CN115461171A - Method for manufacturing casting mold - Google Patents

Method for manufacturing casting mold Download PDF

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Publication number
CN115461171A
CN115461171A CN202180031693.9A CN202180031693A CN115461171A CN 115461171 A CN115461171 A CN 115461171A CN 202180031693 A CN202180031693 A CN 202180031693A CN 115461171 A CN115461171 A CN 115461171A
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CN
China
Prior art keywords
precoated sand
dry
sand
mold
manufacturing
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CN202180031693.9A
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Chinese (zh)
Inventor
前田博信
高间智宏
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Asahi Yukizai Corp
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Asahi Yukizai Corp
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Priority claimed from JP2020080481A external-priority patent/JP7418279B2/en
Priority claimed from JP2020080483A external-priority patent/JP7467221B2/en
Application filed by Asahi Yukizai Corp filed Critical Asahi Yukizai Corp
Publication of CN115461171A publication Critical patent/CN115461171A/en
Pending legal-status Critical Current

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    • 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
    • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
    • 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
    • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
    • B22C1/10—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for influencing the hardening tendency of the mould material
    • 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
    • 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

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mold Materials And Core Materials (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)

Abstract

Provided is a method for industrially advantageously producing a mold having improved mold properties such as strength, moisture resistance and scratch hardness. After forming wet precoated sand in a heated state by adding an aqueous medium to dry precoated sand obtained by covering the surface of a refractory aggregate with a water-soluble binder, the wet precoated sand is filled into a predetermined preheated mold while maintaining the heated state, and molding is performed.

Description

Method for manufacturing casting mold
Technical Field
The present invention relates to a method for producing a mold, and more particularly, to a method for advantageously producing a mold having excellent mold characteristics.
Background
Conventionally, as one of the molds used for casting molten metal, a mold has been used which is formed into a desired shape by using a coated sand (mold material) having a structure in which the surface of a refractory aggregate (molding sand) is covered with a predetermined binder (binder). As the binder in such coated sand, in addition to an inorganic binder such as water glass, an organic binder containing a resin such as a phenol resin, a furan resin, or a urethane resin is used, and a molding method of a self-hardening mold using the binder has been put into practical use.
Among these binders, various methods have been proposed, in which a water-soluble binder is used in the form of an aqueous solution, and kneaded with a predetermined refractory aggregate to form coated sand in a form in which the surface of the refractory aggregate is covered with the water-soluble binder, and then the coated sand is cast. In the molding of a mold using the coated sand, a mold filled with the coated sand is usually preheated to a predetermined temperature in order to quickly cure and harden the coated sand and obtain desired properties such as strength.
For example, japanese patent laid-open No. 2012-76115 proposes the following method: a mold having a desired shape is produced by filling a mold with dry precoated sand having good fluidity, which is obtained by covering a predetermined refractory aggregate with water glass, which is one of the water-soluble binders, blowing steam or supplying water into the mold to wet the binder layer on the surface of the precoated sand, and then heating and curing the binder layer.
However, with this method of manufacturing a mold, the following problems are potentially present: since the precoated sand filled in the mold is humidified by supplying steam or water, it is difficult to uniformly humidify the whole of the filled precoated sand, and thus the physical properties of the molded mold vary depending on the part of the mold, and are not uniform. If the dissolution of the water-soluble binder covering the coated sand is insufficient due to the supply of the water, a concentration difference (concentration difference of the binder component) is generated between the aggregate-side portion of the adhesive layer and the intermediate portion between the aggregates at the bonded portion between the coated sands, and the moisture resistance is deteriorated. In particular, when water glass is used as the binder, the concentration difference is easily caused, and therefore, a large amount of sodium components which are easily dissolved in water are present on the surface of the binder layer, and the silicic acid component remains undissolved on the aggregate side, thereby causing deterioration of moisture resistance. Further, when water vapor or water is excessively supplied or unevenly supplied to moisten the precoated sand filled in the mold, and the excessive water is locally present, it takes time to heat and dry and cure the part, and thus there is a problem that a molding cycle is potentially lengthened, and when the mold is taken out in a state where the filling layer of the precoated sand in the mold is insufficiently dried, there is also a problem that moisture resistance of the mold deteriorates due to the remaining water.
In addition, in japanese patent laid-open No. 2012-501850, the following method is proposed: the target mold is molded by using dry precoated sand obtained by forming a water glass layer on the surface of mineral sand or synthetic sand as a refractory aggregate, filling the sand into a mold preheated to a temperature of 20 ℃ to 160 ℃, and then hardening the filled precoated sand while blowing steam.
Further, the molding method as described above is potentially problematic in that: since the precoated sand charged into the mold is usually supplied at normal temperature, when the precoated sand in the normal temperature state is charged into a preheated mold and molded, heat transfer to the charged precoated sand is likely to become uneven, which causes uneven curing and/or hardening of the precoated sand, and makes it difficult to stably express the physical properties of the mold, such as a decrease in the strength of the obtained mold. Moreover, the precoated sand in the normal temperature state has the following potential problems: even when the molding material is filled into a preheated mold, the temperature is not easily raised immediately, and therefore, there is a fear that the water glass is not sufficiently dissolved, and the adhesion between the coated sands is weakened, and the mold strength cannot be sufficiently exhibited.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2012-76115
Patent document 2: japanese Kohyo publication No. 2012-501850
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a mold having improved mold properties, such as strength, moisture resistance, and scratch hardness (scratch hardness), and to provide a method for industrially advantageously producing a mold having improved mold properties.
Means for solving the problems
In order to solve the above-described problems, the present invention may be suitably implemented in various embodiments described below, and any combination of the various embodiments described below may be adopted. The embodiments and technical features of the present invention are not limited to the contents described below, and may be understood as technical aspects that can be recognized based on the inventive concept understood from the entire description of the specification.
In order to solve the above-described problems, a first aspect of the present invention is a method for manufacturing a casting mold, characterized in that a dry precoated sand obtained by covering the surface of a refractory aggregate with a water-soluble binder is prepared, an aqueous medium is added thereto, and the mixture is kneaded to form a wet precoated sand in a heated state, and then the wet precoated sand is filled into a predetermined preheated mold while maintaining the heated state, and molding is performed.
In the second aspect of the method for manufacturing a mold according to the present invention, the dry precoated sand is preheated, and then the aqueous medium is added and kneaded, whereby the dry precoated sand is moistened, and the moist precoated sand is formed in a heated state.
In a third aspect of the present invention, the preheating temperature of the dry precoated sand is 32 to 150 ℃.
In a fourth aspect of the present invention, the dry coated sand in a normal temperature state is heated while being kneaded, and an aqueous medium is added to form the wet coated sand in a heated state.
In a fifth aspect of the present invention, the kneading and heating of the dry precoated sand are performed in a mixing device, and the mixing device is preheated before the dry precoated sand is charged.
In a sixth aspect of the present invention, a wall surface of the mixing device, which is in contact with the dry coated sand, is heated to a temperature of 50 to 200 ℃.
In a seventh aspect of the present invention, the dry precoated sand is kneaded and heated, and then the aqueous medium is added immediately before the kneading is completed.
In an eighth aspect of the present invention, the addition of the aqueous medium is started 30 seconds to 2 minutes before the end of the kneading time.
In a ninth aspect of the present invention, the aqueous medium is in a liquid state or a vapor state.
In a tenth aspect of the present invention, the wet coated sand in a heated state is 30 to 100 ℃.
In an eleventh aspect of the present invention, the aqueous medium is preheated to a temperature lower than the boiling point thereof.
Furthermore, according to a twelfth aspect of the method for producing a mold of the present invention, the preheating temperature of the aqueous medium is 30 to 100 ℃.
In a thirteenth aspect of the present invention, the aqueous medium is added in a proportion of 0.3 to 6 parts by mass with respect to 100 parts by mass of the dry coated sand.
