US2515284A

US2515284A - Differential cooling in casting metals

Info

Publication number: US2515284A
Application number: US793997A
Authority: US
Inventors: Paul P Zeigler; John Clyde R St
Original assignee: Kaiser Aluminum and Chemical Corp
Current assignee: Kaiser Aluminum and Chemical Corp
Priority date: 1947-12-26
Filing date: 1947-12-26
Publication date: 1950-07-18
Anticipated expiration: 1967-07-18

Description

July 18, 1950 P. P. ZEIGLER ETAL DIFFERENTIAL COOLING IN CASTING METALS 2 Sheets-Sheet 1 Filed Dec. 26, 1947 INVENTORS P. ZE/GLER gLKYDE R.

PAUL

ST JOHN (5 July 18, 1950 P5P. ZEIGLER ET AL DIFFERENTIAL COOLING IN CASTING METALS 2 Sheets-Sheet 2 INVENTORS PAUL P. ZE/GLEI? BQ LYDE R. 37'- JOHN Filed Dec.

Patented July 18, 1950 DIFFERENTIAL COOLING IN CASTING METALS Paul P. Zeigler and Clyde R. St. John, Spokane,

Wash., assignors to Kaiser Aluminum & Chemical Corporation, a corporation of Delaware Application December 26, 1947, Serial No. 793,997

7 Claims.

This invention relates to method for continuously casting metal ingots, billets and the like. More particularly, it relates to the continuous casting of light metal ingots, billets and the like wherein the molten metal is solidified by application of a cooling fluid to the mold and/or to the ingot or billet in a particular manner as herein below described.

In the art of continuous casting of metals the general practice is to provide an open-ended mold, which may be horizontal or vertical but, in the case of large castings (such as rolling ingots and extrusion billets), is preferably vertical; to feed molten metal continuously into one end of the mold (the top end in the case of a vertical mold) and continuously withdraw solid casting from the opposite end of the mold; and to supply a cooling fluid continuously to the mold and/ or to the solid casting as it emerges from the mold. The metal may or may not be completely solidified in the mold; thus, the casting at the point where it emerges from the mold may contain a core or crater of molten metal, which is solidified by cooling the casting below the mold. The coolin fluid may be a liquid, preferably water, or a gas, such as air. Cooling of the mold, and of the casting below the mold, may be accomplished either by the use of a cooling jacket, such as a water jacket, or by delivering coolant directly to the mold or casting, as by means of spray pipes or a perforated tank. The casting procedure may be a strictly continuous process (in which the casting is cut to length without interruption of the casting procedure) or it may be semi-continuous; i. e., a casting of desired length may be cast, the flow of metal stopped, the casting removed and the procedure commenced anew. Continuous" casting as herein used refers to either type of operation.

In the casting of relatively large castings, such as rolling ingots and extrusion billets, it is advantageous to use a liquid coolant, such as water,

and to apply the coolant directly to the mold and to the casting below the mold; and, especially in the casting of large light metal ingots and billets, such as aluminum and magnesium (including their alloys) ingots and billets, it is advantageous to employ a short mold, with a low head of metal in the mold, and to complete solidification of the interior of the casting below the mold.

Whatever the method of cooling used, it has been the practice heretofore, and regarded as essential, to cool the surfaces of the mold and the casting uniformly; that is, to cool each horizontal section (in the case of a vertical casting operation) uniformly about the perimeter of that section. Typically, this is accomplished in the case of a system employing a vertical mold and spraying water onto the sides of the mold and the casting from a perforated spray pipe or spraybox, by providing each spray pipe or spray box surrounding the mold or casting with uniformly spaced holes of uniform shape and diameter.

The most advanced techniques of continuous casting have progressed to a point where rapid casting of large ingots, billets and the like to produce good quality castings is possible. Nevertheless, even with the most advanced techniques heretofore known a substantial amount of rejected castings are produced owing to surface cracks, edge splits and bottom splits of the castings. These defects, when observed, lead to rejection of the casting (i. e., it must be remelted and recast); otherwise, in rolling sheet, extruding or otherwise fabricating the casting, a defective product may result. Even more serious, owing to their latent nature, are internal ruptures of castings. These are not readily observed, and castings having internal ruptures may be rolled, extruded or otherwise fabricated, and even put to their ultimate use, before detection of the defect.

