EP0043817A1 - Self drying aluminium-containing compositions - Google Patents

Self drying aluminium-containing compositions

Info

Publication number
EP0043817A1
EP0043817A1 EP80902297A EP80902297A EP0043817A1 EP 0043817 A1 EP0043817 A1 EP 0043817A1 EP 80902297 A EP80902297 A EP 80902297A EP 80902297 A EP80902297 A EP 80902297A EP 0043817 A1 EP0043817 A1 EP 0043817A1
Authority
EP
European Patent Office
Prior art keywords
composition
aluminium
alkali metal
nitrite
drying
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP80902297A
Other languages
German (de)
French (fr)
Inventor
Michael John Gough
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Foseco International Ltd
Original Assignee
Foseco International Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Foseco International Ltd filed Critical Foseco International Ltd
Publication of EP0043817A1 publication Critical patent/EP0043817A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D7/00—Casting ingots, e.g. from ferrous metals
    • B22D7/06—Ingot moulds or their manufacture
    • B22D7/10—Hot tops therefor
    • B22D7/104—Hot tops therefor from exothermic material only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D7/00—Casting ingots, e.g. from ferrous metals
    • B22D7/06—Ingot moulds or their manufacture
    • B22D7/10—Hot tops therefor

Definitions

  • This invention relates to self drying aluminium- containing compositions, and in particular to shaped self drying aluminium-containing compositions for use in the casting of molten metals.
  • the exothermic compositions generally rely on an aluminothermic reaction for their exothermic properties, and usually contain aluminium, an oxidising agent and a fluoride to reduce the temperature at which reaction between the aluminium and the oxidising agent commences.
  • Some heat insulating compositions may also contain aluminium, particularly compositions used in the casting of steel.
  • Exothermic insulating compositions are also known containing aluminium and oxidising agents which react without the presence of fluorides.
  • Such aluminium-containing compositions may be used e.g. as a cylindrical sleeve for lining a riser, or as an insert to be located in the mould cavity at a point where directional solidification is to be encouraged, and they may be formed to shape by various methods, most of which involve drying the compositions to remove added water.
  • One method of drying the compositions is to utilise the exothermic reaction which takes place between the aluminium and a strong alkali in the presence of an alkali metal nitrate.
  • This method is described in British Patent specification 808400 according to which a mixture of finely divided aluminium, an amount of oxidising agent, including alkali metal nitrate well below the amount necessary to react completely with the aluminium to oxidise it completely, a fluoride and water is formed to shape and a small amount of a strongly alkaline solution e.g. of caustic soda, is applied to the shaped composition.
  • the reaction on addition of the caustic soda is believed to include the following stages:-
  • the hydrogen generated in the first reaction regenerates sodium hydroxide in the second, and a chain reaction is thereby set up so that in practice it is necessary only to apply a few drops of caustic soda solution at a few positions on the shaped composition to bring about the reactions throughout the whole mass and as a result of the heat generated to dry the whole mass.
  • a self drying aluminium-containing composition in which the drying of the composition is to be initiated by an alkaline substance characterised in that the composition contains an alkali metal nitrite.
  • the quantity of alkali metal nitrite present is preferably 6 - 10 % by weight based on the weight of the dry components of the composition.
  • the alkali metal nitrite may be for example sodium nitrite or potassium nitrite.
  • the alkaline substance is preferably applied as a solution.
  • An aqueous solution is preferred but a solution in ethyl alcohol is also effective.
  • suitable alkaline substances are sodium hydroxide, potassiun hydroxide, sodium carbonate, potassium carbonate, sodium aluminate and potassium aluminate.
  • composition will contain other components in addition to the aluminium and the alkali metal nitrite.
  • the composition will usually contain a proportion of an inert refractory filler such as grog, chamotte, alumina or silica, an oxidising agent such as iron oxide or manganese dioxide, and a fluoride such as sodium fluoride, potassium fluoride, sodium aluminium fluoride or potassium aluminium fluoride, and the quantity of aluminium present will be such that only a proportion is utilised in the self drying reaction the remainder being utilised by reaction with the oxidising agent to produce heat.
  • an inert refractory filler such as grog, chamotte, alumina or silica
  • an oxidising agent such as iron oxide or manganese dioxide
  • a fluoride such as sodium fluoride, potassium fluoride, sodium aluminium fluoride or potassium aluminium fluoride
  • the aluminium-containing composition may be an exothermic composition, which, also contains fibres, such as asbestos, calcium silicate fibre, or aluminosilicate fibre, for example as described in British Patents 1 117 977 and 1 218 568.
  • the aluminium-containing composition may also be an essentially non-exothermic heat-insulating composition containing for example aluminosilicate fibre, zircon fibre or silica fibre, and optionally a particulate refractory material, for example as described in British Patent 1 283 692.
  • the same self drying properties can be obtained using less aluminium and less alkali metal salt.
  • similar self drying properties can be obtained from a composition containing about 23% by weight aluminium and 12% by weight sodium nitrate, and one containing about 17% by weight aluminium and 6% by weight sodium nitrite.
  • the amount of sodium nitrite used may be considerably less than the equivalent amount of sodium nitrate less ammonia is produced in the self drying reaction despite the fact that 1 molecule of sodium nitrite and 1 molecule of sodium nitrate each produce 1 molecule of ammonia.
  • compositions containing residual sodium nitrite are less prone to pick up moisture than are the known compositions which contain residual sodium nitrate.
  • the method of the invention is particularly suitable for the production of slabs or sleeves for lining ingot mould hot tops or casting mould risers and also for the production of foundry padding materials which are used to help feed molten metal to those parts of a casting which may be remote from a riser.
  • the application of padding materials is described in British Patent 1 240301 and the method of the invention is particularly useful when applied to rammable or mouldable padding materials.
  • the method of the invention tray also be used to produce linings for molten metal containing vessels such as ladles and launders.
  • a snail proportion of a compound such as boric acid which will passivate the aluminium as described in British Patent 775380.
  • the aluminiumcontaining composition in two parts, one part containing the aluminium, and the other the alkali metal nitrite, and mix the two parts together just prior to use. This is particularly desirable at high ambient temperatures of about 25o C and above. Under such conditions a pre-prepared composition containing both the aluminium and the alkali metal nitrite could become unusable during storage due to premature chBnical reaction taking place.
  • a steel casting 1 having dimensions 110 mm x 110 mn x 110 mm is produced in a sand mould 2.
  • the casting 1 is separated from a cylindrical feeder 3, 100 mm in diameter and 150 mm high by a plate 4, 220 mm high, 110 mm wide and 55 ⁇ rn thick.
  • the cylindrical feeder is lined by a refractory heat-insulating sleeve 5.
  • a composition according to the invention was produced as follows:-

