MX2008006539A - Process for making molds - Google Patents

Abstract

The invention discloses a process for making molds which do not generate toxic gas in pouring a molten metal into the molds equipped with casting cores or the like even when the binder contained therein decomposes and which are excellent in the disintegration characteristics after casting. The process comprises mixing a particulate aggregate with one or more water-soluble binders, a surfactant, a crosslinking agent and water under stirring and foaming to prepare a foamed aggregate mixture, charging the foamed aggregate mixture into a mold-forming cavity, solidifying the charged mixture by evaporating the water contained in the mixture to form a mold, and taking the mold out of the cavity.

Description

PROCESS FOR THE PREPARATION OF MOLDS FIELD OF THE INVENTION The invention relates to a process for the production of molds. More particularly, this invention relates to a process for making a mold to be manufactured from a foamed mixture in which a granular aggregate, a water-soluble binder, a surfactant and water are stirred to foam so that the mold has great strength and offers resistance to high temperatures and generates few unpleasant odors.

BACKGROUND OF THE INVENTION An example of conventional molding processes for the production of hollow cores is described in Japanese Patent Laid-Open Publication No. 63-115649. The method uses sand for uncured molding (a granular mixture) which is composed of silica sand as an aggregate granular material and a binder. The method includes the steps for adding a solution of a surfactant to the uncured molding sand and shaking it so that the aggregate granular material foams, injecting the mixture of foamy granular aggregate material into a heated metal mold, and retaining the injected mold of metal heated for a predetermined time to evaporate moisture therefrom. As a binder usable for the method, the above publication describes a phenolic resin. However, the use of phenolic resin produces harmful gases, for example, formaldehyde, a phenol and ammonia. These represent a biological risk and involve an unpleasant odor when the binder is to be hardened by the heat transferred from the metal mold.

