EP0363375B1 - Continuous casting device - Google Patents

Abstract

A chill mold in a continuous casting apparatus consists of a cast material, which is shrunk onto the cast-in central chill tube as well as the chill tubes which spirally surround the same. Components of the apparatus are re-usable. This is accomplished by a primary and a secondary chill which are offset in the axial direction in relation to each other. Both chills are cooled by separate coolant circuits to their respective chill bodies. The ratio between the length in the continuous casting direction to the external and, respectively, the internal diameter of the primary chill is less than 70:100.

Description

The invention relates to a continuous casting device according to the preamble of claim 1.

Conventional continuous casting devices consist of a mold which is made from a graphite tube or at least has a graphite layer on its inner surface. In order to ensure a flawless and hot metal flow from a holding furnace or a crucible, conventional molds are usually designed to protrude into the melting chamber.

Although this basically has the disadvantage in terms of process technology that considerable amounts of heat are withdrawn from the furnace and, above all, from the material to be cast, which then have to flow off to the surrounding cooler via the mold wall, the one from the EP has nevertheless -A-0158898 known continuous casting device very proven. In addition to the configuration divided in two in the longitudinal direction using a crucible-side feed part and a temperature-adjustable cooling column adjoining it in the casting direction, this known continuous casting device has the essential advantage, which is decisive in comparison with other known devices, that the cooling mold is made of a casting material which is made in the Shrink fit surrounds the cast-in cooling pipe and the spiral cooling pipe surrounding the cooling pipe and through which the coolant medium flows.

A two-part mold has also become known, for example, from DE-A-2058051 and from DE-U1-1854884. In both cases, the mold is divided in two in the longitudinal direction, whereby in the first-mentioned publication the cooling device following the introductory part is divided into two different zones, which differ in the use of different materials on the inner cooling central tube. The much larger and longer part of the cooling central tube is also made of graphite in this prior art, which is why the disadvantages mentioned above exist and occur here.

A continuous casting mold with a primary and a secondary cooler is also from "Soviet Invention Illustrated", Section CH, Week K46, December 28, 1983 Derwent Publications Ltd. (London, (GB) - Summary No. 819305, Class M22 & SU-A-990,411, January 23, 1983 (D1). However, this two-part mold is not suitable for practical operation in many respects due to the conically overlapping arrangement between the primary and secondary coolers and because of the changing inner diameter from the primary to the secondary mold. In addition, due to the overlapping conical arrangement of the primary and secondary coolers, a large heat flow is already caused in the primary cooler.

Finally, a two-part continuous casting mold can also be found in GB-A-1227312, in which the secondary cooler consists of copper or a copper alloy, ie a harder material than graphite. Primary and secondary coolers in this case comprise a cooling device in the form of a plurality of cooling tubes lying transversely to the longitudinal direction of the mold.

In contrast, it is an object of the present invention to provide a continuous casting mold based on the aforementioned prior art, which also improves the quality of the continuous casting compared to conventional continuous casting devices with low manufacturing and operating costs.

The object is achieved according to the features specified in the characterizing part of claim 1. Advantageous embodiments of the invention are specified in the subclaims.

The present invention for the first time creates a continuous casting device in which particularly favorable continuous casting properties can be achieved due to the relatively small axial length of the primary cooler with a comparatively large inner diameter in cooperation with the secondary cooler.

It is only in connection with this short primary cooler that the secondary cooler, which has a much greater axial length, enables optimized, controlled cooling of the continuous casting while avoiding graphite for the cooling central tube. Finally, the use of a cooling coil known per se is just as important as the feature known from EP-A-0158898, in particular, that the central tube, like the cooling coil, is encapsulated by the metal of the heat sink in a shrink fit. This is the only way to achieve the absolutely necessary heat transfer coefficients.

In a preferred embodiment, the tubular feed part anchored to the crucible can extend as far as the secondary cooler, the extremely short primary cooler only surrounding the lower section of the tubular feed part immediately adjacent to the secondary cooler. This front feed part can consist of good heat-conducting, high-quality graphite which is not soluble in the melt. Due to this short length, the graphite costs for this wearing part are kept extremely low. Through targeted control of the cooling temperature, the wall temperature of this short primary cooler can be regulated so high that it completely solidifies over the entire length of the strand without any noticeable shrinkage taking place.

In addition, as a result of the small longitudinal extent of the primary cooler device surrounding the tubular feed part in the form of a disk, less heat is removed from the cooling mold compared to conventional solutions.

