US2747245A

US2747245A - Process for continuous casting of metal billets

Info

Publication number: US2747245A
Application number: US234195A
Authority: US
Inventors: Junghans Siegfried
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-06-29
Filing date: 1951-06-29
Publication date: 1956-05-29
Anticipated expiration: 1973-05-29

Description

May 29, 1956 s. JUNGHANS 2,747,245

PROCESS FOR CONTINUOUS CASTING OF METAL BILLETS Filed June 29, 1951 J E y i 6 m 7 k 5 710a INVENTOR S/EGFR/ED JUNGHANS ATTORNEYS United States Patent 7 PROCESS FOR CONTINUOUS CASTING OF METAL BILLETS Siegfried Junghans, Schorndorf, Germany Application June 29, 1951, Serial No. 234,195

2 Claims. (Cl. 22200.1)

The present invention relates to a process for the continuous casting of metal billets and in particular billets of metals having a high melting point such as iron and steel.

It is an object of the invention to provide a process which renders it possible to produce a billet by continuous casting, which billet is particularly dense and free of pipes or axial cavities, segregations and internal cracks.

It has been found in accordance with the invention that the desired improvement in the properties of the continuous cast billet can be efiected primarily by the applications of pressure upon the molten charge as it solidifies. It was found, furthermore, that continuous casting particularly olfers the possibility of applying an elfective pressure, especially when the following procedure, in accordance With the invention, is employed: The molten metal at the edge zone of the cross-section of the casting is solidified a short distance from the upper surface into a closed, substantially rigid, conveyable casing or crust as it passes through a downwardly open cooled mold, whereas complete solidification of the molten metal in the interior of the casting is only eifected at such a distance from the upper surface of the molten metal that the existing pressure of the liquid head eflectively reduces the possibility of pipes or segregations. In continuous casting, the conditions of casting and cooling must be accurately controlled in comparison to ordinary casting of ingots. It has been found from experience that the continuously cast billet, because of this accurate control, solidified homogeneously with rather irregular orientation of the crystals formed, particularly, at its center. The process, in accordance with the invention, can, therefore, be carried out with columns of molten metal of a height which could not ever be remotely approached in ordinary ingot casting processes because of the danger of interruptions in the fluid column because of bridging as a consequence of dendritic crystal growth.

It was found desirable to carry out the cooling of the solidified casing and its inner fluid core in such a manner that the greatest possible cross-section is subjected to the fluid pressure. Consequently, it was found desirable only to remove so much heat from the billet while it passes through the mold, that the equilibrium temperature reached between the solidified casing and the inner molten portion after it leaves such mold is just below the melting point. An additional characteristic of the invention resides in the regulation of the shape and depth of the molten inner portion of the billet ice cracks. It was unexpectedly found, in accordance withthe invention, that such internal cracks were caused by the mechanical means employed for controlling the billet; speed through the mold. These means, in continuously operating continuous casting plants, normally consistsof clamping rollers which serve to reduce the speed at which the heavy billet descends to the selected rate of casting. Previously, it had not been recognized that proper application of such means is of great importancein the production of sound castings. In accordance with the invention, it was found that the clamping pressure of the means employed can lead to inner axial cracks; because of the squeezing action effected thereby on the insufficiently solidified billet. Consequently, an additional characteristic of the invention is that clamping pressures of the means for controlling the speed of the billet through the mold are only applied at a point where the billet has solidified sufficiently to be able to resist the pressure stresses which might cause damage to its structure. This point normally lies below the tip of the column of molten metal. As the billet with its very deep column of molten metal normally does not have sufficient inherent stiflness to prevent its bending out of its direction of travel before it reaches the clamping rollers or other means employed to control its descent, it can be desirable to provide lateral guiding means for the billet which exert substantially no pressure thereupon.

The casting apparatus for carrying out this modification of the invention should be provided with means for controlling the billet speed through the mold whose distance from the lower end of the mold can be adjusted and, furthermore, with guiding means such as, for example, rollers or similar devices that can be contacted with the billet in accordance with the requirements of the individual instance to prevent sagging or bending of the billet on its way from the mold to the means controlling the descent of the billet.

Further objects and advantages of the invention will become apparent from the following description taken together with the drawings.

In the drawings:

Fig. I schematically shows a vertical section of an apparatus suitable for carrying out the process in accordance with the invention.

Fig. 11 shows a cross-section through a faulty billet.

In Fig. I, runner 1 which is supplied with molten metal from a suitable source, delivers molten metal to the top of the water-cooled, downwardly-open mold 2, wherein the fluid metal is so sharply cooled that a solidified casing S1 is quickly formed around the still fluid core S2 of the billet S being cast, which casing extends substantially up to the upper surface S3 of the molten metal.

