METHOD OF PRODUCING METAL STRANDS AND APPARATUS FOR PRODUCING METAL STRANDS

Abstract

The invention relates to a method of producing elongate metal strands or fibres with a crucible, the method comprising the steps of; directing molten metal through a nozzle having a nozzle direction in a deposition direction at a regulated pressure difference between the inside and the outside of the crucible; depositing said molten metal from said nozzle on a rotating planar surface having an axis of rotation; entraining said molten metal in one plane via said rotating planar surface to form elongate metal strands, wherein said rotating surface is aligned at an alignment angle, to the deposition direction during the entraining of the molten metal; cooling said elongate metal strands to form solidified metal strands; and guiding said metal strands to collecting means to collect the solidified metal strands formed on the rotating planar surface.

Claims

1-18. (canceled)

19. A method of producing at least one of elongate metal strands and fibres with a crucible, the method comprising the steps of: directing molten metal through a nozzle having a nozzle direction in a deposition direction at a regulated pressure difference between the inside and the outside of the crucible; depositing said molten metal from said nozzle on a rotating planar surface having an axis of rotation; entraining said molten metal in one plane about said axis of rotation via said rotating planar surface to form the at least one of elongate metal strands and fibres, wherein said rotating surface is aligned at an alignment angle with regard to the deposition direction during the entraining of the molten metal; cooling said elongate metal strands to form solidified metal strands; and guiding said metal strands to collecting means to collect the solidified metal strands formed on the rotating planar surface.

20. The method according to claim 19, wherein the rotating planar surface is arranged perpendicular to the deposition direction during said steps of entraining and cooling said molten metal, and wherein the rotating planar surface comprises a circular, oval, quadratic, rectangular or triangular shape.

21. The method according to claim 19, wherein the alignment angle of the rotating planar surface is selected to lie in the range of 90° to 1° with respect to the deposition direction and/or the nozzle direction is selected to lie in the range of 0° to 90° with respect to the rotating planar surface.

22. The method according to claim 19, wherein a spacing between a nozzle opening of the nozzle and the rotating planar surface is at least 10 μm.

23. The method according to claim 19, wherein the moving surface is a base interface of a rotating wheel.

24. The method according to claim 19, wherein the axis of rotation is perpendicular to the rotating planar surface when the rotating planar surface is designed as a base interface of a rotating wheel.

25. The method according to claim 19, wherein the deposition position of the nozzle relative to the rotating planar surface is adjusted, while an orientation of the nozzle is of any direction.

26. The method according to claim 19, wherein the rotating planar surface is cooled.

27. An apparatus for producing elongate metal strands and fibres, the apparatus comprising: a rotating planar surface, at least one nozzle having a nozzle direction and a nozzle opening for directing molten metal in a deposition direction onto the rotating planar surface, the rotating planar surface being configured to move under an alignment angle with respect to said deposition direction to entrain and cool the molten metal in one plane via said movement of the rotating planar surface to form solidified elongate metal strands at said rotating planar surface, and collecting means configured to collect the solidified strands of metal formed on the rotating planar surface and separated from the rotating planar surface by a force generated by the movement of the rotating planar surface.

28. The apparatus according to claim 27, wherein the apparatus comprises a rotatable wheel.

29. The apparatus according to claim 27, wherein the rotating planar surface is aligned perpendicular to the deposition direction during the entraining of the molten metal.

30. The apparatus according to claim 27, wherein the rotating planar surface is aligned at an alignment angle with respect to the deposition direction during the entraining of the molten metal, wherein the alignment angle is selected to lie in the range of 90° to 1° and/or the nozzle direction is selected to lie in the range of 0° to 90° with respect to the rotating planar surface.

31. The apparatus according to claim 27, wherein the rotating planar surface rotates around an axis of rotation, which is aligned perpendicular to the rotating planar surface.

32. The apparatus according to claim 27, wherein a spacing between the nozzle opening and the rotating planar surface is at least 10 μm.

33. The apparatus according to claim 27, wherein the rotating planar surface comprises at least one exchangeable plate.

34. The apparatus according to claim 33, wherein a set of exchangeable plates is provided with each plate of the set of exchangeable plates being made from the same material as the remaining plates of the set of exchangeable plates, or wherein a variety of plates made from different materials is provided in the set of exchangeable plates.

