Note: Descriptions are shown in the official language in which they were submitted.
&333~
Background of the Invention
The present invention relates generally to a fluid
cooled casting apparatus for the continuous casting of metallic
strand and, more particularly, to such an apparatus having an
improved cooling 1uid seal which facilitates repair and
maintenance.
lt is well known in the prior art that it is possible
to continuously cast a metallic strand from a molten mass of the
metal by immersing the end of a refractory material die into the
melt and then withdrawing the melt upwardly through the die and
gradually cooling the melt into a solid strand, Generally9 the
cooling is accomplished by surrounding the die with a snuggly
fitting coolerbody made of a material having good thermal con-
ductivity characteristics, and circulating a cooling fluid, such
as water, through the coolerbody to extract the heat of solidifi-
cation thererom. It i~ imperative that this cooling fluid be
sealed completely within the coolerbody. Contact of the fluid
with the strand within the die will contaminate the finished
product; and, contact with the high-temperature melt may produce
an explosion.
In U.S. Patent No. 4,211,270, which has a common
assignee as the present application, there is disclosed a cooler-
body structure which employs a copper-gold brare to effect the
fluid-containing seal. Not only is such a braze an increasingly
more expensive pro~edure, but the more or less permanent nature
of a braze interferes with maintenance or replacement of parts
within the casting appara~us. The removal of the braze to allow
~'
~B3~2~
separation of mating pieces of the coolerbody is a time-consuming
procedure, and the heat and mechanical stresses thus induced
often irretrievably damage element~ of the coolerbody and pre-
vents their reuse. Such waste means unnecessary expense.
The high temperatures experienced by the coolerbody
during a typical casting operation have hindered the effec-
tiveness of conventional O-ring seals. The prolonged exposure of
the O-ring's constituent rubber material to these temperatures
produces deteriora~ion of the material and eventually destroys
the effectiveness of the seal. Because of the potential safety
hazard, such a ~eal has not heretofore been acceptable.
Therefore, it is an object of the present invention to
provide a means for sealing and containing the cooling fluid
within the interior of a coolerbody and to do 60 in a manner that
facilitates disassembly o the coolerbody for repair.
It is a further object of the present invention to pro-
vide a sealing means whose removal during disassembly does not
irreversibly damage adjacent components of the casting apparatus.
~ It is still a further object of the present invention
to provide a simple, reliable sealing means which can withstand
the typically high temperatures associated with metal casting
procedures.
Summary of the Invention
The present invention resides in an improvement to an
apparatus ~or the continuous casting of a metallic strand from a
metallic melt. The conventional apparatus has a die of refrac
tory material in 1uid communication with the melt through which
die the metallic strand is drawn. A thermally conductive cooler-
body surrounds a~ least a portion of the die to extract heat
therefrom. The con~entional casting apparatus also includes a
conduit for passing a cooling fluid through the coolerbody.
Specifically, the improvement of the present inven~ion comprises
O~ring ~eals mounted to the coolerbody for containing the cooling
fluid within the conduit, and a thermal barrier within the cooler-
body adjacent the O--ring saals for maintaining the temperature of
the O-ring at a level insufficient to damage the O-rings.
In a specific embodiment of the invention, two O-ring
seals are used: one surrounding the lower portion of the cooler-
body and the other surrounding the upper portion. The thermal
barrier a~socia~ed with the lswer O-ring consists of an extension
of the cooling fluid-bearing conduit to a point at which it
intersects the portion of the coolerbody between the O-ring and
the die, so as to counteract the transmission of heat from the
die to the O-ring. The thermal barrier associated with the upper
o-ring also includes such an extension of the cooling fluid
conduit to the region between the O-ring and the enclosed
metallic strand. But, this upper barrier also utilizes a hollow
cylindrical insert made of a material with a relatively poor
thermal conductivity, which fit6 into a recess within the
coolerbody and produces two heat-retarding air gaps, one between
the outer surface of the insert and the coolerbody, and a second
between the inner surface of the insert and the metallic strand.
At both the upper and lower O-riny positions, the ~her-
mal barriers limit the temperatures experienced by the O-rings so
_~ .
that they are not subjected to the temperatures which would melt
the O-rings or otherwise deteriorate the seal.
