US3327768A - Horizontal continuous casting apparatus - Google Patents

Description

June 27, 1967 R. T. cRAxG ET AL 3,327,768

HORIZONTAL CONTINUOUS CASTING APPARATUS Filed Jan. 25, 1965 IGIO Richard Craig Y* BY Robe/'T E Dieffenbach ATTORNEY United States Patent O 3,327,768 HGRIZNTAL CONTINUOUS CASTING APPARATUS Richard T. Craig, New Kensington, Pa., and Robert P.

Dieienhach, Davenport, Iowa, assignors to Aluminum Sompany of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jian. 25, 1965, Ser. No. 427,716 4 Claims. (Cl. 164-2810 This invention relates to continuous casting in horizontally disposed molds, ingots of the light metals, aluminum and magnesium, together with alloys in which these metals constitute at least 75% by weight of the composition.

Horizontal continuous casting of ingots has found commercial acceptance because of generally recognized advantages in certain respects over vertical casting. For instance, vertically casting long ingots requires elevating the mold or providing a deep pit beneath it, either method representing a costly installation which is avoided in horizontal casting. Other advantages are the degree of operating continuity and the ingot handling convenience associated with horizontal casting.

In the horizontal casting under consideration here molten metal is provided in a reservoir separated from the horizontal mold by a partial barrier or closure which does not chill the metal, and hence can be conveniently made of an insulating or refractory material. This partial closure, hereinafter referred to as the header plate, has a gate, or opening, for passage of the liquid metal therethrough and directly into a drastically chilled mold wherein the metal is solidified and continuously withdrawn in a horizontal direction. The emerging ingot is then conveniently cut to desired length without interrupting the casting operation, the duration of a casting run depending only on the molten metal supply.

Horizontally cast light metal ingots often exhibit a surface defect called a lap or fold which corresponds to what is called la cold-shut in vertically cast ingots. These lap defects, as explained in more detail hereinafter, appear as repeated band-like irregularities on the ingot surface normal to the axis of the ingot and are generally attributed to variations iri surface tension and metal freezing rates which occur during initial contact of the metal with the drastically chilled mold. The laps or folds extend into or penetrate t-he surface of the ingot which generally necessitates removal of the affected surface portions to an extent commensurate with the depth of penetration before the ingot is further processed, especially if it is to be rolled. The lap penetration problem is generally most severe in horizontally cast ingots having relatively large cross-sections, e.g. one having rectangular dimensions of l x 40, where the lap depth or penetration varies from less than 1A in the top-most surface portion of the ingot to 3A or 1/2 or even more in the lower surface portions of the ingot. The difference in depth of the laps on the bottom and top surfaces of an ingot is considered to be disproportionate. While there are some exceptions, this severe or disproportionate lap penetration is most often observed in light metal alloys having a relatively wide freezing range. While the foregoing condition in the top-most surface portion of the ingot is often considered commercially acceptable from the standpoint of the depth of metal to be removed, the deeper cut associated with the lower surface portions is generally deemed excessive.

It has been discovered that the severe lap penetration prevailing in the lower surface portions of a horizontally cast ingot can be alleviated by proper positioning of the gate opening with respect to the mold.

Accordingly a primary object of the invention is to 3,327,768 Patented .lune 27, 1967 ICC provide apparatus adapted to minimize disproportionate lap penetration into the freezing ingot surface, especially at the lower surface portions thereof, in the continuous horizontal casting of light metal ingots.

Another object of the invention to provide a method for continuously casting light metal ingots in horizontally disposed molds wherein lap penetration, particularly in the surface of the lower ingot portions, is minimized.

Further objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a better understanding of the invention and its objects reference is made to the following description, including the appended claims and the drawings in which:

FIGURE 1 is an elevation view, partly in cross-section, illustrating a horizontal casting apparatus;

FGURE 2 is an enlarged longitudinal cross-section of a portion of a metal ingot freezing in a horizontal mold;

FIGURE 3 is an elevation in cross-section illustrating the invention in more detail;

FIGURE 4 illustrates three ingots in cross-section indicating the peripheral zones of severe and disproportionate lap penetration.

