Patent Publication Number: US-2016235110-A1

Title: Method and apparatus for controlling the flow of product over a product attrition bed

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to the use of augers for controlling the flow of a product over a product attrition device, for example, the flow of potatoes over a potato peeler. 
     2. Background 
     Food attrition devices typically comprise an open chamber where product freely tumbles from entrance to exit making contact with various forms of abrasive to remove the product&#39;s skin. Contact time, movement of product, and bed height are critical in the process. Examples of food attrition devices and various components thereof are illustrated and described in U.S. Pat. No. 4,519,305, U.S. Pat. No. 5,858,429, U.S. Pat. No. 7,197,978, and U.S. Pub. No. 2006/0005715, which are hereby incorporated by reference as illustrative examples. 
     Because the product can tumble freely in the product attrition device after exiting the auger or before entering the auger, the residence time of any individual unit of product can vary greatly from an average residence time for the product in the food attrition device. As a result, the amount of skin removed from each unit of product can vary, which can be undesirable in terms of reduced efficiency, reduced product capacity, and variable product quality. 
     Compounding this problem is the fact that existing product attrition devices supply product to a product attrition apparatus at a variable feed rate. For example, even if an existing product attrition device were to use an auger, the feed rate to the auger is variable, which results in fluctuations in volume of product per auger flight. 
     Previous devices have claimed to use augers to control only a feed rate of product at an entrance of a food attrition device (e.g., U.S. Pub. No. 2006/0005715) or only a discharge rate of a product from the food attrition device (e.g., U.S. Pat. No. 4,519,305). Other devices (e.g., U.S. Pat. No. 5,858,429 and U.S. Pat. No. 7,197,978) have claimed to use an auger to control a feed rate to the food attrition device, but have not provided an auger extending substantially an entire length of a product attrition bed and have not provided a desirable degree of control over the residence time of the product. Nor do these devices provide for feeding a specific volume of product to each pitch length of an auger positioned over a product attrition bed. 
     For these and other reasons, the utilization of augers as currently practiced in the industry can be improved upon. Accordingly, it would be desirable if a product attrition apparatus provided a controlled residence time without substantially inhibiting product tumbling and could maintain a desired bed height from entrance to exit of the product attrition device with a high degree of predictability and repeatability (e.g., low standard deviation in residence time and/or bed height for each pitch length of an auger). 
     For example, it would be desirable if an auger extended the entire length of an abrasive so it could control residence time of particles over the abrasive. 
     It would be desirable if a first auger section had a larger pitch to avoid inhibiting product motion, but a second auger section comprised a flow restriction device to maintain a higher bed height of the product along a greater length of the auger, and thereby maintain a higher bed height along a greater length of an abrasive for removing skin from a product. 
     For example, it would be desirable if the auger comprised a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with a smaller pitch for maintaining the bed height of the product over the abrasive. 
     It would also be desirable if the auger comprised a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with multiple auger flights for maintaining the bed height of the product over the abrasive. 
     As another example, it would be desirable if the auger comprised a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with a rotary gate to maintain the bed height of the product over the abrasive. 
     Furthermore, it would be desirable if a product attrition apparatus were provided with a controlled volumetric feed rate. For example, it would be desirable to limit variations in the volumetric feed rate to the auger and thereby limit fluctuations in volume of product per auger flight. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention provides a product attrition apparatus with improved flow control for a product comprising a plurality of product units. The product attrition apparatus comprises a product attrition bed and an auger positioned above the product attrition bed. The product attrition bed abrades the product while the auger conveys the product in a flow direction. The auger comprises a rotational axis of the auger oriented parallel to the flow direction, an auger flight coiled around the rotational axis, a first auger section, and a second auger section downstream of the first auger section. The auger is configured in relation to the product attrition bed to form a charge space for substantially confining a product charge of the product. As the auger rotates on the rotational axis, the charge space moves in the flow direction, thereby moving the product charge in the flow direction. Additionally, the first auger section comprises a minimum pitch of about 4 times an average equivalent spherical diameter of the product, and the second auger section comprises a flow restriction mechanism to restrict a discharge flow of the product from the auger. 
     In a second aspect, the present invention provides a method for using an auger to control a flow of a product over a product attrition bed. The product comprises a plurality of product units, and the auger conveys the product above the product attrition bed in a flow direction while the product attrition bed abrades the product. The method comprises the steps: feeding the product to the auger to provide a product charge; substantially confining the product charge in a charge space; rotating the auger to move the charge space, and thereby the product charge, in the flow direction; and discharging the product charge from the auger through a flow restriction mechanism to provide a discharge flow of the product. Furthermore, a first end of the charge space and a second end of the charge space are bounded by the auger; a bottom of the charge space is bounded by the product attrition bed; the first auger section of the auger is upstream of a second auger section of the auger; and the second auger section comprises the flow restriction mechanism to restrict the discharge flow of the product. 
     In a third aspect, the present invention provides an apparatus for providing one control volume of a product to an auger per revolution of the auger. The auger extends the length of a product attrition bed for abrading the product as it is conveyed by the auger in a charge space. The charge space is bounded by the auger and the product attrition bed. 
     In a fourth aspect, the present invention provides a method for controlling a volumetric feed rate of product to an auger positioned over a product attrition bed, said method comprising the steps: feeding one control volume of product to an auger per revolution of the auger; rotating the auger to convey the product in a charge space bounded by the auger and the product attrition bed; abrading the product by contact with the product attrition bed; and discharging the control volume from the auger. The auger extends the length of a product attrition bed. 
     The invention described herein provides for several advantages in its various embodiments. In one aspect, the invention provides a controlled residence time without substantially inhibiting product tumbling and maintains a desired bed height from entrance to exit of the product attrition device with a high degree of predictability and repeatability (e.g., low standard deviation in residence time and/or bed height for each pitch length of an auger). 
     In another aspect, the invention provides for an auger that extends the entire length of an abrasive to the control residence time of particles over the abrasive. 
     Additionally, the invention provides for a first auger section comprising a larger pitch to avoid inhibiting product motion, and a second auger section comprising a flow restriction device to maintain a higher bed height of the product along a greater length of the auger. Accordingly, the invention provides for maintaining a higher bed height along a greater length of an abrasive for removing skin from the product. 
     For example, the invention provides for an auger comprising a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with a smaller pitch for maintaining the bed height of the product over the abrasive. 
     As another example, the invention provides for an auger comprising a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with multiple auger flights for maintaining the bed height of the product over the abrasive. 
     Additionally, the invention provides for an auger comprising a first auger section with a larger pitch to avoid restricting product tumbling and a second auger section with a rotary gate to maintain the bed height of the product over the abrasive. 
     In another aspect, the invention provides a product attrition apparatus with a controlled volumetric feed rate. For example, in one aspect, the invention limits variations in the volumetric feed rate to the auger and thereby limits fluctuations in volume of product per auger flight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of one embodiment of a product attrition apparatus with a modified feed chute for controlling the volumetric feed rate of product. 
         FIG. 2  is schematic view of one embodiment of an auger with a second auger section comprising a plurality of auger flights. 
         FIG. 3  is a schematic view of one embodiment of an auger with a second auger section comprising a reduced pitch relative to a first auger section. 
         FIG. 4  is a schematic view of one embodiment of an auger with a second auger section comprising a rotary gate. 
         FIG. 5A  is a plot showing an example of how the total number of product units in a product attrition bed varies with time when the product is conveyed with a single flight, single pitch auger. 
         FIG. 5  is a schematic view illustrating one embodiment of a product attrition apparatus comprising a single flight, single pitch auger and illustrating how the average residence time of product units in a product charge varies along the length of the auger. 