After the embryo billet leaves the lower end of mold 2, its solidified casing S1 must be maintained at a predetermined thickness and it as well as the liquid core S2, must be maintained at predetermined temperatures. For this purpose, the billet is passed through an equalizing chamber 3, which, for example, can be filled with hot air, steam or a hot gas such as nitrogen or other neutral gas. Chamber 3 is merely shown schematically. Appropriate means can be provided therein to effect the cooling at a predetermined rate. For example, the chamber can be subdivided into several zones provided with different cooling media or a cooling medium at different temperatures. The gas chamber 3 must be of suflicient length that a fluid column S2 is maintained which is sufliciently high that its fluid pressure effectively reduces or eliminates the formation of pipes and/or segregations within the billet.

The complete solidification of the billet S occurs at:

metal. In the case of a steel billet having a diameter of 100 mm. and it was found that a column of molten metal of a length L of 2400 mm. provided a fluid pressure head of 1.7 atmospheres gauge pressure. The billet leaves mold 2 with a surface temperature of about 1350 C., and is then passed through a gas chamber, the temperature of which is adjusted to about 600 C. After passing through the gas chamber, the billet has a surface temperature of about 1150 C. The resulting billet was of sound structure in which no spongy spots or segregations could be discovered.

Rollers and 6, whose speed of rotation is controlled by shaft 7, are provided to control the descent of billet S. The rollers 5 and 6, when there is danger of internal cracking, should grip the billet below the lower tip S4 of the liquid core S2.

It is easily ascertainable whether interior cracks in the billet are caused by premature application of the clamping of rollers 5 and 6 by interrupting the casting and permitting a portion of the billet above the rollers to solidify completely. A cross-section of the billet will show an axial inner crack S5 (Fig. II) which extends between points Q1 and Q2 of the clamping pressure if the clamping pressure has been applied prematurely. Consequently, if such a crack is formed, the rollers must be adjusted to a lower position.

As the billet leaves mold 2 with a surface temperature of about 1250" to 1350 C. and with a liquid core and will remain so for several mold lengths,

nonpropelled guide rollers

8a and 8b and 9a and 9b are provided to prevent possible lateral bending or breaking of the billet above rollers 5 and 6. A spraying device 10 is positioned below the mold 2 for the purpose to maintain the solidified casing S1 at a predetermined thickness, i. e. to prevent that the liquid core S2 is melting and finally breaking through the casing S1, until the billet S has entered the gas chamber 3.

Spraying device 10 can be omitted if the billet is cooled by means of the mold 2 to such an extent, that with the gas chamber 3 positioned closely to the mold, there is no danger that the liquid core could break through between the different cooling steps of the billet.

I claim:

1. A process for the continuous casting of metal billets comprising continuously pouring molten metal into an open mold shell, cooling the molten metal and thereby forming an embryo billet composed of a solidified casing about a molten core, withdrawing the embryo billet from the bottom of the mold, then reducing the cooling by hot gas means in order to maintain the molten core at a depth suflicient for its fluid pressure to eliminate segregations, while at the same time laterally supporting the billet without distortion pressure thereon, solidifying said billet adjacent the bottom of said gas means, and then gripping said billet with billet withdrawal means adjacent the lower end of the molten core at a point where the billet has obtained sufiicient solidification to Withstand the pressure of the gripping means without forming fissures in the solidified billet.

2. A process as in claim 1, further comprising water cooling said billet between the mold and the gas means to further preserve said solidified casing.

References Cited in the file of this patent UNITED STATES PATENTS 648,091 Trotz Apr. 24, 1900 894,410 Trotz July 28, 1908 2,195,809 Betterton et al Apr. 2, 1940 2,284,503 Williams May 26, 1942 2,284,703 Welblund et al June 2, 1942 2,284,704 Welblund et al June 2, 1942 2,590,311 Harter et a1 Mar. 25, 1952

Claims

1. A PROCESS FOR THE CONTINUOUS CASTING OF METAL BILLETS COMPRISING CONTINUOUSLY PORING MOLTEN METAL INTO AN OPEN MOLD SHELL, COOLING THE MOLTEN METAL AND THEREBY FORMING AN EMBRYO BILLET COMPOSED OF A SOLIDIFIED CASING ABOUT A MOLTEN CORE, WITHDRAWING THE EMBRYO BILLET FROM THE BOTTOM OF THE MOLD, THEN REDUCING THE COOLING BY HOT GAS MEANS IN ORDER TO MAINTAIN THE MOLTEN CORE AT A DEPTH SUFFICIENT FOR ITS FLUID PRESSURE TO ELIMINATE