US3286310A - Continuous casting mold venting apparatus - Google Patents

Description

NOV- 22, 1966 J. E. DORE r-:TAL

CONTINUOUS CASTING MOLD VENTING APPARATUS Filed oct. 22. 1963 INVENTORS` JAMES E. DORE AVERY L. KEAR/VEV United States Patent 3,286,310 CONTINUOUS CASTING MOLD VENTING APPARATUS James E. Dore, Milford, Conn., and Avery L. Kearney,

Birmingham, Mich., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Oct. 22, 1963, Ser. No. 317,883 5 Claims. (Cl. 22-57.2)

This invention relates to improvement-s in apparatus and method of continuous casting of metals and more particularly to an improved continuous casting mold which provides for the escape of gases or vapors created during the casting process, and to the method of vapor removal.

In the art of continuous casting, many advantages have been derived by disposing the longitudinal axis of the mold in a horizontal orientation so that the casting of the ingot takes place in a horizontal direction from the inlet end of the mold to the outlet end thereof. One of these is that in casting continuously, ingots of great length can be formed without the need for deep pits or other facilities which would be required to receive or handle vertically oriented lengths of ingot. Also, horizontal casting facilities higher production speed as a result of the elimination of casting interruptions inherent in vertical casting techniques due to the nite lengths of ingot which can be formed without removal of these lengths from the casting apparatus.

Production speed, with acceptable quality being understood, is the most important test of a casting process in industrial application. Efforts to increase the output from a casting machine and/ or to reduce the manpower needed to make a given quantity of cast metal are important for the economic feasibility of a particular casting machine or process.

One of the primary factors preventing attainment of higher casting speeds in the horizontal continuous casting of aluminum alloys and other non-ferrous metals is nonuniform heat removal in the mold. This problem has been traced to a vapor barrier or bubble in the top of the mold cavity which is formed by the vaporization of mold lubricant and/or entrapment of air at the start of the cast. The vapor barrier greatly reduces heat transfer from the molten metal to the mold wall and produces a nonsymmetrical solidication front and a weak zone in the top of the forming embryo ingot shell. Casting speed, of course, is limited by the ability of this shell to contain the still liquid metal at the center of the casting as the ingot emerges from the mold.

It is well known in the casting art that one of the principal causes of failure in the continuous direct chill casting of metal is the friction between the work and the casting die, and/or wetting of the casting die by the molten metal which produces welding of the ingot shell to the mold and gauling. It is accordingly a conventional practice to apply 4a lubricating medium, generally oil, to the interface between the ingot shell and mold during the solidication stage of the casting process. A great variety of processes and apparatuses are present in the casting art for applying the lubricant to the ingot-mold interface lat some point within or adjacent to the ca-sting mold. The amount of lubricant used and the point of introduction are both critical factors in conventional processing, and little or no casting difficulty is encountered if these factors are very -closely controlled. However, such close control is difficult to maintain and frequently cannot be achieved due to the many variable circumstances which enter into casting practice. The difficulty, of which it is the basic object of this invention to overcome, is the creation of the aforementioned vapor barrier or bubble formed by the almost instantaneous vaporiza- 3,286,310 Patented Nov. 22, 1966 tion of an excess of lubricant when it contacts the extremely hot surface of the forming ingot, or when lubricant is not introduced at the correct point. The removal of the top gaseous layers in the mold resulting from this lubricant vaporization, or from air entrapment in the mold by the molten metal at the start of casting, broadens the range of operating parameters and makes lubrication less critical, and is essential for uniformity of heat removal in the horizontal casting process. It has been found that a thin gas layer, even on the order of a thousandth of an inch in thickness, can be a controlling resistance to heat conduction and extraction.

This invention provides improved mold constructions which allow the horizontal continuous casting of aluminum alloys and other non-ferrous alloys at speeds substantially higher than those presently possible. These constructions provide for escape of vapor gases trapped in the mold cavity to insure uniform heat removal from the molten metal to the mold Wall thereby resulting in a more symmetrical solidification of the forming embryo ingot shell.

