US2414269A - Method for cooling ingots in continuous casting - Google Patents

Description

Jan. 14, 1947. E. A. NICHOLLS 1 METHOD FOR COM-116G INGOTS IN CONTINUOUS CASTING Filed Aug. 1, 1942 2 Sheets-Sheet 1 Jan. 14, 1947. E. A. N[CHOLL$ 2,414,269

METHOD FOR COOLING INGOTS IN CONTINUOUS CASTING Filed Aug. 1, 1942 2 Sheets-Sheet 2 ZDWl/V Au-wzp Mamas INVENTOR.

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ATTORNEY Patented Jan. 14, 1947 METHOD FOR COOLING moors IN CONTINUOUS oas'rmc Edwin Alfred Nicholls, Alcoa, Tenn., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application August 1, 1942, Serial No. 453,146

Claims. 1

This invention relates to the. casting of ingots by a continuous casting process and it is especially concerned with chilling the mold and the ingot emerging therefrom.

In the continuous casting process molten metal is continuously fed into a suitable open mold shell where it at least partially solidifies and the solid metal body so formed is continuously withdrawn from the mold at approximately the rate at which solidification progresses upwardly. In this manner the solidified metal serves as a bottom to the open mold and holds the pool of molten metal within the mold shell once the casting operation has begun. The rate at which molten metal is introduced into the mold and the rate of withdrawal of the solid metal body are obviously deof water is required and there may be a nonpendent upon the rate at which heat is extracted from the mold and the metal therein. Both the surface condition and internal structure of the solidified metal body are considerably affected by the rate at which heat is extracted. Too drastic a chill may cause a rupture in the metal body due to contraction. An insuflicient chill may permit bleeding of the molten metal to the outside of the freezing metal body. A non-uniform chilling causes an undesirable variation in grain size and distribution of undissolved constituents in the ingot. In casting ingots of light metals, for example, aluminum and magnesium and the alloys wherein these metals predominate, the chilling must be very carefully controlled to maintain the proper rate of heat extraction and thus avoid the foregoing troubles. This requirement is particularly acute where relatively thin walled mold shells are employed, such as those which may be about one-fourth of an inch in thickness, and any changes in chilling conditions are quickly transmitted to the freezing metal within the mold shell.

Methods of chilling molds used heretofore in the continuous casting process have consisted of providing water jacketed molds or directing high pressure sprays of water against the mold shell. The ingots have been cooled either by passing them through tanks of water or allowing water from the mold to run down over the ingot surface. Water jacketed molds are expensive to make and sometimes introduce difficulty in operation because of possible stoppage of the water passages or the accumulation of scale within the passage which interferes with the transmission of heat through the mold wall. Where high pressure sprays have been employed, such as is generally the case when the water comes directly from the main supply line, a considerable volume uniform chilling eifect at the point of impingement of the individual water jets upon the mold and ingot surfaces. Another difiiculty which has been encountered where high pressure sprays are used is that any marked fluctuation in pressure effects the chilling effect, and unless the mold operator maintains a carefulcontrol, the flow of water is uneven, with the result that the freezing of the metal within the mold is not uniform. This variation in chilling conditions may lead to one or more such defects as surface cracking of the ingot, a rupture within the ingot not visible at the surface, or even a visible splitting of the ingot. By surface cracking is meant cracks which extend but a short distance into an ingot, generally only a fraction of an inch. The splitting may not occur at the very beginning of the casting operation but may happen after a considerable portion of metal has been cast. In any event when such splitting occurs, the ingot must be subsequently scrapped and remelted with a consequent loss in time and expense. An uneven flow of water also tends to produce a rough ingot surface known as hot streaking which may introduce diiiiculties in fabricating operations. In casting light metal ingots of relatively large cross sectional area, especially those having a considerable thickness, one or more of the foregoing adverse eiiects sometime occur in spite of the operators efforts to control the chilling properly.

It is an object of my invention to provide a method of uniformly chilling mold shells and ingots in the continuous casting process. Another object is to provide a method for minimizin rough surfaces on ingots made by this process which may lead to diificulty in fabrication of the ingots to finished products. Still another object is to provide a method for minimizing the surface cracking and splitting tendenciesand improving the uniformity of internal structure of ingots made by the continuous casting process. A further object is to produce uniform chilling conditions where ingots of relatively large cross sectional area are made. Still another object is to provide apparatus for carrying out my method, including a novel form of water distributing means by which the novel steps of the method are performed. These and other objects will become apparent in the following description of the invention.

