DE7316110U - Device for heating a vacuum degassing vessel - Google Patents

Description

18,669

DAIDO SEIKO KABUSHIKI DAISHA Nagoya, Aichi (Japan)

. Device for heating a vacuum

- · gassing vessel

The innovation relates to a device for heating a vacuum degassing vessel, for vacuum degassing of molten metal, particularly molten steel.

In a vacuum degassing system, partial amounts of the molten steel is repeatedly sucked up into a vacuum vessel for vacuum degassing. So that the temperature drop of the molten steel when passing through the vacuum vessel is as small as possible and the composition the following batch is not affected by spattered material adhering to the wall of the vessel, the degassing vessel must be heated to a predetermined temperature of at least 1200 ° C.

. ^: So far, for heating such a vacuum degassing vessel, it has been provided with a burner or a graphite electrode and the combustion heat generated by the burner or the V / arm of the arc generated by means of the graphite electrode or that of

The heat generated by the graphite electrode is used to heat the vacuum degassing vessel. Have these arrangements the disadvantage · that they do not allow sufficient heating and the additional devices, for example the graphite electrode, require additional expenditure.

In the inventive device for heating a vacuum degassing vessel, a part or the larger Part of the refractory lining of the vacuum degassing vessel from a suitable number of heating element rings formed, which contain a metal oxide, for example stabilized · tes zirconium dioxide, which at high temperatures an electrical conductivity developed, arranged at vertical distances from one another, and a preheating device, for example a burner is provided.

The innovation thus creates a device for heating a vacuum degassing vessel in which a part or the greater part of the refractory lining of the Vacuum degassing vessel is formed by heating element rings, which are spaced in a suitable number at vertical intervals are arranged from each other and made of a metal oxide, for example stabilized zirconium dioxide, exist, which develops an electrical conductivity at high temperatures, whereby a preheating device, for example a burner is provided.

The innovation is based on the idea of providing a high-melting metal oxide such as zirconium dioxide (ZrO ₂ ) as part of the refractory lining of the vacuum degassing vessel and using it together with added yttrium oxide (Y ₂ ⁰ S ^ ^{0 (or the} like as a high-temperature heating element, so that heating to high temperatures is made possible and an additional device, for example a graphite electrode, can be dispensed with.

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In a furnace which is provided with a conventional "ideretande heating element made of metal, this heating element can, with certain exceptions, only be heated up to a temperature of 1700 ° C, so that the material to be heated cannot be heated sufficiently high. On the other hand, there are various Metal oxide materials, ^x such as ZnOg, ThOg, TiOg, insulators. In contrast to metallic materials, they can withstand high temperatures and their resistance decreases when heated, so that they develop sufficient electrical conductivity. As a result, they can conduct electricity at high temperatures In a heating element consisting of a single oxide, e.g. zirconium dioxide, local melting and resolidification generally takes place even with a very small temperature fluctuation, and when electrical current flows through the heating element with heat generation, the temperature decreases with a slight temperature change Power so that the temperature is continuously ierlich increases, while with a small Ttmperaturabfall the power decreases rapidly, so that the temperature drops continuously. As a result of this instability, such an element can therefore not be used as a heating element. This disadvantage can be avoided if a stabilized heating element made of stabilized zirconium dioxide is used, which consists of the zirconium dioxide itself and, for example, yttrium oxide in an amount of about 10 # ^ At high temperatures (over 1000 ° C) the specific electrical resistance of the stabilized Zirconium dioxide to a value of 1-10 ohmmeters, so that the material develops electrical conductivity. It has grown to temperatures up to 2500 ° C and even under oxidizing conditions temperatures ^ up to 2200 ° C. . ■

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According to the innovation, a metal oxide that has the property given above, for example stabilized Sirkoniuauioxiu, is vsrforat stones, from which several rings are formed in the refractory lining of the vacuum degassing vessel, which are adapted to the cross-sectional shape of the vessel and are spaced apart so that the Metal oxide form part or the larger part of the fire-resistant lining of the degassing vessel. The metal oxide forms heating elements through which an electric current is passed so that the entire vessel is heated to a predetermined high temperature and is kept at this temperature during the vacuum treatment. Thus, the temperature-lowering is "MPACT the vessel on the molten steel is reduced and the heating of the vessel for the subsequent batch, he" entert · v \.

