DE2639378C3 - Water-cooled lid of an electric arc furnace - Google Patents

Description

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The invention relates to a water-cooled lid in box construction, which is from the inside of the furnace Is refractory lined and is supported against a cooled cover ring, for a circular cross-section Electric arc furnace for steel production.

The use of a water-cooled lid of this type for electric arc furnaces is in the journal "Neue Hütte", Volume 9, Issue 2, February 1964, pages 118,119.

From DE-PS 9 29 865 a rectangular arc furnace with an elongated cross section is known, Above which is arranged a metal cover which surrounds the electrodes and which is provided with a single opening is through which all electrodes are passed in such a way that each of them is a distance from the edge of the opening, the cover being divided into units for the circulation of a cooling liquid

From DE-PS 7 08 276 is a water-cooled lid for melting furnace, which is of an annular Strut edged and supported by supporting flanges, known in which the cooling water flowed through Pipeline is designed as a connecting member between the strut and the support flanges

In US-PS 22 22 004 is an oven lid construction with liquid-cooled electrode rings.

During operation, a furnace lid from the working space of the furnace becomes significant thermal and mechanical stresses The operating time of the furnace depends on the service life of the Cover off.

The service life of the lids of electric arc furnaces, which are made of conventional refractory materials is usually between 25 to 300 melts.

The durability of wall lined lids is influenced by many factors, including the geometric covering measurements of the ceiling (diameter and pitch), the type of masonry (rings, Arch sectors or combined), the proportions of the geometrical dimensions of the furnace (cover distance from the metal level to the diameter of the melting chamber, ratio of the diameter of the Circle that runs through the electrode axes, to the diameter of the melting chamber, etc.), from the electrical Operating condition, the type of steels to be produced, the power of the transformer, etc.

The refractory materials wear out faster in the central part of the lid than on the periphery regardless of the type of destructive effect. The service life of the lids is usually around one calendar month under operation.

The realization of modern operating methods of electric steelmaking, which with the increase in dem The power supplied to the furnace and the deoxidation period processes are not carried out in the furnace, but in the pan, as well as with intensive use of oxygen to blow through the metal bath causes difficult operating conditions for the lids of an arc furnace.

In this context, efforts are being made to develop a durable lid. To this end, will at present the work has been carried out in two directions.

One direction sees the search for higher quality refractory materials and perfection the construction of the masonry cover.

The second direction is concerned with further development an artificially cooled cover construction, in which the creation of a cavity for the Flow of a coolant is provided.

Significant successes have been achieved in recent years in the first direction The durability of the lids increases with the improvement in the quality of the refractory materials used in the construction of the masonry be used by lids.

The pace of improving the quality of refractory materials is slowing down but see where you see approaches the highest possible quality. Another significant increase in the durability of the masonry of the furnace lid in the former direction is therefore impossible.

This explains the fact that the second direction has recently been increasingly developed, namely the creation of lids of electric arc furnaces with

provides artificial cooling

There are two types of artificially cooled lid constructions: one from the tube and one from the Box type.

The tubular construction of the lids (Metalworking Weekly Steel, December 9,1963, N 24, V 153, p. 97-98.) contains steel coils in which a coolant circulates. The lid has one on the side of the furnace thermal insulation made of refractory bricks or a refractory mass

Such a lid can withstand 350 melts, while a lid made of bricks containing alumina with a thickness of 225 mm only withstands 26 melts

However, significant difficulties arise in operating the furnace with a lid. The middle part of the Lid wears out faster because, in contrast to the peripheral part of the lid, it has higher thermal values Is exposed to stress.

In addition, this central part is electrically stressed by the electrodes

Since the cover is designed as a whole piece, if the middle part fails, the entire cover must be replaced. In addition, in the event of a short interruption in the supply of the Coolant to the pipes an emergency that could burn the lid.

While the furnace is in operation, the underside of the lid must be coated periodically with shotcrete.

The manufacture of the pipe coils causes great difficulties with the use of additional Equipment and operators are connected.

Attempts have been made to create a cobined lid in which the central portion has a has box-shaped cavity which is filled with coolant, and the peripheral part consists of tubes

Such a lid has a longer service life because the middle part is cooled better than the Tube-type lids are the case (see SU-PS 2 14 560).

However, these covers are also designed as a whole piece and have to be worn after one individual section must be completely replaced.

There is also considerable loss of power due to magnetization reversal and of heat with the Cooling water.

As an example of a box-type lid, the ceiling! in accordance with the USSR certificate 3 65 538.

