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
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/03—Sand moulds or like moulds for shaped castings formed by vacuum-sealed moulding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/12—Treating moulds or cores, e.g. drying, hardening

Definitions

• the present invention relates to a coated sand, a method of producing the same, and a method of producing a casting mold, and more particularly to a coated sand which is in a dry state and which has fluidity at the room temperature, a method of producing the coated sand, and a method of producing a casting mold by using the coated sand.
• a casting mold obtained by forming a coated sand into a desired shape has been used.
• the coated sand used for the casting mold is obtained by coating a molding sand consisting of a refractory aggregate, with a suitable binder.
• a suitable binder inorganic binders such as a cement and a water glass, and organic binders such as a phenolic resin, a furan resin and a urethane resin are disclosed, together with methods of forming self-curing molds by using these binders, on pages 78-90 of Chuzou Kougaku Binran (Handbook of Foundry Engineering) edited by Japan Foundry Engineering Society.
• JP-A-2009-90334 discloses a method of producing the casting mold by using a resin-coated sand obtained by coating the molding sand with a thermosetting resin such as the phenolic resin, which is one of the above-indicated organic binders.
• the intended casting mold is produced by the following steps: filling a forming mold with the resin-coated sand; blowing a steam into the forming mold to raise a temperature of the resin-coated sand; and then blowing a heated gas into the forming mold to evaporate condensation water within the forming mold and to heat the binder of the resin-coated sand to a temperature not lower than a temperature at which the binder is solidified or cured.
• the phenolic resin or other resin is used as the binder, so that the binder may be decomposed at a high temperature at the time of formation of the casting mold or casting of the molten metal, giving rise to a problem of generation of gases due to decomposition of phenol and aldehyde. Odors and stimulants of these gases cannot be completely eliminated, so that the above-described method is not suitable for applications in which the odors and stimulants should be avoided.
• the molding sand (refractory aggregate) is kneaded with an aqueous solution of the water glass used as the binder, to coat surfaces of the molding sand with the binder, and the casting mold is formed by using the thus obtained coated sand in a wet state (a moist state) in which the wet water glass adheres to the surfaces of the molding sand.
• a coated sand has a low degree of fluidity, so that there arise inherent problems of difficulty in filling the forming mold with the coated sand, occurrence of filling defects, and low productivity of the casting mold.
• JP-A-2012-76115 proposes to use, as the binder, a water-soluble inorganic compound selected from a group consisting of the water glass, sodium chloride, sodium phosphate, sodium carbonate, sodium vanadate, sodium borate, aluminum sodium oxide, potassium chloride and potassium carbonate.
• the binder-coated refractory proposed in this publication is obtained by coating surfaces of the refractory aggregate with a solid coating layer containing the water-soluble inorganic compound described above.
• This publication further discloses a method of producing the casting mold, which includes steps of: filling the forming mold with the binder-coated refractory; blowing a steam into the forming mold to heat the binder-coated refractory and to moisten the binder constituting the coating layer; and then solidifying the binder.
• the inventor of the present invention studied the binder-coated refractory described above, and found that even where the surfaces of the refractory aggregate are coated with the solid coating layer of the binder consisting of the water-soluble inorganic compound such as the water glass and sodium chloride, a sufficiently high degree of fluidity of the binder-coated refractory cannot be necessarily secured, and the casting mold obtained by using the binder-coated refractory does not have a sufficiently high degree of strength. Further, in order to coat the refractory aggregate with the water-soluble inorganic compound (binder), the water-soluble inorganic compound is dissolved in water, and the thus obtained aqueous solution is used to coat the refractory aggregate.
• the water-soluble inorganic compound such as the water glass and sodium chloride
• the properties of the binder-coated refractory considerably vary depending on the kind of the water-soluble inorganic compound, so that where the binder-coated refractory is produced by using different kinds of the water-soluble inorganic compounds, under the same conditions, the physical properties of the binder-coated refractory have undesirable variations, giving rise to an inherent problem of difficulty in optimizing the conditions of its production.
• Non Patent Document 1 Chuzou Kougaku Binran, pp. 78-90
• objects of the present invention are to provide: a coated sand which is in a dry state and which has fluidity at the room temperature; a method of advantageously producing the coated sand; and a method of producing a casting mold having excellent properties by using the coated sand.
• Other objects of the present invention are to provide: a coated sand which permits a considerable improvement in ease of filling of a molding cavity of a forming mold used for producing a casting mold, with the coated sand, and a further improvement of a strength of the obtained casting mold; a method of producing the coated sand; and a method of producing the casting mold by using the coated sand.
