CH665788A5 - DEVICE FOR CONTINUOUSLY PRODUCING A LONG-TERM METAL OBJECT. - Google Patents

Description

DESCRIPTION Continuous methods for the shaping processing of metal melts are known in particular in the form of continuous casting processes, about which there is an extensive literature including patent literature. Operational devices are only available to a very limited extent, which has various reasons and is often based on problems of contact of the solidifying melt with the walls of the mold or mold.

In order to overcome the disadvantages of contact of the melt with mold walls, various methods have been described which are based on the use of electromagnetic fields for guiding the metal melt; typical of this is the process described in US Pat. No. 3,735,799, which, like the methods proposed later in accordance with US Pat. Nos. 3,467,166, 3,605,865, 3,735,799, 4,014,379 and 4,126,175, the casting in the downstream direction downwards, ie in the direction of gravity, and has significant operational safety problems, e.g. B. in the event of a power failure and then an uncontrolled outflow of the melt down.

US Pat. Nos. 3,746,077 and 3,872,913 describe processes for the continuous casting of molten metals upwards, that is to say against gravity, in which the molten metals either overcome "gravitationally" hydrostatically (more precisely: "metallostatically") upwards is pressed or sucked. These methods could solve the problem of the operational safety of the continuous casting processes working with electromagnetic fields with regard to uncontrolled outflow of the molten metal downwards, but only at the expense of the inevitable contact of the melt with a molding or molding wall.

From published Japanese patent application No. 48-5413, the task is known to introduce liquid metal from below into an elongated, upwardly moving electromagnetic field for the continuous production of elongated metal objects and to remove solidified product at the upper end of the field. However, an operational solution to the task is not described and is also not possible with the specified means.

This object is achieved according to the invention by a device for the continuous production of an elongated metal object by introducing liquid metal from below into an elongated, upwardly moving electromagnetic field and removing solidified metal at the upper end of the field; the device is characterized by an elongated tubular enclosed molding space (11), the lower end of which is connected to a source (10) for the liquid metal and means are provided for removing the solidified metal from its open upper end; means (28) surrounding the forming space along part of its length for maintaining the electromagnetic field inside the forming space (11) such that the field acts on a column (20) of solidifying metal inside the forming space to control the hydrostatic pressure reduce the column and maintain a majority of its outer surface in pressure-free contact with the surrounding inner surface of the molding space; and a heat exchanger device (30) for removing heat from the molding space (11) in a mass sufficient to solidify the liquid metal.

The pressure-free contact between the column of liquid metal and the inner surface of the molding space surrounding the column, which is essential for the operation of the device according to the invention, is evident in the result, among other things, from the fact that the surface of elongated metal objects obtainable with the device according to the invention, eg. B. rods, does not correspond to the inner surface of the molding space used, but is slightly cross-ribbed or slightly cross-corrugated; In this respect, the usual form terminology of continuous casting technology is not applicable to the device according to the invention, because the surface of a conventional, continuously obtained casting product is completely determined by the inner surface of the mold, that is to say “shaped”, while this is not the case with the device according to the invention the case is. In a typical, with the invented

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Product obtainable according to the device, e.g. In the case of a round bar with a diameter of 8 to 30 mm, for example 15 mm, the outside diameter of the bar is approximately 25 to 50 micrometers smaller than the inside diameter of the inside wall of the molding space.

In the following description, the effect of the electromagnetic field in the device according to the invention is briefly referred to as “lifting action” and the state of practically complete weight compensation or weightlessness of the column achieved with a sufficient lifting action is referred to as “levitation”. Accordingly, a field that is not only capable of holding the metal column contact-free, but also of achieving the practical weightlessness of the column, is briefly referred to as the “levitation field”.

Preferred embodiments of the device according to the invention have the features specified in claims 2 to 7.