Furthermore, this has the advantage that sufficient hot metal always flows into the short hot feed part of the cooling device and the gases released during the solidification and dissolved in the melt can escape in countercurrent without the metal temperature of the melt and, associated therewith, its gas content disadvantageously to have to lift high.

The larger part of the cooling mold, namely the secondary cooler, is designed as a reusable component. It proves to be particularly advantageous here that the use of graphite can be dispensed with in the continuous casting device according to the invention in this secondary cooler, which accounts for the largest part of the longitudinal extent. This saves extreme costs and also ensures that the secondary cooler is continuously reused.

A carbide compound, in particular silicon carbide, is particularly suitable for the cooling central tube in the secondary cooler. The use of aluminum or an AL alloy, which surrounds the inner cooling central tube, preferably made of silicon carbide, as well as the cooling coils in the shrink fit, achieves an optimal thermal conductivity and cooling effect. In addition, this mold is extremely light and therefore easy to handle.

By using the special silicon carbide mentioned, which has extremely high hardness with the lowest thermal expansion coefficient, a high surface quality of the mold wall with a roughness depth of, for example, 2 to 5 μm is also achieved. As a result, the continuous casting which runs through this central cooling tube and which initially solidifies only at the edge is opposed to only a very slight friction.

This, as well as the great hardness of the material, leads to the fact that no attachments which impair the heat transfer can be formed in the cooling central tube. Finally, a constant high heat transfer / heat exchange between the hot, continuously rigid, continuous casting and the secondary cooler is brought about by a radiation figure approximating the "black body", without the strand being inadvertently deterred too much. A process that would lead to the known "white radiation" of the outer cast skin, especially when casting cast iron.

With the continuous casting device according to the invention, the casting performance can also be increased by more than 30% compared to conventional continuous casting devices. The continuous casting device according to the invention is suitable for both horizontal and vertical operation. Above all, it can be used for a continuous continuous casting process, although it is of course also suitable for discontinuous operation. It is precisely here that the particular advantages of the invention are shown by the use of a highly wear-resistant, highly heat-conducting, thermo-shock-resistant and at the same time extremely hard, polishable material such as ceramic material for the inner cooling central tube, which can often be used without otherwise having to rework the inner surface of the casting mold. The otherwise considerable wear of graphite molds during discontinuous continuous casting is obviously avoided here.

Due to the safe supporting and guiding effect of the casting strand which solidifies further in the secondary cooler, this becomes Protected against deflection and mechanical influences and also safely guided and centered in the primary cooling zone. This promotes a uniform, centric primary solidification and uneven wear of the sensitive, soft primary graphite mold is avoided, which is particularly noticeable with a horizontal continuous casting device.

Figur 1:

ein erstes Ausführungsbeispiel einer erfindungsgemäßen Stranggießvorrichtung für Horizontalstranggießen von Rundbolzen;

Figur 2:

eine weitere Ausführungsform einer erfindungsgemäßen Stranggießvorrichtung, insbesondere für Vertikalstranggießen von Rohren aus Metall-, insbesondere Schwermetallegierungen.

Further advantages, details and features of the invention result below from the exemplary embodiments illustrated with the aid of drawings. The following show in detail:

Figure 1:

a first embodiment of a continuous casting device according to the invention for horizontal continuous casting of round bolts;

Figure 2:

a further embodiment of a continuous casting apparatus according to the invention, in particular for vertical continuous casting of pipes made of metal, in particular heavy metal alloys.

Reference is now made to FIG. 1, in which a continuous casting device for horizontal operation is shown in a schematic longitudinal section. 1 denotes the bottom and side walls of a holding furnace in which there is a melt 3. In a front wall of the holding furnace, a feed part 5 of the continuous casting device is provided so as to protrude, the opening of which is provided in a known manner with an insert 7 made of refractory material which is not soluble in the melt and has passages 9.

The end of the feed part 5 opposite the insert 7 in the continuous casting direction is fitted in a conical or cylindrical seat of a primary cooling 11 in the manner of a cooling ring. 13 with thermal insulation is designated, which sits between the furnace wall 1 and the primary cooler 11 designed as a cooling ring. The cooling itself takes place through a cooling spiral 15 provided in the primary cooler 11.

