GB1594977A

GB1594977A - Method of and apparatus for solidifying molten metal or metal alloy

Info

Publication number: GB1594977A
Application number: GB5387377A
Authority: GB
Original assignee: PVL PHYSIKALISCHE VERSUCHSANST
Current assignee: PVL PHYSIKALISCHE VERSUCHSANST
Priority date: 1976-12-29
Filing date: 1977-12-23
Publication date: 1981-08-05
Also published as: BE862424A; IT1089617B; CH626282A5; DE2758350A1; FR2375938A1; SE7714591L

Abstract

The method envisages that a melt consisting of metals and metal alloys be subjected to a macrosonic field, at least at the beginning of the solidification process. This produces a pressure amplitude in the molten material and, as a result, as large as possible a number of crystallisation nuclei is produced. The intention is, by influencing the grain growth, to obtain a fine-grained structure in the solidified melt. The device for carrying out the method contains an ultrasonic system comprising an ultrasound generator (converter) 6 and an oscillatory transmission part in the form of a horn (1), which is connected to the ultrasound generator (6) via an intermediate piece (5), the length of which is matched to the wavelength of the ultrasound. The horn (1) forms an oscillatory bottom to the casting mould, in which it is mounted to allow displacement in the plane of a node of vibration. <IMAGE>

Description

(54) A METHOD OF AND APPARATUS FOR SOLIDIFYING MOLTEN METAL OR METAL ALLOY (71) We, BERTWIN LANGENECK ER, an Austrian citizen of Wenigzell, Sommersgut 23, Steiermark, Austria, and PVL PHYSIKALISCHE VERSUCHSAN STALT DR. B. LANGENECKER, an Austrian Company of Wenigzell, Sommersgut 23, Steiermark, Austria, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to a method and apparatus for solidifying molten metal or metal alloys.

Attempts have already been made to expose molten metal or metal alloys during the solidification process to an ultrasonic field, but these attempts did not give useful results because it was not possible to transmit the ultra-sound to the molten metal undamped or slightly damped.

According to a first aspect of the present invention there is provided a method for the solidification of a molten metal or metal alloy wherein a macro-sonic field is applied to the melt during the solidification thereof.

A macro-sonic field is an ultra-sonic field of high amplitude, see for example the book "Mechanical Radiation" by Robert Bruce Lindsay published by McGraw-Hill Book Co. Inc. 1960. In the method of the invention the melt can be guided through the macro-sound field during its solidification process.

According to a second aspect of the invention there is provided apparatus for solidifying molten metal or metal alloy comprising a mould and at least one macrosound generating apparatus for applying a macro-sonic field to a melt contained, in use of the apparatus, in the mould, the macrosound generating apparatus having a converter and a transmission part which can be set in oscillation by the converter, wherein the transmission part is provided as a part of the mould cavity into which the melt comes into contact or is provided on a wall of the mould.

The transmission part can form the base, the wall or an annular or frame-like part of the wall of the casting mould.

The macro-sound is thus transmitted by the transmission part, e.g. a so called horn, directly to the material to be solidified. The transmission part will be tuned so as to oscillate at the resonant frequency of the macro-sonic field generating apparatus.

Best results are achieved when the surface at which the macro-sound waves contact the melt is located in a so-called vibration antinode. Such an antinode is located where the displacement as a result of the formation of a stationary wave, is greatest. In order to ensure this, the length of the respective transmission part should be a whole multiple of half the wave length of the macrosound used in the respective ultra-sound system.

The application of the macro-sound during the solidification of metals and their alloys makes it possible to considerably refine the hitherto conventional grain sizes formed in conventional casting processes, i.e. without the use of macro-sound. Additionally the macro-sound makes it possible to eliminate undesirable inclusions of gas, which can occasionally lead to cavities of varying size in the metals and their alloys, and also the action of macro-sound facilitates a controlled distribution of the alloy components in metal alloys which consider ably improves the quality and thus the technological properties of metals and their alloys.

Furthermore, the effect of macro-sound makes it possible to produce alloys with a fine-grained structure from different.components which the conventional methods (i.e. without the action of macro-sound) could either not be produce or only under extremely difficult conditions.