This water-cooled lid for an electric arc furnace is made as a whole piece of sheet metal, has a cover ring of rectangular cross-section and is with the side of the furnace chamber Refractory lined.

The cover has a cavity for the flow of a coolant and through openings for Arrangement of electrodes for the supply of gas to the furnace chamber and for the extraction of flue gases. This lid is more reliable in operation and has a longer shelf life than other arc furnace lids. However, the lid causes significant losses of heat and power during magnetization. In addition, its operational safety is due to a large number before. existing angle welds small amount.

With the growing need for metal and the The necessity of increasing the technical and economic indicators for its production arose Problem of extending the service life of arc furnaces by extending the service life the lid.

The invention has for its object to provide a water-cooled cover for electric arc furnaces with a to develop structural design that will significantly extend the life of the furnace To reduce the number of angle welds in the manufacture of cover rings considerably, the

ίο Replacing the middle part of the lid, the maximum is exposed to thermal stresses from the furnace chamber, to simplify and accelerate allowed

This is the case with a water-cooled lid

! 5 initially mentioned type achieved according to the invention in that the cover consists of two concentric components, the disk-shaped central part through which the electrodes are passed by an electrically insulating sealing ring from the annular outer part, which ά: -. Contains exhaust opening, is separated and the Deckelrir-g is circular in profile

The design of the cover ring with a round cross-sectional profile leaves the number of angle welds Significantly reduce and thereby the service life of the cover ring, and consequently of the cover and of the oven.

The middle part wears out faster because there is considerable thermal stress and low electrical energy To absorb carbon copies. The design of the cover from removable parts allows the replacement of the Simplify and speed up the middle part of the cover and increase the service life of the cover.

The disk-shaped central part advantageously consists of three sectors that are electrically isolated from one another.

Such a structural design of the middle part of the cover prevents breakdowns from the electrode the metallic elements of the water-cooled cover and leaves the power losses when Reduce re-magnetization.

Preferably on the ceiling to distribute the water! arranged a collecting vessel, which from the Lid ring is fed and the individual parts with Cooling water supplied.

This simplifies the cooling water supply.

An advantageous development is that each of the sectors of the central part with a Recess is carried out from the side wall of the sector to the electrode opening.

Such recesses in the sectors of the middle part of the cover reduce the power loss during magnetization reduce.

It is advantageous to have nozzle heads in the cover with angles from 70 to 70 to the longitudinal axis of the nozzle heads 75 ° inclined nozzle openings for the introduction of cooling gas.

The presence of nozzle heads in the above-mentioned design enables the heat-absorbing gas To feed the surface of the lid from the side of the furnace chamber.

Gas supply during the deoxidation period of molten metal, where practically none in the furnace If oxygen is present and the gas temperature is 1500 to 1700 ° C, the gas will also decompose

6 ¹ ) the deposition of soot carbon. The gas layer, which contains the carbon black, reduces the effect of the heat flow from the weld pool on the cover.

In other periods of melting, a gas-air mixture can be fed in via the nozzle heads, i. H. the Burn the gas on the lid surface and the heat losses from the working area of the furnace reduce.

A grate for holding the refractory material is preferably formed on the inside of the lid made of edgewise welded zigzag-shaped metal strips.

Such a reinforcement of the underside of the cover results in a reliable support of the lining and prevents them from falling while the furnace is in operation.

Preferably, in the metal strips at the points that form the walls of the cells of the grate, through holes drilled through which wire is passed. The wire inside the cells forms one additional reinforcement, which improves the adhesion of the lining to the underside of the ceiling leaves.

The invention is explained below with the aid of examples, with various possible embodiments of a water-cooled lid of a Arc furnace are described in more detail with reference to the drawings, it shows

F i g. 1 shows a longitudinal section through an oven with a water-cooled lid according to the invention,

2 shows the top view of a water-cooled cover with sectors, with a cutout,

Fig.3 the pressure view of a section of a Sector in the middle part of the lid with a recess on its side wall,

4 shows a longitudinal section through the part of the water-cooled cover with nozzle head which is attached to the The gas line is to be connected,

F i g. 5 shows a cover part with a butt joint, the side wall having an arcuate cross section having,

F i g. 6 a cover part with a butt joint, the side wall having a U-shaped cross section,

F i g. 7 shows a vertical section through the part of the water-cooled cover with cells made of metal strips,

F i g. 8 is a view of the cover part of FIG. 7 seen from below.

The water-cooled cover 1 (FIG. 1) for an electric arc furnace 2 is a box-shaped metallic welded construction which is supported against a cover ring 3 and has a refractory lining 4 on the side of the working space 5 of the furnace 2. The box-shaped construction consists of the middle part 6 ( FIG. 2), which is a hollow disk, and the outer part 7, which is a hollow ring.

