HK1021903B - Smelting installation with an electric arc furnace - Google Patents

Description

Melting device with arc furnace

The present invention relates to a melting apparatus with an electric arc furnace as described in the preamble of claim 1.

A melting device is known from WO 90/10086. In this known melting device, the outer part of the furnace lid is replaced by a cylindrical shaft which is fixed to a holding structure and has a closable charging opening and a gas duct opening in the upper part of the cylindrical shaft. The hot furnace gas is discharged through the cylindrical furnace path, and the furnace burden placed in the cylindrical furnace path is heated according to the heat exchange relationship, so that a large amount of energy can be saved.

In order to be able to carry out the melting process with discontinuous charging, it is advantageous to adapt the total quantity of charge for the weight of liquid metal to be tapped to the total volume comprising the electric arc furnace and the cylindrical shaft. For this reason, in view of the further requirement of limiting the height of the cylindrical shaft, the cross section of the cylindrical shaft is preferably rectangular, and the molten bath section is an ellipse whose one side is defined by a straight line in a plan view. Therefore, the bath section, including the lower part of the bath section, must adopt a new shape compared to the popular circular bath sections.

In the known melting apparatus, the entire furnace cover is movable relative to the bath section, in conjunction with or independently of the clamping structure supporting the cylindrical shaft. It has proven advantageous if the cover is releasably fastened to the holding structure, so that the cover, including the cylindrical shaft, can be rotated or moved linearly relative to the bath section. In the above-described construction, charge material can be purposefully charged through the cylindrical shaft into different regions of the bath section.

In the known melting device, the charge can also be blocked by a stopper arranged in the lower part of the cylindrical shaft, so that the hot waste gas can be used to preheat the raw materials after melting of the charge in the refining stage.

Such a striker is described in detail in WO 95/04910. This application is specifically incorporated herein by reference.

A melting installation with an electric arc furnace in which the furnace cover enclosing the bath section has a first and a second part is known from DE-a-4332913. In each of the two parts of the furnace cover, there is a feed opening for feeding the charge into the furnace section, above which there is a respective cylindrical magazine for preheating the charge fed into the furnace section. These storage containers are fixed to the platform frame above the electric arc furnace, so that the heavy weight of the container filled with charge is directly borne by the support frame, independently of the bath section.

In one embodiment of the cited reference, the furnace cover is segmented in the direction of the electrode support arm and can be pivoted away from the upper part of the furnace body by means of individual wings. This makes it possible to open the upper furnace body in the event of special circumstances or for inspection of the furnace. The magazine, which is suspended on the furnace frame, cannot rotate with it, and only one single electrode opening is provided between the halves of the furnace cover that can be pivoted open. The electrode support arm supporting the electrode cannot be rotated sideways by the magazine, which is suspended from the furnace frame, enclosing the electrode arm. This also eliminates the direct charging of the furnace shaft with charge material by means of scrap cages (Schrottkorb).

The present invention is directed to the proven technology of utilizing existing equipment. The existing arc furnace is modified at minimum cost in such a way that as many parts as possible of the existing plant are used and the plant provided with the melting device is essentially not modified. Thus, with conventional electric arc furnaces with a circular or oval bath section, in which the electrodes are arranged in the center of the furnace lid, there is a particular problem, especially in view of the height of the building, in that the space required for the cylindrical shaft, which serves as a charge preheater and is arranged on the side of the electrodes as the outer part of the furnace lid, is limited, so that it is not possible to provide sufficient volume in the cylindrical shaft for the charge to be heated. The bath section may be made up of one part or may be divided above the slag line into a bottom bath section (lower bath section) and a top bath section (upper bath section). The lid is generally arched and has three channels for the electrodes, arranged coaxially (three-phase ac furnace) or one channel in the centre (dc furnace), called electrode hole.

The object of the present invention is to design a melting apparatus according to the preamble of claim 1, in which as many parts of an existing electric arc furnace as possible are used, i.e. only a minimum number of parts are replaced or modified.

