Abstract:
A stirred ball mill assembly includes multiple vessels each having a body supporting sets of magnets rotatable with respect to the body. Each vessel defines an enclosed milling chamber, and has a stirring arm assembly extending in the respective enclosed milling chamber and connected for rotation with the respective sets of magnets. The sets of magnets and the stirring arm assembly are completely enclosed within the respective vessel. The vessels are configured to be stacked with one another so that adjacent ones of the sets of magnets are magnetically coupled with one another. A drive motor assembly has another set of magnets magnetically coupled with one of the sets of magnets of the stacked vessels. The drive motor can rotate the stirring arm assemblies within the milling chambers of the milling chambers of the stacked vessels via magnetic coupling of the magnets.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a stirred ball mill assembly having multiple vessels that are stirred in parallel via a magnetic drive system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Stirred ball mills (also known as attritors) are commonly used for material processing. They are very flexible machines that can perform mechanical alloying, grinding, particle size control and mixing. They can be configured vertically or horizontally to optimize a particular process. A stirred ball mill works by loading grinding media, which can be spherical, cylindrical, etc., into a vessel along with the material to be processed. This load is then stirred to the appropriate speeds by spinning arms driven by an externally-mounted motor. A typical stirred ball mill is limited to one reaction at a time. This means performing process optimization or running different materials has to be done sequentially, taking a great deal of time. 
         [0003]    If the process needs to be carried out under a controlled atmosphere (e.g., with inert or a specific gas to assist the reaction or process), a seal must be made around the shaft from the driving motor to the stirring arms. If this rotating seal fails, the reaction is ruined. Also, for a small reaction, the vessel is loaded in a glove box, and if the seal is not perfect, it will leak before the user can load the cup on the stirred ball mill and connect an external gas source. Often this is prevented by placing the entire stirred ball mill in a controlled atmosphere, an expensive and cumbersome solution. 
       SUMMARY OF THE INVENTION 
       [0004]    A stirred ball mill assembly is provided that includes multiple vessels each having a body supporting sets of magnets rotatable with respect to the body. Each vessel defines an enclosed milling chamber, and has a stirring arm assembly extending in the respective enclosed milling chamber and operatively connected for rotation with the respective sets of magnets. The sets of magnets and the stirring arm assembly are completely enclosed within the respective vessel. The vessels are configured to be stacked with one another so that adjacent ones of the sets of magnets are magnetically coupled with one another. The stirred ball mill assembly includes a drive motor assembly that has another set of magnets magnetically coupled with one of the sets of magnets of the stacked vessels. The drive motor can rotate the stirring arm assemblies within the milling chambers of the stacked vessels via magnetic coupling of the magnets. Because the stirring arm assemblies are completely enclosed within the separate vessels, multiple different reactions can be carried out in the different stacked vessels, and no leak paths are created that would reduce yield of the reactions. Because the stirring arm assembly does not extend outside of the vessel, there is no rotating seal past which the material can escape from the chambers. 
         [0005]    The stirred ball mill assembly may include a base assembly configured to support the stacked vessels and the motor assembly. In at least one embodiment, the motor assembly may be slidably mounted on shafts of the base assembly, and has locating features that engage with interlocking features of the stacked vessels. This allows a single motor to stir all of the multiple vessels through magnetic coupling of the motor and the stacked vessels. 
         [0006]    Most existing devices used for ball milling do not implement the ability to process multiple samples in parallel, instead processing material in only one milling vessel per motor. One known stirred ball mill that runs multiple vessels using only one motor uses a drivetrain (chains and sprockets, belts and pulleys, gears, etc.) to spin multiple arm shafts off of one motor. However, that design has a large space requirement as the vessels do not stack and thus require a large area to contain the device. Also, because each vessel has its own arm shaft that extends out of the vessel to the pulley, a rotating seal is necessary for each vessel. This creates multiple potential leak points between the seal and the arm shaft and increases the chance of contaminating the material. 