DESCRIPTION OF THE INVENTION Accordingly, an object of the invention is to provide a molding process for the manufacture of a mold. The molding process of the present invention inhibits the generation of harmful gases, which present a biological risk to humans and involve an unpleasant odor. This is because a binder is decomposed when an aggregate granular material including sand and the binder is used for the molding process, or when a molten metal is poured into the mold (such as a core) which is made of granular material aggregate. In addition, the mold that is made by the molding process of the present invention has better collapsibility after casting. In addition, a part of the object of this invention is to provide a molding process capable of making a mold with increased strength. The present invention provides a molding process comprising the steps of mixing, agitating and making the granular aggregate material, one or more types of soluble binders in water, a surfactant, a crosslinker and water to prepare a foam aggregate mixture; filling a molding space with the foamy aggregate mixture; vaporize the moisture in the filled aggregate mixture so that the aggregate mixture is cured to make a mold of it; and remove the mold from the metal mold. Preferably, the surfactant is one which causes a crosslinking reaction with the crosslinker. Preferably, the surfactant is nonionic and one whose HLB value is 8 or more; however, less than 20. The HLB value is an index that denotes the level of affinity with water or an oil, which is an organic compound that does not have water solubility, of a surfactant. The HLB value has a range of 0 to 20. The affinity with the oil is increased by approaching 0, while that of the water is increased by approaching 20. The HLB value can be derived from a calculation. based on the Atlas method or the Griffin method. The HLB value1 can also be determined by the waiting time 'when using a chromatography of high performance liquid. The foamy aggregate mixture can not be obtained if the nonionic surfactant has an HLB value of less than 8. This is because said nonionic surfactant is difficult to distribute in water, and it does not foam enough. In case the nonionic surfactant has an HLB value of 8 or more, it is firmly distributed in water to make sufficient foam. In this way, a mixture of foamy aggregate can be obtained. The molding space can be defined by a metal mold. In this case, the filling step preferably includes a step for filling the foamy aggregate mixture in the molding space upon pressurization. The pressurized filling step may include a step for loading the foamy aggregate mixture into a cylinder and then filling it into the molding space by directly pressurizing it. Alternatively, the pressurized filling step may include a step for filling the foamy aggregate mixture in the molding space by pressurizing it with a compressed gas. In the vaporization step, the moisture in the foamy aggregate mixture is preferably vaporized by means of the heat of the metal mold which is heated. Each binder soluble in water is soluble in water of normal temperature. Each binder soluble in water is saccharide or its derivative. One or more types of water-soluble binders are contained in 0.1 to 5.0 weight percent per 100 weight% of the granular aggregates. Preferably, the crosslinker is a chemical compound having a carboxyl group. The guanic compound having the carboxyl group is selected from a group including an oxalic acid, a maleic acid, a succinic acid, a citric acid, a tetracarboxylic acid butane, a copolymer of methyl vinyl maleic anhydride, and an isobutylene anhydride copolymer malefic With the present invention, the foamy aggregate mixture is prepared by mixing the granular aggregate material, one or more types of water soluble binders, a surfactant, a crosslinker that causes a crosslinking reaction with the water soluble binders. Because the mixture of foamed aggregate can be filled in a molding space (or a molding cavity) in each part, and the amount of gases generated from a mold when a molten metal is poured into it, it can be inhibited, any Defect caused by gas in the mold can be reduced. Because the foamy aggregate mixture includes non-phenolic resin as it exists in the prior art, the generation of harmful gases is prevented. they represent a biological risk to humans and involve an unpleasant odor, even if each binder is decomposed when the foamy aggregate mixture is molded or when the molten metal is poured into a mold (eg, core mold) made from the mixture of aggregate. In addition, a mold with high collapsibility can be produced. The strength of the mold (the core) which is produced by the use of a surfactant, a cationic surfactant, and an amphoteric surfactant becomes undesirably lower than that produced by the use of a nonionic surfactant. Accordingly, the present invention utilizes the nonionic surfactant to facilitate the mixing of foamed aggregate with which the molding space is to be filled in each area and to provide sufficient strength and strength for moisture for the resulting mold. The above and additional features and advantages of the present invention will be further clarified by the following detailed description, with reference to the appended figures.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a longitudinal sectional view of a molding machine used for the first embodiment of the molding process of the present invention. Figure 2 is a longitudinal sectional view of the molding machine used for another embodiment of the molding process of the present invention. Figure 3 illustrates the results of an analysis wherein the components of the gases that are generated from a binder in the molding process of the present invention were analyzed by means of a mass spectrometer.

