Process and apparatus for the continuous production of mineral wool mats

Abstract: 2.1. The objective is to provide a process and an apparatus for the continuous production of mineral wool mats, by means of which a stable flow pattern is created in the chute, thus facilitating a clearly defined, homogeneous layer of deposited mineral wool. 2.2. According to the invention, at least one backflow region (24, 25) is generated in the chute (9) outside the fiber flow (23), which backflow region (24, 25) is sufficient for such a large-volume backflow with such a low mean velocity that appreciable upward fiber transport is avoided. In this connection, a portion (32) of the process air entrained with the fiber flow is deflected upward in the backflow, and another portion (34) of the process air is extracted. 2.3. Production of mineral wool.

Description: The invention concerns a process and an apparatus for the continuous production of mats, particularly mineral wool mats, in accordance with the preambles of claims 1 and 3. In the production of mineral wool mats, e.g. from rock wool or glass wool, not only is the fiberisation process of importance, but also the formation of the mat as such constitutes an important process step. It is customary in this respect for a fiber/gas/air mixture produced by a fiberisation unit to be introduced into a box-like so-called chute to separate the fibers, which chute usually features at the bottom an accumulating conveyor acting as a type of filter screen which is constructed in the form of a gas-permeable, rotating, flat conveyor belt. Under the conveyor belt is located an extraction device which generates a certain partial vacuum. In addition, drum-shaped accumulating conveyors with curved suction surfaces are also known from, for example, DE-A 39 21 399. When the fiber/gas/air mixture - which can also contain a binder - impinges on the accumulating conveyor, the gas/air mixture is sucked through to below the accumulating conveyor acting as a filter, and the fibers are retained on the conveyor in the form of a mat. In the known process for mat production, there are generally a plurality of adjacently arranged fiberisation units which produce fiber flows in a manner familiar per se to a person knowledgeable in the art. For the sake of simplicity, the terms "fiber flow" or "fiber stream" used in the following shall refer to the composite flow comprising fibers, process air, and binder where appropriate, with the term "process air" also covering the propellant gas required in order to attenuate the fibers, the secondary air entrained during fiberisation, and any additional air which may be sucked into the process for the purpose of cooling following fiber attenuation. Into the space bounded by the accumulating conveyor and the side walls of the chute, are thus introduced from the top fiber flows arranged in the form of adjacent core streams which carry fibers which are in the process of production or which have just been produced. In order to facilitate a directed flow and orderly deposition of the fibers as a mat on the accumulating conveyor, it is therefore necessary to extract the introduced process air from below the accumulating conveyor. By this means, one obtains in the chute a vertical stream of the fiber flows, from which the fiber content is trapped at the accumulating conveyor, as if at a filter, to form a mat which is then conveyed away while the process air continues to flow to extraction devices. The extraction process under and in the accumulating conveyor presents certain difficulties as extraction has to be performed through the forming wool mat, so that at the beginning of mat formation there is, of necessity, less flow resistance while after partially completed mat formation, a greater level of flow resistance has to be overcome. Directly above the mat formation zone, therefore, a non-uniform flow pattern prevails owing to the spatially differing thicknesses of the mat lying below. At the entry end of the chute, i.e. above the mat formation zone, the fiber flow is made up of a plurality of core streams, with each core stream initially being assignable to an individual fiberisation unit. The core streams which occur immediately below the fiberisation units, which core streams exhibit the energy of the propellant gas flows injected for fiber production and as a result of their elevated velocity represent regions of reduced static pressure, are located in relatively close mutual vicinity and exert a mutual suction effect which can lead to unstable oscillating flows in the individual core streams or in the fiber flow as a whole. The overall result is a heterogeneous, spatially and temporarily unstable flow pattern above the accumulating conveyor which, although appearing as a downward flow at any one given moment, nevertheless locally exhibits a plurality of different flow components acting in the most varied