Abstract:
An apparatus for the creation of a spiral coil by extruding a hollow tube and cutting the tube in a fixed plane relative to the tube is provided. A fabric made from such spiral coils is also provided.

Description:
BACKGROUND 
     The present invention relates to spiral coils that can be interlaced to create fabrics or seams for use in the papermaking industry. It further relates to a method for extruding and cutting tubes to produce the coils. 
     It has been recognized in the prior art that spiral coils can be used to create all or part of a papermaking fabric. The most common spiral coils are made from extruded monofilaments that are thermally treated and wrapped about a mandrel for shaping into a helical form. The resultant coils and fabrics are sensitive to fluctuations in ambient temperature and moisture which leads to their destabilization in use. This tendency to destabilize is believed to be attributable to orientation of the polymer molecules in the monofilament along the longitudinal axis established during the monofilament extrusion process. Conventional prior art methods generally require a coiling process that limits them to certain materials. In addition, the coiled materials generally require further heat setting to achieve a flat or planer coil array. These conditions generally limit the coiling method to round or oval monofilaments which have lower surface contact areas. 
     SUMMARY 
     The invention is directed to an apparatus or the creation of a spiral coil by extruding a hollow tube and cutting the tube in a fixed plane relative to the tube. Additionally, the invention is directed to a fabric made from such spiral coils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an apparatus for converting an extruded hollow tube into a spiral coil. 
     FIG. 2 is a cross-section taken along line  2 — 2  in FIG.  1 . 
     FIG. 3 is a perspective view of the apparatus of FIG. 1 with a portion of the cutter housing being partially broken away. 
     FIG. 4 is a cross-section taken along line  4 — 4  in FIG.  3 . 
     FIG. 5 illustrates a cutting tool used in the apparatus of FIG.  1 . 
     FIG. 6 illustrates a cutting edge profile for the cutting tool of FIG.  5 . 
     FIG. 7 illustrates a cutting edge with coil smoothing means. 
     FIG. 8 is a top plan view of a fabric fragment having intermeshed spiral coils. 
     FIG. 9 is a cross-section taken along line  9 - 9  in FIG.  8 . 
     FIG. 10 is a cross-section similar to FIG. 2 of a second embodiment of an apparatus for converting an extruded hollow tube into a hollow coil. 
     FIG. 11 is an elevational view, partially broken away, of a third embodiment of an apparatus for converting an extruded hollow tube into a hollow coil. 
     FIG. 12 is a cross-section taken along line  12 - 12  in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described with reference to the drawing figures wherein like numerals indicate like elements throughout. 
     In FIG. 1, a hollow tube  2  is shown having a wall  3  of a desired thickness that surrounds and defines a tube interior  5 . The tube interior  5  is dimensioned to provide an approximately desired space between end curves  9  of a desired coil  10 . Preferably, the tube  2  is extruded from an extruder  4  and is moved at a constant speed through the path of a cutting device  6 , located in an opening  11  in a housing  7 . Mounted within the housing  7  is a cutting tool  8  with a cutting edge  14 . The tool  8  moves in a fixed plane that is perpendicular to the direction of travel of the tube  2 . The tool  8  repeatedly navigates a path normal to the tube wall  3 . The movement of the tube  2  through the perpendicular fixed plane and the movement of the cutting edge  14  in the plane are coordinated so that a uniform spiral coil  10  is cut from the tube  2 . 
     FIGS. 1 and 2 illustrate a first preferred embodiment of the cutting device  6 . The housing  7  supports the cutting tool  8  that creates the coil  10  from tube  2 . A groove  16  is located in housing  7  and receives a drive belt  17 , as shown in FIG.  2 . As shown in FIG. 3, a chamber  19  is located adjacent the groove  16 , and receives a means for driving the belt  17 , such as a drive gear which engages and advances the belt. The cutting tool  8  preferably passes through a slot  18  that extends inwardly from the groove  16  and is advanced by the drive belt  17  as it moves within the groove  16 . The slot  18  is dimensioned to allow passage of the tool  8  through the groove  16  while stabilizing the cutting edge  14  against vibration and other mechanical deflections. This is illustrated in FIG.  4 . The belt  17  may be driven by an electric motor or pneumatic or fluid means, not shown, such as will be known to those skilled in the art. 
     Referring now to FIG. 5, a preferred cutting edge  14  on the tool  8  is shown in detail. The cutting edge  14  on the tool  8  is preferably formed by a notch  20 , having an angled base  22  with a sharp edge  24 . Preferably, the notch  20  is sized to receive the wall  3  of the tube  2 , with the thickness of the wall  3  being approximately equal to or less than the opening of the notch  20 . In a preferred embodiment, the opening of the notch  20  is chamfered to provide a lead-in surface for receiving the wall  3  of the tube  2 . 
     Referring now to FIGS. 6 and 7, an alternate embodiment of the tool  8 ′ is shown. The alternate embodiment of the tool  8 ′ includes smoothing bars  26  and  28  located generally behind the cutting edge  14  in the cutting direction. The smoothing bars  26 ,  28  hold the cut portion of the coil  10 , parallel to the tube  2  in the area directly after the cut is formed to smooth the cut edges and to prevent tearing and/or uneven cutting as the cutting edge  14  is carried through the wall  3  of the tube  2  to form the coil  10 . This provides for a more uniform and consistent cut. Preferably the opening D is equal to the all thickness of the coil  10  and is in the range of about 0.3 to 0.7 mm. 
