Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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"CRYSTALLIZER FOR CONTINUOUS CASTING AND METHOD FOR ITS
PRODUCTION"
* * * * *
FIELD OF THE INVENTION
The present invention concerns a crystallizer for continuous casting, usable
in the
iron and steel making industry to cast billets, blooms or other similar
products, of any
type and cross section. The invention also concerns the method for its
production.
BACKGROUND OF THE INVENTION
Different crystallizers for continuous casting are known, suitable to cast
billets,
blooms or other iron and steel products, each having a tubular body provided
with a
through longitudinal cavity with a desired cross section, corresponding to the
cross
section of the product to be cast, for example circular, elliptical or
polygonal, and in
which the liquid casting metal is suitable to pass. On the wall or walls which
define
the tubular body of the crystallizer and which have a thickness of some tens
of
millimeters, a plurality of channels are normally made longitudinally, which
are part
of a closed cooling circuit in which a cooling liquid, for example water, is
made to
circulate.
Some examples of crystallizers for continuous casting and corresponding
production methods are described in the Italian publication nos. 0001415398
and
0001415767 filed by the present Applicant.
Another example of a crystallizer for continuous casting is described in the
document EP-A-1.468.760 and comprises a first tubular body, or internal
tubular
body, which defines a casting channel for the liquid metal, and a second
tubular body,
or external tubular body, which is associated externally to the first tubular
body.
In particular, the internal tubular body is provided, on its external contact
surface
with the external tubular body, with support ribs and connection ribs
alternating with
the support ribs.
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The support ribs and the connection ribs protrude toward the outside and
extend
along the axial extension of the crystallizer.
The function of the support ribs is to maintain the external tubular body
distanced
from the internal one, while the connection ribs are inserted in attachment
seatings
made on the internal surface of the external tubular body, defining a fixed-
joint
mechanical coupling, making the internal tubular body able to be disassembled
from
the external tubular body.
Moreover, the connection ribs and the support ribs define, between the
internal
tubular body and the external tubular body, a plurality of hollow spaces in
which a
cooling fluid flows.
The fixed-joint mechanical coupling between the internal tubular body and the
external tubular body does not guarantee a hydraulic seal of the cooling fluid
in the
hollow spaces, since the support ribs have only a distancing function for the
external
tubular body and are not able to guarantee the hydraulic seal between adjacent
hollow
spaces.
This disadvantage is linked to the rigidity, and the geometric and dimensional
tolerances of each of the two tubular bodies and to the fact that the latter
are not
intimately coupled to each other.
In particular, document EP-A-1.468.760 provides that the internal tubular body
is
made of metal material, for example copper, while the external tubular body is
made
of a metal or non-metal material, a composite for example, such as laminate
carbon.
Moreover, it is known that traditional crystallizers are affected by a series
of
disadvantages due to the variation in the internal conicity of the
crystallizer, at least
around the meniscus zone. Indeed, mainly in this zone, there is a tendency to
expand
toward the outside, due to the heat stresses deriving from the contact
temperature
between the liquid steel and the wall of the crystallizer. This causes a
reduction in
conicity between meniscus and upper entrance section, and a greater conicity
than the
specification conicity in the lower segment of the crystallizer, always with
respect to
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the meniscus zone. This causes a deterioration in the quality of the cast
product
because of the alteration in the functioning conditions and consequent poor
heat
conduction between the skin of the steel and the cooled wall of the
crystallizer itself.
Consequently, the probability of leakages of liquid steel from the skin, also
called
"breakout", is increased, following the lack of heat conduction which causes
the skin
to stick to the walls of the crystallizer, called "sticking".
One purpose of the present invention is to make a crystallizer for continuous
casting, with cooling channels incorporated in the walls, which overall has an
increased structural rigidity without increasing the thickness of its walls,
in order to
guarantee an increased casting efficiency and an increased quality of the
product
exiting from the crystallizer.
