APPARATUS AND METHOD OF MANUFACTURING METALLIC OR INORGANIC FIBERS HAVING A THICKNESS IN THE MICRON RANGE BY MELT SPINNING

Abstract

Disclosed is an apparatus having a rotatable wheel with a planar external circumferential surface, which is flat in a direction parallel to the axis of rotation of the wheel, at least one nozzle having a nozzle opening for directing a molten metal onto the circumferential surface and a collection means for collecting solidified fibers 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 nozzle has a rectangular cross-section having 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. An apparatus is provided for controlling a gas pressure applied to the liquid metal and delivers it to the circumferential surface of the rotatable wheel.

Claims

1.-15. (canceled)

16. An apparatus for producing elongate microfibers of metal, of metallic glasses or of inorganic material, the apparatus comprising a rotatable wheel having a planar external circumferential surface, which is flat in a direction parallel to the axis of rotation of the wheel, at least one nozzle having a nozzle opening for directing a molten material onto the circumferential surface, with the nozzle having a rectangular cross section and a width of a slit of the nozzle opening in the circumferential direction of the wheel being selected to lie in the range from 10 to 500 m, and a collection means for collecting solidified fibers of material formed on the circumferential surface from the molten material and separated from the circumferential surface by centrifugal force generated by rotation of the wheel, wherein the apparatus comprises a further apparatus that is configured to control a gas pressure applied to the molten material which moves the molten material through the nozzle opening and delivers it to the circumferential surface of the rotatable wheel and wherein the further apparatus is further configured to regulate the mass flow of molten material down to a level at which microfibers of the material are formed on the rotatable wheel by controlling and keeping the mass flow per unit area of the wheel surface of the molten material which is deposited per unit of area onto the circumferential surface of the rotatable wheel in the range from 0.01 to 100 g/(m2*sec) for a surface speed of rotation of the wheel in the range from 10 to 100 m/sec.

17. The apparatus in accordance with claim 16, wherein the nozzle has a length transverse to the circumferential surface of the wheel which is greater than the width.

18. The apparatus in accordance with claim 16, wherein the mass flow per unit area of the wheel surface of the molten material which is deposited per unit of area onto the circumferential surface of the rotatable wheel is controlled and kept in the range from between 0.1 and 50 g/(m2*sec) for a surface speed of rotation of the wheel in the range from 10 to 100 m/sec.

19. The apparatus in accordance with claim 18, wherein the mass flow per unit area of the wheel surface of the molten material which is deposited per unit of area onto the circumferential surface of the rotatable wheel is controlled and kept in the range from between 0.2 and 30 g/(m2*sec) for a surface speed of rotation of the wheel in the range from 10 to 100 m/sec.

20. The apparatus in accordance with claim 18, wherein the mass flow per unit area of the wheel surface of the molten material which is deposited per unit of area onto the circumferential surface of the rotatable wheel is controlled and kept around 0.4 g/(m2*sec) for a surface speed of rotation of the wheel in the range from 10 to 100 m/sec.

21. The apparatus in accordance with claim 16, wherein a controller is provided that is configured to keep the speed of rotation of the wheel constant so that the surface speed of the wheel is in the range from 40 to 60 m/s.

22. The apparatus in accordance with claim 16, wherein the nozzle has a rectangular cross section and the width of the opening of the slit of the nozzle in the circumferential direction of the wheel is selected to lie in the range from 20 to 500 m.

23. The apparatus in accordance with claim 22, wherein the nozzle has a rectangular cross section and the width of the opening of the slit of the nozzle in the circumferential direction of the wheel is selected to lie in the range from 20 to 100 m.

24. The apparatus in accordance with claim 17 in which the length of the slit corresponds to the width of the external circumferential surface of the wheel in a direction parallel to the axis of rotation thereof.

25. The apparatus in accordance with claim 16 in which the temperature of the melt is kept 100 to 400 C. greater than the melting point of the material.

