US2293972A

US2293972A - Manufacture of steel castings

Info

Publication number: US2293972A
Application number: US378810A
Authority: US
Inventors: Edward J Dunn
Original assignee: Individual
Current assignee: Individual
Priority date: 1941-02-13
Filing date: 1941-02-13
Publication date: 1942-08-25
Anticipated expiration: 1959-08-25

Description

. Aug l25, 1942- E. J. DUNN MANUFACTURE OF STEEL` CASTINGS F11-ed Feb. 13, 1941 Patented Aug. 25, 1942 UNITED ySTATES PATENT .OFFICE This invention relates to the manufacture of metallic ingots and, particularly, to an improvedl means for covering the molten metal in the tops of ingot molds .to effect aninsulation 'and exothermic condition.

In the usual practice of casting steel ingots, the molten metal is taken/rom the furnace in a liquid state and carried in a ladle, from which it is pouredinto ingot molds 4generally made of cast in the mold, the carbon and other elementsl in the metaltends to segregate, which is, of course, undesirable in that it reduces the vquality of the ingot and the steel.

iron of a square, rectangular, or round section to form ingots which afterwards are shaped in rolling mills to commercial products. The steel in cooling and solidifying in these'molds will, of course, shrink, and solidication .will start immediately after the steel is poured and comes in contact with the inner Walls of the mold.

In such practice, the top of the metal freezes over, leaving a large shrinkage cavity under the surface and, as a result, when the ingot thus formed has nally cooled there will be, due to this shrinkage of the steel, a cavity commonly known as a pipe in the tcp central part of the ingot of substantially a conical shape tapering toward the bottom. The surface of this pipe, when exposed to the atmosphere after .the pouring has been completed, becomes oxidized and this. part of the ingot will not, in the process of rolling or forming into a commercial product, be welded solidly into a homogeneous mass with the rest of the ingot and, consequently, the end of the ingot, on the dead head or crop, as it is sometimes called, containing such pipe must be discarded as scrap; thus, clearly reducing the usable portion of the ingot.

Various means have been employed to -reduce the pipe and increase the recoverable part of the ingot, but none of .them have proved to be very satisfactory. One of the methods most commonly used is tovplace on toppof the ingot mold a hot top, which is either a hollow tile orfavcastv 40a iron box lined with a suitable refractory material.

. The purpose of such a hot top is, of course, to

retain the temperature of the poured liquid steel as long as possible so that the steel in the upper part of the ingot remains molten for a time after the outside of the ingot in contact with the mold walls solidies, thus tending to ll the shrinkage of ingots.

Furthermore, when the top of the molten metal The present invention relates to a means for preventingexcessive shrinkage and piping of the.

ingot and excessive segregation of the metal as it solidies, so as to provide an ingot which is sounder and free from pipe and segregation of carbon and other elements, thereby producing a higher yield of ingot to iinished product.

Accordingly, it is one of the objects of my invention to provide an improved exothermic covering means for the top of the molten metal in an ingot mold so as to prevent excessive shrinkage of this part of the' ingot as it solidies, and an insulating means which maintains the metal molten for a predetermined length of time.

It is another object of the invention to provide an improved exothermic covering means for the top of the molten steel in an ingot mold so as to I prevent excessive segregation of the carbon and other elements, whereby a better ingot is produced having an extremely high yield.

It is a further object of this invention to -pro' vide an improved exothermic covering means for the top of the molten steel in ingot molds having an ash content related to .the carbon content of the steel with which it is used.

It is still another object of the invention to provide an improved exothermic covering means for the top of the molten metal which is simple and inexpensive and, at the same time, one' which is eflicient and eifective in its use.v

Various other objects andadvantages of my in vention-will become more apparent during the course of the following specification and appendedclaims.

The improved means of my invention for insulating molten metal in the tops of ingot molds emot dry`anthracite^coal whichn ImhaveVJ named Dukite. The anthracitecoal is preferably in the form of finely ground4 anthracite slack which is divided into various grades, according to its asli content. River coal (dried), being a low grade, ne anthracite coal which is recov- -ered from rivers by dredging, it having been run into the river during the Washing process of anthracite lump coal, is very practical for use, but it will be understood that anthracite coal from any other source is satisfactory.