The mold designs of this invention comprise generally an elongate mold of varying cross section having a mold cavity an inlet for molten metal at one end and an outlet for the solidified ingot at the other. The mold cavity is surrounded by a chamber or area for the association therewith of a cooling means, which may take the form of spray quenching apparatus or a simple cooling medium circulation means, either of which facilitates a high rate of heat removal from the mold wall which in turn induces rapid solidification of the molten metal within 4the mold cavity. Means are provided to control the rate of flow of molten metal into the mold, land means are also provided for withdrawing the solidted ingot from the discharge end of the mold.

The improvement of this invention consists generally of providing an escape route for the gases or vapors that accumulate in the mold cavity. This escape route is preferably located around or adjacent the upper portion of the mold, and Aat least at the inlet end thereof, and comprises generally a ported distribution nozzle or ported mold wall, either of which communicates with a vapor collection plenum which in lturn connects with a vacuum system to assist in the removal of vapors collected in the plenum.

Having thus described the .invention in a general manner, it is a primary object thereof to provide a mold design for continuous casting .apparatus which eliminates the aforementioned vapor barrier problem and thus allows substantially higher casting speeds.

It is another object of this invention to provide a horizontal continuous casting mold which will eliminate even an extremely thin gas film surrounding the solidifying ingot so as to improve ingot to mold heat transfer and consequently increase casting speeds.

It is yet another object of this invention to provide a horizontal continuous casting apparatus which provides a vapor escape route for vapors or bubbles created in the mold by vaporization of mold lubricant and/or entrapment of air.

It is still another object of the present invention to provide a horizontal continuous casting apparatus having vapor escape means communicating directly with the ingot-mold interface at the location of highest vapor or air concentration.

It is still another object of the present invention to provide a horizontal continuous casting apparatus in which a vacuum system is in communication with the areas of highest vapor concentration within the mold to facilitate the vapor removal.

It is still another object of the present invention to provide horizontal continuous casting apparatus which is simple in construction, efiicient in operation and economical to manufacture and maintain.

It is still another object of the present invention to provide a method of continuous casting which achieves removal of vapor or gases created in the casting process.

These and other objects and advantages of the invention will be more readily apparent from a consideration of the following detailed description when read in conjunction with the laccompanying drawings, in which:

FIGURE 1 is a vertical sectional view of one embodiment of the invention illustrating the mold and vapor release means during the solidication stage of the casting process;

FIGURE 2 is a vertical sectional view taken on line 2 2 of FIGURE 1;

FIGURE 3 is a view similar to FIGURE 1 illustrating another embodiment of the invention;

FIGURE 4 is a view similar to FIGURES 1 and 3 illustrating still another embodiment of the invention;

FIGURE 5 is a vertical sectional view on the line 5-5 of FIGURE 4; and

FIGURE 6 is a partial sectional view similar to FIG- URE 5, illustrating a further embodiment thereof.

Referring now to FIGURES 1 and 2, wherein one embodiment of the invention is illustrated, the reference numeral 10 indicates generally a horizontal casting apparatus comprising a substantially cylindrical hollow casting mold 12 having inner and outer walls 14 and 16, respectively, which define .a chamber 18 for the circulation therein of a cooling medium 20. Generally, the cooling medium is water, either lat room temperature or at some elevated temperature depending upon various characteristics of the casting process, although other cooling media may be used. The cooling medium 20 enters through an inlet port 22, circulates Within the chamber 18 and all 'or a portion of it is withdrawn through an exit port (not shown).

The discharge end of the casting mold 12 is provided with a plurality of apertures 24 through which a portion being utilized.

The mold 12 is further provided with a ported distribution nozzle 28 having a molten metal inlet end 30 for the introduction of the molten metal into the casting mold. The distribution nozzle 28 has an outwardly tapered surface 32 which terminates at 34 adjacent the inlet end of the casting mold 12. It will be observed from FIG- URE 1 that the terminal portion 34 has an outward flare or taper which is much steeper in degree than the tapered surface 32 which extends over a major portion of the length of the distribution nozzle 28. It is to be understood that this nozzle configuration is merely illustrative of a variety of nozzle designs which may be utilized with the present invention.