35. The apparatus according to claim 27, wherein a deposition position of the nozzle is adjustable at least parallel to the rotating planar surface.

36. The apparatus according to claim 27, wherein the nozzle opening is of any geometry and is aligned in any direction with respect to the rotating planar surface.

37. The apparatus according to claim 27 comprising at least two nozzles, each nozzle having a nozzle opening for directing molten metal onto the rotating planar surface, wherein each nozzle is adjustable at least in parallel to the rotating planar surface.

38. The apparatus according to claim 37 that comprises between 4 and 12 nozzles.

Description

[0037] The invention will now be described in further detail by way of example only with reference to the accompanying drawings. In the drawings there are shown:

[0038] FIG. 1: a first embodiment of an apparatus according to the invention;

[0039] FIG. 2: a second embodiment of an apparatus according to the invention;

[0040] FIG. 3: a top view of an exemplary embodiment with a plurality of nozzles;

[0041] FIG. 4a: an example of a real life apparatus according to the invention;

[0042] FIGS. 4b to 10: different examples of metal strands and fibers, which are produced with an apparatus according to the invention; and

[0043] FIG. 11 to 12: different distributions of the strand thicknesses produced with an apparatus according to the invention.

[0044] FIG. 1 shows a first embodiment of an apparatus 10 for producing elongate metal strands, in particular a melt spinning apparatus, comprising a nozzle 12 with a nozzle opening 14 which deposits drops or streams of molten metal 15 in a deposition direction (see arrow D) onto a rotating planar surface 16. In order to be able to deposit molten metal, the nozzle 12 comprises a heating device 18 which heats the metal inside the nozzle 12 to a temperature where the metal is in its liquid state.

[0045] The nozzle opening 14 may be of any geometry, usually circular, oval, rectangular, quadratic or triangular. The opening width can lie in the range of 10 μto 10 mm, depending on the size of the metal strand 22 or fiber 22 that should be produced. In the case of metal strand 22 production, the width of the nozzle opening 14 is usually chosen from a range of 500 μm to 10 mm, whereas in the case of fiber 22 production the width of the nozzle opening 14 is chosen from a range of 10 μm to 500 μm. Hence, different nozzle opening 14 sizes are possible depending on the desired application of the apparatus 10. The nozzle direction N may vary from 90° with respect to the planar surface 16, i. e. it may be selected to lie in the range from 90° to 0°. Hence, the nozzle 12 could also be aligned parallel to the rotating planar surface 16 and still have a deposition direction D which is perpendicular, or any other angle, to the planar surface 16.

[0046] The planar surface 16 is located on a wheel 20 which rotates around its axis of rotation R, which is aligned parallel to the deposition direction D. Hence, the planar surface 16 is designed to be the radial surface of the wheel 20. It is noted that the wheel 20 can rotate clockwise as well as counterclockwise. Furthermore, it is noted that the planar surface 16 could also be aligned at an alignment angle A with respect to the deposition direction D, wherein the alignment angle A can be selected to lie in the range of 0 to 90°. Additionally, the surface 16 may also comprise an oval, rectangular or quadratic shape.

[0047] The diameter of the wheel can range from centimeter to meters and the wheel material maybe of any choice which withstands the metal molt deposition and fast rotation speed, in particular metal alloys such as copper, copper alloys, brass, nickel, iron, ironoxide, stainless steel or carbon based material such as graphite or carbide, ceramic materials. It is also possible that the wheel 20 is a wheel of a base material having a layer made of a metal or of a metal alloy of a ceramic material or of graphite or a vapor deposited carbon, for example a copper wheel 20 having a layer of graphite.

[0048] Because of the rotation of the wheel 20, the molten metal drops or streams 15, which come into contact with the surface 16 are entrained and thereby elongated by the wheel 20 to form elongate metal strands 22. These strands 22 remain on the surface 16 until they are cooled down enough to solidify. For this purpose the rotating wheel 20 can be cooled by a cooling device C to for example room temperature or even below by cooling with liquid nitrogen in order for the molten metal drops 15 to be able to solidify to metal strands 22. If the wheel was not cooled at all it would eventually heat up because of its contact with the (hot) molten metal 16 and hence prevent the molten metal 16 to cool down sufficiently to solidify. Heating of the wheel can also affect its mechanical stability. The cooling device C is shown inside the rotatable wheel 20, but it is noted that does not necessarily have to be located inside the wheel. There are sufficiently many methods known to cool such devices.