Another purpose of the present invention is to make a crystallizer for
continuous
casting, of the type indicated above, that is simple in construction and at
the same
time has a reduced cost compared to known crystallizers, even when the
crystallizer
has large sizes, for example a diameter or width equal to or more than 800 mm,
reducing to a minimum the use of metal, for example copper, needed to make the
walls of its tubular body.
It is also a purpose of the present invention to make a crystallizer for
continuous
casting that allows to obtain cast metal products of high quality, keeping the
specification conicity substantially unvaried, when both hot and cold.
Another purpose of the present invention is to make a crystallizer for
continuous
casting, of the type indicated above, that can be easily used, without any
contraindication, in association with a mechanical agitator, also called
stirrer.
Another purpose of the present invention is to make a crystallizer for
continuous
casting, of the type indicated above, that is reliable and can be used,
without any
contraindication and with maximum efficiency, even with a radioactive rod used
to
detect the level of liquid metal inside the crystallizer during casting.
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Another purpose of the present invention is to perfect a method to make a
crystallizer for continuous casting, of the type indicated above, that allows
to reduce
production costs without reducing the characteristics of structural rigidity,
safety,
reliability and thermal and thermo-mechanical efficiency of the crystallizer
itself.
Another purpose of the present invention is to perfect a method that allows to
make
a crystallizer for continuous casting, of the type indicated above, easily and
with
simple work steps, that can have any shape and cross section, for example
circular,
elliptical or polygonal.
The Applicant has devised, tested and embodied the present invention to
overcome
the shortcomings of the state of the art and to obtain these and other
purposes and
advantages.
SUMMARY OF THE INVENTION
In accordance with the above purposes, a crystallizer for continuous casting,
according to the present invention, comprises a tubular body with at least a
wall that
defines a through longitudinal casting cavity and a plurality of longitudinal
grooves
made at least on a part of an external surface of the at least one wall and
open toward
the outside thereof.
According to one characteristic of the present invention, a covering binding,
comprising one or more overlapping layers of fiber material, is irremovably
wound
around the external surface of the at least one wall, so as to create an
indivisible whole
between the at least one wall with the longitudinal grooves and the covering
binding.
Here and hereafter, by covering binding we mean a material comprising a
plurality
of fibers adjacent to each other to define one or more bands that, once in
position,
cover at least part of the external surface of the wall.
The layers of fiber can be impregnated with a polymer material, which, once
the
covering binding has been wound around the external surface of the wall, is
polymerized and determines the solid and irremovable attachment of the
covering
binding to the wall.
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This allows to obtain a crystallizer for continuous casting that maintains its
specification conicity unchanged whether it is hot or cold, thanks to the
reinforcement
structure that the external covering binding achieves for the walls of the
crystallizer.
Indeed the covering binding, wound tightly around the crystallizer in a
direction
mainly transverse to its longitudinal direction, limits the deformations and
movements of the walls, maintaining the internal conicity, while allowing the
longitudinal dilation due to heat phenomena for example between 0 and 4 mm.
According to a first form of embodiment of the present invention, the covering
binding is in direct contact with the external surface of the at least one
wall and closes
the longitudinal grooves. Corresponding cooling channels are thus obtained,
configured to make a cooling liquid flow inside them, for example water,
suitable to
cool the tubular body of the crystallizer.
According to a second form of embodiment of the present invention, as an
alternative to the first, the covering binding is in direct contact with a
metal layer
made with electrolytic deposition techniques; the metal layer, in its turn, is
in contact
with the external surface of the at least one wall and closes the longitudinal
grooves
to form a corresponding plurality of cooling channels.
Therefore, unlike the technical solution described in EP-A-1.468.760, which
provides to use electrolytic deposition as a solution to oxidation phenomena,
the
present invention describes the use of electrolytic deposition with the
purpose of
creating sealed cooling channels on the external surface of the walls of the
crystallizer.
In this way, the covering binding makes rigid the whole made by the at least
one
wall of the crystallizer and the metal layer associated thereto.