         FIG. 6A  is a plot showing an example of how the total number of product units in a product attrition bed varies with time when the product is conveyed with an auger comprising a second auger section with a double flight. 
         FIG. 6  is a schematic view illustrating one embodiment of a product attrition apparatus with an auger comprising a double flight and illustrating how the average residence time of product units in a product charge varies along the length of the auger. 
         FIG. 7  is a schematic view illustrating one embodiment of a control volume of product. 
         FIG. 8  is a schematic view illustrating one embodiment of an auger with a truncated drive shaft. 
         FIG. 9  is a schematic view illustrating a coordinate system superimposed over one embodiment of a product attrition apparatus and illustrating how two auger flights can be out of phase. 
         FIG. 10A  is a flow chart illustrating steps for one embodiment of a method for controlling the flow of product in a product attrition bed. 
         FIG. 10B  is a flow chart illustrating steps for one embodiment of a method for controlling the feed of product to an auger. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In developing the invention disclosed herein, the inventors realized that it is useful to design an auger  104  based on the size of product  502  conveyed. For example, using an auger  104  with a smaller pitch  302  (e.g., less than about 4 times the average equivalent spherical diameter  514 ) advantageously produces a lower standard deviation in residence time relative to a larger pitch  202  (e.g., greater than about 4 times the average equivalent spherical diameter  514 ). However, a smaller pitch  302  can be problematic because it restricts product movement due to contact with the auger surface which can prevent exposure of all product surfaces to an abrasive  154 . 
     Accordingly, the inventors worked to develop an auger  104  with a single larger pitch size (e.g., 750 mm pitch) to provide substantially free product mixing and tumbling. The auger  104  was used in a product attrition apparatus with a stationary S shaped exit gate and was positioned about ¼ inch above an abrasive  154 . The auger  104  did not extend the full length of an abrasive  154 ; however, the auger stretched over a substantial portion of the abrasive to help prevent back-mixing, control the residence time of the product over the abrasive, and provide a more uniform degree of product attrition (e.g., peeling). The first end  208  of the auger was a distance (e.g. about a foot) from an entrance to the product attrition bed  102 . Likewise, the second end  210  of the auger was a distance from the exit of the product attrition bed. 
     Using a larger pitch auger helped address the problem of restricted product movement because the larger pitch resulted in less restricted motion. However, because the auger  104  had a single larger pitch, when the last auger pitch opened to discharge product, the bed height  516   b  dropped over a relatively larger distance from the exit of the auger (e.g., the distance across a terminal portion  536  of the auger). 
     This can be undesirable because the loss in bed height reduces the normal force between the product and the abrasive  154 . The reduction in normal force, in turn, results in a loss of potential peeling capacity for a length of the abrasive  154  (e.g., the length under the lower bed height  516   b ). 
     The inventors also realized other problems. For example, since the auger flight  106  did not extend the entire length of the abrasive  154 , free mixing (e.g., loss of control over residence time for product) occurred over the abrasive  154  before the first end  402  of the auger flight  106  and after the second end  404  of the auger flight. 
     In order to address the problem of free mixing, the inventors designed (e.g., using a computer and a discrete elements method to model the product flow) a larger pitch auger  104  with an auger flight  106  that extended the full length of a product attrition bed  102 . For example, the auger flight  106  extended an entire length of an abrasive  154  on the surface of product attrition bed. This advantageously provided plug flow of the product  502  within a flight  106  of the auger  104 . For example, the product  502  formed a plurality of product charges  512  and each product charge was substantially confined in a charge space  510  formed between two portions of the auger  104  and the abrasive  154 . As a result, the auger  104  reduced back-mixing of product from a downstream portion of the product attrition bed  102  to an upstream portion of the product attrition bed. The auger  104  also provided a more controlled residence time of each unit  502  of product in a product charge  512 , and a more uniform attrition (e.g., peeling) of product within each product charge. The auger  104  also enabled operators to decrease residence time, or increase the speed at which product  502  travels across the product attrition bed  102 . 
     Nonetheless, the larger pitch, full-length auger still presented several potential problems. For example, stagnation resulted at a pinch point between the second end  404  of the auger flight  106  and the stationary exit gate of the product attrition bed  102 . Additionally, some back-mixing occurred at the exit gate of the product attrition bed. 
     The inventors addressed these issues by removing the stationary exit gate from the product attrition bed  102  (e.g., using the computer model). This removed the pinch point between the stationary exit gate and the auger  104 . Removing the stationary exit gate also reduced back-mixing. 
     However, the inventors realized that removing the gate without providing the auger  104  with a flow restriction mechanism would result in a loss of bed height  516  within the final pitch length before the exit end of the auger. As a result, the peeling capacity of the abrasive  154  would be reduced along the final pitch length of the auger. 
     In order to mitigate the pinch point problem associated with the stationary gate, while still maintaining bed height at the end of the auger, the inventors decided to add a flow restriction mechanism to the second end  210  of the auger itself (e.g., using the computer model). 
     One example of a flow restriction mechanism is a rotary gate  406  fixed to the second end  404  of a larger pitch, full length auger flight  106 . In one embodiment, the rotary gate  406  is fixed to the second end  404  of the auger flight and located in a plane that is perpendicular to the rotational axis  506  of the auger  104 . The rotary gate  406  extends in the same direction as the auger flight  106 , and the gate has substantially the same radius  138  as the auger flight. 
     The rotary gate  406  blocks the discharge flow  155  of product from a blocked area at the exit of the auger. The blocked area is defined by the sweep of the radius of the rotary gate, which sweeps from the second end  404  of the auger flight for a selected angle (e.g., greater than 0 degrees, greater than 0 degrees but a maximum of 270 degrees, or from about 90 to about 180 degrees, inclusive). 
     Using an auger  104  with a rotary gate  406  results in less stagnation at the second end  210  of the auger and reduces back-mixing. However, the inventors realized that additional improvements were possible. 
     Accordingly, the inventors developed a larger pitch, full-length auger, with another type of flow restriction mechanism (e.g., using the computer model). Namely, the inventors developed an auger  104  that comprises a first auger section  108  (e.g., upstream auger section) and a second auger section  110  (e.g., downstream auger section) with a smaller pitch  302  than the first auger section  108 . As a result of using a smaller pitch  302  in the second auger section  110 , the bed height  516   c  over a first portion  110   a  (e.g., upstream portion) of the second auger section  110  is increased relative to what it would have been if the second auger section  110  did not have a smaller pitch. 
     However, the inventors again realized that additional improvements were possible. For example, if the smaller pitch is ½ the larger pitch in the first auger section  108 , the linear velocity of the product over the product attrition bed  102  is cut in half. This is because product  502  only travels  1  pitch per revolution (or turn) of the auger  104  so the linear velocity of the product in the auger is the pitch divided by the time required for one revolution of the auger. Thus, the linear velocity of product  502  passing through the second auger section  110  becomes a limiting factor (e.g., bottleneck) for the overall linear velocity of the product conveyed by the auger. 
     Accordingly, the inventors developed a different type of flow restriction mechanism for the second auger section  110  (e.g., using the computer model). Namely, the inventors developed a second auger section  110  with a plurality of auger flights  206  (e.g., a double flight). 
     In one embodiment, the second auger flight  204  of the double flight  206  extends for a fraction of a revolution, (e.g., ½ revolution or 180 degrees) from second end  404  of a first auger flight  106 . Additionally, the second auger flight  204  has the same shape as the first flight, but is out of phase with the first flight by a phase shift angle  924  (e.g., 180 degrees). 
     One benefit of using a plurality of flights  206  is that linear velocity of the product in the second auger section  110  is the same as the linear velocity of the product in the first auger section  108 . Accordingly, using a plurality of flights  206  does not result in a bottle neck in the second auger section  110 . 
