Method for forming a groove in a thermoplastic article

Abstract

To make a thin-wall bottom groove in an injection molded plastic article, such as the type of V-shape grooves which define tear-out portions of an article, the space between the groove-defining land of the mold and the opposing part of the mold is changeable. During injection and filling of the mold, the space is large, to enable filling of the mold. As the mold fills, the space is made small, so the desired finished dimension in the part is obtained.

1 . (canceled)  
   
   
       2 . (canceled)  
   
   
       3 . A method of forming a groove in an injection molded article made of a thermoplastic material by means of a land part of the mold which projects into the article defining cavity of the mold, which comprises: 
 providing a mold having 
 a first mold part which comprises said projecting land part;  
 a second mold part opposing and spaced apart from said first mold part;  
 wherein the spacing between the first and second mold parts, in vicinity of said projecting land, is changeable by movement of at least one of said mold parts;  
   injecting hot thermoplastic material into the article defining cavity of the mold while spacing apart the mold parts sufficient to enable thermoplastic to flow by and around said projecting land part;    moving said mold parts closer together, to deform and shape said thermoplastic so the desired dimension article is formed; and,    opening the mold parts and removing the article from the mold.    
   
   
       4 . The method of  claim 3  wherein the first mold part is movable and the second mold part is fixed.  
   
   
       5 . The method of  claim 3 , wherein the spacing between said projecting land part and the opposing second mold part, when the mold parts are moved closer together, is less than about 0.1 inch.  
   
   
       6 . The method of  claim 3  wherein the projecting land part forms a V-shape groove in the article.  
   
   
       7 . The method of  claim 5  wherein the projecting land part forms a V-shape groove in the article.  
   
   
       8 . The method of  claim 1  wherein the thermoplastic material is polypropylene.  
   
   
       9 . The method of  claim 7  wherein the thermoplastic material has a Graves Tear Test value of about 470-500, as determined by ASTM Standard D1004.  
   
   
       10 . The method of  claim 7 , wherein the thermoplastic material is polypropylene.  
   
   
       11 . A method of forming a V-shape groove in an injection molded article made of a thermoplastic polypropylene material by means of a land part of the mold which projects into the article defining cavity of the mold, which comprises: 
 providing a mold having 
 a first mold part which comprises said projecting land part;  
 a second mold part opposing and spaced apart from said first mold part;  
 wherein the spacing between the first and second mold parts, in vicinity of said projection is changeable by movement of at least one of said mold parts;  
   injecting said softened hot thermoplastic material into the article defining cavity of the mold while spacing apart the mold parts sufficient to enable thermoplastic to flow by and around said projecting land part;    moving said mold parts closer together, so the land part is less than about 0.01 inch spaced apart from the opposing mold part, to thereby shape said thermoplastic so the desired dimension article is formed; and,    opening the mold parts and removing the article from the mold.    
   
   
       12 . The method of  claim 11  wherein the first mold part is movable and the second mold part is fixed.