US3144323A - Treatment of molten light alloys - Google Patents

Treatment of molten light alloys Download PDF

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Publication number
US3144323A
US3144323A US24907A US2490760A US3144323A US 3144323 A US3144323 A US 3144323A US 24907 A US24907 A US 24907A US 2490760 A US2490760 A US 2490760A US 3144323 A US3144323 A US 3144323A
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carbon
molten
light alloys
nitrate
molten light
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US24907A
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Albert R Watson
Frederick H Taylor
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Foseco International Ltd
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Foseco International Ltd
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/05Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B21/00Obtaining aluminium
    • C22B21/06Obtaining aluminium refining
    • C22B21/064Obtaining aluminium refining using inert or reactive gases

Definitions

  • This invention relates to the treatment of molten light alloys, by which term is to be understood magnesium, aluminium, alloys of these two metals and alloys of either or both of these metals with other metals in which alloys, magnesium or aluminuim or a mixture of these is the predominant constituent.
  • the present invention has for an object to provide a method of removing the dissolved hydrogen from molten light alloys wherein the foregoing difficulties are avoided or minimised.
  • the operation is referred to hereinafter as de-gassing.
  • a method of degassing light alloys comprises fiushing through the molten light alloys carbon monoxide and/or carbon dioxide. It has been discovered, rather surprisingly, that degassing with the oxides of carbon may be effected without giving rise to undesirable inclusions in the cast metal.
  • the oxides of carbon may be provided as such, e.g., supplied from cylinders of the compressed gases or, in the case of carbon dioxide, supplied in the form of the solid (Dry Ice). These, however, are less preferred methods since the former requires the provision of cylinders and the latter involves a serious reduction in the temperature of the molten metal.
  • the carbon monoxide or dioxide is generated in situ by adding to the molten metal a solid substance which, at the temperature of the molten light alloy, will decompose to yield the required gas, which then bubbles freely through the molten metal.
  • carbon dioxide may be generated in the molten light alloy by adding thereto a carbonate which decomposes at the temperature of the molten light alloy.
  • a carbonate which decomposes at the temperature of the molten light alloy.
  • the alloy will be at a temperature in the range 580 to 800 C.
  • a suitable carbonate for this use is magnesium carbonate.
  • a carbonate which does not itself decompose to yield carbon dioxide at the temperature of the molten light alloy, its decomposition may be achieved by including with it a composition of which the ingredients, at the said temperature, react exothermically (e.g., a mixture of aluminium and an oxidising agent therefor such as iron oxide), the temperature thus achieved by the exothermic reaction being suflicient to decompose the carbonate.
  • a carbonate which does not itself decompose at the temperature of the molten light alloy may be introduced in admixture with a substance which will react with the carbonate, at the said temperature, to generate carbon dioxide.
  • Suitable substances for this purpose are alkali metal (e.g., sodium and potassium) silicofluorides and borofiuorides.
  • an oxalate e.g., calcium or sodium oxalate.
  • These oxalates decompose, at the temperature of the molten light alloy, to generate carbon monoxide and carbon dioxide.
  • the added substance is a mixture of cyanamide and an oxidising agent (e.g., sodium nitrate).
  • an oxidising agent e.g., sodium nitrate.
  • the added substance is a mixture of carbon or carbonaceous material (which is preferably finely divided graphite but may be carbon black) and an oxidising agent, e.g., a nitrate, peroxide, persulphate, chlorate or phosphate, preferably of an alkali metal or less preferably of an alkaline earth metal.
  • an oxidising agent e.g., a nitrate, peroxide, persulphate, chlorate or phosphate, preferably of an alkali metal or less preferably of an alkaline earth metal.
  • the additive compositions may contain a diluent which may be inert or may participate in the reaction to a limited extent, e.g., sodium chloride, calcium fluoride, marble dolomite, zircon or grog (brick dust) but generally at least 5% of the additive will consist of the carbon-generating substance or ingredients.
  • a diluent which may be inert or may participate in the reaction to a limited extent, e.g., sodium chloride, calcium fluoride, marble dolomite, zircon or grog (brick dust) but generally at least 5% of the additive will consist of the carbon-generating substance or ingredients.
  • the moisture content of the additives is preferably not greater than 1% of its weight and optionally does not exceed 0.25% of its weight. It is accordingly often desirable to subject the additive to drying at a temperature below the temperature at which decomposition sets in, in order to reduce its moisture content to within the indicated limits. No difliculty appears to arise in the practice of the invention from the dissociation of moisture in the ambient atmosphere. Especially in the case of carbon dioxide and mixtures rich therein, this may be due in part to a blanketing effect at the surface of the metal.
  • compositions added to the molten light alloy according to the invention may also include substances having other special effects on the light alloy, e.g., grain refining agents or hardeners, e.g., salts of titanium or boron or mixtures thereof may be so included.
  • grain refining agents or hardeners e.g., salts of titanium or boron or mixtures thereof may be so included.
  • compositions serving as the additives according to the present invention may be introduced into the molten light alloy as powders or granulated compositions, loose or in packets, e.g., paper packets, or aluminium containers, or may be preformed to tablet shape and added as tablets.
  • compositions according to theinvention are those of which the active ingredients are carbon, e.g., in the form of graphite, and a nitrate, e.g., an alkali metal nitrate. It is found that the eflicacy of these compositions may be further improved by including in them a small amount, e.g., up to 20 by weight of a fully chlorinated hydrocarbon, e.g., hexachlorethane, which appears to have a catalytic effect on the oxidation of the carbon and tends to reduce the formation of nitrogen oxide fumes.
  • a fully chlorinated hydrocarbon e.g., hexachlorethane
  • the carbon oxide or mixture of carbon oxides need not necessarily be in a pure form.
  • it may, when produced in situ, contain contaminants produced simultaneously, e.g., oxides of nitrogen, or it may be diluted with inert gases such as nitrogen or argon in small proportions or in such proportions that they contribute materially to the de-gassification.
  • compositions for use according to this invention are listed:
  • Example I The following composition was made up from the granulated or powdered ingredients as stated:
  • Example II The following composition was made up from the granulated or powdered ingredients as stated:
  • a method of treating molten light alloys consisting essentially of at least one metal selected from the group consisting of aluminum and magnesium to remove therefrom gases including hydrogen which method comprises generating within the body of molten metal a sufiicient quantity of at least one carbon oxide selected from the group consisting of carbon monoxide and carbon dioxide to remove said hydrogen from said molten alloy by adding to the molten alloy a mixture comprising carbon and an inorganic nitrate, said nitrate being present in at least substantially stoichiometric proportion relative to the carbon.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Description

