Patent Publication Number: US-2009218426-A1

Title: High speed orbiting ball media processors

Description:
BACKGROUND OF THE INVENTION 
     Ball mills are currently used to work generally spherical target particles (e.g., metal particles) into an end product that is generally in the form of a flake (i.e., a particle that has a high diameter-to-thickness aspect ratio). The basic operation of exemplary prior art ball mills is described in U.S. Pat. No. 4,115,107 to Booz. 
     As may be understood from the Booz patent, such prior art ball mills include a cylindrical milling tube, a vibration mechanism for oscillating the tube longitudinally back and forth along the milling tube&#39;s central axis (i.e., the milling tube&#39;s axis of symmetry), and a plurality of milling balls that are used to grind target particles into the desired form. The vibratory motion of the milling tube within these prior art ball mills typically causes the milling balls to move in a generally chaotic manner within the milling tube and/or to move from one end of the milling tube to the other while the ball mill is in operation. Because the milling balls within a typical prior art ball mill tend to move longitudinally along the interior of the ball mill&#39;s milling tube while the ball mill is in operation, there is often a need to constantly re-circulate the milling balls from the trailing end of the milling tube to the leading end of the milling tube in order to assure a proper distribution of milling balls within the milling tube. 
     In addition, prior art ball mills often take a relatively long time (commonly several hours) to transform target particles into flakes. Furthermore, these prior art ball mills are not able to produce flakes with certain desired properties. Accordingly, there is a need for improved ball mills that may, for example, address one or more of the issues stated above. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Various embodiments of the invention will now be described with reference being made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a schematic diagram of a single batch milling machine according to a particular embodiment of the invention. 
         FIG. 2  is a diagram showing the general motion of a milling tube and multiple milling balls according to a particular embodiment of the invention. 
         FIG. 3  is a time lapse photograph showing the motion of seven different milling balls as the milling balls move along orbital paths within a milling tube according to a particular embodiment of the invention. 
         FIGS. 4A-4D  are schematic diagrams showing the progressive movement of a particular milling ball as the milling ball travels about a substantially orbital path within the interior of the milling tube of  FIG. 1 . 
         FIGS. 5A-5D  are schematic diagrams showing the frame-by-frame movements of a milling tube simplified into four basic movements and the resulting movement of the milling ball of  FIG. 1 . 
         FIG. 6  is a schematic diagram of the direction of movement of the milling tube in a downward direction and the resulting location of the milling ball of  FIG. 1 . 
         FIG. 7  is a schematic diagram of a continuous process milling machine according to a particular embodiment of the invention. 
         FIG. 8  is a picture of 300 μm metal target particles before the particles are processed. 
         FIG. 9  is a picture of 300 μm metal particles after the particles have been processed by a milling machine according to a particular embodiment of the invention. 
         FIG. 10  is a picture of polymer target particles before the particles are processed. 
         FIG. 11  is a picture of polymer particles after the particles have been processed by a milling machine according to a particular embodiment of the invention. 
         FIG. 12  is a schematic diagram of the general process by which layered flakes are formed from particles within ball mills according to particular embodiments of the invention. 
         FIG. 13  is a picture of flake-to-flake welding of iron particles that have been processed according to a particular embodiment of the invention. 
         FIG. 14  is a picture of a cross-section of a magnesium particle that has been processed according to a particular embodiment of the invention for one minute. 
         FIG. 15  is a picture of a cross-section of a magnesium particle that has been processed according to a particular embodiment of the invention for two minutes. 
         FIG. 16  is a chart illustrating the particle size distributions of magnesium particles prior to being processed according to one embodiment of the invention. 
         FIG. 17  is a chart illustrating the particle size distributions of magnesium particles after being processed using a 25 mg milling ball according to one embodiment of the invention. 
         FIG. 18  is a chart illustrating the particle size distributions of magnesium particles after being processed using a 35 mg milling ball according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     Single Batch Milling Machine 
       FIG. 1  depicts a single batch milling machine  102  according to a particular embodiment of the invention. As may be understood from this figure, in this embodiment, the milling machine  102  includes a substantially cylindrical milling tube  100  that defines a substantially cylindrical interior portion  103 . The milling tube is dimensioned to house one or more (and preferably a plurality of) milling balls  105 A- 105 C and target particles  110  to be processed by the milling machine  102 . In various embodiments of the invention, the milling tube  100  is configured to be sealed during operation to prevent material from escaping from the milling tube  100  while the milling machine  102  is in use. 