It has been found that the dry anthracite coal I or Dukite, when applied to the top surface of the molten metal in an ingot mold, vacts as an solidies and the freezing proceeds downwardly insulation and causes an exothermic reaction which maintains the steel in the hot top molten for a considerable length of time, thus affording a more efficient feeding of the molten metal down into the shrinkage cavity which forms as the ingot solidif'les. 'I'he feeding of the molten metal with the use of Dukite results in substantially a reduced U-shaped cavity where a V-shaped cavity normally occurs. It also has-been found by comparison that dry anthracite coal of various grades of ash content, in the manner as it is proposed to be used according to the present invention, provides ingots with a far greater yield than ingots using other types of insulating means.

The dry anthracite coal or slack is classified preferably into six grades, according to the ash content, as follows:

Grade No. l-having an ash content up to approximately 16 per cent;

Grade No. Z-having an ash content of from approximately 16 to 19 per cent;

Grade No. 3-having an ash content of from approximately 19 to 23 per cent;

Grade No. 1 -having an ash content of from approximately 23 to 26 per cent;

Grade No. 5-having an ash content of from approximately 26 to 28 per cent; and

Grade No. 6-having an ash content in excess of 28 per cent.

It has been found that grades Nos. l, 2 and 3 of Dukite, that is, anthracite coal having an ash content up to approximately 23 per cent, are satisfactory for use with low carbon steel, namely, steel having a carbon crutent up to approximately 0.14 per cent; that grades Nos. 1, 2, 3, and 4, that is, coal having an ash content up to approximately 26 per cent, are satisfactory for use with medium carbonsteel, namely, steel having a carbon content of approximately 0.40 per cent; and that all six grades, that is, coal having an ash content up to'` and in excess-of 28 per cent, are satisfactory for high carbon steels, namely, steels having a carbon content of approximately 0.96 per cent. 'Ihe proper grade of anthracite coal or Dukite" for steels having a carbon content in between or above those given can be con'- veniently found by experimentation.

'I'he following conventional procedure for casting an ingot isemployed, with which the insulating means of 'the present invention is used. The molten metal is carried from the furnace understood that my insulating means may be used with or without a hot top, but it is preferable that a hot top be used, as better results will be benefits in the elimination of piping and segregation and not too long so as to hold back production. For the average size ingot a grade of Dukite" is selected so that the metal remains molten for a period of about one hour and a half,`

which is just about the proper length of time to obtain the maximum benefits therefrom so as to produce an ingot satisfactory in all respects.

In order to ascertain the advantages of the use of the insulating means or "Dukite of my invention over the use of other insulating means, experiments have been made and it has been compared with other types of insulating materiais. To illustrate the results of these experiments, there is shown in the drawing a graph illustrating the effect of the use of anthracite coal or Dukite on carbon segregation, in which the abscissa represents the inches below the hot in a ladle in a manner well known to those skilled in the art, from which the molten metalis poured into the ingot molds. After the proper amount` of molten metal has been poured into any particular mold, according to the present invention Dukite" is applied loosely to the top surface thereof. The particular grade of anthracite coal upon the carbon content of steel being into the molds and with which it' arte be used. Itis preferable that the grades hereinbefore mentioned for steels having corresponding carbon content be used. The anthracite coal or Dukite,.

whenV disposed upon the top of the molten metal, will tend to distribute itselfuniformly over the entire top surface thereof so as to provide an insulating and exothermic blanket thereon, thereby insulating the same. As the main body of the ingot solidies, the metal in the hot top and in the top portion of the mold is maintained liquid 'due to this insulating blanket of anthracite coal or Dukite, thus affordingl more opportunity for a denser -andlless segregated ingot. It will be top junction in the ingot, and the ordinate represents the percentage in variation from the ladle carbon analysisv in hundredths of one per cent. In this graph the'segregation of the carbon in an ingot with the use of the insulating means or "Dukite (Grade No. 3) of my inventionI is compared with the segregation of carbon in ingots where two commercial types of insulating materials were used, these two insulating materials being ones which have given the highest yield of any known commercial coverings heretofore used. It is common practice, a fact which is well known to those skilled in the art, that steel having more than a 10point variation of carbon from'the ladle analysis, that is, more than .l0 per cent variation, unsatisfactory for use and generally discarded. and that when no insulating means is usedl the hot top and about l0 inches below the hot top junction must be discarded, due to the segregation of the carbon in the upper portion of the mold and in the hot top. Referring to the graph, it will be seen that with the use of the two commercial insulating materials or covers, the hot top and about 4 inches below the hot top junction must be discarded.

