PROCESS AND APPARATUS FOR THE PRODUCTION OF A MINERAL FIBREBOARD

Abstract: An apparatus for the production of single-ply or multiply boards comprises a collecting belt (15) for receiving a fleece (20), a precompression stage (17) for compressing a fleece (20), a compression unit (19) having conveyors (31, 33, 35, 37) each comprising two opposite roller groups comprising two or more rollers for longitudinal or longitudinal/thickness compression of the fleece, a multi-ply unit (21) for forming layers of different densities and a curing oven (25) for fixing the compressed fleece. Compaction is preferably effected by longitudinal compression, and preferably there is no further thickness compression after the compression unit (19). The boards made on the apparatus can be pleated but generally have a substantially random fibre orientation, the fibres being arranged in a corrugated pattern, and good mechanical properties such as high tread, compressive, piercing and tensile strength for comparatively low density.

Description: O 97/36034 POYEP97/01489 Process and apparatus for the production of a mineral fibreboard This invention relates to a process and apparatus for the production of a mineral fibreboard. Various improvements in the production of mineral fibreboards have been disclosed in recent years. A substantial improvement to the properties of mineral fibreboards can be obtained, for example, by reorienting the fibres in the production process so that they are aligned predominantly perpendicularly to the large surfaces of the board. The compressive strength and the tensile strength perpendicularly to the board plane can be substantially increased as a result. It is known to make products having a pleated structure. For instance a pleated product is made in the process described in EP 365,826 by passing the web, with longitudinal compression, between a series of spaced apart rollers. The separation, in the longitudinal direction, between the rollers is sufficient great to allow significant movement of the fibres up between the rollers, and the overall process leads to pleating. It is known that it is generally more desirable to conduct the longitudinal compression substantially without the formation of pleats. Such a process is described in DE 1,635,620. In this a fleece is subjected to thickness compression and is then subjected to longitudinal compression between belts under conditions whereby the thickness of the fleece after longitudinal compression is about the same as or slightly more than the thickness before the longitudinal compression. In many processes involving longitudinal compression it is necessary to subject the longitudinally compressed fleece to thickness compression immediately prior to bonding. For example, in EP 133,083 processes are described in which there is substantial longitudinal compression, the fleece is then subjected to thickness compression, and the fleece is then bonded. Other processes of conducting longitudinal compression substantially without pleating are described in, for instance, US 4,567,078, WO 91/14816 and WO 94/16164. The processes are usually conducted using belt conveyors for performing the longitudinal compression, with the fleece passing between one set of belt conveyors and then through a slower moving set of conveyors. In EP 133,083 it is specifically recommended that belt conveyors should be used in preference to rollers because they tend to clog. Thus, processes of achieving significant longitudinal compression between sets of rollers tend to have the disadvantage that significant amounts of fibres migrate between the rollers and cause blockages and distortions and render the process unsatisfactory. A combination of belt conveyors and rollers is described in WO 94/16162 and WO 94/16164. It is stated that all the rollers should rotate at the same speed. The known processes tend to have the disadvantage that they are difficult to adjust and to operate in an efficient manner. They also tend to have the disadvantage that either only pleated products or products having an isotropic fibre orientation can be produced by them. The object of this invention is to provide an apparatus and a process to enable products to be produced with improved properties. The objective is more particularly further to improve the efficiency of the production processes for mineral fibreboards, i.e., products having specific physical properties, such as improved compressive strength and tensile strength and better insulation values, can be produced with reduced use of resources. The products should have the most homogeneous density possible. Another object of the invention is to provide an apparatus in which the critical compression and other stages can easily be adjusted without dismantling the apparatus, in response to changes in the fleece that is being fed to the apparatus or the product which is desired from the apparatus. By this means it would be desirable to be able to make, on a single apparatus, products having a range of different physical properties without any undesirable down-time or other inconvenience between the production of one grade and another. It would also be desirable to produce products having a random fibre orientation and as far as possible also products having a pleated structure, on a single installation. Novel apparatus according to the invention comprises a fibre production unit for producing a fleece, transport means for transporting the fleece to a bonding station, a bonding station for bonding the fleece, a compression unit for thickness and/or longitudinal compression of the fleece disposed between the fibre production unit and the bonding station, and means to prevent break-out of the fleece between the compression unit and the bonding station, characterised in that the compression unit comprises a plurality of conveyor pairs disposed consecutively in the conveying direction; each conveyor pair comprises two opposite roller groups comprising in each case at least two spaced-apart rollers, so that a conveying path for the fleece is formed by the opposite roller groups, each said roller having a diameter of between approximately 60 and 160 mm, preferably between 80 and 120 mm, the distance between adjacent rollers is so selected as to substantially prevent escape of the fibre felt is not possible, there are drive means in order to drive the rollers of each group at substantially the same circumferential speed. there are means for individually adjusting the circumferential speeds of the conveyor pairs and there are means for adjusting the distance between the opposite roller groups of the conveyor pairs. The invention also includes apparatus for the continuous production of a bonded mineral fibreboard from a mineral fibre felt or fleece comprising a fibre production unit for producing a felt, transport means, for transporting the felt to a bonding station, a bonding station for bonding the felt, a longitudinal or longitudinal/thickness compression unit disposed between the fibre production unit and the bonding station, and means to prevent break-out of the fleece between the compression unit and the bonding station, characterised by a compression-optimising unit comprising a plurality of conveyor pairs, each conveyor pair comprising in each case two opposite rollers or roller groups, in which each roller has a diameter of between approximately 60 and 160 mm, preferably between 80 and 120 mm, and the distance between the rollers is so selected that an escape of the fibre felt is not possible, means for individually adjusting the circumferential speeds of the conveyor pairs and means for adjusting the clearance between the opposite roller groups of the conveyor pairs. The invention also includes a continuous process for the production of a bonded mineral fibre board by production of a mineral fibre fleece, longitudinal and/or thickness compression of the fleece followed by bonding of the longitudinally compressed fleece in a bonding station, the fleece being held to prevent break-out between the compression unit and the bonding station characterised in that the longitudinal compression is effected by the fleece passing through a compression unit comprising a plurality of conveyor pairs disposed consecutively in the conveying direction, each conveyor pair comprising in each case two opposite roller groups each having at least two spaced-apart rollers, so that a conveying path for the fleece is formed by the opposite roller groups, the