Molten metal is fed into the distribution nozzle through any suitable flow control means, and passes from the distribution nozzle into the mold chamber 34 defined by the interior surface of the inner mold wall 14. As the molten metal passes through this chamber, solidification thereof commences adjacent the inner surface of the mold wall 14 and continues through the mass of molten metal toward the center thereof, thereby forming the crater 36 of molten metal surrounded by an annular shell 38 of solidified metal.

In order to provide an escape route for the gases or vapors that accumulate in the mold chamber or cavity,

nozzle 28 is provided with a plurality of radially extending vapor escape ports 40 which connect interiorly in the flared portion 34 of the distribution nozzle located immediately adjacent the inlet end of the casting mold 12, and which extend rearwardly therefrom for a short distance and then outwardly to the outer surface 42 of the distribution nozzle. As will be seen from FIGURE 2, the ports 40 are distributed radially around approximately the upper half of the distribution nozzle, although more or less of the circumferential extent of the distribution nozzle may be provided with vapor escape ports depending upon the amount of lubricant used, the point or method of introduction, and extent of vaporization of mold lubricant or gas or Aair entrapment encountered in the particular casting apparatus to which the invention is applied.

While the escape ports 40 may in some instances be sufficient of themselves to provide adequate vapor removal, it is desirable to assure removal of as much as possible of the vapor or gases in order to reduce to a minimum, if not eliminate, the heat transfer barrier which the vapor or gases create. To facilitate vapor removal, the escape ports 40 communicate with a collection plenum 42 which illustratively comprises -a semicylindrical hood 44 having outlet means 46 adapted to be connected to a vacuum system providing a reduced pressure within the collection plenum of approximately 5 to 125 millimeters of mercury below atmospheric pressure. The molten metal static head, the amount and type of lubricant used, land the point of lubricant introduction into the mold are among the factors which determine the extent of vacuum maintained in the plenum.

It should be noted that the ports 40 must be of such a size that the surface tension of the molten metal will be sufficient to prevent the metal from entering the ports and either solidifyi-ng therein, thereby blocking the passage of vapors to the collection plenum 42, or being drawn by the reduced pressure into the collection plenum 42 and solid-ifying therein. At the same time, the ports 40k must not be of such small size as to prevent free passage of the vapors from the mold cavity to the collect-ion plenum 42.

The extent of sircumferential coverage of the ports 40, the number provided, and the diameter of the ports are all variables which are `determined by the vapor circulation or gas or air entrapment characteristics of the particular casting apparatus being utilized. Accordingly, these features of the vapor escape means will vary from one installation to another.

A second embodiment of the invention is illustrated in FIGURE 3 in which the mold is constructed to have the vapor escape means as an integral part of the mold. More specifically, the mold 1-12 is again divided with interior and exterior concentric walls 114 and 116, respectively, to provide a circulation chamber 118 for the cooling medium 120 which enters through the port 122 and circulates within chamber 118 and exits, at least in part, through ports 124 to provide direct cooling effect upon the solidifying portion of the ingot 126. Molten metal is introduced int-o the mold through distribution nozzle 128, the inlet end of which is associated with appropriate flow control means.

In this embodiment of the invention the inner wall 114 is provided with a continuous slot Ior annulus 146, or, if desirable, an annular series of closely spaced radially extending apertures, which communicates between the mold cavity 134 defined by the inner surface of wall 114 and a collection plenum 142 defined by extensions of inner and outer mold walls 114 and 116, an annular partition wall 117 and the end wall 119 of the mold 112. The collection plenum 142 is connected by means of outlet 146 to a suitable vacuum system as described above in connection with FIGURES 1 and 2. The annulus or slot 140 may be continuous .around the mold wall 114, or it may be confined to as l-ittle as the top 60' of the mold, again depending upon the same factors mentioned above regarding the circumferential extent of ports 40 in distri- -bution nozzle 28. It should also be noted that the annulus or slot 140, or the apertures as the case may be, must be of such a size that surface tension of the molten metal will prevent entry thereof into the slot or passage therethrough into the collection plenum in order to prevent the deleterious effects which this would have upon the vapor escape means and upon the casting itself.

