US3841385A

US3841385A - Method and apparatus for teeming stream protection

Info

Publication number: US3841385A
Application number: US00230797A
Authority: US
Inventors: D Burk
Original assignee: Allegheny Ludlum Industries Inc
Current assignee: Allegheny Ludlum Corp; Pittsburgh National Bank
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15

Abstract

Method and apparatus for excluding air from the teeming stream with the use of an airtight, consumable sheet metal shield purged of air with a non-oxidizing gas and for preventing splashing of an ingot teeming stream. The shield surrounds the teeming stream and can be lifted along its vertical axis such that its upper edge will engage and seal against the bottom of a teeming ladle; while its lower edge rests on or near the bottom of a mold beneath the ladle. The shield is formed from essentially the same alloy as that being teemed and is consumed, starting from its lower end, as the metal rises in the mold.

Description

United States Patent [1 1 Burk Oct. 15, 1974 [54] METHOD AND APPARATUS FOR TEEMING 109.920 11/1964 Netherlands 249/206 STR M PROTECTION 1,132,297 6/1962 Germany 249/206 [75] Inventor: David L. Burk, Pittsburgh, Pa.

[73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa.

[22] Filed: Mar. 1, 1972 [2]] Appl. N0.: 230,797

[57] ABSTRACT 1 Method and apparatus for excluding air from the teeming stream with the use of an airtight, consumable g 164/66 164/ sheet metal shield purged of air with a non-oxidizing 58 Field of Search 164/65, 66, 256,258, 259; gas for Preventing Smashing eeming stream. The shield surrounds the teeming stream and 249/206 can be lifted along its vertical axis such that its upper [56] References Cited edge will engage and seal against the bottom of a teeming ladle; while its lower edge rests on or near the UNITED STATES PATENTS bottom Of a mold beneath the ladle. The shield is 917,257 4/1909 Critchlow 164/65 formed from essentially the same alloy as that being 2,976,587 3/1961 Daussan 164/65 t ed and is consumed tarting from its lower end,

FOREIGN PATENTS OR APPLICATIONS 875,769 8/1961 Great Britain 164/65 as the metal rises in the mold.

11 Claims, 3 Drawing Figures k... VII/IIl/I/I/A III/I 4 PATENIEDHIIHBW j 3.841.385

SHEET 10F 2 PATENTED BUT I 51974 3.841 .385

sum 2 or 2 METHOD AND APPARATUS FOR TEEMING STREAM PROTECTION BACKGROUND OF THE INVENTION In casting steel ingots, it is customary to transfer the molten metal from the furnace to a teeming ladle. This ladle is then transferred by an overhead crane to the pouring floor where successive ingot molds are filled through an opening in the bottom of a ladle equipped with a nozzle, a stopper rod assembly, and a device for raising or lowering the stopper rod assembly to open or close the nozzle.

In the teeming process, the metal in the ingot ordinarily becomes contaminated with reoxidation products due to exposure of the teeming stream to air. That is, the molted'metal, as it passes from the nozzle in the bottom of the ladle to the rising molten metal meniscus in the mold, is in the form of a ragged, turbulent stream which causes substantial splashing as it falls into the molten metal pool in the mold. The result is that considerable surface area of the teeming stream is exposed to air, resulting'in the formation of oxide inclusions in the ingot. The problem is particularly acute in the case of high alloy steels, such as stainless steels, where easily-oxidizable alloy additions form inclusions which show up as stringers in the product rolled from the ingot, causing a relatively large part of the product to be scrapped, unsuitable for critical applications, or such as to require extensive grinding.

In the past, systems have been devised for protecting the teeming stream against oxidation wherein an elongated, consumable splash can or snorkel is provided around the teeming stream between the bottom of the ladle and the rising molten metal meniscus in the mold. One of these systems is shown, for example, in U.S. Pat. No; 2,976,587 wherein a snorkel fits into a conical receptacle at the bottom of the ladle and is pressed against a seal on the bottom of the mold. A cover is placed over the mold and both the mold and snorkel evacuated during teeming.

The system shown in U.S. Pat. No. 2,976,587, while possibly workable, is complicated and requires that the ladle be moved upwardly, its nozzle aligned with the splash can, and then moved downwardly so as to fit the upper end of the snorkel into a conical receptacle each time an ingot is poured. Furthermore, the use of a cover over the mold and the apparent necessity for removing the snorkel from its receptacle after each teeming operation makes the device not altogether satisfactory and possibly explains its lack of commercial acceptance.

