DE1565538A1 - Electric arc furnace and method for stabilizing an electric arc - Google Patents

Description

PATE IJTAlJ WXLTc

DR. E. WIEGAND DIPL-ING. W. NIEMANN * r η ccq Q

DR. M. KOHLER DIPL-ING. C. GERNHARDT> 0 D 0 0 0 Q

MDNCHEN. HAMBURG TELEPHONE 555 <7i 8000 MÖNCHEN 15, TEIEGRAMMB: KARPATENT NUSSBAUMSTRASSE 10

October 16, 1969 W. 12 752/66 15 / Cr P 15 65 538.6

Foseco Tracing AG-Chur, Graubünden (Switzerland)

Electric arc furnace and method of stabilization an electric arc

The invention relates to the stabilization of electric flame arcs or arcs and the Creation of an electric arc device and in particular to the creation of electric arc furnaces that can give the arc better stability.

In the case of the larger direct electric arc melting furnaces in which the arc is struck between a carbon electrode and the metal to be melted, there is a problem in that the large load fluctuation which occurs in the generation of the arc. an apparent short-circuit condition exists ". The extent of the load fluctuation is kept within limits by the presence of a reactance or a reactance in the current circuit; up to 4-q P-QQ KVA ', is the load fluctuation

^BÄD ORJGJNAL

sufficient to work on the feeding or supply system, to cause a clatter. .

The object of the invention is to reduce such load fluctuation effects as well as in the achievement of other advantages, for example one less> improved energy performance and lower electrical consumption. ·

According to the invention, a method for stabilizing. sizing a using at least one carbon electrode formed Q created arc, in which ' a solid substance is incorporated into the carbon electrode, which under the action of the electric arc generates a vapor or a medium or in a vapor or in a medium is transferred that the electrical conductivity of the Arc increased. As the above-mentioned substance, a metal oxide, a metal carbonate or a metal silicate is expedient or a mixture thereof is used. The metal component of the above-mentioned compounds can, for example, barium » Be calcium, magnesium, sodium, or potassium.

The substances can be in one or more of the carbon arc electrodes either as a core in the electrode. "or dispersed in the carbon material from which the Electrode is made to be introduced.

The invention also relates to an apparatus, and more particularly to one
with at least one of the carbon arc lamps "ferö4eÄ ■■" of those listed above

008128/0331

Original

In selecting the substance for inclusion in the electrode or electrodes, the purpose for which the Arc is intended to be taken into account to avoid materials that are harmful or disadvantageous for this purpose, to avoid. In particular, it is desirable to choose a relatively inexpensive material that is easy to process can and is ionized to reduce the resistance of the arc. In one used for melting metal In an electric arc furnace, the substance chosen should be one that is free from contaminants or other harmful substances on the metal to be melted or on the furnace structure. Within these conditions, the above -. The range of substances listed are used. Of these, sodium or potassium carbonate are preferred.

Of course, several substances that make up the conductive medium can be used in a mixture. A particularly useful mixture of substances results from calcined dolomite, which contains calcium and magnesium oxygens.

Inclusion of the above alkali compounds is particularly effective in lengthening the arch and improving it its stability. It is believed that this is due to their low ionization potential, i. on their readiness for ionization in the arc, whereby the electrical conductivity is increased. Rubidium and cesium are also effective, but their practical use is prohibitive because of their high cost.

Bi e active compounds can be in the electrode ,, or Electrodes included in any convenient way

OC982 3/0336 *

BATH ORIGINAL

will. So they can be included as part of the mass from which the electrode is made, or they can Verden provided as a core for the electrode. Generally they are available in part form and with one another Binding agents connected, which e.g. consist of tar or pitch or a paste obtained from anthracite and pitch can.

Particular advantages resulted from the use of a mixture of suitable compounds in an excess of one Carbon paste, for example an anthracite paste and bad luck. When baked or fired to form an electrode, the product shows a cellular or porous structure. When an electrode manufactured in this way is put into use and heated dijbe, the The dispersed compound is easily ionized by the heat generated in the arc, reducing the conductivity of the arc increases.

For most purposes, the chosen substance turned out to be the potassium salt, for example potassium carbonate alone or together with other substances in a carbon electrode as suitable.

The optimal choice of materials and the type and shape is e their introduction is mainly determined by the use for which the arc is intended.

The method according to the invention not only reduces or reduces the load fluctuation described above avoided, but also the flickering and the generation of harmonics also reduced or switched off in the feed or supply system.

