U.S. patent application number 10/493080 was filed with the patent office on 2004-12-23 for method and device for optimizing the cooling capacity of a continuous casting mold for liquid metals, particularly for liquid steel.
Invention is credited to Feldhaus, Stephan, Kopfstedt, Uwe, Mossner, Wolfgang, Parschat, Lothar, Pleschiutschnigg, Fritz-Peter, Rahmfeld, Werner, Wosch, Erwin.
Application Number | 20040256080 10/493080 |
Document ID | / |
Family ID | 26010383 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040256080 |
Kind Code |
A1 |
Rahmfeld, Werner ; et
al. |
December 23, 2004 |
Method and device for optimizing the cooling capacity of a
continuous casting mold for liquid metals, particularly for liquid
steel
Abstract
The invention relates to a method for optimizing the cooling
capacity of a continuous casting mold (1) for liquid metals,
particularly for liquid steel, by homogenizing the thermal load
(22) above the height of the continuous casting mold (1). According
to the method, the cooling medium (5) is guided through a
cross-sectional area of a large number of cooling medium channels
(3) or cooling medium boreholes (4) running approximately parallel
to the cast billet (9). The cooling medium cross-sectional areas
between the mold entry (6) and the mold exit (7) are configured
differently. In order to homogenize the thermal mold load (22), a
smaller cross-sectional area sets the flow rate of the cooling
medium (5), which is conducted from the top downward, inside the
cooling medium channel (3) or inside the cooling medium borehole
(4) higher in the upper area of the continuous casting mold (1)
than in the lower area of the continuous casting mold (1) in which
the flow rate is set lower by a larger cross-sectional area and/or
the covering of the cooling medium is adjusted by a cross-sectional
shape that varies from the top downward.
Inventors: |
Rahmfeld, Werner; (Mulheim
a.d.Ruhr, DE) ; Wosch, Erwin; (Stolberg, DE) ;
Pleschiutschnigg, Fritz-Peter; (Duisburg, DE) ;
Feldhaus, Stephan; (Dusseldorf, DE) ; Mossner,
Wolfgang; (Erkrath, DE) ; Parschat, Lothar;
(Ratingen, DE) ; Kopfstedt, Uwe; (Meerbusch,
DE) |
Correspondence
Address: |
THE FIRM OF KARL F ROSS
5676 RIVERDALE AVENUE
PO BOX 900
RIVERDALE (BRONX)
NY
10471-0900
US
|
Family ID: |
26010383 |
Appl. No.: |
10/493080 |
Filed: |
April 15, 2004 |
PCT Filed: |
October 15, 2002 |
PCT NO: |
PCT/EP02/11481 |
Current U.S.
Class: |
164/485 ;
164/443 |
Current CPC
Class: |
B22D 11/055
20130101 |
Class at
Publication: |
164/485 ;
164/443 |
International
Class: |
B22D 011/055; B22D
011/124 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2001 |
DE |
101 50 919.7 |
Jan 17, 2002 |
DE |
102 01 502.3 |
Claims
1. A method of optimizing the cooling capacity of a continuous
casting mold for liquid metal, especially for liquid steel by
homogenizing the thermal load over the height of the continuous
casting mold in which the coolant is passed through a cross
sectional area of a large number of coolant channels or coolant
bores which run generally parallel to the cast strand, whereby the
coolant cross section between the mold inlet and the mold outlet is
configured differently, characterized in that the flow cross
section of the coolant which is passed through the continuous
casting mold from the top to the bottom, is set to be higher in the
coolant channels or coolant bores of the upper region of the
continuous casting mold as a result of a smaller cross sectional
area than in the lower region of the continuous casting mold in
which the flow velocity is adjusted to be less than a greater cross
sectional area and/or in that the coverage with coolant has a cross
sectional shape which varies from the top to the bottom.
2. The method according to claim 1, characterized in that at a
casting speed of 3 m/min to about 12 m/min a heat flow loading of
the continuous casting mold of a maximum of 8 MW/m.sup.2 and a
coolant speed of 4 m/s to 30 m/s is maintained.
3. The method according to claim 1, characterized in that a maximum
thermal loading of the mold plates at their hot side is less than
550.degree. C. and that the heat transfer coefficient .alpha. is
set up to 250,000 W/m.sup.2.multidot.K.