United States Patent 3,144,323 TREATMENT OF MOLTEN LIGHT ALLOYS Albert R. Watson and Frederick H. Taylor, Birmingham,
England, assignors to Foseco International Limited, a
company of Great Britain No Drawing. Filed Apr. 27, 1960, Ser. No. 24,907
Claims priority, application Great Britain May 1, 1959 3 Claims. (Cl. 75- 67) This invention relates to the treatment of molten light alloys, by which term is to be understood magnesium, aluminium, alloys of these two metals and alloys of either or both of these metals with other metals in which alloys, magnesium or aluminuim or a mixture of these is the predominant constituent.
It is well known that the foregoing light alloys, when melted, dissolve substantial quantities of hydrogen, originating for example from the dissociation of moisture from the atmosephere or introduced with the common additives to such metals. On solidifying the molten light alloys containing dissolved hydrogen, much of the hydrogen comes out of solution, giving rise to the presence of minute bubbles or porosity in the solid metal.
It is common practice to attempt to remove dissolved hydrogen from light alloys whereby an inert gas, for example, nitrogen or argon is bubbled through the molten metal before casting. A drying system for the inert gas is required and, even when the gases are thoroughly dried, light alloys with very low hydrogen content are rarely obtained. Chlorine gas or chlorinated hydrocarbons which volatilise at the temperature of the molten metal have been used for the same purpose, but it has been found that large quantities of unpleasant fumes are produced during their use.
The present invention has for an object to provide a method of removing the dissolved hydrogen from molten light alloys wherein the foregoing difficulties are avoided or minimised. The operation is referred to hereinafter as de-gassing.
According to the present invention a method of degassing light alloys comprises fiushing through the molten light alloys carbon monoxide and/or carbon dioxide. It has been discovered, rather surprisingly, that degassing with the oxides of carbon may be effected without giving rise to undesirable inclusions in the cast metal.
The oxides of carbon may be provided as such, e.g., supplied from cylinders of the compressed gases or, in the case of carbon dioxide, supplied in the form of the solid (Dry Ice). These, however, are less preferred methods since the former requires the provision of cylinders and the latter involves a serious reduction in the temperature of the molten metal.
Preferably according to the invention the carbon monoxide or dioxide is generated in situ by adding to the molten metal a solid substance which, at the temperature of the molten light alloy, will decompose to yield the required gas, which then bubbles freely through the molten metal.
Thus for example, carbon dioxide may be generated in the molten light alloy by adding thereto a carbonate which decomposes at the temperature of the molten light alloy. Usually the alloy will be at a temperature in the range 580 to 800 C. A suitable carbonate for this use is magnesium carbonate. If a carbonate is used which does not itself decompose to yield carbon dioxide at the temperature of the molten light alloy, its decomposition may be achieved by including with it a composition of which the ingredients, at the said temperature, react exothermically (e.g., a mixture of aluminium and an oxidising agent therefor such as iron oxide), the temperature thus achieved by the exothermic reaction being suflicient to decompose the carbonate.
Alternatively a carbonate which does not itself decompose at the temperature of the molten light alloy may be introduced in admixture with a substance which will react with the carbonate, at the said temperature, to generate carbon dioxide. Suitable substances for this purpose are alkali metal (e.g., sodium and potassium) silicofluorides and borofiuorides.
Instead of a carbonate there may be used an oxalate, e.g., calcium or sodium oxalate. These oxalates decompose, at the temperature of the molten light alloy, to generate carbon monoxide and carbon dioxide.
In a further form of the invention the added substance is a mixture of cyanamide and an oxidising agent (e.g., sodium nitrate). Such a mixture, at the temperature here under consideration, will generate carbon dioxide with usually a proportion of carbon monoxide.
In a still further form of the invention the added substance is a mixture of carbon or carbonaceous material (which is preferably finely divided graphite but may be carbon black) and an oxidising agent, e.g., a nitrate, peroxide, persulphate, chlorate or phosphate, preferably of an alkali metal or less preferably of an alkaline earth metal. In this case it is convenient though not critical, to employ the carbon and the oxidising agent in substantially stoichiometric proportions.