SUMMARY OF THE INVENTION In accordance with the present invention, a system is provided for teeming molten metal into a mold by initially placing in the mold a vertically-extending metal sheath device which will isolate a teeming stream from the surrounding air and which can be lifted along its vertical axis, followed by positioning a ladle containing molten metal over the sheath such that a pouring nozzle in the bottom of the ladle is essentially aligned with the vertical axis of the sheath. The sheath device is then raised along its vertical axis until its upper edge engages and is sealed against the bottom of the ladle around the nozzle; whereupon molten metal is discharged through the nozzle such that it will fall through the sheath into the mold. The sheath, after it is raised such that its top edge abuts the bottom of the ladle, is preferably purged with argon or some other inert or non-oxidizing gas.

In the preferred embodiment of the invention, the sheath is made expandable along its vertical axis by forming it in two parts, one of which slides or telescopes into the other. It is necessary only to insert ex pandable sheaths in each mold of a row of molds. As the teeming ladle makes its pass along the row of molds, a simple mechanical clamping and lifting device attached to the ladle bottom engages the top of the sheath beneath the ladle and riases its upper telescoping part into sealing engagement with the underside of the ladle around the nozzle. The lower telescoping part rests on the bottom of the ingot mold. To enhance the exclusion of air from the teeming stream, a purging gas can be introduced into the sheath through a sealing gland surrounding the pouring nozzle.

An advantage of this arrangement is that the ladle need not be raised or lowered to effect a seal between the bottom of the ladle and the sheath. A minimum of bulky mechanical fixtures need be attached to the ladle. In the embodiment of the invention shown herein, a hand-operated tong-like fixture on the ladle acts to bring the upper end of the sheath into contact with the underside of the ladle.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is an elevational view, partly in section, of the system of the invention;

FIG. 2 is an enlarged cross-sectional view of the teeming nozzle and associated sealing means for the metal sheath of the invention surrounding the teeming stream; and

FIG. 3 is a cross-sectional view, taken substantially along line IlI-III of FIG. 1, showing a top view of a tong-type device for manipulating the sheath shown in FIGS. 1 and 2.

With reference now to the drawings, and particularly to FIG. 1, there is shown a ladle 10 formed from an outer steel shell 12 having an inner refractory lining l4 and containing a bath 16 of molten metal to be teemed into ingot molds. One of the molds is shown in FIG. 1 and is identified by the reference numeral 18. Ceramic structures called hot tops are often used on top of the ingot mold. They serve as an extension of the mold and provide a reservoir of molten metal. For clarity the hot top is not shown in the figures. The ladle I0 is carried by means of hooks adapted to engage trunnions 20 on the sides of the ladle and suspended from an overhead crane, not shown. In the bottom of the refractory lining 14 and the steel shell 12 isan opening which carries a refractory nozzle 22. A stopper rod 24, which carries a stopper or plug 26 at its lower end, can move into or out of the opening 28 formed in the nozzle 22. When the stopper rod 24 is raised as shown in FIG. 1, molten metal can flow through the nozzle 22, forming a teeming stream of molten metal which falls into the mold 18. However, when the stopper rod 24 is lowered and the plug 26 inserted into the opening 28, the teeming stream is interrupted.

In most steelmaking practices, the teeming stream is permitted to fall through the air from the nozzle 22 down into the mold 18. This teeming stream is ragged and turbulent; and, when it falls into the bottom of the mold or the rising molten metal within the mold, considerable splashing occurs. As will be understood, this exposes a considerable surface area of the molten metal to air and oxygen, with the result that a considerable amount of reoxidation occurs forming inclusions in the cast ingot.

In order to prevent oxidation of the teeming stream in accordance with the principles of the present invention, a gas-tight metal sheath 30 is placed in the mold 18 prior to the teeming operation and before the ladle is moved over the mold. The sheath 30, in the embodiment of the invention shown in FIG. 1, comprises an upper cylindrical portion 30A which loosely nests into a lower section 30B of larger diameter, the latter being provided to prevent the initial splash from reaching the mold wall. In this manner, the portion 30Bwill always rest on the bottom of the mold 18; however the upper portion 30A may be moved upwardly along the vertical axis of the sheath and into engagement with a seal assembly, generally indicated in FIG. 1 by the numeral 32, which surrounds the lower end of the ceramic nozzle 22.

