A METHOD AND AN APPARATUS FOR FORMING THE PRIMARY WEB OF A MINERAL FIBRE MAT

Abstract: The invention relates to a method for forming the primary web of a mineral fibre mat onto a moving, pervious base by transporting fibres onto the base by means of a stream of air or a corresponding means. In accordance with the invention, the stream of air is adjusted to minimise the pressure difference over the forming base. The invention also relates to an apparatus for the purpose of implementing the method.

Description: A method and an apparatus for forming the primary web of a mineral fibre mat The invention relates to a method for forming the pri a- ry web of a mineral fibre mat from fibres manufactured from mineral melt by using centrifugal force, particu¬ larly by means of several slinger wheels linked in series; i.e. using what may be called the cascade met¬ hod. In accordance with the principle of manufacturing mine¬ ral fibre by using centrifugal force, the molten mineral matter is led onto the periphery of a spinning or slinger wheel in strip form, from which the fibre embryos are drawn outwards by the centrifugal force produced by the great rotational velocity. A high-velocity medium flow is directed to pass close to the disc periphery, which me¬ dium flow finishes the fiber-formation and transports the fibres in the direction of the rotational axis of the wheel away from the fibre formation area. In cascade fiberization more than one slinger wheel is used, generally 2-4 wheels, in which case the molten material is led onto the first slinger wheel, from there to the second wheel rotating in the opposite direction, then to the third, and so on. At each wheel, with the possible exception of the first one, part of the molten material attaches itself in strip form onto the periphery of the wheel, and due to the centrifugal force and the passing medium flow forms fibres so that at the last wheel the entire molten material is fiberized. The medium flow directs the fibres formed in the fiber¬ ization device into a wool chamber, at the opposite end of which the fibres are collected onto a wire or other corresponding air pervious forming-base conveyed in a direction essentially perpendicular to the medium flow direction and onto which the fibres form a thin mat, a primary web. The complete mineral wool blanket is formed by layering a required number of the primary webs one on top of the other. The dispersion of air/fibres obtained from the fiberizat- ion device is essentially cylindrical in shape and in addition generally narrower than the desired primary web. This is why it has been difficult to collect onto for¬ ming bases webs that are of uniform quality right up to their edges. From the standpoint of proper web formation it is considered essential that the transportation of the fibres to the forming-base and their settling down on it is to be achieved by means of a suction force acting through the base. In other words, underpressure is main¬ tained on the evacuation side of the forming-base with respect to the pressure prevailing on the formation side. In this manner, the fibres become settled to that part of the forming base where the suction produced by the under¬ pressure is at its highest, i.e. where the fibre mat thusfar formed onto the base is at its thinnest. This production model requires the implementation of a closed transportation passage, i.e. a tunnel-like wool chamber between the fiberization device and the forming base. On the other hand the dispersion cloud issuing forth from the fiberization device needs to be equalized out over the width of the primary web and on the other hand be¬ cause it is necessary to eliminate disturbing external streams influencing the settling down of the fibres and especially the settling down suction. Moreover, the cham¬ ber has to be relatively long for the desired results to be achieved. The disturbance-free functioning of the wool chamber re¬ quires that its walls be kept clean. This, however, is very difficult because of the heat-hardening glue subs- tance generally added to the fibres in conjunction with fiberization. Fibres coated with the said glue substance easily attach themselves to the walls of the chamber, the glue hardens in the warm conditions, and pre-tempered fibre/glue layers accumulate onto the walls, which layers cause disturbances in the air flow, and if loosened and mixed into the fibre suspension, cause defects in the fibre mat. The Finnish patent application no. 910216 discloses the idea that mat formation can be influenced for instance by means of additional gas medium flows used at the fiber- ization stage. According to the said application, the ad¬ ditional gas medium flows can be used in the wool chamber to influence the flow properties in the wool chamber of the dispersion formed of fibres and the gas medium; for instance to prevent the formation of fibre accumulations. However, the said action model fails to take into account that the powerful suction force acting through the form¬ ing-base essentially delimits the possibilities to use the gas flows to shape and regulate the dispersion cloud issuing from the fiberization device and that shaping can actually be executed solely by means of these gas flows. In accordance with the present invention, the gas medium flows fed into the fiberization stage are regulated to optimize of the fibre formation on the one hand and the web formation on the other hand, while the volume flow rate of the gas medium sucked through the forming-base is regulated to maintain essentially the same pressure on both sides of the forming base on the web formation area. When acting in accordance with the said principle, it is firstly possible to achieve optimum fibre formation con¬ ditions by using an into the fiber formation area direct¬ ed, as to its velocity and direction correctly controlled gas medium flow. Secondly, additional medium