US3515202A - Method for continuous casting of metal ingots - Google Patents

Description

June 2, 1970 K. BICK ETAL 3,515,202

METHOD FOR CONTINUOUS CASTING OF METAL INGOTS Filed Aug. 16, 1967 INVENTOR-$ BY Mam ATTORNEY United States Patent Ofice 3,515,202 Patented June 2, 1970 3,515,202 METHOD FOR CONTINUOUS CASTING 0F METAL INGOTS Klaus Bick, Paderborn, Wolfgang Weinreich, Wilhelmshohe, and Lothar Harmsen, Paderborn, Germany, assignors to Paderwerk Gebr. Benteler, Schloss Neuhaus, Kreis Paderborn, Germany Filed Aug. 16, 1967, Ser. No. 661,503 Claims priority, application Germany, Aug. 20, 1966, P 40,221 Int. Cl. B22d 11/12 US. Cl. 16489 7 Claims ABSTRACT OF THE DISCLOSURE A mold is provided wth a mold cavity having an inlet end adapted to receive a stream of molten metal, and an outlet end downstream from. the inlet end. Cooling channels for circulation of cooling fluid are provided in the walls of the mold for indirectly cooling the molten metal and causing at least partial solidification thereof so that it will issue from the outlet end as a continuous ingot. A cooling system is arranged downstream of the outlet end and comprises a structure which defines a plurality of elongated slots extending in longitudinal direction away from the outlet end. Each of the slots exposes a longitudinally extending strip-shaped surface portion of the ingot. Means is provided for projecting into each slot against the respective surface portion which is exposed therein at least one jet of coolant fluid which impinges directly onto the surface portion over substantially the entire length of the associated slot.

BACKGROUND OF THE INVENTION The present invention relates generally to the continuous casting of metal ingots, and more particularly to a method of continuously casting metal ingots in stationary molds. The invention also relates to an apparatus for carrying out the method.

In the casting art it is known to use stationary ingot molds for the continuous casting of heavy metals, particularly steel and alloy steel. In such arrangements the mold, which generally consists of copper, comprises a mold cavity, having a inlet end into which molten metal is introduced, and an outlet end downstream of the inlet end. A liquid cooling medium is used to cool the mold which latter, depending upon the diameter or the width of the side faces of the desired ingot, may have an axial length ranging between 600 and 1000* mm. Over this length the continuously moving ingot is in contact with the internally cooled smooth inwardly-directed copper faces bounding the mold cavity.

Molds of this type have not been found entirely satisfactory. The reason for this is that, as the molten metal is introduced into the inlet end of the mold, radial heat exchange takes place between the molten metal and the mold with the result that the metal solidifies radially inwardly and forms a shell around the core which initially is still liquid. As this shell-formation takes place it is accompanied by shrinking of the molten material, and this in turn results in withdrawal of the solidified shell out of contact with the cool inner face of the mold. Thus, as the material approaches the region of the outlet end it is no longer in contact with the inner face of the mold which bounds the mold cavity and proper even cooling no longer takes place.

Attempts have been made to avoid this problem by having the mold cavity converge slightly in the direction towards the outlet end to thereby compensate for the aforementioned shrinking. However, this has not been completely satisfactory either because, even if it is possible to thus effect continuous contact between the inner mold face and the solidified shell of the ingot over the entire axial length of the mold cavity, the fact remains that the exterior face of the shell is relatively rough and thus affords only poor heat-exchange characteristics. Furthermore, withdrawal of heat is of course limited also by the ability of the copper mold to conduct heat away from the shell of the solidifying ingot.

For all of these reasons it has been found necessary to subject the ingot either still within the mold cavity or immediately upon its issuance from the outlet end thereof to an additional direct cooling step by spraying a cooling medium, usually a liquid such as water, directly onto the ingot. This, however, also brings with it some disadvantages. By spraying a cooling medium, which for the sake of simplicity will hereafter be simply referred-to as water, onto the exterior surface of the ingot the latter is subjected to uneven cooling which can lead to damage in the material, such as cracks and the like. Furthermore, in cases where water is sprayed against the ingot while the same is still within the mold cavity there exists the danger that if the water is introduced into the mold cavity at excessively high pressure it will rise to the level at which the entire molten metal is still liquid within the mold cavity, and will there cause serious problems. Generally speaking, however, in all instances known to us in which water is directly sprayed onto the ingot interiorly or exteriorly of the mold cavity, we have found that the uneven and usually insufficient cooling of the ingot results from the fact that the water, which runs off immediately downwardly of the point at which it impinges onto the surface of the ingot, is insulated by formation of a layer of steam in accordance with the so-called leidenfrost phenomenon. In the region in which this occurs, the cooling action is negated and, in fact, it is often observed that a re-heating of the solidified shell occurs as a result of heat transfer from the not-yet solidified inner core.

