US2893085A - Methods of casting steel bodies - Google Patents

Description

July 7, 1959 E. JOHANSS'ON ET AL METHODS OF CASTING STEEL BODIES Filed Feb. 17, 1955 ELECTR0DE \C;q :pam

I6 :1: I ELECTRODE INVENTORS Erik Johorzsson.

v. E L115 Erik m'lhelmHeliz-c F 3 (Ya/ 10mm,, wmnlzbn A TTOFPNEYS United States Patent mangoes METHODSOF CASTING STEEL B'ODIES Johansson, Motala, andiElisErik Wilhelm 'Helin, Goteborg; Sweden, assignors to Elektriska Svetsningsgktiebolaget, Goteborg, Sweden, a corporation of we'rlen Application February 17, 1955, Serial No. 488,950

Claims pri'ority, application *SwedenMarch 20, 1954 3 Claims. (Cl. 22- 216) :Thisi'nvention relates to the product-ionof ingots or other castbodies'ofkilled steel. More particularly, the 'invention relates to methods of forming a steel casting in which, after the molten steel has beenpoured into a mold and before the body of :molten 'steel has -a completely solidified, {hfifil energy'is .rapplied to the upper'surface of saidwbodyzin order to maintainapool of liquid steel until i all other parts of the casting-have-solidified.

When castingingots of killed steel itis-customary 'to xemploy a so-called'hot top placed on top of the mold jproper or=inserted in-the upper part of the moldiproper, i inordertoacontrol and tore'duce theipipe formationwan'd to re'duce the=volumeofthe1part of the casting which has --to'-be cropped. It is alsoknown during'solidification of the-ingot-toapplyheat energy to 'themetal containedin the hot top by means of oXy-acetylene flames directed against the surface of the metal or=by-rneans of-an electr-ic arc'maintained betweenthe surface of the metaland :an electrode'the end of whichis submer ged in ablanket -f= slag or flux covering said surface. Said last-mentioned methods have in-many cases proved'zto 'resultin a' substanttial improvement ofthe ,yieldof'sound steel. However, the still remaining metal loss will generally 'be large enough to render further improvement highly desirable, particularly lIlthCIPI'OdllCtiOIl of'1arge"ingots,'=for which a hot .top having a correspondingly large :innerdiameter has tobeemployed.

:Thepresent invention has'for itsigeneral objectto provide 'an improved m'ethodof forming a killed: steel casting resulting in a particularly high yield of sound metal. Another objectis toprovide amethod of torming-a killed s'teelingotinwhich the solidification process of the ingot is so controlled that-the "impurities presentin the metal body will be 'concentratedlto a comparatively thin top stratum of the solidifiedingot. Another object is the provision of a method of forming a-killed steel ingot in which the top end ofthe solidified ingot will-he terminated by-asubstantially flat surface surrounded by athin annular rib only. Still another object is the .provis'ion of a method of forming a killed steel casting in which the amount of heat energy required tobe applied to the upper surface of the metal body for maintaining the pool of liquid steel is comparatively small, even inthe case of large ingots.

According to a principal feature ofthe invention, an improved control of the temperature distribution and of the solidification iprocess in theupper part'of the casting is eifectedthereby that'heat energy-is applied, not only to the upper surface of the metal body as in-the known method, but also*tothe"outside of the part of the mold confiningthe upper-part ofthe metal body.

Other features and advantages of the invention will be clear from the following description of various manners of carrying it out in practice and from the accompanying drawing, in which 'Fig. 1 is a view in vertical -section of the upperpart of a mold provided'with a hot top adapted for carrying out the present invention,

Figs. 2 and 3 are each a'view taken in the same-manner as Fig. 1 of the upper parts of a mold provided with another type of hot top suitable for carrying out the present invention.