     Nonetheless, the inventors realized that further improvements were possible. For example, the inventors realized that the volumetric feed rate to an auger can vary (e.g., +/−15%). Because the bed height in a charge space  510  of the auger is dependent upon the volume of product fed into the charge space, variations in the volumetric feed rate cause variations in bed height from one charge space to another. This, in turn, causes less predictable results (e.g., the standard deviation of the residence time of a product unit  502  can be greater than desired). 
     In order to address this issue, the inventors determined that it would be desirable to provide the auger  104  with one fixed volume of variable sized product units  502  per revolution of the auger. Accordingly, the inventors developed (e.g., using the computer model) a method and apparatus for controlling the volumetric feed rate to an auger. 
     For example, in one embodiment, a container  116 , such as a hopper, can be added to a product attrition apparatus and used to intermittently empty product  502  into the product attrition bed  102 . This advantageously provides each charge space  510  along the auger  104  with approximately the same volume of product, the same product bed height, and the same pressure between the product and the abrasive  154 . 
     However, the inventors realized that retrofitting a product attrition apparatus to include a feed hopper would be expensive. Accordingly, the inventors developed a less costly method for retrofitting a product attrition apparatus. Namely, the inventors added a primary gate  120  (e.g., slide gate) to a downstream portion of a feed chute  118  for an auger  104  and a secondary gate  124  (e.g., slide gate) to an upstream portion of the feed chute. This creates a volume bounded on its bottom and sides by the feed chute, primary gate, and secondary gate. A sensor  128  (e.g., level sensor) is used to measure the volume of product. 
     While product  502  is accumulating between the primary gate  120  and the secondary gate  124 , the primary gate is closed but the secondary gate is open. Then, when a desired volume  112  of product has accumulated, the secondary gate closes and the primary gate opens to discharge the product to the auger  104 . 
     Advantageously, when using some embodiments of the invention described herein, an operator of a product attrition bed  102  can independently control several important parameters that determine the degree of attrition (e.g., peeling) experienced by a product  502 . First, an operator can control the angular velocity  926  (e.g., revolutions per minute) of auger  104 , which, in turn, enables an operator to control residence time for each product charge  512 . Second, an operator can control the volumetric feed rate  122  to the auger (e.g., volume of product fed to the auger per revolution), which, in turn, controls the bed height of product in each charge of the auger. Third, an operator can control the speed an abrasive  154  (e.g., the speed of roller brushes used to abrade the product). 
     An embodiment of the invention will now be described with reference to  FIG. 10A .  FIG. 10A  is a flow chart depicting a method for using an auger  104  to control a flow of a product  502  in a product attrition bed  102 . The auger conveys the product  502  above the product attrition bed  102  in a flow direction  504  while the product attrition bed  102  abrades (e.g. severs and/or removes) the product  502 . The method comprises several steps. 
     First, in a feeding step  1002 , product  502  is fed to the auger  104  to provide a product charge  512 . 
     Second, in a confining step  1004 , the product  502  is completely or substantially confined in a charge space  510 . As illustrated, for example, in  FIG. 1 , a first end  520  of the charge space  510  and a second end  522  of the charge space  510  are bounded by the auger  104 , and a bottom  528  of the charge space  510  is bounded by the product attrition bed  102 . 
     Third, in an abrading step  1006 , the product charge  512  is abraded by an abrasive  154  (e.g., bristles or blades). 
     Fourth, in a rotating step  1008 , the auger  104  is rotated to move the charge space  510 , and thereby the product charge  512 , in the flow direction  504 . 
     Fifth, in a discharging step  1010 , the product charge  512  is discharged from the auger  104  through a flow restriction mechanism (e.g., reduced pitch  302 , a plurality of auger flights  206 , or a rotary gate  406 ) to provide a discharge flow  155  of the product  502 . 
     In some embodiments, the product  502  comprises a plurality of product units  502   a,b  (e.g., potatoes, vegetables, etc.), and the product attrition bed  102  abrades at least an outer surface (e.g., skin and/or peeling) of one of the product units  502   a,b.    
     With reference to  FIG. 10A , the abrading step  2006  can be performed using a variety of methods and types of product attrition beds  102 . For example, the abrading step  2006  can be accomplished by scrubbing, sanding, peeling, cutting or otherwise removing at least a portion of an outer surface of a product  502 . In one embodiment, for example, as illustrated in  FIG. 1 , the product attrition bed  102  comprises a frame  150  on which a plurality of parallel rollers  152  are rotatably mounted in parallel relation to define a longitudinally extending, upwardly opening trough. As another example, the product attrition bed  102  can comprise a frame  150  on which a plurality of blades or some other abrasive  154  is mounted. 
     Similarly, the feeding step  1002 , can be accomplished in a variety of ways. For example, in some embodiments, one control volume  112  of the product  502  is fed to the auger  104  per revolution of the auger to provide a product charge  512 . In one embodiment, the control volume  112  varies by a maximum of +/− about 5% to 20% from a specified volume. In one embodiment, the volumetric feed rate of product to the auger has a standard deviation of approximately 20%. 
     One example of a feeding step  1002 , is illustrated in the flow chart of  FIG. 10B . First, in a conveying step  1020  as illustrated in  FIGS. 1 and 7 , a product  502  is conveyed into a chute  118  while a primary gate  120  of the chute  118  (e.g., downstream gate) is closed and while a secondary gate  124  of the chute  118  (e.g., upstream gate) is open. Second, in a measuring step  1022 , for example, as shown in  FIG. 7 , a volume  702  of the product accumulated upstream of the primary gate  120  and downstream of the secondary gate  124  is measured. For example, in one embodiment, the volume  702  of the product is measured by using a level sensor  128  to measure a level  130  of the product and the level is converted to the volume  702  of the product. Third, in a closing step  1024 , after a control volume  112  or a fraction (e.g., 1/20, 1/10, ⅕, ¼, ⅓, ½) of a control volume  112  of the product has accumulated upstream of the primary gate  120  and downstream of the secondary gate  124 , the secondary gate  124  is closed. For example, this prevents the product  502  from flowing past the secondary gate  124  after the control volume  112  or fraction of a control volume  112  has accumulated. Fourth, in an opening step  1026 , the primary gate  120  is opened to discharge the control volume  112  or fraction of a control volume  112  to the auger to provide the product charge  512 . Fifth, in a repositioning step  1028 , after discharging the control volume  112  or fraction of a control volume  112  to the auger, the primary gate  120  is closed, and then the secondary gate  124  is opened. In some embodiments, the fraction of the control volume provides a specific volume and dividing the control volume by the specific volume results in an integer, for example, so the control volume is evenly divisible by the specific volume. In some embodiments, a container is sized to hold the specific volume. In some embodiments, the container or a plurality of the containers provide a control volume to the auger. 
     Although the invention has been described with reference to a gate, in some embodiments, a flow control mechanism can be used in place of the gate. For example, the secondary gate can be a secondary control mechanism, which can, in turn be any device or structure to regulate (e.g., completely obstruct) the flow of product downstream of the secondary control mechanism and upstream of the primary gate. Examples of secondary control mechanisms include a sliding gate, or a conveyor (e.g., endless conveyor) for the product that can be started and stopped. Accordingly, as used in this context, a secondary control mechanism is open when it enables or causes product to flow past the secondary control mechanism to a position (e.g., along a chute) that is downstream of the secondary control mechanism and upstream of the primary gate. Similarly, as used in this context, a secondary control mechanism is closed when it prevents or stops causing product to flow past the secondary control mechanism to a position (e.g., along a chute) that is downstream of the secondary control mechanism and upstream of the primary gate. 