Still another embodiment of the invention is illustrated in FIGURES 4 and 5 which includes casting mold 2112 having inner and outer concentric walls 214 and 21-6, respectively, defining the circulating chamber 218 for a cooling medium 220 which enters through entrance port 222 and exits through the apertures 224 for direct cooling of the solidifying portion of ing-ot 226. Distribution nozzle 228 receives molten metal at its inlet end 230 from a flow control means and discharges the molten metal into the inlet end of mold 212.

The vapor escape means of this embodiment comprises a series of closely spaced ports or holes 240 which are disposed in a single row located in the uppermost part of the mold and extending substantially from one end of the casting mold to the other. This vapor escape route may also, if desirable, take the form of a continuous slot rather than the series of holes illustrated in FIGURE 4. The holes or slot communicate between the interior of the mold cavity and a collection plenum 242 which is dened in part by a hood 244 mounted on the upper portion of exterior mold wall 216, and in part by a pair of upstanding longitudinally extending Walls 221 and 223 respectively which interrupt the continuity of the circulation chamber 218 along the upper port-ion of the mold 212. The collection plenum 242 is provided with an outlet port 246 which is suitably connected to a vacuum system in orde-r to maintain a reduced pressure in the collection plenum to assist in the removal of vapors and gases.

It is to be noted that this embodiment of the invention offers an advantage over those previously described in that it allows vapor to be collected along the entire length of the mold. Thus, no isolated bubbles or vapor pockets can be formed and exist some distance from the inlet end of the mold and not be accessible to the vapor escape ports located at the inlet end of the mold. Also, in the case of the slot, problems associated with the entry and freezing of metal in the vapor escape ports is minimized. Since the slot is parallel to the direction of cast-ing, any metal that flashes into the slot will be withdrawn with the ingot thus making the slot self cleaning.

AIt should again be remembered that the holes 240, or in the alternative the continuous slot, must be small enough to prevent the entry of molten metal therein.

Further modifications which are deemed to be within the scope of the invention are suggested .by refe-rence to the accompanying drawings. For example, referring to FIGURE l in place of the ported distribution nozzle sh-own therein, a non-ported nozzle may be substituted which is fabricated from a porous material, the material being of such porosity that the accumulated vapor-s or gases will pass therethrough but molten metal will not. Additionally, a porous metal ring or insert may be placed within the upper portion of the nozzle 28 of FIGURE 1 in place of the apertures 40 in order to provide a vapor escape route, in which case the nozzle 28 would be fabricated of non-porous material.

In either of these embodiments, a collection plenum is utilized to facilitate removal of the vapors, the plenum, in the case of the porous nozzle, covering substantially the entire nozzle.

Among the materials su-itable, either for the porous nozzle or for the porous insert or ring for use with a nonporous nozzle are the following: porous carbon, cellular silicon carbide, other cellular or porous ceramic and refractory materials resistant to melting and attack by molten metals.

Referring to FIGURES 3 and 4 it is also contemplated that a porous metal insert be substituted for the continuous annulus of FIGURE 3 or the row of holes 240 of FIGURE 4. The latter expedient is illustrated in the enlarged partial sectional view of FIGURE 6, analogous to FIGURE 5 with analogous structure 214, 2.16, 220, 221, and 223 indicated by the same reference characters primed. Instead of employing holes 240, there is provided a continuous slot 340, in which may be situated a suitably shaped porous metal insert 341.

