US3862657A

US3862657A - Method and apparatus for continuous casting of metal with a considerably lower specific gravity of the strand in relation to the cast metal

Info

Publication number: US3862657A
Application number: US381281A
Authority: US
Inventors: Armin Thalmann
Original assignee: Concast AG
Current assignee: SMS Concast AG
Priority date: 1972-07-27
Filing date: 1973-07-20
Publication date: 1975-01-28
Anticipated expiration: 1992-01-28
Also published as: DE2338218B2; FR2194506A1; ZA735108B; DE2338218A1; BR7305676D0; CH553606A; AT333456B; IT991413B; CA1003185A; GB1444625A; SE383275B; FR2194506B1; JPS4953530A; ATA663373A

Abstract

A method of, and apparatus for, continuous casting of metals with considerably lower specific gravity of the strand in relation to the cast metal, wherein the metal and the additive constituents in the liquid metal pool are introduced into a hollow mold compartment. As the additives there are added porous bodies having a specific gravity less than 1, and upon the porous bodies there is exerted a pressure which at least corresponds to the magnitude of the lift force acting upon the porous bodies upon penetration into the metal. The apparatus for the performance of the method aspects comprises means defining a hollow mold compartment and an infeed device for the metal. In addition to the infeed device for the metal there is provided a device for exerting a pressure upon the porous bodies for infeeding the porous bodies into the liquid metal pool.

Description

United States Patent [1 1 Thalmann 1 1 Jan. 28, 1975 Concast AG, Zurich. Switzerland July 20. 1973 [75] Inventor:

Assignee:

Filed:

Appl. No:

[30] Foreign Application Priority Data July 27, 1972 Switzerland 11245/72 [52] US. Cl 164/86, 164/97, 164/58, 164/275 Int. Cl 822d 11/10 Field of Search 164/58, 79, 80, 86, 97, 164/275 [56] References Cited UNITED STATES PATENTS 3.224.846 12/1965 Fiedler et a1 164/79 X Primary Examiner-R. Spencer Anncar Attorney. Agent. or Firm-Werner W. Klecman 57 ABSTRACT A method of. and apparatus for. continuous casting of metals with considerably lower specific gravity of the strand in relation tothe cast metal. wherein the metal and the additive constituents in the liquid metal pool are introduced into a hollow mold compartment. As the additives there are added porous bodies having a specific gravity less than 1, and upon the porous bod ies there is exerted a pressure which at least corresponds to the magnitude of the lift force acting upon the porous bodies upon penetration into the metal. The apparatus for the performance of the method aspects comprises means defining a hollow mold compartment and an infeed device for the metal. In addition to the infeed device for themetal there is provided a device for exerting a pressure upon the porous bodies for infeeding the porous bodies into the liquid metal pool.

21 Claims, 5 Drawing Figures PATENTED JAN28 I975 SHEEF 10F 2 BACKGROUND OF THE lNVENTlON The present invention relates to a new and improved method of, and apparatus for.the continuous casting of metals with a considerably lower specific gravity of the strand than that of the cast metal, wherein the metal and the additives or additive constituents in the liquid metal pool are introduced into a hollow mold compartment.

A conventional casting process has become known to the art wherein the fillers to be cast into the metal possess a porous carbon structure. Such fillers or filler bodies, primarily in the form of spheres or balls, possess a very small specific gravity have the advantage that they do not or only very slowly react with the liquid metal. A technique for fabricating these porous carbon bodies has been disclosed in German Pat. publication No. 2,038,682. In this patent there are also advanced proposals for the conventional casting in molds.

Furthermore, there is also known to the art a contin uous casting process in which the metal and additives production directly introduced into the liquid metal pool in a mold. As the additive constituents there are mentioned, among others, graphite for the poroduction of metals for bearings. For this purpose the graphite bodies must be small and of compact volume. They are not suitable for producing metals having a low specific gravity. Moreover, the disclosed infeed device does not teach how it is possible to avoid separation in the strand due to the lift or buoyant force of the specifically lighter graphite.