Mixtures of any of these solid additives may be employed. To limit the rate of the reaction, the additive compositions may contain a diluent which may be inert or may participate in the reaction to a limited extent, e.g., sodium chloride, calcium fluoride, marble dolomite, zircon or grog (brick dust) but generally at least 5% of the additive will consist of the carbon-generating substance or ingredients.
It is important that the moisture content of the additives be kept to a very low level. The moisture content of the additive is preferably not greater than 1% of its weight and optionally does not exceed 0.25% of its weight. It is accordingly often desirable to subject the additive to drying at a temperature below the temperature at which decomposition sets in, in order to reduce its moisture content to within the indicated limits. No difliculty appears to arise in the practice of the invention from the dissociation of moisture in the ambient atmosphere. Especially in the case of carbon dioxide and mixtures rich therein, this may be due in part to a blanketing effect at the surface of the metal.
The compositions added to the molten light alloy according to the invention may also include substances having other special effects on the light alloy, e.g., grain refining agents or hardeners, e.g., salts of titanium or boron or mixtures thereof may be so included.
The compositions serving as the additives according to the present invention may be introduced into the molten light alloy as powders or granulated compositions, loose or in packets, e.g., paper packets, or aluminium containers, or may be preformed to tablet shape and added as tablets.
Preferred compositions according to theinvention are those of which the active ingredients are carbon, e.g., in the form of graphite, and a nitrate, e.g., an alkali metal nitrate. It is found that the eflicacy of these compositions may be further improved by including in them a small amount, e.g., up to 20 by weight of a fully chlorinated hydrocarbon, e.g., hexachlorethane, which appears to have a catalytic effect on the oxidation of the carbon and tends to reduce the formation of nitrogen oxide fumes.
It will be appreciated that the carbon oxide or mixture of carbon oxides need not necessarily be in a pure form. For example it may, when produced in situ, contain contaminants produced simultaneously, e.g., oxides of nitrogen, or it may be diluted with inert gases such as nitrogen or argon in small proportions or in such proportions that they contribute materially to the de-gassification.
The following are examples of compositions for use according to this invention:
Example I The following composition was made up from the granulated or powdered ingredients as stated:
Parts by weight Sodium nitrate 36 Graphite 6 Hexachlorethane 3-5 Grog 30 Sodium chloride 23-25 gms. per cc.
Example II The following composition was made up from the granulated or powdered ingredients as stated:
Parts by weight Sodium nitrate 36 Graphite 6 Grog 30 Sodium chloride 28 This composition behaved similarly to that of Example I but was a little less vigorous in action.
We claim as our invention:
1. A method of treating molten light alloys consisting essentially of at least one metal selected from the group consisting of aluminum and magnesium to remove therefrom gases including hydrogen which method comprises generating within the body of molten metal a sufiicient quantity of at least one carbon oxide selected from the group consisting of carbon monoxide and carbon dioxide to remove said hydrogen from said molten alloy by adding to the molten alloy a mixture comprising carbon and an inorganic nitrate, said nitrate being present in at least substantially stoichiometric proportion relative to the carbon.
2. A method according to claim 1 wherein the in0rganic nitrate is an alkali metal nitrate.
3. A method according to claim 1 wherein the mixture includes an inert diluent filler.
References Cited in the file of this patent UNITED STATES PATENTS 1,318,074 Gowdy Oct. 7, 1919 2,160,812 Alden et al. June 6, 1939 2,281,216 Udy Apr. 28, 1942 2,362,507 Steinbeck et a1. Nov. 14, 1944 2,461,937 Strauss Feb. 15, 1949 2,583,533 Hiensch Jan. 29, 1952 2,654,670 Davis Oct. 6, 1953 2,952,534 Quinn Sept. 13, 1960 2,956,873 Emmott Oct. 18, 1960 FOREIGN PATENTS 127,031 Great Britain May 29, 1919 OTHER REFERENCES Carapella, Foundry Technology, Aluminum and Magnesium, August 1946 (pages 11 and 13).
Ser. No. 387,769, Lepp (A.P.C.), published May 4, 1943.

