Until now, these problems have, in principle, been solved according to the following four different methods: -by careful selection of the material used in plywood manufacturing, the surface defects can be minimized; -by making the surface even by machining, e. g. using grinding, in particular, when no deep surface defects oc- cur; -by filling the cavities, the surfaces of the plywood boards have been made even; -by applying a smoothing layer, it has been possible to make the surfaces of plywood boards, chipwood boards, and the like even.

The latter method differs from the others in that it changes the characteristics of the surface as a whole, and in that it adapts to, to express it briefly, to all kinds of boards with wood as their material.

The method can be carried out by, before pressing, apply- ing a fiber matting, essentially comprising a mineral fiber impregnated by a binding material, to one or both sides of the board material. During pressing, the fiber matting will level out all uneven spots and then, after

the binding material has hardened under pressure, form hard and firm board surfaces.

The invention relates to this method and constitutes an improvement of an earlier procedure. In spite of its rather wide use, this procedure has not appeared to be an optimal one.

If the surface upon which a fiber matting is to be applied has a defect in the form of a cavity, one of two extreme phenomena may occur. In the first of these extremes, the fiber matting will act as a liquid. Under pressure, the fiber matting material will flow so that its density, i. e. its material mass per volume unit, remains unchanged the whole time. In reality this extreme case cannot be reached, as the fiber matting, in order to secure its manageability, must remain as a whole. It is not desirable either because the material of the fiber matting could just vanish over the edges if there were no specific obstacles, which in pratice are not obtainable.

In the other extreme, no material transfer takes place in parallel with the surface of the board blank. This results in the fact that the density of the fiber matting in the middle of the cavity will be considerably lower than at the other points of the surface. A weakening will become apparent, after a period of surface wear, in the form of surface unevenness. This is one of the problems which the surface coating should eliminate.

Researches have shown that, in reality, we are quite close to this extreme. The only possibility to compensate for this phenomenon has been to produce oversize fiber mattings so that the weakenings, which emerge in connec- tion with the cavities on the surfaces of the wood material surfaces, do not reach harmful dimensions.

However, in practice there is a condition making this situation more difficult. Fiber mattings for said purpose are manufactured based on mineral wool spread upon a band and then impregnated. It is well known that mineral wool mattings are normally characterized-by unevenness so that the fiber mass varies between different positions. In thick mattings, i. e. those with a large quantity of fiber mass per surface area, there is always a levelling factor in the form of random. If the fiber mass in one layer of the matting is small within a certain area, there is a strong likelihood that in the other layers the masses will be normal, or even bigger than normal, whereby a levelling or compensation has occurred.

In thin mattings, having a surface weight actual for instance in lining of plywood boards, such a levelling does not take place, or its extend is relatively limited.

This means that in any fiber matting, there may usually very well be either too much or too little material in the middle of a cavity in the wood. If there is too much, the consequences will have no importance at all. However, if there is too little material, this will mean that the density in the fiber matting in the middle of the cavity will be even lower than it would have been if the material mass in the fiber matting had been normal.

In practice, it is not possible to achieve an absolutely even fiber matting if the costs have to be taken into consideration. However, it has turned out that this prob- lem can be solved to a satisfactory extent even when the uniformity is not perfect, if it satisfies the condition that the uniformity, measured in the way described below or in any other way with equal results, reaches 20 % at the most, calculated as a variation factor.

However, this requires that in the fiber matting there should be a flowing binding material which will transfer

the pressure from the press to the individual fibers.

Also some form of a filler may be needed to modify the lubricating characteristics of the binding material.

Therefore, the objective of this invention is to provide a fiber matting consisting mainly of mineral fibers, pri- marily intended to be used as a face for plywood and the like in order to reliably level out all of the uneven spots in them in connection with the pressing and curing of the binding material, hereafter called the filling capacity, and to otherwise improve its characteristics, so that the mineral fibers form a uniform structure and are uniformly distributed over the fiber matting so that the scattering of the deformation resistance does not exceed 20 %, calculated as the variation factor, and so that the distribution of the fiber lengths is bimodal.

The uniformity of a fiber matting can be defined in sev- eral different ways. For this purpose the surface weights of small surface elements can be determined. Research has, however, proved that the deformation resistance according to the method described below, supported by Fig. 1A, is a better representation of of the filling capacity of the fiber matting. According to this method, a metal cylinder A with a diameter of 10 mm, fixed to the measuring rod B in a measuring clock C, can from above press against a fiber matting D laying on a horizontal, even base E. The combined weight of the metal cylinder A and the measuring rod B is 200 grams.

