Patent Publication Number: US-2007101846-A1

Title: Compensating stripper rings for material slitting machines

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates generally to slitter machines for slitting sheet materials into strips and, more particularly, to knife arrangements and stripper rings for use on such slitting machines.  
      2. Description of the Invention Background  
      Much of the steel produced by mills is in the form of coiled steel sheet, but rarely does the sheet correspond in width to the multitude of products that are stamped or otherwise formed from it. Accordingly, the steel sheet is usually slit longitudinally to sizes suitable for the particular products. Indeed, special slitting machines are made for this purpose.  
      The typical slitting machine has circular blades or knives arranged in pairs on two powered shafts or arbors, there being one knife of each pair on one of the arbors and the second knife of the pair on the other arbor. The arbors are connected to a drive system for counter-rotation. During operation, sheet metal is moved between the arbors and cut into strips or “mults” by the knives counter-rotating on the arbors. Actually, each knife may be nothing more than a hardened steel disk having flat end faces and a cylindrical peripheral face which intersects the end faces at relatively sharp cutting or shearing edges. The disks of each pair are positioned on their respective arbors, often with a slight overlap. Overlap or not, the knives of each pair are positioned close enough to each other to enable them to cut or shear the metal sheet as it passes between those knives. In other words, the metal sheet is drawn between the two knives of a pair the disk-like knives shear the sheet along the opposite cutting edges, thus producing a clean longitudinal cut in the sheet. Not only are the disk-like knives arranged in pairs, but the pairs of knives are also usually organized into left and right hand configurations to present similar slit burr orientation on the slit strands. That is, on one strip, the slit burrs will face upward and on adjacent strips the burrs will face downward, such that the burr orientation will alternate on the adjacent strips.  
      In many slitting arrangements, stripper rings are journaled on the arbors adjacent each side of the disk-like knife. In practice, the stripper rings are arranged in “male” and “female” pairs with the male stripper ring located on one drive shaft and a corresponding female stripper ring located on the other drive shaft adjacent the cutting edges of the knives. Such stripper rings serve to support the strip material through the cutting operation and provide space to compensate for the required “vertical” travel of the cutting knives. These male and female stripper rings are commonly fabricated from solid rubber or Urethane and, although may have a modicum of flexibility, they are generally not flexible enough to accommodate different thicknesses of metal or other material to be slit without the exchange of smaller or larger female stripper rings selected to compensate for various material thicknesses to be slit. This exchange requires retooling the slitter head for proper stripper ring pinch pressure and leads to undesirable machine downtime and associated labor costs.  
      Thus, as can be appreciated from the forgoing discussion, there is a need for a stripper roll that can accommodate different thicknesses of materials.  
      There is a further need for a knife assembly for use on a material slitting machine that can readily accommodate different material thicknesses.  
      There is yet another need for a slitting method that can accommodate different material thicknesses without having to physically adjust or alter the female stripper ring diameter.  
     SUMMARY  
      In accordance with one embodiment of the present invention, there is provided a stripper ring for use on a material slitting machine. One embodiment of the stripper ring comprises a flexible ring that has a mounting hole extending therethrough. The flexible ring further has a circumferentially extending driving surface and a first lateral face that extends between the circumferentially extending driving surface and the mounting hole. A second lateral face extends from the circumferentially extending driving surface and the mounting hole. A first annular groove is provided in the first lateral face and a second annular a groove is provided in the second lateral face.  
      In accordance with another embodiment of the subject invention, there is provided a stripper ring for use on a material slitting machine. One embodiment of the stripper ring comprises a ring that has a central portion with a mounting hole extending therethrough. The central portion further has a first lateral face with first relief means therein and a second lateral face with second relief means therein and a circumferentially extending driving surface. The first and second relief means serve to enable a portion of the stripper ring to deflect in two different directions upon the application of compressive force to the portion of the stripper ring.  
      In accordance with yet another embodiment of the subject invention, there is provided a knife assembly for a slitting machine having a drive shaft. One embodiment of the knife assembly comprises a knife holder assembly that is attachable to the drive shaft for rotatable travel therewith. A rotary knife is supported by the knife holder assembly. The rotary knife has a shearing face, a circumferentially extending end surface and a mounting face wherein the shearing face and the circumferentially extending end surface form a shearing edge. A female stripper ring is supported by the knife holder assembly adjacent the shearing face of the rotary knife. The female stripper ring has a first circumferentially extending driving surface formed thereon and is constructed to permit at least a portion of the female stripper ring to compress in two different directions upon the application of compressive force to a corresponding portion of the first circumferentially extending driving surface. A male stripper ring is supported by the knife holder assembly adjacent the mounting face of the rotary knife.  
