Background of the Invention
[0001] 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 fluid seal which facilitates repair and maintenance.
[0002] It 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. Generally, the cooling is accomplished by surrounding
the die with a snuggly fitting coolerbody made of a material having good thermal conductivity
characteristics, and circulating a cooling fluid, such as water, through the coolerbody
to extract the heat of solidification therefrom. It is 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.
[0003] In U.S. Patent No. 4,211,270, which has a common assignee as the present application,
there is disclosed a coolerbody structure which employs a copper-gold braze to effect
the fluid-containing seal. Not only is such a braze an increasingly more expensive
procedure, but the more or less permanent nature of a braze interferes with maintenance
or replacement of parts within the casting apparatus. The removal of the braze to
allow separation of mating pieces of the coolerbody is a time-consuminq procedure,
and the heat and mechanical stresses thus induced often irretrievably damage elements
of the coolerbody and prevents their reuse. Such waste means unnecessary expense.
[0004] The high temperatures experienced by the coolerbody during a typical casting operation
have hindered the effectiveness of conventional O-ring seals. The prolonged exposure
of the 0-ring's constituent rubber material to these temperatures produces deterioration
of the material and eventually destroys the effectiveness of the seal. Because of
the potential safety hazard, such a seal has not heretofore been acceptable.
[0005] 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 so
in a manner that facilitates disassembly of the coolerbody for repair.
[0006] It is a further object of the present invention to provide a sealing means whose
removal during disassembly does not irreversibly damage adjacent components of the
casting apparatus.
[0007] 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
[0008] The present invention resides in an improvement to an apparatus for the continuous
casting of a metallic strand from a metallic melt. The conventional apparatus has
a die of refractory material in fluid communication with the melt through which die
the metallic strand is drawn. A thermally conductive coolerbody surrounds at least
a portion of the die to extract heat therefrom. The conventional casting apparatus
also includes a conduit for passing a cooling fluid through the coolerbody. Specifically,
the improvement of the present invention comprises O-ring seals mounted to the coolerbody
for containing the cooling fluid within the conduit, and a thermal barrier within
the coolerbody adjacent the O-ring seals for maintaining the temperature of the O-ring
at a level insufficient to damage the O-rings.
[0009] In a specific embodiment of the invention, two O-ring seals are used: one surrounding
the lower portion of the coolerbody and the other 'surrounding the upper portion.
The thermal barrier associated with the lower 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 fits 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.
[0010] At both the upper and lower O-ring positions, the thermal 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.
[0011] This embodiment also features an annular ring which surrounds the lower portion of
the coolerbody at the location of the lower O-ring and is bolted at several locations
to the coolerbody. The inner surface of the annular ring compresses the lower O-ring
and effects a seal. A threaded bayonet-type coupling receives the threaded upper portion
of the coolerbody and is arranged such that a portion of the coupling compresses the
upper O-ring to effect a seal. The cylindrical insert is press-fit to the coupling
and extends into the interior of the coolerbody. To gain access to the interior of
the coolerbody for maintenance, it is
'a simple matter to remove the mounting bolts holding the annular ring to the lower
portion of the coolerbody, and then to unscrew the upper portion of the coolerbody
from the coupling.
[0012] The structure as described herein is generally acceptable 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 parameters may vary such as, for example, the
rate of flow of cooling fluid through the coolerbody, the length and total outer surface
area of the coolerbody, and the thickness of the refractory material die.
[0013] 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 drawings.
Brief Description of the Drawings
[0014]
FIG. 1 is an elevation view, in section, of a casting apparatus incorporating the
improved seal arrangement in accordance with the present invention;
FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1, showing the finned
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. 1.
