U.S. patent application number 10/487447 was filed with the patent office on 2005-02-17 for method and apparatus for stirring and treating continuous and semi continuous metal casting.
Invention is credited to Dvoskin, Pavel, Nadam, Dror, Zlochevsky, Valery.
Application Number | 20050034840 10/487447 |
Document ID | / |
Family ID | 11075732 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050034840 |
Kind Code |
A1 |
Dvoskin, Pavel ; et
al. |
February 17, 2005 |
Method and apparatus for stirring and treating continuous and semi
continuous metal casting
Abstract
A method and apparatus for stirring and treating continuous and
semi-continuous casting of metallic rods (12). The apparatus
comprising: a stand (30) for suspending at least one electric arc
electrode (24) over the upper surface of a metallic casting (14)
after or during pouring, at least one electrode (24) for forming a
moving electric arc (38) over the upper surface of the mettalic
casting being cast, a second electrode, being the liquid metal
(14), for completion of an electric circuit including said electric
arc (38) and the liquid metal (14); and control means (34),
connected between said apparatus and a power supply (36) and
arranged to supply power to the plasma arc electrodes (14, 24), for
monitoring the parameters of the electric arc (38). The invention
also provides a method for casting the metallic rods (12) by using
the above described apparatus.
Inventors: |
Dvoskin, Pavel; (Sfarim,
IL) ; Zlochevsky, Valery; (Netanya, IL) ;
Nadam, Dror; (Sarid, IL) |
Correspondence
Address: |
EITAN, PEARL, LATZER & COHEN ZEDEK LLP
10 ROCKEFELLER PLAZA, SUITE 1001
NEW YORK
NY
10020
US
|
Family ID: |
11075732 |
Appl. No.: |
10/487447 |
Filed: |
October 12, 2004 |
PCT Filed: |
August 20, 2002 |
PCT NO: |
PCT/IL02/00686 |
Current U.S.
Class: |
164/470 ;
164/508 |
Current CPC
Class: |
B22D 27/06 20130101;
B22D 11/11 20130101 |
Class at
Publication: |
164/470 ;
164/508 |
International
Class: |
B22D 027/02; B22D
011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2001 |
IL |
145099 |
Claims
We claim:
1. A continuous and semi-continuous casting apparatus for the
production of improved-quality rods, including rod cross-sections
having a aspect ratio exceeding 1.8, the apparatus comprising: a) a
stand for suspending at least one electric arc electrode over the
upper surface of the molten metal casting after or during pouring;
b) at least one electrode for forming a moving electric arc over
the upper surface of said metallic casting being cast: c) a second
electrode, being the liquid metal, for completion of an electric
circuit including said electric arc and the liquid metal; and d)
control(s) mean(s) connected between said apparatus and a power
supply and arranged to supply power to the plasma arc electrode(s)
and monitoring the parameters of the electric arc.
2. The continuous and semi continuous casting apparatus as claimed
in claim 1, wherein a second electric circuit is provided to create
a magnetic field urging said plasma arc towards the center of said
upper surface of said molten metal, by said second electric circuit
passes through molten metal held in a reservior and reaches said
metallic component of said mold through a molten metal column
formed in a feed tube.
3. The continuous and semi continuous casting apparatus as claimed
in claim 1, wherein said first electrode is hollow and means are
provided for directing a stream of an inert gas, there through to
impact said upper surface for preventing oxidation of the molten
metal forming said upper surface and for the removal therefrom of
solid impurities and the removal of casting powder if present.
4. The continuous and semi continuous casting apparatus as claimed
in claim 1, further including a refractory guard ring slightly
deeped in the surface of said rod to maintain exclusion of solid
impurities such as casting powder from said upper surface under the
plasma arc, and to electrically insulate an upper portion of said
mold from said plasma arc.
5. A continuous and semi continuous casting apparatus substantially
as described hereinbefore and with reference to the accompanying
drawings.
6. A method for continuous and semi continuous metal casting for
improving quality of metallic continuous rods, said method
comprising; step a) continuously pouring the liquid metal into a
mold for casting rods. step b) providing at least one first
electric arc electrode and positioning same slightly above the
upper surface of the molten metal; step c) providing a second
electrode in electrical contact with a section of the mold being
electrically conductive, and applying an electric current to said
electrodes to form an arc between said first electrode and said
upper surface; and step d) continuously moving said electric arc(s)
over said upper surface.