In a fourteenth aspect of the present invention, the mold is heated to a temperature of 40 to 250 ℃.
In a fifteenth aspect of the present invention, the water-soluble binder is a soluble silicic acid compound.
In a sixteenth aspect of the present invention, the dry coated sand contains a filling property improving agent.
In addition, according to a seventeenth aspect of the method for manufacturing a mold of the present invention, the dry coated sand contains a moisture resistance improver.
Furthermore, according to an eighteenth aspect of the present invention, the prepared dry precoated sand is transported to a molding site as a manufacturing site of a mold, and then the aqueous medium is added to the dry precoated sand and kneaded at the molding site, thereby forming the wet precoated sand in a heated state.
ADVANTAGEOUS EFFECTS OF INVENTION
In this way, in the method for producing a mold of the present invention, the wet-state coated sand is formed in a heated state from the dry-state coated sand obtained by using a water-soluble binder such as water glass as a binder, and then the wet-state coated sand is molded with the preheated mold while maintaining the heated state in the wet state, so that the effect of the water-soluble binder-formed coating layer in the coated sand as a binder can be advantageously improved, the bending strength and the moisture resistance of the obtained mold can be effectively improved, the scratch hardness of the mold can be advantageously improved, and a mold having excellent mold characteristics can be industrially advantageously produced.
Detailed Description
In the method for producing a mold of the present invention, the precoated sand in a dry state prepared in advance is usually produced by mixing a water-soluble binder in an aqueous solution state as a binder with a refractory aggregate and then evaporating moisture from the mixture, in other words, evaporating moisture of the water-soluble binder in an aqueous solution state. The obtained precoated sand is a dry precoated sand in which a dried coating layer formed of a solid component of a water-soluble binder as a binder is formed on the surface of the refractory aggregate in a predetermined thickness, and has good room-temperature fluidity.
In the coated sand, the range of the moisture content for obtaining a dry state differs depending on the properties of the water-soluble binder. Therefore, the dry state in the present invention means a state in which a measured value of the dynamic repose angle can be obtained when the dynamic angle of repose is measured, regardless of the amount of water. Here, the dynamic repose angle is a value obtained by measuring an angle formed between a slope of a precoated sand layer flowing in a cylinder and a horizontal plane when the slope is flat by holding precoated sand in the cylinder in which one end portion in the axial direction is closed with a transparent plate material (for example, putting precoated sand in a container having a diameter of 7.2cm × a height of 10cm to a half of the volume of the container), holding the cylinder with the axis in the horizontal direction, and rotating the cylinder around the horizontal axis at a constant speed (for example, 25 rpm). The dynamic repose angle is preferably 80 ° or less, more preferably 45 ° or less, and still more preferably 30 ° or less. In particular, when the refractory aggregate is spherical, the dynamic repose angle can be easily set to 45 ° or less. When the precoated sand does not flow in the cylinder in a wet state, the inclined surface of the precoated sand layer cannot form a flat surface, and the dynamic repose angle cannot be measured, the precoated sand is referred to as wet precoated sand.
In addition, in the present invention, since the dry precoated sand as described above is used as a molding material, the pot life thereof is long, and the storage stability can be advantageously improved, a large amount of such dry precoated sand can be prepared in advance at a place such as a work place different from a molding site, and a part of the dry precoated sand can be transported to the molding site and used for molding a target mold, which also contributes greatly to the efficiency of the molding work.
As the refractory aggregate constituting the coated sand, any of various refractory granular or powdery materials conventionally used for casting molds can be used, and specifically, specific examples of the refractory aggregate include silica sand and regenerated silica sand, and specific sands such as alumina sand, olivine sand, zircon sand and chromite sand, slag-based granules such as ferrochrome-based slag, ferronickel-based slag and converter slag; artificial grains such as alumina-based grains and mullite-based grains, and regenerated grains thereof; alumina spheres, magnesium frit, and the like. The refractory aggregate may be fresh sand, reclaimed sand or reclaimed sand used once or more times as foundry sand in molding a mold, or mixed sand obtained by adding fresh sand to the reclaimed sand or reclaimed sand and mixing the same, without limitation. The refractory aggregate is generally an aggregate having a particle size of about 40 to 130 in terms of AFS index, and preferably an aggregate having a particle size of about 60 to 110.
The refractory aggregate is preferably spherical, and more specifically, it has a particle shape coefficient (coefficient of orientation) of 1.2 or less, and more preferably 1.0 to 1.1. By using a refractory aggregate having a grain shape coefficient of 1.2 or less, the fluidity and filling property are good, and the number of joints between aggregates increases, so that the amount of binder and the amount of additive required to exhibit the same strength can be reduced. The particle shape coefficient of the aggregate used herein is generally used as a criterion for indicating the shape of the outer shape of the particle, and is also referred to as a particle shape index, and a value closer to 1 means closer to a spherical shape (a regular sphere). The grain size factor is expressed by a value calculated using a sand surface area measured by a known method, and means: the surface area of each 1g of actual sand grains is measured, for example, using a sand surface area measuring instrument (manufactured by Georg Fischer Ltd.), and the surface area is divided by the theoretical surface area. The theoretical surface area is a surface area assuming that all the sand grains are spherical.
The binder covering the refractory aggregate is also referred to as a binder, and in the present invention, a water-soluble binder is used. As the water-soluble binder, any of inorganic polymers, thermosetting resins, saccharides, synthetic polymers, salts, and proteins can be used as long as it is water-soluble. These may be used alone or two or more of them may be used selectively, and an inorganic polymer is particularly preferably used. These water-soluble binders can be used by diluting them with water or a solvent in advance.
Examples of the inorganic polymer used as the water-soluble binder include water glass, colloidal silica, alkyl silicate, bentonite, cement, and the like, and among these, water glass is preferably used. The water glass is a solution of a soluble silicic acid compound, and examples of such silicic acid compounds include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, and the like, and hydrates thereof, such as sodium metasilicate nonahydrate, sodium metasilicate pentahydrate, and the like.
Further, such sodium silicates are generally based on SiO 2 /Na 2 The molar ratio of O is used in the range of 1 to 5. Specifically, sodium silicate No. 1 is SiO 2 /Na 2 Sodium silicate with O molar ratio of 2.0-2.3, and No. 2 SiO 2 /Na 2 Sodium silicate having a molar ratio of O of 2.4 to 2.6, and further sodium silicate No. 3 is SiO 2 /Na 2 Sodium silicate with the molar ratio of O being 2.8-3.3. In addition, sodium silicate No. 4 is SiO 2 /Na 2 Sodium silicate with molar ratio of O3.3-3.5, and sodium silicate No. 5 is SiO 2 /Na 2 Sodium silicate with the molar ratio of O being 3.6-3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS-K-1408. These sodium silicates may be used alone or in combination, and SiO may be arbitrarily adjusted by mixing 2 /Na 2 Molar ratio of O. In addition, siO 2 /Na 2 The molar ratio of O is not limited to the range defined in sodium silicate nos. 1 to 5, and may be, for example, in the range of 0.8 to 4.0.
To say thatIt is clear that, in order to favorably obtain the dry coated sand used in the present invention, siO, which is a sodium silicate constituting water glass used as a binder, is used 2 /Na 2 The molar ratio of O is preferably 1.9 or more, preferably 2.0 or more, and more preferably 2.1 or more, and sodium silicates corresponding to nos. 1 and 2 are particularly advantageously used in the above classification of sodium silicates. The sodium silicate nos. 1 and 2 stably obtained dry coated sand having good characteristics even in a wide range of the concentration of sodium silicate in water glass. In addition, siO of the sodium silicate 2 /Na 2 The upper limit of the molar ratio of O is appropriately selected depending on the characteristics of the water glass in the form of an aqueous solution, and is usually 3.5 or less, preferably 3.2 or less, and more preferably 2.7 or less. Here, if SiO 2 /Na 2 When the molar ratio of O is less than 1.9, the viscosity of the water glass is low, and if the water content is not reduced to a large extent, the water glass is hard to be in a dry state, while when the molar ratio is more than 3.5, the solubility in water is reduced, and the adhesion to the surface of the refractory aggregate is insufficient, so that there is a problem that the adhesive area is not obtained, and the mold strength is reduced.
