Patent Publication Number: US-7712692-B2

Title: Rotary impact mill

Description:
CROSS REFERENCES 
   This Patent Application is a continuation-in-part of U.S. patent application Ser. No. 11/424,833 filed on Jun. 16, 2006 now U.S. Pat. No. 7,416,145 and entitled Rotary Impact Mill, which is herein incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   Hammermills are often used to reduce the size of solid material. Materials often used in hammermills include coal, asphalt, cement, limestone, chemical fertilizer, barks, rocks, minerals, and food products. The materials are often fed into an inlet where the material falls into a milling chamber. The milling chamber typically comprises a plurality of impact hammers and may comprise a screen. The impact hammers are typically fastened at a proximal end to a rotary assembly; they are either rigidly fixed to the rotor assembly or the impact hammers may be free-swinging. As the material is fed into the chamber, the rotary assembly rotates bringing the impact hammers into contact with the material. The size reduction on each impact depends on the differential speed between the hammers and material, size of the material, and hardness of the material. If a screen is present, the screen may allow only the desired material particle size to pass to the outside of the chamber to an outlet where the particles can be collected or funneled to another machine where the material may be further processed. 
   Due to the impact and/or abrasive nature of the material, the impact hammers may wear requiring continual maintenance and down time of the hammermill. 
   U.S. Pat. No. 6,405,950 by Gunderson which is herein incorporated by reference for all that it contains, discloses an improved airflow hammermill assembly for grinding materials. The improved airflow hammermill assembly incorporates one or more diverging ducts communicating with the hammermill housing to provide a more uniform negative pressure within the housing. The improved airflow hammermill assembly allows increased throughput and energy savings. 
   U.S. Pat. No. 5,938,131 by Thom, Jr., et al., which is herein incorporated by reference for all that it contains, discloses a hammermill that includes a housing, a working chamber defined by a polygonal screen, an inlet to the chamber, an outlet and a plurality of free-swinging hammers attached to a driven rotor. Support brackets extend the length of the housing and mount deflectors for eliminating tangential motion of materials being comminuted in the working chamber in the region of the deflectors. 
   U.S. Pat. No. 4,638,747 by Brock, et al., which is herein incorporated by reference for all that it contains, discloses an invention that comprises a coal-fired burner system for use in a drum mix asphalt plant or drum dryer used for producing asphalt paving composition. 
   U.S. Patent Publication 2004/0129808 by Crane, et al., which is herein incorporated by reference for all that it contains, discloses a hammermill for singulating cellulosic fibers from a pulp sheet that comprises a cylindrical housing, a feed slot with a breaker bar positioned therein and a rotor mounted for rotation in the housing. Feed rolls are provided to feed a sheet of pulp into the feed slot upstream of the breaker bar. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect of the invention, a rotary impact mill has a milling chamber defined by a housing with an inlet, an outlet, and at least one wall. A plurality of impact hammers located within the milling chamber are fastened to and longitudinally disposed along a rotor assembly connected to a rotary driving mechanism. At least one of the impact hammers has a plurality of inserts arranged adjacent one another in a row and attached to a body of the hammer, wherein a first end of at least one insert is complementary to a second end of an adjacent insert. 
   The inserts may be bonded proximate a distal end of the impact hammer whereas a proximal end is fastened to the rotor assembly. The inserts may comprise a generally rounded geometry, a generally conical geometry, a generally flat geometry, a generally hemispherical geometry, or a combination thereof The inserts may comprise a coating comprising diamond, polycrystalline diamond, cubic boron nitride, refractory metal bonded diamond, silicon bonded diamond, layered diamond, infiltrated diamond, thermally stable diamond, natural diamond, vapor deposited diamond, physically deposited diamond, diamond impregnated matrix, diamond impregnated carbide, cemented metal carbide, chromium, titanium, aluminum, tungsten, nitride, stelite, cobalt, manganese, or combinations thereof The inserts may be brazed or press fit into recesses of the hammer body and may be compressed together laterally. The inserts may comprise a hardness greater than the hardness of the hammer body. 
