Abstract:
A method of providing for a manually insertable bushing in a spherical joint. By forming slots, strategically located and sized, the bushing may be inserted manually into the race, then rotated into position in the race. The bushing may be disallowed from exiting via the slots by engaging the bushing to a shaft, or by a keeper affixed to cover the slots.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    The present invention relates to hammer mills. More particularly, this invention relates to an improved spherical joint to which hammers in hammer mills are operatively attached. 
         [0002]    Hammer mills are a common tool for crushing, grinding, or comminution of a wide variety of materials. For example, hammer mills are 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, concrete, aggregate materials, and dried distiller grains. 
         [0003]    A typical hammer mill comprises a rotor mounted on a rotor shaft inside a housing. Hammer mills have an advantage over other grinding mechanisms in that, if the material to be reduced fails to yield to a hammer&#39;s blow, that hammer is simply deflected and other hammers will strike the same material until it does yield. 
         [0004]    A typical hammer mill comprises a rotor assembly mounted on a rotor shaft inside a housing. A rotor assembly  1100  is illustrated at rest in  FIGS. 11 and 13  of Plumb et al. U.S. Pat. No. 8,104,177, and U.S. Pat. No. 8,342,435, both of which patents are incorporated herein by reference. 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. As shown in  FIGS. 11 to 13  of the Plumb et al. &#39;177 Patent, the rotor assembly  1100  includes a drive shaft and rows of hammers  1400 , as illustrated in  FIG. 14  of the Plumb et al. &#39;177 Patent. The hammers  1400  are pivotally connected to the rotor  1100  by a steel hammer rod or pin. The hammers are normally flat steel blades or bars, as illustrated in  FIGS. 11 to 14 . The hammers extend out substantially radially from the hammer rods due to inertia when the hammer mill rotates, that is, is in operation, as illustrated in  FIG. 12 . The rotor assembly  1100  is mounted inside a housing, known by those skilled in the hammer art as a grinding or working chamber. 
         [0005]    An apparatus for attaching hammers within a hammer mill is disclosed in U.S. Pat. No. 7,419,109 by Ronfeldt et al., which is also hereby incorporated by reference. 
         [0006]    Present-day cutting plates comprise an upper, linear 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 of the material being comminuted. Particles less than or equal to the desired size exit the chamber though the screens, while material greater than the desired size are further reduced by the rotating hammers  1400  (still referring to the prior art shown in U.S. Pat. Nos. 8,104,177 and 8,342,435). 
         [0007]    Standard hammers, when grinding a product in a hammer mill, impact the product to be pulverized to create a smaller average particle size. 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 spherical joint, comprising a bushing and a race, is used to attach the hammer to the shaft. Such a joint does not support loads to the hammer parallel to the shaft until the spherical joint has reached its limit of travel. Therefore, bushing wear due to said loading is greatly diminished. 
         [0008]    For the purposes of the present document, including the claims, a spherical joint is defined as follows. It comprises a bushing  220  and a race  310  (see  FIGS. 2 and 3  of the present document). The surfaces of the bushing and the race in contact with one other are generally described, mathematically, as portions of a cylindrical surface  110 , depicted in  FIG. 1A . The surface of a cylinder  110  may be described in rectangular coordinates as: 
         [0000]    
       
      
       x 
       2 
       +y 
       2 
       +z 
       2 
       =R 
       2  
      
     
         [0000]    where x, y, and z are the usual Cartesian coordinates shown in  FIG. 1A  and R is the radius (half the diameter) of the spherical surface. The bushing  220  and a race  310  surfaces are confined, geometrically, between two parallel planes  120 ,  130  as shown in  FIG. 1A . These planes  120 ,  130  are depicted as planes of constant x, equidistant from the origin or center  170  of the sphere in  FIG. 1A , but any two parallel planes  120 ,  130 , equidistant from the center of the sphere  170  and spaced appropriately provide the same shape for the bushing  220  and race  310  surfaces. The bushing  220  surface and the race  310  surface, then, are shown in  FIG. 1A  as the portion of the cylinder&#39;s surface residing between the two parallel planes  120 ,  130 . The race  310  surface has a slightly larger diameter or radius than that of the bushing  220  so the bushing  220  may readily move within the race  310  under the influence of a force or torque. The race  310  surface would typically be defined by a closer spacing between the two parallel planes  120 ,  130  compared to the bushing  210  surface. 
         [0009]    For the purposes of the present document, including the claims, a cylindrical coordinate system is defined as shown in  FIGS. 1A and 1B . An axial direction, x  140 , is perpendicular to the two parallel planes  120 ,  130  and passes through the center  170  of the sphere  110 . For instance, when the member is a hammer mill hammer, the x-direction (x-axis)  140  is perpendicular to the broader faces of the hammer mill hammer  100 , as seen in  FIG. 1B . An angular or tangential direction, θ  150 , is orthogonal to the axial direction, x  140 , the rotational direction being in accordance with a right-hand coordinate system. The radial direction, r  160 , is orthogonal to both the z-direction  140  and the θ-direction  150 . The r-direction (r-axis)  160  points in any θ-direction  150  beginning at the x-axis. 