of directions. Minute changes of a boundary condition in this chaotic flow system lead to changes in the flow pattern which are difficult to control from the outside and which, in turn, are undesirable as they adversely affect the degree of uniformity with which the mat is formed. In particular in the boundary zone around the fiber flows, fibers exhibiting rapid upward movements can also be observed. These upward streams in the boundary zone of the fiber flows can be attributed to the fact that, as a rule, only a certain portion of the process air flowing in from above is completely extracted, while another portion at the side of the actual fiber flows is pushed upward again, or is sucked upward by partial vacuum zones in the region of the injected attenuating gas flows. These air streams exhibit high flow velocities in an upward direction and entrain fibers in an upward direction into the area of fiberisation. In the case of fiber production by the blast drawing process, for example, already solidified fibers which are sucked into the nozzle slot together with the secondary air can lead to massive disruptions to production. In addition, the transport of already solidified fibers into the region of binder injection which, in the blast drawing process, is usually located at the entry zone of the chute, can lead to these fiber elements once again coming into contact with binder and then adhering to the chute wall or falling onto the mat as fibers with an excessive accumulation of binder, for example in the form of highly undesirable lumps. In order to achieve orderly fiber deposition under these conditions, it is necessary to perform a plurality of fine adjustments for a given production process, so as to optimise, by trial and error, the fiber deposition conditions. Any change in the production conditions leads to the requirements that new fine adjustment be performed. A process and apparatus of the species indicated in the preamble of claim 1 or claim 3, respectively, has become known from FR-A-2247346, cp. Fig. 2 there. The backflow regions created in accordance therewith, are voluminous and have room at the side to enable them to circulate comparatively slowly, so that the upward velocities generated are reduced, thus diminishing the tendency to entrain fibers in an upward direction. Moreover, disadvantageous encrustations of binder-containing wool accumulations are avoided in that area of wall in which the stagnation point of the branching flow is located. Above the stagnation point, there is a backflow of process air, while below the stagnation point, the process air is extracted through the accumulating conveyor. When the volumes available for the backflow are too small, wool constituents in the region of said stagnation point impinge onto the wall with a high velocity component perpendicular to the wall. This leads to undesirable encrustations which are avoided if this stagnation point is located a sufficient distance away from the external enveloping surfaces of the fiber flows so that the disruptive velocity component of the flow in the vicinity of the stagnation point is drastically reduced. A further and essential aspect of the concept of FR-A-2247346, Fig. 2 there, lies is in the fact that the extended backflow zone should be dimensioned such that the wool to be deposited can no longer follow the backflow in the lower flow deflection area, i.e. it is effectively centrifuged out in a cyclonic flow. In this process, the wool to be deposited is already separated within the actual chute from an appreciable portion of its associated process air. Consequently, this portion no longer needs to be sucked through the mat. This leads to advantages with respect to the necessary suction energy input, which is reduced owing to the substantially lower pressure loss a) of this partial flow, and b) of the remaining process air passing through the mat and/or the accumulating conveyor. Moreover, the differential pressure necessary for extracting the process air from the mat is therefore also reduced, thus making the mats deposited more voluminous and facilitating the manufacture of products with lower bulk densities. The overall result should be a defined limitation of the fiber deposition area and thus of the mat formation zone, provided not by means of the chute walls but by a boundary area formed between the outsides of the fiber flows and those of the backflow regions. However, a marked disadvantage also acknowledged in FR-A-2247346 is the fact that reduction of the energy of upward flow in the backflow regions requires a very substantial input of secondary air from above the chute. Under unfavourable conditions, i.e. when only small amounts of secondary air should be introduced into the chute, this concept is not industrially applicable in view of intolerable amounts of fibers being transported upwardly in the backflow regions. Moreover, another