US3203687A - Apparatus for degassing molten metal - Google Patents

Description

Aug. 31, 1965 P. J. WYNNE ETAL APPARATUS FOR DEGASSING MOLTEN METAL 2 Sheets-Sheet 1 Filed May 16. 1961 llll.

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1965 P. J. WYNNE ETAL 3,203,687

APPARATUS FOR DEGASSING MOLTEN METAL 2 Sheets-Sheet 2 Filed May 16. 1961 United States Patent 3,203,687 APPARATUS FOR DE'GASSING MOLTEN METAL Peter J. Wynne, Pittsburgh, and Patrick J. Wooding and Walter Sieckman, Canonsburg, Pa., assignors to Mc- Graw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed May 16, 1961, Ser. No. 110,539 4 Claims. (Cl. 266-43) This invention relates to apparatus for the vacuum degassing of molten metals and, more particularly, to means for preventing the seepage of air into a vacuum degassing chamber between its metallic shell and refractory lining.

The metallurgy of certain steel alloys requires the reduction of such elements as oxygen, carbon and hydrogen. Because chemical reactions involving these elements have a gas phase and can be made to occur at reduced pressures, their removal can be accomplished expeditiously by treating the melt in a vacuum chamber.

The type of vacuum degassing apparatus used to illustrate the preferred embodiment of the instant invention, is one wherein a vacuum vessel is disposed above a ladle of molten metal and the two are arranged for relative movement toward and away from each other. A nozzle extends downwardly from the lower end of the vessel for immersion below the surface of the molten metal so that upon movement of the chamber and the ladle toward each other a portion of the melt is drawn into the vessel for degasification by the partial vacuum therein. Upon relative movement of the chamber and ladle away from each other, molten metal flows out of the nozzle to intermix with the remaining metals in the ladle. If desired, a new portion of the melt may be redrawn into the chamber by again relatively moving the vessel and ladle toward each other. This process is repeated until the desired degree of degasification has been achieved.

Such degassing chambers generally include a refractory lining which, because of its porosity, is covered with a steel shell to make the assembly gas-tight. A substantially sealed chamber is therefore achieved when the end of the nozzle is dipped into the molten metal which, in elfect, forms a closure for the nozzle opening. However, because expensive cooling apparatus is required if the steel shell of the nozzle is to :come into direct contact with the melt, apparatus of this type are generally provided with a refractory cover for both sides as well as the bottom of the nozzle. As a result of imperfect bonding between the cast refractory material comprising the lining of the nozzle and the metal shell surrounding it, and also because minute cracks may appear during the setting of this nozzle lining material, a serious sealing problem may be created by the creepa-ge of air along the metallic shell and between the shell and the nozzle lining.

It is the primary object of this invention to provide in a vacuum degassing chamber having a nozzle adapted to be dipped into a ladle of molten metal, means for prevent-ing gas leakage between the steel nozzle shell and its castable refractory nozzle lining wherein said means does not interfere with the casting of said nozzle lining.

This and other objects and advantages of the invention will become more apparent from the detailed description of a preferred embodiment of the invention taken with the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section, of vacuum degassing apparatus incorporating the instant invention;

FIG. 2 is a cross section view of the nozzle of the vacuum degassing chamber shown in FIG. 1; and

FIG. 3 illustrates how the ram mix, which surrounds the lower end of the nozzle shown in FIG. 2, flows when it is being cast.

In general terms, the invention comprises in a refractory lined, metal encased vacuum degassing vessel, a metallic refractory lined nozzle for conducting molten metal to and from the interior of the vessel, a plurality of metallic creepage rings alfixed t0 the outer surface of the nozzle and extending obliquely away from its surface and toward the vessel, and a jacket composed of high alumina refractory ram mix surrounding the lower end of the nozzle and covering the metallic rings. In the preferred embodiment of the invention the rings have a frusto-conical.

configuration whose base angle is at least as great as the apex angle of the pressure cone of the ram mix when the latter is in its plastic pre-cast state.

Referring now to the drawings in greater detail, FIG.

1 shows vacuum degassing apparatus comprising a vessel 10, a ladle 11 containing molten metal 12 and a lifting mechanism 14 for supporting the vessel 10 and for lifting it vertically relative to the ladle 11. The degassing vessel l0 includes a steel shell 15 which encloses an inner refractory lining 16. A layer of heat insulating material 18 is disposed between the metallic shell 15 and the refractory lining 16 to minimize heat radiation losses from the vessel 10. The steel shell 15 provides a support for, and hermetically seals the chamber 19 defined by the relatively porous refractory lining 16. A nozzle 20 is atfixed to the lower end of vessel 10 and has a cylindrical bore 22 that communicates with the interior chamber 19.