Generally, my invention consists of chilling the More specifically it has been found that ingots are produced having a more uniform internal structure, i. e. greater uniformity of grain size and jdistribution of undissolved constituents, a smoother surface and fewer surface cracks and splits when a low pressure water spray is employed than where a high pressure spray is used. These advantages are especially evident in making ingots of relatively large cross sectional area, for example, those having an area of over 200 square inches. In referring to a relatively low water pressure, I mean that the pressure of the water at the spray hole is of the order of from a few ounces to a few pounds per square inch, for example, from about 0.5 to 3 or 4 pounds per square inch as compared to a normal line pressure of 40 or 50 pounds per square inch or more. The improvement is accomplished by using a low pressure coolant system that includes a spray chamber as one of the principal parts thereof, said chamber surrounding a substantial portion of the mold but separated therefrom by an air space. The space between the said chamber and mold is preferably from 0.5 to 1 inch. The chamber surrounds that portion of the mold where the ingot is formed and it also, preferably, extends below the bottom edge of the mold shell to provide for a spray on the emerging ingot. The chamber is provided with suitably arranged spray holes whereby at least the external surface of the mold, and preferably the emerging ingot also, are flooded with water from the low pressure sprays. The spray chamber may be referred to as a unitary chamber since all of the coolant for chilling the mold and ingot comes from one chamber instead of from two or more pipes or other conduits whereby individual portions of the spray can be independently controlled.

The use of a single unitary spray chamber surrounding a substantial portion of the mold has particular advantages in that only one water control valve is required to admit water to the chamber, This obviates the necessity for adjustment of several valves, and promotes a uniform flow of water from the chamber, and ec-nsequently, a greater uniformity in the chilling of the mold and the hot metal therein. The use of a single water control means also simplifies the operation where a low pressure water supply system is employed in that the control means may be opened to the maximum position without danger of sudden variatiqns in the water pressure. To provide a low pressure spray the unitary chamber must be of sufiicient size to accommodate a relatively large volume of water so that frictional resistance to flow is low. A relatively large volume of water with respect to the out flow also promotes the settling of any suspended matter. Still another advantage of the unitary chamber in place of a water jacketed mold is that the stream of water which chills the mold can be seen by the operator and any stoppage or other interference with the stream can be easily detected.

A low pressure water supply can be provided in various ways but I have found that a pressure reducing means such as a standpipe with suitable intake and outlet is a convenient means of maintaining a constant low pressure supply of water to the spray chamber.

In using a low pressure water supply it has been found that a satisfactory chilling is obtained so long as that portion of the external surface of the mold shell corresponding to the internal surface which is in contact with or close proximity to the molten and hot solidified metal is flooded with water. By contact with or close proximity to the mold shell by the molten and hot metal within the mold is meant both the region of the mold shell where there is an actual contact and where the solidified metal has contracted slightly and left a small space between it and the mold shell. Furthermore, there is apt to be less variation in pressure in a low pressure water supply than where a high pressure supply is employed. This uniformity, in pressure is of course conducive to a uniformity in chilling. A low pressure supply also tends to permit equalization of the temperature of the water used, particularly where a reservoir is employed as an immediate source of water for chilling. The unitary; water chamber also permits a mixing of the water and tends to equalize any variation in temperature of the liquid. The uniformity of water pressure and temperature is of particular importance in the casting of light metal ingots where relatively thin walled mold shells are used made of metal having a relatively high thermal conductivity, because variations in the chilling' condition on the exterior of the mold shell are quickly transmitted to the metal within the mold.

The invention will be further described both as to method and apparatus in the following detailed description of the accompanying drawings, in which:

' Fig. 1 is a plan view of a preferred form of apparatus used in connection with the casting of ingots;

Fig, 2 is a side elevation of the apparatus shown in Fig. 1;

, Fig. 3 is a cross sectional view taken on the line IIIIII of Fig. 1, together with certain additional casting equipment disclosed for the purpose of clarity;

Fig. 4 is a broken and partial longitudinal sec- H0381 view of the spray chamber and inlet pipes; an

Fig. 5 is an enlarged broken cross sectional view of a spray chamber of the invention,

Referring to Figs. 1 and 2, frame III, which supports mold shells I6 and spray chambers 22 together with the necessary water supply pipes, is mounted on a support 62 and the entire assembly is pivoted on the member I 2 so thatit can move through an are described by the dotted curved line [4. In this manner the assembly can be moved into and out of casting position when desired.