PREFERRED MODALITIES OF THE PRESENT INVENTION The molding process of the present invention will be explained later. This comprises the steps of preparing and stirring a mixture of aggregate including a granular aggregate material, one or more types of a water-soluble binder, an interfacial active agent, a cross-linking agent and water for foaming, filling the foaming mixture In a molding space, evaporate the moisture inside the filled mixture to harden the charged mixture to make a mold, and remove the resulting mold from the molding space. The granular material added in the present invention is a heat-resistant granular material comprising at least one material selected from a group which includes silica sand, alumina sand, olivine sand, chromite sand, zircon sand, mulita sand, any artificial aggregate material, and so on. Each water-soluble binder in the present invention is soluble in water of normal temperature, and acts as a binder which hardens upon evaporation of moisture. It also acts as a thickening agent to adjust the viscosity of a mixture of aggregate that is molded and foamy. The thickening agent means a high polymer that dissolves or is distributed in water to present it sticky, and it is also called adhesive paste. The water-soluble binder may be a sugar group which includes, in particular, starch or its derivatives, polysaccharides such as saponins, or disaccharides such as sugar. The water-soluble binder which is soluble in water of normal temperature can be mixed in a mixture of foamy aggregate without heating it and the water. A water-soluble binder that has no solubility in water at normal temperatures can not be mixed unless it and the water are heated. To use said water-soluble binder which has no solubility in water at normal temperatures, it can be heated once and then blended to prepare a binder solution. soluble in water which is cooled to a normal temperature. The starch is, for example, dextrin or α-starch, which is derived from potatoes, or corn, or tapioca, or flour. The starch derivative is, for example, etherified starch, esterified starch, or a binding starch. Sugar is sucrose which is a saccharide in which a pair of fructose molecules and a couple of glucose molecules are linked. Examples of a saccharide include white sugar and granulated sugar. The water-soluble binders that are to be used in the present invention are readily available. In particular, «-starch, dextrin and sugar are available at low cost. The α-starch, dextrin or its derivatives, saponins, and a sugar are soluble in normal temperature water. Examples of the thickening agent include a starch, a xanthan gum, a guar gum, an Arabica gum, etc. Because the decomposition temperature of the water-soluble binder used in the invention is lower than that of the phenol resin, a mold made by a method of the present invention can be easily decomposed by the heat of the melting process. In this way, the mold can be obtained which has a high collapsibility after having finished the casting process. The aggregate granular material of preference it contains the water-soluble binder from 0.1 to 5.0% by weight based on the total weight of the aggregate granular material. This is because a mold having insufficient strength is provided if the content is less than 0.1% by weight, and a mold having redundant force is produced if the content exceeds 5.0% by weight. With the mold of the present invention, adding the results of the crosslinker between the crosslinking reactions with the water soluble binder increases the bonding of particles of the aggregate granular material which are coated by the water soluble binder. In addition, there is a lower possibility that the water-soluble binders will react with water molecules, thus providing the resulting mold with sufficient property even in a high humidity environment. The granular aggregate material preferably contains the added surfactant from 0.01% to 1.0% by weight based on the total weight of the aggregate granular material. This is because no admixture mixture having sufficient foam is provided and, thus, no frothy aggregate mixture is provided if the content is less than 0.01% by weight. The foamy aggregate mixture has a fluidity if the content is 1.0% by weight. The crosslinker which can be used in the present invention includes a compound which has a group carboxyl which includes one such as oxalic acid, or maleic acid, or succinic acid, or citric acid, all of which cause a crosslinking reaction via an ester linkage. Alternatively, the crosslinker may include a copolymer of methyl vinyl of ether maleic acid and a copolymer of isobutylene maleic anhydride having a carboxyl group when in the phase of a water solution. A preferred crosslinker which can be used in the present invention is a crosslinker which causes the ester linkage to generate less harmful gases, i.e. one which has a carboxyl group. In the present invention, the added amount of the crosslinker is from 5 to 300% by weight based on the total weight of the total content of water soluble binder. This is because no mold that has sufficient strength in a high humidity environment can be produced if the added amount of crosslinker is less than 5% by weight, wherein the advantage of the crosslinking reaction is not sufficient. Although the resulting mold having sufficient strength in the high humidity environment can be produced if the added amount of the crosslinker exceeds 300% by weight based on the total weight of the total content of water soluble binder, its advantage is not more remarkable than when the added amount of the crosslinker is 300% by weight. In this way, add the crosslinker that exceeds 300% by weight can be uneconomic and a practical inconvenience. In the present invention, the crosslinker is used with an aqueous solution. For example, its density may be greater than 10% by weight in case the crosslinking agent is carboxylic acid of tetra butane, or citric acid, or a copolymer of methyl vinyl anhydride maleic ether. In the present invention, the foamy aggregate mixture can be injected into a cylinder by directly pressurizing it, or it can be pressurized by air such that a molding space is filled with the foamy aggregate mixture. Direct pressurization by the cylinder is for injecting the mixture into the cylinder to receive the mixture in a metal mold by directly pressurizing the mixture by pressurizing a plunger (or a piston) of a pressure mechanism in the cylinder. Direct pressurization by compressed air as shown, for