US3888300A

US3888300A - Apparatus for the continuous casting of metals and the like under vacuum

Info

Publication number: US3888300A
Application number: US326056A
Authority: US
Inventors: Claude Guichard; Jean-Claude Soret
Original assignee: Combustible Nucleaire SA Soc I
Current assignee: Combustible Nucleaire SA Soc I; Industrielle De Combustible Nucleaire SA Ste
Priority date: 1970-06-15
Filing date: 1973-01-23
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

An apparatus for the continuous casting of metals and metal alloy materials under vacuum comprising a source of melted metal, an ingot mold, and a dynamic air lock which includes several suction chambers which are separated by diaphragm walls. The improvement comprises an air lock arrangement where the melted product passes between rollers which support and center the existing metal inside the suction chambers of the air lock. This improvement is particularly advantageous for applications where the product to be cast has a large cross section.

Description

United States Patent Guichard et al.

APPARATUS FOR THE CONTINUOUS CASTING OF METALS AND THE LIKE UNDER VACUUM Inventors: Claude Guichard, Voiron;

Jean-Claude Soret, Saint Egreve, both of France Societe Anonyme: Societe Industrielle de Combustible Nucleaire Filed: Jan. 23, 1973 Appl. No.: 326,056

Related U.S. Application Data Continuation-in-part of Ser. No. 153,266, June 15, 1971, abandoned.

Assignee:

Foreign Application Priority Data June 15, 1970 France 70.21933 U.S. Cl. 164/256; 164/83; 164/282,

277/59; 277/79 Int. Cl 822d 27/16 Field of Search 164/64, 83, 256, 282',

References Cited UNITED STATES PATENTS H1945 Renkin 34/242 1 June 10, 1975 2,384,500 9/1945 Stoll 118/49 X 3,032,890 5/1962 Brick et a1. 34/242 X 3,038,219 6/1962 Hudson 164/277 X 3,310,850 3/1967 Armbruster 164/64 3,724,529 4/1973 Chaulet et a1. 164/64 X 3,757,847 9/1973 Sofinsky et a1. 164/277 R21,26l 11/1939 Hazelett 164/277 X FOREIGN PATENTS OR APPLICATIONS 1,458,070 9/1969 Germany 164/64 Primary ExaminerR. Spencer Annear Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT An apparatus for the continuous casting of metals and metal alloy materials under vacuum comprising a source of melted metal, an ingot mold, and a dynamic air lock which includes several suction chambers which are separated by diaphragm walls. The improve ment comprises an air lock arrangement where the melted product passes between rollers which support and center the existing metal inside the suction chambers of the air lock. This improvement is particularly advantageous for applications where the product to be cast has a large cross section.

10 Claims, 8 Drawing Figures PATENTEDJUH 10 1915 SHEET APPARATUS FOR THE CONTINUOUS CASTING OF METALS AND THE LIKE UNDER VACUUM CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 153,266, filed June 15, l97l, now abandoned, and the benefit of the filing date of said prior application is claimed for common subject matter.

BACKGROUND OF THE INVENTION The present invention relates to devices for continuous casting, and, in particular, to apparatus for the continuous casting of metals and metal alloy materials, such as steels (particularly refractory steels), copper and its alloys, zirconium and its alloys, aluminum, uranium and the like, under vacuum, where the material to be cast requires good de-gassing and/or which reacts easily with the air when it is hot. This invention concerns itself in particular with the apparatus used for the implementation of such a method.

In general, the devices used for continuous casting under vacuum include an enclosure for providing a vacuum, or a controlled atmosphere, inside which is disposed a tundish containing melted metal with a tap hole for the flow control of the metal, or any other equivalent device, such as a melting-over technique, using electron bombardment or an arc oven, as heat energy sources, and which permits very accurate control of the metal flow through adjustment of the energy supply to the fusion source. Such devices further include an interchangable, cooled ingot mold, a measuring device for accurately determining the level of metal inside the ingot mold, a dynamic air lock, and lastly, one or several coolant spray stations arranged at the outside of the vacuum chamber.

The dynamic air lock is composed of a succession of vacuum chambers (between one and five chambers, for example), each of the chambers communicating with a vacuum pump, or with a group of vacuum pumps, whose type and size depend on the pressure desired inside the corresponding chamber and on the flow volume to be created. The vacuum chambers are separated from one another by means of diaphragm walls, the apertures in these walls being of such dimensions that the space between the strand of cast metal and the diaphragm wall is small enough to create air flow resistance such that the amount of air flowing past the diaphragm wall is less than the flow volume of the pump. This condition is essential for the proper operation of the device, and it requires in turn that an accurate control be maintained on the level of liquid metal inside the ingot mold, in turn requiring a very accurate control of the position of the tap hole valve in the tundish or, as the case may be, of the energy supplied to the arc oven or to the gun of the electron beam oven.

