DE1758169A1 - Electrode with a protective layer resistant to oxidation and method for covering the electrode with such a protective layer - Google Patents

Description

Electrode with a protective layer resistant to oxidation and methods of covering the electrode with such a protective layer.

Made of graphite or similar carbonaceous material

electrodes are usually prepared gt into electrical light arc furnaces such as in operating with electric arc electrothermal processes, for example Stahlschtnelzöfen used. When such electrodes are used for this purpose, it has been shown that the electrodes are quickly consumed as a result of the oxidation of their surface exposed to the hot atmosphere inside the melting furnace. This loss of the electrode material is of course very disadvantageous, since it considerably reduces the period of use of the electrodes and the purpose of the present invention is now to create an electrode which has at least satisfactory properties with regard to antioxidation, anti-cleavage, I - low specific resistance, low modulus of elasticity and high mechanical strength.

However, it turns out to be quite difficult, if not impossible, to meet these requirements. There two Properties, namely anti-oxidation and anti-cleavage, are incompatible, a dense and less extensive electrode can, to withstand oxidation, but not splitting, while vice versa a large, porous electrode

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Cleavage, but cannot withstand simultaneous oxidation. As a result, any attempt to produce an electrode with some desirable properties will be enhanced at the same time Lead to manufacturing costs, since extremely pure starting material as well as a meticulously controlled manufacturing process must be assumed · To prevent a Oxidation of the electrode is already a surface coating

a material resistant to heat, such as aluminum including bromine, silicon (pebble), titanium, zirconium, chromium or molybdenum has been suggested. The coating can by melting the aluminum onto an electrode holder made of copper. However, Ss has proven

sen that the aluminum surface is easily _{oxidized to Al 2} O; and since such an oxidized surface layer is not electrically conductive, it can have a detrimental effect on the electrothermal process and thus cause sparks which can lead to defects in the aluminum layer and damage to the electrode holder and thus reduce the protective effect of the layer. Because of this, the earlier attempts have not proven successful and consequently have not gained general acceptance in the industry.

The present invention aims to eliminate or at least reduce the disadvantages of known coatings by using coatings based on Fe instead of Al. Fe has the added benefit of being low in price and easy to apply.

As a result, the invention relates to an electrode preferably made of graphite or other carbon-containing material

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rial, which is intended for use in electric arc furnaces or in electrothermal processes that use electric arcs, and which are provided with at least one oxidation-resistant or an oxidation-preventing, electrically conductive layer to protect the surface of the electrode against oxidation. The novelty of the invention mainly consists in the fact that the coating consists mainly of Fe and additionally at least one of the metals Cr, Al or Si, which together form an alloy and / or mixture of double metal type. This alloy or double metal mixture has extremely good antioxidant properties and can be applied to the surface of the electrode without difficulty.

According to a preferred embodiment of the invention, the electrode contains at least one first or inner iron or steel layer and at least one second or outer layer containing Cr and / or Al and / or Si, these two layers preferably being alloyed or mixed with one another. If there is no outer layer, the entire composition of the layer, calculated in% by weight, can contain at least 4 % Cr ™ and / or from 0.2 Jb to 30 Sb Al and / or at least 0.2 % Si, if desired also 0.2% of a further metal, such as Ni, Mn, Mo, W, E, Ti, Zr, V, Nb, Hf, Y, Co, Cu, Be and possibly at least 0.01 / 6 N ₂ , at least 0.005 f> ¥ and / or at least 0.01 jb C; the rest in iron.

The invention further relates to an advantageous electrode coating method and one against oxidation resistant protective layer or layers made of the above metals in the molten state -

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The invention is explained in more detail by means of the following examples.
example 1

After cleaning the electrode surface (e.g. with a Electrode with a diameter of 450 mm) for removal Any of that, dirt, paint and foreign substances, the electrode is in a rotating device such as a lathe. In order to facilitate the application of a protective layer, the electrode surface is first roughened with a wire brush. After that the electrode rotates at a peripheral speed of about 15 m revolutions / minute and becomes molten carbon steel 3US of a spray gun using a wire 3 mm in diameter sprayed at a distance of about 15 cm.