In the case of conventional arc furnaces with a circular or oval lower bath section part, in which the electrodes are arranged concentrically in the central region, the invention seeks to provide a cylindrical shaft volume for the charge to be heated, which volume is sufficient to carry out the melting process as far as possible without a post-charging operation, taking into account the electrode arrangement and the limited space of the building height.

The material stop provided in the cylindrical shaft for stopping the charge material is adapted to the particular factors involved.

The invention also seeks to ensure that the solution of the invention prevents furnace gas from escaping in the cap area.

The invention is characterized by the features of claims 1 and 2. Advantageous configurations of the invention are set forth in the other claims.

In order to provide sufficient volume for the charge to be preheated, the cross-section of the cylindrical shaft in the cylindrical shaft arranged laterally of the electrode on the furnace lid is selected to be large enough so that, in plan view, the inner contour of the rear shaft wall (viewed in the direction of the electrode hole) at least in the upper part of the cylindrical shaft falls outside the inner contour of the upper edge of the lower part of the bath section. The cross-sectional pattern of the upper part of the cylindrical shaft is preferably rectangular or trapezoidal. According to the invention, the upper sector of the bath section below the cylindrical shaft, i.e. the design of the upper part of the bath section with a sector wall converging from the upper edge to the lower edge of the upper part of the bath section, forms a transition from the shaft wall, which falls outside the inner contour of the lower part of the bath section, to the inner contour of the lower part of the bath section, i.e. the upper edge of the furnace, which leads the charge from the outer region of the cylindrical shaft into the lower part of the bath section without hindrance. The transition from a rectangular cylindrical shaft to a circular or oval bath section can be effected in various ways, for example by means of a change in cross section: rectangle-ellipse-circle or rectangle-polygon-circle. The sector-shaped converging walls and the rest of the upper part of the bath section are usually formed by water-cooled walls, which when charging the charge from the cylindrical shaft, feed it into the lower part of the bath section (hearth) which is circular or oval in cross-section.

In plan view, the inner contour of the furnace shaft wall falls outside the inner contour of the upper edge of the lower part of the bath section, the transition from the inner contour of the furnace shaft wall to the lower part of the circular or oval bath section already beginning above the upper edge of the upper part of the bath section, i.e. above the edge of the bath section, in which case the furnace shaft wall remote from the electrode openings is directed obliquely inwardly towards the center of the bath section (center line of the bath section) or the upper edge of the upper part of the bath section. In the lower part of the cylindrical tunnel, this configuration can be provided by means of an elliptically converging wall section or a planar member which transforms the tunnel wall remote from the electrode from a straight line in the horizontal plane into a polygonal, preferably trapezium, shape. The inner contour of the lower edge of the furnace shaft wall remote from the electrodes is preferably substantially identical to the inner contour of the upper edge of the bath section, which contour also corresponds to the contour of the second cover part provided with the cylindrical furnace shaft.

In the melting apparatus of the present invention, in the case of improvement, the lower structure of the entire furnace including the lower part of the bath section, the electrode lifting and rotating apparatus can be continuously used.

If the convergent transition from the rectangular cross section to the cross section of the circular bath section already starts at the upper part of the cylindrical shaft, for example just below the opening in the cylindrical shaft, the front shaft wall must be arranged running parallel to the rear shaft wall, as seen in the electrode direction, so that the inner cross section of the cylindrical shaft is not reduced in the downward direction.

If the linear cross section of the rear wall of the cylindrical shaft, which is rectangular at the top, is transformed into a polygon, preferably a trapezoid, this is also necessary for the front wall to be parallel to the rear wall, in other words, the linear contour of the front wall is transformed in the same way into the aforementioned polygon in a configuration converging towards the center of the bath section. The cross-sectional profile of the lower part of the cylindrical chimney is formed by two sets of parallel polygonal or trapezoidal sides connected by the side wall profile. If, in the lower part of the cylindrical shaft, the rear shaft wall and the adjacent side shaft wall are formed by sectors converging towards the upper edge of the circular or oval bath section, it is even possible to continue to use the already circular or oval upper part of the bath section in the improved operation. This solution is particularly interesting for arc furnaces with a domed cover and for barrel-shaped flues with stoppers.

