Water-soluble binder composition, water-soluble mold material, water-soluble mold, and method for producing the same

Abstract

While improving the mold filling property, enhancing the mold strength of water-soluble cores, providing a water-soluble binder composition capable of withstanding the low-pressure aluminum casting method and the high-pressure aluminum casting method, and improving the easy collapsibility of the mold, the storage stability of the binder, enhancing the cooling effect on the casting, preventing insertion into the mold, hardening the surface hardness of the aluminum casting, etc., providing water-soluble mulled sand and cores excellent in moldability and casting workability. 【Solution means】In a water-soluble binder composition containing a water-soluble salt or an inorganic compound as a binder component, it is composed of one or more selected from phosphates, borates, sulfates, carbonates, nitrates, hydroxide salts, silicate salts, and halides, and the water-soluble binder composition has a viscosity of the binder solution of 100 mPa / s or less and a pH of 2-13 (concentration 2% or more).

Description

Technical Field

[0001] The present invention relates to a water-soluble binder composition used in casting and a core manufacturing method, and particularly relates to a mold material used as a water-soluble binder composition for a mold. More specifically, it relates to a sand mold and die casting method for casting mainly light metals such as aluminum alloys, magnesium alloys, and copper alloys, a green sand casting method, a low-pressure casting method, a high-pressure casting method (die casting method), and a binder composition technology field for manufacturing cores thereof. Furthermore, more specifically, it relates to a water-soluble binder composition based on the use of water-soluble salts and other additives, and a water-soluble core formed by molding using such a binder-coated sand.

Background Art

[0002] For driving motors of HEV / EV vehicles, which are expected to spread rapidly, miniaturization, high output, and high reliability are required. In particular, the temperature rise accompanying the increase in output of the driving motor greatly affects the output and reliability. Therefore, it is required to manufacture complex-shaped castings such as water jackets for driving motor cooling. For this, it is necessary to cast using high-precision cores, and many cores with good dimensional accuracy and complexity are being manufactured. In particular, cores are widely used to provide a space inside precision castings such as mechanical parts. For example, cores are indispensable for creating the internal space of a cylinder made of an aluminum alloy and the cooling medium passage inside the exhaust. As the core molding process for this, currently, shell molds using a phenolic resin as a binder and cold boxes using a phenolic resin and an isocyanate resin as binders are mainstream.

[0003] In the shell mold method, a phenolic resin composition containing a phenolic resin as a resin binder component (binder component) is used as a binder, and it is kneaded with refractory particles (aggregates such as foundry sand) to form a binder layer on the surface of the refractory particles, obtaining resin-coated sand (RCS), and then molded into a desired shape. Today, shell molds produced by this molding method have been generally used. In addition, for the cold box mold, as a two-component organic binder, a binder composed of a phenol resin component and a polyisocyanate component is added to the casting sand, kneaded, and after coating the sand with the binder, the kneaded sand is filled into a molding die. Then, by introducing a curing catalyst such as amine gas into the molding die, the urethanization reaction between the phenol resin component and the polyisocyanate component in the casting sand composition is promoted to produce the target mold. This method is also commonly used.

[0004] However, these shell mold and cold box molds are derived from artificial organic resins made from petroleum. Also, since the shell mold uses hexamethylenetetramine as a curing agent and the cold box mold uses amines as a curing catalyst, when molten metal is poured, decomposition occurs, leading to problems in terms of the environment, such as the generation of gases with bad odors like benzenes, hydrocarbons, ammonia, and amines.

[0005] Furthermore, in the light alloy casting method, after pouring the molten metal, it is necessary to remove the mold from the cast product. However, since the molten metal temperature is low and it is difficult to easily return it to a sandy state, various countermeasures have been taken conventionally. For example, in Patent Document 1, Patent Document 2, and Patent Document 3, resin-coated sand for molds that can be prepared by blending an alkali metal salt of an aromatic carboxylic acid, phosphate esters, and an oxidizing agent with a phenol resin is used. However, depending on the mold strength, particle size index, and resin content, the above-mentioned measures alone may not be sufficient, and there are cases where it does not return to a sandy state. Currently, in many cases, the cast product and the cores encapsulated therein are once subjected to heat treatment or knocking by impact in a firing furnace or the like to return them to a sandy state.

[0006] Therefore, in order to achieve the goal of carbon neutrality (CN) by 2050 and meet environmental compliance, a mold material using an aqueous solution of alkali silicate, particularly an aqueous solution of sodium silicate (hereinafter also referred to as water glass), as a binder for neutrons has been proposed to solve the problems of conventional organic processes. Representative methods for curing water glass in the prior art include the carbon dioxide mold, N process, H process, diecal mold, water glass - ester curing mold, VRH method, heat curing method, etc. In particular, alkali silicate neutrons that can reduce the amount of gas generated during casting are considered by using water glass as the binder for the mold. However, problems in this type of mold process, similar to the organic mold, include gelation and dehydration condensation reactions inside the mold due to heat on the mold surface reaching 700°C or higher and heat after casting, causing part of the binder to melt and vitrify, firmly adhering between the mold sand grains, resulting in poor sand collapsibility after aluminum casting, and extremely poor efficiency in the process of removing the mold. In relation to this, a neutron molding system using a water glass - based binder requires recycling of foundry sand due to the depletion of natural resources in casting. However, as mentioned above, the heat - resistant temperature of the binder is low. Once the binder is vitrified, the foundry sand and the binder adhere firmly. When roasting and mechanical polishing are performed to return it to a sandy state, the sand is often crushed and peeled off together, and the recovery rate of the water glass mold tends to be worse than that of ordinary shell mold and cold box molds. As a result, the particle shape of the recycled sand also deteriorates, and the quality of the recycled sand is lower than that of new sand. Furthermore, fine powder of silicate derived from water glass also has a risk of pneumoconiosis and is difficult to handle from the perspective of environmental risk assessment.

[0007] Therefore, in order to achieve environmental compliance, a water - soluble mold process in which a binder such as an inorganic salt is used for neutrons has been developed in the same way as above. For example, in the mold described in Patent Document 4, drying is carried out under the condition of leaving it at 150°C for 30 minutes. When kaolin and talc clay minerals are added as fillers to magnesium sulfate and sodium phosphate and sugars are used as the secondary binder, the neutron strength is at most 30 kg / mm2 Since the value is extremely low, there is no product that has been put into practical use or mass-produced. The main reasons are that due to the lack of binding force of the binder, it is difficult to obtain the required core strength, and the hardening speed of the formed mold is not sufficient, and there are also problems with the hardenability inside the mold. In addition, when the addition amount of the inorganic powder increases, it not only causes the problem of reducing the mold strength of the coating sand, but also has problems such as mold deformation and moisture absorption deterioration due to the swelling peculiar to clay minerals. So far, it can be used for gravity casting of aluminum, but it cannot obtain the mold strength required for low-pressure casting or high-pressure casting methods, and it cannot withstand practical use as a water-soluble mold, so it has not been popularized or put into practical use.

[0008] Regarding these problems of the mold, in recent years, due to the low expansibility and small specific surface area of spherical bodies, the resin amount can be reduced, so various proposals have been made as the aggregate (casting sand) of the mold, and many types of them are commercially available, enabling the solution of both of the above problems. However, those produced according to Patent Document 5 etc. use spherical bodies with a grain shape coefficient of 1.05 or less, and the mold strength of the water-soluble mold is also difficult to say sufficient at 30 kg / cm 2 or less, and the problem has not been solved yet.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0010] When implementing the inventions according to Patent Document 1 and Patent Document 2, it was found that the strength of the molded mold was low, the core would break due to the pressure during aluminum casting, the filling property of the mold was poor resulting in burn-in defects, and the surface of the mold was roughened by the molten metal during casting due to the low adhesive force of the binder, resulting in sand sticking defects.

[0011] In addition, since it is a water-soluble process, it is sensitive to temperature changes in the surrounding environment. When the temperature drops to 20°C or lower, the viscosity of the binder gradually increases, the filling property during molding deteriorates, not only does the mold strength decrease, but problems such as precipitation and deposition of the binder component also surface, leading to issues with storage stability. In many cases, the salts formed by precipitation in conventional water-soluble compositions are insoluble salts that can hardly be redissolved even by heating, and it has been found that they cannot be reused repeatedly.

