The object of the present invention is a screen, making a circular trajectory, to be used in chipboard and OSB factories, the screen being implemented by means of meshes of different mesh sizes and comprising a number of mesh levels one above another, with which screen wood-based raw material is screened into different-sized fractions after chipping and drying, which screen comprises a frame part and a moving part.

OSB means Oriented Strand Board and is a well known term in this art of technology. In the following, when we use the term "chipboard factory", that could also include OSB factory.

The invention thus relates to a screen, making a circular motion, to be used in chipboard factories, with which screen wood-based raw material is screened into different fractions after chipping and dry ing. By means of the device, the raw material is screened into face particles and core particles to be used in the chipboard manufactur ing process.

Screens making a circular movement to be used in a chipboard fac tory are typically large steel structures in which a welded steel struc- ture forms the frame of the device. The screens in question conven tionally comprise 2-4 screening levels formed from screen meshes that are inclined slightly with respect to the horizontal plane. The angle of inclination is generally 5-10°. The material being screened flows in the direction of the inclination. The screen meshes are de- tachable and replaceable via doors or hatches in the outer sides of the screen. The screen structure is arranged to move on an essen tially circular path on the horizontal plane. The screen in question is not, therefore, a screen vibrating back and forth, but instead is a screen making a circular motion, in which a constant centripetal ac- celeration rotating around an essentially vertical axis gets the mate rial to be screened on top of and through the mesh levels. A typical diameter of an orbit is 40-80 mm and the circulation speed 150-200 r/min. The screens are supported on the frame structure either with suspension means, which are e.g. cables or hinged rods. Another typical support structure is supporting from below on top of flexibly fastened supports that allow the relatively small circular screening motion of the screen with a relatively small resisting force.

These types of screens are manufactured both as single-layered and as double-layered. A screen of double-layered structure is formed from two structures, each functioning essentially as a single-layer screen, one above the other. By means of a double-layered screen, the screening capacity can be substantially increased, in principle doubled, for a certain-sized area.

The screens making a circular movement to be used in a chipboard factory are typically large steel structures in which the width of the frame exceeds 3 m and the length of the frame is generally between 5-10 m. Such large steel structures are demanding to fabricate and, because of their large dimensions, expensive to transport.

With the screen that is the object of the invention, material is pro cessed in a chipboard factory after drying, i.e. the wood-based ma terial is dry and it contains dust. It is possible that a dust explosion will occur inside the screen and for that reason the structure must be designed and manufactured to function safely in a possible dust explosion. Typically, in the top part of a single-layered screen, i.e. in the roof structure of the screen, there are explosion hatches, via which explosion pressure is released in a controlled manner. On the other hand, no solution has as yet been found for the safe and eco nomic management of dust explosion occurring in the lower screen section of a double-layered screen.

The aim of the present invention is to provide a new type of rotary- motion screen for a chipboard factory, with which screen a cheaper manufacturing price and more advantageous transportation are achieved, and with which screen safe and economic dust explosion management in the case of double-layer screens is also realized. The screen according to the invention is characterized in that the moving part of the screen comprises at least two screen modules and at least one frame module.

One preferred embodiment of the screen according to the invention is characterized in that there is one frame module and two screen modules, and in that the frame module is between the screen mod ules.

One preferred embodiment of the screen according to the invention is characterized in that the walls facing towards the frame module of the screen modules are provided with explosion hatches for directing the pressure of a possible dust explosion into the space between the screen modules and from there either upwards or downwards into a free space.

Yet another preferred embodiment of the screen according to the invention is characterized in that the pressure of a dust explosion possibly occurring in a screen module is conducted in the frame mod ule via at least one flame extinguisher.

Other preferred embodiments of the screen according to the inven tion are defined in the dependent claims 5-11.