      In accordance with another embodiment of the subject invention there is provided a material slitting machine that comprises a driven upper shaft and a driven lower shaft that is supported in spaced relation to the driven upper shaft. At least one upper knife holder assembly is mounted to the driven upper shaft. One upper knife holder assembly embodiment includes an upper rotary knife that is supported by the upper knife holder assembly. The upper rotary knife has an upper shearing face, an upper mounting face and a circumferentially extending upper end surface, wherein the upper shearing face forms an upper shearing edge with the upper end surface. An upper female stripper ring is supported by the upper knife holder assembly adjacent the upper shearing face of the upper rotary knife. The upper female stripper ring has a circumferentially extending upper driving surface formed thereon and is constructed to permit at least a portion of the upper female stripper ring to comprises in two different directions upon an application of compressive force to a corresponding portion of said upper driving surface. An upper male stripper ring is supported by the upper knife holder assembly adjacent the upper mounting face of the upper rotary knife. The machine further comprises at least one lower knife holder assembly mounted to the driven lower shaft wherein at least one lower knife holder assembly corresponds to one of the upper knife holder assemblies. In one embodiment, the lower knife holder assembly comprises a lower rotary knife that is supported by the lower knife holder assembly. The lower rotary knife has a lower shearing face, a lower mounting face, and a circumferentially extending lower end wherein the lower shearing face forms a lower shearing edge with the lower end. The lower shearing edge is oriented adjacent to the upper shearing edge of the upper rotary knife corresponding thereto. The lower end of the lower rotary knife is oriented in confronting relationship with respect to the upper driving surface of the upper female stripper ring of the upper knife holder corresponding thereto. A lower female stripper ring is supported by the lower knife holder assembly adjacent to the lower shearing face of the lower rotary knife. The lower female stripper ring has a circumferentially extending lower driving surface formed thereon and is constructed to permit at least a portion of the lower female stripper ring to compress in two other different directions upon application of other compressive forces to a corresponding portion of the lower driving surface that is in confronting relationship with at least a portion of the upper male stripper ring and a portion of the upper rotary knife. A lower male stripper ring is supported by the lower knife holder assembly adjacent to the lower mounting face of the lower rotary knife and is oriented in confronting relationship relative to at least a portion of the upper drive surface of the upper female stripper ring.  
      Accordingly, various embodiments of the invention provide solutions to the shortcomings of other stripper rings and slitting machine arrangements. Those of ordinary skill in the art will readily appreciate, however, that these and other details, features and advantages will become further apparent as the following detailed description proceeds.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the accompanying Figures, there are shown present embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein:  
       FIG. 1  is a perspective view of a metal slitting machine which may employ various stripper ring embodiments of the present invention;  
       FIG. 2  is an end elevational view of the slitting machine of  FIG. 1  with a plurality of stripper rings disclosed herein associated with corresponding knife holder assemblies operably mounted to the machine;  
       FIG. 3  is an end view of a lower portion of the slitter machine showing a knife holder assembly movably mounted thereto;  
       FIG. 4  is a side elevational view of the knife holder assembly depicted in  FIG. 3 ;  
       FIG. 5  is a cross-sectional view of a portion of the upper and lower drive shaft assemblies with knife holder assemblies of the present invention mounted thereon;  
       FIG. 6  is a cross-sectional view of a corresponding pair of upper and lower knife holder assemblies mounted on the upper and lower drive shaft assemblies, respectively;  
       FIG. 7  is a front view of a stripper ring embodiment of the present invention;  
       FIG. 8  is an end view of the stripper ring of  FIG. 7 ;  
       FIG. 9  is a cross-sectional view of a portion of the stripper ring of  FIG. 8 ;  
       FIG. 10  is another cross-sectional view of a stripper ring embodiment of the present invention;  
       FIG. 11  is a partial cross-sectional view of upper and lower knife holder assemblies employing stripper rings of the present invention;  
       FIG. 12  is a cross-sectional view of a stripper ring mounted within a knife holder assembly illustrating the application of forces thereto; and  
       FIG. 13  is a cross-sectional view of a stripper ring mounted within a knife holder assembly with the cross hatching omitted for clarity and illustrating the application of forces thereto which cause the stripper ring to flex and which flexing is represented in phantom lines.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to the drawings for the purposes of illustrating the present embodiments of the invention only and not for the purposes of limiting the same,  FIG. 1  illustrates one type of slitting machine  10  that may employ various embodiments of the stripper rings disclosed herein. Such slitting machine is disclosed in U.S. Patent Publication No. US 2003/0205117, entitled CNC SLITTER MACHINE, the disclosure of which is herein incorporated by reference in its entirety. Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.  
