The present invention reLates to a dry forming system for successiveLy Laying out a Layer of fibers on a moved forming wire, the system being of the kind which comprises a pipe of a perforated c Lassi fi cat ion materiaL and means for estabLishing through this pipe and though a return pipe system a circuLating fLow of an air fLuidized fiber materiaL, which is caused to be succes¬ siveLy discharged through the perforations of the pipe, and means for sucking air down through the forming wire such that the perforated pipe as Located above the wire is pLaced generaLLy in a downwardLy directed air fLow, by which the fibers discharged through the perforations of the pipe are carried downwardLy for deLivery onto the forming wire; inside the pipe is arranged a needLe cyLinder rotating about an ax.is, which is paraLLeL with the axis of the pipe, but preferabLy Located underneath th s axis, such that the needLes of the cy inder sweep across a LongitudinaL, internaL area of the perforated p pe at a smaLL distance from the inner surface of the pipe.

A system of this kind is discLosed in W0 81/02031. The needLe cyLinder serves, for one thing, to agitate the fibers just inside the area, in which the fibres are discharged at a maximum rate, viz. aLong the bottom area of the perforated pipe, such that Lump formations in the fibers wiLL be counteracted, just as the fibers, by the associated vivid reorganizing thereof, wiLL more easiLy get discharged through the pipe waLL with a reasonabLy high capacity. For the dry forming of paper products it is customary to make use of a fiber materiaL consisting of rather short ceLLuLose fibers, having a Length of some 2-5 mm, but even with the use of perforations having a corresponding diameter it has been found that

also Longer fibers, e.g. plastic fibers of a Length of 15-20 mm, may get discharged through these perforations, when the fibers are violently agitated.

However, the thought has come up that the discharge capacity as far as Long fibers are concerned could be further raised ith the use of perforations which are equally long or even longer, when the width of the perforations is kept small enough to sti ll make the pipe wall able to withhold Lump formations from being discharged. For a closer consideration of this possibi li¬ ty it is essential that the general flow-through veLocity of the fiber materiaL in and along the pipe is relative¬ ly low, viz. of the magnitude 2-4 m/sec, while the peripheral tip velocity of the transversely rotating needLe cylinder is desired to be relatively high, viz. of a magnitude some 10 times as high. Hereby the needLe cyLinder wi ll act as a carding cyLinder, which wi ll seek to orient the Long fibres mainly in the moving direction of the needles, i .e. in the cross direction of the perforated pipe. It wi LL be conditioned hereby that the oblong perforations in the pipe wall should be oriented in the circumferential direction of the pipe for obtaining a high discharge capacity of the "cross ca ^* ded" fibers, but experiments have shown that this measure does not provide for any considerable increase or any increase at all of the discharge capacity.

It has been found with great surprise, on the other hand, that an essential increase of the discharge capacity is obtainable with the use of oblong perforations, which are oriented lengthwise of the perforated pipe, i .e. just crosswise of the direction which should be selected based on the above theoretical consideration. For the present it is impossible to explain this effect, but the practical result is remarkable inasfar as the discharge capacity is more than doubled when the oblong perforations are oriented

in the length direction of the pipe.

Thus, the invention is primarily characterized in that the pipe wall is provided with oblong protrusions and that these a r e oriented in the Length direction of the tube.

With the use of oblong perforations having an effective orientation it is thus possible to achieve a considerable discharge capacity for Long fibers, whereby it becomes attractive to produce dry-formed Long fiber products of a high quality and evenness, because the pipe wall wi ll sti ll constitute a clas¬ sification element which will sort off fiber Lumps from the laid out material, whereby the Latter may be even and uniform, also when made with a small thickness. It wi ll be possible, thus, to make use of fiber materials other than cellulose, whereby new and attractive products may be manufactured for different purposes, or at Least such products may be produced at considerably reduced costs due to the remarkably increased discharge capacity of the dry forming system as far as Long fibers are concerned .