The sheath 30 is a simple, sheet metal cylinder which stands in the mold and can extend above the top of the mold or above the hot top (the latter is not shown for clarity) if one is used. It can be fabricated from scrap sheet or strip of essentially the same alloy as that being teemed. The diameter of the sheath 30 should be much greater than that of the nozzle opening 28 since the teeming stream will flare outwardly as it falls down into the mold through the sheath. Otherwise, if the diameter of the sheath were not substantially greater than that of the nozzle opening, contact of the stream with the sides of the sheath would melt it.

As is best shown in FIGS. 1 and 3, the top of the upper portion 30A of the expandable sheath 30 is provided with diametrically opposed lugs 34 which can be engaged by hooked ends 36 of a bifurcated tong 38. As shown in FIG. 1, the tong 38 is suspended from a lug 40 secured to the side of the ladle 10 by means of a flexible chain 42 connected to the tong at 44. With this arrangement, an operator standing on the teeming floor 46 can grasp handles 48 of the tong 38 and move them upwardly into the broken-line position shown in FIG. 1 while positioning the hooked ends 36 of the tongs beneath the pins 34 on the sheath 30. The tong, adjacent the handle 48, carries a weight 50 such that the tong will normally tend to rotate in a clockwise direction as viewed in FIG. 1. Thus, after the hooked ends 36 are positioned beneath the pins or lugs 34, the operator permits the weight 50 to pull the handle 48 downwardly by gravity; whereupon the upper portion 30A of sheath 30 is forced upwardly and into engagement with the sealing assembly 32.

Plates

52 and 54 on the bifurcated tongs are adapted to fit into the interstice between spaced plates 56 on the underside of the ladle so as to position and correctly center the sheath 30 with respect to the sealing assembly 32. As will be appreciated, other and different arrangements can be devised for raising the portion 30A into engagement with the sealing assembly 32.

The details of the nozzle 22 and the sealing assembly 32 are shown in FIG. 2. Surrounding the lower end of the nozzle 22 is a metal retaining ring 58 having a tapered inner opening which engages the tapered outer side walls of the nozzle 22 and holds it in place. The

ring 58 is bolted or otherwise securely fastened to the steel shell 12 of ladle 10 around the nozzle 22. Beneath the retaining ring 58 is an annular metallic ring 60 spaced from the ring 58 and secured thereto by means of an annular metal ring 62 which forms a plenum chamber 64 between a radially-extending flange portion of the ring 58 and the ring 60. An annular space 66 is provided between the ring 58 and the ring 60, pro viding communication between the plenum chamber 64 and the lower end of the nozzle 22. Extending through the annular ring 62 is a conduit 68, equipped with a shut-off valve 69, through which argon or some other purging gas may be introduced.

The seal between the upper end of the sheath 30A and plate 60 can be augmented in several ways. The embodiment shown uses an annular slot 70 having flared, lower edges. The slot 70 receives a tubular seal 72, formed from neoprene or other suitable material, fitted over the top edge of the upper portion 30A of the sheath 30. Thus, when the tongs 38 are moved from the broken-line position to the full-line position shown in FIG. 1, the upper portion 30A is moved upwardly and the seal 72 on its upper edge is forced into the annular slot 70. This occurs with the lower portion 308 remaining on the bottom of the mold.

The sheath 30 may be purged prior to teeming if desired and a positive internal pressure provided during teeming by forcing an inert gas into the annular plenum chamber 64 from whence it passes through space or passageway 66 directly into the sheath 30. After the sheath 30 is thus purged of air, the stopper rod 24 is raised; and metal is teemed into the mold 18 through the sheath 30. Since the sheath excludes the air, very little oxidation of the teeming stream occurs, nor can any substantial splashing occur since the sheath surrounds the stream at its point of contact with the bottom of the mold or the rising molten metal meniscus. The sheath beneath the level of the molten metal will, of course, melt and form part of the ingot; however a portion of the sheath will always exist beneath the molten metal meniscus in order to provide a seal and prevent the entrance of air into the sheath during the teeming operation.

At the completion of the teeming operation, a portion of the sheath 30 will remain unmelted above the level of molten metal in the mold. This, however, can either be taken away or be simply dislodged from the hooked ends 36 of tong 38 and permitted to fall into the molten metal within the mold where it is melted and becomes a part of the resulting ingot. The seal 72, which is preferably formed from neoprene or some other similar material as explained above, simply burns and does not contaminate the ingot.