The amount of cooling water required for cooling is adjusted accordingly by a control valve 19 arranged in the inflow line 17 for the cooling spiral 15, which is regulated and controlled in a known manner by the temperature of the exiting heated cooling water via a thermal sensor 23 arranged in the outlet pipe 21.

As can be seen from the drawing, the primary cooling 11 designed as a cooling ring sits with only a small longitudinal extension at the end of the feed part 5 directly in front of the subsequent secondary cooler 25. A favorable ratio of the length of this cooled primary or feed part 5, which is pressed into the surrounding metal cooler, to the inner diameter the tubular feed part 5 is less than 60: 100; 50: 100, 40: 100 or 35: 100. The mentioned inner diameter of the tubular feed part 5 corresponds to the outer diameter of the casting strand taking into account the shrinkage factor.

The material for the feed part 5 is generally high-quality graphite which is a good heat conductor and is not soluble in the melt.

However, the use of e.g. Boron nitride. Due to the relative shortness of the cooled feed part 5, the temperature in the foremost part of the feed part 5 protruding into the crucible is only approximately 60 ° to 110 ° C. less than the temperature range of the melt 3. This realizes the advantage that the melt is little Heat is removed. The extreme ratio of the short length of the primary cooler to its diameter results in a high ΔT of at least 550 ° C. to 600 ° C. at the inlet of the primary cooler 11 and less than 200 ° C. at the end of the cooler, especially when entering the primary cooler. However, the wall temperature on the short primary cooler is still so high that in this front primary cooler a complete edge rigidity over the entire strand circumference occurs, but no noticeable shrinkage.

In Figure 1, the cooling disc 11 is designed in the manner of a flat cone. It consists of highly thermally conductive metal or a likewise highly thermally conductive metal alloy, e.g. Copper or copper with e.g. 0.5 to 0.7% Si with 1% to 1.2% Ni, i.e. a hardenable, heat-resistant Cu alloy. Discarding this primary cooling disk 11 is almost impossible due to its special, compact shape. The cast-in cooling spirals 15 eliminate the need for expensive machining of cooling channels, as in the case of traditional coolers. Likewise, the welding or brazing otherwise required is not required.

As already mentioned, the primary cooler 11 is followed by the secondary cooler 25, the inner cooling central tube 27 of which consists of highly thermally conductive ceramic material.

The cooling central tube 27 is surrounded by the actual cooler made of highly thermally conductive metal, such as aluminum or an aluminum lining, which are joint-tight to the feed part 5 by means of a snug fit 31 and anchor bolts 33, but are easily detachably connected. The cooling tubes 17 and 21 of the primary cooling circuit are guided in axial alignment through the cooler 25 such that they pass into the cooling spirals 15 in the primary cooler 11.

The cooling coil 35 of the secondary cooler 25, like the inner cooling central tube 27, which is made of ceramic material, is connected in a heat-conducting manner by the metal of the cooler 25 which is shrinking around both. The temperature of the secondary cooler 25 is regulated by a further thermal sensor 39 located in the outlet pipe 37, which controls the control valve 41 in the feed pipe 43 of the secondary cooler 25.

45 with a thermocouple is designated, which is installed between the inner wall of the cooler 25 and the ceramic central cooling tube 27 just behind the transition of the supply part 5 to the secondary cooler 25. This thermocouple 45 influences the casting speed, ie the strand transport and its speed, in such a way that it is ensured that the edge rigidity of the casting strand in the feed part 5 is completed. To clarify the function of this thermocouple, the position of the liquid / solid phase boundary or the liquidus / solidus line is shown schematically in FIG. 47 denotes the position of the phase boundary immediately after the end of the pull period, while line 49 shows the solidification front moved back towards the furnace during the stop period.

The thermocouple 45 effects the regulation of the pull-off speed, for which purpose the thermocouple 45 controls a sensor designated 51 in the drawing, to limit the phase limit at the level of the connection or shortly before the connection between the feed part 5 and the secondary cooler 25. The thermocouple shows 45 an increasing temperature above a set value as a result of the displacement of a phase boundary, the casting speed is reduced via the transmitter 51, as a result of which the temperature measured again at the thermocouple 45 drops. The production of the secondary cooler by simultaneously casting around the inner ceramic cooling central tube 27 and the cooling spiral 35 is particularly cost-saving and efficient. After pouring, the inner cooling central tube 27 forms a firm, non-detachable shrink connection with the surrounding metal of the secondary cooler 25, the inner cooling surface of which no longer has to be machined. Above all, the use of highly thermally conductive ceramic materials, such as silicon carbide, has proven to be particularly favorable. Such materials, such as special silicon carbide, have a high thermal conductivity and low thermal expansion and, at the same time, high thermal shock resistance and aging resistance. They are also extremely hard and can be polished.