The ingot mold illustrated in Fig. 1 consists of a cast iron main body 1, or the mold proper, and of a hot-top or shrink head resting on the upper edge of the mold proper. The hot top is formed by an outer case 2 of refractory material, for instance firebrick, and an inner conical sheet-steel member 3, "the bottom'end of which is provided with a flange 4 inserted between the mold 1 and the outer case 2. The annular space formed between the cone 3 and the outer caseZ contains a filling 50f coke .orcharcoal-or some similar combustible material. To produce an ingot, a charge of killed steel is poured 'into the mold to the level represented by the dotted line 6. Immediately thereupon, a quantity of powdered 'or granulated slag-forming material isdeposited on the surface o'fthemolte'n metal to forrnalaye'r or-blanket'of slag or flu); on said surface, and an electric arc is initiated 'betweenthe surface of the molten metal and an electrode, for instance a graphite electrode, the end of which is-imrnerse'd into said layer or blanket of slag-forming'material. The type of electrode used, the composition 'of'the -slag forming material and the means through which the -arc isinitiated and the electrode is maintained at'a-suitable distance'frornthe level of the liquid metal areall old in the art and need not be described here. The coke -or charcoal filling is ignited by the heat of the molten metal and burns slovvly in the 'air'ga'iningaccess through 'theopenupper end-of the-annular space. The'heatdeveloped by the burning fuel assists the arc'in'maint-aining "a'pool of liquid metal under the slagblanket-during-the period of solidification of the ingot. result of the increased'temperature of the part (cone 3) As a particular of the 'hot 1 top contacting Y the A metal body caused by the surrounding layer of burning fuel, the pool of liquid metal will be substantially'broaderthan in a hottop'of ing to a predeter'r'nined time schedul'e'or according to' obs'erv'ationof the level of the pool of liquid'rnetal. The volume offuel contained in the space 5 should be suflicient f'orthe entire period of treatrnent, as the introduction "of fre'sh -'fuel in the course of the treatment is liable 'to-cause difficulties. Preferably the major 'partof the fuel s'hould still be unconsumed on'termination 0f the -treatment,'that is, when all'parts of theingot have' solidified. Thelin'e 7 represents the outline of the upper surface of the solidifiedingot, the layer of frozen'slagrep'osin'g thereon being'not shown. As shown, said 'surfacehas a substantially'flat shape apart from a thin circumferential flange or rib formed by metal solidified in contact with the cone 3 during the shrinking period. 'For'compaiis'on, the "line 8 indicates the approximate outline of the top portion of an ingot treated in the same ma'nnerbut forthe replacementof'the fuel layer '5 by a layer of refractory sand. The'shape shown maybe'takenastypical for the top :portion of ingots treated with electric arc heating in hot tops of'usual types. It'will'be noted that the'volume 'ofimetal contained in the annular rib of the ingot obtained with the method according totheinvention is much smaller than the volume of the corresponding rib or crater wall of the ingot obtained with the known method. The segregations and impurities which are al ways present in the upper part of a killed steel ingot are substantially concentrated to a thin stratum immediately below the flat upper surface, so that only a thin slice of metal is required to be removed from the upper part of the ingot to obtain a body of perfectly sound metal of homogeneous composition.

Fig. 2 illustrates the carrying out of the invention with a hot top of modified design in which the inner sheet metal member is formed with a cylindrical portion 9 and a conical portion 10. The conical portion serves to bridge or soften the transition between the cross-section of the cylindrical portion 9 and the cross-section of the mold proper 11. The solid fuel layer 12 supports a cast iron ring 13 which maintains the fuel in a uniformly packed condition during the combustion period and which also serves to limit the access of air to the fuel. The volume of molten steel poured into the mold is so adjusted that the top surface 14 of the solidified ingot will be approximately on a level with the lower edge of the cylindrical portion 9 of the sheet metal member. The line 15 indicates the level of the metal as just poured. The temperature conditions should be so adjusted that the volume of metal solidifying on the wall of the cylindrical portion 9 is inappreciable, or not above /2% of the total weight of the ingot. Thus, the volume of the space confined by the cylindrical portion 9 below the level 15 will be substantially equal to the shrinkage of the metal body on solidification.

