[0001] The present invention relates to a melt overflow casting device and method, particularly a device and method for manufacturing a metal non-woven fibre mat.

Background to the Invention

[0002] Melt overflow casting is a type of rapid solidification in which a metal product, such as a thin, short fibre or a wide, continuous strip, is formed by cast ing molten metal against the outer, peripheral surface of a rotating, cylindrical casting wheel. The molten metal solidifies on the casting wheel, is carried out of the molten pool and projected off of the casting wheel onto a surface such as a conveyor. Fibres cast onto the conveyor become entangled, forming a continu ous non-woven mat. Melt extraction rapid solidification is taught in U.S. Patent Nos. 3,871 ,439 and 3,838,185, both to Maringer, et al. and melt overflow rapid solidification is taught in U.S. Patent Nos. 4,930,565 and Re 33,327 to Hack- man, et al. The dimensions of the fibre mat or strip formed by a melt overflow process are controlled by a number of variables. Examples of these variables are the height of the liquid metal interfacing against the casting wheel, the ve locity of the casting wheel and, especially for fibres, a large number of which are formed across the width of the casting wheel, the net width of fibres being pro duced. If a metal piece or slag solidifies in the molten pool near the casting wheel and blocks fibres from being produced in that region of the casting wheel, then the net width is reduced and fewer fibres will be projected from the casting wheel. The total number of fibres projected from the casting wheel per unit of time will decrease. The fibres are commonly projected onto a moving conveyor to form a mat, and fewer fibres being projected onto the conveyor per unit of time will result in a mat of lower density. Usually, the interfering piece of metal or slag which has solidified near the casting wheel and blocks the fibre from be ing produced is eliminated by scraping/dragging away, after which the mat will return to its normal density. However, the overall result of this variation in the number of fibres being projected per unit of time is a fibrous mat having a dis continuous linear density. [0003] To overcome the problem, there is a melt Over flow control system discussed in WO94/04296 (Ribbon Technology Corporation). In WO94/04296, the overflow of the molten metal is controlled by a ceramic plunger which is lowered into the molten metal. Sensors sensing the metal on the casting wheel are linked with the lowering mechanism via a control system to keep the amount of metal flowing onto the casting wheel consistent. However, even with these advances there are still irregularities in the fibre mat produced. The mats pro duced have inconsistently sized fibres and variable density across the width of the mat. [0004] Non-uniformities and observed inconsistencies in the distribution of fibres in continuous fibre networks are unwanted and problematic. They can significantly affect the mechanical integrity of continuous fibre mats and there are likely to be other consequences in terms of heat insulative and noise atten uation capability (depending on the application in which the fibre mats are used). The origin of non-uniformity in continuous fibre mats is currently un known.

[0005] There has now been devised a device and method which substantial ly overcomes and/or mitigates the above referenced and/or other disadvantages associated with the prior art. Summary of the Invention

[0006] In an aspect of the invention there is provided a melt overflow casting device comprising a rotatably driven casting wheel in fluid communication with a source of molten metal, the casting wheel being arranged proximal an opening in a first end of a chamber for receiving solidified metal fibres from the casting wheel, the chamber having an open lower portion comprising a conveyor onto which the fibres are laid down on in use to form a continuous fibre mat, the con veyor being configured for transporting the fibre mat out of the chamber in a di rection opposite the first end of the chamber, the casting device being charac terised in that there is a first nozzle and a second nozzle, the first and second nozzles both being directed inwardly of the chamber and both being in fluid communication with a separate blower configured to blow air into the chamber through the respective nozzle, wherein the first and second nozzles are each mounted to the chamber in the region proximal the opening in the first end by a two way pivot configured to allow the nozzles to pivot controllably about a re spective first axis and a second axis independently of one another, the first axis and second axis being at right angles with one another, and wherein the first and second nozzles are independently operable from one another.

