US3548919A

US3548919A - Continuous casting

Info

Publication number: US3548919A
Application number: US780706A
Authority: US
Inventors: Ivan Gyongyos; Helmut Kotthaus
Original assignee: Alusuisse Holdings AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1965-04-13
Filing date: 1968-12-03
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22

Description

United States Patent [72] Inventors Ivan Gyongyos [50] 164/87, 88, Rikon/Tosstnl, Switzerland; 276, 278, 281

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n UM." BBB [54] CONTINUOUS CASTING ABSTRACT: A continuous casting machine of the grooved rotary wheel mold type has a tundish that feeds molten metal 9 Claims, 4 Drawing Figs.

164/273 in one direction into the mold and has spout that fits for seal- B221! 11/06 ing the walls of the mold. I

PATENTEDuEc22|9m 3,548,919

F1 9 3 Fi g INVENTORS WAN evuev'cis HELMUT mnHAus THEIR ATrOPNEX' CONTINUOUS CASTING Reference is had to our copending application SerJNo. 447,651 filed Apr. 13, 1965, now U.S.Pa t'.'No'. 3,428,111 issued Feb. l8, 1969, of which theinstant application is a divi- SlOl'l. a

The invention relates to continuous casting, and relates more particularly to continuous casting of aluminum alloys; still more particularly, it relates to continuous casting of the type wherein the casting mold is formed by a portion of the groove peripheral annular rim, open towards the exterior, of a rotating cooled casting wheel and a cover band that covers that portion and moves synchronously therewith.

Casting wheels of thistype are known. The cover band is usually endless; the liquid metal to be cast is poured into the mold which is formed between the rim and the cover band, and the' solidified metal leaves the wheel together with the cover band, and is subsequently removed as continuous strip or bar.

Continuousv casting in accordance with rotating watercooled casting wheel molds of the prior art has generally been satisfactory; these molds have, however, been-found to be deficient in that the'rnetal wasdelivered to the mold from a tundish to a point on the wheel that moved downwards so that the metal flowed down through the m m tome'et amass of liquid and solidifying metal located lower down. The surface at the level of this mass of liquid metal was small in comparison with the depth of the mass. This depth, however, is easily affected by very small variations in the feed, and this may result in irregularity of structure in the casting. Moreover, turbulence occurred when the metal flowed down from .the a tundish into the mold and this favored the occlusion of oxide. This was particularly likely to happen if the metal entered the mold under throttle valve control as a thin jet at a point well below the top of the wheel. The metal then tended to trickle onto the base of the mold without coming into contact with the cover band until it reached the mass of molten metal. The distance between the throttling valve and this mass was so great that the formation and entrainment of films ofoxide was almost inevitable.

It is accordingly among the the prior art.

It is another object'of the invention to provide that the sump, namely the liquid metal in'the mold upstream of the solidified part,extends at all times upwardly above the highest pointof the base ofthe mold. a 1 jj I It is afurther object of the invention-to arrange for the aforesaid upward extension of the sump by'adjustment of the rate of rotation of the casting wheel and rate of feeding of the molten metal.

It is still another object of the invention to feed the molten metal in such a manner that it enters the mold at or near the top of the casting wheel.

It is yet a further object of the invention to feed the liquid metal into the mold and tundish in such a manner that the liquid metal'in the mold and the tundish are kept at thesame level, with the tundish extending substantially horizontally and being in liquid-tight contact with the mold;

It is still a further object of the invention to provide such a tundish with side walls extending above the'rim of the wheel and to provide a seal between the frontal parts of the side walls of the tundish and the cover band, whereby the level of the metal in the tundish may be kept above the highest point of the side walls of the mold, so that the liquid metal will come into contact with the cover band before it actually touches any part of the wheel. v

It is yet a further object of the invention to provide for a constant level of molten metal in the tundish, without need for any level regulating devicein the sump itself.

It is another object of the invention to provide for level con-' stancy by means of. a constant-level device in the tundish, which device may includea float. Alternatively, such a device may make use of variations in capacity between an'electrode formed by the surface of the metal and another electrode principal objects of the inven- 'tion to providemeans for avoiding the aforesaid drawbacks of formed by a metal plate arranged above it, signals from the device being used to control the tilting of a ladle or furnace from which the liquid metal is supplied to the tundish. This has the advantage that the liquid metal will be fed from the supply ladle or furnace into the tundish and from there into the mold with but a minimum of turbulence. t

In accordance with a preferred embodiment of the invention, the sump, namely the liquid metal in the mold upstream of the solidified part, extends on both sides of the highest point of the base of the mold. The molten metal is fed through the tundish at a point slightly below said highest point of the base of the mold, thus in advance of that highest point counted in the direction of rotation of the wheel. On the other side of said highest point, the sump is terminated by the solidification front. The position of the solidification front is determined by the cooling adjustment of the casting wheel. I

The mass of liquid metal of the sump is such that the area of the free surface of the metal is large in' comparison with the depth of the sump. The sump is therefore given a greater cushioning or buffer action and is capable of absorbing the small variations in the supply of the molten'metal which are unavoidable in spite of anyautomatic regulation of the level of the surface of the metal.