According to another aspect of the invention, the first cover part with the electrode bores and the second part with the cylindrical shaft are in the form of a combination which are separated from each other by a cover seam and are horizontally movable independently of each other relative to the bath section. In this case, the components of the old cover can continue to be used as modified.

If necessary, the cover gap resulting from the separation of the assembly into two separate bodies which can be rotated or moved horizontally relative to the bath section can be sealed in a simple manner, so that there is no risk of environmental pollution due to furnace gas leakage compared with a cover consisting of one body.

The benefits of the transition from rectangular to circular have been stated by means of a specific configuration or configuration of the striker.

The invention is described in more detail below by means of four embodiments with reference to ten drawings, in which:

FIG. 1 is a side view of a melting apparatus of the present invention with a closed furnace lid,

fig. 2 shows the device of fig. 1, with a second cover part comprising a removed cylindrical chimney,

FIG. 3 is a plan view of a melting apparatus having a section III-III of the cylindrical shaft shown in FIG. 2, with the first lid portion rotated open, and an elliptical transition zone from the rectangular cross-section of the cylindrical shaft to the lower portion of the circular bath section,

fig. 4 shows the section IV-IV in fig. 3 with the furnace lid closed, i.e. with the first lid part screwed in and including the electrodes and the second lid part moved back,

figure 5 is an enlarged view of a portion of figure 4,

fig. 6 is a view corresponding to fig. 3 of a second embodiment, where the transition from the rectangular cross section of the cylindrical shaft to the circular bath section is started in the lower part of the cylindrical shaft below the dam, and the transition zone is polygonal,

fig. 7 is a view corresponding to fig. 6 of a third embodiment, in which the transition from the rectangular cross section of the cylindrical shaft to the circular bath section has been initiated in the upper part of the cylindrical shaft above the dam,

figure 8 is a view of the third embodiment corresponding to figure 4,

figure 9 shows the main parts of section IX-IX in figure 8,

FIG. 10 is a view of a modification of the third embodiment corresponding to FIG. 8 with the circular bath section upper portion without the sector shaped converging wall.

The melting apparatus illustrated in fig. 1 to 5 as a first embodiment comprises an electric arc furnace 1, the electric arc furnace 1 comprising a bath section (hearth vessel)3 mounted on a furnace frame 2 and a dome-shaped furnace cover 4 covering the upper edge of the bath section 3. The bath section 3 comprises a lower bath section part 5 and an upper bath section part 6, the lower bath section part 5 forming a brick-lined hearth for holding molten metal and the upper bath section part being typically formed of water cooled elements. With particular reference to fig. 3-5, the lid 4 comprises a first lid portion 7, the first lid portion 7 being shown in fig. 3 in an outwardly pivoted position, and a second lid portion 8, the second lid portion 8 being in fact formed by the lower end portion of a cylindrical chimney 9 or by a frame 10 housing the lower end portion of the cylindrical chimney 9 (draft) (fig. 1 and 2). In fig. 1 the two-part furnace lid is closed and in fig. 2 the second lid part comprising the cylindrical chimney 9 is open.

Referring in particular to fig. 3-5, the part shown to the right of the center of the bath section corresponds to a conventional electric arc furnace having a circular bath section and into which the electrode 12 can be concentrically moved up to the center 11 of the bath section (central axis of the bath section, see fig. 3 and 4). Compared with the conventional design of an arc furnace with a circular bath section, only the region to the left of the electrode 12 shown in the figure above the lower part of the bath section is modified.

The first cover part 7 is of arched construction and has a so-called core or cover part 13 with electrode openings 14 (fig. 5) for three arc electrodes 12, the arc electrodes 12 being introduced into the bath section, the electrode openings 14 being arranged in a generally triangular manner in the three-phase electric arc furnace. The electrode 12 is mounted on an electrode holder 15 and can be lifted and swung to the side by an electrode lifting and rotating device 16. The first lid part 7 is able to be lifted by the lid lifting and rotating means 17 from the position shown in fig. 4 and 5 at the edge of the bath section and turned to the side position shown in fig. 3 to open the bath section, for example for top charging from above. Suitable lid lifting and rotating means are described in EP-0203339.