         [0010]    The advantages of a spherical joint in hammer mills notwithstanding, the bushing in the race in present-day spherical joints must be pressed or forged together, making manufacture costly and replacement of just the bushing difficult. Heat treating must be done after assembly of the bushing into the race. Hence, there are serious limitations for the materials used for bushing and race. 
         [0011]    Therefore, there is a need for a spherical joint wherein the bushing may be inserted into the race without undue force or material deformation. There is a further need for a method and apparatus whereby the bushing and race may be heat treated separately. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    An object of the instant invention is to provide a method and apparatus for manufacturing and assembling a spherical joint, such as used in hammer mills, such that the bushing may be inserted into the race using only manual force. 
         [0013]    To effect the above objective, slots or broadened regions, centered about a diameter in the circumference of the race—said regions generally slightly wider than the bushing thickness—are formed from a first face of the hammer to the center of the race&#39;s thickness and to the maximum diameter of the race. The second face of the hammer is not modified, so the race appears as a circle at that second face. For assembly, the bushing is inserted in the x-direction into the aforementioned broadened regions in the first face of the hammer to the center of the race where the cylindrical shape of the inner surface of the race disallows further insertion. The bushing is then rotated on an axis parallel to the radial direction, r, to engage it in the race. Once installed on the shaft in the hammer mill, the bushing cannot rotate to a position whereby it may exit the race. 
         [0014]    Because the spherical joint of the present invention may be heat treated before assembly, the heat treatments and materials of the separate bushing and race may be different. 
         [0015]    The novel features believed to be characteristic of this invention, both as to its organization and method of operation together with further objectives and advantages thereto, will be better understood from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood however, that the drawings and examples are for the purpose of illustration and description only, and not intended in any way as a definition of the limits of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]      FIG. 1A  is a plot of a sphere and two parallel planes equidistant from the sphere&#39;s center; 
           [0017]      FIG. 1B  defines a cylindrical coordinate system useful for describing the present invention; 
           [0018]      FIG. 2  is a perspective view of a hammer mill hammer blade with an integral race and bushing installed therein; 
           [0019]      FIG. 3  is a perspective view of the hammer mill hammer blade with an integral race, the bushing is also illustrated but is separated from the race; 
           [0020]      FIG. 4  is a perspective view of the hammer mill hammer blade with an integral race showing how the bushing is inserted into the race; 
           [0021]      FIG. 4A  is a front elevation view of the hammer mill hammer blade with an integral race and bushing installed therein, the bushing features an elongated hole for the shaft; 
           [0022]      FIG. 5  is a front elevation view of the hammer mill hammer blade with an integral race and bushing installed therein; 
           [0023]      FIG. 6A  is a sectioned view of the hammer mill hammer blade with an integral race and bushing installed therein, the section being indicated in  FIG. 5 ; 
           [0024]      FIG. 6B  is the sectioned view of  FIG. 6A  with the bushing removed; 
           [0025]      FIG. 7A  is a sectioned view of the hammer mill hammer blade with an integral race and bushing installed therein, the section being indicated in  FIG. 5 ; 
           [0026]      FIG. 7B  is the sectioned view of  FIG. 7A  with the bushing removed; 
           [0027]      FIG. 8A  is a side elevation view of the hammer mill hammer blade with an integral race and bushing installed therein and the bushing mounted on a shaft showing a range of motion of the hammer mill hammer blade; 
           [0028]      FIG. 8B  is a side elevation view of the hammer mill hammer blade with an integral race and bushing installed therein and the bushing mounted on a shaft, the hammer mill hammer blade shown rotated on the bushing; 
           [0029]      FIG. 9  is a sectioned view of an upper portion of the hammer mill hammer blade with an integral race and bushing installed therein; 
           [0030]      FIG. 10  is a side elevation view of three hammer mill hammer blades with integral races and bushings installed in them, said bushings mounted on a single shaft; 
           [0031]      FIG. 11  is a perspective view of a hammer mill hammer blade with a keeper to maintain the bushing in its installed position; and 
           [0032]      FIG. 12  is a perspective view of the hammer mill hammer blade with the bushing and keeper separated from the race. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIGS. 2-4  show a hammer mill hammer blade assembly  100 , comprising a hammer blade body  210 , and a bushing  220  installed in an integrated bearing race  310 . 
         [0034]    The hammer blade body  210  preferably also comprises a hardened portion  230  where the hammer blade body  210  is likely to impact the material being crushed or ground. 
