently the toothed sprocket ( 1 ) is turned for removing the residual sprue portion ( 8 ) projecting from the sprocket ( 1 ) itself.

1 . A process for manufacturing toothed sprockets for rewinding devices of safety belts, comprising the steps of:
 pressure die-casting a molten metal alloy in a communication runner opening into a molding cavity, so as to define a toothed sprocket associated with a respective die-casting sprue;   removing the die-casting sprue from the toothed sprocket;   lathe-shaping or turning the toothed sprocket so as to remove a residual sprue portion projecting from the sprocket itself.   
   
   
       2 . The process as claimed in  claim 1 , wherein said sprocket has a substantially cylindrical conformation of circular cross-section, extending around a respective longitudinal axis, and defining a circumferential toothing coaxial with said longitudinal axis. 
   
   
       3 . The process as claimed in  claim 1 , wherein in the die-casting step said metal alloy flows into the molding cavity close to the circumferential toothing of the sprocket. 
   
   
       4 . The process as claimed in  claim 3 , wherein in the die-casting step said metal alloy flows into the molding cavity externally of the axial dimensions of said circumferential toothing. 
   
   
       5 . The process as claimed in  claim 3 , wherein in the die-casting step said metal alloy flows into a portion of the molding cavity extending in a continuous circular sector. 
   
   
       6 . The process as claimed in  claim 3 , wherein in the die-casting step said metal alloy flows into the molding cavity at a circular portion coaxial with said toothing and axially offset relative to the same. 
   
   
       7 . The process as claimed in  claim 2 , wherein the residual sprue portion radially projects from a circular portion of the sprocket that is axially offset relative to the toothing. 
   
   
       8 . The process as claimed in  claim 1 , wherein the residual sprue portion radially projects in the form of a continuous arc of a circle from a circular portion of the sprocket. 
   
   
       9 . The process as claimed in  claim 2 , wherein following the turning step, a shoulder axially spaced apart from the toothing is defined. 
   
   
       10 . The process as claimed in  claim 1 , wherein said die-casting step is carried out in a plurality of runners associated with each other and each of which is in communication with a respective molding cavity. 
   
   
       11 . The process as claimed in  claim 2 , wherein removal of the sprue is carried out through cutting out of the diametrical dimension of the circumferential toothing.