A further exemplary embodiment of the invention is explained below with reference to FIG. 2, in which the same components as in FIG. 1 are provided with corresponding reference symbols.

The exemplary embodiment according to FIG. 2 relates to a vertical continuous casting device, in particular for heavy metal alloys. The entire furnace can be protected here by additional floor insulation 61, 63 being a floor plate.

In this embodiment, the feed part is let into the furnace bottom 1 by means of a fitting piece 65. The fitting 65 lies on the cooling ring-like primary cooler 11 or on the insulation 13 provided there. In this embodiment, 67 denotes a hollow casting mandrel, preferably made of graphite, which is precisely in by means of a graphite plug 69 and a centering 71 the middle of the feed part 5 is held. The plug 70 made of refractory cement prevents direct heat flow from the melt to the casting mandrel and prevents possible leakages of melt through the thread 73 into the interior of the casting strand 75.

It is stated above that ceramic materials are particularly suitable for the central cooling pipe. Carbides or carbide compounds are particularly recommended. As a rule, only boron and silicon carbides are considered as covalent carbides, which are hard, difficult to melt and chemically inert. Most metallic carbides are non-stoichiometric compounds of an alloy character. They are resistant to acids, usually harder than the pure metal components and conduct the electrical current. Carbides of chromium, tungsten, hafnium, molybdenum, nadium, niobium, tantalum and titanium are technically important.

Claims (10)

1. A continuous casting apparatus for vertical and/or horizontal operation, comprising a feeder part (5), which is able to be arranged on a ladle (1) and if necessary comprises a casting mandril (67), and an adjacent cooling mold section consisting of a central cooling tube (27), a cooling spiral (35) and of a cooling material cast around the cooling tube (27) and the cooling spiral (35) with a shrink fit, characterized in that in addition to the feeder part (5), with an offset in the axial direction in relation to each other, a primary and a secondary cooler (11 and 25) are provided having a separate coolant circuit (15 and 35) in their cooling members, in that the ratio of the longitudinal extent of the primary cooler (11) in the direction of continuous casting to the internal diameter of the primary cooler (11) is less than 60: 100 and in that the central cooling tube (27), which extends for a greater length than the primary cooler (11), of the secondary cooler (25) consists at least on the inner surface of graphite-free material, whose hardness is greater than that of graphite.

2. The continuous casting apparatus as claimed in claim 1, characterized in that the inner tube of the primary cooler (11) or, respectively, the inner coating thereof consists of boron nitride or preferably, respectively, graphite.

3. The continuous casting apparatus as claimed in claim 1 or claim 2, characterized in that the tubular feeder part (5) extends as far as the central cooling tube (27) of the secondary cooler (25) and in that the primary cooler (11) is designed in the form of a cooling ring surrounding the feeder part (5).

4. The continuous casting apparatus as claimed in claim 1, characterized in that the cooling ring (11) surrounding the feeder part (5) is arranged at the end of the tubular feeder part (5) adjacent to the secondary cooler (25).

5. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 4, characterized in that the ratio of the longitudinal extent to the outer or, respectively, inner diameter of the cooling tube (feeder part 5) of the primary cooling means (11) is less than 50: 100 and preferably less than 40: 100.

6. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 5, characterized in that the material of the central cooling tube (27) consists of an extremely hard material resistant to thermal shock, with a low coefficient of thermal expansion.

7. The continuous casting apparatus as claimed in any one of the claims 1 through 6, characterized in that the central cooling tube (27) consists of or includes carbide, a carbide compound, preferably silicon carbide or ceramic material.

8. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 7, characterized in that a thermosensor (23) is also provided in the cooling circuit of the primary cooler (11) for the control of a regulating valve (19) regulating the coolant rate.

9. The continuous casting apparatus as claimed in claim 8, characterized in that the thermosensor (23) is arranged in the associated outlet tube (21) of the cooling spiral (35) for the measurement of the temperature of the heated coolant.

10. The continuous casting apparatus as claimed in any one of the preceding claims 1 through 9, characterized in that a thermoelement (45) is arranged in the connection between the primary and secondary coolers (11 and 25) for the control of the draw off rate of the solidified cast strip (75).

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