Such an air lock allows the continuous passage of a strand of metal from the vacuum to the atmosphere, or from an area of partial pressure to the atmosphere, the strand having a constant-cross section in the form of either a full bar, a hollow tube, a special profile, or a slab. The range of clearance to be maintained between the cross-section of the cast product and each of the diaphragm walls should normally be about 1 mm, especially in the case of slabs or profiles having a large cross-section, in order to assure that the amount of air entering along the diaphragm apertures is less than the flow volume of the pump which cooperates with the subsequent vacuum chamber.

It should also be noted that the clearance between the cast product and the diaphragm aperture should be approximately the same over the entire contour of the cross-section. Indeed, if a malfunction should occur in the centering of the cast product, the piece would come to be located on one of its sides in immediate proximity to the diaphragm aperture, while on its opposite side, there would appear a clearance of as much as 2 mm, for example, which would mean a considerable reduction of the resistance offered to the air flow, thus greatly increasing the amount of air flowing into the subsequent vacuum chamber and creating the possibility that the amount of air entering would exceed the maximum pumping capacity of the corresponding pump, with the result that some air could enter into the vacuum chamber.

The problems encountered in determining the crosssection of the diaphragm aperture increase both with an increase in the cross-section of the cast product and when the speed of extraction becomes rather high. The cross-section of the product to be cast is determined by the ingot mold, provided no deformation or soiling of the strand occurs after exit from the ingot mold. In the majority of cases, however, the solidification obtained inside the ingot mold produces only skin of comparatively little depth. It follows from this that the solidified shell can become deformed as a result of static pressure in the metal, while its thickness increases. This phenomenon becomes rather important when the cast product has a cross-section with large surface areas, as is the case in the casting of a rectangular slab whose cross-sectional length is more than twice its width. It is also the case, when the cross-section of the cast product is very large, even when the various faces of the section have approximately identical surfaces (square crosssection, for example), meaning that a large proportion of the metal remains in the molten state, thereby exerting a considerable static pressure on the solidified shell of the cast section.

The inventors have found a solution to these difficulties by arranging inside the dynamic air lock a train of guide roller assemblies which are designed to support and accurately guide the cast product in the air lock.

BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantages of the invention will become apparent from the following description of two embodiments, given by way of example, when taken together with the accompanying drawings, wherein:

FIG. 1 represents, schematically, an apparatus of the present invention for the continuous casting of metals under vacuum;

FIG. 1A represents, schematically, in a vertical crosssection, a slab passing through the dynamic air lock of the apparatus of FIG. 1;

FIG. 2 represents an elevational side view, in partial cross-section, of the air lock of FIG. IA;

FIG. 3 represents a horizontal cross-section of an air lock with a rigid support structure;

FIG. 4 shows in an elevational side view an air lock for a square section of large dimensions;

FIG. 5 represents a horizontal cross-section of the air lock shown in FIG. 4;

FIG. 6 represents, schematically, an apparatus of the present invention for horizontal casting; and

FIG. 7 represents, schematically, an apparatus of the present invention for use where the ingot mold itself is curved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a continuous casting apparatus of the present invention comprises a vacuum chamber 100, having located therein a tundish 101 acting as a reservoir for the molten metal 103. In the lower portion of the tundish 101 is located a stopper rod 102 which controls the flow of molten metal from said tundish through a tap holevalve 104, operably connected to a tap hole 105, and is controlled very precisely by a mechanical device operated by a servo-mechanism 111.

Beneath tundish 101 is a funnel 106 which receives the molten metal flowing from the tundish 101 through the tap hole 105 and pours the same uniformly into an ingot mold 125 adapted to shape the molten metal flowing therein. Ingot mold 125 is interchangeable and of a known type; its internal portion is cylindrical and has a cross-section substantially equal to that of an ingot 107 to be cast, taking into account the shrinkage of the solidifying and cooling metal. The internal portion of the ingot mold may also be slightly tapering downwards by an angle of 1-2, so as to partly compensate shrinkage and thus prevent too rapid impairment of the thermal contact between the ingot and the mold. The ingot mold 125 is provided within its walls with a cooling circuit supplied by

ducts

108 and 109 at an adjustable flow rate. A vibrating device, not shown in this figure, but of a known type, is adapted to reciprocate the ingot mold along its axes.