One thus produces in the molten material, the compressive amplitude which is necessary for splitting "nuclei" for the processes of grain growth and one thus obtains as many nuclei as possible, from -which as many crystal grains as possible result, which in the solidified state, finally represent the fine-grained structure.

A further use of the invention is in subjecting moulds for complicated cast parts, for example engine blocks, to macrosound waves. The sound waves are transmitted during the solidification of the metal in the mould. The arrangement is such that macro-sound generating apparatus with the transmission parts are attached to those points of the mould where there is a danger of the formation of cavities or where a particularly fine-grain is desired in the casting.

The drawings illustrate three embodi ments of the invention, by way of example.

In the drawings: Figure 1 shows a chill mould, having a transmission part and associated converter, Figure 2 is a cross section through a chill mould, in which several macro-sound gener ating apparatus act on the wall of the mould; and Figure 3 is a section through a continuous casting apparatus including macro-sound generating apparatus.

As regards practical construction, it is possible to use the arrangement shown diagrammatically in Figure 1. The transmis sion part 1, the horn, is located in an opening in the base of the chill mould 2, which receives the melt 3 in its inside. The part 1 thus forms part of the mould cavity into which the melt 3 comes into contact.

The horn 1 can be completely cylindrical, without any change in its cross section, both in the part located outside the chill mould as well as inside the chill mould, but as shown in Figure 1, it can be modified to correspond to a funnel-shaped chill mould, extending conically outwards or conically inwards. It is not absolutely necessary to screw the horn 1 to the chill mould 2. It is sufficient to insert an asbestos cord 4 between the base of the chill mould and the horn. The weight of the ultra-sound system consisting of the horn 1, intermediate part 5 and converter 6 ensures an adequate seal of the chill mould, or the melt 3 to be cast in the chill mould 2 presses the horn 1 tightly against the asbestos sealing cord and thus against the base of the chill mould.

The positioning of the horn 1 ensures that the macro-sonic field is directed axially with respect to the mould.

In order not to attenuate oscillations in the transmission part due to the mounting in the lower part of the chill mould, it is recommended that contact between the horn and the chill mould, i.e. in the region of the asbestos cord 4, takes plates in a node of vibration of the horn.

The intermediate member 5 is to be recommended if melts of high temperature, for example steel, are to be subjected to ultrasonic sound waves and in which case inadmissibly high temperatures could be transmitted by the horn 1 to the converter 6, if heat were not dissipated by the water cooling arrangement 7, which is appropriately located in the node of vibration of the intermediate member 5. "Inadmissibly high temperatues" are those temperatures at which the converter 6 would sustain damage. The curie point for generally pietzoelectric or pietzo ceramic converters is only several hundred degrees celsius. If the converter is heated to high temperatures, then it sustains permanent damage and is no longer capable of transforming the electrical signals, which emanate from matched (ultra-sound) generators, into mechanical (macro-sound) oscillations.

The horn 1, intermediate member 5 and converter 6 may be interconnected by screws 8. In any case, these components must be tuned to the resonant frequency of the ultra-sound system, in order that the highest possible degree of efficiency is achieved and this is achieved best due to the fact that the components, namely the horn 1 and intermediate member 5 are cut to half the wave length k12 (or a multiple thereof) of the ultra-sound wave X in which case k = C/F in which F is the frequency of the sound field and the sound velocity

is thus proportional to the root of - the modulus of elasticity E and the density p of the material used for these components.

In a modified construction, parts or-the entire wall of a chill mould 2 of any shape, for example of cylindrical construction, as shown in Figure 2, are made to carry out macro-sonic oscillations, which are transmitted to the molten material 3. In this case, several horns 1 can be constructed as projecting parts of the chill mould, which are in turn located in front of the converter 6 by way of intermediate members to be provided if need be (according to part 5 in Figure 1). The molten material 3 is introduced for example through a supply opening in the base 4 and can rise in the mould. It is then subjected to the macro-sound field emanating from the converters 6.

In the embodiment illustrated in Figure 2, the macrosonic field is directed at right angles with respect to the longitudinal axis of the elongate mould.

