Abstract:
An improved grinding apparatus or hammermill utilizing retractable bars as a hammermill screen, or as a support to a conventional hammermill screen. The ability to retract these bars which make up the screen of the hammermill assembly reduces the down time associated with inspecting, replacing, and repairing the bars, and clearing jammed material caught within the screen. When the retractable bars support a hammermill screen, retraction of the bars allows the screen to drop down from the hammermill for repair and cleaning.

Description:
PRIORITY  
       [0001]    This application incorporates by reference and claims priority from previously filed provisional application Ser. No. 60/249,401, filed on Nov. 15, 2000, entitled “Retractable Rod Screens.” 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention generally relates to grinders and hammermills, and, more particularly to grinders with a screen adjacent to a rotating hammermill.  
           [0003]    Grinding machines, including those utilizing grinding means such as hammermills, grinders, drum chippers, and wheel chippers, are used for varying applications. These applications can include, amongst others: grinding tree stumps and slash from logging operations; grinding construction debris from buildings damaged by natural disasters, such as hurricanes or floods; shredding animal feeds, grinding used automobile tires, grinding wood, and grinding landfill material for compaction or disintegration purposes.  
           [0004]    Many different kinds of grinders and hammermills are known in the prior art, including U.S. Pat. No. 4,997,135 to Zehr and U.S. Patent Number  5 , 720 , 440  to Bonner et al. Generally, these grinders/hammermills utilize a hammermill assembly formed of a rotatable shaft to which radially extending hammers are affixed, interfitted within a semicircular hammer mill screen, such as is shown in FIG. 3 of Bonner (U.S. Pat. No. 5,720,440).  
           [0005]    In use, the material to be ground is dropped into a hopper from which it passes into the screen chamber containing the rotating hammermill hammers, where it is broken apart and/or pulverized. Other configurations of grinders and shredders exist, each with a hammermill and a screen. The hammermill screen serves as a sieve, allowing ground material smaller than the sieve hole size of the hammermill screen to pass through, or literally to be thrown through the screen into a chute and onto some sort of discharge system, conveyor, auger, or other device by which it is carried away. Hammermill/grinder screens shown in the prior art include: screens having screen holes (Bonner), a “grate” (Zehr), a plate/grate system (Graveman), and curved ribs and spaced bars (Williams).  
           [0006]    A typical problem with such grinding devices arises when a piece of material becomes lodged between the hammermill screen and the hammers, causing a jam. Material may also become wrapped around the hammermill, or clogged in the holes of the hammermill screen, and wrapped around the screen. The prior art method of relieving such a jam is, as described in Bonner, disassembling the grinding device in order to manually dislodge the material jammed therein. This step is time consuming and labor intensive. Some grinders are designed so that the screen of the grinder is in the shape of a section of a cylinder, which is removed by rotating it from adjacent the hammermill to a position in the feed intake of the hammermill. Even though the screen is typically made of thick metal, it may have been bent during operation, and rotating it and removing it is a demanding and time consuming job.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an improved screen, particularly for hammermills, horizontal grinders, tub grinders, shredders, and other grinding apparatuses. The device of the invention can be utilized in any shredder or grinder which uses a rotating hammermill with an adjacent screen through which material is ejected.  
           [0008]    The device is an improved grinding apparatus for use in grinding or commuting material. The improved grinding apparatus includes a frame for supporting the grinding apparatus, an inlet for receiving material to be ground, and a grinding means which is operatively connected to the inlet and typically mounted on a drive shaft. The grinding means is typically a hammermill and comminutes material to a smaller size. The device also includes a screen mounted around the hammermill or grinding means, and thus defining a screen chamber around the hammermill. Material enters the hammermill and is struck by hammers of the hammermill and driven through or into the screen. The screen of the improved grinding device is formed from a number of bars which extend parallel to and adjacent to the grinding means. The bars have a long axis, and the long axis of the bar is parallel with the long axis of the hammermill or grinding means. One or more of the bars may be extracted from the screen chamber, and inserted into the screen chamber by pulling or pushing on the bar, in a direction parallel with the long axis of the bar.  
