Abstract:
A method and apparatus for chopping long unwound items like fiber, fiber strands, yarn, etc. The chopper has a backup roll, a blade roll and a biasing system for forcing the backup roll and the blade roll together at a desired force during set up and operation. The biasing system contains one or more sensors for sensing a biasing force at set up and during operation.

Description:
[0001]     The present invention includes a chopper for one or more strands, the chopper having an improved biasing system. The improved choppers are used to separate long lengths of strand into short segments. The invention also includes a method of chopping while controlling the bias between a backup roll and blade roll with the biasing system. Each strand can be a single fiber, filament, string, wire, ribbon, or strip, or each strand can contain a plurality of fibers, filaments, strings, wires, ribbons or strips.  
         [0002]     It has long been known to chop continuous fibers or fiber strands into short lengths of about 3 inches or shorter and billions of pounds of chopped products are produced each year in processes and chopping apparatus like or similar to those disclosed in U.S. Pat. Nos. 5,970,837, 4,398,934, 3,508,461, and 3,869,268, the disclosures of which are incorporated herein by reference. These choppers comprise a blade roll containing a plurality of spaced apart blades for separating the fibers into short lengths, a backup roll, often or preferably driven, which the blades work against to effect the separation. The chopping action also pulls the fibers or fiber strands into the chopper at a proper speed to achieve the desired fiber diameter. In some choppers an idler roll is used to pull and to hold the fibers or fiber strands down onto the surface of the backup roll. In the chopped fiber processes disclosed in these patents, the chopper is usually the productivity limiting equipment in the process. These processes typically operate continuously every day of the year, 24 hours each day, except during furnace rebuilds every few years. Therefore, improvements in the chopper, which allow the chopper to pull and chop faster and for longer times between maintenance shutdowns, and/or to pull and chop more fibers or fiber strands at a time, have an extremely positive impact on productivity and production costs.  
         [0003]     In some prior art choppers a mechanical jack operated by a gear motor provided the force needed to bias one of the backup roll or blade roll into the other roll until the blades had penetrated the working layer of the backup roll an appropriate amount. If the blades did not penetrate far enough, double cuts or stringers, long strands, would result, an unacceptable result. If the blades penetrated too far, the chopper would chop the strands properly, but the backup roll life would be shortened substantially. Given these options, at least some operators tended to run the jack motor too long in setting up a rebuilt chopper, or if a chopping problem developed, thus reducing backup roll life substantially below what it could be if the choppers are set up properly. This is a costly situation causing this system to be abandoned in favor of using fluid cylinders with or without shear pins.  
         [0004]     Normally several strands such as up to 14 or more are fed into the chopper, each strand containing 2000 or more fibers. As more fiber strands and fibers are fed into the chopper it becomes more difficult to pull all of the strands and fibers at the same speed, so more pressure is applied to the cylinder pushing the idler roll against the backup roll with more force. Occasionally a glass bead from a fiberizing bushing or a wad of fibers will be pulled to the chopper caught up in the multitude of fiber strands. When this happens, it is necessary for one of the backup roll or blade roll to be able to move away from the other roll to allow this thicker anomaly to pass through the nip between the blade roll and the backup roll. If this separation does not occur the chopper will often lock up causing damage to the drives, belts and/or the rolls.  
         [0005]     Although at least one of the rolls is held in position with a fluid cylinder, the fluid is either not compressible or responds too slowly to the sudden problem to protect the chopper from damage and downtime. In the past the shear pin was used to provide such protection. However, when the shear pin shears the blade roll and backup roll are no longer biased together properly requiring that the chopper be shut down to install a new shear pin. This downtime is costly because of the loss of production during the downtime and due to reduced material efficiency for several minutes following restart. Downtime causes forehearth and bushing temperature upsets because hanging fibers do not pull in cooling air that occurs when the chopper is pulling the fibers from the bushings. Also, there is a tendency on the part of the operator, if the chopper is not chopping the strand properly, to increase the biasing force excessively and this drives the blades of the blade roll too deep into the elastomeric working layer of the backup roll and substantially shortens the life of the backup roll.  
         [0006]     If all of the strands or fibers are not pulled at the same speed, the slower strands and fibers will have a greater fiber diameter which is unacceptable and the bushings of the slower strands frequently will not operate at the proper temperature causing more frequent breakouts and/or additional fiber diameter variations, both of which are unacceptable. Also, fiber slippage can cause some of the fibers to be cut to shorter lengths than desired resulting in an unacceptable product. Therefore, it is very important that the biasing force between the blade roll and the backup roll remain proper and essentially constant.  