     As desired, the steps of  FIG. 10B , or some portion thereof, can be repeated, for example, to provide a single control volume  112  (e.g., product charge  512 ) to the auger  104  per revolution of the auger. Additionally, the components described with reference to  FIG. 10B  can be used to retrofit an existing feed chute  118  of a product attrition apparatus  100 . For example, after adding a primary gate  120  and a secondary gate  124  to an existing chute  118  to provide a control volume  112  or a fraction of a control volume  112 , and after adding a sensor (e.g., level sensor  128 ) to the chute  118  to measure the control volume  112 , the method of  FIG. 10B  can be used to control the volumetric feed rate of a feed  122  of product to a product attrition apparatus  100  (e.g., to an auger  104  of the product attrition apparatus  100 ). 
     As another example of a feeding step  1002 , a control volume  112  or a fraction of a control volume  112  of the product  502  can be fed to the auger  104  from a conveyor  114  comprising a plurality of containers  116 . For example, in one embodiment, the invention comprises a conveyor  114  for feeding a control volume  112  or a fraction of a control volume  112  of product to the auger  104 . The conveyor  114  comprises a plurality of containers  116  (e.g., buckets) and each container  116  is sized to contain (e.g., has a volume equal to) the control volume  112  or a fraction of a control volume  112 . The conveyor  114  feeds the auger  104  one control volume  112  of product  502  from one or more containers  116  in the plurality of containers per revolution of the auger. 
     With reference again to  FIG. 10A , the confining step  1004  and the rotating step  1008 , can be used together to convey a product  502 . For example, as illustrated in  FIGS. 1 and 5 , after product  502  is fed to an auger  104 , the product is conveyed in a charge space  510  from a first portion of the product attrition bed  102  (e.g., first or upstream end  144  of the product attrition bed  102 ) to a second portion of the product attrition bed  102  (e.g., second or downstream end  146  of the product attrition bed  102 ). As illustrated in  FIG. 1 , a first end  520  of the charge space  510  (e.g., upstream or trailing end of the charge space) is initially open to an entrance  132  of the auger  104  as the charge space  510  is charged with product. Then, the first end  520  of the charge space  510  closes to confine the product as the charge space  510  moves toward an exit  134  of the auger. Then, as the charge space  510  approaches (e.g. reaches) an exit  134  of the auger, the charge space  510  opens to provide a path for the product charge  512  to flow to the second end  210  of the auger (e.g., exit  134  of the auger). 
     As illustrated in  FIGS. 1-4 , as the charge space  510  approaches (e.g., reaches) an exit  134  of the auger, a second end  210  of the auger (e.g., downstream or leading end of the auger) becomes a second end  522  of the charge space  510  (e.g., downstream or leading end of the charge space  510 ). Accordingly, as the second end  210  of the auger rotates and opens, the second end  522  of the charge space  510  rotates and opens, thereby discharging the product from the charge space  510 . 
     Turning again to  FIG. 10A , the discharging step  1010  can comprise restricting the flow of the product charge  512  as it is discharged from an auger  104 . For example, as shown in illustrations of  FIGS. 2-4 , a flow restriction mechanism can be used to restrict the flow of the product from the second end  210  of the auger. For example, the flow restriction mechanism restriction mechanism can be used to decrease the length of the auger from the second end that is open to the exit, for example, 50% by using a double flight, or a smaller pitch that is ½ the pitch of a larger pitch section, or by using a rotary gate that sweeps  180  from the second end of the auger flight. 
     In some embodiments, the flow restriction mechanism is selected from the group consisting of a rotary gate  406 , a downstream portion of the auger (e.g., the second auger section  110 ) with smaller pitch  302  than an upstream portion of the auger (e.g. the first auger section  108 ), and a plurality of auger flights  206 . 
     As illustrated in  FIGS. 2-4 , the flow restriction mechanism is provided in a second auger section  110  that is downstream of a first auger section  108 . As shown in  FIGS. 5 and 6 , the charge space  510  has an upstream bed height  516   a  before a charge space  510  opens to an exit  134  of the auger (e.g., second end  210  of the auger). The second auger section  110  provides a higher downstream bed height  516   c  for at least an upstream portion (e.g., the first portion  110   a  shown in  FIGS. 1 and 6 ) of the product charge  512  as the product charge is discharged from the auger. As used in this context, the term higher downstream bed height  516   c  is used to denote that the higher downstream bed height  516   c  in the upstream portion  110   a  of the product charge is higher than a lower downstream bed height  516   b  (e.g., lower downstream bed height  516   b  for an auger  104  without a second auger section  110 ) that would prevail in the upstream portion  110   a  of the product charge  512  if the second auger section  110  were to have the same configuration (e.g., same shape, same pitch, same radius, same structure for providing flow restriction) as the first auger section  108 . 
     In some embodiments, the flow restriction mechanism is positioned downstream of a second end  146  (e.g., downstream end) of the product attrition bed  102  to maintain a minimum bed height (e.g., bed height  516   c ) for substantially an entire length  109  of the product attrition bed. For example, in some embodiments, a portion of an auger  104  comprising the flow restriction mechanism extends downstream of the second end  146  of a product attrition bed  102 . Furthermore, in some embodiments the length  216  of an auger flight  106  is greater than the length  109  of a product attrition bed  102 . 
     In some embodiments, the charge space  510  is divided (e.g., partially or completely) in the second auger section  110  by an additional auger flight  204  to form an upstream division (e.g., first portion  110   a  of the second auger section) and a downstream division (e.g., second portion  110   b  of the second auger section), thereby limiting the amount of the product charge  512  that loses bed height when the second end  522  (e.g., downstream end or leading end) of the charge space  510  is opened. For example, as illustrated in  FIG. 1 , the second end  522  of the charge space  510  opens to the exit  134  of the auger  104 . However, because the charge space  510  is divided by an additional auger flight  204 , only a portion of the product charge  512  can exit the auger when the second end  522  of the charge space  510  is opened. 
     In some embodiments, for example, as shown in  FIG. 3 , a length of the charge space  510  in the second auger section  110  (e.g., pitch  302  of the second auger section) is reduced relative to the length of the charge space  510  in the first auger section  108  (e.g., pitch  202  of the first auger section). For example, this can be accomplished by reducing the pitch  302  of the second auger section  110  relative to the first auger section  108 . As a result of reducing the length of the charge space  510 , the charge space  510  begins to open when the first end  520  of the charge space  510  is positioned closer to the exit  134  of the auger than the first end  520  of the charge space would be positioned if the second auger section  110  had the same configuration as the first auger section  108 . 
     In some embodiments, a rotary gate  406  is provided in the second auger section  110  to constrain the discharge of product  502  from the second auger section  110 . For example, the rotary gate  406  can be positioned at the second end  210  of the auger  104  (e.g., downstream or leading end of the auger). Furthermore, the rotary gate  406  can be positioned at the second end  404  of the auger flight  106 . 
     As illustrated in  FIG. 8 , in some embodiments, the rotation of the auger  104  is driven by applying a force to a drive shaft  518  of the auger. For example, the force can be applied to a drive shaft  518  that extends a shaft length  212  from an end of the auger  208 , 210  wherein the shaft length  212  is substantially less than an entire length  218  of the auger. In some embodiments, the radius of a drive shaft is minimized to avoid restricting the tumbling motion of product in a charge space  510 . In some embodiments, the rotation of the auger  104  is driven by applying a force directly to an auger flight  106  of the auger. 
     One embodiment of the invention will now be described with reference to  FIGS. 1 and 5 , which illustrate a product attrition apparatus  100  with improved flow control for a product  502  comprising a plurality of product units  502   a,b . The product attrition apparatus  100  comprises a product attrition bed  102  and an auger  104 , and the product attrition bed  102  abrades the product  502  while the auger conveys the product in a flow direction  504 . 