SUMMARY OF THE INVENTION Hence, it is a primary object of the present invention to provide an improved method of, and apparatus for, the continuous casting ofmetals having a considerably lower specific gravity of the strand in contrast to the cast metal and which is not associated with the aforementioned drawbacks and limitations of the prior art proposals.

Another and more specific object of the present invention aims at the provision of a new and improved continuous casting method for' the production of strands having low specific gravity wherein there is effectively prevented, or at least substantially minimized, separation or dissociation of specific lighter bodies in the liquid metal.

Another object of the present invention relates to an improved method of, and apparatus for, the continuous casting of metals wherein the proportion by volume of the bodies in the metal and their distribution can be reliably determined.

Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the invention contemplates employing as the additive constituents to be mixed with the metal porous bodies having a specific gravity which is less than 1, and exerting upon the porous bodies a pressure corresponding at least to the magnitude of the lift or buoyant force which is effective upon such porous bodies during penetration into the metal.

With this technique it is possible to fabricate strands having considerably lower specific gravity in relation to the cast metal, and wherein it is also possible to adjust at the strand both a predetermined distribution as well as also a predetermined quantity of the constituents to be admixed. For instance, the specific gravity of an aluminum strand having a 60 percent proportion by volume of carbon spheres amounts to about 1.1. The reduction in the specific gravity therefore amounts to more than one-half. whereas the reduction of the physical properties is considerably-less. The process of this development can be effectively employed for most metals which can be cast by continuous casting techniques, and in particular for aluminum and its alloys. copper and its alloys as well as also for metals formed on the basis of iron. The carbon spheres do not react with, or only slowly react with such metals, wherein during slow reaction, for instance in the case of steel, the rapid solidification which occurs during continuous casting brings with it advantages in contrast to conventional casting techniques.

In order to obtain the desired percentual proportion by volume or porous bodies and therefore the predetermined specific gravity of the strand even with varying casting parameters, according to a further aspect of the invention, thevolume-dependent addition of porous bodies is regulated as a function of the strand withdrawal speed.

In order that, on the one hand, there is available sufficient time for the metal to penetrate into the hollow voids or interstices between the porous bodies and, on the other hand, to prevent premature solidification, a further facit of the invention contemplates introducing the porous bodies into a non-cooled portion of the metal bath or through a non-cooled portion of the metal bath.

Furthermore, in order to additionally reduce the danger of premature solidification, especially in the case of metals which melt at high temperatures, a further aspect of the invention contemplates pro-heating the porous bodies prior to introducing the same into the liquid metal. If such bodies consist of carbon then the preheating step must occur in the absence of air.

According to a further feature of the invention the porous bodies are delivered to the liquid metal pool by means of a fusible or castable container.

For reasons of strength or other reasons, for instance in the case of tubes it can be necessary that the porous bodies are not present at the surface of the metal, rather that the cell-like core is covered by a compact metallic layer. Hence, to realize such layer, a further feature of the invention contemplates solidifying at least a part of the outer marginal layer which contacts the wall of the hollow mold compartment prior to penetration of the porous bodies.

The buoyant force which acts upon the porous bodies at the liquid metal pool can bring about undesired enrichment of such bodies, especially during horizontal casting, so that at the cell-like structure of the strand there can appear considerable irregularities. in order to eliminate this drawback the invention further proposes agitating or moving the porous bodies in the liquid metal pool.

As already alluded to above, the invention is not only concerned with the aforementioned method aspects but also deals with apparatus for the performance thereof and such is manifested by the features that in addition tothe infeed or delivery device for the metal there is provided a device exerting a pressure upon the porous bodies, this pressure exerting device serving for the infeed of such bodies into the metal pool.

According to a further apparatus aspect a thermalinsulating attachment or adapter is associated with the hollow mold compartment. 7

In situations where the cell-like core should be covered by a metallic layer, a furtherembodiment of the invention contemplates providing'the opening for the infeed of the metal at the thermal-insulating attachment beneath the level of the bath.

Since the visual inspection of the bath surface is completely or partially hindered by the porous bodies, but there is however necessary a certain metal head in the attachment for the penetration of the metal between the bodies prior to its solidification, a further aspect of the invention contemplates providing a bath level control for the attachment.

An additional exemplary embodiment of the'invention for preventing premature solidification of the metal between the bodies contemplates providing a heating device for the attachment.