example, in Figure 1, instead of the piston in the previous direct pressurization by the cylinder. In this arrangement, an opening in the upper part of the cylinder (or the piston) 1 is provided with an airtight seal 2 for closing so that it is adjusted by air. The air-adjusted space of the upper part of the cylinder 1 is also provided with a cover 3 It forms an air passageway 3a for connection to a source of compressed air to supply compressed air at the top of the foamy aggregate mixture 6 inside the cylinder 1 to inject it into a molding space 5 of the metal mold 4. In the molding process of the present invention, vaporizing the moisture in the mixture of foamy aggregate that is filled in the molding space, a metal mold or its related element, or both, which define the molding space, can be heated, to a high temperature, or the molding space which is filled with the foamy aggregate mixture can be placed under a vacuum environment. Alternatively, if desired, the molding space can receive there an insufflation of air. In vaporizing the moisture in the foamy aggregate mixture by the metal mold which is heated to high temperature, both the foam and the moisture have been distributed in the aggregate mixture when agitated and are moved to the core of the mold which is made from the mix of aggregate by means of the heat of the metal mold. In this way, the density of the aggregate material that is to be filled in the core of the mold is decreased. A mold having a low density in its core causes the amounts of granular aggregate and water soluble binders to be reduced. Also, it provokes gases generated with the decomposition of water-soluble binders that are going to be easily depleted, because a mold like this tends to have many holes. The surfactant in the present invention can, in general, be classified into four types by the dissociative states of its molecules when dissolved in water: an anionic surfactant, a cationic surfactant, a nonionic surfactant and an amphoteric surfactant. The guímica definition of a surfactant is "a material to mix water and oil." A surfactant has both a hydrophobic and a hydrophilic group within the molecules, and is dissolved or dispersed in a liquid such as water or oil, and absorbs the interface selectively. Therefore, the surfactant in the present invention causes formation or bubbling. The (core) of the mold made by the use of the anionic surfactant, the cationic surfactant or the amphoteric surfactant, among the four types of surfactants, does not cause a crosslinking reaction with the crosslinker because said surfactants do not have hydroxyl group in the molecules , as discussed later. In this case, the mold having insufficient force can then be worked out. In contrast, the mold produced by the use of nonionic surfactant it has sufficient strength, because three three-dimensional networks in the molecules of the water-soluble binders and the surfactant are formed by a cross-linking reaction in which a carboxyl group (COOH) in the molecules of the crosslinker and the hydroxyl (OH), which is a hydrophilic group, are linked by ester. Accordingly, the nonionic surfactant is preferably used in the present invention to make a mold having sufficient strength. By adding the nonionic surfactant which acts as the crosslinker to cause the crosslinking reaction with the water soluble binders, the binding of the granular aggregate particles which are coated with the water soluble binders is increased. In addition, because the reaction between water soluble binders and water molecules can be inhibited, the resulting mold can maintain sufficient properties under a high humidity environment. Although examples of the nonionic surfactant include a sucrose fatty acid ester, a sorbitan fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a fatty alkanol amide, an ester of some polyoxyethylene, an ester of phenyl alkyl polyoxyethylene, a fatty acid ester of glycerin, a fatty acid ester of propylene glycol and so on, and one that have an HBL value of 8 or more is used between them. Preferably, a natural coconut oil or palm oil that is made from vegetable oil has high safety, and is not harmful in practical use. The following embodiments are intended to explain, but are not limited to, the molding process of the present invention. The First Modality Table 1 Composition (except water) of the Aggregate Mixture 11 Silica and (flattening sand): 100% by weight Starch (Dextrin NSD-L, manufactured by Nissi Co., Ltd., Japan): 1.0% by weight Surfactant (polyglycerol fatty acid ester): 0.03% by weight Citric acid (made by Fuso Chemical Co., Ltd., Japan): 0. 5% by weight In the first embodiment, the mixture of aggregate that is compounded as shown in Table 1 and the water of 4% by weight are mixed and stirred with a mixing magulina (a table mixer, made by Aikohsha Manufacturing Co. , Ltd., Japan) at 200 rpm for approximately 5 minutes. In this way, it foams to prepare a foamy aggregate mixture 11. The foamy aggregate mixture 11 is poured into a cylinder 13 of a plunger 12, as shown in Figure 2. This foamy aggregate mixture is then pressurized with approximately 0.4 MPa of the surface pressure by the cylinder so that it is pressure loaded into a molding space 15 with a capacity of approximately 80cm3 in a metal mold for the mixing test 14, which is kept at a temperature of 250 ° C (the filling step). The mixture of foamed aggregate in the heated metal mold is held for about 2 minutes to vaporize the moisture by heat of the latter so that the foamed aggregate hardens (the hardening step). The mold is removed from the molding space 15 of the metal mold 14 after causing the crosslinking reaction between the water soluble binder and the crosslinker. Two specimens are prepared to be used for the mixing test method. The specimens are kept for 24 hours in respective humidity baths at a humidity of 30% and at a humidity of 90% or more, and then the mixing test is carried out. As a result, the forces of 4.9 MPa and 2.3 MPa were measured at a humidity of 30% and a humidity of 98%, respectively. Due to the mixing force of 4.9 MPa at a humidity of 30%, approximate to a mold that is produced from a shell molding (see JFS Foundry Engineer's Handbook, Section 2.1, "Shell Molding "), the normal operation of the mold does not involve a significant problem.If the mold has a strength of 2 MPa or more after it is stored for 24 hours at a humidity of 90% or more, a normal handling of the mold does not involve a significant problem, and can be used as a mold.