      The slitting machine  10  is but one example of a slitting machine on which various embodiments of the stripper rings disclosed herein may be used. As illustrated in  FIG. 1 , the slitting machine  10  is used for shearing metal sheet  12 , such as sheet steel, into multiple segments or mults  14  of a desired width along slits  16 . Those of ordinary skill in the art will understand, however, that the unique and novel aspects of the stripper ring arrangements and knife holder assemblies disclosed herein may also be effectively employed in connection with slitter arrangement for slitting other types of materials without departing from the spirit and scope of the present invention. In the example depicted in  FIG. 1 , the metal sheet  12  is normally provided from a mill or other supplier of mill products in a coil  18 . The coil  18  is supported on a spool  20 . The metal sheet  12  is withdrawn from the coil  18  and fed into the machine  10 . Typically, the metal sheet  12  passes through a straightening machine  22  to remove the coil set. The sheet  12  alternatively may be fed into the machine  10  in individual sections, preferably with the assistance of a skewed roller table (not shown) or the like.  
      As can be further seen in  FIGS. 1 and 2 , the slitting machine  10  may include an upper frame  26  movably coupled at spaced ends thereof to a lower frame  28 . The upper and lower frames  26 ,  28  of the machine  10  include upper and lower drive shaft assemblies  44 ,  46 , respectively, mounted therein for rotation. The drive shaft assemblies  44 ,  46  are supported in the respective frames  26 ,  28  by spaced pillow block bearings  48 . Corresponding ends of the upper and lower drive shaft assemblies  44 ,  46  are coupled to a gear box  50  by separate universal couplings  52 . A motor  54  is connected to the gear box  50  to provide rotational movement through the gear box  50  to the universal couplings  52  and ultimately the drive shaft assemblies  44 ,  46 . The drive shaft assemblies  44 ,  46  are rotated in opposite counter-rotating directions for pulling and slitting the metal sheet  12  passing therebetween.  
      A number of knife holder assemblies  200 ,  200 ′ are supported for movement along the upper and lower drive shaft assemblies  44 ,  46 , respectively, as shown in  FIGS. 2 and 5 . The knife holder assemblies  200 ,  200 ′ are supported in cooperating pairs at spaced positions along the upper and lower drive shaft assemblies  44 ,  46  in the upper and lower frames  26 ,  28 , respectively. To provide the knife holders  200 ,  200 ′ with the ability to be positioned in close proximity to each other along their respective drive shafts, the knife holder assemblies  200 ,  200 ′ may be arranged as illustrated as shown in  FIGS. 2 and 5  on each side of the slitter  10  centerline (CL). The knife holder assemblies  200 ,  200 ′ alternate across the slitter in “right hand” and “left hand” orientations. The right handed knife holder assemblies may be mirror images of the left handed knife holder assemblies and, therefore, the left handed knife holder assemblies  200 ,  200 ′ will only be described in detail herein.  
      The metal sheet  12  (or other material) to be slit passes between the knife holder assemblies  200 ,  200 ′ on the upper shaft  44  and the knife holder assemblies  200 ,  200 ′ on the lower shaft  46  along a pass line PL as indicated in  FIG. 2 . It will be appreciated that the exact number of knife holder assemblies  200 ,  200 ′ is generally dependent upon the desired width and configuration of the mults  14  and the metal sheet  12  or other material being slit. A holder assembly  200 ,  200 ′ may be supported on the upper and lower drive shaft assemblies  44 ,  46  in the manners described in the above-cited U.S. Patent Publication No. US2003/0205117 which has been herein incorporated by reference. In alternative embodiments, however, the knife holder assemblies  200 ,  200 ′ may be non-movably coupled to their respective drive shaft assemblies  44 ,  46 . The reader will further appreciate that the drive shaft assemblies  44 ,  46  may also be configured in sections as described in U.S. Patent Publication No. US2003/0205117 or they may comprise single driven shaft arrangements.  