In this case, steel of the following composition was used C = 0.1C # », Mn = 0.50 #, F» 0.04 jfc, S «0.04; *, Fe * * 99 x 32 / b, and the film sprayed on the surface had a thickness of about 0.2 mm. Thereafter, aluminum on the upper surface of the ψ was carbon steel layer to a thickness of approximately 1.5 mm sprayed. The electrode, thus provided with an inner carbon steel layer and an outer aluminum layer, was used in a steel melting furnace with a capacity of 40 tons and showed electrode wear of 3 * 3 kg per ton of cast ingot.

In the case of an uncoated electrode, its wear was 5 * 4 kg per ton of cast ingot and in comparison to an electrode coated only with carbon steel, the wear was 5-1 kg per ton of cast ingot. The comparison the

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These three results show the substantial reduction in the electrode consumption of electrodes produced according to the invention.
Beispi el 2

After the same surface treatment as in Example 1, a wire with a diameter of 3 ram is made of 13 # Chrome steel is sprayed onto a graphite electrode with a diameter of 350 mm to a thickness of 0.2 do. To this Layer was then sprayed aluminum to a thickness of about 1.5 mm.

The thus obtained double-layer electrode having an outer aluminum film and an inner chromium film of 13 $ thick is used in a steel melting furnace of 25 tons in capacity, and thereby electron wear of 3 x 2 kg per ton ingot became. The wear of an uncoated electrode, on the other hand, was 4-9 kg per ton of cast ingot, and the wear of an electrode coated only with a 13 # chrome layer was 3 × 8 kg per ton of cast ingot. It is thus readily determine that a erfindungsge- ä, Mäss coated electrode gives much better results.

As can be seen from the above statements, according to the invention Manufactured graphite electrode exclusively with an effective double layer forming antioxidant filter are coated, with aluminum in use due to the temperature of the furnace air in the inner surface layer penetrates. Accordingly, this invention realizes a reduction in electrode wear and thus sustains ♦ to reduce steel production costs. Despite the

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The surface coating of the electrode increases the electrical conductivity d ^ r electrode in the use according to the invention not decreased.

When using aluminum as the outer layer, as described in Examples 1 and 2, it is not advisable to use such a double-coated electrode directly in an electric melting furnace, since, as mentioned above, aluminum has a low melting point and a strong affinity with oxygen and _{tends to form Al 2} O; and since this oxidized surface layer does not conduct electricity, dips can occur between the electrode and the half of the electrode, which damage the holder. It is therefore advisable, when using such double-layer electrodes, to undertake a second process for fusing the outer layer of aluminum with the inner layer before using the electrode in the electric melting furnace. When using an aluminum coating, a further method of mixing, ie penetration of the outer aluminum layer with the inner layer, can preferably be carried out, after which the aluminum-coated electrode can be used in an electric melting furnace The conventional way of using aluminum for an electrode coating is that several spray guns are used at the same time for the metallization of two or more types of metal on the same place at the same time.

For example, one can use an alloy of 30 % aluminum and 70 % steel, which is known to be more heat resistant than just

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ir. r, which is considered to be the only two metals, spray onto the elct- ^r .. ■■ ' · However, the metallization process proves to be less effective than a wire spray process, and pulverization of the metal alloys would incur considerable costs.

herd.". c3> i7v, gcn two "iäsuigv-- diameters and spraying speeds with (u τ application of aluminum and steel wires be Λ me ο ce η, k.-ίηη; π > .η without further one-n alloyed Metallfil; i. Nus 3C ι Alurrir.iun, and 70 Jb steel by a simultaneous bocprit-. N jiden Ntt-tllts' = us separate spray guns -on the same as that of the electrode surface obtained in this way on the electrode surface Received: ltv.ner against Warne, metal li'ilri that can be used for red clay causes far lower costs

Since 20 lh aluminum has an affinity for 70 % nickel and an Lc-: ivi, .r.cr of these metals is dense, resistant to * & r: .t. Layer forms can gtwöhnliche-rweise a metallization by means of a Pulverspritzverfehrens take place% which is iccclich with a i'raht may due to its low processing capability. How ow? Table I shows that powder spraying is less effective than wire spraying.
Eg game 5

Metcc 4E type pistols were used for metallization after cleaning the surface of a graphite electrode with a diameter of 400 mm to remove any Dirt, oil, all paint and foreign substances

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had been. The electrode was mounted in a rotating device, for example a lathe. The surface of the rotating graphite electrode was first roughened with a wire brush to facilitate application. The surface of the electrode was then sprayed while rotating the electrode at a peripheral speed of about 10 m per minute by means of two spray guns, one gun with a steel wire with a diameter of 3 mm, composed of 0.10 ib carbon and 0.50 % manganese a spray speed

™ of 5Λ kg per hour, and the other gun was fed with a 99% aluminum wire with a diameter of 2.3 mm at a spraying speed of 2.08 kg per hour. The function of these two guns is to apply two different types of metal at the same time to the same point on the electrode surface.

