Patent Application
20170209918
Melt spinning is a technique used for the rapid cooling of liquids. A wheel may be cooled internally, usually by water or liquid nitrogen, and rotated. A thin stream of liquid is then dripped onto the wheel and cooled, causing rapid solidification. This technique is used to develop materials that require extremely high cooling rates in order to form elongate fibres of materials such as metals or metallic glasses. The cooling rates achievable by melt-spinning are of the order of 104-107 kelvin per second (K/s).
The first proposals for melt spinning originated with Robert Pond in a series of related patents from 1958-1961 (U.S. Pat. Nos. 2,825,108, 2,910,744, and 2,976,590). In U.S. Pat. Nos. 2,825,198 and 2,910,724 a molten metal is ejected through a nozzle under pressure onto a rotating smooth concave surface of a chill block. By varying the surface speed of the chill block and the ejection conditions it is said to be possible to form metal filaments with a minimum cross sectional dimension of 1 μm to 4 μm and lengths from 1 μm to infinity. In U.S. Pat. No. 2,824,198 a single chill block is used, in U.S. Pat. No. 2,910,724 a plurality of nozzles direct flows of metal onto one rotating chill block or a plurality of rotating chill blocks and associated nozzles are provided. In U.S. Pat. No. 2,910,724 no chill block is provided instead the molten metal is ejected downwardly through nozzles into a vertically disposed cooled chamber containing solid carbon dioxide on ledges provided at the side wall of the chamber. By varying the cross sectional shape of the nozzles the cross-sectional shape of the filaments produced can be varied.
The current concept of the melt spinner was outlined by Pond and Maddin in 1969. Although, liquid was, at first, quenched on the inner surface of a drum. Liebermann and Graham further developed the process as a continuous casting technique by 1976, this time on the drum's outer surface.
The process can continuously produce thin ribbons of material, with sheets several inches in width being commercially available.
References to this process can be found in the following publications:
The melt spinning process has hitherto not been used for the commercial manufacture of micron scale metallic ribbons and fibres on an industrial scale.
In this connection it should be noted that a fibre can be understood as an element of which the length is at least twice its width.
Metal fibre reinforced composite materials play a central role in a whole series of applications for the improvement of the most divers properties. Examples of such applications are:
An important aspect for the improvement of fibre based material functions is a large surface area to weight ratio of the meta fibres and the ability to manufacture and process them in an industrially relevant process. This signifies:
Nowadays, the industrially relevant manufacture of functional materials based on metal fibres is restricted to fiber thicknesses of >50 μm. Academic processes exist based on lithographic techniques, glass based template methods and mechanical extrusion process which enable metallic fibres of <50 μm to be achieved. These methods cannot however be utilized industrially because they are restricted to a few materials and in some cases are not repeatable.
The invention described here permits the manufacture of metallic fibres having a width and thickness significantly less than 1 mm, ideally in the range between 1 and 100 μm and an aspect ratio of length to width of greater than 2:1, ideally greater than 10 to 1. Metallic fibres of a size greater than 50 μm are normally produced industrially by a drawing, rolling or extrusion process. Wires with diameters under 50 μm are normally manufactured individually by a mechanically complicated drawing process from a wire of larger diameter to a smaller diameter.
Smaller diameters have hitherto not been realized on a large scale technically by precipitation from the melt. The reason is to be found in the normally very high surface energy and very low viscosity of metallic melts.
The high surface energy and the low viscosity of metallic wires results in a constriction of a metallic jet and the formation of droplets. The wetting of a capillary likewise makes the “spraying” of wires of small diameter difficult as a result of the large capillary forces. Mathematically the droplet formation is described by the Young-Laplace equation.
In contrast to metallic melts, polymer melts can be spun industrially to a diameter of a few tens of nanometers and an aspect ratio of several thousand as a result of the lower surface energy and the significantly higher viscosity of the polymer melt.
The present invention describes an apparatus and a method which enables the manufacture of metallic strands with a width and thickness smaller than 50 μm by a melt spinning method by exploiting the properties of metallic melts, i.e. high surface energy and low viscosity. One particular object of the present invention is to provide a method and an apparatus for manufacturing metal strands which results in a high yield of desired fibres (strands) having a relatively tight distribution of lengths, widths and thicknesses so that a relatively homogenous product is achieved.