Level sensing means 110 is connected to the top cylindrical portion of the mold 125 and is further connected to a servo-mechanism 111 which controls the stopper rod 102. The level of molten metal in the ingot mold 125 is thus controlled by the servo-mechanism which raises and lowers the stopper rod to open and close, respectively, the tap hole valve 104 in order to allow the molten metal to pass from the tundish 101 through the tap hole 105 into the funnel and, thus, filling the ingot mold.

Beneath the ingot mold is a dynamic air lock 112 comprising a plurality of interconnected vacuum cham bers 114, in which the vaccum is maintained by means of vacuum pump 115. The vacuum chambers are separated one from another by means of diaphragm walls 117 having aligned apertures which permit passage of the cast metal from said ingot mold. Support rollers 116 and 116', mounted on a shaft for rotation, are arranged in each vacuum chamber of the dynamic air lock 112 on opposing sides of the diaphragm wall aperture for supporting and centering the cast metal ingot in its passage through said diaphragm wall apertures.

At the exit of the dynamic air lock 112, the metal ingot 113 is driven through a water spray means 118, whereby it is cooled and hardened, and then it is gripped by

roller sets

120, 120', 121, and 121' acting to guide it and to withdraw from the dynamic air lock.

The liquid level detection means 110 is of a known type, and may include, for example, a Geiger counter probe which is connected electrically through a Geiger counter circuit to servo-mechanism 1 11, as indicated in FIG. 1.

The vibrating ingot mold also is of a known type, which may include a cam, driven by an electric motor, that imparts a reciprocating, axial moinm to the ingot mold by means of connecting rods attached to the ingot mold.

As can be seen in FIG. 1A, an ingot 1 o. rectangular crosssection is shown passing through the dynamic air lock of this invention, having three vacuum chambers, the ingot being supported by means of three roller assemblies of at least two rollers each, the rollers 2 and 2' being located inside the bottom chamber 5, the rollers 3 and 3' being located inside the median chamber 6, and the rollers 4 and 4' being located inside the top chamber 7. A diaphragm wall 8 separates the inside of the chamber 5 from the atmosphere. Between the chambers 5 and 6 is another diaphragm 9, and a similar diaphragm 10 is arranged between the chambers 6 and 7. The chamber 7, in turn, is separated from the ingot mold by a diaphragm 11.

The various roller assemblies directly contact the solidified shell of the ingot which is still at a high temperature. For this reason, it is absolutely necessary to provide effective cooling for these rollers. In the embodiment shown, the cooling is obtained by providing inside the cylindrical roller a water intake through an axial channel 12 which leads inside the roller through a hollow shaft. This channel leads to a plurality of radial channels, followed by peripheral channels 13 which are arranged parallel to the roller axis and in close proximity to its periphery. The water is collected at the other extremity of the roller in an axial channel inside the hollow shaft, the intake and outlet channels being generally symmetric with respect to the shaft. The various diaphragm walls which are subjected to intense heat radiation are likewise cooled via flow channels such as the channel 14, for example.

FIG. 2 shows the air lock of FIG. 1A in a side view, portions thereof being shown in cross-section. In it is shown, at 16, a channel for the cooling of the air lock housing. A gasket 17 provides for sealing ween the vacuum chambers 5 and 6. The figure also s iows a portion of the roller 2 as well as the large face 15 of the ingot 1.

FIG. 3 illustrates additional characteristic details of the air lock as required in the case when an ingot of large cross-section is cast. In such a case, a rather high static pressure is exerted inside the solid shell of the ingot. These forces tend to deform the ingot and they must be opposed by correspondingly high pressures exerted on the support rollers. This condition may necessitate considerable reinforcements on the structure of the air lock. In the example of the embodiment shown, two support beams 18 and 18' have been arranged at the level of each stage and facing the two large surfaces of the slab. The support beams 18 and 18' are linked by means of cross pieces 19, the outside beams 20 giving the whole structure additional rigidity.

The air lock housing 21 of FIG. 3 further includes a certain number of characteristic elements: vacuum outlets 22 and 22', a system of cooling channels for the rollers including an axial water intake 12, cooling channels as described further above, and an axial water out let at 12. At 24 is further shown a rotary vacuum seal for the shaft of roller 2. The air lock housing is further cooled by means of a water cooling system 25. Similarly, the vacuum outlet 22 is provided with a cooling circuit 26.

