Extrusion die

Abstract

An extrusion die ( 10 ) includes a die body ( 30 ) having an upstream face ( 32 ) and a downstream face ( 34 ) with an extrusion profile ( 22 ) passing through the body ( 30 ) from the upstream face ( 32 ) to the downstream face ( 34 ). The walls of the extrusion profile ( 22 ) being the bearing ( 46 ) of the die ( 10 ). A pocket ( 40 ) having tapered sidewalls ( 70 ) is formed in the upstream face ( 32 ) of the die ( 10 ) and surrounds the extrusion profile ( 22 ). The configuration of the pocket ( 40 ) improves the material flow through the die ( 10 ). The configuration of the pocket ( 40 ) depends on the configuration of the extrusion profile ( 22 ). The width of the pocket ( 40 ) is small at the fast areas of the extrusion profile ( 22 ) while being large at the slow areas of the extrusion profile ( 22 ). The pocket ( 40 ) alters the entry angle of material as it enters the die ( 10 ) thus reducing friction in the die ( 10 ) and allowing increased extrusion speeds. In conjunction with the pocket ( 40 ), the die ( 10 ) has a continuous bearing ( 46 ) having the length depending on the configuration of the extrusion profile ( 22 ).

We claim:  
     
       1. An extrusion die, comprising: a body having an upstream face and a downstream face; a pocket formed in said upstream face; an extrusion profile in said body extending from said pocket to said downstream face, the depth of said profile defining a bearing having a length; said pocket being of a predetermined configuration dependent on the configuration of said profile so that the flow of material through the die is improved; said extrusion profile having slow fast areas defined by areas of greatest bearing length and fast slow areas defined by areas of least bearing length; said pocket having a width; said width of said pocket being smallest at the fastest area of the extrusion profile and said width of said pocket being largest at the slowest area of said extrusion profile. 
     
     
       2. An extrusion die according to  claim 1 , wherein said body has a tapered undercut cavity in said downstream face, said extrusion profile passing through said body from said pocket to said undercut cavity; said bearing extending directly to said undercut cavity. 
     
     
       3. An extrusion die according to  claim 2 , further comprising and undercut, said undercut extending between said bearing and said undercut cavity. 
     
     
       4. An extrusion die according to  claim 1 , wherein said length of said bearing is dependent on the configuration of said extrusion profile at any given location along the extrusion profile. 
     
     
       5. An extrusion die according to  claim 4 , wherein said extrusion profile has a wall thickness any given point along said extrusion profile; said length of said bearing at said fastest area of said extrusion profile is in the approximate range of 1.4 to 2.0 times the length of the bearing at said slowest area of said extrusion profile when said wall thickness of said extrusion profile at said fastest area is approximately equal to said wall thickness of said extrusion profile at said slowest area. 
     
     
       6. An extrusion die according to  claim 5 , wherein said approximate range of 1.4 to 2.0 is increased by a first factor when said wall thickness of said extrusion profile at said fastest area is larger than said wall thickness of said extrusion profile at said slowest area. 
     
     
       7. An extrusion die according to  claim 5 , wherein said approximate range of 1.4 to 2.0 is decreased by a second factor when said wall thickness of said extrusion profile at said fastest area is smaller than said wall thickness of said extrusion profile at said slowest area. 
     
     
       8. An extrusion die according to  claim 1 , wherein said pocket has tapered sidewalls. 
     
     
       9. An extrusion die according to  claim 1 , wherein said pocket has a depth equal to said width of said pocket at said fastest area multiplied by a number in the approximate range of 1.2 to 2.0. 
     
     
       10. An extrusion die according to  claim 9 , wherein said pocket has a pocket angle at any given point along said extrusion profile; said width of said pocket at said fastest area creating a pocket angle in the approximate range of 25 degrees to 45 degrees. 
     
     
       11. An extrusion die according to  claim 9 , wherein said pocket has a pocket angle at any given point along said extrusion profile; said width of said pocket at said slowest area creating a pocket angle in the approximate range of 45 degrees to 70 degrees. 
     
     
       12. An extrusion die, comprising: 
       a body having an upstream face and a downstream face and a pocket formed in said upstream face;  
       said body also having an extrusion profile formed in said body extending from said pocket to said downstream face, the depth of said profile defining a bearing having a length;  
       said extrusion profile having slower faster areas defined by areas of greater bearing length and faster slower areas defined by areas of lesser bearing length; said pocket having a width; and  
       said width of said pocket being smaller at said faster areas of said extrusion profile than said width of said pocket at said slower areas of said extrusion profile.  
     
     
       13. The extrusion die of  claim 12 , wherein said pocket has tapered sidewalls. 
     
     
       14. The extrusion die of  claim 12 , wherein said extrusion profile has at least one slowest fastest area defined by the areas of greatest bearing length and at least one fastest slowest area defined by the areas of least bearing length; said pocket having a width; said width of said pocket being smallest at the fastest areas of the extrusion profile and said width of said pocket being largest at the slowest areas of said extrusion profile. 
     
     
       15. The extrusion die of  claim 14 , wherein said pocket has a depth equal to said width of said pocket at said fastest areas multiplied by a number in the approximate range of 1.2 to 2.0. 
     
     
       16. The extrusion die of  claim 12 , wherein said pocket has a pocket angle at any given point along said extrusion profile; said width of said pocket at said faster areas creating a pocket angle in the approximate range of 25 degrees to 45 degrees. 
     
     
       17. The extrusion of  claim 12 , wherein said pocket has a pocket angle at any given point along said extrusion profile; said width of said pocket at said slower areas creating a pocket angle in the approximate range of 45 degrees to 70 degrees.