WO1982004371A2

WO1982004371A2 - High performance split electrode circuit for arc furnaces

Info

Publication number: WO1982004371A2
Application number: PCT/CH1982/000069
Authority: WO
Inventors: Max Schafferer
Original assignee: Max Schafferer
Priority date: 1981-05-15
Filing date: 1982-05-14
Publication date: 1982-12-09
Also published as: EP0080463A1; WO1982004371A3

Abstract

She insufficiencies in the electric devices of the split electrode circuit of an arc furnace may be remedied by eliminating the current conductive function of the retaining jaws by means of an axial connection device while shifting the passage of current leads towards a level higher than that of the carrier arm, by introducing a metal core electrode and by providing an agglomerate protection layer. The axial connection device is comprised by a metal core support nut connected by a contact member formed by copper rings having the shape of a truncated cone, to a bell appropriate for said member. The current is supplied to the metal core of the support nut through the contact rings and reaches the electrode through said core. The metal core electrode is of the graphite electrode type wherein a metal core of aluminium alloy is sealed. Such alloy provides for an irreprochable contact with the graphite while avoiding any formation of cracks due to the heating of the alloy beyond its melting point and to its subsequent solidification. Only the use of an axial connection device together with a metal core electrode makes possible the application of said agglomerate protection layer; this layer insures a safe protection against oxydation of the graphite even in the range of temperatures comprised between 350<o>C and 600<o>C. The layer has as constituents an aluminium agglomerate and at least one fusible glass which melts under 350<o>C, and/or a vitrous oxyde. They are applied in a single step by means of a projection machine for the aluminium and by means of a sprayer; the glass and/or the vitrous oxydes are added in solid form, as dry powder to the jet of melted aluminium drops.

Description

High-performance electrode circuit for electric arc furnaces

The invention relates to the electrical devices of the electrode circuit of the arc furnaces in the production of electrical steel. The electrode circuit includes the current guideway, the contact jaws and the graphite electrodes. All these facilities are not easily able to meet the requirements of high and high performance furnaces.

The current track runs directly over the massive support arm. As a result of the strong currents, there are considerable losses due to induction currents,

The contact jaws wear out quickly as a result of uncontrollable, caused by unavoidable impurities, overheating on the contact surfaces, which leads to the jumping of sparks and arcs, to the formation of caverns and ultimately to the melting of the copper. The reduction of the circumferential angle, the increase of the specific pressure, the improvement of the cooling, as well as the use of graphite interstices, which inevitably lead to a reduction in the electrode diameter and thus to a reduction in the furnace performance, could not completely eliminate these disadvantages.

These overheating phenomena occur significantly more strongly in electrodes which are coated with a protective layer due to the strong pressure on the jaws and question the use of the protective layers developed on aluminum basis. The new requirements for a further increase in the current carrying capacity of the electrodes cannot be met by increasing their diameter over 000 mm, as this would lead to a relative increase in the specific power loss density in the area of the electrode surface due to the "skin" and "proximity effect" and thereby cause residual side burn and cracking. With the development of the "ACX" electrodes, the specific ohmic resistance has been reduced to 5.0 - 6.5 ohm mm ² / m, but at the cost of a 17 - 20% price increase.

Attempts are being made to reduce the strong oxidizing corrosion of the graphite electrodes by applying a protective layer of aluminum and / or its alloys or of high-melting oxides, carbides or nitrides. The high resistance to oxidation of aluminum is due to the formation on its surface of a thin, gas-impermeable aluminum oxide layer which holds together firmly due to its extremely high surface tension.

However, the application of an aluminum layer alone cannot adequately protect the graphite electrode in all temperature ranges, since the aluminum oxide layer only forms above 600 ° C, while the graphite begins to oxidize at 350 ° C, so that the electrode heats up for about 2 hours - is exposed to oxidizing corrosion. Various protective layers based on aluminum have been proposed with the purpose of bridging the critical temperature range of 350-600 ° C:

According to such a process, the aluminum layer is applied with an aqueous suspension of titanium, drilling acid, silicon carbide and silicon, the electrodes are then dried in special ovens and then heated with an arc.

In another method, a layer of elemental silicon and then one of aluminum is first applied to the graphite surface, with silicon carbide and silicon-aluminum alloys then becoming so.