A further important characteristic of the device is represented by means for controlling the pressure between the rollers and the ingot, such means including pressure screws 27 and 28 which bear on the shaft of one of the rollers and are adjustable through rotation, to permit adjustment of the pressure on the support roller, while producing a slight displacement of the roller axes. With this displacement, it is possible to compress the solidified shell of the ingot, in order to maintain its dimensions just slightly below the dimension of the diaphragm aperture which is situated immediately downstream of the roller device. These adjustments also permit re-centering of the cast piece relative to the diaphragm apertures.

When it is desired to cast sections of a very large cross-section, it becomes necessary to exert pressure on all sides of the ingot regardless of its cross-sectional form. The FIGS. 4 and 5 illustrate such a case for the casting of an ingot of square cross-section.

In FIG. 4 is shown a dynamic air lock comprising two chambers in superposition. At the bottom of the figure is shown the square ingot 42 exiting from the air lock. At 35 and 36 are shown the axes of the shafts carrying the rollers 31 and 32 (FIG. 5). At 43 is schematically indicated a portion of the intake conduit for the water which is to cool the roller 31. This intake conduit 43 loads, via an elbow piece (not shown), to an axial channel in the hollow shaft of roller 21. Similarly, 44 indicates the axial channel for the water supply to roller 32. The cooling circuit for the lower diaphragm is shown at 14.

In FIG. 5 is shown a horizontal cross-section through one of the vacuum chambers of the air lock illustrated in FIG. 4. It shows two oppositely arranged pairs of support rollers and 31, and 32 and 33, respectively. For reasons of structural arrangement, the

axes

34 and 35 of the

rollers

30 and 31 are arranged at a level which is slightly higher than that of the

axes

36 and 37 for the corresponding rollers 32 and 33. Like the earlier described embodiment, this vacuum chamber comprises two vacuum outlets 38 and 38', as well as the necessary water supply channels described above. The various vacuum chambers are bolted on top of one another by means of screws indicated at 39. They are also centered relative to one another at 40 and 40' by means of matching cylindrical depressions and lugs arranged alternately on adjacent vacuum chamber housing and diaphragm walls. A gasket 41 provides the seal between adjacent faces of the air lock.

It should be understood that the air lock as shown in FIGS. 4 and 5 may be reinforced by exterior structural elements in a manner similar to that shown in FIG. 3. Likewise, the adjustment of the pressure and the centering of the ingot may be provided on any one or on both rollers by means of adjustment screws such as are shown at 27 and 28 in FIG. 3. Other known means may replace these adjustment screws, for example, an eccentric in combination with a counter-spring allowing fine adjustment of the roller axes.

The structure representing the various vacuum chambers of the dynamic air lock as described hereinabove is composed of identical elements, their assembly being facilitated through the provision of gaskets and centering lugs. It is obvious that a dynamic air lock composed of identical elements which can be disassembled is more economical in use in order to enable mounting, adjusting and cleaning operations than a similar device completely welded together.

It is possible, furthermore, to use the device for continuous casting under vacuum, or under controlled atmosphere conditions, in an application for horizontal casting, such as shown in FIG. 6.

The apparatus for continuous casting of metals in a horizontal manner, as can be seen in FIG. 6, includes a vacuum chamber 100, which has a tundish 101 located therein containing molten metal. Stopper rod 102 controlled by means of servo-mechanism 11] allows the molten metal to pass through tap hole 105 from the tundish into a funnel-like container 126. The container 126 is filled to a level determined by a liquid level detection sensing means and has an opening near its bottom and at the side thereof for passing molten metal into a horizontally disposed vibrating ingot mold 125. The ingot mold is cooled, as well as vibrating, in the same manner as that described in FIG. 1. The cast metal ingot 107 passes from the ingot mold in a horizontal direction out of the vaccum chamber into a dynamic air lock 112, such as described in FIG. 1.

Also, the produced ingot may be curved after leaving the ingot mold, or the ingot mold itself may be curved. The former device is fully suitable for use in the latter application. In this case, it is merely necessary to give the air lock a shape that corresponds to the curved strand making sure that the diaphragm walls are perpendicular to the surface of the metal at the points of air restriction in the vacuum chambers. As can be seen in FIG. 7, the apparatus, similar to that of FIG. 1, includes a vacuum chamber 100, with a tundish 101, containing molten metal, said molten metal passing through tap hole 105 upon the release of tap hole valve 104 when stopper rod 102 is raised by the action of servo-mechanism 111 into funnel 106. The molten metal passes from the funnel into vibrating ingot mold which, as shown in FIG. 7, is curved. A curved ingot is produced and passes into a similarly curved dynamic air lock 140, which is of the type of the present invention, and then may be further curved by means of deflecting and

withdrawal rollers

145, and 146, 146'.