[0012] Furthermore, during casting, in the case of magnesium sulfate type, which has been conventionally used as the main component, when used in combination with other inorganic salts, when the mold temperature reaches 450°C or higher due to the heat of the molten aluminum during casting, a part of the binder component reacts and insoluble salts are generated as described above. Therefore, the characteristic of easy collapsibility of the sand, which is also a characteristic of water-soluble cores, is impaired, and problems such as deterioration of collapsibility (sand removal property) and issues in repeated use and regeneration have occurred. However, magnesium sulfate alone can also be used as a binder, but in this case, the problem of moisture absorption deterioration of the mold becomes prominent, and other problems such as storage of the core occur.

[0013] In the aluminum casting method, as described above, conventional organic processes, processes using water-soluble binders, and inorganic binders (water glass / sodium silicate) have characteristics where mold strength and collapsibility are contradictory. There is a problem that when the mold strength is increased, the collapsibility deteriorates. In particular, in the case of organic processes, the cooling of the casting tends to be slow due to the heat generated by the combustion of the binder, and there are many casting defects such as porosity defects and micro-shrinkage defects caused by the gas draw holes in the generated mold. Even in the case of the inorganic water glass (sodium silicate) process, there is a problem that the cooling performance is insufficient and the problems caused by the gas in the organic process have not been solved. Also, in the conventional mold processes, it has been very difficult to achieve both high mold strength and easy collapsibility in organic molds, water glass-based inorganic molds, and water-soluble molds. Therefore, an object of the present invention is to provide a binder composition and a material for controlling the high strength and filling properties of a water-soluble mold and increasing the easy collapsibility and cooling rate of the mold in a mold material using casting sand with a water-soluble salt as a binder.

Means for Solving the Problems

[0014] As a result of repeatedly studying the binder composition for a water-soluble mold in order to solve the problems as described above, the inventor has found that in a water-soluble binder composition containing water-soluble salts as binder components, it consists of one or more of phosphates, borates, sulfates, carbonates, nitrates, hydroxide salts, silicate salts, and halides, and the viscosity of the binder solution is 100 mPa / s or less and the pH is 2 - 13 (concentration 2% or more). The inventor has completed the invention related to the water-soluble binder composition configured as such. As a result, the binder solution has improved stability even when the environmental temperature is in the low - high temperature range. For the mulled sand obtained using such a water - soluble binder composition, if necessary, by combining one or more filler particles and viscosity modifiers, the fluidity of the mulled sand can be effectively increased, and as a result, it is also possible to adjust to increase the strength of the mold. Moreover, it has been found that the sand collapsibility (sand removal property) after casting, which was difficult in conventional organic processes, inorganic binder processes, (sodium silicate / water glass), can be achieved with fine - grained sand that is easily collapsible. Compared with conventional water - soluble cores, the collapsibility after casting is also improved by suppressing the thermal reaction during casting. In addition, by using this water - soluble binder composition, the molded core has higher cooling performance compared to ordinary shell molds and inorganic molds, and it can also be confirmed from the aluminum structure after casting that it is advantageous for improving the hardness of aluminum castings, shrinkage cavities due to shrinkage of the casting during solidification, and gas defects in the mold, thus completing the present invention.

[0015] The present invention has been completed based on the above - mentioned findings, and in order to solve the above - mentioned problems, it can be preferably implemented in various aspects listed below. Moreover, each of the aspects described below can be adopted in any combination. It should be understood that the 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 entire description of the specification and the drawings.

[0016] According to one of the desirable embodiments of the water-soluble binder composition of the water-soluble salts according to the present invention, at least one kind of the water-soluble binder composition is a phosphate or a phosphate hydrate. Phosphate salts may contain, as constituent components, orthophosphoric acid, metaphosphate salts, triphosphate salts, polymeric phosphoric acid and their salts (sodium, potassium, calcium, magnesium, ammonium, ferric) and their hydrates. The phosphate compounds have relatively high solubility and are important in increasing the binder concentration, and increasing the concentration enhances the expression of mold strength. In addition, since many phosphate salts have compounds with increasing viscosity during the process of binder concentration, they also have the effect of increasing the adhesion force inside the mold as dehydration progresses during molding.

[0017] However, when using phosphates such as sodium dihydrogen phosphate, which is one of the orthophosphates, as a binder, when the alkaline earth metal ion Mg 2+ contained in magnesium sulfate dissolves in the binder solution, it immediately reacts to form a white precipitate of an insoluble salt. This is also evident from the fact that phosphates are used as a detector for Mg 2+ ions. Therefore, for combined use, a very small amount of addition is desirable. When adding a large amount, there is a risk that the water-soluble binder component will precipitate, leading to a decrease in concentration and a decrease in mold strength, so care is required for the combination.

[0018] According to one of the desirable embodiments of the water-soluble binder composition according to the present invention, at least one kind of the water-soluble binder composition is a borate or a borate hydrate. Borate salts are characterized by containing orthoborate, diborate, metaborate, tetraborate, and polyborate as constituent components. Dissolved boron in water of the borate compound exists as BO3 3 in the low pH range and B(OH) 4 in the high pH range, and its form also changes depending on the concentration, and polymers are formed in the high concentration range. Furthermore, it forms hydrogen bonds with many ionic compounds and has the effect of increasing mold strength.

[0019] The borates described above have the characteristic that polymers are formed in a high-concentration range, but they have relatively low solubility, and a large amount of solvent is required when preparing a water-soluble binder. Therefore, by combining with other salts, the solubility of the borate is increased, and by reducing the water content as much as possible, a high concentration becomes possible. By increasing the concentration of borate ions in the binder, the concentration can be further increased in the dehydration process of the molding, which is also the reason for the manifestation of mold strength.

[0020] According to one of the desirable embodiments of the water-soluble binder composition according to the present invention, at least one of the water-soluble binder compositions employs a sulfate or a sulfate hydrate. The sulfate hydrates are preferably magnesium sulfate, magnesium sulfate heptahydrate, sodium sulfate, sodium sulfate decahydrate, potassium sulfate, potassium aluminum sulfate 7-12 hydrate, aluminum sulfate, and aluminum sulfate 14-18 hydrate. Since sulfates have high heat resistance, the combination enhances the easy collapsibility.

[0021] The nitrates can be at least one compound selected from potassium nitrate and sodium nitrate. By using such a water-soluble binder mold material, a high concentration of the water-soluble binder is possible and the mold strength can be enhanced. Further, in the water-soluble binder, even if some hardly soluble compounds are formed depending on the presence or absence of coexisting ions unrelated to the reaction, the precipitate can be redissolved and assisted, and the easy collapsibility can be improved by being able to increase the collapsibility and the binder concentration as much as possible.

[0022] Compounds with low solubility such as the hydroxide salts and silicate salts act as filler fine particles, improving the filling property due to the smooth hardening of the mold. In addition, since compounds having a hydroxyl group can also be dissolved by adjusting the pH, by forming a hydrogen bond or the like with the borates, gelation occurs and mold strength is manifested.

[0023] A water-soluble binder mold material is preferably used in which the surfactant is used in a total amount of 20 to 500 parts by mass, more preferably 30 to 80 parts by mass, based on 1000 parts by mass of the foundry sand.

[0024] Conventional thermosetting processes such as thermosetting shell mold castings are filled and cured in a cavity of a mold with a molding temperature of 250 ° C to 400 ° C by a gravity drop method or a blowing method. However, the molding temperature of this water-soluble binder process can be molded in a temperature range of 120 ° C to 220 ° C, preferably 140-180 ° C is good. In molding with a low mold temperature, the expansion and contraction amounts of the resin and aggregate after molding are smaller than those of the conventional shell mold method, and the dimensional accuracy is also good.

[0025] In the practice of the present invention, filler fine particles having an average particle diameter of 100 μm or less may be further contained. The average particle diameter of the filler fine particles is preferably 100 μm or less, more preferably less than 10 μm. In particular, it has been confirmed by experimental verification that the effect of improving the filling property of spherical particles having an average particle diameter of 7 μm or less is large.