The mold shells 5 are provided with lugs I8 having pins 20 therein which register with holes in the frame thereby maintaining the shells in a fixed position. The mold shells preferably have relatively thin walls, say one-fourth inch in thickness, and are made of a metal having a relatively high thermal conductivity such as aluminum or copper or their alloys. Surrounding each mold shell "5 is a. unitary spray chamber 22 having end plates 24 bolted to flanges 26. As best shown in Fig. 5, the spray chamber has outer solid walls 34 and inner walls 32 provided with suitably arranged spray holes through which water is directed at the mold shell and ingot descending therefrom. Inside of the chambers and at both ends thereof, perforated ballle plates 28 are located directly in front of water inlets 56, the baffle plates being held in place by supports 30 attached to the top and bottom of the spray chamber.

A water supply of low pressure is provided from a standpipe 36 mounted on base 38. Water is adlet 44, swivel joint 48, and main line to branch pipes 52 and 54, where it enters the spray chambers through inlets 56, as shown by the arrowed dotted lines. For the purposeof draining the standpipe, a pipe 58 and valve 60 are employed. The entrance of all water to the system, it is noted. is controlled by the one valve 42. The standpipe may be of any convenient height so that the water pressure at the spray may be on the order of from about 0.5 to 3 or 4 pounds per square inch. The main water line from the standpipe must obviously be of suificient size to provide enough water to keep the spray chambers filled and the sprays operating.

Figs. 4 and 5 present detailed views of a spray chamber. Water- supply pipes 50, 52. and 54 are shown in Fig. 4 with inlet pipe 56 threaded into the end plate 24. Water entering through these inlets is prevented from directly striking the inner end walls of the spray chamber by the perforated bafiie plates 28. It will be noted that not all of the water coming from the inlet necessarily passes through the bafiie plates. some of it passing over the top and under the bottom of the plates or around the sides thereof. The water within the spray chamber is discharged in sprays 92 against the mold shell and descending ingot through spray holes 90 in the inner wall thereof. The spray chamber is preferably spaced from the mold shell a distance of about 0.5 to 1 inch, the maximum distance in any event being determined by the distance which the water spray can reach under the pressure employed. It is preferable that the inner wall of the spray chamber be parallel to the mold shell. It has been found that providing two banks of spray holes in the upper portion of the inner chamber wall and a ingle bank near the bottom gives an adequate supply of water to produce satisfactory light metal ingots.

It is preferable to position the holes as shown in Fig. 5 so that the spray strikes the mold and ingot in predetermined locations. However, such positioning i not essential to the use of a low pressure spray, except that the mold shell should be chilled above the level of the molten metal therein in order to avoid a fusion or burning of the shell by the hot metal inside of it. Generally, water should be sprayed on the emerging ingot as well as the mold shell, even though water sprayed on the shell drains down upon the ingot surface. The location of the lowest spray is determined in part by the character of the metal or alloy being cast; in some instances, the spray should strike the ingot a few inches below the bottom edge of the mold, whereas in other cases the spray location is not critical. For the best results the lowest spray holes should be located a sufficient distance above the bottom of the spray chamber to permit the settling of any sediment on the bottom without clogging the holes. It is known that where pipes have been employed to provide a spray, the holes have become clogged with sediment and this seriously interferes with obtaining a uniform chilling effect on the mold shell and ingot. To remove any accumulated iii sediment in the bottom of the spray chamber it is only necessary to remove an end plate and scrape out the dirt, or pipe plug 85 may be removed if the sediment can be easily drained out. This ease of access to the spray chamber greatly facilitates maintaining the chamber in the best operating condition. One or two drilled holes 94 are located at the top of each chamber to provide for the escape of air as the chamber is being filled with water. The outer spray chamber wall 34 is preferably welded to the remainder of the chamher, as shown in Fig. 5. However, any other means of attachment would be suitable providing a leak-proof joint is obtained.