According to a third form of embodiment of the present invention, alternative
to
the first two, it is provided that the longitudinal grooves are closed by at
least a plate
associated to the external surface of the at least one wall so as to define a
corresponding plurality of cooling channels inside which a cooling liquid
flows.
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In this case, the covering binding is in direct contact with the at least one
plate so
as to reinforce and increase the security of the connection between the at
least one
plate and the at least one wall.
According to a fourth form of embodiment of the invention, it is provided that
the
longitudinal grooves are closed by at least a lamina made of a fiber-
reinforced
polymer material, fiberglass for example, associated to the external surface
of the at
least one wall to define a corresponding plurality of cooling channels inside
which a
cooling liquid flows. The covering binding, in this case, is located in direct
contact
with the lamina of fiber-reinforced polymer material in order to make rigid
the whole
made by the at least one wall and the lamina of fiber-reinforced polymer
material.
The covering binding can be wound around the wall defining even variable
thicknesses in a longitudinal direction in the most stressed zones, for
example the
meniscus zone. The variation in thickness in a longitudinal direction of the
covering
binding can even be some millimeters. Merely by way of example the covering
binding, in the non-thickened zone, has a thickness comprised between lmm and
8mm.
The variable thickness of the fibers which surround the crystallizer, after
complete
polymerization of the covering binding, allows to work with machine tools on
the
external containing surface so as to obtain seatings for housing packings or
break-
pins.
The method to make a crystallizer for continuous casting, according to the
present
invention, comprises a step in which a tubular body is made, of metal for
example,
more specifically of copper, with at least a wall that defines a through
longitudinal
casting cavity and a plurality of longitudinal grooves made at least on one
part of the
external surface of the at least one wall and open toward the outside thereof
According to another characteristic of the present invention, the method
according
to the present invention also comprises a step in which a covering binding,
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comprising one or more layers of fiber material, is associated to the external
surface
of the at least one wall.
In particular, the covering binding comprises a band made using at least a
fiber,
impregnated or pre-impregnated with for example a volumetric ratio of fibers
of 60%,
such as carbon, and glue or polymer resin of 40%. The polymer material is the
type
resistant to high temperatures, that is, equal to or more than 100 C, such as
a polymer
for example chosen from the group comprising polyamide, epoxy or polyester
resins.
The fibers can be chosen from a group comprising carbon fibers, glass fibers,
aramid fibers or similar.
The covering binding in fiber, which becomes rigid when the polymer solidifies
by polymerizing, can be applied using any known technique, including the
filament
winding technique.
The polymerization of the polymer can occur through heat polymerization steps,
that is, reticulation of the resin, called curing.
During the curing step, the crystallizer is heated to a temperature comprised
between 30 C and 120 C and kept at this temperature for a period comprised
between
and 200 minutes. These conditions determine the reticulation of the polymer
resin
and therefore a solidarization of the binding to the wall or walls.
This allows to guarantee better characteristics of resistance and heat
consolidation
20 depending on the type of resin applied.
In possible forms of embodiment, after the curing step, a post-curing step can
be
provided during which the crystallizer is heated to a temperature comprised
between
80 C and 200 C and kept at this temperature for a period comprised between 1
hour
and 20 hours.
In possible forms of embodiment, for the whole duration of the curing and/or
post-
curing steps, the crystallizer is kept in rotation around its own axis.
According to one possible implementation, the crystallizer, after the curing
and
possibly post-curing steps, can be subjected to a forced cooling.
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The operation of winding the covering binding on the wall can include the
installation, on a suitable apparatus and by means of a dedicated apparatus,
of the
wall in rotating mode around an axis of rotation and subsequent winding of the
covering binding perpendicularly to the axis of longitudinal development, or
with a
winding angle comprised between 0 and 10 , preferably between 0 and 5 , with
respect to the perpendicular to the axis of longitudinal development of the
crystallizer.
The winding operation can occur with a controlled tension of the fibers, for
example from IN and 50N per fiber.