      In one non-limiting embodiment, the knife holder assemblies  200 ,  200 ′ are supported in cooperating pairs along the upper and lower drive shaft assemblies  44 ,  46  such that one knife holder assembly  200  of each pair is positioned along either the upper drive shaft assembly  44  or lower drive shaft assembly  46  and the complementary knife holder assembly  200 ′ of the pair is positioned along the upper drive shaft assembly  44  or lower drive shaft assembly  46  in complementary relationship thereto as illustrated in  FIGS. 2, 5 , and  6 .  
      As shown in  FIG. 3 , the knife holder assemblies  200  (and  200 ′) are supported for linear movement along bearing rails.  FIG. 3  illustrates one knife holder assembly  200  in front of an adjacent knife holder assembly  200 ′. The knife holder assembly  200  in that Figure includes a bearing arbor  210  that has an outer linear bearing block  214  attached thereto by, for example, cap screws  215  and an inner linear bearing block  216  attached thereto by cap screws  217 . The outer linear bearing block  214  is mounted to a first outer rail  218  which is affixed to the lower frame  28  and extends laterally across the machine  10 . Likewise, the inner linear bearing block  216  is movably received on a first inner rail  220  which is also affixed to the lower frame  28  and extends laterally across the machine  10 . As can also be seen in  FIG. 3 , the adjacent knife holder assembly  200 ′ has a bearing arbor  210 ′ that has an outer linear bearing block  214 ′ and an inner linear bearing block  216 ′ attached thereto. The outer linear bearing block  214 ′ is movably mounted to a second outer rail  218 ′ which is affixed to the lower frame  28  and extends laterally across the machine  10 . Likewise, the inner linear bearing block  216 ′ is movably received on a second inner rail  220 ′ which is also affixed to the lower frame  28  and extends laterally across the machine  10 . By offsetting the bearing blocks from the center line of their respective knife holder assembly, better holder stability can be achieved. In addition, such arrangement enables adjacent holder assemblies to “nest” in the manner described in U.S. Patent Publication No. US 2003/020511. The reader will further appreciate that such linear bearing arrangements serve to enable the positions of the knife holder assemblies  200 ,  200 ′ to be selectively adjusted across the width of the machine.  
      As can be most particularly seen in  FIG. 6 , a conventional bearing assembly  230  is mounted within the bearing arbor  210  to rotatably support a knife shaft  232  within the bearing arbor  210 . The knife shaft  232  has a hub portion  233  that defines a first knife-receiving cavity  234  therein. In addition, a stripper ring retention flange  236  is also formed on one end of the knife shaft  232 . A conventional disk-like knife  240  is mounted within the knife-receiving cavity  234 . The disk-like knife  240  may be fabricated from tool steel and be formed with a shearing face  244 , a mounting face  246  and a circumferentially extending end surface  248 . The circumferentially extending end surface  248  forms a shearing edge or nip  250  with the shearing face  244 . A portion of the knife  240  is supported within the knife-receiving cavity  234  such that the mounting face  246  abuts a lateral wall  235  of the knife-receiving cavity  234 . A removable stripper ring retention flange  260  abuts a portion of the mounting face  246  and a series of cap screws  262  extend through the stripper ring retention flange  260  and knife  240  into the hub portion  233  of the knife shaft  232 . It is conceivable that other fastener arrangements may be employed to affix the knife and stripper ring retention flange  260  to the knife shaft  232 .  
      As can be seen in  FIGS. 5 and 6 , each knife holder assembly  200  further includes a female stripper ring  400  and a male stripper ring  500 . The female stripper ring  400  is oriented between the shearing face  244  of the corresponding knife  240  and the flanged portion  236  of the knife shaft  232 . The male stripper ring  500  is oriented between the mounting face  246  and stripper ring retention flange  260  that is mounted in the position shown in  FIG. 6 , by cap screws or other fasteners  262 .  