The device according to the invention offers various advantages. First of all, it can be manufactured with a structure that is small and comparatively less capital-intensive in comparison to the prior art, and allows economical and reliable processing even with relatively small production quantities. Furthermore, the electromagnetic field can exert an intensive stirring effect on the solidifying melt and thereby a considerable improvement in the grain structure of the products obtained with the device according to the invention.

Furthermore, to remove the solidified product at the upper end of the field, due to the minimization or elimination of heavy, friction and adhesive forces, no special measures or particularly strong pulling devices are necessary and the cooling can be accomplished without any particular problems.

In general, the device according to the invention permits the production of copper and other metal rods, which can then be rolled, annealed and drawn in the usual way for the production of wire, with substantial cost reductions being achievable in certain production areas. For example, welding wires and other products in which the grain size is not of primary importance can be obtained directly in the final form; the composition of the metal is not particularly restricted and e.g. Process copper with high or low oxygen content. Presumably as a result of levitation, the products obtained with the device according to the invention are generally free of pores and cavities.

The invention is explained in more detail with reference to the drawings. Show it:

1 is a partially sectioned front view of the diagram of a device according to the invention together with a hot rolling device,

2 is an enlarged sectional view of part of the device shown in FIG. 1,

3 is a further enlarged schematic representation of the part of the device shown in FIG. 2,

4 shows the schematic representation of a modified form of the part of the device shown in FIG. 3,

5 shows the line network diagram of a coil which can be used in the devices of FIGS. 1 to 4 for generating the levitation field,

6 shows a further modification of the device part shown in FIGS. 3 and 4,

7 shows the photographic representation of a copper rod obtained with the device according to the invention,

8 is an enlarged view of the lower end of the copper rod of FIG. 7.

The molten metal to be cast is held in a tilting holding furnace (not shown in FIG. 1) and from there is brought into the casting crucible 10 as required in order to obtain the desired level of liquid metal in the interior of the molding space 11. The forming space 11 is fastened on the crucible 10 and then extends vertically up to an open upper end through which the product 12 is discharged into the cooling chamber 13, from which it is transferred to the tandem hot rolling stations 14 and 15 cooled and wound up in station 16.

Optionally, the rod 17A can be manufactured directly in the finished size. The molten metal is displaced from the crucible 10 by supplying it with a gradient as a column of liquid metal into the shaping space 11 from the holding furnace, which is tipped at intervals or continuously to release molten metal into the crucible 10, as is required for continuous production. In the preferred mode of operation of the device, the column 20 (FIG. 2) is first produced from liquid metal in this way and is then kept at a level above that level at which the weight reduction or levitation by electromagnetic traveling waves is effective, which affects the hydrostatic ( Metallostatic) pressure of the column reduced or eliminated. The upper end of the column 20 is thus first brought into the lower part of the molding space 11, where at least the upper part of the column 20 becomes essentially weightless when the molding space 11 is supplied with electricity.

The shaping space 11 preferably has an open-ended tube 25, which can consist of heat-resistant material and is attached to the crucible 10. With successive phases of the multi-phase power source of FIG. 5, for example, twelve windings of the coil 28 are arranged in a vertically divided arrangement around the tube 25 substantially perpendicular to the tube axis and connected in groups of three; this creates a magnetic field that induces eddy currents in the tube 25 in the liquid metal, which leads to an upward lifting effect on the metal to be cast. This six-phase levitator is ready for the formation of a progressive traveling wave which moves at a speed proportional to the distance between successive closed river loops and the excitation frequency. The coil 28 is arranged vertically along the tube 25 so that the weight of the liquid metal and the solidified metal in all sections except the lowermost section of the tube 25 is reduced to the desired extent during the entire operation, preferably essentially to zero weight can be.