According to this method, 20 areas of fiber matting with- in the surface area of 210x297 mm (A4) are measured. The mean value M of the distances and the standard deviation s are calculated, and from them the variation factor v is calculated using the formula v = 100 * s/M

A more extensive scattering may lead to the risk of an unreliable filling capacity. Uniformity is importat even on surface covers containing no or only local uneven spots. Thus, in case one, when trying to obtain a strengthened surface, it is essential that there are no weak areas on it as, in practice, the technical outcome will depend on the characteristics of the weakest points.

It is obvious that a certain material mass is required to make the fiber matting effective, whatever material it is made of. For most practical purposes, the surface weight requirement is at least 150 g/m2, preferably at least 250 g/m2.

An important precondition for the good functioning of the fiber matting in practice is that its fiber length dis- tribution is bimodal. It is true that a low average length may result in good filling capacity but it gives insufficient inner coherence to obtain the treatment characteristics required in practice. A high average length gives coherence but lacks in filling characteris- tics. Looking at the problem superficially, it should be possible to find an average length in between, with both sufficient filling characteristics and sufficient treat- ment characteristics, this has, however, not proved viable. Suprisingly it has been proven that a suitable fiber matting can be obtained by providing a bimodal fiber length distribution.

It has been impossible to develop a structurally formu- lated theory for this phenomenon, but it is most likely that bimodality results in a mobility of the shorter fibers forming a mass in relation with the long ones, with a tendency to form a more immobile grid.

By way of definition, such a bimodal fiber length distribution is characterized by two frequency peaks.

Both of these frequency peaks need not be equally high.

If they are not equally high the lower one must, however, be sufficiently high so that the probability a random de- viation of a unimodal distribution is in practice eli- minated.

Bimodality may form the basis for seeing the fiber mass as containing two fiber fractions, one shorter and the other longer.

It has been noted that an increased uniformity down to the variation factors less than 10 per cent and up to 5 per cent will result in observable advantages but also that the excessive uniformity obviously does not mean increased filling capacity, nor any other advantages.

In order to make the longer fibers function optimally and give strength without greatly reducing the inner mobility that contributes to the filling capacity, the relation between those fiber lengths that refer to the two frequency maxima in the bimodal fiber length distribution must be greater than 5, preferably also greater than 10.

In this way, good results have been achieved by the mix- ing of average 25 mm length fibers in a fiber mass, the average fiber length of which is about 3 mm. When the longer fibers were reduced to an average length of 10 mm a large quantity of the longer fibers had to be added to achieve sufficient strength and the filling capacity became too low. As the long fibers normally cost more than the short ones, in this case, even the economy of the production will suffer.

Fig. 1B shows an example of a bimodal fiber length dis- tribution with two frequency maxima, one by 3 mm and the other by 21 mm. The relation between these two fiber lengths is 7 and thus the shown example should satisfy the requirement according to Claim 3. Also Fig. 1C, show-

ing a bimodal fiber length distribution with the fiber length maxima by 3 and 15.5 mm respectively, satisfies the requirement according to Claim 3.

However, and not surprisingly, it ha-s appeared that other characteristics of the fiber matting are also influencing its filling capacity. One such characteristic is the orientation of the fibers. Depending on the way the fibers are grouped in bundles or clusters, their filling capacity is reduced. The same is true if a larger number of fibers is orientated perpendicular or nearly perpen- dicular against the fiber matting level. Further, it is not convenient to let a large number of fibers take a certain direction, e. g. the running direction of the fiber matting. Instead, the fibers in the fiber matting should be mainly randomly orientated on the level of the fiber matting.

It is very difficult to directly observe that the fibers are randomly orientated. Instead, it is preferred to measure the tensile strength of the fiber matting in longitudinal and transversal directions. The relation between these values must not be less than 0.5 and not greater than 2. Preferably, the relation should be between 0.7 and 1.5. Outside these limits the fiber orientation is no longer random enough and the filling capacity may become too minimal.

Treatment of the fiber matting in different phases empha- sizes the tensile strength requirements of the longitu- dinal direction more than those of the transversal direc- tion. Therefore, it is an advantage if, in any given interval, the value of the former is higher than that of the latter.