4. The method according to claim 1, characterized in that the
continuous casting mold is oscillated.
5. The method according to claim 1, characterized in that the cast
strand is lubricated with casting powder slag in the continuous
casting mold.
6. The method according to claim 1, characterized in that the
surface of the cooling channels is provided with increased
roughness from mold inlet to mold outlet.
7. An apparatus for optimizing the cooling capacity of a continuous
casting mold for liquid metal, especially for liquid steel by
homogenizing the thermal load over the height of the continuous
casting mold in which the coolant is passed through a cross
sectional area of a large number of coolant channels or coolant
bores which run generally parallel to the cast strand, whereby the
coolant cross section between the mold inlet and the mold outlet is
configured differently, characterized in that the coolant channels
(3) or the coolant bores (4) respectively have a relatively small
coolant channel inlet cross section (14) and a greater outlet cross
section from the mold inlet (6) to the mold outlet (7) with a
greater coverage of the mold inlet (6) by the coolant (5).
8. The apparatus according to claim 7, characterized in that the
variation of the cross sectional shape from mold inlet (6) to the
mold outlet (7) is continuous.
9. The apparatus according to claim 7, characterized in that the
casting speed in the continuous casting direction is adjustable up
to about 12 m/min.
10. The apparatus according to claim 7, characterized in that a
thermal loading (11) of the continuous casting mold (1) of a
maximum of 8 MW/m.sup.2, a coolant speed (16) of 4 to 30 m/s and a
maximum local thermal loading (11) of the copper plates (2) on the
liquid metal side (11.1) are provided with a heating transfer
coefficient .alpha. of a maximum of 250,000
W/m.sup.2.multidot.K.
11. The apparatus according to claim 7, characterized in that the
coolant channels (3) have rectangular cross sections and increase
in the channel depths (3.1) and/or channel widths (3.2) from mold
inlet (6) to mold outlet (7).
12. The apparatus according to claim 7, characterized in that the
cross sectional areas (19) of the cooling channels (3) are variable
by means of baffles (3.3) through a control or regulation
(3.3.1).
13. The apparatus according to claim 7, characterized in that the
surface of the coolant channels (3) are provided with a roughness
(21) from the mold outlet (7) to the mold inlet (6).
14. The apparatus according to claim 7, characterized in that the
roughness (21) is formed by pits (24) of 0.5 to 3 mm diameter and
0.5 to 2 mm depth.
15. The apparatus according to claim 7, characterized in that the
distribution or the number of pits (24) increases from the mold
outlet (7) to the mold inlet (6).
16. The apparatus according to claim 13, characterized in that the
roughness (21) is variable by chemical or mechanical features.
17. The apparatus according to claim 16, characterized in that the
roughness (21) is variable during the casting process.
Description
[0001] The invention relates to a method and a device for
optimizing the cooling capacity of a continuous casting mold for
liquid metal, especially for liquid steel, so as to make the
thermal load uniform over the height of the continuous casting
mold, in which the cooling medium is fed through a cross sectional
area having a large number of cooling agent channels or cooling
agent bores which run generally parallel to the cast strand,
whereby the cooling agent cross sectional areas between the mold
inlet and the mold outlet are differently configured.
[0002] The continuous casting mold with which the invention is
concerned as a device is known from the German patent DE 41 27 333
C2. The steel melt is poured into a continuous casting mold whose
mold walls which extend from the top downwardly, encloses the
cooling water circulation and are provided with through-going
cylindrical cooling bores whose flow cross section areas are partly
reduced by constricting rods. To reduce the temperature difference
between the higher regions of the mold and thereby reduce the
stresses and increase the life of the mold, the cooling water in
the region of the highest temperature loading is fed at a maximum
speed through the cooling agent bores. Nevertheless only the bores
reduced by the constricting rods leave available only annular cross
sectional areas which are traversed by the coolant. Furthermore,
the coolant is guided only from the bottom to the top.
[0003] By contrast, the invention has as its object to create a
more uniform cooling over the entire height of the continuous
casting mold with the greatest possible cooling intensity and so
control the copper plate skin temperatures at the hot side and the
cold side that the recrystallization temperature of the cold rolled
copper is not exceeded at the hot side while possible evaporation
of the coolant at the cold side is avoided.
