From EP 0 159 618 Al, a device of such kind is known. The forming box of the apparatus described therein is most often an integral part of the entire papermaking plant, which constitutes an essential limitation to the capacity of the plant.

The fibres are blown into the formation head or forming box, from where they are distributed onto an underlying forming wire. A vacuum box is provided underneath the forming wire for drawing the fibres onto the forming wire. For placing the fibres on the forming wire, the forming box is provided with a bottom net or sieve having a number of openings. In order to ensure the passage of the fibres through the bottom of the forming box it is suggested to use wings, rollers or other scraping or brushing devices, which in an active manner removes fibres from the sieve at the bottom of the forming box. Although such mechanical devices do give an increase in the capacity, attempts have been made through many years to increase the capacity further.

The size of the openings in the mesh or sieve in the bottom of the forming box is decided by the fibres which are to be distributed on the forming wire. This is particularly relevant in relation to the use of cellulose fibres in the manufacture of paper products including absorbing products, such as napkins. Thus, there has been a limitation in the length of the fibres used. In practise, it is found that it is not possible to use fibres with a length of more than 18 mm. This also results in a limitation in the kind of non-woven products that can be manufactured on such a plant.

From US 6,233, 787 B1 is known a forming box with an open bottom, i. e. without a bottom mesh or sieve. The distribution of fibres is carried out by a number of rotating spike rolls and according to the forming box disclosed in this document, the spikes are arranged to partly holding back the fibres against the effect from the suction of the underlying vacuum box. The cloud of fibres which is formed inside the forming box of single fibres, which are slit up and mixed in the air stream, are transferred down onto the underlying wire by the application of the rotating spike rollers. This increases the capacity of the forming apparatus significantly.

However, lumps of fibres may pass the spike rollers without being torn sufficiently apart by the spikes. This results in an uneven distribution of fibres on the forming wire.

It is the object of the invention to provide a fibre distributor which ensures an even distribution of fibres on the forming wire in a dry-forming apparatus without compromising the capacity of the fibre distributor. In addition, it is the object to provide a fibre distributor which is reliable in operation and which allows for longer time between overhauls or maintenance.

These objects are achieved by a forming box of the initially mentioned kind, wherein an endless belt screen is provided having an upper run along the at least one row of spike rollers and a lower run closer to the open bottom of the forming box.

By a forming box according to the invention, an efficient disintegration of fibres is achieved and an even distribution of fibres on the forming wire is obtained by the forming box without reducing the capacity of the fibre distributor. The endless belt screen has an upper run, which runs immediately below and/or above a row of spike rollers i. e. for instance between two rows of spike rollers and a lower run in the lower part of the forming box. This ensures an even distribution of the fibres just as fibre lumps or oversized fibres are prevented from being laid down on the forming

wire and retained on the belt screen in the forming box and transported away from the lower portion of the forming box and returned to the spike rollers for further disintegration. In a forming box according to the invention, the endless belt screen provides a sieve or fibre screen member which is self-cleaning since the oversized fibres are retained on one upper side of the lower run of the endless belt screen and released on lower side of the upper run of the endless belt screen because of the vacuum underneath the forming box and the forming wire.

In the preferred embodiment, two rows of spike rollers are provided on each side of the upper run of the belt screen. Hereby, an initial disintegration of the supplied fibres may be provided before the screening by the belt screen and a further disintegration after this first screening.

In a preferred embodiment, the spike rollers in the row immediately below the upper run of the belt screen are positioned with a decreasing distance between their axis of rotation and the belt screen in the direction of travel of the upper run of the belt screen. Hereby, the fibre lumps or clusters of fibres retained on the lower run of the belt screen are graduately re-disintegrated as these retained fibres are returned to the upper part of the belt screen for reprocessing. By starting with a"course"processing of the returned fibres and then graduately reducing the size of the gap between the belt screen and the individual spike rollers, it is ensured that a lump of returned fibres is disintegrated and not compressed and drawn through a gap between two adjacent spike rollers. Hereby, a better disintegration is achieved.

In order to achieved further disintegration of the fibres and thereby more even distribution, two further rows of spike rollers may be provided on each side of the lower run of the belt screen.

In an embodiment of the invention, the spike rollers are provided along at least one of the vertically runs of the belt screen. Hereby, fibres that are drawn along the belt

screen may be re-processed also during the return path and/or the belt screen may be cleaned by the spike rollers provided along the vertical path of the belt screen.