   The body of the impact hammer may comprise a plurality of rows of inserts. The plurality of rows of inserts may be arranged such that a gap between the plurality of inserts forms a pocket. The distal end of the impact hammer may comprise a plurality of faces with at least one face comprising a plurality of inserts. The distal end may comprise a strip of a wear resistant material with a hardness of at least 60 HRc. The strip may be adjacent the plurality of inserts. The distal end of the impact hammer may comprise a distal surface opposite the proximal end and substantially normal to the axial length of the body. This normal distal surface may comprise a hard surface. 
   The wear resistant inserts may protrude beyond the body of the impact hammer 0.010 to 3.00 inches. The inserts may be generally flush with the body of the impact hammer. The inserts may comprise a first end which is flat, angular, slanted, curved, rounded or combinations thereof. The inserts may comprise first and second ends which are generally planar and where first ends are angled so as to be generally parallel to the second ends of the adjacent inserts. The inserts may have first and second ends which are generally planar and angled. The first and second ends of inserts may be generally non-planar. The inserts may have all first ends that are angled with the same angle and all second ends with angles complementary to the angle of the first ends. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional diagram of an embodiment of a rotary impact mill. 
       FIG. 2  is a perspective diagram of an embodiment of an impact hammer. 
       FIG. 3  is a perspective diagram of an embodiment of an insert. 
       FIG. 4  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 5  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 6  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 7  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 8  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 9  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 10  is a perspective diagram of another embodiment of an impact hammer. 
       FIG. 11  is an orthogonal diagram of an embodiment of a row of inserts. 
       FIG. 12  is an orthogonal diagram of another embodiment of a row of inserts. 
       FIG. 13  is an orthogonal diagram of another embodiment of a row of inserts. 
       FIG. 14  is a perspective diagram of an embodiment of an insert. 
       FIG. 15  is a perspective diagram of another embodiment of an insert. 
       FIG. 16  is a perspective diagram of another embodiment of an insert. 
       FIG. 17  is a perspective diagram of another embodiment of an insert. 
       FIG. 18  is a perspective diagram of another embodiment of an insert. 
       FIG. 19  is a perspective diagram of another embodiment of an insert. 
       FIG. 20  is a perspective diagram of another embodiment of an insert. 
       FIG. 21  is a perspective diagram of another embodiment of an insert. 
       FIG. 22  is a perspective diagram of another embodiment of an insert. 
   

   DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT 
     FIG. 1  is a cross sectional diagram of an embodiment of a rotary impact mill  100 . A milling chamber  101  is defined by at least one wall  102  of a housing  103  which may support an internal screen  104 , which is typically cylindrical or polygonal. Within the screen  104  a rotary assembly  105  comprises a plurality of shafts  106  connected to a central shaft  107  which is in turn connected to a rotary driving mechanism (not shown). The rotary driving mechanism may be a motor typically used in the art to rotate the rotor assembly of other hammermills. Although there are four shafts  106  shown, one, two, or any desired number of shafts may be used. A plurality of impact hammers  108  are longitudinally spaced and connected to each of the shafts  106  at the hammer&#39;s proximal end  109 . The hammers  108  may be rigidly attached to the shafts  106  or the hammers  108  may be free-swinging. In some embodiments, the rotor assembly  105  comprises just the central shaft  107  and the impact hammers  108  are connected to it. 
   The housing  103  also comprises an inlet  110  and an outlet  111 . Typically the inlet  110  is positioned above the rotor assembly  107  so that gravity directs the material towards it through an opening  112  in the screen  104 , although the inlet  110  may instead be disposed in one of the sides  113  of the housing  103 . When in the milling chamber  101 , a material may be reduced upon contact with the impact hammers  108 . The screen  104  may comprise apertures (not shown) only large enough to allow the desired maximum sized particle through. Upon impact however, a distribution of particle sizes may be formed, some capable of falling through the apertures of the screen  104  and others too large to pass through. Since the larger particle sizes may not be able pass through the apertures, they may be forced to remain within the screen  104  and come into contact again with one of the impact hammers  108 . The hammers  108  may repeatedly contact the material until they are sized to pass through the apertures of the screen  104 . 
