EP0814925B1 - Process and device for the continuous production of sheet metal strips - Google Patents

Abstract

PCT No. PCT/DE96/00210 Sec. 371 Date Nov. 7, 1997 Sec. 102(e) Date Nov. 7, 1997 PCT Filed Feb. 5, 1996 PCT Pub. No. WO96/27464 PCT Pub. Date Sep. 12, 1996A mother strip with a metallically pure surface is passed through a melt bath of a metal and whereby the coating is smoothed by rolling immediately after leaving the melt bath. The mother strip, having been preheated, to a temperature clearly above ambient temperature, especially above 200 DEG C., is introduced into the metal bath. The preheating is carried out by indirect heat exchange with the melt bath in an oxygen-free environment. The melt freshly supplied to the melt bath has an increased temperature in accordance with the heat lost due to preheating.

Description

The invention relates to a method for the continuous production of band-shaped Sheets, in particular made of steel, with the features of the generic term of Claim 1 and an apparatus for performing this method.

EP 0 311 602 B1 describes a method for producing thin metal strands e.g. known from steel with thicknesses below 20 mm. This procedure uses a Metallic steel strip on the surface with room temperature (Mother band) in the vertical direction from bottom to top or vice versa by a Melted metal. The molten metal can be of the same type or also different material to the mother tape. The dwell time of the Mother tape in the molten metal is like this depending on its temperature dimensioned that a crystallization of metal crystals and an attachment of Melting takes place on the surface of the mother tape without the mother tape melts itself or the already deposited material again is melted. In this way, a band-shaped semi-finished product can be produced its thickness is about 6 to 10 times the original thickness of the mother tape corresponds. Because the solidification process is different from the usual continuous casting This does not run from the outside inwards, but in the opposite direction Form of semi-finished product also known as inversion casting.

Another method of inversion casting is known from WO-A-94 29 048, at a thin steel strip after passing through a steel melt from below above immediately after re-emerging from the melt by a Smoothing roller pair is smoothed in the surface. Following the pair of smoothing rollers the steel strip produced in this way passes through a cooling zone filled with inert gas, in of it in a controlled way to achieve improved material properties is cooled.

Finally, from JP-A-56-151163 (Patent Abstract of Japan, vol.006, no.036) Coating wire with a liquid metal is known.

Since the aim is generally in inversion casting, as much material as possible to crystallize on the mother tape, this is usually at room temperature introduced into the melt. Especially in the production of metal strips it is not different material layers (composite materials) absolutely desirable to achieve the greatest possible coating thickness. Instead of the usual production of a product with about 3 to 6 times Mother tape thicknesses are often considerably smaller in the case of composite materials Layer thicknesses desired. In principle, this could be achieved by: Contact time between the melt and the mother tape is drastically reduced. The but has the disadvantage that the bond between the crystallized material and the mother volume is often insufficient. So it doesn't come with the required Security for complete welding. To the growth rate on the Reduce the surface of the mother band and still be a good one It is possible to ensure that the crystallization is welded to the mother tape preheat the mother tape to reduce its cooling capacity and thus its To reduce crystallization potential. This procedure can in particular for the production of multi-layer materials (e.g. coated with stainless steel Carbon steel) can be used.

In principle, preheating to the desired temperature of the Realize the mother tape before entering the melt in that the A suitable preheating furnace in the form of a continuous furnace as the melt container separate unit is connected upstream. Such a furnace could use fossil fuels Energy sources (e.g. gas or oil) or with electrical energy (e.g. Induction furnace) are heated. The use of a plasma torch would also be imaginable.

Such solutions involve a relatively large additional outlay on equipment with itself, especially since the feed speeds for the mother tape are relatively high. These are usually in the range of 10-100 m / min. Add to that the Requirement that the mother tape introduced into the melt is a pure metal Must have surface. This means that in particular a preheated one Mother band must be protected from the entry of oxygen, otherwise one rapid reoxidation begins. Oxidized surface areas would be required Endanger welding with the crystallized material.

The object of the invention is to provide a method and an apparatus for the same Specify implementation with which a specific preheating of the mother band a preheating temperature well above room temperature (especially above 200 ° C) is possible without this requiring a large outlay on equipment and without the risk of reoxidation of the surface of the mother tape.

This problem is solved for a generic method with the Characteristic features of claim 1. Advantageous further developments of the method are specified in subclaims 2 to 9. A Plant according to the invention for performing this method has the features of claim 10. This can be achieved by the features of claims 11 to 18 Further design the system in an expedient manner.

