Method of making mold

Abstract

To provide a method of making a mold that allows for advantageously reducing the time of molding work as compared with the conventional making method.SOLUTION: A method of making a mold, using a resin-coated sand whose foundry sand is covered at a surface with a coating layer containing at least alkaline resol resin, includes: filling such a resin-coated sand in a cavity of a forming die to give a mold aimed at and then carrying out an operation to feed superheat vapor and carbon dioxide gas into the cavity so as to set the resin-coated sand through the feed operation, thereby obtaining a mold aimed at.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a mold, and more particularly to a method for manufacturing a mold that can advantageously shorten the molding operation time as compared with conventional manufacturing methods.

Background Art

[0002] Conventionally, as one of the molds used for casting molten metal, a coated sand (mold material) having a structure in which the surface of a refractory aggregate (casting sand) is coated with a predetermined binder (adhesive) has been used to mold it into a desired shape. And as such a binder in the coated sand, in addition to an inorganic binder such as water glass, an organic binder made of a resin such as a phenol resin, a furan resin, or a urethane resin has been used. Also, a method of molding a self-hardening mold using these binders has been put into practical use.

[0003] And regarding the method for manufacturing a mold using such coated sand, various methods have been proposed conventionally according to the type of binder and the like. For example, in Patent Document 1 (Japanese Patent No. 6121121), as a method for manufacturing a mold using a binder-coated refractory (resin-coated sand) made of a thermosetting resin such as a phenol resin, such a binder-coated refractory is filled into a molding die, and a high-temperature and high-humidity gas having a temperature of 120°C or higher and a water vapor concentration of 10 to 80% is passed through the molding die. By this, the temperature of the binder-coated refractory is raised by the sensible heat and the latent heat of condensation of the high-temperature and high-humidity gas, and it is continuously heated with the high-temperature and high-humidity gas having the same temperature and water vapor concentration as described above passed through the molding die to evaporate the condensed water in the molding die and cure the binder of the binder-coated refractory. A method for manufacturing a mold has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in recent years, there has been a demand for improving the efficiency and shortening the time required for mold making. Under such circumstances, the inventors of the present invention have intensively studied a method for manufacturing a mold that can complete molding in a short working time based on the conventional method of manufacturing a mold using various binders, and as a result, have completed the present invention. That is, the present invention has been made against such a background, and the problem to be solved is that, compared with the conventional manufacturing method, it is possible to advantageously shorten the molding operation time, and the obtained mold can exhibit excellent strength even after a lapse of time from molding (manufacturing). It is to provide a method for manufacturing a mold.

Means for Solving the Problems

[0006] And the present invention can be preferably implemented in various aspects listed below in order to solve such problems. Further, each of the aspects described below can be adopted in any combination. It should be understood that the aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the description of the entire specification.

[0007] (1) A method for manufacturing a mold using resin-coated sand in which the surface of the foundry sand is covered with a coating layer, wherein the coating layer contains at least an alkali resol resin, after filling the resin-coated sand into the molding cavity of a molding die that gives the target mold, a supply operation of superheated steam and carbon dioxide gas is performed into the molding cavity, and the resin-coated sand is cured by the supply operation to obtain the target mold. A method for manufacturing a mold, characterized by the above. (2) The superheated steam is 1 cm of the volume of the molding cavity 3The method for manufacturing a mold according to the above-described aspect (1), wherein the mold is supplied into the molding cavity at a quantitative ratio of 0.17 to 8.30 L / min per unit area. (3) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein the carbon dioxide gas is supplied into the molding cavity at a quantitative ratio of 0.01 to 2.00 L / min per 1 cm 3 of the volume of the molding cavity. (4) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein the supply operation includes a step of simultaneously supplying the superheated steam and the carbon dioxide gas. (5) The method for manufacturing a mold according to the above-described aspect (4), wherein the simultaneous supply of the superheated steam and the carbon dioxide gas into the molding cavity is performed under the condition that α calculated from the following formula (1) is 4.0 or more. [α]=A / B ···(1) However, in the above formula (1), A is the supply amount of the superheated steam (L / min 3 ) per 1 cm of the volume of the molding cavity, and B is the supply amount of the carbon dioxide gas (L / min 3 ) per 1 cm of the volume of the molding cavity. (6) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein the supply operation includes a step of supplying the superheated steam and the carbon dioxide gas at different times. (7) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein an alkylene carbonate and / or an organic ester is supplied into the molding cavity together with or separately from the superheated steam. (8) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein the mold is heated to 100 °C or higher. (9) The method for manufacturing a mold according to the above-described aspect (1) or (2), wherein the coating layer of the resin-coated sand further contains a novolak-type phenolic resin. ​(10) The method for manufacturing a mold according to the above aspect (1) or aspect (2), wherein the coating layer of the resin-coated sand further contains an alkylene carbonate and / or an organic ester. (11) The method for manufacturing a mold according to the above aspect (1) or aspect (2), wherein the resin-coated sand has a dry state with room temperature fluidity. [Advantages of the Invention]