The solution of using the covering binding, in particular of fiber, around the
tubular
body of the crystallizer, which is new and original, allows to obtain at least
the
following advantages:
- increasing the rigidity of the hollow tubular body of the crystallizer;
- maintaining the internal conicity of the crystallizer both when hot and when
cold;
- maximizing the efficiency of a possible radioactive rod associated to the
crystallizer,
given that the covering binding is transparent to radiations;
- containing the costs of production of crystallizers of any shape, or with
any cross
section, for example polygonal, circular, or elliptical, and even of
considerable sizes,
for example with diameters, or widths, equal to or more than 800mm;
- reducing to a minimum the thickness of the walls which define the tubular
body of
the crystallizer and therefore minimum use of metal, for example copper, of
which
they are made;
- prolonging the life of the crystallizer;
- improving the quality of the cast product;
- possibility of working with machine tools on the solidified covering
binding, for
example to define grooves for sealing rings or holes for the insertion of
break-pins.
According to possible solutions of the method according to the present
invention,
before winding the one or more layers of fiber material it provides to fill
the
longitudinal grooves with disposable material, for example wax, to deposit a
metal
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layer on the external surface of the at least one wall by electrolytic
deposition
techniques, in order to close the longitudinal grooves, and to subsequently
remove
the disposable material from the longitudinal grooves so as to define
corresponding
cooling channels.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other characteristics of the present invention will become apparent
from
the following description of some forms of embodiment, given as a non-
restrictive
example with reference to the attached drawings wherein:
- fig. 1 is a perspective and schematized view of a crystallizer for
continuous casting
according to a first form of embodiment of the present invention;
- fig. 2 is an enlarged detail of the crystallizer in fig. 1;
- fig. 3 is a perspective and schematized view of a detail of a crystallizer
according to
a second form of embodiment of the present invention;
- fig. 4 is a schematized view of a detail of a crystallizer according to a
third form of
embodiment of the present invention;
- figs. 5 and 6 are schematized views of possible variants of the crystallizer
according
to the present invention.
To facilitate comprehension, the same reference numbers have been used, where
possible, to identify identical common elements in the drawings. It is
understood that
elements and characteristics of one form of embodiment can conveniently be
incorporated into other forms of embodiment without further clarifications.
DETAILED DESCRIPTION OF SOME FORMS OF EMBODIMENT OF THE
PRESENT INVENTION
With reference to figs, 1 and 2, a crystallizer 10 for continuous casting
according
to the present invention, in a first form of embodiment, comprises a tubular
body 11
with a wall 12, for example made of copper or its alloys, which defines a
through
longitudinal casting cavity 13. The thickness of the wall 12 is for example
comprised
between 10 mm and 50 mm.
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There is a plurality of longitudinal grooves 14 on at least an external part
of the
wall 12. Each longitudinal groove 14 is open toward the outside of the wall
12.
A covering binding 15, which in this case comprises one or more layers of a
band
16 of fiber, impregnated or pre-impregnated with a polymer resistant to high
temperatures (that is, equal to or higher than 100 C), is in direct contact
with the
external surface of the wall 12 and closes the longitudinal grooves 14 from
the
outside. In this way corresponding channels 17 are made, configured to make a
cooling liquid, for example water, flow inside them. In this specific case, it
is
provided that the band 16 defines a plurality of layers wound on the external
surface
of the wall 12 of the crystallizer 10.
In a second form of embodiment, a crystallizer 110 (fig. 3) according to the
present
invention comprises, interposed between the covering binding 15 and the wall
12, a
metal layer 18 made with electrolytic deposition techniques, for example as
described
in Italian Publication No. 0001415767 cited above.
In this case, it is the metal layer 18 that hermetically closes the
longitudinal
grooves 14 from the outside of the wall 12 and defines the plurality of
cooling
channels 17.
Therefore, in this second form of embodiment, the covering binding 15 is in
direct
contact with the metal layer 18, in order to make rigid the whole made up of
the latter
and the wall 12. This allows to have a very contained thickness of the metal
layer 18,
for example in the range of one or two millimeters. The covering binding 15 in
this
case has a containing function of the metal layer 18 and guarantees the seal
of the
latter even at high working pressures of the cooling fluid circulating in the
channels
17.
