CA1183322A - Fluid cooled casting apparatus having improved fluid seal - Google Patents

Abstract

FLUID COOLED CASTING APPARATUS HAVING IMPROVED FLUID SEAL Abstract of the Disclosure An apparatus for the continuous casting of metallic strand from a melt has a fluid-cooled coolerbody surrounding a casting die, and resilient O-ring seals which surround the upper and lower ends of the coolerbody to contain the cooling fluid within a distribution conduit. Extensions of the cooling fluid distribution conduit are formed within the coolerbody between the O-rings and the heat-dissipating strand, as protective thermal barriers to limit the temperature rise experienced by the O-rings. An annular shield also is disposed intermediate the upper O-ring and the strand to form two air gaps which enhance the thermal barrier effect.

Description

&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

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 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, ~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

Claims (9)

1. In an improved apparatus for the continuous casting of a metallic strand from a melt in which said apparatus is partly immersed, having a die of a refractory material in fluid communication with said melt, the die substantially defining a mold cavity through which mold cavity 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 in a recess of 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 encompass-es only said mold cavity 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 withing said cooler-body in the region between said second O-ring and said mold cavity.

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 mold cavity, 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 mold cavity, thereby producing a first air gap between said mold cavity 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, said die substantially defining a mold cavity through which mold cavity said strand is drawn, a thermally conduc-tive coolerbody having a first end portion positioned below a second end portion when said apparatus is immersed in said melt, with only said first end portion encompassing 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;
a second channel formed within said coolerbody intermediate said second O-ring and said mold cavity, 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 mold cavity, said annular shield having an outer diameter smaller than the dimensions of said recess and an inner diameter greater than the diameter of said mold cavity, thereby producing a first air gap between said mold cavity 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.