• the present invention can be preferably embodied in various modes which will be described below.
• the various modes of the invention described below may be practiced in any combination. It is to be understood that the modes and technical features of the present invention are not limited to those described below, and can be recognized based on the inventive concept disclosed in the specification taken as a whole.
• the water glass is used as the binder, and the aqueous solution of the water glass is used to coat the refractory aggregate.
• the coated sand is obtained in the dry state, such that the entirety of the coated sand has the moisture percentage of not more than 0.5% by mass.
• the strength of the casting mold obtained by using the coated sand can be further improved by reducing the amount of the lumps included in the coated sand, according to the preferable mode of the present invention. Further, by controlling the nonvolatile content in the aqueous solution of the water glass so as to be a low value, the water glass having a high concentration can be diluted with the water, and the thus obtained aqueous solution of the water glass can be used to efficiently and uniformly coat the refractory aggregate with the water glass. Thus, it is possible to advantageously obtain the coated sand including only a small amount of the lumps, and more advantageously improve the strength of the casting mold obtained by using the coated sand.
• the coated sand according to the present invention is obtained by using the water glass as the binder. Accordingly, unlike the conventional resin coated sand obtained by using the organic binders such as the phenolic resin and the furan resin, the coated sand of the present invention can reduce or prevent generation of a gas component which has a low molecular weight and emits an odor, at the time of formation of the casting mold and casting of the molten metal. Therefore, the coated sand of the present invention has an advantage that its use does not result in generation of a gas, tar, odor and the like, and does not give rise to a problem of deterioration of production environment.
• a coated sand according to the present invention is obtained by mixing an aqueous solution of a water glass used as a binder, with a heated refractory aggregate, and evaporating water in the thus obtained mixture, in other words, evaporating the water contained in the aqueous solution of the water glass, for thereby forming a dry coating layer consisting of the water glass which serves as the binder, on surfaces of the refractory aggregate.
• the coated sand is in a dry state and has a sufficiently high degree of fluidity at the room temperature.
• a moisture percentage of the coated sand is controlled so as to be not more than 0.5% by mass, and advantageously not more than 0.3% by mass.
• the moisture percentage is preferably close to zero as far as possible.
• the coated sand which is provided with the coating layer of the water glass and which has the extremely low moisture percentage is used in the dry state in the absence of water, so that the coated sand flows smoothly and has excellent properties such as the sufficiently high degree of fluidity at the room temperature. Accordingly, it is possible to effectively improve ease of filling of a molding cavity of a forming mold used for producing a casting mold, with the coated sand, to advantageously obtain a sound casting mold and effectively improve a strength of the casting mold.
• the coated sand according to the present invention preferably includes only a small amount of composite particles so-called lumps, each of which is formed of a plurality of particles combined with each other, and which are generated during a production process of the coated sand.
• an amount of the coated sand which does not pass through the 20-mesh screen namely, an amount of the lumps left on the 20-mesh screen is not more than 3% by mass, and more preferably not more than 1 % by mass, with respect to a whole amount of the coated sand.
• the refractory aggregate of the coated sand is a refractory material which serves as a base material of the casting mold. Any one of various refractory particulate materials conventionally used for the casting mold may be used as the refractory aggregate.
• Specific examples of the refractory aggregate include: a silica sand; a regenerated silica sand; special sands such as an alumina sand, an olivine sand, a zircon sand and a chromite sand; slag particles such as a ferrochromium slag, a ferronickel slag and a converter slag; artificial particles such as alumina particles and mullite particles, and regenerated particles thereof; an alumina ball; and a magnesia clinker.
• the above-indicated refractory aggregates may be: a new or fresh sand; a regenerated or reclaimed sand which has been used once or a plurality of times as a molding sand to form the casting mold; or a mixture of the regenerated or reclaimed sand and the new or fresh sand.
• the refractory aggregate used in the present invention generally has a grain size of about AFS 40-80, and preferably not larger than about AFS 60 in order to make it easy to pass a steam through the coated sand and dry the coated sand in formation of the casting mold.
• the water glass used as the binder of the coated sand according to the present invention is a soluble silicate compound, and preferably an aqueous solution of an alkali metal silicate, such as sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, colloidal silica and alkyl silicate. It is possible to use a mixture of a plurality of kinds of the alkali metal silicates. Among various kinds of the alkali metal silicates, those having a molar ratio of silicon dioxide to an alkali metal oxide, which molar ratio is not smaller than 1.0 and smaller than 3.0, are preferably used.
