Abstract:
A method of avoiding hammer rod-hole deformation in a hammer mill. Conventional hammers are fitted with a bearing structure that reduces wear while permitting the hammer to pivot about multiple axes. An optional, integral spacer provides spacing between adjacent hammers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0003]    The present invention relates to hammer mills. More particularly, this invention relates to an improved two or three piece hammer that reduces hole elongation and side loading of the hammer. 
         [0004]    Hammer mills have long been used for grinding or comminution of materials. A typical hammer mill comprises a rotor mounted on a rotor shaft inside a housing. A rotor  1100  according to the prior art is illustrated at rest in  FIG. 11  and in motion in  FIG. 12 . A material inlet is generally located at the top of the housing with one or more material outlets located near the bottom of the housing. The rotor  1100  includes a drive shaft and rows of hammers  1400 , normally comprising flat steel blades or bars, as illustrated in  FIGS. 13 and 14 . The hammer  1400  is pivotally connected to the rotor  1100  via a steel rod or pin. The rotor  1100  is mounted inside a typically teardrop shaped enclosure, known by those skilled in this art as a grinding or working chamber. In a reversible hammer mill, this grinding chamber comprises a cutting plate mounted on either side of the material inlet. Reversible hammer mills are capable of rotation in either direction, a feature providing increased life for the hammers  1400 , cutting plates, and screen plates. Present-day cutting plates comprise an upper, linear section connected with a convex section, and do not allow particles to escape. Downstream of the cutting plate, the interior of the working chamber is defined by curved screen plates. The screen opening diameter is selected to match the desired final particle size. Particles less than or equal to the desired size exit the chamber through the screens while material greater than the desired size are further reduced by the rotating hammers  1400 . 
         [0005]    Numerous industries rely on hammer mill grinders or impact grinders to reduce material to a smaller size. For example, hammer mills are often used to process forestry products, agricultural products, minerals, and materials for recycling. Specific examples of materials processed by hammer mills include grains, animal food, pet food, feed ingredients, mulch, wood, hay, plastics, and dried distiller grains. Hammer mills heretofore have long been employed to effect size reduction in such diverse materials as scrap metal, paper, animal and human feed, or anything else that needs to be reduced in size. 
         [0006]    Standard hammers, when grinding a product in a hammer mill, impact the product to be pulverized to create a smaller average size particle. This impact forces material against a perforated screen area that also cuts and sizes the product. Inside the typical hammer mill, numerous forces act. A force exists toward the tip of the hammer, where the hammer impacts the material to be comminuted. Also present inside the mill is a axial force, parallel to the rotor shaft, on a side of the hammer due to the material entering the mill. The combination of these two co-existing forces cause elongation to the pivot hole in the hammer, decreased life, and the eventual failure of the hammer. Accordingly there is a need for a hammer mill design to compensate for impact loading, side loading, wear, and hole elongation. There are also tub grinders and impact crushers that use the hammer setup. 
         [0007]    Manufacturing methods utilizing forgings, rolling, and casting are well known in the art to improve the life and functionality of the hammer. 
         [0008]    The two pieces are preferably forged together in a similar manufacturing process as that disclosed in U.S. Pat. No. 2,728,975, hereby incorporated in its entirety by reference. 
         [0009]    Treatment Methods such as welding weld material to the end of the hammer blade are well known in the art to improve the grinding functionality and life of the hammer. These methods typically infuse the hammer edge, through welding, with a metallic material resistant to abrasion or wear such as tungsten carbide. See, for example, U.S. Pat. No. 6,419,173, incorporated herein by reference, describing methods of attaining hardened hammer tips or edges, as are well known by those skilled in the art. 