     Referring now to FIGS. 8 and 9, there is shown a small portion of a fabric  32  that is comprised of a plurality of intermeshed spiral coils  10  in accordance with the present invention which are retained in the intermeshed condition by a plurality of pintles  40 ,  42 . As shown in FIG. 9, the major axis M represents the length and the minor axis N represents the caliper or height of the coil  10 . The major axis M is preferably in the range of 5 to 10 mms and the minor axis N is preferably in the range of 2 to 4 mm. The wall thickness D of the coil  10  is preferably in the range of 0.3 to 0.7 mm, and is approximately equal to the opening height D of the notch  20  used to form the cutting edge  14  in the tool  8 . Filler strands may be inserted in the open channels  52  if it is desired to further reduce the permeability of the fabric  32 . 
     Those skilled in the art will recognize from the present disclosure that the coils  10  can be utilized to form an entire fabric  32  or may be used to form only a portion thereof, such as a seam to connect two ends of a woven fabric together to form an endless belt. 
     The hollow tube  2  can be made of any extrudable polymer, and in any number of shapes or sizes. Currently, preferred coil shapes are oval with flat top and bottom surfaces. Currently preferred polymers are PET; PA; PPS/PEEK. However, those skilled in the art will recognize from the present disclosure that other suitable materials may be utilized to form the tube  2 , if desired. 
     Preferably, the material is processed through a single screw extruder at the required melt temperature and extruded through a die head having the desired tube profile. The extrudate is then fed directly to the cutting device  6  to form the coil  10 . Preferably, the extrusion process results in either random orientation of molecules in the extruded tube  2 , or, to the extent that the molecule strands are oriented, they are oriented generally in the direction of flow  0 , as shown in FIG.  1 . Because of the cutting and assembling process, the molecules in the final coils  10  and fabric  32  are either randomly oriented or generally oriented perpendicular or transverse to the direction of travel of coil  10  or fabric  32  on a paper making machine. This is similar to what may be found in an injection molded coil. 
     As shown in FIG. 8, the longitudinal portions of the coil  10 , as indicated by coil portions  36 , are oriented in the machine direction and running generally perpendicular to the extruded molecules flow direction, as indicated by arrow  34 . Similarly, the interconnecting portions, as indicated by  38 , are generally oblique to the extruded molecules&#39; flow. The head curves  9  will have intermediate portions of each. No portion of the coil  10  in the fabric  32  has an extended orientation parallel to the orientation of the original tube  2 . 
     Since the extruded tubes are not subjected to a post extrusion draw, the coil  10  will not be oriented in the manner of a conventional monofilament. The lower level of orientation results in a generally tougher coil that is more closely likened to an injection molded product. The absence or reduction of directional orientation reduces the thermal and moisture reactivity in the same direction, and to the extent that any orientation of molecules would generally be in the extrusion direction O (shown in FIG.  1 ), this is transverse to the machine direction in the finished fabric or portion of fabric in which the coil  10  is used. 
     Referring now to FIG. 10, a second embodiment  60  of the cutting device is shown. In the second embodiment of the cutting device  60 , a cutting tool  62  is mounted on a centrally located shaft  64 . Preferably, the cutting tool  62  includes an elongated cutting edge  66 . The cutting tool  62  is rotated by the central shaft  64  to cut the coil  10  from the tube  2 . Preferably, the free end  68  of the cutting tool  62  is constrained to travel within a slot  70 , formed in the housing  72  of the cutting device  60 . The slot  70  is sized to stabilize the cutting tool  62  to prevent vibration or mechanical deflection as the cutting edge  66  cuts the tube  2  to form the coil  10 . Preferably, the feed rate of the tube  2  through the cutting device  60  is coordinated with the rotation speed of the cutting tool  62  in order to form a uniform coil  10  in the same manner as described above in connection with the cutting device  6  in accordance with the first embodiment. The central shaft  64  is preferably rotated via a controllable pneumatic or electric motor. 
     Referring now to FIGS. 11 and 12, a third embodiment of the cutting device  80 , in accordance with the present invention is shown. The cutting device  80  includes a cutting tool  82  having a cutting edge  83 . The cutting tool  82  is mounted on a ring gear  84  for rotary movement about the tube  2 . The ring gear  84  is supported by a roller bearing  88  mounted on a support  90 . The ring gear  84  is driven via a drive motor  92 , having a drive gear  94  which engages the gear teeth  86  of the ring gear  84 . The speed of the motor  92  is coordinated with the extrusion rate of the tube  2  in order to cut the uniform coil  10 . Preferably, the cutting device  80  is located adjacent to the extruder dye face  96  and the cutting tool  82  is moved along the dye face  96  as the tube  2  is being extruded to form the coil  10 . 
     Due to the oval shape of the tube  2 , the cutting edges  66 ,  83  on the cutting tools  62 ,  82  must be elongated since the area of the cutting edge  83  on the cutting tool  82  contacting the tube  2  will vary, depending upon the location of the cutting tool  82 . 
     Preferably, the motor  92  is a controllable electric or pneumatic motor, such that the speed of the motor can be controlled to a desired rate. 
     It will be appreciated by those skilled in the art that changes can be made to the preferred embodiments of the cutting device described above, as well as to the shape and size of the coil formed by the cutting tools, without departing from the broad inventive concept of the present invention. The size of the coils and fabrics made therewith can also be altered, as desired. It is understood, therefore, that the invention is not limited to the particular embodiments disclosed, and is intended to cover modifications within the spirit and scope of the present invention.