[0004] Its object is achieved in accordance with the invention in
that the flow velocity of the coolant, which traverses the
continuous casting mold from top to bottom, is set so as to be
higher in the coolant channels or coolant bores in the upper region
of the continuous casting mold by a smaller cross sectional area
than in the lower regions of the continuous casting mold in which
the flow velocity is less constricted by a greater cross section
area and/or by establishing for a coolant a variable cross
sectional shape running from top to bottom. The advantage resides
in a greater coverage by coolant in the hot region and by
comparison with prior systems a reduced heat obstruction below the
hot region. The consequence is not only a reduction in the shock
load in the hotter upper region of the casting level by a
significant amount but also a greater uniformity of the thermal
load over the entire height of the continuous casting mold. In
addition, neither the recrystallization temperature of the
cold-rolled copper at the hot side is reached nor does the change
arise of an evaporation of coolant at the cold side. The inlet
cross section of the coolant passage can be square or rectangular
and the continuation can respectively be configured as an elongated
rectangle to a square or a circular starting cross section can be
analogously configured.
[0005] In a refinement of the invention, the invention is so
carried out that with casting speeds of 3 m/min to about 12 m/min a
heat flow loading of the continuous casting mold of a maximum of 8
MW/m.sup.2 and coolant speeds of 4 m/s to 30 m/s are
maintained.
[0006] According to further steps it is proposed that a maximum
thermal loading at the hot side below 550.degree. C. be set and
that the heat transfer coefficient .alpha. be set at a maximum of
2500 W/m.sup.2.multidot.K.
[0007] Another feature which influences the heat values is that the
continuous casting mold is oscillated.
[0008] It is provided further that the casting strand be lubricated
with casting powder slag in the continuous casting mold.
[0009] A feature supporting the heat transfer resides further in
that the surfaces of the coolant channels are provided with a
degree of roughness from the mold which increases from the inlet to
the outlet.
[0010] In a device for atomizing the cooling capacity of a
continuous casting mold for liquid metal, especially for liquid
steel by rendering the thermal loading more uniform over the height
of the continuous casting mold, whereby the coolant is passed
through a cross section with a large number of coolant channels for
cooling bores which run generally parallel to the cast strand and
whereby the coolant cross sectional area of the coolant channels is
differently configured between the mold inlet and the mold outlet,
the object which has been set is achieved in accordance with the
invention in that the coolant channels or the cooling bores have a
relatively small coolant channel inlet cross sectional area and a
larger outlet cross sectional area from the mold inlet to the mold
outlet together with a greater coverage by the coolant by the mold
inlet (under "coverage" the ratio of cooling channel width/coolant
channel spacing, that is the effective phase boundary layer
copper/coolant is to be understood). Thus the effect of the decay
of peak temperatures in the copper plate at the region of the
casting level in the mold and the homogenization of the thermal
load over the entire height of the continuous casting mold is
produced.
[0011] An alternative to the transition from the mold inlet to the
mold outlet resides in that there is a change in the cross
sectional area shape from the mold inlet to the mold outlet in a
continuous manner.
[0012] According to a further feature of the invention it is
provided that the casting speed in the continuous casting direction
be adjustable up to about 12 m/min.
[0013] The invention is in addition improved when the thermal
loading of the continuous casting mold is set at a maximum of 8
W/m.sup.2, the coolant speed at 4 to 30 m/s and the maximum local
thermal loading of the copper plates at their sides turned toward
the liquid metal has a thermal transfer coefficient .alpha. of a
maximum of 250,000 W/m.sup.2.multidot.K. A further refinement is
obtained if the coolant channel of rectangular cross section have
channel depths and/or channel widths which increase from mold inlet
to mold outlet.
[0014] An improvement can be obtained in that the cross sectional
area of the coolant channel is made variable by a control or
regulation of baffles. In this manner the flow of the coolant in
the fixed shape of the coolant channel can have a further function
imparted to it. Another further development is provided in that the
surface area of the coolant channel is provided with a roughness
from the mold outlet up to the mold inlet.
[0015] In this case the roughness should consist of small pits of a
diameter of 0.5 to 3 mm and a depth of 0.2 to 2 mm.