In particular, the thicker fiber mattings according to this invention sometimes have the tendency to delaminate

under treatment, i. e. to form layers caused by insuffi- cient inner coherence in their thickness direction. This is due to the fact that an overwhelming part of the fibers, and especially the long ones if any of those are involved, are placed at the level of-the matting and only a few of them have a significant reach in the perpendicu- lar direction against this level. This relationship can be corrected by so-called needling, providing sections of the longer fibers reach through the fiber structure in its thickness direction. This is an efficient means to keep the structure together.

The bimodal fiber length distribution can be achieved by mixing several fiber materials with distinctly different length characteristics. If these fiber materials are also made of different basic materials, e. g. so that one is inorganic and the other organic, it will be easy to determine, even after mixing, their respective proportions, e. g. in volume percentages.

If the bimodal fiber length distribution has been the outcome of something else, or if the two fiber materials to be mixed consist of the same basic material, this can appear more difficult. If the fiber length distributions are so widely separated that there is between them an empty fiber length interval, even in this case the pro- portions between them can be determined. If, on the con- trary, the fiber length distributions are overlapping, there are cases when it will not be possible to determine whether a certain fiber belongs to one portion or to the other. Therefore, to be able to give the mutual propor- tions, a convention is used where the fiber length between the two frequency maxima, showing the lowest fiber frequency, is used as divisor. If this lowest fre- quency covers several fiber lengths, or one fiber length interval, the average value of these fiber lengths or of the fiber length area is used instead.

In the example shown in Fig. 1B, the following fiber lengths between the two frequency maxima are empty: 11, 13,14,15,16, and 18 mm. The average value of these is 14.5 mm, thus giving, by way of definition, the boundary between the two fiber materials.

The example shown in Fig. 1C shows the minima by 9 and 11 mm, respectively, and thus the boundary between the two distributions is, by way of definition, 10 mm.

The researches concerning the present invention show that the proportion of the longer fibers, i. e. of those belonging to the longer of the two fiber length distribu- tions, must be up to at least 8 per cent, preferably at least 15 per cent of the total fiber volume.

Even the length characteristics of the fiber component with long fibers is significant, although the most important is that their average length is considerably more than that of the rest of the fibers. The longer of the two fiber distributions must have its average length within 10 to 80 mm, preferably 20 to 40 mm. Any shorter fibers have a lower strength contribution and any longer fibers do not seem to be beneficial in relation to the material mass they represent.

In the experiments, three categories of long fibers have been shown to be especially advantageous, regarding dif- ferent aspects such as functioning, costs, and willing- ness to be uniformly distributed. In this context, func- tioning means considering the positive effect that the long fibers have on the tensile strength of the fiber matting, and the negative effect they have on its filling capacity, probably due to the fact that they limit the mobility of the relatively shorter fibers. One of these categories comprises organic fibers, e. g. the synthetic fibers of polyester, polypropylene, polyamid or of

polyester/polypropylene, polyester/polyethene, polypropylene/polyethene and polyester/copolyester. This category may also comprise the viscose fibers. Their maximum thickness in this case must be 7 decitex. The second category comprises fibers of-glass, conventional glass fibers or fibers of glass with a basalt like compo- sition. Their maximum thickness must be 3 decitex. Both of these categories are characterized by a smooth fiber surface and a high tensile strength. These result in a good strengthening effect, without a too high reduction of the mobility of the shorter fibers during the pressing process.

Even natural fibers such as cotton, jute, linen, and sisal fiber, or modified natural materials such as cellu- lose fiber, have been shown to be effective. Although their surface is not smooth, they are functional, prob- ably due to the fact that they are, instead, broken by the powers which influence them during the pressing pro- cess.

Not unexpectedly, even the fiber thickness of the compo- nent with long fibers is significant. The optimal value for this parameter has appeared to be within a fairly narrow area, i. e.

-for organic polymer fibers 3 to 7 decitex, preferably 5 to 6 decitex -for conventional glass fibers 0.7 to 3 decitex, prefer- ably 1 to 2 decitex -for fibers with a basalt like composition 0.2 to 3 decitex, preferably 1.2 to 2.2 decitex.

The desirable inner mobility of the fiber matting depends, very significantly, on the fiber morphology of the mineral fiber component. The shorter fibers seem to play a key role here, and their ratio should be limited, i. e. the relation between their length and diameter. This

can be expressed so that the fibers with a length under 5 mm have a relation between their average lengths and their average diameters between 100 and 1000. A lower ratio leads to a structure with a too insufficient inner strength, notwithstanding the positive influence of the long fibers. A too high ratio works against the inner mobility and leads to lowered filling capacity.

