MOVING PAPER WEB

This method relates to edge cutting of paper web in accordance with the introduction of patent claim 1.

Previously known from Finnish patent 12457 is edge cutting by a water jet. From the Finnish publications 83106 and 88417 diagonal cutting of paper web is known, i.e. in the first place longitudinal cut off by means of a water jet.

The construction as per patent 12457 can be applied when the paper web speed is slow and cutting carried out close to the wet end. Then the forces generated by cutting hardly have any impact on the web forward travel. Instead, cutting of dry paper has turned out to be difficult by growing web speeds. Especially, on coating the paper, the edge arrives at cutting only after coating, whereat the uneven edge margin with the coating border is removed. After coating, due to cutting, the advancing web is equal in quality up to the edge. It has been established that a high-speed water jet produces in the edge of a fast moving web braking powers preventing the use of a water jet cutter. The web proceeds undeter inately and the possibility of breaks in the line grows.

With a method and an apparatus according to this invention the above introduced problem has been settled and the invention is characterized in what is presented in the patent claims.

Advantages of the present invention can be considered that it is possible to generate enough counterforces in the web edge in order to compensate the inconvenient forces on the web by the water jet. Cutting can be carried out in dried and even in coated paper web moving even faster than 20 m/s. The cutted edge can be easily after-treated, since after cutting the position of edge is stable on utilizing the method and appa¬ ratus as per this invention are utilized.

In the following the invention is disclosed with reference to the enclosed drawing.

Fig. 1 is a diagonal view of the apparatus.

Fig. 2 is a side view of the apparatus.

Fig. 3 is a cutting top.

In figure 1 the paper web moves from the right to the left and a strip 2 is cut off from its edge. For cutting a high-speed water jet is used, the nozzle portion 3 of which is very close, appr. at 1 mm distance from web 1. The cut off strip 2 is steered to a channel 11, into which an air flow to transport the edge strip is produced, which secures conveyance of strip out from channel. At the channel 11 mouth (not shown) is a control device with a photocell observing faulty motions of strip 2, for instance its getting conveyed along with web 1, whereat different functions go off, e.g. air blasts, striving to steer strip 2 into channel 11 and, in case it does not work, finally nozzle 3 is pulled aside and cutting of edge strip swithed off. Conveyance of strip 2 along with web 1 causes an immediate line break possibility and efforts must be made to prevent such a possibility by means of safety devices.

Cutting water is conveyed to nozzle 3 along piping 6. The whole apparatus rests on a bearer 7 and the cutting line is adjusted moving the bearer sideways.

Along pipe 5 the air jet is guided to the cutting spot, whereat cutting dust and coating peeling off the paper and coating dust are conveyed to channel 11 and into the channel by suction. On the cutting line an after-treatment device is installed consisting of after-treatment pieces 9 and 10 installed on both sides of the web at the edge. In pieces 9,10 there are sharp edges directed against the arriving web to sweep off portions that swell too much from the web surface. Further, about from the middle of these pieces air is blasted

into the space between the pieces and the web in order to prevent full gliding contact. The direction of the air blast into the space between a piece and the web is turned mildly out off the web, whereby the blast residue goes to channel 11. Along pipe 8 compressed air is brought to the apparatus. The lower piece 10 is fixed to cutting top 4, the upper piece 9 attached to the apparatus. The after-treatment equipment is resiliently attached to beam 7 (not shown) so that the appa¬ ratus is freely suspended by piece 9 above the web almost without any friction on an air cushion formed beneath piece 9. The web edge is dried by means of an infrared radiator 12, by means of which possible water jet moisture is lessesned.

Figure 2 shows a side view of the complete apparatus with a sectional view of a part of channel 11. Web 1 travels above cutting top 4 almost touching this cutting top 4. cutting and after-treatment take place above the channel 11 orifice.

Figure 3 shows the cutting table, which is a top level 4 and most significant for the water jet cutting to work well, and most appropriately placed under the web at the cutting point. Water penetrating web 1 is conveyed out through a hole 14. The lower after-treatment piece 10 is placed in hole 18. On the cutting top underside surface there is a L-formed channel 13 into which compressed air is conveyed. From channel 13 compressed air has access to flow out from the underside of lath 16 and along furrows 17 diagonally with respect to the web forward travel. The furrows 17 are separated from one another by ridges 15. When compressed air in furrows 17 flows faster than the web and since it can be discharged into a larger space, i.e. to the outside, negative pressure is generated in the furrows pulling web 1 toward cutting top 4. The simul¬ taneous direction sideways and forward chosen for the furrows produces forces of proper direction into the web compensating the forces generated by the water et, due to which the web travel would otherwise be disturbed.

The compensation forces formed by cutting top 4 are necessary for the web to endure continuous water jet cutting, without trouble, at usually applied speeds. The after-treatment equipment as per embodiments shown in figures 1 and 2 is imerative for reliable cutting operation and its necessity depends on the web quality. When cutting dried paper web this equipment is needed for dusting and for cleaning the coating material and the web edge. Particles hovering in the air may not even begin to accumulate on the surface of the cutting equipment, since they could before long reach into contact with the web and cause interruption in web travel. Dusts and water mist must therefore be blasted or sucked off the cutting point if one wants to secure a reliable long-run function.

Cutting top 4 is shown from the web underside only, it can be located on both sides of the web. Most advatageously the cutting top is made of strong material or coated with such material. After-treatment devices 9,1°,12 may be needed either on one side only or on both sides of the web.