Patent Publication Number: US-9834326-B2

Title: Method for elimination of powder segregation during can filling

Description:
BACKGROUND 
     This invention relates generally to the field of manufacturing. In particular, the present invention relates to the preparation of metallic alloy powder used to create either hot isostatically pressed or extruded metallic alloy logs that are subsequently converted through additional thermomechanical processing and machining into aerospace products, but this invention is also applicable to any product that employ powder constituents as raw material anywhere during its manufacturing process (for example pharmaceuticals, pigment, electronics, catalysts, and others). 
     In preparation for manufacturing, a powder, composed of the particles of a given and rather broad distribution, is introduced through an opening at the top of a can. It falls through an atmosphere in the can, and as it free falls it creates a pyramid shaped cone at the bottom of the can. During the free-fall the powder particles segregate due to the size differentiation (as defined by kinetics-of-flow). The segregation further progresses during the formation of the cone, the coarse particles may be free-flowing while the finer particles can be cohesive with a tendency to accumulate in the center of the cone. In addition, very fine particles are suspended in the can atmosphere and due to the electrostatic attraction to the can walls will with time adhere to the can walls. However, the very fine particles may detach from the walls and fall to the bottom of the can in clumps to further segregate the powder in the cone. 
     This segregation leads to non-homogeneity in a final manufacturing product due to the variability in microstructure and properties of the powder. This non-homogeneity may ultimately result in a final manufacturing product not matching the desired specification. Non-homogeneity of final product is typically undesirable in the final product of metallic alloy powders. 
     SUMMARY 
     A powder filling method includes introducing a tube into a can so that the lower end of the tube is near the bottom of the can. The powder in the can is introduced through the tube. The proximity of the lower end of the tube to the powder is controlled by retracting the tube as the powder fills the can. 
     A powder filling method includes introducing a tube into a can. The powder is supplied through the tube to fill the can. The tube is retracted as the powder fills the can to maintain a consistent distance between the lower end of the tube and the powder. The powder in the can is agitated through rotary agitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a prior art can for preparing powder for a next production step. 
         FIG. 2A  is a schematic view of a can for preparing powder for a next production step according to a first embodiment of the present invention. 
         FIG. 2B  is a schematic view of a can for preparing powder for a next production step according to a first embodiment of the present invention. 
         FIG. 3A  is a schematic view of a can for preparing powder for a next production step according to a second embodiment of the present invention. 
         FIG. 3B  is a schematic view of a can for preparing powder for a next production step according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic view of a prior art can  10  for preparing powder for a next production step. Powder  12  is introduced through the top of can  10  and falls to the bottom of can  10 . Powder  12  may include any material, such as powdered metals such as aluminum or super-alloys, and/or powdered polymers. Can  10  may be filled with inert gas  13  to create a controlled atmosphere within can  10 . An example of inert gas  13  used during the can filling process may include one of nitrogen or argon. As powder  12  falls through can  10 , powder  12  forms cone  14  at the bottom of can  10 . During free-fall the particles of powder  12  segregate due to the size differentiation (as defined by kinetics-of-flow). The segregation further progresses during the formation of cone  14 , the coarse particles of powder  12  may be free-flowing while the finer particles of powder  12  can be cohesive with a tendency to accumulate in the center of cone  14 . As powder  12  falls through can  10 , fine powder particles  16  are suspended in gas  13  and due to the electrostatic attraction to the walls of can  10  will with time adhere to the walls of can  10 . As the filling of can  10  continues, can  10  is periodically vibrated in attempt to homogenize cone  14  and increase tap density. However, fine powder particles  16  may detach from the walls of can  10  and fall in clumps to further segregate the particles of powder  12  in cone  14 . 
       FIG. 2A  is a schematic view of can  10  for preparing powder for a next production step according to a first embodiment of the present invention. Can  10  may be filled with inert gas  13  to create a controlled atmosphere within can  10 . A low pressure vacuum may also be present in can  10 . Free-falling powder  20  is introduced into can  10  through tube  18 . Tube  18  is located in can  10  such that the bottom end of tube  18  extends towards the bottom of can  10 . The proximity of tube  18  to powder  12  at the bottom of can  10  during the filling of can  10  is controlled in such a way as to minimize the formation of cone  14 . The gap between the bottom of tube  18  and powder  12  is kept consistent during the filling of can  10  by retracting tube  18  from can  10 . The retraction of tube  18  is designated by arrow  15  in  FIG. 2A . Tube  18  is retracted from can  10  through mechanical, pneumatic, or hydraulic means. 
     As the level of powder  12  rises, tube  18  is retracted from can  10  to maintain common distance  19  between tube  18  and powder  12 . Tube  18  will minimize the accumulation of fine powder particles  16  at the walls of can  10 . Introduction of powder  20  into can  10  through tube  18  in close proximity to bottom of can  10  minimizes interparticle motion, eliminates cone formation of powder  20 , and eliminates the suspension and plating of fine powder particles  16  on the interior surfaces of can  10 . Eliminating the formation of cone  14  and the plating of fine powder particles  16  on the interior surfaces of can  10  minimizes segregation of powder  12 . The decrease in segregation of powder  12  results in an increased homogeneity of powder  12  used in a process. The homogeneity of powder  12  ultimately provides a more uniform grain growth and provides more consistent mechanical properties of end product. 
       FIG. 2B  is a schematic view of can  10  for preparing powder for a next production step according to a first embodiment of the present invention. Can  10  may be filled with inert gas  13  to create a controlled atmosphere within can  10 . A low pressure vacuum may also be present in can  10 .  FIG. 2B  shows a retracted position of tube  18 . Tube  18  has been retracted as the level of powder  12  continues to rise during the can filling process. Tube  18  retracts during the can filling process so as to maintain common distance  19  between tube  18  and powder  12 . 