An analysis of the coated film showed an aluminum content of 27.15 ^liters and a steel content of 72.08 %. The surface layer had a thickness of about 0.2 mm.

* The graphite electrode thus metallized was used in a 30 ton capacity smelting furnace with a 33% increase in service life compared to an uncoated electrode. Example 4

In the same manner as in Example 3, a graphite electrode with a diameter of 400 ram was rotated at a peripheral speed of about 5 m / minute. Then the electrode was coated with two different types of metal . each sprayed a gun. A spray gun was attached to a wire

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/ Π

of 3 mm diameter and consisting of 97 x 61 #> nickel at a spray speed of 5.08 kg per hour, and the --nd- ^ re spray gun with a diameter of 1.4-5 mm in diameter consisting of 99 % aluminum with a spray sprayed at a speed of 0.75 kg / hour. These two guns simultaneously spray two different metals on the same spot on the electrode surface; the surface coating reaches a thickness of about 0.1 mm. An analysis of the layer shows the content of 1 -, '. B7 jb aluminum and 77 x 32 # nickel. This Metallfün less m porous, but a good seal the electrode surface.

The graphite electrode coated with the above metal coating was used in a melting furnace of 30 ton capacity, and its life was found to be 4-7 % longer as compared with that of an uncoated electrode.

According to one embodiment of the invention, the peripheral Electrode surface consisting of an alloyed film made of two different metals, for example by means of a spray gun, which applies the two metals simultaneously on the " Electrode surface applies, coated.

However, the metallic antioxidant coating can also be produced by spraying metal powder, mainly made of chrome, for example metallic chrome, chrome iron alloys, Chrome pebble alloys, chrome manganese alloys, Chromium aluminum alloys and / or chromium nickel alloys exist.

The antioxidant ability of a chromium alloy is improved as soon as the chromium content exceeds 4%, and

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a considerable amount is sufficient if the chromium content is 20 # exceeds.

The addition of aluminum and silicon to these alloys causes an extraordinary increase in the antioxidant effect.

As indicated above, two metallization methods per se can be used, namely wire spraying and powder spraying, but the cost of the wire spraying process is considerable due to the poor machinability of compositions which can be used for this purpose. For example, an alloy of 30-40 Si chromium, 4-8 % aluminum, 1-3 % silicon and iron is so poor in usability that the wire-shaped product is difficult to manufacture and involves high costs. As a result, the method proposed according to the invention is far more advantageous and economical if the metal is coated by powder spraying of the electrode, the metal composition used being able to be selected solely on the basis of the desired antioxidant ability, regardless of its preparation for use as a wire. As a result, the following metal powder can be used according to the invention for the purpose of improving the antioxidant properties of a graphite electrode by metallizing the electrode surface:

Metal powder consisting of at least 4 JIi Cr and / or 0.2 to 30 $ 6 Al and / or if desired at least 0.2 % Si; at least 0.2 % of one or more of the following components Ni, M, Mo, W, B, Ti, Zr, V, Nb, Hf, Ta, Y ₁ Co, Cu, Be; the rest of iron, with a content of at least 0.01 % Hg and /

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/ ff

or at least 0.005% P and / or at least 0.01 % C.

The method according to the invention is intended to be explained in more detail by the following examples: Example 5

Weight #

Chrome iron (Cr 62.7 V> Si 6.7 #) & 5%

Aluminum (Al 99.6 Jb) 10 %

Silicon iron (. ~ I 75.2 Jb) 5 f>

The above-mentioned mixture of metals was first carried out in a furnace melted and then cooled, and then in a ™ Grind ball mill into a powder. Pulvtr was obtained Ü3s d-inn on the peripheral electrode surface using eir.or Spray gun (type Metco 2P) sprayed in the following way.

After cleaning the surface with a graphite electrode a diameter of 400 mm for removing any oil, Dirt, paint and contaminating substances were placed on the electrode on a rotary device, for example a Lathe, manufactured.

