Abstract:
A method for sharpening radially extending teeth on a disk included: 1) sharpening a tooth by moving the disk relative to a cutting head, 2) separating the disk from the cutting head, 3) indexing the disk to the next tooth, 4) engaging the cutting head with the next tooth, and repeating steps 1)-4) until sharpening is complete. A machine for sharpening teeth includes: a table movable in the x-y plane, an angle plate mounted on the table for holding a disk, a digital indexer for rotating the disk, a cutting head for sharpening the teeth, and a computer for the controlling the movement of the disk relative to the cutting head by sequentially moving the disk via movement of the table and rotation of the disk on the angle plate. A rotary cutting head has a cutting element affixed at a periphery of the head.

Description:
RELATED APPLICATION 
     This application claims the benefit of co-pending U.S. provisional patent application Ser. No. 61/760,687 filed Feb. 5, 2013, incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention disclosed herein is directed to the sharpening of radially extending teeth on the surface of a disk. 
     BACKGROUND OF THE INVENTION 
     There are several processing machines that use disks having a plurality of radially extending teeth on the surface of the disk, see  FIG. 2 , to reduce the size of particles. In general, the equipment uses two disks, with the surface having the teeth facing one another, spaced apart, so the teeth do not touch. The material to be reduced in size is fed between the disks as at least one disk rotates relative to the other. Such equipment may include, for example, pulverizers and powder mills. This equipment may be used to reduce the size on any material, such as, but not limited to, flour, wood, plastic resin, and recycled plastic. 
     During operation, the teeth become dull. With dulling, the efficiency of the equipment&#39;s size reduction capacity is diminished. Accordingly, the teeth are periodically sharpened. To date, the teeth sharpening process has been a ‘grinding’ process. Grinding, as used in the machining arts, refers to an operation using an abrasive wheel. In the grinding process, sharpening is performed by a grinding wheel (typically made with either diamond or poly cubic boron nitride (PCBN)) in a ‘wet’ process. In the wet process, the coolant, for example, oil (for diamond wheels) or synthetic or semi-synthetic oil (for PCBN wheels), is used to cool the grinding wheel and the teeth, and to remove swarf scraped from the teeth by the grinding wheel. These grinding wheels are expense (costing between $1800-3000) and the grinding machine is expensive (typically about $500,000) too. This process is also time-consuming (typically, depending on the extent of wear, from 2-4 hours per disk). Grinding typically requires 2-4 passes of the grinding wheel per tooth to completely sharpen the tooth and the speed of grinding is typically about 12 inches/minute. All of the foregoing makes the typical cost to sharpen the teeth on a disk, by grinding, about 10% of the cost of a new disk each time it is processed, and the lead time for sharpening can be great. 
     Accordingly, there is a need for new method to sharpen the radial teeth on the surface of a disk. 
     SUMMARY OF THE INVENTION 
     A method for sharpening radially extending teeth on a disk included: 1) sharpening a tooth by moving the disk relative to a cutting head, 2) separating the disk from the cutting head, 3) indexing the disk to the next tooth, 4) engaging the cutting head with the next tooth, and repeating steps 1)-4) until sharpening is complete. A machine for sharpening teeth includes: a table movable in the x-y plane, an angle plate mounted on the table for holding a disk, a digital indexer for rotating the disk, a cutting head for sharpening the teeth, and a computer for the controlling the movement of the disk relative to the cutting head by sequentially moving the disk via movement of the table and rotation of the disk on the angle plate. A rotary cutting head has a cutting element affixed at a periphery of the head. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, there is shown in the drawings a form that is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. 
         FIG. 1  illustrates an embodiment of the inventive machine. 
         FIG. 2  illustrates a disk having a plurality of radially extending teeth disposed on a surface thereof. 
         FIG. 3  is an illustration of a cutting head used in the inventive machine/process. 
         FIGS. 4A-4E  illustrate the relative position of the disk in relationship to the cutting head during various steps of the inventive process. 
         FIGS. 5A-5C  illustrate the cycle of sharpening from a new sharpened disk ( FIG. 5A ) to a dulled tooth ( FIG. 5B ) to a sharpened tooth ( FIG. 5C ). 
     
    
    
     DESCRIPTION OF THE INVENTION 
     To better illustrate the instant invention, there is shown in  FIG. 2 , the disk  22  with a plurality of radially extending teeth  24  standing up on a surface  26  of the flat metal disk. This disk  22  may be used in, for example, a pulverizer, as discussed above. The disk  22  may also be referred to hereinafter as a work piece. 