7. A continuous or semi continuous casting method as claimed in
claim 6 including the use of casting powder by: step a)
continuously pouring a liquid metal into a mold and applying
casting powder to the rod; step b) removing the casting powder from
the arc working zone. One of the ways to remove the casting powder
is by blasting an inert gas such as argon over said upper surface;
step c) preventing the return of said casting powder by placing at
list one refractory guard ring on said upper surface; step d)
providing at least one plasma arc electrode and positioning same
slightly above said upper surface of the molten metal, inside each
protecting ring; step f) providing a second electrode in electrical
contact with a section of the mold being electrically conductive,
and applying an electric current to said electrodes to form an arc
between said first electrode and said upper surface; and step e)
continuously moving said electric arc(s) over said upper
surface.
8. A continuous or semi continuous casting method as claimed in
claim 6, wherein said electric current applied to said electrodes
to form a plasma is a DC current.
9. A continuous casting or semi continuous method, substantially as
described hereinbefore and with reference to the accompanying
drawings.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to metal continuous and semi
continuous castings. More particularly, the invention provides an
improved method and apparatus for stirring and treating continuous
and semi-continuous casting to produce a high-quality cast of any
desired length and cross section composed of a ferrous or of a
non-ferrous metal.
[0002] Continuous and Semi-continuous casting are the most commonly
used methods for casting and producing semi-finished products such
as plats, tubs, shits, etc. While continuous casting is the main
method for casting ferrous alloys i.e. low carbon steel, stainless
steel, etc., semi-continuous casting is the preferred method for
casting non-ferros alloys such as aluminium and copper alloys. Both
methods based on continuously pouring metal from a reservoir mostly
known as the tundish or the distributor, to a cooled open mold. The
mold is open both for metal entrance (usually from the top) and for
metal exit (usually from the bottom). Unlike other casting methods
the metal does not solidifies completely in the mold, but rather
receives an initial solidifying shell and continues to cools
outside the mold most commonly by water jets. The cast produced by
continuous or semi-continuous casting such as billet, bloom, bar,
slab etc, hereandafter defined as "rod" is advanced by means of
rollers, gravitation, piston etc. the rod undergo further plastic
deformation for producing the semi-finished products, mentioned
above. The main difference between continuous and semi-continuous
casting regards the length been cast. In continuous casting the
total length can be hundreds of meters in a continuous process. At
the end of the casting the rods, are cut from the casting. While in
semi-continuous casting the length is constant in the size of
several meters, and each billet is cast in a single process.
[0003] A further mentions of continuous casting will refer to
continuous as well as semi continuous casting.
[0004] A further effect in metal alloy casting is the appearance of
dendrites during cooling, these being formed during solidification
as various points in the mass take up a lattice tree like
structure. During the formation of dendrites, alloying elements,
such as C, Cr or Ni are pushed outwardly to form a crystal grain
boundary, these form later a site for the initiation of cracks in a
finished component. A concentration of these alloying elements is
referred to as segregation, which can to some extent be combated by
lower pouring temperatures.
[0005] Impurities from the ladle or the casting powder can form
inclusions and further reduce the mechanical properties of the
products.
[0006] Gases, from the atmosphere or other sources are also present
in the liquid metal, these being the main cause of casting
porosity.
[0007] Applying roller pressure to the rod during continuous
casting is proposed by Fukuoka et al. in Japanese Patent no.
JP56050705A2. Pressure is said to prevent the generation of a crack
on the bottom side of the casting groove. The roller is located at
the point where the bent ingot is straightened. Obviously this
process is of no help in improving the microstructure of the
metal.
[0008] In U.S. Pat. No. 4,756,749 Praitoni et al describe and claim
a process for the continuous casting of steel from a tundish having
several casting spouts. While in the tundish the molten steel is
subjected to further heating, which in claim 5 is a transferred-arc
plasma torch. This patent is for heating the metal in the tundish,
while the present invention is for treating the molten metal in the
mold during the solidification process.
