GB2037412A - Electric arc furnace - Google Patents

Abstract

The invention is to provide a furnace construction which facilitates repair and a secondary objective is to provide for the provision of water cooled panels without the need to modify the furnace roof ring. The primary objective is met by a furnace lining in which the upper part of the furnace walls (3) of refractory material have an upwardly and outwardly sloping stepped configuration overlaid by a sloping refractory monolith (4). The secondary objective is met by so arranging the water cooled panels (6) that their lower edge lies behind the inside edge of the refractory wall, each water cooled panel sloping inwardly from bottom to top so that the top lies inside a conventional roof ring. <IMAGE>

Description

SPECIFICATION Furnaces This invention relates to furnaces and is particularly concerned with electric arc furnaces.

There has been a relatively recent development in electric arc furnaces wherein the upper part of the furnace has been formed from a series of water cooled panels. This has had the effect that far greater power can be applied through the electrodes and which has a significant effect on the time taken to produce a particular weight of melt. The effect has been that whilst the melt time has been considerably reduced, excessively heavy wear has occurred on the lining particularly at or slightly above the slag line. The greater heat generated by the use of increased power has also necessitated enlargement of the roof ring to ensure that it lies outside the outer periphery of the upper part of the furnace formed by the water cooled panels. As a result increased costs have been incurred.

One objective of the invention is to provide a construction of furnace which greatly facilitates repair. A second objective of the invention is to provide a construction of upper part of an electric arc furnace formed by water cooled panels which avoids the need for modification of the roof ring, greatly facilitates furnace construction and which affords a reduced likelihood of damage of the hot working face by abrasion and a reduced possibility of damage at the bottom front edge of each panel.

According to one aspect of the invention, an electric arc furnace comprises a lining including furnace walls of refractory material, the upper part of which have an upwardly and outwardly sloping stepped configuration overlaid by a refractory monolith, the refractory monolith having an upwardly and outwardly curved configuration over that part at least of the wall having a stepped configuration.

The stepped configuration of the wall provides far better keying to the refractory monolith, but of greater significance is the fact that the sloping inner wall of the monolith is considerably easier to repair than is a vertical wall used in conventional arc furnaces.

Refractory material gunned, sprayed or otherwise applied to the sloping surface remains in place to a far greater extent than can be so on a vertical wall.

According to a second aspect of the invention, an upper part of an electric arc furnace comprises a series of water cooled panels, the configuration of each of which is such that when positioned in place on the upper part of the lower refractory wall of the furnace, the bottom edge of the inside (hot) faces lies behind the inside edge of the upper part of the refractory wall, and the upper edge of the inside face lies inside the bottom edge, the inside face of each panel between the top and bottom edges forming an inwardly sloping face, the angle of inclination being such that the upper end of each water cooled panel lies inside a conventional roof ring.

Such a construction offers many advantages over existing designs of furnaces the upper part of which are formed by water cooled panels. By effectively forming a sloping overhang, there is a considerably reduced tendency for there to be damage caused to the inside face of each panel by abrasion from scrap, charged into the furnace from above, and by sloping outwardly in a direction towards the melt, an increasing distance is provided between the panels and scrap charged generally centrally of the furnace, therebyreducing considerably the possibility of an arc being struck between the charged scrap and the face of each panel.By setting the bottom inside edge of each panel outside the upper inside edge of the refractory wall of the furnace, the vulnerable inside front edge is afforded considerable protection against heat damage, which possibility of heat damage can be still further reduced by overlaying the bottom edge with the refractory monolith. Because the upper end of each panel lies inside the position of a conventional roof ring considerable protection is afforded the roof ring against heat damage, thereby totally avoiding the need to provide an enlarged roof ring as a means of ensuring that it lies outside the upper end of the panels, thereby totally avoiding the additional costs that this would entail.An additional advantage of the overhanging configuration is that molten slag thrown from the melt into the furnace atmosphere cannot readily adhere to the inside faces of the panels and be hung up on the panels thereby reducing the likelihood of damage.

The inner sloping face of each panel can be provided by forming each panel of trapezoidal cross-section and when the outer face would be vertical. This would however introduce the need for large amounts of cooling water to completely fill the panels and it is therefore preferred that each panel is of rhomboidal cross-section. Thus, in particular, a supporting ring of; for example, graphite blocks can be placed on the upper edge of the refractory wall, shaped to provide a recess extending towards its rearwardly face, the recess being lined with a metal safety retaining ring.

