EP0187227B1 - Method of and installation for the casting of brittle metal alloys - Google Patents

Description

The invention relates to a method and an apparatus for casting brittle metal alloys, in particular ferro alloys, such as e.g. Ferrosilicon.

After melting or metallurgical production of the melt, ferroalloys are cast in batches or discontinuously into molds. The forms consist of single-use forms, e.g. Sand hearth casting, or from permanent molds, i.e. Molds.

In the case of ferrosilicon, these forms consist of hematite with the dimensions of approximately 1.5 x 1.5 m ² and a thickness of approximately 100 mm. Such molds are on a casting carousel and are filled in portions by the tapping pan. Such a process is associated with a long solidification time, during which analysis segregation occurs. Furthermore, there are procedural disadvantages in that the mold supply on the carousel corresponds to the pan content. If the pan content is large, the casting carousel must be dimensioned accordingly, usually resulting in inappropriately large casting wheels.

The ferrosilicon, which is cast in molds, is crushed into plates in a crusher or grinder to the desired grain size. This results in up to 20 percent unsaleable fines. This fine fraction is melted down again under the known difficulties associated with the use of dusts in metallurgical furnaces.

In terms of plant technology, the investment costs for the casting carousel and the crusher or grinder are relatively high and energy-intensive in operation, and such plants work unsatisfactorily. Due to the circumstances, the state of the art is unsatisfactory in several respects: Batch-wise processing is disadvantageous from an operational process point of view. Technically, the 20% accumulation of fine fraction is extremely disadvantageous. In terms of plant technology, the high investment costs for the casting carousel, crusher and grinder are disadvantageous. Such systems also do not work satisfactorily from an operational point of view. The object of the present invention is accordingly to improve the production and processing of ferroalloys in terms of manufacturing process technology, operational process technology, plant technology and with regard to the necessary investments.

The object is achieved according to the invention by using the process of horizontal continuous casting, as it is e.g. is known from DE-A-32 06 501 and in the melt is passed into a horizontal continuous casting mold and the cast strand produced is essentially drawn at intervals and holding times between the drawing processes are observed, on the casting of brittle alloys, such as ferro alloys or calcium carbide , with the proviso that holding times of 0.5 to 10 seconds are observed in order to produce a desired notch formation in the strand, at intervals which correspond to later piece lengths of the product.

The invention could only be checked for its usability by tests. There are several parameters that preclude the application of continuous casting: ferroalloys have unfavorable flow and solidification properties, also tend to segregate the analysis and impair the structure. Long-term temperature control is difficult with ferroalloys. During the solidification, disadvantageous changes in state occur at temperature intervals. At higher temperatures, the crystal structure can decay (peritectics). There are also dangerous changes in volume during cooling (explosive effect). In the case of ferrosilicon, uncontrolled breakage in the warm state with low mechanical stress must also be expected. All of these disadvantages are avoided by the invention. In addition, it is advantageous that, compared with the known method, the surface solidifies practically without the influence of atmospheric oxygen and forms a metallic surface. In addition, the continuously operating casting process makes the operating process easier because the dust accumulation no longer occurs during continuous casting. Nevertheless, usable portions can be made and the large investment for the casting carousel, crushing or grinding mechanism is avoided.

The portioning problem is solved due to the holding times.

The basis of “continuous casting” is taken into account by inserting shorter holding times between the crushing lengths (piece lengths) compared to the longer crushing length holding times.

In order to avoid an uncontrolled breaking of the casting material, it is proposed that the cooling of the casting strand is slowed down outside the horizontal continuous casting mold.

It is also advantageous that the cooling of the cast strand is controlled in such a way that the temperature after leaving the drawing machine is above the critical value for brittle metal alloys.

Viewed overall, the process according to the invention therefore advantageously leads to a continuous process, i.e. for the continuous casting of materials that previously appeared not to be castable (brittle metal alloys, ferro alloys and non-metals, such as calcium carbide). The process is optimized through the combination of horizontal continuous casting, the possibility of keeping warm with refining and portioning options. The previous fine fraction is eliminated with simultaneous equalization or increase in product quality and dosage. In addition, the structure of the product can be controlled. The device for the application of the horizontal continuous casting process provides a storage vessel for the molten metal with a flanged, short horizontal continuous casting mold and this subsequent drawing machine and is characterized in that after the horizontal continuous casting mold, the drawing machine is arranged at a short distance and that between the horizontal continuous casting mold and the drawing machine and the drawing machine subsequently a device for controlling a dry heat dissipation is provided.