flows can be directed at the flow of formed fibres in order to achieve a proper dispersion of the fibers in the medium. And thirdly, the shape of the dispersion cloud can be modifi- ed beneficially with regard to the web formation, which modifications on the gas medium flow that flows through the formation area are taken into account without distur¬ bance influences being transmitted upstream through the formation area to any of the above functions. The invention will now be described in more detail by means of the appended drawing in which Figure 1 shows a side view of the apparatus employed in the method in accordance with the invention, Figure 2 shows a view from above of the apparatus employed in the method in accordance with the inven- tion, Figure 3 shows a front view of the fiberization apparatus used in the method in accordance with the invention, and Figure 4 shows a schematic presentation of the gas medium flows when acting in accordance with the in¬ vention. The implementation in accordance with Figs. 1 and 2 shows the interlinked group of slinger wheels 6 - 6'" to clar¬ ify the basic principle of the invention. The mutual lo¬ cation of the wheels is shown in Fig. 3. In figures 1 and 2 the mass of molten mineral 7 is led to the periphery of the first or uppermost slinger wheel 6, from which the centrifugal force casts it partly into fibre embryos and draws it in fibre form into the high- velocity stream of air that is led past the periphery surface of the slinger wheel in the direction axis of rotation of the slinger wheel. Part of the molten ma¬ terial is cast onto the next wheel 6 r and so on. The stream of air carries the fibres onto the wire 8 mounted in front of the slinger wheels, the said wire being kept in motion for the purpose of leading away the mat of fibre formed onto it. Air dissipated on the wire from the fibres is removed by means of a suction device 9. When acting in accordance with the invention, the suction de¬ vice's operation is so regulated that the pressure on either side of the wire is essentially the same. In prac¬ tice, the essentially same pressure means understandably that the pressure maintained on the evacuation side of the wire is slightly lower than that on the formation side so that the mat formed can remain on the wire. Nevertheless, excess of the pressure-difference essential for the mat to remain on the wire is to be avoided. In the aforementioned basic state, the different gas me¬ dium flows employed in the fiberization stage can be used as properly as possible with regard to their basic func¬ tion. The effect achieved on the fibre dispersion cloud by the regulation of the gas medium flows is clearly dem¬ onstrated when the shape of the clouds shown in Figs. 1 and 2 is compared. Whereas, in accordance with Fig. 1, hardly any change takes place in the shape of the cloud in the direction of motion of the forming base, Fig. 2 shows that the fibre dispersion cloud has been signifi¬ cantly expanded in the direction of the width of the forming-base, i.e. perpendicularly to the direction of motion of the forming base, as compared to the width that it has when emitted from the fiberization device. In prior art solutions, however, the corresponding expansion is achieved by means of an effective suction force acting essentially through the forming base 8. In the solution in accordance with the invention, however, this expansion is achieved by means of medium blows directed into the fiberization stage, the said blows acting mainly expand- ingly from the inside to make the dispersion cloud form a primary web of the desired width and formed in the de- sired manner on the forming-base. Figure 3 illustrates the optional ways of guiding the various gas mediums (in practice often air) used in the fiberization stage. Firstly, part of the periphery of each slinger wheel 6 - 6' ' r is surrounded, slightly apart from the periphery, by a slit-like orifice 1 via which the fiberization air is blown tangential-ly to the per¬ iphery of the wheel. The purpose of this stream of air is to draw the fibre embryos into fibres, the said embryos having been forced up by the centrifugal force as embryos from the molten material rotating on the periphery of the slinger wheel. While the main direction of the fiberizing stream of air is essentially that of the axis of the sli- nger wheel, it is advantageous for the forming and onward transportation of the fibre dispersion cylinder formed in the stream of air after the slinger wheel if the said fiberizing stream of air is given a component of motion tangential to the slinger wheel, advantageously in the direction of rotation of the wheel. In addition to the aforementioned stream of air essen¬ tial for fiberization, Fig. 3 illustrates on the part of each slinger wheel yet another stream of air blown via nozzles or a uniform nozzle 2 partly surrounding the wheel. The purpose of this "transportation" stream of air is to dilute the fibre dispersion cylinder produced by the fiberizing stream of air and to further shape it into a form advantageous from the point of view of transporta- tion and web formation. While the velocity of the trans¬ portation stream of air is essentially less than the vel¬ ocity of the fiberizing stream of air, the volume flow of the former is greater than that of the latter. The trans¬ portation stream of air can be used to achieve essential changes in the internal fibre distribution of the fibre dispersion cloud after the slinger wheels and in the shape of the cloud perpendicular to its direction of progress. These matters can be influenced mainly by regu¬ lating the velocities of the transportation stream of air with respect to the surrounding streams of air. Another possibility to influence is to direct and/or divide the number of transportation streams of air differently by means of nozzles 2 located in different parts of the apparatus, the