[0026] The filling property can be improved by using at least one compound selected from fumed silica, fumed alumina, hollow filler, spherical iron oxide, iron oxide, boron nitride, aluminum nitride, titanium oxide, potassium titanate, aluminum hydroxide, barium sulfate, silica gel, clay mineral, graphite, and feldspar as the filler fine particles.

[0027] Since the filler fine particles have low reactivity regardless of the type of water-soluble salt, the viscosity of the binder increases due to dehydration by the heat of the mold, crystals are hardly precipitated, and the function of assisting fluidity is strong. Therefore, it contributes to an improvement in mold filling density and high strength is exhibited.

[0028] It is desirable to use the filler fine particles in a total amount of 0.1 to 50 parts by mass based on 1000 parts by mass of the foundry sand.

[0029] In the implementation of the present invention, a viscosity modifier may be added. A surfactant can be used as the viscosity modifier, and at least one compound selected from nonionic type, cationic type, anionic type, and zwitterionic type can be adopted as this surfactant. By using this clay modifier in the water-soluble binder mold material, it has the effect of reducing the surface tension of the water-soluble binder and the viscosity of the binder, and suppressing the evaporation of moisture from the mulled sand, thereby alleviating a significant increase in viscosity and assisting the mold filling property. It is particularly effective under low humidity climate conditions.

[0030] The filler fine particles can also be used as a substitute for casting sand. By using a water-soluble mold material selected from at least one of them alone or in a plurality of combinations, it effectively acts when high-pressure casting methods such as low-pressure casting and high-pressure casting methods with high aluminum casting pressure are adopted.

[0031] The present invention also provides water-soluble binder-coated sand obtained by coating casting sand with the water-soluble binder and being in a wet or dry state.

[0032] The present invention also provides a mold made of the above components and the like. The mold of the present invention is obtained by curing the mold material. It is desirable that the curing includes dehydration curing. After forming the water-soluble coated sand, cycle time can be achieved by heating curing, vacuum suction curing, or micro-heating curing, superheated steam curing, and combining hot air and cold air blowing with them, enabling molding similar to the conventional shell mold.

Effects of the Invention

[0033] The present invention relates to a water-soluble binder composition containing water-soluble salts as a binder component, which consists of one or more of phosphates, borates, sulfates, carbonates, nitrates, hydroxide salts, silicate salts, and halides, and has a viscosity of the binder solution of 100 mPa / s or less and a pH of 2-13 (concentration 2% or more). By configuring such a water-soluble binder composition, the binder solution has improved stability even when the environmental temperature is in the low to high temperature range or the binder concentration is increased. For the mulled sand obtained using such a water-soluble binder composition, if necessary, by combining one or more filler fine particles and viscosity modifiers, the fluidity of the mulled sand is effectively increased. As a result, it becomes possible to adjust the mold to have high strength, and the sand collapsibility (sand removal property) after casting is also made easy even with fine-grained sand that was difficult in the conventional process. It was also confirmed from the aluminum casting structure that the cooling rate is faster than that of the conventional process. It was possible to provide a new mold using such a mold material and a method for manufacturing the mold.

Brief Description of the Drawings

[0034]

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Best Mode for Carrying Out the Invention

[0035] Embodiments of the present invention will be described. This embodiment is an example in which the present invention is applied to a mold for casting an aluminum alloy casting and a method for manufacturing the same. First, a water-soluble casting mold material to which the present invention is applied will be described.

[0036] The mold material for a water-soluble binder according to this embodiment includes casting sand and a water-soluble binder composition. The water-soluble binder composition includes water-soluble salts and filler fine particles. The water-soluble binder composition can further include a viscosity modifier.

[0037] 〔Water-soluble binder composition〕 In the water-soluble binder composition using water-soluble salts used in the present invention, the water-soluble salts of those water-soluble binder compositions are in a solid state (including hydrate form) or a liquid state (when made into a solution) that can be dissolved in the presence of a protic polar solvent (alkaline water, acidic water, neutral water, ionic liquid, etc.). Salts composed of strong acids and strong bases are completely ionized both in the acid component and the base component, and neither the cations nor the anions are hydrolyzed, so they become neutral with a pH of 7. On the other hand, when the ionization degree of one of the acid component or the base component is small, it returns to the free form due to the acid-base balance, so the hydrogen ion concentration deviates from neutrality. That is, a solution of a salt composed of a weak acid and a strong base shows alkalinity due to the hydrolysis of the anion, and a solution of a salt composed of a strong acid and a weak base shows acidity due to the hydrolysis of the cation. In the case of a salt of a weak acid and a weak base, both the cation and the anion are hydrolyzed and depend on the mutual acid-base balance.

[0038] 〔Raw materials of the water-soluble binder composition〕 In addition, the water-soluble inorganic salts used as raw materials of such a water-soluble binder composition (water-soluble binder composition) are phosphates, borates, sulfates, carbonates, hydroxide salts, silicates, nitrates, halide salts (including hydrates), and one of them is used alone or in combination of two or more.

[0039] Phosphates, borates, sulfates, carbonates, nitrates, silicate salts, hydroxide salts, and halides used in the water-soluble binder composition (water-soluble binder composition) according to the embodiment of the present invention are polyatomic ions (polyvalent ions), namely: phosphate ions, borate ions, carbonate ions, nitrate ions, silicate ions (or metasilicate ions), hydroxide ions, and oxonium ions of halogens are contained alone or in plurality in the binder solution. As one of the actions of polyvalent anions, there is an increase in the solubility of sparingly soluble compounds bound with metal ions. For example, NO3 - ions are attracted around the Ag+ ions of the sparingly soluble salt AgCl, and Cl - ions, Na + ions are attracted around them, and the affinity between the ion pairs of Ag + …Cl - decreases, thereby improving solubility. Depending on the presence or absence of coexisting ions unrelated to the reaction, the solubility of water-soluble inorganic salts can be improved even for sparingly soluble compounds, and the binder concentration can be increased as much as possible, leading to an improvement in mold strength. Furthermore, there is suppression of aggregation by dispersing in a suspended state, and it also leads to a stable improvement in binder storage stability, such as a precipitation suppression effect when creating a high-concentration solution.

[0040] 〔Phosphates〕 Phosphates used in the water-soluble binder composition (water-soluble binder composition) according to the embodiment of the present invention are industrially produced by manufacturing phosphoric acid from phosphate ore, and further through a polycondensation reaction by heating or the like or a reaction with salts, phosphates having a chain, cyclic, or network structure are obtained. Phosphates having one phosphorus are orthophosphates, those with two bonded phosphates are pyrophosphates, those with three bonded are tripolyphosphates, and substances with a mixture of 10 or more long-chain bonds and cyclic bonds are hexametaphosphates, and in addition to the main components, phosphates with a degree of polymerization of individual units are included. The pH and solubility of representative phosphates are as shown in Table 1 below. However, in the water-soluble binder composition, they may be adjusted singly or in plurality and used in terms of ease of adjustment to characteristics and improvement of solubility.

[0041]

Table 1

[0042] Furthermore, phosphate is a polyvalent anion and has a high effect of increasing the ionic strength. (The ionic strength quantifies the force of interaction between ions and represents the degree of influence of ions in an aqueous solution.) By dispersing a poorly soluble substance bound to metal ions in a soluble or suspended state, it has the effect of suppressing aggregation and preventing adhesion to other substances. In addition, as one of the characteristics of phosphate, chain-like polymeric phosphates form complex salts in an aqueous solution by complexing various metal ions and causing the so-called sequestering action that makes them lose their function as metal ions. Due to this action, a network structure is formed and the hot strength is improved under high pressure and high temperature during casting, which is effective for preventing core breakage in the aluminum high-pressure casting method. However, for example, when magnesium ions are dissolved in a sodium dihydrogen phosphate solution, a precipitate is formed that reacts and does not contribute to the mold strength. The same applies to combinations of water-soluble binder compositions, and care must be taken to avoid the formation of insoluble salts. For example, magnesium sulfate, magnesium chloride, magnesium hydroxide, polymeric phosphate and iron ions, calcium ions, etc. can be mentioned for sodium dihydrogen phosphate. Also, at least one phosphate compound of the water-soluble binder composition (water-soluble binder composition) according to such an embodiment of the present invention is preferably an orthophosphate. In this case, the phosphates are preferably configured to contain 40 mol% or more, more preferably 50 to 70 mol% of sodium dihydrogen phosphate and sodium dihydrogen phosphate dihydrate. Thus, regarding the detailed mechanism of the influence on the mold strength by using orthophosphates as the main component system and constituting sodium dihydrogen phosphate, it has not yet been elucidated. However, by using such highly soluble orthophosphates, it becomes possible to dissolve other binder components with low solubility even at a low moisture content due to the improvement of solubility by polyvalent anions, and the binder concentration can be increased. As a result, it is possible to increase the mold strength.