[0049] Once the metal strands 22 are solidified the centrifugal forces which act on the metal strands 22 due to the rotation of the wheel 20 will suffice in order to move the metal strands 22 away from the planar surface 16. As the adhesion force between the solidified metal strand 22 and the planar surface 16 is less than a force acting on the metal strand 22 due to the rotation of the planar surface 16. Thus, the solidified metal strands 22 fly away from the wheel 20 in a direction transverse to the circumference of the wheel 20.

[0050] That is why a collector 24 is arranged in such a way to intercept the solidified metal strands 22 and guide them to an opening 26 at the bottom of the collector 24 in order to collect the produced metal strands 22. Guiding of solidified metal strands may also be possible by a flow of gas inside the melt spinning chamber.

[0051] Turbulences may affect the collections of metal strands especially in case of small fibers. This may be prevented by positioning a strong flow of gas or a solid wall which guides the fibers or by evacuating the chamber that no turbulences may occur.

[0052] Depending for example on which type of metal is to be molten, the cooling times can differentiate substantially. That is also why the nozzle is adjustable at least parallel to the planar surface (see arrow 28). When using a rotatable wheel 20 it makes sense to use a nozzle which is adjustable in a radial direction of the wheel 20 in order to decide how dose to the center of the wheel the molten metal 15 should be deposited. Depending on the deposition position, the molten metal undergoes a different acceleration. For some applications the nozzle 12 can also be adjustable in a direction perpendicular to the planar surface 16.

[0053] Although a diameter of the wheel 20 of 20 cm to 55 cm is preferred this is not critical and wheel 20 diameters in the range from 1 to 100 cm can be used. A larger diameter of the planar surface 16 of the rotating wheel 20 increases the circumferential speed of the wheel 20 for outer tracks if the speed of rotation is kept constant and the position of the nozzle 12 relative to the axis of the wheel 20 is changed. Thus a larger diameter of the wheel 20 can result in a smaller width of and shorter length of the metal strands or fibers 22 at constant speed of rotation.

[0054] A controller (not shown) can be provided for maintaining the speed of rotation of the wheel 20 constant so that the surface speed of the planar surface 16 lies in the range between 10 to 100 m/s, especially between 30 and 80 m/s, ideally between 40 to 60 m/s at the circumference of the wheel 20 with a wheel 20 of 20 cm or lager diameter of the external circumference.

[0055] The production of fiber material and metal strands is a combination of the material flow from the nozzle 12 and the speed of rotation of the rotatable wheel 20. If one succeeds in drastically reducing the metal flow from the nozzle 12 then it is also possible to operate with lower speeds of rotation. Accordingly, a speed of rotation of 10 Hz with a wheel 20 of 200 mm diameter is also entirely possible provided the amount of molten material 15 discharged from the nozzle 12 is correspondingly reduced.

[0056] FIG. 2 shows an embodiment of the apparatus according to the invention which mostly corresponds to that of FIG. 1. The only difference between the two embodiments lies in the fact that the rotatable wheel 20 comprises a plate 30, which consequently comprises the planar surface 16. The plate 30 is exchangeable and can thus be easily replaced once the planar surface 16 has worn off too much or if a different material or surface structure of the planar surface 16 is desired. Thus, the versatility of the wheel 20 is enhanced substantially.

[0057] Different plates 30 can also comprise different structures such as grooves or can be made out of different materials. Hence, a plate 30 can be chosen according to the type of metal to be molten and/or according to the type of strand or fibre to be produced.

[0058] Hence, the plate 30 or the plurality of plates 30 can be made out of the same materials as the wheel 20 of FIG. 1. Also the layering of different materials is possible in order to have different plates 30 for different applications or different types of metal to be used for the production of the strands or fibers 22.

[0059] In order to place the plate 30 onto the wheel 20, the wheel 20 comprises a recess 34 in which the plate 30 is arranged. In the case of a rotating wheel 20 like in FIG. 3 the plate can be designed as a circular disc, a ring, a ring-segment or a circular segment. Hence, one wheel 20 can comprise one or more plates 30 at the same time.