[0008] Thus, in the method for manufacturing a mold according to the present invention, when manufacturing a mold using resin-coated sand containing at least an alkali resol resin in the coating layer, superheated steam and carbon dioxide gas are supplied into the molding cavity of the mold filled with such resin-coated sand, and the resin-coated sand is cured by these superheated steam and the like, thereby manufacturing a mold. That is, in the present invention, by using superheated steam, adhesion of casting sand particles, promotion of curing of the alkali resol resin by thermal energy, and promotion of strength development in the cured mold can be advantageously achieved. At the same time, by using carbon dioxide gas, promotion of curing due to neutralization of the alkali component and assistance in the development of mold strength can be advantageously achieved. Therefore, in the method for manufacturing a mold according to the present invention, the curing of the resin-coated sand proceeds rapidly, and thus, compared with the conventional manufacturing method, shortening of the molding operation time is advantageously achieved. Further, the mold manufactured according to the manufacturing method of the present invention exhibits excellent strength even after a lapse of time from molding (manufacturing). The effect of obtaining a mold that exhibits excellent strength even after a lapse of time from molding (manufacturing) can be more advantageously enjoyed by using resin-coated sand containing a novolac type phenol resin in the coating layer together with the alkali resol resin. [Embodiments for Carrying Out the Invention]

[0009] Incidentally, when manufacturing a mold according to the present invention, resin-coated sand (hereinafter also simply referred to as RCS) in which the surface of molding sand is covered with a coating layer containing at least an alkali resol resin is used as a mold material.

[0010] As the molding sand constituting such resin-coated sand (RCS), any refractory granular material that has been conventionally used for molds can be used. Specifically, silica sand, chromite sand, zircon sand, olivine sand, alumina sand, synthetic mullite sand, etc. can be mentioned. These molding sands can be new sand, or recycled sand or recovered sand that has been used once or multiple times for molding a mold as molding sand. Furthermore, even if new sand is added to such recycled sand or recovered sand and mixed to form mixed sand, there is no problem at all. And such molding sand is generally used as having a particle size of about 40 to 80 in terms of the AFS index, preferably about 60 in terms of particle size. If the AFS index is too large, there is a risk of hindering gas ventilation. On the other hand, if the AFS index is too small, the gas supply amount becomes excessive, causing the drying of RCS to proceed more than necessary, and as a result, there is a risk of inhibiting the curing reaction of RCS.

[0011] The resin-coated sand (RCS) used in the present invention is one in which a coating layer containing at least an alkali resol resin as a binder is formed on the surface of the molding sand as described above. The alkali resol resin contained in the coating layer is not particularly limited in the present invention, and it is possible to appropriately select and use one according to the properties required for RCS from various conventionally known alkali resol resins.

[0012] Here, the alkali resol resin is an alkaline resol type phenol resin. Generally, phenols are reacted with aldehydes in the presence of a large amount of alkaline substances as a catalyst, for example, at a ratio where the molar number of the alkaline substance to phenols is about 0.01 to 2.0 times the molar amount, to be synthesized (manufactured). In addition, the blending molar ratio (F / P) of aldehydes and phenols in such a synthesis reaction is appropriately determined according to the type of reaction catalyst used there, etc., but generally, it is selected within the range of 1.1 to 4.0. Further, examples of the alkaline substance used in the synthesis of the alkali resol resin include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, etc., and they can be used alone or in a mixture of two or more. Among the alkaline substances, particularly, potassium hydroxide and sodium hydroxide are preferably used because of their good catalytic activity.

[0013] The resin-coated sand (RCS) used in the present invention is configured such that the surface of the casting sand is covered with a coating layer containing the above-described alkali resol resin. However, such a coating layer can contain known binder components other than the alkali resol resin as long as the object of the present invention is not inhibited. In the method for manufacturing a mold according to the present invention, RCS covered with a coating layer containing a novolak type phenol resin together with the alkali resol resin is preferably used. By manufacturing a mold according to the manufacturing method of the present invention using such an RCS covered with a coating layer containing an alkali resol resin and a novolak type phenol resin as a binder component, the resulting mold will exhibit sufficient strength even after a lapse of time since its manufacture.

[0014] The novolak-type phenolic resin used in the present invention is produced by subjecting phenols and aldehydes to a condensation reaction using an acidic catalyst, such as inorganic acids like hydrochloric acid, sulfuric acid, phosphoric acid, etc., organic acids like oxalic acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, etc., and further acidic substances like zinc oxide, zinc chloride, magnesium oxide, zinc acetate, etc. The blending molar ratio (F / P) of aldehydes to phenols in this synthesis reaction is appropriately determined according to the type of reaction catalyst used, etc., but generally, it is selected within the range of 0.55 to 0.99. Also, the weight average molecular weight (polystyrene-equivalent molecular weight measured by GPC) of the novolak-type phenolic resin used in the present invention is, for example, 800 to 10,000, preferably 1,000 to 9,000, more preferably 2,000 to 8,000. By using a novolak-type phenolic resin having such a weight average molecular weight, it becomes possible to more advantageously enjoy the effects of the present invention.

