US3089209A - Method for continuous casting of metal - Google Patents

Description

May 14, 1963 A. J. PHILLIPS ETAL 3,089,209 METHOD FOR CONTINUOUS CASTING 0F METAL Filed Jan. 6. 1960 4 Sheets-Sheet l TAT-l. 70

S 1? 0) K: qt-BERT J. INVENTOR PHILLIPS RICHARD BFHEE y 4, 1963 A. J. PHILLIPS ETAL 3,089,209

METHOD FOR CONTINUOUS CASTING OF METAL Filed Jan. 6. 1960 4 Sheets-5heet 2 5 110 5 121 f6 720 V W L T 1 :Za "7 114 INVENTORS QLBEET J. PHILLiPS BY RICHARD Ema? 2am w k QTTOQN EY May 14, 1963 A. J. PHILLIPS ETAL METHOD FOR CONTINUOUS CASTING OF METAL 4 Sheets-Sheet 3 Filed Jan. 6. 1960 INVENTORS QLBEET J. FHlLLrPs RICHARD BFHEE 81/25 9 S: I I? QTTO ENEV May 14, 1963 A. J. PHILLIPS ETAL METHOD FOR CONTINUOUS CASTING OF METAL.

4 Sheets-Sheet 4 Filed Jan. 6. 1960 INVENTORS QLeER-r J. HILLIPS ICHHED BFHER HTTO ENE? United States Patent METHOD FOR CONTINUOUS CASTING 0F METAL Albert J. Phillips, Plainfield, and Richard Baler, New

Brunswick, NJ., assignors to American smelting and Refining Company, New York, N.Y., a corporation of New Jersey Filed Jan. 6, 1960, Ser. No. 894 7 Claims. (Cl. 22-2001) This invention relates to a process for continuously casting metal. More particularly, it relates to a process for continuously casting a copper metal, especially low oxygen copper.

Broadly, the invention comprehends, in a method for continuously casting metal in which molten metal is introduced into one end of an open ended mold and cast metal is withdrawn from the other end of the mold, the improvement which comprises introducing a gas containing more than about 40% by volume of hydrogen to that area of the mold wall at which freezing of the introduced molten metal commences during the casting procedure. For best results, such hydrogen gas is continuouslv introduced to said area of the mold.

The invention is especially useful in continuous casting procedures in which the molten metal is introduced into the chilled zone of an open ended, vertically disposed mold and the rate of introduction of the molten metal with respect to the rate of withdrawal of the cast metal is such as to maintain a free mold wall surface in the chill zone of the mold, i.e. a portion of the chill zone mold wall extends above the level of the metal in the mold. In such casting procedures, the molten metal commences to freeze at the meniscus of the metal in the mold; and in accordance with the invention, the hydrogen gas is introduced to that area of the mold wall in which the meniscus of the molten metal is located.

An important advantage of the invention is that it affords a method by which a metal. especially a copper metal such as copper and copper base alloys and particularly low oxygen copper, can be successfully continuously cast either or both for longer periods and at higher speeds than are possible in the absence of the invention. Moreover, the castings produced by the process possess uniformly excellent surface characteristics and this is a further advantage of the process. Another important advantage of the invention is that it affords a method by which low oxygen copper can be continuously cast for longer periods and at higher speeds than have been possible heretofore while at the same time producing a non-porous casting having a uniform surface and a specific gravity higher than 8.85 and readily produces a low oxygen copper of a density above 8.90 and which for all practical purposes is substantially that of the theoretical specific gravity of copper. These and other advantages of the invention will become apparent from the following description thereof.

In practicing the invention, such introduction of such hydrogen gas may be accomplished in any appropriate manner. For example, the gas may be introduced to said area by delivering it as such thereto from an outside source or by releasing such gas at said area in any other suitable manner from any suitable source. For best results in casting procedures in which the meniscus of the metal is located in the chill zone of the mold, introduction of the hydrogen gas is accomplished by conducting the hydrogen gas as such from an outside source to the mold adjacent the mold wall area where the incoming molten metal contacts the chilled wall of the mold. For example, the hydrogen gas may be introduced into the mold cavity above the level of the metal in the mold from a perforated ring disposed over the 3,089,209 Patented May 14, 1963 mold cavity above the metal in the mold or from ports in the mold wall above and adjacent to the metal level intended to be maintained in the mold during the casting procedure; or by diffusion throught the mold wall where the latter is fabricated of a sufiiciently porous material such as, for example, graphite. Most efficient use of the hydrogen is made when it is introduced by diffusion through the mold wall.

In accordance with another important feature of the invention, the instant hydrogen gas is introduced to said mold wall area in controlled amounts. Such control is effected most readily and advantageously by regulating the amount of introduced gas to obtain a surface of a desired character on the casting as is indicated on the latter as it emerges from the mold. in general, with the introduction of increased amounts of the hydrogen gas, the appearance of an irregular pattern of irregularities on the surface of the emerging casting is indicative that introduction of the hydrogen gas is approaching undesirably excessive amounts and an irregular pattern of irregularities on a major portion of the surface of the emerging casting indicates an undesirable excess of the introduced gas. An irregular pattern of irregularities saving the appearance of cold shuts or folds which are perceptible to the touch are typical of such an irregular pattern on the surface of the casting. On the other hand, with the introduction of decreased amounts of the hydrogen gas, the occurrence of small visible surface scoffs on the emerging casting is indicative that the introduction of the hydrogen gas is approaching undesirably small amounts and severe sticking which causes deep tears in the casting indicates the use of an undesirably small amount of gas. In accordance with the foregoing, a further feature of the invention comprises controlling the introduction of the hydrogen gas to said mold wall area to a rate which is below that at which an irregular pattern of irregularities occurs on a major portion of the surface of the emerging casting and above that at which deep tears occur in the casting emerging from the mold.

The invention is most advantageously used in casting procedures employing a vertical mold in which the level of the molten metal in the mold is maintained below the top of the chilled zone of the mold and the level of the meniscus of the molten metal in the chill zone is moved in vertical reciprocal relative movement with respect to the mold wall during the casting procedure. Such reciprocal movement of the meniscus may be obtained by any appropriate relative movement between the mold wall and the metal therein; for example, by horizontal reciprocation of the sides of a segmented mold or, more preferably, by vertical reciprocation of the mold. In the best mode of operating with such casting procedures, the introduction of the instant gas to the mold wall area upon which the meniscus moves is regulated to obtain regular, uniformly spaced ripples on the surface of the emerging casting.

A hydrogen gas containing any amount of hydrogen may be employed in practicing the invention provided the gas contains more than about seas by volume of hydrogen. Preferably. the gas contains at least by volume of hydrogen and most preferably is a substantially pure hydrogen gas such as is available commercially. The concentration of the hydrogen in the instant ga affects the amount of gas employed. In general, to obtain the same results when the concentration of the hydrogen in the gas is decreased, the amount of gas employed is increased and vice versa. The amount of gas employed is also alfected by the manner in which the gas is introduced to the mold Wall area. In casting procedures in which the meniscus of the molten metal is located in the chill zone of the mold during the casting of the metal and the hydrogen gas is introduced to the mold cavity in the space above the metal in the mold by means of a perforated ring located above the mold, the efiiciency of this mode of introduction, due to dilution, or burning or both, is so low that it is difficult, even when using a 100% hydrogen gas, to introduce the gas at a sufficient rate to obtain the above mentioned irregular pattern of irregularities on the surface of the emerging casting. However, such a surface is readily obtainable where, in such casting procedures, the instant gas is introduced through ports in the mold wall close to the metal meniscus and especially where the gas is diffused thereto through the mold wall.

In practicing the invention, it was found that the casting speed is affected by the cross-sectional shape and size of the casting to be produced, the presence or absence of tapers in the chill zone of the mold, and the rate of reciprocation of the metal meniscus or freezing metal in the chill zones as well as by the heat conductivity of the metal being cast and the overall heat extractive capacity of the mold. In general, the reciprocation rate is increased as the casting speed (Le. the net rate of withdrawal of the casting from the mold) is increased and vice versa. The presence of a converging taper on the mold wall defining the mold cavity increases the heat extractive capacity of the mold and permits the use of higher casting speeds than would otherwise be possible. On the other hand, the casting speed is decreased as the least cross-sectional linear dimension of the casting is increased.

