Abstract:
This fiber chopper overcomes the disadvantages of the previous cutting rollers for chopping continuous filaments. The apparatus includes a means for feeding continuous fibers through apertures in a fixed head. End mills engage the continuous fiber and chops them into discrete fiber lengths.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to an apparatus and process for chopping continuous fibers into discrete fiber lengths. More specifically, the apparatus uses an end mill to chop the discrete fiber lengths.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fiber choppers typically use cutting rollers to break continuous rovings into individual short fiber lengths. These choppers use a hard rubber back up roll as an anvil which cooperates with the cutting roller carrying one or more transversely extending blades. The back up roll and cutting roller cooperate to chop a discrete fiber length off the continuous roving each time a rotor blade contacts the back up roll.  
           [0003]    These cutting rollers work well for producing chopped fibers such as conventional chopped glass fibers.  
           [0004]    Continuous filaments include a single filament or a plurality of filaments in a strand, with the filament having continuous length or substantial length, e.g., greater than one foot. A plurality of filaments is a plurality of segments of a single filament in adjacent relationships, such as occurs when a single filament is wrapped around a bobbin tube. Formation of the filaments also normally involves treating the filaments with a size to enhance the properties of the fiberglass in subsequent operations.  
           [0005]    Recent advances, however, in after coatings for continuous filaments make the fibers more difficult to chop. The filaments are stiff and tuff and often have rubbery coatings. Conventional cutting rollers often don&#39;t cut the stiff fibers. Results often leave the fibers bent or kinked. The typical result is not the clean cut industry desires. Further, the cutting rollers often break blades or do not penetrate the rubbery coatings.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    I have developed a process and apparatus which overcomes the disadvantages of the previous cutting rollers for chopping continuous filaments. My apparatus for chopping continuous fibers into discrete fiber lengths includes at least one fixed head having a first side, a second side with at least one aperture through the fixed head. The apparatus also includes at least one means for feeding at least one continuous fiber through the aperture from the first side of the fixed head. At least one end mill on the second side of the fixed head engages the continuous fiber and chops them into discrete fiber lengths.  
           [0007]    Preferably, the fixed head has a plurality of apertures therethrough and a plurality of means feeding continuous fibers to the apertures. Preferably, a plurality of end mills chop the continuous fibers into chopped fibers of a shorter length. The cutting end of the end mills may have flat cutting edges, center cutting edges or specific designs such as ball nose cutting ends with spiral grooves or flutes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a side view of the apparatus for continuously chopping fiber strands into chopped fibers.  
         [0009]    [0009]FIG. 2 is a side view of a conventional end mill.  
         [0010]    [0010]FIG. 3 is an end view of a conventional end mill.  
         [0011]    [0011]FIG. 4 is a side view of a center cutting end mill.  
         [0012]    [0012]FIG. 5 is an end view of a center cutting end mill.  
         [0013]    [0013]FIG. 6 is a side view of an end mill with multiple cutting edges.  
         [0014]    [0014]FIG. 7 is an end view of an end mill with multiple cutting edges. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The apparatus of this invention chops continuous fibers into discrete fiber lengths. The chopper comprises at least one fixed head having a first side, a second side and at least one aperture therethrough. A means feeds at least one continuous fiber through an aperture from the first side of the fixed head. An end mill on the second side of the fixed head engages the continuous fiber and chops them into discrete lengths. Preferably, the fixed head has a plurality of apertures therethrough and a plurality of means feed continuous fibers through the apertures. Preferably, the chopper also has a plurality of end mills for engaging the continuous fibers. Preferably, the fixed head has a circular shape and the end mill rotates in a circular path. Preferably, the apertures in the fixed head are a slot or circular hole. The means for feeding the continuous fiber generally is a pair of nip rollers. In general, the means for feeding the continuous fiber aligns the fiber transverse to the end mill. A hollow tube between the nip rollers and fixed head may be used to feed and align the continuous fibers.  
         [0016]    [0016]FIG. 1 shows chopper  10  having nip rollers  12  feeding continuous fibers  14  through apertures  16  of fixed head  18 . End mill  20  engages fibers  14  and chop them into discrete fiber lengths. Tube  22  aids in feeding fibers  14  to apertures  16 . Preferably, tube  22  extends into aperture  16 . End mill  20  has movement in a horizontal or perpendicular direction with respect to fibers  14  as indicated by the arrows. This movement increases the cutting edge of mill  20 . Tube  22  is an adjustable tube and moves in a vertical direction as indicated by the arrows. Adjustable tube  22  aids in the chopping process of fibers  14 .  
