US3425482A

US3425482A - Continuous casting of non-ferrous metals

Info

Publication number: US3425482A
Application number: US559290A
Authority: US
Inventors: Alfons Capaul
Original assignee: Alusuisse Holdings AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1965-06-23
Filing date: 1966-06-21
Publication date: 1969-02-04
Anticipated expiration: 1986-02-04
Also published as: FI46809C; FR1567011A; IS770B6; DE1508965B1; DK113722B; NL149723B; NL6607206A; AT263244B; GB1096258A; NO115972B; SE317781B; FI46809B; CH456858A; BE682814A; IS1560A7

Description

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United States Patent Othce 3,425,482 Patented eb. 4, 1969 3,425,482 CONTINUOUS CASTING F NON-FERROUS METALS Alfons Capaul, Sierre, Switzerland, assignor to Swiss Aluminium Ltd., Chippis, Switzerland, a Swiss corporation Filed June 21, 1966, Ser. No. 559,290 Claims priority, application Switzerland, June 23, 1965, 8,819/65; Sept. 8, 1965, 12,543/65 U.S. 'Cl. 1644 Int. Cl. B22d 11/10, 17/32; B22c 19/04 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the continuous casting of nonferrous metals, and is particularly applicable to the casting of aluminum and aluminum alloys, utilizing a float or floats to regulate the flow of metal to the mold.

In the continuous casting of slabs of aluminum or aluminum alloys to be rolled in a rolling mill and of round bars every effort is made to obtain as smooth as possible a surface and the thinnest possible layer of columnar crystals at the surface of the strand and for this purpose the strand must be cooled very rapidly. Especially in the case of slabs to be rolled in rolling mills, it is desirable to reduce as far as possible the thickness of the surface layer, which subsequently has to be removed by a machining operation, for example by milling so that the loss of metal is kept to a minimum. In casting metal of anodic oxydation quality, that is to say a metal which can subsequently be anodically oxydized, in the form of sheet or profiled sections, a surface is required which does not produce streaks, spots or the like during the electrolytic oxydizing process, and for this reason also it is highly desirable to arrange that the surface layer containing columnar crystals can be removed reliably by machining the surface to the least possible depth.

When using a method of continuous casting in which there is a float on the liquid metal in the mold to act as a valve controlling the flow of liquid metal from a nozzle or nozzles to the mold, a surface layer of the required nature can be produced for example by using a high speed of descent of the strand, or by casting the strand with a low meniscus in the mold, that is to say with a low height of metal in the mold.

Continuous casting with a high strand speed can, however, easily result in a rupture of the solidified wall of the strand, particularly in the case of a slab suitable for subsequent rolling. This technique can therefore be applied only in certain circumstances that is to say only in the casting of strands of comparatively small cross-section, or in casting rods or plates.

The other technique in which the strand is cast with a low meniscus height, does not involve any risk of rupture, even when the product from the mold is an aluminum slab for the subsequent rolling, with a cross-section of 800 x 150 mm. or more.

Experiments have shown, however, that in the continuous casting of slabs having a cross-section of 800 x 150 mm. or more, and of round bars having a diameter of 200 mm. or more, using the customary procedures, it is very diflicult to use a meniscus height of less than 50 to 60 mm. above the bottom of the mold, because there is not a sufficiently great distance between the float and the dummy bar that closes the mold bottom when the casting operation begins. If this distance is too small the float tends to become frozen in the solidifying metal.

It is accordingly among the principal objects of the invention to avoid the drawbacks of the prior art.

It is another object of the invention to provide for special casting operation steps and conditions to obtain the desired characteristics in the casting that emerges from the mold.

It is a further object of the invention to provide for a continuous casting process using a float for the purpose described earlier wherein, when the casting operation begins with a dummy bar closing the bottom of the mold, the nozzle or nozzles and the float are located so far above the bottom of the mold as to ensure that the molten metal rises to a level at which the float does not freeze into the solidifying metal, and, just after the dummy bar has started to move downwards, the distance between the nozzle or nozzles and the bottom of the mold is reduced for more than 10 mm., by which then is obtained the desired meniscus height relative to the bottom edge of the mold.