The information about the fiber diameters mentioned here- by concern the optical microscope measurements magnified by 500 times. They are given as averages of 200 individ- ual diameter measurements by using good preparation and observation methods.

The fiber length information indicates direct measure- ments from a projection picture with the ability to mag- nify the fiber sample 100 times.

In order to comply with its final function, the fiber matting has to cooperate with a binding material. This invention also comprises a fiber matting with such a binding material. The task of a binding material is obvi- ously to bind, together with the pressing procedure, the compressed fiber matting into a tight and strong layer.

At the time of pressing, the binding material can also have the role of a lubricating medium, transferring and distributing the pressing power to the individual fibers in the fiber matting. To this end, the most suitable binding material should flow, at least at high tempera- tures such as in a thermo-compressing process.

However, the binding material in its cured state has its most significant impact on the surface against which the fiber matting has been pressed under heat. In order to achieve the right combination of tightness, wear resis- tance, and overall resistance against chemical and microbe attacks, preferably unsaturated polyester, but

also vinyl ester, epoxy, phenolformaldehyde, melamine or the like can be used.

The binding material can include fillers, the task of which in this case can be manifold,-as they can partly modify the effect of the binding material to help the inner movements in the fiber matting during the pressing process, and partly modify the mobility of the filler particles in the fiber structure to improve its filling capacity. Furthermore, the filler particles can improve the wear resistance of the ready-made outer surface, other resistances, or some other new or improved charac- teristics. Suitable filler materials are fine-grained mineral powders such as limestone flour, talcum powder and wollastonite flour.

Among the additional characteristics that can be added by suitable choices of filler, the following can be mentioned: fine corn pyrite carbide gives the coating of plywood or chipwood boards high friction characteristics, grains of materials with a high portion of relatively lightly splitting chrystal water can give added fire resistance, graphite flour can improve the release char- acteristics against e. g. concrete.

Even inorganic filler materials can be used. For instance, wood powder can regulate the flow characteris- tics of a flowing binding material and reduce its required quantity.

The filler material must have a fine-grained structure, or more precisely, its average grain diameter must be under 10 ßm, preferably under 5; nm.

The filler material element in the completed mix of the binding material and the filler must be within the range of 15 to 50 weight per cent, preferably 20 to 30 weight

per cent, out of the total weight of the binding material, including the filler.

In order to obtain the highest possible effect from the filler material's ability to increase the final outer surface, the concentration of the filler particles must be higher on the side of the fiber matting which is turned outwards during pressing. On the other hand, in order to obtain the best possible filling capacity the concentration of the filler particles may need to be higher on the side of the fiber matting which is turned inwards during pressing. These two effects can be combined by making the concentration of the filler par- ticles higher on both sides of the fiber matting than in its middle. The concentration of the filler particles needs not be the same on both sides, and not even the same filler material is necessary. As a matter of fact, both the method and the concentration can be individually adapted to the use or to the advantage of strengthening the complete product coated by the fiber matting on one side, and to the need or to the advantage of increasing the inner mobility and the filling capacity.

The part of the binding material without filler must be 50 to 200 weight per cent, calculated with the weight of the fiber material, in order to achieve the right filling and the desired final characteristics.

To make the penetration of the binding material into the fiber matting easier, especially if it is relatively thick and/or of high density, the fiber matting can with advantage be equipped with holes or weakenings, e. g. by driving needles through it. The art of these, as well as their density, or mutual distances, is in this case adapted according to the need of the penetration help required by the actual case.

Normally, a needling with a needle density of 10 to 20 needlings per cm2 may be suitable, provided that the diam- eter of the needle is about 0.3 to 1 mm2. The use of thicker needles brings about deeper penetrations. When striving to obtain improved and even, but not very deep, penetrations, thinner needles and smaller distances should be chosen.

This invention also includes a method of manufacturing a fiber matting, primarily intended for plywood board coat- ings and the like, in order to level out, in connection with pressing under heating, their unevennesses and to improve their characteristics, whereby the fibers in the fiber matting form a coherent structure and are evenly distributed over the fiber matting, so that the scatter- ing of the deformation resistance does not exceed 20 per cent, calculated as a variation factor, and whereby the fiber length distribution is bimodal.

According to the present invention, the mineral fibers are dispersed into the air, together with a fiber compo- nent of long fibers, and then the fiber dispersion is laid on a mobile, perforated receiving means, without using gravitation, as a matting, and using air suction.

