Note: Descriptions are shown in the official language in which they were submitted.
CA 02419069 2007-10-09
Method and Strand Guide for Supporting, Guiding and Cooling Casting Strands
Made of Steel, Especially Preliminary Sections for Girders
The invention relates to a method of and a strand guide for supporting,
guiding and cooling of cast strand made of steel, in particular, beam-blank
preliminary sections for girders, wherein the cast strand, after leaving a
continuous casting mold, is cooled by a secondary cooling in a nil segment and
is further cooled in the following support segments by spray water and is
drawn
out.
JP 42 00 844 discloses providing, in a strand guide, separate support
rollers for longitudinal sides of the cast strand cross-section, in form of
"jog"
rollers and long rollers having a reduced length and arranged in the profile
base.
On the cast strand side, support rollers having a corresponding length are
arranged. This arrangement does not take into account the strand shell
thicknesses associated with the points on cast strand and the necessary
cooling.
It is to be noted that the functions of the strand guide include not only
providing a support for the cast strand against the ferrostatic pressure but
also
removal of the heat of solidification by secondary cooling and retaining of
the
profile geometry produced in a continuous casting mold. However, always,
surface cracks are formed.
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The object of the strand guidance should be obtaining of error-free
surface quality of a cast strand, inner quality without cracks and
segregations,
with maintaining of exact profile.
The object of the invention is to prevent cracks in the microstructure, in
particular cracks caused by cooling, by adapting cooling conditions of the
strand surface to the secondary cooling, in particular, by preventing
undercooling.
With the use of the method according to the preamble of claim 1, this
object is achieved, according to the invention, by adapting the cooling and
support of the beam blank format to the solidification range so that, in order
to
avoid an undesirable solidification structure on the upper flange edges or in
other cross-sectional areas, the cooling and support are provided only in
areas
where a crater is formed.
According to one embodiment of the invention, the cast strand is cooled,
by guiding the temperature in a predetermined manner in upper support
segments, with spray water jets a width of which corresponds to a length of
support rollers on longitudinal and transverse sides of the cast strand cross-
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section, is decreasingly supported on its transverse sides, in analogous
manner
with respect to a strand course length and a cooling state in core areas of
the
cast strand cross-section, and is further cooled with spray water jets
directed
only onto liquid core areas and having a width equal to or smaller than a
width
of a crater side. Thereby, undercooling of the strand shell is prevented, and
the
chance of appearance of cracks, in particular surface cracks, is substantially
reduced.
According to a further embodiment of the invention, the cast strand is
supported, by guiding the temperature in a predetermined manner, in the nil-
segment, on profile ends, in the middle region of the longitudinal sides, and
on
its transverse sides, so that its longitudinal and transverse sides, except
the
profile corner regions, are cooled, and with progressive formation of a strand
shell along the strand course, only middle regions and the two transverse
sides
of the strand cross-section are supported and in a region of lowest points of
craters of core areas, the transverse sides are decreasingly supported and
cooled,
and on the longitudinal sides, there are provided spray water jets directed
only
onto crater areas. Thereby, a predetermined temperature guidance can be
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achieved dependent on cross-sectional areas of the cast strand cross-section
not
only for rectangular cast strand cross-sections but also for profile strands.
Other features of the invention include supporting the cast strand cross-
section in a region of a crater area, on its transverse sides, without the
spray
water cooling. Advantageously, with this feature, the heat flow from hot areas
to the already cooled areas takes place without a large temperature gradient
The predetermined temperature guidance is further achieved by guiding
the cast strand, in condition of its most possible solidification, on a
support
rollers, without the spray water jets and without upper and side support.
An object of the invention is further achieved, with the use of cooling
and support means, by subjecting the cast strand to a predetermined
temperature
guidance in separate support segments so that ffom a support segment to a
support segment, a secondary cooling, which is adapted to a solidification
state
of the strand profile, is provided, with the support segments which follow the
nil support segment being so formed that excessive spray water outflows in a
plurality of directions from the cast strand cross-section.
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Thereby, by using an appropriate secondary cooling as a result of a
predetermined formation of support segments with an optimal arrangement of
strand guiding rollers, the tendency of undercooling of strand corners (flange
corners) with a poor ductile behavior is avoided, and the formation of cracks
in
the microstructure and on the surface is prevented. Also, a homogenous
temperature distribution in the cast strand cross-section is achieved.
With the temperature guided cooling and support according to the invention,
the
following advantages are achieved:
- minimized spray water quantity for removal of the heat of solidification,
- reduction of consumption of the running water as a result of elimination
of undercooling of flange upper sides and-other cross-sectional areas,
- homogenous temperature distribution in a beam-blank cross-section,
- temperature guidance from the mold up to the straightening region,
- adjustment of surface temperatures in favorable ductile region.
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The strand guide segment should meet the requirements of technological
aspects of their manufacturing. Therefore, they are formed as follows:
- With support rollers which provide support only in a crater area,
- With flange surfaces not being covered in the segments,
- With insurance of optimal outflow characteristics of water,
- With water collectors and guide plates on segment upper sides so that the
smallest possible amount of the running water is consumed.
