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United States Patent	3,589,429
Schoffmann	June 29, 1971

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Foreign Application Priority Data

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May 29, 1968 [OE]			A5131/68

Current U.S. Class:	164/471 ; 164/476; 164/486; 396/661
Current International Class:	B22D 11/128 (20060101); B22d 011/12 ()
Field of Search:	164/76,82,270,283,89

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References Cited

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U.S. Patent Documents

2565959	August 1951	Francis et al.
2698467	January 1955	Tarquinee et al.
3333452	August 1967	Sendzimir
3358358	December 1967	Jenks et al.
3491823	January 1970	Tarmann et al.
3315349	April 1967	Cofer

Primary Examiner: Overholser; J. Spencer
Assistant Examiner: Annear; R. Spencer

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Claims

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What I claim is:

1. A method of continuously casting a metal bar for subsequent shaping thereof, comprising the steps of, casting molten metal in a cooled mold to form the continuous cast bar, subjecting said bar upon emergence from said mold to the action of a cooling medium controlled to effect a decrease in surface temperature of said bar of not more than about 200.degree. C. and solidification through from about 85 percent to 95 percent of the cross-sectional area of the bar, and while still retaining the said surface temperature and solidification characteristics imparted by the action of said controlled cooling medium, passing said bar through an uncooled zone to enable heat emission from the unsolidified core of said bar to heat the surface of said bar to a temperature higher than that prevailing upon its entry into said uncooled zone, whereby the temperature gradient over the cross-sectional area of said bar is reduced and subjecting said bar to shaping operations immediately upon emergence from said uncooled zone.

2. The method set forth in claim 1 wherein additional heat is applied to said bar as it traverses said uncooled zone by means selected from burners, induction means and resistance heating.

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Description

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This invention relates to a method of treating cast bars in continuous casting plants outside of the mold, particularly cast bars which are shaped, e.g. cogged down, preceding or following the complete solidification thereof.

When high-melting materials, such as steel, are subjected to continuous casting techniques the melt cast into the cooled mold is first of all cooled to such an extent that a solidified marginal zone is formed. Upon exit from the mold the solidified marginal zone or skin layer of the bar is subjected to further cooling in a cooling zone provided with spray jets, during which cooling procedure the solidified marginal zone thickens gradually to form a completely solidified bar. With this mode of operation the marginal zone or skin layer, being in direct contact with the cooling medium, is always colder than the inner portion of the bar, which retains a liquid core until the bar has solidified completely.

It has been known to control the cooling process, taking place in the cooling zone following the mold, in a way as to maintain a substantially equal surface temperature, at most a decrease in temperature by not more than approximately 200.degree. C., between the exit of the bar from the mold and the complete solidification of the core. This delayed cooling keeps down the stresses usually developing because of the differences in temperature between the marginal zone and the liquid core and thus minimizes the risk of crack formation, unless additional stresses are applied in the course of shaping or the like. If, however, the cast bar, which might still have a liquid core, is subjected to further processing, e.g. bending or cogging down, immediately upon leaving the continuous casting plant, the known controlling method for the cooling process is no longer satisfactory. It has been found that in such cases the temperature differences prevailing throughout the cross section of the bar as well as the resulting stresses lead to an increased liability to crack formation.

The present invention has as its object to avoid these disadvantages and difficulties and relates to a method of treating cast bars in continuous casting plants outside of the mold, particularly cast bars which are shaped preceding or following the complete solidification thereof, said bars being led from the cooled mold into a cooling zone where they are treated with a cooling medium to obtain a substantially equal surface temperature, at most a decrease in temperature by approximately 200.degree. C., said method comprising leading the bar still containing a liquid core from the cooling zone into a subsequent uncooled, possibly heated, equalization zone, where the temperature of the inner portion of the bar causes an increase in the surface temperature thereof, said increased surface temperature being higher than the temperature prevailing upon entrance of the bar into the equalization zone.

According to the invention the control operation known per se for the cooling procedure, during which the surface temperature should not decrease by more than 200.degree. C., is terminated prematurely, i.e. prior to complete solidification of the bar, and thus it is possible to equalize the differences in temperature and stress over the cross section of the bar before subjecting the bar to additional mechanical treatment, such as bending or cogging down. Suitably the cooling procedure is terminated as soon as the bar has solidified over approximately 85--95 percent of its cross section. In these cases the temperature of the skin layer is approximately 950.degree.--1,000.degree. C., the temperature of the liquid core approximately 1,500.degree. C. This temperature of the liquid core is sufficient to give off heat to the solidified marginal zone while passing the equalization zone to an extent which enables heating said marginal zone to a temperature of about 1,100.degree. C. or slightly higher.

The method of the invention is in more detail illustrated in the drawing.

FIG. 1 is a diagrammatical view of the overall setup;

FIG. 2 a diagram of the temperature behavior in core and skin layer;

FIG. 3 shows the temperature distribution over the cross section of the bar .

In FIG. 1 numeral 1 denotes the cooled mold from where a cast bar with a thin solidified skin layer is delivered. Thus primary cooling takes place in the mold area. Numeral 2 denotes the secondary cooling zone, where the bar is cooled from outside by means of spray jets. 3 is the place where the cooling procedure is terminated and the bar enters the equalization zone 4, said equalization zone ending at 5. With the equalization zone the temperature of the skin layer rises due to heat emission from the core being still liquid in part. 6 and 6' denote a shaping plant, particularly a cogging down plant, following the equalization zone. Instead of said cogging down plant a straightening stand may be provided.

In FIG. 2 numeral 7 denotes the temperature behavior curve in the core and 8 the temperature behavior curve in the solidified skin layer. It is evident that the core temperature is essentially equal in both the secondary cooling zone 2 and the equalization zone 4, i.e. a temperature of 1,500.degree. C. is maintained decreasing slightly toward the end. Within the secondary cooling zone 2 the temperature of the skin layer decreases from approximately 1,100.degree. to approximately 950.degree. C., and within the equalization zone rises to about 1,100.degree. C. due to absorption of heat yielded by the liquid core.

FIG. 3 illustrates the temperature distribution over the cross section of the bar. The drawing shows a square bar 9, the inner core 10 of which is still liquid while the exterior region 11 has already solidified. Curve 12 illustrates the temperature distribution prevailing over the square bar cross section at the entrance into the equalization zone, i.e. in position 3 of the diagram shown in FIG. 1. The temperature distribution at the end of the equalization zone, i.e. in position 5 of FIG. 1, is illustrated by the curve 13. In a modified embodiment of the method of the invention, in which additional heating of the equalization zone is provided, e.g. by means of burners, induction means or resistance heating, the temperature distribution in 5 would correspond to the curve 14. Upon comparison of the curves 12 and 13 on the one hand, and 12 and 14 on the other hand, it is seen that after passing the equalization zone the bar exhibits an evenly distributed temperature with the exception of a very small area in the core.

The method of the invention secures an extensive equalization of temperature stresses, reduces the liability to crack formation in the course of further technological processing, such as bending and cogging down, following the continuous casting procedure, and improves the quality of the products.

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