JPS6260179B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recycling foundry sand molds.
More specifically, coexistence of water with (a) a water-soluble polymer having a carboxyl group or a salt thereof, (b) oxides and hydroxides of metals from Groups 1 and 3 of the periodic table, and (c) foundry sand. When a foundry sand mold that has been mixed and molded and hardened is used for casting and then recycled, the unaltered (a) remaining in the foundry sand mold remains in the foundry sand mold.
A foundry sand mold characterized in that the remaining unaltered water-soluble polymer is reused by pouring 0.1 to 20 times the weight of water into the water-soluble polymer, collapsing the sand mold, and molding and hardening it again. Regarding recycling methods. Conventionally, inorganic binders such as water glass have often been used as binders for foundry sand, but when water glass is used, it is extremely difficult to break the sand mold after casting. Instead, the sand particles are destroyed mechanically or with a hammer at the same time, reducing the particle size of the sand and reducing the number of times it can be reused.Also, because the alkali remains, the sand is reused repeatedly. As the sand ages, the accumulation of alkaline substances increases, and when the sand is finally disposed of, it is necessary to treat the alkaline substances. In addition, organic binders such as furan resin, phenolic resin, or polyester resin are sometimes used, but all of them are self-hardening resins, and once they undergo a chemical reaction and harden, it is difficult to crush and reuse the cured product. Since the sand has lost its curing ability, not only can it not be reused by taking advantage of the binding strength of the binder added at the beginning, but also the catalysts such as acids used during the initial curing remain in the sand. However, each time the used sand is reused, new binder and catalyst must be added, resulting in the accumulation of catalyst. In order to improve the disintegrability of foundry sand molds and to avoid the accumulation of toxic substances in the sand after use, the present inventor developed a copolymer mainly composed of α-olefin and maleic anhydride or an acrylic acid polymer. Sand molding is a method of manufacturing foundry sand molds by mixing oxides or hydroxides of metals of Groups 1 and 3 of the periodic table and foundry sand in the presence of water and molding and hardening the mixture. It has been found that this method is satisfactory in terms of moldability, green strength, disintegration of used sand molds, repeatability as foundry sand, and working environment. -A patent application has been filed as No. 145051. The repeated use as foundry sand in these methods involves pouring molten metal into a foundry sand mold made by the above method, casting, and then mechanically destroying the demolded sand mold to obtain foundry sand. The aqueous polymer solution was added again to the mixture (without adding the metal compound) to prepare a foundry sand mixture, which was then filled into a mold and pressure-molded to produce a sand mold. However, this method has drawbacks such as the fact that it still requires a great deal of labor to crush the sand mold after casting, and that the sand becomes fine pieces due to the crushing. The present inventor believes that the amount of the polymer that is exposed to high temperatures and burnt out during casting is limited to those that come into contact with high-temperature molten metal or in the vicinity, and that even after casting, there is a large amount of polymer that does not change in quality during casting. Focusing on the fact that this residual unaltered polymer can regain its cohesive strength by simply adding water, we conducted extensive research to utilize this residual unaltered polymer.
We have arrived at the present invention. That is, the present invention comprises (a) a water-soluble polymer having a carboxyl group or a salt thereof, (b) an oxide or hydroxide of a metal of group 1 or group of the periodic table, and (c) foundry sand in water. When a foundry sand mold that has been mixed and molded in coexistence and hardened is used for casting and then recycled, the amount of the unaltered water-soluble polymer of (a) remaining in the foundry sand mold is 0.1 to This method of recycling foundry sand molds is characterized by reusing the remaining unaltered water-soluble polymer by pouring 20 times its weight of water to collapse the sand mold, molding it again, and hardening it. In the present invention, it is important to uniformly inject water into the sand mold after casting so that the sand mold collapses and can be reused as foundry sand, which will be explained below. The amount of water to be injected should be enough to cause the sand mold to collapse and the sand to be reused to create the sand mold and then perform the next casting. The amount of water-soluble polymers that have carboxyl groups or their salts that remain in reusable sand is sufficient as long as it does not cause any problems when making a sand mold and performing the next casting.
The amount is 0.1 to 20 times by weight, particularly preferably 0.8 to 5 times by weight. When water is poured in an amount within the above range, the water-soluble polymer in the sand mold develops a suitable viscosity and therefore remains attached to the sand, which is very preferable in terms of reusing the polymer. If the amount of water injected exceeds the above range, the sand to be reused will contain a very large amount of water, so that green strength will not be achieved in a short period of time even when molded. Additionally, as the amount of water injected increases, the water-soluble polymer remaining in the sand mold begins to dissolve into the water.
Since it separates from the sand, it becomes difficult to reuse the remaining water-soluble polymer. For example, conventionally, a method of collapsing a sand mold underwater is known as a method for collapsing a sand mold, but in such a case, a large excess of water is used, so that the unique effects of the present invention cannot be obtained at all. . On the other hand, if the amount of water used is too small for the water-soluble polymer, the water-soluble polymer will not be completely dissolved even if the amount of water remaining in the sand mold after casting is taken into account, which may cause problems in the sand mold destruction process. . Also,
Without pouring water into the sand mold after casting, the sand mold is collapsed into sand, and then water is poured in an amount within the above range, and the water-soluble polymer corresponding to the amount burnt out is added or not. It is also possible to prepare and use it for casting. If the sand in a sand mold that has been collapsed by pouring water (after being molded) is left alone, it will form the same mold as a mixture prepared by first mixing a water-soluble polymer, a metal compound, and foundry sand and molding it in the coexistence of water. It exhibits hardening properties and, as a result, exhibits green strength equivalent to that of a molded and hardened sand mold. Specific examples of water-soluble polymers having carboxyl groups or salts thereof that are preferably used in the present invention include polyacrylic acid, copolymers containing α-olefin and maleic anhydride as main components, and alkali metal or alkali thereof. Examples include salts of earth metals and ammonium. Copolymers whose main components are α-olefins and maleic anhydride are copolymers of α-olefins such as isobutylene (including return BB), ethylene, propylene, n-butylene, and styrene, and maleic anhydride. etc. In the present invention, oxides and hydroxides (hereinafter simply abbreviated as metal compounds) of Groups 1 and 2 of the periodic table are used as curing agents for the water-soluble polymer. Examples of the metal compound include oxides or hydroxides of magnesium, calcium, aluminum, zinc, and the like. These may be used alone or in combination of two or more. Among them, magnesium oxide is preferred. In addition, the mixing ratio of the water-soluble polymer (a) having a carboxyl group or its salt, the metal compound (b), and the foundry sand (c) used in the foundry sand mold to be manufactured first is 0.25/100 in a/c. -5/100 (weight ratio) and b/a of 2.5/100 to 1000/100 (weight ratio). In addition, the amount of water used at that time is 19 times the weight or less of the water-soluble polymer having a carboxyl group or its salt,
Preferably, the amount is 4 times or less by weight, that is, the aqueous solution is preferably 5% by weight or more, preferably 20% by weight or more. The viscosity of the aqueous solution at this time is preferably 0.5 to 500 poise at room temperature. The water-soluble polymer can be reused as foundry sand by pouring water into a cast sand mold and crushing it.
The mixture with sand containing a metal compound and water is filled into a mold in a conventional manner with or without addition of the sand lost during casting, the water-soluble polymer, the metal compound and water. After being molded and demolded, it is subjected to casting. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 After mixing 150 parts by weight of silica sand and 7.5 parts by weight of an aqueous polyacrylic acid solution having a concentration of 40% by weight, 1.5 parts by weight of magnesium oxide powder (manufactured by Kyowa Glass Chemical Industry Co., Ltd., Kiyowa Mag 150) was added and mixed. A foundry sand mixture was prepared. This mixture was filled into a mold and molded under pressure (10Kg/cm ² ) to a diameter of 5.
A cylindrical sand mold sample with a height of 5 cm and a weight of approximately 150 g was prepared. After demolding, this sample was left at room temperature for 3 hours and 24 hours, and its green strength was measured. In addition, a sand mold sample prepared under the same conditions and left for 24 hours was
The sample was placed on a red-hot iron plate at 1000°C with the bottom side facing the iron plate and left for 5 minutes. Approximately 0.41 g of polyacrylic acid was burnt out at this time. When 3.9 g of water was poured into this specimen, the specimen maintained a strong and stable shape immediately after the water was poured, but
As time passed, the shape became easier to collapse, and one hour after pouring water, it could be easily touched with the hand. The thus obtained sand (containing unburned polyacrylic acid and magnesium oxide) located away from the scorched iron plate was sieved to obtain a foundry sand mixture again. This mixture was further supplemented with 1.02 g of 40% by weight polyacrylic acid to prepare the next casting sand mixture. A sand mold sample was prepared using this mixture again in the same manner as described above. This sample was demolded and left at room temperature for 3 hours and 24 hours, and then its green strength was measured. On the other hand, a sand mold sample obtained by the same preparation method was placed on an iron plate at 1000°C for 5 minutes. Thereafter, the above-mentioned operations of pouring water, crushing the sand mold sample, replenishing polyacrylic acid (aqueous solution), molding, and placing it on an iron plate at 1000°C were repeated. This operation was repeated several times. In each case, the green strength of the sand mold samples was measured (Table 1). As shown in Table 1, even if foundry sand is repeatedly used, a sand mold with practical moldability and green strength can be obtained by simply replenishing water and a small amount of polyacrylic acid.

