EP0158898B1 - Equipment for continuous casting, and method for its manufacture - Google Patents

Description

18. The invention relates to a continuous casting device and a method for producing a cooling mold or a cooling tube of a continuous casting device according to the preamble of claims 1 and 18 respectively.

Known cooling molds for continuous casting require high-quality, compression-molded and made of electrographite molds, which become more and more expensive depending on the constantly increasing energy costs, since each mold has to be manufactured as a precision turned part for practically every cast.

The upper part of the graphite molds used for the continuous continuous casting processes in use today protrude into the holding crucible or furnace and their cooling part is fitted in a metal cooler. Up to now, graphite has been used almost exclusively, since this material is the only one that has all the properties that are desired and required for these continuous casting processes. These are the non-wettability and insolubility of the graphite due to the metals to be cast, the high, sufficient dimensional stability at the casting temperature, the relatively good thermal conductivity and the self-lubricating or separating properties.

However, graphite molds also have a major disadvantage. The graphite material is not resistant to oxidation in the range above 550 ° C, and its structure is very often flawed. Imperfections, cracks, etc. and is also very sensitive to frictional stress caused by the hard strand shell. As a result, grooves are formed which increasingly impair the surface quality of the cast strands in the course of the continuous casting. Furthermore, graphite molds are very sensitive to impact, beige and tensile loads.

Since the casting performance of a graphite mold depends not only on the properties of the material properties, but above all on the heat transfer through the mold wall, very often in order to increase the casting performance, the mold wall thicknesses are relatively small. But especially with large-sized molds, the large and thin-walled hollow cylinders become very fragile and are not very reliable. Even slight transverse forces or a hard contact with the mold can lead to cracks or breakage, which is often not recognizable before casting, which can result in serious and dangerous accidents, namely breakthroughs or so-called runouts.

Another serious disadvantage of the mold made of graphite is, as already mentioned, on the one hand in the high material costs, and on the other hand is due to the fact that a lot of expertise, care and time are required to manufacture a graphite mold. Expensive tools, special suction devices etc. are also required. Another disadvantage is that each mold must be fitted, ground or pressed in very precisely into the metal cooler surrounding it, in order to ensure adequate heat transfer. Very rarely does one fit fit the other and often the big ones break; thin-walled molds when knocking out of the metal cooler due to the high static friction required.

In addition, there are considerable problems in production with frequent material defects. A disadvantage of the previous systems is the warping of the coolers surrounding the graphite mold, which often occurs after a relatively short period of use. The cooler bulges due to uncontrolled thermal stresses. This creates an air gap between the outer mold wall and the cooler, which greatly reduces the cooling capacity and thus the casting capacity.

Ultimately, mold wear is a major factor in manufacturing cost accounting. On average, the proportionate mold costs are currently at least DM 0.10 per kg of cast iron produced.

Basically, according to DE-OS 20 58 051 and DE-GM 1854884, a mold divided into two or three parts in the longitudinal direction is known, the overall length of which is relatively large due to the different conditions. This is because only a small amount of heat is to be dissipated below the crucible bottom in the first mold section and a large proportion of the heat in the subsequent section for cooling. In addition, these molds have not proven themselves in this respect, since only very poor casting results can be achieved if graphite is not used.

A generic continuous casting device has become known from GB-A 1 307 423. Similar to the prior art documents mentioned above, it has comparable disadvantages. The known continuous casting device has a large overall length. Despite the division into at least three cooling zones, the continuous casting result cannot be satisfactory.

The object of the invention is to overcome the disadvantages of the prior art and to provide a continuous casting device and a method for its production, the manufacturer. Design costs of the mold significantly minimized, the time required for manufacturing is reduced and the quality of the cast products in use of the mold is significantly improved in terms of dimensional accuracy, surface quality and physical properties compared to conventional continuous casting products. The object is achieved according to the device according to the features specified in the characterizing part of claim 1 and with regard to the method according to the features specified in the characterizing part of claim 18. Advantageous embodiments of the invention are specified in the subclaims.

By means of the present invention, in the field of the continuous casting process, a state of the art that has become known up to now technically enormous and can be described as quite surprising. By means of the present invention, metals and metal alloys can be optimally cast, the mold being split and the upper feed part being thermally insulated from the cooling part which follows in the direction of the strand transport. Furthermore, the cooling surface design and above all the geometric shape of the mold as well as the independent temperature control offer further advantages.

