DE10035097A1 - Immersion heating element used for changing, maintaining and/or comparing the bath temperature of a molten metal comprises an inner inductor arranged in a refractory casing having a flat cross-section and closed on its base - Google Patents

Abstract

Immersion heating element comprises an inner inductor (4) arranged in a refractory casing (31) having a flat cross-section and closed on its base. The casing can be inductively coupled. An Independent claim is also included for a process for the production of the heating element comprising packing or molding an inner inductor into an electrical and/or thermal insulation (33), and using as core after isostatically pressing the casing. Preferred Features: The casing has a rectangular, oval or spectacle-like. The casing has an outer structure. The outer surface of the casing has guiding ribs and/or protrusions or grooves. The inductor is formed by a hollow inductor spiral.

Description

The invention relates to an immersion heater for modification (Heating and cooling) and / or compliance and / or Equalization of the bath temperature of a liquid or Melt, especially a molten metal, such as liquid steel, with a fluid-cooled one, for example air-cooled internal inductor, which is in a bottom side closed refractory jacket is used, which for Heating can be coupled inductively at least in some areas.

Such an immersion heater is not pre-published in the Chen older German patent application 499 00 915.5 be wrote. There is a method and an apparatus for Setting and / or maintaining the temperature of a molten steel during continuous casting using a dipped in the melt refractory tubular molding, which is an internal one Induction coil (coil) interchangeably, proposed. The induction coil is fluid-cooled, for example air-cooled cools. To heat the melt, the melt becomes heat transferred by heat conduction from the wall of the molded part, which in turn is due to the induced electromagnetic change field of the induction coil.

When casting steel continuously, it is due to quality reasons Stranges required the liquid steel in a pre given the narrowest possible temperature range from a tundish to cut into the mold. For this, the liquid steel in the Tundish over a long period of time at a temperature level being held. Apart from that, the specified temperature  as evenly as possible in the entire melt pool be set and maintained. To solve the latter The above-mentioned older patent application is problematic not specified.

DE 197 52 548 A1 relates to a method for setting and Keeping the temperature, especially a molten steel, in narrow temperature limits over the casting time during continuous casting, the drop in temperature being compensated for by heating becomes. The process is improved in that the Temperature of the melt at the outlet of the distribution vessel measured, the measurement result with the given lower Temperature limit compared and the melt when reached or the temperature falls below the limit until the temperature is again within the setpoint range. This also involves heating the melt through a mentioned inductive heating device without the necessary means or a corresponding one Device are described.

To influence the temperature of such a molten bath the transfer of large amounts of heat is required. Basically, inductively heated refractories are suitable for this Components with a large surface for heat exchange. For inductive heating of a channel-shaped, i.e. H. in the essential rectangular refractory molding is according to DE 195 26 976 A1 a helical inner inductor suggested that after heating again from the interior the molded part is removed. This is heating the molded part as such, but not his Use to heat a melt.

Based on the aforementioned prior art, the Invention based on the object, an immersion heater slam that the largest possible heat transfer area  has to the efficiency when heating respectively Cool the liquid or melt to improve it. Furthermore, it is an object of the invention to provide an immersion heating element to design and / or use so that in its Temperature controlled liquid or melt bath temperature profile as uniform as possible in one given narrow temperature range at least at the racking opening of the liquid or melt containing Vessel. Finally, it is the object of the invention safe pouring of the liquid or melt, especially a molten metal from a tundish allow even if the temperature of the melt only is a few Kelvin above liquidus.

To solve the problems with the invention a diving zelement suggested whose refractory jacket a has flat cross section. "Flat" should be in this Zu context is called "appreciably longer than wide". Despite his it has a relatively compact design Immersion heating element has a large surface area as heat transfer area with the z. B. molten bath. Because the heat transfer is mainly done by means of heat conduction, the large one offers Heat transfer surface decisive advantages. The narrow, stiff profile of a z. B. rectangular immersion heater enables a thin-walled construction, which consists of energetic Reasons is advantageous.