The method according to the invention provides that the mother tape used in each case after creating a clean metallic surface before introducing it Melt bath heated to a temperature well above room temperature becomes. This preheating should be at least 200 ° C, preferably at least 300 and particularly preferably be at least 400 ° C. If necessary, the Preheating are also significantly higher. The warming is caused by indirect Heat exchange carried out, taking advantage of the heat of the Crystallize metal melt used. For this purpose, however, none direct contact of the melt with the mother tape instead. So reoxidation the mother tape surface is avoided, at least in the area of Heating zone an oxygen-free atmosphere. This can, for example, by the Generation of an appropriate vacuum can be maintained. In most In some cases, however, the use of a protective gas atmosphere should be more advantageous. As Inert gas, in particular argon and possibly nitrogen, are suitable. The preheated mother tape is then in a known manner by the Metal melt performed so that crystallization and entrainment of liquid Melt take place on the surface of the mother tape. By appropriate Regulation of the feed rate of the mother tape taking into account the length of the immersion distance in the molten metal and taking into account the Melt temperature can be the thickness of the coating desired Mother tape can be set. After leaving the weld pool expediently an immediate smoothing of the crystallized coating. Because of that Melting pool the amount of heat required for preheating the mother tape is withdrawn, this must be done when setting the temperature of the weld pool freshly supplied melt are taken into account. The melt temperature must therefore set higher than if the preheating in one separate upstream heating unit (e.g. continuous furnace).

The method is used with particular advantage for the coating of Mother tape made of common carbon steel. The material of the molten metal can be made from of the same material. However, the use is particularly expedient a molten metal made of a different material than that of the mother tape. In particular, the use of higher-alloy materials is recommended for this. The thickness of the mother tape used should be less than 3 mm if possible, preferably less than 2 mm and particularly preferably less than 1 mm. The thinner that material is used, the faster the heating can take place. The means that the preheating section can be kept correspondingly shorter or that a higher preheating temperature can be achieved over the same length.

A procedure is preferred in which the mother tape is passed through the molten bath from bottom to top. However, it is also possible to carry out the reverse procedure or to feed the mother tape laterally into and out of the melt bath. If the mother tape is passed from bottom to top through the melt, it must be ensured at the point at which the mother tape enters the melt that no liquid melt escapes to the outside. The passage point has the shape of a narrow gap, which is largely filled by the cross section of the mother tape. There is a clear temperature gradient near the entry zone due to the cooling effect caused by the mother tape. This area of the melt in the vicinity of the entry of the mother ligament is often referred to as the "meniscus". In order to avoid expensive measures for sealing at this point, it is advisable to set the temperature of the freshly supplied melt in such a way that, taking into account the heat emission due to the preheating of the mother tape, the melt pool has an isotherm in the vicinity of the point where the mother tape enters the melt , which lies between the liquidus temperature T _liq and the solidus temperature T _sol . Under these conditions, the seal can be easily implemented.

Figur 1

einen Längsschnitt durch ein Ausführungsbeispiel einer erfindungsgemäßen Anlage und

Figur 2

die Abkühlgeschwindigkeit von Blechen und Platten aus Stahl durch Wärmestrahlung in Abhängigkeit von Dicke und Oberflächentemperatur des Materials.

The invention is described below with reference to the drawing. Show it:

Figure 1

a longitudinal section through an embodiment of a system according to the invention and

Figure 2

the cooling rate of steel sheets and plates by heat radiation depending on the thickness and surface temperature of the material.

1 shows a possible embodiment of a system according to the invention in schematic form has been shown. The proportions, especially the Lengths in relation to the thickness of the mother tape do not correspond to the real ones Relationships.