As has been found in tests, the cast strands produced with the continuous casting apparatus according to the invention have a fine-wave, uniform, matt, glossy surface without the longitudinal striations which, with a more or less long casting time, otherwise appear with increasing graphite molds.

According to a particularly preferred embodiment according to claim 2, a separate cooling tube is provided inside the body of the cooling mold, which also contains the separating agent comprising at least graphite. As a result, even more simplified manufacturing conditions with optimal continuous casting options are realized.

Improved cooling conditions without adverse effects due to thermal stress are realized according to a development according to claim 3 when the inner cooling tube and the cast body of the cooling mold are fitted via a shrink connection.

Particularly short lengths can be realized in a further development according to claim 6.

By the inventive arrangement according to claim 10 is caused by the increasing distance of the cooling tubes from the inner cooling jacket that in cooperation with the steadily increasing coolant temperature from the inlet side to the outlet side of the cooling tubes analogously also the wall temperature of the cooling part of the mold from the strand outlet side to the strand inlet side increases.

By using the graphitically precipitated carbon and the dispersed release agent in a further development according to claim 13, not only the graphite costs are drastically reduced compared to the prior art, but also excellent sliding and casting properties are achieved with the simplest design of the cooling mold.

In a further development according to claim 14, the surface of the cooling mold or the internal cooling tube is also machined and additionally provided with a lubricant and separating agent which also comprises graphite.

• Figur 1: eine erste schematische Vertikalschnittdarstellung der erfindungsgemäßen Stranggießvorrichtung;
• Figur 2: ein zweites schematisches Ausführungsbeispiel in Vertikalschnittdarstellung der erfindungsgemäßen Stranggießvorrichtung;
• Figur 3 bis 5: drei Beispiele einer auszugsweisen Draufsicht auf die innenliegende Oberfläche der Kühlkokille bzw. des inneren Kühlrohres und eine zugehörige Vertikalschnittdarstellung;
• Figur 6: schematische Schnittdarstellung eines Hohlkörpers zur Oberflächenbehandlung;
• Figur 7: eine Schnittdarstellung durch einen Formkörper zur Herstellung eines Kühlrohres;
• Figur 8: eine schematische ausschnittweise Draufsicht auf die Oberfläche des äußeren Formkörpers.

Claims 18 to 23 relate to a method for producing a cooling mold or a cooling tube of the continuous casting device according to the invention.

• Figure 1: a first schematic vertical sectional view of the continuous casting device according to the invention;
• Figure 2: a second schematic embodiment in vertical section of the continuous casting device according to the invention;
• Figure 3 to 5: three examples of a partial plan view of the inner surface of the cooling mold or the inner cooling tube and an associated vertical sectional view;
• Figure 6: schematic sectional view of a hollow body for surface treatment;
• FIG. 7 shows a sectional illustration through a shaped body for producing a cooling tube;
• Figure 8: a schematic partial plan view of the surface of the outer molded body.

Reference is made below to FIG. 1, in which 1 shows a lower part of an upstream melting container in the form of a holding crucible or furnace, in which a melt 2 is located. In a bore 3 in the crucible or furnace 1, a feed part 4 of a continuous casting mold 7a is fitted, which is suitable for the continuous casting of solid profiles. In the feed part 4, which consists of low heat conductive, refractory material that is not attacked or only slightly attacked or wetted by the melt, channels 15 are incorporated in a known manner, through which the liquid melt enters the cooling part of the cooling mold 7. The feed part 4 of the continuous casting mold 7a is connected to the cooling mold 7 by known components such as e.g. a conical or cylindrical seat 5 and dowel pins 8 or also connected with a suitable conical or cylindrical thread, with insulating seals 6 also being provided for sealing the liquid melt.

The cooling part 7 of the mold consists of a cast body 10 made of highly heat-conducting material, which at the same time comprises cooling spirals 9 and an inner cooling tube 13 made of highly heat-conductive, high-strength metal in the form of a shrink connection. The inner tube has the shape of a rotational paraboloid and has the surface formation typical of the method, as can be seen from FIGS. 3, 4 and 5.