The instant invention therefore offers the advantage that the stream of molten metal passes from the" tundish to join the liquid mass in the mold at a regular rate without falling through air. The metal is accordingly distributed uniformly ,over the width of the mold and flows without turbulence until it solidifies. At the same time, the formation and entrainment of oxide films are effectively and simply prevented.

With the above and other objects of the invention in view, the invention consists in the novel construction, arrangement and combination of various devices, elements and parts, asset forth in the claims hereof, one embodiment of the same being illustrated in the accompanying drawings and described in the specification.

In the accompanying drawing,

FIG. 1 is a schematic view of a continuous casting machine of the rotating wheel type, in accordance with the invention;

FIG. 2 is a large scale fragmentary vertical central sectional view thereof;

FIG. 3 is a fragmentary sectional view on a still larger scale, taken on the line 3-3 of FIG. 2, and a FIG. 4 is a fragmentary sectional view similar to FIG. 3, but taken on the line 4-4 of F IG. 2.

in carrying the invention-into effectin one of the embodiments which has been selected for illustration in the accompanying drawings and for description in this specification, and referring now particularly to FIGS. 1 and 2, there is provided a continuous casting machine of the rotating wheel type. It comprises a casting wheel I which rotates about an axis x in the direction of an arrow A, and has a rim 2. The rim 2 is recessed and defines an annular groove 4 which is open towards the outside. The groove 4 extends throughout the entire circum ference of the wheel 1, and for a sector portion thereof forms a part of the arcuate casting mold. An endless cover band 3 is provided that runs around

guide rolls

7, 8, 9 and 10, and throughout the mold portion of the groove 4, makes contact with the guiding wheel 1 covering the groove 4 thereby completing therewith the arcuate mold.

Metal to be cast is supplied from a supply vessel (not shown) to a tundish 5, and flows from the tundish 5 into the mold. The wheel 1 is internally cooled by a stream of water, and the cover band 3 is cooled by water sprays 11, with the result that the metal solidifies in the mold to form a continu ous casting 6, which leaves the wheel with the cover band 3 as shown in FIG. 1 and thereafter is continuously drawn away from the machine.

Although the groove 4 may have any desired form in cross section, it is preferably substantially U shaped and has a peripheral base and sides that are inclined outwardly (FIG. 3) so that the removal of the casting is facilitated. The cover band 3, which is advantageously made of steel, is preferably driven by the casting wheel 1 and hence moves in synchronism with the rim 2 of the wheel.

The guide wheel 7 is placed immediately above the top of the wheel 1 and presses the band 3 against the wheel 1, so that at its inlet the mold groove 4 is substantially horizontal.

The discharge end of the tundish 5 exactly matches the cross section of the mold 4 and bears against the rim 2 to make an effective seal at a point where the rim 2 is moving upwards. The tundish 5 is substantially horizontal, and is pivotally mounted about a rod 14 which is parallel to the axis x of the wheel 1, so that the delivery end or spout of the tundish 5 is pressed against the rim walls of the groove 4 by gravity. Additional pressure may be exerted by means of a piston 16 that may be subjected to hydraulic or pneumatic pressure, or again the tundish 5 may be loaded by a spring or a weight so that its spout is firmly pressed into contact with the groove 4. It is important that a good seal should be made at the spout l5 and the spout 15, as described below, may be covered with suitable sealing material for the purpose.

The pivotal mounting of the tundish about the rod 14 presents the advantage that a seal is still maintained if the casting wheel is not truly circular of loses its circular shape as a result of thermal distortion. It is desirable that the rod 14 should be at the end of the tundish remote from the spout 15 so that the amplitude of any rocking movement is small.

Because the spout 15 engages the groove 4 of the wheel at a point where this is moving upwards there is a fairly smooth transition .between the base of the tundish 5 and the base of the groove 4, and the metal flows from the tundish 5 to the mold horizontally as a steady smooth stream without turbulence, in contrast to the thin free cascading of the liquid metal onto the bottom of the mold in previous practice (see FIGS. 3 and 4).