The invention may be practiced in any continuous metal casting procedure employing any conventional continuous casting mold fabricated of any conventional material. However, it is most useful in casting low oxygen copper in a mold in which the metal is cast against a graphite surface, especially a tapered graphite surface, by a procedure in which a free mold wall surface is maintained in the chill zone of the mold, especially when employing a cover of a particulate solid material on the surface of the metal in the mold during the casting procedure, and particularly when the meniscus of the metal in the mold during such procedure is moved in a reciprocal movement with respect to the mold wall during the casting of the metal in the mold. Low oxygen copper as used in the specification and claims means a copper containing less than 0.015% oxygen, and includes oxygen free copper and copper which has been deoxidized with a suitable deoxidizing agent such as, for example, calcium, lithium, boron or phosphorous.

In experimenting with the continuous casting of low oxygen copper against a graphite surface in a vertical mold by a procedure in which during the casting the meniscus of the metal was located in the chill section of the mold, reciprocation of the meniscus with respect to the mold wall was employed and a protective layer of solid particulate cover material was maintained on top of the metal in the mold, it was found that, when the introduction of the instant hydrogen gas is adjusted to provide a regular uniformly rippled surface on the emerging casting and thereafter increased amounts of the gas are introduced, the ripple becomes more and more coarse until a point is reached when a further increase in the amount of the introduced gas causes the regular rippled surface pattern to begin to deteriorate into an irregular pattern in that the ripple begins to become scattered or a crazy quilt pattern of surface imperfections having the appearance of cold shuts or folds at disorganized angles begins to appear on the casting. Thereafter such deterioration of the surface increases until a major portion of the surface of the emerging casting is involved; and it has been found that, if, when this latter occurs, the rate of introduction of the gas is quickly reduced, the possibility of rupture of the casting in the mold is avoided. On the other hand, with introduction of decreasing amounts of the gas, the ripple gradually become more and more faint until a point is reached at which the surface of the casting becomes glassy smooth after which small visible surface scuffs begin gradually to appear on the emerging casting followed by the gradual appearance of small visible surface tears thereon due to slight sticking of the casting in the mold. Thereafter, generally within about one hour and usually within about 15 to 30 minutes, sticking becomes so severe that metal casting is stopped due to rupture of the casting in the mold caused by deep tearing of the casting therein. It has been found that, if the rate of introduction of the gas is increased after the glassy smooth surface or the small visible surface scoffs or the small visible surface tears appear on the casting surface, the possibility of rupture of the casting is avoided. Accordingly, in such casting of low oxygen copper the rate of introduction of the instant hydrogen gas is controlled to a rate below that at which an irregular pattern of irregularities occurs on a major portion of the casting and above that at which rupture of the casting occurs due to deep tearing. Preferably, the introduction of the gas is controlled to a rate below that at which said irregular pattern begins to occur and above that at which deep tears, more preferably above that rate at which small visible surface tears, occur on the surface of the emerging casting, and still more preferably above that rate at which small visible surface scuffs occur thereon and most preferably above that rate at which the surface of the casting is glassy smooth. In the best mode of operating, the introduction of the gas is regulated to obtain regular uniformly spaced ripples on the emerging surface of the casting. For best results the gas is introduced at a rate sufiicient to maintain the regular uniformly spaced ripples on the emerging casting surface during the entire casting procedure.

In practicing the invention in casting low oxygen copper, no limit was found to the period during which the casting procedure could be conducted continuously, even when exceptionally high casting speeds were employed. In casting low oxygen copper in accordance with the invention, highest casting speeds were obtained with shapes in which the least cross-sectional linear dimension was less than about 5 inches. Thus, for example, phosphorous deoxidized copper containing less than 0.015% oxygen was readily cast into billets three inches in diameter while continuously withdrawing the casting from the mold at net speeds higher than 29 linear inches per minute and as high as 64 linear inches per minute and more. Such sustained speeds are up to 6 times faster than those obtainable in the absence of the invention. Moreover, the surface and interior characteristics of the cast billet product were of a uniform high quality throughout. Similar results are obtainable with multi-sided shapes such as cakes having a rectangular cross-sectional area in which the least linear dimension, i.e. the thickness, is less than about 5 inches. Comparable speeds are obtained with other shapes and sizes and with other metal casting procedures taking into consideration size, shape and heat conductivity. Preferably, in practicing the invention with such high sustained casting speeds, the least cross-sectiona1 linear dimension of the shape of the casting (the thickness in the case of cakes and similar shapes, and the diameter in the case of circular shapes such as billets) is about 2 to about 5 inches.

In arriving at the present invention, numerous experiments were conducted in which attempts were made to substitute other gases for the instant hydrogen gas. For example, attempts were made to substitute inert gases such as nitrogen and helium; reducing gases such as methane, ethane, acetylene, carbon monoxide; and oxidizing gases such as air and carbon dioxide. No gas or gas mixture was found, other than the instant hydrogen gas, which had a beneficial effect on the operating period or the casting speed. Thus the instant use of a hydrogen gas containing more than about 40% by volume of hydrogen is unique and critically important in the present process.

The reason or reasons for the success of the present process are not understood. Normally, in continuously casting metals, particularly copper, the presence or use of hydrogen is avoided at all costs because of its known detrimental effect on the physical properties of the metal. In the instant process, however, the hydrogen has the beneficial effects described herein. Moreover, so far as we are aware, the hydrogen has no detectable affect on the composition of the metal being cast. Thus, for example, in casting copper containing up to .015 oxygen, there was no perceptible reduction in the oxygen content of the cast copper. While we do not wish to be bound by any particular theory, it is possible that the hydrogen may affect surface tension at the involved mold wall area so as to result in the benefits obtained in practicing the invention.

The invention is further illustrated in the accompanying drawings and examples. It should be understood, however, that the drawings and examples are given for pur poses of illustration and the invention in its broader aspects is not limited thereto.

In the drawings:

FIG. 1 is a diagrammatic view in side elevation and partly in section of a casting system employing the preferred mode of introducing the instant hydrogen gas to the mold;

FIG. 2 is a diagrammatic elevation in section of the mold illustrated in FIG. 1;

FIG. 3 is a half plan section taken on line 33 of FIG. 2, half of the mold being omitted for simplicity of illustration;

FIG. 4 is a diagrammatic view of a portion of the mold and siphon shown in FIG. l and illustrates freezing of the metal in the mold;

FIG. 5 is a view taken on line 5-5 of FIG. 2;

FIG. 6 is a diagrammatic elevation in section illustrating an alternative mode of introducing the instant hydrogen gas to the mold;

FIG. 7 is a view from the bottom of the ring shown in FIG. 6;

FIG. 8 is a diagrammatic elevation in section illustrating another alternative mode of introducing the instant gas to the mold;

FIG. 9 is a view taken on line 9-9 of FIG. 8;

FIG. 10 is a drawing illustrating the surface on a casting produced in accordance with the best mode of practicing the invention; and

FIG. 11 is an enlarged view in side elevation in section further illustrating the surface shown in FIG. 10.

Referring now to the drawings, FIG. 1 illustrates a casting system which is at present preferred for the continuous casting of low oxygen copper. A melting furnace (not shown) supplies holding furnace 10 with the molten metal to be cast. Furnace 10 supplied pouring ladle 11 which in turn supplies siphon 12. The latter supplies mold 13 which is mounted on platform 14 which in turn is mounted for vertical reciprocation on carriage 15. The casting 17 is Withdrawn from the mold by a conventional roll drive mechanism 18 and is cut into desired lengths by a conventional cut-off mechanism, such as is illustrated by cut-oil saw 19. Such conventional mechanism is disclosed in Beterton and Poland U.S. Patent No. 2,291,204, granted July 28, 1942.

Before passing to roll drive mechanism 18, the casting 17 may be passed through chamber 20 which may be provided with a suitable sealing gasket 21. The carriage may be movable horizontally on tracks 16 from over tank to permit installation of molds of different size or shape or otherwise provide access to the mold. A stationary working platform (not shown) may be located on opposite sides of track 16 and at the same level on which workmen may walk during the casting procedure.