Claims (1)

1. A METHOD OF TREATING MOLTEN LIGHT ALLOYS CONSISTING ESSENTIALLY OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND MAGNESIUM TO REMOVE THEREFROM GASES INCLUDING HYDROGEN WHICH METHOD COMPRISES GENERATING WITHIN THE BODY OF MOLTEN METAL A SUFFICIENT QUANTITY OF AT LEAST ONE CARBON OXIDE SELECTED FROM THE GROUP CONSISTING OF CARBON MONOXIDE AND CARBON DIOXIDE TO REMOVE SAID HYDROGEN FROM SAID MOLTEN ALLOY BY ADDING TO THE MOLTEN ALLOY A MIXTURE COMPRISING CARBON AND AN INORGANIC NITRATE, SAID NITRATE BEING PRESENT IN AT LEAST SUBSTANTIALLY STOICHIOMETRIC PROPORTION RELATIVE TO THE CARBON.
US24907A 1959-05-01 1960-04-27 Treatment of molten light alloys Expired - Lifetime US3144323A (en)

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3282680A (en) * 1963-10-01 1966-11-01 Olin Mathieson Process of degassing copper alloys
US3486884A (en) * 1966-10-24 1969-12-30 Foseco Int Modification of aluminum-silicon alloys
US3854935A (en) * 1972-05-17 1974-12-17 Foseco Int Grain refining compositions and method of refining aluminum therewith
US4003738A (en) * 1972-04-03 1977-01-18 Ethyl Corporation Method of purifying aluminum
US4338124A (en) * 1978-11-21 1982-07-06 Swiss Aluminium Ltd. Method of purification of aluminium melts
US4417923A (en) * 1981-09-14 1983-11-29 Spolek Pro Chemickou A Hutni Vyrobu, Narodni Podnik Solid refining agents for the refining of aluminum and alloys thereof and method of preparing said agents
US5989310A (en) * 1997-11-25 1999-11-23 Aluminum Company Of America Method of forming ceramic particles in-situ in metal
US6036792A (en) * 1996-01-31 2000-03-14 Aluminum Company Of America Liquid-state-in-situ-formed ceramic particles in metals and alloys
US6616729B2 (en) * 2001-07-30 2003-09-09 Tetsuichi Motegi Method of grain refining cast magnesium alloy
US6843865B2 (en) 1996-01-31 2005-01-18 Alcoa Inc. Aluminum alloy product refinement and applications of aluminum alloy product refinement

