US2513602A - Exothermic composition for use in molds for casting molten metal - Google Patents

Description

Patented July 4, 1950 UN i ii S TES EXOTHERMIC COMPOSITION FOR USE IN MOLDS FOR CASTING MOLTEN METAL Canada No Drawing. Original application May 10, 1943,

Serial No. 486,431. Divided and this application August 29, 1947, Serial No. 771,387

12 Claims.

This invention relates to metallurgy and has for an object the provision of an improved metallurgical method or process and the provision of an improved metallurgical product. More particularly, the invention contemplates the provision of an improved method or process for producing sound castings of metals such as iron and steel. The invention further contemplates the provision of products which may be employed in casting operations to inhibit or reduce piping during solidification of metal in casting molds and ingot molds. The invention also contemplates the provision of improved exothermic reaction mixtures suitable for use in producing slag products having desirable characteristics and an improved method of improving the ignition and propagation characteristics of exothermic reaction mixtures.

When steel is poured into a mold, it forms almost immediately a thin skin of frozen metal against the cold surface of the sand or iron of the mold. The radiation of heat thereafter necessarily takes place through these surfaces, and, therefore, a casting usually will complete its solidification by the formation of thicker and thicker layers of solid metal around all the sides. The top portion, however, usually will remain molten longer than the rest because the hottest metal is usually at this point, having been the last to leave the ladle, and, also, because the heat is not conducted away by the air as fast as by the walls of the mold. This is especially true where the casting is poured into an iron mold, for example, in the case of ingots. But it is evident that at some period a stage will be reached when all the outside of the ingot, or casting. will be covered by a skin of solid metal while the interior will still be liquid. The liquid interior will continue to freeze and will, at the same time, contract. The result will be the shrinking of the molten mass and, consequently, the formation of a cavity, known as a pipe, in the interior.

The portion of the steel containing the pipe is of .course defective and must be discarded at some time subsequent to casting. In the casting of ingots, the upper part, which contains the pipe, is cut off during the rolling or forging and goes back to the furnace to be remelted as scrap. In the casting of steel castings, there is a large adjunct to the castings situatedabove it, and so regulated in size and otherwise that it freezes after the casting itself, and thus contains a supply of molten metal which is available to fill any cavity that forms in the casting. This adjunct is cut off when the casting has cooled. In other words, the riser or feeder, as this extra part is called, serves the same purpose for a steel casting as the upper part of an ingot does for the ingot.

I have discovered that piping may be inhibited or. reduced substantially by covering the surfaces of molten metal in ingot molds and in the risers and gates of casting molds with layers of slag of controlled fluidity at temperatures initially higher than the melting or freezing temperatures of the molten metals within the molds. The heat of the slag prevents solidification of the metals in the upper portions of the molds and thereafter the slag layers form insulating blankets which prevent rapid dissipation of the heat contained in the molten metal and thus cause the metal to be maintained in the molten state for longer periods of time. Supplies of molten metal for filling cavities formed in the casting, therefore, are maintained for longer periods of time and pipe-forming tendencies are reduced. The sensible heat of the slags applied to the surfaces also aids in maintaining the metal in the molten state.

The use of a fluid slag is objectionable because it may tend to flow with the molten metal into the cavity resulting from shrinkage and thus produce, a defective casting. In practicing my invention, I employ or produce slag of lower fluidity (or higher viscosity) than the molten metal of the casting to which it is applied, thus providing for preferential flow of molten metal into the shrinkage cavity and avoiding the introduction of slag into the cavity. The slag employed may be relatively viscous, plastic or even substantially solid.

In accordance with the invention, slag may be applied to or formed on a molten metal surface in any suitable manner or at any suitable temperature above the melting or freezing temperature of the metal. 'In a preferred method or process of the invention, I employ slag at atemperature at or near, or even above, the casting or pouring temperature of the metal in order to prevent any substantial transfer of heat from the metal to the slag initially. By employing slag at a temperature at or near the casting or pouring temperature of the metal, dissipation of heat from the molten metal is greatly reduced. When the slag is employed at a temperature above the casting or pouring. temperature of the metal, heat is transferred from the slag to the metal. When the molten metal is at a temperature lower than the casting or pouring temperature at the time of application of the slag, heat may be transferred from the slag to the metal even though the temperature of the slag is below the casting temperature of the metal. Slag may be employed in any suitable quantity capable of accomplishing the desired degree of inhibition or prevention of pipe formation.