An experimental model of the device according to the invention, which was used for the continuous production of copper, aluminum and bronze rods to test the operability of the device, had a levator section with thirty-six turns of copper tubing, which were spaced six turns to 2.5 cm were wound, which resulted in a total levitator length of about 15 cm. The twelve phases were shifted by 60 ° to the phase of their immediate neighbors and the length of the lifter corresponded to two wavelengths. The diameter of the weight reduced metal columns was 22 mm and the column was held at a frequency of approximately 1200 Hertz without acceleration (i.e. the weight reduction ratio was essentially 1.0); the total direct current supply to the direct current / alternating current converter used as the current source for the levitator was in the range of approximately 7 to 10 kW. The heat exchanger explained in FIG. 4 was used.

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Although very different heat exchangers can be used for the device according to the invention, the most suitable and consequently preferred heat exchanger has the structure identified by the reference number 30 in the drawings. It is a construction of processed rolled sheet metal with upper and lower annular spaces 31 and 32 and a cylindrical section 33, which is arranged adjacent to the tube 25 in contact with its annular outer surface. Liquid coolant, suitably tap water. is continuously fed into the upper space 31 from a source (not shown), flows through the section 33 during operation and is led into a drain through the lower space 32, removing the liquid metal and leads to the heat absorbed by the freshly solidified metal product. The windings of the coil 28 are arranged outside the central section of the heat exchanger as shown in Fig. 3, extend essentially in an evenly divided ratio from one room to the other and are arranged close to each other radially around the heat exchanger. A suitable material for the heat exchanger 30 is stainless steel, which offers sufficient corrosion resistance and heat exchange effectiveness.

In a preferred embodiment of the operation of the device according to the invention, the crucible 10 is charged with a molten metal, such as copper, for the continuous production of objects with a large length, such as rods. First, the metal is melted and fed to the crucible 10 from the holding furnace to form a column of liquid metal 20 with its upper end inside the levitator of the molding space 11. A start-up rod 40 is inserted through the upper end of tube 25 to bring the lower end of the rod into contact with the top of the liquid metal column. Tap water flowing through the heat exchanger at high speed solidifies the upper part of the liquid column in contact with the rod. The rod 40 and the melted rod end are then pulled up out of the tube 25 at approximately the rate of solid rod formation. The liquid column is kept essentially weightless at least over most of its length and in this way is kept in essentially depressurized contact with the tube 25 when the levitator is operated in this position; continuous operation gives an endless and completely bubble-free metal rod with a smooth, shiny, slightly wavy surface. This rod is guided through the chamber 13 and cooled there by spraying with water to such an extent that it can be finally cooled and wound with or without previous hot rolling.

If the level of the liquid metal column 20 drops during operation, additional melt is introduced into the casting crucible 10 with supply at a gradient and the operation is continued without interruption.

The device according to the invention has proven itself in numerous tests with different metals. In particular, aluminum, copper and bronze alloy were processed according to the procedure described to bars of about 22 mm in diameter, which were completely free of bubbles, had a consistently uniform composition and a smooth, shiny, somewhat wavy surface. However, the electrical power supplied to the levitator was varied according to the metals processed in order to adapt the extent of the weight reduction to the weight of the respective material, i.e. set and maintain a substantially zero acceleration condition. Contrary to expectations, precise control of the electromagnetic field strength is not necessary to maintain this balance of levitation and weight.

5 With regard to weight reduction or levitation, the column of liquid metal is accelerated upwards if the lifting or levitation force is greater than the weight; this leads to a reduction in the lifting force as a result of the reduction in the cross section of the column, while the counterpart is the case when the lifting force is less than the weight. As long as this effect of the levitator field acts on a considerable part of the length of the column of liquid metal and solidified product inside the molding space, those parts of the column at the lower i5 and upper end of the tube 25 where the levitation forces on average are only about half that Above, supported by the pressure drop to increase the liquid column to the initial height or by the lifting force of the starting rod 40. Accordingly, when the liquid column is built up, a small upward acceleration is generated by the levitation forces in the area of the lower end of the column; if the column of liquid metal then slowly moves up to a point approximately equal to the radius of the levitator windings, it will enter fields 25 which are strong enough to bring the column into a substantially weightless condition and maintain it that contact with the inner surface of the molding space, e.g. the pipe 25 is essentially depressurized. By increasing the pressure drop it is therefore possible to increase the upward flow velocities; usually the initial pressure drop can be used to regulate the speed of such a flow, the coil then serving to keep such an initial flow relatively constant over the top of the liquid column.