26. The apparatus in accordance with claim 16 in which the pressure exerted on the melt upstream of the nozzle is controlled to be higher than the pressure prevailing in the melt spinning chamber by an amount in the range from P equal to 0 to 5000 mbar.

27. The apparatus in accordance with claim 16, wherein the rotatable wheel is temperature controlled.

28. The apparatus in accordance with claim 16, wherein the rotatable wheel is temperature controlled to a temperature in the range of 100 C. to +200 C.

29. The apparatus in accordance with claim 16, wherein the wheel is made of a metal or of a metal alloy or of a ceramic material or of graphite or is a wheel of a base material having a layer or tire made of a metal or of a metal alloy or of a ceramic material or of graphite or a vapor deposited carbon.

30. The apparatus in accordance with claim 16, wherein the wheel is made of copper or stainless steel or is a copper wheel having a layer of graphite formed thereon.

31. The apparatus in accordance with claim 16, wherein said wheel is mounted to rotate within a chamber having an atmosphere, the atmosphere being at least one of air, nitrogen, helium and other inert gasses.

32. The apparatus in accordance with claim 16, wherein said wheel is 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.

33. A method for producing elongate microfibers of metal, or metallic glasses or of inorganic material having a median width of 50 m or less, a thickness of 5 m or less and a length at least ten times greater than said width, the method comprising the steps of directing a molten material through a nozzle onto a planar external circumferential surface of a rotating wheel, with the nozzle having a nozzle opening for directing a molten material onto the circumferential surface, with the nozzle having a rectangular cross section and a width of a slit of the nozzle opening in the circumferential direction of the wheel being selected to lie in the range from 10 to 500 m, by applying a gas pressure to the molten material to move it through the nozzle opening and deliver it to the circumferential surface of the rotatable wheel, and collecting solidified fibers formed on the circumferential surface from the molten material and separated from the circumferential surface by centrifugal force generated by rotation of the wheel, the method further comprising the steps of selecting the dimensions and geometry of the nozzle in combination with the gas pressure to regulate the mass flow of molten material which is deposited per unit of area onto the circumferential surface of the rotatable wheel to a value in the range from 0.01 to 100 g/(m2*sec) for a surface speed of rotation of the wheel in the range from 10 to 100 m/sec to form microfibers of the material on the rotatable wheel by reducing the flow rate of molten material onto the circumferential surface of the wheel in a material dependent manner to a level at which it is concentrated by the forces that are acting to produce the desired elongate fibers of the material.

34. The method in accordance with claim 33, wherein the flow of metal is reduced to a level at which the elongated fibers have a width of 200 m to <1 m or smaller.

35. The method in accordance with claim 33, wherein the fibers have a thickness of 5 m to <1 m or smaller.

Description

[0079] 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:

[0080] FIG. 1 a schematic illustration of the basic melt spinning process,

[0081] FIG. 2 a front view of the apparatus used for melt spinning equipped with the rotatable wheel of the present invention,

[0082] FIG. 3 a detail view of the apparatus of FIG. 2 as seen in a front view with the housing removed,

[0083] FIG. 4 a top view of the discharge orifice of the crucible with an explanatory sketch,

[0084] FIG. 5 a photograph of a melt spun ribbon of an Fe40Ni40B20 alloy spun on a copper wheel of 200 mm diameter rotating at 30 Hz, comparative example 1,

[0085] FIG. 6 a table showing important parameters for sixteen experiments comprising one comparative example and fifteen inventive examples,

[0086] FIG. 7 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 2 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0087] FIG. 8 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 3 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0088] FIG. 9 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 4 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0089] FIG. 10 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 5 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0090] FIG. 11 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 6 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0091] FIG. 12 one photograph (top left) and two SEM images top and bottom right) for fibers produced in the experiment of Example 7 with the scale bars in the photograph indicating a length of 10 mm and the scale bars for the top and bottom SEM images indicating lengths of 200 m and 20 m respectively,

[0092] FIG. 13 two SEM images for fibers produced in the experiment of Example 8, with the images being taken at different positions of the sample and with the scale bars in the left and right hand images indicating lengths of 30 m and 20 m respectively.