The thickness of the sheet metal from which the sheath 30 is formed is limited at the upper extreme by internal heat sink considerations. For normal superheat, the total cross section of the sheath should be less than about 5 percent of the ingot cross section. However, practical handling and forming considerations probably limit its wall thickness to something in the neighborhood of about Va inch. At the other extreme, the sheet will have to be thick enough to withstand handling; but the main limitation will be its ability to survive when a teeming stream flares and drops of hot metal impinge on its side. An 1 l-inch diameter cylinder fabricated from 0.070 inch sheet would be typical and weigh about 60 pounds.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

1 claim as my invention:

1. In the method for teeming molten metal into a mold, the steps of placing in a mold a consumable, vertically-extending and gas-tight metal sheath device including upper and lower open-ended telescoping parts vertically movable with respect to one another and which will isolate a teeming stream from the surrounding air, then positioning a ladle containing molten metal over said sheath and aligning a pouring nozzle in the bottom of the ladle with the vertical axis of said sheath device, raising said upper telescoping part into engagement with a seal surrounding said nozzle while the bottom edge of the lower telescoping part remains in contact with the bottom of the mold and a portion of the upper telescoping part remains in the mold, and thereafter discharging molten metal through said nozzle with the seal and upper telescoping part in engagement whereby the molten metal will fall through said sheath device into said mold, the'upper and lower telescoping parts remaining in engagement with one another during their movement with respect to one another, said molten metal causing melting of the lower part of both telescoping parts as the molten metal rises in the mold.

2. The method of claim 1 including the step of purging said sheath device with a non-oxidizing gas after its top engages the bottom of said ladle.

3. The method of claim 2 including the step of continuing the flow of non-oxidizing gas during the filling of the mold with molten metal.

4. The method of claim 2 wherein said non-oxidizing gas is introduced into said sheath through an annular phenum chamber formed in a seal assembly surrounding said nozzle.

5. The method of claim 1 including the step of permitting the upper, unmelted portion of said sheath device to fall into the molten metal within said mold at the termination of a teeming operation.

6. Apparatus for preventing oxidation of a metallic teeming stream, comprising a consumable metallic sheath formed from upper and lower open-ended telescoping parts both positioned within a mold to be teemed with molten metal passing through a nozzle in the bottom of an overhead ladle, said telescoping parts being vertically movable with respect to one another, a seal device surrounding said nozzle, and means suspended from said ladle for forcing the upper telescoping portion of said sheath into engagement with the seal surrounding said nozzle, the upper and lower telescoping parts remaining in engagement with one another during their movement with respect to one another.

7. The apparatus of claim 6 including lugs projecting outwardly from said upper telescoping part adjacent the upper edge thereof for engagement with said means suspended from the ladle.

8. The apparatus of claim 7 wherein said means suspended from the ladle comprises a tong, a flexible chain device connecting the tong to the ladle intermediate the ends of the tong, and a pair of hooked ends at one end of the tong for engaging said lugs whereby arcuate movement of the tong about its connection to said chain device will move the upper edge of said upper telescoping part into engagement with said seal device.

9. The apparatus of claim 6 wherein said seal device comprises a first annular plate surrounding said nozzle, a downwardly depending central portion on said annular plate, a second annular plate beneath said first plate and forming between its inner periphery and said central portion an annular space, an annular wall interconnecting the outer edges of said first and second plates to form a plenum chamber therebetween, the upper edge of said upper telescoping part being adapted to seal against said second plate, and means for introducing a purging gas into said plenum chamber, the purging gas flowing through said annular space into said metallic sheath sealed against said second plate.

10. The apparatus of claim 9 including an annular groove in the bottom of said second plate for receiving and locating the upper edge of said upper telescoping part.

11. The apparatus of claim 9 including a sealing means fitted over the upper edge of said upper telescoping part.

Claims

1. In the method for teeming molten metal into a mold, the steps of placing in a mold a consumable, vertically-extending and gastight metal sheath device including upper and lower open-ended telescoping parts vertically movable with respect to one another and which will isolate a teeming stream from the surrounding air, then positioning a ladle containing molten metal over said sheath and aligning a pouring nozzle in the bottom of the ladle with the vertical axis of said sheath device, raising said upper telescoping part into engagement with a seal surrounding said nozzle while the bottom edge of the lower telescoping part remains in contact with the bottom of the mold and a portion of the upper telescoping part remains in the mold, and thereafter discharging molteN metal through said nozzle with the seal and upper telescoping part in engagement whereby the molten metal will fall through said sheath device into said mold, the upper and lower telescoping parts remaining in engagement with one another during their movement with respect to one another, said molten metal causing melting of the lower part of both telescoping parts as the molten metal rises in the mold.