In a suitable way, the starting point is preferably a thin web of mineral fibers that are dispersed using two or more brush rollers, possibly after a fiber shortening run by crushing them between the rollers.

The receiving part can be made of a band or drums.

In order to achieve sufficient evenness, the dispersing and the recollection may require more than one stage. In that case, the fiber component with long fibers will most conveniently be added before the first dispersing.

It is convenient to add a binding material to the fiber matting in a separate process, by adding at least one thin and tight carrier layer, e. g. polyethene foil, whereby the binding material is inserted between the foil or the foils and the fiber matting before they are put together. After this, when the foil or foils and the fiber matting are put together, at least a partial inserting of the binding material in the fiber matting will take place.

At this stage of the process, it is possible to prepare one or two mixings of binding material and filler that will be laid over one or two foils to be thereafter inte- grated into the fiber web from the first process part, so that the side of the foil or foils coated by the binding material and the filler are turned against the fiber web, whereafter the integrated layers, the fiber web and the foil or foils will be pressed together.

The process itself can be carried out in several ways, according to the prevailing conditions. It is possible either to coat the surfaces of the carrier layer that are against the fiber matting or the carrier layer with the binding material, or apply the binding material to the completed fiber matting before coating the carrier layer or the carrier layers, or to use a combination of these methods so that the binding material is laid directly on the upper surface of the fiber matting and a protective layer is laid on the lower surface which is then combined with the fiber matting.

If the fiber matting is mainly transferred horizontally and the binding material with its possible filler is dry, it can be strewn on the lower foil and/or on the upper surface of the fiber matting before the foil or foils are combined with the fiber matting.

In order to ease and control the penetration of the mix of the binding material and filler in a later phase of the process, a treatment with needles can in some cases provide advantages when thinnings or holes are made in the fiber matting. If there are long fibers, these can be made to better bind the fiber structure together by using needles with barbs that make some of the long fibers stretch through the fiber structure in its thickness direction.

The needling density is most conveniently within the range of 10 to 20 needle impacts per cm2. The preferable cross profile of the needles is the form of an equilat- eral triangle with rounded edges, and thickness 0.5 mm, measured as the height of the equilateral triangle. If it is not just local thinnings but also the orientetation of some fibers in the transversal direction that is re- quired, the needles should be equipped with barbs, pre- ferably projecting out from the needle point.

The needles are preferably placed on one or several needle booms with a density of 1000 to 3000, preferably about 2000 needles per meter, and in about 20 rows, off- set in relation to each other by a half of the needle distances in the rows.

In those cases where it seems to be useful, it is also possible to ease the penetration of the binding material/filling mix into the fiber structure by treat- ment after the combination and pressing together. There are several treatments to be used. Preferably, it can be carried out by passing the fiber matting through two or more rollers, with a relatively light pressure on the fiber matting. Preferably, the rollers can be equipped with thicker sections or spots causing a periodically varying treatment in the form of changing compressions and lowerings of pressure.

The present invention also comprises a use of the fiber matting whereby the fibers form a coherent structure and are evenly distributed over the fiber matting so that the scattering of the deformation resistance does not exceed 20 per cent, calculated as the variation factor, and so that the fiber length distribution is bimodal. The use according to the invention comprises, in the first phase, the one-sided or double-sided impregnation of the fiber matting and, in connection with this, a one-sided or a double-sided coating is applied to it, together with a protective foil. After the protective layer has been removed, a material layer, e. g. a plywood board or a lay- er of wooden particles or fragments, is applied to one or both sides, and then the material layer and the fiber matting or fiber mattings are transferred to a press where the layers are pressed together by high pressure, and the binding material is fixed to it, preferably by heat under the pressing operation.

Thus, the operation comprises three part processes, the manufacturing of the fiber matting itself, its impregnation, and the pressing together of the impregnated fiber matting with a material layer in combi- nation with which it will be used. These three processes can be carried out in one operation, without using any rolling, storing or transportation of the fiber matting between the phases. The manufacturing and the impregnation of the fiber matting can take place in one single phase, and then the impregnated fiber matting is transported, rolled in a suitable way, to its final site of use as e. g. a coating of plywood.

Another alternative is that the fiber matting is manufac- tured at one site and then transported to another site where the impregnation with the binding material and the coating of a material layer takes place, closely connected with each other. In this case it may even be

possible to eliminate the use of a protective foil.