• sodium silicate (silicate of soda) is advantageously used, since the coated sand obtained by using sodium silicate is not likely to suffer from blocking and has a high degree of formability.
• Commercially available sodium silicates are generally classified into No. 1 to No. 5 based on their SiO 2 / Na 2 O molar ratios. Specifically described, the sodium silicate No. 1 has the molar ratio SiO 2 / Na 2 O within a range between 2.0 and 2.3, the sodium silicate No. 2 has the molar ratio SiO 2 / Na 2 O within a range between 2.4 and 2.5, the sodium silicate No. 3 has the molar ratio SiO 2 / Na 2 O within a range between 3.1 and 3.3, the sodium silicate No.
• the sodium silicate No. 4 has the molar ratio SiO 2 / Na 2 O within a range between 3.3 and 3.5
• the sodium silicate No. 5 has the molar ratio SiO 2 / Na 2 O within a range between 3.6 and 3.8.
• the sodium silicates No. 1 to No. 3 are also specified in JIS K1408. Any one or a mixture of the above-indicated sodium silicates may be used in the present invention. It is possible to control the molar ratio SiO 2 / Na 2 O by mixing a plurality of kinds of the above-indicated sodium silicates.
• the sodium silicate used as the binder preferably has the molar ratio SiO 2 / Na 2 O not smaller than 1.0 and smaller than 3.0, and more preferably not smaller than 2.0 and smaller than 3.0, in order to obtain the coated sand which can fill the molding cavity with a particularly high filling density and which can give the casting mold having a high degree of the strength.
• the sodium silicate having the molar ratio SiO 2 / Na 2 O smaller than 2.0 is not commercially available, such a sodium silicate may be formed and used in the present invention.
• the sodium silicates having the molar ratio SiO 2 / Na 2 O not smaller than 2.0 and smaller than 3.0 are preferably used, since they are easily available and they give the coated sand having high degrees of fluidity and formability.
• the sodium silicates Nos. 1 and 2 are advantageously used.
• the sodium silicates Nos. 1 and 2 give the coated sand having satisfactory filling properties and strength properties, with a high degree of stability, within a wide range of concentration of these sodium silicates in the aqueous solution of the water glass.
• the coated sand obtained by using, as the binder, the sodium silicate having the molar ratio SiO 2 / Na 2 O not smaller than 2.0 and smaller than 3.0 has the high degrees of fluidity and formability, but absorbs a larger amount of water than the coated sands obtained by using the other kinds of the sodium silicates. Therefore, the coated sand using the sodium silicate having the molar ratio SiO 2 / Na 2 O not smaller than 2.0 and smaller than 3.0 is preferably used for applications where the coated sand is used right after its production, and suitably used in dry environments such as in dry regions and cold regions. Further, it is recommended to store the coated sand in the absence of water.
• the aqueous solution of the water glass used in the present invention is obtained by dissolving the water glass in water.
• a commercially available aqueous solution of the water glass is used as an undiluted solution, as purchased, or as a diluted solution obtained by adding water to the undiluted solution.
• a solid content in the aqueous solution which is obtained by subtracting amounts of volatile substances such as the water and a solvent contained in the aqueous solution from an amount of the aqueous solution, is called a nonvolatile content and corresponds to an amount of the soluble silicate compound such as the sodium silicate described above.
• a higher ratio of the nonvolatile content (solid content) in the aqueous solution indicates a higher concentration of the water glass in the aqueous solution.
• the nonvolatile content in the aqueous solution corresponds to an amount of a portion of the undiluted solution other than the water contained therein.
• the nonvolatile content in the aqueous solution corresponds to an amount of a portion of the aqueous solution other than the water contained in the undiluted solution and the water used to dilute the undiluted solution.
• the nonvolatile content in the aqueous solution of the water glass is adequately selected depending on the kind of the water glass, for example, but preferably held within a range of 20-45% by mass.
• the surfaces of the refractory aggregate can be evenly and uniformly coated with the water glass component, when the refractory aggregate and the aqueous solution of the water glass are mixed (kneaded) together.
• the casting mold having high degrees of flexural strength and hardness or resistance to scratching of its surface can be advantageously produced.
• the aqueous solution of the water glass is preferably prepared such that the nonvolatile content in the aqueous solution is not more than 45% by mass, and accordingly, a water content is not less than 55% by mass.