In order to satisfy this object there is provided, in accordance with the present invention, an apparatus for producing elongate strands of metal, the apparatus comprising a rotatable wheel having a circumferential surface, the circumferential surface having circumferentially extending edges and recesses formed between or bounded by the edges, at least one nozzle having a nozzle opening for directing a molten metal onto the circumferential surface and a collection means for collecting solidified strands of metal formed on the circumferential surface from the molten metal and separated from the circumferential surface by centrifugal force generated by rotation of the wheel, the apparatus being characterized in that the nozzle (N) has a rectangular cross-section having a width (W) of the nozzle opening in the circumferential direction (C) of rotation of the wheel (B) and a length transverse to the circumferential surface of the wheel which is greater than the width W, and in that an apparatus is provided for controlling a gas pressure applied to the liquid metal which moves the liquid metal through the nozzle opening and delivers it to the circumferential surface of the rotatable wheel.
Also according to the present invention there is provided a wheel having a structured circumferential surface with circumferentially extending edges and recesses formed between or bounded by the edges and adapted for use in the above recited apparatus. The present invention also relates to a method A method for producing elongate strands of metal optionally having at least one transverse dimension of 50 μm or less and a length at least ten times greater than said at least one transverse dimension, the method comprising the steps of directing a molten metal through a nozzle having a rectangular cross-section with a width of the nozzle opening in the circumferential direction of rotation of the wheel and a length transverse to the circumferential surface of the wheel which is greater than the width onto the circumferential surface of a rotating wheel, by applying a gas pressure to the liquid metal to move it through the nozzle opening and deliver it to the circumferential surface of the rotatable wheel, providing the circumferential surface of the rotatable wheel with circumferentially extending edges and recesses formed between or bounded by the edges and collecting solidified strands of metal formed on the circumferential surface from the molten metal and separated from the circumferential surface by centrifugal force generated by rotation of the wheel, the method further comprising the steps of controlling the width of the nozzle opening, controlling thea a gas pressure applied to the liquid metal to move it through the nozzle opening and deliver it to the circumferential surface of the rotatable wheel and controlling the speed of rotation of the wheel to reduce the flow of molten metal onto the circumferential surface of the wheel per unit of time, in a metal dependent manner, to a level at which it is concentrated by the forces that are acting at the said circumferentially extending edges formed between or bounded by the edges and using these edges to concentrate the molten metal at the edges produce the desired elongate strands of metal.
The present invention is thus based on the recognition that the high surface energy of a molten metal brings about a strong capillary effect at boundary surfaces and in particular at edges or corners of substrates, for example in corners wetted by metallic melts. The structuring of the circumferential surface of the rotating wheel leads to such edges and recesses and the capillary forces thus favor the concentration of the molten metal along such edges and recesses which results in the widths and thicknesses of the strands being constrained to lie within relatively close limits so that a uniform product is achieved. Moreover, the uniformity of the thickness and width of the metal strands means that the length of strand produced prior to separation form the wheel and from the following strand due to the action of centrifugal force is also more uniform, which is again more favorable for the production of a uniform metal strand product.
Using the above apparatus and method it has proved possible in laboratory experiments to manufacture metallic microfibers (strands or ribbons) with a width of <10 μm (median) directly from a metallic melt of Al, Zinc, Pb, stainless steel or Fe40Ni40B20 by means of an industrially relevant melt spinning process as will be described later in more detail with reference to the specific description of the figures. In this way the surface area to weight ratio of these microfibers is already 400 times better than the previous industrially utilised metal fibres! The manufacture of metallic fibres with widths and thicknesses <1 μm is considered practical.
The physical principle of this metal fibre production process is based on the separation of a metal melt in thin films on a solid substrate. In theory two possible mechanisms have been discussed for the breaking up of a liquid film on a solid substrate:
(i) The heterogenous nucleation of holes as a result of defects in liquid films H. S. Kheshgi and L. E. Scriven, Chem. Eng. Sci. 46, 519 (1991). These defects can, for example, be provoked by topographies in the substrate and organized laterally to the substrate surface.