According to a further aspect of the invention, when employing the development of the invention for horizontal or vertical casting, it is contemplated to construct the thermal-insulating attachment as a T-element or T-shaped element.

To render more difficult penetration of the porous bodies into the infeed device for the metal during horizontal or vertical casting, a further aspect of the invention proposes arranging the cross-section of the metal inlet of the T-element lower at least by an amount corresponding to the height of the cross-section of the metal outlet. If additionally the infeed channel of the T-element ascends in the direction of the cross-section of the metal inlet at an angle of at least 45 with respect to the horizontal, then such penetration is prevented.

In order to safeguard the infeed device for the porous bodies against the action of the liquid metal and in order to provide for a faultless conveying or delivery of the bodies, the invention also proposes arranging such infeed device above the level of the bath.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, in FIG. 1 there is depicted an installation which, for instance, isvsuitable for the production of cell-like or cellular steel billets. A hollow molding compartment 1', which can be charged from above, is formed by a vertically arranged openended continuous casting mold I. It consists of two components, a water-cooled copper mold 2 and a thermal-insulating attachment 3 formed of refractory material. The open-ended mold I encloses the hollow molding compartment 1 and is oscillated by conventional and therefore not particularly illustrated means. The cast strand 4 with a liquid metal pool 10 and formed in the mold l is withdrawn from such mold l by means of a conventional strand withdrawal unit 5 having a suitable drive mechanism 6, and then such strand 4 is guided into the subsequently arranged roller guide arrangement or roller apron 7 and cooled by a direct water cooling system 8 for obtaining a complete solidification of the strand.

The attachment 3 is closed at the top, so that the liquid pool 10 is protected against contact with air. The cover or top portion 3' of the attachment 3 possesses two openings 9 and 11. The opening 11 cooperates with an infeed or delivery device 12 for the metal. This infeed device 12 consists of a casting vessel 13 in the form for instance of a tundish. A pouring tube 14 is inserted through the opening 11 for conducting the metal, typically steel into the mold l. A mechanism 21 for the delivery or infeed of the constituents or additives 20 to be admixed with the metal cooperates with the other opening 9. This delivery mechanism or device 21 comprises a funnel 22, a conveying worm 23 with a suitable drive mechanism 24 and a chute or slide 25 for the infeed of the additive constituents or components 20. The slide 25 is coupled with a non-illustrated supply vessel or the like for the additive components 20, out of which these components or constituents are dosed and guided into the funnel 22, such that the funnel 22 is always maintained filled during operation.

Furthermore, operatively associated with the attachment 3 is a bath level control 30 of known construction, composed of a radiation source 31 and a receiver 32. This bath level control 30 maintains the bath 33 within the attachment 3 at a-pre-determined height or level, so that in the attachment 3 there exists an uncooled metal bath portion and a hollow compartment filled with the additive constituents 20. The receiver 32 is operatively connected with a control mechanism 34. This control mechanism 34 actuates a non-depicted stopper rod in the tundish 13 for regulating the level of the bath 33. The attachment 3 can also have associated therewith a heating device, for instance in the form of an induction heater 36.

Since for all metals it is not possible to dispense with lubrication between the strand being formed and the walls of the mold, the attachment 3 is provided with a suitable conventional and thus not particularly shown oil lubrication. The combustion residues formed in the hollow compartment between the level of the bath 33 and the cover portion 3' are sucked-off through an opening of such cover portion of the attachment 3. To prevent a negative pressure from forming in this hollow compartment there is also present an opening for the introduction of an inert gas.

The method aspects of the invention will now be considered and are as follows: prior to beginning a casting operation the copper mold 2 is closed in the usual way by the dummy bar head of a conventional dummy bar. A wire grid is placed into the mold 2 above the dummy bar head. This wire grid prevents the additive components 20 from moving forward to the entrainment means of the dummy bar head, however allows the liquid steel to flow-up to the entrainment means. In this way there is obtained a good connection between the dummy bar head and the forming strand 4.

