U.S. patent application number 09/944427 was filed with the patent office on 2003-03-06 for method and apparatus for improving internal quality of continuously cast steel sections.
Invention is credited to Buziashvili, Boris, Hury, Shlomo, Kayam, Samuel, Ponikvar, Philip E..
Application Number | 20030041999 09/944427 |
Document ID | / |
Family ID | 25481377 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030041999 |
Kind Code |
A1 |
Hury, Shlomo ; et
al. |
March 6, 2003 |
METHOD AND APPARATUS FOR IMPROVING INTERNAL QUALITY OF CONTINUOUSLY
CAST STEEL SECTIONS
Abstract
Segregation of carbon or alloying elements in a solidifying
liquid core during casting of a continuous metal strand of high
carbon steel or alloy steel, are disbursed by vibrating hammers
engaged with a solidified shell enclosing a liquid steel core. The
hammers are located before the end of the liquid core. A vibrator
operating at a frequency of between 1000 and 5000 cycles per minute
is coupled to the hammers by a support structure forming a dead
weight mass for maintaining a metal-to-metal contact with the
solidified shell while vibrated by the vibrator. The support
structure is guided for stabilizing the hammers and for
displacement of the hammers between an operative position and
inoperative position.
Inventors: |
Hury, Shlomo; (Noodcliff
Lake, NJ) ; Kayam, Samuel; (Pittsburgh, PA) ;
Ponikvar, Philip E.; (Bridgevill, PA) ; Buziashvili,
Boris; (New York, NY) |
Correspondence
Address: |
CLIFFORD A. POFF
9800B MCKNIGHT ROAD
SUITE 115
PITTSBURGH
PA
15237
US
|
Family ID: |
25481377 |
Appl. No.: |
09/944427 |
Filed: |
August 31, 2001 |
Current U.S.
Class: |
164/477 ;
164/417 |
Current CPC
Class: |
B22D 11/12 20130101 |
Class at
Publication: |
164/477 ;
164/417 |
International
Class: |
B22D 011/12 |
Claims
1. Apparatus for reducing segregation in a solidifying section with
contained a liquid core during casting of a continuous metal strand
of high carbon steel or alloy steel, said apparatus including the
combination of: at least one hammer having a face surface for
engaging a solidified shell enclosing a liquid steel core having
concentrations of carbon or alloying elements; a vibrator having an
operating frequency of between 1000 and 5000 cycles per minute
coupled to said hammer for vibrating said liquid core to disperse
concentrations of carbon or alloying elements during solidification
of said liquid core; a dead weight mass mechanically coupled to
said hammer for maintaining a desired contact force on said
solidified shell by said hammer while vibrated by said vibrator;
and guides for stabilizing said hammer.
2. The apparatus according to claim 1 wherein said at least one
hammer includes two hammers each having face surfaces for engaging
opposed surfaces of said solidified shell, and wherein said
apparatus further includes link arms interconnecting opposed ends
of said two hammers for mechanically coupling said vibrator and
said dead weight mass to said two hammers.
3. The apparatus according to claim 2 further including an actuator
for displacing said hammers between an operating position wherein
said two hammers contact said solidified shell and an inoperative
position wherein said two hammers are remote to said solidified
shell.
4. The apparatus according to claim 2 further including a shaft for
pivotally interconnecting said link arms with said dead weight
mass.
5. The apparatus according to claim 4 further including a platform
including weights for modifying said dead weight mass.
6. The apparatus according to claim 4 wherein said dead weight mass
includes a cross head secured to terminal end portions of spaced
apart rails extending along opposite sides of said solidified shell
and secured by said shaft to said link arms.
7. The apparatus according to claim 6 wherein said guides extend
generally vertically and slidably support said spaced apart
rails.
8. A method for reducing segregation in a solidifying liquid core
during casting of a continuous metal strand of high carbon steel or
alloy steel, said method including the steps of: selecting a site
along a cast strand upstream of the end of a liquid core contained
within a solidified shell of high carbon steel or alloy steel in a
continuous casting installation; and vibrating the solidified shell
at said site at a frequency selected to disperse concentrations of
carbon or alloying elements during solidification of said liquid
core to refine the grain structure during solidification of the
liquid core.