Finally, the manufacturing of the fiber matting, its impregnation, and its final combination with e. g. a ply- wood board can take place at three different sites, using transportation and possibly even storage between each phase.

In the following, the invention is described in more detail with references to Figs. 2 and 3. Fig. 2 shows the manufacturing of a fiber matting, and Fig. 3 a double- sided impregnation of such a fiber matting.

Fig. 2 shows the insertion of a relatively thin mineral wool matting 1. This can be manufactured in a conventional way, by melting minerals, e. g. basalt, with a lesser addition of dolomite or limestone in the furna- ce, e. g. a cupola furnace, to a continuous melt flow from the furnace, leading this flow against the periphery sur- face of the spinning wheel that is the first one in the series of wheels arranged in a cascade. From there, the melt is slung out in the form of e. g. fibers that are then transferred by air streams to a perforated collec- tion band through which the air is sucked away, leaving the mineral fibers as a matting laying on the conveyor band. The surface weight of the mineral wool matting 1 is 50 to 250g/m2 and it is carried by the conveyor band 2 in the direction shown by the arrow 3 in between the two brush rollers 4 and 5.

The brush roller 4 rotates anticlockwise and the brush roller 5 clockwise, although with a lower peripheric speed than the brush roller 4. The peripheric speed of the brush roller 5 is higher than the speed of the band 2 and the peripheric speed of the brush roller 4 is at least three times higher. The density and diameters of the brush rollers can to a certain extent be adapted to

the characteristics and surface weight of the mineral wool matting 1 used as input material.

By the work of the brush rollers 4 and 5, the mineral wool matting 1 is broken to fine small fragments 6 that are slung into a first fiber chamber 7 and deposited in the form of a new fiber matting 8 on its bottom, consist- ing of a conveyor band 9. The band 9 transports the newly formed fiber matting 8 out from the fiber chamber 7 under a tightening roller 10. After having come out from the fiber chamber the fiber matting 8 passes between two rollers 11 and 12 applying such a high adjustable pres- sure against each other that the fibers in the fiber mat- ting are made considerably shorter by breaking them under pressure. The rollers are driven and pressed against each other by conventional arrangements not shown in the fig- ure. After passing between the rollers, the fiber matting 8 is laid down on the conveyor 13. While it is transferred on this, a long fiber component 14 is added to it from above and dosed with a device symbolized in the figure by the conveyor 15.

The dispersing and recollection processes taking place by using the elements indicated here by 2 to 13 can be doubled or tripled. Regarding any dispersing and recol- lection process, by suitably adjusting the mutual distances of the brush rollers and their rotation speed, as well as their tightness and diameters, e. g. the even- ness of the output fiber matting can be made better than that of the input matting.

The surface weight of the rebuilt fiber mattings is important as well. This is regulated by increasing or reducing the speed of the band or the bands 9. The con- venient adjustment of the device is such that the surface weight before the last dispersing, to be described below, remains between 70 to 120g/m-'.

The more or less rolled and once or twice dispersed and recollected fiber matting 8 is now directed, with a long fiber component 14, in between a further pair of brush rollers 16 and 17, corresponding to the brush rollers 4 and 5, in a fiber chamber 18, corresponding to the fiber chamber 7. The brush rollers 16 and 17 now disintegrate the material of the fiber matting 8 and the long fiber component, covering it with a dispersion in the fiber chamber 18. Forced by gravity and an airstream directed downwards, the reason of which will be described later, the particles in the dispersion now move mainly downwards. The possible larger parts and the non-fiber material is cast as far away as possible by the force of the brush rollers and, in principle, they follow the path indicated by the curve 19. On the other hand, the fiber dispersion is sucked by the blower 20, in principle fol- lowing the path of the curve 21, against the perforated band 22 so that a new fiber matting 23 can be formed.

Thereby the air sucked by the blower 21 is separated from the flow and passed through the band 22 via the channel 24 to the blower. After the blower, the air passes a fil- ter 25 and is then led via the channel 26 back to the fiber chamber 18. This is how the airstream downwards and past the brush rollers 16 and 17 is created.

The newly formed fiber matting 23 is now directed by the band 22 over to the conveyor 27 that will remove the fiber matting from the fiber chamber 18 and then feed it under the tightening roller 28.

After this, the fiber matting 23 can be taken for needl- ing in a conventional needling device, here symbolized by the conveyor 29 and the needling tool 30, with its needle plate 31, and a device 32 for its movements up and down.