     The invention uses a dry milling operation to sharpen the teeth. Milling, as used in the machining arts, refers to removal of material with a cutting head, e.g., a rotating cutting head, having one or more cutting elements. Dry refers to a process where no coolant is necessary, but it may be used. Milling is different from grinding. Grinding uses an abrasive wheel to remove material. 
     Referring to the drawings, where like numerals are to like elements, there is shown in  FIG. 1  an illustration of the inventive sharpening machine  10 . 
     Machine  10  generally comprises: a table  12  moveable in the x-y plane, an angle plate  14  mounted on table  12 , a digital indexer  16  associated with angle plate  14 , a cutter head  18  positioned above the angle plate  14 , and a computer  20  for controlling the movement of the disk  22  and the cutter head  18 . Machine  10  is a milling machine purposed for, among other things, the sharpening the radially extending teeth on the surface of a disk. 
     The table  12  is adapted to move in the x-y plane, for example a horizontal plane. Movement of the table, in the x-y plane, is controlled by the computer  20 . Table  12  is conventional as is the control of its movement by the computer. 
     The angle plate  14  rides (or is mounted) on table  12  and may be removably affixed thereto. Angle plate  14  is adapted to hold a disk  22 . The disk  22  is affixed, in any conventional manner, to the angle plate  14  during the sharpening operation, and removed after sharpening is complete. The angle of the plate  14  to the table  12  is adjustable. The angle may be defined by the cut needed to sharpen a tooth  24  on the disk  22 . This angle may be manually set by an operator or may be controlled by the computer  20 . Any angle may be possible, from 0°-90°. Typical angles may be in the range of: 15°-75°, or 20°-70°, or 30°-60°, or any subcombination of angles between 0°-90°. The angle of the disk  22  to the cutting head  18  may be at any angle. For example, if the tooth has a cross section of an equilateral triangle (all angles=60°), then the angle of the disk to the cutting head would be 60°. 
     The digital indexer  16  is associated with angle plate  14 . The digital indexer  16  is adapted to rotate disk  22  from one tooth  24  to next tooth  24  during the sharpening operation. The degree of rotation is controlled by computer  20  and may vary from disk to disk depending upon the number of teeth on the disk. The digital indexer is conventional. 
     The cutter head  18  is positioned above the angle plate  14 . Cutter head  18  is a rotary cutting head. The cutting head  18  may be rotated at any speed. In one embodiment, the rotating speed of the cutting head may be in the range of 200-2000 rpm. Rotating speed will depend on several factors, including, but not limited to: cutter head diameter, surface speed (feet per minute) relative to the outside diameter of the cutter head, material being cut, depth of cut. Cutter head  18  is in a fixed position in relationship to the x-y (i.e., horizontal) plane but may be movable in the z direction (i.e., vertical direction). Disk  22  is moved passed the cutter head  18  by operation of the table  12  and digital indexer  16 , both being controlled by computer  20  as will be discussed in greater detail below, and at a given angle, as defined by the angle plate  14 . 
     One embodiment of the cutter head  18  is illustrated in  FIG. 3 . The cutting head  18  uses at least one cutting element  34  set to make the cut. Cutting (or milling) is accomplished by rotating the head  18  and engaging the cutting element  34  with the work piece (or tooth face on the disk). Generally, cutter head  18  may have a body  30 , for example, a cylindrical body having a peripheral edge (periphery)  32 , and at least one cutting element  34 . The cutting element(s)  34  are located along the periphery  32  of the body  30 . In one embodiment, the cutting element  34  is removably affixed to the body  30  via conventional locking mechanism  36 , but the cutting element  34  may be permanently affixed to the body  30  of the cutting head  18 . 
     The cutting angle (also known as the rake angle) may be a negative, neutral, or positive cutting angle. In one embodiment, the cutting angle is a negative cutting angle. The negative cutting angle (or negative rake angle) may be any negative angle. The negative cutting angle is used to stabilize the cut. In one embodiment, the cutting angle is in the range of 0° to −20°. In another embodiment, the cutting angle is in the range of −10° to −1°. In yet another embodiment, the cutting angle is in the range of −7° to −3°. In yet another embodiment, the cutting angle may be −5°. 