The arrangement may advantageously be such that the cylindrical part of the wall of the smelt container is integral with projections acting as horns, located in one or more lines extending longitudinally of the mould in which case the distance of the outer end face of the projections from the smelt is equal to (n i2), the spacing of the centres of adjacent projections of one row is likewise equal to (n 22) and the spacing of the centres of adjacent rows is likewise equal to (n 22), n being an integer.

When carrying out continuous casting extrusion the arrangement illustrated in Figure 3 can be used, in order to allow macro-sound to act on the solidifying smelt 3. In this construction, the transmission part 1 is constructed as a ring located at the entrance of the chill mould, its inner diameter being equal to the inner diameter of the chill mould and its width in the radial direction amounting to an integral multiple of half the wave length of the macro-sound.

In this case, several converters 6 may be attached in the shape of a star to the transmission part 1 directly or by means of intermediate parts 5 at a spacing corresponding to an integral multiple of half the wave length of the macro-sound. This construction produces an arrangement for casting installations, in which a macro-sound system is attached radially to the ring at several points, where at the time of - the resonant oscillation of the ring, a vibration antinode occurs.

As a result of the contact, the solidifying casting contracts and is detached from the wall 2. The transmission part is located in the region where the smelt 3 "stands", so that it is in contact with the molten material and transmits the macro-sound wave to the latter.

Further effective cooling, which is also useful for the embodiment according to Figure 2, consists in providing channels for cooling water in the transmission parts 1.

The latter is most appropriately provided in the region of a node of vibration, because otherwise the cooling water is subjected to more or less vigorous ultrasonic effects, due to which cavitation phenomena may occur, which leads to wear of the inner wall of the cooling components. If the chill mould has a cylindrical construction in Figure 1, this produces the possibility of firstly raising the macro-sound system, consisting of the horn 1, intermediate member 5 and converter 6 with respect to the base of the chill mould 2 and then lowering the latter with the melt, when the molten material 3 enters, like the piston of any piston or pump motor and during the latter, of transmitting macrosound to the molten material.

It is also possible to operate in the opposite direction by introducing the melt from below with raising of the solidifying molten material in an upwards direction.

Thus, the horn 1 transmits the macro-sonic oscillations continuously to the molten material in its liquid phase, whereas the solidified material is removed at the top.

Similar arrangements are possible with an inclined and horizontal feed direction or for removal from the bottom.

On account of the high temperatures, it is advantageous if the transmission parts 1 consist of titanium, a titanium alloy, of tungsten or a tungsten alloy.

WHAT WE CLAIM IS: 1. Method for the solidification of a molten metal or metal alloy wherein a macro-sonic field is applied to the melt during the solidification thereof.

2. A method according to claim 1, wherein the melt is in an elongate mould and the macro-sonic field is directed axially with respect to the mould.

3. Method according to claim 1, wherein the melt is in a circular mould and the macro-sonic field is directed radially with respect to a mould.

4. Method according to claim 1, wherein the melt is in an elongate mould and the macro-sonic field is directed at right angles with respect to the longitudinal axis of the mould.

5. Method according to claim 1 wherein the melt is guided through the macro-sonic field during the solidification process.

6. Apparatus for carrying out the method of claim 1 comprising a mould and at least one macro-sound generating apparatus for applying a macro-sonic field to a melt contained, in use of the apparatus, in the mould, the macro-sound generating apparatus having a converter and a transmission part which can be set in oscillation by the converter, wherein the transmission part is provided as a part of the mould cavity into which the melt comes into contact or is provided on a wall of the mould.

7. Apparatus as claimed in claim 6, wherein the transmission part is connected directly to the converter.

8. Apparatus as claimed in claim 6, wherein the transmission part is connected to the converter by an intermediate connecting piece.

9. Apparatus as claimed in any one of claims 6 to 8, wherein the transmission part is located at the bottom of the mould cavity and contacts the mould at a node of vibration occuring in use of the apparatus.