[0015] In addition, the phenols used as raw materials for the various phenolic resins described above mean phenol and derivatives of phenol. For example, in addition to phenol, alkylphenols such as cresol, xylenol, p-tert-butylphenol, nonylphenol, etc., polyhydric phenols such as resorcinol, bisphenol F, bisphenol A, etc., and mixtures thereof can be mentioned, and one of them is used alone or two or more of them are combined and used. On the other hand, as aldehydes, in addition to formalin in the form of an aqueous solution of formaldehyde, known aldehyde compounds such as paraformaldehyde, trioxane, acetaldehyde, paraldehyde, propionaldehyde, etc. can be exemplified, and one of them is used alone or two or more of them are combined and used.

[0016] Regarding resin-coated sand (RCS) that uses an alkali resol resin and a novolak-type phenol resin in combination as the binder component constituting the coating layer, if the amount of novolak-type phenol resin used is too small, there is a risk that the above-described effects cannot be enjoyed. On the other hand, if the amount of novolak-type phenol resin used is too large, there is a risk that the effect of the present invention, which is the rapid curing of RCS, cannot be advantageously enjoyed. Therefore, in the present invention, when using RCS that uses an alkali resol resin and a novolak-type phenol resin in combination as the binder component constituting the coating layer, the ratio of the alkali resol resin to the novolak-type phenol resin in the coating layer is preferably 95:5 to 60:40, more preferably 95:5 to 70:30, and most preferably 90:10 to 80:20 in terms of the weight ratio in terms of solid content. In RCS containing an alkali resol resin and a novolak-type phenol resin in such a ratio, it becomes possible to more advantageously enjoy the effect of using these resins in combination.

[0017] Specifically, when implementing the method for manufacturing a mold according to the present invention using resin-coated sand (RCS) containing an alkali resol resin and a novolak-type phenol resin in the coating layer, energy is efficiently applied to the RCS by supplying superheated steam, compared to the case of using general steam. As a result, the RCS becomes hotter more effectively, and as a result, the melting of the novolak-type phenol resin is promoted, making it easier to mix with the alkali resol resin. Since the novolak-type phenol resin does not have reaction points in the thermosetting reaction, the reaction between such a novolak-type phenol resin and an alkali resol resin is considered to be slower compared to the reaction between alkali resol resins. However, due to the supply of a large amount of thermal energy by superheated steam, the reaction between the novolak-type phenol resin and the alkali resol resin proceeds more efficiently than in the case of using general steam. As a result, regarding the mold obtained by the manufacturing method of the present invention using RCS containing an alkali resol resin and a novolak-type phenol resin in the coating layer, excellent strength can be exhibited whether it is immediately after molding or after a certain period of time has elapsed since molding.

[0018] The resin-coated sand (RCS) in which the surface of the casting sand is covered with a coating layer containing at least an alkali resol resin, as described above, can be used in the present invention as long as it is manufactured according to various conventionally known methods. For example, RCS covered with a coating layer containing an alkali resol resin and a novolak-type phenol resin can be manufactured by adding a novolak-type phenol resin and an aqueous solution of an alkali resol resin to the casting sand, kneading or mixing them, coating the surface of the casting sand with an aqueous solution containing a novolak-type phenol resin and an alkali resol resin, and then evaporating the moisture of such an aqueous solution.

[0019] Here, when manufacturing resin-coated sand (RCS) using the aqueous alkali resol resin solution as described above, depending on the state after manufacturing, it is classified into dry-state RCS having normal-temperature fluidity and wet-state RCS having no normal-temperature fluidity. The dry-state RCS having normal-temperature fluidity means RCS for which, regardless of the water content contained therein, when measuring the dynamic angle of repose, the measured value can be obtained. Here, the dynamic angle of repose means putting RCS into a cylinder having one end face with a transparent and flat surface (for example, putting RCS into a container with a diameter of 7.2 cm × height of 10 cm up to half of the volume), rotating it around the axis at a constant speed (for example, 25 rpm), and measuring the angle formed between the inclined plane and the horizontal plane. In addition, as the dynamic angle of repose of such dry-state RCS, 80° or less is preferable, more preferably 45° or less, and particularly preferably 30° or less. In particular, when the casting sand is spherical, a dry-state RCS having a dynamic angle of repose of 45° or less can be easily realized. On the other hand, those in which RCS does not flow in the cylinder in a wet state, the inclined plane of the RCS layer is not formed as a flat surface, and thus the dynamic angle of repose cannot be measured are regarded as wet-state RCS having no normal-temperature fluidity.