The surface and thus the heat exchange surface of the Immersion heating element can advantageously be by means of a oval and in particular by means of an eyeglass-shaped Increase cross-section and, if necessary, continue by means of a suitable structuring of the immersed Surface. For an additional increase in heat The transition surface of the immersion heating element is the upper shell if necessary with a surface structure for  Example in the form of guide ribs and / or guide grooves Mistake.

If these guide elements are at an angle to the longitudinal axis of the immersion heater element are arranged, the contact of the incoming Medium intensifies and with it the heat transfer.

For the most uniform possible temperature application of the Immersion heater elements are flat, in only one level wound or looped internal inductors have proven their worth. Such For example, inductors are so-called pan cake inductors ren, which consist of a rectangular wound metal hollow profile, mostly made of copper. These inductors are characterized by high electrical efficiency.

The construction of inductor loops made of is particularly simple consist of a U-shaped metal tube.

An advantageous combination is approximately in cross section glasses-shaped fireproof coat with a U-shaped Inductor loop, the legs of which are approximately centered in the Cross-sectional enlargements of the jacket extend by one uniform heating or cooling of the jacket possible. The legs protrude above the bath level the coat so that it’s easy to connect to the electrical power source and air cooling can.

An uncomplicated and safe handling in operation enables an inductor firmly connected to the jacket as Unit.

The easiest way to do this is to use the immersion heater as a structural unit Forming a sufficiently stable inductor at the Manufacture of the jacket made. The inductor can be used in the  Coat pressed in, cast in by means of a refractory mass or mortar.

It is advantageous if the refractory material an electrical and / or between jacket and inductor Thermal insulation is, on the one hand, to short circuits prevent and on the other hand the inductor before the radiation to protect the heat of the jacket. The coat itself can also have an inner insulating wall layer.

If the coat is pressed isostatically, it makes sense as the core required in this pressing process as Prefabricated component in an electrical and / or to use thermal insulator wrapped inductor.

Especially with very wide immersion heating elements Insulation as a prefabricated shell is an advantage. If they are out two half shells is made, the inductor can be between these may be used in a form-fitting manner. The Half shells, which absorb the hydrostatic pressure of the Liquid or melt inside stiffening or Support profiles can also serve for Guiding or stabilizing the inductor turns.

The sealing together, for example cemented Half shells with the built-in inductor can then be detached be firmly inserted into the jacket of the immersion heating element.

When using an immersion heating element according to the invention for the desired setting of the temperature of the bath Liquid or a melt such as one Melting steel in a tundish, for example, will Immersion heater immersed as deep as possible in the bathroom and more or less to the flow of the liquid or Melt turned on. This flow arises when tapping  the liquid or melt by itself. The one with electrical energy through the air-cooled inductor loaded jacket is inductively heated and transferred its thermal energy by means of essentially heat conduction the steel flowing around it, for example. The through that Different flow caused by the jacket paths intensify the heat exchange. The same effect has an inclination of the immersion heating element in the bathroom against the Vertical.

The advantages described above also apply to one desired lowering of the bath temperature, if that Immersion heating element or several immersion heating elements in the Immersed liquid or melt and optionally for Flow of the melt at an angle and / or at an angle to the vertical is or will be employed. In this case the electricity Supply of the inductor turned off but the air cooling more or less. The colder coat then cools the liquid or melt flowing around it.

The immersion heater according to the invention has particular advantages ement and its use to set a predetermined Steel bath temperature in a tundish for uniformity the bath temperature, which is usually both horizontal as differentiated in the vertical direction. By the suggestion ne micro and / or macro outer structure of the shell, which for Example projections and / or directed on its outside Has ribs and / or grooves, the steel melt when flowing against the jacket both horizontally and vertically be distracted, so that a mixing effect occurs that leads to a more even bath temperature. This Mixing effect can be done by turning on the immersion heater at an angle to the flow of the melt and / or at an angle to Verticals are reinforced.  

If several immersion heating elements are used, these can coexist other and / or successively offset across the flow direction of the melt are arranged, whereby the ange sought mixed effect is amplified.