The cover parts 6 and 7 are made of metal sheets 8 (FIG. 3) and 9 (FIG. 4), the upper ones correspondingly and form the lower side of these parts. The side walls 10 (Fig.5 and 6) of each cover part 6 and 7 (Fig.2) are by means of weld seam 11 (Fig. 5 and 6) through their end faces with the corresponding upper 8 and The lower 9 metal sheets are butt-connected, which form the upper and lower sides of the lid. Such a one Butt joint is secure enough during operation, while the welded butt joint 11 is strong and durability is not inferior to the metal of the sheets 8 and 9 to be welded.

There are also different profiles of the cross-section the side wall 10, ζ. Β. Curved or U-shaped possible, which reduces the number of welds because it is very important to replace less secure angle welds with butt joints, which have proven themselves better. For secure attachment of the lining 4 (Fig. 1) are to the lower sheets 9 (Fig. 7) zigzag metal strips 12, which form rows of rows 13, which over the entire surface of the cover 1 (FIG. 1) facing the space 5 of the furnace 2, are welded on.

In the metal strips 12 (Fig. 7) are at the points

which form the walls of cells 13, previously drilled through holes, through which wire 14 (Fig. 8) passed is. These cells 13 are filled with refractory material which forms the lining 4 (FIG. 1). Between the middle part 6 and the outer part 7 of the cover 1 is an annular intermediate layer 15 made of electrical insulating material provided.

Since the middle part 6 of the cover 1 is exposed to more intensive wear, it is designed to be removable. This enables it to be replaced quickly and easily. The 'viiiiciici! S is on the annular Outer part 7 placed so that it covers the opening therein and the outer part 7 in turn against each other supports the cover ring 3, which has a round cross section. Such a cross section of the cover ring 3 allows to reduce the number of welds in its manufacture and its operational reliability to increase.

An example of the design of the cover 1 is possible, where? Uas middle part 6 from three electrically from each other isolated sectors 16 (Fig.2) is composed. This prevents electrical breakdowns from the Electrode 17 (Fig. 1) to metallic parts of the cover 1 and leaves the Leisiungsveriusie at Reduce magnetization reversal.

Any of the part? 6 and 7 of the cover 1 has a cavity 18 (Fig. 7) for the flow of a Coolant, for example water from the water supply network (not shown in the drawing) is fed. A collecting vessel 19 is provided for distributing the water in parts 6 and 7 of the cover 1 ■ »ο (Fig. 2) is provided, the inlet of which is connected to the cover ring 3 and the outlets of which are connected to each of the sectors 16 and to the outer part 7 of the cover 1.

Each sector 16 of the middle part 6 of the lid 1 has a recess 20 (FIG. 3) from the side wall 10 of the Sector 16 to the opening for the electrode 17 (F i g. 1). These recesses 20 (FIG. 3) in the sectors 16 (Fig.2) of the middle part 6 of the cover contribute to the reduction of the power losses during magnetization reversal at.

In addition, through channels 22 for nozzle heads are in the middle part 6 and the outer part 7 of the cover 23 (Fig. 4) with flanges for connection to gas supply pipes (not shown in the drawing) In the lower section of the side wall of each nozzle head 23 there are nozzles 24 for the gas outlet present, the longitudinal axes of which form an angle of 70 to 75 ° with the longitudinal axis of the nozzle heads 23. A gas supply to the heat-absorbing surface of the cover 1 takes place through these nozzles 24 (FIG. 1). from the side of the working space 5 of the furnace 2, whereby a gas protective layer is formed, which the Heat losses of the furnace 2 are reduced by its metallic, water-cooled cover 1

The assembly of the cover 1 begins with the installation of the outer part 7 of the cover with the Lid ring 3 on the furnace 2. Since the outer diameter of the central part 6 of the lid 1 is greater than the Inner diameter of the passage opening in the outer

part 7 is. this enables an accurate and fast Centering the electrodes 17.

Water is fed to the cover 1 via the nozzle 25 (FIG. 2) and flows over the circumference of the Cover ring 3 up to a partition wall 26 also arrives in the collecting vessel 19 and is distributed in the Sector f. of the middle part 6 and the outer part 7 of the lid ir. with the help of pipes and hoses (in the Drawings not shown). In the space 18 (Fig. 7) of the cover pipes 27 with holes 28 are insnüieri. the Direct jets of water onto the inside of the heat-absorbing surface of the lid.