It is still another object of the invention to control the relative distance of the float, and of the nozzle or nozzles and tundish, with relation to the bottom of the mold. The distance involved here is thus a relative one and can be changed either by changing the level of the nozzle or nozzles or by changing the level of the mold, or by changing both these levels. For example when casting an aluminum slab of large cross-section for subsequent rolling, initially the meniscus height can be from 60 to mm. above the bottom of the mold and subsequently be reduced to a height of between 25 and 40 mm.

Hitherto in the vertical continuous casting of aluminum slabs of large cross-section the smallest practicable distance has been 50 to 60 mm., so that the distance of the outlet end of the feed nozzle or nozzles above the bottom of the mold has been just a little more than that. At the start of casting operation, the mold was quickly filled with metal up to a height of 50 to 60 mm. above its bottom and at this height the float closed the nozzle or nozzles. As soon as the molten metal had solidified sufiiciently the descent of the dummy bar was commenced, taking the strand with it at a predetermined speed. The height of the nozzles and therefore of the meniscus did not change subsequently. Using a meniscus height of from 50 to 60 mm. above the bottom of the mold, it is not possible to obtain the desired rapid solidification of the metal, and hence the resulting surface of the strand has transverse ridges, cold-set places and the like, and moreover the surface layer containing columnar crystals is rather thick. Under these circumstances it is practically impossible to produce an aluminum slab which can subsequently be rolled satisfactorily without first removing some of the metal on the Wide faces of the slab by a machining operation.

It is still another object of the invention to provide a continuous casting process that permits aluminum or aluminum alloy slabs and round bar stock to be made for example of aluminum/manganese and low alloy aluminum/magnesium, to be cast with a smooth surface, because a very low meniscus is used in the mold during the main part of the casting operation. The slabs thus produced can be rolled into sheet of anodizing quality, because the surface layer of columnar crystals is thin and uniform and can be removed reliably by milling to a comparatively small depth.

A further advantage of the process in accordance with the invention is that the pouring temperature range can be greater than that permissible hitherto, without giving rise to cold-set places or a thicker surface layer of columnar crystals. In the case of pure aluminum for example the pouring temperature range can be increased upwards by about 10 C. and downwards by about 10 C. to 15 C., which corresponds to a doubling of the range. Moreover, when pouring aluminum/manganese and low alloy aluminum/magnesium, a smoother surface is obtained because there is much less sweating out.

In the casting of aluminum slabs for subsequent rolling, having a cross-section of at least 800 x 150 mm., in accordance with a still further object of the invention the mold and the strand are cooled in such a way that the sump of molten metal in the mold is substantially rectangular as seen from above and the thickness of the solidified crust within the mold is substantially the same along both the long and short sides of the slab.

Examples of the process in accordance with the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic plan view of the top of the strand in the mold during a continuous casting process, indicating in a solid curved closed solid line the configuration of the metal sump in accordance with the prior art, and in broken lines in accordance with the instant invention;

FIGURE 2 is a fragmentary vertical sectional view through part of one example of a continuous casting machine for carrying out the process in accordance with the invention;

FIGURE 3 is a plan view of the machine shown in FIGURE 2;

FIGURE 4 is an elevational view of a float forming part of the machine shown in FIGURES 2 and 3;

FIGURE 5 is a plan view of the float shown in FIG- URE 4;

FIGURES 6 to 8 are details of the machine shown in FIGURES 2 and 3;

FIGURE 9 is a plan view of the mold forming par of the machine shown in FIGURES 2 and 3;

FIGURE 10 is a sectional view taken along the line B-B of FIGURE 9;

FIGURE 11 is a sectional view taken along the line 0-6 of FIGURE 9;

FIGURE 12 is a side elevational view of a device for raising and lowering the height of the meniscus of the molten metal in the mold, the device forming a modification of the machine shown in FIGURES 2 and 3;

FIGURE 13 is a plan view of the modified device shown in FIGURE 12;

FIGURE 14 is a schematic diagram of a hydraulic mechanism and conduit operating the device shown in FIGURES 12 and 13;

FIGURE 15 is a vertical sectional view of a part of a modified machine showing a device for raising and lowering the mold;

FIGURE 16 is a plan view of the device shown in FIG- URE 15; and,

FIGURE 17 is a diagram of a hydraulic conduit of the device shown in FIGURES 15 and 16.