     In various embodiments of the invention, the milling balls  105 A- 105 C are substantially spherical, made of steel, and are between 3/16″ and ⅜″ in diameter. However, other milling balls of different materials and sizes may also be suitable for use within certain embodiments of the invention. 
     In various embodiments, the milling machine  102  further comprises a vibration source  115  that is adapted for vibrating the milling tube  100 . This vibration source  115  is preferably configured to vibrate at a relatively high rate (e.g., greater than about 10,000, 12,000, 14,000 or 15,000 oscillations per minute), but may vibrate at any other suitable rate. One suitable vibration source  115  is the sheet Finish Sander (Model Number FS540K) by Black and Decker. 
       FIG. 2  is a diagram showing the general motion of the milling tube  100  and milling balls  105 A- 105 C shown in  FIG. 1 . As may be understood from  FIGS. 1 and 2 , the vibration source  115  is configured to vibrate the milling tube  100  in a substantially circular pattern so that the central axis  119  of the milling tube  100  travels in a substantially circular path. For example, in one embodiment, the milling tube  100  is configured to rest in a home position when the milling tube  100  is not being vibrated by the vibration source  115 . When the milling tube  100  is in this position, the milling tube&#39;s central axis  119  is in a “central axis home position.” However, in various embodiments, when the ball mill  102  is in use, the vibration source  115  moves the milling tube  100  in a substantially circular pattern so that the central axis  119  of the milling tube  100  travels in a substantially circular path about the home position of the ball milling tube&#39;s central axis. 
     The circular movement of the milling tube  100  is depicted generally by the arrows shown on the left side of  FIG. 2 . As may be understood from this figure, in this embodiment, the vibration source  115  is adapted to produce a vibration within a particular tube vibration plane (here, the XZ plane) and to thereby vibrate the milling tube  100  in a direction that is perpendicular (or substantially perpendicular) to the milling tube&#39;s central axis  119 . 
     As may be understood from  FIG. 2 , as a result of the milling tube&#39;s circular vibration, the various milling balls  105 A- 105 C disposed within the milling tube  100  travel about a substantially circular path along the milling tube&#39;s interior surface. In various embodiments of the invention, at least one (and preferably a plurality or all) of the milling balls  105 A- 105 C travel along a circular path that lies substantially within a plane that is substantially perpendicular to the milling tube&#39;s central axis.  FIG. 3  is a time lapse photograph showing seven milling balls traveling along such a path. In this photograph, each circle shows the path of travel of a particular milling ball. 
     The progressive movement of a particular milling ball  105 A according to certain embodiments of the invention is depicted in  FIGS. 4A-4D . As may be understood from these figures, in various embodiments, the vibration of the milling tube  100  is timed so that, at any particular point in time, the milling tube  100  moves in a direction that is substantially opposite to the ball&#39;s current immediate direction of travel. For example, as shown in  FIG. 4A , when the milling ball  105 A is disposed adjacent the leftmost interior surface of the milling tube  100 : (1) the milling ball  105 A travels in a substantially upward vertical direction; and (2) the milling tube  100  travels in a substantially downward vertical direction. As shown in  FIGS. 4B-4D , this moving relationship between the milling ball  105 A and the milling tube  100  is repeated as the milling ball  105 A travels around the interior surface of the milling tube  100 . 
       FIGS. 5A-5D  further illustrate the progressive movement of the particular milling ball  105 A according to certain embodiments of the invention. In particular,  FIGS. 5A-5D  are simplified illustrations of the basic, cyclical movements of the milling tube  100  taken at four different points during a single oscillation of the milling tube  100 . These figures also show the resulting movement of the milling ball  105 A. 
     It is noted that  FIGS. 5A-5D  show the progressive motion of the milling tube  100  and milling ball  105 A in relation to the fixed X and Z axes shown in these figures. In each of these figures, the general motion of the milling tube  100  is indicated by the smaller, central, gray arrow  150 . For example, in  FIG. 5B , the central gray arrow  150  indicates that the milling tube  100  moves vertically downwardly so that the milling tube&#39;s central axis moves from a first vertical position  151  (shown in gray) to a second vertical position  152  (shown in black) that is vertically below the first vertical position  151 . 
     In each of  FIGS. 5B-5D , the respective intial positions of the milling tube  100  and milling ball  105 A (which are shown in gray) correspond to the respective end positions of the milling tube and milling ball (which are shown in black) shown in the previous drawing. For example, the gray milling tube and milling ball positions shown in  FIG. 5B  correspond to the black milling tube and milling ball positions shown in  FIG. 5A . Similarly, the gray milling tube and milling ball positions shown in  FIG. 5C  correspond to the black milling tube and milling ball positions shown in  FIG. 5B , and the gray milling tube and milling ball positions shown in  FIG. 5D  correspond to the black milling tube and milling ball positions shown in  FIG. 5C . 