Thus, the bottom end of the penal can be placed in the recess and positive location means provided to hold the panel against movement. The posiiive location means may be provided by securing one or more generally U or C-shaped members to the outer face of each panel towards the lower end thereof, and a corresponding number of lugs on the safety retaining ring. Thus, the panel can be lowered into place such that the U or C-shaped members fit over the corresponding lugs and a wedge-like member driven into the gap between each lug and the corresponding part of the lower outer edge of the panel. Using a wedge to Icoate the panel greatly facilitates removal and replacement of the panel, it only requiring the knocking out of the wedge to free the panel.At the upper end, each panel on its outer face may be provided with at least one U or C-shaped member the legs of which are adapted to engage in corresponding recesses in the upper edge of an outer retaining frame on being lowered into position. As a means of easing considerably the positioning of each panel, each panel may be provided with at least one lifting lug secured to the upper part of the outer face, the means on the lifting lug for connection to a hoist or the like being so spaced from the outer face of the panel that on being suspended by the hoist it automatically assumes a correct angle of inclination so that each panel can simply be lowered into position.

With conventional water cooled panels, it is usual to provide a coating of refractory material on the inside face, and accordingly, a refractory coating can be applied to the inside face of the panels of the furnace of the invention. It is also usual to provide protuberances on the inside face to serve to catch clag thrown up from the surface of the melt. According to a further feature of the invention, an anchor for a refractory facing applied to a surface of a water cooled panel comprises a length of angle section of a length less than the depth of refractory facing, adapted for securing to the inside face of the water cooled panel, each limb of the angle section have pressed from it a lug, the lugs and the resultant holes in the angle section serving to key to the refractory facing.As the facing wears, the angle section becomes exposed and can catch slag thrown from the surface of the melt, which then serves to protect the inside face at a worn position.

The water supply to each panel can take many forms. It is however preferred to provide a lower bezel ring towards the upper end of the outer face of the refractory furnace wall from which water is fed to each panel, water from each panel being fed into an upper bezel ring, e.g., located in the upper part of the outer retaining frame from which the panels are suspended. Thus water flows continuously around the lower bezel ring and up through the panels, avoiding the need to provide pipework within the panels as has hitherto been the case. The provision of the lower bezel ring has the advantage that it provides additional structural strength and cooling of at least the carbon blocks and safety retaining ring.

Another advantage of this aspect of the invention is that whilst the inside face of the water cooled panels obviously cannot be inspected during service, the rear and bottom faces can from outside the furnace, and any break on the inside face can be detected because, with the bottom of each panel set in a rearwardly open recess, water is prevented from running down the inside face of the refractory wall towards the melt, but runs below the panel and out of the rear of the recess where it can be seen.

When the two aspects of the invention are utilised in combination, an extremely effective and efficient construction of electric arc furnace is realised.

By way of example only one embodiment of the invention will now be described with reference tot the accompanying drawings in which: Figure 1 is a schematic sectional side elevation of an electric arc furnace in accordance with the invention; Figure 2 is an enlarged view of the part of the furnace of Figure 1 at A; Figure 3 is an enlarged view of that part of the furnace of Figure 1 at B; and Figure 4 is a perspective view of an anchor for holding a refractory facing on the water cooled panels of Figure 1.

In the drawings, an electric arc furnace has a lining 1 formed by a refractory brick floor 2 and side walls 3 overlaid by a refractory monolith 4, with an outer retaining frame 5 supporting the walls 3. The side walls 3, towards the upper end, are upwardly and outwardly divergent, and of stepped configuration, the overlaid monolith therefore having an upwardly and outwardly sloping face at least in the area at and above the slag line, where the greatest degree of wear on the lining can be expected to take place.

The sloping, stepped configuration of the side wall 3 greatly facilitates the production of the overlaid monolith 4 there being a greater degree of keying the retention in place of the monolith, than when the monolith is applied to a vertical wall. Also, once wear has taken place, repair of the sloping monolithtface whether by gunning, spraying or otherwise applying a refractory mix to the worn part of the lining, is greatly facilitated, as the refractory mix remains in place to a far greater extent than could possibly be expected on a conventional vertical furnace wall.

The upper part of the furnace is formed by a number of water cooled panels 6. Each water cooled panel is of rhomboidal cross-section such that the panels can be positioned on top of the side walls 3 with their bottom innermost edges 7 lying behind the front face of the wall, and with their top outermost edges 8 lying inside a conventional roof ring 9 supporting the roof 10.

This has the major advantage of avoiding the need to enlarge the roof ring to ensure that it lies outside, and is thus protected by, the water cooled panels. The inward inclination of the panels automatically puts the roof ring on the outside of the panels. In addition to this, by effectively forming an overhang, there is a considerably reduced tendency for there to be damage caused by scrap charged generally centrally of the furnace from above, and a considerably reduced tendency for an arc to be struck between the charged scrap and the inner face of the panels.