     The product attrition bed  102  comprises a first end  144  of the product attrition bed  102 , a second end  146  of the product attrition bed  102 , a cavity  153  (e.g., trough or cylindrically shaped chamber) that extends from the first end  144  of the product attrition bed  102  to the second end  146  of the product attrition bed  102 , and an abrasive  154  that is positioned and oriented to face the auger and that substantially covers the entire surface of the product attrition bed  102 . 
     The auger comprises a rotational axis  506  of the auger oriented in the flow direction  504 , an auger flight  106  coiled around the rotational axis  506 , a first auger section  108 , and a second auger section  110  downstream of the first auger section  108 . 
     As illustrated in  FIG. 1 , the cavity  153  of the product attrition bed  102  is arcuate and has an axis of curvature that substantially coincides (e.g. is concentric with) the rotational axis  506  of the auger  104 . Additionally, a radius of curvature  136  of the product attrition bed  102  is larger than a radius  138  of the auger flight  106 , but the difference between the radii  136 ,  138  is small enough to prevent product  502  from passing through a space  140  between the product attrition bed  102  and the auger flight  106 . 
     As shown in  FIG. 1 , the auger  104  is configured (e.g., shaped, sized, structured, arranged, positioned, and/or oriented) in relation to the product attrition bed  102  to form a charge space  510  for confining (e.g., completely, substantially, or at least partially confining) a product charge  512  of the product  502 . In some embodiments, the auger  104  is positioned above a cavity  153  of the product attrition bed  102 , and the auger is positioned to avoid contacting the product attrition bed  102  while rotating (e.g., throughout an entire full revolution). Additionally, as shown in  FIG. 1 , the auger  104  is positioned at least partially within the cavity  153  of the product attrition bed  102 . 
     In the examples shown in  FIGS. 1 and 5 , as the auger  104  rotates on the rotational axis  506 , the charge space  510  moves in the flow direction  504 , thereby moving the product charge  512  in the flow direction  504 . 
     As illustrated in  FIG. 1 , a charge space  510  can be open on a first end  520  of the charge space  510  (e.g., upstream or trailing end) or a second end  522  of the charge space  510  (e.g., downstream or leading end). When the charge space  510  is not open on one end, the charge space  510  is bounded by the auger  104  and the product attrition bed  102 . For example, a first end  520  of the charge space  510  is bounded by a first portion  524  of the auger flight  106 ; a second end  522  of the charge space  510  is bounded by a second portion  526  of the auger flight  106 ; and a bottom  528  of the charge space  510  is bounded by the product attrition bed  102 . As illustrated, the bottom  528  of the charge space  510  also acts as a first side  530  and second side  532  of the charge space  510  because the bottom and sides are rounded. 
     As shown in  FIG. 1 , the auger comprises a first auger section  108  upstream of a second auger section  110 . In some embodiments, the first auger section  108  provides for a less obstructed motion of the product charge  512 , and the second auger section  110  provides for a relatively more obstructed motion of the product charge  512 . In some embodiments, the second auger section  110  comprises a flow restriction mechanism (e.g., reduced pitch  302 , a plurality of auger flights  206 , or a rotary gate  406 ) to restrict (e.g., limit) the discharge flow  155  of the product  502 , and the first auger section  108  does not comprise a flow restriction mechanism. 
     As illustrated in  FIGS. 1, 2, and 6 , in one embodiment, the second auger section  110  comprises a plurality of auger flights  206  (e.g., a double flight). For example, the second auger section  110  can comprise at least one additional auger flight  204  (e.g., to divide a charge space  510 ). As shown in  FIG. 2 , a length  214  of the additional auger flight  204  (or a length  214  of the plurality of auger flights  206 ) extends from approximately an end of the auger (e.g., the second end  210  of the auger). In some embodiments, the additional auger flight  204  (or the plurality of auger flights  206 ) extends for at least about ¼, ⅓, ½, ¾, or 1 revolution of the additional auger flight  204 . For example, as shown in  FIG. 2 , the additional auger flight  204  extends from a second end  210  of the auger for about 270° of a revolution of the additional auger flight  204 , which is about ¾ of a revolution of the additional auger flight  204 . In some embodiments, a length  214  of the additional auger flight  204  (or a length  214  of the plurality of auger flights  206 ) is at least about ¼, ⅓, ½, ¾, or 1 pitch (e.g., of the first auger flight  106  or the additional auger flight  204 ). 
     As shown in  FIG. 3 , in some embodiments, the second auger section  110  comprises a pitch  302  that is smaller than a pitch  202  of the first auger section  108 . In one embodiment, the first auger section  108  comprises a minimum pitch  202  of about 4, about 5, or about 6, times an average equivalent spherical diameter  514  of the product  502  (e.g., in the product attrition bed  102 , or in the product charge  512 ). As used herein, the equivalent spherical diameter of a product unit is the diameter of a sphere having the same volume as the product unit. Furthermore, the average equivalent spherical diameter is the average of all the equivalent spherical diameters for the product units in a product. 
     In one embodiment, the second auger section  110  comprises a maximum pitch  302  of about 4, about 5, or about 6 times an average equivalent spherical diameter  514  of the product. For example, in a first section it can be useful to have a pitch  202  greater than 5 times an average equivalent spherical diameter  514 , and in a second section it can be useful to have a pitch  302  less than 2.5 times the average equivalent spherical diameter  514 . 
     In some embodiments a pitch  202  of the first auger section  108  is substantially constant for the entirety of the first auger section  108 . Additionally, in some embodiments, a pitch  302  of the second auger section  110  is substantially constant for the entirety of the second auger section  110 . 
     With reference, for example, to  FIGS. 1 and 2 , in some embodiments, the length  218  of the auger  104  extends (e.g., substantially or completely) the entire length  109  of the product attrition bed  102 . In one embodiment, the length  216  of the auger flight  106  is substantially equal to the length  218  of the auger. In one embodiment, a length  216  of the auger flight  106  is substantially equal to the length  109  of the product attrition bed  102  and/or the shaft length  212 . In another embodiment, the length  216  of the auger flight  106  can be greater than a length  109  of the product attrition bed  102  and/or the shaft length  212 . In one embodiment, the length  216  of the auger flight  106  can be less than a length  109  of the product attrition bed  102  and/or the shaft length  212 . 
     As illustrated, for example, in  FIG. 4 , in some embodiments, the auger flight  106  comprises a first end  402  of the auger flight  106  (e.g., upstream end, trailing end) and a second end  404  of the auger flight  106  (e.g., downstream end, leading end), and the second auger section  110  comprises a rotary gate  406  that is fixed to the second end  404  of the auger flight  106 . 
     As illustrated in  FIG. 6 , in some embodiments, as a result of a flow restriction mechanism in the second auger section  110 , a minimum bed height  516   c , for example, a fraction of the bed height (or average bed height) in the first (e.g., most upstream) closed product charge of the auger, is provided from approximately a first end  208  of the auger to within a selected distance  602  from the second end  210  of the auger. The fraction can be, for example, at least about 75%, 80%, 85%, 90%, 95%, or 100%. The selected distance  602  from the second end  210  of the auger can be equal to or less than the length of the pitch  202  in the first auger section  108 . For example, the selected distance  602  can be a maximum of ¼, ⅓, ⅔, or ¾ the length of the pitch  202  of the first auger section  108 . As another example, the selected distance  602  can be a maximum of ¼, ⅓, ⅔, ¾ or one length of the pitch  302  of the second auger section  110  if the second auger section has a different pitch than the first auger section as illustrated in  FIG. 3 . As another example, the selected distance  602  can be a length of a plurality of flights. 