The additive constituents or components 20 can consist of, for instance, spherical, carbonized balsa wood. They can also possess other geometric shapes. Balsa wood is porous and possesses a specific gravity which is less than 1. Production of such porous balsa wood bodies requires a certain expenditure, and it is for this reason that it is even more advantageous to use as the porous bodies the previously discussed porous carbon 1 spheres. They can be produced for instance in a size of 4 to 6 millimeters and possess a mean specific gravity of less than 0.]. Their squeezing strength amounts to about two kilograms. To improve wetting of the carbon spheres it can be advantageous, for certain metals, if such spheres are provided with a metallic coating. Also this technique has been described in the previously mentioned prior art publication.

After the hollow mold compartment has been filled with the additive constituents 20, for instance the porous carbon spheres, then the steel is cast to the intended metal bath level. Due to the inflowing steel the very light spheres have imparted thereto a buoyant or lift force. The kinetic energy of the inflowing steel prevents the spheres or balls from ascending through the pouring tube 14. As soon as the bath level 33 has reached the intended height, then by virtue of a signal generated by the bath level control 30 the drive mechanism 6 of the strand withdrawal unit 5 is placed into operation and the strand 4 which is formed is withdrawn from the casting mold 1. At the same time there is also placed into operation the drive mechanism 24 and thus the worm 23 for conveying the carbon spheres 20 or the like. These spheres, notwithstanding the buoyant force which acts thereupon, cannot escape upwardly and towards the sides owing to the cover portion 3' and the side walls of the attachment 3. However, in order to assure that these spheres will distribute within the liquid metal pool 10 over the entire cross-section a pressure must be exerted by the worm 23 upon the spheres which at least corresponds to the magnitude of the buoyant force. This pressure can be generated by selecting the pitch of the conveying or feed worm 23 and by adjusting its rotational speed. Owing to this pressure the spheres 20 are pressed into the uncooled metal bath portion and into the liquid pool 10 and are distributed thereat over the entire cross-section, before the metal begins to solidify. Prior to placing into operation the worm 23 the funnel 22 is covered by an inert gas which flows from an infeed conduit or line 26, so that there is prevented sucking-in of air by the spheres into the funnel 22.

The drive mechanism 24 possesses a rotational speed regulator of standard design, by means of which there can be adjusted the desired percentual proportion by volume of porous spheres 20 in the strand. Additionally, the drive mechanism 24 is operatively electrically connected by means of a conductor 35 with the drive mechanism 6 of the strand withdrawal unit 5. As soon as the withdrawal speed has been changed then there also correspondingly changes the rotational speed of the drive mechanism 24, so that the adjusted volumegoverned proportion of spheres 20 in the strand remains the same. Since the bath level 33 is located within the thermal-insulating attachment 3 the metal in the upper portion of the liquid pool 10 is not cooled, so that the spheres can be introduced into this uncooled metal bath portion. Consequently, prior to the initiation of the solidification process the metal has sufficient time for its penetration into the hollow voids between the spheres. In order to additionally retard solidification the attachment 3 and therefore the upper portion of the liquid pool 10 can be heated by the induction heater 36. Hence, the spheres are pre-heated. while excluding air, prior to penetration into the metal.

In FIGS. 2 and 3 there is portrayed a further exemplary embodiment of the invention. The decisive difference in theprocess consists in this case in the fact that the outer marginal layer of the strand 4 is at least partially brought to solidify prior to penetration of the spheres. In this way there is produced a type of tubularshaped strand. Instead of the tubular hollow space there is formed however a cell-like inner portion. One advantage of this embodiment resides in the strength characteristics. A further advantage is in terms of the fact that it is possible to produce larger units by welding together, as will be later described.

In FIGS. 2 and 3 there is depicted the casting of an aluminum slab, the specific gravity of which only slightly exceeds the value of 1 due to the selection of the proportion by volume of the porous spheres so as to amount to at least percent. The components of the installation which correspond to those depicted in FIG. 1 have been designated by the same reference characters and therefore will not be further here described. Instead of the covered attachment 3 here the attachment 40 is open at the top. The metal infeed occurs laterally in that an opening 41 is arranged at the thermal-insulating attachment 40 beneath the bath level 33. This opening 41 constitutes the outflow or discharge of a filling compartment 42 which cooperates with the infeed device 12 for the aluminum.