     The cutting element  34  may be any cutting element. Cutting elements are commercially available and come in various shapes and are made from various materials. In an embodiment, the cutting element may be any cutting element with an angle of less than 90°. In one embodiment, the cutting element may be rhombus-shaped. The angle of the rhombus may be any angle; in some embodiments the angle may be 30° or 55°. In another embodiment, the cutting element  34  may be those designated as D or V (rhombus-shaped with 55° and 30° angle, respectively). In yet another embodiment, the cutting element  34  may be designated as DN or VN (the N refers to a negative cutting angle). The cutter element  34  may be made of any material. In one embodiment, the cutting element  34  any material, although carbon based materials, i.e., diamonds, are less preferred. In another embodiment, the cutter element  34  may be made of poly cubic boron nitride (PCBN). In yet another embodiment, the cutting element  34  may have a hardness at least 20 points greater, on a Rockwell scale, than the material being cut. 
     The computer  20  is used to control the movement of the disk  22  (work piece) about the cutting head  18  and raise and lower the cutting head  18  relative to the work piece. The computer  20  may be any computer capable of controlling the movement of the table  12 , the digital indexer  16 , the cutting head  18 , and, optionally, the angle plate  14 . In one embodiment, the computer  20  is computerized numerical controller (or CNC). The computer is programmable, so that after programming and set up, the computer can be used to repeat the steps of the sharpening operation. Programming is conventional and within the skill of the art. 
     The operation of the machine  10  is illustrated in  FIGS. 4A-4E . 
       FIG. 4A  illustrates cutter head  18  positioned above angle plate  14  and disk  22 . Disk  22  is affixed to angle plate  14  using, for example, a plurality of set pins  50  and set screws  52 . The cutter head is movable in the z (vertical) direction  60 . The disk  22  is movable in the x-y plane  62 / 64 . The table  12  (not shown) is moved away (in the figure to the left) from the cutter head  18 , so that the work piece  22  may be affixed to the angle plate  14 . 
       FIG. 4B  illustrates the zeroing (or initializing) operation. In this operation, the cutter head is positioned relative to the tooth of the disk  22  to be sharpened. This information is input into the computer  20 , so that the computer  20  knows the relative position of the cutter head  18  to the work piece  22 . For this zero position, the subsequent movement of the work piece  22  and the cutter head  18  are guided through the sharpening operation. From the position shown in  FIG. 4A , the work piece  22  is moved to the right and the cutter head  18  is moved down. 
       FIG. 4C  illustrates the sharpening (or cutting) operation. After zeroing, the cutter head  18  begins rotation and the work piece  22  is moved (to the left) by operation of the table  12  (not shown). The movement of the cutting head across the surface of the tooth may be at a rate, for example, greater than or equal to 100 inches/minute. 
       FIG. 4D  illustrates the completion of the sharpening of one tooth  24 ′. After the cutting head has made on complete pass over the tooth, the cutting head  18  is lifted from the work piece  18  and the work piece is indexed (arrow  66 ) to the next tooth. 
       FIG. 4E , similar to  FIG. 4B , shows that after the completion of the sharpening of one tooth, the work piece  22  is moved (to the right) and the cutter head  18  is moved down, so that the next tooth may be sharpened. 
     The foregoing series of steps is repeated until all the teeth have been sharpened. By using the foregoing method, sharpening time may be reduced to about 45-60 minutes, and only one pass per tooth is needed. Further, the method may be accomplished without the use of coolant. 
       FIGS. 5A-5C  illustrate the impact of the sharpening operation on the disk  22 . In  FIG. 5A , a new (or newly sharpened) disk  22  with a single tooth  24  standing on the disk&#39;s surface  26 . The height h of the disk is shown.  FIG. 5B  illustrates a worn tooth  24 ′ in need of sharpening, Note that some of the surfaces of the tooth are rounded with wear, but the height h of the disk remains the same as shown in  FIG. 5A .  FIG. 5C  shows a freshly sharpened disk  22 . Note that the height h′ is shorter than h in  FIG. 5A . During the sharpening operation, metal is cut away from the disk, whereby the thickness of the disk is reduced (i.e., h&gt;h′). The disk, thus, may only be sharpened a finite number of times. The number of times for sharpening depends, among other things, on the thickness of the disk and the amount of material cut from the disk during sharpening. 
     The present invention may be embodied in other forms without departing from the spirit and the essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.