Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/186—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents contaming ammonium or metal silicates, silica sols
  • B22C1/188—Alkali metal silicates

Definitions

• the object of the present invention is a powder composition that acts as an activator in foundry binder systems comprising an aqueous solution of sodium silicate.
• the powder composition of the invention comprises sodium silicate having CAS Registry Number 1344-09-8 and a SiO 2 /Na 2 O molar ratio comprised between 3.0 and 3.6, preferably between 3.2 and 3.5, and sodium aluminosilicate having CAS Registry Number 1344-00-9 .
• the powder composition of the invention may furthermore comprise additives.
• Objects of the invention furthermore are the binder systems comprising the powder composition of the invention and aqueous solutions of sodium silicate, optionally comprising additives, the use of said binder systems for the production of foundry moulds, such as cores and/or moulds, and likewise the moulding material mixtures for the production of foundry cores and/or moulds comprising the binder systems of the invention and the silica sand and/or other granular refractory material.
• objects of the invention are a process for the production of said foundry moulds, such as cores and/or moulds, comprising a production step of the moulding material mixtures comprising the binder systems of the invention, together with silica sand and/or other granular refractory material, and a heating step of said moulding material mixtures, and the cores and/or moulds obtainable with said process.
• the foundry moulds such as cores and /or moulds into or around which the molten metal will be poured, are comprised of a granular refractory material, such as, for example silica sand, mixed with a binder system, normally composed of two or more components.
• a granular refractory material such as, for example silica sand
• the foundry moulds must meet various requirements.
• said moulds must furthermore feature stability against moisture present in the processing environment, so as to be usable even some time after the production thereof and after being subjected to the mechanical stress of transportation from the place of production to the place of use thereof.
• the hardening reaction which binds the inert material is accelerated by a chemical catalyst in a liquid or vapour form.
• inorganic foundry binders such as binder systems based on alkali silicate and, in particular, sodium silicate in an aqueous solution.
• the need for totally inorganic-based binder systems is given by the need for binder-based moulds that do not emit hazardous (i.e. harmful, toxic, corrosive, irritant, etc) substances, such as - for example - benzene, toluene, xylene, phenol formaldehyde, when the high-temperature molten metal is poured into (or around) the mould, resulting in the breakdown of the said mould.
• hazardous substances i.e. harmful, toxic, corrosive, irritant, etc
• the organic binder systems deposit a layer of a tarry substance on the metal surfaces, which leads to frequent cleaning, and as a result, a slowdown in production.
• the inorganic binder systems - which should only develop water as a result of the heat - can prevent this slowdown in production.
• the aqueous solutions of alkali silicates are obtained by melting the silica with an alkali carbonate and dissolving the obtained product in water.
• Sodium silicate is the most commonly used alkali silicate, above all for cost reasons. Only in special cases outside the foundry industry potassium silicate is used, for example, in binders for the farming industry, where sodium ion is an undesirable component. Lithium silicate is used in very specific applications, for example for sealing concrete surfaces.
• the aqueous solution of alkali silicate is mixed with the sand and any other optional components/additives: the resulting moist mixture is placed into the core box or in the flask where, depending on the process used, it hardens by effect of the heat and/or a chemical reaction with an external agent.
• blast-furnace cements for the cold hardening of foundry moulds bonded with aqueous solutions of sodium silicate
• Use of blast furnace slag cements as hardening agents for silicate-bonded moulding sands Donald W. and D. Smith, The British Foundryman, January 1968, p. 34-40 , herein incorporated by reference.
• Patent US4226277 herein incorporated by reference, describes a foundry binder system consisting of an aqueous solution of sodium silicate, in which a flow of air, optionally heated, is forced through a mass of sand bonded with said system to accelerate the evaporation of the water contained in the sodium silicate solution and, consequently, accelerate the hardening thereof.
• Patent application WO98/49118 herein incorporated by reference, describes the controlled gelification and subsequent hardening of the sodium silicate solutions for use as adhesives, in particular for outdoor applications when weather-resistance is required.