• the coating layer of the water glass is formed on the surfaces of the refractory aggregate by using the aqueous solution of the water glass preferably in an amount of 0.1-2.5 parts by mass, and particularly advantageously in an amount of 0.2-2.0 parts by mass, in terms of the solid content or the nonvolatile content in the aqueous solution, per 100 parts by mass of the refractory aggregate.
• the solid content in the aqueous solution of the water glass is measured in a manner described below:10g of a sample of the aqueous solution is weighed and put in a sample dish (a length: 90mm; a width: 90mm; a depth of 15mm) formed of an aluminum foil; the sample dish is held on a heating plate whose temperature is held at 180 ⁇ 1°C, for 20 minutes; the sample dish is reversed upside down and held on the heating plate for 20 minutes; the sample dish is removed from the heating plate and cooled within a desiccator; then the sample is weighed.
• a sample dish a length: 90mm; a width: 90mm; a depth of 15mm
• the sample dish is held on a heating plate whose temperature is held at 180 ⁇ 1°C, for 20 minutes
• the sample dish is reversed upside down and held on the heating plate for 20 minutes
• the sample dish is removed from the heating plate and cooled within a desiccator; then the sample is weighed.
• Solid content % Amount g ⁇ of the sample after drying / Amount g ⁇ of the sample before drying x 100
• the coating layer is formed on the surfaces of the refractory aggregate by using the aqueous solution of the water glass described above.
• the coating layer may contain suitable additives as necessary.
• the coating layer containing the additives is formed by: a method of initially mixing the suitable additives into the aqueous solution of the water glass, and then kneading or mixing the thus obtained mixture with the refractory aggregate; or a method of adding to the refractory aggregate, the suitable additives and the aqueous solution of the water glass separately from each other, and then uniformly kneading or mixing the thus obtained mixture.
• Solid oxides and salts are advantageously used as the additives.
• the solid oxides and salts contained in the coating layer permit an advantageous improvement of a moisture resistance of the coated sand. It is effective to use the solid oxides such as oxides of silicon, zinc, magnesium, aluminum, calcium, lead and boron.
• silicon dioxide, zinc oxide, aluminum oxide and boron oxide are particularly preferably used.
• the silicon dioxide is preferably a precipitated silica or a pyrogenic silica.
• examples of the salts include silicofluoride salts, silicates, phosphates, borates, tetraborates and carbonates.
• zinc carbonate, potassium metaborate, sodium tetraborate and potassium tetraborate are preferably used.
• the above-indicated solid oxides and salts are used in an amount of not more than 100% by mass, and preferably about 0.5-5% by mass, with respect to the nonvolatile content in the aqueous solution of the water glass.
• coupling agents which strengthen a bond between the refractory aggregate and the water glass (binder).
• the coupling agents include silane coupling agents, zirconate coupling agents and titanate coupling agents.
• lubricants which serve to improve the fluidity of the coated sand.
• lubricants examples include: waxes such as paraffin wax, synthetic polyethylene wax and montanic acid wax; fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide; alkylene fatty acid amides such as methylenebis stearic acid amide and ethylenebis stearic acid amide; stearic acid; stearyl alcohol; metal stearate; lead stearate; zinc stearate; calcium stearate; magnesium stearate; monoglyceride stearate; stearyl stearate; and hydrogenated oils.
• waxes such as paraffin wax, synthetic polyethylene wax and montanic acid wax
• fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide
• alkylene fatty acid amides such as methylenebis stearic acid amide and ethylenebis stearic acid amide
• mold releasing agents such as paraffins, waxes, light oils, machine oils, spindle oils, insulating oils, waste oils, plant oils, fatty acid esters, organic acids, graphite particulates, mica, vermiculite, fluorine-based mold releasing agents, and silicone-based mold releasing agents.
• Each of the above-indicated additives other than the above-described solid oxides and salts is generally used in an amount of not more than 5% by mass, and preferably not more than 3% by mass, with respect to the nonvolatile content in the aqueous solution of the water glass.
• the coated sand according to the present invention is produced by a method of uniformly kneading or mixing the aqueous solution of the water glass used as the binder and the additives used as necessary, with the heated refractory aggregate, such that the surfaces of the refractory aggregate are coated with the aqueous solution of the water glass and the water in the aqueous solution is evaporated, whereby the coated sand in the form of dry granules having fluidity at the room temperature is obtained.
• the water in the aqueous solution of the water glass (the coating layer) should be rapidly evaporated before solidification or curing of the water glass proceeds.
