Abstract:
A cutter drum for a rotary cutting apparatus comprises a substantially circular-cylindrical portion provided with at least one cutting member having a longitudinal extension, the surface thereof being divided into a body portion having a first and a second side portion, and a main edge portion between said first and second side portions and substantially across the longitudinal extension of the cutting member. In accordance with the invention, an intermediate portion having a predetermined radius is provided on each side of said main edge portion, said intermediate portion connecting said main edge portion directly or indirectly to said body portion. 
     The invention also relates to a rotary cutting apparatus comprising an anvil drum and such a cutter drum.

Description:
TECHNICAL BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a cutter drum for a rotary cutting apparatus comprising a substantially circular-cylindrical portion provided with at least one cutting member having a longitudinal extension, the surface thereof being divided into a body portion having a first and a second side portion, and a main edge portion between said first and second side portions and substantially across the longitudinal extension of the cutting member. 
         [0002]    The invention also relates to a rotary cutting apparatus comprising an anvil drum and such a cutter drum. 
         [0003]    Such a cutter drum is known from JP 11-188698. Other cutter drums are known from JP 2001-269896 and JP 9-267 299. All of them reside in the drawback that the edge/edges of the cutting member are sharp. This is a major drawback, since, sharp edges require a surface roughness R A  on the top of the edge and on the sides that is less then 0.3 μm. Furthermore, sharp edges are fragile and may be chipped away, and may prevent cutting to be performed, requiring re-sharpening of the edge, in turn reducing the life time of the cutter drum as well as of the anvil drum. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is to improve the properties of the cutting member. 
         [0005]    This object has been achieved by a cutter drum of the initially defined kind, which further comprises an intermediate portion having a predetermined radius is provided on each side of said main edge portion, said intermediate portion connecting said main edge portion directly or indirectly to said body portion. 
         [0006]    Hereby is achieved a more robust edge. It furthermore allows higher surface roughness and increases the lifetime of the cutter drum. Surprisingly was also achieved a reduced cutting effort in the range of 20-40%. Furthermore, less pressure is needed during cutting of a web, due to a progressive pressure created by the defined shape. 
     