rollers of each group are driven at substantially the same circumferential speed by drive means connected to the associated group, and the circumferential speeds of the conveyor pairs are individually controlled, the circumferential speed of the rollers of at least one conveyor pair being less than the circumferential speed of the rollers of the preceding or each preceding conveyor pair, and the distance between the opposite roller groups of the conveyor pairs being adjustable. Because the fleece is under significant longitudinal compression, it is liable to buckle-up away from the conveyor by which it is being carried, and so appropriate means have to be applied to constrain the fleece against break-out (ie buckling away from the support) as it is being transported between the longitudinal compression unit and the bonding station. These constraining means can be a belt, rollers or other guides that will adequately confine the longitudinal compressed fleece to the desired longitudinal path and prevent significant deviation of the fleece from the desired path. Although the literature has tended to regard roller conveyors and belt conveyors as potentially being capable of producing similar results except for the disadvantage that roller conveyors may clog and may tend towards pleating, it has surprisingly been found that the use of a compression unit comprising a plurality of consecutively disposed roller groups each comprising two or more rollers as defined in the invention permits both easy adjustability and the manufacture of products with significantly better properties to be produced. In contrast to known longitudinally/vertically compressed products, the new products are distinguished by a particularly homogeneous density. The fibres are uniformly felted and no preferential fibre orientation can be detected (Fig. 11) . On an enlarged scale, it has been found that the random-orientation fibres are arranged in a partially corrugated pattern. The apparatus can, however, also be used to make pleated products. In contrast to the apparatus of EP-A-0 365 826, no freewheeling intermediate stages are used and no gradual bulging out of the fleece web is desired. Nor is a continuous speed graduation in any way necessary, as in the teaching of WO 91/14816. On the contrary, the rollers can be combined into roller groups comprising two or more rollers, the rollers of which are driven at the same speed. In contrast to WO 91/14816, the opposite roller groups are preferably arranged in parallel, or in certain cases, at an inclination relatively to one another, so that a fleece web tapering in the transport direction is obtained. It has been found that because of the low adhesion a certain slip exists between the rollers and the fleece and allows the fleece to slide over the rollers during compression. In these conditions the fleece is thoroughly fulled over a specific distance, i.e. it is repeatedly expanded and compressed. It is assumed that this effect is a reason for the marked improvement in the product properties obtained. The apparatus according to the invention provides an intensive compaction of the fibre felt in the interior and at the surface. It appears to be an important feature of the present invention that the fleece or the fibre felt is subjected to an optimisation, more particularly a longitudinal or longitudinal/thickness compression, by means of a plurality of rollers or rolls. In the apparatus according to the invention, the compression of the fibre felt can take place gradually and over a longer distance than, for example, in belt conveyors. In these circumstances a compression of the fibre felt over a moderate distance appears to be significant. The fibre felt is permanently thoroughly fulled in the compression zone forming during the compression operation, and this has a positive effect on the gross microdensity. Surprisingly, the products produced with the apparatus according to the invention accordingly have a very homogeneous gross microdensity (density distribution in a small unit volume) and very good mechanical properties, such as compressive, piercing and tensile strength, in a weight 15 - 25% lower than with conventional products, so that significant savings of resources are possible. Usually, the roller diameter and the distance between the rollers in the conveying direction is such that any undesired pleating of the fleece and/or clogging of fibres between the rollers is rendered substantially impossible. Products of a corrugated type of structure can be obtained by compression by means of a compact roller array comprising rollers of a relatively small diameter. The dimensions and spacings of the rollers required to produce the corrugated fibre structure depend, inter alia, on the type of fibre and the fibre length. Advantageously, the roller diameter is between approximately 60 and 160 mm, preferably between 80 and 120 mm. The distance between adjacent rollers is advantageously so selected that any escape of the fibre felt is impossible. Preferably, the spacing between two adjacent rollers is therefore between 1 and approximately 50 mm, advantageously between 2 and 30 mm and most preferably less than 20 mm, eg 3 to 10 mm. The permissible roller spacing depends substantially on the fleece density, the degree of longitudinal compression In the compression unit and on the thickness of the board under manufacture. Advantageously, the roller diameter is about 90 mm and the centre-to-centre spacing of two adjacent rollers is about 95 mm. Products of different thickness and high density can be produced with a small roller spacing. Although, for example, 3 to 10 roller conveyor pairs can be provided, each having 2 to 10 rollers, in a preferred embodiment, 3 to 6 conveyor pairs are each provided with 3 to 8 rollers, preferably 4 conveyor pairs with roller groups each of 4 rollers. Although the use of 4 conveyor pairs with roller groups each comprising 4 rollers allows single or multiple speed graduation, the improved product properties can in many cases be achieved simply with a single-stage longitudinal compression. A sufficiently long compression zone is also made available by the use of 4 conveyor pairs. Advantageously, the conveyor pairs are adjustable as to height independently of one another. In one particularly advantageous embodiment, the position of the opposite roller groups of at least one conveyor pair is individually adjustable relatively to the position of the roller groups of the following conveyor pair or pairs. Thus unlike the known apparatus, it is possible to produce not only products having a random fibre orientation but also those having a pleated fibre structure. Advantageously, for the production of substantially pleated products, the spacing of the opposite roller groups of a conveyor pair is adjustable to approximately 0.5 to 0.1 times the spacing of the roller groups of the following conveyor pair and the conveying path defined by the two conveyor pairs is arranged so be substantially approximately in alignment. Although as a rule the roller groups of a conveyor pair can be driven at the same circumferential speed, it may be advantageous to control the circumferential speed of the rollers of each individual group independently of the speed of the rollers in each other group and provide a separate variable drive. Advantageously, the compression unit comprises a support structure on which the conveyor pairs are disposed. The support structure gives the compression unit a compact construction. The compression unit can also be installed subsequently in existing systems. Advantageously, the roller groups of at least one conveyor pair are arranged on the support structure each to be displaceable independently of one another perpendicularly to the conveying direction. The advantage of this is that the production of pleated products is possible inter alia. In one advantageous embodiment, at least two roller groups are each disposed on a separate frame which is adjustable on the support structure perpendicularly to the direction of conveyance. This simplifies the construction and control of the compression unit. Advantageously, the frame is disposed on the support structure so as to be pivotable. This allows simultaneous thickness and longitudinal compression. The individual adjustment facilities are advantageously embodied by means of spindles. It is also possible to use racks and pinions, worm gears or the like. To embody a parallel drive, two or more spindles can