     By the same token, because, in various embodiments, the milling tube  100  and milling ball  105 A continuously circulate in sequence through the positions shown in  FIGS. 5A-5D , the gray milling tube  100  and milling ball  105 A positions shown in  FIG. 5A  correspond to the black milling tube and milling ball positions shown in  FIG. 5D . 
     The motion of the milling tube  100  and milling ball  105 A according to the particular embodiment of the invention shown in  FIGS. 5A-5D  will now be discussed in greater detail. As may be understood from  FIG. 5A , in one embodiment, the milling tube  100  first moves from: (1) a first position in which the central axis of the milling tube  100  is in the upper left-hand quadrant of the X-Z axis shown in  FIGS. 5A-5D ; to (2) a second position in which the central axis of the milling tube  100  is in the upper right-hand quadrant of the X-Z axis shown in  FIGS. 5A-5D . This movement causes the milling ball  105 A to roll along the interior of the milling tube  100  from: (1) a first position in which the milling ball  105 A is adjacent the bottom interior portion of the milling tube  100  (e.g., adjacent, and/or on, a portion of the Z axis) to (2) a second position adjacent the left-hand side of the milling tube  100  (e.g., adjacent, and/or on, a portion of the X axis). 
     Next, as shown in  FIG. 5B , the milling tube  100  moves from the second position to a third position in which the central axis of the milling tube  100  is in the lower right-hand quadrant of the X-Z axis shown in  FIGS. 5A-5D . This movement causes the milling ball  105 A to roll along the interior of the milling tube  100  from the second position described above to a third position that is adjacent the top interior portion of the milling tube  100  (e.g., adjacent, and/or on, a portion of the Z axis). 
     Next, as shown in  FIG. 5C , the milling tube  100  moves from the second position to a third position in which the central axis of the milling tube  100  is in the lower left-hand quadrant of the X-Z axis shown in  FIGS. 5A-5D . This movement causes the milling ball  105 A to roll from the third position described above to a fourth position in which the milling ball  105 A is adjacent the right-hand interior portion of the milling tube  100  (e.g., adjacent, and/or on, a portion of the X axis). 
     As shown in  FIG. 5D , the milling tube  100  then moves from the third position described above to a fourth position in which the central axis of the milling tube  100  is in the upper left-hand quadrant of the X-Z axis shown in  FIGS. 5A-5D . This movement causes the milling ball  105 A to roll from the fourth position described above to the first position described above (in which the milling ball  105 A is adjacent the bottom interior portion of the milling tube  100  (e.g., adjacent, and/or on, a portion of the Z axis). The milling tube  100  then preferably repeats the sequential movement shown in  FIGS. 5A-5D  until the desired milling results are reached. 
     In various embodiments of the invention, the central axis of the milling tube  100  follows an essentially square-shaped path as the milling tube  100  moves between the first, second, third and fourth positions discussed above. For example, in various embodiments, as shown in  FIG. 5B , as the milling tube  100  moves from the first to the second position, the milling tube&#39;s central axis moves to the right a first predetermined distance along a substantially horizontal path. Similarly, as shown in  FIG. 5C , as the milling tube  100  moves from the second to the third position, the milling tube&#39;s central axis moves downwardly a second predetermined distance along a substantially vertical path. By the same token, as shown in  FIG. 5D , as the milling tube  100  moves from the third to the fourth position, the milling tube  100  moves to the left a third predetermined distance along a substantially horizontal path. Similarly, as shown in  FIG. 5A , as the milling tube  100  moves from the fourth to the first position, the milling tube  100  moves upwardly a fourth predetermined distance along a substantially vertical path. In a particular embodiment the first, second, third, and fourth predetermined distances referenced above are substantially the same. 
     In various embodiments, the repeated circular oscillations of the milling tube  100  cause an acceleration with a continuously changing direction away from the central axis of the milling tube, which is indicated by a gray arrow  153 . In turn, this acceleration naturally causes the milling ball  105 A to move (and preferably roll) to the opposite-most point from the direction of movement of the milling tube  100 . This opposite-most point is indicated by the black position of the milling ball  105 A. 