         [0035]    As described above, the surfaces of the bushing  220  and race  310  generally in contact with one another are spherical in shape. The spherical region on the bushing  220  can be described as generally the outer periphery of the bushing  220 . The spherical region of the race  310  may be described as generally the inner periphery of the race  310 . 
         [0036]    Installation of the bushing  220  into the race  310  is illustrated by the series,  FIGS. 3 and 4 . The race  310  is formed in the hammer blade body  210 , and is modified by two diametrically opposite slots  240 , sized and shaped to receive the bushing  220 . The slots extend in the race&#39;s  310  x-direction  140  from one outer surface  250  to a plane at which the race&#39;s  310  diameter is greatest—at the center of the race  310  in the x-direction  140 . The width h of the slots  240  is preferably slightly greater than the thickness, t (see  FIG. 8A ), of the bushing  220  to permit manual installation of the bushing  220  into the race  310 . The bushing  220  is disposed in an appropriate position, as shown in  FIG. 3 , to enter the slots  240 , with the bushing&#39;s  220  axial direction  140  generally perpendicular to the race&#39;s  310  axial direction  140 . The bushing  220  is then inserted parallel to the race&#39;s  310  axial direction  140  into the slots  240  until the bushing&#39;s  220  greatest diameter reaches the race&#39;s  310  greatest diameter, at which point the bushing  220  cannot progress farther due to the narrowing of the race  310  in that direction. The center points  170  of the spherical surfaces of the bushing  220  and the race  310  are then coincident. This point in the process is shown in  FIG. 4 . 
         [0037]    The bushing  220  is then rotated in the direction  410  shown, the axis of rotation of this direction is parallel to the radial direction,  160 . The bushing  220  may be rotated on an axis of rotation parallel to the x-axis  140  before rotating said bushing  220  about the r-axis  160 , but the final position is the same. 
         [0038]    A modification to the spherical surface of the race  310  may be seen in  FIG. 3 . A groove  320  may be machined, stamped, or otherwise formed at the maximum radius point of the spherical surface of the race  310 . 
         [0039]    Further considering  FIG. 3 , since the bushing  220  and race  310  are separate and may be assembled at any time after those two parts  220 ,  310  are created, heat treatment or other surface treatment may be carried out on the bushing  220  exclusive of the race  310  and on the race  310  exclusive of the bushing  220 . (Heat treatment includes quenching and tempering, annealing, and hardening. Surface treatments include shot peening, laser peening, galvanizing, and case hardening. This is not an exhaustive list, and those of ordinary skill in this art are well versed in the various treatments of the metals used in these spherical joints.) Especially due to this fact, the materials used for the bushing  220  are not limited by the heat or surface treatment of the race  310 , nor are the materials used for the race  310  limited by the heat or surface treatment of the bushing  220 . This adds significant flexibility in manufacture, may reduce material and manufacturing costs, and increase the life of the spherical joint. 
         [0040]    Whereas an aperture  260  in the bushing  220  shown in  FIGS. 2-4  is circular in cross section, the aperture  420  in the bushing  220  of  FIG. 4A  is shown noncircular, in an elongated, oval, elliptic, or egg shape. This alternative is disclosed in U.S. patent application Ser. No. 15/093,199, filed Apr. 7, 2016, now U.S. Pat. No. ______, which is hereby incorporated herein by reference in its entirety. 
         [0041]    To clearly depict the noncircular aperture  420  in the bushing  220 , a shaft  430 , which is circular in cross section, or a right circular cylinder in shape, is shown disposed inside the aperture  420  of the bushing  220 . 
         [0042]    The bushing  220  and race  310  assembly of the present invention is shown in a front elevation view in  FIG. 5 . The section at which  FIGS. 6A and 6B  is viewed is shown in  FIG. 5 . 
         [0043]      FIG. 6A  illustrates a section through the coincident center points  170  of the spherical surfaces of the race  310  and bushing  220 . 
         [0044]    The bushing  220  has been removed from the sectional view of  FIG. 6A  in  FIG. 6B . In this view, the spherical race surface  310  and the groove  320  are exposed. One slot  240  is shown extending from the face  250  on the right of the hammer blade body  210  to a plane midway between the right face  250  and the left face  610 . Relative to the spherical surface of the race  310 , the depth of the slots  240  is greatest at the right face  250  of the hammer blade body  210 . The slots  240  preferably become flush with the spherical surface of the race  310  at the plane midway between the right face  250  and the left face  610 . 
         [0045]    The sectional view of  FIG. 7A  is indicated in  FIG. 5 .  FIG. 7A  is another section through the coincident center points  170  of the spherical surfaces of the race  310  and bushing  220 , this time looking along the length of the hammer blade body  210 . The spherical surface of the race  310  is shown without a groove  320  in  FIG. 7A . 