Table 2 Composition (except water) of the Aggregate Mixture Synthetic sand (Espar # 60 made by Yamakawa Sangyo Co., Ltd., Japan): 100% by weight Starch (Dextrin NSD-L, manufactured by Nissi Co., Ltd., Japan): 1.0% by weight Surfactant (polyglycerol fatty acid ester): 0.03% by weight Citric acid (made by Fuso Chemical Co., Ltd., Japan): 0. 5% by weight In the second embodiment, the aggregate mixture which is compounded as shown in Table 2 and the 2.5% by weight water are mixed and stirred with a mixing machine (a table mixer, made by Aikohsha Manufacturing Co. , Ltd., Japan) at 200 rpm for about 5 minutes and, in this way, lather it to prepare a foamy aggregate mixture (the step of preparation) . The foamy aggregate mixture is poured into a cylinder 13 as shown in Figure 2. This foamy aggregate mixture is then pressurized with approximately 0.4 MPa of a cylinder surface pressure so that it is pressure loaded into a molding space 15 with a capacity of approximately 80cm3 in a metal mold for the mixing test 14, which is kept at a temperature of 250 ° C (the filling step). The mixture of foamed aggregate in the heated metal mold is preserved for approximately 90 seconds to vaporize the moisture by heat thereof, so that the foamed aggregate hardens (the molding step). The mold is removed from the molding space 15 of the metal mold 14 while giving two specimens, after causing the crosslinking reaction between the water-soluble binder and the crosslinker. Both specimens are kept for 24 hours in respective humidity baths at a humidity of 30% and at a humidity of 90% or more, and then the mixing test is carried out. As a result, the forces of 9.5 MPa and 3 MPa were measured at a humidity of 30% and a humidity of 98%, respectively. With these values, a normal handling of the mold does not involve a significant problem, and can be used for the same purposes as the mold. The Third Modality Table 3 Composition (except water) of the Aggregate Mixture Silica and (flattened sand): 100% by weight Starch (Dextrin NSD-L, made by Nissi Co., Ltd., Japan): 1.0% by weight Surfactant (ester) of polyglycerol fatty acid): 0.03% by weight Citric acid (made by Fuso Chemical Co., Ltd., Japan): 0.5% by weight In the third embodiment, the mixture of aggregate which is compounded as shown in Table 2 and the water of 4.5% by weight are mixed and stirred with a mixing magulina (a table mixer, made by Aikohsha Manufacturing Co., Ltd., Japan) at 200 rpm for about 5 minutes and, in this way, makes it foam to prepare a mixture of foamy aggregate. The foamy aggregate mixture is poured into a cylinder 13 as shown in Figure 2. This mixture of foamy aggregate is then pressurized with approximately 0.4 MPa of the surface pressure by the cylinder so that it is charged with pressure in a space of molding 15 with a capacity of approximately 140cm3 in a metal mold for the mixing test 14a, which is preserved at a temperature of 270 ° C (the filling step). The mixture of foamy aggregate in the heated metal mold is preserved for 90 seconds to vaporize the moisture by heat of the latter, so that the foamy aggregate hardens (the molding step). The mold as a specimen A is removed from the molding space 15 of the metal mold 14a (the removal step). The surface layer of the removed specimen was scraped with a metal file to a depth of 1 mm to take a sample of approximately 1 gram. The amount of any disintegration gas is derived based on the method to convert a gas pressure to a capacity according to the method to measure the amount of gas generated by using the JACT M-5 inspection standard, which is defined by the Japan Association of Casting Technology to calculate the molecular weights. Table 4 shows this result.