This e~bodiment al60 features an annular ring which
surrounds the lower portion of the coolerbody at the location of
the lower O-ring and i5 bolted at several locations to the
coolerbodyO The inner surface of the annular ring compresses the
lower O-ring and efects a seal. A threaded bayonet-type
coupling receives the threaded upper portion of ~he coolerbody
and is arranged such that a portion o the coupling compresses
the upper O-ring to effect a seal. Th~ cylindrical insert is
prass-fit to the coupling and ex~ends into the interior of the
coolerbody. To gain access to the interior of the coolerbody for
maint~nance, it is a simple mat~er to remove the mounting bolts
holding the annular ring to ~he lower portion of the coolerbody,
and then to unscrew the upper portion of the coolerbody from the
coupling.
The structure as described herein is generally accep-
-- table for production of a metallic strand having a diameter up to
2 1/2 inches. Depending on the mass of the particular strand
being cast, certain operating parameter~ may vary such as, for
example, the rate of flow of cooling fluid through the cooler-
body, the leng~h and total outer surface area of the coolerbody,
and the thicknes~ of the refractory material dieO
The objects and features of the invention will be more
fully understood from the following detailed description which
should be read in light of the accompanying drawingsO
~3~
Brief Description of the Drawin~s
FIGc l is an elevation view, in section, of a casting
apparatus incorporating the improved ~eal arrangement in accord-
ance with the present invention;
FIG. 2 is a cross-sectional view taken along lines ~-2
of FIG. l, ~howing the inned outer surface of the coolerbody,
and
FIG. 3 is a detail view, showing the! placement of the
heat shield insert within the apparatus of FIG. l.
Description of the Pr~ferred Embodiment
P~eerring to FIG. l, a hollow, genexally tubular die
11, is oriented in a vertical direction with its lower end lla
protruding into a melt 12 of the particular metal being cast.
The melt is drawn upwardly through the die in any conventionally
known manner, and is cooled into a metallic strand 14. The upper
portion of the die ll is tightly contained within a cylindrical
cavity 13 formed in the interior of a coolerbody 15. Typically,
the die is made of a refractory material, such as graphite, which
can withstand the thermal shock generated by the casting process,
while the coolerbody i8 made of a metal having exceptionally good
thermal conductivity characteri~tics, ~uch as copper, or a copper
alloy. The die 11 fits snuggly within the cavity 13 to provide
maximum contact between the outer ~urface of the die and an inner
surface 15a of the coolerbody, across which interface extraction
of the heat of solidification from the strand 14, throu~h the die
ll, is accomplished. Insulating insertæ or bushings 17, 17a
surround the die 11 at th-e location where the die ll enters into
~333;Z ~
the coolerbody 15. ~hese bushings 17 are formed of a refractory
material having a relatively low coefEicient of thermal expansion
Ruch as, for example, cast silica glass (SiO2)~ They prevent
expansion of the die at this location and maintain a uniform
cross-section of the cast strand. Without these insulators the
die would thermally expand, due to the extreme heat of the melt
in which it is deposited, and would produce a strand having a
diametex larger than the inner diameter of the rest of the die
Were this the case, this larger diameter strand could wedge
within the narrower upper portion of the die causing blockage of
the die and interruption of the casting process.
In order to dis~ipate the heat ex~racted by the cooler-
body 15 from the die 11, it i5 necessary to direct a flow of
cooling water or other acceptable cooling fluid across an outer
surface 15b of the coolerbody 15. In the embodiment of FIG. 1,
and as shown more in detail in FIG. 2, the outer surface 15b of
the coolerbody con~lists of a series of thirty-two radially
extending fins 19 of equal height, which are distributed at equal
spacings around the outer periphery of the coolerbody. It is
intended that alternate heat dissipating surface configurations
be used as well such as, for example, the configuration disclosed
in the coolerbody of the above-mentioned U~S. Patent No.