The holding furnace 10 shown may be an upright low frequency induction furnace rotatable about a horizontal axis and having a pouring spout 25. It may receive molten metal through a launder or a bull ladle (not shown) from a suitable melting furnace. The construction and operation or the pouring ladle 11 and siphon 12 illustrated in FIG. 1 are disclosed in copending application, Serial No. 724,114, filed March 26, 1958 by Richard Baler and entitled, Continuous Casting. Such a ladle and siphon are preferred as the pouring mechanism for high speed casting, especially high speed casting of shapes in which the least cross-sectional linear dimension is less than about 5 inches although, if desired, other pouring mechanism may be used, especially for slow casting speeds or larger shapes. The general construction and operation of mold 13 illustrated in FIGS. 2 and 3 are also disclosed in said copending application in that the preferred mold 13 is provided with at least two cooling zones, in the first of which the metal being cast is cooled solely by contact with the cooled mold walls, then by contact both with the cooled mold wall and with water or other fluid coolant in a second zone, and preferably also solely by direct contact with the coolant in a third zone. In addition, the mold wall defining the mold cavity preferably is tapered to converge toward the end of the mold from which the casting emerges and the second cooling zone is provided with nozzles for discharging the coolant against the emerging casting at such an angle with respect thereto as to provide a venturi action as disclosed in said copending application.

As shown in FIGS. 1 and 4, the pouring ladle 11 may comprise an enlarged bowl 26 constituting a reservoir for the molten metal, and a trough 27 which supports the siphon 12. The ladle also has a skim gate 28. The ladle 11 is supported by a mechanism which permits tilting the ladle to change the elevation of the reservoir with respect to the siphon; raising and lowering the entire ladle without tilting it; and swiveling the entire ladle from a position (shown in FIGS. 1 and 4) with the siphon 12 over the mold 13 to a position over a slag pot (not shown) alongside the mold.

In the ladle supporting mechanism illustrated in FIG. 1, there is provided an elevator cylinder 31 whose lower end is fixed; cylinder 31 having a piston connected to pedestal carriage 32. Operation of elevator cylinder 31 raises and lowers the entire pedestal carriage 32 as a unit. The pedestal 32 cariers an arcuate guide track device 33 on which is movably mounted a ladle carriage 34. Arcuate track 33 is laid out on the arc of a circle whose center is the center of siphon cup 42.

The ladle carriage 34 carries rollers 35 which ride on the arcuate guide 33. A tilting cylinder 36 connects with a cross member 37 secured to the pedestal 32; and its piston connects with the ladle carriage 34. The pedestal carriage 32 is rotatable about the vertical axis of elevator cylinder 31 to permit the operator to swing the ladle 11 in a horizontal plane.

Operation of elevator cylinder 31 raises and lowers the ladle 11 without tilting it. Operation of tilting cylinder 36 causes ladle carriage 34 to ride on arcuate track guide 33 and thus to tilt the ladle 11 in a vertical plane about the center of siphon cup 42; this tilting may be accomplished in any position of the ladle 11 in its arc of swing around the vertical axis of elevator cylinder 31, and in any elevation of pedestal carriage 32.

It will be understood that with the cup 42 in register with the mold cavity, when the elevator cylinder 31 reaches its lowermost position, the cup 42 is automatically at the proper level within the mold 13 regardless of angle of tilt of the ladle 11. Proper positioning of the cup 42 in the mold causes the cup to be completely submerged in the molten metal when the molten metal occupies its normal position of about 1 /2 inches below the top of the mold. See FIG. 4.

Any operation of the tilting cylinder 36 to tilt the ladle 11 in either direction operates to change the level of the metal in the ladle and, with the pedestal carriage 32 at its lowermost position, does not change the elevation of the cup 42 from its proper position in the mold.

Thus, with the cup 42 in its proper position in the mold, metal level in the ladle 11 may be changed either by tilting the ladle, or by adding metal to the ladle or by removing metal from the ladle. The control of metal level in the ladle is used to control rate of metal flow through the siphon 12. The ladle may be tilted back- Ward (i.e. carriage 34 lowered) far enough to stop flow through the siphon.

To prevent loss of suction during a startingup operation, cup 42 is provided with overflow means. As shown in FIG. 4, cup 42 has a lower discharge opening provided with a steatite washer or nipple 53'. The lower end of the siphon tube 40 has three circumferentially evenly distributed notches 54 and three corresponding lugs 55, to which the overflow cup 42 is welded, forming three cuplike overflow openings 56. Thus, provision is made for the siphon to discharge molten metal through both the lower steatite opening 53 and the three cup-like overflow openings 56.

Siphon tube 40 of siphon 12 is preferably made of stainless steel with an intermediate arched portion as shown. For melting out frozen metal in case of an accidental freeze-up, the siphon tube 40 may be provided with shroud 43 (see P16. 4). The shroud is U-shaped in cross section for the greater part of its length and follows the arched portion of the siphon tube. The shroud is suitably attached to the siphon tube in spaced relationship thereto and is fitted into the ladle wall lining 46 where the siphon passes through the wall, to prevent loss of liquid metal when pouring molten metal through the siphon. In addition, the shroud is provided with dam 47 which closes the shroud cross-section. The forward end of shroud 43 has an upright front wall 49 which emerges from tubular extension 50. The front wall 49 and the tubular extension 50 may have a series of holes 51 and the lower end of the tubular extension may be squeezed around siphon tube 40 to provide a restricted passage 52 or a series of such restricted passages, to assist in melting out a frozen siphon.

As shown in FIG. 1, mold 13 is supported by a frame 14 which is vertically oscillated by a reciprocating mechanism. A suitable prime mover (omitted for simplicity) is mounted on carriage 15, which reciprocates connecting rod 61. Rod 61 is pivoted to a series of hell crank levers 62 on one side of the frame 14. A series of bell crank levers 63 are pivoted to the carriage on the other side of frame 14. Links 64 and 65 pivotally connect bell crank levers 62 and 63 to oscillatory frame 14. A connecting rod 66 connects bell crank levers 62 and 63. A series of guide posts 67 are supported on carriage 15, and slidably engage guides on frame 14 to insure vertical reciprocation of the mold in a substantially vertical straight line. Any suitable means may be provided to vary stroke and frequency of vertical reciprocation of the mold. For example, to vary stroke, the drive motor may have a crank arm whose length is adjustable. To vary frequency, motor speed may be changed.

Mold 13, as shown in FIGS. 2 and 3, is a composite mold. Metal block 79 provided with removable graphite sleeve 94 is mounted on bottom annular manifold 70 by means of bottom ring 72 which is bolted to the manifold at 73. The manifold 70 rests on suitable cross pieces forming part of platform 14 reciprocatably mounted on carriage 15.

Sleeve 94 may be made of any suitable commercial graphite and is machined to the desired shape. Preferably, the interior mold surface 80 is machined to provide a taper which converges toward the bottom of the sleeve although the surface 80 may, if desired, be a true cylinder. In order to obtain optimum heat transfer, the sleeve 94 is carefully fitted into block 79; the contacting surfaces being cylindrical and carefully machined so that solid-to solid contact is obtained between sleeve and block without any fluid layer at the interface which will interfere with excellent heat transfer.

Preferably, in molds for casting round shapes-for example, billets which are circular in transverse cross section, sleeve 94 is made oversize with respect to the block 79 and is assembled into the latter by forcing it axially into the block. Preferably, also, the compression fit between the assembled sleeve and block is sufficiently severe to provide the solid-to'solid, fluid-free contact at operating temperatures. If desired, the sleeve 94 may be omitted and the block 79 made unitary with the molding surface 80 machined directly into the block; such a unitary structure being preferred in molds for casting shapes such as cakes which in transverse cross section are square or rectangular or for other multi-sided shapes.

The shape of manifold 70 is in general conformity with that of block 79. At its upper and inner corner manifold 70 is provided with an extension ledge 81 facing the interior of the mold and has an inlet passage 82 having a flange for connection with a pipe (not shown) which supplies the manifold with cold water. Additional inlet passages located at equidistant points along the outside periphery of the manifold may be provided, if desired, for the large quantities of water supplied to the mold.