Description of the Preferred Embodiment
[0015] Referring to FIG. 1, a hollow, generally 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 11 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
is made of a metal having exceptionally good thermal conductivity characteristics,
such as copper, or a copper alloy. The die 11 fits snuggly within the cavity 13 to
provide maximum contact between the outer surface of the die-and an inner surface
15a of the coolerbody, across which interface extraction of the heat of solidification
from the strand 14, through the die 11, is accomplished. Insulating inserts or bushings
17, 17a surround the die 11 at the location where the die 11 enters into the coolerbody
15. These bushings 17 are formed of a refractory material having a relatively low
coefficient of thermal expansion such as, for example, cast silica glass (SiO
2). 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 diameter 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.
[0016] In order to dissipate the heat extracted by the coolerbody 15 from the die 11, it
is 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 consists 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. There, instead of fins, the coolerbody has two concentrically 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 strands larger than 3/4 inch for which a significantly longer coolerbody
is required to properly cool the larger mass strand. The longer the coolerbody, the
more difficulty it becomes to drill long, straight, parallel holes through the coolerbody
because of the tendency of the longer drill bit to vibrate and wander or deviate from
a straight line. In such a situation, the external fin configuration is preferable
because it can more easily and quickly be machined on a milling apparatus and, therefore,
is less costly to fabricate.
[0017] Two concentric annular passageways or conduits 21, 23, for transporting the cooling
fluid which passes over the finned outer surface 15b of the coolerbody, are formed
by a concentric arrangement of 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 upper end to a manifold (not shown) which
constitutes the source of the cooling fluid to be circulated through the passageways
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 rate of flow of the cooling fluid varies,
depending on such factors as the size of the strand being cast, the wall thickness
of the die, or the length of the coolerbody. However, the design objective sought
is that the cooling fluid temperature increase from inlet to outlet shall be in the
range of 10° to 15°F. The rate of flow is adjusted to achieve this objective.
[0018] Referring again to Fig. 1, the outer coolant sleeve
29 extends downwardly from the cooling fluid manifold and encompasses almost the entire
coolerbody 15. A positioning ring 33, secured by bolts 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 central lip portion 39 which creates two recesses
41, 42. The outer recess 41 accommodates 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 to 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 19a (see FIG. 2) of
the fins 19 to.maximize the surface 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 19a as well.
[0019] 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 prevent
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 continues to emanate from
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.
[0020] An outer casing or protective cap 47 made of a suitable ceramic material surrounds
the entire 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 from 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 sleeve 29, the effectiveness of the
liquid cooling system would be negated.
[0021] As discussed above, it is very important that the cooling fluid be contained to the
two annular passageways 21, 23. Any contact of the fluid with the strand would have
detrimental effects on its physical properties such as, for example, the surface smoothness
of the strand. Even more importantly, if the cooling fluid were to escape from the
casting apparatus into the high temperature molten metal, an explosion may result
upon contact. To contain the cooling fluid within the described boundaries, 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 projection 53 also provides a shoulder which determines the lateral placement
of the positioning 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 inwardly facing and oppositely
directed surface 33a of the positioning ring 33. When properly formed, the seal will
prevent passage of the cooling fluid below the level of the O-ring 48.
[0022] Referring now to FIG. 3, the upper O-ring 49 similarly is seated within a circular
recess 55 formed within an outward lobe 57 extending 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 has a receptacle portion 63 with a mating thread
65 which receives the threaded neck portion 60 of the coolerbody. The neck portion
59 is threadably engaged within the coupling ring 45 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 of the coupling ring. In this position, the O-ring is compressed
between an outwardly facing surface 55a of the circular recess 55 and an inwardly
; facing surface of a vertical flange 71 integrally formed with the coupling ring 45.
[0023] A particularly suitable material used for the sealing 0-rings 48, 49 is Viton (a
trade name of E.I. duPont de Nemours and Company, Inc. for synthetic rubber). In order
for this material to maintain proper resiliency and other sealing qualities, the temperature
to which it is exposed must not exceed 350°F. Unless compensated for, the extremely
good thermal conductivity characteristics of the coolerbody may cause the temperatures
at the O-rings to exceed the 350°F danger point during casting. A thermal barrier,
in the form of a circular channel 73 cut into the coolerbody 15, is provided to protect
the lower O-ring 48. The channel 73, which forms an extension of the inner passageway
21, is 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 so close to the recess 51, it
also provides for_localized cooling of the coolerbody immediately adjacent the O-ring
48. Thus, the channel has a dual effect on the temperature experienced by the O-ring
48. The cooling water, after passing through the fins 19, circulates within the channel
73 before continuing through the transverse passage 31 into the outer annular passage
23, and then finally out through the outlet (not shown).