In the simplest case, the device for controlling the dry heat dissipation consists of thermal insulation.

In the preceding method, the holding times are matched to produce a programmed notch formation, with a more or less strong notch effect being controlled via the holding times. The notches mainly result from the long solidification time and the cooling of this point to low temperatures, which no longer allow melting by subsequent liquid metal. With a corresponding recoil, the newly formed strand shell is bent inwards and thus offers a similar effect of the notching.

The device according to the further invention is now matched to these procedural measures by arranging a mechanical or thermal separating device following the drawing machine.

It is advantageous here that the mechanical separation device consists of a crushing device that takes advantage of the notch effect.

It is also advantageous that the thermal separation device consists of a cooling device that uses the shock effect.

• Fig. 1 einen schematisiert dargestellten Verfahrensablauf des bisherigen Verfahrens zum Herstellen von Ferrosilizium, mit einem körnigen Endprodukt,
• Fig. 2 den erfindungsgemäßen Verfahrensablauf mit einem in Portionen anfallenden Endprodukt,
• Fig. 3 einen Längsschnitt durch den in der Horizontalstranggießkokille erzeugten Gußstrang in der Phase der Strangschalenbildung nach einem ersten Verfahren,
• Fig. 4 denselben Schnitt gemäß Fig. 3 nach einem alternativen Verfahren,
• Fig. 5 ein Ausziehdiagramm für den Gußstrang in Abhängigkeit von Produktlänge und Zeit für das gemäß Fig. 3 angewendete Verfahren A und das gemäß Fig. 4 angewendete Verfahren B,
• Fig. 6 einen teilweisen Längsschnitt durch eine Horizontalstranggießkokille für das erfindungsgemäße Verfahren mit Rückstoß-Schritten,
• Fig. 7 einen teilweisen Längsschnitt wie Fig. 6 in konstruktiv veränderter Ausführungsform,
• Fig. 8 einen teilweisen Längsschnitt durch die Horizontalstranggießkokille für ein Verfahren ohne Rückstoß und
• Fig. 9 einen teilweisen Längsschnitt durch die Horizontalstranggießkokille wie Fig. 8, ebenfalls für ein Verfahren ohne Rückstoß.

Embodiments of the invention (process engineering and device engineering) are shown in the drawing and are described in more detail below. Show it:

• 1 shows a schematically illustrated process sequence of the previous method for producing ferrosilicon, with a granular end product,
• 2 shows the process sequence according to the invention with an end product obtained in portions,
• 3 shows a longitudinal section through the cast strand produced in the horizontal continuous casting mold in the phase of the strand shell formation according to a first method,
• 4 shows the same section according to FIG. 3 according to an alternative method,
• 5 is a pull-out diagram for the cast strand as a function of product length and time for the method A used according to FIG. 3 and the method B used according to FIG. 4,
• 6 shows a partial longitudinal section through a horizontal continuous casting mold for the method according to the invention with recoil steps,
• 7 shows a partial longitudinal section as in FIG. 6 in a constructionally modified embodiment,
• Fig. 8 is a partial longitudinal section through the horizontal continuous casting mold for a process without recoil and
• Fig. 9 is a partial longitudinal section through the horizontal continuous casting mold as Fig. 8, also for a method without recoil.

1 shows the process sequence before the filing date of the present invention. The ferroalloy is transported from the melting furnace 1 in the pan 2 via a casting carousel 3 and poured into the rotating molds 4. After solidification, the ingots 5 are brought into the crusher 6 and then into the grinder 7, whereupon the end product 8 is a spectrum of fine and coarse-grained material.

2, due to the method according to the invention, the plant has the melting furnace 1, a pan 2, a storage vessel 9, a flanged horizontal continuous casting mold 10, a drawing machine 11 and a separating device 12. The drawing machine 11 can e.g. be carried out in the manner described in DE-A 32 06 501. The end product 8 here consists of solid bodies 8a, which in this form (cylindrical round, cylindrical square and the like) are fed directly to alloying processes.

In the horizontal continuous casting mold 10, the metal melt 13 is solidified from the outside inwards. In this way, the strand shell 14 is formed. During the cooling in the horizontal continuous casting mold 10, the casting strand 15 which is formed is pulled out in steps at intervals for depth-controlled notch formation, stopped (0.5 to 10 seconds), possibly. pushed back (0.5 to 3 mm) and pulled out again. The selected cycles are repeated. In the case of horizontal continuous casting of steel, the holding times generally serve to form the strand shell or to accelerate the cooling of the material. Shorter holding times “a” (lifting marks 16) are provided for such cooling. Longer holding times “b”, on the other hand, produce notches 17 which run around the cast strand 15 and which can widen to form visible grooves. While the cast strand 15 is being pulled out at intervals “c”, the holding times “b” are in each case longer than the holding times “a”. A e.g. doubled interval distance 18 later gives the length of the body 8a. The interval distance 18 maintained during the casting therefore corresponds to the later breaking length in the separating device 12. The extraction methods according to FIG. 3 analogously to the diagram A in FIG. 5 work without recoil of the casting strand 15.