         [0007]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic cross-sectional illustration of a milling vessel for use in a parallel stirred ball mill assembly of  FIGS. 5 ,  7  and  8 ; taken at arrows  1 - 1  in  FIG. 7 ; 
           [0009]      FIG. 2  is a schematic perspective view of a top assembly of the milling vessel of  FIG. 1  with a cover removed; 
           [0010]      FIG. 3  is a schematic perspective illustration of the milling vessel of  FIG. 1  with the top assembly removed; 
           [0011]      FIG. 4  is a schematic perspective illustration of a stirring arm assembly of the milling vessel of  FIG. 1 ; 
           [0012]      FIG. 5  is a schematic perspective view of an unloaded parallel stirred ball mill assembly in a load/unload position, including a motor assembly; 
           [0013]      FIG. 6  is a schematic perspective view of the motor assembly of  FIG. 5 ; 
           [0014]      FIG. 7  is a schematic perspective view of the parallel stirred ball mill assembly of  FIG. 5  fully-loaded with vessels like that of  FIG. 1 , and in an engaged (nm) position; 
           [0015]      FIG. 8  is a schematic cross-sectional view of the fully-loaded parallel stirred ball mill assembly of  FIG. 7  taken at lines  8 - 8  of  FIG. 7 ; and 
           [0016]      FIG. 9  is a schematic cross-sectional fragmentary view of a portion of the fully-loaded parallel stirred ball mill assembly of  FIG. 8 , showing the motor assembly magnetically coupled with one of the milling vessels for rotating the stirring arm assembly. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  shows a cross-sectional view of milling vessel  10  for use in a parallel stirred ball mill  180  shown in  FIG. 5  (also referred to as a parallel attritor). As described herein, multiple vessels  10  stack for use in the parallel stirred ball mill  180  to establish a parallel stirred ball mill assembly  205 , as shown in  FIG. 7 . Stirring of material in the vessels  10  is via a magnetic drive system, as described below. 
         [0018]    The milling vessel  10  of  FIG. 1  has a body  15  that includes two end plates: a bottom plate  20  and a top plate  30 , as well as a cylindrical portion, milling cylinder  120 . Bearings  40  are assembled into the plates  20 ,  30 . The bearings  40  may be sealed ball bearings. The top plate  30  and bottom plate  20  can be made out of any material that is compatible with the synthesis to be performed (e.g., hardened tool steel, stainless steel, plastic, and ceramic). The bearings  40  are press fit into the bottom plate  20  and the top plate  30 , and allow rotation of magnet carrier members  70  relative to the plates  20 ,  30 . In alternate embodiments, the bearings  40  can be replaced with bushings made out of brass, plastic, etc. There are two carrier members  70  per vessel  10 , and these are also referred to as rotatable members. 
         [0019]    The top plate  30  is part of a top plate assembly  50  that includes the bearings  40  and carrier member  70  covered by cover  60 , as well as magnets  80  and seal members discussed below.  FIG. 2  shows the top plate assembly  50  without the cover  60 . The magnet carrier members  70  are pressed into the internal diameter of the bearings  40 . The magnet carrier members  70  can now spin relative to the bottom plate  20  or top plate  30 . First and second sets of magnets  80  are inserted into bores  85  (i.e., spaced openings) cut or otherwise formed into the respective magnet carrier members  70  of the top plate  30  and the bottom plate  20 , respectively, in a circular pattern. In other embodiments, the magnets  80  may be in an alternative pattern. The magnets  80  can be held in place by adhesive, set screws, or any other method of mechanical attachment. In the embodiment shown, the magnets  80  are all installed in the same direction. That is, all are installed with their poles oriented the same way. Alternatively, the magnets  80  can be installed in an alternating manner: north, south, north, south, etc. Since the magnets  80  are fixed in magnet carrier member  70 , they spin with it. The rotating magnet carrier members  70  with magnets  80  along with a drive motor assembly  210  discussed below establish a magnetic drive system that is the driving force for ball milling in the vessel  10 . 
         [0020]    Referring again to  FIG. 1 , the top plate assembly  50  and the equivalent bottom plate assembly  55  also each contain a sealing member, referred to herein as a secondary sealing ring  90 , that is pressed or otherwise attached into a groove in magnet carrier member  70 . The secondary sealing rings  90  are pressed between magnet carrier members  70  and the bottom plate  20  and top plate  30 , respectively, to provide backup contaminant protection for the bearings  40 . The sealing rings  90  could alternatively be lip seals. After all of the subcomponents are assembled into the top plate assembly  50  or the equivalent bottom plate assembly  55 , another sealing member, o-ring  100 , is placed in o-ring grooves  110  of the top plate assembly  50  and bottom plate assembly  55 . Covers  60  are then attached to bottom plate  20  and top plate  30 . The covers  60  can be attached using bolts or clamps, etc. Covers  60  squeeze o-rings  100  and prevent air leakage when the vessel  10  is in use. 
         [0021]      FIG. 3  shows the milling vessel  10  without the top plate assembly  50 . The milling cylinder  120  is attached to the bottom plate assembly  55  through the use of fasteners or clamps (or any other means of mechanical assembly) so that there is a rigid connection. The milling cylinder  120  can be made out of any material that is compatible with the material to be processed, such as hardened tool steel, stainless steel, plastic or ceramic. A sealing member, such as an o-ring  125  (shown in  FIG. 1 ) is located in o-ring groove  128 . A similar o-ring  125  is located in o-ring groove  128  of cylinder  120  adjacent the bottom plate assembly  55 , as shown in  FIG. 1 . When the milling cylinder  120  is fixed to the top and bottom plate assemblies  50  and  55 , the o-rings  125  are compressed and provide a seal between the mating components (milling cylinder  120  and bottom plate assembly  20  or top plate assembly  30 , respectively). 