The above metal powder was ge'sprüht mm on the surface of the animal ro- A forming electrode by means of a spray gun at a distance of about 150 mm was obtained whereby a film having a thickness of 0.25. The electrode thus produced was used in a melting furnace with a capacity of 30 tons, and it was found that the electrode wear F was about 2.6 kg / ton of ingot.

In the case of an uncoated electrode, however, it could a wear of 5 · 4 kg / ton cast ingot can be determined. A comparison of these two results immediately shows that one

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BATH ORIGINAL

considerable progress is achieved by the coating according to the invention.
Example 6

Weight -; *

Metallic chrome powder (99.1%) 40 %

Aluminum powder (99 3 %) 10 %

Silicon powder (99 3 %) 5 %

Iron powder (99.0 #) 45 %

The above metal powders were injected intimately mixed in a mixer in the same manner as in Example 5 onto the surface of a graphite electrode. In this case the thickness of the layer formed on the surface was also about 0.25 mm. The electrode coated in this way was used in a melting furnace with a capacity of 30 tons, with electrode wear of 2.4 kg / ton of cast ingot being found.
Example 7

% By weight chrome iron (Cr 62.7 % Si 6.7 %) 100 %

After pulverization in a ball mill, the above metal was sprayed onto the electrode surface in a layer thickness of about 0.2 mm. In addition, an aluminum wire (Al 99 %) with a diameter of 3.2 mm was sprayed onto the surface with a spray gun in a layer thickness of 0.2 mm with a capacity of 30 tons, with electrode wear of 2.9 kg / ton cast ingot

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BATH

could be determined.

Both electricity and gas as a heat source, e.g. acetylene, are suitable for metallization by means of a wire Oxygen and Propane Oxygen. In the case of metallization by means of powder, gas is preferably used as the only heat source. As can be seen from Table II, which compares the heat sources especially electricity for wire and gas for powder, far, the electrical heat source is more advantageous than Gas as a heat source, as the former is almost seven times as effective as a gas source.

Taking into account that a Cr base alloy is a possesses superior antioxidant ability in spite of poor workability and utility as a wire, and that a electric spray process is more effective than gas process, the invention enables a significantly more economical one Application of a powder coating, mainly consisting of chrome with a steel or aluminum coating

In order to be able to provide the alloy powder, which has a composition with good antioxidant properties but poor usefulness as a wire, with a coating of steel or aluminum, it is possible to use a special powder wire form, which is more profitable than the powder spraying method when spraying using electricity as a heat source. Example 8

A core made of chrome iron powder (Cr «62.7 #» Si = 6.7 %) with a particle size of less than 50 mesh, produced in a ball mill, was placed in a cylindrical shell made of 15 mm wide, 0.20 mm thick sheet steel (0.1 % C, 0.04 % Si)

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applied. From this combination of core and sheath, a wire with a diameter of 3 × 2 mm was produced and placed on the surface of a graphite electrode is metallized using a spray gun (Arcoa S.A., type sprayOmatic) in the following way.

The surface of the graphite electrode is first cleaned, any dirt, oil, paint, contaminating substances removed, etc. The graphite electrode is then placed on a ho-

^ tation device, such as a lathe, and the said wire is metallized by means of a spray gun at a distance of about 250 mm, so that a film about 0.3 ft. thick is formed. The electrode coated in this way was used in a melting furnace with a capacity of 30 tons, with electron wear of 2.9 kg / ton casting block, ie a very low value compared to the 5.4 kg / ton casting block for uncoated electrodes.
Example 9

W A core of metallic chromium powder (99%) in egg nem stainless steel jacket (18 j * Cr - 8 j6 Hi) in a zy Fora lindrisch bent sheet (15 mm wide, 0.2 mn thick) arranged. The combination of core and sheath was sprayed as a wire with a diameter of 3.2 mm onto the surface of an electrode with a diameter of 450 mm for the purpose of forming a layer about 0.3 nm thick, as in Example 8. The electrode wear with the upper part described above amount 2.6 kg / ton cast ingot.