In contrast, the method according to FIG. 4 works analogously to diagram B in FIG. 5 with recoil, the recoil time “d” being short relative to the holding times a and b (FIG. 5).

The cooling of the cast strand 15 outside the horizontal continuous casting mold 10 is slowed down by the fact that there is initially no conventional secondary cooling section. However, heat radiation can be largely prevented by thermal insulation. As a result, the cooling of the cast strand 15 is controlled in such a way that after leaving the drawing machine 12 the assembly temperature is above the critical value for brittle metal alloys. In the case of ferrosilicon, this critical temperature is around 700 ^° C.

The device (Fig. 2 and 6 to 9) consists of the storage vessel 9 with pre-flanged water-cooled horizontal continuous casting mold 10 and the proven drawing machine with jaws and hydraulic control according to DE-A-32 06 501.

The drawing machine 11 is located at a short distance 19 from the short horizontal continuous casting mold 10. The horizontal continuous casting mold 10 or the drawing machine 11 is followed by a device 20 for controlling a dry heat dissipation. Such thermal insulation can e.g. consist of an insulating tube.

The mechanical or thermal separator device 12 effects the separation of the body 8a by further sawing, breaking off or selective strong cooling, whereby no otherwise occurring dust is generated. In this way, the cast strand 15 is subdivided into commercially available sizes or weights of the bodies 8a.

Suitable horizontal continuous casting molds 10 (FIGS. 6 to 9) consist of graphite on the inside of the mold (if there is no C-solubility of the molten metal) or of copper. The metal melt 13 flowing in at the casting speed or in the direction of production V is introduced through the refractory wall 21 or the jacket 22 of the distributor 9 and through the rear wall 23 of the horizontal continuous casting mold 10. The rear wall 23 is designed according to FIG. 7 as a separate ring 24. The horizontal continuous casting mold 10 has water cooling 25. This embodiment of the horizontal continuous casting mold 10 permits recoil of the casting strand 15.

The horizontal continuous casting mold 10 according to FIGS. 8 and 9 is provided for pulling out without recoil.

A pan 2 is used when, in addition to the temperature setting, the use of a metallurgical treatment is advantageous. The storage vessel 9 does not fully offer these conditions. In this case, the pan 2 forms a treatment vessel 26 with a heating device 27, which consists of a plasma torch 27a, a channel or coil inductor or a pan lid heating device. Furthermore, a refining device 28, which e.g. can also be formed from the plasma torch 27a.

Claims (8)

1. Process application, in horizontal continuous casting, for brittle, e.g.: ferro-aloys and/or calcium carbide, characterized by: the melt being introduced into a horizontal continuous casting mould, the cast strand being essentially withdrawn at intervals, there being pauses from 0.5 to 10.0 second(s) between the draw cycles in order to achieve specific notches in the strand at spacings corresponding to the finished lengths of the cast products.

2. Process application, to claim 1, characterized by: the halts corresponding to the cast lengths (b) being intersperced by shorter ones (a).

3. Process application, to claims 1 and 2, characterized by: the cooling of the strand outside the horizontal mould being retarded.

4. Process application, to claims 1 to 3, characterized by: cooling being controlled so that the cast strand emerging from the withdrawal machine retains a temperature above the critical value for brittle metal alloys.

5. Facility for working the process application, to claims 1 to 4, using a storage vessel forthe metal melt, a flanged-on short horizontal continuous casting mould, and a withdrawal machine following the latter, characterized by: the horizontal continuous casting mould (10) being closely followed by a gap (19) and the withdrawal machine (11) with an appliance (20), for dry heat dissipation control, also arranged between the aforesaid horizonal mould (10) and the above mentioned withdrawal machine (11).

6. Facility, to claim 5, characterized by the dry heat dissipation control appliance (20) consisting of thermal insulation.

7. Facility, to claims 5 and 6, characterized by: the withdrawal machine (11) being followed by a mechanical or thermal cut off (12), familiar as such, the mechanical cut off (12) being a breaker utilising the notch effect, the thermal cut off (12) being a cooling unit utilising the shock effect.

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