9. The method according to claim 8 wherein said solidified shell is
vibrated at a frequency selected to propagate vibrations to said
solidified shell upstream and downstream of the site selected by
said step of selecting.
10. The method according to claim 8 wherein said solidified shell
is vibrated at a frequency of between 1000 and 5000 cycles per
minute.
11. The method according to claim 8 wherein said solidified shell
is vibrated at a frequency of between 3000 and 4000 cycles per
minute.
12. The method according to claim 8 wherein said solidified shell
is vibrated at opposed sites.
13. The method according to claim 8 wherein said step of vibrating
the solidified shell includes contacting the shell under a
predetermined dead weight contact force with a face surface coupled
to a vibrator at opposed sites to maintain a metal to metal
contact.
14. The method according to claim 8 wherein said step of vibrating
the solidified shell breaks dendrite tips occurring during
solidification of the high carbon steel or alloy steel to
accelerate solidification by the seeding of the liquid core with
the broken dendrite tips.
15. A method for reducing segregation in a solidifying liquid core
during casting of a continuous metal strand of high carbon steel or
alloy steel, said method including the steps of: using an
electromagnetic field to stir a body of liquid high carbon or alloy
steel in or below a mold of a continuous casting installation;
selecting a site along a cast strand produced by said mold
downstream of said electromagnetic field and essentially upstream
of the end of a liquid core contained in a solidified shell of the
continuous casting; and vibrating the solidified shell at said site
at a frequency selected to disperse concentrations of carbon or
alloying elements during solidification of said liquid core to
refine the grain structure during solidification of the liquid
core.
16. The method according to claim 15 wherein said solidified shell
is vibrated at a frequency selected to propagate vibrations to said
solidified shell upstream and downstream of the site selected by
said step of selecting.
17. The method according to claim 15 wherein said solidified shell
is vibrated at a frequency of between 1000 and 5000 cycles per
minute.
18. The method according to claim 15 wherein said solidified shell
is vibrated at a frequency of between 3000 and 4000 cycles per
minute.
19. The method according to claim 15 wherein said solidified shell
is vibrated at opposed sites.
20. The method according to claim 15 wherein said step of vibrating
the solidified shell includes contacting the shell under a
predetermined dead weight contact force with a face surface coupled
to a vibrator at opposed sites to maintain a metal to metal
contact.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and an apparatus
to improve the internal quality of a continuously cast steel
section and, more particularly, to mechanically vibrate a
solidified shell of such a steel section at a site upstream of the
end of a contained liquid steel core consisting of high carbon
steel or alloy steel to reduce segregation by dispersing carbon or
alloying elements during final solidification of the liquid
core.
[0004] 2. Description of the Prior Art
[0005] Inherent internal conditions in the process of continuous
casting of steel sections such as billets, blooms, rounds and slabs
have a significant influence on the internal quality of the steel
section especially when casting high carbon steel and alloy steel.
The inherent conditions are center looseness, center segregation,
and equiaxed grain ratio. While center looseness and center
segregation are not desirable, obtaining an equiaxed grain ratio is
very desirable. Several methods of combating or enhancing the above
mentioned conditions are known to produce a varying degree of
success. Two such known methods are electromagnetic stirring and
soft reduction. Electromagnetic stirring is accomplished by
applying a magnetic field to the cast section liquid core to
agitate the steel causing the breakage of the dendrite tips and
dispersion of inclusions. This action promotes recrystallization in
the solidification process and minimizes center segregation. The
soft reduction method involves progressively squeezing a mushy zone
in the solidifying section to refine the grain size at the center
of the section, which also influences center segregation and center
looseness. Electromagnetic stirring and soft reduction methods are
capital intensive, when initially installing the necessary
equipment into a new facility or when retrofitting the necessary
equipment into an existing facility.
[0006] It is an object of the present invention to provide a method
and an apparatus to introduce vibration by physically impacting a
continuously cast section at a location before final
solidification.
