U.S. patent application number 13/266042 was filed with the patent office on 2012-02-23 for process and apparatus for the continuous casting of a slab.
This patent application is currently assigned to SMS SIEMAG AKTIENGESELLSCHAFT. Invention is credited to Christian Bilgen, Tilmann Bocher, Christian Klinkenberg, Luc Neumann.
Application Number | 20120043049 13/266042 |
Document ID | / |
Family ID | 42238664 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120043049 |
Kind Code |
A1 |
Klinkenberg; Christian ; et
al. |
February 23, 2012 |
PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF A SLAB
Abstract
The invention relates to a process for the continuous casting of
a slab (1), in particular of steel, wherein the cast slab (1) is
conveyed through a furnace (2) and the slab (1) is subjected to a
descaling operation. To increase the quality of the slab by
reducing scale, the invention provides for the slab surface to
undergo reduction in at least one section (3) of the furnace (2) as
a result of an atmosphere consisting of an inert gas and hydrogen
(H.sub.2) or of pure hydrogen being maintained in said section (3)
of the furnace (2). The invention further relates to an apparatus
for the continuous casting of a slab.
Inventors: |
Klinkenberg; Christian;
(Herdecke, DE) ; Bilgen; Christian; (Dusseldorf,
DE) ; Bocher; Tilmann; (Dusseldorf, DE) ;
Neumann; Luc; (Dusseldorf, DE) |
Assignee: |
SMS SIEMAG
AKTIENGESELLSCHAFT
Dusseldorf
DE
|
Family ID: |
42238664 |
Appl. No.: |
13/266042 |
Filed: |
April 19, 2010 |
PCT Filed: |
April 19, 2010 |
PCT NO: |
PCT/EP2010/002369 |
371 Date: |
October 24, 2011 |
Current U.S.
Class: |
164/471 ;
164/253; 164/474; 164/507 |
Current CPC
Class: |
F27B 9/047 20130101;
B22D 11/04 20130101; B21B 1/46 20130101; B21B 2045/006 20130101;
C21D 9/0056 20130101; B22D 11/14 20130101 |
Class at
Publication: |
164/471 ;
164/474; 164/253; 164/507 |
International
Class: |
B22D 11/12 20060101
B22D011/12; B22D 27/15 20060101 B22D027/15; B22D 11/14 20060101
B22D011/14; B22D 11/00 20060101 B22D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2009 |
DE |
10 2009 018 683.2 |
Claims
1-17. (canceled)
18. A method for continuous casting of a slab, comprising the steps
of: conveying a cast slab through a furnace in a conveying
direction; subjecting the slab to a descaling operation; subjecting
a surface of the slab to a reduction in at least in one section of
the furnace by maintaining in the section of the furnace an
atmosphere which consists of an inert gas and hydrogen (H.sub.2) or
of pure hydrogen (H.sub.2); and, subjecting the slab surface to
oxidation in a section of the furnace in front of and/or behind, in
the conveying direction, the at least one section of the furnace
with reducing atmosphere.
19. The method according to claim 18, wherein the reducing
atmosphere has a proportion of hydrogen (H.sub.2) between 3% and
99.5%.
20. The method according to claim 19, wherein the proportion of
hydrogen (H.sub.s) is between 5% and 50%.
21. The method according to claim 18, wherein the inert gas is
nitrogen (N.sub.2).
22. The method according to claim 18, wherein the inert gas is
argon (Ar).
23. The method according to claim 18, wherein the section of the
furnace with oxidizing atmosphere contains oxygen (O.sub.2) at
least partially.
24. The method according to claim 18, including heating the slab in
the furnace takes place by induction.
25. The method according to claim 18, wherein the continuous
casting takes place as a casting/rolling process.
26. The method according to claim 18, including heating the slab
following a casting process and in front of a rolling process in
the conveying direction.
27. The method according to claim 18, including conveying the slab
continuously.