     With reference to  FIGS. 1 and 6 , in some embodiments, a minimum bed height  516   c  is provided from approximately a first end  144  of the product attrition bed  102  to within a selected distance  602  from a second end  146  of the product attrition bed  102 . Again, the selected distance  602  can be less than the length of the pitch  202  in the first auger section  108 . For example, the selected distance  602  can be a maximum of ¼, ⅓, ⅔, or ¾ the length of the pitch  202  of the first auger section  108 . As another example, the selected distance  602  can be a maximum of ¼, ⅓, ⅔, ¾ or one length of the pitch  302  of the second auger section  110  if the second auger section has a different pitch than the first auger section as illustrated in  FIG. 3 . 
     In some embodiments, the minimum bed height  516   c  is a minimum fraction of the average bed height of the product  502  over the length  109  of the product attrition bed  102 . For example, in one embodiment, the minimum fraction is at least about 75%, 80%, 85%, 90%, 95%, 100%. 
     In some embodiments, a minimum bed height is a minimum fraction of the bed height (or average bed height) in the first (e.g., most upstream) closed product charge of the auger. For example, in one embodiment, the minimum fraction is at least 75%, 80%, 85%, 90%, 95%, 100%. 
     In some embodiments, as illustrated for example in  FIG. 5 , the auger comprises a drive shaft  518 . Although the drive shaft  518  can extend along an entire length of an auger, as shown in  FIG. 8 , the drive shaft  518  can also be a truncated drive shaft  518  that extends a shaft length  212  from an end of the auger (e.g., the second end  210  of the auger). Additionally, in some embodiments, the auger does not comprise a drive shaft  518 . 
       FIG. 8  illustrates a truncated drive shaft  518  that does not extend along an entire length of an auger. The auger comprises a first end  208  of the auger and a second end  210  of the auger downstream of the first end  208  of the auger. The auger also comprises a first end  402  of the auger flight  106  and a second end  404  of the auger flight downstream of the first end  402  of the auger flight  106  (for reference, see the first end  402  and second end  404  of an auger flight shown in  FIGS. 2-4 ). The drive shaft  518  extends a shaft length  212  from the second end  404  of the auger flight  106 , and the shaft length  212  is substantially less than an entire length  218  of the auger and substantially less than an entire length of the auger flight  216  (for reference see an auger flight length  216  shown in  FIG. 2 ). In some embodiments, the shaft length  212  is a fraction of the length  218  of the auger or a fraction of the length  216  of the auger flight. For example, if a plurality of auger flights is used, the shaft length can be the length of the plurality of auger flights. Using a truncated drive shaft  518  or eliminating a drive shaft  518  can be useful, for example, to provide less obstructed mixing, more effective bed height for a product, and more effective volume available to serve as a charge space  510  between an auger  104  and a product attrition bed  102 . In some embodiments the drive shaft is fixed to an end of the auger flight, but the drive shaft does not extend along the length of the auger flight. 
     As illustrated, for example, in  FIGS. 1 and 8 , the auger  104  does not contact the product attrition bed  102 . In some embodiments, the auger  104  (e.g., auger flight  106 , or any truncated drive shaft  518 ) has a sufficiently high mechanical rigidity that the auger can be supported from one end (e.g., first end  208  or second end  210 ) of the auger and thereby suspended a substantially fixed distance above the product attrition bed  102  (e.g., distance  140  between the auger flight  106  and product attrition bed  102 ) for the entire length  218  of the auger. This can be useful to prevent the auger from contacting an abrasive  154  on the surface of the product attrition bed  102 . 
     As illustrated in  FIG. 1 , in some embodiments, the invention also comprises a feed control device for controlling a volumetric feed rate of product  502  to the product attrition apparatus  100 . For example, in one embodiment, the invention comprises a container  116 , and the container comprises a feed chute  118  for feeding product  502  to the auger  104 , a primary gate  120  (e.g., a downstream sliding gate) for controlling (e.g. blocking) a second feed  122  of product from the chute  118  to the auger  104 , and a secondary gate  124  (e.g. an upstream sliding gate) for controlling (e.g. blocking) a first feed  126  of product to the chute  118 . In the illustration of  FIG. 1 , the primary gate  120  is downstream of the secondary gate  124 . 
     Although the invention is described herein in terms of a charge space  510 , the charge space  510  can be one of a plurality of charge spaces  510 . For example, in one embodiment, the product (e.g., a product charge  512 ) is confined in at least one charge space  510 . As another example, in some embodiments, the auger  104  is configured in relation to the product attrition bed  102  to form a plurality of charge spaces  510  for confining a plurality of product charges  512 , respectively. 
     Similarly, although the invention is described in terms of a product charge  512 , the product charge  512  can be one of a plurality of product charges  512 . For example, in one embodiment, the auger  104  conveys at least one product charge  512 . As another example, in some embodiments, the auger  104  is configured in relation to the product attrition bed  102  to convey a plurality of product charges  512 . 
     COMPARATIVE EXAMPLES 
     With reference to  FIGS. 5 and 6 , the advantages provided by the invention can be better understood by comparing a first product attrition apparatus  100   a  (e.g., first peeler) and a second product attrition apparatus  100   b  (e.g., second peeler) that are identical except for their augers  104 . The first product attrition apparatus  100   a  comprises a first product attrition bed  102  (e.g., first bed comprising an abrasive  154 ) and a first auger  104 . Meanwhile, the second product attrition apparatus  100   b  comprises a second product attrition bed  102  (e.g., second bed comprising an abrasive  154 ) and a second auger  104 . 
     The second product attrition bed  102  is identical to the first product attrition bed  102 . Furthermore, the first auger  104  and the second auger  104  have the same auger length  218  and radius, and an initial portion  534  of the first auger is identical to a first auger section  108  of the second auger. Additionally, a terminal portion  536  of the first auger has generally the same configuration (e.g., same pitch, same number of auger flights, same radius, and/or absence of flow restriction mechanism such as rotary gates) as the initial portion  534  of the first auger and the first auger section  108  of the second auger. 
     However, the second auger section  110  of the second auger  104  advantageously differs from the first auger section  108  of the second auger, the terminal portion  536  of the first auger, and the initial portion  534  of the first auger. For example, the second auger section  110  of the second auger comprises a flow restriction mechanism, which is beneficial because it helps to maintain a minimum bed height  516   c  of product  502  over the product attrition bed  102 . A minimum bed height  516   c , in turn, increases the weight of product  502  over the product attrition bed  102  and helps maintain a desirable level of force (e.g., pressure, static head) between an abrasive  154  of the product attrition bed  102  and the product  502 . 
     As illustrated in  FIGS. 5 and 6 , there is a general correlation between the amount of a product unit  502   a,b  that is abraded (e.g., peeled) and the residence time of the product unit  502   a,b  over the product attrition bed  102 . For example, a product unit  502   a  with a shorter residence time will have experienced less attrition (e.g., abrasion) than a product unit  502   b  with a longer residence time. 
       FIGS. 5 and 6  illustrate the average residence times  551   a,b,c,d,e,f  for a plurality of product charges  512   a,b,c,d . In  FIG. 5 , a first product charge  512   a  (e.g., the most upstream product charge) is in an open charge space  510   a  because it has just been fed to the auger. It has a first average residence time  551   a  in the product attrition bed (e.g., over the abrasive) that is the lowest average residence time of the product charges. The second product charge  512   b  (e.g., the second most upstream product charge) is in the first closed charge space  510   b . It has a second average residence time  551   b  that is the second lowest average residence time. The third product charge  512   c  (e.g., the third most upstream product charge) is in the second closed charge space  510   c . It has a third average residence time  551   c  that is the third lowest average residence time. The fourth product charge  512   d  (e.g., the most downstream product charge) is in the second open charge space  510   d  (e.g., most downstream charge space). It has a fourth average residence time  551   d  that is the highest average residence time. However, the residence time spend in the fourth product charge is not as effective for abrading the product charge, because the bed height is lower. 
