JPS6192758A - Long-sized metallic product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to metal melting and solidification technology, and in particular to a novel continuous casting method for manufacturing long metal products, a unique apparatus for carrying out the method, and the resulting It concerns new products.

Continuous casting has been one of the technologies that has been actively researched in the metallurgy field for a long time, and a relatively large number of patents and technical documents have been published. However, for a number of reasons, only very few of the concepts described in these numerous documents have been translated into industrial implementation. Continuous metal casting processes that have been put into practice have typically utilized some type of mechanical contact mold to contact, confine, or form the molten steel while it solidifies. These molds took the form of casting wheels, casting belts, and, in the case of so-called dip molding, seed rods useful as internal molds.

As will be discussed in more detail below, the present invention utilizes alternating electromagnetic fields to create, support, and confine continuous contact between an upwardly moving column of molten metal and an enclosing surface, so that the casting wheel,
It has features that make casting belts, seed rods, or other contact molds used in industry today unnecessary.

In addition to simplifying continuous casting for metal forming and other industrial production systems, the method of the present invention can replace the more expensive billet casting and hot rolling methods commonly used today. This opens the door to the possibility of producing small to medium quantities of brass, nickel and other metal rods.

With much the same purpose as the present invention, it has therefore been proposed to utilize an electromagnetic mold to maintain a pool of metal melt at the top of the downwardly moving ingot, while allowing the lateral outside of the pool to solidify. . This method is described in U.S. Patent No. 3467.
No. 166 (Gettzeleb et al.), and No. 36 of the same
It was further developed in No. 05865 (Getzeleb); No. 3735799 (Carlson) - No. 4014379 (Getzeleb); No. 4126175 (Getzeleb). In both cases, the addition increase is longitudinal and the melt is fed semi-continuously or continuously by gravity flow to the top of the descending ingot. One of the significant drawbacks of this method is the lack of fail-safe properties of upward casting. That is, in the event of a sudden power failure, the molten metal would simply flow back into the holding vessel in the present invention, whereas in the above method it would spill out of the downward casting apparatus. Also, since there is a possibility of breakout if there is melt overflow in downward casting, both the melt feed rate and the ingot removal rate must be carefully controlled at all times. Moreover, these speeds are severely limited by heat exchange problems, thus reducing the possibility of industrial implementation of this type of continuous casting.

U.S. Patent No. 37460 assigned to Autokunpo Oi
According to another method described in No. 77 (Rohikoski et al.) and No. 13872913 (Rohikoski), a freshly formed and cooled cast product is discontinuously and occasionally interspersed with the upper end of a mechanical mold containing molten metal. When removed from physical contact, the molten metal is forced buoyantly into an open, vertical mechanical mold or is sucked up by a vacuum. Fail-safety is thus obtained, but the major drawbacks of external contact molds must be accepted.

The discovery of the present invention, as will be described in detail below with reference to the accompanying drawings, allows various advantages to be obtained at all times in continuous metal casting operations. These results are also achieved when producing rods of copper and other metals that are conventionally rolled, annealed, and drawn to make wire. Furthermore, there is no economic disadvantage; on the contrary, substantial savings in production costs are possible for certain production lines. For example, the present invention allows the production of welding rods or other products in which particle size is not critical by direct continuous casting to the desired final size. Yet another important advantage is that the present invention is generally compositionally free and suitable for the production of copper rods of high to low oxygen content copper, as well as other metals and alloys such as aluminum, aluminum-based alloys, copper Applicable to the production of base alloys, steel and other rods, or other long objects.

The basic idea of the invention is to move a liquid metal column to and through a forming zone where it is sequentially cooled and solidified while being exposed to an electromagnetic field, which field is necessary for removing the resulting casting from the forming zone. The continuous upward casting method helps to reduce the force. This important new effect of the electromagnetic field is achieved in accordance with the invention either by levitation or by confining the molten metal column over most of its length, especially in the area where its solidification is taking place. Flotation is accomplished by electromagnetic traveling waves applied in a preferred embodiment of the invention so that a large portion of the length of the liquid metal column remains substantially weightless throughout the entire casting operation. In containment methods, the electromagnetic field is steady-state, but still applied continuously, such that a large portion of the total length of the liquid metal column is maintained without any contact with the physical mold structure. In yet another aspect of the present invention, flotation and confinement effects are utilized simultaneously such that a large portion of the length of the molten metal column is rendered and held in a substantially weightless state and is connected to the physical mold structure. Avoid contact. Thus, the electromagnetic means functions both as a lifting action and a confinement or molding action.