said nozzles being controllable and/or their flow cross-sections being variable or adjustable. The transportation streams of air can also be controlled via more than one radially, one-inside-the-other located nozzles 2, which can also be located axially, slightly shifted with respect to one another. In accordance with one special characteristic of the in- vention, part of the transportation air can be led through the axis of the slinger wheel. The said function is possible in a slinger wheel structure in which the rotor of the drive motor is mounted directly onto the axis of the slinger wheel so that the motor surrounds the axis of the slinger wheel. The aforementioned measures make it possible to achieve an essential influence on the fibre dispersion cloud formed after the slinger wheels. An example of this is extending the width of the cloud but still retaining evenness of the fibre concentration inside the cloud. The said extension of width can be executed so that it is greater in one cross-section, advantageously in the hori¬ zontal plane, in which case the fibre dispersion cloud can be used to form an advantageously shaped and usable primary web on the forming-base, which is located essen¬ tially closer to the fiberization device than has been hitherto been possible when employing known art procedu¬ res. In practice this distance can be achieved within a range of c. 0.8 - 1.2 metres, although distances greater than these are, of course, within the scope of the inven¬ tion. In equipment complying with the operational prin- ciples of state-of-the-art technology, the said distance is generally of the order of at least 2 metres if the width of the primary web is 2 metres. The distance between the fiberization device and the for¬ ming base is related to the width of the forming base (measurement made perpendicularly to the direction of motion) such that the distance from the forming base to the fiberization device can be within the range of c. 0.2 - 1, advantageously 0.3 - 0.6) times the width of the forming base. A practical guideline for the distance is c. 0.8 - 1.2 metres and 0.8 - 4.5 metres for the width. This fact, and the fact that no subsidiary flows occur due to the extra suction through the forming base, (more than 80% of the stream of air passing through the forming base has been observed to originate from the air from the fans) result in that the fibre dispersion can be made to pass from the fiberization device to the forming base in a space that has essentially no walls. This entirely eli¬ minates problems resulting from the accumulation of ma¬ terial onto the walls of previously used wool chambers. Naturally, it is necessary to use an instrument, a trough or the like, for collecting and leading away non-fiberiz- ed pearls of material. The lack of a powerful suction force helps the said pearls to become separated from the stream of fibre. Here, too, the short distance between the fiberization device and the forming base does not cause any problems. In addition to the aforementioned measures, it is advan¬ tageous for the entire fiberization device to be located in a tunnel-like enclosure so that two other auxiliary streams of air can be made use of. One of the two strea- ms of air (air stream 3 in Fig. 3) is led outside the nozzles 2 inside the enclosure focusing the transporta¬ tion stream of air and into the interspace of the slinge- r wheels 6. A separate fan is used to produce this stream of air. The ejection effect produced by the other streams of air and the slinger wheels inevitably influences this stream of air and results in a more or less uncontroll- able flow regulating factor, but the said factor can, nevertheless be reduced by means of the aforementioned controlled blowing. The other stream of air can be achieved outside the enclosure as a kind of a curtain flow to border the fibre dispersion path should such a flow be felt necessary in a particular application. In an application in accordance with the invention, the streams of air used in connection with the fiberization stage have been illustrated in a manner corresponding to the above and with respect to their flow volumes in the appended Fig. 4. The figure also shows an evacuation fan 9 and a schematic presentation of the regulating device for controlling its functioning in accordance with the invention's operational principle. In principle, the said control can, for example, function according to the data provided by pressure-sensing sensors mounted on either side of the forming base 8. This data is compared to the set default value and the fan equipment 9 is then regu¬ lated accordingly. When forming the fibre mat in accordance with the inven¬ tion, it has been observed that the volume of the over¬ all flow of air can be reduced in comparison with pre¬ vious methods. In the aforementioned modes of execution the forming base 8 has been depicted as being essentially a plane wire, but it is, of course, entirely within the scope of the invention for the forming-base to be for instance curved in the manner of a segment of a large-diameter drum. Similarly, it is not necessary for the forming-base to move precisely in the same plane as where the slinger wheels 6 - 6"' rotate; instead, the forming base can be moved at an angle deviating somewhat from the said plane. In the above modes of execution the forming base has been presented as being moved vertically and the fibre disper¬ sion cloud as being distributed horizontally. The imple¬ mentation of the invention is still possible even if the forming base were to be moved, for instance, horizontal¬ ly past the fiberization device or at any angle between the vertical and the horizontal planes, using which modes of moving it is possible to seek out the optimum situ¬ ation between the mutual functioning of the cascade • wheels .on the one hand and the shaping of the fibre dis¬ persion cloud on the other.