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Example 10

A grain of chrome iron powder (62.7 % Cr, 6.? JL Si) was arranged in a stainless steel casing (18 jb Cr, 8 % Ni) in the form of a cylindrically curved sheet (15 mm wide, 0.2 ram thick) and the core and sheath to a wire having a diam £ 5or of 3 x <~ 'processed mn which thereafter sprayed on the electrode surface was to form a layer of about 0.25mm thickness, as in example 6. in addition, an aluminum wire (Al ^l,' 9 jb) sprayed onto the electrode surface with a diameter of 3 * 2 mm, to a layer thickness of % t-twrt 0.15 nm. The electrode sliver with the above coating was 2.4 kg / ton cast block.
Example 11

A core of metallic chromium powder (99.1 *) was wrapped in an aluminum casing, which was formed as a cylindrically bent sheet metal, 10 rr.tc wide, O. ^ ^r ? rr.rr. thick) is shaped; arranged and this combination was molded into a wire with a diameter of 5 × 2 mm and the surface of an electrode with a diameter of 450 mm was sprayed on until a layer thickness of about 0.4 μm was achieved, as in example 6 The electrode closure; with this coating was 2.0 kg / ton cast ingot.

All percentages given in the description and the claims relate to percentages by weight.

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Table I.

For spraying used

alform

Used Fistole type

Metal type used for spraying

Greatest
the

3pri.tzp3rtilcel

Consumption per hour

metal

(oaucrstoif)

tyltn

Splashed surface area per hour for 1 mm thickness

Ir ant Met co
4E aluminum
nickel 2 mm in
By-
mtsser
5 mm in
Diameter 4th
5 · 17 th
Whether sweep • 1.
1. 67 m ⁵ o.iy
O.e5 m ³ 1
0 .60 m ² fulver Metco
2P alloy
made of aluminum
minium
and nickel -170 + 270
mesh 4th te 1. 30 th ^5th 0.80 0 .42

S. i

OO

(D

Table ll
Comparison of spray processes

Specification of i-lectric Gaseous Gaseous

Spray gun type Spray gun type Soritz gun type

i for wire for powder for wire

J ₀ spray gun: Ar cos :. Type I - '. Ttco 2: F net co cE

- ^ Injected material steel steel steel

, * Injected amount 50 kg per hour 4 kg per hour ^ .9 kg per SLande

ο ■ ζ-

co

Claims (10)

Claims 1. Electrode made mainly of graphite or other carbonaceous material Materials for use in electric arc furnaces or electrical methods using electrical arcs, wherein the electrode is provided with at least one oxidation-resistant or oxidation-preventing, electrically conductive layer is provided, characterized in that the main component of the layer is made of Pe and for the purpose of Formation of a double metal alloy and / or a double metal product from at least one of the metals Cr, Al or Si consists. 2. Electrode according to claim 1, characterized by at least one first or inner iron or steel layer and at least one second or outer layer containing Cr and / or Al and / or Si, the first and second layers preferably are mixed or alloyed with one another. 3. Electrode according to claim 1 or 2, but without the outer layer described in claim 2, characterized in that the layer or layers, apart from iron, consist of at least 4 6 Cr and / or 0.2% to 30 % Al and / or, if desired, at least 0.2 % Si, at least 0.2 % of one or more of the metals Ni, Mn, Mo, W, B, Ti, Zr, V, Nb, flf, Ϊ, Co, Cu, Be and optionally at least 0.01 # N ₂ , at least 0.005 H> P and / or at least 0.01 $ C. 009183/0843 4. Process for coating electrodes with least; cimr protective layer resistant to oxidation mch claims 1 to 3i characterized in that the Electrode coated with the metals in a molten state w ei. !>. Method according to Claims 2 and 4, characterized in that the outer layer is at least partially mixed or alloyed with the base layer. ^ O. The method according to claim 4 or 5, characterized in that it is applied by spraying or both layers are applied by spraying. 7. The method according to claim 6, characterized in that the:; dis net ill or the metals are sprayed in powder form. 8. The method according to claim 6, characterized in that ils Beschichtungsmateri-al metal or Netalle in Drahtiorm consists of nd vorlegiv.rtem metal or metals or VeT-band wire or bare metal to be applied and several \ re Spritzpistoler, at the same time for applying of the coating can be applied to the electrode in the case of using a simple metal 9 * The method according to claim 6, characterized in that that a bandage wire, consisting of an inner powder core made of metal, metals and / or metal alloys as well as a Outer material made of iron and / or iron alloys and / or aluminum and / or aluminum alloy is used. 10. The method according to claim 6, characterized in that one or more metals are sprayed alternately and repeatedly for the purpose of forming the layer composition specified in claim 3. 00 83/0 $ 43 BAD OBlGlNAL