A coolant inlet or outlet is designated 11 and 12. Insulating seals of the crucible, with respect to the upper part of the cooling mold 7, are denoted by 14. Furthermore, thermocouples 16 and 17 are firmly cast in, by means of which the temperature at the inlet or outlet end of the cooling mold 7 is measured and by means of which the coolant temperature and quantity can be regulated. Details of the relationship of the crucible, as well as the arrangement and insulation are not shown in detail since they are of no importance for the invention.

Reference is made below to FIG. 2, in which an embodiment of a continuous casting installation according to the invention is shown in a further exemplary embodiment, as is particularly suitable for the casting of larger hollow cross sections or hollow profiles.

The feed part 4 of the continuous casting mold 7a is seated here in the opening or bore 3 of a highly refractory insert 1a in the furnace bottom 26, which is thermally insulated against the lower part 28 of the steel structure of the furnace floor by an insulating layer 27. As in FIG. 1, the feed part 4 is provided with a conical seat 5 and dowel pins 8 and is insulated and sealed from the cooling mold 7 by means of insulating seals. With 14 an insulating seal of the opening 3 against the cooling part 7 of the mold 7a is designated. The feed part 4 consisting of low heat-conducting material that cannot be wetted by the melt takes place through a precisely centered element, eg. B. a conical thread 22 on the refractory insert 21, to which preferably a hollow casting mandrel 25a, which has proven to be favorable, is fastened by means of a thread 24 and the centering 23.

This can consist of highly refractory, low heat-conducting material, its surface being specially prepared for receiving a release agent, which can be done by means of a tube such that the release agent is applied in the manner described in the claims. Likewise, this hollow casting mandrel 25a can also consist of a highly refractory, non-wettable material with self-lubricating or / and separating properties, the thermal expansion of which is equal to or greater than that of the insert 21.

As can be seen from FIG. 2, the casting mandrel 25a is also formed in two parts like the mold and comprises the upper insert 21 and the lower part 25 fastened underneath.

The remaining elements are designed analogously to FIG. 1 and provided with corresponding reference numbers.

In order to achieve a sufficient sliding and separating effect in a continuous casting process with an even simpler construction and simplified manufacture of the cooling mold or the internal cooling tube, it is provided that the cooling mold 7 or, in the case of a design with an internal cooling tube 13, at least this one made of iron or Copper alloy with integrated finely divided release agent is produced in a solid dispersion. Iron alloys with an addition of carbon are particularly suitable for this purpose, for example an iron alloy with 2 to 3.2% C, 0.4 to 2.2% Si and 15 to 25% Cr. In this case, the carbon is present as a fine-laminar graphite in a pearlitic matrix, whereby in this heat-resistant gray cast iron, graphite crystals are also provided in addition to the graphitically precipitated carbon as an alloying component in an evenly finely distributed form.

Austenitic cast iron grades with preferably laminar graphite layers have also proven to be particularly favorable. In particular the gray cast iron alloys (DIN 1694).

GGL-Ni Cu Cr (1562) with a content of 3.0% C, 1.0 to 2.8% Si, 1.0 to 1.5 Mn, 13.5 to 17.5% Ni, 1.5 up to 2.5% Cr, 5.5 to 7.5% Cu, or

GGL-Ni Cu Cr (1563) with an identical composition as above, but with a chromium content of 2.5 to 3.5%, which results in increased corrosion and erosion resistance, or

GGL-Ni Cr (202), with the same copper, silicon and manganese content, but the nickel content deviates from 18 to 22% and the chromium content is 1 to 2.5%.

It proves to be particularly favorable if the separating agent is used in grain sizes between 0.01 and 0.5 mm, which is ultimately preferably statistically predominantly oriented in the cooling tube or in the cooling mold 7 with its preferred sliding plane parallel to the longitudinal axis of the inner cooling tube.

The manufacture of such a cooling mold or in particular the internal cooling tube 13 is explained in more detail below with reference to FIGS. 7 and 8.

FIG. 7 shows in vertical section a heat-resistant molded body 50 with an internal molded body half 50a and an external molded body half 50b.

The arrangement is such that the two molded body halves 50a and 50b can rotate relative to one another, for example in such a way that the inner molded body half 50a rotates while the outer molded body half 50b is stationary. The rotating molded body half, in the exemplary embodiment shown the inner one, is furthermore provided with vertical ribs 53, as is shown in detail in FIG. 8, which leaves slightly wedge-shaped gaps, the meaning of which will be discussed below.