In the interest of limiting the size of the device according to the invention and in particular the coil for the levitator field and also to reduce the power required to hold the column, a maximum heat exchange efficiency is expedient; the heat exchanger described above can cause a state approximately equivalent to water quenching and is achieved by enveloping the rising column of liquid metal with a rapidly flowing, turbulent stream with a relatively small annular cross section of liquid coolant. The heat exchange between the metal column 20 and a surrounding graphite tube 25, which carries the inner wall of the heat exchanger arrangement made of stainless steel on the cylindrical surface, offers such a very effective heat transfer. In the described embodiment of the heat exchanger, this capability can be increased by means of short annular inner fins 43 which prevent laminar flow and cause turbulence in the cooling liquid which flows from the upper annular space 55 31 through the heat exchanger to the lower annular space 32.

Although the cross-sectional size of the products obtainable with the device according to the invention is theoretically unlimited, more practical considerations are used in the production of rods with a diameter range from 5 mm to 50 mm, with diameters from 8 to 30 mm being preferred for copper rods. If necessary, the desired rod diameter can be reduced by hot rolling and a fine grain structure sufficient for drawing wire can be achieved. The inner diameter of the tube 25 and the process parameters are preferably selected such that a minimal annular gap is present between the liquid metal of the column 20 and the tube 25

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is there. This is below the point at which solidification of the liquid metal causes the cross section of the column to shrink, although this shrinkage is quite small. The gap designated by reference numeral 45 in FIGS. 2 and 3 is merely schematic in nature and is not intended to reflect the position or the dimensions of the annular gap.

In tests to test the suitability of the device according to the invention for the production of essentially homogeneous alloy products with a tendency to selectively separate and solidify in separate components, an aluminum-bronze alloy was melted and processed at three different times with the device according to the invention with the change that (1) the heat exchanger was a simple copper tube wrapped around and in heat exchange contact with the tube 25 (as shown in Fig. 4) and (2) that a column 20 was constructed from liquid metal and by displacing the Melt from the crucible 10 was maintained with a flask instead of being fed from a holding furnace. The analysis results of the alloys used to produce the melt and the three rod-shaped products are given in the table; it can be seen that the alloy composition is preserved within the accuracy of the sampling and the analysis methods.

table

element

Source material

Vers. I

Vers. 2

Vers. 3

Fe

2.64%

2.69%

2.65%

2.71%

Sn

0.01%

0.03%

0.01%

0.02%

Zn

0.01%

0.03%

0.02%

0.02%

AI

10.35%

10.12%

10.02%

10.05%

Mn

0.49%

0.76%

0.68%

0.72%

Si

0.028%

0.049%

0.039%

0.046%

Ni

5.00%

4.99%

4.90%

4.99%

Other

0.03%

0.03%

0.03%

0.03%

Cu

rest

rest

rest

rest

The device of FIG. 4 is a device that includes a tube 50 and a series of twelve separate copper 52 cooling tubes that are wound on the tube 50, distributed along its length and separately supplied with cooling liquid, e.g. tap water (not shown) will. The tubes 52 are also connected in groups of three to successive phases of the multi-phase electrical power source according to FIG. 5. As in FIG. 3, the individual windings are designated with the letters A, B, C, which relate to the three phases of FIG. 5. This device replaces the tube 25 of the heat exchanger 30 and the twelve coils 28 of the device of Fig. 3. Again, the column of liquid metal 55 is weightless for most of its length, but because of the annular gap 57 over the same length without contact Pipe 50 held.

A protective gas can be introduced into the space 57 in any way; when casting copper, nitrogen or a mixture of nitrogen, hydrogen and carbon monoxide is preferred.