4,211,270. Th~re, instead of ~ins, the coolerbody has two con-
centrically arranged groups of parallel cylindrical holes which
extend down into the coolerbody. However, the fin configuration
of FIG. 1 is particularly suitable for the casting of larger
diameter ~trands larger than 3/4 inch for which a significantly
longer coolerbody i~ required to properly cool the larger mass
~33~
strand. The longer the coolerbody, the more difficulty it
becomes to drill long, straight, parallsl holes through the
coolerbody because of the tendency of the longer drill bit to vi-
brate and wander or deviate from a straight linel In such a sit
uation, the external in configuration i8 preferable because it
can more easily and quicXly be machined on a milling apparatus
and, tharefore, is less costly to fabricate.
Two concentric annular passageways or conduits 21, 23,
for transporting the cooling fluid which passes over the finned
outer surface 15~ of the coolerbody, are formed by a concentric
arrangement o three coolant sleeves, an inner sleeve 25 (see
Fig. 1), a middle sleeve 27, and an outer sleeve 29, which fit
one within another. Each of these coolant sleeves is attached at
its upp~r end to a manifold (not shown) which constitutes the
source of the cooling fluid to be circulated through the pass-
ageways 21, 23. A fluid inlet (not shown~ communicates with the
inner passageway 21 while a fluid outlet (not shown) communicates
with the outer passageway, so that the cooling fluid is pumped
downwardly into the inner passageway 21, across the fins 19,
thereby extracting heat therefrom, through a transverse passage
31, and upwardly through the outer passageway 23 to be
discharged. The rat~ of flow of the cooling fluid varies,
depending on such factors as the size of the strand bein~ cast,
the wall thickness of the die, or the length of the coolerbody.
However, the design objective sought i5 that the cooling fluid
temperature increase from inlet to outlet shall be in the range
of 10 to 15~F~ The rate of flow i9 adjusted to achieve this
objective.
33~
Referring again to Fig. 1, the outer coolant sleeve 29
extends downwardly from the cooling fluid manifold and encom-
passes almost the entir2 coolerbody 15. A posî~ioning ring 33,
secured by holts 35 to a shoulder 37 machined in the coolerbody
15, anchors the bottom end of the outer coolant sleeve 29. The
positioning ring 33 has an upwardly extending cen~ral lip portion
39 which creates two recesses 41, 42. The outer recess 41 accom-
modates the bottom end of the outer coolant sleeve 29; and, the
inner recess 42 receives the bottom portion of the middle coolant
sleeve 27. The outer coolant sleeve 29 is welded or joined in
any other suitable fashion to the positioning ring 33 ~o increase
the structural integrity and stability of the assembly. The
middle coolant sleeve 27 is merely press-fit into the inner
recess 42. A small clearance space 43 is provided between the
outer edges l9a (see FIG. 2) of the fins 19 to maximi~.e the sur-
face area contacted by the cooling fluid~ In other words, the
cooling fluid contacts not only the radially extending walls of
the fins, but also the outer circumferential edge surfaces l9a as
-~ well.
- 20 The bottom end of the inner coolant sleeve 25 is welded
at 44 to a coupling ring 45, which mechanically engages the upper
portion of the coolerbody in a manner described hereinafter in
greater detail. The weld 44 provides a fluid-tight seal to pre-
vent the passage of cooling fluid into the interior of the sleeve
25. Not only does the inner coolant sleeve 25 form part of the
inner passageway 21, but its bore 46 serves to guide the movement
of the cast strand after emergence of the strand from the snug-
fitting confines of the die 11. Within this bore 46 heat con-
~a~
tinues to emanata rom the strand, is transmitted by convection
to the inner coolant sleeve 25, and is dissipated by the cooling
fluid passing over the inner coolant sleeve outer surface.
An outer casing or protective cap 47 made of a suitable
ceramic material surround~ the ~ntire casting apparatus, at least
to the level to which it is normally immersed in the melt. This
cap serves to insulate the overall casting apparatus Erom the
potentially damaging temperatures of the molten metal.
Obviously, if the heat of the melt 12 were to be transferred
directly to the outer cooling ~leeve 29, the effectiveness of the
liquid cooling system would be negated.
As discussed abovel it is very important that the
cooling fluid be contained ~o the two annular passageways 21, 23.