Referring to FIGURE 1, a mold is shown at 10 and a continuous line 11 represents the edge of the sump of liquid metal in the mold at a level just under the surface of the melt. FIGURE 1 shows how, in the conventional continuous casting process, the molten metal solidifies much more rapidly near the four corners of the strand than it does near the center portions of the long and short sides. This effect has been called running cold at the corners. There is a good deal of cold set near the corners. In contrast to this, a broken line 12 represents the edge of the sump of liquid metal in the strand during a process in accordance with the invention, in which the cooling of the mold and strand is regulated to obtain this effect. Here the liquid sump is substantially rectangular as seen from above and the four edges of the strand run true. There is no premature cold setting of the short sides and the height of the meniscus can be lowered to about 35 mm. above the bottom of the mold without the molten metal breaking through, for example, at a place near the middle of a face of the strand.

The cooling arrangements for the short sides of the strand are preferably separate from those for the long sides. Moreover, in this example, the dilferential cooling is further encouraged by using different spacing and different diameters for spray holes from which water is sprayed onto the short and long sides of the mold and strand.

In the continuous casting machine shown in FIGURES 2 to 14, the distance of the meniscus above the bottom of the mold is adjusted by raising and lowering a tundish with nozzles through which the metal is supplied to the mold.

As shown in FIGURES 2 and 3 a tundish 13, is supported on the short sides 16 of a rectangular slab mold 17, by means of a cranked beam 14 and lifting devices 15. In FIGURES 2 and 10 the short sides 16 of the mold are shown in section. The long sides of the mold are shown at 18. A dummy bar 20 is mounted on a raising and lowering piston 21.

Example In this example the internal dimensions of the mold are 1020 by 265 mm., to produce slabs having a crosssection of 1000 x 260 mm. The internal wall 19 of the mold is in this example smooth, but it may alternatively be vertically fluted. This wall has a height of mm.

The apparatus for supplying the molten metal to the mold comprises the tundish 13 having a body 22, of grey cast iron which is coated inside with mold wash or facing composition. The molten metal reaches the tundish 13 from a pouring spout 23, and leaves the tundish through two outlet nozzles 24, from where it flows on to raised bafile plates 26 in the bottom of a float 25. The baflle plates 26 act in conjunction with the nozzles 24 to regulate the flow of molten metal, the flow being stopped when the meniscus in the mold reaches a predetermined maximum height in relation to the nozzles 24. At the beginning of the casting operation the pouring spout 23 is disposed horizontally, so that when the tundish 13 is subsequently lowered the spout does not take up too steep an angle.

The float 25 is supported by its ends 27 on angle brackets 28, which are themselves supported from the cranked beam 14, by means of slotted bars 29 and bolts 30 with nuts. The float 25 can be raised and lowered, relative to the cranked beam 14 by means of slots 31 in the bars 29 and the angle brackets 28.

The construction and operation of each of the lifting devices 15 are best described with reference to FIGURES 6, 7 and 8. Actuation of a lever 32 rotates cam discs 33 with the result that a support 37 for the cranked beam 14 is raised or lowered, by means of rollers 34, a roller support 35 and a slide plate 36. In this movement, the plate 36 and the support 37 are guided by sleeves 38 which are fixed to the plate 36, and fit over and slide on pins 39.