be connected to shafts, thus reducing the number of drives required. Advantageously, the circumferential speeds of at least the conveyor pairs and the spacings of the opposite conveyors are individually adjustable. Advantageously, the drive means for the conveyors and the means for adjusting the spacing between the conveyors are connected to a microprocessor control system. Particularly advantageously, the microprocessor control system comprises at least two read/inputting units, one of which is disposed in the region of the compression unit and the other, for example, in a control room. In this way it is possible to optimise a process directly in situ or intervention in the process is possible. The microprocessor control system may comprise memory means to store the process parameters, such as the speeds and spacing of the conveyors, so that customer- specific products can be reproduced at any time. Advantageously, means, e.g. an isotope system, can be provided before the compression unit in order to determine the quantity of fibre per unit area. These means for determining the quantity of fibre can be associated with the fibre production unit or with the microprocessor control system so that the quantity of fibre per unit area can be controlled and rendered uniform. According to a particularly preferred embodiment, a separating device for separating the fleece into two or more sub-webs is provided between the compression unit and the bonding station, at least one compression stage is provided for thickness and/or longitudinal compression of at least one sub-web, and conveyors to prevent break-out of the compressed fleece between the compression unit and the bonding station. Multi-ply products can be produced with this apparatus. The compression stage for compressing the at least one subweb advantageously comprises at least two independently driven conveyor pairs. Longitudinal compression can thus also be effected in addition to thickness compression. Advantageously, at least the separating device and the following conveyor are vertically adjustable in the region of the multi-ply unit. This has the advantage that the apparatus can be used both for the production of single-ply and multi-ply products. Although the adhesion of the sub-webs due to the curing of the binder adhering to the fibres is normally sufficient, means can be provided to provide the contact surfaces of the sub-webs with binder before they are combined. Basically, the combined webs held together by suitable means can be thickness-compressed once again. Advantageously, however, the webs are longitudinally compressed before bonding. The longitudinal compression can be effected in a ratio of 1.1 : 1 to maximum 2 : 1. The contact surfaces can be increased in size by a final longitudinal compression so that the bonding of the sub-webs is improved. The apparatus can be used for making unpleated or pleated products. In one advantageous process variant, for the production of substantially pleated products, the spacing of the opposite rollers of a conveyor pair is set to approximately 0.5 to 0.1 times the spacing of the roller groups of the following conveyor pair, the conveying path defined by the two conveyor pairs being disposed substantially in alignment and the circumferential speed of the following conveyor being less than the circumferential speed of the preceding conveyor. Also, at least one of the roller conveyors can be inclined relatively to the conveying direction, for example to produce a fleece web tapering in the conveying direction. This may be of importance in the production of products having a density less than approximately 100 kg/m3. Advantageously, before entry to the compression unit the fleece is precompressed to approximately 0.8 to 1.5 times, preferably 0.9 to 1.3 times, and quite particularly preferably to the approximate nominal thickness of the finished product, so that there is substantially only a longitudinal compression by the roller conveyor. The thickness compression set refers to the spacing of the opposite roller groups. There is preferably no further thickness compression before the curing oven, so that the fibre structure once set is maintained. Advantageously, before entry to the curing oven and already in the compression unit respectively the fleece has a nominal thickness corresponding to 0.9 to 1.3 times, preferably to the approximate thickness of the finished product. The products produced in this way have a very good tensile and compressive strength for a comparatively low weight. Although the speed can be repeatedly graduated in the conveying direction, most products having a random fibre orientation can be produced by single-stage speed graduation. The mineral fibre fleece is advantageously compressed in length by a factor of 2 to 6, preferably by a factor of 2.5 to 5, and quite particularly preferably by a factor of about 2.5 to 3.5. Only in the case of products having a density of less than approximately 90 - 100 kg/m3 may a multi-stage speed graduation be more advantageous than a single-stage. The degree of thickness compression in the compression unit is preferably less than 2 and preferably less than 1.5. Before entry into the bonding station, e.g. a curing oven, the fleece preferably has a nominal thickness of about 0.9 to 1.3 of the finished product. For the production of products having a pleated fibre structure the spacing between the opposite roller groups of a conveyor pair is adjusted to approximately 0.5 to 0.1 times the spacing between the following roller groups, the conveying path defined by the two conveyor pairs being substantially in alignment and the circumferential speed of the following roller groups being less than the circumferential speed of the preceding roller groups. In a particularly advantageous variant, the fleece is stretched in the conveying direction after longitudinal compression. Unwanted pleating of the fleece web, for example on transition to the bonding station, can be prevented by expanding the compressed fleece. In some cases, hold-down belts which are otherwise required can be partially or completely dispensed with after a decompression. In many cases, a decompression of up to approximately 20% - 40% is sufficient. A decompression may be important in the case of relatively thin products of high density, e.g. of more than 140 kg/m3. In another process variant, the compression zone is moved at certain intervals, i.e. the longitudinal compression is carried out by means of varying conveyor pairs. A certain self-cleaning effect can be achieved in this way by the slip existing between the rollers and the fleece so that the rollers are cleaned of any possibly adhering binder. The fleece may consist of glass wool, rock wool, or other synthetic fibres. Preferably, the fleece consists substantially of man-made vitreous fibres, preferably rock wool fibres, and contains non-cured binder. The binder content by weight can be between approximately 0.7 and 7%, often 1 to 4%. The binder is preferably curable in a curing oven. However, bonding of the fleece can be effected by needling or felting instead of or in addition to bonding by curing a bonding agent. Advantageously, mineral fibres of an average length of between approximately 0.3 and 50 mm, preferably between approximately 0.5 and 15 mm and of a thickness between approximately 1 to 12 μm, preferably between approximately 3 and 8 μm are used. It is, however, also possible to use mineral fibres of an average length between approximately 1 and 10 mm, preferably between approximately 2 and 6 mm and of an average thickness of between approximately 2 to 10 μm, preferably between approximately 3 to 6 or 7 μm. The average length of rock wool fibres, which are usually shorter than glass fibres, is as a rule 2 to 4 mm, and the average diameter is 3 to 4 μm. Advantageously, during the deposition of the fleece on the conveyor the predominant orientation of the fibres is changed or partially evened out. This can be effected, for example, by means of a spinning member adapted to swing at an angle to the direction of transport, or by an air curtain. In this way the density distribution of the fleece can be improved and the fibre orientation changed, this having a favourable effect on the mechanical properties of the resulting products. Advantageously, the primary fleece is deposited on the collecting belt in layers by means of a pendulum belt adapted to swing at an angle to the direction of transport. Thus preferably