Further goals, features, advantages and possible applications the invention result from the following description of exemplary embodiments with reference to the drawing. In doing so all described and / or illustrated features for itself or in any combination the subject of Invention, regardless of its summary in individual claims or their relationship.

Show it

Fig. 1 is a perspective view of a tundish ementen with the arrangement of this invention Tauchheizel,

Fig. 2 shows an inventive immersion heater with an average of about brillenförmigem coat and a U-shaped inductor in plan view,

View Fig. 3, the immersion heater according to FIG. 2 in pages,

FIGS. 4a to 4d schematically a wound in a plane inductor (Pfannenkucheninduktor) and its of order in an insulator and in a right-corner-shaped casing,

Fig. 5 shows a monoblock plug of a stopper rod closure as immersion heater, and

Fig. 6 shows a rotor or stator of a Stopfendrehver circuit as an immersion heater.

According to Fig. 1 comprises a tundish 1 in the vicinity of its one short side 11 in a Tundishdeckel 13 an inlet opening 12 for liquid steel 2, which is tapped from a superimposed controlled to parent not shown pan so that in the tundish 1, a steel bath 21 sets 22 of certain bath height. In a tundish floor 14 , a tap opening 16 is provided near the narrow side 15 opposite the first narrow side 11 , through which liquid steel 2 flows into a mold, not shown, arranged below, where it solidifies and is drawn off as a strand (not shown). Even the steel 2 flowing into the tundish 1 can have different temperatures due to the process. In addition, there is a cooling of the steel 2 in the tundish 1 as a result of heat losses through the tundish walls 17 , the tundish cover 13 and the tundish base 14 , which are inevitable despite good insulation. In addition, the temperature of the steel bath 21 is not homogeneous. The consequence of this can be a reduction in the quality of the strand.

If the steel temperature does not comply with a certain setpoint range, quality losses can also be expected. If the liquid steel 2 cools down too much, it freezes in the tap opening 16 and interrupts the continuous casting. On the other hand, overheating of the liquid steel 2 is not least undesirable for energy reasons. For certain types of steel, however, it is advisable to cast as close as possible to the liquidus temperature of the steel type.

The arrangement and operation of immersion heating elements 3 according to the invention, which are preferably provided in the flow direction upstream of the tap opening 16 , as shown in the example of FIG. 1, enables the steel bath 21 to be kept in a certain temperature range. It is possible to compensate for temperature differences in the steel bath, so that the temperature of the liquid steel 2 in the inlet of the tap opening can be reduced by 16 to 6 Kelvin and less above the liquidus temperature without the steel freezing.

In order to regulate the temperature of the steel bath 21 , it is necessary that large amounts of heat are transferred from the immersion heating elements 3 to the liquid steel. For this purpose immersion heating elements 3 with large heat exchanger surfaces are used, which have an essentially elongated rectangular cross section.

Such an immersion heating element 3 is shown in FIGS . 2 and 3. The elongated, fireproof jacket 31 of the immersion heating element 3 , which projects over the steel bath 21 in use and possibly reaches the tundish floor 14 , has a large surface area with its approximately spectacle-shaped cross section. The jacket 31 has a closed bottom 32 at its end to be immersed and it is open at its opposite end, which projects over the steel bath 21 . An inner inductor 4 , in this case a simple U-shaped metal tube (inductor loop 42 ), which is generally made of copper, is firmly connected to the jacket 31 . The legs 43 of the inductor loop 42 run approximately centrally in the spectacle-shaped extensions of the refractory jacket 31 , as a result of which the jacket 31 is uniformly heated or cooled inductively. In the closed bottom 32 of the jacket 31 , which can be flat or rounded, the two legs 43 are connected to each other, for example by means of a U-shaped crossbar 44 . At their free ends, the legs 43 protrude from the jacket 31 so that they can be provided with the electrical connections, not shown, and the connections for air cooling, which are marked with 48 (supply air) and 49 (exhaust air).

Between the jacket 31 and the inductor loop 42 , thermal insulation resistant to high temperatures 33 is provided in order to protect the inductor loop 42 from the heat radiation from the heated jacket 31 . The insulation 33 likewise has the properties of an electrical insulator in order to exclude short circuits between the inductor loop 42 and the electrically conductive jacket 31 .