[0007] In another aspect of the invention there is a method of manufacturing a continuous metal fibre mat comprising the steps of a) operating a rotatably driven casting wheel which is in fluid communica tion with a source of molten metal, the casting wheel being arranged proximal an opening in a first end of a chamber for receiving solidified metal fibres from the casting wheel, the casting device being characterised in that there is a first nozzle and a second nozzle, the first and second nozzles both being directed inwardly of the chamber and both being in fluid communication with a separate blower, wherein the first and second nozzles are each mounted to the chamber in the region proximal the opening in the first end by a two way pivot configured to allow the nozzles to pivot controllably about a respective first axis and a sec ond axis independently of one another, the first axis and second axis being at right angles with one another, and wherein the first and second nozzles are in dependently operable from one another. b) blowing air into the chamber through the respective nozzles, c) forming a continuous fibre mat by laying down the fibres onto a con veyor at an open lower portion of the chamber, and d) transporting the fibre mat out of the chamber.

[0008] The pivotability of the nozzles allows for directional control of the air being delivered into the chamber. It means that the first and second nozzle are each able to swing controllably within a first arc and a second arc, wherein the first and second arcs are at right angles with one another. Operating the re spective blowers to blow air through the first and second nozzles and into the chamber, blows the fibres around inside the chamber. The device and method of the invention are therefore advantageous primarily because they result in a metal fibre mat having inconsistently sized fibres. More importantly the con- sistency of the mat as a whole is greatly and surprisingly improved. In other words, the mat produced is uniform and homogenous across all of its dimen sions and therefore is devoid substantially of any inconsistencies in density, tangling or fibre dimensions. As a result of these advantages the temperature performance of the mat is greatly improved than that of the mat produced by the prior art methods, and uses less material in the manufacture. Furthermore, the mat attenuates a much greater range of sound frequencies than the mats pro duced by the prior art methods. So when the mat is used, say for example around exhausts, it can function as a much more efficient sound and thermal insulator than any previous mat.

[0009] Independently operable within the context of the invention means that the movement and/or rotational displacement of the first and second nozzles about their respective pivots is independent of one another. Independently op erable within the context of the invention also means that the air flow through the first and second nozzles as delivered by the respective blower is independ ent of one another. Thus the airflow through the respective nozzles may be the same or substantially different. Independent does not preclude equality.

[0010] Preferably the rotational displacement of the first and second nozzles about their respective pivots is fixedly adjustable. This allows for the angle of each of the nozzles to be fixed so that whilst air can be delivered into the cham ber from different directions it can be maintained in those directions in order to maintain a consistent fibre mat produced.

[0011] Preferably the rotational displacement ‘X’ of the first and second noz zles about their respective pivots is ± approximately 75 degrees, and the rota- tional displacement Ύ of the first and second nozzles about their respective pivots is ± approximately 75 degrees. More preferably the angle ‘X’ is between approximately +25 degrees and approximately -8 degrees and angle Ύ’ is be tween approximately +26 degrees and approximately -26 degrees.

[0012] Preferably the fibres have a length of approximately 100mm to approximately 300mm. This is preferable because the longer the fibres are the greater chance that they can hold neighbouring parts of the mat together. In other words it makes the mat less likely to break apart on folding during winding operations for future processing and means it can be wrapped easily around an object or inside a tube such as an exhaust for example. Preferably, the length of fibres within the mat are different. This is advantageous as the different lengths attenuate noise at different frequencies, and therefore the overall effect is a mat with a broad range of noise attenuation capabilities. This can therefore reduce the overall weight over conventional fibre mats.

[0013] Preferably the fibres have a diameter of between approximately 40pm and approximately 120 pm. This is advantageous because this dimension has been found to improve durability and temperature capability of the fibres and therefore the mat.

[0014] Examples of suitable metals include but are not limited to aluminium, nickel based alloys, alloy steels, and copper alloys. Preferably the metal fibres are stainless steel. This is because of the anticorrosive features and durability of stainless steel and its strength. Due to its ability to form fibres consistently and surface tension when molten, it is suited to the invention.

[0015] The device may be contained within an inert atmosphere. And similar ly the method of the invention may be carried out in an inert atmosphere. This is so that fibre mats manufactured from alloys susceptible to oxidation can be manufactured in a similar way and without corrosion occurring by exposure to air or moisture. This allows the possibly for making Iron Chromium alloys, nickel based alloys and copper based alloys.