This fundamentally new approach has important advantages. Electromagnetic levitation is a process in which a metal column is virtually weightless, and the newly solidified part of the metal product can be cooled to gain enough force to support the weight of the metal below, or the product can be shaped. It is also unnecessary to withstand tensile forces to overcome mold friction during removal from the area, opening the door to high productivity. In other words, the work required to peel the solidified metal product from the mold is greatly reduced in this mode of operation, since this work is a function of the mold casting friction, which is a function of the friction at the interface. This is because it is proportional to the compressive force.In the practice of the present invention, the molten metal column is in a weightless state, and therefore, there is pressureless contact between the metal column and the mold, so the compressive force is almost nonexistent. Therefore, without compromising the heat exchange effect of the physical mold, the main advantage of electromagnetic confinement is the need to create a large space or gap between the physical mold and the molten metal column over most of the total length of the molten metal column. There are no benefits.

New opportunities for high productivity are provided in the confinement aspect of the present invention as well as in the combined aspect of both electromagnetic levitation and confinement. In each case, the newly solidified product is removed and the molten metal column is advanced into the solidification zone (
The required force becomes extremely small because frictional force and adhesive force are eliminated. Further, in terms of heat exchange effect, better heat exchange can be achieved by reducing the gap between the molten metal column and the surrounding physical mold in any of the embodiments.

Another advantage of the combination embodiment is that flotation is easily performed over a wide range of power input conditions and kept under tight control. Thus, the inventors unexpectedly discovered that this embodiment has remarkable self-regulating properties, with confinement and buoyancy forces being related to its effectiveness. If the diameter of the liquid metal column is set to a certain desired value, if the upward movement speed of the molten metal column increases, its cross-sectional size will decrease, and therefore the electromagnetic lifting force applied to the metal column will decrease. . As the upward velocity becomes slower and therefore the cross-sectional area of the metal column becomes larger, the lifting force increases, so that the system itself becomes somewhat
Even if the product exhibits a tendency to disorder, equilibrium cannot be reached, and the cross-sectional size and shape of the product will be substantially uniform.

As generally stated above, the inventors have disclosed that preferred embodiments of the present invention, or alternative embodiments, provide novel continuous casting methods for metals, metal mixtures, metal alloys, and virtually any other electrically conductive molten material. Another closely related and unexpected finding is that the removal of heat from a column of liquid metal under conditions of virtually zero hydrostatic head. In the presence of sufficient induced eddy currents, solidification proceeds rapidly and the liquid in the metal column is agitated as the metal column is moved through the levitation zone, thus exhibiting a highly selective tendency for segregation and solidification. Even in the case of metal mixtures, cast products with a high degree of homogeneity can be obtained.

Generally speaking, the method of the present invention that utilizes the above knowledge and discovery is to create an alternating electromagnetic field that extends upward in a narrow direction, introduce a liquid metal into the lower part of this electromagnetic field, and move the metal upward in the electromagnetic field. The process consists of solidifying and extracting the solidified metal product from the top of the electromagnetic field.

As already mentioned, in a preferred embodiment, the present invention provides each of the steps described above, in particular the step of applying a liquid metal in an electromagnetic field to the extent that most of the metal becomes substantially weightless and in pressureless contact with the surrounding physical mold structure. Continuous casting is carried out by an electromagnetic curved levitation process.

Additionally, the present invention provides each of the above steps, particularly the step of electromagnetically levitating most of the liquid metal to a substantially weightless state, and at the same time electromagnetically holding the weightless liquid metal so that it does not come into contact with horizontal supporting structures. including.

In a further aspect of the method of the invention, a large portion of the surface of the liquid metal within the electromagnetic field is maintained free from contact with the supporting mold structure (particularly in the portion of the length of the liquid metal column where platinum metal assimilation is taking place). An electromagnetic field is applied to

In this method, which includes only containment features, the liquid metal is not electromagnetically levitated.