To prepare the immersion heater 3 by a fixed connection of the refractory shell 31 with the inductor 4, the inductor 4 is used in the pre-made, for example, isostatically pressed and subsequently annealed casing 31 and provided with a suitable refractory insulation 33, shed, for example, mortared or pressed. In this way, the inductor 4 is festge in the jacket 31 .

In FIGS. 4a to 4d, another embodiment is a rectangular dip heating element 3 is shown having a wound in a plane Pfannenkucheninduktor 41st This design also enables use in the flat, approximately rectangular, refractory jacket 31 . The required insulation 33 consists of two prefabricated, for example pressed and fired, half-shells 35 made of a suitable temperature-resistant material, into which the inductor 4 is inserted, after which they are joined to form a tight shell 34 . A cemented tongue and groove connection has proven itself.

Already during production 35 stiffening ribs 36 are formed on the inside of the half-shells, onto which at least some of the inductor turns 45 are pushed during installation. The stiffening ribs 36 not only stabilize the inductor 4 , but also the walls of the insulation 33 . The adjoining stiffening ribs 36 also absorb the external pressure which is exerted on the walls of the insulation 33 via the jacket 31 due to the ferrostatic pressure of the melt. In the installed state, the shell 34 of the insulation 33 is detachably connected to the jacket 31 .

In order to adjust the temperature of the steel bath 21 in the tundish 1 in front of the tap opening 16 to a predetermined temperature window and to make it uniform, the following procedure is followed: in the tundish 1 , a plurality of immersion heating elements 3 , in the exemplary embodiment of FIG. 1 two immersion heating elements 3 , are transversely aligned installed in front of the tap opening 16 or immersed in the steel bath after filling the tundish 1 with liquid steel 2 . The rectangular, elliptical or spectacle-shaped immersion heating elements 3 are positioned at an angle to the steel flow S in the tundish 1 , which is formed from the area of the inlet opening 12 to the area of the tap opening 16 . The immersion heating elements 3 can be staggered in depth, with an immersion heating element 3 in the middle and to the left and right of it in the flow direction behind and laterally offset, in each case a further immersion heating element 3 . In order to deflect the steel flow S laterally as far as possible, the immersion heating elements 3 are arranged to overlap.

The fireproof jacket 31 of the immersion heating elements 3 is heated inductively when the steel temperature of the steel bath 21 drops below a predetermined value. If the temperature is too high, for example when pouring a new pan, the electrical energy of the immersion heating elements 3 is switched off, but not the air cooling of the inductors 4 . It can be reinforced by external cooling, for example by cooling channels in the jacket 31 or in the insulation 33 . However, the cooling channels can also be provided in the boundary layer between the jacket 31 and the insulation 33 as a groove in the jacket and / or the insulation, which are then closed on the longitudinal side when the insulation is inserted into the jacket 31 . Depending on the prevailing temperature distribution in front of the immersion heating elements 3 , the flow can be deflected from the inside out or from the outside in to compensate for different temperatures and / or temperature losses. For a better efficiency of the heat transfer, the surface of the refractory jacket 31 can be provided with an outer structure 37 . The effective heat exchanger area is further increased by guide ribs or guide projections 38 or also by guide grooves 39 on or in the jacket 31 . This outer structure 37 or guide elements 38 , 39 can have the additional function of deflecting the steel flow S in the vertical direction in order to compensate for temperature differences in the depth of the steel bath 21 . For this purpose, they are arranged at an angle to the bathroom mirror on or in the jacket 31 .

The same and / or a supporting effect has an immersion heating element 3 inclined against the steel flow.

By means of the measures mentioned, immersion heating elements 3 according to the invention allow a predetermined temperature range in the steel bath 21 to be set uniformly, at least before the tapping, colder strands of the steel, for example in the region of the tundish base 14 , can be compensated, so that there are no steel and / or alumina approaches in the region of the tap opening 16 or the monoblock stopper 51 above it, where appropriate a stopper rod closure 5 comes. Overall, the temperature of the steel bath 21 in the tundish 1 can be lowered very low, since it is difficult to freeze the liquid steel in the tapping area.