[0043] 〔Orthophosphates〕 Incidentally, the orthophosphates preferably used in the present invention are phosphates in monomer form. Specifically, examples include sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, trisodium phosphate, potassium phosphate, and formulations mainly composed of these. Such orthophosphates can be obtained from the market and used, for example, "sodium dihydrogen phosphate dihydrate" (manufactured by Daihachi Chemical Industry Co., Ltd.). Incidentally, the condensation reaction of such orthophosphoric acid can also be conceptually shown by the following formula (Chemical Formula 1).

[0044] JPEG0007713748000003.jpg38161

[0045] In addition, phosphates used in combination with the above-mentioned orthophosphates include polymeric phosphates. Specifically, examples include sodium pyrophosphate, sodium polyphosphate, acidic sodium pyrophosphate, sodium hexametaphosphate, etc. Further, as tripolyphosphates, specifically, sodium trimetaphosphate, potassium trimetaphosphate. Further, as substances containing a mixture of 10 or more long-chain bonds and cyclic bonds, specifically, sodium hexametaphosphate, potassium hexametaphosphate, and sodium ultraphosphate can be mentioned. In the market, commercially available products such as "sodium hexametaphosphate" from Yoneyama Industry Co., Ltd., "potassium metaphosphate" from Taiheiyo Chemical Industry Co., Ltd., "sodium ultraphosphate (ultrapolyphosphate)" from Taiheiyo Chemical Industry Co., Ltd. can be selected and used.

[0046] [Phosphates] In the practice of the present invention, instead of the above orthophosphates, at least one of borates, sulfates, carbonates, silicates, hydroxides, and nitrates can also be used. Further, it is recommended to use these in combination with the above orthophosphates. Thus, by containing borates and / or other salts together with orthophosphates, the mold strength can be advantageously increased. As long as the water-soluble binder concentration % (parts by mass) is 2% or more, and the viscosity is 100 mPa·s / 5°C or less, and the pH is 2 to 13, even if borates and other salts are used in combination and contained as a component of the water-soluble binder composition, there is no problem at all. Furthermore, it is also possible to blend and contain orthophosphates as a component of borates or other salts. Here, even if these orthophosphates, borates, and other salts all contain hydrates in their molecules, there is no problem.

[0047] [Borates] Next, borates are salts of boric acid (B(OH)3), or salts of metaboric acid or polyboric acid formed by dehydration condensation of boric acid and their hydrated form compounds. They are in the form of borates. Examples include boric acid, sodium tetraborate (borax), sodium metaborate, dipotassium tetraborate, lithium tetraborate, etc., and other known borate compounds can also be appropriately used. And these borates can be used alone, or in combination of two or more kinds or in combination with other salts, without any problem.

[0048] Borates can exist in many forms in an aqueous solution. Dissolved boron ions in water are BO3 in the low pH range 3 . Polyborate anions are formed when the boron concentration becomes about 0.025 mol / L or more at pH 7 - 10. The most well-known is the tetraborate ion, which exists as B(OH)4 in the high pH range found in borax. Furthermore, its form also changes depending on the concentration, and polymers are formed in the high concentration range, and a network structure is formed by dehydration condensation, making it possible to improve the mold strength. When the water-soluble binder solution dehydrates and becomes highly concentrated due to heating from the mold during molding, borate ions can increase the mold strength through hydrogen bonding with compounds having hydroxyl groups and other interactions between polyvalent ions.

[0049] [Decomposition reaction system of inorganic compounds] In the water-soluble binder composition according to the present invention, as characteristics of the water-soluble salts contained as the binder component, the decomposition reaction system of the inorganic compound is considered as follows. (1) Dehydration reaction (for example: Mg(OH)2 → MgO + H2O). (2) Decarboxylation reaction (for example, MgCO3 → MgO + CO2). (3) Dehydrogenation reaction (for example: MgH2 → Mg + H2). (4) Denitrification reaction (for example: Mn5N2 → 5Mn + N2). (5) Deoxygenation reaction (for example: Mn2O3 → 2MnO + 0.5O2). (6) Dehalogenation reaction (for example: MoCl6 → Mo + 3Cl2) (7) Deammoniation reaction (for example, NaCl·5NH3 → NaCl + 5NH3) In each reaction, when the endothermic quantity is calculated from the thermodynamics data, the endothermic quantities of the (1) dehydration reaction and the (3) dehydrogenation reaction are large. Among them, those with a small atomic weight of the metal in the atomic substance (Li>Na>Mg>Al>K>Ca) and a large reaction molar number of the hydrate have a large endothermic quantity. As an example of a reaction with a large endothermic quantity, (Na2SO4·10H2O → Na2SO4 + 10H2O) can be cited. Reactions with a large endothermic quantity like this have high cooling performance. As a result, it is effective as a measure for improving the hardness of aluminum castings, preventing shrinkage cavities due to casting shrinkage during solidification, and gas defects from the mold. Therefore, in the practice of the present invention, it is preferable to add one or more water-soluble salts with a small metal atomic weight in the hydrate form. In the water-soluble binder composition according to the present invention (water-soluble binder composition), the cooling rate of the mold becomes faster, so that a chill layer is formed or becomes thicker than normal on the casting surface, the hardness of the aluminum casting is increased, and a solidified layer is formed at the interface between the mold and the molten aluminum, which is also advantageous for preventing the intrusion of mold gas and for preventing the core from breaking due to the pressure during low-pressure casting and high-pressure casting.

[0050] [Borates of other salts] Furthermore, examples of borates of other salts, which are components used in place of or in combination with orthophosphate, include those containing boric acid, sodium tetraborate (borax), sodium metaborate, dipotassium tetraborate, lithium tetraborate, and their hydrates, etc. can be listed as specific examples. In addition, examples of sulfates include those containing sodium sulfate, potassium sulfate, magnesium sulfate, lithium sulfate, aluminum sulfate, potassium aluminum sulfate, and their hydrates, etc. Furthermore, examples of carbonates include those containing sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, dipotassium carbonate, disodium carbonate, magnesium carbonate, calcium carbonate, and their hydrates, etc. Examples of nitrates include potassium nitrate, sodium nitrate, and those containing their hydrates, etc. Examples of silicates include those containing sodium silicate, potassium silicate, lithium silicate, sodium metasilicate, potassium metasilicate, lithium metasilicate, silicone resin, ethyl silicate, and their hydrates, etc. Examples of hydroxides include those containing aluminum hydroxide, sodium hydroxide, potassium hydroxide, sugars, and their hydrates, etc. Examples of halides include sodium chloride, sodium perchlorate, potassium chloride, potassium bromide, and potassium iodide.

[0051] 〔Concentration of solute in water-soluble binder solution, etc.〕 In the present invention, the solute concentration of such a water-soluble binder solution (hydrates are calculated as solvents) is preferably 2.0% or more, more preferably 20% or more, still more preferably 35% or more, and is preferably selected within the range of 20.0 to 55.0. Here, the water-soluble binder concentration (%) is specifically determined by the following formulas 1 and 2. 〔Formula 1〕 Water-soluble binder concentration (%) = [(weight of solute in binder) / (weight of added water + weight of hydrate) × 100] [Formula 2] Weight of solute (g) = [(amount of salt added g) × (solute molecular weight / total molecular weight (including hydrate)]

[0052] When used as a water-soluble binder solution, it is necessary to use one with a viscosity of 100 mPa·s / 5°C or less, preferably 50 mPa·s / 5°C or less, more preferably 20 mPa·s / 5°C or less, 100 mPa·s / 5°C or less and a concentration of 2.0% or more and a pH of 2 to 13.