[0093] Turning now to the schematic drawing of the melt spinning process shown in FIG. 1 it can be seen that the metal A to be spun is heated in a crucible K by an electrical heating device I. A gas pressure P presses the molten metal through the nozzle N of the crucible K onto the rotating wheel B. The wheel B has a planar external circumferential surface (S), which is flat in a direction parallel to the axis of rotation of the wheel (B). I.e. the circumferential surface S of the wheel corresponds to a surface of revolution obtained by rotating a straight line in a circle about an axis of rotation parallel to the straight line. As shown in FIG. 4 the nozzle N of the crucible K, which is typically made of boron nitride, has a nozzle opening O of rectangular shape. From the schematic diagram of FIG. 4 it can be seen that the length direction L of the nozzle opening is oriented transversely to the circumferential direction C of the circumferential surface S of the wheel B and extends over a substantial part of the axial width of the circumferential surface of the wheel, and in a practical example over at least most of the axial width of the wheel, so that the nozzle opening distributes molten metal across the axial width of the surface of the wheel B. The width W of the slot can be chosen within relatively wide limits, e.g. 500 m and 10 m to control the rate of flow of the molten metal from the nozzle N onto the structured surface S of the wheel B. When the width W is relatively large a relatively higher flow rate for the molten metal onto the structured surface of the wheel B is obtained and, for a given speed of the wheel, the strands produced are of relatively large cross-section. As the width W is reduced, which is achieved by substituting one crucible K for another one with the desired nozzle width W, the flow rate of the molten metal onto the structured circumferential surface S of the wheel B is reduced and, for the same speed of rotation of the wheel, the strands produced are relatively smaller in cross-section.

[0094] 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 P between the pressure applied to the melt and the pressure prevailing in the chamber 12 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.

[0095] The actual apparatus used is shown in FIGS. 2 and 3. Apart from the design of the wheel B the apparatus shown in FIGS. 2 and 3 is basically a commercially available melt spinner obtainable from the company Edmund Buehler GmbH, Hechingen, Germany. It consists of a metallic chamber 10 having a cylindrical portion 12 and a tangentially extending collection tube 14 with a closable port 16 at the end remote from the cylindrical portion 12. The crucible K with the electrical heating system I and the gas pressure supply P are mounted within a short cylindrical extension 18 of the chamber 10 above the cylindrical portion 12 and are provided with the necessary supply lines for a pressurized gas such as argon, for electrical power and control of the gas flow valve determining the pressure P, for the power of the heating system I and for the monitoring of parameters such as gas pressure and temperature of the melt. The wheel B is mounted on the inside of and concentric to the cylindrical portion 12 and is supported by bearings (not shown) on an axle 20 driven by an electric motor 22 flanged to the rear of the cylindrical portion 12 (see FIG. 3). The front side 24 of the cylindrical portion, i.e. the side 26 opposite the drive motor 22 is made of glass so that the spinning process can be observed and filmed by a high speed camera. The chamber 10 can be evacuated by a vacuum pump via an evacuation stub 28 and can be supplied with a flow of an inert or reactive gas via a further feed stub 30. Thus a desired atmosphere at a desired temperature and pressure can be provided within the chamber 10.

[0096] 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. In all experiments the copper wheel was not cooled.

[0097] The following experiments were conducted:

EXAMPLE 1COMPARATIVE EXAMPLE

[0098] 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 at S n FIG. 1 and seen in plan view in FIG. 3) having the shape of a right cylinder. A melt of Fe 40Ni40B20 is formed by the heating system I within the boron nitride crucible K. The crucible K has a slit orifice with nominal dimensions, length L=10 mm and width W=400 m. Once the metal has melted gas pressure is applied to the molten gas by the pressure source P to expel the molten metal through the orifice and onto the copper wheel B. The copper wheel B was rotated by the drive motor at a surface speed of 18.8 m/s. The mass of the metal sample was ca. 10 g. As shown in FIG. 5, a single continuous ribbon was generated, which had a length of >1 m, a typical width of 9.3+10.1 mm, and a typical thickness of 42+12 microns. FIG. 5 shows that the ribbons manufactured in this way are of good quality However they are of much larger width and thickness than the dimensions aimed at in the present invention and thus the example is classified as a failed example.