[0020] In the method for manufacturing a mold according to the present invention, it is possible to use either the above-described dry-state resin-coated sand (RCS) having normal-temperature fluidity or wet-state RCS having no normal-temperature fluidity. However, since it is easy to handle and the curing reaction of RCS proceeds more effectively and rapidly by supplying superheated steam and carbon dioxide gas described later into the mold (in the molding cavity), in the present invention, dry-state resin-coated sand (RCS) having normal-temperature fluidity is advantageously used.

[0021] Then, the above-mentioned resin-coated sand (RCS) is filled into the molding cavity of the mold, and the molding of the target mold is carried out. In the present invention, the curing of RCS is promoted by supplying superheated steam and carbon dioxide gas (CO2 gas) into the molding cavity. That is, by supplying superheated steam into the molding cavity, the adhesion of casting sand particles, the promotion of the curing of the alkali resol resin by thermal energy, and the promotion of the strength development of the cured mold can be advantageously achieved. Also, by supplying carbon dioxide gas, the promotion of curing due to the neutralization of the alkali component and the assistance in the development of mold strength can be advantageously achieved. Therefore, in the method for manufacturing a mold according to the present invention, the curing of RCS proceeds rapidly, and thus, compared with the conventional manufacturing method, the molding operation can be advantageously shortened in a short time.

[0022] Regarding the supply order and the like of superheated steam and carbon dioxide gas into the molding cavity filled with resin-coated sand (RCS) in the present invention, it is not particularly limited. However, from the viewpoint of more advantageously enjoying the effects of the present invention, a) First, start the supply of superheated steam, and after a predetermined time has elapsed, stop the supply of such superheated steam or continue it while starting the supply of carbon dioxide gas, and stop the supply of superheated steam and carbon dioxide gas simultaneously, or b) Start the supply of superheated steam and carbon dioxide gas simultaneously, and after a predetermined time has elapsed, stop the supply of superheated steam and carbon dioxide gas simultaneously. Such procedures are advantageously adopted.

[0023] Also, regarding the supply amount per unit time and per unit volume when supplying each gas into the molding cavity filled with resin-coated sand (RCS), although the present invention is not particularly limited, if each supply amount is too small or too large, there may be the following disadvantages. Specifically, first, regarding superheated steam, if the supply amount per unit time and per unit volume is too small, the curing of RCS may be insufficient even after the supply ends, and the resulting mold may not be able to exhibit the intended performance (strength). On the other hand, if such a supply amount is too large, the alkali resol resin (and novolak-type phenol resin) on the surface of the casting sand particles may be detached (peeled off) from the casting sand particles due to the heat and flow rate of the superheated steam, and the adhesiveness of the casting sand particles by the alkali resol resin or the like may decrease. As a result, the resulting mold may not be able to exhibit the intended performance (strength). Also, regarding carbon dioxide gas, if the supply amount per unit time and per unit volume is too small, the curing of RCS may be insufficient even after the supply ends, and the resulting mold may not be able to exhibit the intended performance (strength). On the other hand, if such a supply amount is too large, the drying of RCS may proceed more than necessary, and as a result, the curing reaction of RCS may be inhibited. Therefore, in the method for manufacturing a mold according to the present invention, the supply operations of carbon dioxide gas and superheated steam into the molding cavity filled with RCS are preferably carried out as follows: a) for superheated steam, at a quantitative ratio of 0.17 to 8.30 L / min per 1 cm 3 of the volume of the molding cavity, and b) for carbon dioxide gas, at a quantitative ratio of 0.01 to 2.00 L / min per 1 cm 3 of the volume of the molding cavity, respectively.

[0024] Furthermore, regarding the supply of superheated steam and carbon dioxide gas (CO2 gas) into a molding cavity filled with resin-coated sand (RCS), when the process of simultaneously supplying superheated steam and carbon dioxide gas is involved, such simultaneous supply is preferably carried out under the condition that α calculated from the following formula (1) is 4.0 or more, preferably under the condition that α is 200 or less, and most preferably under the condition that 10.0 ≦ α ≦ 200. When α calculated from the following formula (1) is less than 4.0, the supply amount of carbon dioxide gas relative to superheated steam becomes excessive, and the drying of RCS may proceed more than necessary, resulting in the risk of inhibiting the curing reaction of RCS. On the other hand, when α exceeds 200, the supply amount of carbon dioxide gas relative to superheated steam becomes too small, and the curing of RCS remains insufficient even after the supply is completed, and the resulting mold may not exhibit the intended performance (strength). Here, both superheated steam and carbon dioxide gas are considered as ideal gases, and the concentration of the gas supplied from cylinders or devices is considered to be 100%. [α]=A / B ···(1) However, in the above formula (1), A is the supply amount of superheated steam per 1 cm 3 of the volume of the molding cavity (L / min ), and B is the supply amount of carbon dioxide gas per 1 cm 3 of the volume of the molding cavity (L / min) ).