(ii) The spontaneous breaking up of a liquid film under the influence of long range forces, known as spinodal dewetting (see E. Ruckenstein and R. K. Jain, J. Chem. Soc. Faraday Trans. II 70, 132 (1974).
In the method proposed here both mechanisms are exploited. In this connection use is made of the established process of melt spinning. Traditionally amorphous metals in the form of macroscopic bands are produced. In the present invention the melt spinning process is modified in the following ways:
The surface topography of the wheel, the forces which arise due to surface tension and in particular the high centrifugal forces bring about the control of the de-wetting laterally of the wheel surface and perpendicular to the axis of rotation. Different process parameters result in different thicknesses and thickness distributions of the metal fibres. In this connection the reduction of the deposition rate of the metallic melt onto the wheel by a smaller nozzle width, by an appropriate applied pressure to expel the metal melt from the crucible and an increase in the peed of rotation of the wheel lead to a significant reduction of the fibre thickness.
The width of the nozzle opening can lie in the range from 1 mm to 10 μm, preferably in the range from 400 μm to 10 μm especially 200 μm to 10 μm and most preferably from 100 μm to 10 μm. The smaller the outlet width of the nozzle the finer are the fibres produced.
The circumferential recesses defining the edges have a radial depth greater than 50 μm and preferably in the range from 50 μm to 1000 μm.
The circumferential recesses defining the edges have a width in the range from 1000 μm to 50 μm and especially in the range from 1000 μm to 100 μm. Most preferred is when the wheel has a profile with a structure size greater than 100 μm, i.e. the depth of the grooves, the width of the grooves and the width of any lands between the grooves should all be greater than 100 μm.
At this point reference should also be made to EP-A-1 146 524 and Japanese patent application JP-A-09271909. EP-A-1 146 524 is directed to the manufacture of magnetic ribbon by the melt spin process. For good magnetic material oxidation must be prevented. For this reason the process is operated under inert gas. This inert gas disturbs the process of making uniform layer thicknesses, which are in turn important for the magnetic properties of the material. It is important to note that EP-A-1 146 524 discloses a nozzle with a circular orifice. The EP document utilizes a technique by which the gas is directed away from the ribbon on the roll. For this purpose grooves are provided on the wheel. The generally circumferential grooves have an average depth in the range 0.5 to 20 μm and an average pitch of 0.5 to 100 μm. The ribbons produced have average thicknesses between 8 and 50 μm and are clearly elongate because 5 cm samples are taken and subsequently milled to form magnetic powder. No real information is given on the width of the ribbons. JP-A-09271909 discloses a similar concept for removing air from the forming ribbon, but here the grooves are arranged in chevron form (V form) on the surface of the wheel. So far as can be seen there is no discussion in either of these patent specifications that the ribbons should be constrained laterally (widthwise) nor any suggestion as to how this can be done. In both documents (JP-A-09271909 and EP-A-1 146 524) the inventors are concerned with recesses in the surface of the wheel to lead gas away from the wheel surface and the metal and to increase the contact area between the wheel surface and the metal (EP-A-1 146 524 [0043-0044, 0046] and JP-A-09271909 [0003]). EP-A-1 146 524 explicitly states that the grooves should have a depth of 0.5 to 20 μm, more preferably 1 to 10 μm, and that if the depth of the groove is increased huge dimples result. This is a clear indiction to the person skilled in the art that he should not increase the groove depth beyond the value quoted.
In contrast to the production of relatively wide ribbons the present invention is concerned with narrow fibres having relatively accurately and uniformly reproducible thicknesses and width, the thicknesses and widths of at least a high proportion of the fibres each lying in the range between 50 and 1 μm. That this can be achieved can be seen from the median values and the standard deviation values entered in
Neither EP-A-1 146 524 nor JP-A-09271909 describes a lateral restriction of the ribbons produced there. Neither reference suggests that recesses could be exploited to generate a lateral constriction of the ribbons, so that fibres are formed. Both references show relatively wide ribbons with a width much greater than their thickness, see EP-A-1 146 524, FIG. 1 and JP-A-09271909, FIG. 2a).