The slag employed maybe formed and applied to the metal surfaces in any suitable manner, but

I prefer to form slag layers by placing in con'-,

tact with the molten metal within casting molds exothermic reaction mixtures capable of igniting upon contact with the metal and capable upon ignition of reacting exothermi'cally to produce slag products having suitable compositions and temperatures. Exothermic reaction mixtures of the invention preferably are of such compositions 'as to be capable of reacting upon ignition to produce slags having temperatures not substantially lower than the temperatures of the molten metals at the times of application of the slag thereto.

In carrying out a method or process of the invention, an exothermic reaction mixture of any suitable composition capable of reacting upon ignition to produce slag having a suitable composition and temperature may be employed. The preferred exothermic reaction mixtures of the invention are mixtures capable of reacting to produce iron oxide-bearing 'slags. Such reaction mixtures may comprise iron oxide, oxidizing material such as sodium nitrate or sodium chlorate.

non-carbonaceous reducing material, heat-absorbingmaterial and a small amount of finely.

ably is present in amount suilicient to quickly.

thicken any fluid slag produced as the result of the reaction. Heat-absorbing material may be employed in amounts equal to about five to ten percent to more or less. of the weight of the complete mixture. Finely divided carbon for aiding in initiating and propagating the reaction may be employed in any suitable small amount. Usually an amount equal to less than about one percent of the weight of the complete mixture produces satisfactory results.

Finely divided carbon may be incorporated in any suitable reaction mixture in accordance with the invention for the purpose of improving the ignition and propagation properties. Reaction mixtures of the invention may be employed for producing any modifying slag products in any suitable metallurgical operations.

Iron oxide may be employed as ferric oxide (F6203) or as magnetite (Feaoili The iron oxide may be obtained from iron ore or from mill scale or from any other suitable source. Mill scale is a highly satisfactory source of iron oxide. The reducing material may be aluminum, silicon, magnesium or calcium or a mixture or alloy containing two or more of these elements and which may contain one or more other elements. When aluminum is employed as the reducing agent, oxidizing material such as sodium nitrate may be omitted from the mixtures. Ferrosilicon may be 4 employed advantageously and economically as reducing material. Any grade of ferrosilicon may be employed, but I prefer to employ ferrosilicon containing silicon in an amount in the range fifty to seventy-live percent by weight. Suitable heatabsorbing materials include carbon .and quartz. Carbon in the form of crushed electrodes, charcoal or coke may be employed satisfactorily.

The components of the reaction mixtures of the invention, other than the heat-absorbing material, preferably are intimately. mixed (as by grinding together) in the form of particles small enough to pass a -mesh screen. Heat-absorbing materials preferably are employed in the form of particles as large as about one-half inch or'larger in size and not smaller than those capable of passing a 20-mesh screen. A .mixture of particles in the range 4 to 20-mesh 0r 20-mesh to one-half inch produces satisfactory results. The reaction mixtures may be employed in the form of loose powders or in the form of agglomerates in which the particles are bonded together by means of the oxidizing material or by other suitable bonding means.

A reaction mixture of the invention, for all practical purposes, may be considered as consisting of two component parts, namely, (1) a heat-generating and slag-producing part comprising reducing material, oxidizing material and slag-forming material and (2) a heat-absorbing part. The function of the heat-generating and slag-producing part is to generate a. substantial amount of heat and develop a high temperature substantially instantaneously, and the function of the heat-absorbing part is to thicken liquid or relatively viscous slag. which will retain the heat generated and remain in place as a porous insulating covering for the metal.

When a reaction mixture of the invention is contacted with the surface of molten metal, such as iron or steel in a mold, the components of the heat-generating and slag-producing part react immediately to generate heat and produce a hightemperature slag. Because of the necessity of producing a high-temperature slag to insure maintenance of the upper surface portion of the metal in the molten state, the fluidity of the slag will be undesirably high initially. The heatabsorbing material commences to function substantially immediately after production of the slag to absorb heat and thus reduce the temperathe metal and the relatively low-temperature slag produced by thickening will insure maintenance of the metal in a properly molten state.