However, it will' be seen that with the use of anthracite coal or Dukite, according to my invention, that only the metal in the hot top need be discarded, due tothe fact that the metal belowv the hot top junction is within the 10point variation. Thus, it will be seen that with the use of my insulating means there is considerable savings in metal and`th`ere is also considerably less variaanthracite coal having an ash content of over 23 per cent, the average midway carbon variation was 0.036 per cent and the average center variation was 0.074 per cent. Thus, it will be seen that in the low carbon steels the carbon variation was much less in the use of anthracite coal having a low ash content (less than 23 per cent) than with the use cf coal having a higher ash content (over 23 per cent);

With theuse of a grade of anthracite coal or Dukite" having an ash content up to 26 per cent for insulating steelhaving a medium carbon content (approximately 0.40 per cent) it was found that the average midway carbon variation from the ladle analysis was 0.042 per cent; that the average center carbon variation from the ladle analysis was 0.058 per cent; and that with the use of anthracite coal having an ash content in excess of 26 per cent, the average midway variation was 0.039 per cent and the average center variation, 0.138 per cent. Thus, it will be seen that in the medium carbon steel, the carbon variation was much less in the use of anthracite coal having a low ash content (less than 26 per cent) than with the use of coal having a high ash content (over 26 per cent) With the use of any grade of anthracite coal for insulating high carbon steel (approximately 0.96.per cent)it was found that the average midway carbon variation from the ladle analysis was 0.020 per cent and that the average center carbon variation was 0.060 per cent. Accordingly, it will be seen that it is important that a grade of anthracite coal having the proper ash content be used, in order to obtain an ingot having the least carbon variation. That is to say, the anthracite coal used for insulating should be selected in view of the carbon content of the particular steel with which it is adapted to be used. Therefore, it will be seen that the ash content of the anthracite' coal is critical with respect to the carbon content of the steel.

While the insulating means or Dukite of my invention may be used without the use of a refractory hot top, the benefits derived therefrom are not as pronounced as if a hot top were used.

As a result of my invention, it will be seen that there is provided an improved and inexpensive means for insulating the molten metal in the tops of ingot molds which reduces and practically eliminates the pipe in the top of the ingot and at the same time reduces segregation of the carbon and other elements in the steel to a minimum, thereby producing an ingot having a greater yield and one of much better quality. With the use of the insulating material of my invention, it has been found that the yield of an ingot is as much as 90 per cent, which is much greater than the yield obtained by the use of any otherinsulating means.

From the above description of my invention, it o y.

will be apparent that many modifications of the same may be devised within the scope thereof and all such modifications are contemplated as may fall within the scope of the appended claims.

1. In the manufacture of metallic castings, the method of casting the same which comprises pouring the molten metal into a mold, selecting a ry anthracite coal in the form of slack having an sh content in an amount which is related to the carbon content of the metal, and applying said slack loosely to the top surface of the molten metal so as to provide a uniform insulating blanket over the entire top surface thereof, whereby excessive piping and excessive segregation of the metal is prevented. y

2. In the manufacture of'steel castings, the method 'of casting the same which comprises pouring the molten metal into a mold, selecting a dry anthracite coal in the form of slack having an ash content inan amount related to the carbon content of the steel, said slack having an ash content up to approximately 23 per cent for steel having a carbon content of .approximately 0.14 per cent, and an ash content up to approximately 26 per cent for steel having a carbon content of approximately 0.40 per cent, and applying said' slack loosely to the top surface of the molten steel so as to provide a uniform insulating blanket over the entire top surface thereof whereby excessive piping and excessive segregation of the steel is prevented.

3. In the manufacture of steel castings and the like, the method of casting the same which comprises pouring the molten metal into a mold, selecting a dry anthracite slack having an ash content of a predetermined amount and in rela'- tion to the carbon content of the steel being cast with said slack having an ash content of up to approximately 26 per cent for steel having a carbon content of approximately 0.40 per cent, and applying said slack loosely to the top surface of the molten metal so as to provide a uniform insulating blanket over the entire top surface thereof whereby excessive piping and excessive segregation of the metal is prevented.

4. In the manufacture of steel castings and the like, the method of casting the same which comprises pouring the molten metal into a mold, selecting a dry anthracite slack having an ash content in an amount which is relatedto the carbon content of the steel being cast, said slack having an ash content up to and in excess of 28 per cent. for steel having a carbon content in excess of approximately .40 per cent, and applying the said slack loosely to the top. surface of the moltenl metal in the mold so as to provide a uniform insulating blanket over the entire top surface thereof whereby excessivepiping and excessive segregation of the metal are prevented.

EDWARD J. DUNN.