Machine for slitting plane packaging blanks

A machine for slitting plane packaging blanks made of corrugated board comprising:

• a driving roller assembly for advancing said packaging blanks;
• at least one rotatable slitting roller with at least one knife for producing a front edge slit and/or a rear edge slit in each packaging blank, said knife being sector-shaped, and defined by two knife end edges, a first knife portion adjacent a first knife end edge being adapted to cut the front edge slit out in a front edge of said blank and a second knife portion adjacent a second knife end edge adapted to cut a rear edge slit out in a rear edge of said blank and rearwards through said rear edge while said blank is advanced through the machine at a uniform speed, wherein the sector-shaped knife extends over a per se known central angle (v) of approx 225-300°;
• a driving motor connected to the slitting roller;
• a program timer for controlling the driving motor and rotation of the rotatable slitting roller, wherein the program timer controls the driving motor such that the first knife end edge is initially positioned at a predetermined angle (x) from a cutting nip site, the predetermined angle (x) corresponding to a desired slit length taken along an outer radial edge of the slitting roller, where the arc π/180 rx and r is the radius of the knife, and when the front edge of the blank has reached a cutting site the program timer turns the rotatable slitting roller forward until the front edge slit has been cut, and wherein said knife is retarded when a knife gap is positioned above the blank and wherein the rotatable slitting roller is turned such that the second knife end edge of said second knife portion is turned from an initial angular position (y) and downwards into the blank at the cutting site for the production of the rear edge slit, and is subsequently turned an arc substantially corresponding to a length (b) of the rear edge slit of said blank, where said second knife end edge is retarded and then turned in such a manner that the first knife end edge reaches the initial position ready to make slits in a subsequent packaging blank;
• a back-pressure roller having a resilient coating comprising rubber provided below the slitting roller, said backpressure roller including two relatively thin, circular disks interspaced a distance corresponding to the thickness of the knife, the knife extending a distance into the space between the two circular disks and forming the cutting nip site;
• and
• at least one sensor provided upstream of said at least one rotatable slitting roller for detecting said packaging blanks and for activating said at least one rotatable slitting roller accordingly.