[0024] In the case of the upper O-ring 49, because of a smaller 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 is provided
to allow the cooling fluid to intersect the coolerbody 15 in the region between the
upper O-ring 49 and the closest point on the inner surface 15a. An additional thermal
barrier member is provided in the form of a hollow cylindrical heat shield insert
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, so that an air gap 79 separates the outer surface 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 so that there is provided a second air gap 81 separating
the strand from the insert.
[0025] The air gaps form discontinuities in the highly thermally conductive path provided
by the coolerbody between the casting and the O-ring 49, and thus retards the heat
flow. However, an even more significant amount of resistance to the heat flow is provided
by the presence of stagnant films of air which form 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 strand and the inner surface of the coolerbody, and
therefore only two such air films on the respective surfaces. However, with the second
air gap, two additional intervening surface films are created, namely on the inner
and outer surfaces of the shield insert 77. Doubling the number of surface films effectively
cuts in half the heat flux passing between the strand and the coolerbody.
[0026] A typical material, out of which the insert may be fabricated, is #304 stainless
steel, having a heat conductivity of about 0.036 cal-cm/cm
2/°C/sec, considerably lower than the heat conductivity of a copper coolerbody, which
is about 0.94 cal-cm/cm
2/°C/sec. The upper end of the heat shield insert 77 is press-fit within a mating recess
in the coupling ring 45, so that when the coolerbody is unscrewed from the coupling
ring 45, the insert 77 remains within the coupling ring. Therefore, the total thermal
protection provided to the upper O-ring 49 is the combination of the inner air gap
81, the low-conductivity heat shield insert 77, the outer air gap 79, the four stagnant
surface air films and the cooling fluid passageway extension 75.
[0027] Not only are the upper and lower O-ring seals cheaper and easier to fabricate than
the previously used brazed seals, but they also facilitate disassembly of the casting
apparatus for maintenance. For example, if access is desired to the inner portion
of the coolerbody, it is a simple matter, after removing the 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 positioning
ring 33, to unscrew the coolerbody from the coupling ring 45 and remove it as an integral
unit from the interior of the coolant sleeve 27. Because there is no permanent-type
joint, such 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 apparatus. For example, a deformation
of the closely matched contours of the positioning ring 33 and the mating projection
53 of the coolerbody might preclude proper repositioning of these two units relative
to each other. However, such a situation is avoided by the easily removable O-ring
seal structure. At the very most, replacements of the O-rings themselves would be
required upon reassembly of the casting apparatus, a more or less standard procedure
when using 0-rings.
[0028] It is possible to enhance further the seal provided between the upper portion of
the coolerbody and the inner annular passageway 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 0-ring 49 compressed within its recess to form a seal,
but the abutting 16 micro-inch surfaces similarly provide a sealing action. A small
cutout 89 can be provided to reduce the total contact area between these two surfaces
and thereby to increase the pressure therebetween and enhance the seal.
[0029] A space 91 shown between the bottom of the heat shield insert 77 and a lower lip
93 of the recess 78 is of such a magnitude that the thermal expansion experienced
by the shield insert 77 during operation 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.
[0030] While the invention has been described with reference to its preferred embodiment,
it will be understood that'modifications 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
situations. Such modifications and variations are intended to fall within the scope
of the appended claims. What is claimed and desired to be secured by letters patent
is:
1. In an improved apparatus for the continuous casting of a metallic strand from a
melt having a die of a refractory material in fluid communication with said melt through
which said strand is drawn, a thermally conductive coolerbody, surrounding at least
a portion of said die to extract heat therefrom, and conduit means for passing a cooling
fluid through said coolerbody, the improvement comprising:
O-ring sealing means mounted on said coolerbody for containing said cooling fluid
within said conduit means; and
thermal barrier means within said coolerbody adjacent said O-ring sealing means for
maintaining the temperature of said O-ring sealing means at a level insufficient to
damage said O-ring sealing means.