The water glass used in the present invention is a solution of a silicic acid compound dissolved in water, and may be used as it is in a commercially available stock solution, or may be used in a diluted state by adding water to such stock solution. The solid content (water glass component) obtained by removing volatile substances such as water and solvents from such water glass is referred to as a nonvolatile content, and corresponds to a soluble silicic acid compound such as sodium silicate. Further, the higher the proportion of such nonvolatile components (solid components), the higher the silicate compound concentration in the water glass becomes. Therefore, when the nonvolatile component of the water glass used in the present invention is constituted only by the stock solution, the ratio corresponds to the amount of water removed from the stock solution, and when a diluted solution obtained by diluting the stock solution with water is used, the amount of water removed from the stock solution and the amount of water used for dilution correspond to the nonvolatile component of the water glass used.
The nonvolatile content of the water glass is preferably contained in an appropriate ratio depending on the kind of the water glass component (soluble silicate compound), and is preferably 20 to 50 mass%. By appropriately making the water glass component corresponding to the nonvolatile component present in the aqueous solution, the water glass component can be uniformly and uniformly coated on the refractory aggregate at the time of mixing (kneading) with the refractory aggregate, and thus the desired mold can be favorably formed by the present invention. When the concentration of the water glass component in the water glass is too low and the total amount of nonvolatile components is less than 20 mass%, it is necessary to increase the heating temperature or extend the heating time for drying the coated sand, which causes problems such as energy loss. In addition, when the proportion of the nonvolatile component in the water glass is too high, it becomes difficult to uniformly coat the surface of the refractory aggregate with the water glass component, which causes a problem in improving the properties of the intended mold, and it is desirable to prepare the water glass in the form of an aqueous solution so that the nonvolatile component becomes 50 mass% or less, and the moisture content becomes 50 mass% or more.
Examples of the thermosetting resin which is one of the water-soluble binders other than the inorganic polymer include a resol-type phenol resin, a furan resin, a water-soluble epoxy resin, a water-soluble melamine resin, a water-soluble urea resin, a water-soluble unsaturated polyester resin, and a water-soluble alkyd resin. In addition, it is also possible to improve the thermosetting property of the thermosetting resin by mixing a curing agent such as an acid or an ester with the thermosetting resin. Among these thermosetting resins, a resol-type phenol resin is preferably used, and this phenol resin can be produced by reacting a phenol and a formaldehyde in the presence of a reaction catalyst. In the present invention, a water-soluble alkaline resol resin is given as a suitable example of the phenol resin. When such an alkaline resol resin is used, a mold that can be used in a wide range of fields such as cast iron/cast steel can be provided.
Further, as the saccharide which is another example of the water-soluble binder, known saccharides such as monosaccharides, oligosaccharides, and polysaccharides can be used, and 1 kind of the saccharides can be selected from various monosaccharides, oligosaccharides, and polysaccharides and used alone, or a plurality of kinds can be used in combination, and there is no limitation. Among these, examples of the monosaccharide include glucose (glucose), fructose (fructose), galactose, and the like, and examples of the oligosaccharide include disaccharides such as maltose (maltose), sucrose (sucrose), lactose (lactose), cellobiose, and the like. Examples of the polysaccharide include starch sugar, dextrin, xanthan gum, curdlan, pullulan (pullulan), cyclodextrin, chitin, cellulose, and starch. Gums (gum) of plant mucilages such as gum arabic may be used, and carboxylic acids may be used as a curing agent for saccharides, particularly polysaccharides.
Further, examples of the synthetic polymer used as the water-soluble binder include polyethylene oxide, poly- α -hydroxyacrylic acid, acrylic copolymer, acrylate copolymer, methacrylate copolymer, polyacrylamide, anionic polyacrylamide, cationic polyacrylamide, polyaminoalkyl methacrylate, acrylamide/acrylic acid copolymer, polyvinylsulfonic acid, polystyrenesulfonic acid, sulfonated maleic acid polymer, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyvinylmethyl ether, polyether-modified silicone, polyvinyl acetate, and modified products thereof. Further, they are used alone or in combination.
Further, as the salt, a salt obtained by adding water and then drying and solidifying the salt can be used, and examples thereof include sulfate such as magnesium sulfate and sodium sulfate, bromide such as sodium bromide and potassium bromide, carbonate such as sodium carbonate and potassium carbonate, chloride such as barium chloride, sodium chloride and potassium chloride, and the like. Examples of the protein include gelatin and gelatin.
The water-soluble binder is preferably used in an amount of 0.1 to 5 parts by mass, in terms of solid content only in view of nonvolatile components, based on 100 parts by mass of the refractory aggregate, and particularly preferably 0.2 to 2.5 parts by mass, to form a predetermined coating layer on the surface of the refractory aggregate. The measurement of the solid content is carried out in the same manner as in the conventional art, and can be carried out, for example, according to the method described in international publication No. WO 2019/132006.
If the amount of the water-soluble binder is too small, it becomes difficult to form a coating layer on the surface of the refractory aggregate, and there arises a problem that it becomes difficult to sufficiently cure and/or harden the coated sand. In addition, when the amount of the water-soluble binder is too large, not only is it difficult to form a uniform coating layer by attaching excessive water-soluble binder to the surface of the refractory aggregate, but also there is a fear that coated sand sticks to each other and is agglomerated (composite granulation), which adversely affects the physical properties of the mold and causes a problem that the core is difficult to fall out after casting the molten metal.
The present invention is directed to dry coated sand in which a coating layer obtained by forming a coating layer on the surface of a refractory aggregate using the water-soluble binder, and the coating layer may contain various additives as needed. In order to incorporate such an additive into the cover layer, the following method can be used: a method of mixing a water-soluble binder with a predetermined additive in advance and then kneading or mixing the mixture with a refractory aggregate; a method of adding a predetermined additive to the refractory aggregate separately from the water-soluble binder and uniformly kneading and/or mixing the whole with the water-soluble binder. The water-soluble binder and the additive may be simultaneously kneaded and/or mixed, or kneaded and/or mixed with a time difference.
As one of such additives, a filling property improver is favorably used in the present invention. The above-mentioned filling property improving agent is a granular substance, and the filling property improving agent is present on the particle surface of the obtained precoated sand, in other words, on the surface of the water-soluble binder layer covering the refractory aggregate so that a part of the agent is exposed, and therefore, when the precoated sand is fluidized for filling the precoated sand into a mold (mold), the precoated sand comes into contact with each other via the filling property improving agent, whereby the friction between the particles of the precoated sand can be effectively reduced, the fluidity thereof can be favorably improved, and effects such as improvement of the filling property of the precoated sand to the mold and prevention of the adhesion of the precoated sand to a molding device such as the mold can be favorably enjoyed. Examples of the filling property improving agent include spherical silicone resin powder (particles) and inorganic oxide particles, and spherical silicone resin powder (particles) is particularly favorably used.
The spherical shape in the spherical silicone resin powder is a spherical shape of a degree that is generally recognized, and is not necessarily a regular spherical shape, and a silicone resin powder having a sphericity of usually 0.5 or more, preferably 0.7 or more, and more preferably 0.9 or more is used. Here, the sphericity is an average value of aspect ratios (ratio of short diameter/long diameter) obtained by randomly selecting 10 single particles and projecting the particles on a scanning electron microscope.
As such a spherical silicone resin powder, a silicone resin powder having a particle size smaller than the refractory aggregate and an average particle size of usually 0.01 μm or more and 50 μm or less, preferably 0.05 μm or more and 25 μm or less, more preferably 0.1 μm or more and 10 μm or less, and still more preferably 0.2 μm or more and 3 μm or less is favorably used. Since the spherical silicone resin powder having such an average particle diameter is smaller in particle diameter than the mixed refractory aggregate, it is easily incorporated into the refractory aggregate, and can be uniformly dispersed and uniformly present on the particle surface of the coated sand.