In the exemplary embodiment, not only the bath section 3 but also the lid lifting and rotating device 17 and the electrode lifting and rotating device 16 are mounted on the furnace frame 2, so that the bath section can be tilted together with the electrodes.

Thus, without modifying the electrode arrangement during the transition operation, the structure of the first embodiment provides a first cover portion which is an ellipse 19 defined by a chord (chord)18, which portion comprises the usual electrode structure. When the first cover part is mounted to the bath section, the chord 18 must be in the direction of oscillation, i.e. perpendicular to the plane of the paper shown in fig. 2. In this way, the bath section can be tilted to carry out tapping or deslagging operations, while the cover portion 7 is closed and the cover portion 8 is not displaced. In this case, the cylindrical shaft 9 needs only a slight lifting. This can reduce heat losses due to radiation or allow hot furnace gases to be the main part of the preheating shaft. When the shaft 9 is raised, the gap which occurs between the lower edge of the shaft or second cover part 8 and the edge 39 of the bath section (in fig. 5) can be sealed by a baffle or other device fitted to the shaft or bath section edge.

The cylindrical shaft 9 is fixed in a frame structure 20 which surrounds the cylindrical shaft 9 in a cage-like manner, the frame 10 of the second cover part 8 shown in fig. 1 and 2 representing a part of the frame structure. The frame structure 20 supporting the cylindrical shaft 9 is only schematically illustrated in the drawings and is mounted in a holding device 21 in such a way that the frame structure 20 can be raised and lowered together with the cylindrical shaft by means of a lifting device 22. For this purpose, a connecting location 24 for the lifting device 22 fixed to the holding device 21 is provided on the cross member 23 of the frame, so that the cross member 23 and thus the frame structure 20 supporting the shaft furnace can be lifted from the lower position shown in fig. 1 to the upper position shown in fig. 2. In this case, the required guiding operation is provided by the guide rod 25.

The holding device 21 of the cylindrical shaft 9 is horizontally movable. For this purpose, guide rails 27 are provided on the support structure 26, and wheels 28 are mounted on the gripping device 21 so that the gripping device 21 can be moved in the horizontal direction.

The cylindrical furnace channel 9 is closed at the top by a cover 29, which cover 29 is horizontally movable on rails 30 in the illustrated embodiment to open the upper furnace opening for charging by means of a crane 31 (fig. 4). On the rear side in fig. 1, the cap-shaped or roof-shaped cover part 29 has an air passage hole 32, which air passage hole 32 communicates with an exhaust gas pipe 33 when the cylindrical flue 9 and the frame 10 are in the position shown in fig. 1.

Fig. 3 shows a cylindrical furnace path 9 of rectangular sectional shape. As will be described in more detail hereinafter, the lower part of the cylindrical shaft is preferably rectangular when the assembly has a striker to block the feed. The shaft walls of the cylindrical shaft 9 are thus arranged rectangular at least in the lower part, while when the furnace lid is closed, the front shaft wall 34 is close to the chord 18 (fig. 1, 4 and 5) of the first furnace cover part 7, the rear shaft wall 35 is remote from the chord 18, and the lateral shaft walls 36 and 37 are connected to the shaft walls. According to this arrangement, the forehearth wall 34 is substantially the same length as the chord 18, i.e., the hearth wall 34 is adjacent the chord 18 with a narrow cover seam 38. The lid seam is shown enlarged in fig. 5.

It should be noted at this point that when the roof cover is roof-shaped, as shown in fig. 4 and 5, the upper chord in plan view is only a straight line, but may be other lines that vary in shape with the roof cross-section, and the lower edge of the front flue wall 34 is also the same shape.

