Abstract:
A cutting apparatus for severing a web has a first moveable cutting blade, a second stationary cutting blade and a rotatable cutting cylinder, which has on its circumference at least one first cutting blade, wherein the first and second cutting blades each have at least one cutting edge, wherein the first cutting blade cooperates with the second stationary cutting blade to sever the web in a transverse direction and at least one of the first and second cutting blades is self-resilient.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority of European Patent Application No. 03405758.8, filed on Oct. 20, 2003, the subject matter of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a cutting apparatus for severing a web and is of the type which has a rotatable cutting cylinder provided at a circumference thereof with at least one first cutting blade which cooperates with a stationary second cutting blade for severing the sheet material in a transverse direction.  
         [0003]     A cutting apparatus of the above-outlined type is disclosed in the assignee&#39;s European Patent Document No. 1 186 561 A. The cutting apparatus serves for severing paper or film webs and has been proven in practice. The cutting cylinder is supported in side plates by tapered roller bearings. During cutting, heat is transmitted by the tapered roller bearings to the side plates, and as a consequence of the resulting heat expansion of the side plates, an increase of the distance between the two cutting blades occurs. As a rule, such a distance increase causes the cutting quality to deteriorate. By reducing the distance while the machine is warm, the distance can again be optimally set and thus the desired high cutting quality can be restored. This, however, has the disadvantage that at the beginning of the morning shift, when the cutting apparatus is restarted, a relatively large wear at both cutting blades occurs, since the distance has decreased due to the then cold machine. Heretofore this difficulty has been resolved by installing heatable bearings. Such heatable bearings, however, involve substantial expense and installing problems. Further, the heaters for pre-heating the lateral bearings have to be turned on hours before operation.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the invention to provide a cutting apparatus of the above-outlined type which avoids the discussed disadvantages and which thus makes possible a simplification of the maintenance and servicing, while ensuring a high cutting quality.  
         [0005]     The above and other objects are accomplished according to the invention by the provision of a cutting apparatus for severing a web, comprising: a first moveable cutting blade; a second stationary cutting blade; and a rotatable cutting cylinder which has on its circumference at least one first cutting blade; wherein the first and second cutting blades each have at least one cutting edge, the first cutting blade cooperates with the second stationary cutting blade to sever the web in a transverse direction and at least one of the first and second cutting blades is self-resilient.  
         [0006]     Thus, according to the invention, the above-described conventional cutting apparatus is improved in that at least one of the two cutting blades are self-resilient. In the cutting apparatus according to the invention the self-resilient cutting blade essentially works like a spring during the cutting operation and therefore such a self-resilient cutting blade is significantly more tolerant as concerns distance variations between the two cutting blades. While the self-resilient cutting blade cuts with the required high quality when the cutting apparatus is warm, in case of a cold cutting apparatus and thus at reduced distance between the cutting blades, the latter are not worn out in a short period of time and thus a high cutting quality may be obtained.  
         [0007]     According to an advantageous feature of the invention it is the stationary cutting blade which is self-resilient. Basically, however, the cutting blade mounted on the cutting cylinder may also be self-resilient.  
         [0008]     According to a further feature of the invention, the self-resilient cutting blade has at least one opening which, in accordance with a further feature of the invention, is a slot extending at least approximately parallel to one cutting edge into which the self-resilient cutting blade may resiliently penetrate. The slot is preferably so structured that it extends between the two cutting edges. It is a particular advantage of this construction that the self-resilient cutting blade may be particularly simply re-sharpened, since two surfaces forming cutting edges lie in one plane. One of such surfaces may be used, with one of the bordering abutment surface, for positioning the self-resilient cutting blade, while the other cutting edge is active. By inverting the cutting blade the cutting edges may be exchanged.  
         [0009]     According to a further embodiment of the invention, the self-resilient cutting blade has two slots, each arranged between two cutting edges which resiliently penetrate into the common slot. In such a cutting apparatus the self-resilient cutting blade has four cutting edges which may be exchanged by inverting the cutting blade. For this purpose only two cutting edge-forming surfaces are required and, accordingly, re-sharpening is relatively simple. For this embodiment too, it is provided that an inactive cutting edge lies against an abutment surface and thus positions the self-resilient cutting blade.  
         [0010]     According to a further feature of the invention, on the self-resilient cutting blade a cover bar is disposed which has a frontal edge extending essentially parallel to and spaced from, a cutting edge. By means of the cover bar the active cutting edge and thus the resilient region of the cutting blade may be stabilized. The cover bar is preferably shiftable, so that undesired oscillations of the resilient region of the cutting blade are effectively prevented.  
         [0011]     According to a further feature of the invention, the self-resilient cutting blade is staggered. This arrangement provides for a resilient region supported in a free-standing manner. In such a construction the self-resilient cutting blade preferably has two cutting edges which may be exchanged.  
         [0012]     According to a further feature of the invention, the self-resilient cutting blade is relatively thin at least in the region of an active cutting edge and is supported in a free-standing manner in such a region. Such a cutting blade preferably has four cutting edges. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Further advantageous features appear in the dependent claims, the specification which follows and the drawing.  
         [0014]     Several embodiments of the invention will be discussed in more detail in the following specification in conjunction with the drawing, wherein:  
         [0015]      FIG. 1  is a schematic view of a cutting apparatus according to the invention,  
         [0016]      FIG. 2  is an enlarged detailed schematic of  FIG. 1 ,  
         [0017]      FIG. 3  is a detailed schematic of a variation of the cutting apparatus according to the invention and  
         [0018]      FIG. 4  is a detailed schematic of an additional variation of the cutting apparatus according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The cutting apparatus  1  illustrated in  FIGS. 1 and 2  serves for severing an endless web  12 , particularly a paper web, into uniform portions. Feeding of the web  12  occurs continuously in the direction of arrow  13  by pushing and pulling. Means for feeding the web  12  is well known to those skilled in the art and need therefore not be discussed in further detail. The web  12  is thus advanced from the left to the right in the direction of the arrow  25 .  