It is an object of the present invention to provide an improved method for continuous casting of metals.

It is a further object of the invention to pro vide a method for casting large castings, particularly of light metals, by a continuous casting process which greatly diminishes defects in the castings.

It is a particular object of the invention to provide a method for continuously casting ingots, billets and the like, particularly of light metals, of large cross section and of square, rectangular or other angular shape, while minimizing defects such as surface cracks, edge cracks, bottom splits and internal ruptures.

These and other objects of the invention will be apparent from the ensuing description, the accompanying drawings and the appended claims.

We have discovered that defects in castings are substantially reduced in the case of castings of square, rectangular or other angular cross-section, by employing a suitable continuous casting procedure and by causing substantially greater cooling of the surface of the mold and/or of the casting, at and near the angles or corners of the mold and/or casting than at points more widely spaced therefrom. And we have further discovered that a simple apparatus, employing spray pipes, a spray box or the like surrounding the mold or the casting, effectively accomplishes the objects of the invention, it each pipe, spray box or the like is provided with a. greater number or size of orifices for delivery of coolant at and near these angles or corners than at points more widely spaced therefrom.

For convenience, this cooling feature of the invention whereby certain areas of the mold and casting receive excess cooling. is hereinafter referred to as differential cooling.

In the accompanying drawings several embodiments of the invention are shown. In these drawings;

Fig. 1 is a cross sectional view in elevation of a mold and ingot showing a spray pipe cooling arrangement;

Fig. 2 is a cross sectional plan view taken along the line 2--2 of Fig. 1, showing the mold and piping arrangement.

Fig. 3a is an enlarged .cross sectional view in elevation taken along the line 3-3 of Fig. 2.

Fig. 3b is a fragmentary elevational view of the pipes of Fig. 3a;

Figs. 4a and 4b are similar views taken along the lines 4-4 or |'4' of Fig. 2;

Fig. 5 is a plan view, "partly in cross section, of a second and preferred embodiment of the invention showing a spray box type of cooling mechanism;

Fig. 6 is a front elevation of a fiat pattern of the interior or working surface of the spray box of Fig. 5;

Fig. '7 is a cross sectional viewin elevation taken along the line of Fig. 5;

Fig. 7a is a cross sectional view in elevation taken along the line '|a'|q. of Fig. 5; and

Fig. 8 is a plan view of a third embodiment of the invention, showing a square mold and spray box.

Referring now to Figs. 1 to 4b of the drawings, a roughly rectangular, vertical open-ended mold generally designated as l is supported from pouring platform 2 by any suitable means (not shown). Mold I has relatively short, rounded end portions 1a and relatively long, straight side portions lb. Within the mold and extending below it-is an embryo ingot 3 comprising a pool of molten metal 4 and solidified casting 5, the pool 4 extending downwardly into and forming a, liquid core or crater within the ingot. Surrounding and closely adjacent to the mold, is an upper spray pipe generally designated as 6 and surrounding and closely adjacent to a lower portion of the mold adjacent the lower edge of the same is a similar, lower spray pipe generally designated as 1. Spray pipe 6 has relatively short rounded end portions 60, and relatively long, straight side portions 6b conforming generally to the configuration of mold I, and spray pipe 1 has similar end portions 1a and side portions 1b. Each spray pipe is provided with an inlet pipe 8.

Referring to Figs. 3a and 3b, illustrating the mid-sections of side portions 6b of spray pipe 6, each mid-section is provided with a single horizontal row of circular orifices ll, of uniform diameter and uniformly spaced. The mid-sections of side portions 1b of spray pipe I are similarly provided with circular orifices l2, which may be of the same or different diameter and spacing as in spray pipe 6. As indicated, the angles of orifices H are 70 from the verti- The size, shape, spacing may, however, vary from case to case, being selected in the light of the pressure of the coolant, its temperature and heat capacity and other factors well known in the art.

