|Title of Invention||
METHOD AND DEVICE FOR PRODUCING HOT METALLIC STRIP, IN PARTICULAR FROM LIGHTWEIGHT STRUCTURAL STEEL
|Abstract||The object of the invention is to improve the quality of cast hot strips. The object is achieved in terms of the method by a method for producing hot metallic strips in particular of lightweight structural steel, wherein a melt is charged in the presence of inert gas by means of a runner onto a circulating casting belt of a horizontal strip casting facility, solidifies to form a pre-strip with a thickness of between 6 and 20 mm and, after thorough solidification, the pre-strip undergoes a hot rolling process. The invention is characterized in that the heat transfer and the contact (surface area, time) between the strand solidified to form a pre-strip and the casting belt is reduced, and by a device for carrying out the method.|
Method And Device For Producing Hot Metallic Strip, In Particular From Lightweight Structural Steel
The invention relates to a method of producing hot metallic strips, in particular of lightweight structural steel according to the preamble of claim 1, and to a device according to the preamble of claim 7.
A device of a type involved here for producing hot metallic strips of lightweight structural steel is known (steel research 74 (2003), No. 11/12, page 724-731).
Melt is fed in the known method from a feed vessel via a runner onto a circulating casting belt of a horizontal strip casting facility. The fed melt solidifies when undergoing intense cooling to form a pre-strip with a thickness in the range between 6-20 mm. After thorough solidification, the pre-strip undergoes a hot rolling process.
During solidification, material stress causes warpage of the pre-strip, adversely affecting the quality of the hot strip. In particular, some steels experience on their strand underside irregular and large-area contractions as a result of rapid cooling.
Furthermore, there is the possibility of an excessive friction between the casting belt and the solidifying strand, causing an excessive deviation in the synchronous speed between casting belt and rolling speed, so that the strand tears off in the worst case scenario.
This problem of adjustment of the synchronous speeds is always relevant when in-line casting and rolling is involved.
It is an object of the invention to provide a method and a device for producing hot metallic strips, in particular of lightweight steel, obviating the afore-stated problems.
Based on the preamble, this object is solved in combination with the characterizing features of claim 1. Advantageous improvements as well as an apparatus for producing hot strips are the subject matter of the other claims.
According to the teaching of the invention, the heat transfer as well as the contact (surface area, time) between the strand solidified to a pre-strip and the casting belt is reduced. There are various ways to achieve this, with each single measure being effective by itself or also in combination.
The method according to the invention is basically suitable for the production of hot strips of various metallic materials, in particular also for lightweight structural steel.
A first proposal aims to reduce the contact time between casting belt and solidifying strand. This is realized by causing the casting belt to locally vibrate with the aid of an electromagnetic system. This involves the arrangement of an electromagnetic system which function like a loudspeaker, below the casting belt. It is crucial for proper operation to install the system at a site where a solid strand shell has already been formed.
A further proposal is directed to the reduction of the heat transfer. This involves charging a gas, in particular a mixed gas of inert and reducing gas, in the charging zone of the melt between runner and casting belt. The reducing gas is preferably hydrogen.
Gas acts advantageously across the entire width of the casting belt. The gas volume flow is slight and resembles more a blanketing. When the volume flow is
excessive, the planar formation of the strand's underside would be adversely affected. The applied mixed gas provides for the strand to have an underside surface which is substantially scale-free. A blank surface means less heat radiation so that the heat transfer is significantly reduced between the solidifying band and the casting belt.
A third proposal involves a structuring of the casting belt and has also proven to be very effective. Longitudinal embossments are advantageously impressed in the casting direction. As an alternative, nubs may be arranged in spaced-apart relationship across the casting belt. The application of longitudinal embossments has the advantage of a fairly simple production by drawing a smooth band through the profiled pair of rolls.
It is ensured that any kind of structuring of the casting belt leads to a decrease of the heat transfer between the solidifying strand and the casting belt. The reproduction of the embossments by the melt causes, as a result of shrinkage during solidification, a local detachment of the casting shell and accompanying reduction of the contact surface. This means a decrease in the heat transfer and friction between stand and casting belt and this can be exploited to enhance the process reliability in in-line manufacturing of casting and rolling.
The casting speed should ideally be in synchronism with the rolling speed in in-line manufacturing. In reality however, there are oftentimes deviations which must not be excessive as the pre-strip would otherwise tear off. Deviations of the synchronous speed of > 0.5 m/s for example are considered problematic. If such deviations cannot be controlled, a buffer, also called looper, must be installed interiorly of the roll stand.
The method according to the invention will now be described in greater detail with reference to a drawing, in which:
Figure 1a shows a frontal view of the structure of the casting belt in accordance with the invention,
Figure lb a cross section in the direction A - A in Figure 1a,
Figure 2 shows a length section of the arrangement according to the invention of an electromagnetic system,
Figure 3 shows a length section of the blanketing of the strand's underside,
Figure 4 shows a top view of Figure 3.