[0009] Lowry et al in U.S. Pat. No. 4,770,724 describe an unusual
continuous casting method for metals which claims to eliminate
voids and flaws and to produce a dense homogeneous product. This is
achieved by forcing the metal to flow upwards, against gravity, by
means of an electromagnetic field which also provides containment
forces. The method disclosed includes electromagnetic stirring of
the molten metal; this aspect of the process is in common
industrial use, and is known to improve homogeneity and produce a
fine grain structure.
[0010] However electromagnetic stirring consumes much electric
power, cannot be applied to very large castings and has limited
influence on ingots having aspect ratios (width/breadth ratio) in
excess of 1.8
[0011] In U.S. Pat. No. 5,963,579 Henryon discloses a method of
heating a molten metal in a continuous casting tundish, using a
plasma torch and a special tundish. Other prior-art casting systems
are referred to in this specification which also apply a plasma arc
to metal held in the tundish. As with the Praitoni disclosure, such
heating and/or stirring does not effect the solidification process
in the mold.
[0012] PCT/IL97/00023 describes an electric arc which could be used
in the present aparatus.
OBJECTS OF THE INVENTION
[0013] It is therefore one of the objects of the present invention
to obviate the disadvantages of prior art for stirring and treating
continuous casting rods and to provide an improved method and an
apparatus for producing better quality rods, without the need to
consume great quantities of electric power.
[0014] It is a further object of the present invention to provide
an apparatus that will stir the metal during the solidification
process and thus, increase homogeneity, decrease gas porosity and
break up dendrites into small pieces and thereby reduce the grain
size of the finished rod.
[0015] Yet a further object of the invention is to improve the
production of a continuous rods having aspect ratios exceeding
1.8.
SUMMARY OF THE INVENTION
[0016] The present invention achieves the above objects by
providing a stirring and treating continuous casting apparatus for
the production of improved-quality rods from molten metal,
including rod cross-sections having a aspect ratio exceeding 1.8,
the apparatus comprising:
[0017] a) a stand for suspending at least one electric arc
electrode over the upper surface of a metallic casting after or
during pouring;
[0018] b) at least one electrode for forming a moving electric arc
over the upper surface of said metallic casting being cast:
[0019] c) a second electrode, being the liquid metal, for
completion of an electric circuit including said electric arc and
the liquid metal; and
[0020] d) control(s) mean(s) connected between said apparatus and a
power supply and arranged to supply power to the plasma arc
electrode(s) for monitoring the parameters of the electric arc.
[0021] The invention also provides a method for improving quality,
such as: reducing voids, inclusions, porosity, dendrite and grain
size in metallic continuous rod casting and for improving
homogeneity therein, the method comprising
[0022] step a) continuously pouring the liquid metal into a mold
for casting rods.
[0023] step b) providing at least one first electric arc electrode
and positioning same slightly above the upper surface of the molten
metal;
[0024] step c) providing a second electrode in electrical contact
with a section of the mold being electrically conductive, and
applying an electric current to said electrodes to form an arc
between said first electrode and said upper surface; and
[0025] step d) continuously moving said electric arc(s) over said
upper surface.
[0026] Yet further embodiments of the invention will be described
hereinafter.
[0027] It will thus be realized that the novel device of the
present invention improves rod quality by stirring the liquid metal
in the mold. The electric power required for this purpose is
moderate. For example, in a test carried out in producing a
semi-continuous slab, aspect ratio 2, made of copper nickel alloy,
the plasma-arc consumed only 2 kWh per ton.
[0028] It is to be stressed that the method and apparatus of the
present invention have been tested in practice, and castings
produced by the new method have been examined and compared to the
same castings produced by conventional methods. Test results, also
to be found in the description, leave no doubt as to the improved
quality achieved by use of apparatus constructed according to the
present invention.
SHORT DESCRIPTION OF THE DRAWINGS
[0029] The invention will now be described further with reference
to the accompanying drawings, which represent by example preferred
embodiments of the invention.
[0030] Structural details are shown only as far as necessary for a
fundamental understanding thereof. The described examples, together
with the drawings, will make apparent to those skilled in the art
how further forms of the invention may be realized.
[0031] In the drawings:
[0032] FIG. 1 is a partially section of a preferred embodiment of
the apparatus according to the invention;
[0033] FIG. 2 is a detail section of the first electrode suspended
over the rod;
[0034] FIG. 3 is a partially sectional view of an embodiment of the
apparatus wherein a second electric circuit is provided to create a
magnetic field urging said plasma arc towards the center of the
upper surface.