Since the entire amount of water that is required for the operation of the lid, through the lid ring 3 (Fig. I) flows, there are greater water velocities in the latter, which effectively dissipate the heat allow, which claims the surface of the cover ring 3 from the working space 5 of the furnace 2.

The arrangement of the middle part 6 of the cover 1 over the outer part 7 enables a uniform distribution of thermal stresses on the surface of the cover 1 during the operation of the Furnace 2 and consequently the same working conditions for the lining 4.

The refractory lining 4 (for example, refractory concrete) is on the reinforced surface of the Underside 9 (Fig. 7) of the lid applied. The metal strips 12 are on the heat-absorbing Surface of the lower plates 9 welded in the form of an uninterrupted seam so that they the Form cells 13 with a depth of 40 to 65 mrn. In the Walls of the cells 13 are holes at a distance of 20 mm from the surface to be cooled executed, through which wire 14 (Fig. 8) is passed. This reinforcement prevents the ramming or falling out Sealing compound before starting the furnace. The ramming mass wears out during operation.

The metal and slag vapors that form in the burning zone of the arc condense on the surface of the rammed earth and rise through the pores under the action of capillary forces to the cooling surface. In addition, metal and slag splashes get onto the surface of the rammed earth, the z. B. arise when the metal is blown with oxygen. This leads to the A crust forms when rammed. the further wear of the remaining part of the ramming mass prevented. The strength (and thus the thermal resistance) of the crust depend on the temperature maintenance during operation of the oven and will automatically adjusted so that the amount of heat that the surface of the lid from the furnace working space is applied, with which the cooling water is discharged.

Technical circulating water is required to cool the lid. The gas is coming over from the gas pipe a regulating element is supplied to the nozzle heads 23 (FIG. 4) which have nozzles which are designed such that they direct the gas onto the heat-absorbing ceiling surface.

The number of nozzle heads 23 and their arrangement on the cover surface is such that the whole lined surface of the lid 1 is covered by a Schiilzgassschicht.

During the deoxidation period of molten metal In the furnace, the nozzle heads 23 are supplied with gas that is at a high temperature without Oxygen (conditions of the deoxidation period of metal melting) with deposition of soot particles is dismantled.

The resulting gas layer, which contains soot particles, reduces heat loss through the water-cooled lid. In the remaining periods of Melting metal in the furnace, a gas-air mixture is supplied via the nozzle heads 23, which is on the cover surface from the side of the working space 5 (Fig. 1) of the furnace 2 burns and the heat loss from the Reduced the working space of the furnace 2.

Tests of the lid according to the invention showed that the durability 6500 melts compared to 240 melts when operating with conventional magnetic chromite lids with a thickness of 225 mm. The consumption of electrodes decreased from 5.3 to 4 J kg per ton of steel.

The hermetic seal of the furnace has improved, which is particularly important for vacuum furnaces. Of the Consumption of alloying elements when melting stainless steels became lower. The downtime the furnace became shorter and the labor involved in bricking the lids was avoided.

For this purpose 3 sheets of drawings

Claims (7)

Patent claims: 1. Water-cooled box-type lid with a fire-proof lining on the inside of the furnace and is supported against a cooled cover ring for an electric arc furnace with a circular cross-section for steel production, characterized in that the cover consists of two concentric components (6, 7), the disk-shaped central part (6) through which the electrodes are passed by an electrically insulating sealing ring (35) from the annular outer part (7) which contains the exhaust gas opening, is separated and the cover ring (3) is circular in profile. 2. Water-cooled cover according to claim 1, characterized in that the disc-shaped Middle part (6) consists of three sectors (16) that are electrically isolated from one another 3. Water-cooled lid according to claim 1 and 2, dadü-ch characterized in that for water distribution a collecting vessel (19) is arranged on the lid, which consists of the lid ring (3) is fed and the individual components (6,7,16) with Cooling water supplied. 4. Water-cooled lid according to claims 1 to 3, characterized in that each the sectors (16) of the central part (6) with a recess (20) from the side wall (10) of the Sector (16) is executed up to the electrode opening (21) 5. Water-cooled lid according to claims 1 to 4, characterized in that im Cover nozzle heads (2J) with the longitudinal axis of the nozzle heads (23) at Winkvin from 70 to 75 ° inclined nozzle openings (24) are arranged for the introduction of cooling gas. 6. Water-cooled lid according to claims 1 to 5, characterized in that on the Inside of the lid a grate for holding the refractory material made of edgewise welded zigzag metal strips (12) is arranged. 7. Water-cooled lid according to claims, characterized in that in the metal strips (12) at the points which the walls of the Form cells (13) of the grate, through holes are drilled through which wire (14) is passed