The system consists of a melt container 9, the bottom of one Sealing device 10 is formed. Of course, the melt container 9th also be equipped with its own floor in which the sealing device 10 is installed. The sealing device 10 consists essentially of a flat Housing with an approximately cuboid interior according to the cross-sectional geometry of the mother tape to be coated 1. The broad side walls of the Sealing device 10 are designated by reference number 11. The interior of the Sealing device 10 is open from below and upwards, so that it is narrow Feedthrough channel for the mother tape 1 represents. At least the broad side walls 11 are resistant to a metal melt 14 to be used Refractory material formed. This refractory material should expediently be so be selected that it has the highest possible thermal conductivity, since the Broad side walls 11 in the sense of a heat exchanger as radiant heating surfaces should serve. In principle, it would be possible to use the broad side walls 11 To extend the entire width of the melt container 9, so that in extreme cases narrow side surfaces, along which the longitudinal edges of the mother tape 1 pass, omitted. A shielding box 6 is flanged tightly below the sealing device. This shielding box 6 has a gas connector 8 through which a Inert gas at overpressure (arrow 7) into the inside of the shielding box 6 can be initiated. So that when the inert gas is introduced, it is not unnecessarily large Leakage losses occur, is in the area of the passage gap for the mother tape 1 in advantageous development of the invention on the shield box 6 a special Sealing system provided. This can be done, for example, as shown in the left part of the Picture is shown in the form of lamellar seals 4 or, as in the right part the picture is shown, in the form of a pair of elastic sealing rollers 3 (preferably made of hard rubber). To the mother tape 1 in the Introducing molten metal 9 located molten metal 14 is the mother tape 1 via drive roller pairs 2.5 a corresponding feed movement in the vertical Direction from bottom to top granted. The molten metal 14 is over several Melt inlet connector 13, which is located near the lower part of the Sealing device 10 are located and with their outlet opening on the broad side walls 11th are directed into the melt container 9. This is through appropriate Arrows indicated. Heat through direct contact with the molten metal 14 the broad side walls 11 to a correspondingly high temperature. The means that thus the lead-through channel 12 to a heating channel for the mother tape 1 to be introduced. Due to the intense heat radiation of the Broad side walls 11 finds an extremely rapid heating of the Mother tape 1 instead. This effect can be seen from the graphical representation of the Figure 2 can be easily estimated.

Figure 2 shows the cooling rate of strip or plate-shaped semi-finished products made of steel by heat radiation depending on the surface temperature and the thickness of the objects. This graphic can also be reversed apply for a statement about the heating rate, if appropriate molded objects from room temperature by using a heat radiation source is heated to a surface temperature, as indicated in the illustration. From this it can be seen that a 1 mm thick steel band with a Radiation temperature of e.g. 1426 ° C at a speed of approx. 250 ° C / sec is heated. So if the duct and thus the heating section is a length of a = 1 m and the feed speed of the mother tape at 60 m / sec, would be until the mother tape enters the molten metal 14 can be heated to about 250 ° C when the radiation temperature the broad side walls are around 1426 ° C and the strip thickness is 1 mm. By a corresponding design of the channel length a can thus be set Influence preheating temperature. With a reduction in the thickness of the mother tape a higher temperature would occur with the same channel length a. So there would be as shown in Figure 2 at a radiation temperature of 1426 ° C and a mother tape thickness of 0.8 mm with a residence time of 1 sec in Feed-through channel 12 (corresponding to a feed speed of 60 m / sec and a channel length of 1 m) a temperature increase of about 316 ° C.

Shortly after entry into the molten metal 14, the crystallization of melt begins, which grows to form the coating provided with the reference number 16. To smooth the surface of the coated product produced, a pair of smoothing rollers 15 is expediently used immediately above the weld pool. The coated tape with a smoothed surface is designated 17. In addition to the preheating temperature, the thickness of the coating 16 that can be achieved essentially depends on the length of contact time between the mother tape 1 and the molten metal 14. The contact time in turn depends on the feed rate and the length of the immersion distance b of the mother tape 1. The meniscus already mentioned above, which forms in the entrance area of the mother tape 1 into the molten metal 14, is designated by 18. Some isotherms are indicated in the form of dashed lines. The isotherm with the liquidus temperature is identified as T _liq . In some cases, it may be expedient to make the clear width of the feed-through channel 12 narrower in the exit area of the mother tape 1 to prevent melt from escaping than in the remaining area over the channel length a. This should be at least 0.5 m. expediently at least 1 m, so that a sufficiently high preheating temperature can be achieved at a sufficiently high feed rate.

The invention makes it possible to apply thin coatings to a mother tape with a secure weld to the base material without space-consuming separate heating units must be used for this.

Rather, the preheating of the mother tape takes place in the immediate vicinity of the Entry into the molten metal through indirect heat exchange with the one used Melt instead.

