A PERFORATOR WHEEL

Abstract: A perforator wheel (31) for perforating thin materials, such as paper. The perforator wheel (31) is provided with a plurality of peripheral teeth (32) interspaced by means of intermediate slots (36). The teeth (32) are provided with two outer lateral faces (34, 35) bevelled so as to form a cutting edge (36). The length of the two lateral faces (34, 35) of the teeth is different from each other.

Description: Title: A Perforator Wheel. Technical Field The present invention relates to a perforator wheel for perforating thin materials, such as paper, and comprising a plurality of peripheral teeth interspaced by means of outer lateral faces bevelled so as to form a cutting edge. Background Art As it is commonly known, such perforator wheels are provided with a cutting edge along the periphery. The cutting edge is formed of a plurality of teeth interspaced by means of intermediate slots. When perforating a workpiece, such as a sheet of paper, said piece is fed in between the rotating perforator wheel and a support, usually a rotating roller. As a result, the cutting edge perforates the workpiece, the slots between the teeth forming non-slit portions on the workpiece between the comparatively longer slit portions. Subsequent to perforation, the workpiece is weakened along the line, in which the perforation was carried out. This weakening or perforation line is thus formed of a plurality of slit, narrow, elongated portions and intermediate, non-slit portions. Due to the weakening, the line of perforation may be used for severing the workpiece. It is vital for easy and effortless severing of the workpiece that the perforation line is narrow, i.e. the teeth need be sharp, and that the non-slit portions are short. It is thus commonly known to regrind the perforator wheel, when the cutting edges of the teeth are worn and no longer sharp. When regrinding, material are removed on both lateral faces of the symmetrical teeth, until said teeth are sharp once again. Having being been sharpened a few times, for instance three or four times, the height of the teeth is reduced to such a degree that continuous use of the perforator wheel results in complete severing of the workpiece instead of a perforation thereof. The known perforator wheels are thus discarded after three to four regrindings. Yet another problem in known perforator wheels is that the bottom of the slots between the teeth is essentially perpendicular to the plane of the cutting edges of the teeth, i.e. parallel to the axis of the perforator wheel. Consequently, the residues from the paper are accumulated in the slots and cause poor perforation, the perfora- tor wheel severing the workpiece instead of perforating these, when the slots are filled up with residues. US 3,978,753 discloses a perforator wheel formed as two mutually rotatable halves, whereby long cutting teeth and corresponding short slots are provided along the periphery. However, such a perforator wheel is encumbered with the same short- comings as conventional perforator wheels, as said wheel also have to be discarded after three or four regrindings. The problem of accumulating residues also exists in these perforator wheels, the bottom of the slots being perpendicular to the plane of the cutting edges. Brief Description of the Invention The object if the present invention is thus to provide a perforator wheel of the above type, in which the shape of the teeth is such that more regrindings of the perforator wheel may be carried out than on the known perforator wheels, and in which the problem of the accumulating residues between the teeth is avoided. The perforator wheel according to the invention is characterised in that the length of the two lateral faces of the teeth is different from one another. This entails that the bottom of the slots between the teeth form an acute angle with the plane through the cutting edges of the teeth or in other words the bottom is not parallel to the axis of the perforator wheel. A perforator wheel is thus obtained, which only need be ground on the short face of the two lateral faces at sharpening, whereby more regrindings may be carried out than on known perforator wheels. This is a particular advantage in perforator wheels for the formation of so-called mini or micro perfora¬ tions, i.e. perforations with very small slit portions and non-slit portions, for instance in the order of 0.15 mm to 0.30 mm, as such wheels are comparatively expensive. At the same time, the inclined bottom of the slots between teeth reduces the risk of accumulating residues in the slots between the teeth. According to the invention, the first lateral face of teeth may be three and preferably essentially five times longer than the second lateral face. In practice, this embodi- ments has proved particularly advantageous. Moreover, according to the invention, the bottom of the slots between the teeth are essentially parallel to the longest of the two lateral faces. A perforator wheel is hereby obtained, in which the radial tooth height is not altered at regrinding and in which the risk of residues from the paper accumulating in the slots between the teeth is minimized. Further, according to the invention, the lateral faces may be rectilinear as seen in a radial cross-sectional view, whereby a perforator wheel, which is easy to sharpen, is obtained. Finally, according to the invention, the two opposing lateral faces may form an angle with each other at essentially 60°. In practice, impeccable perforations are obtained at this angle. Brief Description of the Drawings. The invention is explained in detail below with reference to the drawings, in which Fig. 1 is a partial, radial sectional view between the two teeth and a partial side view of a perforator wheel according to prior art. Fig. 2 illustrates the same view as in Fig. 1 of a perforator wheel according to the invention, and Fig. 3 is fractional view of the perforator wheel according to the invention seen from the left-hand side of Fig. 2. Best Mode for Carrying Out the Invention Fig. 1 illustrates a conventional perforator wheel 1 being provided with a plurality of teeth 2 having cutting edges 3 along the periphery. Each tooth 2 is provided with two faces of equal length and converging with each other in a radially outward direction. A slot 6 is provided between each pair of teeth 2a, 2b. Each slot has a bottom 7 being essentially perpendicular to a plane through the cutting edges 3 of the teeth, i.e. essentially parallel to the axis 9 of the perforator wheel. The perfora¬ tor wheel 1 is further provided with an axial through-going hole 8 adapted to receive an axle. Figs. 2 and 3 illustrate a perforator wheel 31 according to the invention in the same manner as the known perforator wheel 1 shown in Fig. 1. Along the periphery, the perforator wheel is provided with teeth 32 forming the cutting edges 33. The teeth 32 have two lateral faces 34 and 35 converging in relation to each other in a radially outward direction. The lateral faces 34, 35 form an angle of essentially 30° to a plane comprising the cutting edges of the teeth. The length L34 of the first lateral face 34 is essentially longer than the length L35 of the second lateral face 35. A slot 36 is provided between each pair of teeth 32a, 32b. As it is evident from Fig. 2, the bottom 37 of the slot is essentially parallel to the longest face of the tooth 34. The height H 32 of the teeth is essentially 0.5 mm. The perforator wheel is further provided with a central, through-going hole 38. The perforator wheel 31 according to the invention is preferably made of a alloyed, hardened steel, such as UBH Arne . The perforator wheel according to the inven¬ tion is preferably used for paper, but may also be used for other materials, such a plastic. The perforator wheel may be provided with an optional number of teeth, said wheel usually having 25 to 94 teeth per inch. The edge life of the perforator wheel is generally about 500,000 A4 sheets. As mentioned above, the known perforator wheel 1 is reground on both lateral faces 4, 5 and can be sharpened three to four times. The perforator wheel 31 according to the invention is only reground on the short lateral face 35. Depending on the length L34 of the long lateral face 34, the perforator wheel according to the invention may be reground about twenty to twenty-five times. The tool life of a perforator wheel according to the invention is thus improved by five to six times relative to conventional perforator wheels. In addition, in case a perforator wheel of the conventional type is dropped on the floor, the teeth are deformed to such an extent that the perforator wheel no longer is usable. However, if the perforator wheel according to the invention is dropped on the floor, it is often possible to remove the deformed portion of the teeth by regrinding and still make use of the perforator wheel. The invention has been described with reference to an example of an embodiment. Many modifications can be carried out without thereby deviating from the scope of the invention. The angles of the two lateral faces with the plane may thus differ through the cutting edges of teeth from one another and said faces may mutually form other angles than the said 60°. Moreover, the long lateral face and the bottom of the slot need not be parallel to each other, but may form an angle with each other.