     As shown in  FIG. 6 , the milling ball  105 A is aligned with the direction of acceleration such that the tangential line drawn at the ball&#39;s contact with the milling tube  100  is substantially perpendicular to the milling tube&#39;s direction of acceleration. However, to sustain the orbiting motion, it is preferable that this alignment not be disturbed by significant external forces (e.g., external forces outside certain small leniencies). 
     With a continuous change in the direction of the acceleration of the milling tube  100 , the position of the milling ball  105 A likewise changes continuously. Ultimately, this motion causes the milling ball  105 A to roll along (and preferably not slide along) the inside interior surface of the milling tube  100  at substantially the same frequency as the oscillation of the milling tube  100 . 
     In various embodiments of the invention, at least two (and preferably all) of the milling balls  105 A- 105 C orbit along the interior surface of the milling tube  100  at substantially the same rate (as measured, for example, in rotations per minute). In addition, in certain embodiments, the ball mill  102  is configured so that: (1) a first milling ball  105 A follows a first respective, substantially orbital path about the central axis of the milling tube  100 ; and (2) a second milling ball  105 B follows a second respective, substantially orbital path about the central axis of the milling tube  100 ; and (3) as the first milling ball  105 A follows the first orbital path and the second milling ball  105 B follows the second orbital path, the first and second milling balls  105 A,  105 B are maintained in a substantially aligned relationship along a line that is substantially parallel to the central axis of the milling tube  100 . In various embodiments: (1) a third milling ball  105 C follows a third respective, substantially orbital path about the central axis of the milling tube  100 ; and (3) as the first milling ball  105 A follows the first orbital path, the second milling ball  105 B follows the second orbital path, and the third milling ball  105 C follows the third orbital path, the first, second, and third milling balls  105 A,  105 B,  105 C are maintained in a substantially aligned relationship along a line that is substantially parallel to the central axis of the milling tube  100 . 
     To use a milling tube  100  according to this embodiment of the invention, a user first unseals the milling tube  100  and places one or more (and preferably a plurality of) milling balls  105 A- 105 C and target particles  110  to be milled into the milling tube&#39;s interior  103  (see  FIG. 1 ). The user then seals the milling tube  100 . Next, the user activates the vibration source  115 , which causes the milling balls  105 A- 105 C to travel in a substantially circular path along the milling tube&#39;s interior surface as described above, and as shown generally by the dashed arrows in  FIG. 1 . In the meantime, the target particles  110  are forced against the milling tube&#39;s interior surface due to the circular motion of the milling tube  100 . As the milling balls  105 A- 105 C travel along the milling tube&#39;s interior surface, the milling balls  105 A- 105 C forcibly roll over the various target particles. Over time, this serves to work each of the various target particles  110  into the form of a flake. 
     After a pre-determined period of time, the vibration source  115  is stopped, the milling tube  100  is unsealed, and the resulting flake product is removed from the milling tube  100 . 
     Continuous Process Milling Machine 
       FIG. 7  depicts a continuous-process milling machine  202  according a particular embodiment of the invention. In this embodiment, the milling machine  202  includes a milling tube  200  and vibration source  215  that are configured to operate generally in the manner described above in regard to the single-batch milling machine  100  of  FIG. 1 . However, in this embodiment, the milling machine  202  further comprises a target particle loading bed  203  that is in gaseous communication with an inlet portion  207  of the milling tube  200  (e.g., via a target particle inlet tube  236 ). 
     In this embodiment, the milling machine  202  further comprises a virtual particle separator  230  that is in gaseous communication with the milling tube&#39;s outlet portion  209 , the milling machine&#39;s target particle inlet tube  236 , and a flake product storage bin  240 . In various embodiments of the invention, the virtual separator  230  is attached adjacent the milling tube&#39;s outlet  209 , and is adapted to separate finished flake particles from intermediate particles (e.g., based on the aerodynamic characteristics of the particles). The virtual separator  230  is also preferably configured: (1) to route intermediate particles  210 B back to the milling tube&#39;s inlet portion  207  (e.g., via an intermediate particle recycling passage  234 ) for further processing within the milling tube  200 ; and (2) to route finished flake particles  210 C into the flake product storage bin  240  (e.g., via a finished particle outlet  232 ) for later pickup by a user. 
     To use the continuous-process milling machine  202  shown in  FIG. 7 , a user first loads target particles  210 A into the milling machine&#39;s target particle loading bed  203  and then activates the milling machine  202 . Once the milling machine  202  is activated, the vibration source  215  begins to vibrate as described above and a carrier gas begins to flow from a carrier gas inlet  201  and into the target particle loading bed  203 . The carrier gas then carries target particles  210 A from the target particle loading bed  203  through the particle inlet tube  236 , through the milling tube&#39;s inlet  207 , and into the interior portion of the milling tube  200 . 