EP-A-1 146 524 admittedly gives no accurate value for the width of the ribbons, however one can conclude from FIGS. 1 and [0098] that the ribbons are very much wider than they are thick. As the thickness of the ribbons lies between 8 and 50 μm, the reference contains no suggestion for the skilled person that he should produce lateral constriction of the ribbons in the preferred range of 3 to 25 μm. Furthermore, the FIGS. 12 and 15 of EP-A-1 146 524 show embodiments which are in no way suited for a lateral restriction of the ribbons. The apertured surface structure in FIG. 15 is described in paragraph [0155] in such a way that it functions just as well as the other structured surfaces shown in the EP document, which actually leads the person averagely skilled in the art away from providing circumferential grooves for the purpose of lateral constrainment.
JP-A-09271909 describes similar art to EP-A-1 146 524 and shows in
In both documents the manufacture of the powdery magnetic particles is based on a comminution process which follows the melt spinning process. This has nothing to do with the melt spinning process itself. It is a completely different application of the melt spinning process and the prior art references are simply not concerned with the preparation of fibres to which the present application is directed.
EP-A-0 227 837 describes the coiling of a wire which is created by extrusion through a nozzle in a melt spinning apparatus. The wheel is not structured and thus this reference is irrelevant for the claimed process:
The US reissue patent Re_33,327 relates to a special construction of the container from which molten metal is drawn by the rotatable wheel from the surface layer of the molten material in the container. I.e. the molten material is not dropped or ejected under pressure through an orifice onto the wheel (as is the case in the present invention), which is described as disadvantageous in the reissue reference. The grooves formed on the surface of the wheel are said to have a pitch in the range from 22 to 40 per inch corresponding to a groove pitch in the range from approximately 1100 μm to 630 μm.
The Liebermann reference “Liebermann h. h. et al Production of amorphous alloy ribbons and effects of apparatus parameters on ribbon dimensions XR002736061, November 1996” relates to the production of bands as opposed to fibres.
The structured circumferential surface of the wheel may also comprise peripherally (circumferentially) extending lands, each land being disposed between two circumferentially extending recesses. The presence of such lands forms a reservoir of melt material between the circumferentially extending edges and this material can be concentrated into the metal strands by the capillary action generated at the edges. Thus the presence of the lands and their width can be selected to influence the width of the metal strands that are produced. The lands typically have widths of I mm or less. The lands also provide surface area for additional heat removal from the molten metal and can thus also influence the size of the strands produced, since the size does not change after solidification has taken place.
The cross-sectional shape of the recesses does not appear to be critical. Thus the recesses can have a cross-sectional shape selected from the group comprising semi-circular, symmetrically v-shaped, asymmetrically v-shaped, rectangular and trapezoidal. The volume of the recesses is, however, another important criteria determining the width and thickness of the metal strands that are produced.
The metal strands typically have the form of ribbons having a thickness of 10 μm or less and a width of 200 μm or less.
Generally speaking the metal strands typically have at least one transverse dimension of 50 μm or less and a length at least ten times greater than said at least one transverse dimension.
For the sake of completeness reference should also be made to two further prior art documents:
DE3443620 describes a method of making a round wire by a melt spinning process. In that method the circumferential surface of a rotatable wheel is provided with a groove extending in the direction of rotation and a plurality of nozzles aligned in series along the groove are used to deposit molten metal into the groove as the wheel rotates. With a surface speed of 25 m/sec a wire of oval cross section with a major diameter of 1 mm and a minor diameter of 0.7 mm is produced and is subsequently drawn to a round wire of 0.5 mm diameter. This document does not disclose the function of utilizing the edges formed by the groove to separate a stream of molten metal into thin strands or ribbons of material by appropriate choice of the operating parameters such as the surface speed of the wheel.