The amount of the spherical silicone resin powder used is usually 0.1 to 500 parts by mass, preferably 0.3 to 300 parts by mass, more preferably 0.5 to 200 parts by mass, still more preferably 0.75 to 100 parts by mass, and most preferably 1 to 50 parts by mass, based on 100 parts by mass of the solid content of the water-soluble binder constituting the coating layer on the surface of the refractory aggregate. In this way, by containing the spherical silicone resin powder having a predetermined average particle diameter at a predetermined ratio in the water-soluble binder coating layer on the surface of the refractory aggregate, the effects of the present invention can be more advantageously enjoyed. The average particle diameter of the silicone resin powder can be determined from a particle size distribution measured by a laser diffraction particle size distribution measuring apparatus or the like.
The spherical silicone resin powder is not particularly limited as long as it is spherical and has binder repellency, and various known silicone resin particles can be appropriately selected and used. The silicone resin is preferably an organopolysiloxane as a main component, and more preferably an organopolysiloxane formed from silsesquioxane. Further, it is particularly desirable that the silsesquioxane is polymethylsilsesquioxane. By using silsesquioxane as the organopolysiloxane constituting the spherical silicone resin powder and polymethylsilsesquioxane as the silsesquioxane, spherical particles having effective binder repellency, a high silicon content and excellent heat resistance can be obtained. Further, by providing such characteristics, thermal decomposition and melting due to heat during mold formation are less likely to occur, so that the spherical shape can be favorably maintained during molding and casting, and therefore, the effects of improving filling properties and strength can be favorably maintained, and odor and smoke during molding can be suppressed, so that the effects of preventing sand adhesion and improving the surface of a casting can be more favorably exhibited even during casting.
The inorganic oxide particles may be spherical particles or non-spherical particles, and spherical particles are preferable in terms of obtaining a cast product having a more satisfactory cast surface. The material constituting the inorganic oxide particles is not particularly limited, and an inorganic metal oxide is preferable. As the particles formed of the inorganic metal oxide, particles formed of silica, alumina, titania, or the like are favorably used. The silica includes crystalline silica and amorphous silica, and preferably amorphous silica, and examples of the amorphous silica include precipitated silica, fired silica produced in an arc or flame hydrolysis, and ZrSiO 4 Silica produced by thermal decomposition of (a), silica produced by oxidizing metal silicon with a gas containing oxygen, silica glass powder produced from crystalline quartz by melting and then rapidly cooling, and the like. The range of the spherical state, average particle diameter, and amount of the inorganic oxide particles is the same as that of the spherical silicone resin powder.
In the present invention, it is preferable to use as an additive a moisture resistance improver together with or separately from the filling property improver. By thus including the moisture resistance improver in the coated sand, the moisture resistance of the finally obtained mold can be further improved.
As such a moisture resistance improver, any moisture resistance improver that has been used in coated sand may be used as long as the effect of the present invention is not impaired. Specifically, examples of the inorganic salt include phosphates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, sodium carbonate, and the like, borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, magnesium metaborate, and the like, borates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, copper sulfate, and the like, sulfates such as sodium phosphate, sodium acid phosphate (sodium hydrogen phosphate), potassium acid phosphate (potassium hydroxide), lithium phosphate, lithium acid phosphate (lithium hydrogen phosphate), magnesium phosphate, titanium phosphate, aluminum phosphate, magnesium hydroxide, calcium hydroxide, strontium hydroxide, zinc hydroxide, aluminum hydroxide, zinc hydroxide, lithium hydroxide, silicon hydroxide, aluminum hydroxide, lithium hydroxide, silicon hydroxide, aluminum hydroxide, silicon hydroxide, lithium hydroxide, iron oxide, calcium hydroxide, zirconium oxide, and the like. Among these, basic zinc carbonate, sodium tetraborate, potassium metaborate, lithium sulfate, and lithium hydroxide, in particular, when water glass is used as a water-soluble binder, can more favorably improve moisture resistance. The moisture resistance improver may be used alone or in combination of 2 or more. The moisture resistance improver described above also includes a compound that can be used as a water-soluble adhesive, and when a water-soluble adhesive different from the above-described compound is used, the compound can function as a moisture resistance improver.
The amount of the moisture resistance improver to be used is usually preferably about 0.5 to 50 parts by mass, more preferably 1 to 20 parts by mass, and particularly preferably 2 to 15 parts by mass, based on 100 parts by mass of the solid content of the liquid water-soluble pressure-sensitive adhesive, in total. In order to favorably enjoy the effect of adding the moisture resistance improver, the amount is preferably 0.5 parts by mass or more, while if the amount is too large, there is a risk that bonding of the water-soluble binder is inhibited and the strength of the finally obtained mold is lowered, and preferably 50 parts by mass or less.
In addition, it is also effective to contain, as another additive, a coupling agent for reinforcing the binding between the refractory aggregate and the water-soluble binder, and for example, a silane coupling agent, a zirconium coupling agent, a titanium coupling agent, or the like can be used. In addition, it is also effective to contain a lubricant which contributes to the improvement of the fluidity of the coated sand, and for example, waxes such as paraffin wax, synthetic polyethylene wax, montanic acid wax, and the like; fatty acid amides such as stearic acid amide, oleic acid amide and erucic acid amide; alkylene fatty acid amides such as methylene bis stearamide and ethylene bis stearamide; stearic acid, stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; glycerol monostearate, stearyl stearate, hydrogenated oil, and the like. Further, as the release agent, paraffin wax, gas oil, engine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agent, silicone-based release agent, and the like can be used. The other additives are each usually contained in a proportion of 5% by mass or less, preferably 3% by mass or less, relative to the nonvolatile components in the water-soluble binder.
In the present invention, when producing the dry coated sand prepared in advance, the following method is generally employed: a refractory aggregate is kneaded and/or mixed by a conventional method with a water-soluble binder as a binder and additives used as needed, uniformly mixed, the surface of the refractory aggregate is covered with the water-soluble binder, and the water-soluble binder is allowed to adhere to the surface of the refractory aggregateIn the present invention, it is desirable that the water-soluble binder in the form of an aqueous solution is added (mixed) to the refractory aggregate, and then the contained water is dispersed within 5 minutes, more preferably within 3 minutes, to thereby produce the dry powdery coated sand. This is because, if the time for the evaporation is long, the following problems arise: the mixing (kneading) cycle becomes long, the productivity is lowered, and the water-soluble binder comes into contact with CO in the air 2 The time becomes long, and thus deactivation occurs.
In the production process of such dry precoated sand, as one of effective means for rapidly evaporating water in the water-soluble binder, the following method is suitably employed: the refractory aggregate is heated in advance, and a water-soluble binder in the form of an aqueous solution is kneaded and/or mixed therein to mix. By kneading and/or mixing a water-soluble binder with the preheated refractory aggregate, the water in the water-soluble binder can be evaporated extremely rapidly by the heat of the refractory aggregate, and therefore, the water content of the resulting coated sand can be effectively reduced, and a dry powder having room-temperature fluidity can be advantageously obtained. The preheating temperature of the refractory aggregate is appropriately selected depending on the moisture content of the water-soluble binder, the blending amount thereof, and the like, and it is desirable to heat the refractory aggregate to a temperature of about 100 to 160 ℃, preferably about 100 to 140 ℃. If the preheating temperature is too low, the water cannot be effectively evaporated, and it takes time to dry, so that it is preferable to use a temperature of 100 ℃ or higher, and if the preheating temperature is too high, the hardening of the water-soluble binder component is accelerated when the obtained coated sand is cooled, and the composite granulation is also performed, so that there arises a problem in the function as the coated sand, particularly in the physical properties such as strength.