The manifold 70 delivers Water to the main cooling tubes 83 disposed in passages 96 which are bored into block 79 and to five levels of water sprays. For this purpose the manifold has a series of top holes 84; a series of bottom holes 85; its ledge 81 has a series of drilled passages 86; the ledge contains holes 78 to clear the main cooling tubes 83.

For water delivery to the top or first level sprays, block 79 is provided with a series of horizontal radial passages containing cross tubes 88, each of the latter having a nozzle tip 89 having a downwardly directed discharge passage disposed at an angle which is less than about 30 to the vertical and preferably is about 20 thereto. The passages 88 connect with elbows 90 which are connected to fittings 91 connected to the top holes 84 in the manifold 70. The inner face of the lower portion of sleeve 94 has clearance bays below the discharge nozzles 89 providing, in effect, vertical ribs or projections 92 which are available to support the casting while the water sprays are directed between the ribs onto the surface of the casting before it leaves the mold. With high casting speeds, this insures cooling the surface of the casting below the plastic range while so supported.

The second level of sprays is provided by nozzle holes 87 drilled into the ledge 81 and connecting with the passages 86 in the manifold. The axes of the nozzle holes 87 also may have an angle which is less than about 30 with the vertical, said angle preferably being about 20. The third, fourth and fifth levels of sprays are provided by openings 103, 104 and 105 located in cooling tubes 83 and in the return bends 93. All of these spray openings direct water against the emerging casting in the directions indicated by the arrows. The return bends 93 connect lower openings 85 with inner tubes 83.

In accordance with the most preferred mode of practicing the present invention, mold 13 is also provided with means for diffusing the instant hydrogen gas through graphite sleeves 94 to introduce the gas to that area of the mold wall 80 at which freezing of the introduced metal commences during the casting procedure. As shown in FIGS. 2, 4 and 5, the outside surface of liner 94 is provided with a plurality of machined horizontal grooves through 114 extending around the outside surface of the liner. Such grooves may be V-shaped and are suitably spaced from each other, preferably by a distance of about /2 inch. The horizontal grooves are connected by a plurality of machined vertical grooves 115 disposed around the outside surface of sleeve 94 and produce a wafile-like pattern in the sleeve. Such vertical grooves may also be V-shaped and are suitably spaced from each other preferably also by a distance of about /2 inch. T he instant hydrogen gas from an outside source (not shown) is conducted through pipe preferably to the uppermost horizontal ring 110 through at least one passage 121 machined in block 79, and preferably through at least three such passages distributed equi-distantly arouid the periphery of block 79. The gas thus supplied to the uppermost groove flows around this groove to the remaining grooves from whence it is distributed by diffusing through the pores of the graphite to the inner surface area of the liner whici is embraced by the grooves; such diffusion taking place even under slight pressurefor example, as little as V2 pound per square inch, gauge, or less. For best results in this mode of introduction of the gas, a sufficient number of the horizontal grooves are employed to insure the bracketing with such grooves of that area of the mold wall at which the introduced metal commences to freeze during the process. In mold 13 the entire length of sleeve 94 is chilled and, as illustrated in FIG. 4, the introduced molten metal commences to freeze at the meniscus. As shown in FIG. 4, a suflicient number of horizontal grooves, preferably at least five, are employed to accommodate reciprocation of the meniscus and also to permit change of the mean operating level of the metal in the mold.

Alternative modes of introducing the instant hydrogen gas are illustrated in FIGS. 6 through 9. As shown in H68. 6 and 7, the gas may be introduced to the mold Wall area at which freezing of the introduced metal commences by conducting it from a source (not shown) to ring 125 from which it is discharged into the mold cavity above the metal therein through a series of downwardly directed perforations 126 of suitable size, for example, about 0.1 inch in diameter, spaced at regular intervals around the ring, preferably about /2 inch apart. Alternatively, the gas may be introduced as illustrated in FIGS. 8 and 9 by conducting it from an outside source through passage 139 drilled in block 79 to annular channel 131 machined in the outer face of sleeve 94 from which it is discharged into the mold cavity above the metal therein through downwardly directed ports 132 of suitable size, for example, about .01 inch in diameter, which are drilled in the sleeve and spaced at regular intervals around the periphery thereof, preferably at /2 inch intervals.

In starting the casting system illustrmed in FIG. 1, a conventional starting bar of appropriate length and having a cross section of a size and shape conforming to that of the mold cavity defined by mold surface 80 and preferably also having a conventional threaded tip of reduced size on the top thereof is employed. The top of the starting bar is inserted into the bottom of the mold a sufiicient distance to cover the ribs 92 on sleeve 94 with the lower end of the bar extending below with drawal rolls 18 so that. as the initial molten metal is fed into the mold, it freezes around the threaded tip and the frozen product is pulled downwardly and out of the mold by rolls 18.

Thereafter, the siphon 12 is primed. In priming the siphon it is first heated at least to a dull red heat, and preferably to the melting point of the metal being cast, with a torch. Ladle 11 hearing the thus heated siphon is then swiveled into a position over a slag pot and the ladle, which in the meantime has been filled with molten metal from holding furnace 16, is tilted forward sulficiently to bring the molten metal level in the ladle higher than the highest part of the arched portion of siphon tube 4%} with the dam 47 serving to retain the molten metal, thereby causing copious flow of molten metal through siphon tube 40 and through lower orifice 53 and upper orifices 56 in nozzle 42.

The size of orifice 53 in nozzle 42 is governed by the flow rate desired for the particular mold. The relationship between the effective areas of orifice 53 and of the cross section of the siphon tube 46 is such as to build up sufficient head in the cup 42 to keep the level of molten metal in cup 42 above the end of the siphon tube during priming. The combined effective area of the overflow orifices 56 and bottom orifice 53 should be greater than the effective cross sectional area of the siphon tube 40, so that maximum flow and velocity are obtained in the tube 40 in order to flush out gases. If orifice 53 is too small, the velocity through the siphon tube will be too low, allowing gas separation at the top of the arch of the siphon tube and loss of siphoning action or possible freezing of the metal in the siphon tube. It will be understood that by effective area is meant the area which controls the rate of flow through the several parts of the siphon, namely, the siphon tube 40, discharge orifice 53 and overflow orifices 56.

For example, in a siphon for feeding a three inch billet mold, the size of orifice 53 was not greater than of the effective area of the siphon tube 40. The best operating ratio was found to be between 30% and 60%. The effective area of the overflow orifices 56 was not less than 50% of the effective siphon tube area. For best results, the sum of the effective areas of orifice 53 and of the overflow orifices 56 should be nearly equal to (not less than 80%), or preferably greater than, the effective area of the siphon tube 40.

It will be understood that, if discharge orifice 53 is too small, the flow through the siphon will not be fast enough to flush entrapped gases from the siphon tube. The cross section of the siphon tube at the top of its arch should be small enough to cause the velocity of the metal flow at this point to be sufiiciently high to prevent entrapped gases from collecting. On the other hand, there should be sufificient flow through the overflow orifices 56 to seal the end of the siphon conduit, particularly when the molten metal does not wet the metal of the siphon conduit.

The function of the shroud 43 and overflow holes 51 and S2 is to remelt a frozen siphon tube 40. Due to error in preheating can-sing freeze-up, or in event of a foreign body becoming lodged in the siphon tube, the flow of copper during priming may cease before full metal flow can be established. If this condition occurs, the ladle is tilted to an elevation permitting molten metal to flow over the dam .7 and around the siphon tube.

Freezing can also occur between the shroud 43 and the tube 40, and progressive melting is required to remelt this metal. This is accomplished by allowing the molten metal to overflow the front wall 49 of the shroud 43 and flow, in succession, from the holes 51 and 52 in the front of the shroud. The frozen metal is quite rapidly remelted and in a few minutes any frozen area in the siphon tube becomes remelted and flow conditions are established.

