ROOF FOR AN ELECTRIC ARC FURNACE AND METHOD OF MANUFACTURING SAME

FIELD OF THE INVENTION The invention relates to a roof for an electric arc furnace and more particularly, but not exclusively, to a roof assembly for an electric arc furnace made from a plurality of segments. The invention also relates to a method of manufacturing a roof for an electric arc furnace, more particularly a roof comprising a plurality of segments.

BACKGROUND TO THE INVENTION

Electric arc furnaces are, amongst other uses, commonly used in the steel and ferro alloy production industry. An eiectric arc furnace comprises one or more electrodes extending into the furnace towards a furnace load, for supplying the energy required during operations.

Electric transformers are generally located outside the furnace and electric power is conducted from such transformers to the electrodes by means of contact shoes that are circumferentially arranged about and releasably engaged with the electrodes.

The furnace comprises a receptacle in which the furnace load is loaded and in which the melting of the furnace load occurs. The receptacle

may be partially or fully covered by a furnace roof. The furnace roof defines apertures for receiving the contact shoes and the electrodes, as well as openings for loading chutes for admitting the load into the furnace, it will be appreciated that the furnace roof is exposed to excessive temperatures and harsh conditions due to its exposure to heat generated during operation of the arc furnace.

Many different materials have in the past been utilised to manufacture roofs for fully or partially closed arc furnaces. In most prior art arrangements, stainless steel is utilised as the structural base materia! and which may be lined with a suitable heat resistant refractory material. However, it has been found in practice that the liner often becomes detached from the stainless steel structure, resulting in the stainless steel being directly exposed to the interior of the furnace, and therefore causing rapid damage due to stainless steel not being capable of withstanding the harsh conditions. Mild steel has also been suggested, but suffers the disadvantage of melting when being exposed to induction currents generated during operation of the arc furnace.

OBJECT OF THE INVENTION

Accordingly it is an object of the invention to provide a roof assembly for an electric arc furnace and a method of manufacturing a roof assembty for an arc electric furnace with which the applicant believes the aforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION

According to the invention there is provided a roof assembly for a furnace comprising at least one segment comprising a single integral metal body comprising copper.

The term 'copper' shall, in the context of this specification, be interpreted to include pure high conductivity copper as well as various copper alloys comprising at least 80% copper and other elements, such as stiver and/or chrome.

The body may have opposed first and second faces and the body may define channels for a cooling fluid drilled into the body, to extend between the first and second faces.

At least one of the channels may comprise at least first and second circular channel parts, each having a respective centre. The channel

parts are preferably intersecting and the respective centres are on a line extending between the first and second faces.

The line is preferably a centre line between the first and second faces.

The first and second faces may be flat and parallel to one another.

The roof assembly may comprise a plurality of segments arranged in juxtaposition relative to one another and interconnected with one another.

Also included within the scope of the present invention is a segment for a roof assembly for an electric arc furnace, the segment comprising a single integral metal body comprising copper.

Yet further included within the scope of the present invention is a method of manufacturing a roof assembly for an arch furnace, the method comprising the steps of: providing a plurality of roof segments, each segment comprising a single integral metal body comprising copper;

arranging the segments in juxtaposition relative to one another; and interconnecting the segments with one another to form the assembly.

Each body may be forged or cast in the form of a copper slab or block.

The method may comprise the step of drilling into each body at least one cooling channel comprising at least first and second circular channel parts, each part having a respective centre. The channel parts are preferably intersecting and the respective centres are preferably on a line extending between opposed first and second faces of the body.

The copper segments may be interconnected and secured to one another by connecting devices, the connecting devices connecting the copper segments mechanically and at least some devices being electrically insulated from the copper segments, so as to prevent electricai bridging between at least some of the juxtaposed copper segments.

The connecting devices may be in the form of stainless steel straps having opposite ends that are secured to adjacent located copper segments.

Gaps may be left between adjacent segments, and the gaps may be filled with an insulating material, to prevent electrical contact between at least some adjacent segments.

The method may comprise the steps of forming at least one aperture in the interconnected segments; providing a copper sleeve adapted to fit the aperture, the copper sleeve defining an opening for receiving an electrode therethrough; and securing the sleeve to the interconnected segments.

The copper sleeve may comprise a plurality of arcuate copper sleeve parts and wherein the parts are secured to one another, so as to form a tubular sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now further be descried, by way of example only, with reference to the accompanying diagrams wherein:

figure 1 is a diagrammatic perspective view of the roof assembly in accordance with the invention; figure 2 is a diagrammatic plan view of the assembly, illustrating juxtaposed copper segments forming part of the assembly; figure 3 is a diagrammatic perspective view of one embodiment of a copper segment; figure 4 is a diagrammatic side view of another embodiment of a segment; figure 5 is a diagrammatic end view of yet another embodiment of a segment; and figure 6 is a diagrammatic end view of yet another embodiment of a segment.

DETAILED DESCRIPTION Of THE INVENTION

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of a roof assembly in accordance with the invention is indicated by reference numeral 10.

The roof assembly 10 comprises a plurality of juxtaposed copper segments 12.1 to 12.n that are interconnected so as to form the roof assembly. The segments and/or roof assembly may have any suitable

profile and may for example be substantially planar. The assembly defines apertures 14 for receiving electrode rings 18 and apertures 16 for receiving loading chutes (not shown).

