US2401075A - Process of casting ingots - Google Patents

Description

Patented May 28, 194

George Walter H umes, Sharon, Pa., assignor to Carnegie-Illinois Steel Corporation, a corporation of New Jersey No Drawing. Application May 6, 1942,

Serial No. 441,954

v Claims. In thejcasting or ferrous metal ingots, the importance of elimination of internal defects in the casting and the obtaining of a maximum mold life have been given considerable study and attention, because, obviously, the minimizing of internal defects in the ingots and maximum pos sible' mold life mutually contribute importantly to increased production, which in times of emergencies is of paramount importance.

The present invention introduces an addi tional factor to the above considerations in that it not only reduces internal .defects in the ingots and increases mold life, but also increases production by enabling a more rapid stripping of the cast ingots from the molds, thereby preparing the molds more quickly to receive further charges of metal, consequently reducing very materially the casting time, and also, through the rapid transfer of the ingots from the molds to the soaking furnaces enables the attainment of substantially improved operating economies and increased eillciencies.

In the usual castingof ingots, it is customary, when the molds employed are of the big-enddown type of molds, to remove the cast ingot by stripping the mold off the ingot by holding theingot down while the mold is being lifted forcibly from the ingot, the ram or plunger of the stripping crane bearing against the ingot during the lifting of the mold.

ferrou metals, and more particularly killed forrous metals as poured into open-topped ingot molds.

By the operation of the present invention, there is enabledto be obtained a'substantially higher yielcLof sound product after the ingots I are rolled, and at the same time, securing other important operating advantages, such as increased life of the ingot molds; quicker moving of the'moldsfrom the pouring platform; having the ingots hotter a charged into the soaking pits; less fuel and time required for heating the ingots to rolling temperature, and thus practi'callydoubling the effective capacity of the soaking pits; requiring less scaling and damage to the surfaces of the ingots during such heat ing; and finally obtaining a much shorter time interval between the pouring of the ingots and their rolling in the mill, thus reducing delays on the mill while waiting for hot ingots to roll.

In general, 'thepresent invention consists of the following three essential steps, the combination of'the second and third of which is contrary topped mold.

Consequently, it has been considered essential that the solidification of the ingot must have reached completion in the mold, the length of time required for this solidification depending obviously upon the size'of the ingots. Thus,"for an ingot measuring 21 inches by 23 inche in cross section this length of time averages from about 90 minutes to 120 minutes.

In accordance with the practice of the pres- 1 cut invention, this complete solidification of the ingot in the mold is not required, as the invention is based upon the discovery that a thick solidified layer may be produced at the top of the ingot by chilling the ingot adjacent its top,

' thereby solidifying enough metal to withstand the holding pressure of the ram of the stripping crane during lifting of the molds from the ingot. leaving the interior of the ingot still molten. In this condition the ingots are transferred to the soaking pits while the ingot is still partially,

molten, resulting in there being required less fuel and time for the heating of the ingots to rolling temperature.

It will be apparent, therefore, that the present invention relates to a method of solidifying tothe teaching of the prior art and prior mill Practices:

1. Pouring a killed ferrous metal in an open- Water, so as to solidify the areas containing thenon metallic inclusions. V

As has been pointed out above. herein, the practiceof the present invention is particularly applicable to big-end-down molds, since, as i well known, this type of mold tends to produce an elongated pipe or hrinkage cavity in the ingot, which, if it is contaminated with non-metallic matter, will not weldwhen the ingot is rolled, thus causing large losse'sfor' laminations.

In the operation of the present invention, itis preferred to equip the molds with any suitable type or hot-top to assist in keeping the steel liquid in the top of the ingot until the step of causing it to solidify is completed." Additionally to assist in keeping the steel suitably liquid, it is preferred to 'cover the top of the steel, after the ingot is poured, with a suitable insulating medium; such as small-sized anthracite coal,

- the mammum benefit from the invention and that at least certain of the;benefits can be secured without their aid.

The length oftlme which is allowed to elapse between pouring the ingot and applying the cooling medium is not particularly critical, since some of the non-metallic matter rises to the top almost as soon as the ingot is poured, and this separa ,tion may continue until the ingot is solidified completely. In the practice of the present invention, however, it is found that substantially all of the benefits. of the present improved procedure are secured by using a time interval of 20 to 45 minutes for an average size ingot, for instance, 21 inches by 23 inches in cross section, although substantial benefits are secured by shorter or longer times, and smaller or larger ingots could employ proportionately shorter or longer time intervals.

It will be obvious that the choice of a cooling medium is of convenience only, and may be a gas, or liquid, or solid, since the whole object of the cooling step is to entrap the non-metallic metal in the top of the ingotby causing it to solidify, so that it cannot drain down into and contaminate the lower parts of the central shrinkage cavity.

It is this promptness with which ingots made by the improved process of this invention can be handled and further processed after pouring, that produces the substantial operating benefits referred to earlier herein, such as longer life of ingot molds, for example. In this connection it may be noted that mold life is reduced somewhat It is found in practice that 'the method of the present invention is applicable toferrous metals of any analysis, but is particularly beneficial when used with steels which tend to have large or deep' shrinkage cavities. Steels having considerable silicon content, for instance, 0.10% or more, especially are benefited, as are those steels which are killed by the use of killing agents in I amounts suificient to fully kill, or over-kill the steel, such as is the case with fine-grain or non-aging steels.