The infeed 0f the porous bodies 20 takes place by means of the mechanism 44 which consists of a container 45, which guides such bodies through the uncooled metal bath portion in the attachment 40 into the liquid metal pool 10. This container 45 is formed of three

walls

46, 47, 48 formed of steel wire grids. The mesh width of the wire grids is smaller than the diameter of the balls or spheres. The

walls

46 and 47 are movable wide side walls and wall 48 is a movable narrow side wall. The other narrow side wall 49 is in alignment with the narrow side of the open-ended mold 1 and is constituted by a rigidly arranged iron plate. This container 45 thus constitutes a castable container, i.e., the melting point of the material forming the container is greater than that of the cast metal. The

walls

46, 47 and 48 are advanced towards the hollow mold compartment via the deflecting

rollers

50, 51 and 52. Sheet metal guides or

plates

53, 54, 55 impart to the container the required shape. Transverse walls 60 formed of wire grids are secured in spaced relationship at the wall 47. The wall 46 is provided with supports 61 which elevationally fix the transverse walls 60. The

walls

46, 47 and 48 are arranged at the spacing 65 from their corresponding mold walls.

Prior to the start of the casting operation the container 45 which is formed is introduced into the hollow mold compartment up to the region of the dummy bar head 70, whereby at the same time the compartments or chambers 71 formed by the transverse walls 60 are filled with spheres 20. At the casting vessel 13 the stopper is opened. The buoyant or lift force generated by the inflowing aluminum is absorbed by the transverse walls 60 and the prevailing laterally acting forces by the walls of the compartments 71. Owing to the cooling of the mold 2 the aluminum solidifies and the spheres, as well as also the container 45, are cast, whereby the container serves as a reinforcement for the strand 4. As soon as the necessary bath level has been reached the strand withdrawal unit is placed into operation by the bath level control described heretofore in conjunction with the embodiment of FIG. 1. The cast container 45 is entrained and the compartments 7] which continuously form are filled with spheres 20. The relevant transverse wall 60 generates a counter pressure at the spheres which corresponds to the buoyant lift force, so that the same do not alter their position. In order to protect the spheres against oxidation the charging side of the mold l is covered with an inert gas as heretofore described.

Since the container 45 is located at a distance or spacing 65 from the mold walls there solidifies a marginal layer'of the strand which is free of spheres 20. In the exemplary embodiment under discussion this marginal layer is missing at the side of the wall 49, so that the formed cells with spheres are partially visible. Two such respective open sides of the slab sections can contact one another and the thus contacting marginal layers welded. However, it is also possible for both narrow sides to be cast open, so that specifically light plates of every desired dimension can be produced. Such plates are particularly interesting if their specific gravity is beneath l and thus can float.

The described method of FIGS. 2 and 3 can be also employed for producing spheres which are distributed over the entire cross-section. In such case the container 45 consists of, for instance, meltable or fusible material, such as aluminum sheet which, during casting of steel, simultaneously can serve as a deoxidation agent. The spacing 65 is smaller than the sphere diameter, so that the spheres cannot ascend over the level of the bath. With this technique the deflecting

rollers

50, 51 and 52 for conveying the container 46 must be driven. The spacing 65 can also amount to null when the container 45 is not fusible, rather serves as a covering for the cell-like strand and for this purpose should be welded with the strand.

The attachment 40, for certain low melting metals, is not necessary and can be omitted, especially in cases where there is desired a marginal layer without cast spheres.

As is well known in this particular technology, openended molds for casting of thin slabs are only of limited suitability, which explains why in the field of continuous casting there have already been developed different techniques for casting between revolving bands. With such technique the hollow mold compartment is formed by such revolving bands. One such technique which can be used with the invention has been disclosed, for instance, in the U.S. Pat. No. 3,452,809 and serves as an example for the use of the inventive process of FIG. 4 for producing slabs with low specific gravity. The components for the continuous casting process with revolving bands will only be considered to the extent necessary for explaining the underlying principles of the invention. Hence, it will be understood that reference character designates both of the narrow side bands associated with the hollow mold compartment. The bands of the long sides of the mold compartment have been conveniently omitted from the showing in the drawing to provide clarity in illustration. The bands confronting the hollow mold compartment are supported by the rollers 81. At the region of the bath level 33 there is not carried out any cooling.