         [0022]    A stirring arm assembly  130 , as shown in  FIG. 4 , is made up of a drive shaft  140  and multiple milling arms  150 . The arm assembly  130  can be made out of any material that is compatible with the material to be processed, such as hardened tool steel, stainless steel, plastic or ceramic. The arm assembly  130  has the first or primary sealing rings  155  pressed onto each end. Alternatively, the lip seals could be located in the top plate  30  and bottom plate  20  and configured to seal against the rotating drive shaft  140  of the arm assembly  130 . The arm assembly  130  is assembled into the magnet carrier members  70  of  FIG. 1  by splines  160  on the ends of the drive shaft  140 , as shown in  FIG. 1 , to prevent rotation of the arm assembly  130  relative to the magnet carrier members  70 . Thus, the arm assembly  130  rotates with the magnet carrier members  70 . 
         [0023]    Once the bottom plate assembly  55 , the milling cylinder  120  and the arm assembly  130  are assembled together, a bowl-like enclosed milling chamber  170  is formed where milling balls and raw materials can be loaded. The raw materials are generally in powder form, but could be pellets or granular. If the materials to be milled are air sensitive, the powders can be loaded with the vessel  10  in an inert atmosphere, such as in a glove box. After the milling balls and raw materials are loaded, o-ring  125  is located in o-ring groove  128  and the top plate assembly  50  is then attached by fasteners, clamps or other method of mechanical attachment. Once the entire milling vessel  10  is together (as shown in  FIG. 1 ) it is completely sealed from the environment by the robust static o-ring seals  100  and  125 . If the vessel  10  was put together in a controlled atmosphere, that atmosphere will remained sealed inside the chamber  170 . Once loaded and sealed, the milling vessel  10  is ready for milling. In an alternate embodiment, a valve is included to enable the atmosphere within the chamber  170  to be changed. For example, the valve could be mounted in the top plate  30 . The milling chamber  170  could then be evacuated and filled with a milling gas at higher than atmospheric pressures or left under vacuum. 
         [0024]      FIG. 5  shows the parallel stirred ball mill  180  without any milling vessels  10  loaded onto the mill  180 . The parallel stirred ball mill  180  includes a base assembly  185  that has a holder  190  for the milling vessels  10 . In this embodiment, the holder  190  holds three milling vessels  10 , as shown in  FIG. 7 , but can easily be scaled to hold a much larger number of vessels  10 . If necessary for the processing conditions, coolant can be run through the holder  190  to keep the milling vessels  10  at an optimum temperature. The base assembly  185  also has a base plate  200  to which the holder  190  is mounted. The base plate  200  provides a base for the mill  180  as well as location control for all the components of the mill assembly  205 . 
         [0025]    The mill  180  also includes a motor assembly  210 . The motor assembly  210  is shown in more detail in  FIG. 6 , and includes a motor  220 , a locating plate assembly  230  and various features to interface with the milling vessels  10 . The motor  220  is shown only schematically, but may be an electric motor with a stator and rotor, as is known. The motor assembly  210  is located on two guide shafts  240  of the base assembly  185  (see  FIG. 5 ) through linear bearings  250  mounted in the locating plate assembly  230 . This arrangement allows the motor assembly  210  to freely slide up and down the shafts  240  while remaining centered above the holder  190 . The motor assembly  210  moves from a load/unload position (shown in  FIG. 5 ) to the engaged (or run) position as shown in  FIG. 7 . In this embodiment the motor assembly  210  is moved from position to position by hand and locked in place by a screw or clamp. In other embodiments the motor assembly  210  may be driven by a motor/lead screw to automatically set its position. 