The refractory lining of the vacuum degassing vessel has a high alumina content. There is, however, a considerable difference in conductance between the stabilized zirconia heating element and the Al ₃ O ₅ at 1000-2000 ° C. In this temperature range, the stabilized zirconia has a conductance of 0.1-1 ohm "cm" and the Al ₀ O, one

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Conductivity of 10 to 10 ~ * ohm cm ", so that the stabilized zirconium dioxide is conductive, but the Al ₂ O ₅ acts as an insulator. Therefore, the performance cannot be reduced by the fact that a large part of the current due to the lack of insulation flows through the iron skin.

The subject of the innovation is described below with reference to the exemplary embodiments shown in the drawings. In these shows

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Pig. 1 schematically in longitudinal section an embodiment of the device according to the innovation,

Pig. 2 shows a cross section along the line II-II in Fig. 1 and

FIG. 3 shows, in a cross section similar to FIG. 2, an arrangement in which the one shown in FIGS and 2 'shown heating element on the inner circumference of the vacuum degassing vessel in several successive ones in the circumferential direction Parts is divided.

The drawings show a degassing vessel 1 with an alumina-rich, refractory lining 2. With 3 and 4 removable burners are designated. Part of the refractory lining is formed by heating elements 5, which consist of stabilized zirconium dioxide and their distances from one another to the lower part of the vessel 1 to remove. With 6 insulators are designated, which are locally cooled by a cooling device, 'for example by a suitable one, not shown

Cold blower. Electrical connection parts 7 make this possible

}: Conducting an electric current through the heating elements 5 ·

With 8 is a power source, with 9 a receiving opening for the upper burner and with 10 an evacuation opening referred to, which is connected to a vacuum source via a vacuum valve, not shown.

If operation is with a low voltage, according to ^"2 3 Ig each of Heizelementkränze used in the device according to the innovation in ^sev-. Eral parallel pieces to be split, which follow one another in the circumferential direction of the refractory lining.

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The following is the use of the Device described. Before the first vacuum degassing treatment the degassing vessel 1 is still very cold. It is therefore in the usual way at one temperature heated from 1000-1200 ° C, at which the heating element 5 develops a conductivity. To this end is the product of the combustion of light oil, for example, from the one sitting in the receiving opening 9, upper burner 2 and via the down in the vessel provided channels 11 for the entry and exit of the Molten steel introduced from the separator 4 into the vessel, so that its wall on a predetermined Temperature is heated. When a voltage is applied to the heating element 5 from the power source 8 via the connector the conductivity of the heating element rises 5 nd with it the temperature. At 1000-1200 ° C flows in Current ir of a predetermined amperage through the heating element. As a result, the electric power utilized in the heating element itself to generate heat. Then the burners 3 and 4 are removed and the Reception opening 9 for the upper burner is closed in a square shape, while the vessel is closed by means of the heating elements 5 is further heated. As a result, the degassing vessel 1 is heated to an even higher temperature until a temperature suitable for degassing treatment has been reached. When the lower part of the degassing vessel 1 is heated to about 1600 ° C, the lower <& nden the channels 11 for the entry and exit of the molten steel are immersed in a ladle or the like, so that under the action of one over one not shown Vacuum valve connected to the evacuation opening, vacuum pump not shown, the vacuum degassing treatment is initiated. Since that generated by the heating elements 5 during the degassing treatment Heat only that dissipated through the degassing vessel 1

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Needs to replace heat, the voltage of the power source 8 is reduced to such a value that the The temperature of the vessel is kept approximately constant »The temperature of the degassing vessel 1 is thereby increased kept constant at a high value, so that in the subsequent batches there is almost no preheating by means of the burner is required and the vacuum degassing> treatment can be carried out continuously.