       FIG. 6  is similar to  FIG. 5 , except the fourth product charge has been subdivided. For example, a first product charge  512   a  (e.g., the most upstream product charge) is in a first open charge space  510   a  because it has just been fed to the auger. It has a first average residence time  551   a  in the product attrition bed (e.g., over the abrasive) that is the lowest average residence time of the product charges. The second product charge  512   b  (e.g., the second most upstream product charge) is in the first closed charge space  510   b . It has a second average residence time  551   b  that is the second lowest average residence time. The third product charge  512   c  (e.g., the third most upstream product charge) is in the second closed charge space  510   c . It has a third average residence time  551   c  that is the third lowest average residence time. The fourth product charge (e.g., the most downstream product charge) is in the second open charge space (e.g., most downstream charge space). However, the fourth product charge has been divided into a first portion  512   e  (e.g., an upstream portion) and a second portion  512   f  (e.g., a downstream portion). Similarly, the fourth charge space has been divided into a first portion  510   e  (e.g., an upstream portion) and a second portion  510   f  (e.g., a downstream portion). The first portion  512   e  of the fourth product charge has a fourth average residence time  551   e  that is the fourth lowest average residence time. The second portion  512   f  of the fourth product charge has a fifth average residence time  551   f  that is the highest average residence time. Although the downstream portion  512   f  of the fourth product charge has a lower bed height, the upstream portion  512   e  of the fourth product charge has a higher bed height  516   c.    
       FIGS. 5A and 6A  illustrate the total number of product units  502  in a product attrition bed over time as calculated by a computer using the discrete elements method to model the product flow.  FIG. 5A  corresponds to the product attrition apparatus  100   a  illustrated in  FIG. 5 .  FIG. 6A  corresponds to the product attrition apparatus  100   b , illustrated in  FIG. 6 . At startup, the number of product units increases fairly steadily (for example, because a continuous feed of product is fed to the auger at a constant rate). Then, once product begins to be discharged from the product attrition bed (e.g., by the second end of an auger), if the discharge rate exceeds the feed rate, the total number of product units in the product attrition bed starts to decrease. Then, as the discharge rate goes down, or as the feed rate increases, the feed rate exceeds the discharge rate, and the total number of product units in the product attrition bed starts to increase. 
     The increase and the decrease in the total number of product units over time can be seen in the curves plotted in  FIGS. 5A and 6A . For example, the variation in the total number of curves from a local maximum to a subsequent local minimum in the number of product units provides an amplitude 550,650 of a charge-discharge cycle for an auger. 
     As can be seen, both product attrition beds have an average steady state count of around 143 product units. However, the amplitude for the single pitch, single flight auger illustrated in  FIG. 5A  is about 20 product units while the amplitude of the single pitch, double flight auger illustrated in  FIG. 6A  is about 10 product units. In other words, the total number of product units in the product attrition bed of  FIG. 5A  varies by about 14% of the average steady state number of product units. Meanwhile, the total number of product units in the product attrition bed of  FIG. 6A  varies by about 7% of the average steady state number of product units. 
     Given an average particle size, the number of particles in a product attrition bed is proportional to the volume of the particles. Furthermore, given a substantially constant bed height until the exit end of the auger, the total number of particles in the auger varies primarily with the bed height at the second end of an auger. Accordingly, the product attrition bed of  FIG. 6A  has a lower variability in bed height at the second end of the auger. For example, the variability in bed height at the second end of the auger in  FIG. 6A  is about ½ the variability in the bed height at the second end of the auger in  FIG. 5A . Because, some details of the invention are easier to understand with reference to a coordinate system, a Cartesian coordinate system has been provided in  FIG. 9 . The coordinate system has three mutually perpendicular axes, X, Y, and Z, whose directions are given by X, Y, and Z unit vectors, respectively. The Cartesian coordinate system follows the right-hand rule (e.g., the cross-product of the X unit vector and the Y unit vector points in the direction of the Z unit vector). The X-axis is horizontal and points in the flow direction  504  (e.g., parallel to the rotational axis  506  of the auger and/or axis of curvature of the product attrition bed  102 , which is shown in  FIG. 1 ). The Y-axis is horizontal and perpendicular to the flow direction  504 . The Z-axis is vertical and perpendicular to the flow direction  504 . In the embodiment shown, the auger  104  is shaped to convey the product  502  in the flow direction  504  when the auger rotates with a negative angular velocity  926  (e.g., the rotation of the auger is described by an angular velocity vector  508  that is parallel to but opposite the flow direction  504 ). However, the auger  104  can also be shaped to convey the product  502  in the flow direction  504  when the auger rotates with a positive angular velocity  926 . In some embodiments, the magnitude of the angular velocity of the auger is about 1 to about 30 rpm (rotations per minute). 
     With reference to  FIGS. 1, 2 and 9 , one embodiment of the invention comprises a plurality of auger flights  206 . As shown, a second auger section  110  comprises an additional auger flight  204  (e.g., a second auger flight with the same rotational axis  506 , shape, and pitch  202  as the first flight) extending a length  214  of the additional flight along the rotational axis  506  of the auger from the second end  210  of the auger toward the first end  208  of the auger. Both auger flights  106 , 204  have substantially constant radii to provide the auger  104  with a substantially constant radius over a length  218  of the auger. 
     As illustrated in  FIG. 9 , the additional auger flight  204  is out of phase with the first auger flight  106 . For example, given a reference point  902  on the rotational axis  506  of the auger  104  and a normal plane  904  that is perpendicular to the rotational axis  506  at the reference point  902 , the outer edge  906  of the first auger flight  106  intersects the normal plane  904  at a first point of intersection  908 , and a first vector  910  (e.g., straight line with direction and magnitude) drawn from the reference point  902  to the first point of intersection  908  is at a first angle  912  to a reference vector  914  in the plane (e.g., horizontal vector in the plane) originating at the reference point  902 . Additionally, the outer edge  916  of the second auger flight (e.g., additional auger flight  204 ) intersects the normal plane  904  at a second point of intersection  918 , and a second vector  920  drawn from the reference point  902  to the second point of intersection  918  is at a second angle  922  to the reference vector  914  in the plane. Furthermore, the first angle  912  is out of phase with the second angle  922  by a phase shift angle  924  (e.g., 180 degrees, as illustrated in  FIG. 9 ). 
     In some embodiments, an auger flight  106  begins to open (e.g., discharge a product charge  512  at the second end  210  of the auger) when at least a portion of a second end  404  of the auger flight  106 ,  204  rotates into a position below horizontal (e.g., a position below parallel to the reference vector  914  in  FIG. 9 ). For example, in some embodiments, when an auger  104  has a negative angular velocity  926  (as shown in  FIG. 9 ), the auger flight  106 ,  204  begins to open when at least a portion of a second end  404  of the auger flight  106 ,  204  rotates to an angle less than 0° (with a 0° angle defined by the reference vector  914 ). In other embodiments, when an auger  104  is a mirror image of the auger  104  shown in  FIG. 9  (e.g., mirror image reflected across a vertical plane passing through the rotational axis  506 ) and when the auger  104  has a positive angular velocity  926  (e.g., opposite of angular velocity  926  shown in  FIG. 9 ), the auger flight  106 ,  204  begins to open when at least a portion of a second end  404  of the auger flight  106 ,  204  rotates to an angle greater than 180° (with a 0° angle defined by the reference vector  914 ). 