Table 4 The amount of a disintegration gas (cc / g) The specimen A 18 The Fourth Mode A mixture in which a starch (Dextrin NSD-L, manufactured by Nissi Co., Ltd., Japan), a surfactant (polyglycerin fatty acid ester) and citric acid (prepared by Fuso Chemical Co., Ltd., Japan) are mixed in ratios of 1: 0.3; 5 is preserved at a high temperature, baked at 250 ° C for 10 minutes to then be removed. The stirred mixture is preserved for five seconds under an atmosphere of helium in a pyrolyzer at 590 ° C. The pyrolysis gas is stored for 10 minutes at 50 ° C, and is heated to 240 ° C at the rate of heating 10 ° C / min. The type of gas is analyzed with a mass spectrometer, while the heated gas that passes through a column under the temperature of 240 ° C is preserved for 15 minutes. As shown in Figure 3, carbon dioxide and furfural are detected as a result of the analysis of the components of the pyrolysis gas of the binder with the mass spectrometer. In the conventional shell molding process, unpleasant odors are generated, such as ammonium, formaldehyde and phenols, which are sources of odor, by the pyroosis of a phenolic resin and hexamine (a curing agent) when a core is baked. In contrast, it was found that said gases are not generated from the mold of the present invention.

The Fifth Modality In the fifth mode, the experiments are carried out to confirm whether various types of surfactants cause crosslinking reactions with a crosslinker.

Table 5 Composition of the Aggregate Mixture Silica sand (flattened sand): 100% by weight Nonionic surfactant (a polyglycerol grade acid ester): 0.03% by weight Citric acid (prepared by Fuso Chemical Co., Ltd., Japan): 0.5% by weight The granular material of aggregate, as shown in Table 5, and the water are mixed and stirred with a mixing magna (a table mixer, made by Aikohsha Manufacturing Co., Ltd., Japan ) at 200 rpm for about 5 minutes. In this way, it foams to prepare a mixture of foamy aggregate. The foamy aggregate mixture is filled, manually, into the metal mold which is adapted to prepare a specimen for the mixing test and is defined by the JACT M-l inspection (the filling step). The metal mold is then preserved in a constant temperature bath for 45 minutes to dry and cure the foamy aggregate mixture (the molding step). The resulting mold as a specimen for the mixing test is then removed. For comparison, the reference specimens are prepared in the same manner from the composition as shown in Table 5. However, instead of the nonionic surfactant in said composition, the respective reference specimens include an anionic surfactant (sodium alkyl ether sulfate ester), a cationic surfactant (trimethyl alkyl ammonium salt), and an amphoteric surfactant (amino alkyl oxide). The specimen of the mixing test and the reference specimens are preserved in a humidity bath at a humidity of 30%. Then the mixing forces are measured. Table 6 shows these results.