In a third method, an intermediate layer of tantalum, hafnium and titanium carbides is applied to the graphite surface and the entire electrode is then heated to 300 ° C. in an oven filled with inert gas. An aluminum layer is then applied. A gas-impermeable intermediate layer should then be formed in the furnace from a transition compound C-TaC-AI and Ta-Al.

All of these protective layers have decisive disadvantages, such as high manufacturing costs, complicated manufacturing processes, incomplete protection in the temperature range of 350-600 ° C and cause malfunctions and strong corrosion phenomena as a result of the inevitable adhesion of the aluminum layer to the copper surface of the contact jaws. All of these protective layer processes have the following common characteristics:

- heating the graphite surface to improve the adhesion of the protective layer to it; - Application of the aluminum according to the known Fiamm or arcing retal injection processes;

- Use when applying the protective layer of lathe-like devices.

All of these three characteristics cannot be patent claims.

According to the invention, the stated shortcomings of the electrical devices of the electrode subcircuit are remedied in the following manner:

- Elimination of the current-carrying function of the holding jaws by means of an axial current connection device, with simultaneous laying of the current supply path to a higher level via the support arm,

- Development of the metal core electrode and

- Development of the agglo protective layer

The axial power connection device - Fig. 2, 3 and 4 consists of a support nipple (1) which is connected to the melted metal core (2) via the conical contact ring made of copper (4) and the copper bars (3). The metal core consists of an alloy of aluminum and an additional metal.

The bell (5) sits above the support nipple and is provided with a conical water-cooled copper contact ring (6) which fits on the corresponding contact ring of the support nipple (4). The bell has a segment-shaped slot (7) in which the cable (10), which carries the support nipple with the screwed-on electrode column (8), can move in and out sideways. The bell, to which the current-carrying cables or pipes (9) are connected, can be fixed in its uppermost position by means of remote-controlled clamps, which are fastened to the upper frame, or if they are fixed with a light telescopic column - Fig. 1 - on the support arm connected, can be arrested by the latter. By lowering the rope, the two parts of the device are separated from each other and the support nipple with the screwed-on electrode column is transported to the electrode stand, where a second electrode column with the screwed-on support shaft is waiting to be transported back, connected to the bell and after releasing the locking device into the oven to be lowered.

The current is fed to the metal core of the support nipple via the contact rings and the contact rails and reaches the electrode via this and the threaded connection.

The metal core electrode is a graphite electrode in which a metal core is melted parallel to its axis. The metal core consists of an alloy of aluminum and one or more metals, such as 90.5% Al and 9.5% Cu. The determination of the specific ohmic resistance of a metal core electrode (25x220mm) gave 3.7269 Ohm mm ² / m to 2.1608 ohm mm ² / m versus 7.922 Ohm mm ² / m at the same electrode without MetaIlkern, ie 52, 6% to 72.8% lower specific ohmic resistance - test report No. 121'525 / 2 of December 16, 1981 by the Swiss Electrotechnical Association.

Only the introduction of the axial current connection device and the metal core electrode enables the effective use of the agglo-protective layer, which severely limits the oxidizing corrosion of the graphite and leads to a 14 to 25% reduction in electrode consumption.

The protective agglomer layer consists of an agglomerate of aluminum and at least one additive that melts at a temperature below 350 ° C. Glasses and glassy oxides with a low melting point are used as additives. The critical temperature range of 350 - 600 ° C, in which the aluminum is still solid and therefore gas-permeable, is bridged by the protective effect of the additives, which have already melted below 350 ° C. Aluminum oxide is preferably produced at 600 ° C and the additives form a molten emulsion with the molten aluminum, provided they have not evaporated. As the temperature increases further, glass molds that melt more and more are formed, which in turn improve the protective effect. The process for producing the protective agglomeration layer consists in that the electrode rotating on a lathe is guided past the stationary tools. The aluminum is applied to the roughened graphite surface using a flame or arc spray device. In the jet of molten aluminum drops, the additives are applied in a solid, dry, powdery state via an atomizer. After solidification, the sprayed-on mixture forms a coherent, solid agglomerate layer on the graphite surface from the grains of the additives and the aluminum, which acts as a binder.

A protective layer is applied in one operation. With a graphite electrode 508x1900 mm, this process only takes 36 minutes and is therefore approx. 50% shorter compared to the previously known methods. For a system with an annual productivity for single-shift work and 2-man operation of 1600 t graphite electrodes 508x1900 mm, the footprint required for production is only 90 m ² , the installed capacity 50 kVA and the cost of the protective layer below 30 SFR / m ² - price- and wage level in Switzerland 1981.