the primary fleece is formed by cross-lapping. In this way the fibres are partially re-oriented and the homogeneity (transverse distribution) of the fleece deposited on the collecting belt can be improved. Advantageously, 2 to approximately 60 layers, preferably between 2 and 40 to 50 layers, can be deposited one upon the other. This produces a certain re-orientation of the fibres. The fleece can be deflected, for example, transversely of the direction of transport, while a compression, more particularly longitudinal compression, can take place simultaneously. The invention also relates to mineral fibreboards produced by the process according to the invention, particularly such boards having a corrugated fibre structure. The invention also includes apparatus for performing the process described above and comprising at least one collecting belt to receive a fibre felt, a precompression stage for compressing a fibre felt, at least two consecutive conveyors driven at different speeds for the longitudinal or longitudinal/thickness compression of the fibre felt and a curing oven for fixing the longitudinally and thickness-compressed fibre-felt, characterised by an optimisation unit (19) comprising conveyors each having two opposite roller groups each comprising two or more rollers, so that during operation a continuous or quasi-continuous compression zone extending over a plurality of rollers or roller groups is obtained wherein the rollers have a diameter of between approximately 60 and 160 mm, preferably between 80 and 120 mm and the distance between the roller is so selected that any escape of the fibre felt is impossible. Exemplified embodiments of the invention are described below with reference to the drawings wherein: Fig. 1 shows a mineral wool product produced by thickness compression and having a fibre orientation substantially parallel to the surface. Fig. 2 shows a pleated product comprising a majority of fibres disposed perpendicularly to the surfaces. Fig. 3 shows a two-ply product, the upper layer of which has increased density. Fig. 4 shows a product with substantially homogeneous density and random-orientation fibres. Fig. 5 shows a product in which a layer having random- orientation fibres is combined with a layer of increased density. Fig. 6 is a diagram showing the principle of an apparatus for the continuous production of a multi-ply mineral fibreboard of different densities; a) in a continuous process and in a continuous compression zone respectively and b) in a single-stage process. Fig. 7 is a front elevation of a compression unit in detail. Fig. 8 is a side elevation of the compression unit of Fig. 7. Fig. 9 is a plan view of the compression unit of Fig. 8. Fig. 10 shows the breaking zone of a) a board having a substantially parallel fibre orientation and b) and c) rock wool boards made by the new process and pulled apart perpendicularly to the board plane. Fig. 11 is a perspective section through a two-ply board, the fibre structure being shown on an enlarged scale and Fig. 12 is a diagram showing various possible arrangements of four conveyor pairs disposed consecutively in the conveying direction. Figs. 1 to 5 illustrate the fibre orientations frequently occurring in softboards. Boards having fibres disposed parallel to the surface (Fig. 1) have comparatively poor mechanical properties. To compensate for the disadvantages, the fibres are frequently strengthened with binder and the density increased. Products having fibres arranged perpendicularly to the surface can be obtained if a board of the kind shown in Fig. 1 is cut into strips, the strips are turned through 90° and are then bundled. This type of manufacture is complex and correspondingly uneconomic. According to another type of manufacture, the fleece is pleated (pleating process. Fig. 2) . These products have a substantially better compressive and tensile strength perpendicularly to the board plane than boards of the kind shown in Fig. 1. Boards having pleated fibres can bend and can therefore be used for insulating pipes or for lining curved areas. A disadvantage, on the other hand, is that these products tend to break along the pleats, and the piercing strength is inadequate. Another disadvantage of the known products of this kind is that there may be relatively considerable differences in density within the board. Fig. 3 shows a two-ply product, the top layer of which has an increased density. These products are suitable for applications requiring high tread strength or enhanced surface protection. As a result of the increased density of the top layer the average density can be reduced. Fig. 4 shows a product with substantially isotropic fibre orientation with a substantially random fibre orientation. These products have excellent mechanical properties, such as high compressive, tread, and piercing strength, and high tensile strength perpendicularly to the board plane. They do not break and their thermal conductivity is substantially the same as the products shown in Fig. 1. Generally, these products are lighter than comparable products having substantially parallel fibres for comparable or improved mechanical properties. Fig. 5 shows a product in which the advantages of increased density of the top layer and of the fibre structure shown in Fig. 4 are combined. The object of the invention is particularly further to improve the properties of products of the kind shown in Figs. 4 and 5. The apparatus 11 shown in Fig. 6 for the production of mineral fibre boards comprises essentially, arranged consecutively in the direction of conveyance F, a pendulum belt 13 and a collecting belt 15 for the respective deposition and reception of fibres produced by a fibre production unit (not shown in detail) , and a precompression stage 17 and an optimisation or compression unit 19 for forming a felt or fleece 20 having optimised fibre orientation and homogeneity. The compression unit 19 for optimising the compression is followed by an optional multi-ply unit 21 which can be used for the production of multi-ply mineral fibre boards. The multi-ply unit 21 is followed by transport means 23 which hold the compressed fleece clamped at the opposite large surfaces and feed the same to a bonding station, e.g. a curing oven 25. The above-mentioned fibre production unit serves for the continuous production of fibres by one of the known methods, e.g. the cascade spinning process. The fibres produced, also termed the "primary fleece", are sprayed (not shown) with a binder and pass by means of a conveyor (not shown) to the pendulum belt 13. The latter belt is situated above the collecting belt 15 and swings transversely to the direction of transport of the collecting belt 15. A different orientation of the pendulum movement, e.g. in the transport direction, is however also possible. As a result of the pendulum movement, the primary fleece 26 is deposited in layers, as will be seen from Fig. 6, on the forwardly moving collecting belt 15, depending on the speed of the latter and the frequency of the pendulum movement. Other means, for example gas jets, are however possible for the production of the most random possible fibre orientation on the collecting belt. As a result of the advance movement of the collecting belt 15, the orientation of the fibres is predominantly at an angle to the direction of transport. Viewed from above, the fibres of two superposed fleece layers extend substantially crosswise. The precompression stage 17 consists of a lower conveyor belt 27 and a pressing belt 29. The latter is adjustable as to height so that the fleece 26 can be precompressed to different degrees. The precompression stage 17 provides precompression and a certain ho ogenisation of the relatively loose fleece 20 before the same is introduced into the compression unit 19. The two belts 27, 29 preferably have separate independent drives so that they can be operated at different circumferential speeds. According to the exemplified embodiment shown, the compression unit 19 consists of a plurality of conveyors or conveyor pairs 31, 33, 35, 37. Each pair 31, 33, 35, 37 has a lower and an upper roller group 31", 33'', 35", 37" and 31', 33', 35', 37' respectively each consisting of four rollers 39. The clearance between the individual roller groups 31', 31"; 33', 33"; 35', 35"; 37', 37" is adjustable. The roller groups are also adapted to be inclined relatively to one another preferably in the direction of transport. The latter property enables the fleece 