[0025] In addition, the supply time of superheated steam and carbon dioxide gas into the molding cavity will be appropriately determined according to the above-mentioned supply ratio, etc. Usually, about 10 to 120 seconds is adopted. Also, as the temperature of the superheated steam supplied into the molding cavity, generally, a temperature of 100 to 450 °C is adopted, and preferably a temperature of 150 to 400 °C is adopted. As for the temperature of carbon dioxide gas, usually, a temperature of room temperature or higher is adopted.

[0026] On the one hand, in the method for manufacturing a mold according to the present invention, it is desirable that the resin-coated sand (RCS) filled in the molding cavity of the mold is cured by superheated steam and carbon dioxide gas under a heated state. For this purpose, advantageously, it is desirable that such a mold is heated, and generally, it is desirable that it is heated to a temperature of 100 °C or higher, particularly to a temperature of 110 to 150 °C. By using a mold heated to such a temperature, the curing of the filled RCS can proceed more effectively, making it possible to more advantageously enjoy the effects of the present invention.

[0027] Thus, in the method for manufacturing a mold according to the present invention, the curing of the resin-coated sand (RCS) filled in the mold proceeds by the supply of superheated steam and carbon dioxide gas. However, if necessary, alkylene carbonate and / or organic ester can be supplied into the mold together with superheated steam and / or carbon dioxide gas, or separately from superheated steam or the like, to achieve more rapid curing of the RCS. It should be noted that these alkylene carbonates and organic esters are only used supplementarily, and when using them, special consideration should be given to ensure that their leakage does not have an adverse impact on the environment.

[0028] Here, the alkylene carbonates and organic esters used in the present invention are all known as curing agents for alkali resol resins, and are appropriately selected and used from among various known ones. Among them, for example, alkylene carbonates include ethylene carbonate, propylene carbonate, 4-ethyldioxolone, 4-butyldioxolone, 4,4-dimethyloxolone, 4,5-dimethyldioxolone, etc., and organic esters include methyl formate, ethyl formate, ethyl acetate, ethyl lactate, triethyl citrate, dimethyl succinate, dimethyl malonate, dimethyl sebacate, dimethyl oxalate, methyl acrylate, ethylene glycol diacetate, diacetin, triacetin, etc. carboxylic acid esters, and lactones such as γ-butyrolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, β-propiolactone, ε-caprolactone, etc. Among them, methyl formate, triacetin, γ-butyrolactone, ethylene carbonate, propylene carbonate, etc. are preferably used. Such alkylene carbonates and organic esters can also be contained in the coating layer of resin-coated sand (RCS) together with alkali resol resins and the like.

[0029] Thus, in the method for manufacturing a mold according to the present invention, when manufacturing a mold using resin-coated sand containing at least an alkali resol resin for the coating layer, superheated steam and carbon dioxide gas are supplied into the molding cavity of a mold filled with such resin-coated sand, and the resin-coated sand is cured by these superheated steam and the like, thereby manufacturing a mold. That is, by supplying superheated steam, adhesion of casting sand particles, promotion of curing of the alkali resol resin by thermal energy, and promotion of strength development in the mold as a cured product can be advantageously achieved. Also, by supplying carbon dioxide gas, curing promotion due to neutralization of the alkali component and auxiliary expression of mold strength can be advantageously achieved. Therefore, in the method for manufacturing a mold according to the present invention, curing of the resin-coated sand proceeds rapidly, and thus, compared with the conventional manufacturing method, shortening of the molding operation time is advantageously achieved.

Example

[0030] Hereinafter, several examples of the present invention will be shown to clarify the present invention more specifically. Needless to say, the present invention is not subject to any restrictions by such descriptions of the examples. Also, it should be understood that in addition to the following examples, various changes, modifications, improvements, etc. can be added to the present invention based on the knowledge of those skilled in the art without departing from the gist of the present invention, other than the above specific descriptions. In the following examples and comparative examples, "parts" and "%" are all shown on a mass basis unless otherwise specified.

[0031] First, preparation of an aqueous alkali resol resin solution and production of novolak-type phenol resins a to d were each carried out according to the procedures shown below. Next, five types of resin-coated sand (RCS) were produced using the obtained aqueous alkali resol resin solution (and, if necessary, novolak-type phenol resin) and cerabeads (product name: Itochu Ceramtec Co., Ltd.) as casting sand.