         [0010]    Increasing the hammer strength with the addition of edge weld and increasing the hardness of the hammer material decreases the fatigue strength of the hammer when subjected to dynamic loading. In the prior art, the roundness of the rod hole deteriorates, leading to elongation of the hammer rod hole. Elongation of the hammer rod hole continues until the material yields and yielding in operation causes failure/fracture of the hammer at the rod. The fracture is catastrophic and causes mechanical failure in the mill, damage to the housing, screens and other hammers, as well as safety concerns to workers near mills. Design changes including making the hammer wider at the rod, such as disclosed in U.S. Pat. No. 7,140,569 which is hereby incorporated by reference, have been attempted but still experience field failure due to the side loading of the hammer. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Rod-hole deformation is overcome by providing a two- or, optionally, three-piece design. It is therefore an object of the present invention to provide an end bearing structure comprising a race with an integrated spacer, and a hammer blade with an integrated bearing surface. An additional object is to provide an optional third piece comprising a separate liner installed between the bearing and race surfaces in order to mitigate elongation of the hammer blade pivot hole immediately adjacent to the pivot rod, the liner can also serve as a coating to reduce the friction and wear between the race and the blade to increase service life in elevated dynamic loading situations. A further object is to improve the ease and safety of installation and maintenance of hammer blades within a hammer mill. Still another object is to eliminate unnecessary spacers between the hammer blades when installed onto the pivot rods. 
         [0012]    Effecting the above objects results in a stronger bearing structure designed to deflect and lessen the dynamic side loading on the hammer blade when in motion and under load. Reduction in wear on the leading, bottom, and trailing edges of the hammer by infusing an unyielding material ultimately increase the life cycle of the hammer blade and reduces costs associated with replacement and maintenance of the hammer mill. 
         [0013]    In a hammer mill, including a housing defining a hammer mill grinding chamber with at least one inlet and one outlet, a rotor is disposed centrally in the housing for rotation about a rotor axis of rotation. A screen is disposed at a predetermined radial location relative to the rotor&#39;s axis of rotation. Operatively, pivotally attached to the rotor is a plurality of hammers grouped in sets and disposed periodically about the rotor&#39;s axis of rotation. All hammers within a single set have a common axis of rotation lying parallel to the rotor&#39;s axis of rotation. The hammers&#39; axes of rotation are disposed at a common radial distance relative to the rotor&#39;s axis of rotation. At least one of the hammers in each group has an opening in one end corresponding to the common hammer axis of rotation. 
         [0014]    The present invention may be manufactured using methods of forging, casting or rolling, as are well known by those having skill in the art. 
         [0015]    The hammers require no new installation procedures or equipment. The present invention eliminates the need to utilize spacers. This is accomplished through a variable length race with an integrated spacer. The width of the race with the integrated spacer may range from one quarter to ten inches. This design feature reduces installation time and improves the overall safety to the personnel assembling or maintaining the hammer mill due to the lessening of the need to align hammers, spacers and rods during installation. The installation is also safer for users as with a typical setup, rods must be forced through holes using impact devices while the operator manually holds the spacers. Utilizing the incorporated spacers the operators&#39; hands are clear from pinch points within the mill. 
         [0016]    Established forging techniques, well known in the art of fitting two-piece bearing like structures together, are used in the manufacture of the two-piece end bearing structure disclosed herein. 
         [0017]    The inner race, with the integrated spacer, augments the two-piece end bearing structure by maintaining a predetermined distance between one or more hammer blades when installed on the pivot rod within the hammer mill. The inner race also improves the two-piece end bearing structure by assisting in the dispersal of anticipated dynamic forces that ultimately affect the hammer blade assembly and the hammer mill pivot rod. This additional feature reduces fatigue, and stress and enhances resistance to deformation and inordinate wear acquired through use. The life of the hammer blade assembly is, therefore, extended. 