The possible larger parts and the non-fiber material fall down onto the band 33 and are taken out from the fiber

chamber 18 under the tightening roller 34 as waste 35.

By adjusting the rotation speed of the blower 20, or by a damper in the channel 26, the air flow circulating through the fiber chamber 18 can be-adjusted so that a suitable separation grade is achieved. With a small flow, mainly just the totally free fibers are caught on the band 22 and a major part of the fiber material falls down onto the band 33. On the contrary, if the flow is bigger the balance between the influence of the virtually upwards directed airstream in the vicinity of the band 22 and gravity is offset so that a larger part of the fiber material is sucked up towards the band 22.

The waste 35 may contain considerable quantities of fibers. Especially because of small air flows and the high purity of the material collected on the band 22 caused by this, a significant quantity of the fibers, that would as such still be usable, may be directed to the waste side. They can then be recovered to the process with or without a separation process set between. One of the ways to recover them is to disperse the waste in an airstream and then direct it to a cyclon where an adjust- able part of the solid materials is separated, while the rest of them, containing most of the fibers, are recol- lected to a matting that in turn may be taken back to the process together with the input fiber material 1.

Due to the fact that gravity does not contribute to the depositing of the fiber material on the band 22, the influence of the airstream will be the only force to bring the material there. As the airstream through a cer- tain part of the active band surface is reduced the more fiber material is deposited onto it, the airstream becomes relatively bigger through those parts of the active band surface where the fiber material quantity is not so large. Therefore, relatively, the depositing will

increase there. In this way a levelling of the surface weight takes place so that, in the end, it will be suffi- cient.

Thus, the evenness is largely a function of the efficiency of the dispersing and of the formation of the depositing process. The important aspect of the latter is that the gravity force does not contribute to it. This does not mean that the active band surface of the band 22, i. e. that part of the band through which the airstream is flowing, should be horizontal when the air flow, in principle, is vertical in an upwards direction.

The active band surface can also be vertical when the airstream, in principle, is horizontal. All forms between these can also be considered, e. g. an active band surface that forms a 45° angle against the horizontal level and an airstream that is in principle streaming through it in a direction diagonally upwards.

In more detail, the evenness also depends on certain pro- cess parameters, like the rotation speed of the brush rollers, the surface weights of the various parts in the process etc. It is not possible to give a general deter- mination of these, as they have to be adapted to the respective fiber materials input in the process. Several variations can be considered. For any professionals, it should anyway be possible to find out, with a limited input, in which way the process parameters and the number of dispersings should be chosen in order to achieve the desired results.

The fiber matting 23 manufactured in this way can be rolled to the rolls for intermediate storage and trans- portation to an impregnation plant to be impregnated with a binding material or to be transported directly to the plant if the plants are located near each other and it is otherwise desirable to do so.

It can also be taken away to other operations or uses, for instance to become a capillar-breaking layer in building constructions exposed to humidity.

Fig. 3 shows the principal layout of a plant for impreg- nating a fiber matting manufactured by the method described here, or by some other method within the range of the invention. The binding material is pumped out from three binding material tanks 36 by dosing pumps 37 and 38 into a guiding system 39 and 40. The binding material pumped out may contain just one binding material or a mixture selected freely within a certain range. The num- ber of the binding material tanks, three in the figure, can be chosen according to needs. The guiding system 39 leads the binding material or the binding material mix into a mixer 41. A filler or a mix of various fillers is added to this. From the beginning, the fillers are stored in filler silos 42. The filler is taken from these by the dosing input devices 43 and 44 to the horizontal conveyors 45 and 46. These can be of a screw type. The conveyor 35 supplies the filler or the filler mix to the mixer 41 via the feeder pipe 47.

In a similar way the pipe system 40 conducts the binding material or binding material mixture from the metering pumps 38 to the mixer 48, to which also the horizontal transport 46, which is fed from the dosing feeders 44, leaves a filler or a filler mixture via the feeder pipe 49.

The binding material and the filler are mixed in the mixers 41 and 48 to form an even mix. This mix is then pumped from the mixer 41 by a peristaltic pump 50 via a pipe 51 to a sweeper 52. This spreads an adjustable quan- tity of the binding material/filler mix to form a thin and even layer on a carrier layer 53 coming out from a storage roll 54.