     
       DRAWING SUMMARY 
         [0007]    In the following, the invention will be described in more detail with reference to the accompanying drawings, in which 
           [0008]      FIG. 1  is a lateral cross-section of a first embodiment of a cutting member of the rotary cutter drum of a rotary cutting apparatus. 
           [0009]      FIG. 2  is a lateral cross-section of a second embodiment of the cutting member; 
           [0010]      FIG. 3  is a lateral cross-section of a third embodiment of the cutting member; 
           [0011]      FIG. 4  is a lateral cross-section of a fourth embodiment of the cutting member; 
           [0012]      FIG. 5  is a lateral cross-section of a fifth embodiment of the cutting member; 
           [0013]      FIG. 6  is a lateral cross-section of a sixth embodiment of the cutting member; 
           [0014]      FIG. 7  is a lateral cross-section of a seventh embodiment of the cutting member; 
           [0015]      FIG. 8  is a lateral cross-section of a eighth embodiment of the cutting member; and 
           [0016]      FIG. 9  is a perspective view of a rotary cutting apparatus provided with a rotary cutter drum and a cutting member according to any one of  FIGS. 1-8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is a cross-section of a cutting member  10  of a rotary cutter drum  2  (see  FIG. 9 ). The cutting member  10  is provided with a body portion  12  and an edge portion  14 . The body portion has on each side of it a first side portion  16  and a second side portion  18 , whereas the edge portion  14  is provided with a main edge portion  20  and intermediate portions  28 ,  30  on each side of the main edge portion  20 . 
         [0018]    The main edge portion  20  is relatively linear, as seen in the lateral cross-section according to  FIG. 1 , and has a lateral extension L. 
         [0019]    The lateral extension of the intermediate portions  28 ,  30  is denoted I 1  and I 2 , respectively. The intermediate portions  28 ,  30  also have a curved surface of a desired radius r 1  and r 2 , respectively. 
         [0020]    The angle of the side surfaces  16 ,  18  with respect to a radial plane of the cutter drum  2  is denoted γ 1  and γ 2 , respectively. 
         [0021]    The shape of this cutting member is symmetrical, for which reason I 1 =I 2 ; r 1 =r 2  and γ 1 =γ 2 . 
         [0022]      FIG. 2  illustrates a second embodiment, which is very similar to that of the first embodiment, however being different in the main edge portion  20  is curved between the intermediate portions  28 ,  30 . The curved main edge portion has a radius R. 
         [0023]      FIG. 3  illustrates a third embodiment, which in turn is very similar to that of the second embodiment. The difference lies however in a non-symmetrical shape of the cutting member  10 . The broken line B in  FIG. 3  is a centre line in case of symmetry. 
         [0024]    Accordingly, the angle γ 2  is larger than γ 1 , causing the first side portion  16  to have a steeper slope than the second side portion  18 . Furthermore, the second radius r 1  of the second intermediate portion is smaller than the radius r 2  of the first intermediate portion, and the lateral extension I 1  of the second intermediate portion  30  is larger than the lateral extension I 2  of the first intermediate portion  28 . 
         [0025]    It should however be noted that it would be possible that I 1 =I 2  and that r 1 =r 2 . 
         [0026]      FIG. 4  illustrates a fourth embodiment, according to which the edge portion  14  is not only provided with the first and second intermediate portion  28 ,  30  on each side of the main edge portion  20 , but also with a first side edge portion  22  between the first intermediate portion  28  and the first side portion  16 , and with a second side edge portion  24  between the second intermediate portion  30  and the second side portion  18 . 
         [0027]    As in the previous embodiments, the angle of the side surfaces  16 ,  18  with respect to a radial plane of the cutter drum  2  is denoted γ 1  and γ 2 , respectively. 
         [0028]    Furthermore, the angle of the first and second side edge portions  22 ,  24  with respect to a radial plane of the cutter drum  2  is denoted α 1  and α 2 , respectively. 
         [0029]    The shape of this cutting member is symmetrical, for which reason I 1 =I 2 ; r 1 =r 2 ; γ 1 =γ 2  and α 1 =α 2 . 
         [0030]      FIG. 5  illustrates a fifth embodiment, which is very similar to that of the fourth embodiment, however being different in the main edge portion  20  is curved between the intermediate portions  28 ,  30 . The curved main edge portion has a radius R. 
         [0031]      FIG. 6  illustrates a sixth embodiment, which is very similar to that of the first embodiment. The difference lies however in a non-symmetrical shape of the cutting member  10 . The broken line B in  FIG. 6  is a centre line in case of symmetry. 
         [0032]    Accordingly, the main cutting edge  20  is not arranged centrally, but the lateral extension L thereof is pushed to the right. Furthermore, angle γ 2  is larger than γ 1 , causing the first side portion  16  to have a steeper slope than the second side portion  18 . Furthermore, the second radius r 1  of the second intermediate portion is smaller than the radius r 2  of the first intermediate portion, and the lateral extension I 1  of the second intermediate portion  30  is larger than the lateral extension I 2  of the first intermediate portion  28 . 
         [0033]      FIG. 7  illustrates a seventh embodiment, which is very similar to that of the sixth embodiment, i.e. what is stated in connection with the embodiment of  FIG. 6  regarding the relationships of I 1 , I 2 , r 1  and r 2  also relates to the embodiment of  FIG. 7 . It is however different in that the edge portion  14  is not only provided with the first and second intermediate portion  28 ,  30  on each side of the main edge portion  20 , but also with a first side edge portion  22  between the first intermediate portion  28  and the first side portion  16 , and with a second side edge portion  24  between the second intermediate portion  30  and the second side portion  18 . 
         [0034]    The angle of the first and second side edge portions  22 ,  24  with respect to a radial plane of the cutter drum  2  is denoted α 1  and α 2 , respectively, and α 2 &gt;α 1 . 
         [0035]    For the corresponding reasons as those relating to the embodiment of  FIG. 6 , γ 2 &gt;γ 1 . On the other hand, even though α 2 &gt;α 1 , it is possible in the embodiment of  FIG. 7 , that γ 2 &gt;γ 1 . 
         [0036]      FIG. 8  illustrates an eighth embodiment, which is very similar to that of the seventh embodiment, i.e. what is stated in connection with  FIG. 7  regarding the angles and the lateral extensions also relates to the embodiment of  FIG. 8 . It is however different in that the main edge portion  20  is curved between the intermediate portions  28 ,  30 . The curved main edge portion has a radius R. 
         [0037]    In all the above embodiments the following ranges are suitable: 
       L=10-60 μm 
     R=10-80 μm 
     I 1 =5-50 μm 
     I 2 =5-50 μm 
       [0038]    r 1 =5-50 μm
 
r 2 =5-50 μm
 
         [0039]      FIG. 9  illustrates a rotary cutting apparatus  1  provided with a rotary cutter drum  2  and an anvil drum  3  in cutting relationship with one another, for which reason the rotary cutter drum is provided with one or more cutting members  10 , having the shape of articles to be cut from a web introduced between the rotary cutter drum  2  and the anvil drum  3 . 
         [0040]    It has surprisingly been proven that the cutting effort was reduced in the range of 20-40% by means of the cutter drum according to the invention. 
         [0041]    Furthermore, a more robust edge than according to the prior art was achieved. 
         [0042]    Yet furthermore a better surface roughness was achieved, which in turn increases the lifetime of the cutter drum. 
         [0043]    The cutting member  10  according to any one of the above embodiments can be manufactured by grinding a non-shaped member protruding substantially radially from the cutter drum by means of e.g. a diamond wheel shaped to a rounded form, for creating the rounded shape according to the invention. Alternatively, the cutting member is first provided with e.g. sharp edges. The edges are then treated by brushing or by sputtering of abrasive particles for achieving the desired widths and radii of the edges. 
         [0044]    Prior art cutting members having sharp edges on either sides of a flat surface, causes the fibre material of the web to be pressed against the anvil. The flat surface and sharp edges prevent the fibre material from escaping laterally away from the edges. This requires a high applied pressure and two cuts on each side of the flat surface, i.e. the compressed portion will be cut along the two sharp edges. 
         [0045]    The cutting member according to the invention will instead allow the compressed material to move side-wards, depending on the fact that the rounded edges will create a progressive pressure on the web, and will surprisingly cause the web to tear somewhere between the rounded edges  28 ,  30  at less pressure than what is the case regarding the prior art cutting members having sharp edges. 
         [0046]    This progressive pressure is enhanced by the first and second side edge portion  22 ,  24 .