Generally, cutting the material web in a paper machine or the like takes place at the reel-up during reel change. At a so-called Pope reel-up or at the so-called second generation reel-ups developed from that, in a continuous reel-up of the material web, a new reel spool is often changed into the place of a full reel in such a manner that it is accelerated substantially into a rotating speed corresponding to the web speed of the web and it is lowered or in some other manner taken into contact with the means forming a reeling supporting surface, such as the reeling cylinder.

Reel change can be performed, for example, in such a manner that when the full paper reel, the so-called machine reel, is separated from the reeling cylinder, its speed decreases and a bag begins to form in the material web between the reeling cylinder and the full reel, which bag is blown around an empty reel spool, in which case the web at the same time tears.

Web cutting with a full width percussive blade cutting device is also often used so that as small amount as possible of the material web is wasted and that the changing event would be neat without any loose material resulting from the tearing. After cutting, the material web is directed around the new reel spool.

When the speeds of the paper machine increase, a fast and controlled cutting of the web is challenging and requires very fast functioning special devices for full width cutting. Web tearing during free draught after an edge tear has been made is uncontrollable. In known cutting methods, the web is forced to always be cut substantially after the reeling nip, either during freed draught or supported onto the surface of the roll.

By means of the method according to the invention, it is possible to decrease the above-mentioned problems. The method according to the invention is characterized in that the web is weakened at the latest when the dry matter content of the web is at least 8 % lower than the web dry matter content for the reel-up. The apparatus according to the invention is characterized in that the apparatus for weakening the material web is placed before the dryer section of the paper machine or the like, or at the latest in the area of the calender section.

By means of the method according to the invention, the material web can be cut in a controlled manner and with a uniform quality. When web cutting is performed by means of the method according to the invention, it is possible that the web can be cut in the nip only by means of a stress peak caused in the web in the machine direction by the deformation.

A paper machine or the like in this application refers to, in addition to an actual paper machine, also a soft tissue machine and a board machine, and the material web is the product received from these machines.

The phases of paper manufacturing are described briefly in the following. A paper machine comprises, starting from the beginning of paper manufacturing, a headbox, a wire section, a press section, a dryer section, a coating section, a calender section and a reeling section. The fibre suspension from the headbox is arrange to spread on the wire and in the wire section, the paper is formed into a web- like form, and water is removed from it by means of gravity and suction. In the press section, excess water is further pressed from the web and the fibres are forced into contact with each other. In the dryer section after the press section, water is removed by evaporation and fibre bondings are formed in contact with hot surfaces. In the calender section the paper is calendered, in which case paper becomes thinner, i. e. it is pressed together and it receives a smooth surface. In the reeling section, the finished

material web is reeled. The above-described sections are typical sections of a paper machine, and it is possible that there are other sections besides the ones described in a paper machine. In addition, in an on-machine solution the above-mentioned sections may be repeated, e. g. the coating and dryer sections.

The fibre orientation of the web has an effect on how easily the web is cut. Especially when using gap formers, the fibres are oriented in such a manner that the tensile strength in the machine direction becomes great. This is, of course, disadvantageous from the point of view of cutting the web, because cutting the web requires more power.

In the method according to the invention, the material web is cut in such a manner that the material web is weakened before its dry content matter has risen so high that its strength has reached its substantially normal strength. Thus, cutting the web is controlled and of even quality in the cross machine direction. Generally, the moisture of a finished paper is below 12 %. Weakening is performed on a very narrow area in the longitudinal direction of the web.

In the method according to the invention, the weakening is caused in the pulp forming into a web by affecting the orientation of wood fibres or their amount per unit volume. The weakening can also be performed by temporarily changing the dosage of some additive.

This kind of an agent can be, for example, a retention aid. The weakening can be performed over the area of the entire web width or a part of the web width, for example, only on the edges of the web or in the centre of the web. If the weakening is performed for the entire width of the web, conveying the web forward in the paper machine in a supported manner can be necessary.

Weakening can be performed by dosing liquid onto the web in a controlled manner, by using gas blowing, by affecting the physical or chemical properties of the fibres or by using a device, which contacts the web mechanically. When liquid is dosed on the web, it is advantageously water, and it can be, for example, sprayed with

nozzles onto the forming web. The gas used in gas blowing is advantageously air, and in air blowing, a narrow weakened place is formed on the web. The physical properties, which can be affected are, for example, the strength properties of the fibres or their electric properties. The mechanically contacting device can be, for example, a percussive blade, which causes a local weakening. In practice, the web weakening can be arranged in such a manner that in the cross direction of the web, a beam runs over the web close to it, to which beam the means performing the above-mentioned functions are mounted. Liquid or gas nozzles can be mounted on the beams, or electrodes taking part in forming an electric field or devices required for forming a magnetic field. It is also possible that the weakening is, for example, in the shape of an arrowhead. This kind of a shape can be created through the combined effect of the web movement with the nozzles mounted on the beam and moving in the cross direction of the web. Web weakening can also be implemented by dosing agents temporarily weakening the web into the fibre pulp coming from the headbox, by changing the speed difference between the headbox discharge and the receiving wire, or by temporarily weakening the flow of the fibre pulp from the headbox. Alternatively, the agent weakening the web can be dosed among the liquid brought onto the web, or the agent can be brought onto a certain point of the web in a dry form, for example as a powder. The web weakening agent can affect the chemistry between the fibres, for example the ability of the fibre fibrils to form bonds between fibres, or other fibre properties. The formation of bonds between fibres can be affected, for example, by changes in the pH.

The weakened web can be cut advantageously in the reeling nip by means of the stress peak caused in the web in the machine direction by the deformation. It is also possible that the cutting takes place only by means of web tension. It is also possible to cause an edge tear in the web in order to start the cutting event. The edge tear is usually made at such point of the process where the web travels unsupported, for example at the reel-up. Most advantageously the invention can be applied in processes where the web transfer is entirely closed before the reel-up, in which case the risk of a break is

minimized. Since the weakening is very short-term, it does not disturb the on-line measuring devices.

The above description does not restrict the invention, but the invention may vary within the scope of the claims. The controlled weakening according to the invention can be utilized in all other situations where the web is desired to be cut in a controlled manner, such as, for example when running the web to a pulper. The main idea in this invention is that the material web is weakened before the dryer section of a paper machine, or at the latest when the dry matter content of the web is at least 8 % lower than the dry matter content of the web at the reel-up, i. e. before the strength of the material web has risen close to the strength of the material web.