     Additionally, during the filling process of can  10 , can  10  is periodically vibrated in order to increase the tap density of powder  12 . Tap density of powder  12  includes a volume specific weight powder  12  has after it has been settled or packed. Increased tap density of powder  12  helps to provide more consistent mechanical properties of the end product by reducing the flow inconsistencies of powder  12  with a lower tap density. 
       FIG. 3A  is a schematic view of can  10  for preparing powder for a next production step according to a second embodiment of the present invention. Can  10  is filled with inert gas  13  to create a controlled atmosphere within can  10 . A low pressure vacuum may also be present in can  10 . Tube  18  includes fan  22 . Fan  22  includes fan shaft  24  and small fan blades  26 . Fan shaft  24  extends down through tube  18  and attaches to small fan blades  26 . Small fan blades  26  are attached to fan shaft  24  such that small fan blades  26  are positioned below the bottom of tube  18 . Small fan blades  26  continuously rotate about fan shaft  24  during the can filling process. As free-falling powder  20  exits tube  18 , small fan blades  26  strike free-falling powder  20  to mechanically agitate free-falling powder  20 . Operation of fan  22  disturbs the free-fall kinetics of free-falling powder  20  through mechanical agitation, creating powder dispersion  28 . The mechanical agitation of free-falling powder  20  creates powder dispersion  28  and minimizes cone formation and segregation of powder  12  in can  10 . The material used to form fan  22  is the same composition as powder  12 , which will prevent contamination of powder  12 . 
     Small fan blades  26  provide a mechanical agitation of free-falling powder  20  to create powder dispersion  28 . Small fan blades  26  are sized so that the outer diameter of small fan blades  26  is less than the inner diameter of tube  18 . Small fan blades  26  are sized smaller than the inner diameter of tube  18  so that fan  22  can be retracted through tube  18  and out of can  10 . Retraction of fan  22  out of can  10  facilitates preparation for the next step in a process once the can filling process of can  10  is complete. During the filling of can  10 , tube  18  is retracted from can  10  to maintain common distance  19  between tube  18  and powder  12 . The retraction of tube  18  and fan  22  is designated by arrow  15  in  FIG. 3A . Additionally, can  10  is periodically vibrated in order to increase the tap density of powder  12 . 
       FIG. 3B  is a schematic view of can  10  for preparing powder for a next production step according to a third embodiment of the present invention. Can  10  is filled with inert gas  13  to create a controlled atmosphere within can  10 . A low pressure vacuum may also be present in can  10 . Fan  22  includes fan shaft  24  and large fan blades  30 . Free-flowing powder  20  is introduced into can  10  through tube  18 . Large fan blades  30  provide a mechanical agitation of free-falling powder  20  to create powder dispersion  28 . Large fan blades  30  are sized so that the outer diameter of large fan blades  30  is greater than the outer diameter of tube  18 . Fan  22  with large fan blades  30  is retracted through tube  18  and out of can  10  by folding large fan blades  30  with a motion similar to that of an umbrella. Once large fan blades  30  are folded, the outer diameter of large fan blades  30  becomes smaller than the inner diameter of tube  18 , thus allowing fan  22  to be retracted through tube  18  and out of can  10 . Retraction of fan  22  out of can  10  facilitates preparation for the next step in a process once the can filling process of can  10  is complete. During the filling of can  10 , tube  18  is retracted from can  10  to maintain common distance  19  between tube  18  and powder  12 . The retraction of tube  18  and fan  22  is designated by arrow  15  in  FIG. 3B . Additionally, can  10  is periodically vibrated in order to increase the tap density of powder  12 . 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 
     DISCUSSION OF POSSIBLE EMBODIMENTS 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A powder filling method includes a tube is introduced into a can so that the lower end of the tube is near the bottom of the can. A powder is introduced into the can through the tube. The proximity of the lower end of the tube to the powder in the can is controlled by retracting the tube as powder fills the can. 
     The powder filling method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components: 
     the powder filling method further includes agitating the powder in the can by rotary agitation; 
     the rotary agitation is performed by a fan located near the lower end of the tube; 
     the fan comprises a same composition as the powder; 
     the fan is driven by a fan shaft that extends through the tube; 
     the tube is retracted at a rate that maintains a consistent distance between a lower end of the tube and the powder; 
     the tube is retracted either mechanically, pneumatically, or hydraulically; 
     the fan is retracted at a rate equal to the tube; 
     the powder filling method further includes a vacuum present in the can; 
     the powder filling method further includes an inert atmosphere present in the can; 
     the can is periodically vibrated during the powder filling of the can; and 
     the powder comprises a metallic powder. 
     A powder filling method includes a tube introduced into a can. A powder is supplied through the tube to fill the can. The tube is retracted as the powder fills the can to maintain a consistent distance between a lower end of the tube and the powder. The powder is agitated in the can by rotary agitation. 
     The powder filling method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components: 
     the powder filling method further includes the rotary agitation performed by a fan; 
     the fan comprises a same composition as the powder; 
     the powder is agitated as it exits the tube; 
     the fan is driven by a shaft that extends through the tube; 
     the fan is retracted at a rate equal to the tube; 
     the tube is retracted either mechanically, pneumatically, or hydraulically; 
     the powder filling method further includes a vacuum present in the can; 
     the powder filling method further includes an inert atmosphere present in the can; and 
     the can is periodically vibrated during the powder filling of the can.