According to the form of embodiment in fig. 6, the metal layer 18 can be
replaced
by a lamina 23 made of a fiber-reinforced polymer material which, closing the
longitudinal grooves 14 from the outside, defines the corresponding plurality
of
cooling channels 17. The covering binding 15 is wound intimately in direct
contact
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with the lamina 23 to make rigid the whole constituted by the wall 12 and the
lamina
23.
According to a third form of embodiment, a crystallizer 210 (fig. 4) according
to
the present invention comprises a tubular body 211 provided with a plurality
of walls
212 defining a longitudinal casting cavity 213. The longitudinal grooves 14,
open
toward the outside, are made on the external surface of the walls 212, by
removing
material. At least one plate 219, in this specific case four plates 219, are
associated
to the external surface of the tubular body 211, for example welded or glued,
and are
provided to close the longitudinal grooves 14 made on the walls 212 of the
tubular
body 211 from the outside and to define the cooling channels 17.
The plates 219 can be associated to the external surface of the tubular body
211,
for example, by braze welding or structural gluing, in the same way as
described in
the Italian publication 0001414954 in the name of the Applicant.
In this case too, as in the first form of embodiment, the covering binding 15
is in
direct contact with the surface of the plates 219 that is external during use,
to reinforce
them and increase the secure seal of the braze welding.
Forms of embodiment of the present invention provide that the covering binding
15 has a constant thickness along the longitudinal extension of the tubular
body 11,
211.
Other forms of embodiment, one of which is shown in fig. 5, provide that the
covering binding 15 is provided with a thicker portion 20 that has a greater
thickness
than the thickness along the longitudinal extension of the tubular body 11 or
211. In
this way it is possible to generate zones of the crystallizer 10 with variable
resistance
and rigidity along its longitudinal extension that are determined, for
example,
depending on a variable development of the pressure of the cooling fluid in
the
cooling channels 17 or on different conditions of mechanical and/or heat
stress to
which it can be subjected during normal use.
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According to other forms of embodiment of the present invention, shown for
example in fig. 6, mechanical workings, for example to define circumferential
seatings 21 for housing sealing rings or holes 22 for the insertion of break-
pins, can
be made on the covering binding 15.
The method for producing each of the crystallizers 10, 110, 210 for continuous
casting described heretofore comprises a step in which the tubular body 11,
211 is
made, with the wall 12 or walls 212 that define the longitudinal cavity 13,
213 and
the plurality of longitudinal grooves 14, made for example by removing
material,
such as milling, at least on one part of the wall 12 or walls 212, and open
toward the
outside thereof.
The method also comprises a step in which a covering binding 15, as described
heretofore, is associated to the external surface of the wall 12 or walls 212.
In particular, the binding 15 comprises the band 16 made with one or more
overlapping layers, using at least a fiber impregnated or pre-impregnated with
a
polymer resistant to high temperatures, as indicated above, that is chosen for
example
from a group comprising polyamide, epoxy or polyester resins.
It can be provided, for example, that the wall 12 or walls 212 is or are
installed on
a winding machine, for example by means of clamps or specific equipment to
allow
the subsequent winding operation of the fibers around it.
The fibers can be polymerized in different curing passes, for example a curing
at
30-120 C for 20-200 minutes, followed by a post-curing at 80-200 C for 1-20
hours
depending on the resin applied.
For example the covering binding 15 can be applied using the filament winding
technique.
It is clear that modifications and/or additions of parts may be made to each
of the
crystallizers 10, 110, 210 for continuous casting as described heretofore,
without
departing from the field and scope of the present invention.
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It is also clear that, although the present invention has been described with
reference to some specific examples of embodiments, a person of skill in the
art shall
certainly be able to achieve many other equivalent forms of crystallizer for
continuous casting and/or other methods to make them, having the
characteristics as
set forth in the claims and hence all coming within the field of protection
defined
thereby.
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