Briefly, the invention resides in the discovery that the severe and disproportionate lap condition prevailing in the lower surface portions of horizontally continuous cast ingot can be minimized by introducing the molten metal at a low flow rate in very close proximity to the inner mold wall surface of an open ended mold shell using a gate opening only slightly smaller than the internal dimensions of the mold entrance. The stream of molten metal moving into the mold should have a considerably horizontal attitude which, it has been found, exerts a disturbing influence on the laps penetrating into the ingot. Another factor is that the shape of the gate opening deilects the angular position of the laps penetrating into the ingot toward an attitude parallel .to the mold axis.

Referring now to the drawings, the general arrangement of a horizontal casting apparatus embodying the invention is shown in FIGURE 1. Therein is shown an open top molten metal reservoir 2 having walls of a suitable refractory material 6, and having the general transverse shape of a U and of sufficient width to embrace all of gate 20 in the header plate 18. The header plate 18 consists of a vertical plate-like refractory heat insulative material having an apperture 20 to permit the transfer of metal 8 from the reservoir 2 through the header plate and into the chilled mold 10. The choice of refractory will be determined by the nature of the metal being cast, in the case of casting aluminum and aluminum base alloys the commercial asbestos-silica product sold under the trade name Marinite is satisfactory. It is to be understood that while the header plate is most conveniently fashioned from refractory material, such is not an absolute necessity, It is only essential that the header plate does not significantly chill the liquid metal before it reaches the drastically chilled mold and hence the member is described functionally in the claims as a nonchilling header plate. On the opposite side of the header plate 18 and compressed against it in a sealing position is the chilled mold 10 which can be made of a suitable heat conductive material such as aluminum or copper or alloys in which these metals predominate. Although the mold can be made as an assembly, a more convenient arrangement is to make the mold as an integral casting and machine the surfaces where required, as well as any passageways. The mold is generally quite short even where large ingots are cast, typical mold lengths ranging from about one to four inches. The mold has a lip or step at its entrance. This inwardly extending step may be provided by a separate metallic gasket 32 which has a slightly smaller opening than the mold 10 as shown. The use of such a gasket is described and claimed in co-pending application Ser. No. 286,349. Typical dimensions for this inwardly extending short step are about l/ length (gasket 32 thickness) and 0.010" step extension into the mold opening. The mold may be cooled by circulation of water or other coolant supplied through pipe 14 to chamber 16 in the mold Wall. The coolant is discharged from chamber 16 and projected as a sheath 52 onto the emerging ingot through channel S0. Alternatively, the mold without a surrounding cooling chamber may be chilled by suitably positioned water sprays. Also seen in FIG. l is passageway 58 for continuously supplying lubricant to channel 34 from where it is fed to the head of the mold at the inner wall surface through suitable small openings which may be fashioned by cutting a series of radially disposed notches 33 into the mold face to connect the oil channel 34 with the mold interior. Suitable means, not shown, are provided for refractory back-up, structural support, etc.

The molten metal supply in relation to the solidified ingot is also evident in FIG. l where molten metal 8 in the reservoir passes through the gate 20 in the header plate 1S and establishes a molten head of metal 36 within the mold 10. lt should be noted that the molten metal level in the reservoir is above the mold thereby furnishing a positive liquid metal head. The metal coming in contact with theinner mold wall surface freezes almost immediately to form the walls of the embryo ingot, the freezing starting at 42 next to the header plate 18. The head of molten metal generally extends beyond the exit end of the mold, the boundary between liquid or semiliquid and solid metal being generally illustrated for the ideal case by line 38. The molten metal progessively freezes forming a solid ingot 40 which is moved away from the mold at a continuous rate by means of power actuated rollers 54, or the like. While there has been described a particular species of horizontal continuous casting apparatus, it is not intended that the invention be necessarily limited thereto.