           [0009]    A bar extraction means is also utilized. Typically, the bar extraction means would be formed from a bar extraction tool of various designs. Bar extraction tools can be formed based on propulsion from hydraulic cylinders, mechanical pullers which use leverage or mechanical advantage, electrically driven screws, or pneumatically driven drives. The bar extraction tools of the invention attach to the bars which form the screen chamber and either push the bars into place around the hammermill, or pull them out of the hammermill region. The grinding device of the invention can be configured to include one extraction tool which is attachable sequentially to each of the bars around the hammermill, and is thus able to insert or remove any of the bars around the hammermill. The bar extraction tools can be configured so that there is one bar extraction tool for each of the bars around the screen chamber of the hammermill. The device of the invention may also include a first end wall and a second end wall which are attached to a right rail and a left rail of the frame. The first and second end walls further define the screen chamber. The first and second end wall contained openings, called bar passages, through which the bars pass in and out of the screen chamber, and on which the bars rest for support and positioning around the hammermill.  
           [0010]    In one form, the present invention is utilized on a particular type of grinding apparatus known as a tub grinder. This tub grinder is utilized for comminuting a supply of material. Such a tub grinder will have a frame supporting the grinder&#39;s components, and may have the frame mounted on a locomotion means such as tires or treads. One type of tub grinder has a rotatable drum assembly which is mounted to the frame, with the drum assembly configured to rotate in relation to the frame. Although the device works equally well with stationary tubs, one configuration of the device operates with a rotating drum. The drum assembly has a rotatable sidewall adjacent to the frame, as well as a stationary tub bottom surface inside the side wall. The side wall is open at the top and able to receive the supply of material into a rotating drum space defined therein. The device of the invention also works with horizontal grinders, and other types of hammermills.  
           [0011]    Although the operation of the device is described in use primarily with a tub grinder, it would work equally well with a variety of grinder configurations. The bottom surface of the tub grinder includes an opening in which the hammermill assembly is mounted. The hammers of the hammermill assembly typically extend into the rotating drum space, in the case of a drum grinder, and grind material which is brought into contact with the hammers of the hammermill. The rotatable drum assembly attaches to the frame and its rotation causes material to be pushed into the hammers in the hammermill opening, and by agitation prevents the bridging or arching of material over the hammermill. Such a tub grinder has a drive mechanism for rotating the rotatable sidewall, which causes material inside the sidewall to be pushed into contact with the hammermill assembly. Versions of hammermills with non-rotating drum assemblies are also possible, and may go by the name of shredders, horizontal grinders, chippers and mills. The retractable rod screen of the invention may also be utilized with these non-rotating drum assemblies.  
           [0012]    The grinding mechanism of the invention comprises a hammermill assembly having a rotatable hammermill with attached hammers. Positioned below such a rotatable hammermill is a hammermill screen which is attached to the frame of the grinder, which may be a tub grinder. The hammermill screen comprises a plurality of bars mounted in the frame compartment adjacent to the hammermill. The bars act as any hammermill screen does, and are for impacting and breaking material thrown from the hammermill and hammermill hammers, and for rejecting material pieces which do not fit between the bars back to the hammermill for additional comminution. The hammermill screen and rotatable hammer define a hammermill chamber.  
           [0013]    The frame further includes at least one bar extraction tool attachable to the frame and attachable to at least one of the bars. The bar extraction tool is for selectively removing the bars from the hammermill (or “working”) chamber. In one embodiment, the bar extraction tool is one or more hydraulic cylinders which are attachable to the frame and to the bars for extraction and insertion of the bars into and out of the hammermill chamber from and to the side chamber. This allows the bars to be removed for installation, replacement, inspection, apparatus maintenance, and/or repair. It is preferred that the bars of the hammermill screen be positioned in the frame in an arc corresponding to an arc of rotation of the hammers of the hammermill, thereby defining a generally partially-cylindrical hammermill chamber.  
           [0014]    Another version of the invention uses the retracting bars of the hammermill to support a conventional curved hammermill screen, which is suspended from two or more of the retractable bars. By this version of the device, the hammermill screen can be dropped out the bottom of a hammermill, instead of being rotated to the exposed upper portion of the hammermill for removal. The retractable rods are withdrawn, and the hammermill screen drops out for cleaning, repair, and replacement. The hammermill screen used in this way and supported by the retractable rods can be used with a rotating type grinder, or another configuration of grinders such as a horizontal grinder.  
           [0015]    Accordingly, it is an object of the present invention to provide a hammermill screen with a reduced frequency of jamming, the option of changing the sizing of product, and a quicker removal of screens. It is another object of the present invention to provide a hammermill screen for quickly and easily clearing jams should they occur. It is another object of the present invention to simplify the installation, replacement, inspection, maintenance and/or repair of the hammermill screen.  
           [0016]    Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a partial, cross-sectional view of the hammermill assembly of a grinder type known in the prior art.  