substantial disadvantage also acknowledged in FR-A-2247346 is the fact that the backflow necessarily leads to an uneven fiber distribution on the accumulating mats in view of uncontrollable locally different air flow characteristics. The object of the invention is to provide a process of the species indicated in the preamble of claim 1, and also to create an apparatus for performing said process as indicated in the preamble of claim 3, in which a properly defined, homogenous fiber deposition is enabled without intolerable adverse effects by fiber backflow upwardly in the chute. This object is achieved by means of the characterizing features of claim 1 and of claim 3, respectively. The extraction of air outside the mat formation zone inevitably withdraws process air from the backflow region at its entry, and thus reduces the upward velocity of the process air in the backflow regions with the possible consequence of undesirable fiber transport. Moreover, the extraction of large quantities of air is facilitated. The fact that the chute walls are situated outward into a deliberately created dead flow zone, however, means that wool material which contains binder and has become deposited on the wall in the course of a certain time can bake onto the wall more readily. If, in contrast, the chute walls mechanically limit the actual main flow, then they are also exposed to the stream forces acting here which, being mainly parallel to the wall surface, are more appropriate so that fiber encrustations become less probable. With the walls being positioned in a distance from the main streams, the cooling of the walls as claimed in claims 2 and 4 therefore becomes even more important as a means of preventing binder-containing fiber material, in accordance with the teaching of DE-A 35 09 425, from baking onto the circumferential chute walls. With respect to further details, features and advantages of the cooling system for the chute walls, express reference is made to DE-A 35 09 425, the full contents thereof being hereby incorporated by reference. Further details, aspects and advantages of the present invention are revealed in the following description of an embodiment by reference to the drawing in which Fig. 1 is a schematic representation illustrating the process according to the invention and the apparatus according to the invention, with an accumulating conveyor in the form a flat conveyor belt, and Fig. 2 is a further embodiment of the apparatus according to the invention with a drum-shaped accumulating conveyor. As is apparent from Fig. 1, free jets 5, 6, 7 and 8, which are roughly wedge-shaped in their geometry, are produced by, in this illustrative example, four fiberisation units 1, 2, 3 and 4 operating in accordance with the blast drawing process, said free jets 5, 6, 7 and 8 consisting of a fiber/gas/air/ binder mixture and being surrounded by a box-shaped chute 9, the upper terminations 9a to 9e of which are formed by covers 9a to 9e which limit the entry of ambient air. The chute covers 9a to 9e are of moveable design with respect to their cover area, and are also water-cooled in order to minimise the occurrence on them of encrustations of binder-containing wool constituents. Through their limiting effect on the sucked-in additional air, signified by 48 to 51, backflows are generated, the extent of which is determined by the position and size of the remaining upper inlet cross-sections of the chute. The bottom termination of the chute is formed by an accumulating conveyor 10 featuring a gas-permeable conveyor belt 12 which rotates in the direction indicated by arrow 11. When the fiber/gas/air mixture, which may also contain a binder, impinges on the accumulating conveyor 10, the gas/air mixture is extracted from below the accumulating conveyor 10 acting as a filter by, in this illustrative example, two extraction devices 13, 14, and the wool is deposited with the formation of a mat onto the accumulating conveyor 10 as a wool mat 15. With respect to further details, features and advantages of the chute 9 and the possible injection there of water and binder, and of the construction of the fiberisation units 1 to 4, reference is made to DE-A 41 41 625, and DE-A 41 41 627, the full contents thereof being hereby incorporated by reference. The free jets 5 to 8, which are initially still wedge-shaped in their geometry, produced by the fiberisation units 1 to 4, form at the entry zone of the chute 9 fiber flows 16, 17, 18, 19 with interposed eddy zones 20, 21, 22 of entrained process air. After dropping a certain distance in the chute 9, the individual fiber flows 16 to 19 come into contact with one another and eventually join to form a main flow 23 which likewise features, on its outside, eddy zones 24, 25 with backflow regions 26, 27. According to the invention, the lateral limiting walls 28, 29 of the chute 9 are positioned at a sufficiently large distance