The present invention relates to an arrangement for reducing the thickness of a moving material web along a longitudinal region by cutting away a material strip by a rotating cylindrical cutter. The cutter is arranged on one side of the material web with its axis of rotation substantially in the direction of movement of the web.
In the packing industry a packing material which comprises layers, inter alia, of paper and thermoplastics is used for the manufacture of packing containers for e.g. liquid contents such as milk. In the conversion of the packing material to finished packing containers the longitudinal edges of the material are sealed to one another in an overlap joint. In order to avoid contact of the contents in the packing container with the centrally situated carrier layer of the material, the edge region of the material layer facing the inside of the packing container is folded double so that in the sealing the edge ends up inside and consequently cannot make contact with the contents. Even if the packing laminate has only a total thickness of approx. 0.4 mm, this double folding means that the material obtains an undesirable thickness in the sealing regions which is disadvantageous, especially when two sealing regions cross one another, since in that case channels which entail leakage can easily be produced.
In order to avoid this, it has been suggested that the thickness of the material should be reduced in a longitudinal region which corresponds to the edge region wherein the folding subsequently is to take place. This reduction of the thickness of the material web is done appropriately with the help of a rotating cylindrical cutter, which during the manufacture of the container is made to rest against the material web passing by, in such a manner that by means of the active part of its periphery it cuts off a strip of desired thickness from one side of the material web. The material web passing by can be provided in this manner with one or more longitudinal regions of reduced thickness at the edges of the material web or at those parts of the material web which after dividing up of the same into narrower material webs will form the edge regions.
The cutting away of a material strip with the help of a rotating cylindrical cutter can take place at very high web speeds, which is in fact necessary since the material web on the occasion during the manufacturing process where the reduction of thickness takes place, is fed through the manufacturing machines at a speed of over 300 m/minute. At this high speed a correspondingly high speed of the cylindrical cutter is required. The cutter's peripheral speed should be approx. 50 m/min. It is obvious that it is very difficult at such high working speeds to maintain an exact depth of cut of e.g. 0.25 mm, since this is influenced by inaccuracies in the material passing by, as well as by inaccuracies in the support and in the design of the rotating cylindrical cutter. It has indeed proved practically impossible to maintain a correct depth of cut under such conditions and with the means available up to now. Presently a guide pulley situated inside the rotating cylindrical cutter and freely rotatable in the direction of movement of the material is used. The distance to the cutting edge determines the thickness of the material strip cut off, and an air nozzle arranged at the same level as the cutting edge, but on the opposite side of the material web, is adapted so as to press the material web passing by against the guide pulley. In addition to the difficulties mentioned earlier concerning inaccuracies in the movement of the material web and in the support of the cutter, there are now also inaccuracies in the guide pulley which make the maintaining of a constant depth of cut even more difficult. Even if this were possible in itself immediately after an adjustment of the position of the cutting pulley and the rest of the interacting parameters, the accuracy would be lost after a short period of operation so that non-acceptable thickness variations would occur in the reduced region of the material web.
It is an object of the present invention, whilst retaining the basic construction of the arrangement, to design the different parts of the arrangement in such a manner that the cutting away of the material strip can take place with sufficient accuracy even during prolonged periods of operation.
It is a further object of the present invention to provide a simple and effective arrangement for the adjustment of the thickness of the strip cut away and hence of the thickness of the remaining material in the thickness-reduced region of the material web.
It is a further object of the present invention to provide an arrangement which can operate at especially high material speeds, in particular up to 600 m/min.
Finally it is an object also to provide an arrangement which is uncomplicated and stable as well as inexpensive to manufacture and to maintain.
These and other objects have been achieved in accordance with the invention by providing an arrangement for reducing the thickness of a moving material web along a longitudinal region by the cutting away of a material strip by means of a rotating cylindrical cutter which is arranged on one side of the material web with its axis of rotation substantially in the direction of movement of the web. A guiding device for the control of the thickness of the strip cut away is arranged close by the edge of the cylindrical cutter and is upheld by a supporting unit which is in contact with the cylindrical cutter.
Preferred embodiments of the arrangement in accordance with the invention have been given the further characteristics which are evident from the description below.