Any contact of the fluid with the strand would have detrimental
eff0cts on its physical properties such as, for example, the æur-
face smoothness of the strand. Even more importantly, if the
cooling fluid were 1:o e~cape from the casting apparatus into the
- high temperature mo:Lten metal, an explosion may result upon con
tact. To contain the cooling fluid within the described boun-
daries, a lower and an upper O-ring seal, 48, 49 respectively,
made of a resilient compressible material, are provided. The
lower O-ring 48 fits within a recess 51 provided in a projection
53 integrally formed within the lower portion of the coolerbody
15. It can be seen that this pro~ection 53 also provides a
shoulder which determines the lateral placement of the position-
ing ring 33. Thus, the lower O-ring 48 is compressed into a seal
between an outwardly facing surface 51a of the recess 51 and an
--10--
3~
inwardly facing and oppo~itely directed surface 33a o.f the posi=
tioning ring 33. When properly formed, the seal will prevent
passa~e of the cooling fluid below the l.evel o the O-ring 48~
Referring now to FIG. 3, the upper O-ring 49 similarly
is seated within a circular reces3 55 formed within an outward
lob~ 57 ~xtending from an upwardly directed neck portion 59 of
the coolerbody 15. The neck portion is threaded directly above
this lobe at 60~ The coupling ring 45 ha~ a receptacle portion
63 with a mating thread 65 which receives the threaded neck
portion 60 of the coolerbGdy. The neck portion 59 is threadably
engaged within the coupling ring ~5 and is advanced to the fully
seated position, as determined by the engagement of a top edge 67
of the neck with an inner .surface 69 o the coupling ring. In
this position, the 0-ring is compre~sed between an outwardly
facing surface 55a of the circular recess 55 and an inwardly
ac.ing surface oE a vertical flange 71 integrally formed with the
~oupling ring 45.
- A particu:larly suitable material used for the sealing
o~ m~
~ O-rings 48, 49 is V:Lton ~a trade ~ of E.I. duPont de Nemours
and Company, Inc. for ~ynthetic rubber). In order for this
material to maintain prope.r resiliency and other sealing quali-
ties, the temperature to which it is ~xposed must not exceed
350F. Unless compensated for, the extremely good thermal con-
ductivity characteri~tics of the coolerbody may cause the tem-
peratures at the O-rings to exceed ~he 350F danger point during
ca~ting~ A thermal barrier, in the form of a circular channel
73 cut into the coolerbody 15, is provided to protect the lower
--11--
3~i~
O-ring 48. The channel 73, which forms an ex~nsion of the inner
passageway ~ intermediate the O-ring 48 and the die 11 from
which the heat of solidification is being extracted. Not only
does the channel 73 interrupt the direct metallic path between
the die and the O-ring 48 but, by extending ~o close to the
recess 51, it also provides for localized cooling of the cooler-
body immediately adjacent the O-ring 48. Thu~, the channel has a
dual effect on the temperature experienced by the O-ring 48. The
cooling water, after pa~sing through the fins 19, circulates
within the ch~nnel 73 before continuing through the transverse
passage 31 into the outer annular passage 23, and then finally
out through the outle~ (not shown)~
In the case of the upper O~ring 49t because of a smal-
ler diameter and a closer proximity to the strand being cast,
dual thermal barriers are provided. As in the case of the lower
O-ring seal, an extension 75 of the inner annular passageway 21
ic provided to allow the cooling fluid to intersect the cooler-
body 15 in the region between the upper O-ring 49 and the closest
point on th~ inner surface 15a. An additional thermal barrier
member is provided in the form of a hollow cylindrical heat
shield in3ert 77 inboard of the O-ring 49. A recess 78 within
the upper portion of the coolerbody, at a height above the end of
the die 11, accommodates the downwardly protruding insert 77.
The outer diameter of the insert 77 is smaller than the inner
diameter of the recess 78, ~o that an air gap 79 separates the
outer ~urface of the insert 77 from the coolerbody 15. The heat
shield insert 77 has an inner diameter which is larger than the
diameter of the strand 90 that there i~ provided a second air gap
81 separating the strand from the in~ert.
33~
The air gaps form discontinuities .in the highly ther
mally conductive path provided by the coolerbody between the
casting and the 0-ring 49, and thu~ retards the heat flow.