An evacuating apparatus 24 is connected to the chamber 19 within vessel 10 by a conduit 26 which is connected in a hermetically sealed relation to the shell 15 adjacent an aperture 28 in the roof 29 of the refractory lining 16. A car 30, movably mounted on rails 32 below vessel 10, is provided to support and position the ladle 11. The lifting mechanism 14 includes a platform 34 upon which the vessel v10 is afi'ixed and a plurality of co ordinated hydraulic rams 36 for moving the platform 34 and the vessel 10 vertically. Control of the hydraulic rams 36 is effected by an operator stationed at a remote location. While the vessel 10 is shown to be vertically movable in the illustrated embodiment, it will be appreciated that the device would operate equally as well if the vessel 10 were stationary and the ladle 11 movable.

Operation of the vacuum degassing apparatus will now be described. After the ladle 11 of molten steel 12 has been positioned below the vessel 10, the latter is lowered until the nozzle 20 extends a predetermined distance below the surface of the melt 12. The evacuating apparatus 24 is then actuated to produce a partial vacuum within the chamber 19. As a result of the difference in pressure between the interior of chamber 19 and the atmosmelt 12 has been degassed for a predetermined length of time, the vessel 10 is raised thereby causing the melt 12' to discharge back into the ladle 11 to produce a vigorous stirring within the remainder of the melt 12. However, the lower end of the nozzle 20 remains below the surface of the melt 12 to maintain the partial vacuum within chamber 19. This process may then be repeated by successively lowering and raising the vessel 10 until the desired degree of total degasification has been achieved.

Reference is now made to FIG. 2 which in greater detail shows the nozzle 20 to include an inner lining consisting of a plurality of courses of high alumina refractories 38 and a layer of high alumina mix 39 between the Patented Aug. 31, 1965 3 outer surface of the refractories 38 and a concentrically spaced steel shell 40.

It will be appreciated that the lower end of the nozzle 20 is to be dipped into molten metal which is at a very high temperature. In order to prevent the steel shell 40 from being damaged by contact with this molten metal, a refractory jacket 42 is disposed on the outer surface of the shell 40 and extends below its lower end and into contact with the lower course of the refractories 38. The jacket 42 is formed by forcing a high alumina refractory ram mix between a mold and the shell 40.

It has been found that in the setting of such ceramic ram mixes small fissures or cracks appear in it at the surface of the steel shell 40. These fissures can provide a more or less continuous creepage path for air extending around the outer and inner surfaces of the steel shell 40 and into the chamber 19. For this reason, a plurality of steel rings 44 are affixed to the outer surface of the shell 40 and spaced apart longitudinally to provide a plurality of discontinuities in the otherwise smooth outer surface of said shell. As a result, the likelihood of a continuous fissure along the entire surface between the jacket 42 and the shell 40 is substantially reduced. In addition, the rings lengthen the leakage path around the surface of the shell 40 to further substantially decrease the amount of air that can penetrate into the chamber 19.

These rings 44, however, create difiiculties in the casting of the jacket 42 because of their tendency to block the even flow of the refractory ram mix and thereby prevent the formation of an even homogeneous mixture and create voids at the surface of the shell 40 and beneath the rings 44. For this reason, the rings 44, according to the instant invention, have a frustro-conical configuration.

Reference is now made to FIG. 3 which shows a portion of the jacket 42 being cast in a mold 45. It is known that a force F applied to the surface of a plastic material such as the ram mix 42, when the same is in its plastic uncast state, is transmitted throughout the material from the point of application downwardly and outwardly in all directions in an ever widening path. Further, the material itself flows in the direction of these lines of force. This is known as the pressure cone and its apex angle 9 is determined by the particular physical properties of the material. For example, Coralite, a high alumina ram mix, has a pressure cone whose apex angle is approximately 90 degrees. In order, therefore, to obtain a homogeneous texture of ram mix in the jacket 42 and to prevent the formation of voids, the rings 44 are afiixed to the steel shell 40 so that the base angle of the frustro-conical section of each ring is equal to or greater than one-half the pressure cone apex angle or 2. In this manner, at least some of the forces of the pressure cone will act in a direction parallel to the sides of each creepage ring 44 and thereby flow portions of the ram mix 42 along its upper and lower surfaces and against its junction with the shell 40. Hence, because the upper and lower surfaces of the creepage ring 44 will be parallel to at least some of the forces of the pressure cone, the ram mix 42 will flow along said upper and lower surfaces to provide a dense packing of material on either side of the ring 44 and at its junction with the shell 40.