All these circumstances allow the protective layer to be applied by any steelworks themselves using the "do it yourself" method, and this on electrodes from any manufacturer. The new design of the electrode subcircuit according to the invention by moving the current guideway to a higher level, by introducing the axial power connection device and the use of an agglomer protective layer made possible thereby corresponds to the growing requirements of the high and maximum performance furnaces.

The figures represent variants of moving the current guideway to a higher level via the support arm and an exemplary embodiment of the axial power connection device.

In Fig. Ia, the current is supplied to the axial current connection device via flexible cables, while in Fig. 1b the current is supplied via copper pipes, which are mounted on the vertical telescopic column, which is mounted on the support arm and is rigidly connected to the bell of the axial current connection device.

2 illustrates the individual parts of the axial power connection device in a separate position: bell with contact ring (a), support nipple with metal core and contact nipple (b) and electrode column (c).

Fig. 3a shows a vertical section through the screwed together and nippled current connection device.

The individual parts of the axial power connection device are unscrewed and nippled on FIG. 3b. The corresponding cross sections can be seen from FIG. 4.

Claims

1. Axial power connection device to the graphite or carbon electrodes of the arc furnaces, characterized in that the current is supplied via the support nipple, which has a contact ring made of copper and a rod-shaped or tubular metal core made of an alloy of aluminum and one or more Additional metals is provided.

2. Power connection device according to claim l, characterized in that the current supply to the metal core of the support nipple takes place via a gap which is stranded with a conical contact ring made of copper, to which the current-carrying cables or pipes are connected.

3. Power connection device according to claims l and 2, characterized in that the bell has a segment-shaped Schiitz in which the cable carrying the support nipple can move freely in and out laterally.

4. Current connection device according to claims I to 3, characterized in that the bell in its uppermost position can be locked by remote-controlled clamps which are fastened to the upper frame, or on a telescopic column mounted on the support arm.

5. Metal core electrode for arc furnaces, characterized in that one or more metal cores made of an alloy of aluminum and one or more additional metals, which are rod-shaped or tubular can be melted parallel to their longitudinal axis.

6. Metal core electrode according to claim 5, characterized in that instead of the metal cores in the outer jacket of the electrode, metal balls evenly distributed in the graphite are melted from an alloy of aluminum and one or more additional metals.

7. Metal core electrode according to claims 5 and 6, characterized in that the electrode according to the

Melting of the metal cores or the metal balls is thermally treated.

8. Protective layer against oxidation of graphite electrodes for electric arc furnaces, characterized in that the protective layer consists of an agglomerate of aluminum and at least one or more of our glass or glassy oxides melting at 350 ° C.

9. The method for producing the protective layer according to claim 8, characterized in that the protective layer is applied with the aid of an aluminum spraying device, the solid powdery additives being added by means of an atomizer into the jet of molten aluminum drops.

10. A method for producing the protective layer according to claims 8 and 9, characterized in that the rotating electrode is moved past the stationary mounted tools on a lathe-like device by applying a protective layer in one operation. High-performance electrode circuit for arc furnaces Summary.

The inadequacies of the electrical devices of the electrode subcircuit in the case of arc furnaces are eliminated according to the invention in the following manner: elimination of the current-carrying function of the holding jaws by means of an axial current connecting device, at the same time laying the current supply path to a higher level via the support arm,

- Introduction of the MetaI core electrode and

- Introduction of the agglo protective layer.

The axial power connection device consists of a support nipple with metal icons, which is connected via a contact made of conical copper rings to a bell fitting on it. The current is fed through the contact rings to the metal core of the support nipple and reaches the electrode via it.

The metal core electrode is a graphite electrode in which a metal core made of an aluminum alloy is melted. This alloy ensures perfect contact with the graphite while avoiding any crack formation in the latter when the alloy is heated above its melting point and subsequently solidifies.

Only the introduction of the axial current connection device and the metal core electrode enables the effective use of the agglo protective layer, which guarantees reliable protection against the oxidation of the graphite even in the temperature range 350 ° C - 600 ° C. It consists of an agglomerate of aluminum and at least one glass and / or melting below 350 ° C