28. An apparatus for continuously casting a slab, comprising: a
furnace through which the slab can be conveyed; descaling means for
descaling the slab surface, wherein the furnace has at least two
sections; means provided in at least one of the sections of the
furnace for maintaining a reducing atmosphere; and means provided
in at least another of the sections of the furnace for maintaining
an oxidizing atmosphere.
29. The apparatus according to claim 28, wherein the means for
maintaining a reducing atmosphere includes at least one supply line
for hydrogen (H.sub.2).
30. The apparatus according to claim 29, wherein the means for
maintaining a reducing atmosphere additionally includes at least
one supply line for an inert gas.
31. The apparatus according to claim 28, wherein the means for
maintaining an oxidizing atmosphere includes at least one supply
line for oxygen (O.sub.2).
32. The apparatus according to claim 28, wherein the furnace is a
muffle furnace.
33. The apparatus according to claim 28, wherein the sections of
the furnace are formed by steel pipes.
34. The apparatus according to claim 28, wherein the furnace
includes inductive heating means.
Description
[0001] The invention relates to a method for the continuous casting
of a slab, in particular of steel, in which the cast slab is
conveyed through a furnace, and in which the slab is subjected to a
descaling operation, wherein in at least one section of the furnace
the slab or strand surface is subjected to a reduction by
maintaining in the section of the furnace an atmosphere which
consists of an inert gas and hydrogen or of pure hydrogen. The
invention additionally relates to an apparatus for the continuous
casting of a slab.
[0002] A method of the above described type is disclosed in U.S.
Pat. No. 5,816,311 A. In the manufacture of a steel strip, the
direct rolling from the casting heat is known in the art. In this
connection, the method is more interesting the greater the casting
speed. The method is known, for example, from EP 0 889 762 B1 and
from WO 2006/106376 A1. In this method, initially a slab is
manufactured in a continuous casting machine, wherein the slab is
discharged from a mold perpendicularly downwardly and is then
deflected into the horizontal position. The strip which is still
hot is then conducted to a rolling train. A thickness reduction
then takes place in each roll stand, until the strip having the
desired thickness is produced. The advantages of this method of
continuous casting/rolling are a relatively compact construction of
the plant and the attendant lower investment costs. Moreover,
energy can be saved during the production of the strip. The method
makes it possible to produce products which are difficult to roll,
for example, very thin strips (thickness of, for example, 0.8 mm),
to further process high-strength special materials, and to
fabricate strips which are wide and thin in combination.
[0003] The aforementioned technology is also called CSP-technology.
Among these is the manufacture of a steel strip in a thin strip
casting/rolling plant which facilitates an efficient production of
hot strip if the rigid connection of continuous casting plant,
conveying furnace for temperature compensation, and rolling train
and its temperature pattern through the total plant can be managed.
Accordingly, in this case, the roll stands are arranged directly
following the casting machine and the conveying furnace. By using
the above mentioned casting/rolling plant, a coupled, fully
continuous, direct casting/rolling process is possible.
[0004] For achieving a sufficient surface quality of the strip to
be manufactured, the development of scale is very disadvantageous.
The surface scale forming during casting and solidification and
during heating and remaining in the slab furnace on the steel
strand or on the slab has to be removed prior to hot rolling.
[0005] A particular disadvantage is the fact that in the
aforementioned casting/rolling process, the scale formed during
casting and during the solidification of the strand or the slabs
cannot be removed. The strand or the slab are cast and heated in an
oxidizing atmosphere which causes the surface to form scale. Scale
formed on the bottom side of the strand or slab can be pressed in
on the support surface in the furnace (rollers, shuffle bars) and
may thereby result in a mechanical damage of the surface. The
cleaning of the surfaces by means of a scale washer used in the
classic manner can take place only outside of the furnace. In
addition the removal of scale by means of a scale washer in front
of and/or following the furnace leads to a cooling of the strand or
slab which must be compensated by a greater introduction of energy
into the furnace.
[0006] DE 199 59 688 A1 discloses a method for heating blanks from
metal materials for a rolling or deforming process in which heating
is effected by electrical or magnetic fields or by an electric
resistance heater, wherein a protective atmosphere is used. In this
case, the protective atmosphere is composed especially of carbon
dioxide, of argon, of nitrogen, of sulfuric hexafluoride, or of
helium.