Table 6 Table 6 denotes that the nonionic surfactant is one that causes a crosslinking reaction with a crosslinker having a carboxyl group. The mold that uses other surfactants collapsed when it was removed from the metal mold. In this way, it has no practical force.

The Sixth Modality Table 7 Composition of Silica Sand Aggregate and (Flaking Sand) Aggregate: 100% by weight Starch (Dextrin NSD-L, made by Nissi Co., Ltd., Japan): 1.0% by weight Nionic Surfactant Respective as shown in Figure 8: 0.03% by weight Citric acid (made by Fuso Chemical Co., Ltd., Japan): 0.5% by weight The granular aggregate material, as shown in Table 7 and the water are mixed and stirred with a mixing machine (a tabletop mixer, made by Aikohsha Manufacturing Co., Ltd., Japan) at 200 rpm for about 5 minutes. The visual inspections were carried out to confirm that the foamy aggregate mixtures were obtained. Table 8 shows these results. In Table 8"Excellent" denotes a mixture of excellent sparkling aggregate, "Good" denotes that a mixture of sparkling aggregate is obtained as is in stirred; however, its foam is dissolved immediately upon stopping the agitation, and "Deficient" denotes that no foamy aggregate mixture was obtained.

Table 8 Nonionic Surfactant HLB Sparkling Aggregate Mixture Polyglycerol fatty acid ester 15.5 Excellent Polyoxyethylene alkyl ether 10.5 Excellent Sodium polyoxyethylene lauryl ether 8.1 Excellent Sorbitan fatty acid ester 6.7 Well Sorbitan fatty acid ester 5.0 Poor Glycol propylene fatty acid ester 3.9 Deficient Table 8 shows that a foamy aggregate mixture can not be obtained unless the HLB value of a nonionic surfactant to be used is 8 or more.

The Seventh Modality Table 9 Composition (except water) of the Aggregate Mixture Silica Sand and (Flaking Sand): 100% by weight Starch (Dextrin NSD-L, manufactured by Nissi Co., Ltd., Japan): 1.0% by weight Nonionic Surfactant (Sunsoft M-12, manufactured by Taiyo Kagaku Co., Ltd., Japan): 0.03% by weight Citric acid (made by Fuso Chemical Co., Ltd., Japan): 0.5% by weight In the seventh embodiment, the mixture of aggregate that is compounded as shown in Table 9 and the water of 4% by weight are mixed and stirred with a mixing machine (a tabletop mixer, made by Aikohsha Manufacturing Co., Ltd., Japan) at 200 rpm for about 5 minutes and, thus, the resulting mixture foamed to prepare a foamy aggregate mixture ( the preparation step). As shown in Figure 2, the foamy aggregate mixture 11 is poured into a cylinder 13. This mixture of foamy aggregate is then pressurized with approximately 0.4 MPa of the surface pressure by the cylinder so that it is charged with pressure in a molding space 15 with a capacity of approximately 80cm3 in a metal mold for the mixing test 14, which was presd at a temperature of 250 ° C (the filling step). The mixture of foamed aggregate in the heated metal mold was presd for 2 minutes to vaporize the moisture by heat of the latter so that the foamed aggregate hardens (the molding step). The mold was removed from the molding space 15 of the metal mold 14 as a specimen. For comparison, the reference specimens were prepared in the same way from the granular material added as shown in Table 9. However, instead of the nonionic surfactant in said composition, the respective reference specimens include an anionic surfactant, a cationic surfactant and an amphoteric surfactant. The specimen of the mixing test and the reference specimens are presd in a humidity bath at a humidity of 30% for 24 hours, and a humidity bath with a humidity of 90% or more for 24 hours. The mixing forces were then measured. Table 10 shows these results.