Claims: Claims 1. A perforator wheel (31) for perforating thin materials, such a paper, provided with a plurality of peripheral teeth (32) interspaced by means of interme¬ diate slots (36), said teeth (32) having with two outer lateral faces (34,35) bevelled so as to form a cutting edge (33), characterised in that the length of the two lateral faces (34,35) of the teeth is different from each other. 2. A perforator wheel (31) according to claim 1, characterised in that the first lateral face (34) is essentially three and preferably five times longer than the second lateral face (35). 3. A perforator wheel (31) according to claim 1 or 2, characterised in that the bottom of the slots (36) between the teeth (32) is essentially parallel to the longest of the two lateral faces (34,35). 4. A perforator wheel (31) according to one or more of the preceding claims, characterised in that the lateral faces (34,35) are rectilinear, when seen in a radial cross-sectional view. 5. A perforator wheel (31) according one or more of the preceding claims, characterised in that the two outer lateral faces (34,35) form an angle with each other of essentially 60°.

Inventors: JAHN BIRGER, JAHN, BIRGER
Applicants: JAHN BIRGER, SVEND CARSTENSEN SLIBERI OG MA, JAHN, BIRGER, SVEND CARSTENSEN SLIBERI OG MASKINFABRIK APS
Application year: 1995
Main classification: B26F1
IPC codes: B26F1