Abstract

Une composition amelioree a auto-sechage contenant de l'aluminium dans laquelle le sechage est amorce par une substance alcaline, est obtenue en remplacant le nitrate de metal alcalin que l'on ajoute habituellement a une telle composition par un nitrite de metal alcalin. La composition est particulierement appropriee comme materiau moulable de rembourrage utilise pour contribuer a amener le metal en fusion vers les parties d'une piece coulee qui sont eloignee d'une masselotte. La composition est tasse, dans une cavite dans un moule a sable (2) pour produire une piece coulee (1), seche puis se durcit pour former une surepaisseur ou rembourrage (6) qui isole le metal en fusion coule dans le moule.An improved self-drying aluminum-containing composition in which the drying is initiated by an alkaline substance is obtained by replacing the alkali metal nitrate which is usually added to such a composition with an alkali metal nitrite. The composition is particularly suitable as a moldable cushioning material used to help convey molten metal to those parts of a cast part which are away from a weight. The composition is cup, in a cavity in a sand mold (2) to produce a cast part (1), dries and then hardens to form a thickening or padding (6) which isolates the molten metal flowing in the mold.

Description

SELF DRYING ALUMINIUM - CONTAINING COMPOSITIONS
This invention relates to self drying aluminium- containing compositions, and in particular to shaped self drying aluminium-containing compositions for use in the casting of molten metals.
It is comron in the production of metal castings to utilise exothermic and/or heat-insulating compositions as liners for mould risers and/or as inserts in the moulds to ensure feed of molten metal to all parts of the castings and hence sound castings.
The exothermic compositions generally rely on an aluminothermic reaction for their exothermic properties, and usually contain aluminium, an oxidising agent and a fluoride to reduce the temperature at which reaction between the aluminium and the oxidising agent commences. Some heat insulating compositions may also contain aluminium, particularly compositions used in the casting of steel. Exothermic insulating compositions are also known containing aluminium and oxidising agents which react without the presence of fluorides.
Such aluminium-containing compositions may be used e.g. as a cylindrical sleeve for lining a riser, or as an insert to be located in the mould cavity at a point where directional solidification is to be encouraged, and they may be formed to shape by various methods, most of which involve drying the compositions to remove added water.
One method of drying the compositions is to utilise the exothermic reaction which takes place between the aluminium and a strong alkali in the presence of an alkali metal nitrate. This method is described in British Patent specification 808400 according to which a mixture of finely divided aluminium, an amount of oxidising agent, including alkali metal nitrate well below the amount necessary to react completely with the aluminium to oxidise it completely, a fluoride and water is formed to shape and a small amount of a strongly alkaline solution e.g. of caustic soda, is applied to the shaped composition.
The reaction on addition of the caustic soda is believed to include the following stages:-
Al + NaOH + H20→NaA102 + 3H + heat
NaNO3 + BH→4Na0H + NH3 + 2H20
The hydrogen generated in the first reaction regenerates sodium hydroxide in the second, and a chain reaction is thereby set up so that in practice it is necessary only to apply a few drops of caustic soda solution at a few positions on the shaped composition to bring about the reactions throughout the whole mass and as a result of the heat generated to dry the whole mass.
It has now been found that contrary to what is stated in British Patent specification 800400 an alkali metal nitrate is not essential, and that there are advantages to be gained from using an alkali metal nitrite instead.
According to the invention there is provided a self drying aluminium-containing composition in which the drying of the composition is to be initiated by an alkaline substance characterised in that the composition contains an alkali metal nitrite. The quantity of alkali metal nitrite present is preferably 6 - 10 % by weight based on the weight of the dry components of the composition.
The alkali metal nitrite may be for example sodium nitrite or potassium nitrite.
The alkaline substance is preferably applied as a solution. An aqueous solution is preferred but a solution in ethyl alcohol is also effective. Examples of suitable alkaline substances are sodium hydroxide, potassiun hydroxide, sodium carbonate, potassium carbonate, sodium aluminate and potassium aluminate.
The composition will contain other components in addition to the aluminium and the alkali metal nitrite.