     Additional Embodiments 
     The following clauses are offered as further description of the disclosed invention: 
     1. A product attrition apparatus with improved flow control for a product, wherein the product comprises a plurality of product units, said product attrition apparatus comprising: 
     a product attrition bed; and 
     an auger positioned above the product attrition bed; 
     wherein the product attrition bed abrades the product while the auger conveys the product in a flow direction; 
     wherein the auger comprises:
         a rotational axis of the auger oriented parallel to the flow direction;   an auger flight coiled around the rotational axis   a first auger section; and   a second auger section downstream of the first auger section;       

     wherein the auger is configured in relation to the product attrition bed to form a charge space for substantially confining a product charge of the product; 
     wherein, as the auger rotates on the rotational axis, the charge space moves in the flow direction, thereby moving the product charge in the flow direction; 
     wherein the first auger section comprises a minimum pitch of about 4 times an average equivalent spherical diameter of the product; 
     wherein the second auger section comprises a flow restriction mechanism to restrict a discharge flow of the product from the auger. 
     2. The apparatus of clause 1 or 24, wherein the auger flight extends substantially an entire length of the product attrition bed.
 
3. The apparatus of clause 1 or 24, wherein an entire length of the auger flight is greater than an entire length of the product attrition bed.
 
4. The apparatus of clause 1 or 24, wherein the flow restriction mechanism is positioned downstream of a downstream end of the product attrition bed to maintain a minimum bed height for an entire length of the product attrition bed.
 
5. The apparatus of clause 1 or 24, wherein the second auger section comprises at least one additional auger flight.
 
6. The apparatus of clause 1 or 24, wherein the second auger section comprises a pitch that is smaller than a pitch of the first auger section.
 
7. The apparatus of clause 1 or 24, wherein the second auger section comprises a maximum pitch of about 6 times an average equivalent spherical diameter of the product.
 
8. The apparatus of clause 1 or 24, wherein the auger flight comprises a first end of the auger flight and a second end of the auger flight downstream of the first end of the auger flight; wherein the second auger section comprises a rotary gate, and wherein the rotary gate is fixed to the second end of the auger flight.
 
9. The apparatus of clause 1 or 24, wherein a drive shaft of the auger is fixed to a second end of the auger flight, and wherein the drive shaft of the auger does not extend along a length of the auger flight.
 
10. The apparatus of clause 1 or 24, wherein the auger comprises a first end of the auger flight and a second end of the auger flight downstream of the first end of the auger flight; wherein the auger comprises a drive shaft, wherein the drive shaft extends along the auger flight for a shaft length from the second end of the auger flight; and wherein the shaft length is substantially less than an entire length of the auger flight.
 
11. The apparatus of clause 1 or 24, wherein the auger flight does not contact the product attrition bed.
 
12. The apparatus of clause 1 or 24, further comprising:
 
     a container for providing one control volume of the product to the apparatus per revolution of the auger. 
     13. The apparatus of clause 1 or 24, further comprising: 
     a conveyor for feeding a control volume of product to the auger; 
     wherein the conveyor comprises a plurality of containers; 
     wherein each container is sized to contain a specific volume; 
     wherein the specific volume is not greater than the control volume; 
     wherein dividing the control volume by the specific volume results substantially in an integer; 
     wherein the conveyor feeds the auger one control volume of product per revolution of the auger by feeding the auger the specific volume from at least one container in the plurality of containers per revolution of the auger. 
     14. The apparatus of clause 1 or 24, further comprising: 
     a container, 
     wherein the container comprises: 
     a feed chute for feeding product to the auger; 
     a primary gate for controlling a feed of product from the chute to the auger; and 
     a secondary control mechanism for controlling a feed of product to the chute; 
     wherein the primary gate is downstream of the secondary control mechanism. 
     15. A method for using an auger to control a flow of a product over a product attrition bed, wherein the product comprises a plurality of product units, wherein the auger conveys the product above the product attrition bed in a flow direction while the product attrition bed abrades the product, said method comprising the steps: 
     feeding the product to the auger to provide a product charge; 
     substantially confining the product charge in a charge space, wherein a first end of the charge space and a second end of the charge space are bounded by the auger, and wherein a bottom of the charge space is bounded by the product attrition bed; 
     rotating the auger to move the charge space, and thereby the product charge, in the flow direction; and 
     discharging the product charge from the auger through a flow restriction mechanism to provide a discharge flow of the product; 
     wherein a first auger section of the auger is upstream of a second auger section of the auger; and 
     wherein the second auger section comprises the flow restriction mechanism to restrict the discharge flow of the product. 
     16. The method of clause 15 or 25, further comprising: 
     dividing the charge space in the second auger section to form an upstream division and a downstream division, thereby limiting the amount of the product charge that loses bed height when the second end of the charge space is opened; 
     wherein the second end of the charge space is a downstream end of the charge space. 
     17. The method of clause 15 or 25, further comprising: 
     reducing a length of the charge space in the second auger section relative to the length of the charge space in the first auger section. 
     18. The method of clause 15 or 25, further comprising: 
     using a rotary gate to restrict the discharge flow of product from the second auger section. 
     19. The method of clause 15 or 25, further comprising: 
     driving the rotation of the auger by applying a force to a drive shaft fixed to a an end of an auger flight of the auger, wherein the drive shaft does not extend along a length of the auger flight. 
     20. The method of clause 15 or 25, further comprising: 
     driving the rotation of the auger by applying a force to a drive shaft that extends a shaft length from an end of an auger flight of the auger, wherein the shaft length is substantially less than an entire length of the auger flight. 
     21. The method of clause 15 or 25, wherein the feeding step further comprises: 
     feeding a control volume of the product to the auger to provide the product charge. 
     22. The method of clause 15 or 25, wherein the feeding step further comprises: 
     feeding a control volume of the product to the auger from a conveyor comprising a plurality of containers, wherein each container has a volume not greater than the control volume. 
     23. The method of clause 15 or 25, wherein the feeding step further comprises: 
     conveying the product into a chute while a primary gate of the chute is closed and while a secondary control mechanism of the chute is open, wherein the secondary control mechanism is positioned upstream of the primary gate; 
     measuring a volume of the product accumulated upstream of the primary gate and downstream of the secondary control mechanism; 
     closing the secondary control mechanism after a specific volume of the product has accumulated upstream of the primary gate and downstream of the secondary control mechanism, wherein the specific volume is not greater than the control volume; 
     opening the primary gate to discharge the specific volume of the product to the auger to provide at least a portion of the product charge; 
     closing the primary gate and opening the secondary control mechanism after discharging the specific volume of product to the auger. 
     24. An apparatus for providing one control volume of a product to an auger per revolution of the auger, wherein the auger extends the length of a product attrition bed for abrading the product as it is conveyed by the auger in a charge space, and wherein the charge space is bounded by the auger and the product attrition bed, said apparatus comprising: 
     a container; and 
     a conveyor for feeding product to the container; 
     wherein the container is sized to hold a specific volume; 
     wherein dividing the control volume by the specific volume results substantially in an integer; and 
     wherein the container comprises at least a portion of a feed chute for the auger. 
     25. A method for controlling a volumetric feed rate of product to an auger positioned over a product attrition bed, said method comprising the steps: 
     feeding one control volume of the product to the auger per revolution of the auger, wherein the one control volume is accumulated in a hopper before being fed to the auger; 
     rotating the auger to convey the product in a charge space bounded by the auger and the product attrition bed; 
     abrading the product by contact with the product attrition bed; and 
     discharging the control volume from the auger; 
     wherein the auger extends the length of the product attrition bed. 
     While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.