         [0018]    Installation of hammers with races integrated with the spacer is also made easier and quicker, whether the installation is initial or replacement. It is also predicted to improve the safety of this procedure in the field by reducing the number of parts and alignment issues associated with existing hammer blades and hammer mills. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective view of a hammer mill hammer blade with an integrated, internal bearing surface; 
           [0020]      FIG. 2  is a cross sectional view of the hammer mill hammer blade with an integrated, internal bearing surface; 
           [0021]      FIG. 3   a  is a perspective view of an individual race without an integrated spacer; 
           [0022]      FIG. 4   b  is a cross sectional view of the individual race without the integrated spacer; 
           [0023]      FIG. 3   c  is a perspective view of the individual race with the integrated spacer; 
           [0024]      FIG. 3   d  is a cross detail of the individual race with the integrated spacer; 
           [0025]      FIG. 4  is a perspective cross sectional view of a sub-assembly comprising the hammer mill hammer blade with the integrated, internal bearing surface, and the inner race without the integrated spacer; 
           [0026]      FIG. 5  is a perspective cross sectional view of the sub-assembly comprising the hammer mill hammer blade with the integrated, internal bearing surface and the inner race with an integrated spacer; 
           [0027]      FIG. 6  is a perspective view of the hammer mill hammer blade assembly on a shaft without the integral spacer; 
           [0028]      FIG. 7  is a perspective view of the hammer mill hammer blade assembly on the shaft with the integral spacer and additional material added to the lower leading, trailing, and bottom sides; 
           [0029]      FIG. 8  is a side elevation view illustrating the rotational capabilities of the hammer mill hammer blade assembly when installed onto a sub-assembly rod; 
           [0030]      FIG. 9  is a cross-sectional view of the hammer mill hammer blade assembly of  FIG. 8 ; 
           [0031]      FIG. 10  is a perspective view of the inner race inside an outer race, integral with the hammer mill hammer blade body, prior to forging the parts together; 
           [0032]      FIG. 11  is a perspective view of an assembled hammer mill rotor of the prior art at rest; 
           [0033]      FIG. 12  is a perspective view of an assembled hammer mill rotor of the prior art in motion; 
           [0034]      FIG. 13  is a perspective view of an exploded view of a hammer mill rotor of the prior art; and 
           [0035]      FIG. 14  is a detail view of a partial exploded view of a hammer mill rotor of the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  shows a hammer mill hammer blade assembly  10 , comprising a hammer blade body  11 , and an integrated outer bearing race  14 , the outer bearing race comprising an inner surface or cup  15 . The cutaway view of  FIG. 2  provides an additional angle showing that the outer bearing race  14  is integrated with the hammer blade body  11 . Voids  13 , in the hammer blade body  11 , are optional to reduce the weight of the hammer blade assembly  10  and/or to enhance the milling process by increasing the dynamic movement of particles from rod to screen in the mill and providing additional impact surfaces. The voids can be round, rectangular, pentagonal, or multiple of shapes and achieve the same function. 
         [0037]      FIGS. 3   a  and  b  illustrate an inner bearing race  16 , which in use, is disposed within and concentric to the outer bearing race  14 , as shown in  FIG. 4 . The cup  15  conforms to the shape of the outer surface of the inner bearing race  16 . 
         [0038]      FIGS. 3   c  and  d  illustrate an inner bearing race assembly  17 , comprising the inner bearing race  16  and a spacer  18 . In the preferred embodiment, these two parts: the inner bearing race  16  and the spacer  18 , are integral. That is, they are made from the same mass of material to form the inner bearing race assembly  17 . 
         [0039]    The outer surface of the inner bearing race  16 , with or without the integral spacer  18 , is convex to mate with the concave inner surface  15  of the outer bearing race  14  as illustrated in  FIGS. 4 and 5 , where the optional integral spacer  18  is included in  FIG. 5  but not in  FIG. 4 . The concavity of the outer bearing race  14  is a result of a manufacturing process, as described below. The choice of curvature of the convex and concave surfaces is well understood by those versed in the present art, to permit the hammer blade body  11  to adequately pivot on axes  810 ,  820  not parallel to the axis of rotation of the rotor  1100  (see  FIGS. 10-12 ), as shown in  FIGS. 8 and 9 . Such shapes include and elliptical segment and circular arc. Because of the additional degrees of freedom of the hammer mill hammer blade  11  of the present invention, side loading on the hammer assembly  10  is relieved by rotation, and the load is thus transferred to the rod  24  (see  FIG. 6 ) holding the hammer assembly  10  as a linear load. 
         [0040]    The inner race  16  without the integral sleeve  18  is shown installed in the hammer mill hammer blade body  11  in  FIG. 6 . The method used to unite these two parts is described below. 
         [0041]    The inner bearing race assembly  17  is shown installed in the hammer mill hammer blade body  11  in  FIGS. 6 and 7 . In  FIG. 6 , the optional integral spacer is not included, whereas in  FIG. 7 , the inner bearing race assembly  17  includes the optional integral spacer. The method used to unite the inner bearing race assembly  17  and the hammer mill hammer blade body  11  is described later. In  FIG. 7 , additional material  22  has been added to particular wear points, preferably by welding, to increase the life of the hammer mill hammer body  11 . 