     Next, the target particles  210 A are forced against the milling tube&#39;s interior surface due to the circular motion of the milling tube  200 . Meanwhile, the milling balls  205 A- 205 C travel along the milling tube&#39;s interior surface and, in the process, forcibly roll over the various target particles  210 A. Over time, this serves to flatten each of the target particles into the form of a flake. 
     As the milling tube  200  continues to rotate, the target particles  210 A move slowly toward the milling tube&#39;s outlet  209 . During this process, the target particles  210 A are flattened further by the various milling balls  205 A- 205 C. 
     After the various target particles  210 A exit the milling tube&#39;s outlet  209 , the target particles  210 A enter the virtual separator  230 , which: (1) routes finished flake particles  210 C into the flake product storage bin  240  (e.g., though the finished particle outlet  232 ); and (2) routes intermediate particles  210 B back to the inlet  207  of the milling tube  200  (e.g., via the particle recycle passage  234 ) for further processing. The process above may continue, for example, until the milling machine  202  produces the desired amount of flake product. 
     Appearance of Particles and Resulting Flakes 
       FIG. 8  is a picture of 300 μm metal particles before the particles are processed.  FIG. 9  is a picture of 300 μm metal particles after the particles have been processed by a milling machine according to a particular embodiment of the invention. 
       FIG. 10  is a picture of polymer particles before the particles are processed.  FIG. 11  is a picture of this same type of polymer particles after the particles have been processed by a milling machine according to a particular embodiment of the invention. 
     Production of Layered Flakes 
       FIG. 12  is a schematic representation showing how milling machines according to various embodiments of the invention may be used to produce layered flakes through the mechanical alloying of a binary alloy mixture. In such embodiments, a mixture of loose target particles  303  is placed into a milling tube  100 ,  200  and processed as described above. During the milling process, the individual target particles  305 ,  307  first undergo plastic deformation and are flattened into flakes  315 ,  317 . The flakes  315 ,  317  are then bound together (e.g., via coalescence or welding effect) into a single flake  325  having alternating layers of material as shown in  FIG. 12 . This technique can be used to produce layered flakes having a variety of different properties. Such flakes may, for example, be useful in hydrogen storage applications, fuel cell electrode production, and in pharmaceutical production (such layered flakes can facilitate the expedited, simultaneous delivery of multiple drugs).  FIG. 13  further illustrates exemplary flake-to-flake welding according to one embodiment of the invention using iron particles. In this embodiment, loose flakes of iron are joined with other loose flakes of iron. However, in an alternative embodiment, layered flakes of different materials can also be made by forming flakes using different starting materials. 
     Exemplary Operation of a Milling Mechanism 
     In an exemplary operation of a milling mechanism according to one embodiment of the invention, the mechanism&#39;s flake producing capability is measured by determining how quickly a spherical target particle can be processed into a flake of a particular thickness. For example, in one embodiment in which the mechanism utilizes milling tube having a diameter of between about 8 mm and about 12 mm, a milling ball having a diameter of between about 4 mm and about 8 mm, a milling radius of between about 1 mm and about 3 mm, and a milling speed of between about 10,000 RPM and 15,000 RPM. In a particular example in which the mechanism utilizes a milling tube having a diameter of about 10 mm, a milling ball having a diameter of about 6 mm, a milling radius of about 1.5 mm, and a milling speed of about 13,000 RPM, an initially spherical Magnesium particle of 300 μm is processed into a 12 μm mean-thickness flake in approximately two minutes. A cross-sectional view of the example Magnesium flake cast in a solid epoxy after approximately one minute of processing is shown in  FIG. 14 , and a cross-sectional view of the example flake after approximately two minutes of processing is shown in  FIG. 15 . 
     In addition, according to one embodiment, the particle morphology, or size, may be controlled in part by processing time and in part by other operating parameters. For example, the particle size distributions of Magnesium are shown before processing in  FIG. 16 , by changing the loading of the milling ball to about 25 mg and processing for approximately two minutes in  FIG. 17 , and by changing the loading of milling ball to about 35 mg and processing for approximately two minutes in  FIG. 18 . When the particle undergoes the process, the thickness reduces while the projected area increases. For example, as shown in  FIGS. 17 and 18 , the equivalent particle size becomes larger as the loading increases. 
     CONCLUSION 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended listing of inventive concepts. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.