      As can be seen in  FIG. 6 , the knife holder assemblies  200  also include drive flange  270  that is jounaled onto the respective upper drive shaft  44  or lower drive shaft  46 , whichever the case may be. The drive flange  270  has a flanged portion  272  that may be affixed to the end of the hub portion  233  of the knife shaft  232  by a series of fasteners  276  or the like. See  FIGS. 3 and 6 . The drive flange  270  may further have a key  274  for receipt within a keyway  45  in the upper drive shaft  44  or a keyway  47  in the lower drive shaft  46 , whichever the case may be. In alternative embodiments, the drive shafts  44 ,  46  may be square in cross-section or have another cross-sectional shape to enable the drive shafts to be received thereon without the need for keys and associated keyway arrangements. Regardless of which method is employed, such arrangement causes the drive flange  270 , the knife shaft  232 , knife  240  and female and male stripper rings  400 ,  500  to rotate with the drive shaft  44  or  46 , whichever the case may be. The reader will further appreciate that the bearing assembly  230  enables the knife shaft  232 , knife  240 , and female and male stripper rings  400 ,  500  to rotate relative to the bearing arbor  210  as the drive shafts  44 ,  46  rotate. As can also be seen in  FIGS. 5 and 6 , in one embodiment, the knife holder assemblies may also include self lubricating bearings  480  journaled on the respective upper and lower drive shafts  44 ,  46  to between for mounting the corresponding bearing arbors  210  thereon. In other embodiments, however, such bearings may not be employed. Also, a separate bearing mounting flange  290  may be journaled on a hub portion  211  of the bearing arbor and the drive flange  270 . The bearing mounting flange  290  serves to clamp the inner bearing race of bearing assembly  230  and serves to house the O-ring grease seal therefor.  
      The knife holder assemblies  200 ′ are essentially identical in construction to the knife holder assemblies  200  except that the female stripper rings  400  are supported between the shearing face  244  of the knife  240  and the stripper retention flange  260  and the male stripper ring  500  is mounted between the mounting face  246  and the flange portion  233  of the knife shaft  232 . The knife holder assemblies  200  and  200 ′ forming an upper and lower pair of assemblies are thus oriented such that the shearing edge  250  of the upper knife  240  and the shearing edge  250  of the lower knife  240  are essentially aligned with each other as shown in  FIGS. 5 and 6 , or they may be oriented with a slight vertical overlap—for example 0.025 inches open (negative)—0.025 inches overlap (positive). Accordingly, the knives  240  of each pair of knife holder assemblies  200 ,  200 ′ are positioned close enough to each other to enable them to cut or shear the metal sheet  12  (or other material) as it passes between those knives  240 . The point at which the two knife edges  250  come together is referred to in the industry as the “nip”. The nip points have been generally designated as  251  in  FIGS. 5, 6  and  11 . In other words, the metal sheet  12  (or other material) is drawn between the two knives  240  of a pair of the knife holder assemblies  200 ,  200 ′ and the disk-like knives  240  shear the sheet  12  along the opposite cutting edges (the nip point  251 ), thus producing a clean longitudinal cut in the sheet.  
       FIGS. 7-10  illustrate one embodiment of a female compensating stripper ring  400  of the present invention that may be employed in connection with the knife holder assemblies  200 ,  200 ′ to accommodate or compensate for different material thicknesses. One female stripper ring  400  disclosed herein may be fabricated from a flexible material such as, for example, molded BUNA-N rubber material having a durometer of, for example, approximately 60-65. However, other materials with similar characteristics could be used. As can be seen in those Figures, a flexible female stripper ring  400  has a mounting hole  402  extending therethrough to enable the female stripper ring  400  to be journaled on the hub portion  233  of a knife shaft  232  (for knife holder assemblies  200 ) or on the stripper ring retention flange  260  (for knife holder assemblies  200 ′). In one embodiment for example, the female stripper ring  400  may have an outer diameter “OD” of approximately 13.240-13.245 inches (336.3-336.4 mm) and an inner diameter of approximately 11.499-11.501 inches (292.07-292.125 mm) and a central axis CA-CA. However, the female stripper ring  400  may be provided in other sizes that are tailored for a specific application.  
      The female stripper ring  400  also has a circumferentially extending driving surface  404  and a first lateral face  410  that extends between the mounting hole  402  and the circumferentially extending driving surface  404 . A second lateral face  430  extends opposite to the first lateral face  410  between the mounting hole  402  and the circumferentially extending driving surface  404 . See  FIG. 8 . A first relief means or first annular groove  412  is formed in the first lateral face  410  and a second relief means or annular groove  432  is formed in the second lateral face  430 .  
