Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 BACKGR~UND OF THE INVENTION
Field of the Invention
This invention relates to a continuous casting mold
having a removable insert constituting the entry end thereo~_
Descri~tion of the Prior Art
In the continuous casting of molten material,
particularly metals and alloys such as steel, the apparatus
for this purpose includes a tundish for receiving the molte~
material to be cast. The tundish has a refractory,
horizontally disposed nozzle through which the molten metal
leaves the tundish for casting. The nozzle at the end
opposite that connected to the tundish is connected to a fl~w-
through continuous casting mold. The continuous casting mold
is made of a heat-conducting material, usually copper or
copper alloys, and provision is made for circulation of
liquid, usually water, to cool the mold. As the molten metal
enters the mold and contacts the cooled, interior mold
surfaces, it is solidified to form a solidified skin of the
molten metal with the interior portion remaining in the molten
condition. The thickness of ~he solidified skin increases
progressively along the length of the mold. As this partially
solidified or embryo casting leaves the mold, the skin is
sufficiently thick to prevent the breakout of molten metal.
Thereafter, the embryo casting is progressively cooled and
25eventually complete solidification of the casting is achieved.
The refractory material ~f the nozzle which is in
contact with the molten metal leaving the tundish is at
extremely high temperatures. In contrast, the mold abutting
1 the refractory nozzle is at significantly lower
temperatures. ~onsequently, it is conventional practice to
place on the interior of the mold a break ring to serve as a
transition material between the refractory of the nozzle and
the heat-conducting material of the cooled mold. ~he break
ring functions to define the point at which the shell of the
casting begins to form when the molten metal initially enters
the mold. It prevents solidification and hang-up of the metal
at the end of the nozzle at the interface of the nozzle and
10 mold. More specifically in this regard, as is well known,
relative oscillation or vibration of the mold and casting is
provided longitudinally to facilitate withdrawal of the
partially solidified casting from the mold. If metal enters
l- and solidifies at the interface or connection between the
i 15 nozzle and mold a solidified metal projection, commonly termed
a "fin", is formed. This, during withdrawal of the casting
from the mold, results in surface irregularities of the
casting skin, which can cause cracking with resulting molten
metal break-out. In addition, the break ring prevents the
20 molten metal from freezinq within the pores of the refractory
material adjacent the continuous casting mold. In summary,
the break ring prevents damage to the newly formed solidified
casting skin at the entry end of the mold. For this purpose,
~ and particularly in the continuous casting of molten alloys,
,` 25 such as steel, the break ring must have chemical resistance to
the steel, high resistance to thermal shoc~, low thermal
conductivity, high resistance to
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l wear and erosion and accurately conform to the surface on which
it is mounted. To meet these requirements, the break ring is
conventionally constructed from refractory oxides or nitrides,
such as boron nitride, silicon nitride and zirconia, and is
machined to the proper contour to achieve the required accurate
mounting.
The continuous casting mold in typical steel casting
operations is of a generally round and/or rectangular
configuration to permit the casting of slabs or billets which are
subsequently reduced to flat-rolled sheet and strip or long
structured products, including bars and beams, respectively. The
configuration of the mold may also conform generally with the
shape of other products to be cast. Consequently, the interior
cross section of the continuous casting mold must conform to this
desired configuration. Each mold, however, due to inaccuracies
in construction will vary somewhat in dimension. Therefore, the
break ring requires either machining to very close tolerances to
mate with the interior of each continuous casting mold or may be
formed integrally with the mold in accordance with U,S. Patent
' No. 4,744,406 which issued May 17, 1988 to L.F. Rostik. If
the break ring is not accurately dimensioned with respect to
the mold interior onto which it i9 mounted, this will result
in the molten metal propagating between the connection of the
' break ring and the mold interface surface. As discussed herein,
this may prevent withdrawal of the casting.
