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:-

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Mold Materials And Core Materials (AREA)
• Processing Of Solid Wastes (AREA)
• Floor Finish (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10510756

Family Applications (1)

Country Status (9)

Cited By (1)

Citations (4)

Family Cites Families (1)

• 1980
  • 1980-12-11 EP EP80902297A patent/EP0043817A1/en not_active Withdrawn
  • 1980-12-11 BR BR8009022A patent/BR8009022A/pt unknown
  • 1980-12-11 WO PCT/GB1980/000213 patent/WO1981001971A1/en not_active Application Discontinuation
  • 1980-12-11 JP JP56500122A patent/JPS57500006A/ja active Pending
  • 1980-12-11 GB GB8122374A patent/GB2082200A/en not_active Withdrawn
  • 1980-12-15 ZA ZA00807842A patent/ZA807842B/xx unknown
  • 1980-12-31 KR KR1019800005054A patent/KR830004051A/ko unknown
• 1981
  • 1981-01-15 IT IT8167038A patent/IT8167038A0/it unknown
  • 1981-01-19 ES ES498627A patent/ES8201048A1/es not_active Expired

Patent Citations (4)

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