         [0046]    The maximum diameter of the bushing  220  is shown in  FIG. 7A  as L 1 . 
         [0047]    In the sectional view of  FIG. 7B , the slots  240  may be seen extending from the face  250  on the right of the hammer blade body  210  to a plane midway between the right face  250  and the left face  610 . The remainder of the surface of the race  310  is spherical. 
         [0048]    The distance between the surfaces of the slots  240  is indicated in  FIG. 7B  as L 2 . This distance is preferably slightly greater than the maximum diameter of the bushing  220 , L 1 , in  FIG. 7A  to admit the bushing  220  into the slots  240  without binding. 
         [0049]    The hammer blade body  210  may rotate about the center point  170  of the spherical surface of the bushing  220  as shown in  FIG. 8A . The center points  170  of the spherical surfaces of the bushing  220  and race  310  coincide as long as the bushing  220  is engaged properly in the race  310 . The hammer blade body  210  may rotate until the edges of the race  310  contact the shaft  430 , thereby providing a range of motion  810  and disallowing the bushing  220  to rotate to a position that it may exit the race  310  via the slots  240 . To reach the position required for the bushing  220  to slide out the slots  240 , the x-axis of the bushing  220  surface must be normal to the x-axis of the race  310  surface. It is impossible for the bushing  220 , when engaged to the shaft  430 , to be disposed in this orientation. 
         [0050]    Shown in  FIG. 8B  is the hammer blade body  210  rotated about a radial direction  160  different from the radial direction  160  rotated about in  FIG. 8A . It should be noted, the hammer blade body  210  may be rotated about any radial axis  160 —that is, any radial axis at any angle, θ  150 . 
         [0051]      FIG. 9  shows the detail indicated in  FIG. 6A . The hammer blade body  210  is shown with its integral race surface  310 . The bushing  220  is installed and the groove  320  in the otherwise spherical race surface  310  is indicated. 
         [0052]    A single hammer mill hammer assembly  100  is not typically used alone. A set of three hammer mill hammer assemblies  100  installed on a shaft  430  are illustrated in  FIG. 10 . Material to be ground, shredded, or crushed is struck in different places simultaneously or at different times by the plurality of hammer mill hammer assemblies  100  installed on a shaft as well as hammer mill hammer assemblies  100  installed on other shafts within the hammer mill. Any of the bushings  220  installed in the integral races  310  in these hammer mill hammer assemblies  100  may be removed after the hammer mill hammer assembly  100  is disengaged from the shaft  430  by reversing the process illustrated in the series of figures,  FIG. 3  through  FIG. 4 . 
         [0053]      FIG. 11  illustrates another aspect to the present invention. The integral race  310  is formed in the hammer blade body  210 , and is modified by the two diametrically opposite slots  240 , sized and shaped to receive the bushing  220  just as above. However, the hammer  210  or other item in which the integral race is formed may be used in applications in which the shaft  430  is sometimes removed. In this case, the bushing  220  may be held in place in the race  310 —even when the bushing is rotated to align with the slots  240 —by a keeper  1110 . The keeper  1110  may be attached to the hammer blade body  210 , or other item in which the integral race is formed, by fasteners  1120 , such as machine screws, rivets, or bolts. 
         [0054]    Since little or no load is typically anticipated when the bushing  220  is not engaged on the shaft  430 , the keeper  1110  typically need not be heavy. The race  310  is made adequately strong to withstand the stresses experienced by the hammer blade body  210  or other item when the shaft  430  is engaged in the bushing  220 . 
         [0055]    Assembly of the hammer mill hammer blade assembly  100  with the keeper  1110  is illustrated in  FIG. 12 . The bushing  220  is disposed in an appropriate position, as shown in  FIG. 12 , to enter the slots  240 , with the bushing&#39;s  220  axial direction  140  generally perpendicular to the race&#39;s  310  axial direction  140 . The bushing  220  is then inserted parallel to the race&#39;s  310  axial direction  140  into the slots  240  until the bushing&#39;s  220  greatest diameter reaches the race&#39;s  310  greatest diameter, at which point the bushing  220  cannot progress farther due to the narrowing of the race  310  in that direction. The center points  170  of the spherical surfaces of the bushing  220  and the race  310  are then coincident. 
         [0056]    The bushing  220  is then rotated in the direction  410  shown in  FIG. 4 , the axis of rotation of this direction is parallel to the radial direction,  160 . The bushing  220  may be rotated on an axis of rotation parallel to the x-axis  140  before rotating said bushing  220  about the r-axis  160 , but the final position is the same. Finally, the keeper  1110  is applied and operatively fastened by fasteners  1120 , such as machine screws, rivets, or bolts, to the hammer blade body  210  to maintain the bushing  220  in place even if it rotates to be aligned with the slots  240 . 
         [0057]    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.