Fig. 3 shows another type of a hot box which may be used for the purpose of the invention. In this case, the space between the sheet metal member 16 and the refractory outer case 17 contains a filling of foundry sand, dolomite grit or some similar loose refractory material 18 having embedded therein an annular electric heater 19 supplying the additional heat energy required according to the invention. Preferably said heater should be switched on in advance so as to thoroughly heat the hot top before the pouring of the steel.

When a layer of solid fuel is employed to provide the additional heat energy required, as in the cases illustrated in Figs. 1 and 2, the rate of heating obtained is influenced by several factors, as the composition and the piece size of the fuel and the supply of air to the fuel, any or several of which factors may be utilized for adjusting the heat. In some cases it may be expedient to employ a mixture of pieces of fuel and pieces of refractory, as dolomite, instead of fuel alone. To provide the amount of air required for the combustion it will sometimes be useful or necessary to arrange special ducts or ports for admitting the air to the fuel and/ or for leading away the combustion products, particularly when the height of the fuel layer is comparatively large. For in stance, a hot top of the general type illustrated in Fig. 1 may be provided with radial ports in the lower portion of The outer case of the hot top does not have to be constructed of refractory material and may consist, for instance, of cast iron or steel.

Instead of a fuel requiring air for its combustion, it is within the invention to use some exothermically reacting mixture having a comparatively low rate of reaction, so that it will develop heat substantially during the entire period of solidification of the ingot. It is also possible to provide the required heat energy by the combustion of a combustible gas supplied to a space provided between the inner wall and the outer case of the hot top.

According ,to still another modification of the invention, the supplementary heat energy required may be provided by means of an inductor disposed outside a metallic inner wall of the hot top. Said inductor may consist of a coil of water cooled copper tubing disposed substantially in the same manner as the ohmic heater 19 of Fig. 3. The inductor may be adapted to be energized by a high-frequency alternator, or by the network through a stepping-down transformer. The inductor will cause heat to be developed not only in the inner wall of the hot top but also in the volume of metal enclosed thereby.

In carrying out the method according to the invention, it is generally preferable to apply the are energy as well as the additional heat energy as soon as possible after the metal has been poured. It is sometimes difiicult, however, to avoid some delay, which may cause the formation of a more or less complete roof or vault above the body of liquid metal. To melt said roof or vault, or to prevent the same from forming, a quantity of some exothermically reacting mixture, such as one of the usual anti-pipe compounds, may be applied on top of the metal body after pouring.

While the invention has been described above with particular reference to ingot melds provided with hot tops, it should be understood that the invention is not limited to the use of hot tops and that the invention comprises any method covered by the appended claims irrespective of the means required for carrying out said method.

We claim:

1. A method of forming a steel casting which comprises the steps of pouring a body of killed steel into a mold; maintaining a blanket of flux over said body of steel; maintaining a pool of liquid steel immediately below said flux blanket by applying electrical energy to the upper portion of the body through at least one electrode spaced therefrom and extending through said blanket of flux until all other portions of the casting have solidified, said electrical energy input being insufiicient, in the absence of any additional source of heat, to prevent a rim zone of frozen metal having a substantial thickness 1 from progressively forming around said pool during the the external case 2, or spacers may be inserted between the case 2 and the bottom flange 4 of the cone 3 to provide an annular slot between said members. In another variant, a perforated extra cone or sleeve is disposed be tween the fuel layer and the external case so as to provide a free space or duct therebetween to which the air has access at its upper end. These various possibilities are mentioned by way of example only. Suitable valves or dampers may be provided to allow easy adjustment of the rate of supply of the air to the fuel.

The inner sheet-metal member of thethot top may be provided with a coating of refractory material on one or both sides, preferably on the side facing the fuel, in order to prevent direct contact between the fuel and the liquid metal if the sheet metal member should melt or be burnt through. It is also possible to construct the inner wall of the hot top entirely of refractory material, such as sintered alumina.

sinking of the pool level attending the gradual shrinking of the body of steel, whereby the formation of pipes is substantially suppressed, and heating the part of the mold confining the upper portion of the metal body by means of an additional source of heat energy disposed outside of said part of the mold to a temperature at which said pool of liquid steel extends during substantially all of the period of shrinking of the steel body over substantially all of the cross-section of the space enclosed by said part of the mold.