U.S. Pat. No. 6,622,777 describes a way of making metal fibres by “dropping a metal plate vertically onto the blades of a rotary disc thereby extracting metal fibre therefrom”. The metal plate passes through a pair of induction coils which has a melting function but there is no description of molten metal being dispensed onto the blades of the rotary disc. The structure and dimension of the blades are not indicated in the above mentioned patent. The authors of the reference use the blades for “cutting” metal out of a metal plate. The reference does not discuss the use of a nozzle of defined geometry which is an important feature of the present invention, nor does it discuss the use of a profiled circumferential surface having a defined structure or geometry, another important feature of the present invention. Also there is no discussion of the metal plate being completely melted. In contrast, the melting of the metal upstream of a nozzle is another important feature of the invention as it allows a controlled gas pressure to dispense the molten metal through a nozzle of defined geometry, which is not present in the reference. The nozzle geometry and amount of pressure applied to the liquid metal regulates (controls) the amount of liquid metal material which passes through the nozzle and hits the rotating wheel. This control is critical for obtaining small fibre width dimensions and controlling the geometry as well as the distribution of geometry dimensions (small distribution!) Certainly it is not clear that the referenced operates with liquid metal. Although the word “melt” is used it seems to be more important for the authors of the reference that a solid metal plate is in contact with the blade, although the end of the plate might be in a melted or softened state. The reference also does not disclose the inventive concept of separating the solid metal from the liquid metal.
The reference does not disclose the concept of dispensing a drop of molten metal and does not provide any way of controlling the volume of metal brought into contact with the rotating blade. There certainly does not seem to be any disclosure of the controlling of the amount of metal deposited on the blades. In addition there is no suggestion in the reference that edge effects be used to generate metal ribbons. Equally there is no disclosure of the use of appropriate wheel speeds to ensure the specific metal being used is separated into ribbons of the desired size. This is again an important element of the present invention, namely that the wheel speed is selected in dependence on the nozzle size, the gas pressure and the specific metal being converted into ribbons of the desired size
The rotatable wheel is usefully temperature controlled and preferably cooled e.g. to a temperature in the range of −100° C. to +200° C. Controlling the temperature of the wheel permits the solidification rate of the molten material to be controlled and this again favors the manufacture of uniform metal strands.
The wheel is expediently made of a metal, for example copper or aluminium, or of a metal alloy or of a ceramic material or of carbon such as graphite. Also layers of one of these materials on a base wheel are possible such as carbon evaporated layers on a copper base wheel. Such materials have good thermal conductivity which again favors the solidification process.
If desired the structure of the circumferential surface of the wheel can be made by lithographic technique which can enable sharp structures of small dimensions to be made more easily than by milling or turning.
The wheel is conveniently mounted to rotate within a chamber having an atmosphere at a pressure corresponding to the ambient atmospheric pressure, or to a lower pressure than ambient pressure or to a higher pressure than ambient pressure. The atmosphere in the chamber affects the formation of the solidified metal strands and can be used to fine tune the geometry of the metal strands that are produced. For metals which react with the constituents of air it can be favorable to use an inert gas atmosphere in the chamber. Also, under some circumstances a reactive gas atmosphere could be beneficial, for example a nitrogen or carbon containing atmosphere could be used to nitride or carburize suitable steel materials if hardened metal strands are desired. A deflector such as a scraper blade or doctor blade can optionally be provided upstream of the nozzle in the direction of rotation of the wheel to deflect boundary air from the circumferentially extending surface prior to depositing molten metal on the surface via the nozzle. Such a deflector, which only needs to have a minimum spacing from the circumferential surface of the wheel to avoid damaging the structure thereof (and the function of which can also be provided by the nozzle if this is positioned close to the circumferential surface of the wheel), can prevent the boundary air carried along with the wheel from undesirably affecting the flow of molten metal from the nozzle onto the circumferential surface, for example thereby reducing cooling of the metal material prior to it reaching the surface of the wheel.
Generally speaking a gas pressure is applied to the molten metal to force it through the nozzle. Such a gas pressure is generally necessary because the high surface tension/energy of the molten metal will inhibit its flow through a small nozzle. The additional gas pressure (additional to the weight of the molten metal) causes the molten metal to flow through the nozzle. When reference is made here to the pressure applied to the molten metal the pressures recited will be understood to be the amount by which the pressure is higher than the pressure prevailing in the chamber of the apparatus, which is frequently kept below atmospheric pressure, e.g. at 400 mbar. The expression delta P or ΔP refers to the pressure difference between the pressure operating on the molten metal in the crucible and the internal pressure in the chamber.
The gas pressure is typically selected in the range from 50 mbar to 1 bar overpressure relative to the pressure external to the nozzle. The gas pressure regulates the deposition rate of molten metal onto the rotating wheel. This parameter controls the dimension of the metal ribbon as well.