20 to be continuously compressed in thickness or be decompressed on passage through a conveyor pair 31, 33, 35, 37. A number of different formulations for the fleece optimisation can be obtained as a result of the possibility of adjusting the distance between the opposite roller groups and their speeds. In this way the product properties can be quite different. Also, because of these adjustment facilities, the fibre structure can be controllably optimised and, for example, undesirable pleating at the fleece surface can be prevented. At least the lower and upper roller groups 31" and 31' respectively of the first conveyor pair 31 are independently adjustable as to height. This enables the fleece to be subjected to bending, as shown in Fig. 6, for example in order to smooth and compact the fleece surface. A particularly interesting process variant can be obtained if, for example, the spacing of the roller groups 31', 31" of the first conveyor 31 is set to approximately 0.6 to 0.1 times the spacing of the following roller groups 33', 33", and the conveying path defined by the conveyor pairs 31, 33 is arranged in alignment (Fig. 12: centre line 69). If the speed of the following conveyor pair 33 is less than that of the conveyor pair 31, it is possible to produce products having a pleated fibre structure, the pleating being effected between the conveyors 31 and 33. The upper and lower roller groups 31', 31"; 33', 33"; 35', 35"; 37', 37" of the conveyor pairs 31, 33, 35, 37 each have a separate drive not shown in detail in Fig. 6. The drives used are preferably infinitely variable within a specific range, so that, for example, the upper and lower roller groups can have different circumferential speeds. A slightly higher circumferential speed of the upper roller group is necessary, for example, if the same is disposed, not horizontally, but at an angle to the lower roller group. Figs. 7 to 9 show an exemplified embodiment of a compression unit 19 in which the conveyors with the roller groups 31', 31"; 33', 33"; 35', 35"; 37', 37" having the rollers 39 are disposed on a supporting structure 71. Chain wheels 115 (Fig. 9) are provided at one end of each of the rollers 39. Each four or five rollers 39 are interconnected by drive chains (not shown) and form a roller group. A drive 117', 117", 117"', 117"", 118', 118'', 118''', 118"'' is provided for each roller group. The upper and lower roller groups 31', 31" of the first conveyor pair 31 considered in the direction of conveyance (Fig. 8, arrow F) are vertically adjustable. The vertical adjustment of the upper roller group 31' is effected by means of a drive member 81 which drives the spindles 73, 73' via the Cardan shafts 77, 77'. A drive member 83 driving the spindles 75, 75' via the Cardan shafts 79, 79' is used for the vertical adjustment of the bottom roller group 31". Unlike the first roller groups 31', 31'', the position of the remaining roller groups is either not adjustable (at the bottom) or adjustable only jointly (at the top) . As will be seen particularly from Figs. 7 and 8, the rear bottom three rollers groups 33'', 35", 37'' as considered in the direction of conveyance are disposed on a stationary frame 85 while the upper three roller groups 33', 35', 37' are disposed on a vertically adjustable frame 87. The latter frame 87 is vertically adjustable at the top part of the supporting structure 71. Linear guides 93 at the columns 95, 95', 97, 97' provide vertical guidance of the frame 87. A drive member 103 which by way of the Cardan shafts 99, 99', 101, 101' drives the spindles 89, 89', 91, 91' arranged in pairs on the supporting structure 71 is provided for vertical adjustment of the frame 87. The upper roller groups 33', 35', 37', the last of which has 5 rollers 39, are disposed on support rails 105 pivotally connected to the frame 87 by the pivot 107. In the exemplified embodiment illustrated, the front end of the rails 105 as considered in the direction of conveyance is connected to the vertically adjustable frame 87 by another pair of spindles 109, 109'. By adjustment of the spindles 109, 109' it is possible to swing the support rails 105 upwardly or downwardly out of the horizontal so that, for example, it is possible to form a path tapering in the direction of conveyance F. The spindles 109, 109' are also interconnected via Cardan shafts 111, 111' so that here again one drive 113 is sufficient to adjust them. Fig. 12 shows various possibilities of how four conveyor pairs can be arranged in principle. The adjustments according to Figs. 12b and 12c, however, cannot be made with the compression unit according to Figs. 7 to 9. An arrangement of the roller groups 31', 31", 33', 33", 35', 35", 37', 37" according to Fig. I2d is advisable, for example, if light products are to be made. With an arrangement of the roller groups 31', 31", 33', 33", 35', 35", 37', 37" as shown in Fig. 12f, it is possible, for example, to produce a pleated fibre structure or fleece web. The compression unit 19 comprising a plurality of conveyor pairs is followed by the optional multi-ply unit 21, which in the exemplified embodiment illustrated is in the form of a dual density device. This comprises a separating device 41, for example, a band saw or a band knife, which is shown only in outline in Fig. 6, for separating the compressed fleece 20 into two sub-webs 43 and 45. The multi-ply unit 21 also comprises conveyors 47, 49, 50 and 51, e.g. conveyor belts, which fix the compressed sub-webs 43, 45 in thickness. Any gaps occurring for geometric reasons between the separating device and, for example, the conveyor belt 49 or 50 can be bridged where possible by guide plates. These prevent the fleece web 43, which is compressed to varying degrees, from breaking out. The separating device 41 and following conveyor 49 is preferably adjustable as to height, so that the fleece emerging from the compression unit 19 can be cut into lower and upper webs 43, 45 of practically any thickness. In addition, the separating device 41 and the conveyor belt 49 can also be displaced independently of one another and upwardly to an extent such that they are disposed outside the range of transport of the fleece. The conveyor belt 49 then serves as a hold-down belt. Owing to the vertical adjustability, the apparatus 11 can be used optionally for the production of single-ply or multi-ply boards. Basically, a plurality of separating devices and corresponding hold-down belts can be provided to enable boards to be produced with three or even more layers. Also, the distance between the upper and lower rollers is adjustable so that outer layers of different thicknesses can be made. Two conveyor pairs 53, 54 provided after the conveyors 50, 51 serve for thickness and longitudinal compression of the upper web 45. The conveyor pairs 53, 54 preferably comprise rollers 55, which are combined in each case to form upper and lower roller groups with three rollers in each case. The conveyor pairs 53, 54 are each drivable at different circumferential speeds so that the elongations which may occur as a result of thickness compression can be compensated by subsequent longitudinal compression. Also, the distance between the upper and lower rollers is adjustable so that outer layers of different thicknesses can be made. Conveyor belts, chutes and/or guide plates (not shown in detail) reco bine the compressed web 45' with the lower web 43. In most cases a hold-down belt for the highly compressed web 45' can be dispensed with. A metering device 57 for a binder is provided in the zone where the webs 43, 45 meet. With this arrangement it is possible to apply binder to the contact surfaces of the upper and/or lower webs 43, 45' so that a better bonding is obtained after curing of the binder. In most cases, particularly if any elongations occurring have been compensated previously, a metering device 57 can also be dispensed with. Feed belts 59, 61 and feed rollers 63, 65 press the combined webs 43, 45' together and transport the same into the curing oven 25. The circumferential speeds of the feed belts 59, 61 and feed rollers 63, 65 are advantageously individually adjustable so that compression or decompression of the compressed webs 43, 45' can be effected as required. At least the feed rollers 63, 65 are preferably coolable. Air-permeable conveyor belts 67, 67' are preferably provided in the curing oven 25. The belts 67, 67' hold the webs 43, 45' together during the curing process and thus substantially