In addition, the rings 44 will form a support for the ramming mix 42 in the mold 45 to prevent its sliding. For this latter reason, too, a plurality of weld spots 46 are formed by affixing small portions of welding material to the inner surface of the shell 40 to help support the ram mix 39.

While only a single embodiment of the instant invention is shown and described and while it has been illustrated in connection with one particular type of vacuum degas- 4 sing apparatus, it is not intended that the scope of the appended claims be limited thereto.

We claim:

1. In a refractory lined, metal encased vacuum degassing vessel having a nozzle for conducting molten metal to and from the interior thereof, said nozzle having a metallic shell and a refractory lining, a plurality of metallic creepage rings surrounding the outer surface of said metallic shell and affixed thereto, said rings extending obliquely away from their line of attachment to the surface of said metallic shell and upwardly toward said vessel, and a ramplaced jacket surrounding the lower end of said nozzle and covering said metallic rings, said jacket being composed of a high alumina refractory material.

2. In a refractory lined, metal encased vacuum degassing vessel having a nozzle for conducting molten metal to and from the interior thereof, said nozzle having a metallic shell and an inner refractory lining, a jacket surrounding the lower end of said nozzle and composed of a high alumina refractory ram mix, said nozzle having a plurality of metallic rings surrounding the outer surface of said metallic shell and affixed thereto beneath said jacket, each of said rings having a frustro-conical configuration and being inclined upwardly from their line of attachment to said nozzle.

3. In a refractory lined, metal encased vacuum degassing vessel having a nozzle for conducting molten metal to and from interior thereof, said nozzle having a metallic shell and a refractory lining, a jacket surrounding the lower end of said nozzle and composed of a high alumina refractory ram mix having an initial plastic state, and a plurality of metallic rings surrounding the outer surface of said metallic shell and affixed thereto beneath said jacket, each of said rings having a frustro-conical configuration whose base angle is at least as large as one-half the apex angle of the pressure cone of the refractory rammix when the latter is in its initial plastic state, said rings being inclined upwardly from their line of attachment to said vessel.

4. In a vacuum degassing vessel having a nozzle extending from its lower end and means for producing relative movement of said vessel and a ladle of molten metal disposed therebelow so that a reduction in the relative distance between said vessel and ladle will draw molten metal through said nozzle and into said chamber for degasification, said nozzle having a metallic shell and a refractory lining, a jacket surrounding the lower end of said nozzle and composed of a high alumina refractory ram mix having had an initial plastic state, a plurality of metallic rings affixed to the outer surface of said metallic shell beneath said jacket and each having a frustro-conical configuration whose base angle is at least as large as one-half the apex angle of the pressure cone of the refractory ram mix when the latter is in its initial plastic state, said rings being inclined upwardly from their line of attachment to the nozzle.

References Cited by the Examiner UNITED STATES PATENTS 1,960,042 5/34 Andrus 264274 XR 2,416,490 2/47 Molique 26643 2,906,521 9/59 Harders 26634 3,056,595 10/62 Knuppel 26634 FOREIGN PATENTS 1,113,855 12/55 France.

MORRIS O. WOLK, Primary Examiner.

RAY K. WINDHAM, Examiner.

Claims (1)

1. IN A REFRACTORY LINED, METAL ENCASED VACUUM DEGRASSING VESSEL HAVING A NOZZLE FOR CONDUCTING MOLTEN METAL TO AND FROM THE INTERIOR THEREOF, SAID NOZZLE HAVING A METALLIC SHELL AND A REFRACTORY LINING, A PLURALITY OF METALLIC CREEPAGE RINGS SURROUNDING THE OUTER SURFACE OF SAID METALLIC SHELL AND AFFIXED THERETO, SAID RINGS EXTENDING OBLIQUELY AWAY FROM THEIR LINE OF ATTACHMENT TO THE SURFACE OF AID METALLIC SHELL AND UPWARDLY TOWARD SAID VESSEL, AND A

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