After the siphon is primed, cooling water is circulated through mold 13 flowing thercthrough in the direction indicated by the arrows in FIG. 2 and discharging therefrom through orifices 89, 87, 103, 164 and into tank 20. Thereafter the tilt of ladle 11 is reduced to reduce the priming flow of metal to a volume more suitable for starting the casting operation, usually to a value not less than about half the flow to be employed during the casting operation, such flow being generally indicated by an intermittent or very small trickle through upper orifices 56 while full flow from bottom orifice 53 continues. Then without changing the ladle angle of tilt and with molten metal continuing to flow through the siphon, the ladle, as rapidly as possible, is swiveled into registry over mold 13 and is lowered until siphon tip 42 is in its normal operating position in the mold. If reciprocation of the mold is to be employed, reciprocation is commenced after swiveling the siphon in registry with the mold and the latter is partly filled. When the metal covers cup 42 and reaches its normal operating level, usually about 1 inches below the top of the mold and generally no higher than about V: inch below the top of mold 13, the operator starts withdrawal rolls 18 to withdraw the starting bar at a pre-sclected reduced starting speed; the reduced priming flow of metal through the siphon automatically adiusting to the pro-selected starting speed when cup 42 is submerged in the molten metal. When the operator is ready, he increases the lowering rate of the starting bar to full running speed and at the same time raises the liquid level in ladle 11 to provide sufficient head to deliver metal at the increased rate.

When the level of the metal in the mold has reached its normal operating level therein, introduction of the instant hydrogen gas is preferably begun and continued during the casting procedure, the gas being introduced at a sufficient rate during the procedure to provide the surface described earlier herein on the emerging casting. Also, where employed, a cover of solid material is placed in the mold on top of the metal therein when the latter has reached its normal operating level. Where the cover is comprised of discrete particles as is illustrated in FIG. 4, sufficient additional material of this type is added from time to time during the casting procedure to provide and maintain on the metal a protective cover of substantial thickness which generally is not less than about A; inch thick.

With the high heat extractive capacity provided by a mold of the type illustrated in FIG. 2 and with the sustained high casting speeds obtainable by practice of the present invention, the casting 17 emerging from the mold is red hot and is rapidly chilled by the series of pressurized water sprays 89, 87, and 103-105, and the large volume of water is collected in tank 20. This water is removed at any desired level as by a suitable drain line 57 and may be circulated by a circulation and pumping system, through a cooling device, and back to the water manifold 70 on the mold 13. The intensity of cooling of mold 13 is so high that, even at the sustained high casting speeds obtainable with the present invention, the molten metal congeals practically as soon as it touches the mold wall, causing the edge of the crater shell 101 (see FIG. 4) to extend substantially to the free surface 24.

In practicing the invention with a mold provided with such sprays, it is very desirable that the sprays operate with such high velocity and proper tangential direction that the cooling is effected by warming the water, not by generating appreciable steam. Low velocity sprays used in the uppermost position would result in steam at sufficient pressure to force its passage upward in the mold between the casting and mold wall. This results in shallow scalloping of the surface of the billet, if the steam reaches the solidifying surface. Accordingly, both pressure and direction are used to create a downward venturi action which eliminates this effect. Preferably, in practicing the invention with such sprays operated to provide such venturi action, the mold is provided with a taper, most preferably employing a forced taper operation as hereinafter described. Preferably also the downward direction of the first and second level sprays 89, 37 is suilicient to insure overall venturi action.

it will be noted that the top level of sprays 89 applies cooling while the wall ribs 92 are still available to contact and support the crater shell. it will be understood that, even when shrinkage of the casting due to cooling causes the casting to tend to lose contact with the ribs 92, the ribs still fit the casting sufficicntly closely to remove substantial amounts of heat. Thus, at the zone defined by the ribs 92, heat is removed from the casting by Contact with both liquid medium and solid medium. In other words, the zone of cooling by contact with a solid medium overlaps the zone of cooling by a liquid medium.

Preferably, in practicing the invention, the mold, as is illustrated in FIG. 2, is provided with a taper, especially when high speed casting is employed and particularly in the high speed casting of low oxygen copper. Where a taper is employed it may be a so-called natural taper or a forced taper.

With a natural taper the inner surface 80 of mold 13 is designed to follow the shrinkage pattern of the casting, as it passes through the mold, rather closely at any par ticulzu" linear billet speed. With such a construction, a

slow linear casting rate which produces in the casting a well cooled cross section permits the use of a steeper mold taper (Le. at a larger angle to vertical) than a rapid linear casting rate where the shape is emerging from the mold at a higher temperature. With natural tapers, a small but finite clearance is highly desirable between the billet and mold wall along the major length of contact in such molds.

Higher casting speeds are obtainable with forced taper and, for this reason, a forced taper operation is preferred. In a forced taper operation a linear casting speed is employed which, in relation to the steepness of the mold taper, is such that the shrinkage taper on the cast product, caused by the freezing and cooling of the latter, is forceably wedged against the taper on the mold wall so as to plastically deform the hot tube comprising the crater shell 101 enclosing the liquid core 162 as shown in FIG. 4.

Such a forced taper operation, in a sense, is similar to wire-drawing. It requires the establishment of a crater shell with a long and deep V which extends in the mold at least as far as the mold taper therein, with a strong but plastic shell wall surrounding a soft liquid center, a combination that is readily deformed by pulling it through the tapered mold. Such conditions are readily established in a forced taper operation due to the improved contact between shell 101 and mold wall 80 which so improves the rate of heat extraction from the shell to the mold wall that the shell wall congeals sufiiciently strong and thick to resist rupture at the high operating speeds which create the deep V.

In order to obtain maximum effect throughout the operating length of the mold in a forced taper operation, the angle of the mold taper at each level in the mold should be steeper than the corresponding natural shrinkage taper on the cast product caused solely by the freezing and cooling of the latter at that level. In practice, a uniform mold taper which extends throughout the entire length of the mold, as illustrated by the taper of surface 80 on sleeve 94 in FIG. 4, has been found to operate satisfactorily. Such a taper has the advantage of providing the proper taper angle on that part of the mold wall surrounding the free surface of the molten metal, regardless of variation in the level of this surface, thus obtaining good contact between mold Wall and crater shell even at its point of formation.

Where reciprocation is employed and especially in reciprocation of the metal meniscus in the chill zone of the mold, the reciprocation is preferably obtained by vertical reciprocation of a vertical mold on the casting as is illustrated in FIG. 1. in such a procedure, the amplitude and the frequency of reciprocation of the mold is related to the cross section being cast, the amount of taper and the casting rate. In general, higher reciprocation rates are employed with higher casting speed. Also, in general, it has been found that the ratio of reciprocation frequency (in number of cycles per minute), to casting speed (in inches per minute), should be at least about eight to one. Freferably, the ratio is 1G-l4 to l and at present, a ratio of about 11 to l is considered ideal, especially in casting low oxygen copper. Higher ratios may also be employed although the benefits obtained by higher ratios are usually not warranted by the extra wear and tear on the reciprocation mechanism. Thus, for example, in employing a ratio of ll to l, 220 cycles per minute are employed at a linear casting rate of 20 inches per minute, or 440 cycles per minute at a linear casting rate of 40 inches per minute. A short stroke is generally to be preferred since this avoids excessive clearance between mold and casting on the downward portion of the stroke. Preferably, the stroke is about A; to H inch; :1 stroke of "i inch being most preferred.

By stroke or cycle of a vertically reciprocated mold is meant a complete round trip movement of the mold from bottom position back to bottom position. The movement is preferably simple harmonic, varying from zero speed at upper and lower ends to maximum speed between the upper and lower ends of the amplitude of movement.

When, in a casting system such as is illustrated in FIG. 1, vertical reciprocation of the mold is employed in conjunction with a cover of particulate solid material as illustrated in FIG. 4, it is desirable that the maximum instantaneous downward speed of the mold be greater than the uniform downward linear speed of the casting to provide a small gap between mold taper and casting taper and thus to permit a controlled amount of the cover 23 to feed down the mold wall between mold and cast product.

