Arrangement in the sheet cutter of a pulp-drying machine The present invention relates to an arrangement in the sheet cutter of a pulp- drying machine to enable an increase in the web speed of the pulp-drying machine, said sheet cutter comprising a slitter and a cross-cutting mechanism as well as a take-up conveyor for carrying cut sheets and overlapping the same for reducing the speed thereof prior to setting the sheets on a bale table. The invention relates further to a method for composing sheets into bales in a sheet cutter, said sheet cutter comprising a slitter and a cross-cutting mechanism, a bale table as well as a take-up conveyor between the cross-cutting mechanism and the bale table for carrying cut sheets and overlapping the same for reducing the speed thereof prior to setting the sheets on the bale table.

The mechanism that is a principal limiting factor to increasing the speed of pulp- drying machines is the sheet cutter. In practice, the current sheet cutters do not allow running speeds of more than 200 m/min. One limiting factor is mainly the fact that, upon leaving a sheet cutter, the cut sheets are ejected by means of an ejector roll against a backing grid, whereafter the sheets fall onto a bale table to compose a bale and, thus, the ejection speed should not exceed 100 m/min and, preferably, should remain at the rate of about 80 m/min. In case the sheets are ejected at a speed higher than this, the edge thereof develops an impact mark or indentation as the sheets collide with the backing grid, resulting in a cumulative deterioration of the bale shape as the bale edge rises higher. When pressing such a bale in a bale press, the bale develops a lip, which in turn complicates its wrapping and shipping.

Following the cross-cutting of sheets, the presently available machines, which typically run at a rate of 100-120 m/min, are provided with an overlapping sequence for sheets, wherein the successive sheets are set in a slight overlap relative to each other and, thus, it is possible, by ejecting the sheets against a backing grid, to set said sheets on top of each other for bales while also reducing the web running speed as a result of the overlap. This action is sufficient when the machine has a web speed which is in the same category as those employed

today. However, when the machine speed is increased, an overlap as currently used is not able to achieve a desired result as it develops running problems because of excessive sheet deceleration/a speed difference between successive sheets.

Hence, one object of the present invention is to provide an arrangement in the sheet cutter of a pulp-drying machine, whereby it is possible to increase the web speed of a machine to a rate of even more than 200 m/min while maintaining the ejection speed of sheets at a desired rate of less than about 100 m/min, preferably at a rate of about 80 m/min. In order to achieve this objective, an arrangement of the invention is characterized in that the take-up conveyor comprises a number of sub-assemblies in such a way that the running speeds of sheets within various sub-assemblies are differentiable from each other for dividing the sub-assemblies in terms of the sheet running speed thereof in at least three different groups in order to achieve the overlapping of sheets in at least two separate stages. On the other hand, a method of the invention is characterized in that the method comprises overlapping the cut sheets in at least two separate stages. Preferably, the sheets are overlapped in said at least two separate stages to provide an overall overlap of about 50% or more.

The invention will now be described in more detail with reference made to the accompanying drawing, in which fig. 1 shows a sheet cutter of the prior art in a schematic lateral view, and fig. 2 shows schematically one embodiment for an arrangement of the invention in a sheet cutter.

Figs. 1 and 2 display the same reference numerals for corresponding components.

In the prior art sheet cutter shown in fig. 1, a web emerging from a drying machine is fed by means of a tail feed device 1 to a slitter assembly 2 and further

to a feed press 3. From the press 3 the web progresses to a cross-cutting mechanism, comprising a cross-cutting apparatus 4 and a bed knife beam 5. From the cross-cutting mechanism the sheets travel through a roll 6'and a set of press-rollers 6 over a hydraulically driven reject gate 7 onto a take-up conveyor 8 and further by way of press rolls, a roll mechanism, and a throwing roll 9 onto a bale table 14 between divider plates 10. In such a prior art sheet cutter, an overlapping device 6 is normally used for implementing an overlap of about 20- 30% in a single sequence or stage (in prior art, the rolls of roll-pressroller pairs in the conveyor 8 are co-driven, e. g. by means of a chain extending over each roll).

The bale table 14 can be designed e. g. as a type of chain conveyor. At the same time, an evener device 11 is used for pressing the pile of sheets against a backing grid 12 in the purpose of alignment. The piles of sheets stacked on top of the bale table are carried by means of the bale table further to a bale handling station. If necessary, the sheets discarded through the reject gate 7 are transferred onto a broke conveyor 15 and further to a pulper.

In the schematic exemplary embodiment shown in fig. 2, the sheets have a speed which is increased preferably downstream of the cross-cutting by means of a roll- pressroller pair 6,6'to momentarily exceed the web speed for creating between the cut sheets a distance D, which is substantially larger than a"cutting line" caused by the actual cutting. This is followed by reducing the speed of a sheet to less than the web speed by means of a roll-pressroller pair 21', 20', whereby the sheet emerging from the preceding station at a speed higher than the web speed can be guided in an overlapping fashion on top of the sheet travelling at a speed lower than the web speed. The take-up conveyor 8 for sheets has been provided with a sub-assembly constituted by a roll 21 and a set of overhead press rollers 20, whereby the advancing speed of sheets can be decelerated further for overlapping the sheets more, for example by about 30-40%, i. e. the total overlap, together with the first overlap, will be about 50-70%, preferably about 60%. Fig. 2 shows an arrow A, by which the travelling speed of sheets has fallen by about 20-30%, as consistent with the first overlap, and by an arrow B, the second overlap established by means of the roll-pressroller pair 21,20 has reduced the running speed of sheets respectively by about 30-40% more, i. e. the web speed

at this point is about 30-50% of what it was originally. Thus, when the web speed of a web arriving in the sheet cutter is for example about 200 m/min and the total overlap is about 60% (web speed about 40% of the original), the cut sheets will have a web speed of about 80 m/min at the throwing roll 9. By implementing the overlap in accordance with the invention, for example as described above, the overlap can be increased in several stages 20", 21" ; 20,21; 20"', 21"'for maintaining the ejection speed against the backing grid of a bale table at < about 100 m/min, preferably at about 50-80 m/min. The overlap of the invention, implemented in at least two stages, can be used for reducing the advancing speed of a sheet flow by about 40-70 m/min per overlapping stage.

In the arrangement of the invention, between the successive pressroller-roll pairs is fitted a support member 22, e. g. a support plate, for supporting a sheet flow progressing in the sheet cutter.

In the embodiment of fig. 2, the conveyance and transport of sheets are carried out by means of underneath rolls extending across the entire sheet width and by means of loaded set of rollers thereabove, comprising a number of rollers crosswise of the sheet. According to the invention, the rolls 21' ; 21" ; 21; 21"'may all be driven either in an independently variable fashion or connected to a drive motor with a given appropriate transmission ratio for implementing a multi-step overlap and deceleration of the invention. The transmission ratio can be either a given preset standard gear ratio or for example a variator or the like gear ratio, the overlap and deceleration being regulable and controllable by means of appropriate parameters while the machine is running.

Above, the roll-pressroller pair 20,21 has been described as a further overlapping mechanism, but such further overlap is conceivable by using other implements as well, such as for example by a conveyor belt by appropriately regulating the conveyor speed. In addition, the conveyor section 8 can be provided with two or more successive press-pressroller pairs to implement the overlap, for example in the embodiment of fig. 2, the roll-pressroller pairs 21", 20" and 21"', 20"'can be conceivably used for implementing such a further overlap.