The device shown in FIG. 6 can also be used instead of the corresponding device of FIG. 3 if an electromagnetic weight reduction is not required but an electromagnetic holding is desired or is necessary for the continuous production. The column 60 made of liquid metal is held without contact to the tube 61 over at least part of the column, in which the column surface solidifies. Here, the electromagnetic shaping effect, as in the case of the operation explained in FIG. 4, generally extends well below the solidification limit of the column surface because of the annular gap 63.

Similar to FIG. 4, the device according to FIG. 6 has a series of copper tube windings 62, which, however, are connected to a single-phase electrical power source 64 and additionally serve for cooling by being in good heat transfer with the graphite tube 61, in terms of structure and function corresponds to the pipes 25 and 50. In operation, water is fed into the windings 62 from a suitable supply source (not shown) at maximum flow rate. The water, which contains the heat absorbed by the hot metal within the tube 61, is either passed out of the windings 62 into a reservoir for cooling and recirculated, or passed into a drain channel.

FIGS. 7 and 8 show a copper rod produced continuously with a device according to the invention according to FIG. 3. The procedure was as described in connection with FIGS. 1 to 3. The slightly wavy, smooth, shiny surface of the rod comes about because the column made of liquid copper does not exert any pressure on the inner wall of the molding space in the area of the solidification of its surface; presumably the eddy currents induced in the solidifying copper also contribute to the characteristic appearance of the product; the otherwise completely dense (measured density = 8.9) and accordingly bubble-free product had an apparently uniform composition throughout. The rod diameter was almost exactly 16 mm, which corresponded to the inner diameter of the tube 25. In the area of the smooth matt tape at the bottom, i.e. in the figure, the left end of the rod had a diameter of about 50 | in the larger diameter than in the shiny, wavy area of the rod surface; in the area of this matte band, the rod had solidified below the effective levitation area and in pressure contact of the molten copper with the inner surface of the molding space.

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Claims (7)

665 788 PATENT CLAIMS 1.Device for the continuous production of an elongated metal object by introducing liquid metal from below into an elongated, upwardly moving electromagnetic field and removing solidified metal at the upper end of the field, characterized by an elongated, tubular, enclosed molding space arranged in an upright position ( 11), the lower end of which is connected to a source (10) for the liquid metal and means are provided for removing the solidified metal from its open upper end; means (28) surrounding the molding space along part of its length for maintaining the electromagnetic field inside the molding space (11) such that the field acts on a column (20) of solidifying metal inside the molding space to control the hydrostatic pressure reduce the column and maintain a majority of its outer surface in pressure-free contact with the surrounding inner surface of the molding space; and a heat exchanger device (30) for removing heat from the molding space (11) in a mass sufficient to solidify the liquid metal. 2. Device according to claim 1, characterized in that the molding space (11) has an upright, elongated tube (25, 50, 61) for receiving the column of solidifying metal and surround the tube by a heat exchanger for solidifying the liquid metal The device (28) for maintaining the electromagnetic field is a coil (28, 52, 62) comprising the tube (25, 50, 61). 3. Device according to claim 2, characterized in that the coil has a plurality of windings (28, 52) for connection to successive phases (A, B, C) of a multi-phase electrical power source. 4. Device according to one of claims 2 or 3, characterized in that the tube (25, 50, 61) consists of heat-resistant material and has a substantially uniform inner diameter. 5. The device according to claim 1, characterized by a crucible (10) for receiving molten metal (20), which crucible communicates with the lower end of the molding space (11, 25), and by a device to liquid metal in the molding space up to to move up a height above the lower end of the winding (28). 6. The device according to claim 3, characterized in that the current source is a three-phase generator which is capable of generating a uniform symmetrical electromagnetic field. 7. The device according to claim 2, characterized in that the coil (52, 62) has hollow turns which are capable of passing coolant and to function as a heat exchanger.