The raising and lowering of the tundish 13 must of course take place equally at both sides of the machine. This equalization of movement is ensured by a mechanical stop system 40 which functions in conjunction with a series of holes 41, arranged to form a scale. Before actuating the lever 32, the operator first pushes a lever 42 to draw a pin 43 out of one of the holes 41. As soon as the lever 32 has been rotated as far as is required, the lever 42 is released and the point of the pin 43 moves under the action of a spring 44 and engages in another of the holes 41, so that the lever 32 is locked. The levers 32 on both sides of the machine are actuated successively and are moved through equal angles.

In the mold 17 shown in FIGURES 2, 3, and 9 to 11 the long sides 18 consist of hollow extruded sections made of aluminum/magnesium/silicon alloy. Cooling water is admitted to the interiors 46 of the hollow sections through connections 45, and issues through bores 47, which spray the cooling water against the long sides of the strand as it emerges from the mold. The water is admitted to both ends of the hollow sections and therefore a region of higher pressure is produced near the center portion of the sections. This results in a greater cooling effect here. The distribution of the cooling is further influenced by the absence of bores for 2 /2% of the length of the sections 18 at both ends. The first bores situated at each end along the first 8% of the length hollow sections, starting from the end and moving towards the middle, each have a diameter of 2 mm., whereas the bores nearer the middle have diameter of 2.5 mm. each. The short sides 16 of the mold consist of angle sections in the form of aluminum/ magnesium/ silicon alloy castings. These members are cooled by a spray of water issuing from a spray tube 48, which has two rows of spray holes so arranged that the cooling water is directed, both on to the angle section member and also on to the face of the strand itself just below the bottom edge of the mold. The cooling water is supplied to the stray tube 48 through a connection 49, and the supply of water is controlled by a valve 50. The four sides of the mold are screwed together and are located relatively to each other by dowel pins. The inner surfaces 19 are machined smooth. The mold is mounted on its supports by means of brackets 51.

FIGURES 4 and 5 show how the float 25 is constructed so that the molten metal issues horizontally towards the narrow sides of the mold. The float is made of black iron plate 1.5 mm. thick coated with mold wash composition.

Before the beginning of the casting operation, the tundish body 22 and the pouring spout 23 are removed and the float 25 is adjusted in height relative to the cranked beam by moving the supporting brackets 28 up or down, that is to say the float is set to set the gap between the nozzles 24 and the baffle plate 26 when the tundish body 22 is replaced. The whole tundish and float assembly is then raised to its highest position by actuating the lifting devices by means of the levers 32. As already mentioned, at the beginning of the casting operation the level of the meniscus of the melt must be high in the mold, in order to prevent the float from becoming frozen in near the bottom of the mold. As soon as the surface of the melt has risen far enough to lift the float off the brackets 28, that is to say as soon as the float is floating, the lowering of the dummy bar on the supporting piston 21 may be commenced. After the strand has emerged from the mold for a length of about 5 cm. the tundish 13 with the nozzles 24 and the float 25, is lowered slowly until the height of the meniscus level above the lower edge of the mold has decreased to the distance required for the remainder of the casting operation. This lowering must be effected evenly, and this can be done without difficulty with the help of the rows of holes 41. As soon as the required meniscus height is obtained, the levers 32 are locked.

Towards the end of the casting operation the tundish and float assembly must be raised'again, to prevent it from freezing in, This is done in one movement by means of the levers 32, which lifts the float out of the pool of molten metal in the mold. This lifting movement also causes the residue of molten metal in the pouring spout 23 to run back into the furnace or ladle.

When the series production of ingots is required the machine shown in FIGURES 2 and 3, however, has the disadvantage that it needs to be controlled at a numbe of different places.