The nozzle expediently has a rectangular cross-section having a width in the circumferential direction of rotation of the wheel of less than 1 mm. The length direction of the nozzle is oriented perpendicular to the direction of rotation of the circumferential surface of the wheel.
An electric motor is conveniently used to drive the wheel at a frequency up to 95 Hz for a wheel having a diameter of 200 mm, i.e. more generally at circumferential speeds of up to and above 60 m/s.
The circumferential surface of the wheel may have transversely extending features to control the length of the strands produced. Such features could for example comprise a number of transverse, regularly spaced, grooves interrupting the circumferentially extending edges and recesses at the circumferential surface of the wheel.
The material of the wheel is selected so that it does not readily bond to the molten metal, for example a wheel of copper can be used for Fe40Ni40B20 alloy, aluminum, or lead.
In the melt spinning process of the invention one applies the metallic melt through the opening of a crucible onto a very quickly rotating metallic wheel. The wheel normally consists of copper and can be well cooled. In particular one can exploit the particularly strong capillary forces of metallic melts for the manufacture of strands of smaller diameter. One does not use a smooth spinning wheel but rather a melt spinning wheel, which is structured with elongate circumferentially extending grooves (recesses). If now the quantity of metallic melt incident on the rotating wheel is reduced to the extent that only one recess or a few recesses, and/or the land or lands between adjacent recesses are wetted then one obtains a lateral braking up of the planar metallic (liquid) film as a result of the recesses formed in the wheel and the capillary forces that are acting. To a first approximation the lateral dimension of the resulting strand reflects the lateral dimension of the structuring of the wheel. However, a further reduction of the quantity of melt which strikes the wheel per unit of time results in the amalgamation or collection of the quantity of metallic melt at a corner or an edge of the structure on the wheel as a result of the capillary forces that are acting. Thus the melt deposits along a corner such as an edge of a recess of the wheel or along the base of a recess in the wheel. This makes it possible to obtain very much smaller geometries of the strands than might be expected from the dimensions of the actual structuring of the wheel. Thus, with a lateral structure size of 1 mm it is possible to obtain a ribbon of 0.4 mm width. The deposition rate of the metallic melt on the copper wheel and the structuring of the wheel are thus of decisive importance for the invention. The deposition rate of the metallic melt can be controlled by the speed of rotation of the wheel, by the size of the opening of the crucible and by the pressure with which the melt is pressed through the opening of the crucible. As the length of the nozzle opening transverse to the structured circumferential surface of the wheel extends typically over a plurality of grooves and or lands plural stands can be formed at any one time due to the lateral breaking up of the molten metal on the circumferentially structured surface of the wheel. Reducing the width of the nozzle in the circumferential direction of the wheel reduces the amount of metal forming each strand per unit of time and thus results in the strands becoming finer, i.e. having a reduced transverse dimension or dimensions.
The structure on the wheel can generally be produced by a technical turning operation such as on a lathe, by milling or by laser ablation. The abrupt solidification of the metallic melt and the high centrifugal forces resulting from the rotation of the wheel lead to the capillary forces becoming unimportant and thus to the wire that is forming being flung away from the wheel, so that it can then be collected in a known collection device. After the solidification of the melt the metal normally forms no droplets and the wire can now be further processed, e.g. worked into a textile fleece or felt. Thus the melt spinning method can be combined with a method of manufacturing textiles.
Preferred embodiments of the invention are set forth in the subordinate claims.
The invention will now be described in further detail and by way of example only with reference to the accompanying drawings and various examples of the method of the invention. In the drawings there are shown:
Turning now to the schematic drawing of the melt spinning process shown in
The pressure P applied to the molten metal can also be used to change the flow rate. Clearly a relatively large pressure leads to a higher flow rate than a relatively lower pressure. A minimum pressure P is always required in order to force the molten metal through the nozzle N, as gravity alone is not normally sufficient to ensure adequate flow, particularly with a relatively small width W of the nozzle opening. In fact this is advantageous because otherwise some form of valve would be necessary and a valve for regulating the flow of molten metal is technically challenging. It should be noted that the pressure difference ΔP is dependent on the metal used and on the width of the nozzle opening in the circumferential direction. It is also dependent on the length of the nozzle opening in a direction parallel to the axis of rotation of the wheel. The length of the nozzle opening can be varied within wide limits. For laboratory experiments values of 10 to 12 mm have been found useful. In production much greater lengths could be selected in dependence on the axial width of the circumferential surface of the wheel.