For best results in practicing the invention in casting procedures employing a cover on the top of the metal in the mold, the cover is a solid particulate material, preferably one which has free flowing characteristics, especially under the casting conditions. For best results in casting low oxygen copper against a graphite mold wall, the layer 23 is a layer of discrete particles of carbonaceous material such as, for example, flake graphite, lamp black, pulverized anthracite, fine carbon particles, etc., or mixtures of such material. Fine bead-like carbon particles obtained by flash distillation of a liquid petroleum material such as still bottoms and known as Micronex beads are preferred. A mixture of flake graphite and such beads, especially a mixture containing at least about 25% by weight of the latter, is most preferred as the cover in casting low oxygen copper. Preferably, such particulate cover material is employed in amounts suflicient to maintain a protective blanket about /2 to 2 inches thick on the top of the metal in mold 13. It is possible to employ the cover material as a means for the introduction of the instant hydrogen gas. For example, where the absorption characteristics of the cover material are sufficient, such material may be suitably treated outside the mold, as for example, with an appropriate gas, to releasably provide therein the instant hydrogen gas, and then adding the cover material to the mold and removing it therefrom at a sufficient rate to release therein, under the temperature conditions therein obtaining, the instant hydrogen gas in suflicient quantities to provide the instant results. However, such a procedure is cumbersome and is not preferred.

In practicing the invention, it is advantageous to maintain the temperature of the molten metal introduced into the mold as close as practicable to the freezing point of the metal inasmuch as excess superheat, to the extent that it exists in the molten metal, increases the heat extractive load on the mold and results in lower casting speeds than would otherwise be possible in a given mold. In general, the temperature of the molten metal introduced into the mold is preferably less than about 200 F. above the freezing point of the metal. For best results in casting low oxygen copper at casting speeds above about 29 inches per minute, the temperature of the metal introduced into the mold is below about 2150 F., preferably below about 210i) F., and more preferably in the range of about 20110 to 2070 F.; a temperature of about 205l F. being at present considered ideal.

The invention is further illustrated in the following examples.

Example 1 Phosphorous deoxidized copper having a total oxygen content of less than .015% oxygen was cast into billets 3 inches in diameter in the casting system shown in FIG. 1 employing the mold illustrated in FIGS. 2 and 3 except that the mold was not provided with means for introducing the instant gas and none of the latter was used. Sleeve 94 was machined from a block of commercial graphite and was sufliciently oversized so that when inserted into copper block 79 it was under suflicient compression to insure excellent contact between the sleeve and jacket under the casting conditions. The sleeve was also provided with a uniformly converging taper of .087 inch per linear inch of the sleeve throughout the length of inner surface to provide forced taper casting of the billets at the speed employed. The temperature of the copper fed into the mold was maintained at about 2050 F. The level of the copper in the mold was maintained above the top of cup 42 and about 1% inches from the top of the mold but was not allowed to rise to a level closer than /2 inch from the top of the mold. The mold above the level of the metal therein was kept filled with a mixture of flake graphite and Micronex heads; the mixture containing at least 25% by weight of the latter. In reciprocating the mold a stroke inch in length was employed and the ratio of the frequency of reciproca tion in cycles per minute to casting speed in inches per minute was eleven to one. The cooling in the mold in relation to the casting speed employed was such as to maintain a V-shaped crater (crater 382 in FIG. 4) of molten metal in the mold which extended just below the bottom of sleeve 94 as shown in FIG. 4. In cooling the mold, cooling water at 80 F. was introduced into manifold 82 and was circulated through the mold at the rate of 600 gallons per minute.

In commencing the casting procedure a conventional starting bar was inserted in mold 13, siphon 12 was printed, water circulation through the mold was initiated, the siphon was moved into pouring position, vertical reciprocation of the mold was begun, the carbonaceous cover material was added when the top of nozzle 42 was covered with metal, and the casting speed was brought up to operating speed, all as described earlier herein.

Initially, an operating speed of 40 inches per minute was employed. The billet emerging from the mold at the beginning of the run had a light but uniformly spaced ripple on its surface. As the run continued, the surface on the emerging billet began to deteriorate, at first becoming glassy smooth after which small visible scufls began to appear on the surface which were followed by small visible tears and thereafter the billet began sticking in the mold to such an extent that, at the end of the first hour of operation, the casting procedure could not be continued.

Thereafter, numerous experiments were made in an attempt to extend the operating period and to maintain uniformly spaced ripples on the surface of the casting. In the course of such experimentation, the operating conditions were changed to employ higher and lower temperatures in the metal introduced into the mold, higher and lower phosphorous in the copper, higher and lower ratios of reciprocation to casting speed, diiferent levels of the metal in the mold as well as changing the metal level during the casting procedures, increased and decreased depth of the carbonaceous cover 011 the metal as well as various carbonaceous covers of different composition, increased and decreased tapers as well as no taper, and higher and lower casting speeds. No one or combination of these or other operating conditions were found which were successful.

Example 2 The procedure and operating conditions described in Example 1 for the operating speed of 40 inches per minute were repeated except that, in this instance, the instant hydrogen gas was employed. Mold 13 was provided with the means for introducing the gas illustrated in FIGS. 2, 4 and 5. As illustrated by the dimensions shown in N6. 4, the top horizontal channel groove lit was located /2 inch from the top of the mold and horizontal grooves 1lll14 were located below it at spaced intervals of V2 inch; lowermost groove 114 being located 2 inches from the top of the mold. Vertical grooves 115 extending from horizontal groove 119 to 114 were spaced around the outside periphery of sleeve 94 at intervals of /2 inch. Groove was /8 inch wide and 15 .030 inch deep. Grooves 111--l15 were .030 inch wide and .030 inch deep.

After primed siphon 12 was placed in operating position in the mold and the introduced metal had covered cup 42, the carbonaceous cover material mixture was added and introduction of the hydrogen gas was begun, and thereafter the casting speed was brought up to the operating speed of 40 inches per minute. During the casting procedure, the level of the metal in the mold was maintained at about one and one-half inches from the top of the mold and the space in the mold above the metal was kept full with the carbonaceous cover. As in Example 1, the ratio of reciprocation frequency to casting speed was eleven to one and the stroke was 1 inch in length. The hydrogen gas was commercially pure hydrogen and was continuously introduced to the mold during the casting operation at the rate of 315 cc. per minute, measured at standard conditions, i.e. room temperature and pressure, such total flow being approximately equally divided through the three passages 121 spaced equidistantly about the perimeter of block 79.

The run was continued without interruption for twentytwo hours at which time it was stopped only because the available supply of molten metal was exhausted; the continuous billet produced being cut into convenient lengths by saw 19 as the billet passed below withdrawal rolls 18. All of the surface on the continuously cast billet possessed the uniformly spaced ripples encircling the billet as illustrated by FIGS. and 11. FIG. 10 is a scale drawing illustrating the appearance of the surface to the naked eye. As shown in the enlarged view of FIG. 11, the ripples comprised a valley portion 140 and a relatively flat portion or land 141. Upon examination it was found that the vertical length of each land portion 141 was about four times that of the adjacent valley portion and that approximately 11 lands occurred on each linear inch of the casting. The specific gravity of the casting was found to be 8.92. The interior of the casting was found to be free of detectable voids and had a uniform radial grain structure extending substantially to the center of the billet and the billet was free of center porosity and pipe. The severed lengths of the billet were used for the production of tubes in a conventional manner by hot piercing and subsequent cold drawing to finished sizes and resulted in the production of tubes of superior quality which readily met the exacting standards required of tubing for use in air conditioning apparatus and the even more exacting standards required for rolled finned tube production.

In a large number of subsequent runs under the same operating conditions, the results were found to be exactly reproducible for all practical purposes. No upper limit was found to the casting period and in each case the casting was stopped only when the supply of available molten metal was exhausted. The rippled surface and the interior characteristics were the same as those obtained in the first run described in this example. The specific gravity was found to be 8.92 to 8.93. In further runs under the same operating conditions except that the ratio of reciprocation frequency to casting speed was varied from 8 to l up to 14 to l and more. it was found that the results were substantially the same except that the number of lands 141 which occurred per linear inch of casting corresponded to the employed ratio but that the width of the lands increased at the ratio decreased and vice versa. Thus. when this frequency was reduced to 8 to l, eight lands occurred in each linear inch of the casting but the lands were correspondingly wider whereas when the ratio was increased to 14 to l, fourteen correspondingly narrower lands occurred per linear inch of casting.