[0016] The casting wheel is cooled preferably with water as it is rotated. Other cooling methods may be used such as cooling blasts of air or other liq- uids. This has the effect of cooling the metal very fast after it leaves the casting wheel. Preferably the metal is cooled after it leaves the casting wheel at an ini tial rate of approximately 1000000°C/s. This is beneficial in that it is then possi ble to produce very fine grained, homogenous metal fibre structures or in the case of some materials an amorphous structure. This super-cooling also allows the possibility of adding alloy additions to much higher levels in order to en- hance physical and mechanical properties that would otherwise not be possible using conventional casting methods.

[0017] The device of the invention may comprise one or more further noz zles mounted to an upper portion of the chamber and directed downwardly into the interior of the chamber. This helps prevent fibres collecting at the top of the chamber or blowing out of the top of the chamber. The one or more further air nozzles are preferably in communication with their own separate blower, to en able air to be blown into the chamber independently of all the other nozzles, in cluding the first and second nozzles. [0018] The chamber may be open at its top or have one or more openings at its top. This is to prevent the temperature inside the chamber from increasing too much and affecting the operation of the conveyor. In instances where the materials of the device can be made temperature stable, the chamber may be closed at its top, as this helps to improve the consistency of the mat. Brief Description of the Drawings

[0019] The invention will now be described by way of example and/or illus tration only with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an embodiment of the device according to the invention. Figure 2 is a perspective view of the underside of the chamber as shown in Figure 1.

Figure 3A is a view of the nozzles as shown in Figure 1 from above,

Figure 3B is a view of the nozzles as shown in Figure 1 and 3A from the side; and Figure 4 shows a set of photographs of the mat produced by the prior art device and that produced by the device shown in Figure 1 using an embodiment of the method of the invention.

Detailed Description of the Illustrated Embodiment

[0020] Figure 1 illustrates an embodiment of the melt overflow casting device according to the invention. The device is generally designated 1 and includes a cylindrical casting wheel 10 that is rotatably driven by, for example, a variable speed electric motor 12. A hearth or crucible 14 is also included in the melt overflow apparatus and has four walls and a bottom. One wall 15 of the hearth 14 has a portion with a top edge that is lower than the other walls. The hearth 14 is filled with molten metal 16 and the wall 15 is placed very near the outer circumferential surface of the casting wheel 10. A height control means, prefer ably a ceramic plunging melt displacement means 18 for displacing molten metal 16, is submerged into the molten metal 16 by a suitable driving means 19 causing the molten metal 16 to initially rise and overflow over the top edge of the wall 15, and then maintain a constant level during steady state operation.

[0021] The device 1 also includes a chamber 20. The chamber 20 is a steel enclosure having a first end wall 21 , an opposite second end wall 22, two oppo site sides 23, 24 and a roof 25 which connects the walls 21, 22, 23 and 24 to gether. The chamber 20 is open at its base (shown as Ό’ in Figure 2), but has mounted thereto a conveyor 26. Whilst the side walls 23, 24 and second end wall 22 are vertical in orientation and the roof 25 is horizontal in orientation (i.e. at right angles to the side walls) and the first end wall 21 is sloped from the ver tical. The conveyor 26 is approximately 2.5 cm from the bottom of either side

23, 24. The roof 25 is provided with a number of openings in order to let heat escape during use. In another embodiment the roof 25 is completely open.

[0022] The dimensions of the chamber 20 are variable depending on the di mensions of the mat being required to manufacture. In this example the length of the chamber 20 is approximately 6 m. The height of the chamber 20 is ap proximately 1.5 m and the width is approximately 20 cm. In other examples the device is substantially the same except that the chamber 20 could be made wider or thinner depending on the width of the fibre mat to be produced. A spout 27 is connected to the lower portion of the first end wall 21 , i.e. the portion of the first end wall 21 closest to the open base. The spout 27 is a small piece of steel having a “U” cross section. One end of the spout 27 is connected to both the lower portion of the first end wall 21 , and the lower portion of the sides 23,