[0032] - Preparation of Aqueous Alkaline Resol Resin Solution - To 752 parts of phenol, 1021 parts of 47% formalin and 178 parts of water were added to form an aqueous solution, and 133 parts of 48% NaOH aqueous solution as an alkaline catalyst was gradually added to this aqueous solution to obtain a reaction solution. After gradually heating this reaction solution to 80 °C, the liquid temperature was maintained and the reaction was carried out under reflux. When the viscosity of the reaction solution reached 500 mPa·s / 50 °C, cooling of the reaction solution was started and the synthesis of the alkaline resol resin was completed. Thereafter, 246 parts of water for viscosity adjustment was added to the reaction solution containing the alkaline resol resin, and urea was added in a proportion of 1.8% based on the total mass of the reaction solution after the addition of such water, and 3-glycidoxypropyltrimethoxysilane was added in a proportion of 0.5% respectively. Further, 200 parts of 48% NaOH aqueous solution was added as a pH adjuster to prepare an aqueous alkaline resol resin solution.

[0033] - Production of Novolak-Type Phenol Resin I - Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 400 parts of phenol, 160 parts of 47% formalin, and 3 parts of oxalic acid were charged. Next, while stirring the inside of the container, the reaction vessel was gradually heated to reach the reflux temperature, and then reflux reaction was carried out for 90 minutes while maintaining the reflux temperature. Further, by heating under reduced pressure and concentrating until the temperature of the content reached 180 °C, 470 parts of novolak-type phenol resin I having a weight average molecular weight of 1183 was obtained.

[0034] - Production of Novolak-Type Phenol Resin II - Into a reaction vessel equipped with a thermometer, a stirring device and a condenser, 400 parts of phenol, 215 parts of 47% formalin, and 3 parts of oxalic acid were charged. Next, while stirring the inside of the container, the reaction vessel was gradually heated to reach the reflux temperature, and then reflux reaction was carried out for 90 minutes while maintaining the reflux temperature. Further, by heating under reduced pressure and concentrating until the temperature of the content reached 180 °C, 453 parts of novolak-type phenol resin II having a weight average molecular weight of 3765 was obtained.

[0035] -Production of Novolak-Type Phenol Resin III Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 400 parts of phenol, 93 parts of 92% paraformaldehyde, and 2 parts of zinc chloride were charged. Next, while stirring the inside of the vessel, the reaction vessel was gradually heated to reach the reflux temperature, and then reflux reaction was carried out for 90 minutes while maintaining the reflux temperature. Further, by heating under reduced pressure and concentrating until the temperature of the content reached 180°C, 463 parts of novolak-type phenol resin III having a weight average molecular weight of 2328 were obtained.

[0036] -Production of Novolak-Type Phenol Resin IV Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 150 parts of phenol, 240 parts of bisphenol A, 118 parts of 47% formalin, and 3 parts of oxalic acid were charged. Next, while stirring the inside of the vessel, the reaction vessel was gradually heated to reach the reflux temperature, and then reflux reaction was carried out for 90 minutes while maintaining the reflux temperature. Further, by heating under reduced pressure and concentrating until the temperature of the content reached 180°C, 425 parts of novolak-type phenol resin IV having a weight average molecular weight of 2431 were obtained.

[0037] -Production of Resin-Coated Sand a (RCS-a) The foundry sand preheated to 170°C (manufactured by Itochu Ceramatec Co., Ltd., trade name: Nigai Cerambeads) was put into a mixer (Speed Muller manufactured by Enshu Iron Works Co., Ltd.), and while stirring, 2.0 parts of an alkaline resol resin aqueous solution in terms of solid content was added to 100 parts of such foundry sand, and they were stirred and mixed. After 30 seconds had elapsed since the start of mixing, 0.04 part of an ethylene carbonate / γ-butyrolactone mixed solution was further added, and 20 seconds after such addition, blowing into the mixer was started, and this blowing was continued for 50 seconds to evaporate moisture with the heat of the foundry sand while discharging the evaporated moisture to the outside, thereby obtaining dry resin-coated sand a (RCS-a) having normal temperature fluidity.

[0038] -Production of Resin-Coated Sand b (RCS-b) The foundry sand preheated to 170°C was put into a mixer (Speed Muller manufactured by Enshu Iron Works Co., Ltd.), and while stirring, 0.4 part of novolac-type phenolic resin I was added to 100 parts of such foundry sand. After stirring for 20 seconds, 1.6 parts of an alkaline resol resin aqueous solution in terms of solid content was added and stirred and mixed. After 30 seconds had elapsed since the start of mixing, 0.04 part of an ethylene carbonate / γ-butyrolactone mixed solution was further added, and 20 seconds after such addition, the blowing into the mixer was started. By continuing this blowing for 50 seconds, while evaporating the moisture with the heat of the foundry sand, the evaporated moisture was discharged to the outside to obtain dry resin-coated sand b (RCS-b) having normal temperature fluidity.

[0039] -Manufacture of resin-coated sand c (RCS-c)- Except that novolac-type phenolic resin II was used instead of novolac-type phenolic resin I, in accordance with the same method as the manufacturing method of the above-mentioned resin-coated sand b (RCS-b), dry resin-coated sand c (RCS-c) having normal temperature fluidity was obtained.