[0053] Thus, when the water-soluble binder composition is composed of a plurality of salts compounds, the water-soluble binder concentration (%) requires obtaining the weight of the solute of each salt, multiplying the molecular weight ratio of the solute added to the weight g of the salt added respectively, and obtaining it as the sum of the values obtained from these. The viscosity (5°C or 30°C) and pH of the water-soluble binder need to be actually measured and obtained.

[0054] In addition, if a binder with a water-soluble binder concentration of less than 2% is used, it will cause the influence of the decrease in the mold strength of the mold, and deterioration in productivity such as an extended molding time during molding will be caused. Also, under molding conditions in a low-temperature range of the environmental temperature, if a water-soluble binder with a viscosity higher than 100 mPa·s / 5°C is used, the mold filling property will become insufficient, and problems such as casting surface defects such as poor filling will be caused. Similarly, a viscosity of 100 mPa·s / 30°C or more due to moisture evaporation in summer will also cause problems such as a decrease in the fluidity of the mulled sand during mold molding, a decrease in the filling property, a decrease in the mold strength, and a deterioration in workability due to clogging of the blow head and blow port in the molding machine.

[0055] [Blending amount of water-soluble binder] When manufacturing coated sand for an aluminum mold using the water-soluble binder composition, the water-soluble binder composition is kneaded into predetermined refractory particles (aggregates such as foundry sand) according to a conventional method. Here, the blending amount of the water-soluble binder composition according to the present invention is appropriately determined in consideration of the type of the composition used, the required strength of the mold, etc., and thus cannot be defined univocally. Generally, it is in the range of about 20 to 500 parts by mass, preferably 30 to 150 parts by mass, and more preferably 40 to 80 parts by mass with respect to 1000 parts by mass of the refractory particles.

[0056] In the present invention, the foundry sand used includes all foundry sands for casting, such as silica sands mainly composed of quartz such as natural silica sand, artificial silica sand, and recycled sand used for casting, ceramic sands such as mullite and alumina, special sands such as zircon sand, chromite sand, and olivine sand, and slag sand produced from slag produced during the production of ferronickel and ferrochrome. Spherical bodies with a grain shape coefficient of 1.4 or less and a pH of 11 or less function as aggregates in the mold material. Various artificial spherical bodies that have been conventionally proposed and used as such aggregates can also be appropriately selected and used in the present invention. For example, Albani-sand (manufactured by Touchu Co., Ltd.; trade name) with a grain shape coefficient of 1.2 made of high-purity silica sand, a natural mineral, DB-sand (manufactured by Meia Sangyo Co., Ltd.; trade name) with a grain shape coefficient of 1.05 obtained from molten steel slag, Esperal (manufactured by Yamakawa Sangyo Co., Ltd.; trade name) and TYCO-sand (manufactured by Tsuchiyoshi Sangyo Co., Ltd.; trade name) with a grain shape coefficient of 1.03 mainly composed of molten mullite, Lunamos (manufactured by Kao Corporation; trade name), TY-sand (manufactured by Tsuchiyoshi Sangyo Co., Ltd.; trade name) with a grain shape coefficient of 1.09 mainly composed of sintered mullite, CPS (manufactured by Kyushu Tsusho Co., Ltd.; trade name), and spherical particles commercially available under names such as Cerabeads (manufactured by Itochu Ceramtec Co., Ltd.; trade name) can be mentioned. Of course, it is not limited to these, and any natural and artificial refractory spherical particles that satisfy the grain shape coefficient and pH defined in the present invention can be used. Also, since the particle size of the foundry sand is determined by factors such as the casting surface and gas defects, the effects of the present invention are not inhibited regardless of the particle size of the foundry sand used. Desirably, the AFS index is 30 to 250. Note that the particle size of the foundry sand shown in Fig. 1 is only an example, and the present invention should not be understood restrictively based on this. Generally, the effects of the present invention are not inhibited even if materials such as red iron oxide, iron sand, coal powder, graphite powder, starch, sugars, wood powder, surfactants, thickeners, and disintegration accelerators commonly added to foundry sand are used.Using casting sand in the form of spherical bodies with a particle size coefficient close to 1 makes it possible to cover the surface of the particles with a small amount of binder. As a result, it can exhibit characteristics such as maintaining sufficient strength and forming a mold with good collapsibility after casting.

[0057] Here, the particle shape coefficient of the spherical bodies used in the present invention is generally used as a measure indicating the outer shape of the particles and is also referred to as the particle shape coefficient. The closer its value is to 1, the closer it means to approach a spherical shape (true sphere). Such a particle size coefficient is measured by various known methods. After measuring the particle images with an optical microscope or SEM image, the particle size coefficient "(perimeter length)^2 / (4π × area)" can be measured using free software such as ImageJ.

[0058] The pH measurement of the water-soluble binder solution is the value measured in accordance with JIS Z 8802 (2011) "Method for Measuring pH" when the water-soluble binder composition is made into an aqueous solution. The pH here is to detect the degree of influence on the aggregate during mold manufacturing, the mold during molding, and the aluminum casting after casting. It dissolves H+, OH- metal ions, etc. in the binder into water and measures the pH of the aqueous solution to define it as the pH of the water-soluble binder.

[0059] 〔Water-soluble cores and their manufacturing method〕 The water-soluble cores of the present invention and their manufacturing method will be described with reference to FIG. 1. The figure shows the case where only a water-soluble binder is added to the casting sand, and the surface of the casting sand is coated with the water-soluble binder. The bonding force between the casting sands depends on the amount of the water-soluble binder present at the contact points between the casting sands and the filling rate of the mold. Even if a large amount of binder is added, the binder coated on the surface other than the contact points does not contribute to the bonding. In contrast, FIG. (b) shows the case where a binder and filler fine particles are added to the casting sand. The surface of the casting sand is coated with the water-soluble binder, and filler fine particles are present on the surface between the casting sands. This alleviates the frictional resistance due to the mold-sand, sand-sand, and the viscosity of the binder during blow filling, and functions as a so-called slip effect (bearing effect or dimple effect) to improve the filling density of the mold. In particular, the filling density of the mold is improved, and the contact area between the casting sands is increased. The bonding force between the casting sands is exerted by both the water-soluble binder and the filler fine particles. Compared with the case of only the water-soluble binder, the mold strength is particularly improved in the high binder addition amount region.

[0060] As the surfactant used as the viscosity modifier in the present invention, various surfactants can be used as long as they have the function of reducing the surface tension of the solvent and imparting the functions of improving the fluidity of the kneaded sand and suppressing the evaporation of moisture. Regarding the surfactant, when used in combination with the product of the present invention, a better filling property and an effect of suppressing moisture evaporation can be obtained. Surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. In the present invention, examples of anionic surfactants include sodium fatty acid, monoalkyl sulfate, alkyl polyoxyethylene sulfate, alkylbenzene sulfonate, monoalkyl phosphate, etc. Examples of cationic surfactants include alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, etc. Examples of amphoteric surfactants include alkyldimethylamine oxide, alkyl carboxy betaine, etc. Even when polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglucoside, fatty acid diethanolamide, alkyl monoglyceryl ether, etc. are used in combination as nonionic surfactants, the effects of the present invention are not inhibited, and a further improvement effect on the filling property can be obtained. In addition, when implementing the present invention, it does not exclude the use of surfactants for purposes other than imparting fluidity and suppressing moisture evaporation.