24. The back side of the spout 27 is open as shown on Figure 2. The opposite end of the spout 27 is open and thus provides a first opening to the chamber 20. The open end of the spout 27 is arranged proximal the circumference of the casting wheel 10 on the opposite side of the casting wheel 10 to that of the cru cible 14. The spout is arranged tangentially with the casting wheel 10, in a posi tion able to receive the molten metal 16 as it is projected off the casting wheel 10 in an upwards direction. [0023] The conveyor 26 is a belt conveyor running from one end of the chamber 20 to the other. The conveyor 26 is driven by a motor (not shown) and configured to transport fibre mat 40 from the region of the first end 21 of the chamber 20 to the second end 22, where the conveyor extends out of the chamber 20. The conveyor 26 is driven by a motor (not shown). Any gas within the chamber 20 can escape through the opening at the base where the convey or 26 is as it is not sealed in an air tight manner with the remainder of the chamber 20. Density of the mat laid down on the conveyor 26 is measured us ing an optical sensor device and software for interpretation.

[0024] The chamber 20 has a first air nozzle 31 and a second air nozzle 32. Both air nozzles 31 , 32 are mounted at a single opening (not shown and sepa rate to the spout 27) in the chamber 20. The opening is at the interface between the spout 27 and the first end 21 of the chamber 20.

[0025] Each air nozzle 31 , 32 is tubular with a rectangular shape cross sec tion and having one open end 31a, 32a which is in fluid communication with the interior of the chamber 20 and an opposite end 31 b, 32b external of the cham ber which is connected to a respective blower 33a, 33b and in fluid communica tion therewith. Each of the open ends 31a, 32a are at right angles to the re mainder of the respective main tubular part of the nozzle 31 , 32. Ends 31 b, 32b are shown circular in Figure 1 which is for ease of connection to a round pipe for communication with the blower, but otherwise the ends 31b, 32b may be square or rectangular in cross section. In other words - dependent on the shape of the pipe to which they are connected.

[0026] Both air nozzles 31 , 32 are mounted side by side one another at the opening formed in the chamber 20, as shown more clearly in figure 3A, which shows an overhead view of the mounting of the air nozzles within the chamber. Figure 3B shows a view from the left of the chamber. [0027] To enable the mounting of the air nozzles 31 , 32 to the chamber, mounted to the underside of each open end 31a, 32a is a two way pivot (p) which pivotally connects the respective nozzle 31 , 32 to the chamber. Each piv ot (p) is a hinged joint which allows the respective nozzle 31 , 32 to rotate about an axis (y-y) running parallel with the side wall 23 of the chamber 20 and at right angles with the conveyor 26, and an axis (x-x) running at right angles to the side wall 23 of the chamber 20 and parallel with the conveyor 26. Both axis y-y and x-x run through the pivot P. Each of the pivots are controlled by computer con trolled actuators in order to mechanically move each of the nozzles 31 , 32, in dependently of on another.

[0028] Each air nozzle 31 , 32 can therefore swing in a first arc (indicated by the dotted lines in figure 3a and solid arrows) about the pivot P and axis y-y, and in a second arc (indicated by the dotted lines in figure 3b and solid arrows) about the pivot P and axis x-x. The axis x-x is at right angles to the axis y-y and therefore the first arc and the second arc are at right angles to one another.

[0029] The angle of displacement (X) of each air nozzle 31 , 32 within the first arc is measured by the angle which forms between the opening to the chamber in the front wall 21 where the nozzles 21 , 32 are mounted and the open end 31a, 32a. In the example shown the angle X can be anything from +25 degrees to -8 degrees. In other examples, the device 1 is substantially as described but the dimensions of the respective nozzles 31, 32 are different to that described herein, therefore the angle X can be anywhere up to approximately ± 75 de grees.

[0030] The angle of displacement (Y) of each air nozzle 31 , 32 within the second arc is measured by the angle which forms between the open end 31a, 32a and the right angle of the conveyor 26. In the example shown the angle Y can be anything from +26 degrees to -26 degrees. In other examples, the de vice 1 is substantially as described but the dimensions of the respective nozzles 31 , 32 are different to that described herein, therefore the angle Y can be any where up to approximately ± 75 degrees. - IQ -

10031] A third nozzle 34 is mounted to the roof 25 of the chamber 20. The nozzle 34 is substantially the same as nozzle 31 or nozzle 32, but is only pivot able about the x-x pivot to give an angle Y which is the angle between the front face of the open end and the roof 26. Nozzle 34 is directed downwardly into the interior of the chamber 20 and slightly rearwards towards the end 22 of the chamber. In fact the nozzle 34 forms an angle of 86 degrees between it and the roof of the chamber. This is to keep the airborne fibres progressing towards the rear of the chamber (second end wall 22) and to improve consistency of the re sultant mat. Nozzle 34 is connected to its own separate blower 33c. In use the blower 33c blows air through the nozzle 34 and into the chamber. This air pre vents the fibres which are present within the chamber from blowing out of the roof and further helps to create and maintain a turbulent flow of fibres within the chamber in use.