This disadvantage has been observed in a prior-art arrangement wherein the mold is provided in the region of its outlet end with longitudinally extending grooves in which water is sprayed onto the surface of the advancing ingot, the intention being that the water can run off through the grooves along the surface of the ingot. We have found that strong cooling takes place wherever water impinges upon the surface of the ingot or, rather, of the shell surrounding the still-liquid core. We have also found, however, that in this arrangement the cooling effect downwardly of the point of impingement is insufficient because the water is reflected by bouncing off the surface of the shell. Once this has taken place the water no longer contributes to coo ing and either runs off through the grooves remote from the surface of the advancing shell, or is insulated by the steam layer which develops in accordance with the leidenfrost phenomenon. Thus, cooling at the point of impingement is followed by development of a zone downstream of this point at which the COOliIlg effect is inadequate. When this takes place the aforementioned re-heating as a resu t of heat transfer from the hot core to the solidified outer shell will occur.

SUMMARY OF THE INVENTION The present invention overcomes these disadvantages which have been outlined above.

More particularly, the present invention provides a method of continuously casting metal ingots in which all parts of the advancing ingot are coo ed evenly and intensely.

The present invention also provides an apparatus for carrying out this method.

The apparatus according to the present invention is relatively simple and requires neither great technological nor high economic expenditures, thus making its utilization feasible in a wide range of circumstances.

In accordance with one feature of our invention we provide a method of continuously casting metal ingots in a mold which has a cavity provided with an inlet end and an outlet end. The method involves the steps of continuously feeding molten metal into the inlet end of the cavity, and indirectly cooling the molten metal in the cavity intermediate the inlet end and the outlet end thereof. By so doing the molten metal is at least partly solidified and continuously issues from the outlet end in the form of an ingot which moves in a predetermined direction, namely away from the outlet end. In further accordance with the novel method jets of fluid coolant are directed directly against circumferentially adjacent relatively narrow but elongated stripshaped portions of the ingot surface and in a region which is elongated downstream from the outlet end and extends in the predetermined direction. The jets of fluid coolant are caused to impinge onto the strip-shaped surface portions with high kinetic energy and their width is so selected that they are narrower than the width of the strip-shaped portions.

We have conducted tests with an arrangement utilizing this method and have found that the method makes it possible to cool an ingot within a relatively short cooling range or area so evenly and intensively that the problems discussed earlier are completely eliminated. In particular, the formation of an insulating steam layer, that is the leidenfrost phenomenon, is prevented at all points of the ingot surface because closely adjacent strip-shaped surface portions of the surface have the fluid coolant directly sprayed thereonto with high kinetic energy and over the entire longitudinal extension of the cooling zone. By selecting the width of the jets of fluid coolant narrower than the width of the strip-shaped surface portions the fluid coolant is propelled without any impairment and impinges with full force onto the exposed surface portions, while on the other hand any coolant which is reflected by contact with the ingot surface is free to run off alongside the impinging jet and thus also does not interfere with the incoming coolant. Our tests have shown that with our novel method we can obtain optimum cooling if the kinetic energy of impingement of the jets amounts to at least but preferably up to approximately kp. rn./min. cm. While we prefer to utilize jets which provide a relatively narrow and flat but elongated area of contact with the ingot surface, we have found that we can also utilize a plurality of point-contact jets as long as these are arranged spaced in longitudinal direction of the cooling zone. Evidently it is also possible to use the first-mentioned type of jets and to provide a plurality of these spaced in longitudinal direction of the cooling zone.

The apparatus for carrying into effect our novel method comprises a mold which defines a cavity having an inlet end adapted to receive a stream of molten metal, and an outlet end which is located downstream from the inlet end. Indirect cooling means is provided for cooling the mold so as to at least partially solidify the molten metal which enters the cavity whereby such metal issues from the outlet end in the form of a continuous ingot moving in predetermined direction. Finally, we provide a cooling system which is arranged downstream of the outlet end and which comprises a structure defining a plurality of elongated slots which extend in the aforementioned predetermined direction. Each of these slots exposes a longitudinally extending strip-shaped surface portion of the ingot. Means are provided for projecting into each of the slots and against the respective surface portion which is exposed therein at least one jet of coolant fluid which impinges directly onto the surface portion over substantially the entire length of the associated slot.