In order to create the cooling tube 13, a corresponding alloy with a temperature above the liquidus line, preferably a temperature which is only slightly above the liquidus line, is poured into the space 54 remaining between the two molded body halves. The release agent is then added to the inner molded body half 50a with constant rotation of at least one molded part half, the above-mentioned powdered release agent being Mixing in particular using graphite may be considered, and the grain spectrum should also be at least 70% between 0.01 and 0.5 mm. At the same time, the temperature is lowered below the liquidus line. The rotation results in a uniform distribution of the release agent, since the pulp-like alloy is carried along in particular by the ribs 53 of the inner molded body half 50a. The centrifugal forces also produce the effect that, on the one hand, the lighter release agent components diffuse inward due to the centrifugal forces and thus come to lie with a higher density on the inner surface of the inner cooling tube 13. Likewise, the density of the release agent parts with a low specific weight increases due to gravity from bottom to top. The thyxotropic behavior - similar to a sludge - of the supercooled alloy reduces the separation through buoyancy and centrifugal force.

This also results in connection with the above-mentioned advantages that the sliding and separating properties are improved due to the denser attachment of the release agent bodies to the inner surface of the cooling mold. The location, the distribution and orientation of the lubricant body, so z. B. control the graphite crystals by appropriate optimal choice of the temperature of the speed and the cooling intensity in a wide range.

Furthermore, it should also be noted that the ribs 53 not only create the above-mentioned orientation and condensed accumulation of the finely divided release agent particles in the cooling mold to be produced, but above all also an improved and increased heat transfer surface to achieve a shrink connection. If the outer molded body half 50b is also insulated or heated accordingly, slow cooling of the melt can be achieved in a targeted manner. Since the release agent has a much lower thermal expansion than the surrounding metal alloy, the sliding and separating particles are shrink-wrapped by the metal alloy as it cools down.

As shown in FIG. 7, the pouring into the rotary casting mold (molded body 50) can also take place from top to bottom through a partially hollow internal molded body 50a (casting mandrel) which at the same time serves in its lower part as a brake core and ejector. After its solidification, the inner cooling tube 13 is shrunk onto its refractory jacket, the hollow core serving as the inner molded body 50a then being pushed off from the cooling tube 13 thus produced. Due to the shrinkage process, the hollow core is usually destroyed, especially in the case of larger dimensions. B from sand grains bound with furan resin, from clay graphite and z. B. alumina compounds.

In a departure from the methods explained, the separating agent, which essentially consists of graphite, can also be previously introduced into the liquid iron or, for example, copper alloy at a temperature above the liquidus line before it is poured into the moldings.

After the manufacturing process, the release agent is thus internally deposited with an increased concentration on the cooling mold or on the cooling pipe, so that sufficient sliding properties can be achieved. Some of these can be improved by etching the inner surface of the cooling mold 7 or the cooling tube 13, the graphite portions emerging from the pearlitic matrix by this etching process. Surface treatment is also possible and sometimes useful.

In the following, reference is made to FIGS. 3 to 5, which show greatly enlarged sections (approx. 10: 1) of the process-typical surfaces of the cooling surfaces of the mold (or of the inner cooling tube 13), as can be seen after processing and coating, that is to say in the ready-to-cast state appearance. (The hollow part 25 of the casting mandrel 25a can also be provided with this surface).

FIG. 3 illustrates a surface typical of the method, such as is obtained by preparing the surface according to the invention by cutting a multi-thread saw or tooth thread with a low pitch after smoothing and applying the separating layer, in 10 times magnification.

The thickness or thickness of the shrinked cooling tube 13 and the depth of the thread turns after the smoothing process, in particular grinding, are illustrated by 43. With 31 the valleys fully pressed with the release agent are designated, while with 32 the raised, ground thread tips are shown. In all three enlarged representations, the counter-conicity appears to be greatly exaggerated due to the shape of the paraboloid of revolution according to the invention.