At this point a brief explanation is set forth as to what are believed to be the nature and the causes of lap development in ingot casting together with how such is affected by the practice of the invention. It is observed in FIGURE l that laps appear on the ingot surface as a series of bands, typified by the numeral 110, extending around the periphery of the ingot in a plane substantially normal to the ingot axis. In cross-section it is observed that the laps appear as a series of linear penetrations into the ingot and that a typical lap penetration 130 across the top-most portion of the ingot is less than that 208 at the bottom. For clarity purposes only a few laps are illustrated in FIG. l; however, it is to be understood that the lap defects prevail along the entire ingot length and that those shown are merely typical. The penetration at the top is typified by depth of generally not more than about 1A; to 1,/4 of an inch as opposed to the condition at the bottom portions where the penetration runs as deep as 3A" to 1/2" or more in large ingots. While the precise reason for this condition is not completely understood, the zones of maximum lap penetration appear to be associated with the most drastically chilled regions which in turn are probably determined by a combination of thermal and gravitation effects. The disproportionate lap penetration problem is generally most pronounced with ingots of relatively large cross-section, for instance, by 40" rectangular cross-section. Also, while there are exceptions to this general rule, alloys having relatively broad freezing ranges (80 F. to 200 F. and higher) are generally most susceptible to the disproportionate lap penetration. FIGURE 2 is an enlarged cross-section of the lower portion of a freezing ingot emphasizing lap growth 208 into the ingot. It can be seen that a band of discontinuities in grain structure and composition, schematically typified by dotted lines paralleling the lap itself and the ingot surface and designated by the numeral 209, ex-

tend a little further into the ingot than the actual lap itself and must be considered in removing surface material to prepare the ingot for further processing. The zone of severe lap penetration is described herein as the lower surface portions but also generally extends around the entire periphery excepting the top-most portion. For example FIGURE 4o illustrates the periphery of an ingot of rectangular cross-section and the zones of minimal lap penetration, the top-most surface portion 840, together with the zone of severe and disproportionate lap penetration, the lower surface portions 810. Similarly FIGURES 4b and c respectively illustrate this zone for circular and polygonal cross-sections. rfhus the term lower surface portions is intended'to encompass this zone which not only includes the bottom itself but extends up the sides and generally around the top corners.

It is believed that laps are caused by fluctuations in the surface skin of the ingot vas freezing is initiated. Referring to FIGURE 2 the liquid metal at the junction of the non-chilling or refractory header plate 18 and the mold 10, the liquid surface is shown as forming fa submerged free liquid meniscus 220 which also forms 'the boundary of meniscus void 210. The insert gasket 32 is not shown completely in FIG. 2 so that the meniscus effects may be more clearly illustrated. As the liquid metal is chilled, its surface becomes semi-solid, or plastic, a condition wherein it does not function as a liquid but cannot be considered a solid. By the effect of factors such as increased surface tension, freezing shrinkage and others, a freezing plastic meniscus 216 forms and extends or grows into the embryo ingot substantially along the wall of header Iplate 18. This causes the meniscus gap 210 to significantly increase thus curtailing heat flow out of the freezing plastic meniscus zone which is thus weakened especially at the innermost portion 218. The ifreezing or plastic meniscus then ruptures or fails probably at or near the inner portion 218 and liquid metal again fills the area behind the freezing meniscus restoring the submerged free liquid meniscus 220. The freezing metal surface which formed the freezing plastic meniscus 216 generally is not completely redissolved by this inrushing action and remains as a permanent discontinuity extending from Ithe surface to a considerable depth into the solidified ingot.

In accordance with the invention the solution to the problem of severe and disproportionate lap penetration resides in Ithe provision of a gate opening only slightly smaller than the internal dimensions a-t the mold as indicated in FIG. l and shown in more detail in FIG. 3. Within the limits set forth herein, such will alleviate the disproportionate lap penetration associated with the lower surface portions of horizontally cast ingot. Referring to FIG. 3 it is seen that the edge 312 of the gate opening 20 is only slightly inward of the inner mold wall surface. In laccordance with the invention this distance, the A dimension in FIG. 3, is highly critical and ranges broadly from 1,/64" to J/g" and is preferably 1/16 to g". The A dimension is measured from the inside surface 310 of any step at the mold entrance as indicated in FIGURE 3, since as the step seldom exceeds 0.020 into the mold opening, its surface is considered the inner mold wall surface at the mold entrance. The slope at which the gate diverges into the mold can range from nil, or an attitude substantially parallel to the ingot axis, to a slope of 60 with respect to the ingot axis although a range of 0 to 45 is preferred. The edge 312 should be fairly sharp Iand is preferably not rounded more .than $64. Since the stream of molten metal will be moving quite slowly through such a large gate, the slope of the mold opening in the header plate is only important at the discharge side of the plate. Hence the gate opening on the reservoir side of the plate may have a different slope than on the opposite side of the plate. For example, referring to FIG. 3, the mold side slope 316 only extends for a portion through the gate opening, the reservoir side portion 320 being straight or having a different slope.