from the outside edge 30, 31 of the fiber flows, i.e. the main flow 23, so that there is at least sufficient room for the eddy zones 24, 25 to ensure that the backflow regions 26, 27 which occur exhibit small mean velocities. In this way the problem is avoided whereby fibers from the main flow 23 are transported back up into the entry zone of the chute via the eddy zones 24, 25, in which entry zone they are sprayed anew with binder. The shape of the eddy zones 24, 25 leads, in the edge zone of the main flow 23, to a division in the downwardly directed air stream into a portion 32 which is returned upward in the backflow region 26, and a portion 33 which is extracted in the vicinity of, but outside, the mat formation zone 35, namely in a zone 36 with a width a in the illustrative example, by the extraction device 13. The remaining portion 34 is sucked through the mat 15 in the mat formation zone 35 with a width b by extraction device 14. Depending on requirements, instead of extraction device 14, several such extraction chambers can, of course, be provided, duly designed and arranged in accordance with the layer growth of the mat. Moreover, extraction chamber 13 in particular can be dispensed with or take the form of a - if necessary throttlable - part of extraction device 14. As shown in the right-hand part of the illustration, a large-volume flow is also generated in the region of maximum mat layer thickness, in accordance with the invention, so that appreciable upward wool transport is avoided. To this, a zone c where there is no mat formation can be connected in a similar manner, from which zone c a further partial flow of process air 33b can be extracted by an extraction device 13b which is not shown in any further detail and which is located outside the mat formation and conveying region. The distance of the lateral limiting walls 28, 29 of the chute from the outside edge 30, 31 of the main flow 23, and also the width a of zone 36, and the width b of the mat formation zone 35 are dimensioned in this respect such that disruptive velocity components perpendicular to the limiting wall 28, 29 in the vicinity of the stagnation point signified by 37 are drastically reduced. It is known from earlier measurements that these velocities can easily lie in a range from approx. 10 to 20 m/s. According to the invention they are reduced to below 10 to 20% of these values. The following data are provided to serve as an indication of the volumes involved in the case of the claimed backflow regions: Given a process gas volume flow of, for example 9,000 m 3 /h (STP) per fiberisation unit, the volume of circulating backflow generated between the end walls 28, 29 and the enveloping surfaces 30, 31 near to the wall is approx. 2,500 m 3 /h (STP). According to the previously customary design with respect to the distance between fiberisation units 1 and 4 on the one hand, and the end walls 28 and 29 respectively on the other hand, maximum velocities of the upward flows near to the wall of approx. 4 m/s are known to have occurred. These velocities are higher than the drop velocity of wool flakes, so that a substantial proportion of wool is repeatedly carried upward into the chute entry zone. With the creation in accordance with the invention of sufficiently sized backflow regions, the circulating backflow volumes of 2,500 m 3 /h (STP), although only having undergone an insignificant change, feature substantially reduced upward velocity with values falling to below 2 m/s and preferentially below 1 m/s. As a result of the likewise advantageous introduction of a mat-free extraction region a and/or c, approx. 20 to 80%, and preferably 40 to 60%, of the process air volume from the fiberisation units 1 and 4 near the wall is, in addition, extracted outside the mat formation zone b, without the need to overcome a pressure loss as a result of flow resistance at the mat. In the case of the four fiberisation units in the illustrative example, a portion of 10 to 40% of the process air is extracted without any appreciable pressure loss, and thus with extreme cost-efficiency. As a further advantage, reference is made to the fact that, if the edge zone extension according to the invention is not provided, the 9,000 m 3 /h (STP) process air per fiberisation unit mentioned in the example numerical data above can only be maintained in the case of very coarse wool (such as is required, for example, for automotive exhaust mufflers) featuring correspondingly higher drop velocities and a lower level of permeation resistance. In the case of finer wool, the proportion of additional air sucked into the chute per fiberisation unit has to be increased by approx. 3,000 to 6,000 m 3 /h (STP) in order to avoid upward wool transport. By this means, the position of the backflow regions which are formed is shifted so far down that wool egress out of the chute cover area no longer takes place. Compared with these practical operating data, the invention results in an advantageous reduction of the requisite total volume of exhaust air per fiberisation unit of approx. 