When the furnace lid is closed, i.e. in the state shown in fig. 1, 4 and 5, the outer shape of the furnace lid is formed by the lower edge of the rear chimney wall 35, the lower edges of the two adjoining side chimney walls 36 and 37 and the oval portion 19 of the first lid portion 7. The upper edge 39 of the bath section, i.e. the upper edge of the upper part 6 of the bath section, is adapted to the shape. Thus, in this embodiment, the contour of the upper edge 39 of the bath section coincides with an ellipse defined by a straight or shallow arc 40 with rounded corners 41.

The transition from the region of the bath section edge defined by the straight line 40 and the oval connecting portion to the corresponding circular cross-sectional region of the bath section lower part is effected by means of a fan-shaped converging wall 42 of the bath section upper part 6 (see fig. 3).

In fig. 5 it has been mentioned and shown that the first lid part 7 and the second lid part 8 are separated by a gap 38 parallel to the chord 18, so that the bath section can be tilted in the direction determined by the furnace frame, in which bath section a tapping hole 43 and an operating hole 44 are arranged, which, viewed in the direction of the center 11 of the bath section, are not blocked by the front wall 34 of the adjacent cylindrical shaft 9. The cylindrical chimney 9, as the second cover part 8, is fixed in a clamping device supported by the support structure 26, not on the hob, which part of the cover is also not able to perform a tilting movement. However, a slight elevation of the lower edge of the cylindrical shaft away from the upper edge 39 of the bath section is sufficient to allow a slight tilting movement of the bath section with the first cover part and retracted electrode thereon.

In order to prevent furnace gas from escaping through the gap 38 between the two cover parts, it is provided according to the invention that means for sealing the cover gap 38 are provided on at least one of the adjacent edges 45 and 46 of the first and second cover parts. Such a sealing device is described later.

One such means blows a sealing gas 47 into the slit 38. For this purpose, a duct 48 with a slot-type nozzle opening or a row of holes facing the cover slit 38 is provided along the edge 46, i.e. on the forehearth wall 34. In the illustrated embodiment, the conduit is formed by a hollow profile portion 49 mounted to the forehearth wall 34. The nozzle opening is arranged on the underside of the hollow profile section, indicated by reference numeral 50.

An alternative arrangement may be used to assist in providing a strip arrangement 51 of cooling tube on the edge 45 of the first cover part which fills the slot 52 with a clearance fit when the cover is closed. In this case, the groove 52 is formed by the underside of the hollow profile section 49 together with a bevel sealing strip 53 provided on the hollow profile section 49.

The cylindrical shaft 9 is preferably equipped with a burden stop 54 (finger). The striker described in WO95/04910 is particularly suitable for this purpose.

However, these dams require special construction and alignment depending on the shape of the respective upper edges 39, 40, 41 of the bath sections and the configuration of the sector-shaped converging walls 42.

In the first embodiment, which changes from the rectangular cross-section of the cylindrical shaft through an ellipse to a circular shape in the lower part of the bath section, the sector-shaped converging wall 42 in the upper part of the bath section also has the further requirement of guiding the charge when the finger is turned into the release position. The angle of rotational movement of the outer fingers is limited.

In order to match the shape of the sector wall 42 of the upper part 6 of the bath section, the device has, in addition to the rotatable fingers 54, fixed fingers 55 which act as deflectors.

The rotatable fingers 54 are mounted in spaced parallel arrangement (fig. 3) on a rotating bracket 56, the bracket 56 being disposed in the frame structure 20 on the rear hoistway wall 35. The rotatable fingers 54 are rotatable downwardly from a closed position shown in solid lines in fig. 5, in which the inner sides of the fingers extend into the interior space of the cylindrical shaft and prevent charge material from passing therethrough, to a release position shown in dotted lines in fig. 5, in which the inner sides of the fingers are downwardly directed and allow charge material to pass through the cylindrical shaft. In the closed position, the rotatable fingers may also be tilted downward by about 20 ° relative to horizontal.