The relatively coarse particles of heat-absorbing material form nuclei on which fluid slag produced by the exothermic reaction collects with the result that a portion of the heat is absorbed and the slag is thickened. By employing relatively coarse heat-absorbing material, heat absorption is relatively slow, sumcient heat being absorbed to effect thickening of the slag without undesirable initial reduction of the temperature of the slag and without dissipation of the heat generated. The use of finely divided heat-absorbing material such as quartz would result in an undesirable reduction of the temperature of the slag through too rapid absorption of heat and probably through endothermic reactions with the slag. Finely divided carbon such as charcoal reacts with the oxidizing material to generate heat, while coarse carbon is substantially nonreactive in the presence of the finely divided noncarbonaceous reducing agent and functions initially substantially entirely as a heat absorption agent.

In the preferred exothermic reaction mixtures of the invention, I employ coarse carbon, such as coke, as the heat-absorbing material. After ignition and thickening of such a reaction mixture and during subsequent cooling and solidification of the molten metal, the carbon oxidizes through contact with the air to generate additional heat and causes the production of porous slag both of which factors improve the insulation properties of the slag,-causing the cooling period to be prolonged.

It is desirable, particularly for use in small ingot molds and in the gates and risers of casting molds, that the reaction mixture be applied to the metal immediately after pouring has been completed and that it be capable of reacting to develop a high temperature substantially instantaneously to prevent the formation of a skin of solid metal on the surface of the molten metal.

Reaction mixtures comprising sodium nitrate, ferro-silicon, iron oxide and heat-absorbing material such as coke or quartz and which also contain small amounts of finely divided carbon may be employed with particular advantage. Such mixtures ignite substantially instantaneously when placed in contact with molten iron or steel. They react rapidly to generate large quantities of heat and produce high-temperature, fiuid iron silicate slags which are thickened substantially immediately through the action of the heat-absorbing material. Such mixtures, when placed in contact with molten iron or steel, react to produce slags having temperatures of about 2900 F.

In the production of large ingots, the heatgenerating and slag-producing part and the heat-absorbing part of'the reaction mixture may be placed on the surface of the metal separately. Thus, for example, the heat-generating and slag producing part may be placed in contact with the molten metal to produce a high-temperature fluid slag, and the slag may be thickened by the subsequent addition of heat-absorbing material to form slag of lower fluidity than the molten metal.

The following example illustrates exothermic reaction mixtures of the invention which have been employed effectively in carrying out the method or process of the invention, proportions of the components being shown in parts by weight:

Sodium nitrate (NaNOa) 25- Ferrosilicon (75% Si) 25 Mill scale '70 Coke Charcoal 0.5

The above components were intimately mixed by grinding charcoal, sodium nitrate, ferrosilicon and mill scale together in a ball mill to form a mixture consisting of particles about ninety-five percent of which were small enough to pass a 100- mesh screen, and the resulting mixture was uniformly mixed with coke consisting of particles small enough to pass a 4-mesh screen and too large to pass a 20-mesh screen. The complete mixture was applied to the surfaces of molten metals in the hot tops of ingot molds and in gates and risers of casting molds immediately after the metals had been poured. In each case the mixture was ignited immediately and the reactions proceeded smoothly to completion, forming hightemperature slag layers which completely cov-- ered the surfaces of the metals. After the metals had solidified, the castings were examined to ascertain the extent of piping. It was found that only about forty percent (40%) of the upper portions of the hot tops contained pipe. Comparative tests were conducted employing similar molds, metals and casting temperatures but employing so-called pipe eliminator materials proposed heretofore for use in casting operations with the following results:

Per Cent of Hot To Length mmraining Pipe Prior Art Pipe Eliminator HUGH! FP coazowo the invention, an exothermic reaction mixture is,

contacted with the upper surface of molten metal in a riser or gate or hot top immediately after casting of the metal. The reaction mixture preferably is of such composition as to be capable upon ignition of reacting to produce slag having a temperature higher than the temperature of the molten metal at the time of application of the slag thereto. The slag preferably is maintained in contact with the metal until the metal has solidified.