[0007] It is a further object of the present invention to provide a
method and an apparatus to apply mechanical vibrations to an outer
shell of a continuously cast section to vibrate an internal mushy
zone sufficiently to cause the breakage of dendrite tips and
thereby promote recrystallization and to enhance refinement of the
grain structure by dispersion of segregated carbon or alloying
elements, to produce an equiaxed and dense structure, and to reduce
porosity by facilitating the floatation of gas bubbles to the top
of the mold.
SUMMARY OF THE INVENTION
[0008] According to the present invention there is provided an
apparatus for reducing segregation in a solidifying section with a
contained liquid core during casting of a continuous metal strand
of high carbon steel or alloy steel, the apparatus including the
combination of at least one hammer having a face surface for
engaging a solidified shell enclosing a liquid steel core having
concentrations of carbon or alloying elements, a vibrator having an
operating frequency of between 1000 and 6000 cycles per minute
coupled to the hammer for vibrating the liquid core to disperse
concentrations of carbon or alloying elements during solidification
of the liquid core, a dead weight mass mechanically coupled to the
hammer for maintaining a desired contact force on the solidified
shell by the hammer while vibrated by the vibrator, and guides for
stabilizing the hammer.
[0009] The present invention further provides a method for reducing
segregation in a solidifying liquid core during casting of a
continuous metal strand of high carbon steel or alloy steel, the
method including the steps of, selecting a site along a cast strand
upstream of the end of a liquid core contained within a solidified
shell of a continuous casting installation for high carbon steel or
alloy steel, and vibrating the solidified shell at the site at a
frequency selected to disperse concentrations of carbon or alloying
elements during solidification of the liquid core to refine the
grain structure during solidification of the liquid core.
Preferably, the solidified shell is vibrated at a frequency of
between 1000 and 6000 cycles per minute.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] The present invention will be more fully understood when the
following description is read in light of the accompanying drawings
in which:
[0011] FIG. 1 is an elevational view of a continuous casting
installation embodying the present invention;
[0012] FIG. 2 is an enlarged elevational view of an apparatus to
vibrate a newly formed continuously cast strand at a site along a
secondary cooling section of a continuous casting installation as
shown in FIG. 1;
[0013] FIG. 3 is a sectional view taken along lines III-III of FIG.
2;
[0014] FIGS. 4, 5 and 6 are schematic illustrations of the
transition of the apparatus to vibrate the casting between an
inoperative position and an operative position;
[0015] FIG. 7 is a photograph of a cross section of a high carbon
continuous steel casting produced by an ordinary or standard
casting method;
[0016] FIG. 8 is a photograph of a cross section of a high carbon
continuous steel casting produced by a modified casting method
incorporating the present invention;
[0017] FIG. 9 is a photograph of a cross section of a high carbon
continuous steel casting produced by an ordinary casting method
with electromagnetic stirring; and
[0018] FIG. 10 is a photograph of a cross section of a high carbon
continuous steel casting produced by a modified casting method
incorporating the present invention combined with electromagnetic
molds stirring.
DETAILED DESCRIPTION OF THE INVENTION
[0019] FIGS. 1 and 2 illustrate one form of a continuous casting
installation 10 suitable to practice the method and incorporates
one embodiment of the apparatus according to the present invention
to produce a continuously steel casting comprised of high carbon
steel or alloy steel. The term high carbon steel is defined to mean
carbon steel with a carbon content of 0.45% or greater and the term
alloy steel is defined to mean an alloyed steel having enhanced
properties by the presence of one or more special alloying elements
or due to the presence of larger portions of elements such as
manganese and silicon than are ordinarily present in carbon steel.
The continuous casting installation 10 includes a ladle turret 12
for delivering molten steel in ladles 13 and 14 into and from a
position directly above a tundish 15. The tundish delivers a stream
of liquid steel into a water-cooled mold 16 and a continuous strand
S made up of a solidified shell surrounding a liquid core passes
from the mold along a curved secondary cooling section 17. The
continuous strand S has a well-known cross sectional configuration
such as a billet, a bloom, a round or a slab. The secondary cooling
section 17 contains spaced apart guide rollers 18 interleaved with
water spray headers, not shown, to continue the cooling process.