The moisture content of the thus obtained dry powdery precoated sand is usually about 5 to 55% by mass, preferably 10 to 50% by mass, based on the solid content of the water-soluble binder. In particular, when the water-soluble binder is water glass, the water content is adjusted to 20 to 50 mass% to form coated sand. On the other hand, if the moisture content is less than 5 mass%, the water-soluble binder such as water glass is vitrified, and the binder does not return to a solution state even if the moisture is added again, whereas if the moisture content is more than 55 mass%, the binder is in a wet state rather than a dry state and does not have room-temperature fluidity. Depending on the type of the water-soluble binder, the coated sand may be in a dry state even if the amount of water in the dry coated sand exceeds 55 mass% with respect to the amount of solid content of the water-soluble binder. Here, whether the film is dry or not is judged by whether or not the film has a dynamic repose angle.
In the present invention, the dry coated sand obtained as described above is used, and after being transported to a molding site as a manufacturing site of a mold, an aqueous medium is added to the dry coated sand at the molding site, and the mixture is kneaded, whereby the target wet coated sand is formed in a heated state.
First, in an advantageous method (I) of obtaining a target wet precoated sand in a heated state, the dry precoated sand is heated (preheated) to a predetermined temperature, then put into an appropriate mixer (mixing device), and kneaded/mixed in the mixer (mixing device) together with a subsequently put aqueous medium, thereby making the dry precoated sand wet to form the target wet precoated sand. Therefore, as a method for heating the dry precoated sand, any known method may be used as long as the dry precoated sand can be heated to a predetermined temperature, and for example, a heating method using a thermostat, a heating method using a temperature adjusting means described in japanese patent laid-open nos. 2001-321886, 2009-142830, and international publication No. WO2010/143746, and the like may be suitably used.
As a mixer serving as a mixing/kneading means used here, a known mixing device that can sufficiently stir/mix (knead) the charged precoated sand and, if necessary, includes a heating means such as a heater or a blowing means such as hot air to heat the kneaded precoated sand can be suitably selected and used. It is preferable that the mixer is preheated before the dry precoated sand is charged, and specifically, the preheating temperature of the precoated sand contacting the wall surface of the mixer is usually heated to a temperature of about 32 to 150 ℃, preferably about 35 to 120 ℃, more preferably about 40 to 110 ℃, by using a heater provided in the mixer, a heating means such as a circulating heat medium, or a blowing means such as hot air, so that the charged dry precoated sand can be favorably kept at the temperature or further heated.
Then, a predetermined aqueous medium is added to the dry precoated sand charged into the mixer under kneading, thereby making the precoated sand wet. The kneading of the dry precoated sand and the aqueous medium in the mixer is usually carried out for about 0.5 to 30 minutes, preferably about 1 to 15 minutes, and more preferably about 3 to 10 minutes, whereby the wet precoated sand can be efficiently wetted with the aqueous medium added thereto, and the wetted precoated sand can be taken out from the mixer in a hot state and thus at a temperature effective for molding. In addition, in the case of wet-state formation of the dry-state precoated sand, a water-soluble binder may be added as a further additive in order to readjust the mold strength. When the strength of the mold is to be increased depending on the shape and size of the mold to be produced by adding the water-soluble binder also at the time of mold formation, the strength can be improved by further adding the water-soluble binder.
In order to wet the dry coated sand as described above, the aqueous medium added to the mixer may be water itself, or an aqueous solution and/or an aqueous dispersion containing various known additives added to water as needed. Examples of the additives to be used as needed include various surfactants such as cationic, anionic, amphoteric, nonionic, silicone, and fluorine surfactants, and polyols such as ethylene glycol, polyethylene glycol, and glycerin, and by adding these, the fluidity of the wet-state coated sand and the properties such as moisture retention can be improved. The amount of such an additive is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, based on the aqueous medium. As is well known, it is also advantageous to add a curing agent such as an acid or an ester, a curing accelerator such as a metal salt or a metal powder. Further, addition of spherical particles such as inorganic oxide particles of silica, alumina, titanium oxide, or the like, and resin particles such as spherical silicone particles, is also effective, and this addition of spherical particles can contribute favorably to improvement in filling properties of the coated sand during mold molding. The filling property improving agent such as inorganic oxide particles or spherical silicone particles may be added to the dry coated sand or may be added together with the aqueous medium.
The amount of the aqueous medium used for the above-mentioned wet treatment is appropriately set according to the degree of wet treatment of the dry precoated sand in the mixer, and is usually appropriately determined in a proportion of 0.3 to 6 parts by mass, preferably 0.5 to 4 parts by mass, and more preferably 0.75 to 3.5 parts by mass, relative to 100 parts by mass of the dry precoated sand. If the amount of the aqueous medium added is too small, the dry precoated sand cannot be sufficiently wet, and therefore, the mutual adhesion between the precoated sand becomes weak, and the flowability of the precoated sand deteriorates to deteriorate the filling property into the mold, resulting in problems such as a decrease in the strength of the obtained mold. On the other hand, if the amount of the aqueous medium to be used (added) is too large, not only is it difficult to fill the mold, but also the drying operation after filling the mold takes time, which causes problems such as a long molding time.
Further, for kneading with the preheated refractory aggregate, the aqueous medium added to the mixer is desirably heated to a temperature lower than the boiling point thereof, and a preheating temperature in the range of usually 30 to 100 ℃, preferably 35 to 95 ℃, more preferably 40 to 90 ℃ is employed. In this way, the preheated aqueous medium is kneaded with the heated dry precoated sand, whereby the effect of the coating layer made of the water-soluble binder on the surface of the precoated sand as a binder can be advantageously enhanced, and the effect of the present invention can be more advantageously achieved. In particular, by adopting such a kneading form, the viscosity of the water-soluble binder can be maintained in a low state, and thus if the spherical silicone resin powder used as an additive is present in the coating layer, it is easily exposed on the surface of the formed wet coated sand, and thus the effect of adding the silicone resin powder can be more favorably exhibited.
On the other hand, in another advantageous method (II) of obtaining the target wet-state precoated sand in a heated state, the dry-state precoated sand is put into an appropriate mixer (mixing device) having a heating means such as a heater or a circulating heat medium, or a blowing means for hot air at normal temperature, and heated while kneading in the mixer (mixing device), and a predetermined aqueous medium is added and further mixed/kneaded, thereby making the dry-state precoated sand wet, and the target wet-state precoated sand is formed.
As in the case of the method (I), the mixer serving as the mixing/kneading means used here may have any configuration as long as it can be preheated to a predetermined temperature, and a known mixing device that can sufficiently stir/mix (knead) the charged precoated sand and can heat the kneaded precoated sand by using a heater, a heating means such as a circulating heat medium, a blowing means such as hot air, or the like can be suitably selected and used.
The dry precoated sand in the mixer is kneaded usually for about 0.5 to 30 minutes, preferably about 1 to 15 minutes, and more preferably about 1.5 to 10 minutes, to be uniformly heated. By heating under such kneading, the dry precoated sand is heated to a temperature of usually about 32 to 150 ℃, preferably about 35 to 120 ℃, and more preferably about 40 to 110 ℃. In addition, in kneading and heating the dry precoated sand, the mixer is preferably preheated before the dry precoated sand is charged, specifically, a heater provided in the mixer, a heating means such as a circulating heat medium, or a blowing means such as hot air is used, and the preheating temperature of the wall surface of the mixer in contact with the precoated sand is usually heated to about 50 to 200 ℃, preferably about 70 to 150 ℃, so that the charged dry precoated sand can be efficiently and quickly heated.
