The present invention relates to an arrangement as defined in the preamble of claim 1.

In the sheet cutter of a chemical-pulp dryer, the pulp web is first passed to a slitting unit, where the pulp web is cut into longitudinal web sections. Af- ter this, the web sections are passed to a cross cutting unit, where they are cut into sheets of desired length.

The sheets are passed further to a stacking unit, where they are stacked.

Prior-art sheet cutters have several drawbacks.

Especially the cross cutting unit generates so much noise that the noise level near the sheet cutter is as high as over 100 dB. As the noise generated by the cross cutting unit is effectively propagated via the sheet cutter frame structures, the result is a high noise level in a large area. Moreover, the sheet cutter has many moving and rotating parts, so, in view of work safety, it has to be reliably fenced in or otherwise isolated to prevent inadvertent access to the vicinity of the sheet cutter. In addition, the sheet cutter pro- duces plenty of dust, which readily spreads all over the space around it. Furthermore, especially in the cross cutting unit, temperature variations cause problems in the long cutting blade.

The object of the present invention is to eliminate the drawbacks described above. A specific ob- ject of the present invention is to disclose a new type of arrangement in conjunction with the sheet cutter of a chemical-pulp dryer, so as to obtain a pulp dryer unit that minimises the disadvantages to the rest of the working environment and functions effectively and relia- bly.

As for the features characteristic of the in- vention, reference is made to the claims.

In the arrangement of the invention in conjunc- tion with the sheet cutter of a chemical-pulp dryer, the sheet cutter comprises a slitting unit, a cross cutting unit and a stacking unit, all mounted on the machine floor. According to the invention, the slitting unit, cross cutting unit and stacking unit are substantially completely encased by providing them with a continuous protective casing with both sound and dust insulating properties so that at least the side walls of the pro- tective casing extend to the machine floor without any direct contact with or support on the frame or other parts of the sheet cutter. The walls of the protective casing preferably extend to the machine floor and are supported by it, so that the protective casing consti- tutes a sound insulating envelope completely detached, at least as regards its side walls, from the sheet cut- ter and surrounding it practically on all sides. Thus, at least the side walls of the protective casing do not receive any direct impulses from the vibrations of the frames. Sound propagation is thus minimised at least in a direction where the operating personnel of the machine mainly have to move.

To maximise the intended total effect to be achieved by the invention, the protective casing is preferably provided with a mechanical air exhaust system whereby air is continuously removed from inside the pro- tective casing. An amount of air corresponding to the amount removed by the mechanical air exhaust system is supplied into the space inside the protective casing via routes selected in advance. Preferred routes are e. g. the web entry aperture and an aperture possibly provided for a conveyor for rejected material etc., the air flow in the apertures in the protective casing being directed toward the inside of the casing. A preferred mechanical air exhaust system is one in which the pressure inside the protective casing is lower than the pressure pre- vailing outside the protective casing.

In a preferred case, apertures which have to be kept continuously open, such as the web entry aperture, are arranged to be of appropriate size. In this way, both the noise generated by the sheet cutter and the amount of cutter dust escaping out of the protective casing are minimised, and also a controlled ventilation in the protective casing for maintaining a substantially uniform air temperature as required for proper operation of the cutting apparatus is achieved. It is thus possi- ble to combine a mechanical air exhaust system and a dust removal unit.

Thus, the protective casing preferably consists of walls supported by the machine floor and a top. The protective casing may also comprise sound insulating structures under the sheet cutter, thus damping even the noise propagated via the machine floor, which generally is made of concrete.

The protective casing preferably comprises an entry aperture through which the pulp web is passed to the sheet cutter inside the protective casing. The entry aperture is preferably so dimensioned and fitted that the pulp web can pass through it without touching the edges of the aperture.

The protective casing preferably also has an exit aperture through which the sheet stacks proceeding from the sheet cutter are conveyed out of the protective casing. The exit aperture may be provided with a shut- ter, such as a door or flap door, in which case the exit aperture is generally kept closed and only opened when a sheet stack or a set of sheet stacks is being removed out of the protective casing.

The protective casing may further be provided with various light transmitting wall sections in suit- able parts of the casing to admit light into the protec- tive casing, but of course it is also possible to use illumination inside the casing as necessary.