      In various embodiments, the first annular groove  412  has a first outer wall  414  and a first inner wall  416 . As can be seen in  FIG. 9 , the first outer wall  414  is closest to the circumferentially extending driving surface  404  and is spaced from the circumferentially extending driving surface  404  a first distance “A”. In one example, the first distance “A” maybe approximately 0.19 inches (4.9 mm) and the first outer wall  414  may be substantially concentric with the circumferentially extending driving surface  404 . The first inner wall  416  may be spaced a first inner distance “B” of approximately 0.25 inches (6.35 mm) and may be arranged such that the first inner wall  416  is not substantially parallel to the first outer wall  414 . In the example illustrated in  FIG. 9 , the first annular groove  412  may have a first depth “D” of approximately 0.25 inches (6.35 mm) and have a radiused bottom  418 . In one example, the radius “R” may be approximately 0.06 inches (1.52 mm) and the angle “Q” between the first inner wall and first outer wall may be, for example, approximately 25°. See  FIG. 10 .  
      Similarly, the second annular groove  432  has a second outer wall  434  and a second inner wall  436 . The second inner wall  436  is closer to the mounting hole  402  than the second outer wall  434  and is spaced from the mounting hole  402  a second distance “E” that may be substantially equal to the first distance “A” or it may differ from the first distance “A”. In the example depicted in  FIG. 9 , the distances “A” and “E” are substantially equal. The second outer wall  434  may be spaced from the second inner wall  436  a second inner distance “F” that may be substantially equal to the first inner distance “B” or it may differ from the first inner distance “B”. The second outer wall  434  may also be arranged such that it is not parallel to the second inner wall  436  and yet be substantially parallel to the first inner wall  416 . Thus, in various embodiments, angle “Q” may be approximately 25°. In one embodiment, the second annular groove  432  may have a depth “G” that is substantially equal to the first depth “D” or it may differ from the first depth “D”. In the embodiment depicted in  FIG. 9 , depths “D” and “G” are substantially equal.  
      In female stripper ring embodiments disclosed herein, the first and second annular grooves are shaped to achieve “parallelogram-type” compression which serves to prevent or otherwise minimize point loading when the stripper rings are compressed. For example, the offset annular grooves  412 ,  432  with the tapered inward walls allow the female stripper ring to compress and move in a vertical direction (vector arrow “V” in  FIG. 12 ) and also move in a horizontal direction (vector arrow “H” in  FIG. 12 ).  
      As can be seen in  FIG. 10 , the circumferentially extending driving surface  404  has a first width “W”. The first annular groove  412  serves to define a first outer hub portion  440  in the first lateral face  410 . Likewise, annular mounting surface  403  formed by mounting hole  402  in a central portion  405  has a second width “W” that is longer than first width “W” to form an inner hub portion  450  in the second lateral face  430 . The inner hub portion  450  protrudes outwardly a distance “X” from the second lateral face  430 . See  FIG. 10 . Such distance “X” serves to provide a gap which can accommodate the horizontal movement of the stripper ring  400  when under compression. Such unique and novel arrangement serves to facilitate the application of a constant vertical pinch (compression) load across the portion of the drive surface  404  under compression and thereby apply a slight tension to the strip material entering the slitter nip  251 .  
      In various embodiments, the female stripper ring  400  in one knife holder assembly  200  is oriented adjacent one side of its corresponding knife  240  and the female stripper ring  400  in the complementary knife holder assembly  200 ′ is located on the opposite side of its corresponding knife  240 . For example, as can be seen in  FIG. 6 , the female stripper ring  400  in the upper knife holder assembly  200  is oriented adjacent the left side (which is adjacent to the shearing face  244 ) of that knife  240 . The female stripper ring  400  of the lower knife assembly  200 ′, however, is located on the right side (which is adjacent to the shearing face  244 ) of that knife  240 . Thus, as can be seen in that Figure, the upper (left) female stripper ring  400  is free to move horizontally toward the right (arrow—“H”) when placed under compression during operation and the lower (right) stripper ring  400  is free to move horizontally (arrow “H”) toward the left when placed under compression during operation. Such flexing of the female stripper rings in opposing horizontal directions serves to apply a slight horizontal loading to the material and keep it relatively tight as it enters the nip  251 .  