[0016] Finally the distribution or the number of pits is provided
to increase from the mold outlet to the mold inlet.
[0017] The heat transfer can be made more intensive according to a
further feature in that the roughness is variable by chemical or
mechanical means.
[0018] In that case it is additionally of advantage that the
roughness be variable during the casting process.
[0019] In the drawing embodiments of the state of the art and the
invention are shown which are explained in greater detail in the
following. In the drawing:
[0020] FIG. 1A (respectively from left to right) is a vertical
section through the present continuous casting mold in the upper
part having two horizontal partial sections for coolant channels
and coolant bores in the upper mold region and in the lower part
having two horizontal partial sections for coolant channels and
coolant bores of the lower mold region and showing the temperature
pattern in the copper plates,
[0021] FIG. 1B is analogous to FIG. 1A (respectively from left to
right) showing a vertical section through the continuous casting
mold, in the upper part three horizontal partial sections for
coolant channels and coolant bores in the upper mold region and in
the lower part three horizontal partial sections for coolant
channels and coolant bores in the lower mold region and the new
surface temperature pattern which contrasts with the previous
surface temperature pattern and the difference between the previous
surface temperature pattern and the new surface temperature
pattern.
[0022] FIG. 2A is a diagram of the thermal transfer coefficient
.alpha., the maximum thermal loading and the pressure loss in the
coolant,
[0023] FIG. 2B is a diagram of the heat transfer coefficient
.alpha., the pressure loss .DELTA.P with respect to coolant speed
and
[0024] FIG. 2C is a diagram of the reduction of the maximum thermal
loading with increased coolant velocity.
[0025] In the continuous casting of liquid metal, especially liquid
steel, a continuous casting mold 1 is used (FIG. 1A) which is
comprised of copper plates 2 each with a large number of coolant
channels 3 or coolant bores 4 with or without displacement or
constricting rods 4.1 through which the coolant 5 is fed.
[0026] At the casting level 8 in which the shell 9 of the cast
strand begins its formation, there is the greatest local heat flow
10 (J) and simultaneously the largest value of the thermal mold
loading T.sup.cu-max 11 both on the hot side 11.1 and also one cold
side of the copper plate 2.
[0027] The thermal loading at the casting level 8 or the maximum
heat flow 10 ("J") can, especially at high casting speeds of about
12 m/min amounts to as much as 8 MW/m.sup.2 and requires as a
result special cooling features so that the copper plate skin
temperature at the hot side 11.1 and the cold side 11.2 are so
controlled that the recrystallization temperature of the cold
rolled copper is not exceeded on the hot side 11.1 and so that
possible evaporation of the coolant 5 on the cold side 11.2 can be
avoided.
[0028] The cooling capacity or the cooling effect are determined by
mechanical characteristics like for example the copper plate
thickness 12, the coolant channels 3 or coolant bores 4 with or
without displacement rods 4.1, the spacing 13 (A) of the coolant
channels 3 or coolant bores from one another, the cross sectional
areas 14 (F) of the coolant channels 3 or the coolant bores 4 and
the lengths of the coolant channels 3 or the coolant bores 4, which
correspond to the mold length 15 (L). As state of the art, up to
now the coolant channel cross sectional areas 14 were provided as
constant between the mold inlet 6 and the mold outlet 7. The
process determining influential parameters for the cooling capacity
of the continuous casting mold 1 are, aside from the coolant
temperature, the coolant speed or velocity 16 which is an important
value for the heat transfer coefficient 17 (.alpha.) measured in
W/m.sup.2.multidot.K.
[0029] The relationships are illustrated in FIGS. 2A, 2B and 2C in
diagrams.
[0030] To set a desired heat transfer with the aid of a certain
coolant seed 16 in the continuous casting mold 1 by the cross
sectional area 14 of the coolant channel 3 or the coolant bores 4
and a predetermined mold width 18, here normalized to 1 m, and
spacing 13 of the coolant channel, a pressure drop 19 (.DELTA.P) in
the coolant between the mold inlet 6 and the mold outlet 7 is
established.
[0031] This pressure drop rises superficially with the coolant
velocity 16 (V) or with the coolant volume rate of flow 20 (Q)
measured in m.sup.3/h.multidot.m.