A practical embodiment of the method carried out with the aid of the device according to the invention is described below. In an RH vacuum degassing vessel with an inside diameter of 1100 mm, an outside diameter of 1 .00 mm, a clearance height of 4400 mm, a construction height of 5000 mm and a capacity for the treatment of 50 t of molten steel, the stabilized zirconium dioxide Heating elements that use the in * ig. 2, in the cross section shown in Pig. 1 arranged so that they can be used to heat the degassing vessel. The stabilized zirconium dioxide is shaped into stones, which, as indicated in Fig. 2 at 5, to form a ring

2 are stacked, which has a cross-sectional area of 12,000 mm and an inner diameter of 1250 mm. Electrical connection parts 7 are provided at symmetrically arranged points. As it is in ^ JLg. 1, four such rings are used, which are arranged at decreasing distances from one another towards the lower part of the vessel and are embedded in the lining of the furnace, which consists predominantly of a high-alumina, refractory material, so that they form part of this lining, - ^ read heating elements connected in parallel to the power source 8 effectively form ten semicircular heating elements connected in parallel, so that the applied voltage can be reduced.

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The procedure was carried out as follows j

1. The burners 3 and 4. were operated until the heating elements 5 had become conductive. This was the pail when, after the addition of light oil with a calorific value of 10300 lccal / kg in an amount of 200 l / h (normally 100 l / h) and under a pressure of 4 kp / cm for a period of five hours the refractory lining e:
had enough.

Lining has a surface temperature of 1200 ° C

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2. At the two ends of each of the now conductive A voltage of 470 V was applied to heating elements 5, so that a current was generated at an output of 260 kW rlt a total current of 560 A flowed. This became daa vacuum degassing vessel within two hours so heated 'that on its inner circumference a temperature of 1200 ° C in the upper part and a temperature in the middle part of 1400 ° C and its temperature in the lower part of 1600 ° C prevailed.

3. During the treatment carried out after heating, the voltage became 320 V and thereby the power is reduced to 120 kW, whereby the temperature of the degassing vessel is approximately constant at the specified, high value could be maintained. Eb is useful to open the vessel with the help of burners 3 and 4 to heat the temperature of 1000-1200 ° C, at which the heating elements 5 according to the innovation provided electrically become conductive, but one can also be made of metal, for example Kanthai, in the area of the heating elements 5 Provide a heating element and use it to heat the stand.

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Since the high-alumina lining is also electrically conductive at high temperatures in cases where the application of a high voltage is permissible, not only the above-mentioned

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I high alumina refractory material of the refractory material

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I ■> As can be seen from the description above

1.4 goes, may in the application of modern renewal ^v or-

I direction in which a heating element made of a metal oxide

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I the additional equipment, e.g. a graphite electrode,

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do not adhere to the container before each batch, for example must be preheated wisely with burners that are only used for initial preheating until the Heating elements -are required so that the degassing treatment carried out continuously and even during the degassing treatment to generate electricity by the Heating elements, a current can be conducted, the current strength of which is chosen so that a temperature drop of molten steel is prevented.

Claims (1)

oo ο ο oo oo n ϊ * ο ο η γ. "Λ O O Γ - 10 - Protection claim: Device for heating a vacuum degassing vessel, characterized in that one part or the greater part of the refractory lining of the Vacuum degassing vessel is formed by heating element rings, which are spaced in a suitable number at vertical intervals are arranged from each other and made of a metal oxide, for example stabilized zirconium dioxide, exist, which develops an electrical conductivity at high temperatures, whereby a Preheating device, for example a burner, is provided. 731S1102I.7.7I