[0007] WO 2007/054,237 A1 discloses for a combined casting/rolling
process to descale the pre-rolled hot strip immediately prior to
the entry into a temperature adjusting device, wherein the strip
pretreated in this manner is held in the temperature adjusting
device in a protective gas atmosphere.
[0008] A method for continuously manufacturing strip steel or steel
plates is also disclosed in WO 89/11363. A similar method is shown
in WO 98/00248. Further similar solutions are shown in WO 02/04145
A2, EP 1 134 296 A2 and CN 101 091 958 A.
[0009] The present invention is based on the object of reducing the
formation of existing scale layers and to prevent the formation and
the build up of a scale layer during the annealing treatment.
Moreover, it is desirable to avoid or at least reduce surface
errors caused by scale.
[0010] This object is met by the invention with respect to method
technology in that in front of and/or behind the at least one
section of the furnace with reducing atmosphere in travel
direction, a section of the furnace follows in which the slab
surface is subjected to an oxidation. This section of the furnace
with oxidizing atmosphere may contain oxygen at least
partially.
[0011] The proportion of hydrogen can be between 3% and 100%,
preferably between 5% and 50%. The inert gas is preferably nitrogen
or argon.
[0012] Heating of the slab in the furnace can take place by
induction.
[0013] The above described method preferably is the continuous
casting in the casting/rolling process. Heating or equalizing
annealing of the slab then takes place preferably following the
casting process and before the rolling process as seen in travel
direction. The slab is conveyed continuously.
[0014] The apparatus for continuously casting a slab, which
includes a furnace through which the slab can be conducted, wherein
additionally descaling means are provided by means of which the
slab surface can be descaled, is characterized according to the
invention in that the furnace has at least two sections, wherein
means are provided for maintaining a reducing atmosphere in at
least one section of the furnace, and wherein means are provided
for maintaining an oxidizing atmosphere in at least another section
of the furnace.
[0015] The means for maintaining a reducing atmosphere preferably
includes supply lines for hydrogen and preferably also for an inert
gas. The means for maintaining an oxidizing atmosphere preferably
includes at least one supply line for oxygen.
[0016] The furnace may be a muffle furnace. The portions of the
furnace can also be formed by steel pipes; this has the advantage
that there are no open flames. The furnace may also comprise
inductive heating means.
[0017] With the proposed procedure it is possible to produce a
steel strand or a steel slab with improved surface characteristics.
This results from a targeted adjustment of the furnace atmosphere
during the heating or the equalizing annealing in a stationary
furnace or in a roller hearth furnace.
[0018] In accordance with this proposal, an existing scale layer is
reduced and the formation and build up of a scale layer during the
annealing treatment is substantially prevented. In addition,
smaller surface defects can be removed through a targeted
combination of scaling and reducing.
[0019] As a result, the surface quality of the strand or slab can
be improved, which is particularly applicable to directly rolled
strip, for example, from the CSP casting-rolling process. This
makes it possible to meet high requirements of the surface quality
as they exist, for example, with respect to steel plates for outer
skin parts in automobile construction.
[0020] The scale build up on the support surfaces in the furnace
(rolling, shuffle bar, etc.) can be avoided or at least
reduced.
[0021] By avoiding scale losses and avoiding reductions in quality,
a higher output of the plant can be achieved.
[0022] There is also a savings of energy due to an improved heat
transfer in the furnace. An energy savings and also a savings of
water result from the fact that any scale washers that may still be
required are operated with reduced water quantity. The resulting
lower temperature loss of strand or slab permits the indication of
a lower furnace temperature with constant temperature of the slab
when entering the first roll stand.
[0023] Embodiments of the invention are illustrated in the drawing.
In the drawing:
[0024] FIG. 1 schematically illustrates a plant for casting/rolling
a slab with a casting device, a roller-hearth furnace and a hot
rolling train; and
[0025] FIG. 2 schematically illustrates a plant for the
conventional hot rolling process with a casting machine, a slab
storage, a heating furnace and a rolling train.