         [0020]     For the purpose of severing the web  12  transversely to the feeding direction, the cutting apparatus  1  includes a cutting cylinder  8  which is continuously rotated in the direction of the arrow  11  about a rotary axis  10 . The drive for rotating the cutting cylinder  8  as well as the side plates and bearings for the cutting cylinder  8  are known by themselves and are not shown.  
         [0021]     On a circumference  9  of the cutting cylinder  8  at least one bar-shaped cutting blade  4  is mounted which has at least one cutting edge  14 , having a length that at least equals the width of the web  12 . Such width is, for example, in the range of from 520 mm to 740 mm. The cutting cylinder  8  has at least one cutting blade  4 , but it may have several such cutting blades  4 , so that relatively narrow strips may also be severed from the web  12 .  
         [0022]     The cutting blade  4  cooperates with a likewise bar-shaped cutting blade  5  which is affixed to a carrier  15 . For positioning the cutting blade  5  on the carrier  15 , the latter has an abutment surface  22  against which the cutting blade  5  lies with a surface  23 . Further, the cutting blade  5  engages face-to-face a surface  31  of the carrier  15 .  
         [0023]     The cutting blade  5  is provided with two slots  20  and  21  which extend preferably over the entire length of the bar-shaped cutting blade  5  and which are both open at their end. The slot  20  is situated essentially centrally between an active cutting edge  18   a  and an inactive cutting edge  18   b . The slot  20  forms two regions  32  and  33  which are relatively thin-walled and which may be resiliently deflected. The region  33  is inactive (quieted) as shown in  FIG. 2 , while the region  32  may be deflected toward the slot  20 . In case the cutting blade  4  hits the cutting edge  18   a , the latter may resiliently penetrate into the slot  20  in the direction of the arrow  19 . The deflection in the direction of the arrow  19  is, to be sure, relatively small and amounts to a few hundreds of one mm. The cutting blade  5  may be inverted to situate the cutting edge  18   a  in the region of the abutment surface  22 , thus rendering it inactive, while the cutting edge  18   b  will be active.  
         [0024]     The cutting blade  5  has a further slot  21  as well as two further cutting edges  18   c  and  18   d . Thus, the cutting blade  5  has a total of four cutting edges  18   a ,  18   b ,  18   c  and  18   d . All cutting edges may be exchanged. Re-sharpening is performed at the surfaces  23  and  24 , so that simultaneously two cutting edges may be sharpened.  
         [0025]     The cutting blade  5  has a planar surface  26  oriented parallel to the surface  31  of the carrier  15 . A cover bar  16  lies against the cutting blade  5  at the surface  26  and in the vicinity of the cutting edge  18   a . A frontal edge  17  of the cover bar  16  extends parallel to the cutting edge  18   a . By means of the cover bar  16  the resilient region  32  is stabilized and thus undesired oscillations of the region  32  are prevented. The cover bar  16  is preferably shiftable for adjusting the distance of the edge  17  from the cutting edge  18   a . Such a construction ensures an optimal support of the resilient region  32 .  
         [0026]     While as a rule, the two cutting blades  4  and  5  and thus the cutting edges  14  and  18   a  do not extend axially parallel, it is feasible to arrange them in an axially parallel manner.  
         [0027]     The cutting blade  5  is, in view of the above-described construction, self-resilient, and it is thus ensured that the cutting blade  5  behaves as a spring and is significantly more tolerant to distance variations. Thus, if the axis  10  moves upward or downward due to temperature changes at the side plates, such distance variations may be taken up by the cutting edge  18   a  by a resilient deflection thereof without an appreciable additional wear and without a deterioration of the cutting quality. In this manner the service life of the cutting blade  5  may be substantially extended.  
         [0028]     In the cutting apparatus  1  the cutting blade  5  is of self-resilient construction. In the alternative, it is basically feasible to design the cutting blade  4  as being self-resilient and the cutting blade  5  as being rigid. Further, basically an embodiment is feasible where both cutting blades  4  and  5  are self-resilient.  
         [0029]      FIG. 3  illustrates a part of a cutting apparatus  2  showing a variant of the invention. In this embodiment a self-resilient cutting blade  6  is supported on a carrier  15 ′ which has, in the region of a cutting edge  27 , an aperture  28  permitting a deflection of the cutting edge  27 . The cutting blade  6 , which is relatively thin, thus making possible a resilient deflection thereof, is positioned on the abutment surface  22 . Therefore, upon deflection, the cutting blade  6  rubs against the abutment surface  22 .  
         [0030]      FIG. 4  illustrates a part of a cutting apparatus  3  showing a further variant of the invention. In this embodiment a self-resilient cutting blade  7  is provided which is supported on a carrier  15 ″. The cutting blade  7  is of staggered design and has an active cutting edge  29   a  and an inactive (quieted) cutting edge  29   b . Between a resilient region  34  and the carrier  15 ″ a gap-like intermediate space  30  is provided which makes possible a deflection of the resilient region  34  during cutting. Similarly to the earlier-described embodiments, in the cutting apparatus  3  too, a cover bar  16  is provided. In this embodiment the cutting blade  7  has only two exchangeable cutting edges  29   a  and  29   b . The positioning of the cutting blade  7  is effected at an abutment surface  35 .  
         [0031]     The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.