• the hardening of said solutions is brought about by adding additives such as amorphous silica or an amorphous metal silicate, chosen from magnesium silicate, calcium silicate or aluminium silicate.
• patent application EP1802409 herein incorporated by reference, describes a foundry moulding mixture comprising a granular refractory material, a sodium silicate solution and a hardener consisting of a metal oxide in particulate form, chosen from silica, alumina, titanium oxide, and zinc oxide.
• foundry moulds such as the cores and/or moulds obtained with the binder systems and/or moulding material mixtures of the invention, feature high moisture resistance during storage, thus allowing later use thereof, some time after the production thereof, including after the transportation from the place of production to other places for the subsequent use thereof.
• the binder systems and the moulding mixtures of the invention are totally inorganic-based and therefore furthermore meet recent environmental safety standards requiring limited release of hazardous and/or toxic substances into the environment.
• the object of the invention is therefore a powder composition comprising sodium silicate ( CAS Registry Number 1344-09-8 ) and a SiO 2 /Na 2 O molar ratio comprised between 3.0 and 3.6, preferably between 3.2 and 3.5, and a sodium aluminosilicate powder ( CAS Registry Number 1344-00-9 ).
• the sodium silicate powder has an average grain size comprised between 60 and 100 ⁇ m, preferably between 70 and 90 ⁇ m, and still more preferably of 80 ⁇ m, and/or the sodium aluminosilicate powder has an average grain size comprised between 2 and 15 ⁇ m, preferably between 5 and 10 ⁇ m, and still more preferably of 7 ⁇ m.
• Sodium silicate powder is scarcely soluble in cold water, but becomes soluble when warm. Therefore, this component does not negatively affect the storage potential (bench life) of the moulding material comprising said component, since, thanks to its high molar ratio, it acts as an accelerator during the subsequent heating process (baking).
• the sodium aluminosilicate powder is insoluble in water.
• the powder composition of the invention comprises 60 to 90% by weight of sodium silicate with a SiO 2 /Na 2 O molar ratio comprised between 3.0 and 3.6, preferably between 3.2 and 3.5, and 10 to 40% by weight of sodium aluminosilicate, wherein said percentages refer to the total weight of the powder composition.
• the powder composition may comprise additives.
• additives are understood as substances and/or compounds which are useful for improving the flowability of the moulding material mixtures comprising the powder composition of the invention, such as for example mica and/or silver graphite, substances and/or compounds which are useful for improving the surface of the castings, such as - for example - iron oxides, or substances and/or compounds which are useful for improving the breakdown (shake-out) of cores or moulds after casting.
• carbohydrates are used, such as sucrose, cereal flours, coke powder, and/or wood powder.
• the powder composition of the invention comprises 1 to 25% by weight of additives, preferably 5 to 15 % by weight of additives, wherein said percentages refer to the total weight of the powder composition of the invention.
• the powder composition of the invention is obtained by mixing sodium silicate and sodium aluminosilicate and any optional additives, as defined above, in a powder mixer, preferably of the conical type, which is activated until a homogeneous powder is obtained.
• the powder composition of the invention enables the hardening of a moulding material mixture comprising aqueous solutions of sodium silicate and sand and/or other granular refractory material, thereby allowing foundry moulds to be obtained, such as cores and/or moulds, which are safe for the environment and for the workers in the industry, feature resistance to ambient moisture, and which extend the storage potential for use thereof for some time, subsequently to the time of production.
• the object of the invention is a binder systems comprising the powder composition of the invention, as defined hereinabove, and an aqueous solution of sodium silicate.
• the aqueous solution of sodium silicate comprises 25 to 50% by weight of sodium silicate, more preferably, 35 to 45% by weight of sodium silicate, and between 50 to 75% by weight of water, wherein said percentages refer to the total weight of the aqueous solution of sodium silicate.
• the aqueous solution of sodium silicate has a SiO 2 /Na 2 O molar ratio comprised between 1.9 and 2.5, preferably between 2.0 and 2.4, and more preferably between 2.1 and 2.3, and/or the aqueous solution of sodium has a density at 20°C comprised between 1.30 and 1.50 kg/dm 3 , preferably comprised between 1.35 and 1.45 kg/dm 3 .