When the mono-block stopper 51 of a known stopper rod shutter 5 (Fig. 5) or the standing within the steel bath 21 rotor 61 and stator 62 of a per se known rotary plug closure 6 (Fig. 6) equipped with an air-cooled helical interior inductor 4, as Tauchheizel ement 3 alone or better in combination with other, described immersion heating elements 3 , the efficiency of the temperature control is particularly great, since the steel temperature can be influenced directly in the outlet area of the tap opening 16 .

LIST OF REFERENCE NUMBERS

1

tundish

11

first narrow side of the tundish

12

inlet opening

13

Tundishdeckel

14

Tundishboden

15

second narrow side of the tundish

16

tapping opening

17

Tundishwände

2

molten steel

21

Stahlbad

22

Stahlbadhöhe

3

immersion heater

31

fireproof coat

32

Bottom of the refractory jacket

33

insulation

34

Bowl

35

Half shell of the insulation

36

Stiffening rib / support projections

37

Outside structure

38

Guide rib, guide ledge

39

Leitauskehlung

4

interior inductor

41

Induktorspirale

42

inductor

43

Leg of the inductor loop

44

Cross bar of the inductor loop

45

inductor windings

46

groove

47

feather

48

supply air

49

exhaust

5

Stopper rod closure

51

Monoblock stoppers

6

Rotary plug closure

61

rotor

62

stator
S flow of molten steel

Claims (22)