The grooves or recesses G can have a cross-sectional shape selected from the group comprising semi-circular, symmetrically v-shaped, asymmetrically v-shaped, rectangular and trapezoidal and grooves G of this kind are shown in
When lands are provided they generally have widths of I mm or less.
As can be seen from
The overall aim of the tests carried out to date is to investigate whether the melt spinning process can produce thin fibers with diameters in the micron range, for industrial applications such as light weight, mechanically strengthened textiles (textiles reinforced by the metal strands), filters and catalytically active materials. The actual apparatus used is shown in
The cover for closing the port 16 can be a hinged or removable glass cover permitting the material collected in the cylindrical extension 18 to be observed, removed and filmed as required.
The following experiments were conducted:
In the first experiment melt spun ribbons were generated on a standard copper wheel B with a diameter of 200 mm and a smooth circumferential surface 32 (indicated in
The specific parameters used were as follows:
Using the same apparatus as in
To investigate the microstructure of the melt-spun ribbons shown in
For this example the aim was to make the single ribbons finer by promoting the break-up of the liquid melt on the copper wheel by reducing the volume of the liquid pool forming on the wheel between the wheel surface and the orifice of the crucible K. This concept was based on the recognition that single ribbons with 1 mm widths would have been generated on the flat surfaces in between the semicircular grooves, if the breakup of the ribbon material could be promoted to reach completion. In this example, this was achieved using the same structured surface as in Illustrative Example 1, and the same set of parameters as in Comparative Example 1 but by increasing the speed of rotation of the wheel B to 60 Hz corresponding to a surface speed of the wheel of 37.5 m/s. The resultant ribbons are shown in
The mass and size distribution of the strands shown in the photograph of
Total mass=9.70 g (100%)
Mass of agglomerated strands=2.83 g (29%);
Length of the strands: plural centimetres (10 cm);
Typical width: ca. 1.3 mm
Mass of remaining material: 6.73 g (69%) Mass of material lost; =0.14 g (1%).
The diagrams of
In this example the same basic set-up was retained as for Inventive Example 1 but the pressure on the melt was reduced to 100 mbar in order to reduce the deposition rate of the melt onto the spinning wheel. This resulted in two types of metal strands:
Metallic strands in the form of agglomerations of similar strands with homogenous diameters and of several cm's length and strands in the form of a fiber mix including all the remaining fiber products.
The following results were obtained:
Total mass 6.06 g (100%),
Mass of agglomerated strands 4.18 g (69%)
Average width 389 μm+/−167 μm
Average thickness 28 μm+/−7 μm
Length of strands ca 10 cm
Residual mix 1.66 g (27%)
Length several mm's,
Average width of ca. 20 μm
Material loss 0.22 g (4%)
In this case the parameters used were as follows:
Material lead (Pb)
Surface structure, size and speed of rotation of copper wheel as in inventive example 1
The ribbons produced in this way are shown in
In this case the parameters used were as follows:
Material Aluminium (Al)
In the following further examples will be given of fibres produced using different parameters of the melt spinning process using a structured wheel. In all the following examples the wheel is a copper wheel having various groove configurations which are illustrated in the summary of
The textured ribbon produced in this experiment is shown in photographs with different magnifications in
The textured ribbon produced in this experiment is shown in photographs with different magnifications in
The fibres produced in this experiment are shown in photographs with different magnifications in
The fibres produced in this experiment are shown in photographs with different magnifications in
The fibres produced in this experiment are shown in photographs with different magnifications in
The fibres produced in this experiment are shown in photographs with different magnifications in
The values of all the examples 5 to 11 are summarized—together with other relevant values—in the Table of
| Number | Date | Country | Kind |
|---|---|---|---|
| 14180273.6 | Aug 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/068194 | 8/6/2015 | WO | 00 |