[0032] In addition, it is to be noted with an increasing roughness
21 (R) of the surfaces of the coolant channels 3 or the coolant
bores 4, the transfer coefficient 17 (.DELTA.P) rise.
[0033] The target of the invention is to minimize the pressure drop
19 (.DELTA.P) while controlling the maximum thermal loading 11
(T.sub.cu-max) both on the hot side 11.1 and the cold side 11.2 and
thereby to homogenize the thermal mold loading 22 or the thermal
profile 23 over the mold length 15. In FIGS. 2A, 2B and 2C, the
heat transfer coefficient 17 (.alpha.) and the maximum thermal
loading 11 of the copper plate has been shown as a function of the
structural and process parameters like for example
[0034] the coolant velocity 16 (V)
[0035] the coolant volume flow rate 20 (Q)
[0036] the pressure drop 19 (.DELTA.P)
[0037] the roughness 21 (R) of the surfaces
[0038] under respective predetermined and constant boundary
conditions.
[0039] The cast strand 9 is poured according to FIG. 1B with a
casting speed 9.1 of about 12 m/min, for example, in a casting size
corresponding to thin slabs with a thickness between 20 mm and 100
mm. During the casting, casting powder 1.2 as well as an
oscillation 1.1 can be used. The casting process loads the
continuous casting mold 1 with a maximum heat flow 10 ("J") at the
casting level 8 of 2 to 8 MW/m.sup.2 which is a maximum thermal
loading 11 at the casting level and the hot side 11.1 on which the
liquid steel is located as well as at the cold side 11.2 at which
the current 5 is located.
[0040] The process gives rise to a thermal mold loading 22 and a
heat flow profile 23 over the mold length 15 (L). The coolant
channel cross sectional area 14 (F) in the cooling channel 3 or
cooling bores 4 with or without displacement rods 4.1 are in the
state of the art system (FIG. 1A) constant over the mold length 15
and give rise to a constant coolant velocity 16 (V) and to a
defined coolant pressure drop 19 (.DELTA.P) which has been
designated as unity "1".
[0041] In the extreme right hand illustration of FIG. 1B, the
temperature pattern of the surface temperature has been shown by
comparison with that of FIG. 1A in which the heat quantity carried
off is the same in the two tests.
[0042] So that the thermal loading 22 of the mold is homogenized
and the pressure drop 19 (.DELTA.P) of the coolant 5 is minimized,
the cross sectional area 14 (F) of the coolant channels 3 or the
coolant bores 4 are increased from the mold inlet 6 to the mold
outlet 7 (FIG. 1B). In addition the roughness 21 (R) can also
selectively increase from the mold outlet 7 to the mold inlet 6
over the mold length 15.
[0043] The roughness 21 can be produced by pits 24 of a maximum
diameter of 1 to 3 mm and depth of 1 to 2 mm to produce cavitation
effects in the flowing coolant 5 (for example the water) at the
phase boundary between the copper (for side 11.2) and the coolant 5
and thereby give rise to an increase heat transfer coefficient 17,
(.alpha.) as brought about by forced convection in the lamina,
seeded boundary layer in which the energy transport occurs by
thermal conductivity.
[0044] The increase in the cross sectional area 14 of the coolant
channel 3 or the coolant bores 4 over the length of the mold can be
effected in the case of cooling channel 3 by means of the variation
in the channel depth 3.1 and/or of the channel width 3.2 in the
case of the coolant bores 4, the cross sectional enlargement can be
effected by increasing the diameter of the coolant bores 4 and/or a
reduction in the diameter of the displacement rods 4.1.
[0045] Another configuration provides that baffle plates 3.3 of the
coolant channels 3 can be set manually or automatically
mechanically to vary the cross sectional areas 14 of the coolant
channel 3 over the mold height 15, for example, using an on-line
process control with a control or regulation 3.3.1 to adjust the
positions of the baffles 3.3.
[0046] After carrying out this described embodiment, the thermal
mold loading 22 over the mold length 15 is lowered through the
homogeneous thermal profile 22.1 which has been shown in the
right-hand part of FIG. 1B in a graph.