2. The improved apparatus as set forth in claim 1 wherein said coolerbody has a first
end portion which encompasses said die and a second end portion which encompasses
only said strand at a position beyond the end of said die, and wherein said O-ring
sealing means comprises:
a resilient first O-ring surrounding said first end portion of said coolerbody;
an annular positioning member secured to said coolerbody and surrounding said first
O-ring in compressive engagement therewith;
a resilient second O-ring surrounding said second end portion of said coolerbody;
and
a coupling member which receives said second end portion of said coolerbody and surrounds
said second O-ring, in compressive engagement therewith.
3. The improved apparatus as set forth in claim 2 wherein said thermal barrier means
comprises:
means for circulating said cooling fluid in the regions of said coolerbody adjacent
both said first and second O-rings.
4. The improved apparatus as set forth in claim 3 wherein said means for circulating
forms an extension of said conduit means.
5. The improved apparatus according to claim 4 wherein said thermal barrier means
further comprises:
means for providing air gaps within said coolerbody in the region between said second
O-ring and said strand.
6. The improved apparatus according to claim 5 wherein said air gap providing means
comprises:
an annular shield fixed to said coupling member and protruding within a recess in
said second end portion of said coolerbody so as to enclose said strand, said annular
shield having an outer diameter smaller than the dimensions of said recess and an
inner diameter greater than the diameter of the enclosed strand, thereby producing
a first air gap between said strand and said annular shield, and a second air gap
between said coolerbody and said annular shield.
7. The improved apparatus according to claim 6 wherein said annular shield has a thermal
conductivity less than that of said coolerbody.
8. The improved apparatus according to claim 7 wherein said recess has a shoulder
portion opposing the lower end of said annular shield and spaced sufficiently closely
thereto, whereby a vapor seal is formed by said lower end of said-shield pressing
against said shoulder upon thermal expansion of said shield during operation of the
apparatus.
9. In an improved apparatus for the continuous casting of a metallic strand from a
melt, having a die of a refractory material in fluid communication with said melt
through which said strand is drawn, a thermally conductive coolerbody having a first
end portion encompassing said die and a second end portion encompassing only said
strand at a position beyond the end of said die, and a conduit formed within said
coolerbody for accommodating the flow of a cooling fluid therethrough, the improvement
comprising:
a resilient first O-ring surrounding said first end portion of said coolerbody adjacent
said conduit;
an annular positioning member secured to said coolerbody and surrounding said first
O-ring, in compressive engagement therewith, thereby forming a first seal for containing
said cooling fluid within said conduit;
a first channel formed within said coolerbody intermediate said first O-ring and said
die, said first channel intersecting said conduit whereby cooling fluid can circulate
within said first channel;
a resilient second O-ring surrounding said second end portion of said coolerbody,
adjacent said conduit;
a coupling member receiving said second end portion of said coolerbody and surrounding
said second O-ring in compressive engagement therewith, thereby forming a second seal
for containing said cooling fluid within said conduit; Claim 9 cont'd.
a second channel formed within said coolerbody intermediate said second O-ring and
said strand, said second channel intersecting said conduit whereby cooling fluid can
circulate within said second channel; and
an annular shield fixed to said coupling member and protruding within a recess in
said second end portion of said coolerbody so as to enclose said strand, said annular
shield having an outer diameter smaller than the dimensions of said recess and an
inner diameter greater than the diameter of the enclosed strand, thereby producing
a first air gap between said strand and said annular shield, and a second air gap
between said coolerbody and said annular shield,
whereby the temperatures of said O-rings are maintained at a level insufficient to
damage said O-rings.