It will be appreciated that the use of the oblong perforations will not in any way involve an restriction of_the discharge capacity for such short cellulose fibers which might be present in the fiber material. Such short fibers, whether being used alone or in admixture with longer fibers, may easi ly be discharged through the oblong perforations, which - due to their small width - wi ll sti ll be "classif ing" also as far as the short fibers are concerned.

There are two important consequences of this, viz. both that a given standard pipe having axiaLly elongated perforations will be usable for a classified laying out or down of materials of short as well as long fibers, i.e. the pipe may be standardized irrespective of which kinds of fibers it should handle, and that such a pipe

may work with a fiber materiaL containing both short and Long fibers, e.g. both cellulose and plastic fibers. It is possible to hereby build up some special products, which may show special characteristics when subjected to some suitable af er-treatment, e.g. showing a good porosity and therewith a good hygroscopic effect due to the cellulose fibers, combined with a good mechanical strength resulting from spotwise bindings between the long plastic fibers, which, in the areas between these binding spots, will act to mechanically hold the shorter cellulose fibers .

Thus, the use of the oblong perforations wiLL promote the possibilities of exploiting fiber materials, which hold fibers of different Length and characters, for the production of webs of particular characteristics On this background it is a special feature of the invention that such a web material may be provided by a mixing together of different kinds of fibers, which are deLivered from individual defibration devices for respective short-'and long-fibered pulp materials. It is hereby important that a cellulose pulp materiaL may be worked into short fibers e.g. in a hammer mill, while a pulp materiaL consisting of Long plastic fibers ar-e move suitably defibrated in a special tearing-up unit, which separates the fibers without breaking them into smaller pieces.

Both the short and the long fibers, therefore, may be brought into an air fluidized condition by separation in an optimized manner from respective pulp materials, and thereafter it will be sufficient to move the fluidized fibers together and intermix them not later than by their admission into the perforated pipe. In practice it is preferred to bring the air flows holding the respective short and long fibers from the respective defibrators together in a mixing unit prior to their admission into the perforated tube, because it will be

secured hereby that the mixing of the fibers wi ll be carried out effectively already before the fibers enter the perforated pipe, thereby enhancing the uniformity of the fiber materiaL Layer Laid out on the forming wire. In the following the invention is described in more detai l with reference to the drawing, in which:

Fig. 1 is a perspective view of a known dry forming system,

Fig. 2 is a cross section thereof, Fig. 3 is a Longitudinal sectional view of a corresponding system according to the invention, and

Fig. 4 is a schematic diagram of further detai ls. In Fig. 1 is shown a foraminous forming wire 2, which in a closed path has a horizontal run through a forming unit 4 comprising a Lower suction box 6, from which air is exhausted through a pipe 8, and an upper housing 10, in which there is arranged a pair of parallel pipes 12 which are perforated and extend crosswise over the wire 2. In end walls 14 of the housing 10 are mounted rotation bearings 16 for the pipes 12, and outside the end walls 14 the ends of the neighboring pipes 12 are interconnected through respective U-pipes 18 and 20. The Latter is connected wi-th a supply pipe 22, through which an air fluidized fiber materiaL may be blown into one of the pipes 12, whereafter the fiber material is movable in a circulation path through the pipes 12.and the U-pipes 18 and 20. The ends of the pipes 12 are provided with non- perforated sleeve members 24, which are rotatable in the bearings 16 and are drivingly connected, through driving belts 26, with a motor pulley 28 for rotating the pipes 12. In the top side of the oblong housing 10 is provided a pair of longitudinal air intake slots 30 located above the respective pipes 12 and optionally provided with adjustable valve or air guide flaps 32 (Fig. 2) .

Inside each of the pipes 12 is arranged a needle cylinder 34, see also Fig. 3, which is provided with needles 36 arranged along a screw line. The cylinders 34 have outer shafts 38 projecting through rotation bearings 40 in the U-pipe 18, the shafts 38 outside these bearings being provided with pulleys 42. The cylinders 34 are mounted eccentr cally in the pipes 12 such that the needles 36 sweep over the interior bottom side of the pipes 12 of a short distance therefrom. As shown in Fig. 2, outside and adjacent the top side of the pipes 12 may be provided some blowing nozzles 44 arranged on stationary nozzle pipes 46, whi le internally in the pipes 12 there may be provided stationary air screens 48 st retching through the pipes near the top portions thereof.