Next, a predetermined aqueous medium is added to the dry coated sand heated as described above, and the mixture is moistened. The timing of adding such a wet aqueous medium is appropriately selected depending on the amount of the aqueous medium to be added, the form of the aqueous medium to be added, and the like, and it is particularly preferable that a predetermined aqueous medium is introduced (added) into a mixer in a liquid state or a vapor state immediately before the completion of the kneading time as described above, and is mixed with the coated sand that has been kneaded and heated, whereby the wetting is performed and the wetting of the coated sand can be performed by the added aqueous medium effectively. It is preferable that the addition of the aqueous medium immediately before the completion of the kneading is started 30 seconds to 2 minutes before the completion of the kneading time, whereby the wet precoated sand is taken out from the mixer at a temperature effective for molding.
In addition, as in the case of the method (I), water itself may be used and, if necessary, an aqueous solution and/or an aqueous dispersion containing various known additives may be added to the water. The additives used as needed include, for example, the surfactants and polyols described above, and by adding them, the fluidity of the coated sand in a wet state and the properties such as moisture retention can be improved. In addition, addition of a known curing agent or curing accelerator is also advantageously used. Further, as in the case of the method (I), the addition of spherical particles such as inorganic oxide particles and resin particles such as spherical silicone particles is also effective, and the addition of the spherical particles can contribute favorably to the improvement of the filling property of the coated sand at the time of mold molding. The inorganic oxide particles and the spherical silicone particles may be added as a filling property improving agent to be contained in the dry coated sand as described above, or may be added together with an aqueous medium to be present on the surface of the coated sand. The amount of the aqueous medium used for the above-mentioned wet-state treatment is also the same as in the case of the method (I), and the aqueous medium to be added to the mixer for kneading with the preheated refractory aggregate is preferably preheated to a temperature lower than the boiling point thereof, and the same as in the case of the method (I) is true together with the preferable preheating temperature used therefor.
The moisture content of the thus obtained wet coated sand having no room-temperature fluidity can be appropriately adjusted to a level of being wet, and the moisture content is usually adjusted to more than 55 mass%, preferably 70 to 900 mass%, and more preferably 95 to 500 mass% with respect to the solid content of the water-soluble binder. The wet precoated sand adjusted to such a moisture content can effectively prevent drying due to blowing gas at the time of filling into the mold at the time of mold molding and prevent the filling into the mold from being hindered, and can maintain the wettability as wet precoated sand, and a mold molded using such precoated sand is also provided with excellent characteristics.
In the present invention, the wet precoated sand obtained by taking out the wet product of the dry precoated sand formed as described above from the mixer is charged into a predetermined preheated mold, specifically, a molding cavity of the mold while keeping the wet precoated sand in a heated (hot) state without cooling, and the wet precoated sand is dried and solidified and/or hardened, whereby the properties of the obtained mold can be effectively improved. That is, the wet coated sand taken out from the mixer at a still hot temperature of about 30 to 100 ℃ is directly filled into the preheated molding die while being heated to such a temperature, so that heat transfer to the filled wet coated sand can be efficiently performed, and the coated sand can be favorably bonded to each other, whereby the mold strength can be stably realized, and further, the moisture resistance of the mold and the scratch hardness can be favorably improved.
Here, the term "filling the wet precoated sand into the mold while keeping the heated state thereof means that the wet precoated sand taken out from the mixer is at a temperature of 30 to 100 ℃, and therefore the wet precoated sand is filled into a predetermined mold while keeping the temperature within such a temperature range, in other words, at a temperature of 30 ℃ or higher. Therefore, the distance between the mixer and the molding die is not particularly limited as long as it is maintained within such a temperature range. If the temperature of the wet precoated sand taken out from the mixer is lower than 30 ℃, it is difficult to suppress the occurrence of uneven heat transfer in the mold, while if the temperature is higher than 100 ℃, the evaporation of water from the wet precoated sand increases, and then the viscosity of the water-soluble binder increases due to the evaporation of the water, so that the adhesive area by the binder is not sufficiently obtained, which causes problems such as a decrease in strength.
In addition, when the molding of the target mold is performed by drying, curing and/or hardening the wet precoated sand filled in the mold in this manner, a mold heated in advance may be advantageously used in order to favorably dry the wet precoated sand. By using the preheated molding die, the drying of the filled wet coated sand can be efficiently performed, and thereby the molding time can be advantageously shortened. The heating temperature of the mold is usually in the range of 40 to 250 ℃, preferably 70 to 200 ℃, and more preferably 100 to 175 ℃. If the heating temperature is less than 40 ℃, there are problems that it is difficult to sufficiently exhibit the drying acceleration effect by heating and the molding time becomes long, and if it is higher than 250 ℃, there are problems that the filling property is deteriorated because the wet coated sand filled into the mold is cured and/or hardened too quickly, and the wet coated sand loses adhesiveness due to excessive drying and the adhesive effect is lowered, and the strength of the obtained mold is lowered.
Further, in order to promote drying of the wet precoated sand filled into the mold, it is effective to directly heat the filled wet precoated sand with microwaves, and particularly, when the mold is a resin mold, it can be suitably used. Further, it is effective to introduce heated air or dry air into the mold filled with the wet precoated sand and pass the heated air or the dry air through the filling layer of the wet precoated sand, thereby promoting drying and more rapidly curing and/or hardening the filled wet precoated sand. Further, the drying under reduced pressure in the mold by suction under reduced pressure of the mold filled with the wet precoated sand is also one of effective drying means, and particularly, it can be advantageously employed in a mold made of a material susceptible to heat, such as a resin mold.
Further, in the present invention, as described above, when the target mold is formed by removing the moisture of the aqueous medium used for making the wet precoated sand filled in the mold from the wet precoated sand, the water glass constituting the surface of the precoated sand is usually cured by evaporation and drying of water without adding any additive, and is cured by adding an oxide, a salt or the like as a curing agent. In addition, in order to cure the water glass, it is also effective to circulate carbon dioxide or an organic ester gas in a mold filled with wet coated sand, and thereby, the water glass can be rapidly cured in the same manner as in the conventional art, and the molding speed can be advantageously increased. As the organic ester gas, for example, methyl formate, ethyl formate, propyl formate, γ -butyrolactone, β -propiolactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerol triacetate, propylene carbonate, and the like can be used in a gaseous state or in a mist state.
In addition, according to the present invention, the dry precoated sand is wet-conditioned by kneading and heating, and then filled into a preheated mold in a specific heated state, and various known molding methods can be suitably used as a method for molding, whereby the target mold can be industrially advantageously produced.
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not to be construed as being limited to the specific descriptions of the embodiments. The present invention may be implemented in various forms such as modifications, alterations, and improvements based on the knowledge of those skilled in the art, and such embodiments are within the scope of the present invention unless they depart from the gist of the present invention.
Examples
The present invention will be described more specifically with reference to the following examples, but it should be understood that the present invention is not to be construed as being limited thereto. In the following examples and comparative examples, "%" and "part(s)" are expressed on a mass basis unless otherwise specified. The flexural strength and scratch hardness of the molds obtained in examples and comparative examples were measured as follows.
Flexural Strength (kgf/cm) 2 ) Measurement of
Width of the green precoated sand obtained in examples and comparative examples, which was molded: 25.4mm × height: 25.4mm × Length: the breaking load of a test piece having a size of 200mm was measured using a measuring instrument (digital sand strength tester, manufactured by gaku corporation), and the bending strength (bending strength) was calculated as follows using the breaking load obtained by the measurement.
Flexural Strength =1.5 XLW/ab 2
[ wherein, L: distance between fulcrums (cm), W: breaking load (kgf), a: width (cm) of test piece, b: thickness (cm) of test piece
Then, the mold immediately after the molding, and further the mold after the molding, which was held for 1 hour or 24 hours in an environment of 3 ℃x60% rh was subjected to the measurement of the above-mentioned bending strength, and the ratio of the bending strength after 24 hours and the bending strength after 1 hour of the molding thus obtained was used to obtain the strength retention ratio, and the moisture resistance of the obtained mold was evaluated.