The infeed mechanisms for the metal and the porous spheres 20 are analogous to those considered above with regard to the embodiment of FIG. 1, and for which reason the same components will not be here again described. Instead of the attachment 3 of FIG. I, in the arrangement of FIG. 4 there is provided an attachment in the form of an insert 82 for sealing the hollow mold compartment toward the top. It fulfills the same functions as the cover portion of the attachment 3. The bath level control 30 of FIG. I (which has not been shown in FIG. 4) maintains the bath 33 at the desired level or height and carries out the same functions as already heretofore described.

The process is analogous to that described in conjunction with the embodiment of FIG. 1. The spheres 20 are again delivered from the infeed or delivery device 21 under pressure to the liquid metal pool 10 and distribute themselves, prior to itssolidifrcation, over the entire cross-section. The process features described in conjunction with FIGS. 2 and 3 and which differ from that of FIG. 1 are also usable with the process of FIG. 4 employing revolving bands.

Now in FIG. 5 there is depicted the use of the inventive process for horizontal casting, wherein as an example of the casting operation there is here assumed the casting of a cell-like or cellular round bar of cast iron. With a 55 percent proportion of porous spheres or balls there is obtained a specific gravity of the strand of 3.2 in contrast to 7.2 for a solid cast strand. The horizontal casting process is generally known to the art and further details have been disclosed, for instance, in U.S. Pat. No. 2,837,791 to which reference may be readily had. Hence, this particular process will only be explained to the extent necessary for understanding the underlying concepts of the invention.

A horizontal, water-cooled open-ended mold 85 possesses a graphite insert 86 which forms the hollow mold compartment. Ahead of the mold 85 there is arranged a thermal-insulating attachment 87 formed of refractory material. This attachment 87 is constructed as a T-element or T-shaped element. The cross-section of the metal outlet or discharge 88 is identical to the cross-section of the hollow mold compartment of the mold 85. The cross-section of the metal inlet 89 can likewise be identical, however advantageously possesses a square cross-section, so that at the attachment 87 the infeed channel 90 for the cast iron transforms from a square into a round cross-section. The attachment 87 is connected at the inlet side with a metal infeed device 91 in the form of a vessel for the cast iron.

The attachment 87 is provided with an additional inlet 92. At the inlet 92 there is arranged the delivery device or mechanism 21 for the infeed of the porous spheres or balls 20, as the same has been described in detail in conjunction with the embodiment of FIG. 1. The attachment 87 also is equipped with the heater 36. The upper edge 95 of the inlet 92 possesses at least the height of the edge 96 of the vessel 91 for the metal, so

that the infeed device 21 for the spheres 20 is arranged above the metal bath 100.

The conveyor or feed worm 23 presses the desired proportion by volume of spheres 20 i from above, against the action of the buoyant force, through the uncooled metal bath portion at the inlet 92 into the uncooled infeed or delivery channel 90. From that location they are moved, with the further aid of the inflowing metal, into the hollow mold compartment and into the liquid metal pool 10. In order that the spheres or balls 20 cannot move in the direction of the inlet 89, owing to the pressure exerted upon such spheres by the conveying worm 23, it is possible to mount in front of the inlet 92, especially in the case of metals having a low melting point, a sieve. A more advantageous construction contemplates having the upper boundary or upper wall 97 of the infeed channel 90 ascend, after the cross-section of the metal inlet 89, at an angle 98 of at least 45 with respect to the horizontal. The crosssection of the inlet 89 is located lower at least by the height of the cross-section of the outlet 88. At this upper boundary 97 there is present a component,'

which assists the spheres in their movement in the direction of the hollow mold compartment, so that such cannot penetrate into the vessel 91.

In order to avoid irregularities in the cell-like structure of the produced strand, owing to the lift forces which act upon the porous spheres 20 at the liquid metal pool and to ensure for the distribution of such spheres over the cross-section, these spheres are moved or displaced in the liquid metal pool. For this purpose there is employed for instance an electromagnetic field which is generated by a coil 102, and which imparts a circular motion to the metal in the casting head 10. Due to this movement the spheres 20 are moved downwardly. Together with the buoyant or lift force these spheres are distributed over the entire region of the cross-section and are solidified into the cast strand through the action of the increasing solidification process.