The method or process and the products of the invention may be employed advantageously to reduce the depths of hot tops employed in ingot casting operations. Thus, the invention permits a substantial saving in operating costs by reducing the quantities of metal which must be removed from ingots and remelted as scrap. The invention also permits substantial savings in operating costs in the production of castings by providing for the maintenance of a sufiicient supply of molten metal in risers to insure the filling-of cavities formed during cooling and solidification of the castings and thus insuring the production of sound castings.

This application is a division of my application Serial No. 486,431, filed May 10, 1943 (U. S. Patent No. 2,426,849, dated September 2, 1947).

I claim:

1. An exothermic reaction mixture suitable for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse heat-absorbing material, the iron oxide, sodium nitrate and non-carbonaceous reducing material being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of 76 reacting exothermically to produce molten slag,

7 the heat-absorbing material being present in amount sumcient to-thicken the slag and the finely divided carbon being present in amount sufilcient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

2. An exothermic reaction mixture suitable for use in providing slagilayers on the surfaces of molten metals in castin molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse carbon, the iron oxide, sodium nitrate and non-carbonaceousreducing material being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce molten slag, the relatively coarse carbon being present in amount sufficient to thicken the slag and the finely divided carbon being present in amount suflicient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

3. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material comprising silicon and relatively coarse heat-absorbing material, the iron oxide, sodium nitrate and non-carbonaceous reducing material being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce molten slag; the heat-absorbing material being present in amount sufficient to thicken the slag and the finely divided carbon being present in amount sufficient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

4. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse heat-absorbing material, the reducing material being present in the reaction mixture in amount sufilcient to react with a portion of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce iron oxide-bearin slag, the heat-absorbing material being present in amount suflicient to thickenthe slag .and the finely divided carbon being present in amount sufllcient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

5. 4n exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse carbon, the reducing material being present in the reaction mixture in amount sufilcient to react with a portion of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and beingsoastobecapableuponigiiition ofthereactionmixtureof reacting exothermically to produce iron oxide-bearing sing, the relatively coarse carbon being present in amount sufilcienttothiaentheslagandthe finely divided carbon helm present in amount sufiicient toreactwithaportionofthesodiumnitrateto generate heat and came the reaction mixture to ignite and burn readily.

6. An emothermiereaction mixture forv use in providing slag 1am on the surfaces of molten metalsincastingmoldsandingotmoldstoinhibit or reduce 1191M. comprising finel divided iron oxide, sodium nitrate, finely divided carbon and non reducing material and relatively coarse cite, the reducing material being present in the reaction mixture in amount sufiicient to react with a portion of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proporflrmed as to be capable upon ignition oi the reaction mixture of reacting exothermically to produce iron oxide-bearing slag, the coke being present in amount sufilcient to inhibit or prevent the producflon of fluid slag and the finely divided carbon being prment in amount sumcient to react with a. portion oi the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

7. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely, divided iron oxide, sodium nitrate. finely divided carbon and non-carbonaceous reducing materialv comprising silicon and relativel coarse heat-absorbing materiaL the reducing material being present in the reaction mixture in amount suflicient to react with a portion of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermicall to produce iron' oxide-bearing slag, the heat-absorbing material being present in amount suilicient to thicken the slag and the finely divided carbon being present in amount sufiicient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily. Y