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1 Because the temperature of the molten metal issuing from
the nozzle through the continuous casting mold is highest at
the entry end of the mold, this end of the mold is subjected
to more rapid wear than the remainder of the mold body.
Consequently, it is the wear at the mold inlet end that first
causes deterioration of the mold sufficient to require
replacement thereof. In this instance, the remainder of the
mold body is generally not worn to the extent requiring
replacement. Also, thermal shock resulting at the interface
at the entry end of the mold may cause a crack in the newly
formed skin of the casting which remains during progressive
solidification. This may result in a site for crack
propagation during subsequent rolling.
SUMMARY OF THE INVENTION
It is accordingly a primary object of the present
invention to provide a continuous casting ~old having at the
mold inlet end a removable insert which may be of a material
more wear resistant than the remainder or body portion of the
mold, which insert upon wear may be replaced without requiring
20 replacement of the entire mold.
A more specific object of the invention is to provide a
continuous casting mold having at the entry end a removable
insert which insert may be provided with an integral break
ring of nonconductive material.
The invention relates to an apparatus particularly
adapted for the horizontal continuous casting of molten
material, such as metals and alloys, particularly steel. The
apparatus includes a tundish for receiving a quantity of
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1 molten metal to be cast. A refractory nozzle is provided as a
molten material outlet from the tundish to a flow-through mold
of heat-conducting material having an inlet end contacting the
nozzle for receiving the molten material and an outlet end for
discharging an embryo casting of the molten material. The
embryo casting results from the cooling of the molten material
during passage through the mold. In accordance with the
invention a removable insert comprising the mold inlet end is
provided with one end of the insert contacting the nozzle and
10 an opposite end of the insert connected to the body portion of
the mold. The insert may be constructed from a material
having higher wear resistance and/or thermal conductivity or
controlled thermal conductivity with respect to the body
:~ portion of the mold. By controlled thermal conductivity, the
15 conductivity of the insert may be varied along its length and
specifically may increase progressively from the end
contacting the nozzle to the opposite end. The body portion
of the mold may be constructed from copper or a copper alloy
in the conventional manner, with the insert constructed from a
20 material that may be a second copper alloy having higher wear
, resistance and different or higher thermal conductivity than
the copper or copper alloy of the body portion of the mold.
For this purpose, the insert material may for example be
; composite material, ceramic or alloys, such as copper alloy
` 25 including at least one alloying element providing increased
wear resistance and/or thermal conductivity, which alloying
elements may include zirconium and silver. The composite
material may be for example composites of copper ceramic
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1 alloys. The insert may be constructed fro~ a conductive
ceramic having higher wear resistance than the body portion of
the mold. In this embodiment, the insert ~ay be less
conductive than the body portion of the mold. The insert may
include a break ring and specifically a non-conductive,
ceramic break ring, formed integrally on the insert at the
inlet end thereof adjacent the nozzle, without any
intermediate bonding layer being provided between the break
ring and the insert.
BRIEF DESCRIPTION OF THE DR~.WINGS
Figure 1 is a somewhat schematic vie~ in vertical cross
section of a portion of a continuous casting apparatus with an
embodiment of applicant's mold structure enployed therewith;
and
Figures 2, 3 and 4 are similar cross sections showing
,i alternate embodiments of applicant's mold structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With respect to Figure 1 of the drawings, there is shown
an assembly of a portion of a continuous, horizontal steel
20 casting apparatus, designated generally as 10. The apparatus
includes a tundish 12 containing therein a quantity of molten
steel 14. A refractory nozzle 16 is connected at an outlet
end to the interior of the tundish 12 and at the opposite end
to the inlet end of a horizontally disposed, continuous
25 casting mold 18. The mold 18 has a generally round and/or
rectangular configuration and const~tutes a copper body
portion 20 having an interior water circulation chamber 22
communicating with water inlet 24 and water outlet 26. This
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l structure provides for the circulation of water throuqh the
chamber to cool the mold. As the molten metal 14 enters the
mold 18 and contacts the copper water-cooled mold body 20, it
begins to solidify to form a solidified skin 28 with the
5 interior constituting molten metal 14. A break ring 30 is
provided at the entry end of the mold.