[Table] I can do things. Example 2 150 parts by weight of silica sand and 7.5 parts by weight of an aqueous solution of a copolymer of isobutylene and maleic anhydride (hereinafter abbreviated as IBM) with a concentration of 40% by weight were mixed, and then magnesium oxide powder (Kyowa Gas Chemical Industry Co., Ltd.) was mixed. 1.5 parts by weight of Kiyowa Mag 20) manufactured by Co., Ltd. was mixed, filled into a mold, molded under pressure (10 Kg/cm ² ), and demolded to a diameter of 5 mm.
A cylindrical sand mold sample with a height of 5 cm and a weight of 150 g was prepared. This sample was heated at room temperature for 3 hours and 24 hours.
The green strength was measured after being left for a period of time. A sand mold sample prepared in the same manner was placed on a red-hot iron plate at 1000°C and left for 5 minutes. IBM was burnt out when analyzed.
The amount was 0.45g. 3.8 g of water was poured into the sample placed on the iron plate and the sample was crushed to obtain a foundry sand mixture. Furthermore, 40% by weight IBM aqueous solution was added to this mixture.
1.12g was replenished to make a foundry sand mixture. This sand mold sample was subjected to the same operations as in Example 1, including pouring water, crushing, replenishing IBM (aqueous solution), molding, and placing it on a steel plate at 1000° C., and the green strength of the sand mold was measured each time. Table 2 shows the relationship between this repeated operation (that is, the number of repeated uses of the foundry sand) and the green strength of the sand mold sample.