[0060] The dimensions of the recess 34 depend on the dimensions of the plate (or plates) 30, which are used, i. e. the recess 34 can either have the form of a ring or of a circle. Accordingly, the recess 34 for the corresponding plate 30 (or plates 30) can have a diameter which is almost the same as the diameter of the wheel 20 itself, i.e. preferably between 20 and 35 cm. The exact dimensions for a recess 34 in the form of a ring depend on the dimensions of the plate 30. The inner radius of such a ring lies in the range of 1 to 30 cm, whereas the range of the outer radius of such a ring lies in the range of 5 to 35 cm—always depending on the actual size of the wheel 20. This means that for a wheel of 200 cm diameter, the outer diameter of the plate may be up to 198 cm, and the inner diameter of the ring shaped plate may be as little as 5 cm. The recess 34 material can be different from the plate 30 material, i. e. the recess 34 material may be a mechanically very strong material such as Tungsten while the plate 30 material may be weaker like copper, such that the recess stabilizes the plate mechanically. This would allow the wheel 20 to rotate at speeds where the recess 34 is still stable but the inner plate 30 would be destroyed because of centrifugal forces.

[0061] In the case of a plurality of plates 30 for one wheel 20 it can be preferred that all of the plates 30, which are in use at the same time, are made out of the same material. Hence, with the use of a plurality of identical plates 30 the apparatus 10 gets way more versatile in its handling, because the single plates 30, which together form the planar surface 16, can be exchanged separately in the case of wear or when a different type of metal is used for the production or when different kinds of fibres are produced.

[0062] FIG. 3 shows a top view of another embodiment of the invention where one rotatable wheel 20 is provided together with nozzles 12 which are radially adjustable along the respective arrows 28. With such an arrangement eight metal strands can be produced at the same time. This makes the apparatus much more efficient compared to known apparatuses from the state of the art.

[0063] In principle every angle of arc for arrangement of the nozzles 12 is possible around the circumference of the moving surface 16. It has proven to be an advantage when the nozzles 12 are arranged evenly around the circumference of the wheel 20. Hence, possible angles for the arrangement of the for example eight nozzles 12 shown in FIG. 4 are 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315°.

[0064] Also other angles like 30°, 60°, 120°, 150°, 210°, 240°, 300° and 330° are possible, if there are for example twelve nozzles 12 present. Hence, one can see that since the wheel 20 is rotating around its axis of rotation R, the exact angles for the placement of the nozzles 12 can be chosen as desired as long as the nozzles 12 are arranged evenly around the circumference of the moving surface 16.

[0065] FIG. 4a shows a photograph of an example of a real life apparatus 10 with a wheel 20, which is aligned horizontally to the ground, i. e. its axis of rotation R is aligned parallel to the deposition direction D of the molten metal. FIG. 4a shows an example of a real life application of the apparatus 10 described in connection with FIGS. 1 and 2.

[0066] FIGS. 4b to 10 show different examples of metal strands and fibers 22, which were produced with an apparatus 10 according to FIG. 1.

[0067] FIG. 4b shows two pictures made of fabricated metal fibers 22 inside a collector 24. One can see that the produced fibers 22 are directed in the direction of the opening 26 where they can be collected by an operator or by a (not shown) container. About 90% of the produced fibers 22 could be collected with the collector 24.

[0068] FIGS. 5 to 7 additionally show enlarged pictures of the fibers 22. One can see that the fibers 22 produced comprise a width of several tens to several hundreds of micrometers.

[0069] The fibers shown in FIGS. 4b to 7 were produced out of FeNiB with a nozzle 12 having a nozzle opening of 17×0,05 mm. The fibres 22 shown in FIG. 8 were produced out of an Al-alloy, whereas the fibres 22 shown in FIGS. 9 and 10 were produced out of a Cu-alloy.

[0070] Thus, it is noted that with an apparatus 10 according to the invention not only metal strands 22 can be produced, but also fibers 22, which are noticeably smaller in width.

[0071] Some distributions of the thicknesses and widths of the Al- and Cu-fibres 22 (see FIGS. 7 and 8) produced out of Al-alloy (FIG. 11) and out of a Cu-alloy (FIG. 12) with an apparatus 10 according to the invention are shown in FIGS. 11 and 12. One can see that the widths of the fibres 22 lie in the range of several tens to several hundreds of micrometers, whereas the thickness of these fibres 22 lies more in the range of 0,1 to 10 micrometers.