• the water in the aqueous solution of the water glass is evaporated within five minutes, and preferably within three minutes, after the aqueous solution is added to (mixed with) the refractory aggregate, to obtain the coated sand in the form of the dry granules.
• productivity of the coated sand is lowered due to an increase of a time required for the mixing (kneading) operation, and a risk of deactivation of the aqueous solution of the water glass is increased since the aqueous solution is exposed to CO 2 in the air for a longer period of time.
• the above-described method of producing the coated sand according to the present invention includes the steps of: preheating the refractory aggregate; and kneading or mixing the preheated refractory aggregate with the aqueous solution of the water glass.
• a temperature to which the refractory aggregate is preheated is adequately selected depending on the water content in the aqueous solution of the water glass and the amount of use of the aqueous solution, for example. It is desirable to preheat the refractory aggregate to a temperature of generally about 100-150°C, and preferably about 100-120°C. Where the preheating temperature of the refractory aggregate is excessively low, the water cannot be effectively evaporated, so that a time required for drying the coated sand is undesirably increased. Therefore, it is desirable to preheat the refractory aggregate to a temperature not lower than 100°C.
• the refractory aggregate is preheated to an excessively high temperature, curing of the water glass proceeds while the obtained coated sand is cooled, and the composite particles are formed, so that the coated sand has problems in terms of its function, particularly in its strength or other physical properties.
• the amount of the lumps in the form of the composite particles is effectively reduced.
• the coated sand according to the present invention is produced as described above, such that the moisture percentage of the coated sand is controlled so as to be not more than 0.5% by mass, and preferably not more than 0.3% by mass, whereby the coated sand can more easily fill the molding cavity of the forming mold used for producing the casting mold, and the casting mold formed by using the coated sand is given excellent properties.
• the casting mold is produced by a method including the steps of: filling the molding cavity of the forming mold which gives the intended casting mold, with the coated sand; blowing a steam into the molding cavity such that the steam is passed through the filler phase of the coated sand; and holding the coated sand within the forming mold until the coated sand is dried and solidified or cured.
• the forming mold such as a metallic forming mold or a wooden forming mold to be filled with the dry coated sand is preferably preheated and kept at an elevated temperature, to advantageously dry the coated sand moistened with the steam.
• the forming mold is generally preheated to and kept at a temperature of about 60-140°C, preferably about 80-130°C, and particularly preferably about 100-120°C. Where the forming mold is kept at an excessively high temperature, the steam does not sufficiently reach a surface of the filler phase of the coated sand which has been filled into the forming mold. On the other hand, where the forming mold is kept at an excessively low temperature, an undesirably long time is required for drying the formed casting mold.
• the coated sand is preferably held within the forming mold for a predetermined period of time, before the obtained casting mold is removed from the forming mold.
• the coated sand is preferably held within the forming mold for 30-300 seconds, and more preferably for 30-180 seconds, after passing of the steam through the coated sand, such that the coated sand is dried while being held within the forming mold.
• the coated sand moistened with the steam has a high degree of thermal conductivity, so that by holding the coated sand within the preheated forming mold, the coated sand can be uniformly heated and solidified or cured.
• the dry coated sand used to fill the forming mold is preferably preheated.
• the forming mold is filled with the coated sand heated to a temperature not lower than 30°C, a flexural strength of the obtained casting mold can be advantageously improved.
• the coated sand is preferably heated to a temperature of about 30-100°C, and advantageously about 40-80°C.
• a pressurized steam is blown into the molding cavity through inlets provided in the forming mold, such that the steam is passed through the filler phase of the coated sand formed within the molding cavity, to moisten the filler phase and bond together particles of the coated sand, whereby a mass of the coated sand (a mass of the bonded particles of the coated sand) in the form of an integral casting mold is obtained.
• the water glass is generally solidified by evaporation of the water to dryness.
• the oxides and the salts are used as a curing agent, the water glass is cured.
• the curing agent is added, so that the filler phase of the coated sand is cured.
• the filler phase of the coated sand may be merely solidified.
• the steam may be a saturated steam or a superheated steam.
• the superheated steam is used in the state of a wet steam containing water drops.
• the superheated steam in the state of a dry steam which does not contain the water drops is not used to moisten the coated sand, but may be used to dry the coated sand.
• a temperature of the steam blown into the molding cavity through the inlets in the forming mold and passed through the filler phase of the coated sand is generally held within a range of about 80-150°C, and preferably about 95-120°C.
• the steam having a temperature around 100°C is advantageously used, since the steam having an excessively high temperature requires a large amount of energy for its production.