The support and secondary cooling in accordance with further features
are so effected that in the nil support segment, longitudinal sides of the
cast
strand cross-section are supported by centrally symmetrically arranged paired
long support rollers, corner regions of the cast strand profile are supported
by
pairs of "jog" rollers, having a smaller length, and transverse sides of the
cast
strand cross-section are supported by support roller pairs a length of which
somewhat corresponds to the transverse side length.
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Such a support is particularly favorable, e.g.. at strand shell thicknesses
between 30 and 50 mm. The support is effected practically from all sides only
in the crater area in order to prevent the undesirable undercooling.
According to a further embodiment, in the following support segments,
on the longitudinal sides of the cast strand cross-section, only centrally
arranged
long support roller pairs are provided, and on its transverse sides, there is
provided a pair of support rollers, a length of which somewhat corresponds to
a
side length. With this support, the strand shell thicknesses already between
40
and 60 mm can be handled, and the corner areas of the cast strand cross-
section
need not be supported any more.
A further avoidance of support forces is achieved in accordance with
further features, by shortening, in the following support segments, rollers of
the
support roller pairs, respectively, which are arranged on the transverse
sides.
This assumes that the central areas of the cast strand have already
solidified,
and the strand shell has, in the outer regions, a thickness of about from 50
to 70
mm.
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With a further progressive solidification, it is contemplated that in the
following support segments, the pairs of symmetrical, shortened, support
rollers
are provided only on the transverse sides. In a cast strand of the preliminary
section, according to the invention, in the corner areas of the cast strand
cross-
section, already a strand shell thickness from 70 to 90 mm has been provided.
It is further contemplated that the cast strand is supported, in sections
having a most possible core solidification, only by support rollers provided
on
its lower side.
A further improvement is achieved by effecting spraying during the
secondary cooling analogous to a cast crater in a core area. This prevents a
too
high water impact.
Advantageously, the excess spray water is carried away. Thereby, only a
minimal amount of water remains in the center of a cast strand, e.g. on the
profile web of a preliminary section after the strand is not any more
supported.
According to a further development of the present invention the spray
water jets have a width equal to or wider than the length of associated
support
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rollers. This feature can be used in particular for relatively thin strand
shells of about
from 30 mm to 60 mm.
Finally, the "jog" rollers can be provided only in the support segment
following the nil support segment.
In another aspect, the invention provides a strand guide for a steel cast
strand,
comprising:
a nil support segment adjoining a continuous casting mold;
a plurality of further, following each other, support segments dimensions of
support
means of which are reduced in accordance with solidification state of the cast
strand
as it is displaced along the strand guide so that it is supported only in an
area of a
liquid phase;
means for cooling the cast strand only in the area of liquid phase and
comprising
water jets means; and
drawing means, wherein the water jets means is so arranged in the nil support
segment that water jets completely impact longitudinal sides of a middle
region of the
cast strand, and is arranged in the further support segments so that water
jets impact
only corner regions of the longitudinal sides of the middle region of the cast
strand;
wherein the water jet means is so arranged on transverse sides of the cast
strand that
water jets have a width corresponding to a length of support means of
respective
support segments on the transverse sides of the cast strand, with the length
of
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respective support means of the respective support segments corresponding to a
liquid
phase formation.
= The drawings show embodiments of the invention which would be described
in detail below.
It is shown in:
Fig. 1 a side view of a cast strand with strand shell
thicknesses associated with a cast strand
path for a preliminary section;
Fig. lA a cast strand cross-section in a continuous
casting mold;
Fig. 2A a cast strand cross-section at the outlet of
the continuous casting mold;
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Fig. 2B a cast strand cross-section with an
arrangement of support rollers and
secondary cooling in nil-segment;
Fig. 2C a cast strand cross-section with an
arrangement of support rollers and
secondary cooling in a following support
segment.
Fig. 2D a cast strand cross-section with an
arrangement of support rollers and
secondary cooling in a further support
segment; Fig. 2E a cast strand cross-section with an
arrangement of support rollers and
secondary cooling in a still further support
segment;
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Fig. 2F a cast strand cross-section before
solidification without secondary cooling;
Fig. 2G a cast strand cross-section at almost
complete solidification;
Fig. 2H a cast strand cross-section after complete
solidification and supported on a roller
table;
Fig. 3 a perspective view of a support segment;
Fig. 4A a perspective view across a support segment
with "jog" rollers;
Fig. 4B a perspective view across a support segment
without "jog" rollers;
Fig. 5 a perspective side view across the nil
support segment in an open design; and
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Fig. 6 a perspective view of a nil support segment
in an open design.
Fig. I and lA show an example of a cast strand I for a preliminary
section 2 for a to-be-rolled girder. The cast strand 1, after leaving the
continuous cast mold 3, is cooled in a nil support segment 4 as a result of
secondary cooling, is then cooled, in further support segments 5, 6,7, with
water
jets 8, and is drawn out by driven rolls of a drawing machine 9.
