This invention concerns a device for levelling a particulate material web, such as a wood-fibre mat laid out on a wire and intended for the production of wood- fibre boards, said material web being moved in relation to the device.

In the production of wood-fibre boards, glue-coated wood fibres are pneumatically conveyed from a container to a forming station. In this station, the wood fibres are laid out in the form of a mat on a wire, by means of which the fibres are conveyed to a pressing plant, where they are pressed into fibre boards under given pressure and temperature conditions. On its way to the pressing plant, the fibre mat passes a milling roller which is arranged transversely of the direction of conveyance and which mills the fibre mat to give it a smooth upper sur¬ face as well as a suitable thickness and a suitable weight before the pressing operation. The fibres removed from the fibre mat in the milling operation are recycled to the container, so as to subsequently be returned to the forming station and be laid out on the wire. The amount of wood fibres separated by the milling roller is fairly large and may, in some applications, be up to 25%. Since the amount of fibres separated and thus recirculat¬ ed is fairly large, the fibres are worn and dehydrated to a disproportionate extent. Furthermore, the glue consump¬ tion and the power requirement of the fibre conveyance become excessive.

The object of this invention is, therefore, to pro¬ vide a levelling device complementing the prior-art mill- ing roller, thereby to considerably reduce the amount of fibres separated and recirculated.

According to the invention, this object is achieved by a device which is of the type mentioned by way of in¬ troduction and which is characterised by a rotary shaft, which is adapted to be arranged transversely of the

direction of movement of the material web and on which a plurality of elliptic discs, through the centres of which extends the shaft, are mounted at an axial distance from one another so as to rotate with the shaft, the discs being so inclined about their minor axes in relation to the shaft as to have a circular axial projection.

In a preferred embodiment, the discs are mounted at such an axial distance from one another that adjoining discs overlap in the axial direction. Conveniently, the discs are inclined at an angle of 45-80°, preferably about 60°.

The invention will now be described in more detail with reference to the accompanying drawings, in which

Fig. 1 is a side view of a device according to the invention, and

Fig. 2 is a schematic perspective view illustrating in more detail the geometric relationships of the compo¬ nent parts of the device.

Thus, Fig. 1 shows a levelling device 1 according to the invention, which is mounted above a wire 2 on which is laid out a material web 3 in the form of a wood-fibre mat. The material web 3 passes the device 1 on its way from a forming station (not shown) to a pressing plant (not shown) for the production of fibre boards. The device 1 comprises a shaft 4, which has a cir¬ cular cross-section and extends transversely of the direction of conveyance of the wire 2 and the material web 3 and which, at its ends, is rotatably mounted in a frame 5. In a manner not shown in detail, the shaft 4 is vertically adjustable to enable the device to be adapted to the thickness of the material web 3.

The shaft 4 supports a plurality of identical discs 6, which are fixed to the shaft 4 with an axial spacing. The discs 6 are evenly distributed along the shaft 4 in such a manner that adjoining discs 6 overlap in the axial direction.

Each disc 6 has the shape of an ellipse. The shaft 4 extends through a centre hole 7 (only illustrated in the case of a disc shown in section in Fig. 1) in each disc 6, this centre hole 7 having the shape of an ellipse whose major axis coincides with that of the ellipse of the disc. About its minor axis Al (Fig. 2), which in Fig. 1 is perpendicular to the plane of the drawing, each disc 6 is inclined at an angle α to the shaft 4. This angle α may vary between 45° and 80° but preferably is 60°, as in the embodiment illustrated in Fig. 1.

The discs 6 have such an elliptic shape and are so inclined about their minor axes Al (see Fig. 2) as to have a circular axial projection, which in Fig. 2 is illustrated with the aid of two broken-line circles C. When the shaft 4 rotates about its axis A (Fig. 2), which extends through the centres of the discs 6, each point on the circumferences of the discs 6 thus describes, as seen in axial projection, a circle whose diameter equals the length of the minor axis Al of the ellipse of the disc. During this rotation, the discs 6 perform an axially reciprocating throwing movement inside the imaginary, horizontal and straight tube T whose cross-section is defined by the two circles C (see Fig. 2 ) . The lowermost point of the discs 6, which is located on the circumfe- rential surface of the imaginary tube T, is then axially reciprocated along a straight line L and levels the mate¬ rial web 3 to the level of this line.

When vertically adjusted in suitable fashion and used as a complement to the prior-art milling roller described by way of introduction, the above levelling device according to the invention considerably reduces the amount of fibres separated and recirculated.

In each of the examples illustrated in Figs 1 and 2, all the discs 6 occupy the same rotational position as regards rotation about the shaft 4. This need not, how¬ ever, be the case, and the discs 6 may separately or in groups occupy different rotational positions with respect

to the shaft 4, if only the inclination about the minor axis Al of the ellipse is the same (60° in Fig. 1) for all the discs 6, such that the axial projection of all the discs 6 consists of one and the same circle.