8. An exothermic reaction mixture for use in providing slag flyers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non reducing material comprising aluminum and relatively coarse heatabsorbing material, the reducing material being present in the reaction mixture in amount sufficient to react with a portion of the sodium niilcient to thicken the slag and the finely divided carbon being present in amount sufficient to react with a portion of the sodium nitrate to generate heat and-cause the reaction mixture to ignite and burn 9. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate, finely divided carbon and ferrosilicon and relatively coarse heat-absorbing material, silicon being present in the reaction mixture in amount sufiicient to react with a portion of the sodium nitrat and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in'such quantities and being so proportioned as .to be capable upon ignition of the reaction mixface of molten metal within the mold an exothermic reaction mixture comprising finelydivided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse heat-absorbing material and thereby forming a layer of hot slag in contact with the molten metal, and maintaining the metal and slag in contact until the metal has solidified, the reducing material being present in the reaction mixture in amount suificient to react with a portion of the sodium nitrate and to reduce a portion only of the iron oi the iron oxide. the components of the reaction mixture being present in such quantities and being so propor- ,tioned as to be capable upon ignition of the reaction mixture of reacting exothermicaily to produce iron oxide-bearing slag, the heat-absorbing material being present in amount suilicient to inhibit or prevent the production of fluid slag and the finely divided carbon being present in amount suilicient to react with a portion of the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

11. The method of producing sound metal casta suitable mold, contacting with an upper suri0 ing material being present in the reaction mixture in amount suificient to react with a portion ofthe sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantitles and being so proportioned as to be capable upon ignition of the reaction mixtur of reacting exothermically to produce molten iron oxidebearing slag, the carbon being present in amount sumcient to inhibit or prevent the production of fluid slag and the finely divided carbon being present in amount suiiicient to react with a portion 01 the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

12. The method of producing sound metal castings which comprises pouring molten metal into a suitable mold, contacting with an upper surface of molten metal within the mold an exothermic reaction mixture comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse coke and thereby forming a layer of hot slag in contact withthe molten metal,

and maintaining the metal and-slag in contact until the metal ,has solidified-the reducing material being present in the reaction mixture in amount suiiicient to react with a portion of the sodium nitrate and to reduce a portion only oi ings which comprises pouring molten metal into a suitable mold, contacting with an upper surface of molten metal within the mold an exothermic reaction mixture comprising finely divided iron oxide, sodium nitrate, finely divided carbon and non-carbonaceous reducing material and relatively coarse carbon and thereby forming a layer of hot slag in contact-with the molten metal. and maintaining th metal and slag in contact until the metal has solidified, the reducthe iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermicall'y to produce iron oxide-bearing slag. the coke being present in amount suificient to thicken the slag and the finely divided carbon being present in amount suflicient to react with a portion oi'the sodium nitrate to generate heat and cause the reaction mixture to ignite and burn readily.

MARVIN J. UDY.

REFERENCES CITED The following references are oi record in the file or. this patent:

UNITED STATES PA Number Name Date 2,142,031 Lorange Dec. 27. 1988 2,243,784 Udy May 27, 1941 2,243,786 Udy May 27, 1941 2,247,262 Udy June 24, 1941 2,276,671 Rentschler Mar. 17, 1942 2,294,169 Francis Aug. 25, 1942 2,426,849 Udy Sept. 2. 1947

Claims (1)

1. AN EXOTHERMIC REACTION MIXTURE SUITABLE FOR USE IN PROVIDING SLAG LAYERS ON THE SURFACES OF MOLTEN METALS IN CASTING MOLDS AND INGOT MOLDS TO INHIBIT OR REDUCE PIPING, COMPRISING FINELY DIVIDED IRON OXIDE, SODIUM NITRATE, FINELY DIVIDED CARBON AND NON-CARBONACEOUS REDUCING MATERIAL AND RELATIVELY COARSE HEAT-ABSORBING MATERIAL, THE IRON OXIDE, SODIUM NITRATE AND NON-CARBONACEOUS REDUCING MATERIAL BEING PRESENT IN SUCH QUANTITIES AND BEING SO PROPORTIONED AS TO BE CAPABLE UPON IGNITION OF THE REACTION MIXTURE OF REACTING EXOTHERMICALLY TO PRODUCE MOLTEN SLAG, THE HEAT-ABSORBING MATERIAL BEING PRESENT IN AMOUNT SUFFICIENT TO THICKEN THE SLAG AND THE FINELY DIVIDED CARBON BEING PRESENT IN AMOUNT SUFFICIENT TO REACT WITH A PORTION OF THE SODIUM NITRATE TO GENERATE HEAT AND CAUSE THE REACTION MIXTURE TO IGNITE AND BURN READILY.