In accordance with the invention, there is provided at
the entry end of the mold a removable insert 32. The insert
32, in accordance with the embodiment shown in Figure 1,
constitutes an alloy containing copper and having higher wear
resistance than the copper or copper alloy constituting the
body portion 20 of the continuous casting mold. Since the
inlet end of the mold is subjected to greater wear than the
body portion of the mold because of the higher temperature of
lS the molten metal as it enters the mold and comes into contact
~; with the inlet end thereof, the insert 32 is subject to
greater wear and degradation from the molten metal. Since the
insert is removable, it may be replaced when it becomes worn,
without replacing the body portion of the mold which is
subjected to less wear than the entry end of the mold. This
results in a more economical casting practice, since the
entire mold does not have to be replaced because of wear at
the entry end thereof.
Figure 2 describes an alternate embodiment of the
invention. In Figure 2 an insert 32 of a conductive ceramic
is provided. Integral with the insert 32 is a break ring 34
constructed of a nonconductive ceramic. The integral break
ring 34 may be formed by conventional thermal spraying, such
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1 as plasma spraying, of the refractory compound onto the
refractory of the insert 32. Plasma spraying, as is well
known, includes providing a powder charge of the refractory
compound to be used in the manufacture of the integral break
ring. The powder charge is introduced to a high-temperature
gas plasma which melts the particles and sprays them onto the
surface to be coated ~ith the refractory compound. Spraying
of the refractory compound to deposit the same is achieved by
- accelerating the molten refractory compound by the plasma
arc. Although various techniques are known for this purpose
and the invention embodies any equivalent practice, various
conventional thermal spraying practices suitable for use in
the practice of the invention are disclosed in the article
"Tomorrow's Surface Coatings," Iron Age, June 21, 1985, pages
35-49. This could also be achieved by various other
techniques, included powder metallurgy and processes based
thereon.
Although the break ring 34 is shown having a cross
section of generally rectangular configuration, other cross
sectional shapes maybe used and are well known in the art.
For example, the surface of the break ring in contact with the
molten metal may be rounded or slanted rather than being at
right angles as shown in the embodiment of Figure 2. Also, as
is well know in the art, the break ring may be positioned
other than as shown in this Figure. For example, it may be on
the outer end surface of the mold adjacent the nozzle.
Although various ceramic compounds may be suitable for
use in the practice of the inventiGn for constructing the
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1 insert 32 and break ring 34 examples of suitable, conventional
compounds for this purpose are molybdenum and copper alloys,
alloys of titanium boride and the like. Likewise, suitable
`~ alloys of copper for use in constructing the insert 32 in the
embodiment of Figure 1 may be copper silver bearing or
zirconium bearing alloys. Specifically in this regard, Figure
3 shows the insert 32 having an integral break ring 36 with
the cross-sectional area thereof decreasing progressively from
the end thereof contacting the nozzle to the opposite end. In
lC this manner, controlled thermal conductivity is achieved,
; whereby with a break ring of nonconductive material as the
cross-section of the break ring decreases relative to the
cross-section of the insert the thermal conductivity of the
insert correspondingly increases. This may also be achieved
15 with the embodiment of Figure 4 where the break ring is of
uniform cross-section along its entire length by varying the
thermal conductivity of the break ring material from end to
end thereof by using materials of different thermal
conductivity in constructing the break ring. This may be
20 achieved for example by flame spraying the different materials
,~ during construction of the break ring. Alternately, the break
ring may be constructed by powder metallurgy techniques where
different materials of varying thermal conductivity in powder
form are consolidated to form the break ring. Consolidating
25 techniques may include conventional hot isostatic pressing as
, by the use of a gas pressure vessel, commonly termed an
; autoclave.
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