In an embodiment of the invention, the belt screen extends beyond the housing in the downstream direction with respect to the travelling direction of the forming wire.

Hereby, an extra cleaning effect of the belt screen can be achieved without interfering with the forming process depending on the type of fibres used. This may be advantageous with respect to some types of products. Alternatively, the belt screen is provided inside the housing.

The fibres of the fibre material may be natural fibres, such as cellulose fibres, synthetic fibres or any combination thereof as well as granular material in any kind possible.

The belt screen may be driven with the same or in the opposite direction of movement of the lower run as the underlying forming wire. Herby, different laying formation of the fibres may be achieved for forming fibreboard with a particular desired surface pattern.

Moreover, the belt screen may be either continuously driven, e. g. with a constant speed, or intermittently driven. These different modes of operation of the forming box also allows for different fibre formation patterns on the forming wire.

In a first embodiment of the invention, two further rows of spike rollers may be provided on each side of the lower run of the belt screen. Hereby, a possibility of providing extra disintegration of fibres or lumps of fibres is made available, which may be advantageous for some applications.

The belt screen is preferably provided with grid openings in a predetermined pattern.

In one embodiment, the belt screen may be a wire mesh having a predetermined

mesh opening. In another embodiment, the belt screen has transversely orientated grid members with openings in between.

In an embodiment of the invention, the lower run of the belt screen is immediately above the forming wire so that the belt screen makes contact with the upper side of the fibre formation being air laid on the forming wire. Hereby, the vacuum is screened in some areas in the bottom opening of the forming box and a predetermined surface structure of the laid product may be achieved. These vacuum screened areas are determined by the screen pattern of the belt screen.

In the following, the invention is described in more detail with reference to the accompanying drawings, in which: Fig. 1 shows a schematic perspective view of a forming box according to a first embodiment of the invention; fig. 2 shows a schematic side view of a forming box according to a first embodiment of the invention; fig. 3 shows a detailed view of the forming box shown in fig. 2; fig. 4 shows a detailed view of a second embodiment of a forming box according to the invention; fig. 5 shows a detailed side view of a third embodiment of the invention; and fig. 6 shows another embodiment of the forming box, shown in fig. 3.

In fig. 1 and fig. 2, a forming box according to a first embodiment of the invention is shown. The forming box comprises a housing 1 into which fibres 3 are supplied from an inlet 2. The forming box is positioned above a forming wire 4 onto which the fibres 3 are air laid due to a vacuum box 5 underneath the forming wire 4 to form a fibreboard 6 in a dry forming process. In fig. 1, the forming box is shown with the interior elements visible in the housing. However, it is realised that the housing walls may be made either from transparent or opaque materials.

The fibreboard 6 may be made or at least include from natural fibres, such as cellulose fibres, animal hair, fibres from flax, hemp, jute, ramie, sisal, cotton, kapok, glass, stone, old newsprint, elephant grass, sphagnum, seaweed, palm fibres or the like. These fibres have a certain insulating capacity that may be useful in many applications. The fibreboard 6 may also be made from or at least include a portion of synthetic fibres, such as polyamide, polyester, polyacrylic, polypropylene, bi- component or venniculite fibres or the like as well as any kind of granular material.

Fibreboards with such synthetic fibres may be used for providing the fibre product with certain properties, e. g. absorbent products. Moreover, the fibres may be pre- treated with a fire retardant or a fire retardant may be supplied directly in the fibre mixture which is blown into the forming box.

The fibres 3 are blown into the housing 1 of the forming box via the inlet 2. Inside the forming box a number of spike rollers 7 are provided in one or more rows, e. g. four rows of spike rollers 71,72, 73,74 as shown in figs. 1 and 2. In the housing, an endless belt screen 8 is also provided. This endless belt screen 8 is provided with a conveying path including an upper run 85, a vertical section 88 where the belt screen 8 moves in a downwards direction, a lower run 86 where the belt screen 8 travels substantially parallel with the underlying forming wire 5 and an upwardly oriented run 87, as shown in fig. 3.

Adjacent the upper run 85 of the belt screen 8, at least one row of spike rollers 71 is provided. In the embodiment shown two upper rows of spike rollers 71,72 and two lower rows of spike rollers 73,74 are provided at different levels in the housing 1.