[0032] In use, molten metal 16 within the crucible is pulled off the melt me- niscus and projected up the entry spout 27. The height control means, in the preferred embodiment comprising the plunging melt displacement mechanism 18 and the driving means 19, may alternatively be a tilting hearth which tilts to ward the casting wheel 10 in order to cause the molten metal 16 to overflow on to the casting wheel 10. Control of the tilting rate of the hearth controls the height of the molten metal 16. The tilting hearth requires a drive means which would be a substitute for the drive means 19.

[0033] The fibres are ‘catapulted’ by the wheel 10 into the chamber 20 via the spout 27 as described as part of the melt-overflow process. The blowers 33a and 33b are operated and these then blast air into the chamber 20 through the air nozzles 31 , 32.

[0034] The respective blower 33a, 33b, 33c blows air through the air nozzles 31 , 32, 34 and into the chamber 20. The flow rate of the air leaving each of the air nozzles 31 , 32 into the chamber 20 is approximately 160m/s. The flow rate of the air leaving the air nozzle 34 into the chamber 20 is approximately 22 m/s. The pivotability of each of the air nozzles 31 , 32 allows for directional control of the air being blown into the chamber by the above referenced computer con- trolled actuators. The incoming fibres are thought to be caused to mix homoge nously with each other by the action of the air from the air nozzles 31 , 32, 34. The (gauge) pressure in the air nozzles 31 , 32 is approximately 46 inches of water or more which is equal to a (gauge) pressure of approximately 11.46 kPa or more. The fibres are then free to move around within the chamber 20 (via their interactions with the flow field and the chamber 20 walls, and via fibre-fibre interactions). The fibres eventually deposit on the moving belt conveyor 26 as a continuous non-woven fibre mat 40 at the base of the chamber 20 around about the mid part of the chamber 20. It is postulated that the positioning and angle and direction of the air nozzles 31 , 32 is such that a turbulent air flow is created within the chamber 20. This is thought to cause the fibres to mix evenly. This has the result that when the fibres are eventually deposited on the conveyor 26 as a continuous non-woven mat 40, the mat 40 has a much improved degree of homogeneity over that for the mats produced by the prior art techniques. Alt- hough the mechanism of action of the invention is likely to be a combination of factors. This is no way limits what is understood to be the mechanism of action of the invention. The conveyor 26 then transports the mat 40 of fibres in contin uous line out of the chamber 20 where the length of mat 40 is collected onto a spool (not shown). [0035] Two samples of mat were compared, one manufactured using the prior art process as described in WO9404296 and one 40 using the device and method of the invention as described above. Photographic evidence is provid ed showing the difference in the two mat samples in figure 4. Figure 4A and B shows the mat produced using the method substantially as described in WO9404296. Figure 4C and D shows the mat 40 produced using the device and method of the present invention. It can be seen that the mat in Figure 4C and D is more consistent in overall density across its width and length. There are none of the patches of less dense fibre matting as shown in Figure 4A and labelled P. Also there is a more defined boundary at the edge of the mat, which means that wrapping or coiling of the mat will be easier and more consistent.

[0036] Further experiments were conducted to investigate the effect of dis placement angles x and y on the formation of the fibre mat 40. Various different displacement angles were set for the nozzles 31 , 32 and the resultant mat ana lysed quantitatively for density and qualitatively for appearance. The results are shown below in Table 1 .

Table 1 : Results of experimentation to show effect of different X and Y angles on mat production (values for X and Y are provided as percentages of

32.659 and 23.749 respectively) [0037] The results showed that roll 10 and roll 15 produced the best visual results. Even though the density was not the highest it was the most consistent along its overall length and when it comes round to noise or heat attenuation, consistency is the most important factor.