The disadvantage is overcome by using the control system shown in FIGURES 12 to 14. This control system is mounted directly on a frame 52 of the casting machine. The tundish assembly 13 is supported by a control frame 53 made of angle iron. The frame 53 is raised and lowered by means of four hydraulic cylinders 55 having pis tons 54. The lifting stroke in this example is mm. The pistons 54 are all lifted simultaneously by means of a pump, such as for instance a manually operated pump 56 that delivers through an equalizing valve 57. The lowering movement is elfected by the weight of the assembly acting on the pistons 54, and the return flow of the oil to the tank 58 is controlled by a control valve 59. With this arrangement, the control frame 53 can be operated from a single operating station, and can be held in place at any desired height.

FIGURES 15, 16 and 17 show a modification in which instead of the tundish assembly being movable upwards and downwards, the mold is movable. In this modification there is a mold 60, a float 61 and a tundish 62 with two feed nozzles 63. The mold 60 rests on two beams 64 the ends of which are connected to a frame 65 which is itself connected by brackets 66 to hydraulic lifting devices 67 in such a way that actuation of the lifting devices 67 raises and lowers the frame 65 as required. The tundish 62 is supported by bars 68 that are supported, in turn, by fixed beams 69.

The hydraulic lifting devices 67 and the beams 69 are supported by a frame 70 which rests on the upper part of a housing 71 of the continuous casting machine. The pouring spout has been omitted from the drawing for the sake of greater clarity. The lifting devices 67 have in this example a lifting stroke of 100 mm. Pistons of the lifting devices 67 are simultaneously lifted by a pump such as a manual pump 72 which delivers through a pressure equalizing valve 73, so that the mold 60 is raised or lowered to bring it to the required height relative to the feed nozzles 63 and thus relative to the tundish, The lowering of the mold is effected by the weight of the mold assembly on the pistons of the lifting devices 67, and the return flow of oil into an oil tank 74 is controlled by a control valve 75.

The strand is usually lowered into water, the surface of which can be brought to within about 10 cm. of the bottom edge of the mold. Coolants other than water can of course be used if desired and further jets of water can be used for directly cooling the strand.

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.

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

1. In a process for continuously casting non-ferrous metal strand, particularly aluminum and aluminum alloys, with the aid of a tundish having at least one nozzle pouring the molten metal into a vertical open-ended mold in which the flow of metal through the nozzle and thereby the height above the mold bottom of the meniscus level in the mold is controlled by a float in the liquid metal in the mold, wherein the casting operation is begun with the lowering of a dummy bar initially closing the bottom of the mold, the steps comprising, locating during the beginning of the casting operation the nozzle and the float so far above the bottom of the mold as to ensure that the molten metal rises in the mold to a level sufiiciently high so that the float remains free from freezing into the solidifying metal and subsequently, shortly after the dummy bar together with the forming metal strand began the casting operation by moving downwards, reducing the distance between the nozzle and the bottom of the mold for more than 10 mm., to a reduced height desired for the remainder of the casting operation.

2. A process according to claim 1 in which the height of the meniscus level above the mold bottom is adjusted by vertically moving the mold.

3. A process according to claim 1, in which the height of the meniscus level above the mold bottom is adjusted by vertically moving the tundish.

4. A process according to claim 1, in which the distance between the level of the meniscus relative to the mold bottom is adjusted by vertically moving both the mold and the tundish.

5. A process according to claim 1 for the casting of aluminum slabs of large cross-section in which the height of the meniscus level at the beginning is from 60 to 80 mm. above the bottom of the mold, and is subsequently reduced to from 25 to 40 mm.

6. A process according to claim 1, for the casting of slabs for subsequent rolling or round bar in which the height of the meniscus level above the bottom at the mold is reduced after the strand has emerged from the mold for a distance of about 5 cm.

7. A process according to claim 1, for the casting of aluminum slabs having a cross-section of at least 800 x 150 mm., the steps of cooling the mold and the strand in such a way that the sump of molten metal in the mold is substantially rectangular as seen from above and the thickness of the solidified skin within the mold is substantially the same along both the long and short sides of the strand.

References Cited UNITED STATES PATENTS 15 J. SPENCER OVERHOLSER, Primary Examiner.

R. SPENCER ANNEAR, Assistant Examiner.

US. Cl. X.R.