US3720552A - Exothermic composition for use in steelworks and in foundries - Google Patents

Abstract

THIS EXOTHERMIC COMPOSITION CAN BE USED IN CASTING MOLTEN METALS IN STEELWORKS AND IN FOUNDRIES SO AS TO DELAY SOLIDIFICATION AND TO FILL UP THE CAVITIES CAUSED BY THE SHRINKAGE OF THE METAL DURING SOLIDIFICATION. IT CONTAINS IN A KNOWN MANNER ALUMINUM, AT LEST ONE OXIDISING AGENT AND AT LEAST ONE FILLER. IT ADDITIONALLY CONTAINS A SOLID EASILY COMBUSTIBLE CARBONACEOUS MATERIAL IN A FINELY DIVIDED STATE. THIS MATERIAL CAN BE PAPER OR PLASTIC. IN CASE OF PAPER, THE PROPORTION AS USED IS AT LEAST 5%. THIS PROPORTION IS COMPRISES BETWEEN 0.2 AND 5% IN CASE OF PLASTIC. THE COMPOSITION ADVANTAGEOUSLY CONTAINS FINE PARTICLES OF A COMPOSITE CONSISTING OF A FILM OF ALUMINUM DEPOSITED ON A SUPPORT OF A SOLID EASILY COMBUSTIBLE CARBONACEOUS MATERIAL SUCH AS PAPER OR PLASTIC.

Description

United States Patent 3,720,552 EXOTHERMIC COMPOSITION FOR USE IN STEELWORKS AND IN FOUNDRIES Simon Lustigue, 28 Avenue Leman, Lausanne, Switzerland No Drawing. Filed Mar. 15, 1971, Ser. No. 124,508 Int. Cl. C06b 19/02 US. Cl. 1493 Claims ABSTRACT OF THE DISCLOSURE This exothermic composition can be used in casting molten metals in steelworks and in foundries so as to delay solidification and to fill up the cavities caused by the shrinkage of the metal during solidification. -It contains in a known manner aluminum, at least one oxidising agent and at least one filler. It additionally con- The present invention generally relates to the technique of casting molten metals in steelworks or in foundries. It is well known to use compositions which are exothermic and/or insulating and/or refractory when casting molten metals, so as to delay solidification. Thus, in the case of casting steel into ingot moulds, the upper part of the steel charge contained in the ingot is kept liquid so as to fill up the cavities caused by the shrinkage of the steel during solidification, thus producing a corresponding reduction in the rejected top end of the ingot. In foundries, a feedhead, acting in a similar manner, is kept in the liquid state so as to yield sound castings.

Such compositions are employed in various forms, either as a covering powder which is poured onto the metal after casting, or in the form of a lining applied to the walls of an ingot mould, or in the form of a sleeve or the like. Such a lining can be produced by attaching prefabricated sheets of lining or by tamping powder into a casing.

The known exothermic compositions contain aluminum in the pure state and/or in the form of aluminum dross, fluorides, oxidising agents such as chlorates, iron oxide, manganese dioxide and the like, and generally one or more fillers such as alumina, sand, chamotte, perlite and the like, depending on the operating conditions and on the desired results.

One object of the invention is to provide a new exothermic composition which can be used in steelworks and foundries when casting metals.

Another object of the invention is to provide an exothermic composition which can be used during the casting of metals, of the type which contains, in a known manner, aluminum or an aluminum compound, at least one oxidising agent and at least one filler, characterised in that it furthermore contains a solid easily combustible carbonaceous material in a finely divided state. This material can be paper or a plastic.

According to the invention, if this composition contains paper, the amount of paper is at least 5% relative to the total composition.

If this composition contains a plastic, it is advisable for the amount of plastic to be between 0.2 and 5%. The said composition can also simultaneously contain paper and a plastic. The investigations which have resulted in the invention have shown that such a proportion of paper or plastic, in a finely divided state, in the exothermic composition makes it possible to achieve more uniform combustion of this. composition.

It is in fact known that under the influence of the heat provided by the metal, for example by liquid steel, which is at about 1600 C. at the time of casting, the aluminum and the oxidising agents react so as to produce an additional evolution of heat. This reaction is well known. It forms the basis of aluminothermy. The investigations indicated above have shown that this reaction by combustion is rendered more uniform through the presence of paper and/or of plastic. Furthermore, the incorporation of paper and/or of plastic in the composition makes it possible to obtain markedly lower densities, which can for example be as low as 0.35-0.40.

According to an example given without implying a limitation, the composition can contain more than 15%, and in particular about 20%, of pure aluminum, or an amount of aluminum dross representing about 20% of aluminum, 15 to 20% of oxidising agents, for example chlorates, iron oxide, manganese dioxide, fluorides and the like, 50 to 65% of fillers such as alumina, sand, chamotte, perlite and the like, and at least 5% of paper in a finely divided state. At least a part of the paper of this composition can be replaced by the plastic. However, in this case the proportion of plastic will generally be less than 5%.

It is already known to incorporate paper or equivalent cellulosic fibres into refractory or insulating linings used in steelworks. On contact with the liquid steel, the paper or the fibres undergo combustion and thus allow the lining to be disintegrated after the ingot has solidified. In the composition which forms the subject of the invention, the paper and/or the plastic fulfill an additional function because the presence of a proportion of paper and/or of plastic in a finely divided state in the composition ensures, in an intrinsically noteworthy manner, that the combustion is more uniform. Furthermore, the density of the composition is reduced.