[Table] As shown in Table 2, practical formability and green strength can be obtained by adding an aqueous solution of IBM and water corresponding to the amount of burned IBM. Example 3 In Example 2, the cylindrical sand mold sample was placed on a red-hot iron plate at 1000°C, left for 5 minutes, the sand mold sample was mechanically pulverized, and only 3.8 g of water was added to give an IBM concentration of 40% by weight. The mixture was filled into a mold without adding an aqueous solution, molded under pressure (10 Kg/cm ² ), demolded, left at room temperature for 3 hours, and measured for green strength. This sand mold was repeatedly crushed, poured with water, molded, and heated (placed on an iron plate heated to 1000°C), and the green strength was measured (Table 3). As shown in Table 3, it has a green strength that is acceptable for practical use even after repeated use four times.

【table】

Claims (1)

[Claims] 1. Mixing (a) a water-soluble polymer having a carboxyl group or a salt thereof, (b) an oxide or hydroxide of a metal of group 1 or group of the periodic table, and (c) foundry sand in the presence of water. After the molded and hardened foundry sand mold is used for casting, when recycling it, 0.1 to 20 times the weight of the unaltered water-soluble polymer (a) remaining in the foundry sand mold is added. By pouring water, collapsing the sand mold, shaping and hardening again,
A method for recycling foundry sand molds characterized by reusing residual unaltered water-soluble polymer.