The operating conditions under which the low pressure water spray is employed are illustrated in Fig. 3. where the molten metal from any convenient source is delivered to a pouring trough I2. From this trough it passes through downspouts I4 to partially fill the mold shells and form a pool of metal 86 therein. The pool is maintained at substantially the same level during the casting operation. The flow of molten metal is conveniently controlled by raising and lowering the valve stem 18 through the support mounted on bracket 82, which in turn rests upon the pouring trough. The molten metal is discharged from the downspout through ports 16. Pool of metal freezes at the mold shell walls, and the thickness of frozen zone increases as the bottom edge of the mold shell is approached, however, the entire cross section of metal within the shell. may not be solidified at the level of said bottom edge of the mold shell. The frozen zone is thick enough at this location under proper .chilling conditions to prevent any molten metal from leaking to the surface. The ingot formed in this manner is lowered from the mold shell by the hydraulic elevator at a predetermined rate.

In addition to the foregoing features, Fig. 3 shows a cross section of Fig. 1 on line III-III. The frame It on which mold shells it are supported can be seen. Pipe 50, 52, and 54 are shown as well as the manner of supporting pipe 54 from a T-member by welded construction. Flanges 26 at one end of the spray chambers with ibolt holes provided therein are evident. The spray chambers having spray holes in the inner wall can also be seen. The ingots 88 rest on mold bottom 64 which in turn are mounted on platform 66. This platform is supported on plate 68 against which bears the hydraulic ram arm III which raises or lowers the platform. The hydraulic cylinder which operates the ram is located in the casting pit which is not shown in the figures.

The water supply to the spray chambers is provided by filling the standpipe to the desired height above the outlet 44 and maintaining that level throughout the casting operation. Automatic means may, of course. be used to maintain any predetermined level of water such as a float valve. However, an overflow pipe placed :at the desired height, as shown in Fig. 2, provides a simple means of providing a constant pressure if the inflow of water is maintained in just a sumcient volume to cause a slight overflow.

Although one form of apparatus has been described, my invention is not limited thereto but extends to other structures possessing the same essential features which in operation produce the same result, namely, ingots having uniform internal structure which are relatively free from surface cracks and splitting. More particularly, the invention is not restricted to the casting of rectangularly shaped ingots but is applicable to other shapes and sizesv of ingots.

Water has been referred to hereinabove as the cooling medium employed. However, other fluid coolants can be used so long as the requisite chilling eilect is obtained.

I claim:

1. In the method of making ingots in open mold shells by a continuous casting process wherein the mold shell is chilled by a water spray, the step which comprises chilling said mold shell with a water spray under a pressure of from about 0.5 to 4 pounds 'per square inch, said water spray being directly delivered, in the form of a multiplicity of jets, from a relatively large body of water maintained adjacent the mold.

2. In the method of making light metal ingots in thin walled open mold shells by a continuous process .wherein the mold shell and emerging ingot are chilled by a water spray, the step which comprises chilling said mold shell and ingot with a water spray under a pressure of from about 0.5 to 4 pounds per square inch, said water spray being directly delivered, in the form of a multiplicity of jets, from a relatively large body of water maintained adjacent the mold.

. 3. In the art of making ingots by a continuous casting process in open mold shells, the method of minimizing splitting and surface cracking of an ingot and improving the uniformity of its internal structure comprising introducing molten metal into the mold shell, chilling the exterior of the mold shell andthe emerging ingot with a water spray under a pressure of from about 0.5 to 4 pounds per square inch, said water spray being directly delivered, in the form of a multiplicity 'of jets, from a relatively large body of water maintained adjacent the mold, said chilling being applied to at least that portion of the external surface of the mold shell corresponding to the portion of the internal surface in contact with or in close proximity to the hot metal within the mold shell, and continuously withdrawing the ingot from said mold shell.

' 4. In the art of making light metal ingots of relatively large cross sectional area by a continuous process in thin walled open shell molds made of a metal having a high thermal conductivity, the method of minimizing splitting and surface cracking of an ingot and improving the uniformity of its internal structure comprising partially filling the mold shell with molten metal and maintaining the pool of said molten metal at substantially the same level during the casting operation, chilling the exterior of the mold shell and emerging ingot with awater spray under a pressure of from about 0.5 to 4 pounds per square inch, said water spray being directly delivered, in the form of a multiplicity of jets, from a relatively large body 0! water maintained adjacent the mold, said chilling being applied to at least that portion of the external surface of the mold shell corresponding to the portion of the internal surface in contact with or in close proximity to the hot metal within the mold shell, and continuously withdrawing the ingot from said mold shell at the same rate at which freezing of the metal within the mold shell progresses upwardly.

EDWIN ALFRED NICHOLLS.

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