Example 3 The procedure of Example 2 was repeated employing the eleven to one ratio of reciprocation frequency to casting speed. After the 40 inches per minute operating speed was reached, the casting was continued for two hours while introducing the pure hydrogen gas to the mold at the 315 cc. per minute rate as described in Example 2 to produce the regular, uniformly spaced ripples on the billet surface. The rate of introduction of the hydrogen gas was then decreased. It was found that as the rate of introduction was decreased, the surface of the emerging casting gradually and progressively deteriorated. ln thus deteriorating, the ripples on the surface of the emerging billet became lighter and less pronounced until they finally disappeared and, at a rate of gas introduction into the mold of 25 cc. per minute, the emerging surface became glassy smooth. With continued decrease in the rate of introduction of the gas, small visible surface scuffs began to appear on the emerging casting. The sculfs were small abraded areas which were in general sequential alignment with the axis of the emerging billet; such generally aligned scuffs occurring at irregular intervals around the periphery of the casting. After the scuffs appeared, small visible shallow surface tears, caused by slight sticking of the casting in the mold, began to appear on the emerging casting surface. Thereafter the tears became progressively more deep and, thirty minutes after the initial appearance of the small tears, sticking became so severe that metal casting was stopped due to deep tearing of the billet in the mold resulting in its rupture therein. As was the case with the scutfs, the shallow tears and the deep tears, were in general spaced sequential alignment with the longitudinal axis of the billet and such aligned tears occurred at irregular intervals about the billet periphery.

Sleeve 94, which was damaged by the rupturing of the billet, was replaced and the run was repeated as before but in this instance the rate of introduction of the gas was decreased until the emerging billet surface became glassy smooth and thereafter the rate of introduction of the gas was not further decreased. An hour after the emerging billet surface had become glassy smooth, oasting Was stopped as before due to rupture of the billet.

Sleeve 94 was again replaced and the run repeated as before. In this instance after the emerging billet surface became glassy smooth the rate of introduction of the gas was increased to the 315 cc. per minute rate which was employed initially in the run and the normal uniformly spaced ripple was quickly restored on the surface of the emerging casting. The rate of introduction of the gas was then reduced until the small surface scuffs ap peared on the surface of the casting. The rate of gas introduction was then increased to the 315 cc. per minute rate and the normal rippled surface was quickly restored. Thereafter the rate of gas introduction was reduced until the small visible tears appeared after which the rate was returned to the 315 cc. per minute. Again the normal ripple was quickly restored to the casting surface. In additional runs, such reduction and increase of the rate of introduction of the gas was repeated numerous times without damaging mold wall (see FIG. 2). In each case the surface of the emerging billet deteriorated as described and the deteriorated surface was quickly restored to the normal uniformly spaced ripple when the rate of introduction of the gas was restored to that originally employed in the run.

Attempts were then made to restore the uniform rippled surface after deep tears were produced on the casting. The rate of introduction of the gas was reduced sufficiently to produce deep tears and was returned to the 315 cc. per minute rate before rupture of the casting occurred. In a minor number of the attempts, the rippled surface was restored to the casting surface when the gas rate was increased to the 315 cc. per minute rate. However, in a major number of the attempts, sticking of the deeply torn billet caused the mold wall 80 to be scarred to such an extent that the normal ripple could not be restored and casting was stopped due to rupture of the billet in the mold Within an hour after the introduction of the gas was returned to the 315 cc. per minute rate.

Sleeve 94 was again replaced and the run started and operated as before for two hours with the 315 cc. per minute rate of introduction of the gas. Thereafter, the rate of gas introduction was continuously increased. It was found that, as the rate was increased, the surface of the ripple on the emerging casting became more and more coarse until, at a rate of introduction of the gas at 850 cc. per minute, the ripple on the emerging casting began to scatter and to assume a crazy quilt pattern of surface imperfections which were perceptible to the touch and which had the appearance of cold shuts and folds at disorganized angles. With further increases in the rate of introduction, this irregular pattern increased until, at a rate of gas introduction of 1320 cc. per minute, it involved a major portion of the surface of the casting. A further increase in the rate of introduction of the gas was then made. Within five minutes thereafter, casting was stopped due to rupture of the billet in the mold. In repeating this run after replacing sleeve 94 and starting up the system as before, it was found that higher rates of introduction of the gas were required to cause the irregular pattern to appear on the casting surface and to involve a major portion of the surface therewith when more severe cooling conditions were employed in the mold; more severe cooling being obtained in this instance by lower temperatures in the available supply of cooling water.

In a further run sleeve 94 was replaced, the system was started and run for the two hour period as before. Thereafter, the rate of introduction of the gas was again continuously increased and the uniformly spaced ripple on the surface of the emerging casting deteriorated as before. However, when a major portion of the surface became involved with the irregular pattern above noted, the rate of introduction of the gas was quickly reduced to the 315 cc. per minute rate initially employed and the normal uniformly spaced ripple was restored on the surface of the emerging casting. In additional runs, such increase and reduction of the rate of introduction of the gas was repeated numerous times with the same results. Thereafter in another run, the rate of introduction of the gas was controlled to produce at will the above noted irregular pattern of irregularities, the smooth surface, the small visible surface scuffs and tears, checks, and the uniformly spaced ripple, on the surface of the emerging casting.

Additional runs at speeds from 30 to 64 inches per minute were made; the heat extraction required of the mold at the latter speed being close to the maximum heat extractive capacity of the mold being used. The ratio of the reciprocation frequency to the casting speed was varied from 814 to 1 during these runs. No limit was found to the period during which the casting procedure could be conducted continuously at these speeds and it was found that the rate of introduction of the gas could be controlled to produce at will the uniformly spaced ripple, the irregular pattern of irregularities as well as the smooth surface and the small visible surface scuifs and tears on the surface of the billet. In addition, it was found that, when the rate of introduction of the gas was adjusted to provide the normal uniformly spaced ripples on the surface of the casting at a given speed, the speed could thereafter be varied over a comparatively wide range without further adjustment of the rate while still maintaining such a surface on the casting. It is believed that the forced taper reduces or prevents loss of hydrogen to the zone of reduced pressure in the bottom of the mold established therein by the venturi effect of nozzles 89 and 87.

Example 4 The procedure of Example 2 was again repeated but in this instance the mold was provided with the means illustrated in FIGS. 8 and 9 for introducing the hydrogen gas, employing ports 132 which were .010 to .012 inch in diameter. It was found that the rate of introduction of the gas could be controlled to produce at will the irregular pattern of irregularities, the smooth surface, the small visi- Example 5 The procedure of Example 2 was repeated employing the means illustrated in FIGS. 6 and 7 for introducing the gas; the downwardly directed perforations 126 being .010 inch in diameter. Inasmuch as the mold was not shielded from the atmosphere, burning of the gas occurred at the top of the mold. It was found that the rate of introduction of the gas could be controlled to produce at will the small visible surface scuffs and tears as well as the uniformly spaced ripple on the surface of the casting. However, it was not possible to introduce the gas at a sufficiently high rate to produce the irregular pattern of irregularities on the emerging billet. It is believed this latter was due to the dilution effect of the products of combustion or air or both.

Example 6 The procedure of Example 2 was repeated employing the eleven to one ratio of reciprocation frequency to casting speed. After the 40 inches per minute operating speed was reached, the casting was continued for two hours while introducing the commercially pure hydrogen gas to the mold as described in Example 2 to produce the normal uniformly spaced ripple on the surface of the billet as described therein. Thereafter, the introduced hydrogen gas was progressively diluted with nitrogen gas. As the concentration of the hydrogen in the gas mixture was decreased, no apparent change took place in the character of the rippled surface until the hydrogen concentration in the gas wasreduced to about 79% by volume, thereafter the ripple became progressively more faint. When the hydrogen concentration in the gas reached about 40% by volume, the billet surface possessed the glassy smoothness which, as noted in Example 3, preceded deep tearing and ultimate rupture of the casting in the mold and it was not possible to improve the surface of the emerging billet with increased rates of introduction of the thus diluted gas. The run was repeated employing helium as the diluent gas and the same results were obtained. The results from these runs illustrate the critical importance of the concentration of the hydrogen in the introduced gas in practicing the invention.