As already pointed out above, the nozzles utilized for projecting the jets are preferably of the type which produces a generally fan-shaped jet of coolant fluid which is relatively narrow but elongated so that the coolant fluid impinges over a relatively narrow but elongated area of the surface. We can, however, also utilize two or more of such jets which are spaced from one another in the longitudinal direction of the slots and these nozzles may be of the type providing fan-shaped jets, as mentioned before, or point-shaped jets. If two or more nozzles are used, however, it is necessary that the coolant fluid overlap at the points of impingement whereby to obtain continuous area of contact which extends over the length of each slot. In accordance with the invention the width of this area of contact, whether it be provided by a single nozzle or a plurality of nozzles should be significantly less than the width of each slot.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view of an apparatus embodying our invention in somewhat schematic representation; and

FIG. 2 is a section taken on the line IIII of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail it will be seen that the metal ingot is shown in FIG. 2 and identified with reference numeral 1. In FIG. 1 the ingot has been omitted for the sake of clarity of illustration. The ingot moves in downward direction through the mold cavity defined by the mold 2 (compare FIG. 1) and is actually formed in this mold cavity by introducing molten metal into the upper or inlet end of the cavity, which metal solidifies during passage towards the lower or outlet end of the cavity. Such solidification is facilitated by indirectly cooling the molten metal. To this end the mold 2, which consists of copper in the illustrated embodiment, is provided with internal channels 4 for circulation of a cooling fluid therethrough. The channels 4 are connected with an inlet 5 and an outlet 6 for the cooling fluid which will generally be water, but may be another type of fluid. The mold cavity is bounded by mutually inclined surfaces 7 of the mold, these surfaces 7 being smooth and being cooled by the cooling fluid circulating through the channels 4.

Arranged immediately downstream of the outlet end of the outlet end of the mold cavity, and in the illustrated embodiment releasably connected with the mold 2, is a cooling structure 3 which, in the illustrated embodiment, consists of a plurality of hardened steel plates 8. Different materials are suitable for this purpose but we have found that a hardened steel such as the type known as St. 60 is particularly well suited for this purpose. The plates 8 have a wall thickness ranging between 5 and 10 mm., and preferably on the order of 6 mm. They are circumferentially spaced from one another in parallel planes. The spacing is preferably on the order of 10 mm. but may range between 7.5 and 15 mm. To maintain the plates 8 in their predetermined position relative to one another they are connected by means of anchoring rods 9 and distancing sleeve 10 which are placed onto the rods 9 intermediate the respective plates 8.

It is evident both from FIGS. 1 and 2 that the plates 8 have inwardly-directed edge faces 8a which, as shown in FIG. 2, serve to engage and support the already solidified ingot 1, thus serving the dual function of guide surfaces.

In the illustrated embodiment the upper region of the structure 3 is surrounded exteriorly by a manifold 11 into which the cooling water is fed under high pressure through the inlet 11a. The inner side of the manifold 11, that is the side which faces the outwardly-directed edge faces of the plates 8, carries a plurality of nozzles 12 which, in the illustrated embodiment, are constructed so as to produce substantially flat, narrow fan-shaped jets 13 of cooling fluid at a spraying angle of approximately 90 measured in the vertical, which jets 13 contact the strip-shaped surface portions of the ingot 1 intermediate the respective plates 8 over the entire axial height of the structure 3. FIG. 2 shows that the width of each of the jets 13 is significantly smaller than the distance between the adjacent plates 8. By inclining the nozzles 12 in the direction of movement of the ingot 1, that is downwardly away from the outlet end of the mold cavity, and by so providing the nozzles that they will produce the aforementioned spraying angle of 90, we assure that the liquid which impinges onto the strip-shaped surface portions of the ingot in the region closer to the outlet end of the mold cavity is of greater density and has a higher kinetic energy of impingement than in the region downwardly spaced therefrom. Thus, the density and/or the kinetic energy decreases in the direction away from the outlet end of the mold cavity, and it is preferable that such decrease should be progressive. In accordance with the invention the cross section of the nozzles 12 will be so selected that at any given speed of advancement of the ingot the ingot surface will be maintained at a temperature between 700 and a maximum of 1250 C. when the nozzles 12 are in use.