If the composition is an exothermic composition, for example of the type described in British Patent 800400, the composition will usually contain a proportion of an inert refractory filler such as grog, chamotte, alumina or silica, an oxidising agent such as iron oxide or manganese dioxide, and a fluoride such as sodium fluoride, potassium fluoride, sodium aluminium fluoride or potassium aluminium fluoride, and the quantity of aluminium present will be such that only a proportion is utilised in the self drying reaction the remainder being utilised by reaction with the oxidising agent to produce heat.
The aluminium-containing composition may be an exothermic composition, which, also contains fibres, such as asbestos, calcium silicate fibre, or aluminosilicate fibre, for example as described in British Patents 1 117 977 and 1 218 568. The aluminium-containing composition may also be an essentially non-exothermic heat-insulating composition containing for example aluminosilicate fibre, zircon fibre or silica fibre, and optionally a particulate refractory material, for example as described in British Patent 1 283 692.
The use of an alkali metal nitrite instead of a nitrate provides a number of advantages.
Firstly the same self drying properties can be obtained using less aluminium and less alkali metal salt. For example similar self drying properties can be obtained from a composition containing about 23% by weight aluminium and 12% by weight sodium nitrate, and one containing about 17% by weight aluminium and 6% by weight sodium nitrite.
Secondly since the amount of sodium nitrite used may be considerably less than the equivalent amount of sodium nitrate less ammonia is produced in the self drying reaction despite the fact that 1 molecule of sodium nitrite and 1 molecule of sodium nitrate each produce 1 molecule of ammonia.
Thirdly, shaped compositions containing residual sodium nitrite are less prone to pick up moisture than are the known compositions which contain residual sodium nitrate.
The method of the invention is particularly suitable for the production of slabs or sleeves for lining ingot mould hot tops or casting mould risers and also for the production of foundry padding materials which are used to help feed molten metal to those parts of a casting which may be remote from a riser. The application of padding materials is described in British Patent 1 240301 and the method of the invention is particularly useful when applied to rammable or mouldable padding materials. The method of the invention tray also be used to produce linings for molten metal containing vessels such as ladles and launders.
In order to delay corrmencement of the chemical hardening reaction, it may be desirable to include in the composition forming the ratτmable or mouldable material a snail proportion of a compound such as boric acid which will passivate the aluminium as described in British Patent 775380.
In padding and other applications in which a mouldableor ramm able material is formed to the required shape in situ and then hardened it may be desirable to provide the aluminiumcontaining composition in two parts, one part containing the aluminium, and the other the alkali metal nitrite, and mix the two parts together just prior to use. This is particularly desirable at high ambient temperatures of about 25º C and above. Under such conditions a pre-prepared composition containing both the aluminium and the alkali metal nitrite could become unusable during storage due to premature chBnical reaction taking place.
The invention is illustrated by way of example with reference to the accompanying drawing which is a sectional view of a metal casting mould.
Referring to the drawing, a steel casting 1 having dimensions 110 mm x 110 mn x 110 mm is produced in a sand mould 2. The casting 1 is separated from a cylindrical feeder 3, 100 mm in diameter and 150 mm high by a plate 4, 220 mm high, 110 mm wide and 55 πrn thick. The cylindrical feeder is lined by a refractory heat-insulating sleeve 5. A composition according to the invention was produced as follows:-
Percent by weight
Alumino-silicate fibre 51 .3
Aluminium foil 5.0
Aluminium powder 12.2
Colloidal silica sol 5.9
(30% by weight solids content)
Sodium nitrite 6.0
Calcined chamotte 8.4
Calcined alumina 8.0
Ball Clay 3.0
Boric acid 0.2
60 parts by weight of water were added to 100 parts by weight of the composition to produce a mouldable mixture, and the mixture was rammed into a cavity in the sand mould 2 having dimensions 200. mm in height, 110 mm in width and tapering in thickness from 45 mm at the upper end to 15 mm at the lower end. A few spots of an alkaline solution were applied to the exposed face of the moulded mixture. The composition of the alkaline solution was:
Percent by weight
Sodium nitrite 10
Sodium hydroxide 10 Water 80
As a result of the ensuing chemical reaction the moulded mixture dried and hardened to form a pad 6. Previous tests using the same composition had produced pads having a density of 0.90 g/cm3. Two hours after application of the alkaline solution molten steel was poured into the mould 2 and the resulting steel casting 1 was sound.