Table 10 As seen in Table 10, the molds with forces of 4.9 MPa and 2.3 MPa were measured at a humidity of 30% and a humidity of 98%, respectively. Due to the mixing force of 4.9 MPa at a humidity of approximately 30%, a mold that is produced from a shell molding (see Foundry Engineer's Handbook, Section 2.1, "Shell Holding"), the operation Normal mold does not involve a significant problem. In case the mold has a mixing force of 2 MPa after keeping it for 24 hours at a humidity of 90% or more, the normal handling of the mold does not involve a significant problem and can be practically used as the mold. In contrast, the mixing force of the mold that is produced using other surfactants was lower. In particular, it was less than that of a mold that is produced by the conventional coke molding process, because said surfactants do not cause crosslinking reaction with the crosslinker. further, it was also found that said mold does not have sufficient strength in a high humidity environment. With the molding process of the present invention, the generation of any harmful gas, which poses a biological risk to humans and involves an unpleasant odor can be inhibited, in case a binder is pyrolyzed when a molten material is poured into it. mold. Accordingly, the molding process of the present invention can be applicable to produce a light metal mold using, for example, aluminum or magnesium. It should be appreciated, additionally, that the number of tabs for the mold that is produced by the molding process of the present invention can be remarkably reduced. Because the foregoing embodiments are intended to be illustrative and not to limit the scope of the present invention, those skilled in the art conceive, in this manner, various changes and modifications in the embodiments within the scope of the appended claims.

Claims (13)

1. NOVELTY OF THE INVENTION
2. Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as property:
3. CLAIMS 1.- A molding process characterized in that it comprises the steps of: mixing, agitating and frothing the granular aggregate material, one or more types of water-soluble binders, a surfactant, a crosslinker and water to prepare a foamy aggregate mixture.; filling a molding space with said foamy aggregate mixture; vaporizing the moisture in said aggregate mixture so that the aggregate mixture is cured to make a mold of the cured aggregate mixture; and removing said mold produced from said molding space. 2. - The process according to claim 1, characterized in that said surfactant is one that causes a crosslinking reaction with said crosslinking agent. 3. The process according to claim 2, characterized in that said surfactant is a nonionic surfactant whose HLB value is 8 or more but less than 20.
4. 4.-. The process according to any of the preceding claims, characterized in that said molding space is defined by a metal mold, and characterized in that said filling step includes a step for filling said foamy aggregate mixture in said molding space when pressurizing said mold. mixture of sparkling aggregate.
5. 5. - The process according to claim 4, characterized in that said filling step includes a step for loading said mixture of foamy aggregate in a cylinder, and filling said mixture of charged aggregate in said molding space when pressurizing, directly , said mixture of charged aggregate.
6. 6. The process according to claim 4, characterized in that said filling step includes a step for filling said foamy aggregate mixture in said molding space by pressurizing said foamy aggregate mixture with a compressed gas.
7. 7. The process according to claim 5 or 6, characterized in that said vaporization step includes a step to vaporize the moisture in said foamy aggregate mixture by means of the heat of said metal mold which is heated.
8. 8. - The process according to claim 7, characterized in that each water-soluble binder is dissolved in water at normal temperatures.
9. 9. The process according to claim 7, characterized in that each water-soluble binder is a saccharide or its derivative.
10. 10. The process according to claim 7, characterized in that said one or more types of water-soluble binders contain 0.1 to 5.0% by weight per 100% by weight of said granular aggregates.
11. 11. The process according to claim 7, characterized in that said crosslinker is a compound having a carboxyl group.
12. 12. The process according to claim 7, characterized in that said compound having the carboxyl group is selected from a group which includes an oxalic acid, a maleic acid, a succinic acid, a citric acid, a carboxylic acid of tetra-butane, a maleic vinyl ether anhydride copolymer and an isobutylene maleic anhydride copolymer.
13. 13. The process according to claim 4, characterized by said step of vaporization includes a step to vaporize moisture in said mixture of foamed aggregate by means of the heat of said metal mold which is heated.