The invention relates to a sheeter or sheet cutter for a chemical pulp drying machinery.

In a chemical pulp drying machine's sheet cutter, a pulp web is cut lengthwise and cross direction into sheets, which then are stacked as bales for storage and transportation immediately after the cutting. The speed of the process has been constrained by the stacking phase, problems related to which have been eliminated by arranging a conveying section where the sheets' speed is slowed down between the cutter and the piling Interleaving of overlapping of the sheets in the running direction is a prerequisite for slowing down the speed, i.e. successive sheets are arranged slightly on top of each other. Such a sheet cutter and overlapping arrangement is presented in the patent specification FI111446B, for example.

The overlapping of the sheets is done by implementing a step down on the track level and by slowing down the speed after the step, thereby settling the sheets partly on top of each other on the overlapping level after running past the step. This known arrangement has reached operating speed of approximately 200 - 250 m/min. When the speed is increased above this, the trajectory of the sheets no longer follows a desired flow. The problem is that the relatively heavy sheet strives to maintain its trajectory as it passes the overlapping step and the sheet's trailing edge does not descent sufficiently, so that the leading edge of the following sheets easily hits the trailing edge of the previous sheets and thus disturbs the overlapping.

A solution for previously described problem has been achieved by, at the point of dropping the pulp sheet, arranging an essentially free discharge for the air that compresses under the sheet at least at the region of the sheet's trailing edge. As a special feature of the invention, the discharge of the compressing air is enhanced with suction The length of this section of the track does not need to be very long, e.g. having a magnitude of approximately half of the sheet's length. If suction is used, it does not need to be very strong. What is essential is to get the trailing edge of a sheet that has passed the overlapping step to descend below the level of the followings sheet's leading edge on the track section. By utilizing this track section running stabilizes and speeds of over 300 m/min and even over 400 m/min can be achieved at the cutter.

The object of the present invention is also a pulp drying machine's sheet cutter for cutting pulp web into pulp sheets and overlapping and stacking pulp sheets into pulp bales, which sheet cutter comprises a slitting machine and a cross section cutter arranged to cut the pulp web into pulp sheets, a step down in the track level for overlapping the pulp sheets on the overlapping level located after the down step, and a receiving conveyor arranged to receive the overlapped pulp sheets and to convey them to be stacked at the sheet layer It is characteristic of the sheet cutter that at least an essential part of the overlapping level's initial section's surface has an flow connection to the surroundings.

In a sheet cutter according to a specific feature of the invention, the corresponding basic components and the characterizing flow connection to the surroundings have been implemented by perforations penetrating the initial section of the overlapping level. According to a specific feature of the invention, the perforations penetrating the initial section of the overlapping level are connected to suction means.

For carrying out the invention, a broke lid's top, equipped with perforations and included in the broke sheet route, acts as an overlapping level, the space underneath the broke lid advantageously having a vacuum.

The solution according to the invention is particularly suitable for handling chemical pulp sheets because chemical pulp sheets are sufficiently heavy and have a rigid structure, so they react to suction in a favorable manner.

A further advantage invention is that the height of overlapping step can be diminished compared to previously applied structures, which makes the trajectory of the pulp sheets straighter in the horizontal plane.

• Figure 1 shows a side view of a sheet cutter according to the prior art.
• Figure 2 shows a sheet cutter according to an embodiment of the invention.

In a known sheet cutter described in figure 1, a web from a drying device is fed to a slitter 2 aided by a drawing device 1, and further on to a drawing press 3. The web advances from the drawing press 3 to a cross section cutter, which includes a cross section cutter drum 4 and a fixed counter blade 5. The sheets pass from the cross section cutter between sheet guiders 6 over a broke lid 7 to a receiving conveyor 8. A step down is arranged on sheets' conveying section between the broke lid and the receiving conveyor. The sheets advance further to a sheet layer 14 for stacking via press wheels, a roller arrangement and a sheet conveyor 9. On the section between the receiving conveyor 8 and the sheet conveyor 9 the movement of the sheets is decelerating, the slowing down thus enabling the stacking to be done at a sufficiently low sheet progression speed and therefore without problems while the machine speed remains in the previously mentioned range. The broke lid 7 on the conveying section can be flipped up and it is intended to guide cut sheets during a malfunction on to a broke conveyor 15 located beneath the sheet cutter.

Figure 2 illustrates a part of the track section, to which a drop down is arranged on the conveying section enabling the overlapping of the sheets. In this embodiment, the broke lid described in the context of figure 1, located on the conveying section slightly differing from the arrangement according to figure 1, is utilized as a step down. The top surface of the lid 21, operating as a overlapping level, is located below the sheet's trajectory set by sheet guide rollers 6 for forming a step down.

A narrow (short in the running direction of the sheets) perforation section 23, from which an essentially free flow connection to the surroundings has been arranged, is made to the leading side of the lid. This perforation can prevent the formation of an air cushion under the sheet passing over the lid, so that the sheet can descend without obstructions on lid's surface and the trailing edges of the sheets can descend after the step down. Thus, the overlapping occurs on the broke lid's top 21. The track speed after the overlapping step is descending and therefore, above the broke lid's top, the leading edge of each sheet settles on top of the trailing edge of the sheet in front resulting in the sheets to partly overlap each other. In consequence of preventing the formation of the air cushion, the sheets gravitate after the step immediately towards the surface of the broke lid's top without bouncing or otherwise distracting the overlapping of following sheets.

It is possible to achieve the structure described above alternatively by utilizing a vacuum device 22. Also in this structure, on the leading side of the lid, a narrow (short in the running direction of the sheets) perforation section (23) is made, from which a mild suction effect is achieved underneath the falling sheet through the broke lid 21, which arrangement enables an effective descending of the trailing edge of the sheets after the step down.

A sheet cutter according to the invention can process a pulp web having a weight per square meter of e.g. 800 - 1300 g/m². The pulp sheets can have a length of e.g. 800 - 920 mm and a width of e.g. 670 - 800 mm. However, the invention is not limited to using these exemplary parameters.