Some of the advantages of the invention that can be mentioned are that because the center frame and the screen modules are different structures and are also manufactured in different ways, the manu facturing of them can be done in a factory specialized in the relevant manufacturing method for reducing manufacturing costs. The auxil iary means to be used in manufacture, e.g. welding jigs, are smaller and more ergonomic. Correspondingly, repairing a screen comprised of separate modules in the event of possible damage is less expen sive than in screens according to prior art.

In the following, the invention will be described in more detail by the aid of some preferred embodiments with reference to the attached drawings, wherein Fig. 1 presents an oblique view from above of the screen according to the invention.

Fig. 2 presents the frame module of the screen according to the invention, and the drive devices of the frame mod ule.

Fig. 3 presents the screen according to the invention as viewed from the end.

Fig. 1 thus presents the screen according to one embodiment of the invention. It comprises a frame structure and a moving part sus pended from it. The moving part of the screen could also be sup ported from below instead of being suspended. The suspension here is implemented with hinged rods 3. The moving part comprises two screen modules 4 and a frame module 5 between them. A screen module comprises one screening chamber or a number of screening chambers essentially one above another separated structurally from each other, e.g. with a solid intermediate level, in each of which chambers the material for screening is screened into at least two fractions. In the drawings an embodiment is presented wherein the screen is double-layered, in other words there are two screening chambers, one above the other, in each screen module 4.

The material to be screened is fed into the feeder hoppers in the manner indicated by the arrows 6 and the screened fractions are removed from the other end of the screen in a manner that is per se known in the art. Each fraction to its own conveyor.

The screen modules 4 comprise screening levels 7 (Fig. 3) compris ing screen meshes in a manner known in the art. The screens and their screening levels 7 are inclined e.g. approx. 5-10° with respect to the horizontal plane, in which case the material being screened flows in the direction of the inclination when a horizontal rotating movement is induced in the moving part of the screen. Suspension from above or support from below permits the rotating movement in question.

The rotating movement can be brought about with at least one, but in the embodiment according to Fig. 2 with two, drive machineries 8 that are eccentric in their mass and at least mostly situated inside the frame module 5, the drive machineries having rotating shafts 9 that are essentially vertical and that produce in the screen a rotating force in relation to the vertical axis and thus a rotating trajectory on essentially the horizontal plane. The eccentric masses of the rotation shafts 9 are marked with the reference number 10 and they are sit uated inside the frame module 5 thus reducing the space required by the screen.

Additionally, the center of mass of the one or more rotating drive shafts 9 disposed in the frame module 5 can be on essentially the same plane as the center of mass of the screen modules 4, which is the plane in the direction of mesh levels 7 of the screen module 4.

The screen in Fig. 3 is presented as viewed from the end and partly opened/sectioned. There is a dust explosion risk in screens screening wood-based products. For this reason, the screening chambers of the screen modules are provided with explosion hatches that are per se known in the art. The screen structure according to the invention, having a frame module 5 in the center and screen modules 4 on both sides of the frame module, makes it possible that the walls facing towards the frame module 5 of the screen modules 4 or towards their screening chambers can be provided with explosion hatches 11 for directing the pressure of a possible dust explosion into the space between the screen modules (into the frame module 5) and from there either upwards or downwards into a free space. In the embod iment of Fig. 3 it is directed upwards, as the arrows indicate. The pressure of a dust explosion can additionally be conducted via at least one flame extinguisher 12 in the frame module 5. The screen modules 4 and the frame module 5 are dimensioned for transporting in a standard-sized sea container, which is advanta geous for transporting them. It is obvious to the person skilled in the art that the invention is not limited to the embodiments described above, but that it can be var ied within the scope of the claims presented below. One alternative is that the screen has two drive shafts 9 that have rotating masses of different magnitudes to each other, in which case the resultant of the forces producing a rotational movement is directed at the center of mass of the moving structure.

Presented above is an embodiment comprising one frame module 5 and two screen modules 4. These numbers can, however, vary within the scope of the invention in such a way that there are at least two screen modules 4 and at least one frame module 5.

The characteristic features possibly presented in the description in conjunction with other characteristic features can also, if necessary, be used separately to each other.