   After passage through the screen  104  the size-reduced particles may be funneled through the outlet  111  for collection. In other embodiments the particles may be directed towards another machine for further processing, such as when coal is the material being reduced and fine coal particles may be directed towards a furnace for producing power. It may be necessary to provide low pressure in the vicinity of the outlet  111  to remove the particles, especially the fine particles, through the outlet  111 . The low pressure may be provided by a vacuum. 
   As shown in  FIG. 1 , the rotor assembly  105  is positioned such that it is substantially perpendicular to the flow of material fed into the inlet  110 . In other embodiments, the rotor assembly  105  may be positioned such that it is substantially parallel or diagonally disposed with respect to the flow of feed material. In some embodiments, there are multiple rotor assemblies. 
   The impact hammers  108  comprise a plurality of wear resistant inserts  114  bonded to a body  115  of the impact hammer  108 . At least one of the inserts  114  has a first end which is complementary to a second end of an adjacent insert  114 . Although the embodiment of an impact hammer  108  in  FIG. 1  comprises a generally rectangular shape, the impact hammer  108  may comprise any general shape including, but not limited to generally cylindrical, generally triangular, tapers, beveled, generally conical, generally stepped, or combinations thereof. In some embodiments of the present invention, the hammer is a bar hammer, a T-shaped hammer, a ring-type hammer, a toothed type-ring hammer or combinations thereof. The wear resistant inserts  114  are believed to reduce wear of the hammer body  115 . The body  115  of the hammers may be made of steel, stainless steel, a cemented metal carbide, manganese, hardened steel, metal, hardox  600 , or combinations thereof Typically hardened steel is used. The distal end  116  of the hammer body  115  is typically more susceptible to wear because it travels the farthest distance per rotation of the rotor assembly  105  causing the distal end  116  to travel at a higher velocity than the rest of the hammer body  115  and causing it to be more susceptible to wear. Although other regions of the hammer body may be less susceptible to wear, they may still come into contact with the material being reduced and may benefit from having a wear resistant insert bonded to it. 
     FIG. 2  is a perspective diagram of a preferred embodiment of an impact hammer  108  and discloses a plurality of domed inserts  114  bonded proximate the distal end  116  of the hammer body  115 . Though  FIG. 2  discloses domed inserts, the inserts may comprise a generally rounded geometry, a generally conical geometry, a generally flat geometry, a generally hemispherical geometry, or a combination thereof Impacting the material with a domed insert  114  may generate a more explosive impact than a sharper insert. The desired balance of blunt inserts to sharp inserts would depend on the type of material being reduced, the rate that material is fed into the milling chamber, and the differential speed between the material and insert. At least one of the inserts  114  comprises a first end which is complementary to a second end of an adjacent insert  114 . 
   The distal end  116  may comprise a single row of inserts  114 , or as disclosed in  FIG. 2 , a plurality of rows of inserts  114 . The inserts may comprise a hardness greater than the hardness of the hammer body  115 . Cavities may be formed in the body  115  on the impact side  202  of the body  115 . The inserts  114  may be brazed within the cavities or press fit. The inserts  114  may be brazed using a braze material comprising silver, gold, copper, nickel, palladium, boron, chromium, silicon, germanium, aluminum, iron, cobalt, manganese, titanium, tin, gallium, vanadium, indium, phosphorus, molybdenum, platinum, or combinations thereof. In some embodiments, where the inserts  114  are brazed in, there may be a gap of 0.005 to 0.040 inches between the inserts at the narrowest point. Press fitting the inserts  114  together in a row where the first and second ends press against each other may cause the inserts to compress together laterally. 