As best shown in figures 3 to 6, each copper segment comprises a body 22 in the form of a planar block or slab made of copper. It is an important aspect of this invention that the copper segment bodies are integrally made or formed of copper, for example by forgings in the form of forged slabs or blocks, or, casting in the form of cast slabs or blocks, etc.

Referring to figure 4, the segment 12.k comprises body 22 defining tapered or dovetail grooves 24 in an operative bottom face 26 of the body. A body 27 of a suitable heat resistant material, such as a refractory material, is used to fill the grooves. In another embodiment

12.j shown in figure 3, a layer 28 of a suitable heat resistant material is applied to the face 26, to clad the face. Complementary formations or keys of the layer 28 engage the grooves 24, so as to ensure that the layer does not become detached from the body 22. However, it is believed that the copper segments are able to withstand the conditions in the arc furnace for a substantial time, even were the layers to become detached from the segments.

Referring to the segment 12.1 in figure 5, cooling channels 50 for a cooling fluid are formed in the segment body 22 by drilling holes from and end of the body 22 to extend between operative bottom face 26 and opposed operative upper face 29 of the body. In a preferred form of the invention, each channel comprises at least first and second intersecting circular parts 52 and 54, each having a respective centre. The centres may fall on a line extending between the bottom and upper face. In one preferred embodiment, the line is a centre line between the faces. The cooling channels 50 in the segment 1 2.m shown in figure 6 comprise three intersecting circular parts 52,54 and

56 of which the centres lie on a line between the opposed faces 26 and 29. In other embodiments, even more such intersecting circular parts may be provided to increase the transverse cross sectional area of the channel 50, whilst not compromising the lateral thickness of the body 22.

As best shown in figure 3, a plurality of spaced parallel channels 50.1 to 50.7 are drilled into the body as hereinbefore described. An iniet 60 for the cooling fluid is made into the top face 29 to communicate with the first channel 50.1 at one end thereof. A connection channel 62 between the first channel 50.1 and the second channel 50.2 is cut or machined into the body 22 at the opposite end of channel 50.1 . The

connecting channel is then covered by a copper cover 64. The second channel 50.2 and the third channel 50.3 are similarly linked at the opposite end of the body. In this manner all the parallel channels are interconnected. In some cases, the channels may not be drilled to extend from the one end of the body 22 to the opposite end thereof

(as is the case with channels 50.1 and 50.2), but some channels may be blind, as is the case with channels 50.4 and 50.5. in these cases, the connection channel 66 may be machined or cut into the body 22 from the top face of the body. The connection channel 66 is thereafter covered with a copper cover. The covers may be welded to the body

22. An outlet 68 from the interconnected channels 50.1 to 50.7 is drilled or machined into the body 22 from the top face 27 thereof, to communicate with the channel 50.7.

As stated hereinbefore, apertures 1 6 are defined in the copper segments. These apertures are configured to receive the loading chutes, so as to enable the furnace load to be introduced into the furnace. Some of the copper segments 12.1 to 12.n are also configured to have arcuate edges 30 (shown in figures 1 to 3) in order collectively to define the circuiar apertures 14 when the copper segments 12.1 to 12.n are positioned in juxtaposition relative to one

another as shown in figures 1 and 2. These apertures 14 are provided in order to receive electrode rings 18 therein.

The copper segments 1 2.1 to 1 2.n are interconnected by way of connecting devices 32, in the form of stainless steel and/or carbon stee! brackets or straps, for example. The connecting devices 32 are suitable for preventing lateral movement of adjacent copper segments

1 2.1 to 1 2.n relative to one another, but also for providing structurai rigidity, in that it can accommodate bending moments induced between adjacent copper segments 12.1 to 12.n.

Referring to figure 1 , the electrode rings 18 are in the form of composite copper sleeves. Each copper sleeve comprises a plurality of arcuate copper sleeve parts 34 collectively forming a ring or sleeve when positioned adjacent to one another. The arcuate sleeve parts 34 are connected to one another by means of connecting devices 36. The connecting devices or brackets 36 also connect the sleeve parts 34 to the segment body 22. Insulating materia! (not shown) is provided between the electrode rings 18 and the segment bodies 22, to ensure that there is no electrical bridging. Similarly, gaps 38 are provided between immediately adjacent copper segments 12.1 to 12.n. These gaps are also filled with an insulating material, to prevent

electricai bridging between adjacent copper segments. The connecting devices 32 are also electrically insulated from the copper segments 20, so as to ensure that the brackets 32 do not provide an electricity conducting path between adjacent copper segments 12.1 to 2.n interconnected thereby. The level (number) of insulating connections between two electrodes or one electrode and the rest of the furnace structure may vary according to customer requirements.

During manufacturing, the copper segment bodies 22 are formed from copper billets, and are forged so as to enhance the mechanical and conductive properties thereof. The copper segment bodies 22 are then cut into the desired shapes, so that a composite roof assembly

10 as shown in figures 1 and 2 can be formed. The apertures 16, tapered grooves 24 and cooling channels are also formed in the copper segment bodies. Once formed, the copper segments are located in juxtaposition relative to one another in a desired configuration as shown in Figure 2. The segments 12.1 to 12.n are interconnected or secured to one another by means of the connecting devices 32. Gaps

38, deliberately left between immediately adjacent copper segments 12.1 to 12.n, are filled with an insulating material. Once the copper segments 12.1 to 12.n have been assembled, the electrode rings 18

are located in the apertures 14 and secured to the copper segments

12, 1 to 1 2.n by the insulated connecting brackets 36.