In yet another preferred embodiment of the invention, the flotation effect is selected such that at least a portion of the liquid metal column is substantially hydrostatic headless, ie, substantially weightless. The buoyancy force applied to move the metal column upwardly out of the forming area is provided by a starter rod that is joined to the liquid metal column early in the process, causing the liquid metal column to solidify in contact with the lower end of the rod. . As the lower end of the liquid metal column is continuously produced in a stable manner in the continuous casting process, the rod is also drawn upwardly over the successively solidified portions of the cast body by suitable means.

In another embodiment of the present invention, in which a substantial electromagnetic levitation effect is not applied to the liquid metal column, a substantial portion of the entire length of the dragon-shaped metal column, especially the portion where solidification occurs, is removed from the surrounding mold structure. kept from coming into contact with surfaces.

That is, the liquid metal column is electromagnetically confined by a stationary electromagnetic field that serves as a structureless mold, the cross-sectional size of the metal column is therefore easily controllable, and the length of the liquid metal column thus confined is simply It is possible to use one electromagnetic field or many adjacent stationary electromagnetic fields, so the choice is free.

In any of these various embodiments of the method of the present invention, the length of the electromagnetic field is appropriately larger than the diameter of the electromagnetic field,
It is also preferred that it be fairly large, and best that the length of the floating metal column is greater than its diameter.

Briefly, the novel apparatus of the present invention comprises: an elongated cylindrical casting vessel placed in an upright position to receive liquid metal for solidification; means for directing the liquid metal to a lower portion of the vessel; heat exchange means associated with the vessel for cooling and solidifying the metal, means for removing the solidified metal from the top of the vessel, and electromagnetic field generating means disposed around the vessel along part of its length. Become.

The electromagnetic field generating means includes a number of electromagnetic coils connected to successive phases of the multiphase current source to produce an upward lifting effect on the liquid metal column within the container.

The term "lift effect" means that a continuous column of liquid metal is forced upwardly into contact with the lower end of the forming product rod. Pores and pipe flows are thus avoided. More specifically, the apparatus of the invention has a crucible for containing a bath of molten metal communicating with the lower end of the casting vessel, and is associated with the crucible for producing a column of liquid metal and suspending the column within the casting vessel. It includes means for pushing upwardly to a certain level above the lower end of the means. In a preferred embodiment, the means for creating the metal column takes the form of a hydrostatic pressure source, which serves to move the liquid metal and hold it in place to form the metal column.

The novel product of the present invention is a long metal body that is fully dense, of substantially uniform diameter, and of identical composition from piece to piece. In as-cast conditions, such bars, rods, etc. are held electromagnetically out of contact with the lateral supporting structures in preferred embodiments, where the metal being formed before, during, and immediately after assimilation. Also, since the solidifying liquid metal is constantly stirred by the induced eddy currents, it has a smooth and somewhat corrugated surface. In a preferred embodiment, the product is a rod of highly phase-separable composition, resulting in a high degree of homogeneity due to induced eddy currents.

In the practice of the present invention, the average error in the diameter of the rod that is kept buoyant and in physical contact with the tube is about 0.001 to O,OO2.
It has been discovered that it is in.

This and the unique surface texture demonstrate that solidification of the bar product was accomplished without contact with the cooling tube surface.

As shown in FIG. 1, the molten metal to be cast is placed in a tiltable holding furnace (not shown) from which the molten metal is deposited in the amount necessary to maintain the desired level of liquid metal within the casting assembly 11. However, ity builders are supplied to 10. This casting assembly is mounted on top 10 and extends vertically upwardly from there to an open top end through which new cast bars 12 are discharged into a cooling chamber 13 from which tandem Hot rolling station 14
and 15, and finally cooled and coiled at a coiling station 16. Alternatively, rod 17A is directly cast to the final desired size for use.

The molten metal is fed into the crucible 10 by tilting the holding furnace to the charging position from time to time or continuously as needed during the continuous casting process, and is fed into the crucible 10 by gravity flow from the holding furnace.
Cast assembly 11 as liquid metal column from crucible 10
Sent inside. In a preferred embodiment of the invention, the liquid metal column 20 (see FIG. 2) is initially created in this manner and then (electromagnetic traveling wave levitation is performed to a height above which the hydrostatic head of the metal column is reduced or eliminated). In other words, from the beginning, the upper end of the metal column 20 is contained within the lower part of the assembly 11, and when the flotation device of the casting assembly is connected to the power source, at least the upper end of the metal column 20 is substantially It becomes essentially weightless.

The casting assembly 11 has an open ended revitator tube 2.
5, which is made of refractory material and has a crucible 1
0 to receive liquid metal for solidification from there, and from the upper end of the cooling chamber 13 as a cast product.
Finally, the product is sent to

For example, 12 coil groups 28 are vertically spaced around the levitation tube 25 as windings arranged substantially perpendicular to the tube axis, and are arranged in successive phases of the polyphase power supply in FIG. They are connected in groups of three to create a magnetic field that generates a Foucault current in the liquid metal in the tube 25 and gives an upward lifting effect to the metal being cast. The coils 28, which form the heart of the reviator means, are arranged vertically along the length of the reviator tube and are operable to create a progressive traveling wave that moves at a speed proportional to the excitation frequency and the distance of the reviator. All of the liquid metal, with the exception of the lower part, as well as the solidified metal product, is buoyed during the casting operation to the desired extent, preferably to substantially weightlessness.

An experimental model of the method and apparatus of the invention was used to manufacture copper, aluminum and bronze rods in continuous casting to demonstrate the effectiveness of the apparatus. A floating section of 36 rotations and an overall length of 6 inches was provided. Each of the 12 phases was offset 60' in phase from its immediate neighbor, and this section was effectively two wavelengths long. The floating metal column The diameter of the metal column was 22cm, and the total DC power supplied to the motor alternator AC leveler power source was approximately 7 to 10 kilowatts, so at frequencies around 1200 Hz, this metal column had no acceleration (i.e., levitation rate). The heat exchanger shown in FIG. 4 was used.

Although heat exchangers of various designs and configurations may be used in the apparatus of the present invention, the one best suited to the purpose and therefore preferred for this combination is that shown in FIG. upper and lower annular air chambers 31 and 32;
and a cylindrical portion 33 formed around the reviator tube 25 and in contact with its annular outer surface. A liquid coolant, preferably tap water, is continuously supplied from a source (not shown) to the upper chamber 31 and flows through the section 33 during the metal casting operation and is drawn through the lower chamber 32 to a drain pipe 25. carries away the heat absorbed from the liquid metal within and the newly solidified metal product.

As shown in FIG. 3, a coil 28 is provided outside the central section of the heat exchanger and extends substantially from one chamber to the other at narrow intervals evenly spaced around the heat exchanger. The preferred material for constructing the heat exchanger 30 is stainless steel from the standpoint of corrosion resistance and heat exchange performance.

In carrying out the method of the present invention, an elongate product, such as a continuously cast rod, and a melt of a metal, such as copper, are placed in a crucible 10. That is, first, as a preliminary step, metal is melted and the molten metal is sent from the holding furnace to the crucible 10 to form a liquid metal column 20 whose upper end is within the floating part of the casting assembly 11. A starter rod 40 is inserted through the upper end of tube 25 so that the lower end of the rod contacts the top of the liquid metal column. Tap water is passed through the heat exchanger at full speed to solidify the top of the liquid metal column while remaining in contact with the rod. Rod 40 and attached rod end are then withdrawn upwardly from tube 25 at approximately the same rate as solid rod formation. The liquid metal column is kept substantially weightless over at least a large portion of its length by operating the levitator means in this manner and is kept in substantially pressure-free contact with the tube 25, and by continuing this operation. A continuous length of metal rods having a smooth, shiny, somewhat corrugated surface and being sufficiently dense throughout is made. The bar is passed through a chamber 13 where the temperature is lowered by water spray to the point where it is suitable for final cooling and coiling, during which time an intermediate hot rolling may be carried out. It may not be done.

As this process progresses, as the height of the liquid metal column 2o decreases, additional melt is pumped into the casting crucible 10 by gravity flow.
The casting operation thus continues uninterrupted.

It has been demonstrated that the method of the present invention can be successfully carried out in a number of experiments involving various metals using this apparatus. In particular, aluminum, copper and bronze alloys were cast into bars in the operations described above. In each case, the bar products were uniform in diameter, about 22 mm, fully dense, of uniform composition throughout, and had a smooth, shiny, and somewhat corrugated surface. However, the power input to the levitator is varied for different casting materials in order to make the levitation force approximately equal to the weight of the object being levitated, ie, to create and maintain a substantially zero acceleration levitation condition. Contrary to expectations, it was not necessary to precisely limit the strength of the electromagnetic field to maintain the levitation car's balance.

If the levitation force is greater than the force of the weight, the liquid metal column will be accelerated upward and the cross-sectional area of the metal column will become smaller, reducing the lifting force, and if the lifting force is less than the force of the weight, the opposite is true ( This will happen.

While the full effect of this flotation means is applied to most of the total length of the liquid metal column and to the solidified bar product in the levitator tube, the metal column sections at the lower and upper ends of the levitator tube, where the flotation force averages about 7 (only 1.5 mm) is supported by the pressure head provided to raise the liquid column to its original height and by the lifting force applied through the starter rod 40, respectively. Thus, these lower end levitation forces provide a small upward acceleration as the liquid column is being formed, and as the liquid metal column gradually moves upward to a point approximately equal to the radius of the levitation coil, The metal column is subjected to an electromagnetic field strong enough to render and maintain it substantially weightless, so that its contact with the levitating tube is substantially pressureless. Therefore, by increasing the pressure head, the upward flow velocity can be increased, and the initial pressure head can be used to adjust the velocity of the flow, and the initial flow can be spread over a certain length above the liquid column. Flotation means can be made useful to maintain a relatively constant value.

Maximum heat exchange efficiency is desirable in order to reduce the size of the casting equipment, especially the flotation assembly, and to minimize the amount of power input for maintaining the liquid column during the surfaceization stage, and for this purpose the heat exchanger is By effectively enclosing the liquid metal column in a rapidly flowing, turbulent, and fairly small cross-section liquid coolant reflux, conditions virtually approximate water cooling. The heat exchange between the metal column 20 and the surrounding graphite tube 25, which rests against the cylindrical surface of the stainless steel inner wall of the heat exchange assembly IJ-, can perform a very effective heat exchange. In the improved heat exchanger shown, heat exchange is further improved by short internal annular ribs 43, which serve as a barrier to the laminar flow moving downward through the heat exchanger from the upper chamber 31 to the lower chamber 32. Creates turbulence in the coolant liquid.

Although there is no theoretical limit to the cross-sectional size of the product cast by the method of the present invention, from a general practical point of view, the diameter of the as-cast rod is approximately 5 mm to 50 Vrm; It is preferably 8 to 30 mm. The rod is then hot rolled to the desired bar diameter and to the fine grain structure required for wire drawing. However, in any event, the internal diameter and operating parameters of the levitating tube 25 are selected in accordance with a preferred embodiment of the invention such that the clearance between the metal column 20 and the tube 25 is the minimum annular gap number. This is selected as described above below the point where solidification of the liquid metal causes contraction of the cross-sectional area of the metal column, albeit to a very small extent. The gap designated by 45 in FIGS. 2 and 3 is schematic and does not accurately represent the location of the annular gap or its dimensions.

For the purpose of testing the applicability of the method of the present invention to substantially homogeneous castings of alloys in which the respective components tend to selectively segregate and solidify, an aluminum-bronze alloy was melted and The same equipment as above was used, except that 1) the heat exchanger was a single piece of steel pipe wrapped around the revitator pipe 25 so as to be in heat exchange contact; see Figure 4), (2)
) The liquid metal column 20 was created and held by moving the melt from the crucible 10 by piston action instead of by gravity flow from a holding furnace, and three castings were carried out in accordance with the method of the invention. The results of the analysis of the alloy used to make the molten metal as well as the results of the analysis of the three bar products are shown in Table 1 below, or within the accuracy of the sampling and analytical methods available from this table, the alloy composition. It was found that the consistency was sufficiently maintained.

Table 1 Fe 2.64%2.69%2.659G 2.71
%SnO,010,030,010,02Zn
O,010,030,020,02Ai 10.351
0.1210.0210. O5Mn Q, 49 0.
76 0.68 0.72Syu 0.028
0.049 0.039 0.04
6Ni 5.00 4.99 4.90 4.99 Others 0.03 0. O'3 0,03
0.03 Cu Residue Residue Residue ResidueThe apparatus of FIG. This is a subassembly consisting of 12 copper cooling pipes 52 connected to (not shown). The tube 52 also has a fifth tube for the upward lift effect mentioned above.
The successive phases of the polyphase current source shown in the figure are connected in groups of three, thus serving two practical purposes.As also shown in FIG. The components and their power sources are represented by A, B, and C, which relate to the three phases of FIG. 28, but in use provides both floating and containment or molding functions. In other words, this device
A liquid metal column 55 similar to 0 is weightless over most of its length, but unlike the metal column 20, over the same length it is separated from the tube 50 by an annular gap 57, preferably of small radius dimension. It is used so that it is held apart and not in contact with it.

A cover gas that does not deleteriously react with the metal being cast is used and supplied into space 57 in any desired manner. Preferred for steel casting is nitrogen or a mixed gas of nitrogen, hydrogen and carbon monoxide obtained by burning natural gas and separating and removing H2O and CO2 from the gas.

The subassembly of Figure 6 may also be used in place of the corresponding subassembly of Figure 3 when electromagnetic levitation is not required in an upward casting operation, but electromagnetic confinement is desirable or necessary in the production of continuous cast metal products. used. That is, as shown in FIG. 6, the liquid metal column 60 is held so that at least the solidified portion of the surface of the metal column does not come into contact with the levitator tube 61. In fact, in this embodiment of the method of the invention, the electromagnetic mold effect is maintained well below the surface solidification level of the metal column and the annular gap 63 is created, as in the operation shown in FIG.

Similar to the device of FIG. 4, the device of FIG. 6 includes a series of steel tube coils 62 connected to single phase power J64;
A graphite tube 6 which also serves as a cooling means and corresponds in structure and function to the revitator tubes 25 and 50
1 and has good heat exchange contact. In operation, water is also continuously supplied to coil 62 from a suitable source (not shown) at a maximum flow rate. Water carrying heat absorbed from the hot metal in tube 61 is discharged from coil 62 into a cooling circulation sump or drain.

Continuously cast copper rod products of the present invention, shown in FIGS. 7 and 8, were made by the method of the present invention using the apparatus of FIG. In particular, when an upward casting operation as described in connection with FIGS. 1-3 is carried out, the electromagnetic levitation mode keeps the liquid steel column weightless, but the entire top of the column is brought into pressureless contact with the levitation tube. used. Holding the liquid steel column free from pressure on the horizontal support structure at the point where the steel column surface was solidifying resulted in a smooth, shiny bar product surface with some undulations. This is also the result of eddy currents induced in the solidifying copper by the levitation field. This sufficiently dense product (8.9 in actual measurements and calculations) had an apparently homogeneous composition throughout.The diameter of the rod was close to the 16 mm inner diameter of the revitator tube 25 in which the rod was made. The smooth matte band at the lower or left end of the bar is about 2 mils larger in diameter than the shiny rippled surface area that solidified without pressure contact with the levitator tube. This short, smooth, matte band at the lower end of the rod, solidified in the heat exchanger zone below the buoyancy zone, was therefore in pressure contact with the levitation tube.The apparent pressure and non-pressure contact areas are The above difference is clear.

[Brief explanation of the drawing]

1 is a schematic elevational view of the apparatus of the present invention in combination with a hot rolling mill; FIG. 2 is an elevational view of the casting assembly of the apparatus of FIG. 1; and FIG. 4 is an enlarged sectional view of a casting container portion of an apparatus according to another aspect of the present invention; FIG. 5 is an enlarged sectional view of a casting container portion of an apparatus according to another embodiment of the present invention;
6 is a wiring diagram of a levitation coil used in the assembly of the device shown in the figure; FIG. 6 is a cross-sectional view of the casting vessel portion of the device according to yet another aspect of the invention; and FIG. This is a photograph of the obtained copper rod, and Figure 8 is a photograph of the copper rod obtained.
Of the copper rod in the figure, / 1. -;) Medium 1. a.

Claims (1)

[Claims] 1. Continuously cast long metal products that are sufficiently dense throughout, have a homogeneous composition throughout, and have a corrugated pattern on the surface.