The composition according to the invention can be used in the form of a covering powder intended to be poured over the liquid metal immediately after casting, or in the form of a powder intended to be tamped or pressed into a casing, for example inside an ingot mould, or in the form of a pulverulent composition which can be mixed with one or more suitable binders so as to manufacture lining elements or exothermic feedheads in a manner which is in itself known.

The composition according to the invention can be prepared simply by mixing the constituents of which it consists. These constituents are used in a manner which is known for the production of compositions of this type, in the form of powders or in a finely divided state, and, for example, the paper and/or the plastic, especially in the form of scrap, can be chopped or ground so as to reduce them to a suitable particle size, allowing them to be well distributed in the entire composition.

However, a different embodiment consists of starting from an already existing aluminum-paper or aluminumplastic composite.

It is known to deposit a film of aluminum on a paper or plastic support for certain industrial or commercial uses, for example for packaging certain commercially supplied products. In industry, there exists relatively large amounts of scrap of a composite consisting of an aluminum-paper laminate or aluminum-plastic laminate. Attempts have already been made to recover the aluminum from this composite, in view of the fact that this material is expensive. The solutions proposed have for example consisted of burning the said composite so as to destroy the paper or plastic support and thereafter to recover the aluminum. However, this combustion changes the properties of the aluminum. The result is no better if attempts are made to destroy the paper or the plastic by chemical means.

The invention provides a particularly simple means of recovery, which makes it possible to use to optimum effect the amounts of waste aluminum-paper or aluminum-plastic composite which exist in industry. According to the invention, this waste composite is ground so as to reduce it to a sufficiently small particle size for it to be incorporated into a pulverulent composition such as that described above, and the said particles are incorporated into such a composition.

Certain composites, of the type in question, contain about 30 to 35% by weight of aluminum and 65 to 70% by weight of paper. Other composites comprise an aluminum film deposited on an extremely thin plastic support film, so that this composite contains, for example, 65 to 70% by weight of aluminum. The incorporation of the finely divided product obtained by grinding such composites thus introduces into the composition at least a part of the aluminum required in the exothermic compositions of this type and a not insignificant proportion of paper or of plastic.

Furthermore, it is possible to establish that the grinding carried out in fact does not separate the aluminum from the paper or from the plastic and that, in a certain number of particles, aluminum and paper or plastic are simultaneously present, even though these constituents cannot be detected with the naked eye if the size of the particles are expressed in microns, as is the case for powders, so that the paper is perfectly distributed in the mass of the composition and provides optimum uniformity of combustion.

According to yet a further characteristic, aluminumpaper or aluminum-plastic composites in a finely divided, chopped or ground, state used in the exothermic composition which forms the subject of the invention are of the type in which the aluminum film is at least partly protected by printing, by application of a varnish or in some similar manner.

In fact, the greater is the contact surface between the aluminum and the oxidising agents which provide oxygen and which are present in the exothermic composition, the faster is the exothermic reaction between the aluminum and these oxidising agents, and the greater is the amount of heat evolved per unit time, thereby allowing higher temperatures to be obtained. Conversely, the lower is the contact surface, the slower is the reaction and the lower is the temperature reached.

The heat evolved at the time of reaction is partly transferred to the liquid steel so as to replace the calories lost on leaving the ladle when casting into the ingot mould, but the greater part of the heat produced is furthermore transferred to the constituents which surround the thermogenic materials consisting of the aluminum and the oxidising agents, especially to the insulating and refractory constituents which are intended to preserve this heat. It is easily understood that the more rapidly the amount of heat produced by a given charge of aluminum and oxidising agents is involved, the higher is the temperature reached by the steel and by the abovementioned insulating and refractory constituents, so that optimum preservation of the heat is ensured.

In the case of aluminum shot or aluminum powder used without special precautions, a layer of oxide is found to be present on the surface of the aluminum particles, which interferes with the almost pure aluminum employed coming into contact with the oxidising agents and which hence counteracts maximum evolution of heat. This is also the case for scrap aluminum-paper and aluminum-plastic composites in a finely divided state, for example in the form of fibres or of extremely narrow strips. The presence of a varnish, for example, prevents the oxidation of the surface of the aluminum. At the time of contact with the steel, this film of varnish is removed under the influence of heat, and the aluminum is directly in contact with the oxidising agents, which allows a rapid reaction and maximum evolution of heat within a very short space of time, with the advantages of a high temperature which result therefrom.

This result is particularly discernible in the case where the composite, cut into fibres or extremely thin strips, is used in the manufacture of exothermic feedhead slabs. The experiments carried out show that in such a case an improvement of about 20% in the results obtained is achieved.

Modifications can be introduced into the embodiments described, within the scope of technical equivalence.

What is claimed is:

1. In an exothermic composition for use when casing molten metals, comprising an intimate admixture of fine particles of aluminum, at least one oxidizing agent, at least one filler, and at least one solid easily combustible carbonaceous material selected from the group consisting of paper and plastic; the improvement in which at least a portion of said aluminum and at least a portion of said carbonaceous material are in the form of a composite of a layer of aluminum on a layer of said carbonaceous material.

2. An exothermic composition as claimed in claim 1, in which said composite is a film of aluminum deposited on a support of said carbonaceous material.

3. An exothermic composition as claimed in claim 1, and a protective film on the free surface of the aluminum of said composite.

4. An exothermic composition as claimed in claim 1, in which said composite consists essentially of 30-35% by weight of aluminum and -70% by weight of carbonaceous material.

5. An exothermic composition as claimed in claim 1, in which said composite consists essentially of 65-70% by weight of aluminum and 30-35% by weight of carbonaceous material.

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