Claims (18)

1. Process for the continuous production of strip-shaped metal sheets, in particular of steel, in which a starting strip (1) with a metallically pure surface is passed through a molten bath of a metal (immersion length b), wherein the speed of the starting strip (1) is regulated in accordance with the immersion length b and the temperature of the metal melt (14) to obtain a desired total thickness of a coating being deposited in the form of crystals and melt at the surface of the starting strip (1), and wherein the coating is smoothed by rolls immediately after leaving the molten bath,
   characterised in that the starting strip (1) is introduced into the molten bath having been preheated with a temperature lying above 200°C, wherein the preheating is carried out through indirect heat exchange with the molten bath (14) in an oxygen-free environment, and that the temperature of a metal melt freshly supplied to the molten bath is raised according to the heat loss for the preheating.
2. Process according to claim 1,
   characterised in that the starting sheet is passed through the molten bath from the bottom upwards.
3. Process according to one of claims 1 and 2,
   characterised in that the oxygen-free environment is created by an atmosphere of an inert gas, in particular argon or nitrogen, maintained at a slight overpressure.
4. Process according to one of claims 1 to 3,
   characterised in that the preheating is carried out to at least 300°C, in particular at least 400°C.
5. Process according to one of claims 1 to 4,
   characterised in that a material consisting of a regular carbon steel is used for the starting strip.
6. Process according to one of claims 1 to 5,
   characterised in that the metal melt of a material of the same type as the starting strip is used as the molten bath.
7. Process according to one of claims 1 to 5,
   characterised in that the metal melt of a steel material which is more highly alloyed than the material of the starting strip is used as the molten bath.
8. Process according to one of claims 1 to 7,
   characterised in that the starting strip which is used is of a thickness of less than 3 mm, preferably less than 2 mm, with a thickness of less than 1 mm being particularly preferred.
9. Process according to one of claims 1 to 8,
   characterised in that the temperature of the freshly supplied melt is set such that, taking account of the heat yield for preheating the starting strip, the molten bath exhibits an isotherm in the vicinity of the point of entry of the starting strip into the metal melt (region of the "meniscus") which lies between the liquidus temperature T_liq and the solidus temperature T_sol.
10. Plant for carrying out the process according to claim 1, with a melt vessel (9), with a sealing appliance (10) in the region of the outer wall of the melt vessel (9), through which the starting strip (1) can be introduced into the metal melt (14) or removed from the latter, with a feed appliance (drive rollers 2, 5) for the starting strip (1) and with a rolling appliance (pair of smoothing rolls 15) for smoothing the coating deposited in crystal form,
    characterised in that the sealing appliance (10) is in the form of a shallow, substantially cuboid housing which projects a long way into the metal melt (14) in the transport direction of the starting strip (1) and whose broad side walls (11), which extend parallel to the plane of the starting strip (1), consist of a refractory material and surround the starting strip (1) at a small distance as radiant heating surfaces, while forming a shallow feed-through channel, and that an appliance for maintaining an oxygen-free atmosphere is connected to the sealing appliance (10) in the region of the feed-through channel (12).
11. Plant according to claim 10,
    characterised in that the sealing appliance (10) is disposed in the bottom region of the melt vessel (9) and the conveying direction of the transport appliance (pair of drive rollers 2, 5) is directed vertically upwards.
12. Plant according to claim 10 or 11,
    characterised in that the sealing appliance (10) is formed from a refractory material with a comparatively high coefficient of thermal conductivity.
13. Plant according to claim 12,
    characterised in that the supply system for the metal melt (14) is constructed in the vicinity of the bottom of the melt vessel (9), in particular in the form of a plurality of melt inlet branches (13), the exit direction of which is directed at the lower part of the broad side walls (11).
14. Plant according to one of claims 10 to 13,
    characterised in that the appliance for maintaining an oxygen-free atmosphere is formed as an inert gas shield.
15. Plant according to claim 14,
    characterised in that the inert gas shield comprises a shielding box (6) which arches over the region of entry for the starting strip (1) at the feed-through channel (12), to which box inert gas at a slight overpressure can be supplied through a gas connection branch (8) and into which the starting strip (1) can be introduced through a slit-shaped opening.
16. Plant according to claim 15,
    characterised in that the slit-shaped opening in the shielding box (6) is sealed off towards the outside by a laminated seal (4) or a pair of elastic rollers (sealing rollers 3), in particular a pair of hard rubber rollers.
17. Plant according to one of claims 10 to 16,
    characterised in that the sealing appliance (10) projects into the metal melt (14) by at least 0.5 m, in particular at least 1 m (length a).
18. Plant according to one of claims 10 to 17,
    characterised in that the inside width in the exit region of the starting strip (1) at the feed-through channel (12) is narrower than in the remaining region over the length a of the feed-through channel (12) in order to prevent the exit of melt.

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