Preferably, though not necessary, mold 16 also includes an
electromagnetic coil assembly 19 to provide electromagnetic
stirring of the liquid core in the continuous strand S. The rollers
and spray headers of the secondary cooling section 17 are supported
by consecutively arranged frames 20, each having anchor rods 21
supported on pedestals 22 mounted on an underlying foundation. The
secondary cooling section extends to a straightener section 23
provided with motor driven straightenering rolls 24 for
straightenering and delivering the continuous strand S to a runout
table 25.
[0020] In accordance with the present invention there is provided
an apparatus 26 to vibrate the continuous strand S in the
continuous casting installation 10 at selected site upstream of the
end of the liquid core within the solidified shell. The end of the
liquid core is generally within or close to the straightener
section 23. The selected site in the embodiment shown in FIGS. 1
and 2 is in a gap that exists between the last of the guide rollers
18 of the secondary cooling section 17 and the first pair of motor
driven straightener rolls 24 of a straightener section 23. The
selected site can be located in a space between driven straightener
rolls 24, or past the last pair of straightener rolls and before
the point of solidification of the liquid core.
[0021] As shown in FIGS. 2 and 3, the apparatus 26 essentially
includes an oscillating dead weight mass, driven by a vibration
actuator 27 which can be electromagnetic or eccentrically driven by
an air, hydraulic, or electric motor. The vibration actuator 27 is
mounted on a vibrating head 29, which pivots on a frame 28, and is
engaged and disengaged by a linear actuator retained at the
selected site through the use of supporting structure provided by
the existing foundation of the casting machine. However, the
selected site may be located in an area behind, i.e. downstream of,
the straightener rolls in the event that the liquid core extends
into this area. When engaged and activated, the mass undergoing
oscillation is comprised of the frame 28 and the vibrating head 29
will undergo dynamic impacting with the continuous strand S at a
preselected and relatively low frequency typically at a frequency
in the range of 1000 to 6000 cycles per minute, preferably in the
range of 3000 to 4000 cycles per minute. The magnitude of the
dead-weight mass required for static contact with the continuous
strand S, the oscillation stroke and force of the vibration
actuator 27 are chosen relative to the physical dimensions of the
continuous strand S. The oscillation cycle, stroke and force are
controllable parameters of the vibration actuator 27. The
construction of the frame 28 and vibrating head 29 are specifically
engineered to establish a predetermined dead weight required for
exerting contact forces by hammer face surfaces on the casting. A
plate P may be added to support a counterweight W to modify the
dead weight and center of gravity of head 29, such modification to
the center of gravity to compensate a change to the metallurgical
composition of the continuous strand or a change to the thickness
of the continuously cast strand. However, it is to be understood
that the hanging weight of the dead weight mass and the center of
gravity can be modified by the addition of weight to the cross head
36 and/or by the counterweight W. The vibrations generated by the
vibration actuator 27 are transmitted from the vibrating head 29 by
a shaft 30 to the frame 28. The shaft 30 pivotally interconnects
head 29 with spaced apart rails 32 of frame 28 extending along
opposite sides of the of the continuous strand S where the rails
slidably engage with guides 33 extending generally vertically for
stabilizing the frame 28. The link arms 31 extend from the shaft 30
in a cantilevered fashion along opposite sides of the continuous
strand S for rigidly mounting the opposite ends of two hammers 34
and 35 in a spaced apart relation to thereby mechanically couple
the hammers to the vibration actuator 27. The hammers 34 and 35
have face surfaces arranged for engaging the upwardly and
downwardly directed face surfaces of the continuously moving steel
casting. It is sufficient to provide at least one hammer although
two hammers are preferred. The vibration imparted to the hammers
serves the additional and essential function of reducing friction
between the hammers and the continuously moving steel casting which
allows unimpeded forward movement of the casting without damage to
the hammer support structure including the guides 33.