10. Apparatus according to any one of claims 6 to 8, which is a continuous casting

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. emanating from the converters 6. In the embodiment illustrated in Figure 2, the macrosonic field is directed at right angles with respect to the longitudinal axis of the elongate mould. The arrangement may advantageously be such that the cylindrical part of the wall of the smelt container is integral with projections acting as horns, located in one or more lines extending longitudinally of the mould in which case the distance of the outer end face of the projections from the smelt is equal to (n i2), the spacing of the centres of adjacent projections of one row is likewise equal to (n 22) and the spacing of the centres of adjacent rows is likewise equal to (n 22), n being an integer. When carrying out continuous casting extrusion the arrangement illustrated in Figure 3 can be used, in order to allow macro-sound to act on the solidifying smelt 3. In this construction, the transmission part 1 is constructed as a ring located at the entrance of the chill mould, its inner diameter being equal to the inner diameter of the chill mould and its width in the radial direction amounting to an integral multiple of half the wave length of the macro-sound. In this case, several converters 6 may be attached in the shape of a star to the transmission part 1 directly or by means of intermediate parts 5 at a spacing corresponding to an integral multiple of half the wave length of the macro-sound. This construction produces an arrangement for casting installations, in which a macro-sound system is attached radially to the ring at several points, where at the time of - the resonant oscillation of the ring, a vibration antinode occurs. As a result of the contact, the solidifying casting contracts and is detached from the wall 2. The transmission part is located in the region where the smelt 3 "stands", so that it is in contact with the molten material and transmits the macro-sound wave to the latter. Further effective cooling, which is also useful for the embodiment according to Figure 2, consists in providing channels for cooling water in the transmission parts 1. The latter is most appropriately provided in the region of a node of vibration, because otherwise the cooling water is subjected to more or less vigorous ultrasonic effects, due to which cavitation phenomena may occur, which leads to wear of the inner wall of the cooling components. If the chill mould has a cylindrical construction in Figure 1, this produces the possibility of firstly raising the macro-sound system, consisting of the horn 1, intermediate member 5 and converter 6 with respect to the base of the chill mould 2 and then lowering the latter with the melt, when the molten material 3 enters, like the piston of any piston or pump motor and during the latter, of transmitting macrosound to the molten material. It is also possible to operate in the opposite direction by introducing the melt from below with raising of the solidifying molten material in an upwards direction. Thus, the horn 1 transmits the macro-sonic oscillations continuously to the molten material in its liquid phase, whereas the solidified material is removed at the top. Similar arrangements are possible with an inclined and horizontal feed direction or for removal from the bottom. On account of the high temperatures, it is advantageous if the transmission parts 1 consist of titanium, a titanium alloy, of tungsten or a tungsten alloy. WHAT WE CLAIM IS:

1. Method for the solidification of a molten metal or metal alloy wherein a macro-sonic field is applied to the melt during the solidification thereof.

installation with a mould of circular section, wherein the transmission part is constructed as a ring located at the entrance to the mould, the ring having an inner diameter equal to that of the mould and a radial width equal to an integral multiple of half the wave length of the macro-sound which the transmission part applies, in use of the apparatus, to a melt.

11. Apparatus according to claim 10, wherein a plurality of converters are located around the ring at positions at which a vibration antinode occurs in.use of the apparatus.

12. Apparatus according to any one of claims 6 to 8, wherein the mould is cylindrical and a plurality of transmission parts formed as projections on the outer surface of the cylinder are provided, said transmission parts being arranged in at least one line extending longitudinally of the cylinder with the spacing between the centres of adjacent transmission parts of the same or an adjacent line being equal to an integral multiple of half the wavelength of the macro-sound applied in use of the apparatus, this also being the spacing between an outer surface of each projection and the melt in use of the apparatus.

13. Apparatus according to any one of claims 6 to 12, wherein the transmission part is cooled.

14. Apparatus according to any one of.

claims 6 to 12, wherein the transmission part is of titanium, titanium alloy, tungsten, or a tungsten alloy.

15. Method for solidifying molten metal or metal alloy substantially as hereinbefore described with reference to any one of Figures 1 to 3 of the accompanying drawings.

16. Apparatus for solidifying molten metal substantially as hereinbefore described with reference to any one of Figures 1 to 3 of the accompanying drawings.