In FIG. 4, the reference number 13 shows the inner cooling pipe with the saw thread threads cut in crosswise fashion (left and right) with an incline of approximately 15 °. Here, the area 31 filled with the release agent predominates by far the surface of the stubbed truncated pyramids 32, the flanks of which are intentionally more and more rounded by the grinding and polishing process according to the manufacture, by the subsequent hard chrome plating and by use, until a state is reached which not changed or hardly changed.

Figure 5 illustrates a ready-to-cast surface as it results from cords. The thickness of the inner mold tube, which in practice is between 3.5 and about 16 mm, depending on the starting diameter and the alloy to be cast, is again indicated at 43.

With 34 the original wall thickness of this inner cooling tube before smoothing the tips and 33 with the surface layer removed by the smoothing process is named. Reference number 32 in turn relates to the remaining truncated cones and reference number 31 to the cooling surface occupied by the separating agent.

Furthermore, it is pointed out that the thermocouples cast on the strand entry and exit sides allow the amount of coolant to be regulated according to the principle of differential control so that the casting speed is controlled and optimized solely according to the strand exit temperature.

Particularly suitable as coolant is softened water, which is fed through the quantity-controllable feed pump under pressure to the cooling coils of the mold depending on the temperature difference - as explained above - in such an amount and temperature that the coolant on its way in countercurrent through the coil of the mold evaporates according to the forced flow principle and in the upper turns to the desired rule bare, optimal temperature is heated. This results in a strand quality according to the invention which is not predictable and clearly improved compared to the prior art.

During the start-up process (start) of the casting process with appropriately low wall temperatures of the mold, an amount of coolant adjusted to idle value is first conveyed by the control system through the cooling coils, as a result of which the mold wall heats up to the desired operating temperature very quickly and without any signs of condensation, and then increases as the casting speed increases The required amount of coolant can be readjusted infinitely depending on the increasing temperature values using the differential control described above.

It has also been found to be advantageous that the cooling coils mentioned can be provided in a single-thread manner in the case of smaller molds, but can also be wound in a multi-thread manner in the larger ones.

In FIG. 6, a hollow punch 45 with openings 47 for the release of the separating agent is shown in part and schematically, via which the cooling tube 13 or, if the mold is used without a cooling tube, the surface of the cooling mold 7 itself is appropriately surface-treated.

The desired controllable temperature control can be achieved by means of the feed pump 49 shown in FIG.

In certain cases, it can also be advantageous not to let the internal cooling tube 13 run from the lower end of the cooling mold 7 to its upper end, but rather to let it end at a certain distance in front of the upper end of the cooling mold 7. In this case, a graphite ring can be used up to the height of the mold 7.

Claims (23)

1. A continuous casting apparatus comprising a continuous casting die (7a), which is adapted to be mounted on the crucible bottom (1) of an upstream melt container, which is divided into at least two parts, and which is subdivided into a supply part (4), possibly receiving a casting mandril (25a) and, transversely in relation to the direction of continuous casting, into a chill die (7), whose temperature is able to be regulated, with a chill means surrounding it, said supply part (4) being made of a refractory material, which preferably has a low thermal conductivity and is practically not attacked by the melt, and the chill die (7) consists of a basis material of metal, or, respectively, a metal alloy with a good thermal conductivity, characterized in that the chill die (7) is provided with encircling cooling tubes (9), which for the purpose of providing a shrink fit, have the alloy material of the casting (10) forming the chill die (7) cast around them, and in that the alloy material of the chill die (7) comprises a stripping agent, which preferably contains graphite and in that the chill die is thermally insulated in relation to the feed part (4) and also to the crucible bottom (1) or, respectively, under the insert (1a) provided there with a sealing means (6 and 14).

2. The continuous casting apparatus as claimed in claim 1, characterized in that the chill die (7) possesses an external casting (10) which surrounds the chill tubes (9) and internally possesses a chill tube (13), only the internal chill tube (13) containing a stripping agent which is preferably made of graphite.

3. The continuous casting apparatus as claimed in claim 1 or claim 2, characterized in thatthe inner chill tube (13) and the casting (10) are fitted using a shrink joint.

4. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 3, characterized in that the chill tube (13) extends along at least part of the height of the chill die (7) from its lower end upwards.

5. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 4, characterized in that the chill die (7) consists of a casting (10) of material with a high thermal conductivity and the inner chill tube (13) consists of a material with a high strength and good thermal conductivity or of such an alloy.