Determination of scratch hardness (mm)
Width of the green precoated sand obtained in examples and comparative examples, which was molded: 25.4mm × height: 25.4mm × Length: a test piece having a size of 200mm, the scratch hardness (n =3, average value) of the test piece held for 1 hour in an environment of 23 ℃ × 60%RH after the molding was measured using a scratch hardness tester (GF formula). Specifically, the scratch hardness was measured as follows: first, the teeth at the tip of the scratch hardness tester were pressed against the surface of the test piece, the upper black bar was rotated clockwise for 1 cycle, then counterclockwise for 1 cycle, and this rotation operation was repeated 5 times, whereby the teeth were slowly inserted, and the insertion depth of the teeth was read by the scale (mm) of the side surface. The smaller the measured value, the higher the scratch hardness, and the larger the measured value, the lower the scratch hardness.
Production example 1 of Dry Coated Sand (DCS)
As a refractory aggregate, commercially available artificial sand for casting, ESPEARL #60L (trade name: manufactured by shanchuan industrial co., ltd.) was prepared, and as a water glass used as a binder (water-soluble binder), commercially available products were prepared: sodium silicate No. 2 (trade name: siO, product of Fuji chemical Co., ltd.) 2 /Na 2 Molar ratio of O: 2.5, solid content: 35%). Then, 100 parts of the ESPEARL #60L was heated to a temperature of about 120 ℃ and then charged into a Kawakawa universal mixer (model 5 DM-r) (manufactured by DALTON CORPORATION), and 1.0 part of the water glass was added thereto and kneaded, thereby obtaining dry coated sand (DCS 1) having free fluidity at room temperature. The moisture content of DCS1 was measured, and as a result, it was 32% relative to the solid content of water glass in DCS.
Production example 2 of Dry precoated Sand
A dry coated sand (DCS 2) free-flowing at room temperature was obtained in the same manner as in the above-mentioned "production example 1 of dry coated sand" except that 0.05 part of spherical silicone resin particles Tosperl 120 (trade name: 2.0 μm particle diameter manufactured by MOMENTIVE PERFORMANCE MATERIALS JAPAN LLC) as a filling property improver was further added as an additive. The moisture content of the DCS2 thus obtained was 33% based on the solid content of water glass in DCS.
Production example 3 of Dry precoated Sand
A dry coated sand (DCS 3) having free fluidity at room temperature was obtained in the same manner as in "production example 2 of dry coated sand" except that 0.1 part of zinc carbonate as a moisture resistance improver was further added as an additive to "production example 2 of dry coated sand". The water content of DCS3 was measured, and as a result, it was 33% of the solid content of water glass in DCS.
Molding example 1 of mold
(example 1)
First, 100 parts of DCS1 obtained in "production example 1 of coated sand in a dry state" was preheated to a temperature of about 50 ℃, and then charged into a mixer. Then, water at normal temperature was added to the preheated DCS1 at a ratio of 1.0%, and the mixture was kneaded to wet the DCS1, thereby obtaining Wet Coated Sand (WCS) having no normal-temperature fluidity. The moisture content of the WCS obtained was measured, and as a result, it was 317% based on the solid content of the water glass in the WCS.
Next, the Wet Coated Sand (WCS) having no normal temperature fluidity obtained by the humidification of DCS1 was taken out of the mixer, and was immediately pressurized in a hot state without cooling: the mold was dried and solidified by blowing and filling the mixture into a molding die preheated to a temperature of 150 ℃ at a gauge pressure of 0.3MPa, holding the mixture for 30 seconds, blowing hot air at about 120 ℃ for 30 seconds, and then taking out the mixture from the molding die to obtain a mold as a test piece.
(example 2)
A WCS having a moisture content of 318% with respect to the solid content of the water glass in the WCS was formed in the same manner as in example 1 except that DCS2 obtained in "production example 2 of coated sand in a dry state" was used and the preheating temperature of DCS2 was set to about 30 ℃, and then the WCS in a hot state taken out from the mixer was directly molded in the same manner as in example 1 without being cooled, to obtain a mold as a test piece.
(examples 3 to 6)
A casting mold as a test piece was produced in the same manner as in example 2, except that the preheating temperature of DCS2 was changed to about 40 ℃, about 50 ℃, about 70 ℃, or about 90 ℃, and the WCS having a moisture content of 316%, 310%, 305%, or 293% to the solid content of water glass in the WCS was formed by humidifying the WCS in the same manner as in example 2, and then molding the WCS taken out from the mixer in a hot state.
(example 7)
A mold as a test piece was produced by wetting DCS2 in the same manner as in example 4 except that the temperature of water added to DCS2 was set to about 50 ℃, forming a WCS having a moisture content of 305% with respect to the solid content of water glass in the WCS, and then molding the WCS in a hot state taken out from the mixer in the same manner as in example 4.
(example 8)
A mold as a test piece was produced by wetting DCS2 in the same manner as in example 4 except that the temperature of water added to DCS2 was set to about 80 ℃, forming a WCS having a moisture content of 304% with respect to the solid content of water glass in the WCS, and then molding the WCS in a hot state taken out from the mixer in the same manner as in example 4.
(example 9)
A mold as a test piece was obtained in the same manner as in example 4 except that DCS3 obtained in "production example 3 of coated sand in a dry state" was used, and WCS having a water content of 302% based on the solid content of water glass in WCS was formed, and then, the WCS was taken out from the mixer and directly molded in a hot state without cooling in the same manner as in example 4.
Comparative example 1
In example 1, DCS1 was wet-conditioned in the same manner as in example 1 except that DCS1 was used in the normal temperature state without preheating DCS1, and the obtained WCS (moisture content: 319%) was filled in a mold and molded in the same manner as in example 1 to prepare a mold as a test piece.
Comparative example 2
In example 2, a mold as a test piece was produced by wetting DCS2 in the same manner as in example 2 except that DCS2 was used in a room temperature state without preheating, and the obtained WCS (moisture content: 320%) was filled in a mold and molded in the same manner as in example 2.
Evaluation of mold Properties 1-
The flexural strength and scratch hardness of each of the molds (test pieces) obtained in examples 1 to 9 and comparative examples 1 to 2 were measured by the methods described above, and the results thereof are shown in tables 1 and 2 below.
[ Table 1]
Figure BDA0003913754830000251
[ Table 2]
Figure BDA0003913754830000261
From the results of said tables 1 and 2 it is clear that: the casting molds (test pieces) of examples 1 to 9, which were molded using a preheated mold using Wet Coated Sand (WCS) obtained by preheating dry coated sand (DCS 1 to 3) and then adding and kneading water, were excellent in bending strength and scratch hardness, and also in moisture resistance and further in strength retention with time.
In contrast, it can be seen that: in the molds obtained by molding the Wet Coated Sand (WCS) obtained by wetting the dry coated sand (DCS 1-2) at room temperature without preheating as in comparative examples 1-2, the bending strength immediately after molding was low, the bending strength after 1 hour and 24 hours after molding was insufficient, the strength retention rate after moisture absorption was poor, and the scratch hardness of the mold after 1 hour of molding was insufficient.
Molding example 2 of mold
(example 10)
First, 100 parts of DCS2 in the dry state obtained in production example 2 of precoated sand described above was previously blown with hot air at a temperature of 200 ℃, and was put into a pinchuan universal mixer (5 DM-r type) having a wall surface temperature (average of measured values of 5 parts of the inner wall surface) of about 50 ℃, and kneaded while continuing to blow the hot air for 5 minutes, and after heating the kneaded DCS2, water at normal temperature was added at a ratio of 1.0% to DCS2, and further kneaded for 1 minute, whereby the kneaded DCS2 was moistened in the mixer, and wet precoated sand (WCS) having a moisture content of 182% to the solid content of water glass in WCS was obtained.