Figure la shows a frontal view of a structure of the casting belt 1 in accordance with the invention. The trailing deflection pulley 2, as viewed in transport direction, can be seen as well as the casting belt 1 placed thereupon and advancing in arrow direction 3. Illustrated are the conjointly moving side boundaries 4, 4' on the top side.
Rolled into the casting belt 1 are embossments 5 arranged in length direction. The cutaway illustration Figure lb provides easy depiction of a detail of the cross section in direction A -A in Figure la.
Figure 2 shows a second proposal for reducing the heat transfer, with the illustration depicting a length section of the charging zone of a horizontal strip casting facility. The facility includes as main element a melting vessel 6, an inlet 7 with attached runner 8. Melt 9 contained in the melting vessel 6 exits the runner 8 and is fed onto a circulating casting belt 1.
To excite local vibrations of the casting belt 1, an electromagnetic system 10 is arranged beneath the casting belt 1. It operates in accordance with the principle of a loudspeaker and causes the casting belt 1 to vibrate. This results in a
shortening of the contact tines of the solidifying melt with the casting belt 1. The excitation of vibrations is possible only when the melt bath has formed a sufficiently solid casting shell on the underside. The electromagnetic system 10 must therefore be arranged further away from the charging zone.
A third proposal for solution shows Figure 3, in which a same length section is shown of a strip casting facility like in Figure 2 so that same reference signs are used for same parts.
The third proposal for solution is characterized by a blanketing with a mixed gas before melt 9 is charged onto the casting belt 1. For that purpose, a hollow body 12 is arranged beneath the runner 8 and above the leading deflection pulley 11. A brush 13 is placed in front of the hollow body 12 for sealing and better distribution across the width of the casting belt 1.
The hollow body 12 is connected to a feed conduit 14 (Figure 4) for supply of gas. After starting the gas supply, the mixed gas exits the hollow body 12 and flows along the gap between casting belt 1 and underside runner 8 directly to the charging zone. As a result, the casting shell that initially solidifies is prevented from scaling. It remains substantially blank.
List of Reference Signs
1 Casting belt
2 Trailing deflection pulley
3 Rotation direction
4,4' Side boundary
5 Longitudinal embossment
6 Melting vessel
10 Electromagnetic system
11 Leading deflection pulley
12 Hollow body
14 Feed conduit
1. Method of producing hot metallic strips in particular of lightweight structural
steel, wherein a melt is charged by means of a runner onto a circulating
casting belt of a horizontal strip casting facility in the presence of inert gas,
solidifies to form a pre-strip with a thickness between 6 to 20 mm, and after
thorough solidification the pre-strip undergoes a hot rolling process,
that the casting belt is caused to locally vibrate, with the heat transfer as well as the contact (surface area, time) between the strand solidifying to form a pre-strip and the casting belt is reduced.
2. Method according to claim 1,
that the casting belt is excited electromagnetically.
3. Method according to claim 1-2,
that a gas Is fed between runner and casting belt before charging the melt.
4. Method according to claim 3,
that the gas is a mixed gas of an inert gas as carrier and a reducing gas.
5. Method according to claim 4,
that the reducing gas is hydrogen.
6. Device for producing hot metallic strips, in particular of lightweight structural
steel, according to the method of claims 1-6, comprising a feed vessel which
contains the melt and has a horizontal runner, a primary cooling zone which
is comprised of two deflection pulleys and a circulating cooled casting belt
and is followed by a secondary cooling zone which is comprised of an
enclosed roller table and is followed by a first roll stand,
that the casting belt (1) is provided with a structure and that an
apparatus (10) is arranged beneath the casting belt (1) to excite vibrations.
7. Device according to claim 6,
that the structure has embossments (5) extending in length direction.
8. Device according to claim 6,
that the structure has nubs distributed across the surface.
9. Device according to claim 8,
that the apparatus is an electromagnetic apparatus.
10. Device according to claim 9,
that the electromagnetic apparatus is installed at a site in the region of the already solid casting shell.
11. Device according to claim 6,
that a hollow body (12) is arranged in the region of the leading defection pulley (11) of the strip casting facility beneath the runner (8) transversely to the casting belt (1) and has a broad slit, for connection with a gas feed line (14).
12. Device according to claim 11,
that the hollow body (12) extends across the entire width of the casting belt(1).
13. Device according to claim 11 and 12,
that there is a seal which is arranged beneath the discharge zone of the hollow body (12) and which is connected with the hollow body (12) and rests upon the casting belt (1).
14. Device according to claim 13,
that the seal is a brush (13).
|Indian Patent Application Number||3856/CHENP/2008|
|PG Journal Number||48/2013|
|Date of Filing||23-Jul-2008|
|Name of Patentee||SALZGITTER FLACHSTAHL GMBH|
|Applicant Address||EISENHUTTENSTRASSE 99, 38239 SALZGITTER|
|PCT International Classification Number||B22D11/06|
|PCT International Application Number||PCT/DE06/02082|
|PCT International Filing date||2006-11-22|