         [0007]     As the pulling speed is increased, and/or as the number of strands and fibers are increased, above about 3000-4000 ft./min. (FPM), depending on the product, the present state of the art choppers begin to vibrate and the idler roll begins to allow one or more of the strands to slip some thus reducing the pulling speed of one or more of the strands. Also, if all of the strands are not pressed between the idler roll and the elastomer layer of the backup roll, a strand can slip partially out of the nip leaving some of the fibers unchopped, producing double cuts and stringers in the chopped product and causing the product to be scrapped.  
         [0008]     U.S. Pat. No. 3,731,575 teaches an air cylinder with an adjustable stop to bias the blade roll against the backup roll so that the blades penetrate the backup roll the desired distance and no further. However, with this arrangement, the pressure in the cylinder increases when a wad or bead or other thicker strand set passes through the chopper and forces the backup roll to back away from the blade roll. Also, an air cylinder bias is subject to permitting vibration at high speeds and is therefore not desirable. Finally, this system suffers the same problem as the mechanical jack system in that it requires an operator to set the mechanical stop limiting the distance the blades can penetrate the working layer of the backup roll.  
         [0009]     It would be very desirable for the chopper operator to know what the magnitude of force or bias is, when he is first setting up the chopper and when the chopper is operating. With that information the operator could tell if something has changed and needs adjustment, and the operator could then properly manipulate the assembly providing the biasing force to raise the biasing force back to the desired level. Alternatively, the control system could use that feedback signal to automatically adjust the assembly providing the bias to keep the magnitude of force or bias at the desired level  
         [0010]     The present invention comprises a chopper for separating long a long strand or strands, the strand or strands comprising one or more fibers, filaments, wires, strings, ribbons or strips, into short segments, the chopper having a biasing system that comprises a strain gauge as part of the biasing system. One or more strain gauges detect, either directly or indirectly, the magnitude of force biasing the backup roll and the blade roll toward each other, i.e. the magnitude of force holding the two rolls in operating or chopping engagement. The strain gauge(s) can be of any suitable type and placed in one or more of numerous locations that will provide a reading of the magnitude of force on a mechanical jack providing the biasing force or on a structural member transmitting the biasing, the engaging force.  
         [0011]     The invention also includes a method of separating a strand or strands, each strand comprising one or more fibers, filaments, wires, strings, ribbons or strips, or combinations of two or more thereof, into short segments using the improved chopper of the invention. In the method one or more strands are guided into a nip formed between a backup roll and a blade roll of the chopper biased together with a biasing system comprising one or more strain gauges and using the output of the one or more strain gauges to set and/or control the biasing force during set-up and operation of the improved chopper. The more constant biasing force between the backup roll and the blade roll optimizes the life of the backup roll and significantly improves productivity of the chopped fiber forming operation.  
         [0012]     The strain gauge, using an analog output to a PLC, provides a real time display to the operator and process engineers informing them concerning forces optimum for cutting and/or protection of equipment. The strain gauge data can be used to set up the chopper for operation after installing one or both of a new blade roll and a new backup roll, as an informational process optimization tool and also for process control and bias magnitude control during operation of the chopper of the invention.  
         [0013]     When the word “about” is used herein it is meant that the amount or condition it modifies can vary some beyond that stated so long as the advantages of the invention are realized. Practically, there is rarely the time or resources available to very precisely determine the limits of all the parameters of one&#39;s invention because to do so would require an effort far greater than can be justified at the time the invention is being developed to a commercial reality. The skilled artisan understands this and expects that the disclosed results of the invention might extend, at least somewhat, beyond one or more of the limits disclosed. Later, having the benefit of the inventors&#39; disclosure and understanding the inventive concept and embodiments disclosed including the best mode known to the inventor, the inventor and others can, without inventive effort, explore beyond the limits disclosed to determine if the invention is realized beyond those limits and, when embodiments are found to be without any unexpected characteristics, those embodiments are within the meaning of the term “about” as used herein. It is not difficult for the artisan or others to determine whether such an embodiment is either as expected or, because of either a break in the continuity of results or one or more features that are significantly better than reported by the inventor, is surprising and thus an unobvious teaching leading to a further advance in the art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an elevational front view of a chopper of the present invention.  
         [0015]      FIG. 2  is a partial elevational view of the interior of the chopper shown in  FIG. 1  and shows the support for the backup roll and backup roll spindle and a some typical embodiments of the biasing system of the present invention.  
         [0016]      FIG. 3  is a blown up elevational view of the biasing systems shown in  FIG. 2 .  