[0072] In detail, it can be seen in FIG. 11 that most of the fibres 22, which were produced out of an Al-alloy, could be produced with a width smaller than 50 μm with a thickness smaller than 2,5 μm. In FIG. 12, on the other hand, it can be seen that the fibres 22, which were produced out of a Cu-alloy, comprise widths which lie in the range of 70 to 200 μm with a corresponding thickness of about 1 to 8 μm. Hence, it could be shown that the choice of metal can have an impact on the width of the produced fibers.

[0073] A real life embodiment of the method to produce metal strands according to the invention is described in the following: casting molten metal 15 by defined flow on a fast rotating planar surface 16. In particular, this is obtained by mounting a melt spinning wheel 20 such that the rotation axis R is oriented approximately in line with the deposition direction D of the molten metal 15 originating from the opening 14 of a crucible; practically, the rotation axis R is oriented vertically and the top and bottom sides of the wheel rotate horizontally, i.e. parallel to the ground. This is why an apparatus 10 according to the invention can also be called a “horizontal melt spinner”.

[0074] In the case of conventional melt spinner the rotation axis R is mounted perpendicular to the deposition direction D of molten metal 15 originating from the opening of a crucible 14. The rotation axis R is oriented horizontally and the sides of the wheel 20 are oriented vertically to the ground. This is why the well-known melt spinner are also called “vertical melt spinner”.

[0075] In the case of the horizontal melt spinner 10 the motel metal 15 is dropped on one of the planar base surfaces 16 of the cylindrical wheel 20 which is the surface 16 through which the rotation axis R is aligned centrically and perpendicular to the rotating planar surface 16. This results in the pulling of centrifugal forces on the deposited melt 15 in a way which makes it more spread on the wheel's base surface 16 than in the case of dropping the melt on a circumferential surface of a rotating wheel of a vertical melt spinner. Consequently, the thickness of metal strands 22 is significantly reduced. The geometry of the metal strands 22 is not straight but curved along the elongation of the objects. The curvature is the one picked from the circular path on the base surfacel6 of the wheel 20 at which the metal melt 15 is deposited. The contact time of strands 22 is extended over the one obtained by traditional melt spinning. This cools the strands 22 more before leaving the rotating wheel 20. This reduces the damage of the wheel since less wheel material is moved from the surface 16 with the leaving strands 22.

[0076] Eventually, also the exchange and polishing of the wheel 20 is drastically simplified in case of the horizontal meltspinner. Finally, the mechanical impact of the wheel 20 on its bearing is in favour of a more precise and stable rotation since nearly no momentum is placed on the rotation axis R.

[0077] A rotating wheel 20 or plate 30 has a circumference and two round base plates through which the rotating axis R points. It is the object of this invention to deposit the metal melt 15 not on the circumferential but on one of the base plate surfaces 16 at a distance from the rotation axis R. The rotation axis R and the metal deposition direction D will usually be the same but may also form an angle different from 0°. Thereby, centrifugal forces act on the molten metal 15 which wets the rotating wheel 20. In case of dropping metal 15 on a circumferential surface centrifugal forces point away from the surface working against wetting of the circumferential surface by the metal. In case of dropping molten metal 15 on one of the base plate surfaces 16 centrifugal forces on the molten metal 15 act along the surface 16. Thereby, flatting the metal liquid on the surface 16 and leaving it on the wheel 20 for longer times. In the case of to traditional melt spinner, on the other hand, the molten metal 15 is dropped on the circumferential surface and the melt is moved away from the circumferential surface due to the centrifugal forces.

REFERENCE SIGNS

[0078] 10 apparatus

[0079] 12 nozzle

[0080] 14 nozzle opening

[0081] 15 molten metal

[0082] 16 planar surface

[0083] 18 heating device

[0084] 20 wheel

[0085] 22 metal strand

[0086] 24 collector

[0087] 26 opening

[0088] 28 adjustability

[0089] 30 plate

[0090] 34 recess

[0091] A alignment angle

[0092] C cooling device

[0093] D deposition direction

[0094] N nozzle direction

[0095] R axis of rotation