0 0 9 8 2 3/0336 ^B M> Orj _G i _Nal

The more steady arc conditions make this possible Development of a greater energy in a given time and result in an improvement in the load factor. This higher stress factor causes the melt rate or the degree of melting increases, causing a higher output of the arc furnace. Also, the noise will of the arc is considerably reduced, which is an important advantage, especially for indirect electric arc furnaces, represents.

In addition, the electrode regulator system need not be so be sensitive or easily approachable and therefore can be of simpler construction or simpler execution.

The following examples are provided for further explanation the invention, .

example 1

A test was carried out on an indirect electric arc furnace of the single-phase type of 150 KVA, ie a furnace in which the arc is struck between two tubular electrodes. The electrodes in this case were made of graphite and were approximately 10 * 16 cm (4 inches) in diameter. The electrodes were eine'm with concentric hole of about 4.44 cm (1 3/4 ") diameter _r of the pierced with a core of 60 ° / o anthracite, 20 ·? £ pitch mi" t a Söhmelagunkt of 5Q ⁰ C , 16 $ powdered glass and 4 f * comb carbonate was packed or filled »These materials were prepared and placed in, the hole in the electrode,« the preceding for the creation of a mechanical

BATH ORIGINAL

Key for the core had been incised, pulped and heated ^{to 40 "to 50 0 O.}

The arc conditions were determined using Standard graphite electrodes observed with the furnace turned to Smelting 340 kg batch (750 Ib) of phosphorus copper was used became. Under these conditions, the furnace load fluctuated between 105 and 145 KVA, with fluctuations were most pronounced at the start of melting when the charge or batch was cold. The waveform of the power supply was extremely irregular, and the sound made by the arc was very noticeable.

This experiment was repeated using the cored electrodes made in the manner described above but with the same charge of phosphorus copper. A remarkable improvement was immediately observed. The waveform of the power supply was practically sinusoidal, the load fluctuations were reduced to within the limits of 140 to 150 KVA, and the noise emitted by the arc was reduced to a very low level. The melting time was reduced by 15 ° β and the energy consumed in melting the charge or batch was reduced by more than T0 $.

Example 2

The following composition was made with MgO (about 15 g)
Coke (about 5g)

10 ⁰ A Sodium Silicate "<ο, ^

0 0 9823/0336

This mixture was tamped into holes about 0.95 mm (3/8 ") in diameter and about 5.8 cm (1.5") deep in graphite electrodes, which were then baked ^{at 20O 0 O for 2 hours} .

A first experiment was carried out with two comparison electrodes. This was achieved by igniting and expanding the arc. Due to the fading of the arc, this procedure was repeated three times before sufficient heat was obtained in the furnace. Considerable fluctuations in the electrical load in the range from 15 to 30 KVA were observed. The maximum length of the arch * was 4.7 mm (3/16 ").

Then electrodes having the composition according to this Example included, used. There was a considerable improvement as the KVA heater was steadily at 22 and a maximum arc length of about 50.8 mm (2 ") was immediately obtained. Copious amounts of white fumes were produced observed over a 7 minute period and the oven remained silent for 15 minutes Fluctuations in operation. After 15 minutes the KVA reading had taken decreased to 18.

Although for the sake of simplicity the present invention has only been described with reference to the method, the conductivity-increasing substance being the core in an electrode is provided, this can also be done according to any of the other working methods listed below with corresponding Results are executed.

BAD ORIGINAL 0 0 9 8 Γ "J / 0336" Γ

Claims (6)

Claims * ■■ ■ '■. ' 1. Method of stabilizing a using at least one carbon electrode arc formed, characterized in that a solid substance is incorporated into the carbon electrode, which under the action the arc generates a vapor or a medium or converts it into a vapor or a medium, which increases the electrical conductivity of the arc. 2. The method according to claim 1, characterized in that * net that the 'mentioned substance is a metal oxide, metal carbonate or metal silicate or a mixture thereof is used. 3 · The method according to claim 1 or 2, characterized in that the substance mentioned is potassium carbonate or use magnesium carbonate. 4. The method according to claim 1 or 2, characterized in that the said substance is burned dolomite used. 5. The method according to any one of claims 1 to 4, characterized in that said substance as Takes up the core in the carbon electrode. 6. The method according to any one of claims 1 to 4, characterized in that said substance in the Carbon material from which the sheet is formed is dispersed. 9B23 / 03? 8