   The wear resistant inserts  114  may be of a solid material or a combination of materials. Preferably the insert  114  comprises the combination of a cemented metal carbide substrate with a superhard coating  204  bonded to it, such as polycrystalline diamond. However, the insert  114  may also comprise a coating  204  selected from the group comprising diamond, polycrystalline diamond, cubic boron nitride, refractory metal bonded diamond, silicon bonded diamond, layered diamond, infiltrated diamond, thermally stable diamond, natural diamond, vapor deposited diamond, physically deposited diamond, diamond impregnated matrix, diamond impregnated carbide, cemented metal carbide, chromium, titanium, aluminum, tungsten, and combinations thereof. The coating  204  of solid hard materials, in some cases, may be made harder by doping or infiltrating the materials with higher or lower concentrations of metals and/or hard materials to achieve a desired hardness. The hardness of the coating  204  may have a hardness greater than the hardness of the hammer body  115 . In some embodiments, the hammer body  115  has a hardness of 35 to 50 HRc. Preferably the insert substrates have a hardness of at least 60 HRc, and the superhard coating has a hardness of at least 2000 HK. 
   The coating  204  may be bonded to the substrate with a non-planar interface to increase the strength of the bond. Also the superhard material may be a sintered body, such as in embodiments where a polycrystalline diamond is used, and may be made thermally stable by removing a thin layer of metal binders by leaching in the hard surface. It is believed that the thin layer of metal binders may have a higher coefficient of thermal expansion than the grains of the superhard material. In other embodiments, the hard surface may comprises a metal binder concentration less than 40 weight percent. In embodiments where polycrystalline diamond is used, a higher concentration of cobalt typically reduces the brittleness of the polycrystalline diamond but as a tradeoff increases its susceptibility to wear. Preferably the polycrystalline diamond has a cobalt concentration of four to ten weight percent. Adjusting the metal binder concentration in the cemented metal carbide may also have the same effect. Preferably the carbide is a tungsten carbide comprising a cobalt concentration of 6 to 14 weight percent. Polycrystalline diamond grain size distribution may also play an important role in the strength of the diamond and also in its failure mode. Preferably, the grain sizes are within 0.5 to 300 microns. Preferably, the coating  204  is also polished to reduce crack initiation starting points that may be created during manufacturing. Although several preferred characteristics have been identified, any concentrations and characteristics of coatings  204  are encompassed within the claims. 
   In some embodiments a gap between a plurality of inserts forms a pocket  203 . It is believed that when material is fed through the mill that the pocket  203  fills with material. This material in the pocket  203  is believed to protect the body  115  of the impact hammer  108  between the inserts  114   
   In  FIG. 3  a perspective embodiment of an insert  114  is shown with a first end  300  that is generally flat and complementary to a second end of an adjacent insert. The flat first end  300  allows inserts  114  to be positioned close together. In this way the wear between inserts  114  is reduced by substantially eliminating the momentum of material flowing between the inserts  114 . Because inserts  114  with a diamond coating  204  have a much greater wear resistance than the body  115  of the hammer, wear occurs around the inserts  114  before the inserts  114  wear themselves. Therefore it is believed that by reducing the amount and velocity of aggregate impacting on the body  115  proximate the inserts the overall life expectancy of the hammer  108  will increase. A radius  301  or conic is shown opposite the coating  204 . An insert  114  may comprise any combination of flatted ends in order to be complementary to adjacent inserts. 
     FIG. 4  discloses an embodiment of a hammer  108  where a plurality of faces  400  is disposed on the distal end  116 . By adjusting the angle between the plurality of faces  400  the angle of impact between the insert  114  and the material can be adjusted. It is believed that different face angles  401  may adjust the aggressiveness of the impact. By using multiple faces it is believed that impact angles may be manipulated to achieve maximal crushing effect on the material without creating undue wear on the inserts  114 . 