Another form of fixed fingers 55 are resiliently mounted in the frame structure adjacent the side shaft walls 36 and 37 and extend through the side shaft walls 36 and 37 into the cylindrical shaft, the fingers also being spaced from one another. When the rotatable fingers 54 are in the closed position (solid line position in fig. 5), the fixed finger ends 57 are adjacent to the two outer rotatable fingers 54. In this way, a charge stopper is formed in the lower part of the shaft, which stopper extends over the entire cross-section of the shaft and allows hot furnace gas to enter the blocked charge column in the shaft to heat the charge column. When the rotatable fingers 54 are rotated together downwardly from the closed position shown in solid lines in fig. 5 to the open position shown in dotted lines, the downwardly falling charge is directed centrally, i.e. into the lower part of the circular bath section, by both the rotatable fingers 54 and the fixed fingers 55, thereby protecting the sector walls 42 of the upper part of the bath section from damage by excessive loads.

In the second embodiment illustrated in fig. 6, the transition from the rectangular cross section of the cylindrical shaft 9 to the circular cross section of the lower part 5 of the bath section is accomplished through a polygonal cross section, in this case a trapezoid (trapezoid). The transition has furthermore already started above the upper edge 39 of the upper part of the bath section to such an extent that, in the lower part of the cylindrical shaft below the dam 54, the angles between the shaft walls 35 and 36, 35 and 37 are of a shape converging towards the center of the bath section. The sector-shaped convergent channel walls are indicated by reference numerals 58 and 59. The transformation of the rectangular section into the profile of the section of the walls 36, 35 and 37 of the shaft is a planar transformation, the latter being trapezoidal, the plane reflecting the profile of the upper edge 39 of the bath section by means of the rectilinear portions 40a and 41 a. A further transition from the shape of the upper edge 39 of the upper part of the bath section, which is trapezoidally shaped in the lower part of the shaft, to the circular cross-section of the lower bath section part is accomplished by a sector-shaped converging wall 42 a.

According to the transition shape shown in fig. 6, the fixing finger 55 serving as the deflector of the first embodiment may be omitted. The fingers 54 disposed above the scalloped flue walls 58 and 59 cannot deflect downward like the middle fingers. The release position of finger 54 is illustrated in solid lines and the closed position is illustrated in dashed lines in fig. 6. As can be seen in the example, the three fingers, which show the maximum opening position and are respectively adjacent to each of the flue walls 36 and 37, cannot be turned downwards like the middle fingers. A prerequisite is that the rotation of the fingers is effected separately, while the intermediate fingers can be rotated together.

In the second embodiment, the transition from the rectangular cross section to the circular cross section has been initiated in the lower part of the cylindrical shaft below the dam, whereas the wall 34 close to the electrode opening has not changed compared to the first embodiment. However, if the cover is of an arched configuration, the lower edge of the shaft wall 34 follows the arch, and the cross-section of the cylindrical shaft channel at the lower part of the cylindrical shaft does not at least decrease in any noticeable manner.

In the embodiment illustrated in fig. 7-9, the transition from a rectangular section to a circular section has taken place in the upper part of the cylindrical shaft (immediately below the upper opening of the cylindrical shaft, as shown in fig. 8), while in this case, as in the second embodiment, the rear shaft wall 35, seen in the direction of the electrodes, has been transformed into the sides of a trapezium. So that the cross-section of the shaft is not reduced in the downward direction (but rather can be enlarged in order to allow an unobstructed emptying), it is also possible in the third embodiment for the forehearth wall 34, viewed in the direction of the electrode openings, to converge in such a shape towards the center of the bath section, in particular parallel to the rear hearth wall 35. The converging portions of the walls of the rear channel are indicated by reference numerals 60 and 61 and the converging portions of the walls of the front channel are indicated by reference numerals 62 and 63.

In this embodiment, the transition has started above the fingers 54, which are arranged in a plane in which the profile of the back shaft wall 35 and the front shaft wall 34 is the sides of a trapezium. In order to match the cross section, the horizontal frame elements of the frame structure 20 adjacent to the rear shaft wall 35 and in which the swivel supports 56 of the swivel fingers 54 are arranged are also arranged parallel to the trapezoidal shape of the rear shaft wall 35, all fingers being equally far openable compared to the second embodiment, as in the first embodiment. The release position of the fingers 54 shown in fig. 7 and 9 is shown in solid lines and the closed position is shown in phantom lines.