The system so far described is known from W0 81/02031, to which reference is made for a detai led description of the operation of the system. The main function is that the blown-in and circulated fiber materiaL is brought to be successively discharged through the perforated pipe 12 by the action of the air which, from the suction box 6, is sucked down through the housing 10 from the slots 30, this air flowing do.wnwardly both through the perforated pipes 12 and through the areas outside these pipes, whereby the fibers discharged from the pipes wi LL be conveyed down to be deposited on the forming wire 2 and thus, on that wire, be moved away from the forming unit in an even fiber layer on the wire. The discharge of the fibers from the perforated pipes 12 is greatly promoted by the action of the needLe cyLinder 34, the needles 36 of which, by the rapid rotation of the cylinder, wi ll agitate and reorganize the fibers and even act centrifug- ally on the fibers. Moreover, by the screw-Like arrangement of the needles on the cyLinder, the cylinder will contribute to ^" the general transportation of the

fiber material through the associated pipe 12.

In the said known system the pipes 12 are made of a suitable classification screen materiaL having small holes of a dimension of 2-5 mm in both the Longitudinal and the circumferential direction of the pipes, irrespective of the holes being circular or quadratic. These holes are primarily adapted to the use of correspondingly short cellulose fibres, though as already mentioned they may well allow for a certain discharge of considerably Longer fibers.

Such a discharge of Long fibers, however, may be promoted partly by an increased rotational speed of the needle cylinders and partly with the use of oblong perforations in the walls of the pipes 12. A rapid rotation of the needle cylinders, whereby the tip velocity of the neddles 36 will be some ten times the axial velocity of the fiber materiaL through the pipe 12, will produce a cross oriented carding effect on the fibers inside the pipe 12, but as already mentioned the fiber discharge capacity will be even very low if the oblong perforations of the pipe 12 a re corresponding¬ ly oriented in the transverse or circumferential direction of the pipe, while the capacity is surprising¬ ly. high when the oblong perforations are oriented in the Longitudinal direction of the pipe.

Such an orientation of the oblong perforations is shown in Fig. 3, in which it is also shown in different area sections of the tube 12 that these perforations may be arranged in different patterns in the tube wall, the perforations preferably being provided as punched holes in a pipe plate materiaL; alternatively they may be constituted by correspondingly open areas in a pipe wall made of a net wire materiaL.

For the invention it is possibly not decisive whether the oblong perforations are oriented exactly in the longitudinal direction of the pipe 12, even though

with such an orientation an unexpected high discharge capacity has been observed; the perforations may be slightly oblique with respect to the said longitudinal direction, though without practically approaching the circumferential direction of the pipe.

The oblong perforations wiLL allow for long fibres to be discharged from the pipe 12 with a desired high capacity, but at the same time, of course, they will also allow for shorter fibers to be discharged. It is perfectly possible, therefore, to make use of a mixture of short and Long fibers, whereby, as mentioned, products of advantageous special characteristics may be manufactured.

It is an associated problem how the pipes 12 can be supplied with a fiber materiaL consisting of both short and long fibers. With the invention this problem is solved by providing for separate flows of air fluidized fibers originating and defibrated from respective separate pulp materials, these flows being individually fed to a mixing unit, from which the resulting flow is fed to the forming unit. This principle is schematically i llustrated in Fig. 4, in which the two individual defibrators are designated 52 and 54 and the mixing unit 56. It would be possible to make use of a single defibrator handling a mixed pulp of short and long fibres, but the system as shown and described is highly advantageous in that the two separate defibrators may be individually adapted to work with respective specific pulp materials in a speciaLi zed and optimized manner with respect to both energy consumption and gentleness towards the fibers. If required, more than two defibrators may be used.