Referring, now to Figs. 4a and 4b, these views illustrate the orifice design of spray pipes 6 and I at their end portions 60 and la, respectively, andalso at the end sections of each side portion 6b and lb. That is to say, considering Figs. 3a, 3b, 4a and 4b together, Figs. 3a, and 3b show the orifice design at the mid-sections of side portions of pipes 5 and while Figs. 4a and 4b show the orifice design at the end portions of these pipes and at the extremities of the side portions adjacent the end portions,

Eachend portion 6a and the adjacent end sections of side portions 6b of pipe 6 is provided with a double horizontal row of orifices II and Ila. Similarly, each end portion la andthe adjacent end sections of side portions '|b is provided with a double row of horizontal orifices I2 and |2a. As indicated, each upper row of orifices is at an angle of 45 from the vertical and each lower row of orifices is also at an angle of 45 from the vertical.

Referring now to Figs. 5 to 7. there is here shown a preferred embodiment of the invention involving a set or gang of three molds instead of a single mold and a spray box or chamber instead of spray pipes. Referring more particularly to Fig. 5, showing a plan view, a gang of three molds 2| of roughly rectangular horizontal section, having rounded end portions and straight side portions, are encased by a spray box 22 provided with an inlet pipe or conduit 23 and having three wells or openings 24 of the same shape as the molds and each being concentric with its mold but of larger dimensions to allow an annular space between the mold and the interior or working surface 25 of the spray box. Molds 2| are supported by a suitable pouring platform (not shown).

Referring to Fig. 5, and to Fig. 6 showing in front elevation a fiat pattern of the interior surface 25 of the spray box 22, sections A1 and A2 of the interior surface 25 are disposed opposite the end portions and adjacent segments of the side portions of mold 2|, as shown more clearly in Fig. 5. Similarly, sections B1 and B2 are disposed opposite the mid-sections of the side portions of mold 2|. As shown in Figs. 6 and 7a, an upper double row of relatively large orifices 3| and 3 a aredrilled in sections A1 and A2 opposite about the mid-portion of mold 2| and a lower double row of relatively

large orifices

32 and 32a are drilled in sections A1 and A2 and opposit about the bottom portion of mold 2 Upper an lower single rows of relatively small orifices 33 are drilled in sections 31 and B2 opposite about the mid-portion and bottom portion, respectively, of mold 2|. As indicated, the upper rows of orifices 3| and 3|a are at an angle of 45 from the vertical and the lower rows of

orifices

32 and 32a are also at an angle of 45 from the vertical. The upper rows of orifices 33 and the lower rows of orifices 33 in sections B1 and B2 are at angles of 70 and 60 respectively from the vertical.

Referring now to Fig. 8, showing an embodiment of the invention adapted to casting square ingots, there is shown in plan View an approximately square mold 2|, having rounded corners; a spray box 22' provided with an inlet pipe or cal and of orifices l2, 60 from the vertical. 7 conduit 23 and having a well or opening 24 and and angles of the orifices Y an interior or working surface 25 defining said well and surrounding the mold so as to leave an annular space between the interior surface and the mold. Interior surface 25 is divided into corner areas A1, A1, A: and A4 adjacent the corners of the mold and casting, and intermediate areas B1, Ba, Ba and B4 adjacent the mid-sections of the mold walls and casting walls. Larger orifices are drilled in corner areas A1, etc. than in intermediate areas B1, etc., so as to supply a greater flow of coolant to the four corner sections of the mold and casting than to intermediate areas.

In operation, and referring to the embodiments of Figs. 1 to 4b, the casting operation is commenced by means well known in the art. Thus, a bottom portion (not shown), operated hydraulically, may be brought up against, and seal the bottom of mold 2. Water or other suitable cool ant is caused to fiow through inlet pipes 8 into spray pipes 8 and l, thence through orifices H, Ha, l2 and 12a to the mold and to an area below the mold. Molten metal may then be caused to flow from a melting furnace or holding vessel (not shown) through a trough and a suitable throttling valve (not shown) into mold i to fill it to a certain, predetermined level. Then, while pouring continues, the aforementioned bottom piece is continuously lowered, the rate of pouring and lowering being so correlated as to maintain the desired level of metal in the mold. As the ingot emerges from the bottom of mold i, it is struck by coolant flowing through orifices i2 and 12a, the mold being meanwhile cooled by coolant fiowing through orifices I i and Ila, sufficiently to produce a solid shell or skin of metal about the ingot so that, below the mold, the ingot serves as its own mold. The ingot or billet may be cut to length by suitable saw arrangement well known in the art, without interrupting the casting procedure or, when an ingot or billet of desired length has been cast, the pouring may be stopped and the solidified casting removed.