[0022] The lower end portions of the spaced apart rails 32 are
secured to a cross head 36 provided with an arm 37 having a lateral
projection overlying a linear actuator 38 which can be
electrically, pneumatically or hydraulically powered to displace an
actuator rod 39. The actuator is supported by a bracket 40
extending from the underside of a frame 41, which extends in the
direction of the flow of the casting for support by adjacent
pedestals 22 at the boundaries of the gap at the selected site. The
frame 41 includes upstanding frame 42, which includes the guides 33
for supporting the rails 32. Channels, one of which is identified
by reference numeral 43, for coolant water are strategically placed
at diverse locations to cool the apparatus 26 during the operation
of the continuous casting installation 10.
[0023] As shown in FIG. 4, the actuator rod 39 of the linear
actuator 38 is extended to hold the upper hammer 34 in an
inoperative position at a location above the casting. The
cantilevered relation of the hammers relative to the shaft 30
allows the lower hammer 35 to rotate to an inoperative position
below the casting by rotation of the link arms 31 about the shaft
30 and the upper hammer 34 to rotate to an inoperative position
above the casting. The apparatus 26 is moved into an operative
position by retracting the actuator rod 39 and, as shown in FIG. 5,
this allows downward travel of the rails 32 along the guides 33
with the receding movement by the actuator rod. The upper hammer 34
rotate to an operative position contacting the upper surface of the
casting S and the lower hammer rotates toward an operative position
for contact with the lower surface of the casting S. When the
actuator rod 39 is fully retracted, as shown in FIG. 6, the upper
hammer 34 remains in contacts the upper surface of the casting and
the lower hammer 35 pivots about shaft 30 into contact with the
lower surface of the casting. The dead-weight mass of the assembly,
which moved to allow contact with the casting by the two hammers,
establishes a metal-to-metal contact with the casting under a
dead-weight load. At the position shown in FIG. 6, the actuator rod
39 is disengaged with arm 37 and thereby the entire weight of the
head 29 and the frame 28 is hanging on the strand S.
[0024] The vibration imparted to the steel shell propagates to the
internal liquid core and in directions of toward the mold and
oppositely to essentially the end of the liquid core to disperse
concentrations of carbon or alloying elements occurring in the
continuous casting of high carbon steel or alloy steel,
respectively. FIG. 7 illustrates extensive center segregation of
the grain structure in a continuous strand produced without
practicing the method or use of the apparatus of the present
invention. FIG. 8 illustrates a very favorable refined central
grain structure in a continuous strand S produced by the same
casting machine used to produce the steel casting of FIG. 7 but
modified by practicing the method and the use of the apparatus of
the present invention. The absence of voids in the central area of
the casting shown in FIG. 8 is a note worthy advancement as
compared with high concentrations of voids and segregated grain
structure visible in the cross section of FIG. 7.
[0025] Experimental use of the present invention further included a
trial to examine the benefits of vibrating the casting in a
continuous casting machine equipped with electromagnetic stirring
of the steel residing in the mold which produced the equiaxed and
densely refined grain structure as shown in FIG. 9. The operation
of the continuous casting installation was altered by placing the
apparatus to vibrate the casting in the inoperative position but
use of the electromagnetic stirring was continued to recover a
casting and examine the grain structure, which is shown in FIG. 10.
The benefits of breaking dendrite tips during cooling of the
central core of the high carbon steel or alloy steel are readily
apparent which also was found to accelerate the solidification
process by the seeding of the liquid core with the broken dendrite
tips. Additionally, vibrating the continuously cast strand promoted
the discharge of gas bubbles from the core during
solidification.
[0026] While the present invention has been described in connection
with the preferred embodiments of the various figures, it is to be
understood that other similar embodiments may be used or
modifications and additions may be made to the described embodiment
for performing the same function of the present invention without
deviating there from. Therefore, the present invention should not
be limited to any single embodiment, but rather construed in
breadth and scope in accordance with the recitation of the appended
claims.
* * * * *