The thickness data of the thicknesses of the strand shell are given with
spacing of 2 m. The length L designates the entire length of the plant from
the
continuous casting mold 3 to the drawing machine 9. In addition, the radii RI,
R2 and R3 of the arches of the strand course are set.
The cast strand 1 is subjected in the (upper) nil support segment 4, by
guiding the temperature n a predetermined manner, to action of the spray water
jets 8 having a width 10 equal to or greater than the length 1 I of a pair of
support rollers 12. The spray water jets 8 are provided on both the
longitudinal
side 13 and the transverse -side 14 of the cast strand cross-section 1 A
(Figs. 2A-
2H). The transverse sides 14 are decreasingly supported (Figs. 2D-2F) in an
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analogous manner with respect to the strand course length and the cooling
state
in core areas 15, which still contain viscous melt in the cast strand cross-
section
1 a, with the spray water jets being directed only onto the core areas (Fig.
2D).
In accordance with the best possible process (Figs. 2A-2H), the exact
cast strand 1, which was produced in the continuous casting mold 3, enters the
nil support segment 3 (Fig. 2B) in which the cast strand I is supported on its
longitudinal side 13 by support rollers 17 arranged in the middle regions 16
of
its longitudinal sides, and is supported on the transverse sides 14 by support
rollers 18. At that, the profile corner regions 19 of the cast strand I are
not
cooled but are supported by "jog" rollers 20. The spray water jets 8 form,
with
respect to the strand, which is still in a liquid or viscous condition, and
its strand
width or strand thickness, an angle opening in the flow direction. Thereby,
only
there a large amount of heat is removed where the still fluid or viscous melt
is
present inside the cast strand 1, whereas the already solidified regions of
the
remaining strand shell 21 are spared. As a result, a gentle cooling of the
strand
corners takes place, and no surface cracks or few cracks are formed. In
accordance with Fig. 2C, the spray water jets 8 are still retained with a wide
angle. In Fig. 2D, one immediately sees that only the middle region 16 of the
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cast strand cross-section 1 a is supported by the support rollers 17, but it
is not
cooled any more. The spray water jets 8 are directed only to the core areas
15.
The support rollers 18 are shorter. This purposeful temperature guidance
continues in the strand course (Fig. 2E) until the spray water jets 8 are
directed
only onto the core areas 15 in the longitudinal side 13. Finally, the core
areas
15 (Fig. 2F) becomes very small, and the cast strand 1 needs not to be cooled
any more and is guided only by the support rollers 18 on the transverse sides
14. In Fig. 2G, the core areas 15 are further reduced and the cast strand 1 is
guided only by horizontal support roller 22. In Fig. 2H, the cast strand 1 is
solidified. The thickness of the strand shell 21 is, e.g., (dependent from
respective sizes of the cast strand cross-sections) 38.2 mm in Fig. 2B, 54 mm
in
Fig. 2C, 66.1 mm Fig. 2D, 76.4 mm in Fig. 2E, 85.4 mm in Fig. 2F, 93.5 mm
in Fig. 2G, and 101 mm in Fig. 2H.
Fig 2 shows one of the support segments 5,6,7. The essential
components are an upper frame 23, a lower frame 24, side frames 25, rollers
26,
and spray bars 27.
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Figs. 4A and 4B show outflow of the spray water 29 in the direction of
arrows 28. The outflow becomes possible in particular by the open profile of
the support segments 5,6, 7, with the cast strand cross-section 1 a being
surrounded, toward an open frame, on its four sides, by outer ribs 30,
reinforcing members 31, inner ribs 32, and respective nozzle connections 33.
The view in Fig. 4A corresponds somewhat to the strand course in Figs.
2B and 2C. The view in Fig. 4B corresponds to the strand course in Fig. 2D.
Fig. 5 shows a transverse section of the segment 5, 6, 7 shown in its
operational position, in which an open shape of the support segment 5, 6, 7
can
be clearly seen. The spray water 29, which is injected through the nozzle
connections 33 in form of the spray water jets onto the cast strand cross-
section
I a, can easily circularly flow away between the reinforcing members 31.
Fig. 6 shows a support roller strand 5, 6, 7 described with reference to
Fig. 3, in its operational position.
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List of reference signs
I. Cast strand.
1 a. Cast strand cross-section.
2. Preliminary profile (strand profile).
3. Continuous casting mold.
4. Nil support segment.
5. Support segment.
6. Support segment.
7. Support segment.
8. Spray water jet.
9. Drawing machine.
10.Width (of the spray water jet).
11.Length.
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12.Pair of support rollers.
13.Longitudinal side (of the cast strand).
14.Transverse side (of the cast strand).
15. Core area.
16.Middle region of the longitudinal sides.
17. Support roller.
18. Support roller.
19.Profile corner region of the cast strand.
20. "Jog" roller.
21. Strand shell.
22.Horizontal support roller.
23.Upper frame
24.Lower frame.
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25. Side frame
26.Displacement roller.
27. Spray bar
28. Arrow direction.
29. Spray water.
30.Outer rib
31. Reinforcing member
32.Inner rib.
33.Nozzle connection.
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