The dynamic air lock arrangement may be used with continuous casting equipment which includes a tundish for molten metal maintained under vacuum, or a controlled atmosphere, having a vibrating, interchangeable ingot-mold equipped with a water cooling system and including a level detecting device and a device to maintain constant the static pressure in the metal which exists at the level of the air lock by adjusting the level of molten metal in the ingot mold in response to the output from the level detector, so as to maintain within a predetermined tolerance the difference obtained between the cross-section of the cast product and the diaphragm aperture of the air lock arrangement.

What we claim is:

1. In a device for the continuous casting of metals or metal alloy materials under vacuum, or under a controlled atmosphere, where degasing of the materials is required and/or the materials react easily with the surrounding air when they are hot, including a tundish for molten metal which is maintained under a vacuum, or under a controlled atmosphere; and interchangeable ingot mold associated with said tundish and equipped with a water cooling system and a level detecting device for detecting the level of molten metal in said mold; a dynamic air lock comprising a plurality of interconnected vacuum chambers whose inside pressures are reduced by means of a large capacity vacuum pump, the vacuum chambers being separated from one another by means of diaphragm walls having aligned apertures to permit passage of material from said mold, and support rollers mounted for rotation on shafts arranged in each vacuum chamber of the dynamic air lock on opposing sides of said diaphragm wall apertures, cooling means for cooling said support rollers and centering means for adjusting the position of said rollers to center said material with respect to said diaphragm wall apertures; a water spray means arranged at the outside of the dynamic air lock; and means for maintaining constant the static pressure in the metal which exists at the level of the dynamic air lock by adjusting the level of molten metal in the ingot mold in response to the output from said level detector, so as to maintain within a predetermined tolerance the difference obtained between the cross-section of the cast product and the diaphragm wall apertures.

2. The device of claim 1, wherein said cooling means for the support rollers includes a water circulation system, having a water passage entering through a hollow shaft of the support rollers and extending radially toward the roller periphery, and parallel to the axis of the rollers through a plurality of peripheral channels, and returning at the exit side to a single axial exit channel.

3. The device of claim 1, wherein said centering means includes pressure screws adjustable through rotation which exert pressure on the shaft of said rollers, thus affecting a displacement of small amplitude of the shaft in its support.

4. The device of claim 3, wherein said dynamic air lock comprises an assembly of removable vacuum chambers, each chamber having sealing gaskets and centering means, the air lock further including at least one roller assembly.

5. The device of claim 1, wherein the cast product is curved at the exit of the ingot mold, and wherein the diaphragm walls of the vacuum chambers in the dynamic air lock are respectively perpendicular to the surface of the cast product at the point of the aperture in said diaphragm walls.

6. A dynamic air lock for use in a device for the continuous casting of metals and metal alloy materials under a vacuum, or under a controlled atmosphere, where degasing of the materials is required and/or the materials react easily with the surrounding air when they are hot, comprising a plurality of interconnected vacuum chambers whose inside pressures are reduced by means of a large capacity vacuum pump, diaphragm walls having aligned apertures therein for separating said vacuum chambers from one another, roller means mounted for rotation on shafts in each vacuum chamber on opposed sides of said diaphragm wall apertures for supporting and centering a cast metal product passing through the diaphragm wall apertures of said vacuum chambers, and cooling means for cooling said roller means, said cooling means including a water circulation system, having a water passage entering through a hollow shaft supporting said roller means and extending radially toward the roller periphery, and parallel to the axis of the roller through a plurality of peripheral channels, and returning at an exit side to a single axial exit channel.

7. The dynamic air lock of claim 6, wherein centering means are provided for centering the rollers about the aligned apertures on each diaphragm wall.

8. The dynamic air lock of claim 7, wherein said centering means includes pressure screws adjustable to rotation which exert pressure on the shaft of the roller means, thus affecting a displacement of small amplitude of the shaft in its support.

9. The dynamic air lock of claim 6, wherein the plurality of vacuum chambers are removable from one another, each chamber having sealing gaskets and centering means, and including at least one roller means.

10. The device of claim 1, wherein said ingot mold vibrates along its axis.

* i i i

Claims

3. The device of claim 1, wherein said centering means includes pressure screws adjustable through rotation which exert pressure on the shaft of said rollers, thus affecting a displacement of samll amplitude of the shaft in its support.

10. The device of claim 1, wherein said ingot mold vibrates along its axis.