US3431971A - Continuous casting machine of the rotatable wheel type - Google Patents

Description

March 11, 1969 l. evc'iwcsvs CONTINUQUS CASTING MACHINE OF THE ROTATABLE WHEEL TYPE I of 2 Sheet Filed Sept. 2, 1965 1 n M Y R m m 0 T V/ A G n H. W 1

March 11, 1969 1. GYdNGYS CONTINUOUS CASTING MACHINE OF THE ROTATABLE WHEEL TYPE Sheet g or? Filed Sept.

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A /'5 ATTOENEX United States Patent 3 Claims ABSTRACT OF THE DISCLOSURE A continuous casting machine for molten metal has a cooled Wheel with an annular groove open at the circumference, and a cover band that moves synchronously with the groove throughout a portion thereof, covers the circumference and forms with said groove portion the casting mold. The tundish that delivers the molten metal to the mold has a spout that is closed on all four sides and has a form that matches for sealing the form of the groove and band near the point of the mold entrance.

This is a continuation-in-part of the application Ser. No. 447,651, filed Apr. 13, 1965.

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 grooved 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 this :type 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.

Continuous 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 metal was delivered to the mold from a tundish to a point on the Wheel that moved downwards so that the metal flowed down through the mold to meet a mass of liquid and solidifying metal located lower down. The surface at the level of this mass of liquid metal was small incomparison 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 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 of oxide was almost inevitable.

It is accordingly among the principal objects of the invention to provide methods of and means for avoiding the aforesaid drawbacks of the prior art.

It is another object of the invention to provide that the sump, namely the liquid metal in the mold upstream of ICC the solidified part, extends at all times upwardly above the highest point of the base of the mold.

It is a further 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 the same 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.

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 device in the sump itself.

It is another object of the invention to provide for level constancy by means of a constant-level device in the tundish, which device may include a 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 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.

It is still a further object of the invention to provide an improved seal for the molten metal between the bath in the tundish and the mold, by closing the top of the discharge portion of the tundish, thus forming a discharge portion of the tundish in the shape of a nozzle or spout with a curved upper wall that passes beneath the endless band of the mold.

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.

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 any automatic 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 distrilbuted 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 etfectively and simply prevented.

With the above and other objects of the invention in view, the invention consists in the novel methods, construction, arrangement and combination of various devices, elements and parts, as set 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 showing one embodiment;

FIG. 3 is a fragmentary sectional View on a still larger .scale, taken on the line 33 of FIG. 2;

FIG. 4 is a fragmentary sectional view similar to FIG. 3, but taken on the line 4-4 of FIG. 2;

FIG. 5 is a fragmentary sectional view, similar to FIG. 4, but embodying a modification;

FIG. 6 is a fragmentary perspective view of the tundish with a discharge spout in accordance with the modification of FIG. 5;

FIG. 7 is a large scale fragmentary sectional view, similar to FIG. 2, but embodying a further modification;

FIG. 8 is a fragmentary sectional view, taken on the line 8-8 of FIG. 7; and

FIG. 9 is a fragmentary perspective view, similar to FIG. 6, but showing the spout of the modification of FIGS. 6 and 7.

In carrying the invention into effect in the embodiments which have 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 1 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 circumference 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 continuous 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 forms a spout that 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 15 is firmly pressed into contact with the groove 4. As it is important that a good seal be made between the spout 15 and the mold entrance of the groove 4, the spout 15, as described below, may be covered with suitable sealing material for the purpose. The mold entrance is characterized therein that there the mold has a smaller cross section than any point upstream thereof in point of molten metal feeding.

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 or 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 met'allostatic 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 1 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 solidification front is 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 exemplification; 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 sideward 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, shown in FIGS. 4 and 5, the concave frontal portions 21 may be provided with sealing material 23 of compressible elastic refractory properties, for instance material available under the trade names Marinite or Fiberfrax.

As best shown in FIGS. 5 and 6, the sealing material 23 may be connected to the side walls 20 by means of a dovetail construction. 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.

In the modifioation shown in FIGS. 7 to 9, there is used a spout or nozzle 25 which is closed by a top wall 26 that spans the side walls. This top wall 26 is curved concavely, so that it passes below the band 3, and the tip of the nozzle 25 may advantageously terminate at the highest point 18 of the wheel 1. In this case, the metal that passes through the spout 25 into the mold 4 is drawn largely from below the surface and, accordingly in contrast to the earlier embodiment, there is not the same need for a stripping bar; it is, however, still preferred to provide a stripping bar 27 (FIG. 7) which, in contrast to the stripping bar 17 of FIG. 2, is spaced somewhat further away from the band 3.

I wish it to be understood that I 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. For example, the discharge end of the tundish 5 may be extended to make contact with the wheel 1 at a point Where the wheel is moving downwards, though it is always necessary for the surface of the liquid metal in the mold 4 to be positioned above the base of the tundish 5. Again, although the top of the spout of the tundish 5 may come into contact with the cover band 3, there may the a small gap defined therebetween.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

1. A continuous casting machine comprising a cooled wheel rotatable about an 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 and defining with said groove portion a continuous casting mold, said cover Iband including a portion [disposed at least in part above said tundish and having a convex curvature, and a tundish for the supply of molten metal to the mold including at one end a spotut fitting for sealing said base and side walls of the mold, said spout being composed of one piece and comprising integral side wall portions and a top wall portion and a bottom wall portion, said top and bottom wall portions spanning said side wall portions, thereby defining a discharge passage, said top Wall portion being ourved concavely matching the convex curvature of said cover band portion, said top wall thereby sealing the molten metal inside said tundish against said band before the metal is discharged into said mold.

2. In a continuous casting machine, as claimed in claim 1, the front end of said spout terminating near the highest point of said wheel.

3. In a continuous casting machine, as claimed in claim 1, the front of said spout extending near the mold en tnance portion of said groove, said entrance portion having a smaller cross section than any cross section extending between the wheel and the band upstream of the groove.

References Cited UNITED STATES PATENTS 1,507,456 9/1924 Brasted 22--57.4 1,531,747 3/ 1925 Hazelett 22--57 .3 1,600,668 9/1926 Hazelett 2257.3 1,702,528 2/ 1929 Walters -2257.4 2,804,665 9/1957 Harter et al 22-200.1 X 2,128,941 9/ 1938 Hudson 162277 2,206,930 7/1940 Webster 164-278 2,956,320 10/ 1960 Pulsifer 164-87 FOREIGN PATENTS 569,390 1/ 1959 Canada. 230,406 9/ 1960 Australia.

I. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

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