During horizontal casting there is generally employed an intermittent withdrawal of the strand. Also such strand withdrawal operation can be synchronized with the drive mechanism 24. By appropriately extending and imparting the desired shape to the metal outlet side of the attachment 87 constructed as a T-element the inventive process also can be employed in a vertical casting installation. It is, however, to be observed that the tip at the liquid metal pool 10 does not reach the bath level 100 at the infeed device 91 and at the inlet 92 for the balls or spheres 20. In the case of ascending casting the lift force additionally assists in bringing the porous bodies into the liquid metal pool 10, so that their distribution over the cross-section is facilitated.

lt is of course to be clearly understood that the principles of the invention are not strictly confined to the exemplary embodiments given herein. They also can be employed for arc-, inclined-, or tubecontinuous casting operations.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

Accordingly. what is claimed is:

l. A method of continuously casting metals with a considerably lower specific gravity of the cast strand than that of the cast metal, wherein the metal and additive constituents are introduced into the liquid metal pool of the metal bath in a hollow molding compartment, the improvement comprising the steps of: introducing as the additive constituents porous bodies having a specific gravity which is less than I, and exerting a pressure upon the porous bodies which at least corresponds to the magnitude of the buoyant force acting upon the porous bodies upon penetration into the metal.

2. The method as defined in claim l. further including the step of withdrawing the cast strand and regulat' ing in accordance with the desired proportion by volume of the porous bodies in the strand the volumedependent infeed of such porous bodies as a function of the strand withdrawal speed. i

3. The method as defined in claim 2, including the step of introducing the porous bodies into an uncooled part of the metal bath.

4. The method as defined in claim 1, including the step of guiding the porous bodies through an uncooled part of the metal bath.

5. The method as defined in claim 1, including the step of pre-heating the porous bodies prior to their introduction into the liquid metal.

6. The method as defined in claim 1, including the step of employing an approximately vertically arranged hollow mold compartment, and delivering the porous bodies by means of a fusible container into the liquid metal pool.

7. The method as defined in claim 2, including the step of pre-heating the porous bodies prior to their introduction into the liquid metal, employing a substantially vertically arranged hollow casting mold, and introducing the porous bodies by means of a castable container into the liquid metal pool.

8. The method as defined in claim 2, including the step of initiating solidification of the metal in at least a part of the outer marginal layer contacting the wall of the hollow mold compartment prior to the penetration of the porous bodies.

9. The method as defined in claim 1, including the step of moving the porous bodies at the liquid metal pool.

10. A method of continuously casting metals with a considerably lower specific gravity of the cast strand than that of the cast metal, wherein the metal and additive constituents are introduced into the liquid metal pool of the metal bath in a hollow molding compartment, the improvement comprising the steps of: employing an approximately vertically arranged hollow mold compartment, introducing as the additive constituents porous bodies having a specific gravity which is less than 1 into the liquid metal pool in the hollow mold compartment by means ofa castable container, and exerting a pressure upon the porous bodies which at least corresponds to the magnitude of the buoyant force acting upon the porous bodies upon penetration into the metal.

11. A method of continuously casting metals with a considerably lower specific gravity of the cast strand than that of the cast metal, wherein the metal and additive constituents are introduced into the liquid metal pool of the metal bath in a hollow molding compartment, the improvement comprising the steps of: initiating solidification of the metal in at least a part of the outer marginal layer contacting the wall of the hollow molding compartment prior to the penetration of porous bodies, introducing as the additive constituents porous bodies having a specific gravity which is less than 1, and exerting a pressure upon the porous bodies which at least corresponds to the magnitude of the buoyant force acting upon the porous bodies upon penetration into the metal.

12. An apparatus for the continuous casting of metals having a considerably lower specific gravity of the strand than that of the cast metal, comprising means defining a hollow mold compartment for confining the metal to be cast, an infeed device for the metal to be cast. and a mechanism for the delivery of the porous bodies into the metal to be cast and for exerting a pressure upon the porous bodies.