Claims: Patent claims: 1. A method for forming the primary web of a mineral fibre mat from fibres transported from a fiberization de- vice by a gas medium and formed of molten mineral matter by means of centrifugal force, the said primary web being formed onto a wire or a corresponding pervious forming base in motion in front of the fiberization device, char¬ acterised in that the fibre dispersion cloud is, by means of air streams directed into the fiberization stage and under forming guidance of the air streams, blown onto the forming-base, and that a state in which there is essen¬ tially .no pressure difference is achieved and is main¬ tained through the forming base on the web forming area. 2. A method as claimed in claim 1, characterised in that at least three gas medium flows, essentially unidirec¬ tional in terms of their main direction of flow, are in¬ troduced into the fiberization stage, the said flows be- ing independently adjustable and/or controllable in terms of their direction, velocity and/or volume flow, the vel¬ ocities of the said flows being inversely proportional to the distance from the fibre forming area in the direction of the centrifugal force. 3. A method as claimed in claim 2, characterised in that part of the gas medium flow is led through at least one area defined by a fibre forming area subjected to the centrifugal force. 4. A method as claimed in claims 2 or 3, characterised in that the web forming is controlled by controlling the mu¬ tual velocities and/or directions of gas flows. 5. A method as claimed in any of the above claims 1-4, characterised in that the gas medium flows are led chan¬ nelled. 6. An apparatus for implementing the method according to claim 1, the apparatus consisting of at least one driven slinger wheel (6 - 6 , , r ) for the purpose of receiving molten mineral mass (7) , a slit orifice (1) for blowing the fiberization gas medium tangentially with respect to the slinger wheel and surrounding the slinger wheel in an arc-like manner at a small distance from the periphery or part of the periphery, transportation gas medium nozzles (2) located radially with respect to the slinger wheel outside the fiberization gas medium orifice and surround¬ ing the fiberization gas medium orifice in an arc-like manner, a forming wire (8) located essentially in front of the slinger wheel (6 - 6 ' ' ' ) or wheels in a plane es- sentially parallel with the rotation plane of the said wheel(s), and devices (9) for evacuating the gas medium through the forming wire, characterised by means for regulating and/or controlling the gas medium flows in the fiberization stage and by control devices for maintaining a predetermined pressure difference over the forming wire by controlling the suction devices (9) , for the purpose of creating an essentially wallless area for shaping the fibre dispersion cloud between the fiberization device and the forming area (8) . 7. An apparatus as claimed in claim 6, characterised in that the axis of at least one slinger wheel (6 - 6"') acting as a centrifugal fiberizer is hollow to allow part (4) of the gas flow of the fiberization stage to be di- rected via the said axis. 8. An apparatus as claimed in claims 6 or 7 , characteris¬ e in that the control devices for the gas medium flows comprise an enclosure (10) surrounding the fiberization equipment in a tunnel-like manner. 9. An apparatus as claimed in claim 8, characterised in that the cross-sectional form of the enclosure (10) has been adapted to guide the shaping of the fibre dispersion cloud to be formed. 10. An apparatus as claimed in claims 8 or 9, charact¬ erised in that the equipment includes a fan for achieving the adjustable stream of air (3) through the tunnel en¬ closure. 11. An apparatus as claimed in any of the claims 6 - 10, characterised in that the distance between the forming- base (8) and the slinger wheels (6 - 6 // ') is c. 0.2 - 1.0 times the width of the forming base, advantageously c. 0.3 - 0.6 times the width of the forming base.

Inventors: AOSTRAND ERIK, HOIKKA TIMO, NURMI TOM, WALLI BJARNE, AASTRAND, ERIK, HOIKKA, TIMO, NURMI, TOM, WALLI, BJARNE
Applicants: PAROC OY AB
Application year: 1993
Main classification: C03B37
IPC codes: C03B37, D04H1