The operation of the gang mold-spray box apparatus of Figs. 5 to 7a and of the square moldspray box of Fig. 8 are essentially the same except that, in the gang mold apparatus, the three molds are operated simultaneously.

The several drawings illustrate the apparatus of the invention diagrammatically. In practice, to secure optimum results, a modicum of trial and error will determine the optimum design; e. g., with reference to Fig. 6, whether the lengths of sections A1 and A2, B1 and B2 of the interior surface of the spray box, and whether

orifices

3i, 3m, 32 and 32a shall have 50, 100 or 150% greater area than orifices 33. The particular, optimum angle of the orifices may also vary from case to case.

As shown by Fig. 8, square molds receive differential or excess cooling adjacent the corners only whereas, as shown by the preceding figures, rectangular molds having relatively long side portions and relatively short end portions receive differential cooling adjacent the corners and all along the end portions. As a general "working rule, where the mold presents long and short sides, if the ratio of the long side to the short side exceeds about 2 or 2 to 1, the short sides (or end portions) will receive differential cooling over their whole extent; but if this ratio is less than about 2 or 2 to 1, or the cross section approaches an equilateral polygon, only the corner sections will receive differential cooling, as shown in Fig. 8.

With the foregoing general description and the following specific examples, no difllculty beyond a modicum of trial and error will be encountered in designing the spray mechanism to achieve optimum results.

Further, the principle of the invention, 1. e., differential cooling, although preferably embodied in procedure and apparatus such as illus- .trated above, and used in conjunction with appurtenant apparatus such as disclosed in Ennor, U. S. Patent No. 2,301,027, and Nicholls et al., U. S. Patent No. 2,414,269, and applied to the casting of light metals such as aluminum, magnesium and their respective alloys, and employing water as the coolant, is applicable to other procedures, apparatus, metals and coolants. Thus, the coolant may be other than water, e. g., air, brine, oil or ethylene glycol. Also, the coolant may be enclosed in a jacket, as in Coats, U. S. Patent No. 1,503,479. Further, instead of using a greater orifice area adjacent the angles of the mold and casting, other methods of differential cooling may be employed, e. g., coolant may be supplied through the same orifice area but under greater pressure, or colder coolant or a coolant having greater heat capacity may be applied to the critical areas. Similarly, the mold wall may be made thinner, or of more heat conductive material at these areas. Other metals (including alloys of the same) which may be cast are copper, lead, zinc, and steel.

Following are specific illustrative examples of the invention.

Example 1 Mold and spray boa: design.--Each mold was constructed of a sheet aluminum alloy (35), thick. It was of rectangular horizontal cross section having straight, long sides and rounded ends. Depth (vertical) was 7", greatest length (horizontal) 32%," and width (horizontal) 10%;". Radius of curvature of the ends was 10%;". Three such molds were used.

The spray box was of the type illustrated in Figs. 5, 6 and 7, being provided with three wells to enclose the three molds. This spray box was constructed of sheet steel and was connected with a low pressure supply of water to deliver water to the mold and casting at about 4 to 5 lbs. sq. in. The annular space between the interior surface of the box and the mold was inch. Under these conditions, all the jets of water struck the mold or ingot and ran down their sides without splashing.

The. orifice design will be best understood by reference to Figs. 5 and 6 of the drawings. Each interior surface 25 defining a well 24 containing a mold 2| was drilled to present four sections; that is, 'two end sections A1 and A2 and two side sections B1 and B2. Each end section A1 or A: was disposed opposite and end portion of the mold and opposite adjacent end segments of the sides of the mold. Each of these four end segments covered by a section A1 or A: extended 3%" along a straight side of the mold, measuring from the point at which curvature of the end portion commenced.

In each of the end sections A1 and A2 were drilled an upper double row of orifices 3i and 3i a adapted to deliver water to the mold about midway between its top and bottom, and a lower double row of

orifices

32 and 32a adapted to deliver water to the ingot at the bottom of the mold. These orifices were centered 4 inches apart, the angle of upper orifices 3|, 3ia being 45 and also of

lower orifices

32, 32a being 45 from the vertical. Regarding A1 as the section lying nearer water inlet 23, the orifices in section A1 were of 95 diameter and the orifices of section A: were of is" diameter.