         [0026]    When the parallel stirred ball mill  180  is in the load/unload position, milling vessels  10  can be loaded into holder  190 . Holder  190  has locating features  260  cut into its bottom that mate with interlocking features, also referred to as locating fingers  270  (see  FIG. 1 ), on the bottom plate  20  of the milling vessel  10 . Top plate  30  of the milling vessel  10  also has locating interlocking features, also referred to as locating features  280 , that mate with the locating fingers  270  of an adjacent bottom plate  20  when vessels  10  are stacked. As the milling vessels  10  are stacked in the holder  190  the mating locating features  280  and the locating fingers  270  interlock to prevent the stack from rotating and lock it in place. Once the milling vessels  10  are assembled into the holder  190 , the motor assembly  210  is moved into the engaged (or run) position, as shown in  FIG. 7 . Referring to  FIG. 6 , the motor  220  has a motor adapter  290  rigidly attached to its front face  300 . The motor adapter  290  has locating features  310  similar to locating fingers  270 . Locating features  310  engage in the locating features  280  of the top plates  30  of the milling vessels  10 . The locating features  310  will engage with the top plate  30  of the milling vessel  10  that is on the top of the stack in the holder  190 . Once the motor assembly  210  is locked in the run position, the motor adapter  290 , holder  190 , and the stack of milling vessels  10  are all locked together and cannot move.  FIG. 8  shows a cross sectional view of this state. 
         [0027]      FIG. 9  shows a cross-sectional view of a portion of the motor assembly  210  engaged with the top milling vessel  10  of the stack. The motor  220  has a drive shaft  315  with a motor magnet carrier member  320  rigidly attached to the drive shaft  315 . The motor magnet carrier member  320  has the same circular pattern of magnet bores  330  as does magnet carrier member  70 . Magnets  340  are assembled into the magnet bores  330 . The magnets  340  can be held in place by adhesive, set screws, or any other method of mechanical attachment. Since the magnets  340  are fixed in magnet carrier member  320 , they spin with it. As can be seen in  FIG. 9 , the magnets  340  in the motor assembly  210  and the magnets  80  in the top plate assembly  50  are directly aligned over the respective magnet on the opposite part. If the magnets  80  are all installed in the magnet carrier members  70  with their poles oriented in the same direction, then all of the magnets in the motor assembly magnet carrier member  320  will also be oriented in the same direction. Magnets in the magnet carrier member  320  and the vessels  10  will be oriented so that opposite poles will face each other. For example, all the magnets  340  in the motor assembly  210  may have their north poles facing out and all the magnets  80  in the milling vessels may have their south poles facing out. Alternatively, the magnets  340  can be installed in an alternating manner: north, south, north, south, etc. if the magnets  80  of the milling vessels  10  are also oriented in this manner. Because of this alignment, the magnets  80  and magnets  340  will be attracted to each other, causing the magnet carrier members  70  and the magnet carrier member  320  to rotate together as if they were attached. To maximize the attraction, only covers  60  separate the sets of magnets  80  and  340 , and the adjacent sets of magnets  80  of the top plate assembly  50  and the bottom plate assembly  55  of adjacent vessels  10 . The covers  60  are optimized to be very thin, and are made out of a non-magnetic material. 
         [0028]    When the shaft  315  of the motor  220  spins, the magnet carrier member  320  and the magnets  340  spin with it. Because of the magnetic attraction, magnet carrier members  70  also spin, which spins the arm assemblies  130  through the splines  160 . The spinning of the arm assemblies  130  causes milling balls and raw materials in the milling chambers  170  to be knocked into motion by the arms  150 . These impacts will then cause mechanical alloying, grinding or mixing depending on the processing conditions. Because of the magnetic drive system, there are no rotating seals that could become contaminated by powders and create a leak path out of the vessels  10 . This makes the stirred ball mill assembly  205  very robust. The only rotating seals are primary sealing rings  155  and secondary sealing rings  90 . Because the arm assemblies do not extend outside of the vessels, the sealing rings  90 ,  155  can be entirely enclosed within the vessels  10  to ensure that the material that is being processed stays in the milling chamber  170 . This prevents any material from getting out of the chamber  170 , which would reduce the yield of the reaction. Thus, all of the rotating seals (i.e., sealing rings  90 ,  155 ) are completely enclosed within the milling vessels  10 , and the vessels  10  are sealed by robust static seals (i.e., o-ring seals  100 ,  125 ), unlike traditional attritors that are dependent upon less robust rotating seals to seal the milling vessel. 
         [0029]    When multiple milling vessel assemblies are stacked as in  FIG. 8 , it can be seen that the magnets  80  in the bottom plate assembly  55  of one milling vessel  10  will be attracted to the magnets  80  in the top plate assembly  50  of the milling vessel  10  below it. In this manner, one motor  220  can drive a large stack of milling vessels  10 . The magnets  80  and  340  would be selected with an appropriate strength to handle the torque of driving multiple arm assemblies  130  through all of the milling balls and raw materials. Because each milling vessel  10  is completely sealed and separate from the others, many different reactions can be run in parallel, providing a high-throughput method of mechanical synthesis. Even higher throughput can be achieved by stacking multiple milling vessels  10  and driving multiple stacks off one motor (with belts/pulleys, gears, chains/sprockets, etc.). 
         [0030]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.