determine the nominal thickness of the finished boards. The belts 67, 67', like the conveyors 59, 61, 63, 65, are vertically adjustable and can thus be adjusted to the fleece thicknesses coming from the multi-ply unit 21 or the compression unit 19. The production of the multi-ply board can be carried out as follows: the primary fleece delivered from a collecting chamber (not shown) and provided with binder and, in the case of rock wool fibres, usually of a weight of about 200 - 800 g/m2, preferably 200 400 g/m2, with an approximate average thickness of 1520 mm, or frequently up to 75 mm, is fed to the pendulum belt 13. The latter deposits the primary fleece on the continuously advancing collecting belt 15. Depending on the speed of the latter belt 15 and the frequency of the pendulum belt 13, a larger or smaller number of fleece layers is formed on the belt 15 in the vertical direction. The number of layers is selected according to the required board properties, e.g. weight, compressive strength etc. , of the end product. The number of layers also depends on the fibre formulation, i.e. the individual fibre processing stages between the fibre production unit and the curing oven 25. Usually 2 to 40 to 50 layers are deposited on the collecting belt 15. Depositing the primary fleece 26 by means of the pendulum belt 13 not only provides good transverse distribution of the fibre material on the collecting belt 15, but also contributes to uniform fibre orientation and a certain homogenisation. The fibre orientation can be further controllably influenced by changing the direction of the pendulum movement. The deposited fleece is subjected to a precompression in the precompression stage 17. The precompression is usually such that the fleece can still be engaged by the rollers of the first conveyor pair (required nominal thickness plus at maximum approximately 40% of the roller diameter) . Some deflection of the fleece after precompression is desirable so that, on entry into the compression unit, sufficient adhesion between the fleece and the rollers is achieved to give the required reorientation of the fibres. Since, in the case of products having a density of less than approximately 80 to 90 kg/m3, the expansion forces prevailing in the fleece during longitudinal compression are much lower, a moderate thickness compression in addition to the longitudinal compression is usually necessary in the production of these products in order to set the required tension and avoid undesirable pleating at the fleece surface. In the case of doubling, i.e. when the primary fleece is deposited in layers, the fleece surfaces have steps showing to varying degrees. These steps can be at least partially evened out in the precompression stage 17, by driving the upper belt 29 at a slightly higher speed than would be necessary for further transport. The partially smoothed fleece can be subjected to further smoothing in the compensation unit 19. To this end, for example, the first and second conveyor pairs can be disposed so as to be out of alignment. It is also possible for any other pairs of conveyors to be disposed out of alignment. The out-of-alignment arrangement subjects the conveyed fleece 20 to a bending or transverse deflection, which can effect smoothing of the fleece surfaces. The smoothing effect can be enhanced if the second conveyor pair runs somewhat more slowly than the first. Preferably, a longitudinal compression of 2:1 to 6:1 (corresponding to the circumferential speeds of the first and the last conveyor pairs 31 and 37) is effected in the optimisation or compression unit 19 substantially with a roller spacing corresponding to the nominal thickness of the board being produced (i.e. compaction by longitudinal compression without thickness compression) . Although the speed graduation may be multi-staged, the required properties can usually be achieved with a single-stage longitudinal compression. In the case of lighter products, however, a longitudinal compression together with simultaneous moderate thickness compression may be advantageous. In the case of a single speed graduation, each two conveyor pairs 31, 33 and 35, 37 can be driven jointly by one drive. Surprisingly, rollers 39 have proved particularly advantageous as conveyor means. The fleece can be greatly longitudinally compressed with rollers 39 without appreciable pleating at the fleece surface. One possible explanation for this is that there is only a slight adhesion between the rollers and the fleece. The rollers also promote the reorientation of the fibres, since the fleece can expand somewhat between the rollers in each case but without pleating. This results in good compaction of the fibre felt in the interior and at the surface. In the multi-ply unit 21 the compressed fleece can be separated into two or more webs 43, 45. It is also possible to omit the multi-ply unit or position it outside the conveying path and feed the fleece with the optimised fibre structure to the curing oven direct. Separation of the fleece 20 is effected by a band saw or a band knife in manner known per se. The upper web 45 with the optimised fibre structure is then subjected to a thickness and longitudinal compression. In this, the fibres of the upper layer 45 are further compacted by the thickness and subsequent longitudinal compression. The thickness-compressed web 45' is then returned to the continuously moving lower web 43. The compressed fleece 43, 45', more particularly the web 43 under tension, is guided between the compression stage 19 and the curing oven 25 by the conveyors 47, 49, 59, 61, 63, 65, for example belts, chains or roller systems, preferably conveyor belts, in order to prevent any break-out or bulging. In the curing oven 25 the binder in the fleece is cured. Curing of the binder takes place at temperatures between 180 and 300°C, preferably at about 200 to 250°C. The binder also ensures a firm bonding between the two webs 43, 45' of low and high gross density. To improve the adhesion of the webs 43, 45', the contact points thereof can be provided with a solid or liquid adhesive (metering device 57) on the multi-ply unit before being combined. Alternatively, or in addition, the bonding between the two webs 43 and 45' can be improved if the webs are contracted somewhat before the curing oven 25. Depending on the degree of contraction, this may result in some pleating of the webs. The contraction results in the contact surfaces increasing in size and the adhesion/felting of the webs can thus be improved. The apparatus according to the invention can be used for single-stage or multi-stage longitudinal compression of a mineral fibre fleece. Alternatively, the apparatus can also be so operated that a continuous compression zone forms. Products preferably having a density of between approximately 40 and 200 kg/m3 can be produced. Example 1: Board type 2-ply Fibre material Rock wool Board thickness 100 mm Outer layer thickness About 20 mm Substrate thickness About 80 mm Average gross density About 90 kg/ro.3 Outer layer gross density 155 kg/m3 Substrate gross density 75 kg/m3 Binder Modified phenolic resin Average fibre length From about 0.5 to 10 mm Average fibre diameter From 3 to 6 μm Precompression Approximately 1.5 nominal thickness Thickness compression 1.8 : 1 to 1.1 : 1 Longitudinal compression 3 : 1 Compressive strength at 10% deflection 0.025 - 0.030 N/mm2 Pull-off strength 0.013 - 0.018 N/mm2 (Delamination) Example 2: Board type Single-ply Fibre material Rock wool Board thickness 100 mm Gross density About 90 kg/m3 Binder Modified phenolic resin Average fibre length From about 3 to 4 mm Average fibre diameter From 3 to 4 μm Precompression Approximately nominal thickness Longitudinal compression 3 : 1 Compressive strength at 10% deflection 0.035 N/mm2 Pull-off strength 0.020 N/mm2 (Delamination) In comparison with boards having a non-optimised fibre structure and density, the weight of boards produced by the new process can be reduced by up to 25 to 40% for otherwise substantially identical mechanical properties. The tensile strength perpendicularly to the board plane is greatly improved, this being evident from the highly structured breaking zone (Figs. 10b and 10c) . Products according to the invention can be used for any of the conventional purposes of synthetic fibres, e.g. for boards, webs, used for thermal insulation, fireproofing and fire protection or soundproofing and sound control, or in suitable form in horticulture as a growth medium.