2. A method of forming a steel casting which comprises the steps of pouring a body of killed steel into a mold having a restricted upper part; maintaining a blanket of flux over said body of steel; maintaining a pool of liquid steel immediately below said flux blanket in the portion of the body contained in said restricted upper part by applying electrical energy thereto by means of at least one electrode spaced therefrom and extending through said blanket of flux until all other portions of the casting have solidified, said electrical energy being insufiicient in the absence of any additional source of heat to prevent a rim zone of frozen metal having a sub sta'ntial thickness from progressively forming around said pool during the sinking of the pool level attending the gradual shrinking of the body of steel, whereby the formation of pipes is substantially suppressed, and heating the restricted upper part of the mold by means of an additional source of heat energy disposed outside of said part of the mold to a temperature such that a thin shell only of solidified metal will form on said part of the mold throughout the shrinking period of the steel body.

3. A method of forming a steel casting which comprises the steps of pouring a body of killed steel into a mold having a restricted upper part formed by a thin wall member surrounded by a layer of combustible matter; maintaining a blanket of flux over said body of steel; maintaining a pool of liquid steel immediately below said flux blanket in the portion of the body contained in said restricted upper part by applying electrical energy thereto by means of at least one electrode spaced therefrom and extending through said blanket of flux 20 until all other portions of the casting have solidified, said electrical energy being insufficient in the absence of any additional source of heat to prevent a rim zone of frozen metal having a substantial thickness from progressively forming around said pool during the sinking of the pool level attending the gradual shrinking of the body of steel, whereby the formation of pipes is substantially suppressed, and additionally heating the thin wall member through combustion of the combustible matter to a temperature at which said liquid pool extends during substantially all of the period of shrinking of the steel body over substantially all of the cross-section of the restricted part of the space enclosed by the restricted part of the mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,192,617 Gathmann July 25, 1916 1,789,883 Roth Jan. 20, 1931 2,240,405 Kinzel Apr 29, 1941 FOREIGN PATENTS 565,154 Great Britain Oct. 30, 1944 698,303 Great Britain Oct. 14, 1953

Claims (1)

1. A METHOD OF FORMING A STEEL CASTING WHICH COMPRISES THE STEPS OF POURING A BODY OF KILLED STEEL INTO A MOLD; MAINTAINING A BLANKET OF FLUX OVER SAID BODY OF STEEL; MAINTAINING A POOL OF LIQUID STEEL IMMEDIATELY BELOW SAID FLUX BLANKET BY APPLYING ELECTRICAL ENERGY TO THE UPPER PORTION OF THE BODY THROUGH AT LEAST ONE ELECTRODE SPACED THEREFROM AND EXTENDING THROUGH SAID BLANKET OF FLUX UNTIL ALL OTHER PORTIONS OF THE CASTING HAVE SOLIDIFIED, SAID ELECTRICAL ENERGY INPUT BEING INSUFFICIENT, IN THE ABSENCE OF ANY ADDITIONAL SOURCE OF HEAT, TO PREVENT A RIM ZONE OF FROZEN METAL HAVING A SUBSTANTIAL THICKNESS FROM PROGRESSIVELY FORMING AROUND SAID POOL DURING THE SINKING OF THE POOL LEVEL ATTENDING THE GRADUAL SHRINKING OF THE BODY OF STEEL, WHEREBY THE FORMATION OF PIPES IS SUBSTANTIALLY SUPPRESSED, AND HEATING THE PART OF THE MOLD CONFINING THE UPPER PORTION OF THE METAL BODY BY MEANS OF AN ADDITIONAL SOURCE OF HEAT ENEEGY DISPOSED OUTSIDE OF SAID PRT OF THE MOLD TO A TEMPERATURE AT WHICH SAID POOL OF LIQUID STEEL EXTENDS DURING SUBSTANTIALLY ALL OF THE PERIOD OF SHRINKING OF THE STEEL BODY OVER SUBSTANTIALLY ALL OF THE CROSS-SECTION OF THE SPACE ENCLOSED BY SAID PART OF THE MOLD.

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