The former practice in making fully killed steels usually hasbeen to allow the hot-topped ingots to solidify completely at the pouring platform without moving the molds. For ingots 21 inches by. 23 inches in cross section this waiting period usually requires at least 90 minutes, and more often 120 minutes, as has been indicated above, as compared with, for instance, 20 to 45 minutes, required for the same size of ingots in accordance with the practice of the present invention. The reasons for the usual practice of causing the ingots to solidify completel before removing .from the moldhave been, first, the fullest possible feeding of liquid metal from the hot-top to the ingot proper was believed to be,

essential, and this could be achieved only by waiting until all of the metal had solidified; second, in the case of big-end-down molds, since the metal in the hot-tog was the last to solidify, any attempt to strip the mold oil the ingot while this latter was not fully solidified, by using theram or plunger of the stripping crane to hold the ingot down while the mold was being lifted forcibly off the ingot, would cause the; ram to be .lf-forced into the still-liquid metal ofthe hot top land the liquid or mushy metal of the ingot proper,

v thus producing a large hole in the-upper part of the ingot, and this portion of the ingot, of course, would be renderedworthless. L

In-accordance with the present improved process, there is caused a substantial layer of steel to solidify above the still-liquid meta1 inthe ingot proper, so that the ingot can be moved to the stripping crane, the mold strippedoil, and he ingot charged into the soaking pit while the ingot still'is-partly molten, all without damage to the ingot, since the stripper ram will not be forced through this solidified layer of steel.

to a point adjacent to the top of the metal in tofore.

in proportion to the time during which the whitehot ingots remain in the molds. Other advantages have been mentioned above, such as less pouring platform surface required, ingots delivered hotter to the pits, requiring less fuel and heating time, with greater resultant capacity of the soaking pits, and fewer mill delays, all of which follow from the quicker handling of the ingots made by the improved process, as will be apparent.

The reason for the success of the improved operations isnot definitely known, but apparently when water is applied to the top part of the ingot in the manner described above, it permits the ingot to be stripped and charged into the soaking pits before a secondary internal contraction of the metal takes place. Apparently also, the hot top acts as it is expected to do, that is, as a reservoir of liquid steel to fill up any void caused by contraction, but by the process of the present invention the outside skin of the ingot is shrunk to a greater degree than in normal cooling so that there are less voids permitted to form within the ingot. The process of solidification appears to be, first, contraction of the skin of the ingot, followed by a secondary con! traction from the inside outwardly, so that any increase in the outside contraction would reduce the seriousness of the inside contraction. Apparently, also, in the present process, the greatly reduced time from pouring to rolling which is obtained by the present invention prevents some of the secondary contraction taking place, and the steel may be somewhatv mushy in the center when rolled, thus permitting a compression of the center of the ingot and elimination of voids.

As has been indicated above herein, production is increased substantially by the method of the present invention. The present invention also enables a rapid moving of the ingots through the soaking pits and a substantially efi'ective doubling of ingot capacity in the same pits coupled with about 25% to 30% longer mold life than here- Additionally, the process of the present invention results in substantially decreased fuel consumption for resoaking.

I claim:

1. The process of producing ferrous ingots of killed metal, which comprises pouring the killed meta1 into open-topped molds, providing a hot top for each of the molds, allowing the metal in the molds to stand until at least the major portion of the non-metallic inclusions rise to the top of the metal, chilling the metal adjacent to the top portions thereof until a solidified layer of substantial thickness is formed at the top of the ingot sufiicient to withstand pressure exerted thereon by a plunger of a stripping ram employed to remove the mold, removing the mold from the ingot while the said'ingot is still molten internally, and transporting the still partially molten ingot to a soaking pit.

2. The process of casting ferrous metal ingots r of killed metal, which comprises casting molten metal into and open-topped mold provided with a hot top, allowing the metal tostand until segregation of the non-metallic inclusions rises the mold, applying a chilling method to'the upper portions of the metal in the mold until there is formed a solidified layer of metal of suificient thickness to withstand holding pressure ring the ingotwhile still interiorly molten to a portion of the metal while leaving the metal interiorly molten, and removing the thus partially solidified ingot from the mold. V

4. In the casting of ingots 01 killed steel, the

- tion of a substantially thick layer of solid steel.

steps which consist in pouring molten killed steel into an open-topped ingot mold, mounting a hot top for the mold the molten steel to an ingot from the mold.

stand in the mold until segregationroi non metallic inclusions rises to a. point adjacent to the top of the molten steel, chilling the top portions of the molten steel to cause solidification of a substantially thick layer 'ofsolid steel thereon, while leaving the ingot interiorly molten, and removing the resulting partially solidified'ingot from the mold.

' 5. In the casting of ingotsor killed steel, the

steps which consist in pouring molten killed steel into an open-topped ingot mold,- mounting a not top for the mold allowing the molten steel to stand in the mold until at least the major portion of inclusions have. risen to the top of the molten steel, chilling the top portions by directing water against the said top portions to cause solidiflca thereon, while leaving the ingot interlorly molten, and removing the resulting partially solidified GEORGE WALTER HUMIS.