[0035] FIG. 4 is a detail sectional view of an embodiment with a
refractory guard ring arranged to prevent solid impurities such as
casting powder from reaching the upper surface under the plasma
arc;
[0036] FIG. 5 is a detail sectional view of an embodiment arranged
to provide a stream of inert gas for preventing oxidation of the
molten metal;
[0037] FIG. 6 is a photographic view of a section of a slab cast by
conventional methods; and
[0038] FIGS. 7a and b are photographic views of a section of a slab
cast from the same material using the method and the apparatus of
the present invention.
FULL DESCRIPTION OF THE INVENTION
[0039] There is seen in FIGS. 1 and 2 a continuous casting
apparatus 10 for the production of improved-quality rods 12 from
molten metal 14.
[0040] A water-cooled mold 16 has a cavity open at its upper end 20
to receive molten metal 14 and open at its lower end 22 to release
the partially solidified rod 12 being formed. The mold 16 is
electrically conductive, and functions as one of the components of
a electric circuit.
[0041] A first plasma arc electrode 24 is positioned so that its
lower face 26 thereof is disposed in proximity to the upper surface
28 of the molten metal 14 having been poured into the mold 16.
[0042] A stand 30 is provided for supporting the first plasma arc
electrode 24 above the upper surface 28, leaving a gap of between
2-20 mm between the first electrode 24 and the upper surface 28 of
the molten metal 14.
[0043] A second plasma arc electrode 32 is attached to the
electrically conducting mold 16 or to the metal 12 or 14.
[0044] Control means 34 are connected between the apparatus 10 and
power supply source 36. The control means 34 controls the electric
circuit parameters, thus enabling an operator to increase or
decrease power in accordance with the needs of the process. The
plasma arc 38 is formed between the upper surface 28 of the molten
metal 14 and the lower face 26 of the first electrode 24. The
plasma arc 38 completes an electric circuit, and causes stirring of
the molten metal 14 in the mold 16.
[0045] The rod 12 continuous to grow in length as long as required
and as long as further molten metal 14 is available from the
tundish 46 through the nozzle 48.
[0046] With reference to the rest of the figures, similar reference
numerals have been used to identify similar parts.
[0047] Referring now to FIG. 3, there is seen a continuous casting
apparatus further provided with a second electric circuit 68,
requiring less power than the first electric circuit, is provided
to create a magnetic field urging the plasma arc 38 (see FIG. 2)
towards the center of the upper surface 28 (see FIG. 2) of the
molten metal 14.
[0048] The second electric circuit 68 passes through the molten
metal held in the tundish 46 and through the nozzle 48 and reaches
the molten metal 14 in the mold 16.
[0049] FIG. 4 shows a detail of a continuous casting apparatus 10,
further provided with a refractory guard ring 54 arranged to
prevent solid impurities such as casting powder 56 from the upper
surface 28 under the plasma arc 38; The refractory guard ring 54
submerged to a level below the upper surface 28 of the molten metal
14 contained in the mold 16.
[0050] FIG. 5 shows a detail of a continuous casting apparatus 10,
further provided with a stream of inert gas 76 device for
preventing oxidation of the molten metal 14; The first electrode 24
is hollow and a jet tube 78 is provided for directing a stream of
an inert gas 76, The gas jet 78 impacts the upper surface 28 of the
molten metal 14 of the rod 12 in the mold 16. The inert gas
prevents oxidation of the molten metal forming the upper surface
28, and removes therefrom any solid impurities, particularly any
casting powder if present.
[0051] Any combination of the embodiments described and illustrated
in FIG. 3, FIG. 4 and FIG. 5 can be applied.
[0052] FIG. 6 is a photograph 90 of a copper-nickel slab section of
400*200 mm cast by conventional semi-continuous casting.
[0053] FIGS. 7a and b are photographs of the same alloy been
treated by the method and apparatus of the present invention. The
improved macrostructure is evident.
[0054] The scope of the described invention is intended to include
all embodiments coming within the meaning of the following claims.
The foregoing examples illustrate useful forms of the invention,
but are not to be considered as limiting its scope, as those
skilled in the art will readily be aware that additional variants
and modifications of the invention can be formulated without
departing from the meaning of the following claims.
* * * * *