In accordance with the method of the invention, molten metal is introduced through the large gate opening at a slow linear rate which is substantially the same as the ingot withdrawal rate. Typical withdrawal rates can range from one to ten inches per minute depending on the size of the ingot. The peripheral portion of the molten metal is introduced in close proximity to the mold wall, 1&4 to 1/s and preferably 1746" to 3/32 from the mold inside wall at the mold entrance. Another consideration is 'the attitude at which the surface portion of the molten metal reaches .the mold. This attitude is generally diverging into the mold at an angle of 0 to 45 with respect to the mold axis. Thus the attitude is described as having a substantial component parallel to the mold axis. This method may be contrasted to the practice where the gate is relatively small in respect -to the cross-sectional dimension of the mold, and spaced `at a distance from the mold wall. There the peripheral or surface metal is introduced at a distance from the mold greater than the maximum delined herein and moves outwardly over the header plate where it contacts the mold at an attitude substantially normal to the ingot axis. Thus in accordance with the method of the invention molten metal is introduced into the mold in a manner such that the peripheral or surface portions thereof enter Ithe mold at a slow linear ow rate and in close proximity to its inner wall surface and further at an attitude having a substantial component parallel to the mold axis. Another aspect is the action of the laps as they tend to grow into the ingot whereby they are deflected by the edge 312 of the gate opening toward an attitude parallel to the mold axis but in the direction opposite the molten metal flowing through the gate opening. This deflection together with proper molten metal introduction as set forth above serves to minimize disproportionate lap penetration into the ingot. At this point it should be understood that the theoretical discussions and explanations as to the nature and cause of laps together with the mechanism by which the invention achieves its objects are merely intended to illustrate the invention with greater perspective land are not necessarily intended to place any limitation on the invention. The benefits achieved by the invention are observable phenomena and need not be tied to `any theory.

To more clearly illustrate the practice of the invention the following example will proceed.

Example 1,-Several ingots of an aluminum alloy containing 3.5 to 5.0% magnesium, the balance being aluminum and impurities, were continuously cast in horizontal molds. The ingots generally had rectangular crosssections of about 16" x 39". In addition to magnesium some ingots contained about 0.2 to 0.7% manganese and 0.05 to 0.25% chromium. Using the apparatus of the general type shown in FIGURE 1, but without including the limits required by the practice of the invention, several ingots were cast at an ingot withdrawal rate of about two inches per minute. These ingots all exhibited nonuni-form lap defect depth in that the depth across the midtop portion averaged around V16 but the depth at the top corners, the sides and bottom, the zone designated 810 in FIG. 4a is about Additional ingots were cast using the same basic casting apparatus with the gate opening modified in accordance with the invention. Very good results were achieved where, referring to FIG. 3, A is ym" to 1%2 and angle x is about 45, the ingots exhibiting a maximum lap penetration of about Ms to Still further improved results are obtained by holding the slope, angle x, within the range of to 25 which is considered a preferred embodiment of the invention, not only for the particular alloy composition specied in this example but for any almninum alloy.

It is to be understood that while reference to aluminum and to particular alloys thereof appear in this description, such is not a limitation thereon. The invention will find application in the horizontal continuous casting of any light metal which has a tendency to form disproportionately deep laps in the lower surface portions `of horizontal continuously cast ingot. By the light metals and their alloys is meant aluminum and magnesium or alloys thereof containing at least 75% base metal. Also, while there have been shown and described what are presently considered to be preferred embodiments of the invention together with some minor variations, further modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements described and the appended claims are intended to include any modifications or variations as fall within the true scope and spirit of the invention.