The two sections B1 and B2 disposed opposite the mid-sections of the mold sides were each drilled with an upper single row of orifices and lower single row of orifices 33. The upper orifices were at angles of 70 and centered inch apart, while the lower orifices were at angles of 60 and centered inch apart, positioned to deliver water to the mid-portions and bottom of the mold, respectively. All orifices were of 3," diameter.

Casting procedure-Metal poured was in some instances the well-known aluminum alloy 248,

in others 758. Lowering rate of the casting was 2%" per minute. Temperature of the metal delivered to the mold was 1290 to 1320 F. in the case of 24S, 1320 to 1340 F. in the case of 75S. Pouring was commenced after the usual preparations had been made; e. g., after the pouring trough and valves had been brought to the proper temperature, a supply of water in the range of about 40-60 F. had been turned on and the bottom of the mold was in place. When the metal in the mold reached a level of about 4" above the bottom of the mold, lowering of the mold bottom was commenced and continued at the rate indicated. After a standard length of sheet ingot had been cast, (about 110"), pouring ceased and the ingot was lowered out of the mold.

Example 2 x 39" ingots and 8" x 42" ingots were cast similarly, the molds and spray boxes being similar to that of Example 1 but designed to accommodate the different size of ingot. Lowering rate in the case of 10" x 39" ingots was 2%" per minute and, in the case of 8" x 42 ingots, it was 4 per minute.

In a variation of the previously described casting processes, it is possible to continuously cast molten metal using only the top spray means, i. e., for example, spray pipe 6 as shown in Fig. 1.

By casting procedures as described in these examples and as generally employed in the art, and by the use of the differential cooling apparatus and method as described herein, it has been wherein molten metal is continuously supplied to an angular mold, the molten metal is cooled while in the mold at least sufficiently'to form a skin of olid metal about the casting, and a casting having corners corresponding to the angular shape of the mold is continuously withdrawn from the mold, the improvement which comprises cooling the metal substantially more rapidly at and near the corners formed by the mold than at points more widely removed from the said corners.

2. The improvement of claim 1, wherein the metal isa light metal.

3. In the continuous casting of metals to .produce angular castings of relatively large crosssection, wherein molten metal is continuously supplied to the upper part of an angular. vertical mold, at least partly solidified casting is continuously withdrawn from the bottom of the mold, and liquid coolant is continuously sprayed onto the mold and onto the casting below the mold, the improvement which comprises spraying substantially more. coolant onto areas of the mold and the casting close to and including the corners thereof than onto areas farther removed therefrom.

4. A method of producing rectangular light metal ingots oi relatively large cross-section, which comprises continuously supplying the molten metal to the upper .part of a'n'open-ended vertical mold of approximately rectangular horizontal cross section and having a maximum horizontal length at least twice the width of the mold, continuously spraying liquid coolant onto the sides and end portions of the mold and the sides and end portion of the ingot below the mold, and so maintaining an excess supply of coolant to the end portions of the mold and casting and to adjacent portions of the sides of the mold and ingot lying close to the end portions as to substantially reduce cracking of the ingot.

5. The method of claim 4, wherein said light metal is predominantly composed of aluminum. 6. A method of producing rectangular light metal ingots of relatively large cross-section, which comprises continuously supplying the molten metal to the upper part of an open-ended vertical mold of rectangular horizontal cross section and having horizontal dimensions such that no one such dimension exceeds any other by a factor of more than two, continuously spraying liquid coolant onto the sides of the mold and of the ingot below the mold, and so maintaining an excess supply of coolant to the corner sections of the mold and ingot as to substantially reduce cracking of the ingot.

7. The method of claim 6, wherein said light metal is predominantly composed of aluminum.

PAUL P. ZEIGLER. CLYDE R. ST. JOHN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,074,812 Sendzimer Mar. 23, 1937 2,127,515 Hazelett Aug. 23, 1938 2,301,027 Ennor Nov. 3, 1942 2,304,258 Junghan Dec. 8, 1942 2,310,893 Brenner Feb. 9, 1943 2,414,269 Nicholls Jan. 14, 1947 FOREIGN PATENTS Number Country Date 884,498 France Apr. 27, 1943