[0047] The diagram 2A plots the heat transfer coefficient 17
(.alpha.) measured in W/m.sup.2K, pressure losses 19 (.DELTA.P) and
the liquid maximum thermal loading 11 of the copper plate 2 at the
casting level 8 as a function of the roughness 21 of the surfaces
of the coolant channels 3 or the coolant bores 4 at a constant
copper plate thickness 12, coolant speed 16 (V in m/s), heat flow
10 (J) cross sectional areas 14 for the coolant channels 3 or the
coolant bores 4, the mold length 15 and the spacing 13 of the
coolant channel 3 or coolant bores 4 from one another. The graph
makes clear that with increasing roughness 21 (R) the heat transfer
coefficient 17 (.alpha.) and also the pressure drop 19 (.DELTA.P)
increase steadily but also that simultaneously the copper plate
temperature 11 (T.sub.cu-max) at the hot side 11.1 and the cold
side 11.2 fall rapidly.
[0048] In graph 2B, the variation of the heat transfer coefficient
17 (.alpha.) and the pressure loss 19 (.DELTA.P) with the coolant
velocity 16 (V) or the coolant flow quantity 20 (Q) with increasing
roughness 21 at constant cross section 14 (F), mold lengths 15 and
spacing 13 (A) is shown. It is clear from this that with increasing
coolant speed 16 (V), coolant flow quantity 20 (Q) and roughness 21
(R) the heat transfer coefficient 17 (.alpha.) and also the
pressure loss 19 (.DELTA.P) have fallen superproportionally.
[0049] In FIG. 2C the drop in the maximum thermal loading 11 at the
casting level 8 of the copper plate 2 with increasing coolant speed
16 (V), coolant quantity 20 (Q) and roughness 21 (R) at constant
the flow 10 (J) has been shown in the heat flow profile 23 over the
mold length 15 the copper plate thickness 12, the coolant channel
cross section 14 (F) and the spacing 13 (A) of the coolant channels
3 or the coolant bores 4.
[0050] The partial illustration in FIG. 2C makes clear that the
liquid maximum thermal loading 11 at the casting level 8 with
rising roughness (R) the coolant speed 16 (V) or the coolant
quantity 20 (Q) sinks easily.
[0051] The principle of the invention also operates with strip
casting devices which operate with speeds of up to 100 m/min. All
of the features which are applicable over the height of the
continuous casting mold are applicable to the periphery of the twin
rollers.
Reference Character List
[0052] 1. Continuous casting mold
[0053] 1.1 Oscillation
[0054] 1.2 Casting powder, casting slag
[0055] 2 Copper plate
[0056] 4 Coolant channel
[0057] 3.1 Channel depth
[0058] 3.2 Channel width
[0059] 3.3 Baffle
[0060] 3.3.1 Control/regulation of the position of the baffle
[0061] 4 Coolant bore
[0062] 4.1 Displacement tube, bar, round body
[0063] 5 Coolant
[0064] 5.1 Coolant flow direction
[0065] 6 Mold inlet (upper edge of mold)
[0066] 7 Mold outlet (lower edge of mold)
[0067] 8 Casting level
[0068] 9 Stand shell, strand
[0069] 9.1 Casting speed
[0070] 10 Local maximum heat flow "J" at casting level
[0071] 11 Local maximum thermal loading at casting level
(T.sub.cu-max)
[0072] 11.1 Side turned toward the molten steel (hot side)
[0073] 11.2 Side turned toward the coolant (cold side)
[0074] 12 Copper plate thickness (between hot side and cold
side)
[0075] 13 Spacing of coolant channels (3) or coolant bores (4) from
one another
[0076] 14 Cross sectional area (F) of the coolant channel (3) or
the coolant bore (4)
[0077] 15 Length of the coolant channel, coolant bores, the
mold
[0078] 16 Coolant speed (V in m/s)
[0079] 17 Heat transfer coefficient .alpha. in
W/m.sup.2.multidot.K
[0080] 18 Mold width (in m)
[0081] 19 Pressure loss of the coolant, .DELTA.P
[0082] 20 Coolant quantity Q in m.sup.3/h.multidot.m
[0083] 21 Roughness R, in mm of the surface
[0084] 22 Thermal mold loading over the mold length
[0085] 22.1 Homogeneous thermal profile (T.sub.cu-max)
[0086] 23 Heat flow profile over the mold length
[0087] 24 Pits, pockets
* * * * *