We have found it advantageous in tests conducted with our novel device that for every 100 mm. of circumference of the ingot 1 between 3 and 9, and preferably 6 of the jets 13 be directed against the ingot surface.

'Of course, in the embodiment illustrated in FIGS. 1 and 2 the nozzles 12 are arranged in the region of the upper end of the structure 3, that is adjacent the outlet end of the mold cavity. This is possible because of the fanshaped configuration of the jets 13. If, on the other hand, two or more nozzles are to be provided for each space between two adjacent plates 8 and, if these are then spaced from one another in longitudinal direction of the structure 3, then it is necessary that the liquid projected by these nozzles overlap at the point of impingement onto the strip-shaped exposed surface portions of the ingot 1. If two or more nozzles are used in this manner they can be of the general type shown in FIG. 1, but providing smaller fan-shaped jets, or they can be of the point-shaped jet-producing type.

We have also found that with the novel arrangement the copper mold, which is rigidly but preferably releasably connected with the structure 3, can be shortened as compared with conventional mold constructions to the extent that it will be either shorter or, preferably, approximately as long as twice the diameter of the ingot. If the ingot is of rectangular or quadratic cross section, then the length of the mold may preferably be twice as long as the width of a side face of the ingot. The axial length of the structure 3 can be approximately the same as the axial length of the mold 2, but it can also be longer than the same.

In tests conducted with the novel apparatus disclosed herein we have produced an ingot having side faces of 160 mm. width. For each of these side faces we utilized nine plates-corresponding to the plates 8 in the drawing-of 6 mm. thickness and spaced 10 mm. apart from one another. This required a total of 40 fan-jet producing nozzles with a total water consumption of 8 m. /h. With this apparatus we have found that even at very high speeds of advancement of the ingot we obtained a very intensive and completely even cooling effect. Thus, we were able to utilize speeds of advancement of up to 2.8 m./min. and in no case did the temperature of the ingot shell exceed 1000 C. upon leaving the cooling structure 3 and at any point of its shell surface.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in an apparatus for continuous casting of metal ingots, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of continuously casting metal ingots in a mold having a cavity provided with an inlet end and an outlet end, comprising the steps of continuously feeding molten metal into the inlet end of said cavity; indirectly cooling the molten metal in said cavity intermediate said inlet end and said outlet end to thereby at least partly solidify the molten metal which continuously issues from said outlet end in the form of an ingot moving in predetermined direction; and directly cooling said ingot only downstream of said outlet by directing circumferentially spaced jets of fluid coolant with high kinetic energy and directly against longitudinal relatively narrow stripshaped portions of the ingot surface which alternate in circumferential direction of said ingot with other portions of said ingot surface against which such jets of fluid coolant are not directed.

2. A method as defined in claim 1, and comprising the step of supporting said ingot along elongated surface portions extending in said downstream direction and each located between adjacent area of said strip-shaped portions.

3. A method as defined in claim 1, wherein the step of directing jets of fluid coolant against strip-shaped surface portions comprises directing against each of said strip-shaped surface portions at least one jet of fluid coolant which impinges against the respective strip over substantially the entire length of said region.

4. A method as defined in claim :1, wherein the step of directing jets of fluid coolant against said strip-shaped surface portions comprises flaring said jets in direction of elongation of said surface portions so that said jets impinge against said strips substantially over the entire length of said region.

5. A method as defined in claim 4, comprising the step of directing said jets against said strip-shaped surface portions from points which are spaced from said surface portions in direction transversely of said predetermined direction.

6. A method as defined in claim 4, wherein flaring said jets comprises flaring each of said jets to a greater extent in said predetermined direction and to a lesser extent oppositely said predetermined direction.

7. A method as defined in claim 1, wherein the step of directing jets of fluid coolant against said strip-shaped surface portions comprises directing against each of said surface portions a plurality of jets spaced from one another in said predetermined direction.

(References on following page) 8 References Cited J. SPENCER OVERHOLSER, Primary Examiner UNITED STATES PATENTS R. S. ANNEAR, Assistant Examiner 2,946,100 7/1960 Baier et a1. 164-283 X 3,098,269 7/1963 Baier 164283 3,124,855 3/1964 Baier 16489 5 164283 FOREIGN PATENTS 1,055,763 4/1959 Germany.

970,284 9/1964 Great Britain.

Images