20 to 60%, and on average approx. 30%. Fig. 2 shows a further embodiment of the apparatus according to the invention, in which the accumulating conveyor 10 is designed in the form of drums 38, 39. The drums 38 and 39 each feature a rotating, perforated (gas-permeable) rotor 40 and 41, each of which is powered by a motor (not depicted in any further detail in Fig. 2) in the direction of the arrows 42, i.e. the conveying direction. Furthermore, arranged inside the drums 38 and 39 is an extraction device, not depicted in any further detail, the suction pressure generated by which is active only in suction chambers 45 and 46 located below the curved suction areas 43 and 44. The distance between the two drums 38 and 39 creates a so-called discharge gap 47, the width of which is essentially to be matched to the thickness of the mat 15 to be produced. In order to adjust the width of the discharge gap 47, one of the two drums 38, 39 may be of a pivoting design. In order to optimise the large-volume flow structure, the extraction devices 45 and 46 may, in particular, be divided such that the suction pressure in the mat-free suction zones a is adjustable. In this embodiment, the extraction zone a shown in example 1 (see Fig. 1) is arranged to particular advantage as, owing to the two, initially mat-free perforated surfaces entering the chute, there are two extraction zones a formed which, without any great degree of design sophistication, serve the purpose according to the invention of extracting a considerable portion of the process air from outside the mat deposition surface. This eliminates what would be, in itself, a more difficult problem, namely that of providing a further extraction device 13b analog to region c in Fig. 1. By this dual utilisation of the advantages of a mat-free zone a, the formation of zones c in this concept can be avoided to advantageous effect. With respect to further details, features and advantages of such drums, express reference is made to DE-A 41 41 627, the full contents thereof being hereby incorporated by reference.

Claims: A process for the continuous production of wool mats (15), preferentially mineral wool mats, in which, to form the mat (15) there is, in at least one chute (9), at least one fiberisation unit (1, 2, 3, 4) in each case, in which process the fibers, under the effect of a suction pressure, are deposited on at least one accumulating conveyor (10), and in which process, in the chute (9) at the outside of the fiber flow (23), at least one such backflow region (24, 25) is created as is sufficient for a sufficiently large-volume backflow with a sufficiently low mean velocity such that appreciable upward fiber transport is avoided, with a portion (32) of the process air entrained in the fiber stream being deflected upward in the backflow, and another portion (34) of the process air being extracted, characterized in that a portion (33) of the extracted process air is extracted outside the mat formation zone. A process as claimed in claim 1, wherein at least a portion of the circumferential walls (28, 29) of the chute (9) is cooled. An apparatus for performing a process for the continuous production of wool mats, in particular for the production of mineral wool mats (15), which, for the formation of the mats, features in at least one chute (9) at least one fiberisation unit (1, 2, 3, 4) in each case, in which apparatus the fibers may be deposited on at least one gas-permeable accumulating conveyor (10) under the effect of a suction pressure, and in which apparatus within the lateral limiting walls (28, 29) of the chute (9) such a distance to the outside edge (30, 31) of the fiber flow (23) is provided as is sufficient for a sufficiently large-volume backflow (24, 25) with a sufficiently low mean velocity to prevent appreciable upward fiber transport, a portion (32) of the process air being deflected upward in the backflow, and another portion (34) of the process air being extracted through the mat (15) within the mat formation zone, characterized in that an extraction device (13, 13b), acting also outside the mat formation zone, is provided for extracting a further portion (33) of the process air. An apparatus as claimed in claim 3, wherein a cooling arrangement for cooling at least a portion of the limiting walls (28, 29; 9a to 9e) of the chute (9) is provided. An apparatus as claimed in claim 3 or 4, wherein the chute (9) features shaft covers (9a to 9e) which are of movable design with respect to their covering area.

Inventors: HIRSCHMANN KLEMENS DR, MELLEM JOACHIM, HIRSCHMANN, KLEMENS, DR., MELLEM, JOACHIM
Applicants: GRUENZWEIG & HARTMANN, GRUENZWEIG + HARTMANN AG
Application year: 1992
Main classification: D04H1
IPC codes: D04H1, C03B37, F16L59