         [0017]    Tube  22  oscillates up and down and coordinates with the revolution of end mill  20 . End mill  20  also revolves to prevent the cutting edge from heating up. Revolutions typically are about 60 rpm&#39;s. The tube&#39;s inside diameter usually rasnges from {fraction (1/1000)} to a few 10000&#39;s of an inch.  
         [0018]    [0018]FIGS. 2 and 3 show a conventional end mill tool with flat cutting edges. End mill  30  is made of cylindrical rod stock which has been ground to form distinctive portions. At one end of tool  30  is shank portion  32 , suitable for chucking to the spindle of a milling machine (not shown) for rotating and advancing tool  30 . At the other end of tool  30  is cutting end  34  which is provided with flat cutting edges  36  and  38 . Between shank portion  32  and cutting end  34  is body portion  40  which is helically ground to have a number of flutes  42  and  44 . A “boundary” between body portion  40  and shank portion  32  is designated  46  in the drawing.  
         [0019]    Any of the end mills used in this invention may be made of polycrystalline diamond (CBN) or polycrystalline cubic boron nitride (PcBN) and may be manufactured using conventional methods.  
         [0020]    [0020]FIG. 4 shows ball nose end mill  50  using these materials. Mill  50  comprises end mill body  52  having four helical flutes  54  circumferentially and equidistantly spaced around body  52 . Body  52  of ball nose end mill  50  may be fabricated from a hard and tough material such as cemented tungsten carbide. The term “diamond” is used herein interchangeably to denote polycrystalline diamond, polycrystalline cubic boron nitride, or both. Groove  56  is formed in leading edge  58  adjacent flutes  54 . A sintered polycrystalline diamond or PcBN  60  is formed in situ in the helically formed groove  58 . Cutting edges  62  are ground into the sintered diamond material  60  in grooves  58  in end mill body  52 . Tungsten carbide end mill body  52  may then be metallurgically bonded to a steel or carbide shank  64  along juncture  66 . The metallurgical bond may, for example, be a braze.  
         [0021]    [0021]FIG. 5 shows end  68  of ball nose end mill  50  and further illustrates grooves  58  adjacent leading edge  58  of flutes  54 . Polycrystalline diamond or polycrystalline cubic boron nitride  60  is compacted and sintered within the grooves  58 . Flutes  54  and cutting edge  62  are ground into the PCD or PcBN material after the sintering process is complete. The PCD or PcBN cutting edge can be formed by methods which include grinding, wire electrical discharge cutting (wire EDM), and electrical discharge grinding (EDG).  
         [0022]    [0022]FIGS. 6 and 7 show end mill  80  having multiple cutting edges. FIGS. 6 and 7 show end mill  80  including shank portion  82 , point  84  and body portion  86 . End mill  80  has two flutes  88  and  90  extending from point  84  towards shank portion  82 .  
         [0023]    First flute  88  and second flute  90  are formed at a helix angle extending the length of body  86  of end mill  80 . At point  84 , flutes  88  and  90  terminate and define a pair of flat cutting edges  92  and  94 , commonly referred to as end teeth cutting edges.  
         [0024]    End mill  80  has two additional end teeth cutting edges  96  and  98  which extend from two ears  100  and  102  at an angle  90 E from the body  86 . Cutting edges  96  and  98  are formed without a first or second flute as provided with cutting edges  92  and  94 . It will be appreciated by those skilled in the art that the specific number of additional cutting edges  96  and  98  are largely a matter of design choice and subject to variation. Additional cutting edges originate from grinding off two flutes (not shown) of a four flute tool and leaving the end teeth or cutting edges. Cutting edges  96 ,  98  extend to outside diameter  104  of shank  82  and body  86 . When the flutes (not shown) are ground down, a length of outer diameter  104  preferably is left extending downward from the cutting edge  96 ,  98  to form ear  106  and  108 .  
         [0025]    This unique chopper was designed for processing reinforcements having a specific coating thereon. Preferably, the mixture is an epoxy/polystyrene mixture developed for coating glass fiber reinforcements for thermoset resins such as polyesters. First, the glass is coated and dried. After drying, the roving then is wrapped around chilled mandrels and chopped into an appropriate length.  
         [0026]    These after coated reinforcements are described in U.S. patent application Ser. No. 09/829,095, filed Apr. 9, 2001 and herein incorporated by reference.  
         [0027]    In addition to these embodiments, persons skilled in the art can see that numerous modifications and changes may be made to the above invention without departing from the intended spirit and scope thereof.