      Also in various non-limiting embodiments, the knife holder assemblies  200 ,  200 ′ each further include a male stripper ring  500 . See  FIG. 11 . The male stripper rings  500  have a mounting hole  502 , a first lateral face  504  and a second lateral face  506  and a circumferentially extending driving surface  508 . In various embodiments, the male stripper rings  500  may be fabricated from 70 to 75 durometer material. In various embodiments, the male stripper rings  500  are preferably stiffer (less compressive) than the female stripper rings  400  and are 0.010 inches to 0.020 inches large in diameter than the slitter knives  240  to prevent the non-cutting knife edge from marking the slit product.  
       FIG. 11  is an enlarged view illustrating the orientations of the male and female stripper rings  400 ,  500 , respectively, in a knife holder assembly  200  relative to the female and male stripper rings  400 ,  500  in a knife holder assembly  200 ′ of a corresponding pair of knife holder assemblies  200 ,  200 ′. As can be seen in that Figure, the female stripper ring  400  of the knife holder  200  is mounted on the hub portion  233  of the knife shaft  232 . The second lateral face  430  of the female stripper ring  400  is located adjacent to the shearing face  244  of the knife  240 . The end of the inner hub portion  450  of the female stripper ring  400  abuts the shearing face  244  and serves to form a clearance distance “CD” between the shearing face  244  and the second lateral face  430  of the female stripper ring  400 . The reader will appreciate that in an “unflexed” or “uncompressed” state, the clearance distance “CD” will be substantially equal to distance “X”. The circumferentially extending driving surface  404  of the female stripper ring  400  is in confronting relationship with the circumferentially extending surface  248  of the knife  240  in the corresponding knife holding assembly  200 ′ and also in confronting relationship with a portion of the circumferentially driving surface  508  of the male stripper ring  500  in the knife holding assembly  200 ′. The female and male stripper rings  400 ,  500  of one knife holder assembly  200  do not have to overlap the corresponding male and female stripper rings  400 ,  500  in a corresponding knife holder  200 ′. However, those rings will tend to overlap more as the knives are reconditioned (face ground) to a thickness of 0.50 inches from their original 0.75″ or whatever the case may be. As can be seen in  FIG. 11 , the female stripper ring  400  in the knife holding assembly  200 ′ is similarly oriented relative to the knife  240  and the male stripper ring  500  in the knife holding assembly  200 .  
      As the material passes between the knife assemblies  200 ,  200 ′ on the upper and lower drive shafts  44 ,  46 , the unique and novel female stripper rings  400  can essentially flex or compress in separate vertical and horizontal directions. The arrows “T” in  FIGS. 12 and 13  represent the application of compression forces to the circumferentially driving surface  404  when the material  12  enters between the female stripper ring  400  and the opposing knife  240  and male stripper ring  500 . As the female stripper ring  400  is compressed, it can deflect in a parallelogram-like fashion moving in a vertical direction (i.e., in a direction away from central axis CA-CA) which is represented by the vector arrows “V” in  FIGS. 12 and 13  and also in a horizontal direction (in a direction essentially parallel to the central axis CA-CA) represented by the vector arrow “H”. As can be seen in  FIG. 13 , the female stripper ring  400  may move in a direction that is the resultant of the vertical and horizontal vectors (represented by the vector “R” in  FIG. 13 ) such that the portion of the drive surface  404  that is under compression is substantially parallel with a corresponding portion of the mounting surface  403  thereby causing the female stripper ring to slightly “collapse” while retaining a parallelogram-like shape.  FIG. 13  illustrates the parallelogram-like deflection in phantom lines. Such “multi-directional” defection of the female stripper rings  400  is accommodated by virtue of the first and second annular grooves  412 ,  432  and their diagonal orientation relative to each other. Thus, the reader will appreciate that such unique and novel compensating stripper ring arrangement enables the slitter to accommodate materials of varying thickness (within a range of acceptable thicknesses) without the need to exchange one diameter stripper rings with stripper rings having another diameter to enable the machine to accommodate different material thicknesses.  
      The invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. The embodiments are therefore to be regarded as illustrative rather than restrictive. Variations and changes may be made by others without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such equivalents, variations and changes which fall within the spirit and scope of the present invention as defined in the claims be embraced thereby.