13. The apparatus as defined in claim 12, wherein said hollow mold compartment includes a thermalinsulating attachment means.

14. The apparatus as defined in claim 13, wherein the thermal-insulating attachment means is provided with an opening for the infeed of metal which is located beneath the level of the molten metal.

15. The apparatus as defined in claim 13, further including a bath level control means operatively associated with said attachment means for maintaining the level of the molten metal bath at a predetermined height.

16. The apparatus as defined in claim 13, further including heating means provided for the attachment means.

17. The apparatus as defined in claim 13, wherein the means defining said hollow mold compartment comprises a substantially horizontal open-ended mold, said thermal-insulating attachment means comprising a T- element.

18. The apparatus as defined in claim 17, wherein the T-element possesses a metal inlet and a metal outlet. and wherein the cross-section of the metal inlet of the T-element is located lower than the metal outlet at least by the height of the crosssection of the metal outlet.

19. The apparatus as defined in claim 17, further including an infeed channel for the T-element having an upper boundary, and wherein the upper boundary of the infeed channel ascends at an angle of at least 45 with regard to the horizontal at a location following the metal inlet.

20. The apparatus as defined in claim 12, wherein the delivery mechanism for the porous bodies is arranged above the level of the molten bath of metal.

21. An apparatus for the continuous casting of metals having a considerably lower specific gravity of the strand than that of the cast metal, comprising means defining a substantially horizontal open-ended hollow mold compartment for confining the metal to be cast, an infeed device for the metal to be cast, a substantially T-shaped element interposed between said infeed device and said hollow mold compartment for supplying the metal to be cast from said infeed device to said hollow mold compartment, and a mechanism for the delivery of the porous bodies into the metal to be cast and for exerting a pressure upon the porous bodies.

Claims

1. A method of continuously casting metals with a considerably lower specific gravity of the cast strand than that of the cast metal, wherein the metal and additive constituents are introduced into the liquid metal pool of the metal bath in a hollow molding compartment, the improvement comprising the steps of: introducing as the additive constituents porous bodies having a specific gravity which is less than 1, and exerting a pressure upon the porous bodies which at least corresponds to the magnitude of the buoyant force acting upon the porous bodies upon penetration into the metal.

2. The method as defined in claim 1, further including the step of withdrawing the cast strand and regulating in accordance with the desired proportion by volume of the porous bodies in the strand the volume-dependent infeed of such porous bodies as a function of the strand withdrawal speed.

10. A method of continuously casting metals with a considerably lower specific gravity of the cast strand than that of the cast metal, wherein the metal and additive constituents are introduced into the liquid metal pool of the metal bath in a hollow molding compartment, the improvement comprising the steps of: employing an approximately vertically arranged hollow mold compartment, introducing as the additive constituents porous bodies having a specific gravity which is less than 1 into the liquid metal pool in the hollow mold compartment by means of a castable container, and exerting a pressure upon the porous bodies which at least corresponds to the magnitude of the buoyant force acting upon the porous bodies upon penetration into the metal.

12. An apparatus for the continuous casting of metals having a considerably lower specific gravity of the strand than that of the cast metal, comprising means defining a hollow mold compartment for confining the metal to be cast, an infeed device for the metal to be cast, and a mechanism for the delivery of the porous bodies into the metal to be cast and for exerting a pressure upon the porous bodies.

13. The apparatus as defined in claim 12, wherein said hollow mold compartment includes a thermal-insulating attachment means.

17. The apparatus as defined in claim 13, wherein the means defining said hollow mold compartment comprises a substantially horizontal open-ended mold, said thermal-insulating attachment means comprising a T-element.

18. The apparatus as defined in claim 17, wherein the T-element possesses a metal inlet and a metal outlet, and wherein the cross-section of the metal inlet of the T-element is located lower than the metal outlet at least by the height of the crosssection of the metal outlet.

19. The apparatus as defined in claim 17, further including an infeed channel for the T-element having an upper boundary, and wherein the upper boundary of the infeed channel ascends at an angle of at least 45* with regard to the horizontal at a location following the metal inlet.