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB127031A (en) * 1916-11-24 1919-05-29 Ernest Edouard Frederic Berger Improvements in the Obtainment of Fumes, or Vapours, by the Combustion of Mixtures of Chemical Substances.
US1318074A (en) * 1919-10-07 Egbert clyde gowdy
US2160812A (en) * 1938-03-09 1939-06-06 Aluminum Co Of America Making castings of aluminum and aluminum-base alloy
US2281216A (en) * 1940-05-28 1942-04-28 Marvin J Udy Metallurgy
US2362507A (en) * 1942-10-27 1944-11-14 Steinbock Method and means for producing commercial castings
US2461937A (en) * 1946-01-09 1949-02-15 Foundry Services Ltd Degassing and grain refining of magnesium
US2583533A (en) * 1945-04-17 1952-01-29 Hiensch Johannes Nathanael Method of destroying patterns
US2654670A (en) * 1950-04-01 1953-10-06 Pennsylvania Salt Mfg Co Flux for treating aluminum and aluminum alloys
US2952534A (en) * 1957-06-03 1960-09-13 Quinn Treatment of molten metals
US2956873A (en) * 1957-02-04 1960-10-18 Foundry Services Int Ltd Method of removing hydrogen from molten metal

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1318074A (en) * 1919-10-07 Egbert clyde gowdy
GB127031A (en) * 1916-11-24 1919-05-29 Ernest Edouard Frederic Berger Improvements in the Obtainment of Fumes, or Vapours, by the Combustion of Mixtures of Chemical Substances.
US2160812A (en) * 1938-03-09 1939-06-06 Aluminum Co Of America Making castings of aluminum and aluminum-base alloy
US2281216A (en) * 1940-05-28 1942-04-28 Marvin J Udy Metallurgy
US2362507A (en) * 1942-10-27 1944-11-14 Steinbock Method and means for producing commercial castings
US2583533A (en) * 1945-04-17 1952-01-29 Hiensch Johannes Nathanael Method of destroying patterns
US2461937A (en) * 1946-01-09 1949-02-15 Foundry Services Ltd Degassing and grain refining of magnesium
US2654670A (en) * 1950-04-01 1953-10-06 Pennsylvania Salt Mfg Co Flux for treating aluminum and aluminum alloys
US2956873A (en) * 1957-02-04 1960-10-18 Foundry Services Int Ltd Method of removing hydrogen from molten metal
US2952534A (en) * 1957-06-03 1960-09-13 Quinn Treatment of molten metals

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3282680A (en) * 1963-10-01 1966-11-01 Olin Mathieson Process of degassing copper alloys
US3486884A (en) * 1966-10-24 1969-12-30 Foseco Int Modification of aluminum-silicon alloys
US4003738A (en) * 1972-04-03 1977-01-18 Ethyl Corporation Method of purifying aluminum
US3854935A (en) * 1972-05-17 1974-12-17 Foseco Int Grain refining compositions and method of refining aluminum therewith
US4338124A (en) * 1978-11-21 1982-07-06 Swiss Aluminium Ltd. Method of purification of aluminium melts
US4417923A (en) * 1981-09-14 1983-11-29 Spolek Pro Chemickou A Hutni Vyrobu, Narodni Podnik Solid refining agents for the refining of aluminum and alloys thereof and method of preparing said agents
US6036792A (en) * 1996-01-31 2000-03-14 Aluminum Company Of America Liquid-state-in-situ-formed ceramic particles in metals and alloys
US6843865B2 (en) 1996-01-31 2005-01-18 Alcoa Inc. Aluminum alloy product refinement and applications of aluminum alloy product refinement
US5989310A (en) * 1997-11-25 1999-11-23 Aluminum Company Of America Method of forming ceramic particles in-situ in metal
US6723282B1 (en) 1997-11-25 2004-04-20 Alcoa Inc. Metal product containing ceramic dispersoids form in-situ
US6616729B2 (en) * 2001-07-30 2003-09-09 Tetsuichi Motegi Method of grain refining cast magnesium alloy

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