In order to avoid constriction of the channel cross-section, the forehearth wall is also of downwardly converging configuration, so that the profile of the lower edge of the hearth wall 34, as seen in plan view, is a side of a trapezium, the adjacent edge (chord 18a) of the first lid portion 7 also being of the same shape. Thus, when the two lid portions 7 and 8 are in the inwardly pivoted and retracted positions as shown in figure 9, the gap between the two lid portions is as narrow as in the previous embodiment over its entire length.

Fig. 10 shows a modification of the third embodiment. In this case, it is even possible to continue to use the already existing round or oval bath section upper part for the improvement. In the embodiment shown in fig. 10, the rear shaft wall 35 below the fingers 54 converges to the circular cross-sectional shape of the upper edge of the upper bath section 6 of the circular or oval bath section. In other respects, the embodiment of fig. 10 corresponds to the third embodiment. The desired structure is an arch-shaped furnace cover which prevents the inner cross-section of the cylindrical shaft from decreasing in the lower part; and a rotatable finger 54 which, when rotated downwardly, directs charge material towards the centre of the bath section to protect the upper edge of the bath section from falling charge material.

Claims (23)

1. Melting device with an arc furnace (1)

Comprising a bath section (3) comprising a lower bath section part (5) and an upper bath section part (6), and a furnace cover (4) comprising a first and a second cover part (7 and 8), wherein the first cover part (7) comprises at least one electrode opening (14) and the second cover part (8) comprises a cylindrical shaft (9) which is fastened to a holding device (21), the upper part of the cylindrical shaft having a closable charging opening and a passage opening (32) for preheating the charge to be charged into the bath section, and further wherein the holding device (21) and the bath section (3) are horizontally movable relative to each other,

the method is characterized in that: in a cylindrical shaft, the inner contour of the cross section of a part of the cylindrical shaft in a vertical projection is located outside the inner contour of the upper edge of the lower part of the bath section, the upper part (6) of the bath section below the cylindrical shaft (9) and/or the rear shaft wall (35) viewed in the direction of the electrode openings (14) have sector walls (42, 42a, 58, 59, 60, 61) which converge towards the center (11) of the bath section.

3. A melting apparatus as defined in claim 1 or 2, wherein: the first cover part (7) can be lifted and turned sideways by the cover lifting and rotating device (17).

4. A melting apparatus as defined in claim 3, wherein: the electrode lifting and rotating means (16) can be rotated outwards together with the lid lifting and rotating means (17).

5. A melting apparatus as defined in any one of claims 1 to 4, wherein: the second cover part (8) can be lifted and lowered together with the cylindrical furnace shaft (9) in the clamping device (21), and the clamping device (21) can be moved horizontally.

6. A melting apparatus as defined in any one of claims 1 to 5, wherein: the holding device (21) can be moved perpendicular to the cover seam (38).

7. A melting apparatus as defined in any one of claims 1-6, wherein: means for sealing the lid seam (38) are provided on at least one of the two adjacent edges (45, 46) of the first and second lid parts (7 and 8).

8. A melting apparatus as defined in claim 7, wherein: a groove (52) extending along one edge (46) of two adjacent edges (45, 46) of the first and second cover parts (7 and 8) is provided on said edge, and a strip-shaped part (51) extending along said edge is provided on the other edge (45) of said edge (45, 46), which strip-shaped part fills the groove (52) with a clearance fit when the cover is closed.

9. A melting apparatus as defined in claim 7 or 8, wherein: on at least one edge (46) of the adjacent edges (45, 46) of the first and second cover parts (7 and 8) is placed a conduit (48) extending along the edge, the conduit having at least one nozzle opening (50) facing the cover slit (38) through which sealing air is blown into the cover slit (38).

10. A melting apparatus as defined in claim 9, wherein: an edge extending slit-type nozzle orifice (50) is provided.

11. A melting apparatus as defined in claim 9, wherein: an array of apertures extending along the rim (46) is provided as nozzle apertures.