We claim:

1. An apparatus for the continuous casting of light metal ingot comprising a molten metal reservoir, a Ihorizontally disposed mold in communication with said reservoir, said mold having chilled walls and an entrance and exit, and having at its entrance a small inwardly extending step, a common non-chilling header plate between said reservoir and said entrance of said mold except for a gate opening in said header plate for the passage of molten metal from said reservoir to said mold, said gate opening being `only slightly smaller than the internal dimensions of the mold entrance such that the distance from the edge of the gate opening outwardly to the inner mold wall surface at the mold entrance ranges from %4 to Ms", the slope of the gate opening diverging into the mold at an angle of from 0 to 60 with respect to the mold axis, means for applying lubricant to the inner mold wall surface at the entrance portion of said mold and substantially around the periphery thereof, means for cooling said mold and the ingot within and emerging therefrom substantially around the periphery thereof, and means for withdrawing the ingot from the mold at a relatively continuous rate.

2. 'Ihe apparatus as in claim 1 wherein the light metal contains at least 75 aluminum.

3. An apparatus for the continuous casting of aluminum alloy ingot comprising a molten metal reservoir, a horizontally disposed mold in communication with said reservoir, said mold Ihaving chilled walls and an entrance and exit and having at its entrance a small inwardly extending step, a common non-chilling header plate between said reservoir and said entrance of said mold except for a gate opening in said header plate for the passage of molten metal from said reservoir to said mold, said gate opening being only slightly smaller than the internal dimensions of the mold entrance such that the distance from the edge of the gate opening outwardly to the inner mold wall surface at the mold entrance ranges from 1/16 to %2, the slope of the gate opening diverging into the mold at an angle of from 0 to 45 with respect to the mold axis, means for applying lubricant to the inner mold wall surface at the entrance portion of said mold and substantially around the periphery thereof, means for cooling said mold and the ingot within and emerging therefrom substantially around the periphery thereof, and means for withdrawing the ingot from the mold at a relatively continuous rate.

y4. The apparatus as in claim 3 wherein the slope of the gate opening diverges into the 4mold at an angle of from 15 to 25 with respect to the mold axis.

References Cited UNITED STATES PATENTS 2,565,959 8/1951 Francis et al. 2257.2 X 2,996,771 8/ 1961 Armand et al. 22-572 3,022,552 2/ 1962 Tessmann 22-57.2 3,045,299 7/1962 Steigerwald 22-57.2 3,076,241 2/ 1963 Simonson et al. 22-57.2 X 3,263,283 8/ 1966 Allard 2257.2

J. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, Assistant Examiner.

Claims (1)

1. AN APPARATUS FOR THE CONTINUOUS CASTING OF LIGHT METAL INGOT COMPRISING A MOLTEN METAL RESERVOIR, A HORIZONTALLY DISPOSED MOLD IN COMMUNICATION WITH SAID RESERVOIR, SAID MOLD HAVING CHILLED WALLS AND AN ENTRANCE AND EXIT, AND HAVING AT ITS ENTRANCE A SMALL INWARDLY EXTENDING STEP, A COMMON NON-CHILLING HEADER PLATE BETWEEN SAID RESERVOIR AND SAID ENTRANCE OF SAID MOLD EXCEPT FOR A GATE OPENING IN SAID HEADER PLATE FOR THE PASSAGE OF MOLTEN METAL FROM SAID RESERVOIR TO SAID MOLD, SAID GATE OPENING BEING ONLY SLIGHTLY SMALLER THAN THE INTERNAL DIMENSIONS OF THE MOLD ENTRANCE SUCH THAT THE DISTANCE FROM THE EDGE OF THE GATE OPENING OUTWARDLY TO THE INNER MOLD WALL SURFACE AT THE MOLD ENTRANCE RANGES FROM 1/64" TO 1/8", THE SLOPE OF THE GATE OPENING DIVERGING INTO THE MOLD AT AN ANGLE OF FROM 0* TO 60* WITH RESPECT TO THE MOLD AXIS, MEANS FOR APPLYING LUBRICANT TO THE INNER MOLD WALL SURFACE AT THE ENTRANCE PORTION OF SAID MOLD AND SUBSTANTIALLY AROUND THE PERIPHERY THEREOF, MEANS FOR COOLING SAID MOLD AND THE INGOT WITHIN AND EMERGING THEREFROM SUBSTANTIALLY AROUND THE PERIPHERY THEREOF, AND MEANS FOR WITHDRAWING THE INGOT FROM THE MOLD AT A RELATIVELY CONTINUOUS RATE.

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