[0061] 〔Kneading〕 And when manufacturing the target coated sand using the water-soluble binder composition according to the present invention, the manufacturing method is not particularly limited. In the present invention, in particular, in a kneader such as a muller mixer or a speed mixer, after kneading refractory particles (aggregates such as foundry sand) and silica fume (fine filler particles), then, for the purpose of adding an aqueous solution of the water-soluble binder composition and a surfactant and dispersing the lubricant content, high-speed stirring is applied, and the adoption of the cold coat method is recommended. The timing of kneading the binder binding component (phosphate, borate, etc.), fine filler particles, and viscosity modifier constituting the water-soluble binder composition according to the present invention with the refractory particles can be appropriately selected based on the knowledge of those skilled in the art. They can be kneaded alone or sequentially, or can be kneaded in an appropriate combination.

[0062] 〔Molding〕 Furthermore, when using the coated sand obtained as described above to mold a predetermined mold such as a water-soluble binder mold, in order to heat-cure such coated sand, the molding of the target mold will be performed under heating. Such a heating molding method is not particularly limited, and any conventionally known method can be advantageously used. For example, the coated sand as described above can be filled into a mold heated to about 120°C to 220°C having a desired shape space for providing the target mold by a slurry addition method, a pressurization method, a gravity drop method, a blowing method, etc., and decompression or suction can be performed as necessary and molded according to a conventional method. At that time, as an advantageous dehydration method for the water-soluble binder solution, a molding machine that blows the mixed sand containing the mold material of the present invention into a pre-heated mold and then purges it with cold air or warm air is suitable. The purging of cold air or warm air can be either a pressurization method or a decompression or suction method. After curing, the cured mold can be removed from such a mold to obtain the target casting mold. And in the mold obtained in this way, excellent characteristics as described above can be advantageously imparted. Also, the heating of the mold can be either electric heating, gas heating, or a method using hot oil. Such a molding machine has already been developed and can be easily obtained. Using superheated steam instead of cold air or warm air makes the curing even faster. It is possible to heat and cure the mold using microwave heating, high-frequency heating, or far-infrared heating, and then ventilation can be performed, or decompression can be performed for dehydration and curing. Curing by a vacuum freeze dryer is also possible.

Example

[0063] Several embodiments of the present invention will be shown below to more specifically clarify the present invention. Needless to say, the present invention is not limited in any way by such descriptions of the embodiments. In addition to the following embodiments, various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art without departing from the spirit of the present invention, even beyond the above specific descriptions.

[0064] In the following description, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified. Each property of the manufactured water-soluble binder mold was measured according to the following test methods.

[0065] Measurement of flexural strength Using each water-soluble mold, according to the JACT test method: SM-1, a JIS type test piece (10 mm × 10 mm × 100 mm, firing conditions: 170 °C, 60 seconds) was prepared, and the flexural strength (kgf / cm 2 ) of the obtained JIS type test piece was measured. The higher this flexural strength, the higher the strength of the mold. The core was placed on the fulcrum between L (50 mm), and P (kgf) was applied from above to the center. From the following formula, the flexural force σ (kgf / m 2 ) was obtained with a: test piece width and H: test piece height. σ = 3 / 2 × L / a·H 2 × P

[0066] Confirmation of collapsibility JIS type test pieces (width: 10 mm × thickness: 10 mm × length: 100 mm, firing temperature time: (170 °C × 60 seconds)) were prepared from each water-soluble coating sand, and the obtained JIS type test pieces were directly placed in a high-temperature electric furnace at a predetermined temperature (600 °C) and heated for 1 minute each. Then, immediately after taking out the test pieces and under the condition of cooling to room temperature, they were each put into cold water, and the time until the mold collapsed was measured.

[0067] Measurement of Binder Viscosity The Brookfield viscosity is the value measured using the model Brofield DV-II+Pro owned by the Western Hiroshima Industrial Technology Center, based on the measurement principle of the B-type rotation method, when the water-soluble binder composition is made into an aqueous solution. It is the value measured in accordance with the "Method for Measuring Viscosity of Liquids". The Brookfield viscosity is the resistance torque when stirring the aqueous solution, meaning that the higher the value, the more energy is required for stirring.

[0068] Measurement of Binder pH The pH measurement of the water-soluble binder composition is the value measured using the device IM-32 type, manufactured by Toa DKK Corporation, in accordance with JIS Z 8802 (2011) "Method for Measuring pH" when the water-soluble binder composition is made into an aqueous solution. Here, the pH is to detect the degree of influence on the aggregate during mold manufacturing, the mold during molding, and the aluminum casting after casting. It is defined as the pH of the aqueous solution obtained by dissolving H + , OH - metal ions, etc. in water and measuring the pH of the aqueous solution as the pH of the water-soluble binder.

[0069] (Comparative Examples 1 and 2) [Manufacture of Water-Soluble Binder Solution] Water-Soluble Binder Production Example 1 Into a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 170 parts of magnesium sulfate heptahydrate, 122.5 parts of sodium tetraborate decahydrate, 49 parts of sodium sulfate decahydrate, and 100 parts of distilled water as a solvent were respectively added. Then, the temperature of the reaction vessel was gradually raised, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 441.5 parts of water-soluble binder solution A1 were obtained.

[0070] (Example 1) Water-Soluble Binder Production Example 2 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 312 parts of sodium dihydrogen phosphate dihydrate, 244.5 parts of sodium tetraborate decahydrate, 100 parts of sodium sulfate decahydrate, and 200 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 856.5 parts of water-soluble binder solution A2 were obtained.

[0071] (Examples 2, 3) Water-soluble Binder Production Example 3 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, 160 parts of sodium sulfate decahydrate, and 230 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 905 parts of water-soluble binder solution A3 were obtained.

[0072] (Example 4) Water-soluble Binder Production Example 4 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 820 parts of sodium tetraborate decahydrate and 1700 parts of distilled water were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 2520 parts of water-soluble binder solution A4 were obtained.

[0073] (Example 5) Water-soluble Binder Production Example 5 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 180 parts of sodium dihydrogen phosphate dihydrate, 550 parts of sodium tetraborate decahydrate, and 300 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 1110 parts of water-soluble binder solution A5 were obtained.

[0074] (Example 6) Water-soluble Binder Production Example 6 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, and 300 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated to reach 45 °C, and after stirring for 3 h - 5 h until the solute was completely dissolved, 815 parts of water-soluble binder solution A6 were obtained.

[0075] (Example 7) Water-soluble Binder Production Example 7 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 234 parts of sodium dihydrogen phosphate dihydrate, 249 parts of sodium tetraborate decahydrate, and 300 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated to reach 45 °C, and after stirring for 3 h - 5 h until the solute was completely dissolved, 783 parts of water-soluble binder solution A7 were obtained.

[0076] (Example 8) Water-soluble Binder Production Example 8 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 281.5 parts of sodium dihydrogen phosphate dihydrate, 132.5 parts of sodium tetraborate decahydrate, and 300 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated to reach 45 °C, and after stirring for 3 h - 5 h until the solute was completely dissolved, 714 parts of water-soluble binder solution A8 were obtained.

[0077] (Example 9) Water-soluble Binder Production Example 9 Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 335 parts of sodium dihydrogen phosphate dihydrate and 300 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and 635 parts of water-soluble binder solution A9 were obtained.

[0078] (Example 10) Water-soluble Binder Production Example 10 Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, 18 parts of potassium sulfate and 300 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 833 parts of a water-soluble binder solution A10 were obtained.

[0079] (Example 11) Water-soluble binder production example 11 Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, 34.5 parts of potassium sulfate and 300 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 849.5 parts of a water-soluble binder solution A11 were obtained.

[0080] (Example 12) Water-soluble binder production example 12 Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 187.3 parts of sodium dihydrogen phosphate dihydrate, 26.6 parts of sodium pyrophosphate, 30.5 parts of sodium hexametaphosphate, 246 parts of sodium tetraborate decahydrate, 27.2 parts of sodium metaborate tetrahydrate and 300 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 817.6 parts of a water-soluble binder solution A12 were obtained.

[0081] (Example 13) Water-soluble binder production example 13 Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 80 parts of sodium sulfate decahydrate, 10.1 parts of potassium sulfate, 187.3 parts of sodium dihydrogen phosphate dihydrate, 246 parts of sodium tetraborate decahydrate and 400 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 937.2 parts of a water-soluble binder solution A13 were obtained.