It is, however, also possible to feed the molten metal instead to a point downstream of the highest point 18 of the base of the groove 4, by leading the spout 15 of the tundish 5 to a point to the left (of FIG. 2, though not shown) of said highest point 18, provided, however, that the level of the sump will at all times be above any point of the base of the groove 4.

In both cases, the narrow spaces between the spout 15 and the groove 4 are subject to a metallostatic pressure and need good sealing. The spout 15 therefore needs to be made of a proper material for proper sealing. The spout 15, may, as shown in FIG. 2, be made of a separate piece, and may be composed of a material, namely a sealing material, that may be different from the material of the remainder of the tundish 5. If the tundish 5 is made of a material that does provide enough sealing, then the spout 15 may be made of one piece with the tundish 5. If, on the other hand, the tundish 5 is made of a material that does not provide the needed sealing, then those surfaces of the tundish 5 that make contact with respective surfaces of the groove 4 may be provided with a sealing layer or coating.

The molten metal is supplied from the tundish 5 through a trough 12 and a nozzle 19 thereof, and the supply is controlled by a valve member that cooperates with the nozzle 19, and which includes a circular float 13. The float control ensures that the surface of the liquid metal in the tundish 5 is kept at a substantially constant level.

It is desirable to restrain oxide on the surface of the molten metal from entering the mold, and for this purpose a stripping bar 17 may be provided just above the spout 15. There is thus substantially no opportunity for reoxidation of the metal that actually enters the mold.

In operation, the rate of feed of the metal to the mold and the speed of rotation of the wheel I are correlated so that at all times there is molten metal on both sides of the highest point 18 of the base of the mold. The actual solidification front, that is to say the point where the metal starts to solidify, is preferably maintained fairly close to the top of the wheel.

As best shown in FIG. 2, the'solidiflcation frontis to the left of the highest point 18 of the base of the groove 4 of the wheel 1 The front in FIG. 2 is shown'merely by way of exemplifica tron; the front may, in practice, extend instead further in the direction of the arrow A of FIG. 2, throughout an angle of 40 or even 50.

If the metal level in the tundish 5 is higher than the plane where the cover band 3 makes contact with the rim 2 near the point 18, the forward portions 21 of the side walls 20 of the tundish 5 will make sealing contact with the lateral extensions of the cover band 3. The side walls 20 extend above the rim 2 of the wheel 1. These portions 21 will be concavely shaped (see FIG. 2), in order to match the convex bend of the cover band 3. In accordance with a preferred embodiment, the concave frontal portions 21 may be provided with sealing material of elastic refractory for instance material available under the trade names Marinite or Fiberfrax. The tundish 5 will thus be sealed against the cover band 3, and the liquid metal will come into contact with the cover band 3 before it actually touches any part of the wheel 1.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

We claim: M

1. A continuous casting machine comprising a cooled wheel rotatable about a substantially horizontal axis and having an annular groove, including a base and side walls recessed in its rim open towards the outside, a cover band moving substantially synchronously with said rim throughout a portion of said groove starting substantially at the top of the wheel and defining with said groove portion a continuous casting mold with a substantially horizontal inlet and a tundish extending substantially horizontally for the supply of molten metal above the base of said groove in one direction including at one end a spout being in liquid-tight contact with said mold and fitting for sealing said walls of the mold to restrain flow of metal in any other direction.

2. A machine according to l claim 1, in which the tundish is pivotably mounted near its end opposite said spout end about an axis parallel to the wheel axis.

3. A machine according to claim 1, in which the spout terminates in the mold at a point at which the wheel is moving upwards.

4. A machine according to claim 1, and means operable for exerting pressure on the tundish to urge the spout into contact with the mold.

5. A machine, as claimed in claim 1, at least said spout of the tundish being composed of sealing material.

6. A machine, as claimed in claim I, and a layer of sealing material disposed between said spout and the mold.

7. A machine, as claimed in claim 1, said spout including a separate piece projecting into said mold and being composed of material different from that of the remainder of the tundish.

8. A machine according to claim 1, and a stripping bar provided in the tundish operable to restrain oxide on the surface of the molten metal from entering the mold.

9. In a machine, as claimed in claim 1, said tundish having side walls including frontal portions adjacent the sides of said cover band, and sealing means connected to said frontal portions composed of elastic refractory material and operable to complete a seal with said cover band for restraining the exit of molten metal from the tundish before it reaches the mold.