     FIG. 5  discloses an embodiment of a hammer  108  where the inserts  114  may protrude from a face  400  by 0.010 to 3.00 inches. It is believed that protruding inserts  114  may create a bending moment on impacting material. This bending moment is believed to more effectively break the material Inserts  114  with a generally rounded geometry are believed to contribute to the bending moment. In addition, it is believed that the generally rounded inserts are less susceptible to chipping from contaminants in the material feed. It is believed that chipping of the inserts  114  occurs proximate the edge  501  of the distal end  116  of the hammer  108 . Rounded inserts  114  may resist the chipping. In some embodiments the hammer  108  has rounded inserts  114  near the edge  501  in combination with flat inserts  114  placed more proximal on the hammer. In some embodiments the inserts  114  may not protrude from the face  400 , but may be flush with the face  400 . In some embodiments, the inserts may be simply bonded to a flat surface of the body  115 . 
   Referring now to  FIG. 6 , in some embodiments of the invention a rectangular strip  601  of hard material at high wear regions of the hammer  108  may provide wear resistance, allowing for protection from impact and shearing forces due to the flow of material. In some embodiments, the strip  601  may be segmented. The strip  601  may be casted or molded prior to fastening and/or bonding it to the hammer  108 . Graphite or ceramics may be placed in the casted or molded material such that holes are formed in the strip  601  and the inserts  114  may be brazed or press fit into them. The strip  601  may be adjacent the plurality of inserts  114  in more than one direction and may be disposed between rows of inserts  114 . By positioning the strip  601  in areas of high wear around the inserts  114  the wear resistance of the hammer  108  may be increased without increasing the number of inserts  114 . In some embodiments the strip  601  may be disposed on a distal surface  602  opposite the proximal end and substantially normal to the axial length of the body  115 . In some aspects of the invention the distal surface  602  may comprise a plurality of inserts  114 . This may be advantageous for reducing wear of the distal end  116  of the hammer  108  in situations where the distal end  116  of the hammer body  108  comes into contact with the screen  104  (see  FIG. 1 ) or if a material particle braces itself between the screen  104  and the hammer  108 . 
   Referring now to  FIG. 7 , the distal end  116  may comprise a plurality of inserts  114  disposed along a longitudinal edge  701  of the body  115 . In addition to the distal end  116  of the impact side  202 , the longitudinal edges  701  of the hammer  108  may also experience great amounts of wear. It is believed that placing inserts along the longitudinal edge  701  will reduce the wear along those edges  701  and increase the life expectancy of the hammer  108 . A hard surface  702  may be disposed adjacent the plurality of inserts in any direction in order to protect the body  115  from wear without increasing the number of inserts. In some embodiments, the hard surface  702  comprises carbide. Also in certain embodiments, the hard surface matches the profile of inserts. 
   Referring now to  FIG. 8  the distal end  116  of the hammer  108  may comprise a single row of inserts  114 . The production cost of hammers  108  may be correlated to the number of inserts  114  on the hammer  108 . In applications of the invention that cause less wear it may be advantageous to have only one row of inserts  114 . 
   Referring now to  FIG. 9 , the body  115  may comprise a plurality of longitudinal wear resistant plates  901 . Material particles may pass over the longitudinal edges  701  and cause them to be susceptible to wear. In some applications the longitudinal wear plates  901  may be sufficient to reduce wear in that region. Although the embodiment of  FIG. 9  discloses a long single solid wear resistant plate  901  bonded to a longitudinal edge  701 , in other embodiments smaller plates may be positioned adjacent one another along the edge  701 . Furthermore, any geometry of plates may be used. These wear plates  901  may be disposed adjacent a plurality of inserts  114 . Preferable a longitudinal wear plate  901  is as close to its longitudinal edge  701  as possible. To achieve this, the plate  901  may be bonded to the body  115  such that a small portion of the plate  901  hangs over the edge  701 , which overhang is then removed by grinding. The overhang may be allowable, depending on the spacing of the impact hammers  108  along the rotor assembly  105  (See  FIG. 1 ). If the overhang doesn&#39;t interfere with adjacent longitudinally spaced hammers, the grinding step may not be necessary. In some embodiments, the edge  701  may be rounded or chamfered. 