• the steam is passed through the filler phase of the coated sand at a gauge pressure of about 0.01-0.3MPa, and preferably about 0.01-0.1 MPa.
• the gauge pressure within the above-described ranges makes it possible to pass the steam through the entirety of the casting mold formed within the forming mold, and to reduce times required for passing of the steam and drying of the casting mold, and accordingly reduce a time required for formation of the casting mold. Further, the gauge pressure within the above-described ranges permits formation of the casting mold even in the case where the coated sand does not allow the steam to easily pass therethrough. An excessively high gauge pressure causes occurrence of staining around the inlets, while an excessively low gauge pressure gives rise to a risk that the steam cannot be passed through the entirety of the filler phase of the coated sand, so that the coated sand cannot be sufficiently moistened.
• the steam is blown into the molding cavity through the inlets provided in the forming mold, and passed through the coated sand (filler phase) which has been filled into the molding cavity, as described above.
• a period for blowing the steam is adequately selected depending on the size of the forming mold and the number of the inlets, for example, so as to sufficiently moisten the water glass which covers the surfaces of the coated sand and serves as the binder, by blowing the steam to the surfaces of the coated sand, and accordingly to bond (bind) together the particles of the coated sand.
• the steam is generally blown into the molding cavity for a period of about 2-60 seconds. Where the period for blowing the steam is excessively short, it is difficult to sufficiently moisten the surfaces of the coated sand.
• the period for blowing the steam is excessively long, there arises a risk of dissolution and discharge flow of the binder covering the surfaces of the coated sand.
• Passage of the steam through the coated sand which has been filled into the forming mold may be further improved by blowing the steam into the forming mold while sucking out an atmosphere within the forming mold through an exhaust vent provided in the forming mold.
• the method of moistening the coated sand is not particularly limited, but the above-described method of passing the steam through the coated sand is advantageously employed, from standpoints of the time required for forming the casting mold and simplicity of the process for forming the casting mold.
• the steam may be blown into the molding cavity while a dry air, a heated dry air, a nitrogen gas or an argon gas is simultaneously blown into the molding cavity and passed through the filler phase of the coated sand, in order to actively dry the filler phase of the coated sand moistened with the steam.
• a dry air, a heated dry air, a nitrogen gas or an argon gas is simultaneously blown into the molding cavity and passed through the filler phase of the coated sand, in order to actively dry the filler phase of the coated sand moistened with the steam.
• the dry air, the heated dry air, the nitrogen gas or the argon gas is preferably blown into the molding cavity and passed through the filler phase of the casting mold, after the blowing of the steam into the molding cavity, in order to actively dry the filler phase of the coated sand moistened with the steam.
• the filler phase of the coated sand is rapidly dried even in its central part, whereby curing or solidification of the filler phase is more advantageously accelerated to advantageously increase a curing rate of the filler phase.
• the flexural strength or other properties of the obtained casting mold can be advantageously improved, and the time required for formation of the casting mold can be advantageously reduced. Blowing of the dry air or the like into the molding cavity is desirably carried out simultaneously with the blowing of the steam, and continued after termination of the blowing of the steam.
• At least one of a carbon dioxide gas (a CO 2 gas), an ester gas, and a carbonate gas may be blown into the molding cavity, between a moment of initiation of the blowing of the steam and a moment of termination of the blowing of the dry air or the like. Solidification of the binder can be further accelerated by neutralizing the binder with the carbon dioxide gas, the ester gas, or the carbonate gas. Blowing of the carbon dioxide gas, the ester gas, or the carbonate gas may be carried out simultaneously with the blowing of the steam, or after termination of the blowing of the steam. Also, the blowing of the carbon dioxide gas, the ester gas, or the carbonate gas may be carried out simultaneously with the blowing of the dry air or the like, or with a time lag with respect to the blowing of the dry air or the like.
• a carbon dioxide gas a CO 2 gas
• an ester gas an ester gas
• a carbonate gas may be blown into the molding cavity, between a moment of initiation of the blowing of the steam
• a pressure within the molding cavity may be reduced to a pressure preferably lower than the atmospheric pressure.
• a production machine of the casting mold may be provided with an apparatus for sucking the air from the molding cavity.
• the casting mold formed as described above may be heated with a micro wave to selectively evaporate the water only. If the water exists within the casting mold, the binder may be redissolved in the water, giving rise to a risk of deterioration of the flexural strength of the casting mold. Further, the water within the casting mold may be decomposed by the heat at the time of pouring of a molten metal, with a result of generation of a hydrogen gas, giving rise to an inherent problem of occurrence of a gas defect in the obtained cast product. Therefore, heating the formed casting mold with the micro wave to remove the water within the casting mold is an effective means for storage of the casting mold and an improvement of the quality of the cast product.