[0082] (Example 14) Production Example 14 of Water-Soluble Binder Into a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 80 parts of sodium sulfate decahydrate, 187.3 parts of sodium dihydrogen phosphate dihydrate, 246 parts of sodium tetraborate decahydrate, 21.2 parts of sodium metasilicate pentahydrate, and 350 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 884.5 parts of water-soluble binder solution A14 was obtained.

[0083] (Example 15) Production Example 15 of Water-Soluble Binder Into a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 160 parts of sodium sulfate decahydrate, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, 21.2 parts of potassium nitrate, and 350 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 996.2 parts of water-soluble binder solution A15 was obtained.

[0084] (Example 16) Production Example 16 of Water-Soluble Binder Into a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 160 parts of sodium sulfate decahydrate, 210 parts of sodium dihydrogen phosphate dihydrate, 305 parts of sodium tetraborate decahydrate, and 350 parts of distilled water as a solvent were respectively charged. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 50 parts of an antifoaming agent (silicone resin: MK-72M) diluted 400-fold with distilled water was further added to obtain 1025 parts of water-soluble binder solution A16.

[0085] (Example 17) Production Example 17 of Water-Soluble Binder Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 170 parts of magnesium sulfate heptahydrate, 49 parts of sodium sulfate decahydrate, 60 parts of sodium dihydrogen phosphate dihydrate, 315 parts of sodium tetraborate decahydrate, 12.4 parts of boric acid, 15.6 parts of aluminum hydroxide and 150 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 50 parts of an antifoaming agent (silicone resin: MK-72M) diluted 400-fold with distilled water was further added to obtain 774.7 parts of a water-soluble binder solution A17.

[0086] (Example 18) Water-soluble binder production example 18 Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 170 parts of magnesium sulfate heptahydrate, 49 parts of sodium sulfate decahydrate, 60 parts of sodium dihydrogen phosphate dihydrate, 315 parts of sodium tetraborate decahydrate, 12.4 parts of boric acid, 15.6 parts of aluminum hydroxide and 150 parts of distilled water as a solvent were respectively added. The reaction vessel was gradually heated, and after reaching 45 °C, it was stirred for 3 h - 5 h until the solute was completely dissolved, and then 50 parts of a viscosity modifier (antifoaming agent silicone resin: MK-72M) diluted 400-fold with distilled water was further added to obtain 774.7 parts of a water-soluble binder solution A18.

[0087] 〔Production of water-soluble coated sand〕 (Comparative Example 1, Example 2) To 2000 parts of new sand (fused artificial sand, trade name: TYCO-ceramic sand #650), 80 parts of the above water-soluble binders A1 and A3 were added, and after mixing by stirring and kneading with a speed mixer under the condition of 50 Hz for 60 seconds, they were discharged from the mixer to obtain water-soluble coated sands CS1 and CS3 respectively.

[0088] 〔Production of other water-soluble coated sands〕 (Comparative Example 2, Example 1, Examples 3 to 18) To 2000 parts of new sand (fused artificial sand, trade name: TYCO Ceramic Sand #650 or fused slag sand, trade name: DB-SAND #85), 80 parts of the above water-soluble binders A2, A4 to A17 and 20 parts of silica fume as a filler were added, and they were stirred and kneaded in a speed mixer for 60 seconds under the condition of 50 Hz. After mixing, they were discharged from the mixer to obtain water-soluble coated sands CS2, CS4 to CS18 respectively.

[0089] For molding, a mold of 10 mm×10 mm×100 mm was formed using a blowing molding machine. The kneaded sand was blown into the mold with a blowing pressure of 3.0 kg / cm2 and a blowing time of 1 second. In Comparative Examples 1 to 2 and Examples 1 to 17, the kneaded sand was filled into a mold preheated to 170 °C in advance, and the moisture in the kneaded sand was removed and cured by performing molding with a firing time of 60 seconds.

[0090] Regarding the various mold materials for water-soluble binders according to Comparative Examples 1 to 2 and Examples 1 to 18 obtained, the flexural strength, specimen density, disintegration time, and as binder characteristics, the binder concentration, pH, and binder viscosity were measured respectively, and the obtained results are shown in the following respective tables.

[0091]

Table 2

[0092]

Table 3

[0093] As is clear from the comparison of the results in Tables 2 to 3, in Comparative Example 1 and Examples 1 to 18, compared with the conventional magnesium sulfate-based (Comparative Example 1) binder, the binder mainly composed of phosphate and borate can further increase the mold strength by combining with other salts and adjusting the addition amount. Similarly, in terms of collapsibility, the conventional magnesium sulfate-based binder has high heat resistance for each component alone, but it was revealed that when exposed to heat exceeding 400 °C, the collapsibility of the mold deteriorates rapidly, and it does not collapse when exceeding 600 °C. This is because depending on the combination of binder components, reactions occur between the binder components, leading to the formation of insoluble salts. Therefore, this time, by examining the combination of multiple salts, it became possible to effectively increase the concentration of the binder and manufacture a water-soluble mold with higher strength and improved heat resistance than conventional water-soluble binder molds.

[0094] Detailed descriptions of FIGS. 1 to 9 are shown below. FIG. 1 is a SEM image of the aluminum structure of a shell mold and a water-soluble mold. Cooling effect of water-soluble binder Casting evaluation using joint water was carried out using a shell core and a water-soluble core in the aluminum gravity casting method. SEM observation of the hose part, which is a weak part of the product, was performed, and analysis of the chill layer thickness and dendrite arm spacing (DAS) was carried out to confirm whether there is a difference in the cooling rate between the water-soluble core and the shell core. The SEM images were measured at magnifications of 50 times, 200 times, and 500 times, and the difference in cooling rate was judged from the tissue state of the casting-mold interface. From the casting results this time, it was confirmed that the chill layer is thicker in the water-soluble core compared to the shell core. The place in contact with the normal mold is the place with the fastest cooling rate, so it is likely to have a fine structure, which is called the chill layer, and the crystal grains extend in the horizontal direction from there towards the center. This represents the temperature gradient of cooling as it is. Therefore, it was demonstrated that the water-soluble core with a large chill thickness has a faster cooling rate than the normal shell core, and as a result, the gas shielding effect from the mold and the effect of preventing shrinkage cavities are higher than those of the normal shell core, and it was confirmed that it is also effective in countermeasures against casting defects, which are problems in the organic process.

[0095] Figure 2 is a chart of the DAS measurement results. Primary crystal Al exhibits a dendritic morphology, and its solidification proceeds as the generation and growth of α-Al dendrites. And the proportion of the α-Al dendrite phase in the structure is very high. As an indication of the size of the microstructure of the casting, the dendrite arm spacing (secondary dendrite arm spacing, DAS) has been measured. The dendrite arm spacing generally measures the spacing between secondary arms. These arm spacings and cell sizes are used to estimate the cooling rate, solidification rate, solidification time, and mechanical properties during the solidification of the casting. This time, when comparing the water-soluble grains and the shell grains, it can be seen that the solidification rate and cooling rate are faster because the interval of the dendrite arm spacing is narrower than that of the shell grains.

[0096] Figure 3 is a schematic diagram of the hydrogen bond of the borate compound. When sodium tetraborate is dissolved in water, tetraborate ions such as B(OH) 4- are generated. These tetraborate ions have the property of being easily bonded by hydrogen bonds with hydroxyl groups. For example, they partially react with phosphates (orthophosphate: sodium hydrogen diphosphate) which are compounds having hydroxyl groups, and form a network structure, so it is considered that they have the effect of easily gelling and enhancing the curability and mold strength.

[0097] Figure 4 is an explanatory diagram (common ion effect) of the action of the present invention based on the redissolution image diagram of the sparingly soluble salt. The common ion effect refers to the effect that ions coexisting in a solution affect the dissociation and solubility of electrolytes. When a completely unrelated salt (ions) dissolves, it is the phenomenon that the solubility of the ionic compound changes due to the environmental change caused thereby. For example, when an inert salt such as KNO3 is added to a sparingly soluble salt such as silver chloride, K + and NO3 -Due to the shielding effect, the affinity between ion pairs decreases, resulting in a decrease in the effective charge and, as a result, an increase in solubility. In the water-soluble binder component, by combining various salts (ions), the concentration of the binder component can be increased, the mold strength can be improved by the binder, and the solubility can be improved, thereby improving the storage stability in the binder solution. It is conceivable.