In a similar way, the mixing of the binding material from the pipe system 40 and the filler from the feeder pipe 49 takes place to make it to an even mix. This mix is then pumped from the mixer 48 by a peristaltic pump 55 via a pipe 56 to a sweeper 57. This spreads out an adjustable quantity of the binding material/filler mix to form a thin and even layer on a carrier layer 58 coming out from a storage roll 59.

The carrier layer 58 coated this way is now transferred by the transferring rollers 60 over to a conveyor 61.

A fiber matting 63 manufactured using the method described, or by any other method, is rolled out from the storage roll 62. It can also come direct, without any intermediate rollings or rollings out. The fiber matting is laid down by the transferring rollers 64 onto the car- rier layer 58 on the conveyor 61. Thus, the carrier layer 53 is laid down on the fiber matting 63 by using the transferring rollers 65. The combination 66 with three layers is now directed under the band press 67, compris- ing an upper band 68 and a lower band 69. The band press 68 presses the three layers together so that the mix of the binding material and the filler is pressed into the fiber matting.

After the pressing together, the fiber matting 70 equipped with the binding material, the filler, and the carrier layer, is now lifted from the conveyor 61 using conveyor rollers 71. At the treatment station, comprising a series of lower rollers 72 and a series of upper rollers 73, the fiber matting can be treated 67 in a con- trolled way whereby the penetration of the binding material in the fiber matting increases. Finally, the fiber matting 70 is rolled up into a roll 74 and is now ready to be used according to its purpose.

The described impregnation can also be applied on one side only.

The invention can also be operated by using dry, powderlike binding materials, possibly mixed with a fil- ler in a way that is, in principle, compatible with what is shown in Fig. 3. The means of preparing and transfer- ring the binding material and the mix of the binding material and the filler, respectively, are in that case composed accordingly. They may, advantageously, be closed pneumatic systems. Fig. 4 shows one such arrangement. The arrangement of the main parts complies with the one shown in Fig. 3, the difference being that the upper side of the fiber matting is covered by a binding material in powder form using a delivery device 75 that, with a cell feeder connected to a vibrator, not shown in the figures, delivers the binding material in powder form, with or without the filler mixed in, over the width of the fiber matting 63 and to be deposited on it. It is then covered by the carrier layer 53, the task of which, in this case, is mainly to act as a protective or covering layer. When this layer has been laid, the pressing together takes place in the band press 67.

Fig. 5 shows an arrangement where the binding material in powder form is applied to both sides of the fiber matting 63. This is done by feeding both the fiber matting 63 and the carrier layers 53 and 58 from above and with a cer- tain distance between them. The carrier layer is then moved against the fiber matting using the press rollers 76. Immediately before the carrier layer and the fiber matting are pressed together by the rollers, the binding material in powder form is added to the mixture from the feeders 75. After this, the combination of the carrier layer, the fiber matting, and the binding material can continue downwards towards the conveyors 61 and into the band press 67.

Designations used in figures and text: A metal cylinder B measuring rod C measuring clock D fiber matting E base 1 mineral wool matting 2 band 3 direction arrow 4 brush roller 5 brush roller 6 fragment of fiber matting 7 fiber chamber 8 fiber matting 9 band 10 tightening roller 11 roller 12 roller 13 conveyor 14 long fiber component 15 conveyor 16 brush roller 17 brush roller 18 dispersion of fibers 19 curve for non-fiber material 20 blower 21 curve for fibers 22 perforated band 23 fiber matting 24 channel 25 filter 26 channel 27 conveyor 28 tightening roller 29 conveyor 30 needling tool

31 needle plate 32 arrangement for needle plate movement 33 band 34 tightening roller 35 waste 36 binding material tanks 37 dosing pumps 38 dosing pumps 39 pipe system 40 pipe system 41 mixer 42 filler silos 43 dosing feeder 44 dosing feeder 45 conveyor 46 conveyor 47 feeder pipe 48 mixer 49 feeder pipe 50 peristaltic pump 51 pipe 52 sweeper 53 carrier layer 54 storage roll 55 peristaltic pump 56 pipe 57 sweeper 58 carrier layer 59 storage roll 60 conveyor rollers 61 conveyor 62 storage roll 63 fiber matting 64 conveyor rollers 65 conveyor rollers 66 combination of carrier layer and fiber matting 67 band press

68 upper band 69 lower band 70 fiber matting with carrier layer 71 conveyor rollers 72 lower rollers 73 upper rollers 74 roll of fiber matting 75 delivery device for binding material in powder format, with/without filler 76 pressing rollers