         [0018]    [0018]FIG. 2 is a partial, cross-sectional view of one embodiment of the present invention.  
         [0019]    [0019]FIG. 3 is a perspective, partial view of one embodiment of the present invention.  
         [0020]    [0020]FIG. 4 is an end view of a screen chamber first end wall utilized with the present invention.  
         [0021]    [0021]FIG. 5 is a side, environmental view of an embodiment of the present invention.  
         [0022]    [0022]FIG. 6. is a side view of an embodiment of the invention.  
         [0023]    [0023]FIG. 7 is an end view of the invention in which retractable rods support a conventional hammermill screen.  
         [0024]    [0024]FIG. 8 is a perspective view of a hammermill screen which is supportable by retractable rods. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.  
         [0026]    Referring initially to FIG. 1, shown is a prior art type of grinding apparatus, namely a tub grinder. This tub grinder has a hammermill assembly  4  utilizing a driven, rotating hammermill having a plurality of hammers  24  which break apart refuse until it is small enough to fit through holes  6  within a hammermill screen  2 . This arrangement is fine for certain applications, but other applications require much larger holes. In a screen such as this, which is formed into a semi-cylindrical shape which wraps around the hammers of the hammermill, removing the screen for repairs, replacement, or to remove jammed materials can become problematic. If it is jammed sufficiently tight, the hammermill itself may have to be removed so that the screen  2  can be accessed and freed. The normal procedure for replacing the hammermill screen  2  is to rotate the screen into the open region above the hammermill. This can be very difficult to do if the screen is warped or bent.  
         [0027]    Referring now to FIG. 2, one embodiment of the present invention is shown. The improved grinding apparatus  10  has a frame  12  to which a housing  20  is attached. Located within the housing  20  is a grinding means, preferably a rotatable hammermill assembly  30 . The rotatable hammermill assembly is formed of a driven, rotatable shaft  32  to which radially extending hammers are attached in the standard manner for either swinging or fixed hammers. Located within the housing  20  is a hammermill screen  40 . This hammermill screen defines a screen chamber  42  which exists between the screen (a plurality of retractable bars  44 ) and the rotatable hammermill itself.  
         [0028]    In one configuration of the invention, these retractable bars  44  are retractable from the screen chamber  42  and away from the hammermill to a region adjacent to the screen chamber. These bars have first and second ends, wherein the second end  54  of the bars are supported by the screen chamber second end wall  48 , and the first ends  52  of the bars  44  are supported by the screen chamber first end wall  46 . Being so supported, the bars  44  serve as a rigid screen means for use in comminuting material. The preferred bars are rectangular in cross-section, and are oriented with one of the narrower sides of the rectangle facing the hammermill, as shown in FIG. 3 and FIG. 4. Other cross-sectional shapes of bars are possible, such as round, square, triangular, oval, etc.  
         [0029]    Referring back to FIG. 2, located above the hammermill assembly is a rotatable drum assembly  80 . In other embodiments, the drum assembly itself may not rotate or other assemblies may be utilized instead of a rotating drum, such as horizontal oriented grinders. Other configurations might include feeding directly into the hammermill, or feeding horizontally into the hammermill. The rotatable drum assembly  80 , shown in FIG. 2, has a rotatable sidewall  82  which is rotatably connected to a stationary bottom surface  84 . The sidewall, the bottom surface and the open top  86  define a rotating drum space  88 . In use, material to be ground is placed within the rotating drum space  88  for ultimate feeding through an inlet or opening  22  and into the screen chamber  44  for comminution. In this configuration of such a grinder, the hammers partially extend into the rotating drum space  88 , and as the rotatable sidewall turns, material is brought into contact with the partially exposed hammers.  
         [0030]    Referring now to FIG. 3, a portion of one preferred embodiment of the present invention  10  is shown in perspective view. This figure shows the improved hammermill screen  40  with other structures absent. In this view, the screen chamber first end wall  46  and screen chamber second end wall  48  are shown. These would be mounted on the grinder frame  12 . These end walls  46  and  48  further define a plurality of bar passages  18  for receiving the retractable bars  44  utilized with the present invention. The retractable bars  44  furthermore are attachable to one or more bar extraction means, which is a bar extraction tool  60 . One bar extraction tool  60  could be interconnected to one or to all of the of retractable bars  44 . Individual bar extraction means, or bar extraction tools  60 , could be connected to each individual bar  44 , as shown in FIG. 3. The bar extraction tool(s) could comprise any number of devices, including but not limited to cables, electric or hydraulic motor driven screws, mechanical pullers, explosive pullers, pneumatic pullers, levers, hydraulic rams, etc. The embodiment shown in FIG. 3 shows one hydraulic cylinder bar extraction tool  60  attached to each retractable bar  44 . As shown in FIG. 3, the retractable bars  44  can be pulled from the screen chamber towards the left of the drawing in FIG. 3 or FIG. 2. This would normally be the practice in order to clean or inspect a retractable bar  44 . Another desirable alternative is to be able to push the retractable bars  44  to the right of the view shown in FIGS. 2 and 3, so that the bars may be replaced from that end, and the replacement bars pulled into place in the screen chamber  40 . Pushing the bars to the right of the view shown in FIGS. 2 and 3 could also be utilized for repairs, cleaning, and inspection of the retractable bars  44 .  