Example 7 The procedure of Example 2 was again repeated employing the eleven to one ratio of reciprocation to casting speed. After the 40 inches per minute casting speed was reached, the casting procedure was continued for two hours while introducing the commercially pure hydrogen gas to the mold at the 315 cc. per minute rate to produce the uniformly spaced ripple on the surface of the emerging casting described in Example 2. Thereafter, an equal how of commercially pure carbon monoxide was substituted for the commercially pure hydrogen. Within 15 minutes, the introduction of the carbon monoxide gas had to be discontinued due to the rapid deterioration of the billet surface and introduction of the pure hydrogen gas at the rate of 315 cc. per minute was immediately begun to restore the normal ripple surface to the casting. The procedure was repeated employing changes in the casting conditions as described in Example 1 as well as various rates of introduction of the carbon monoxide in an attempt to extend the operating period. In all such tests the introduction of the carbon monoxide had to be discontinued within 15 minutes due to deterioration of the surface of the billet and no set of operating conditions or rates of introduction of the gas were found which would enable the carbon monoxide gas to maintain the uniformly spaced ripples on the surface of the casting provided by the use of the instant hydrogen gas.

The foregoing procedure was repeated employing, as a substitute for the hydrogen, various gases such as, for example, nitrogen, helium, air, carbon dioxide, steam,

19 methane, ethane, propane, acetylene, etc. and mixtures thereof. in all cases introduction of the substituted gas had to be discontinued within 15 minutes to one and onehalf hours and no set of operating conditions were found which would enable a substituted gas to maintain the uniformly spaced ripple on the surface of the casting.

In conducting the foregoing test with steam, it Was found that the steam condensed in passage 121 and in grooves 110-115. Steam was therefore introduced employing the introduction means shown in FIGS. 6 and 7. Within 15 minutes introduction of the steam had to be discontinued due to the explosion hazards arising from condensation of the steam against the cold mold walls. It was also noted in testing gaseous hydrocarbons, that copious amounts of carbon black were produced in the mold. The foregoing runs were repeated employing methane, ethane, propane and acetylene as a substitute for the hydrogen gas but in each case in this instance the cover material was skimmed from the top of the metal before the introduction of these gases was begun and no cover material was added. With each of these gases the surface of the bare metal quickly became covered with carbon black. However, in all these additional runs, introduction of the gas had to be discontinued within an hour and one-half due to deterioration of the surface of the emerging billet. The same results were obtained when attempts were made to substitute lubricating oil for the instant hydrogen gas by adding the oil to the cover material or to the bare metal in the mold. The results from the foregoing runs in this example further illustrate the unique and critical importance of the instant hydrogen gas in the present invention.

Example 8 The procedure of Example 2 was repeated employing the eleven to one ratio of reciprocation frequency to casting speed. After the 40 inches per minute operating speed was reached, the casting procedure was continued for two hours while introducing the pure hydrogen gas to the mold at the 315 cc. per minute rate as described in Example 2 to produce the billet surface described therein. Thereafter, the metal level in the mold was raised and lowered from the normal level of 1% inches from the top of the mold. Higher levels caused coarsening of the rippled surface of the emerging billet, the effect being that obtained by an increase in rate of introduction of the gas at the normal level of 1% inches from the top of the mold. Lowering the level below the normal level caused the ripple on the surface to become increasingly faint; the effect being that of a decrease in the rate of introduction of the gas. When the metal level was lowered to and below the lower limit of the effective hydrogen diffusion zone in the mold (such lower limit occurring below the level of groove i113 and above that of groove 114 of the mold illustrated in FIG. 4), the effect was the same as that obtained when no hydrogen was introduced into the mold. These results further illustrate the critical importance of introducing the instant hydrogen gas to that area of the mold wall at which freezing of the introduced metal commences.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that various omissions,

20 substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a method for continuously casting copper base metal in which molten copper base metal is fed into the top of a vertically disposed open-ended mold having a chill section for casting the molten metal and cast metal is withdrawn from the other end of the mold while maintaining the level of the metal in the mold below the top of the chill section, said chill section presenting a graphite face to the metal cast therein, and the meniscus of the metal in said chill section is vertically reciprocated with respect to the wall of the chill section, the improvement in combination therewith which comprises feeding said molten metal to said chill section at a temperature which is less than about 200 F. above the freezing point of the metal being cast, introducing a gas containing more than about 40% by volume of hydrogen to the meniscus of the metal in the chill section during the casting procedure, and controlling the amount of hydrogen which is delivered to said meniscus by controlling the amount of said hydrogen delivered to the meniscus during the casting procedure to a rate of introduction which is between that rate which produces an irregular pattern of irregularities on a major portion of the surface of the casting emerging from the mold and that rate which produces deep tears on the surface of the emerging casting.

2. A method according to claim 1 in which a cover is maintained above the molten metal being cast in the mold.

3. A method according to claim 2 in which said metal is low oxygen copper, said hydrogen gas is introduced to said meniscus beneath a cover of solid particulate material which is added to and maintained on top of the metal in the mold during the casting procedure in amounts sufiicient to provide a cover of said material which is not less than about A; inch thick and the casting emerging from the mold possesses a rippled surface.

4. A method according to claim 3 in which said cover material is a carbonaceous material and the gas providing said hydrogen gas at said meniscus is led into the mold cavity above the metal level therein.

5. A method according to claim 3 in which said cover material is a carbonaceous material and said hydrogen gas is introduced to said metal meniscus by diffusion through said graphite face of said mold.

6. A method according to claim 5 in which said metal is phosphorus deoxidized copper, said hydrogen gas introduced to said meniscus contains at least hydrogen by volume.

7. A method according to claim 6 in which said hydrogen gas is substantially pure hydrogen gas.

References Cited in the tile of this patent UNITED STATES PATENTS 2,131,307 Behredt Sept. 27, 1938 2,135,183 Junghans Nov. 1, 1938 2,376,518 Spence May 22, 1945 2,740,117 Smart Apr. 3, 1956 2,743,494 Rossi May 1, 1956 2,871,534 Wieland Feb. 3, 1959 2,946,100 Baier et al. July 26, 1960

Claims (1)

1. IN A METHOD FOR CONTINUOUSLY CASTING COPPER BASE METAL IN WHICH MOLTEN COPPER BASE METAL IS FED INTO THE TOP OF A VERTICALLY DISPOSED OPEN-ENDED MOLD HAVING A CHILL SECTION FOR CASTING THE MOLTEN METAL AND CAST METAL IS WITHDRAWN FROM THE OTHER END OF THE MOLD WHILE MAINTAINING THE LEVEL OF THE METAL IN THE MOLD BELOW THE TOP OF THE CHILL SECTION, SAID CHILL SECTION PRESENTING A GRAPHITE FACE TO THE METAL CAST THEREIN, AND THE MENISCUS OF THE METAL IN SAID CHILL SECTION IS VERTICALLY RECIPROCATED WITH RESPECT TO THE WALL OF THE CHILL SECTION, THE IMPROVEMENT IN COMBINATION THEREWITH WHICH COMPRISES FEEDING SAID MOLTEN METAL TO SAID CHILL SECTION AT A TEMPERATURE WHICH IS LESS THAN ABOUT 200*F. ABOVE THE FREEZING POINT OF THE METAL BEING CAST, INTRODUCING A GAS CONTAINING MORE THAN ABOUT 40% BY VOLUME OF HYDROGEN TO THE MENISCUS OF THE METAL IN THE CHILL SECTION DURING THE CASTING PROCEDURE, AND CONTROLLING THE AMOUNT OF HYDROGEN WHICH IS DELIVERED TO SAID MENISCUS BY CONTROLLING THE AMOUNT OF SAID HYDROGEN DELIVERED TO THE MENISCUS DURING THE CASTING PROCEDURE TO A RATE OF INTRODUCTION WHICH IS BETWEEN THAT RATE WHICH PRODUCES AN IRREGULAR PATTERN OF IRREGULARITIES ON A MAJOR PORTION OF THE SURFACE OF THE CASTING EMERGING FROM THE MOLD AND THAT RATE WHICH PRODUCES DEEP TEARS ON THE SURFACE OF THE EMERGING CASTING.

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