         [0042]    In  FIGS. 8 and 9 , a set or subset of hammer mill hammer assemblies  10  on a shaft  24 . The illustrated hammer assemblies  10  include integral spacers  18  to provide the necessary spacing between the hammer bodies  11 . However, separate spacers may also be used with hammer assemblies  10  without integral spacers  18 , such as those illustrated in  FIGS. 4 and 6 . 
         [0043]      FIGS. 8 and 9  also illustrate the extra degrees of freedom by which the hammer body  11  may pivot. Axes of rotation  810 ,  820  are not parallel to the longitudinal axis of the shaft  24  on which the hammer assemblies  10  are mounted. Pivotal motion about these axes of rotation  810 ,  820  is permitted by sliding the outer bearing race  14  relative to the inner bearing race  16  due to the appropriate curvature of the mating surfaces of these races  14 ,  16 . 
         [0044]    The inner race  16  is manufactured utilizing a lathe. The inner race  16  is preferably made of 1030, 1040, 52100 or similar carbon steel, but the present invention is not limited to a particular race material. The inner race  16  is manufactured to needed width when incorporating the integrated spacer  18  design. The arc of the inner race  16  is designed so as to conform to the material malleability characteristics of the hammer blade body  11 . 
         [0045]    The hammer mill hammer blade  11  is manufactured by forging to required dimensions, coining the hammer blade  11  for tolerances, and drilling the hole  12  to its required tolerance. The hammer blade  11  is forged and machined with a cylindrical hole  12  with excess material around the hole  12  on both sides of the hammer blade  11 . 
         [0046]    An initial step in assembling the inner bearing race  16  to the hammer blade  11  is to heat the hammer blade  11 , thus allowing the cooled inner bearing race  16  to be placed inside the hole  12  as depicted in  FIG. 10 . 
         [0047]    The next step in the manufacturing process is to final forge the hammer blade  11  and move excess material around the hole  12  in contact with the inner race  16 , thus making the hammer blade  11  the cup to the outer race  14 . 
         [0048]    The next step is to heat the hammer blade  11  and utilizing a forging press or drop hammer forging, wherein two dies are pressed together. The dies are manufactured to hold the inner race  16  center and the material of the hammer blade  11  is rolled at 45° to 60° relief to match the curvature of the inner race  16 . The end result is that of  FIG. 4  or  5 , depending on whether or not the hammer assembly  10  includes the integral spacer  18 . 
         [0049]    The next step is heat treatment and loading of the hammer blade assembly  10 . The heat treatment process at designated temperature creates expansion and contraction throughout the forged part. The material deformation stress is relieved and the inner race  16  outside diameter reduces and the hammer blade inside diameter increases. The forged hammer cup  15  loses 10% of the original deformation. At this point, the hammer mill blade body  11  may pivot about the inner race  16  about the pivot axis  820  with approximately 1-2 degrees of movement. In some applications that race will be manufactured with 0 degrees of movement after heat treatment to increase start-up behavior in some mills, the hammer mill blade body  11  will still achieve full pivot when loaded. In other applications, the outside hammer will be manufactured to achieve full rotation after heat treatment for mills with high start-up impact loading. 
         [0050]    Full pivot of the hammer mill blade body  11  is achieved when loaded into the hammer mill. A loading, preferably greater than 100 ft·lbs, deforms the material on a 45-60 degree relief until the material of the hammer mill blade body  11  reaches its yield point. At this point, the inner race is fully set, and any side loading of the hammer mill blade body  11  is relieved by rotation, and the load is transposed to a linear load on the rod  24  on which the hammer blade assembly  10  is mounted. This change in directional force, as well as the increase in bearing surface relative to the prior art, reduces the working stress of the hammer blade body  11  well below the yield point so the hammer blade body  11  experiences no inelastic deformation and failure as seen with hammers  1300  in the prior art. Toward the hammer assembly&#39;s life the inner race  16  will be able to rotate approximately 15°. 
         [0051]    Although only an exemplary embodiment of the invention has been described in details above, those skilled in the art will readily appreciate that many modifications are possible without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.