[0098] The figure is a scatter diagram chart showing the relationship between the molar ratio of phosphate and borate used in the present invention and the mold strength. When sodium dihydrogen phosphate dihydrate and sodium tetraborate decahydrate are used as the binder component, the preferred optimal mixing ratio at which the mold strength is the highest is such that the molar ratio % of sodium dihydrogen phosphate dihydrate is 40% or more, more preferably 50 - 70% of the molar ratio %. By mixing at the optimal molar ratio %, it becomes possible to dissolve sodium dihydrogen phosphate and sodium tetraborate decahydrate with low solubility at a low water content (coexisting ion effect), and it is considered that the mold strength is increased by the concentration of the binder component and the interaction such as hydrogen bonding between tetraborate ions and the hydroxyl groups of phosphates. However, since sodium dihydrogen phosphate has low heat resistance and there is a risk that the binder component will be vitrified by the heat during aluminum casting, further improvement in solubility and heat resistance can be achieved by adding other salts with high heat resistance, such as sodium sulfate and potassium sulfate. It is conceivable.

[0099] Figure 6 is a chart showing the relationship between the temperature and viscosity of the water-soluble binder of Production Example 1. It can be seen from the above figure that the water-soluble binder solution has the characteristic that its viscosity changes with temperature. Usually, as the air temperature decreases, the water temperature of the binder also decreases, resulting in an increase in the viscosity of the water-soluble binder. The increase in viscosity can also be a factor that inhibits the fluidity of the aggregate during mold making, and can cause a decrease in mold strength due to deteriorated filling properties and sand biting defects due to insufficient filling. Therefore, it is necessary to always control the viscosity and ensure fluidity regardless of environmental changes.

[0100] Figure 7 is a diagram showing the relationship between temperature and viscosity by adding a viscosity modifier to the water-soluble binder. As a countermeasure for improving the fillability with the increase in viscosity, by adding a small amount (0.5%) of a viscosity modifier diluted 300 times with respect to the binder (main component of the detergent: sodium alkyl ether sulfate, antifoaming agent, reagent: polyoxyethylene (20) sorbitan monooleate), it is possible to lower the binder viscosity under low-temperature conditions, and it becomes possible to improve the fillability and mold strength by improving the fluidity of the kneaded sand.

[0101] Figure 8 is a temperature distribution diagram of the water-soluble binder mold. Using the water-soluble binder mold, a casting test was carried out on an actual product by the aluminum gravity casting method. For the purpose of confirming the temperature applied to the water-soluble mold, thermocouples were installed at two locations, the surface layer part and the middle part of the water-soluble core, to confirm the temperature change of the mold. The casting temperature was 710 °C, the mold temperature was 380 °C, the casting time after tilting was 5 seconds, and the solidification time was 90 seconds. The temperature of the mold after casting was such that only the surface layer part was 600 °C immediately after casting, and the maximum temperature of the central part was 450 °C around 3 minutes. As for the whole mold, it was found that the cooling was fast. After casting and completely cooling the casting, a sand removal test was carried out by immersion in water. As a result, the magnesium sulfate-based binder (Comparative Example 2) had poor collapsibility, and it was possible to remove the sand after leaving it for more than one day, but it did not completely return to a sandy state, and the sand was discharged partially in a lump-like state. As a result of carrying out the casting test under the conditions of Examples 2 and 3 in the same way, it was also confirmed that the sand could be removed within 1 minute.

[0102] Figure 9 is a diagram showing the relationship between the temperature and the collapse time of the water-soluble binder. The collapsibility of the water-soluble binder mold was tested under temperature conditions (170°C, 450°C, 500°C, 550°C, 600°C) with a firing time of 1 minute. After firing, the test specimens were taken out and air-cooled until they reached room temperature. The mold test specimens were immersed in water, and the time until the test shape collapsed was measured. It was revealed that the conventionally used magnesium sulfate-based binder (manufacturing condition 1, Example 2) had high heat resistance as a single component system, but its collapsibility deteriorated rapidly when heated above 450°C. This is due to the reaction of the binder components (magnesium sulfate and magnesium tetraborate) to form an insoluble salt. Therefore, depending on the salts combined, the combination design of the binder composition components considering not only the heat resistance of the single salt but also the reactivity due to heat after casting becomes important. This time, by newly combining various salts with phosphates and borates, it became possible to manufacture a water-soluble binder that achieves both high strength and collapsibility of the mold. The above is the result of the collapsibility test of (manufacturing condition 3, Example 3), and compared with the conventional binder, the collapsibility was good up to around 600°C.

Claims

1. In a water-soluble binder composition for a water-soluble mold containing water-soluble salts as a water-soluble binder component, the water-soluble binder component is composed mainly of at least one kind of phosphates and at least one kind of borates, the main components account for 71% by weight or more of the entire water-soluble binder component, with the total of the phosphates and the borates being 100, the molar ratio of the phosphates being 53.5 to 83.7, and the viscosity of the binder solution at 5 °C being 100 mPa / s or less and the pH being 2 to 13. A water-soluble binder composition characterized by this.

2. The water-soluble binder composition according to claim 1, wherein the water-soluble binder component contains, in addition to the main components, one or more compounds selected from sulfates, carbonates, nitrates, hydroxide salts, and halides.

3. The water-soluble binder composition according to claim 1 or 2, characterized in that the binder solution contains at least one selected from the group consisting of sulfate ions, hydroxide ions, carbonate ions, nitrate ions, and halide ions, borate ions, and phosphate ions.

4. The water-soluble binder composition according to any one of claim 1 or claim 2, wherein at least one of the phosphate compounds is at least one selected from orthophosphates, metaphosphates, and polymeric phosphates, or is at least one compound or hydrate selected from orthophosphates, metaphosphates, and polymeric phosphates.

5. The water-soluble binder composition according to claim 1 or 2, wherein the borates are at least one selected from orthoborate, diborate (metaborate), triborate, tetraborate, and polyboric acid, or are at least one compound or hydrate selected from orthoborate, diborate (metaborate), triborate, tetraborate, and polyboric acid.

6. The water-soluble binder composition according to claim 1 or 2, wherein at least one of the water-soluble salts contains a hydrate of the water-soluble salt.

7. A water-soluble binder solution containing one or more of the water-soluble binder compositions according to claim 1 or 2, characterized in that its concentration (mass concentration) is 2.0% or more. A water-soluble binder solution.

8. A water-soluble binder composition according to claim 1 or 2, foundry sand, and filler fine particles, wherein the filler fine particles are at least one compound selected from fumed silica, fumed alumina, hollow fillers, spherical iron oxide, iron oxide, boron nitride, aluminum nitride, titanium oxide, potassium titanate, aluminum hydroxide, clay, and graphite, characterized by a water-soluble mold material.

9. A water-soluble binder composition according to claim 1 or 2, foundry sand, and a viscosity modifier, wherein the viscosity modifier is a surfactant, and the surfactant is at least one compound selected from nonionic type, cationic type, anionic type, and zwitterionic type, characterized by a water-soluble mold material.

10. A water-soluble binder composition according to claim 1 or 2 and foundry sand, wherein the water-soluble binder composition is used in a proportion of 20 to 500 parts by mass in total with respect to 1000 parts by mass of the foundry sand, characterized by a water-soluble mold material.

11. A water-soluble binder composition according to claim 1 or 2 and foundry sand, wherein the water-soluble binder composition coats the foundry sand in a slurry state, wet state, or dry state, characterized by a water-soluble binder-coated sand for a water-soluble mold.

12. A water-soluble mold characterized by being composed of a water-soluble mold material containing the water-soluble binder composition according to claim 1 or 2.

13. In a method for manufacturing a water-soluble mold using the water-soluble binder-coated sand according to claim 11, after press molding, injection molding, or blow molding, molding is performed by at least one of heat curing, vacuum suction curing, micro-heat curing, superheated steam curing, and hot air and cold air blowing, characterized by a method for manufacturing a water-soluble mold.

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