         [0017]      FIG. 4  is a partial side view of the embodiments shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows a front elevation view of a typical chopper  2  used in making chopped strand glass fiber. It comprises a frame and front plate  4 , feet  5 , a blade roll  6  with spaced apart blades  7  contained in slots and projecting from the periphery of a blade holder integrated into the blade roll  6 , a backup roll  8  and an idler roll  13 . The blade roll  6  is mounted on a rotatable spindle  17  and held in place with a large nut  19 . The blade roll  6  is usually made of metal and thermoplastic material such as the blade rolls shown in U.S. Pat. Nos. 4,083,279, 4,249,441 and 4,287,799, the disclosures of which are herein incorporated by reference.  
         [0019]     The backup roll  8  is comprised of a hub and spoke assembly  9  with an integral metal rim  10  on which is cast or mounted a working layer  11  of an elastomer or thermoplastic material such as polyurethane. The backup roll  8  is mounted on a second spindle  18  and held in place with a large nut  20 . To operate the spindle  18  of the backup roll  8  is moved towards the spindle  17  of the blade roll  6  until the blades  7  of the blade roll  6  press into the working layer  11  of the backup roll  8  a proper amount forming a nip  14  to break or separate fiber strands  12  into an array of short lengths.  
         [0020]     One or more, usually eight or more and up to  20  or more strands  12 , such as glass fiber strands, each strand containing 400-6000 or more fibers and usually having water and/or an aqueous chemical sizing on their surfaces, are pulled by the backup roll  8 , in cooperation with a knurled idler roll  13 , into the chopper  2  and the nip  14 . The strands  12  first run under a grooved oscillating, separator and guide roll  16 , preferably with one or two strands in each groove, and upward and over the outer surface of the backup roll  8 . The working surface of the back up roll  8  is typically wider than the oscillating path of the glass fiber strands  12 . The strands  12  then pass under the outer knurled surface of the idler roll  13 , which is pressed against the strands at a desired pressure to enable pulling of the glass fiber strands. The strands remain on the surface of the working layer  11  and next pass into the nip  14  between the backup roll  8  and the blade roll  6  where they are separated with the razor sharp blades  7  wherein the strands are usually cleanly cut or broken into an array of chopped strand  15  having the desired length.  
         [0021]     The improved chopper  2  of the present invention and illustrated in  FIGS. 1-5  comprises a novel biasing system such as a preferred biasing assembly  24 . The backup roll spindle  18 , in turn holding the backup roll  8  in a rotatable manner, is supported with multiple bearings in a known manner on a pivoting beam  20  that is held in a pivoting manner with a pin  22 . As the pivoting beam  20  is raised, the outer working surface of the backup roll  8  is pressed against the blades  7 . The biasing assembly  24  is attached to the pivoting beam  20  in a manner that will be described later and a mechanical jack  26  is manipulated to bias the backup roll  8  against the blades  7  of the blade roll  6  in the manner shown in  FIG. 2 .  
         [0022]      FIGS. 3-5  show the most typical embodiment of the biasing assembly of the present invention in more detail. The preferred biasing assembly  24  is comprised of a mechanical jack  26 , such as an Acme screw jack called a having a rotatable input shaft  35  for extending or retracting a rod  34  of the screw jack, a rotating means such as a conventional stepping motor, conventional motor and gear reducer or gearhead motor combination  28  having an output shaft  29 , conventional controls for the gear motor (not shown), a conventional coupling (not shown) for connecting the gear motor  28  to the rotatable shaft  35  and means for securing one end of the screw jack  26  to the frame of the chopper and the other end to the pivoting beam  20 . When a stepping motor is used as the motor  28 , a conventional programmed control can be used allowing the operator to key in the number of steps for the stepping motor to advance or backoff. All motors used are reversable motors.  
         [0023]     The means for securing mechanical extenuating means or screw jack  26  to the pivoting beam  20  preferably comprises a clevis mount  38  having a hole therethrough and an opening for a clevis attached in any known suitable manner to the underneath surface of the outer end of the pivoting beam  20  as shown in  FIG. 2 . A clevis  36  is rotatably attached to the end of the mechanical jack rod  34  in a known manner. The clevis  36  is then pivotly attached to the clevis mount  38  according to one embodiment of the invention with a strain gauge pin  48  having a load cell pin or bolt  45 ″. This load cell pin or bolt contains a strain gauge and can be of many types. One type is a load cell pin or bolt produced by the Strainsert Company of West Conshokocken, Pa. When a load is applied to the load cell pin  45 ″, a strain gauge wire mounted inside the pin or bolt senses the amount of force and transmits an electrical signal indicating the magnitude of force. As will be seen later, the strain gauge can be in other locations, such as a compression load cell  54  placed under a clevis bracket  44 , or a load cell pin or bolt  45  used to mount the jackscrew  26  to the clevis bracket  44 . Also, a strain gauge can be attached to any part of the biasing assembly that will be under load during operation or set up for operation such as on the pivot beam  20 , e.g. see the strain gauge  58  attached to the underneath side. More than one strain gauge can be used at the same time, but usually not necessary. Normally only one strain gauge or strain gauge load cell placed in a manner to sense the biasing force is necessary and its type and location can be a matter of choice.  