Claims

1. A self drying aluminium-containing composition in which the drying of the composition is to be initiated by an alkaline substance characterised in that the composition contains an alkali metal nitrite.
2. A composition according to claim 1 characterised in that the quantity of alkali metal nitrite present is 6 - 10
% by weight based on the weight of the dry components of the composition.
3. A composition according to claim 1 characterised in that the alkali metal nitrite is sodium nitrite or potassium nitrite.
4. A composition according to claim 1 characterised in that it also contains fibres.
5. A composition according to claim 4 characterised, in that the fibres are asbestos, calcium silicate fibre, aluminosilicate f ibre, zircon fibre or silica fibre.
EP80902297A 1980-01-19 1980-12-11 Self drying aluminium-containing compositions Withdrawn EP0043817A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8001860 1980-01-19
GB8001860 1980-01-19

Publications (1)

Publication Number Publication Date
EP0043817A1 true EP0043817A1 (en) 1982-01-20

Family

ID=10510756

Family Applications (1)

Application Number Title Priority Date Filing Date
EP80902297A Withdrawn EP0043817A1 (en) 1980-01-19 1980-12-11 Self drying aluminium-containing compositions

Country Status (9)

Country Link
EP (1) EP0043817A1 (en)
JP (1) JPS57500006A (en)
KR (1) KR830004051A (en)
BR (1) BR8009022A (en)
ES (1) ES8201048A1 (en)
GB (1) GB2082200A (en)
IT (1) IT8167038A0 (en)
WO (1) WO1981001971A1 (en)
ZA (1) ZA807842B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2134729B1 (en) 1996-07-18 2000-05-16 Kemen Recupac Sa IMPROVEMENTS INTRODUCED IN OBJECT APPLICATION FOR A SPANISH INVENTION PATENT N. 9601607 FOR "PROCEDURE FOR THE MANUFACTURE OF EXACT SLEEVES AND OTHER ELEMENTS OF MAZAROTAJE AND FEEDING FOR CAST MOLDS.

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2490327A (en) * 1947-10-14 1949-12-06 Peter J Soffel Exothermically reactive mold insert
GB775380A (en) * 1954-10-22 1957-05-22 Foundry Services Ltd Improvements in or relating to exothermic mixtures
GB808400A (en) * 1956-01-20 1959-02-04 Foundry Services Ltd The production of moulded exothermic compositions
FR1394847A (en) * 1964-02-22 1965-04-09 Exothermic mixture for metallurgy
DE2853817C2 (en) * 1978-12-13 1985-06-20 Erwin Kampf Gmbh & Co Maschinenfabrik, 5276 Wiehl Device for the simultaneous, biaxial stretching of film webs made of thermoplastic material

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8101971A1 *

Also Published As

Publication number Publication date
IT8167038A0 (en) 1981-01-15
WO1981001971A1 (en) 1981-07-23
ES498627A0 (en) 1981-12-01
BR8009022A (en) 1981-11-24
ES8201048A1 (en) 1981-12-01
ZA807842B (en) 1981-12-30
GB2082200A (en) 1982-03-03
KR830004051A (en) 1983-07-06
JPS57500006A (en) 1982-01-07

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Effective date: 19820120

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Withdrawal date: 19830105

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Inventor name: GOUGH, MICHAEL JOHN