[0099] In the following examples will be given of fibers produced by melt spinning using a smooth flat wheel and an Fe40Ni40B20 metallic glass (examples 3 to 7 and 9 to 14), for stainless steel (V2A example 8) as well as for Zn and Al (examples 15 and 16). Where reference is made to the median width this value is obtained in accordance with the usual definition. In all cases the thickness of the majority of the fibers was less than 5 m. As yet no attempts have been made to more accurately determine the thicknesses

EXAMPLE 2INVENTIVE EXAMPLE

[0100]

TABLE-US-00001 Material: Fe40Ni40B20 Experiment MS048 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 400 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 600 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 1296 m, min 6.3 m Thickness of the resultant fibers <5 m

EXAMPLE 3INVENTIVE EXAMPLE

[0101]

TABLE-US-00002 Material: FE40Ni40B20 Experiment MS047 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 200 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 600 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 335 m, min 3 m Thickness of the resultant fibers <5 m

EXAMPLE 4INVENTIVE EXAMPLE

[0102]

TABLE-US-00003 Material: Fe40Ni40B0 Experiment MS045 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 100 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 800 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 216.1 m, min 3.1 m Thickness of the resultant fibers <5 m

EXAMPLE 5INVENTIVE EXAMPLE

[0103]

TABLE-US-00004 Material: Fe40Ni40B20 Experiment MS051 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 75 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 1000 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 94 m, min 2.3 m Thickness of the resultant fibers <5 m

EXAMPLE 6INVENTIVE EXAMPLE

[0104]

TABLE-US-00005 Material: Fe40Ni40B20 Experiment MS050 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 50 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 1400 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 148.3 m, min 2.7 m Thickness of the resultant fibers <5 m

EXAMPLE 7INVENTIVE EXAMPLE

[0105]

TABLE-US-00006 Material: Fe40Ni40B20 Experiment MS049 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 25 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1400 C. Ejection pressure 1900 mbar Surface speed of wheel 59.4 m/s Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 180.7 m, min 2.1 m Thickness of the resultant fibers <5 m

EXAMPLE 8INVENTIVE EXAMPLE

[0106]

TABLE-US-00007 Material: Stainless steel V2A Experiment MS058 Nominal length of nozzle opening 10 mm Nominal width of nozzle opening 75 m Temp of wheel RT (~23 C.) Gas in chamber Argon Pressure in chamber 12 400 mbar Temp. of gas in chamber 12 RT Ejection temperature 1550 C. Ejection pressure 1200 mbar Sirface speed of wheel 59.4 m/s95 Hz Diameter of wheel 200 mm Distance between nozzle and wheel 0.3 mm Width of the resultant fibers Max 143.9 m, min 2.3 m Thickness of the resultant fibers <5 m

[0107] The values for both the comparative example 1 and for the inventive examples 2 to 8 are summarizedtogether with other relevant valuesin the Table of FIG. 6 classified by the experiment number. Further inventive examples 9 to 16 are included in the table of FIG. 6. Where available SEM micrographs and photographs of the relevant fibers are shown in FIGS. 7 to 13 and identified by the Experiment number (MS plus three digits).

[0108] The Table of FIG. 6 also includes mean values for the width of the microfibers that are produced.

[0109] Although the spacing between the nozzle opening and the wheel was 300 m in the Examples given experiments have shown that choosing spacings between 100 and 300 mm; has not had any measurable influence on the microfibers produced.

[0110] In all experiments the diameter of the wheel was 200 mm.