[0040] -Manufacture of resin-coated sand d (RCS-d)- Except that novolac-type phenolic resin III was used instead of novolac-type phenolic resin I, in accordance with the same method as the manufacturing method of the above-mentioned resin-coated sand b (RCS-b), dry resin-coated sand d (RCS-d) having normal temperature fluidity was obtained.

[0041] -Manufacture of resin-coated sand e (RCS-e)- Except that novolac-type phenolic resin IV was used instead of novolac-type phenolic resin I, in accordance with the same method as the manufacturing method of the above-mentioned resin-coated sand b (RCS-b), dry resin-coated sand e (RCS-e) having normal temperature fluidity was obtained.

[0042] -Manufacture of resin-coated sand f (RCS-f)- Instead of using 0.4 part of novolak type phenol resin II, 0.8 part of novolak type phenol resin IV was used, and except for using 1.2 parts of an aqueous alkali resol resin solution in terms of solid content, a dry resin-coated sand f (RCS-f) with normal temperature fluidity was obtained according to the same method as the manufacturing method of the above-mentioned resin-coated sand c (RCS-c).

[0043] Using the resin-coated sand obtained as described above, a mold was manufactured according to the method shown below.

[0044] - Mold manufacturing examples 1 to 6 (Examples 1 to 6)- Using any one of the previously prepared resin-coated sands (RCS-a to e), this was blown into a mold (molding die, cavity size: 2.54 cm × 2.54 cm × 20 cm) heated to 110°C at a blowing pressure of 0.3 MPa to fill the resin-coated sand into the molding cavity of the mold. Next, the supply of superheated steam (350°C) into the molding cavity was started at a volumetric ratio of 0.80 L / min per 1 cm 3 of the volume of the molding cavity. After 60 seconds had elapsed since the start of the supply of superheated steam, the supply of carbon dioxide gas (CO2 gas) was started at a volumetric ratio of 0.08 L / min per 1 cm 3 of the volume of the molding cavity. Note that the supply of superheated steam was continued even during the supply of carbon dioxide gas. After continuously supplying superheated steam and carbon dioxide gas for 60 seconds (in other words, after 120 seconds had elapsed since the start of the supply of superheated steam), the supply of superheated steam and carbon dioxide gas into the molding cavity was stopped, and then the mold was held for 60 seconds. After such holding, a mold as a cured product of the resin-coated sand was taken out from the mold (molding die).

[0045] - Mold molding example 7 (Example 7)- The previously prepared resin-coated sand-a (RCS-a) was blown into a mold (molding die, cavity size: 2.54 cm × 2.54 cm × 20 cm) heated to 110°C at a blowing pressure of 0.3 MPa to fill the resin-coated sand into the molding cavity of the mold. Subsequently, the supply of superheated steam (350°C) into the molding cavity was started at a quantitative ratio of 0.15 L / min per 1 cm 3 of the volume of the molding cavity. After 60 seconds had elapsed since the start of the supply of superheated steam, the supply of carbon dioxide gas (CO2 gas) was started at a quantitative ratio of 0.005 L / min per 1 cm 3 of the volume of the molding cavity. Note that the supply of superheated steam was continued even during the supply of carbon dioxide gas. After the supply of superheated steam and carbon dioxide gas was continued for 60 seconds (in other words, after 120 seconds had elapsed since the start of the supply of superheated steam), the supply of superheated steam and carbon dioxide gas into the molding cavity was stopped, and then the mold was held for 60 seconds. After such holding, a mold, which was a cured product of the resin-coated sand, was taken out from the mold (molding die).

[0046] -Mold manufacturing example 8 (Example 8)- Simultaneously with the supply of carbon dioxide gas, the supply of methyl formate gas, which is an organic ester, was started at a quantitative ratio of 0.08 L / min per 1 cm 3 of the volume of the molding cavity. A mold was obtained according to the same method as in Mold manufacturing examples 1 to 6, except that the supply of methyl formate gas was stopped simultaneously with the stop of the supply of superheated steam and carbon dioxide gas.

[0047] -Mold manufacturing example 9 (Comparative example 1)- A mold was obtained according to the same method as in Mold manufacturing examples 1 to 6, except that the supply of carbon dioxide gas (CO2 gas) into the molding cavity was not carried out.

[0048] -Mold manufacturing example 10 (Comparative example 2)- A mold was obtained according to the same method as in Mold manufacturing examples 1 to 6, except that nitrogen gas (N2 gas) was used instead of carbon dioxide gas.

[0049] -Mold manufacturing example 11 (Comparative example 3)- A mold was obtained in the same manner as in Mold Production Examples 1 to 6, except that steam was used instead of superheated steam and carbon dioxide gas (CO2 gas) was not supplied into the molding cavity.