The belt screen is arranged with an upper run path 85 between the two upper rows of spike rollers 71,72 and the lower run path 86 between the lower rows of spike rollers 73,74. The fibres 3 may be supplied into the housing 1 in lumps. The spike rollers 7 then disintegrate or shredder the lumps of fibres 3 in order to ensure an even distribution of fibres 3 in the product 6 formed on the forming wire 5. The fibres pass the spike rollers 71 in the first row and then the belt screen 8 and the second row of spike rollers 72 as the fibres are sucked downwards in the forming box. In the lower

run 86 of the belt screen 8, oversized fibres are retained on the belt screen 8 and returned to the upper section of the forming box for further disintegration. The retained fibres are captured on the top of the lower run 86 of the belt screen 8 which then become the lower surface of the upper run 85 and the fibres are suck off the belt screen 8 and the lumps of fibres are shredded by the spike rollers one more time.

As shown in fig. 3, the row of spike rollers 72 immediately below the upper run 85 of the belt screen 8 in inclined. This row 72 receives the retained,"oversized"fibres being returned from the retention below. In order to ensure that the fibres 3 are shredded efficiently in this row 72, the first spike rollers 72', 72", 72"', 72""in the row 72 are provided with different distances between the axis of rotation of the individual spike rollers 72', 72", 72"', 72""and the upper run 85 of the belt screen 8.

The first spike roller 72'in the row is positioned with the largest distance and graduately the subsequent spike rollers 72", 72"'and 72""are positioned with closer distances, so that fibres in the lumps of returned, oversized fibres are"peeled"off gently whereby it is ensured that the lumps are shredded and disintegrated rather than being sucked and dragged off the belt screen and in between two adjacent spike rollers.

The endless belt screen 8 includes closed portions 81 and openings 82 provided in a predetermined pattern. Alternatively, the belt screen 8 could be a wire mesh. By a particular pattern of openings 82 and closures 81 of the belt screen 8, a predetermined surface pattern on the fibreboard 6 formed by the dry-forming process may be achieved by arranging the lower run 86 of the belt screen 8 so that it makes contact with the top surface of the fibres which are laid on the forming wire 4, as shown in fig. 4.

In fig. 5, another embodiment of a belt screen 8 in the forming box is shown.

According to this embodiment, the belt screen 8 is made from pivotable elements 81 retaining the fibres. By pivoting the elements 81 between an open position 81'and a closed/flat position 81", the opening between the elements may be changed. Hereby,

a"course"sieve function may be obtained on the upper run path of the belt screen 8 and a"fine"sieve on the bottom run path.

As shown in fig. 4, the belt screen 8 may be guided along a path taking it outside the housing 1 as indicated by reference 9. This allows for the possibility of installing cleaning means for cleaning the belt screen without interrupting the forming process.

The vacuum box is extended in the downstream direction beyond the forming box.

Hereby, loose fibres may be laid in a finishing layer on the top surface of the formed fibreboard.

In the vertically oriented paths of travel 87, 88, one or more spike rollers (not shown) may be provided adjacent the belt screen 8 for loosing fibres on the belt screen. The configuration of the spike rollers may be chosen in accordance with the kinds of fibres which are to be air-laid by the forming box.

The bottom of the forming box may be provided with a sieve 11 as shown in fig. 6, and the belt screen 8 may accordingly be provided with brush means (not shown) for removing retained fibres. Hereby, the belt may additionally be used for cleaning a bottom sieve. The brush means may be members provided for sweeping the fibres off the upper side of the lower run path of the belt screen. Alternatively or in combination, the belt screen may be provided with means for generating a turbulent airflow stirring up the retained fibres on the sieve. In this manner, a forming box with a bottom sieve may be provided with a cleaning facility for the bottom sieve and the belt may additionally be used for preventing that the sieve is clogging up.

In the above-described embodiments, the inlet is shown positioned above the belt screen and the spike rollers. However, it is realised that the inlet may be positioned below the upper run of the belt screen, and/or that a multiple of inlets may be provided, e. g. for supplying different types of fibres to the forming box. The spike rollers and indeed the belt screen will then assist in mixing the fibres inside the forming box.

In another embodiment, a granulate or another type of fibre may be supplied into the forming box above the fibre inlet 2 and mixed with the fibres adjacent the inlet opening inside the forming box. Such granulate is supplied separately to the forming box since it must be transported at a separate (higher) airflow velocity. This granulate may include vermiculite, rubber, plastic, glass fibre, rock wool, etc. The granulate may also include metal fibres, such as aluminium or brass, steel, etc.

The present invention is described above with reference to some preferred embodiments. However, it is realised that many variants and equivalents may be provided without departing from the scope of the invention, as defined in the accompanying claims.