         [0031]    [0031]FIG. 4 shows an end view of one embodiment of a screen chamber first end wall  46  utilized with one embodiment of the present invention. Such an end wall  46  would be attached to the grinding apparatus or tub grinder through attachment to the frame of the apparatus. A second end wall  48  would be likewise oriented and attached. In the embodiment shown, the frame further comprises subcomponents: a left rail  14  and right rail  16 . Attachment could be through any of the standard manners including but not limited to welding, bolting, or other fastening means. The bar passages  18  located within the screen chamber first end wall  46  are shown in a position wherein they would be adjacent to the rotating hammermills of the rotatable hammermill assembly when installed, and in the preferred radial and partially cylindrical orientation. The bars  44  could be shaped to have a rectangular cross-section, as shown in the figures, or other cross-sectional shapes, such as square, triangular, round, etc. In one preferred embodiment, the bars  44  are four inches by six inches in cross-sections, of solid steel, and are ten feet in length. The bar extraction tools  60  are five inches by ninety-two inches in size. The end walls  46  and  48  are of two-inch thick steel.  
         [0032]    Referring now to FIG. 5, an environmental view of one embodiment of the present invention is shown. This embodiment shows the typical configuration of a portable grinding apparatus or tub grinder  10 , being able to move to tracks  96  on wheels. Other configurations might include a stationary grinding apparatus or tub grinder  10 . This figure shows that the driven shaft  32  attaches to a drive means or engine  8 . Grinding apparatuses or tub grinders  10 , such as shown here, are typically able to move on tracks  96  or wheels. Such a drive shaft  32  can be driven as shown in the prior art, including, but not limited to: electric motors, hydraulic drives, gas engines, and diesel engines. As shown in FIG. 5, when the bars  44  are in operation, they are pushed into the screen chamber  42 . The bars  44  can be pulled from the screen chamber  42  to the region right or left of the screen chamber  42 , for cleaning, repairing, replacing, etc. The bars  44  are connected to hydraulic cylinder bar extraction tools  60  which are connected to each individual bar  44 . The hydraulic cylinder bar extraction tool  60  is attached to and mounted on the frame  20  of the grinding machine. When retracting the bars  44 , material is removed by the sidewall  46  so that any material jammed or wrapped around the bars  44  falls down to the discharge system below the screen chamber  42 .  
         [0033]    [0033]FIG. 6 shows another preferred embodiment of the invention. In this embodiment, the retractable bars  44  support a conventional hammermill screen. The hammermill screen  2  is configured to rest on retractable rods  44  by rod brackets  64 , which may encircle the retractable rods  44 , or may partially encircle retractable rods  44 . In this embodiment, when retractable rods  44  are withdrawn, the hammermill screen  2  drops down from the hammermill, and does not have to be rotated around it and lifted up for removal. The hammermill screen can be installed in the reverse manner, by raising the hammermill screen  2  into position adjacent the hammermill, and then extending the retractable rods  44  through rod brackets  64 . Although FIG. 6 shows the hammermill screen  2  supported by  2  retractable rods  44 , more or fewer retractable rods can be used to support and position the hammermill screen  2 .  
         [0034]    [0034]FIG. 7 shows another version of the device in which four of the retractable bars  44  are used to support a conventional hammermill screen  2 , which further includes support brackets  90 . FIG. 8 shows a perspective view of this conventional hammermill in a version which has fairly large sized holes. The support brackets  90  define bar passages  92  through which the retractable bars  44  extend in order to support and position the hammermill screen  2 . A hammermill screen, as shown in FIG. 8, would be utilized to grind a number of materials, including wood, solid waste, building materials, and any other type of material for which hammermills are utilized.  
         [0035]    While there is shown and described the present preferred embodiment of the invention, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims.