DE1056841B - Electromagnetic stirring process - Google Patents

Description

kl. 4Od 1/30

INTERNAT. KL. C 22 pounds

W 19212 VI / 4Od

REGISTRATION DAY: JUNE 11, 1956

NOTICE
THE REGISTRATION
AND ISSUE OF THE
ACSLE FONT:

6. Sl A I 1 9 5 9

The invention relates to electromagnetic stirring methods and is suitable for "use in Stirring liquids at elevated temperatures when using mechanical agitators would cause undesirable contamination of the liquid or inconvenient for other reasons were.

The invention described here uses a reactive force which results from the interaction between an electrical current flowing through the material to be stirred and a magnetic field applied at an angle relative to the direction of current flow, transverse to the liquid material. Processes in which liquid materials can be suspended by a counterforce resulting from the interaction between a current flowing through the liquid and a magnetic field applied above the liquid are known per se. In such methods, it is important that the retroactive force or counterforce be uniform or symmetrical in order to provide motion to the liquid body as a whole.

In the methods outlined here it is necessary to create a fluid flow in the body, that the forces causing the flow become asymmetrical. The general way in the one Such asymmetry is created within the liquid body - results from the use of a magnetic field that is not uniform over the length de? Body is and is in interaction with a current density which is uniform over the cross-sectional area of the body. Because the opposing force the product of the field and the component of the current flowM? s is proportional to the counterclockwise is advanced by an angle of 90 ° against the field, it can be seen that when using a non-uniform field with essentially parallel lines of force a differential of the force effect, measured in the direction of the Change of the created field, results. Although in principle a quantitative change in the value of the Counterforce on the other hand also in a uniform, transverse to the liquid field with a, in a changing current density can be achieved perpendicular to the field plane, so it is in general Convenient to rely mainly or solely on the change in field strength. It is natural equally possible, both a non-uniform current density a / s as well as a non-uniform magnetic one Field to use.

It is already a so-called crucible-free Schm elz traversed n, known for metals and metal alloys, wherein, in a metal pellets by high-frequency fields of high intensity coil eddy currents er-electromagnetic agitating

Applicant:

Western Electric Company, Incorporated,
New York, NY (V. St. A.)

Representative: Dr. Dr. R. Herbst, lawyer,
Fürth (Bay.), Breitsoheidstr. 7th

Claimed priority:
V. St. v. America July 22, 1955

William Gardner Pfann, Basking Ridge,

NJ (V. St. A.),
has been named as the inventor

so that the bead is held freely floating and without any contact with the coils or other fixed parts of the environment can be melted floating freely. When melting the bead assumes the shape of a children's top, while stirring vigorously at the same time of the molten metal takes place. This is because the induced in the metal bead Eddy currents interact with the high frequency coil fields, creating a force of gravity compensating counterforce is generated, which keeps the bead in suspension. It is essential that that the currents induced in the metal are not affected by the high-frequency coil currents that generate them are independent and therefore cannot be regulated independently of them.

Furthermore, a method and a device for stirring a metallic melt in a non-metallic crucible with the aid of an alternating field , more precisely a rotating field, and a dv

1 056 84!

molten metal current flowing through it.

By the interaction of the rotating field with the field of the molten metal flowing direct current, opposing forces are generated, which cause the molten metal body to rotate.

Furthermore, a method for pulling crystals from the melt is already in use proposed an electromagnetic stirring process in which the stirring is carried out by an electrical and a transverse, preferably perpendicular to this magnetic field is generated.

The invention also relates to a method for electromagnetic. Stirring melts, whereby the melt is switched into an electrical circuit and where a magnetic field (generated by one or more permanent or electromagnets) is arranged perpendicular to the direction of the electrical current conducted through the melt so that a the stirring causing electromagnetic counterforce is generated. This process is particularly important in the treatment of semiconductor materials, especially in the so-called zone melting process or in the zone separation process, and is characterized by the fact that when a rod is melted in zones, it is switched into the circuit and the magnetic field runs alongside the melting zone. The new method works roughly in the following way: A substantially parallel current flow is achieved in a liquid body by applying a voltage to two electrodes, one on each side of the body, while a non-uniform magnetic field across the body is achieved by opposing magnetic poles Polarity is applied , which are applied transversely to the body at an angle of substantially 90 ° to the axis of the voltage electrodes, the axis of the pole faces being arranged in such a way that there is a non-uniform flux density within the body. The interaction between the current and the magnetic field results in a non-uniform counterforce which forms an angle of 90 ° with the field plane and the current and decreases in the direction of the decreasing field strength. This gradient of the counterforce across the liquid body results in a flow of liquid in the direction of the counterforce at the point where the force is greatest.

Electromagnetic stirring methods are from. special Significance in the treatment of metals and semiconductor materials, including molten ones Phases of the alaterials to be treated in question come. One such process, known as the "zone melting process," with a widely used industrial one Application is in the treatise, the American Institute for Mining and Metal Engineers, Vol. 194, pp. 747 to 753, from 1952. Since the stirring method according to the invention in particular in connection with zone melting plumes are advantageous and can also find widespread application in this context, it appears useful to the invention mainly to be described in terms of such procedures. It is clear, however, that those here methods described are not limited to this.

In the zone melting process, a molten zone is passed through a block of fusible material. This crossing is achieved by a ring-shaped or other heating device, which is moved relative to the block, o that a toilet of the block melts within the area of influence of the heating device. During the treatment, the zoo is arranged in such a way that there are two moving interfaces between the liquid and the solid phase. One is as SchmelztreTUiflächi? known and represents the interface between the molten zone and the solid part of the block in Wanderrichiunii

ίο represents. The other is referred to as the solidification interface, which denotes the other interface between the molten zone and the solid area will.

Since the solubility and consequently the concentrations of constituents present in minor quantities in the block and in the adjacent solid and molten areas are different, as the molten zone traverses the solid block there is a redistribution of these constituents present in smaller quantities. In the more common case in which these constituents are more soluble in the liquid phase than in the solid, the concentration of these constituents in the molten zone increases as this zone is stirred through the block, thereby removing it Components from your solid part of the block. This property is described by a distribution coefficient h , which is defined here by the concentration of the constituent present in small quantities in the solid phase divided by the concentration of this constituent in the liquid phase, both concentrations at the interface from the solid to be measured to the liquid state. Such a distribution coefficient can be measured under equilibrium conditions, in which case the symbol k is used, or in the steady state, in which case the symbol k _eil is used.

There are two known zone melting processes. In one method, the composition of the molten phase is kept constant in order to obtain a treated block with a uniform concentration of impurity elements, this method also being known as the zone leveling method. The other method is called "zone refining", where the molten phase tends to accumulate the constituents present in smaller quantities or to release these constituents into the solid phase. In the latter method, dx> e are present in small quantities Constituents concentrated either at the beginning or at the end of the passage of the molten zone, the concentration being in the last one that solidifies. Part .in a system in which the distribution coefficient k has a value 'less than 1, while the concentration in the first solidifying part occurs when the distribution coefficient has a value greater than 1.

Like the zone melting process. is known to those skilled in the art, the relative concentrations of constituents present in small amounts on each side of the interfaces between the liquid and solid phases in the steady state are measured by the term of the effective partition coefficient, which is referred to herein as k _elt . It is further -clear that in general during zone melting, the effective \ ⁷ grant coefficient in the steady state to the equilibrium value approximates k, but this is not the same. One leads

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conditions that are not ideal, such as If, for example, essential useful times for these constituents are in the liquid phase, then it follows that the numerical value of ', «approaches the value 1. It is evident that. the more the numerical value of k _ci! 1, the concentrations of these constituents in the two phases at the interface are almost the same, so that the separation achieved in the passage through the molten zone is therefore all the more ineffective. As mentioned earlier with regard to the two types of zone smelting method, effective separation is desirable in the zone separation method and only of secondary importance in the zone equalization method. However, one often wants to influence the value of k _e ii to some extent in the zone balancing process, if only for the purpose of achieving a uniform composition. It has already been proposed to overcome the undesirable feature of the all-round diffusion of the constituents present in small amounts in the liquid phase, at least in part, by stirring within this phase. Suggested stirring methods are e.g. B. mechanical stirring, and inductive stirring, in the latter case the inductive source can also serve as a heating source. In any event, agitation of the material in the molten zone results in a more even distribution of the minor constituents in the zone and tends to overcome the inherent property of this process, enriched or depleted layers of these constituents. build up the solidifying interface between solid and liquid phase. In a system in which the separation coefficient k is less than 1, this layer is enriched.

The stirring methods according to the invention have many advantages over those already proposed Procedure. Inductive stirring methods are z. B. known: from "Iron Smelting Process." By John L. Well done, published by John Wiley and Sons, NewYork, 1954, p. 359. This method lacks the Control and adaptability of the method according to the invention, and it requires an inductive Heating source that is relatively expensive and bulky, which is not justified as long as the heating device not also z. B. is required because of their large heat generation. The ones described here Process can e.g. B. in the resistance zone chmete procedure that only relatively cheap equipment is required, and in many respects is preferable to the inductive zone melting process.

Mechanical stirring of liquid materials can be undesirable, especially when handling high-melting or reactive materials. Construction materials that are suitable for coming into contact with the liquid to be stirred must withstand high temperatures and must not contain any undesirable elements, d ^! ie would result in contamination of the melt. In addition, the insertion of a rod or other agitator through the wall of a crucible can be a difficult problem to solve when a protective atmosphere is to be maintained in the crucible.

_ Although some of the difficulties of the mechanical Agitation method by using a magnetic part within the melted area can be avoided with an outside of the crucible, not mechanically with the second magnetic part connected to the first part cooperates, the avoidance can nevertheless contamination is a problem. Furthermore, the melting temperatures of many materials are which are now being treated by zone melting, such as B. silicon,.-O high that the residual magnetism ferromagnetic! · materials is negligibly small.

The present process deals with the interaction of a through the melted area flowing current with a magnetic field applied over the molten area deals, avoids all of the disadvantages of mechanical processes, avoids the scale and cost of inductive process and avoids direct contact of the magnetic materials with the material to be stirred Liquid and also has other special advantages.

The three contributions which are made by the method according to the invention for the treatment technique, can be represented as follows:

1. In the zone precipitation process or in ordinary freezing, stirring the molten ones results Zone a higher efficiency in the separation at a given speed or allows a greater rate of solidification with a desired separation.

2. Electromagnetic agitation within the molten zone diminishes in zone melting processes the frequency and magnitude of non-uniformities in concentration in wines Amounts of constituents present over the entire solidification interface.

An even concentration of such ingredients in this cross-sectional plane of the finished block is particularly desirable in zone leveling materials.

3. The stirring of the molten material in a molten zone by electromagnetic Stirring causes the thickness of the diffusion layer of the dissolved substance to decrease in the immediate vicinity Neighborhood of the advancing or receding interface between the solid and liquid phase. As already stated in section 1 above, it is generally advantageous to reduce the thickness of this layer. However, it is also possible to change the desired concentration changes or gradients within to achieve the zone-melted material by changing the thickness of this Difi'usionsschicht or by changing the stirring current or the applied field during the treatment or is taken away.

The invention will now be described in more detail with reference to the drawings. It shows

1 shows a schematic representation of a fusible body through which a separating surface is sandwiched liquid and solid phase moves (the diagram in which on the coordinates the concentration is plotted against the distance in the body, is detailed in the theoretical part of the description explained),

Figure 2 is a schematic view of one for creating an agitated melting zone according to the invention suitable facility.

Fig. 3 _e j _ne schematic view of another embodiment of Fig. 2,

Figure 4 is a schematic view of another embodiment similar to the devices according to Fig. 2 and 3 works,

Fiji. 5 a schematic view a .-- Cross. ^ Chnittvs by means of melting and stirring of the melted areas. ··.

6A and 6B show a front end; and a plan view an effective means of generating a shallow molten zone in motion,

Fig. 7 is a schematic representation of a device for use in agitated, pushed Material at the interface between molten and solid material in a normal solidification process and

8 is a schematic view of a suitable arrangement with magnetic poles and heating devices to create a stirred, molten zone.

FIG. 1 further goes into connection with a discussion of the parameters of the solidification process which affect the value of k _elf , which is defined here as the ratio of the concentration of solutes in the solidifying solid to the concentration in the main part of the liquid is. Furthermore, the relationship between the electromagnetic stirring methods and k _e ii will be discussed. It is evident that for systems with a value of k less than 1, a value of km has a favorable effect on the separation efficiency. 1 shows a solid body 1 which is advancing into a melt of liquid material 2 with a concentration Ci in the steady state of dissolved substances for k less than 1. The concentration of the solidifying solid body should be IeC ₀ , where k is the distribution coefficient in the equilibrium state and C _{0 is} the concentration of the melt at the interface.

A layer rich in dissolved substances in the liquid zone 2 is formed from the separating surface 3 to the cross-sectional surface 4 with the thickness due to an accumulation of dissolved substances in the liquid at the separating surface. If there is no stirring, the thickness of layer 3-4 decreases with increasing diffusivity of the dissolved substances in the liquid phase. Because of the accumulation of solutes in layer 3-4, k _{cll assumes} a value that is greater than? the distribution.> coefficient k in the equilibrium state, so that this results in a reduced separation effect. Any method that causes a decrease in the distance C ₀ -Cl also results in a decrease in the value \ * on k _e n. The height C ₀ -C _{L of} the layer 3-4 increases in the steady state for a given chemical system and for a given solidification rate with increasing thickness of the layer δ increases. Hence, a decrease in ö results in a decrease in the value / (■ <, (■ /.

Stirring the liquid in molten zone 2 has the effect of reducing <3. The greater the stirring speed, ie the greater the speed of the liquid parallel to the interfaces: .- t, the smaller d, The theory of enriched layers and the effect of rotating stirring on ό and k _et1 is in the American journal for chemistry and Physik, Vol. 21. 1953, pp. 1987 ff., described. Information about characteristic.? Interfering elements for germanium can also be found there. From this publication it appears, for example, that the growth rate R for germanium-antimony chips grown by crystal pulling can be increased from 38 to 62 microns per second without increasing k _ell if the rotational speed of the crystals is 57 revolutions per minute would be increased to 104 revolutions per minute, l'for lower rotational speeds> I result in a larger proportional ·? » Increase in R for a given increase in the speed of rotation. As a first approximation, when pulling crystals, the stirring speed can be assumed to be proportional to the speed of rotation of the crystal,

ίο In the; method described here, the agitation speed V in the vicinity of a given interface depends on many factors, namely on the value of the field strength //, the value of the stirring current /, the physical dimensions of the melted zone, the viscosity of the liquid, the the exact type of the stirring process achieved by the interaction between // and / and the slope and size of the gradient of the magnetic field strength ΔΗ within the zone. In general, many of these factors are determined by the nature of the system and the desired properties of the starting product. Although it is understandable per se that one chooses the dimensions, ie the length and the cross-section of the zone with a view to desirable stirring properties in industrial applications, it is more likely that the designer of a stirring device is mainly concerned with the parameters of the stirring current / and the change in field strength along the axis of current flow, dHldx, where the distance χ in the molten zone is measured along the axis of current flow. In general, the value of the stirring current / depends on practical considerations, such as e.g. B. on the available voltage and the maximum permissible thermal effect from I ² -R. There may, of course, be applications where the thermal effect from I ² -R is used either in part or entirely as a heat source in the molten area. Some embodiments of this latter possibility are described below.

The maximum value of the field strength H _{max also} depends on practical considerations relating to the size and strength of commonly available commercial permanent magnets or on the size of the current available if an electromagnet is used, as well as on the size of the air gap between the poles above the zone , the size of the air gap in turn depending on the dimensions of the zone. If the material to be treated has a high melting point, e.g. B. germanium or silicon with melting points of 937 or 1412 ° C, which are significantly above the Curie point of common ferromagnetic substances.

the smallest permissible air gap is determined by the maximum working temperature for the magnetic material. It can be desirable to cool the magnetic surfaces using a water jacket, for example. The use of commercially available bar magnets results in a field strength of the order of 25,000 Örsted with an air gap of 2.5 cm. The variable that is easiest to control is, assuming the best possible magnetic material and the greatest, practically realizable stirring current, the change in the field strength along the axis of the current flow and the location of a maximum value of H. In general, the stirring speed is the greater, the greater the change in the field strength along the current flow axis is greater. Taking

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a pair of bar magnets that astride the molten zone at a beckoning! of 90 to the current flow, a maximum stirring effect results when H has a maximum value in the area of a separating surface and when H m reaches the value U in any other area of the zone. As can be seen from the description of the Iigures, the best practical way to do this is by straddling the magnetics

ground surfaces of a horseshoe magnet. Dk interaction between that created by the magnets. 14 and 15, the field strength H and the stirring current 16, which is supplied by a source not shown, results in stirring of the molten material in the zone 11.

In the example shown, is there moving? in the Center between the magnets 14 and 15 located material in a direction away from the viewer, the

flat surfaces other than astride the zone are, are oh-so-dear to the expert. Some of these embodiments are; n the Corridors shown and described.

In practice it has been found that a sharp change in field strength II can be achieved by moving the area of a permanent magnet in λ »ViW Af * blocks nvt a distance of about ϊ S'i Dbi ll dr

20th

For "corresponds to the arrangement shown in FIG this is a wandering of the zone from right to left. In the one shown in this and the other figures Device is the relationship of the element producing the magnetic field to the heating device set. Stop at zone shrinkage

*. KHhe de. Small block with a distance of «w * the magnets and the heating device are attached relatively 6 3 W ϊ> 1 mm from the dielectric. The 25 should be _{moved towards the} body so that the molten magnet moves as small a part of the molten zone as possible through the solid mass. ^ So ^ rdeäe, It found that then, J ^ * ^ ™ * ^^^ £

A interaction between the magnetic field the astride magnets 21 and 22 and the stirring current 23 generated asymmetrical krait is stirred. In the device shown, the liquid area 20 is heated by a heating device 24 and 25 generated. You can see in the

dji'ä tw ^ ^ RTI '^' ^ ndTanWMnder perpendicular th device 35, that two separate kinds of Steherι It 4heint also to be such that a liquid flow "* arise because the by eichte BevorluTung for a vertical magnetic _Magne * _{te 21 and} 22 produced ^ g «** ^ ¹ ^ Fe, d gives, w / nn, the molten zone horizontal ^ ₃₅ ^ to ^ axis ^^^ fi.

Fi "2 to 9 are suitable magnetic 40 _S pj _€ l shown flowing the liquid between c. Generally right _and 22 are away from the observer and in the As

cKug ^ au. _?., .._. λι ■ _the parting surfaces 27 and 28 towards the observer.

In Fi "4 is the heating device 30, which the molten Area 31 is created between this molten zone and the astride magnets 32 and 33, which are arranged at a certain distance fn in the vicinity of the separating surface 34 of the block 35 are. Although this means lends itself to easy control of the location of the interface 34

zenenz-one ui> era corner. ts «" '^ ö ^ -— ";> ■

if the area of the magnet is less than? the Half of the length of the zone, a relatively field-free area is created at the other end of the zone.

Since the stirring results from the interaction only between the components of the current and the field * strength H , which are perpendicular to one another, a maximum stirring effect results when

In the

45

Angular cross-sections, in which the short dimension of the zone is perpendicular to the magnetic field, is preferable, which results in relatively short air gaps.

The current / can be introduced into the body by means of electrodes made of non-contaminating material made of graphite, stainless steel, for example

or tungsten, or via the end te Je easy control uex α - «^ u ^. - _r »

the batch in which the electrodes are embedded or at 50 it may still be necessary ^dl «£« f ",

to which they are attached, these end parts being cooled during 33 to keep them below de, cune point

of the process remain firm. Consider it special. Stirring within the melted

sensitive cleaning processes or for processes, is determined by the interaction between the zone

bd which small amounts of interfering elements create a field of the magnets 32 and 33 and the current flow 36

can produce harmful pollution, one is produced.

the part used as an electrode of the body of I _n Fig. 5 is choose a cross section of "me Ejnnchdem degree of purity, to reach the one _processing with a molten zone 40 illustrated, the _wü n" CHT is generated by heating elements 41 and 42. The Lmp; g -7 ze-Vt e ^; ne plan view of a body is allowed to stir from this by the interaction to 1-e-NEM material 10 with a molten portion 60 _sc hen one in the molten zone through 11 of the ζ B astride mounted a molten zone in the zone magnets 33 and 44 are generated melting represent canoe. The molten zone 11 causes a field and a current flow which is longitudinally generated in the solid block 10 by an annular axis through the zone 40 perpendicular to the character-shaped heating element 12, which extends for example plane. This arrangement allows low levels of resistance to be used. A magnet between the magnet and the zone is allowed and avoids t. ^: >c'.v.-s field above the molten zone 11 will interfere with the heating elements in the vicinity of the interface 13 between th 41 and 42. _ solid and liquid phase by the magnets 14 and Figs. 6A and 6B show a Facility created for Jir-15, the z. B. along a common axis generation and for stirring a relatively ttaclien lying bar magnets or from the parallel liquid zone. In this facility a

909 509385

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oval liquid zone 50 in a solid body 51 generated by a heating element 52. The interaction between a lengthways through Jen Body 51 by means of a voltage wave and electrodes (both not shown) generated: current 53 and a magnetic FiUJ vertical extension, the is caused by -a magnet 54, results, seen from above, a -e liquid flow in the opposite direction clockwise in the liquid zone 50. The oval shape of the liquid zone. d: e by a similar Shaped heating element 52 is caused, supports the stirring effect.

In Fig. 7 a normal solidification process is shown, with that one? Cooling is carried out at the solidification interface. In this facility will a molten zone 60 is created in a body 61 by a furnace 62. If the body is 61 in. The specified Direction pulled out of the furnace, the part 63 crystallizes out. The magnetic field, that above the body 61 in the vicinity of the interface between the liquid and solid phase 64 generated by the magnets 65 and 66, delivers along with d'em axially through the body 61 of one current source, not shown, from flowing stream 67 a stirring effect in the liquid part 60 at the Separation surface, whereby the accumulation of solvents, the separation coefficient of which is less than 1, is kept as small as possible while at the same time or alternatively on the same slope a depletion of solvents occurs whose separation coefficients are greater than 1.

In the arrangement shown in Fig. 8, there are two pairs of horseshoe magnets with poles 71, 72 and 73, 74 mounted astride a heater 75 which has a molten zone 76 in the block 77 generated. The magnetic field of the pole pairs 71,72 and 73, 74 results together with that not shown by Means generated stirring stream 78 stirring in the vicinity of the parting surfaces 79 and 80 between the liquid and the solid phase. Such a method is particularly effective when when the length of the zone in the direction of current flow compared with the dimension perpendicular to the current flow is large.

In general, the greater the density or the A ⁷ iscosity of the liquid to be stirred, the greater the field strength gradient AH in the molten area of the zone to produce a given agitation speed and, accordingly, to produce a given effective partition coefficient in a given system. Although the frictional effects retarding the flow of liquid are proportionally greater in the vicinity of the container walls, a given size of AH gives a more powerful stirring effect if the dimensions of the zone are reduced within reasonable limits. For a molten zone 2 cm long and 1 cm ² cross-section, a stirring speed of the order of 20 cm per second results from the interaction between a stirring current of approximately 20 amps. and a value of AH of about 200örsted across the zone in a liquid with a density of about 12 resulting in counterforce.

Di-ε -electromagnetic stirring method according to Invention were previously with the terms of a Aufrecht-Erhal.tung the solidification conditions, so that the liquid and solid material compositions at the solidification interface in the are essentially in the steady state. As i> erv ·: '.- Ijv.-chrii'] «. '!!. is: such an ancestor insiK'ion.lere with Zuiienaus ^ l-calibrating or with the zone elimination applicable with advantage.

Other applications of the methods described here will come about by themselves. For example, leave it alone di-c elimination coercion of solvent-solvent systems in the vicinity of the interface η between the liquid and solid phase continuously or change discontinuously in that the stirring current modulates the magnetic field or is applied discontinuously. Such controlled, effective elimination coefficients can be a result in desired mixture change in the crystallizing solid material or can be used for this purpose the accumulation or depletion of solvents during a normal solidification process in the remaining molten material.

If the stirring action is to be interrupted quickly, the living force of the stirred To cancel the liquid, suddenly changing the direction of the magnetic field or the direction of the current flow reverses.

When producing NP or NPN junctions in semiconductor materials by the process of changing the growth rate, which can also include melting back or a negative growth rate, it is often desirable to take up a very high growth rate with the melting back. A particularly effective method of achieving this end is to use the agitation current through the block to control the location of the separating tabs. If the heating by 1 - R in the vicinity of the interface is considerable due to this current and the temperature gradient at the interface is large, e.g. B. in the order of 10 to 1000 ° C / cm, then sudden changes in the stirring current I result in a rapid change in the growth rate. If it is desired to change the value of k _eif without affecting the growth rate, this change can be achieved by changing the magnetic field strength or by changing the current / if the current I is small enough to cause only slight heating Deliver PR.

Claims (5)

Patent claims: 1. Method for electromagnetic stirring of melts, the melt in an electrical circuit is switched and being perpendicular to the direction of the through the Melt conducted electrical current (by one or more permanent or electromagnet generated) magnetic field is arranged so that in a zone of the melt a Stirring causing electromagnetic counterforce is generated, characterized in that • when a rod melts in the zone, it is switched into the electrical circuit and 'the magnetic field runs alongside the melting zone. 2. The method according to claim 1, characterized in that the liquid on at least one Separation surface adjoins a solid body and wets it. 3. The method according to claim 2, characterized in that that the interface from the liquid to the solid phase in the liquid progresses is moved on. 4. The method according to claim 1, characterized in that that the liquid at two interfaces, .1. H. a «each end of the liquid? the Acii.-e of the flow of current, to a solid body borders and lienetzt. 5. The method according to claim 4, characterized in that both parting surfaces progressively be moved on in such a way that one becomes one solid body solidifies while the other melts into the liquid. Documents considered: German Auslegeschrift No. 1 004 818; German patent specification Xr. 632,582; Iron Age, July 1952, pp. 85/86. 1 sheet of drawings