1. Immersion heating element for changing (heating or cooling) and / or maintaining and / or equalizing the bath temperature of a liquid or melt, in particular a molten metal, such as molten steel ( 2 ), with a fluid-cooled, for example air-cooled inner ductor ( 4 ) in a fire-proof jacket ( 31 ) closed at the bottom, which can be coupled inductively at least in some areas, characterized in that the jacket ( 31 ) has a flat cross section. 2. immersion heating element according to claim 1, characterized in that the jacket ( 31 ) has an approximately rectangular or oval or glasses-shaped cross section. 3. immersion heating element according to claim 1 or the preamble of claim 1, characterized in that the jacket ( 31 ) has an outer structure ( 37 ). 4. immersion heating element according to claim 3, characterized in that the outer surface of the jacket ( 31 ) has guide ribs or guide projections ( 38 ) and / or guide grooves ( 39 ). 5. immersion heating element according to claims 2 and 3, characterized in that the outer structure ( 37 ) and / or the guide ribs or guide projections ( 38 ) or the guide grooves ( 39 ) of the jacket ( 31 ) extend obliquely to its longitudinal axis. 6. immersion heating element according to the preceding claims, characterized in that the internal inductor ( 4 ) is wound or ground in or approximately in one plane. 7. immersion heating element according to claim 6, characterized in that the inner inductor ( 4 ) is formed by a hollow inductor spiral ( 41 ) (pan cake inductor). 8. immersion heating element according to claim 6, characterized in that the internal inductor ( 4 ) by a z. B. U-shaped inductor loop ( 42 ) is formed. 9. immersion heating element with an approximately eyeglass-shaped jacket ( 31 ) and an inductor loop ( 42 ) according to one of the preceding claims, characterized in that the legs ( 43 ) of an inductor loop ( 42 ) approximately centrally in the region of the cross-sectional enlargements of the jacket ( 31 ) extend that the legs ( 43 ) are connected in the area of the closed bottom ( 32 ) of the jacket ( 31 ) by means of a crossbar ( 44 ) and project beyond the jacket ( 31 ) at their other end. 10. immersion heating element according to claims 1 to 9, characterized in that the internal inductor ( 4 ) with the jacket ( 31 ) is fixedly connected. 11. immersion heating element according to claims 1 to 9, characterized in that the internal inductor ( 4 ) with the jacket ( 31 ) is positively releasably connected. 12. immersion heating element according to claim 10, characterized in that the internal inductor ( 4 ) in the jacket ( 31 ) is molded, for example pressed, poured or mortar. 13. immersion heating element according to claims 10 and 12, characterized in that the internal inductor ( 4 ) in an electrical and / or thermal insulation ( 33 ) is molded or wrapped and molded in the jacket ( 31 ). 14. A method for producing an immersion heating element ( 3 ) according to claim 13, characterized in that the internal inductor ( 4 ) in an electrical and / or thermal insulation ( 33 ) packed or molded and after solidification of the insulation ( 33 ) as a core for pressing , for example for isostatic pressing, of the jacket ( 31 ) is used. 15. immersion heating element according to one of claims 1 to 13, characterized in that the inner inductor ( 4 ) is packed in an electrically and / or thermally insulating shell ( 34 ). 16. immersion heating element according to claim 15, characterized in that the shell ( 34 ) consists of two half-shells ( 35 ) and the inner inductor ( 4 ) is inserted between them in a form-fitting manner. 17. immersion heating element according to claim 16, characterized in that the half-shells ( 35 ) for guiding and holding inductor windings ( 45 ) and for receiving the hydrostatic pressure on the inside have stiffening ribs and / or support projections ( 36 ). 18. Use of an immersion heating element ( 3 ) or more immersion heating elements ( 3 ) according to one of the preceding claims to increase and / or maintain and / or equalize the bath temperature of a liquid or melt, for example of liquid steel ( 2 ), in a vessel, for Example in a tundish ( 1 ), characterized in that the immersion heating element ( 3 ) or the plurality of immersion heating elements ( 3 ) is or are immersed in the liquid or melt, the immersion heating element or the immersion heating elements ( 3 ) being transverse or at an angle the flow (S) of the liquid or melt and / or obliquely to the vertical in the vessel, e.g. B. Tundish ( 1 ), is or will be, and that the jacket ( 31 ) of the immersion heating element ( 3 ) or the immersion heating elements ( 3 ) is heated inductively. 19. Use of an immersion heating element ( 3 ) or more immersion heating elements ( 3 ) according to one of claims 1 to 17 for lowering and / or maintaining and / or equalizing the bath temperature of a liquid or melt, for example of liquid steel ( 2 ), in a vessel , for example in a tundish ( 1 ), characterized in that the immersion heating element ( 3 ) or the plurality of immersion heating elements ( 3 ) is or are immersed in the liquid or melt, the immersion heating element or the immersion heating elements ( 3 ) being transverse or at an angle to the flow (S) of the liquid or melt and / or obliquely to the vertical in the tundish ( 1 ), and that the internal inductor ( 4 ) of the immersion heating element ( 3 ) or some or all of the immersion heating elements ( 3 ) is reduced or switched off heating power is cooled further. 20. Use of an immersion heating element ( 3 ) according to one of the preceding claims, characterized in that the jacket ( 31 ) has an outer structure ( 37 ) and / or guide ribs and / or guide projections ( 38 ) and / or guide grooves ( 39 ) such that a part of the jacket ( 21 ) of flowing and flowing liquid or melt, for example liquid steel ( 2 ), is deflected in the vertical direction. 21. Use of a plurality of immersion heating elements ( 3 ) according to one of the preceding claims, characterized in that the immersion heating elements ( 3 ) in the bath in the direction of the flow (S) of the liquid or melt, for example liquid steel ( 2 ), in such a manner, if appropriate overlapping jacket surfaces are optionally arranged offset that part of the flowing or flowing liquid or melt, for example liquid steel ( 2 ), is deflected in the horizontal direction. 22. Use of an inductively connectable monobloc stopper ( 51 ) of a known stopper rod closure ( 5 ) or an inductively connectable rotor ( 61 ) or stator ( 62 ) of a known stopper closure ( 6 ) with a fluid-cooled, e.g. B. air-cooled internal inductor ( 4 ) as immersion heating element ( 3 ), in particular according to one of the preceding claims, characterized in that the immersion heating element (s) ( 3 ) in a bath in the direction of the flow (S) of the liquid or the melt , for example liquid steel ( 2 ), are arranged offset with overlapping lateral surfaces.