Feedstock materials for semi-solid forming

Abstract

Disclosed is a method for producing feedstock materials for semi-solid forming comprising reducing the size of raw material, introducing the raw material into an extruder and extruding the raw material to produce feedstock material having a non-dendritic microstructure. Further disclosed is an apparatus for producing feedstock materials for semi-solid forming comprising an extruder, a feeder with means for maintaining raw material under a protective atmosphere, a nozzle on an end of the extruder with means for maintaining an extrudate under a protective atmosphere, temperature control means within the extruder and a pelletizer for pelletizing the extrudate. Additionally disclosed is a system for producing feedstock materials for semi-solid forming comprising a size reduction station, a magnetic screen, an extruder comprising a semi-solid raw material and a pelletizer.

1 . A process for producing feedstock materials for semi-solid forming, comprising: 
 (a) providing solid-state raw material;    (b) reducing a size of said raw material to produce particles of raw material of a size suitable for further processing;    (c) introducing said particles of raw material into an extruder; and    (d) extruding said particles of raw material to form an extrudate feedstock material, wherein the extrudate is in semi-solid state.    
     
     
         2 . A process for producing feedstock materials according to  claim 1 , further comprising removing magnetic contaminants from said particles of raw material.  
     
     
         3 . A process for producing feedstock materials according to  claim 1 , wherein said raw material comprises a magnesium alloy.  
     
     
         4 . A process for producing feedstock materials according to  claim 1 , wherein said raw material includes a sprue, runner, ingot, scrap or a combination thereof.  
     
     
         5 . A process for producing feedstock materials according to  claim 1 , wherein said reducing comprises mechanical reduction of said raw material with a reduction machine.  
     
     
         6 . A process for producing feedstock materials according to  claim 1 , wherein reducing includes reducing said raw material to particles of a first size with a first shearing machine to provide first reduced particles, and reducing the first reduced particles to a second size less than the first size with a second shearing machine.  
     
     
         7 . A process for producing feedstock materials according to  claim 1 , further comprising separating the particles by a physical characteristic.  
     
     
         8 . A process for producing feedstock materials according to  claim 1 , further comprising, during said extruding, adding elemental metal or an alloy to said raw material to affect the metallurgical properties of at least one of said raw material and said extrudate.  
     
     
         9 . A process for producing feedstock materials according to  claim 8 , wherein said metal or alloy includes manganese, zinc, silicon, aluminum, chromium, cobalt, lead, platinum, titanium or a combination thereof.  
     
     
         10 . A process for producing feedstock materials according to  claim 8 , wherein said metal or alloy is added at a temperature greater than ambient temperature but below a liquidus temperature of said raw material.  
     
     
         11 . A process for producing feedstock materials according to  claim 1 , wherein said introducing comprises introducing the particles under an inert atmosphere and tumbling the particles over a distance in the inert atmosphere.  
     
     
         12 . A process for producing feedstock materials according to  claim 1 , wherein said particles are introduced into said extruder under an inert atmosphere at a rate less than a maximum rate possible for said extruder.  
     
     
         13 . A process for producing feedstock materials according to  claim 1 , wherein the raw material is extruded at a rate of movement along a barrel of said extruder that is substantially independent of a shearing rate of said raw material.  
     
     
         14 . A process for producing feedstock materials according to  claim 1 , wherein said extruding includes maintaining a shear rate of said raw material of about 500 to 2000 reciprocal seconds.  
     
     
         15 . A process for producing feedstock materials according to  claim 1 , wherein said extruding comprises extruding at a rate of rotation of about 50 to about 250 rpm with an extruder including two rotatable screws arranged in an intermeshing configuration.  
     
     
         16 . A process for producing feedstock materials according to  claim 1 , wherein said extruding comprises extruding with an extruder comprising a flash zone between a feeding throat and discharge orifice of said extruder.  
     
     
         17 . A process for producing feedstock materials according to  claim 16 , wherein said extruder includes a vacuum to draw off volatiles at said flash zone.  
     
     
         18 . A process for producing feedstock materials according to  claim 1 , further comprises flashing said raw material to remove volatile contaminants.  
     
     
         19 . A process for producing feedstock materials according to  claim 1 , wherein the temperature of the raw materials does not exceed a liquidus temperature during the extruding of the raw materials.  
     
     
         20 . A process for producing feedstock materials according to  claim 1 , further comprising cooling said extrudate under an inert atmosphere.  
     
     
         21 . A process for producing feedstock materials according to  claim 1 , further comprising pelletizing said extrudate.  
     
     
         22 . A process for producing feedstock materials according to  claim 21 , wherein said pelletizing comprises dividing said extrudate with a mechanical cutter.  
     
     
         23 . A process for producing feedstock material according to  claim 21 , wherein said pelletizing comprises dividing said extrudate with a non-mechanical cutter.  
     
     
         24 . A process for producing feedstock material according to  claim 1 , wherein the extruder, excluding a vacuum stage, if present, is generally maintained under an inert atmosphere.  
     
     
         25 . A process for producing feedstock material according to  claim 1 , wherein said extruding further comprises exposing incoming raw material to a series of kneading blocks arranged in a forwarding fashion so as to provide sufficient shear to remove at least a portion of the dendritic structures present in said incoming raw material.  
     