[0050] - Mold Production Example 12 (Comparative Example 4)- The previously prepared resin-coated sand a (RCS-a) was blown into a mold (molding die) heated to 110°C at a blowing pressure of 0.3 MPa, and the molding cavity of the mold was filled with the resin-coated sand a. Thereafter, the supply of steam and carbon dioxide gas (CO2 gas) into the molding cavity was started simultaneously at the following volumetric ratios: 1) for steam, at a rate of 0.80 L / min per 1 cm 3 of the molding cavity volume, and 2) for carbon dioxide gas (CO2 gas), at a rate of 0.08 L / min per 1 cm 3 of the molding cavity volume. Twenty seconds after the start of the supply of steam and carbon dioxide gas, only the supply of steam was stopped. Forty seconds after the stop of the supply of steam (60 seconds after the start of the supply of steam and carbon dioxide gas), the supply of heated air (120°C hot air) into the molding cavity was continued for 120 seconds, and then the supply of superheated steam and carbon dioxide gas into the molding cavity was stopped. Thereafter, the mold was held for 60 seconds. After such holding, a mold, which was a cured product of the resin-coated sand, was taken out from the mold (molding die).

[0051] For each of the above-described production examples, the obtained mold was visually observed and evaluated as "moldability" according to the criteria shown below. The evaluation results are shown in Tables 1 and 2 below. ○: No chipping or cracking is observed at the end of the mold. △: Slight chipping or cracking is observed at the end of the mold. ×: Marked chipping or cracking is observed at the end of the mold.

[0052] Also, for the obtained mold, the flexural strength A1 (N / cm 2The flexural strength: A2 (N / cm 2 ) was measured, and the flexural strength was also measured for the mold (hereinafter referred to as the mold after the accelerated deterioration test) that had been allowed to stand for 72 hours in an environment of air temperature: 40 °C and relative humidity: 80%. The measurement results of each mold are shown in Tables 1 and 2 below.

[0053]

Table 1

[0054]

Table 2

[0055] As is clear from the results of Tables 1 and 2, in the method for manufacturing a mold according to the present invention, it is recognized that the curing of the resin-coated sand proceeds rapidly. Therefore, in the method for manufacturing a mold according to the present invention, compared with the conventional manufacturing method, the molding operation can be advantageously shortened in a short time. Further, it is recognized that the mold manufactured according to the manufacturing method of the present invention exhibits excellent mold strength even after a lapse of time from molding.

Claims

1. A method for manufacturing a mold using resin-coated sand in which the surface of the foundry sand is covered with a coating layer, wherein the coating layer contains at least an alkali resol resin, after filling the resin-coated sand into a molding cavity of a mold for providing a target mold, a supply operation of superheated steam and carbon dioxide gas is performed into the molding cavity, and the resin-coated sand is cured by the supply operation to obtain the target mold. A method for manufacturing a mold, characterized by the above.

2. The superheated steam is supplied into the molding cavity at a quantitative ratio of 0.17 to 8.30 L / min per 1 cm 3 of the volume of the molding cavity. The method for manufacturing a mold according to claim 1.

3. The carbon dioxide gas is supplied into the molding cavity at a quantitative ratio of 0.01 to 2.00 L / min per 1 cm 3 of the volume of the molding cavity. The method for manufacturing a mold according to claim 1 or claim 2.

4. The method for manufacturing a mold according to claim 1 or claim 2, wherein the supply operation includes a step in which the supply of the superheated steam and the supply of the carbon dioxide gas are performed simultaneously.

5. The method for manufacturing a mold according to claim 4, wherein the simultaneous supply of the superheated steam and the carbon dioxide gas into the molding cavity is performed under the condition that α calculated from the following formula (1) is 4.0 or more. [α]=A / B...(1) However, in the above formula (1), A is the supply amount of superheated steam per unit volume (1 cm³) of the molding cavity (L / min) 3 ​ ) and B is the supply amount of carbon dioxide gas per 1 cm 3 of the volume of the molding cavity (L / min) ).

6. The method for manufacturing a mold according to claim 1 or claim 2, wherein the supply operation includes a step in which the supply of the superheated steam and the supply of the carbon dioxide gas are performed at different times.

7. The method for manufacturing a mold according to claim 1 or claim 2, wherein alkylene carbonate and / or organic ester is supplied into the molding cavity together with or separately from the superheated steam.

8. The method for manufacturing a mold according to claim 1 or claim 2, wherein the mold is heated to 100°C or higher.

9. The method for manufacturing a mold according to claim 1 or claim 2, wherein the coating layer of the resin-coated sand further contains a novolac-type phenol resin.

10. The method for manufacturing a mold according to claim 1 or claim 2, wherein the coating layer of the resin-coated sand further contains alkylene carbonate and / or organic ester.

11. The method for manufacturing a mold according to claim 1 or claim 2, wherein the resin-coated sand is in a dry state having room temperature fluidity.

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