Next, the Wet Coated Sand (WCS) having no normal temperature fluidity obtained by the wetting with DCS2 was taken out from a cotta universal mixer at a temperature of about 30 ℃, and immediately heated under pressure: the mold was filled with air at a gauge pressure of 0.3MPa, preheated to a temperature of 150 ℃, held for 30 seconds, dried and cured by blowing hot air at about 120 ℃ for 30 seconds, and then taken out of the mold to obtain a mold as a test piece.
(example 11)
A WCS having a moisture content of 180% with respect to the solid content of water glass in the WCS was obtained in the same manner as in example 10 except that the preheating temperature of the inner wall surface of the "kawa" type universal mixer by blowing hot air was set to about 70 ℃, the heating and kneading time of the DCS2 to be charged was set to 6 minutes (water at normal temperature was added, and further 1 minute), and the temperature to be taken out from the mixer was set to about 50 ℃, and then a mold as a test piece was obtained in the same manner as in example 10 while maintaining the above-mentioned taking-out temperature using this WCS.
(example 12)
In example 10, a WCS having a moisture content of 177% to the solid content of water glass in the WCS was formed in the same manner as in example 10 except that the preheating temperature of the inner wall surface of the "gotu" type universal mixer was set to about 90 ℃, the heating and kneading time was set to 7 minutes (adding water at normal temperature, and further 1 minute), and the temperature of taking out from the mixer was set to about 70 ℃, and then the WCS was taken out from the mixer and directly molded in a heated state without cooling in the same manner as in example 10 to obtain a mold as a test piece.
(example 13)
A mold as a test piece was produced in the same manner as in example 11, except that DCS2 kneaded in a "kawa" type universal mixer was heated by circulating a heat medium of 100 ℃ through a temperature control device provided in the mixer instead of blowing hot air, to form WCS having a moisture content of 179% with respect to the solid content of water glass in the WCS, and then the WCS was taken out of the mixer in a heated state of about 50 ℃. The preheating temperature of the inner wall surface of the mixer was about 70 ℃ and the heating and kneading time was 6 minutes.
(example 14)
In example 10, the preheating temperature of the inner wall surface of a "pin chuan" type universal mixer by blowing hot air was set to about 70 ℃, and after 6 minutes of heating and kneading, DCS2 was further kneaded for 2 minutes while blowing steam, thereby forming a WCS having a moisture content of 182% with respect to the solid content of water glass in the WCS, and then the WCS was taken out from the mixer in a heated state at about 50 ℃, and a mold as a test piece was produced by directly molding in the same manner as in example 10. In addition, since the moisture content of the WCS taken out was the same as that of example 10, the water was added at a ratio of 1.0% to DCS2, with respect to the amount of water added for aeration with steam.
(example 15)
A WCS having a moisture content of 182% with respect to the solid content of water glass in the WCS was obtained in the same manner as in example 11 except that the heating and kneading time of DCS2 to be charged was set to 6 minutes, and water at 50 ℃ was added for 1 minute, and then a mold as a test piece was obtained in the same manner as in example 11 while maintaining the above take-out temperature using this WCS.
(example 16)
A WCS having a water content of 181% with respect to the solid content of water glass in the WCS was obtained in the same manner as in example 11 except that the heating and kneading time of DCS2 to be charged was set to 6 minutes, and water at 80 ℃ was added for 1 minute, and then a mold as a test piece was obtained in the same manner as in example 11 while maintaining the above take-out temperature using this WCS.
Comparative example 3
In example 10, the inner wall surface of a "Pinchuan" type universal mixer was kept at room temperature (20 ℃) without blowing hot air (without heating), and the mixing time was as follows: DCS2 was moistened for 1 minute, and the obtained WCS (moisture content: 185%) was filled in a mold in the same manner as in example 10 at room temperature to prepare a mold as a test piece.
Evaluation of mold Properties 2-
Using the respective molds (test pieces) obtained in examples 10 to 16 and comparative example 3 described above, the flexural strength and scratch hardness of each mold were measured by the methods described above, and the results thereof are shown in table 3 below.
[ Table 3]
Figure BDA0003913754830000301
From the results of said table 3 it is clear that: the casting molds (test pieces) of examples 10 to 16, which were obtained by molding Wet Coated Sand (WCS) obtained by kneading and heating dry coated sand (DCS 2) while making the wet coated sand wet, in this heated state, with a preheated molding die, had excellent flexural strength and scratch hardness, and also excellent wet strength and strength retention over time.
In contrast, it can be seen that: as shown in comparative example 3, the mold obtained by molding Wet Coated Sand (WCS) obtained by humidifying dry coated sand (DCS 2) at room temperature without preheating had low bending strength immediately after molding, had insufficient bending strength after 1 hour and 24 hours of molding, had poor strength retention after moisture absorption, and had insufficient scratch hardness after 1 hour of molding.

Claims (18)

1. A method for producing a casting mold, characterized by preparing dry precoated sand obtained by covering the surface of a refractory aggregate with a water-soluble binder, adding an aqueous medium thereto, kneading the mixture to form wet precoated sand in a heated state, and then filling the wet precoated sand into a preheated predetermined mold while maintaining the heated state, thereby molding the mold.
2. A method for manufacturing a casting mold according to claim 1, wherein the dry precoated sand is preheated, and then the aqueous medium is added and kneaded to wet the dry precoated sand, thereby forming the wet precoated sand in a heated state.
3. A method for manufacturing a casting mold according to claim 2, wherein the preheating temperature of the dry precoated sand is 32 to 150 ℃.
4. A method for manufacturing a casting mold according to claim 1, wherein the wet coated sand is formed in a heated state by heating the dry coated sand in a normal temperature state while kneading the same, and adding an aqueous medium.
5. A method of manufacturing a casting mold according to claim 4, wherein the mixing and heating of the dry precoated sand are performed in a mixing device, and the mixing device is preheated before the dry precoated sand is charged.
6. A method of manufacturing a casting mold according to claim 5, wherein a wall surface of the mixing device that comes into contact with the dry precoated sand is preheated to a temperature of 50 ℃ to 200 ℃.
7. A method for manufacturing a casting mold according to any one of claims 4 to 6, wherein the aqueous medium is added to the dry precoated sand immediately before the completion of kneading after kneading and heating.
8. The method of manufacturing a casting mold according to claim 7, wherein the addition of the aqueous medium is started 30 seconds to 2 minutes before the end of the kneading time.
9. A method of manufacturing a casting mold according to any one of claims 4 to 8, wherein the aqueous medium is in a liquid state or a vapor state.
10. A method for manufacturing a casting mold according to any one of claims 1 to 9, wherein the wet precoated sand in a heated state is 30 to 100 ℃.
11. A method of manufacturing a casting mould according to any of claims 1 to 10, characterized in that the aqueous medium is preheated to a temperature below its boiling point.
12. A method for manufacturing a casting mold according to claim 11, wherein the preheating temperature of the aqueous medium is 30 ℃ to 100 ℃.
13. A method for manufacturing a casting mold according to any one of claims 1 to 12, wherein the aqueous medium is added in a proportion of 0.3 to 6 parts by mass with respect to 100 parts by mass of the dry coated sand.
14. A method of manufacturing a casting mold according to any one of claims 1 to 13, wherein the molding die is preheated to a temperature of 40 ℃ to 250 ℃.
15. A method for manufacturing a casting mold according to any one of claims 1 to 14, wherein the water-soluble binder is a soluble silicic acid compound.
16. A method of manufacturing a casting mold according to any one of claims 1 to 15, characterized in that the dry precoated sand contains a filler improver.
17. A method for manufacturing a casting mold according to any one of claims 1 to 16, wherein the dry precoated sand contains a moisture resistance improver.
18. A method of manufacturing a casting mold according to any one of claims 1 to 17, characterized in that the prepared dry precoated sand is transported to a molding site as a casting mold manufacturing site, and then the aqueous medium is added to the dry precoated sand and kneaded at the molding site, thereby forming the wet precoated sand in a heated state.
CN202180031693.9A 2020-04-30 2021-04-28 Method for manufacturing casting mold Pending CN115461171A (en)

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