• the method of forming the casting mold by using the coated sand according to the present invention it is possible to employ various known methods other than the above-described method of filling the forming mold with the coated sand.
• a multilayer molding method specifically, a method of directly forming a three-dimensional casting mold by stacking layers of the coated sand, and curing a part of a stack of the layers of the coated sand, which part corresponds to the intended casting mold, as disclosed in JP-T-7-507508 and JP-A-9-141386 , for example.
• the CS obtained in each example was sieved with a 20-mesh screen to obtain composite particles (lumps) whose diameter is not smaller than 20-mesh and which were left on the screen.
• the amount of the lumps was obtained as a percentage value of the mass of the lumps with respect to the mass of the kneaded sand.
• Amount % ⁇ of the lumps Mass of the lumps / Mass of the lumps + Mass of the sand not larger than 20 - mesh ⁇ x 100
• a test piece having a width of 25.4mm, a thickness of 25.4mm and a length of 200mm was formed, and measured of its breaking load by using a measuring device (a digital molding sand strength tester available from TAKACHIHO SEIKI CO., LTD., JAPAN).
• the test piece formed by using each CS and having the width of 25.4mm, the thickness of 25.4mm and the length of 200mm was measured of its scratch hardness by using a scratch hardness tester (GF type). Initially, a tooth provided at a distal end of the scratch hardness tester was pressed against a surface of the test piece. Then, a black lever provided in an upper portion of the tester was revolved one turn in the clockwise direction, and then revolved one turn in the counterclockwise direction. This set of operations of revolving the lever was repeated five more times, so that the tooth was gradually embedded into the test piece. A depth (mm) by which the tooth was embedded into the test piece was read on a scale provided on a side surface of the tester. A smaller depth indicates a higher degree of the scratch hardness of the test piece, while a larger depth indicates a lower degree of the scratch hardness.
• GF type scratch hardness tester
• the filling percentage was calculated as a percentage value of a specific gravity (calculated by dividing a mass of the test piece by its volume) of the above-described test piece with respect to an absolute specific gravity of an aggregate.
• Filling percentage % Mass g of the test piece / Volume cm 3 ⁇ of the test piece / Absolute specific gravity g / cm 3 ⁇ of the aggregate x 100
• a commercially available artificial molding sand LUNAMOS #50 (Trade Name; available from Kao Corporation, JAPAN) was provided as a refractory aggregate.
• An aqueous solution of a water glass was prepared by diluting commercially available sodium silicate No. 1 (Trade Name; available from Fuji Kagaku Corp., JAPAN) used as a binder, with water, such that the aqueous solution of the water glass has a nonvolatile content (an amount of a portion of the aqueous solution except the water contained therein) of 46.1%.
• a Shinagawa-shiki universal stirrer (5DM-r type; manufactured by DALTON CO., LTD., JAPAN) was charged with the LUNAMOS #50 heated to a temperature of about 120°C, and the above-described aqueous solution of the water glass was introduced into the stirrer in an amount of 0.5 part, in terms of its nonvolatile content, with respect to 100 parts of the LUNAMOS #50.
• the contents in the stirrer were kneaded for three minutes to evaporate the water. After the contents were stirred and mixed until an aggregate structure of the sand particles collapsed, the contents were taken out of the stirrer, whereby a dry coated sand (CS) No. 1 having free flowing characteristics at the room temperature was obtained.
• CS dry coated sand
• the amount of the lumps included in the thus obtained CS and the moisture amount in the CS were measured. Further, the conditions of adhesion of the sand to the surface of the kneading pot were observed. Results of the measurements and observation are shown in a table given below.
• CS Nos. 2 to 9 were obtained by the same procedure as in the Production Example 1, except that aqueous solutions of the water glass were prepared by diluting the commercially available sodium silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 44.0%, 41.6%, 39.7%, 37.5%, 33.5%, 30.0%, 25.0% and 20.0%.
• aqueous solutions of the water glass were prepared by diluting the commercially available sodium silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 44.0%, 41.6%, 39.7%, 37.5%, 33.5%, 30.0%, 25.0% and 20.0%.
• CS Nos. 10 to 15 were obtained by the same procedure as in the Production Example 1, except that aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 46.3%, 44.1%, 41.3%, 38.3%, 26.9% and 20.0%.
• aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 46.3%, 44.1%, 41.3%, 38.3%, 26.9% and 20.0%.
• CS Nos. 16 to 18 were obtained by the same procedure as in the Production Example 1, except that aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 37.5%, 25.6% and 12.8%.
• aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 37.5%, 25.6% and 12.8%.
• CS Nos. 19 to 21 were obtained by the same procedure as in the Production Example 1, except that aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 33.2%, 27.3% and 20.0%.
• aqueous solutions of the water glass were prepared by diluting commercially available sodium silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solutions have the respective different nonvolatile contents of 33.2%, 27.3% and 20.0%.
• CS No. 22 was obtained by the same procedure as in the Production Example 1, except that a commercially available alumina-based spherical aggregate ESPEARL #60 (Trade Name; available from Yamakawa Sangyo Co., Ltd., JAPAN) was used as the refractory aggregate, and that the nonvolatile content in the aqueous solution of the water glass was 33.5%.
• ESPEARL #60 Trade Name; available from Yamakawa Sangyo Co., Ltd., JAPAN
• CS No. 23 was obtained by the same procedure as in the Production Example 1, except that MIKAWA KEISA No. 7 (Trade Name; available from Mikawa Keisa K.K., JAPAN) was used as the refractory aggregate, and that the water glass was used in an amount of 1.0 part, in terms of its nonvolatile content, with respect to 100 parts of the MIKAWA KEISA No. 7, while the nonvolatile content in the aqueous solution of the water glass was 33.5%.
• MIKAWA KEISA No. 7 Traffic Name; available from Mikawa Keisa K.K., JAPAN
• CS No. 24 was obtained by the same procedure as in the Production Example 1, except that an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 15.0%.
• an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 15.0%.
• CS No. 25 was obtained by the same procedure as in the Production Example 1, except that an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 13.3%.
• an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 13.3%.
• CS No. 26 was obtained by the same procedure as in the Production Example 1, except that an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 9.6%.
• an aqueous solution of the water glass was prepared by diluting the commercially available sodium silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used as the binder, with the water, such that the aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 9.6%.
• CS No. 27 was obtained by the same procedure as in the Production Example 1, except that the commercially available sodium silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used as the binder was diluted with the water, such that the thus prepared aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 15.0%.
• the commercially available sodium silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used as the binder was diluted with the water, such that the thus prepared aqueous solution has the nonvolatile content (the amount of the portion of the aqueous solution except the water contained therein) of 15.0%.
• Each of the CS Nos. 1 to 27 obtained in the above-described Production Examples and having a temperature of 20°C was blown into a forming mold heated to 110°C, at a gauge pressure of 0.3MPa, such that the forming mold was filled with the CS. Then, a steam having a temperature of 99°C was blown into the forming mold, at a gauge pressure of 0.05MPa for five seconds, such that the steam was passed through the filler phase of the coated sand which has been filled into the forming mold. After blowing of the steam was terminated, a hot air having a temperature of 150°C was blown into the forming mold, at a gauge pressure of 0.03MPa for two minutes, to cure the CS which has been filled into the forming mold. The thus produced casting mold was used as a test piece (25.4mm x 25.4mm x 200mm).
• test pieces produced by using the respective CS Nos. 1 to 27 were measured of their filling percentage, flexural strength and scratch hardness, according to the methods described above. Results of the measurements are shown in Tables 1 to 3 given below.
• the coated sand can be produced with a high degree of freedom of choice of its composition, and the obtained coated sand has a high degree of formability.
• the sodium silicate Nos. 3 to 5 having the SiO 2 /Na 2 O molar ratios within a range between 3.0 and 4.0 are used, as in the Examples 16 to 21, sufficiently high degrees of the physical properties and formability are achieved only within a narrow range of the nonvolatile content in the aqueous solution of the water glass. Accordingly, it is understood that the use of the sodium silicate Nos. 3 to 5 results in reduction of the freedom of choice of the composition of the coated sand.

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• 2013
  • 2013-12-18 WO PCT/JP2013/083903 patent/WO2014098129A1/fr active Application Filing
  • 2013-12-18 CN CN201380067209.3A patent/CN104903023B/zh active Active
  • 2013-12-18 JP JP2014553179A patent/JP6193884B2/ja active Active
  • 2013-12-18 EP EP13864998.3A patent/EP2937160A4/fr not_active Withdrawn
• 2015
  • 2015-05-07 US US14/706,296 patent/US20150231691A1/en not_active Abandoned

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