• aqueous solutions of sodium silicate which have a SiO 2 /Na 2 O molar ratio comprised between 2.1 and 2.3, with a density at 20°C comprised between 1.35 and 1.45 kg/dm 3 .
• the aqueous solution of sodium silicate is prepared by taking an aqueous solution of sodium silicate having a molar ratio within the above cited range easily available on the market, and appropriately diluting it with water in a mixer equipped with a stirrer, with no need of heating.
• aqueous solution of sodium silicate may furthermore comprise additives.
• the aqueous solution of sodium silicate comprises 0.1 to 10% by weight of additives, wherein said percentages refer to the total weight of the aqueous solution of sodium silicate.
• additives are understood as substances and/or compounds which are useful for improving the flowability of the moulding material mixture, for example sodium 2-ethylhexyl sulphate, which is preferably added in aqueous solution at 40% by weight, in an amount comprised between 0.1% and 1.0% by weight, preferably between 0.2% and 0.6% by weight, with respect to the total weight of the aqueous solution of sodium silicate, or monophenyl glycol, which is preferably added in an amount comprised between 0.5% and 5.0% by weight, preferably between 1.0 and 4.0% by weight, with respect to the total weight of the aqueous solution of sodium silicate.
• sodium 2-ethylhexyl sulphate which is preferably added in aqueous solution at 40% by weight, in an amount comprised between 0.1% and 1.0% by weight, preferably between 0.2% and 0.6% by weight, with respect to the total weight of the aqueous solution of sodium silicate
• monophenyl glycol which is preferably added in an amount comprised between 0.5% and 5.
• the aqueous solution of sodium silicate may furthermore comprise additives which improve bonding with the grains of refractory material with which said aqueous solution of sodium silicate is mixed and which improve the storage potential of the manufactured articles in a humid environment, such as, for example, silane compounds.
• Silane compounds of particular interest are, for example, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-(diethoxymethyl-silyl)propylamine, 3-glycidoxypropyltrimethoxysilane and mixtures thereof, which are preferably added in amounts of between 0.1% and 1.0% by weight, preferably between 0.2 and 0.6% by weight, with respect to the total weight of the aqueous solution of sodium silicate.
• the aqueous solution of sodium silicate may furthermore comprise additives which facilitate the breakdown (shake-out) of the cores and moulds after casting, said additives usually being carbohydrates, such as sucrose, which is preferably added in an amount comprising between 1.0% and 10.0% by weight, preferably between 3.0% and 6.0% by weight, with respect to the total weight of the aqueous solution of sodium silicate.
• additives which facilitate the breakdown (shake-out) of the cores and moulds after casting
• said additives usually being carbohydrates, such as sucrose, which is preferably added in an amount comprising between 1.0% and 10.0% by weight, preferably between 3.0% and 6.0% by weight, with respect to the total weight of the aqueous solution of sodium silicate.
• room temperature means a temperature comprised between approximately 0 °C and + 40 °C, preferably between +15°C and + 30°C
• the aqueous solution of sodium silicate as described above is very fluid and scarcely reactive and it provides the moulding mixture containing it, i.e. to the mixture comprising the aqueous solution of sodium silicate, the powder composition, and the sand and/or other refractory material, with good flowability and a long "bench life".
• the invention therefore relates to the use of binder systems as defined above for the production of foundry cores and/or moulds.
• the moulding material mixtures which furthermore represent an object of the invention, comprising the binder systems of the invention, as defined above, together with the silica sand and/or other granular refractory material, such as zirconium sand (zirconium silicate) or chromite, are obtained by mixing silica sand and/or other granular refractory material with the aqueous solution of sodium silicate, as defined above, and subsequently adding the powder composition of the invention.
• the moulding material mixtures of the invention can be obtained by mixing silica sand and/or other granular refractory material with the powder composition of the invention and subsequently adding the aqueous solution of sodium silicate as defined above.