6. The continuous casting as claimed in any one of the preceding claims 1 through 5, characterized in that the chill die (7) extends as far as the direct vicinity of the crucible bottom (1) or, respectively, of an insert (1 a) located there and the chill die (7) is arranged in the crucible bottom (1) or, respectively, in an insert (1a) arranged there.

7. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 6, characterized in that the inner chill surface, which is preferably circular in cross section, of the chill die (7) or, respectively, of the internal chill tube (13) has essentially the form of a concave paraboloid of revolution in longitudinal section.

8. The continuous casting apparatus as claimed in any one of the preceding claims 7, characterized in that the geometrical form of the inner surface of the chill die (7) or, respectively, of the inner chill tube (13) conforms to a concave paraboloid of revolution, whose internal diameter, which decreases downwards, is functionally dependent on the shrinkage of the cast material related to its speed of draw.

9. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 8, characterized in that the distance of the chill tubes (9) apart decreases in the axial direction of the chill die (7) in the direction of casting of the cast material.

10. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 9, characterized in that the distance of the chill tubes (9) from the inner surface of the die decreases in the direction of casting and accordingly the upward slope of the inner surface, formed as a paraboloid of revolution, is exaggerated.

11. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 10, characterized in that in the chill die (7) both on cast material inlet side and also on the cast material outlet side thermoelements (16 and 17) are cast in place for controlling the flow rate of the coolant in accordance with the differential principle as a function of the cast material output temperature.

12. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 11, characterized in that the chill die (7) as a whole or, respectively, the chill tube (13) consists of a perlitic, finely laminar alloy, more especially cast iron and comprises 2 to 3.2% C, 0.4 to 2.2% Si and 15 to 25% Cr.

13. The continuous casting apparatus as claimed in claim 12, characterized in that the alloy comprises as an alloy component graphitically precipitated carbon and equally finely distributed graphite crystals in a disperse phase.

14. The continuous casting apparatus as claimed in any one of the preceding claims 13, characterized in that the inner chill tube (13) consists of austenitic types of cast iron.

15. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 14, characterized in that the metallic inner surface of the chill die (7) or, respectively, of the inner chill tube (13) is provided with a roughened surface or, respectively, with depressions (31) in the form of craters or waves, whose crests (32) are smoothed away, the inner surfaces of the chill die (7) or, respectively, of the inner chill tube (13) being coated with a lubricant and a stripping agent.

16. The continuous casting apparatus as claimed in claim 15, characterized in that additives of carbonates, oxides and nitrides, preferably with a high melting point, are mixed with the lubricant and stripping agent in accordance with the metal to be cast or, respectively, the metallic alloy to be cast.

17. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 16, characterized in that more especially for small cast material cross sections with a diameter of preferably less that 50 cm the inner chill tube (13) is made of thin-walled steel or of aluminium bronze.

18. A method for manufacturing a chill die or of a chill tube of a continuous casting apparatus as claimed in any one of the preceding claims 1 through 17, characterized in that the liquid alloy is cast at a temperature above the liquidus line while continuously stirring into a mold (50) consists of an inner and an outer die half (50a and 50b) of refractory material, the stripping agent being added before or after teeming into the die (50) while performing further stirring of the liquid alloy and the melt is cooled at a controlled rate under the liquidus line.

19. The method as claimed in claim 18, characterized in that the stirring operation is performed by turning the two die halves (50a and 50b), that is to say an inner and an outer die half (50a and 50b) in relation to each other.

20. The method as claimed in claim 18 or claim 19, characterized in that the inner die half (50a) rotates while the outer die half (50b) is stationary.

21. The method as claimed in any one of the preceding claims 18 through 20, characterized in that for the process of stirring a rotating die half (50b) is used with substantially vertically extending ribs (53) to be placed on the molding.

22. The method as claimed in any one of the preceding claims 18 through 21, characterized in that for the inner die half (50a) use is made of a hollow casting mandril for the supply of the liquid alloy.

23. The method as claimed in any one of the preceding claims 18 through 22, characterized in that when the stripping agent and lubricant have been used up for restoring the continuous casting apparatus the perforated surface to be treated (chill die (7) or, respectively, the inner chill tube (13)) is removed by brushing and fresh lubricant and stripping agent are applied.

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