Claims: CLAIMS 1. Apparatus for the continuous production of a bonded mineral fibreboard from a mineral fibre fleece comprising a fibre production unit for producing a fleece, transport means (19, 23) for transporting the fleece to a bonding station (25) , a bonding station (25) for bonding the fleece, a compression unit (19) for thickness and/or longitudinal compression of the fleece disposed between the fibre production unit and the bonding station (25) , and means (61, 65) to prevent break-out of the fleece between the compression unit (19) and the bonding station (25), characterised in that the compression unit comprises a plurality of conveyor pairs (31, 33, 35, 37) disposed consecutively in the conveying direction; each conveyor pair (31, 33, 35, 37) comprises two opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") comprising in each case at least two spaced-apart rollers (39) , so that a conveying path for the fleece is formed by the opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37"), each said roller has a diameter of between 60 and 160 mm, preferably between 80 and 120 mm, the distance between adjacent rollers (39) is so selected that as to substantially prevent escape of the fibre felt (20) , there are drive means (117', 117", 117'", 117"", 118', 118", 118'", 118'"') are provided in order to drive the rollers (39, 39') of each group at substantially the same circumferential speed, there are means for individually adjusting the circumferential speeds of the conveyor pairs (31, 33, 35, 37) and there are means for adjusting the distance between the opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") of the conveyor pairs (31, 33, 35, 37). 2. Apparatus according to claim 1 in which the distance between adjacent rollers in a group is from 2 to 30 mm, preferably less than 20 mm. 3. Apparatus according to claim 1, characterised in that the roller diameter is 90 mm and the centre-to-centre distance between two adjacent rollers is 95 mm. 4. Apparatus according to any preceding claim, characterised in that the compression unit (19) comprises at least three conveyor pairs, preferably four conveyor pairs (31, 33, 35, 37) with roller groups of in each case three to eight rollers (39) , preferably four rollers (39) in each case. 5. Apparatus according to any one of claims 1 to 4, characterised in that the position of the opposite roller groups (31', 31") of at least one conveyor pair (31) is individually adjustable relatively to the position of the roller groups (33', 33"; 35', 35"; 37', 37") of the following conveyor pair or pairs. 6. Apparatus according to claim 5, characterised in that the distance between the opposite roller groups (31', 31"; 33', 33"; 35', 35") of a conveyor pair (31, 33 35) is adjustable to approximately 0.5 to 0.1 times the distance between the roller groups (33', 33"; 35', 35"; 37', 37") of the following conveyor pair (33, 35, 37) and in that the conveying path defined by the two conveyor pairs is substantially in alignment. 7. Apparatus according to any one of claims l to 6, characterised in that means are provided to control the circumferential speed of the rollers (39) of each individual group (31', 31", 33', 33", 35', 35", 37', 37'') independently of the speed of the rollers in each other group. 8. Apparatus according to any one of claims 1 to 7, characterised in that the compression unit (19) comprises means for inclining at least two opposite roller groups (31', 31"; 33, 33"; 35', 35"; 37', 37") relatively to one another in order, for example, to produce a fleece web tapering in the conveying direction F. 9. Apparatus according to any preceding claim , characterised in that the roller groups of at least one conveyor pair (31) are each disposed on a support structure (71) so as to be displaceable independently of one another perpendicularly to the conveying direction. 10. Apparatus according to claim 9, characterised in that at least two roller groups are each disposed on a separate frame (87) adjustable on the support structure (71) perpendicularly to the conveying direction. 11. Apparatus according to claim 10, characterised in that the frame (87) is disposed pivotally on the support structure (71) . 12. Apparatus according to claim 10 or 11, characterised in that the frame (87) is vertically adjustable by means of first spindles (89, 89', 91, 91') disposed on the support structure (71) . 13. Apparatus according to any one of claims 10 to 12, characterised in that four first spindles (89, 89', 91, 91') are provided which are interconnected by shafts (99, 99', 101, 101'). 14. Apparatus according to any one of claims 10 to 13, characterised in that second spindles (109, 109') are provided on the vertically adjustable frame (87) to pivot the frame (87) relatively to the support structure (71) . 15. Apparatus according to any one of claims 10 to 14, characterised in that guides are provided to guide the frame (87) vertically on the support structure (71) . 16. Apparatus according to any one of claims 9 to 15, characterised in that except for one roller group (31") the lower roller groups (33", 35", 37") are fixedly disposed on the support structure (71) . 17. Apparatus according to any one of claims 1 to 16, characterised in that the circumferential speeds of all the conveyor pairs and the distances between the opposite conveyors are individually adjustable. 18. Apparatus according to any one of claims l to 17, characterised in that the drive means for the conveyors (31, 33, 35, 37) and the means for adjusting the distance between the conveyors are connected to a microprocessor control system. 19. Apparatus according to claim 19, characterised in that the microprocessor control system comprises at least two read/inputting units in combination, one being disposed in the region of the compression unit and the other, for example, in a control room. 20. Apparatus according to claim 19, characterised in that the microprocessor control system comprises memory means for storing the process parameters such as the speeds and spacing of the roller groups (31', 31"; 33', 33"; 35', 35"; 37' 37") 21. Apparatus according to any one of claims 1 to 20, characterised in that means, e.g. an isotope unit, for determining the quantity of fibre per unit area, are provided before the compression unit ( 1 9 ) . 22. Apparatus according to claim 21, characterised in that the means for determining the quantity of fibre are connected to the fibre production unit or to the microprocessor control system. 23. Apparatus according to any one of claims 1 to 22, characterised in that a separating device (41) for separating the fleece into two or more sub-webs is provided between the conveyor pairs (31, 33, 35, 37) and the bonding station (21), in that at least one compression stage (53, 54) for thickness and/or longitudinal compression of at least one sub-web is provided and in that conveyors (47, 49, 50, 51) are provided to prevent break-out of the compressed fleece between the compression stage (19) and the bonding station (25) . 24. Apparatus according to claim 23, characterised in that at least the separating device (41) and the following conveyor (49) are vertically adjustable in the region of the multi-ply unit (21) . 