     
         26 . A process for producing feedstock material according to  claim 1 , wherein said extruding further comprises exposing said raw material to polygonal elements or high pitched forwarding elements in a vacuum vented barrel segment in order to remove volatile organic components present with said raw material.  
     
     
         27 . A process for producing feedstock material according to  claim 8 , wherein said extruding, after adding the metal or alloy to the raw materials, further comprises: 
 (i) forwarding said raw material with high pitched forwarding elements;    (ii) compressing said raw material with moderate pitched forwarding elements; and    (iii) compacting said raw material with low pitched forwarding elements to forward said raw material to a discharge orifice to form the extrudate.    
     
     
         28 . An extrudate produced according to the process of  claim 1  having a non-dendritic microstructure.  
     
     
         29 . The extrudate of  claim 28  wherein the extrudate includes a globular microstructure.  
     
     
         30 . The extrudate of  claim 28 , wherein the extrudate includes a crystalline microstructure.  
     
     
         31 . The extrudate of  claim 28 , wherein the extrudate is in pellet form and has an aspect ratio between about 0.5:1 and about 4.0:1.  
     
     
         32 . A process according to  claim 1 , further comprising introducing said feedstock material into an injection molding process.  
     
     
         33 . A method of injection molding using extrudate from the process of  claim 1 .  
     
     
         34 . An apparatus for producing feedstock materials for semi-solid metal forming, comprising: 
 (a) an extruder;    (b) a feeder attached to and in communication with said extruder for introducing raw material into said extruder;    (c) means for maintaining said raw material under an inert atmosphere in said feeder and as said raw material is fed into said extruder;    (d) a discharge orifice affixed to said extruder and through which said raw material exits said extruder as extrudate having a temperature below the liquidus temperature of the raw material and greater than the solidus temperature;    (e) means for controlling a temperature of the raw materials within the extruder and said extrudate at less than liquidus temperature;    (f) means for maintaining said extrudate under an inert atmosphere as said extrudate exits said discharge orifice; and    (g) a pelletizer for dividing extrudate.    
     
     
         35 . An apparatus according to  claim 34 , wherein said extruder comprises a barrel having a plurality of longitudinally spaced heating zones and a flash zone.  
     
     
         36 . An apparatus according to  claim 34 , wherein said extruder comprises at least one heater.  
     
     
         37 . An apparatus according to  claim 36 , wherein said heater includes a ceramic band heater or an induction heater.  
     
     
         38 . An apparatus according to  claim 34 , wherein said extruder comprises a single, stationary screw mounted in said barrel.  
     
     
         39 . An apparatus according to  claim 38 , wherein said extruder further comprises a plunger for forcing raw material through said extruder along said stationary screw.  
     
     
         40 . An apparatus according to  claim 34 , wherein said extruder comprises at least one screw that is capable of rotary movement relative to said barrel and is suitable for moving said raw material along said barrel from in the direction of the feeder to the discharge orifice.  
     
     
         41 . An apparatus according to  claim 34 , wherein the extruder includes a barrel that includes a non-corrosive lining.  
     
     
         42 . An apparatus according to  claim 34 , wherein the extruder includes at least one screw having a hardening material on an outer surface of said screw.  
     
     
         43 . An apparatus according to  claim 34 , further comprising a gear pump fitted to the discharge orifice nozzle of said extruder for aiding in the removal of extrudate from said extruder.  
     
     
         44 . An apparatus according to  claim 34 , further comprising means for carrying extrudate exiting the discharge orifice of said extruder away from said extruder, optionally under an inert atmosphere.  
     
     
         45 . An apparatus according to  claim 34 , further comprising means for maintaining all stages of said extruder, other than a vacuum stage, if present, under an inert gas atmosphere.  
     
     
         46 . An apparatus according to  claim 34 , wherein said pelletizer comprises a mechanical cutter with blades constructed from a compatible alloy.  
     
     
         47 . An apparatus according to  claim 34 , wherein said pelletizer comprises a non-mechanical cutter.  
     
     
         48 . An apparatus according to  claim 34 , wherein said extruder comprises a screw having a modular design such that a plurality of elements may be arranged along a shaft to produce a screw of a predetermined length.  
     
     
         49 . An apparatus according to  claim 48 , wherein said elements comprise at least one of a high pitch forwarding element, a moderate pitch forwarding element, a low pitch forwarding element, a polygonal element, a distributive comber, a kneading block, or a blister ring.  
     
     
         50 . An apparatus according to  claim 34 , further comprising a size reduction apparatus for reducing a size of said raw material.  
     
     
         51 . A system for producing feedstock materials for semi-solid forming, comprising: 
 (a) raw material;    (b) a size reduction station for reducing said raw materials into particles;    (c) a separation apparatus for removing particles by a physical characteristic;    (d) an extruder comprising a screw and containing semi-solid raw material; and    (e) a pelletizer.    
     
     
         52 . A system for producing feedstock materials according to  claim 51 , wherein said separation apparatus includes a means for removing magnetic elements.  
     
     
         53 . An extruder for semi-solid metal extrusion, wherein said extruder converts raw material to a feedstock and comprises a downstream feeder for introducing alloying elements to the raw material after the raw materials have been at least partially processed in the extruder.