Fiber cutter
FIELD OF THE INVENTION 
     This invention relates to the cutting into uniform short lengths of fibers constituting a tangled mass. 
     BACKGROUND OF THE INVENTION 
     It is known in the prior art to cut short lengths of fibers from a tangled, non-oriented, mass using a device known in the art as a granulator. It is also known in the prior art to cut regimented lengths of fiber into short lengths using a cutter roll (e.g., U.S. Pat. No. 2,719,336). Finally, it is known to use carding rolls in order to orient fibers. 
     SUMMARY OF THE INVENTION 
     I have discovered that very uniform short lengths may be cut from a batt of non-oriented fibers by passing the batt between a feeder roll and a first knife blade spaced from a rotating picker roll carrying at least a second knife positioned for cutting action operatively with the aforementioned blade. 
     I have discovered also that the pieces cut off may be suitably classified to separate too-short pieces and satisfactory pieces by providing, in combination, a dropout below and just downstream of said aforementioned first knife blade and drawing satisfactory pieces through the device thereover with the help of downstream vacuum. 
     PREFERRED EMBODIMENT 
     I turn now to a description of the drawing, structure, and operation of a preferred embodiment of the invention. 
    
    
     DRAWING 
     The single FIGURE illustrates diagrammatically a device according to the invention. 
    
    
     STRUCTURE 
     There is shown in the FIGURE a tangled mass or batt of non-oriented long thermoplastic (e.g., polyester) fibers F. Feed roll 10 (elastomeric covered, 4 11/16 inches in diameter) acting against feed plate 12 advances the batt F against blade 14 and into contact with pins 16 of picker cylinder 18; pins 16 project 3/4 inch from the surface of picker cylinder 18, and are pointed. Fixed belly portion 20, pivotal belly portion 22, and slidable belly portion 24 define with picker cylinder 18 a path through the device. Downstream thereof are a pair of evacuated perforated rolls 26 and a pair of delivery rolls 28. Fly knife 30 is mounted on picker roll 18 and extends 2 millimeters further radially from the surface of the drum than do pins 16. Doctor blade 32 prevents recycling. 
     OPERATION 
     In operation, tangled batt F is fed by feed roll 10 (rotating at 11 rpm) over doctor blade 14. Picker roll 18 rotates (at 720 rpm) so that the pins 16 thereof comb batt F as it is held between feed roll 10 and blade 14. Blade 14 is set at a distance away from picker roll 18 corresponding to the length of the desired finished product, here 0.23 inch. 
     Feed roll 10, which is 4 11/16 inches in diameter in the preferred embodiment, rotates slowly, so that 1/4 inch is fed for each full rotation of the forty-inch diameter picker wheel 18 (720 rpm), knife 30 cooperating with the knife edge of blade 14 in a slight shearing action (blade 30 has a 3° skew) to cut the fibers to the desired length after pins 16 have combed them into alignment. 
     The size, both in a generally radial direction and in a generally circumferential direction, of the opening just downstream of blade 14, is regulated by pivoting the portion 22 and sliding the portion 24. A third variable is the rate at which a fan (not shown) exhausts air through the perforated rolls 26. In the preferred embodiment evacuation rate is 4,000 cubic meters per minute, the device being 4 feet in width. The nature of the opening 33 and the amount of evacuation are adjusted so that desirably short bits of fiber drop out through the opening 33, while the undesirably long pieces of fiber are entrained and pass on through the device. 
     The device and the method of its operation are especially advantageous for thermoplastic fibers. For one thing, the large diameter of the picker roll 18 and its slow rate of rotation provide for cooling between successive cuts. This cooling is further aided by the air drawn through the cut fiber passage by the vacuum pulled at perforated rolls 26. The device and method are, however, quite useful with non-thermoplastic fibers. 
     OTHER EMBODIMENTS 
     If desired, more than one knife 30 may be spaced equally around the periphery of the picker roll 18; with two, for example, the same rate of rotation of the roll 18 would produce cut pieces half as long. 
     The pinch point between feedroll 10 and blade 14 should be positioned as closely to picker roll 18 as may be accomplished consistently with pin clearance of blade 14. Because of this, for shorter lengths of cut pieces, a smaller diameter feedroll 10 should be used.