However, an even more significant amount of reqistance to the
heat flow is provided by ~he presence of stagnant films o air
which orm on each of the surfaces defining the air gaps~ Absent
the shield insert 77, there would be only one such air gap,
namely between the outer surface of the strantl and the inner sur-
face of the coolerhody, and therefore only two such air films on
~he respective surfaces~ However, with the second air gap, two
additional intervening surface films are creatad, namely on the
inner and outer surfaces of the shield insert 77. Doub.ling the
n~tmber of qurface films effectiv~ly cuts in half the heat flux
passing between the ~trand and ~he coolerbody.
A typical material, out of which the insert may be
fabricated, is #304 stainless steel, having a heat conductivity
of about 00036 cal-cm/cm2/5C/sec, considerably lower than the
heat conductivity of a copper coolerbody, which is about 0.94
cal-cm/cm2/~C/sec. The upper end of the haat shield insert 77 is
- 20 press-fit within a mating recess in the coupling ring 45, so that
when the coolerhody is unscrewed from the coupling ring 45, the
insert 77 remains within the coupling ring. Therefore, the total
thermal protection provided to the upper 0-ring 49 is the com-
bination of the inner air gap 81, the low-conductivity heat
shield insert 77, the outer air gap 79, ths four stagnant surface
air films and the cooling fluid passageway extension 75.
Not only are the upper and lower 0 ring seals cheaper
and easier to fabricate than the previously us2d br~ed seals,
-13
~3;~2~
but they also facilitate disassembly of the casting apparatus for
maintenance~ For example, if access is desired ~o the inner por-
tion of the coolerbody, it is a simple matter, after removing ~he
outer ceramic protective cap 47 (see FIG. 1), to unbolt the
series of bolts 35 extending around the periphery of the lower
portion of the coolerbody, to detach the coolerbody from the
po~itioning ring 33, to unscrew the coolerbody from the coupling
ring 45 and remove it as an in~egral unit from ~he interior of
the coolant sleeve 27. Because there is no permanent-type joint,
~uch as a braze, to be removed from the interface between the
coolerbody 15 and the positioning ring 33, there is minimal
possibility of damage to these components to preclude their reuse
upon reassembly of the apparatusO For example, a deformation of
the closely match~d contours of the positioning ring 33 and the
mating projection 53 of the coolerbody might preclude proper
repositioning of these two units relative to ~ach other.
Rowever, such a situation is avoided by the easily removable
0-ring seal structure. At the very most, replacement~ of the
-~ o-rings themselve~ ~would be required upon reassembly of the
casting apparatu~, a more or less standard procedure when using
~ 0-rings~
It is possible to enhance further the seal provided
between the upper portion of the coolerbody and the inner annular
pa~sageway 21 by providing a 16 micro-inch surface finish to both
the downwardly facing inner surface 69 of the coupling ring 45
and the abutting upwardly-facing edge 67 of the threaded portion
60 of the coolerbody 15. When the coolerbody is threaded fully
within the coupling ring and seated in its final position, not
only is the O-ring 49 compressed within its recess to form a
seal, but the abutting 16 micro-inch surfaces similarly provide a
sealing action~ A small cu~out 89 can be provided to reduce the
total ~ontact area between these two sur~aces and thereby to
increase the pressure therebetween and enhance the seal.
A space 91 shown between the bGt~om of th~ heat shield
insert 77 and a lower lip 93 of the recess 78 i 9 of such a
mag~itude that the thermal expansion experienced by the 8hi eld
insert 77 during opera~ion of the casting apparatus will close up
this gap and provide a barrier against contaminating vapors such
as, for example, the zinc vapors which are by-products of the
brass-casting process~ Containment of the gaseous vapors
minimizes the possibility of their condensation within the
casting apparatus and facilitates their evacuation therefrom.
While the invention has been described with reference
to its preferred embodiment, it will be understood that modifica-
tions and variations will occur to those skilled in the art. For
~-- example, the shape or configuration of the extensions of the
cooling fluid passages may vary depending on the application and
the spacings between the heat shield insert and the coolerbody
may vary depending on heat transfer characteristics. Similarly,
the shape of the heat shield insert may be varied to adapt to
particular situationsO Such modifications and variations are
intended to fall within the scope of the appended claimsO
-15-