25. Apparatus according to claim 23 or 24, characterised in that the compression stage for the compression of the at least one sub-web comprises at least two independently driven conveyor pairs (53, 54). 26. Apparatus according to claim 25, characterised in that the conveyor pairs (53, 54) are roller conveyors, the roller spacing thereof being adjustable. 27. Apparatus according to any one of claims 24 to 26, characterised in that means (57) are provided for the metered supply of a binder to the mutual contact surfaces of the sub-webs. 28. Apparatus for the continuous production of a bonded mineral fibreboard from a mineral fibre felt or fleece comprising a fibre production unit for producing a felt, transport means (19, 23) for transporting the felt to a bonding station (25) , a bonding station (25) for bonding the felt, a longitudinal or longitudinal/thickness compression unit (19) disposed between the fibre production unit and the bonding station (25) , and means (61, 65) to prevent break-out of the fleece between the compression unit (19) and the bonding station (25) , characterised by a compression-optimising unit comprising a plurality of conveyor pairs (31, 33, 35, 37), each conveyor pair (31, 33, 35, 37) comprising in each case two opposite rollers or roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37''), in which each roller has a diameter of between approximately 60 and 160 mm, preferably between 80 and 120 mm, and the distance between the rollers (39) is so selected that an escape of the fibre felt (20) is not possible, means for individually adjusting the circumferential speeds of the conveyor pairs (31, 33, 35, 37) and means for adjusting the clearance between the opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") of the conveyor pairs (31, 33, 35, 37). 29. Apparatus according to claim 28, characterised in that drive means (117', 117", 117'", 117"", 118', 118", 118"', 118"") are provided for driving the rollers (39) of each group at substantially the same circumferential speed. 30. A continuous process for the production of a bonded mineral fibre board by production of a mineral fibre fleece, longitudinal and/or thickness compression of the fleece followed by bonding of the longitudinally compressed fleece in a bonding station (25) , the fleece being held to prevent break-out between the compression unit (19) and the bonding station (25) characterised in that the longitudinal compression is effected by the fleece passing through a compression unit (19) comprising a plurality of conveyor pairs (31, 33, 35, 37) disposed consecutively in the conveying direction, each conveyor pair (31, 33, 35, 37) comprising in each case two opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") each having at least two spaced-apart rollers (39) , so that a conveying path for the fleece is formed by the opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37"), in that the rollers (39) of each group are driven at substantially the same circumferential speed by drive means connected to the associated group, and in that the circumferential speeds of the conveyor pairs (31, 33, 35, 37) are individually controlled, the circumferential speed of the rollers of at least one conveyor pair (31, 33, 35, 37) being less than the circumferential speed of the rollers of the preceding or each preceding conveyor pair, and the distance between the opposite roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") of the conveyor pairs (31, 33, 35, 37) being adjustable. 31. A process according to claim 30, characterised in that at least one of the roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") is inclined relatively to the opposite roller group, for example to produce a fleece web tapering in the conveying direction. 32. A process according to claim 30 or 31, characterised in that the fleece is compressed by the compression unit (19) to approximately the nominal thickness of the finished product. 33. A process according to any one of claims 30 to 32, characterised in that before entry to the compression unit (19) the fleece is precompressed to approximately 0.8 to 1.5 times, preferably 0.9 to 1.3 times, and quite particularly preferably to the approximate nominal thickness of the finished product. 34. A process according to any one of claims 30 to 33, characterised in that for the production of products having a random fibre orientation the speed graduation is single-staged. 35. A process according to any one of claims 30 to 34, characterised in that for the production of products having a pleated fibre structure the spacing between the opposite roller groups (31', 31"; 33', 33"; 35', 35") of a conveyor pair (31, 33, 35) is adjusted to approximately 0.5 to 0.1 times the spacing between the following roller groups (33', 33"; 35', 35"; 37', 37"), the conveying path defined by the two conveyor pairs being substantially in alignment and the circumferential speed at least of the roller groups (31', 31"; 33', 33"; 35', 35"; 37', 37") of the directly following conveyor pair being less than the circumferential speed of the preceding roller groups (31', 31") . 36. A process according to any one of claims 30 to 35, characterised in that the fleece is stretched in the conveying direction (F) after longitudinal compression. 7. A process according to any one of claims 30 to 36, characterised in that the compression zone is moved at certain intervals. 38. A process according to any one of claims 30 to 37, characterised in that the fleece consists substantially of man-made vitreous fibres, preferably rock wool fibres, and contains non-cured binder and the binder is cured by heating in the bonding station (25) . 39. A process according to any one of claims 30 to 38, characterised in that during the primary fleece is formed by cross-lapping. 40. A process according to any one of claims 30 to 39, characterised in that the fleece is longitudinally compressed in the compression unit (19) by a factor of 2 to 10, preferably 2 to 6, and most preferably 2.5 to 4. 41. A process according to any one of claims 30 to 40, characterised in that the thickness and longitudinally compressed fleece is divided into two or more sub-webs parallel to the large surfaces, in that in order to prevent a deformation in the direction of the thickness the sub-webs are each held at the opposite large surfaces, in that at least one of the webs is compressed in the direction of the thickness and/or longitudinally and in that the sub-webs are combined and then bonded. 42. A process according to claim 41, characterised in that the contact surfaces of the sub-webs are provided with binder before being combined. 43. A process according to claim 41 or 42, characterised in that the combined webs are longitudinally compressed before bonding. 44. Mineral fibre boards made by the process according to any one of claims 30 to 43.

Inventors: WYSS PETER, ZIMMERMANN FREDY, WYSS, PETER, ZIMMERMANN, FREDY
Applicants: FLUMROC AG, ROCKWOOL INT, WYSS PETER, ZIMMERMANN FREDY, ROCKWOOL INTERNATIONAL A/S, WYSS, PETER, ZIMMERMANN, FREDY
Application year: 1997
Main classification: D04H1
IPC codes: D04H1