12. A melting apparatus as defined in any one of claims 2-11, wherein: the rear furnace wall (35) viewed in the direction of the electrode openings (14) has a sector-shaped wall (58, 59, 60, 61) which converges towards the upper edge of the lower part (5) of the furnace section.

13. A melting apparatus as defined in any one of claims 1-12, wherein: in plan view, the first cover part (7) is oval defined by a chord (18, 18a), the contour of the lower edge of the forehearth wall (34) as seen in the direction of the electrode aperture (14) corresponding to the contour of the chord (18, 18 a).

14. A melting apparatus as defined in any one of claims 1-13, wherein: the shape of the lower edge of the rear furnace wall (35) and the adjacent side walls (36, 37) viewed in the direction of the electrode openings corresponds in the region of the second cover part (8) to the shape of the upper edge (39) of the bath section.

15. A melting apparatus as defined in any one of claims 1-14, wherein: the cross section of the upper part of the cylindrical shaft (9) is rectangular, and the shape of the rear shaft wall (35) and the adjacent side shaft walls (36, 37) viewed in the direction of the electrode openings (14) is transformed by an oval downward convergence into a circular shape of the upper edge of the lower part (5) of the bath section or of the upper part (6) of the bath section.

16. A melting apparatus as defined in any one of claims 1-14, wherein: the cross section of the upper part of the cylindrical shaft (9) is rectangular, and the shape of the rear shaft wall (35) and the adjacent side shaft walls (36, 37) viewed in the direction of the electrode openings (14) is transformed by a polygon to a circular shape of the upper edge of the lower part (5) of the bath section or the upper part (6) of the bath section, converging downwards.

17. A melting apparatus as defined in claim 16, wherein: the polygon is a trapezoid.

18. A melting apparatus as defined in any one of claims 1-17, wherein: the front furnace wall (34) seen from the electrode hole (14) converges in a direction parallel to the rear furnace wall (35).

19. A melting apparatus as defined in any one of claims 1-18, wherein: the lower part of the cylindrical shaft (9) has a striker (54, 55) for the material to be heated, which is movable from a closed position, in which gas can pass and the charge material is blocked, to a release position, in which the striker allows the passage of the material from the cylindrical shaft (9).

20. A melting apparatus as defined in claim 19, wherein: the dam (54, 55) comprises fingers (54) arranged parallel to each other at a distance, which are mounted on a rotary support (56) and can be turned downwards from a closed position, in which the inner parts of the fingers (54) project inside the cylindrical shaft to block the passage of charge therethrough, to a release position, in which said parts of the fingers are directed downwards and release the charge to pass through the cylindrical shaft (9).

21. A melting apparatus as defined in claim 20, wherein: a swivel bracket (56) mounting the rotatable fingers is provided in the frame structure (20) on the rear chimney wall (35), the fixed fingers (55) extending from the adjacent side chimney walls (36, 37) into the interior of the cylindrical chimney (9), the ends (57) of the fixed fingers being disposed adjacent the two outer rotatable fingers (54) when the rotatable fingers (54) are in the closed position.

22. A melting apparatus as defined in claim 21, wherein: in the closed position, the inner portions of the rotatable fingers (54) are inclined downwardly, and the fixed fingers are inclined substantially in line towards the inner ends (57) of said rotatable fingers (54) with the inclination of the two outer rotatable fingers (54) in the closed position.

23. A melting apparatus as claimed in claim 20, characterized in that the individual control of the rotation by means of the outer fingers (54) adjacent to the lateral furnace walls (36, 37) causes the fingers to rotate downwards less far than the intermediate fingers (54) between them, which are co-rotating.

24. A melting apparatus as claimed in claim 20, characterized in that in a shaft furnace, in which the rear furnace wall (35) and the lateral furnace walls (36, 37) connected thereto, viewed in the direction of the electrode openings (14), converge from top to bottom into a circle through a polygon following a trapezoid, the horizontal cross-members of the frame structure (20) adjacent to the rear furnace wall (35) with swivel supports (56) for the swivel fingers (54) extend parallel to the trapezoid contour of the rear furnace wall (35).