• the moulding material mixtures of the invention which if stored out of direct contact with the air, are usable for up to ten hours from the production thereof, comprise from 1.6 to 2.4 parts by weight of the aqueous solution of sodium silicate and from 0.5 to 1.5 parts by weight of the powder composition of the invention, as defined above, and 100 parts by weight of silica sand and/or other granular refractory material.
• said mixtures comprise from 1.8 to 2.2 parts by weight of the aqueous solution of sodium silicate and from 0.7 to 1.2 parts by weight of the powder composition of the invention, as defined above, and 100 parts by weight of silica sand and/or other granular refractory material.
• the cores and/or moulds of the invention comprise a heating step (baking) of said moulding material mixtures comprising the binder system of the invention and the silica sand and/or other granular refractory material.
• the foundry cores and/or moulds thus obtainable which furthermore represent an object of the present invention, show good strength and do not degrade during storage in humid environments.
• the moulding material mixtures of the invention are placed, either manually or by means of compressed air systems, inside a core box already heated to 150 to 200 °C and/or treated with a flow of hot air at 150 to 180 °C, which quickly hardens said mixture.
• the mixtures were prepared in the laboratory, adding first the silica sand, then the aqueous solution of sodium silicate, and finally the powder composition of the invention, using a Kitchen Aid rapid mixer (Artisan model).
• the sand and the aqueous solution of sodium silicate were mixed for 1 minute and then the powder composition of the invention was added and mixed for 1 minute.
• Standard identical bars were prepared with each one of the mixtures. Each mixture was compacted with five strokes of a Georg Fischer rammer PRA model in the individual core box and the resulting standard bars had a 5 cm 2 square breakage section.
• the bars were placed on 220 x 60 mm rectangular steel plates with a thickness of 3 mm, and were baked for 6 minutes at 260 °C in a laboratory oven.
• the bars in the first group were stored for 24 hours in a dryer, while the bars in the second group were stored for 24 hours in a climate chamber ClimaCell 111 model manufactured by MM, which was set at 25 °C with 60% of relative humidity.
• Solution A dry, after 15 minutes at 650 °C had a sodium silicate content equal to 37.68%.
• Solution A1 a variant of Solution A containing additives and having the following percentage composition: Solution A 99.3% by weight of the weight of Solution A1 Sodium 2-ethylhexyl sulphate in 40% aqueous solution 0.2% 3-glycidoxypropyltrimethoxysilane 0.5%
• the sodium silicate powder used in the composition in the examples is a sodium silicate with the following chemical-physical characteristics: - SiO 2 /Na 2 O molar ratio: 3.2-3.5 - SiO 2 : 61.7-66.1% by weight - Na 2 O: 18.0-20.3% by weight - loss on ignition, 800 ° C: ⁇ 20% by weight - average grain size: 80 ⁇ m
• the sodium aluminosilicate powder used in the composition in the examples is a sodium aluminosilicate with the following chemical-physical characteristics: - SiO 2 (on ignited substance): ⁇ 80% by weight - Al (on ignited substance): 6.0% by weight - Na (on ignited substance): 5.5% by weight - loss on ignition: ⁇ 10.0% by weight - average particle size: 7 ⁇ m
• Table 1 below provides a summary of the results obtained in Examples 1-9: Table 1 Flexural strength in N/cm 2 24 hours at 25°C, dry 24 hours at 25°C and 60% RH Mixture in Example 1. 510 90 Mixture in Example 2. 565 60 Mixture in Example 3. 500 105 Mixture in Example 4. 0 0 Mixture in Example 5. 435 430 Mixture in Example 6. 470 395 Mixture in Example 7. 510 385 Mixture in Example 8. 475 400 Mixture in Example 9. 395 360

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Citations (11)

• 2016
  • 2016-04-01 IT ITUA2016A002227A patent/ITUA20162227A1/it unknown
• 2017
  • 2017-03-29 EP EP17163617.8A patent/EP3225327B1/de active Active

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