         [0024]     As shown in  FIG. 3 , he means for attaching the mechanical jack means, screw jack  26  and jackscrew-housing  47  for the jackscrew that is the lower portion of shaft  34  is a plate  42  having on one end an integral eye  42 . The other end of the plate  42  is attached to the underneath side of the mounting plate  27 , preferably centered under the body of the screw jack  26 , in any suitable manner, such as with threaded metal bolts whose heads are recessed in the top portion of the mounting plate  27 . The plate  42  has a cutout portion  49  so the plate  42  can straddle the jackscrew housing  47  as shown in  FIG. 3 . This preferred means for securing the mechanical jack  26  to the frame of the chopper comprises pivotly attaching the eye  45  of plate  42  to a mounting bracket  44  with a clevis pin or a load cell pin or bolt  45 . The mounting bracket  44  can be attached in a known manner to a lower frame member  46  of the chopper and can alternatively set on a compression load cell  54 , according to the invention. As seen in  FIG. 4 , a transmitter  50  is mounted onto the clevis pins  45  and  45 ′ outside the brackets  44  and  36  respectively. The transmitter  50  sends a signal to a display, and optionally also to an input of a controller circuit, in a control panel (not shown) via a wire or wirelessly in a known manner.  
         [0025]     Referring to  FIG. 4 , a motor  28  is energized and rotates its output shaft, coupled to the input side of the screwjack  26  in a known manner.  
         [0026]     This biasing system also optionally comprises a toothed gear  30  attached to a rotatable output shaft  41  of the mechanical jack  26 , a tooth sensor and counter  32  for counting the number of passing teeth of the toothed gear  30 , a bracket  33  for holding the tooth sensor and counter  32  in the proper location, and a mounting plate  27  for mounting the mechanical jack  26 , the gear motor  28  and the bracket  33 .  
         [0027]     To operate the preferred chopper biasing system described above, the operator first either selects a desired amount of force to use in manually driving the motor  28  and screwjack  26  applying the bias forcing the backup roll and blade roll together, or optionally sets the desired force limit in the control panel to automatically achieve the same objective. A force limit for the type of chopper shown in  FIG. 1  is one that will allow the screw jack  26  to exert about 1000 pounds force, but again this depends upon the design of the chopper and the hardness of the elastomeric working layer on the backup roll. In the biasing system shown in this embodiment of the invention, the motor  28  turns in a direction that will cause the screw jack  26  to raise the jackshaft  34  thus raising the pivoting beam  20 . The screw jack  26  will continue to raise the backup roll  8  into the blades  7  until the resistance of the blades penetrating the elastomer layer of the backup roll  8  reaches level where the torque on the input shaft  35  of the screw jack  26  reaches the desired force limit, which is the force required to force the blades  7  the desired distance into the working layer  11  of the backup roll  8 . In other embodiments of the invention, the blade roll  6  is moved towards the backup roll  8 , and both the backup roll  8  and the blade roll  8  are moved towards each other at the same time or sequentially. The stepping motor is usually stopped when the chopper is shut down and reversed to back the backup roll  8  away from the blades  7  when it is desired to remove the blade roll  6  and/or the backup roll  8 .  
         [0028]     Any kind of mechanical jack can be used in the inventive biasing system, but it is preferred to use one of lower mechanical advantage, i. e. preferably less than about 10:1 to minimize the pressure that can build up in the nip between the backup roll  8  and the blades  7  due to a thicker feed before it is relieved and to reduce the reaction time to relieve the pressure. A preferred screw jack is a Duff-Norton 2-ton Machine Screw Actuator #TM-9002-4, 6:1 ratio with a 4 inch stroke available from the Duff-Norton Co. of Charlotte, N.C.  
         [0029]     Different embodiments employing the concept and teachings of the invention will be apparent and obvious to those of ordinary skill in this art and these embodiments are likewise intended to be within the scope of the claims. The inventor does not intend to abandon any disclosed inventions that are reasonably disclosed but do not appear to be literally claimed below, but rather intends those embodiments to be included in the broad claims either literally or as equivalents to the embodiments that are literally included.