It will .be apparent fr-om the foregoing description and accompanying drawings that there has been provided an improved mold for high speed horizontal continuous casting which is believed to provide a solution to the foregoing problems and achieve the aforementioned objects. It is to be understood that the invention is not limited to the illustrations described and s-hown herein which are deemed to be merely illustrative of the best modes of carrying out the invent-ion, and which are susceptible of modification of form, size, arrangement of parts and detail of operation, but rather is intended to encompass all such modifications as are within the spirit and scope of the invention as set forth in the appended claims.

What we claim and desire to secure by Letters Patent is:

1. Casting apparatus comprising:

(A) an elongate mold having a Wall defining a molten metal solidiication cav-ity therewithin, said mold hav-ing (1) an inlet .and an outlet end and (2) cooling means disposed in heat transfer relationship with said cavity for rapidly inducing so'l-idification of molten metal Within said cavity,

(B) `a distribution nozzle associated with said inlet end of said mold,

(C) vapor escape means disposed in said mold and communicating between said mold cavity and arnbient atmosphere for removing vapor or gases from said solidiiication cavity formed during solidification of molten metal therewithin whereby said cooling means is in more effective heat transfer relationship with said solidifying metal, and

(D) a collection plenum communicating with said vapor escape means and maintained at a subatmospheric pressure, said collection plenum comprising an elongate chamber overlying said vapor escape means and traversing the longitudinal extent of said mold cavity, said chamber being deiined by integral radial extensions of said mold wall.

2. Casting apparatus as set forth in claim 1 wherein said vapor escape means comprises a passageway extending through said mold wall and communicating with at least said inlet end of said mold cavity.

3. Casting apparatus as set forth in claim 2 wherein said passageway comprises a plurality of longitudinally aligned lholes formed in an upper portion of said mold wall.

4. Casting apparatus as set forth in claim 2 wherein said passageway comprises a longitudinally extending slot disposed in the uppermost portion of said mold wall.

5. Casting apparatus as set forth in claim 2 wherein said passageway comprises a longitudinally extending porous metal insert disposed in the uppermost portion of said mold Wall.

References Cited by the Examiner UNITED STATES PATENTS 3,022,552 2/ 1962 Tessmann 22-572 FOREIGN PATENTS 814,435 6/ 1959 Great Britain.

I SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

Claims (1)

1. CASTING APPARATUS COMPRISING: (A) AN ELONGATE MOLD HAVING A WALL DEFINING A MOLTEN METAL SOLIDIFICATION CAVITY THEREWITHIN, SAID MOLD HAVING (1) AN INLET AND AN OUTLET END AND (2) COOLING MEANS DISPOSED IN HEAT TRANSFER RELATIONSHIP WITH SAID CAVITY FOR RAPIDLY INDUCING SOLIDIFICATION OF MOLTEN METAL WITHIN SAID CAVITY, (B) A DISTRIBUTION NOZZLE ASSOCIATED WITH SAID INLET END OF SAID MOLD, (C) VAOR ESCAPE MEANS DISPOSED IN SAID MOLD AND COMMUNICATING BETWEEN SAID MOLD CAVITY AND AMBIENT ATMOSPHERE FOR REMOVING VAPOR OR GASES FROM SAID SOLIDIFICATION CAVITY FORMED DURING SOLIDIFICATION OF MOLTEN METAL THEREWITHIN WHEREBY SAID COOLING MEANS IS IN MORE EFFECTIVE HEAT TRANSFER RELATIONSHIP WITH SAID SOLIDIFYING METAL, AND (D) A COLLECTION PLENUM COMMUNICATING WITH SAID VAPOR ESCAPE MEANS AND MAINTAINED AT A SUBATMOSPHERIC PRESSURE, SAID COLLECTION PLENUM COMPRISING AN ELONGATE CHAMBER OVERLYING SAID VAPOR ESCAPE MEANS AND TRAVERSING THE LONGITUDINAL EXTENT TO SAID MOLD CAVITY, SAID CHAMBER BEING DEFINED BY INTEGRAL RADIAL EXTENSIONS OF SAID MOLD WALL.

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