To provide adequate protection for the bottom front edge 7 of each panel, 6, a supporting ring 11 of graphite blocks is provided on the wall 3 having a recess 12 lined with a metal lining 13, into which the bottom of the panel is placed, and the top edge of the refractory monolith extended to overlie the graphite blocks 11 and the bottom end of the panel. To provide for the positive location of each panel, one or more U or C-shaped brackets 14 are provided on the outer face of the lower end of each panel 6, with a corresponding number of lugs 15 provided either on the retaining frame 5 or on the metal lining 13 of the recess 12 in the graphite blocks 11. A wedge 1 6 is driven between the lug 1 5 and the panel 6.At their upper end, each panel 6 on its outer face has at least one U or C-shaped bracket 17, the legs of which engage in recesses formed in an upper edge of an upper, outer retaining frame 18. For ease of positioning each panel, a lug 1 9 is provided on the outer face of each panel, the lifting point on each lug being so spaced from the outer face of the panel, that when suspended by appropriate lifting gear, the panels assumes the angle of inclination that it is required to have when in position.

Although not shown, it is intended that each panel 6 should have at least the innermost face coated with refractory material. Thus, as is shown in Figure 4, refractory anchors 20 are provided secured to the inner face of the panels 6, and are of a length less than the thickness of refractory coating. When wear of the costing takes place, the anchors are exposed and serve as protruberances to catch slag thrown from the surface of the melt, thereby providing additional protection of a worn position.

The water supply to the panels 8 is through a lower bezel ring 21, from where water is fed to the bottom ends of the panels to rise inside the panels to an upper outlet connected to an upper bezel ring 22. As shown, the lower and upper bezel rings form part of the outer retaining frame of the furnace, adding considerably to the strength of the frame, the lower bezel ring being positioned near the carbon blocks 11 to provide additional cooling at that point.

Another advantage of the invention is that by locating the lower end of each panel 6 in a respective recess 12, any break on the inside face of a panel results in water running down the panel not reaching the melt, but running out through the recess 12 below the bottom of the panel where it can be seen.

Claims (14)

1. An electric arc furnace comprising a lining including furnace walls of refractory material, the upper part of which have an upwardly and outwardly sloping stepped configuration overlaid by a refractory monolith, the refractory monolith having an upwardly and outwardly curved configuration over that part at least of the wall having a stepped configuration.

2. An electric arc furnace as in Claim 1, wherein an upper part of an electric furnace comprises a series of water cooled panels, the configuration of each of which is such that when positioned in place on the upper part of the lower refractory wall of the furnace, the bottom edge of the inside (hot) face lies behind the inside edge of the upper part of the refractory wall, and the upper edge of the inside face lies inside the bottom edge, the inside face of each panel between the top and bottom edges forming an inwardly sloping face, the angle of inclination being such that the upper end of each water cooled panel lies inside a conventional roof ring.

3. An electric arc furnace as in Claim 2, wherein the inner sloping face of each panel is provided by forming each panel of trapezoidal cross-section and when the outer face would be vertical.

4. An electric arc furnace as in Claim 2, wherein each panel is of rhomboidal cross-section.

5. An electric arc furnace as in any of Claims 2 to 4, wherein a supporting ring is placed on the upper edge of the refractory wall, shaped to provide a recess extending towards its rearwardly face, the recess being lined with a metal safety retaining ring.

6. An electric arc furnace as in any of Claims 2 to 5, wherein positive location means are provided for the lower ends of the panels, to hold them against movement.

7. An electric arc furnace as in Claim 6, wherein one or more generally U or C-shaped members are secured to the outer face of each panel towards the lower end thereof, adapted to engage corresponding locating lugs.

8. An electric arc furnace as in Claim 7, wherein the lugs are provided on the safety retaining ring in the recess in the graphite blocks.

9. An electric arc furnace as in Claim 7 or Claim 8, wherein a wedge-like member is driven between each lug and the panel.

10. An electric arc furnace as in any of Claims 2 to 9, wherein at the upper end, each panel on its outer face is provided with at least one U or C shaped member the legs of which are adapted to engage in corresponding recesses in the upper edge of an outer retaining frame on being lowered into position.

11. An electric arc furnace as in any of Claims 2 to 10, wherein each panel is provided with at least .one lifting lug secured to the upper part of the outer face, the means on the lifting lug for connection to a hoist or the like being so spaced from the outer face of the panel that on being suspended by the hoist it automatically assumes a correct angle of inclination so that each panel can simply be lowered into position.

12. An electric arc furnace as in any or Claims 2 to 11, wherein a refractory coating is applied to the inside face of the panels.

13. An electric arc furnace as in Claim 12, wherein an anchor for a refractory facing applied to a surface of a water cooled panel comprises a length of angle section of a length less than the depth of refractory facing, adapted for securing to the inside face of the water cooled panel, each limb of the angle section have pressed from it a lug, the lugs and the resultant holes in the angle section serving to key to the refractory facing.

14. An electric arc furnace as in any of Claims 2 to 13, wherein the water supply to each panel is provided by a lower bezel ring towards the upper end of the outer face of the refractory furnace wall from which water is fed to each panel, water from each panel being fed into an upper bezel ring, e.g., located in the upper part of the outer retaining frame from which the panels are suspended.

1 5. An electric arc furnace substantially as hereinbefore described with reference to the accompanying drawings.