   Referring now to  FIG. 10 , the distal end  116  of the hammer  108  may comprise a first row  1000  of inserts  114  that each have an end  1001  complementary to a junction  1002  of inserts  114  in a second row  1003 . It is believed that the momentum of material flow between inserts  114  causes wear. By offsetting the first and second row the momentum of material flow between inserts will be substantially eliminated. The first row  1000  of inserts  114  may also be disposed such that a gap is formed at the junction  1002  of the three inserts. The arrangement of the first row  1000  of inserts  114  at the junctions  1002  of the second row  1003  of inserts may be desirable when a fewer number of inserts  114  provides adequate protection for the distal end  116 . 
     FIGS. 11 to 13  are different embodiments of first and second complementary ends of the inserts  114 . The inserts  114  may have a first end which is flat, angular, slanted, curved, rounded or combinations thereof.  FIG. 11  is an embodiment of a row of inserts in which a first end  1101  is generally rounded complementary to a second end  1102  of an adjacent insert  114 . Since the first end  1101  is interlocked with the second end  1102  it is believed that an impact to one of the inserts will be shared by its adjacent inserts. By distributing the force of aggregate impact throughout an entire row  1103  it is believed that the inserts  114  will have a greater resistive force and a longer life. Additionally, the complementary first and second ends  1101 ,  1102  serve to reduce the space between the inserts  114  thus reducing the amount of aggregate flowing between the inserts  114 . 
     FIG. 12  is an embodiment of a row of inserts  114  in which all of the first ends  1201  are generally planar and angled with the same angle and are complementary to the second ends  1202  of an adjacent inserts. This design not only attempts to reduce wear by reducing the space between the inserts  114  but is also believed to change the flow between the inserts, which will reduce the energy of the flowing material. It is therefore believed that the embodiment of inserts  114  shown in  FIG. 12  will cause a reduction in the momentum of aggregate flowing between the inserts  114 . 
     FIG. 13  is an embodiment of a row of inserts  114  in which a first end  1301  is generally planar and angled complementary to a second end  1302  of an adjacent insert  114 . This arrangement creates a middle insert  1303  that comprises a wedge between two adjacent inserts  1304 . 
     FIGS. 14-22  all disclose various embodiments of geometries of the inserts  114 . Each geometry may be advantageous depending on the material and application of the rotary impact mill. These inserts may be bonded or otherwise attached anywhere on the hammer body, although they are preferably attached proximate its distal end. In embodiments, where the rotation of the rotor assembly is reversible, it may be beneficial to have the wear resistant inserts bonded to the side of the body opposite of the impact side. The insert  114  may comprise a geometry with a generally domed shape, as in the embodiment of  FIG. 14 ; a generally conical shape, as in the embodiment of  FIG. 15 ; a generally flat shape, as in the embodiment of  FIG. 16 ; a generally pyramidal shape, as in the embodiment of  FIG. 17 ; a generally paraboloid shape, as in the embodiment of  FIG. 18 ; a generally frustoconical shape, as in the embodiment of  FIG. 19 ; an elliptical wedge shape, as in the embodiment of  FIG. 20 ; a generally scoop shape, as in the embodiment of  FIG. 21 ; a rectangular wedge shape, as in the embodiment of  FIG. 22 ; a generally asymmetric shape; a generally rounded shape; a generally polygonal shape; a generally triangular shape; a generally rectangular shape; a generally concave shape; a generally convex shape; a chamfer; a conic section; or combinations thereof. The diamond surface  204  may be bonded to a substrate in a high temperature high pressure press at a planar or non-planar interface  1800  of the insert  114 . Preferably the diamond surface is a cobalt infiltrated polycrystalline diamond bonded to a tungsten carbide substrate. 
   Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.