[0026] In FIG. 1, a casting/rolling plant is illustrated, which is
known per se. A slab is cast in a casting machine 5, wherein the
slab is discharged from a mold vertically downwardly and is then
deflected into the horizontal direction by a plurality of rollers,
wherein the cast strand further solidifies. As seen in the
conveying direction F, a hot rolling train 6 follows further back,
and further in the conveying direction F a cooling group 7 and a
reel 8 for the finished strip.
[0027] In the solution according to FIG. 1, a roller-hearth furnace
2 is arranged between the casting machine 5 and the hot rolling
train 6.
[0028] In the alternative solution according to FIG. 2,
conventional hot rolling process is used in which the slabs are
initially stored behind the casting machine 5 in a slab storage 9.
The slabs are conveyed from there into a furnace 2 which is
constructed as a reheating furnace. Subsequently, the additional
process described in connection with FIG. 1 follows, i.e., the
rolling, the cooling and the coiling of the strip.
[0029] The surface scale formed in the slab furnace while the slab
is heated and remains the furnace must be removed prior to hot
rolling. This takes place classically by means of a scale washer by
spraying with water under high pressure (220-400 bar). In contrast
to the conventional manufacture by means of strand casting, cooling
and subsequent reheating and hot rolling (in accordance with FIG.
2), slabs from the casting/rolling process (see in particular the
above mentioned CSP process and FIG. 1) are supplied in a
continuous method by means of a roller-hearth furnace directly to
the hot strip finishing train. As a consequence, it is no longer
possible prior to hot rolling to remove surface defects by flaming
or grinding the slabs.
[0030] With respect to both processes explained above it is
intended that a furnace 2 is used in which at least in one portion
3 of the furnace (see FIG. 1), the slab surface is subjected to a
reduction by maintaining in the section 3 of the furnace 2 an
atmosphere which consists of an inert gas and/or hydrogen
(H.sub.2).
[0031] Accordingly, in the section 3 of the furnace 2 mentioned
above, a reducing furnace atmosphere is adjusted by means of which
a reduction of the surface scale can be effected. The hydrogen
(H.sub.2) being used may have a content of about 3% to 100%.
[0032] In the conveying direction F in front of the section 3 with
reducing atmosphere is arranged in the embodiment according to FIG.
1 and FIG. 2 (however, illustrated only in FIG. 1), a section 4
with oxidizing surface. Accordingly, oxygen (O.sub.2) is introduced
at this location; it is also possible that the entry of the
(oxygen-containing) atmosphere is facilitated at this location.
Consequently, smaller surface defects of strand or slab caused
during the casting or solidification process can be removed by
targeted descaling. By a targeted combination of furnace zones with
oxidizing and reducing atmospheres, a clean metallically bright
slab surface is achieved following the furnace 2.
[0033] A separation of the combustion chamber and the furnace
chamber can be achieved by using a muffle furnace or by using spray
pipes. Alternatively, it is also possible to carry out heating and
equalizing annealing totally or partially by means of inductive
heating elements.
[0034] In this embodiment, two furnace sections or chambers 3, 4
are arranged so that--as explained--preferably initially the
oxidation of the slab 1 takes place first and the reduction thereof
takes place thereafter. It is also possible that more than two
sections, especially three sections, are provided in the furnace 2
(not illustrated), in which respectively different atmospheres for
the reduction or oxidation are maintained.
LIST OF REFERENCE NUMERALS
[0035] 1. Slab/strand [0036] 2. Furnace [0037] 3. Section of
furnace [0038] 4. Section of furnace [0039] 5. Casting machine
[0040] 6. Hot rolling train [0041] 7. Cooling group [0042] 8. Reel
[0043] 9. Slab bearing [0044] H.sub.2 Hydrogen [0045] N.sub.2
Nitrogen [0046] O.sub.2 Oxygen [0047] F Conveying direction
* * * * *