Methods and systems for forming pyrotechnic material extrudates

Abstract

A method for improving the quality of a pyrotechnic material extrudate in accordance with an embodiment of the present technology includes flowing metal powder, fluoropolymer powder, binder, and wax powder in separate respective feed streams toward an extruder. The wax powder includes a wax with a melting point temperature that is greater than the temperature experienced during the extrusion process. During the extrusion process, the wax powder acts as a lubricant to avoid accumulation of the shear forces acting on the mixture as it moves towards and through a die, thereby reducing the velocity gradient across the material passing through the die. The resulting pyrotechnic extrudate is free of internal cracks or other discontinuities.

It is claimed: 
     
         1 . A method for improving the quality of extrudate during a process for making a pyrotechnic material extrudate, the method comprising:
 flowing a metal powder along a first transportation tube extending toward an extruder;   flowing a fluoropolymer powder along a second transportation tube extending toward the extruder;   flowing a binder along a third transportation tube extending toward the extruder;   flowing a wax powder along a fourth transportation tube extending toward the extruder;   forming a uniform powder mixture with the metal powder, fluoropolymer powder, binder, and wax powder in a mixer downstream from the first, second, third, and fourth transportation tubes and upstream from the extruder, wherein the wax powder has a melting temperature; and   passing the uniform powder mixture through an extrusion die of an extruder to form an extrudate, wherein the uniform powder mixture is subjected to pressure and an elevated extrusion temperature, wherein the extrusion temperature is less than the melting temperature of the wax powder, and wherein the extrudate is free of substantive internal discontinuities.   
     
     
         2 . The method of  claim 1  wherein flowing the wax powder comprises metering the wax powder so the wax powder constitutes approximately 0.8-1.5% by weight of the uniform powder mixture. 
     
     
         3 . The method of  claim 2  wherein the wax powder constitutes approximately 1.0% by weight of the uniform powder mixture. 
     
     
         4 . The method of  claim 1  wherein passing the uniform powder mixture through an extrusion die of an extruder, further comprising forming with the material of the wax powder a lubricious layer along a surface of the extrusion die to reduce sticking of the uniform powder mixture to the surface and to reduce a velocity gradient within the extrudate exiting the die. 
     
     
         5 . The method of  claim 1  wherein the wax powder in the uniform powder mixture does not melt during extrusion of the extrudate. 
     
     
         6 . The method of  claim 1  wherein the extrudate is free of substantive internal cracks spaced apart from an external surface of the extrudate. 
     
     
         7 . The method of  claim 1  wherein the metal powder is magnesium, the fluoropolymer powder is a polytetrafluoroethylene powder, the binder is a copolymer including vinylidene fluoride and hexafluoropropylene monomers, and the wax powder is an amide wax powder. 
     
     
         8 . The method of  claim 1  wherein the wax powder is:
 a carnauba wax, 
 a paraffin wax, or 
 an amide wax. 
 
     
     
         9 . The method of  claim 1  wherein the wax powder acts as a lubricant to avoid accumulation of at least shear forces in the powder mixture passing through an extrusion die of an extruder during formation of the extrudate. 
     
     
         10 . The method of  claim 1 , further comprising shearing the binder to increase contact between an adhesive material in the binder and the metal powder. 
     
     
         11 . A system for improving the quality of extrudate during a process for making a pyrotechnic material extrudate, the system comprises:
 an extruder;   a metal powder;   a first transportation tube configured to flow the metal powder toward the extruder;   a fluoropolymer powder;   a second transportation tube configured to flow the fluoropolymer powder toward the extruder;   a binder;   a third transportation tube configured to flow the binder toward the extruder;   a wax powder having a melting temperature;   a fourth transportation tube configured to flow the wax powder toward the extruder;   a mixer downstream from the first, second, third, and fourth transportation tubes and upstream from the extruder, to form an extrudable powder mixture, wherein the mixer is coupled to an inlet of the extruder and configured to deliver the extrudable powder mixture to the extruder through the inlet;   wherein the extruder has an extrusion die, and the extruder is configured to advance and force the extrudable powder mixture through an extrusion die to form an extrudate, wherein during formation of the extrudate, the extrudable powder mixture is subjected to pressure and elevated extrusion temperature, wherein the elevated extrusion temperature is less than the melting temperature of the wax powder so the wax powder does not melt during extrusion, and wherein the extrudate is free of internal discontinuities caused by extrusion through the die.   
     
     
         11 . The system of claim  11  wherein the wax powder constitutes approximate 0.8-1.5% by weight of the extrudable powder mixture. 
     
     
         13 . The system of  claim 11  wherein the wax powder constitutes approximately 1.0% by weight of the extrudable powder mixture. 
     
     
         14 . The system of  claim 13  wherein the wax powder is configured to form a lubricious layer along a surface of the extrusion die without melting to reduce sticking of the extrudable powder mixture to the surface and to reduce a velocity gradient within the extrudate exiting the die. 
     
     
         15 . The system of  claim 11  wherein the extrudable powder mixture is configured so the extrudate is free of substantive internal cracks spaced apart from an external surface of the extrudate. 
     
     
         16 . The system of  claim 11  wherein the metal powder is magnesium, the fluoropolymer powder is a polytetrafluoroethylene powder, the binder is a copolymer including vinylidene fluoride and hexafluoropropylene monomers, and the wax powder is an amide wax powder. 
     
     
         17 . The system of  claim 11  wherein the wax powder added to the powder mixture is:
 a carnauba wax, 
 a paraffin wax, 
 an amide wax, or 
 any other high-temperature melting point wax. 
 
     
     
         18 . A pyrotechnic extrudate formed by an extrusion of a powder mixture comprising a metal material, a fluoropolymer material, a binder material, and an unmelted wax material, wherein the unmelted wax material constitutes approximately 1% by weight of the powder mixture, wherein the extrudate is free of internal cracks within the extrudate. 
     
     
         19 . The pyrotechnic extrudate of  claim 18 , wherein the metal material is magnesium, the fluoropolymer material is a polytetrafluoroethylene powder, the binder material is a copolymer including vinylidene fluoride and hexafluoropropylene monomers, and the wax material is an amide wax powder having a melting temperature greater than the extrusion temperature to which the extrudate is exposed during extrusion through a die.