GB2051327A

GB2051327A - An improved electric metal smelting furnace

Info

Publication number: GB2051327A
Application number: GB8017202A
Authority: GB
Original assignee: Mannesmann Demag AG
Current assignee: Mannesmann Demag AG
Priority date: 1979-05-29
Filing date: 1980-05-23
Publication date: 1981-01-14
Also published as: JPS55162586A; DE2921702A1; ZA803183B; GB2051327B; DE2921702C2

Abstract

An electric arc furnace comprises a furnace vessel 1 having a cover 2 through which pass electrodes 3, and support means 4a for the electrodes and the cover. At least one tap hole 5 is arranged in the bottom of the furnace vessel so as to be closable by a closure member operable by a drive mechanism. <IMAGE>

Description

SPECIFICATION An improved electric metal smelting furnace This invention relates to an electric metal smelting furnace.

An electric arc furnace is known for the production of steel which has a furnace vessel and a cover through which pass electrodes used to supply heat to the metal bath within the furnace vessel. The vessel is pivotally supported so that it may be tilted in order to pour the melt into a ladle.

However, the larger the furnace, the more complicated and more expensive is the pivotal support on which it is mounted. Another disincentive for increasing the size of such a furnace is the fact that the devices for holding and adjusting the electrodes are connected to the furnace and participate in its movement. Not only does this result in the need to move large masses, but also bending forces act on the electrodes during tilting of the furnace. The diameter of the electrodes and hence the maximum furnace output are therefore limited by the need to ensure that unacceptable stresses are not placed on the electrodes during tilting. These difficulties have therefore led to attempts being made to use more than three electrodes, for example six to nine electrodes.

A further problem caused by the movements performed by the electrodes during tilting of the furnace is that of providing a satisfactory power supply system to the electrodes. The need to take into account the mobility of the furnace also complicates the design of the lifting mechanism for the cover, as well as the electrodes and the tubes for feeding material into the furnace, and the furnace gas outlet.

In order to overcome these problems, the present invention provides an electric furnace comprising a furnace vessel having a cover through which electrodes extend, and support means above the furnace vessel for the electrodes and the cover, the vessel having at least one tap hole closable by a closure member operable by a drive mechanism. This arrangement achieves a number of advantages which lead to a simplification in overall design and an improvement in the mode of operation. These include the fact that the molten metal may be discharged from the furnace in substantially less time than hitherto because the invention avoids the need to move large masses, which can only be done slowly.Further, because the path through which the melt travels from the furnace to the ladle may be substantially shorter than hitherto, temperature losses are also reduced and the melt absorbs less oxygen than if it were poured through the casting spout and guide channels of a conventional furnace. Because the ladle may now be supported on the floor a short distance below the tap hole which remains fixed in space, there may be arranged in the intervening region a device which uses a suitable gas to protect the metal being teemed from the furnace. Also, a hood may be easily fitted on the underside of the furnace so as to surround the tap hole and collect the exhaust gas.

Because it is not necessary for the furnace vessel to tilt in order to discharge the melt, it is unnecessary for a refractory lining to extend up to the rim of the vessel. Instead, the lining may terminate a short distance above the surface of the metal bath within the vessel the wall of the vessel above the lining being formed by hollow cooling elements through which flows a coolant.

With this arrangement, not only is an improved cooling effect achieved, but also the heat absorbed by the coolant may be recovered.

As it is unnecessary to take into account the forces applied to the electrodes during a tilting action, this consideration no longer places a limit on the electrode diameter, so that thicker electrodes may be used and the furnace output thereby increased. Nevertheless, it is also possible to make use of more than three electrodes particularly since the current supply arrangement may be of an improved design and the current supply may be at an optimum.

Afurnace in accordance with the invention is capable of being operated either as an arc furnace in which the electrodes terminate above the metal bath or as a resistance or reduction furnace in which the electrodes are immersed in the bath.

The invention will now be described in greater detail but by way of example only with reference to the drawings in which; Figure 1 is a schematic vertical section through a first embodiment of furnace in accordance with the invention, Figure 2 is a section similar to Figure 1 but through a second embodiment of furnace, Figure 3 is a partial section showing a modified vessel bottom in vertical section, and Figure 4 is a view similar to Figure 3 but showing a second modification of vessel bottom.

Referring to Figure 1, a furnace vessel 1 is supported fixedly in a raised position on supports 1 7 providing a space for a movable ladle 20. The vessel is conveniently oval or rectangular when viewed in plan and is provided with a suitable cover 2 for closing the open top of the vessel. A plurality of electrodes 3 extend through the cover, as do ancillary devices, such as feed tubes, not shown. The cover, the electrodes and the feed tubes and other ancillary devices are supported on a cross member 4 which extends above the vessel and is mounted on a vertical column beside the vessel, by means which permit these components to be raised and lowered.

The electrodes extend through apertures in the cover and are adjusted during use of the furnace to keep pace with the erosion of the electrodes.

The cross member is rotatable together with or relative to the column in order to remove the cover, electrodes and ancillary devices from the vicinity of the vessel after they have been raised into a position in which they cannot foul the sides of the vessel.