The arrangement preferably comprises a dust re- moval unit for removing dust produced inside the protec- tive casing. The dust removal unit may comprise internal air circulation systems provided with filters, or vari- ous exhaust fans and replacement air equipment, so that, while the exhaust fans are blowing dusty air out of the protective casing, a corresponding or smaller amount of clean air is admitted into the casing through replace- ment air valves, which means that the pressure inside the casing is equal to or lower than the pressure of am- bient air, thus preventing dust from drifting out through the apertures. The arrangement may further com- prise an air conditioning unit to maintain a temperature as constant as possible inside the protective casing, thereby protecting e. g. the cutting blades against large temperature variations and temperature differences, which would significantly impair the cutting result.

As compared with prior art, the arrangement of the invention has significant advantages. By encasing the entire sheet cutter in a protective casing separate from the sheet cutter as provided by the invention, a sufficiently low noise level, i. e. below 85 dB, outside the sheet cutter is achieved while at the same time ef- fectively preventing propagation of structure-borne sheet cutter noise. A good level of industrial safety of the sheet cutter is achieved by enclosing the entire sheet cutter in a casing. As the sheet cutter is housed in a space with constant temperature and no draught, temperature problems in the cutter bars are avoided. The use of a protective casing also allows complete control of dust removal while preventing dust from spreading to other parts of the plant.

In the following, the invention will be de- scribed in detail by referring to the attached drawing, which presents a diagrammatic sectional view of a sheet cutter with a protective casing according to the inven- tion.

The drawing shows a sheet cutter comprising a slitting unit 2, a cross cutting unit 3 and a stacking unit 4, all mounted on the machine floor. The dried pulp web 9 supplied to the sheet cutter is passed via a guide roller unit 15 to the slitting unit 2, where the pulp web is cut into longitudinal web sections. After this, the pulp web advances to a drawing-in roll unit 16, from where it is passed on to the cross cutting unit 3, which cuts the web sections into sheets 17 of a desired length. Using a number of guide roller units 18, the sheets are conveyed to the stacking unit 4, to be packed in bales.

The three basic units of the sheet cutter, which are supported by the machine floor 1, are sur- rounded by a substantially impervious and sound damping protective casing 5 comprising at least walls 6 extend- ing to the machine floor 1 and a top 7. In the protec- tive casing, no part of at least the vertical walls has any direct contact with any part of the sheet cutter it- self. Preferably no part of the protective casing has any direct contact with any part of the sheet cutter, but the only fixed connection between them is via the machine floor 1. Direct contact or fixed connection here means a connection having essential significance regard- ing suspension of the protective casing. Thus, there may be e. g. cable shelves, supporting beams for hydraulic equipment etc. between them. The wall 6 of the protec- tive casing 5 is provided with an entry aperture 8 dis- posed near the slitting unit 2, through which aperture the pulp web 9 can be passed in to the slitting unit 2 in the protective casing without the web touching the casing.

In addition, the protective casing 5 is pro- vided with an exit aperture 10 with a door 12, disposed in the path of the bale conveyor 19 of the baling unit 4, through which aperture the bales can be removed out of the protective casing. The operation of the door is

preferably so connected to the control system of the baling table of the stacking unit that the door is auto- matically opened only for the time it takes to remove the bale from the baling table. Regarding the operation of the arrangement as a whole, this minimises the time that the large apertures for removing the pulp bales from inside the protective casing are kept open, thus reducing unnecessary flow of ambient air into the casing and at the same time permitting finished bales to be passed further in the process. The door can be so imple- mented that it can move aside from the path of the bales, being pushed by the bales themselves, but it is also possible to use a shutting element of flexible ma- terial instead of a solid door. At other times except during removal of bales from the baling table, the exit aperture is substantially closed. Moreover, the wall comprises light transmitting wall sections 13, i. e. win- dows having appropriate sound insulating and light transmitting properties. In addition, disposed inside the protective casing is a dust removal unit 14, allow- ing dust produced by the sheet cutter to be removed from the air inside the protective casing by circulating the air through the dust removal unit.

The embodiment presented in the figure is also provided with a mechanical air exhaust system 20 for sucking air out of the protective casing. With this ar- rangement, the pressure prevailing inside the protective casing remains constantly lower than the pressure out- side it, thus preventing any uncontrolled, dusty air currents from getting out of the casing.

In the arrangement of the invention, as the cutting of the pulp web takes place in a practically completely closed space while only the narrow entry ap- erture 8 for the pulp web is continuously open to the space outside, the disadvantages normally associated with the sheet cutter regarding noise, dust and safety risks are practically completely eliminated.

In the foregoing, the invention has been de- scribed by way of example by the aid of the attached drawings, but different embodiments of the invention are possible within the scope of the inventive idea defined by the claims.