The bottom of the vessel is provided at its centre with a tap hole 5 provided with a closure and a drive mechanism for opening the closure in order to teem molten metal from the vessel.

An exhaust gas hood 16 is provided on the underside of the furnace in surrounding relationship to the tap hole.

The vessel has a refractory lining which covers the bottom of the vessel and extends upwards slightly beyond the surface of the bath of molten metal 7. Above the level of the refractory lining, the wall 9 of the furnace consists of an array of juxtaposed tubes which are exposed to the furnace interior.

When the furnace is in use, coolant is pumped through the tubes in order to keep the wall cool and recover heat. The tubes are arranged outwardly with respect to the inner edge 10 of a shoulder 11 formed on the upper side of the refractory lining in order to protect the tubes from sprays of molten metal.

Arranged on the upper side of the wall 9 and extending throughout the circumference of the vessel is a tube 13 surmounted by a gas-tight seal against which the cover 2 bears when in its lowered position. The tube 13 is connected with a pump for withdrawing air from the tube whereby dust laden furnace gas is drawn into the tube by way of a slot or plurality of openings 14 facing inwardly of the furnace. The gas extracted from the furnace is passed through a dust separating device before being discharged. In a modification, the tube 1 3 is carried by the cover.

Referring now to Figure 2, the construction of the vessel of this second embodiment is essentially the same as that shown in Figure 1, but the cover 2 and the electrodes 3 and ancillary devices are carried on a bridge member 4a supported on columns arranged on both sides of the vessel and provided with wheels 19 adapted to run on rails 1 8 to facilitate removal of the cover, electrodes and ancillary devices from the vicinity of the vessel.

In a further embodiment not shown in the drawings, the cross member 4 is supported on a single fixed column or bridge-like on a pair of fixed columns and the supports 17 of the vessel are provided with running wheels which engage with rails along which the vessel may be moved from beneath the cover and electrodes when the latter have been raised.

Although in accordance with the invention it is unnecessary for the vessel to be tilted to extract the molten metal, a limited amount of tilt may be permitted under the action of suitable drive means in order to permit a sump of metal to be retained in the vessel or to separate slag from the metal.

As shown in Figures 3 and 4, the bottom of the vessel may be provided with a plurality of tap holes associated with respective closures, not shown, capable of being opened and closed independently of one another. In the case of either modification, it is possible to open the tap hole or tap holes located at the highest levels only, once again in order to retain a sump of molten metal within the vessel as is necessary with certain modes of operation.

Claims

1. An electric metal smelating furnace comprising a furnace vessel having a cover through which pass electrodes, support means for the cover, electrodes and ancillary devices, the vessel having in its lower part at least one tap hole associated with a closure provided with a drive mechanism.

2. A furnace according to Claim 1, wherein the tap hole is arranged substantially centrally of the vessel bottom.

3. A furnace according to Claim 1, wherein the bottom has a plurality of tap holes.

4. A furnace according to Claim 3, wherein the bottom of the furance is concave or inclined, so that the tap holes are arranged in a number of different levels.

5. A furnace according to any preceding claim, including an exhaust gas hood disposed beneath the vessel bottom in surrounding relationship to the tap hole or tap holes.

6. A furnace according to any preceding claim, wherein the furnace vessel has a refractory lining which terminates at a short distance above the intended level of the metal bath, the wall above the lining being formed at least in part of hollow elements exposed to the interior of the furnace and adapted to be supplied with coolant.

7. Afurnace according to Claim 6, wherein the elements comprise tubes which bear tightly against one another.

8. A furnace according to any preceding claim, wherein the outline of the furnace vessel when viewed in plan is other than circular.

9. A furnace according to Claim 8, wherein the vessel is oval in outline.

10. Afurnace according to Claim 8, wherein the vessel is rectangular in outline.

11. A furnace according to any preceding claim, wherein a vacuum pipe is arranged in the region of the rim of the vessel wall or in or on the cover.

12. A furance according to Claim 11, wherein the vacuum pipe extends throughout the periphery of the vessel or cover and communicates with the interior of the furnace, the pipe being connected to a device for reducing pressure within the pipe.

13. A furnace according to any preceding claim, wherein the vessel is pivotal to a limited extent so as to ensure the retention of a sump of molten metal in the vessel during tapping.

14. A furnace according to any preceding claim including a structure movable from a position above the vessel to a position remote from the vessel and arranged to support the cover, electrodes, or feed tubes.

1 5. A furnace according to Claim 14, wherein said structure is in the form of a movable bridge.

1 6. A furnace according to any of Claims 1 to 13, wherein the furance vessel is movable from beneath the cover, while retaining a level position.

1 7. A furnace according to any preceding claim, wherein the vessel is capable of being lowered on one side to separate slag from metal.

1 8. A metal smelting furnace substantially as hereinbefore described with reference to and as iliustrated in Figure 1 or Figure 2 alone or as modified by either of Figures 3 to 4 of the accompanying drawings.