JP2016147287A - Casting sand regeneration process, and polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a convenient and highly productive regeneration process for manufacturing regenerated casting sand capable of being used even in a cold box process.SOLUTION: A casting sand regeneration process for regenerating casting sand to be used in a casting mould, comprises: a step of crushing a casting mould covered with a binder composed mainly of water glass, to attain crushed chips; and a polishing step of polishing said casting sand by adding an acid solution to said crushed chips.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for reclaiming foundry sand and a polishing apparatus used therefor.

  For example, as a method of producing a mold for a core for casting an engine cylinder head, a gas curable casting is obtained by adding two types of binders such as a phenol resin dissolved in a solvent and a polyisocyanate compound to sand and kneading them. Sand is formed, and the foundry sand is blown into the mold by air blowing and then filled, and then a curing accelerating gas composed of triethylamine or the like is passed through the mold to cure the two binders by the action of this gas. Thus, a method for producing a mold is conventionally known (for example, Patent Document 1). This method is called a cold box method because it does not require heating when the mold is cured.

  In the mold using the organic binder described above, the binder burns due to heat during casting, and gas is generated. Since this gas has a strange odor, a process of collecting and processing the gas so that it is not discharged to the outside as it is is necessary, and the processing cost is high, which is expensive.

  Therefore, a molding material mixture for a mold using an inorganic binder instead of such an organic binder has been proposed (for example, Patent Document 2). The molding material mixture for a mold disclosed in Patent Document 2 is cured by removing moisture by heating to form a mold. And in order to harden a casting_mold | template in the time suitable for an industrial use, hot air is blown in into the shaping | molding type | mold, and the removal of a water | moisture content is accelerated | stimulated.

  In addition, a recycling method for reusing a molding material mixture for a mold using the above-described inorganic binder has also been proposed (for example, Patent Document 3). In Patent Document 3, in order to recycle used foundry sand to which water glass is attached, the used foundry sand to which a binder containing fine metal oxide is added based on water glass is brought to a temperature of at least 200 ° C. Regeneration is performed by heating and heat treatment.

JP 2008-149352 A Special table 2011-500330 gazette Special table 2010-519042 gazette

  However, when the foundry sand regenerated by Patent Document 3 was used as a mold for the cold box method, it did not harden at all, and there was a problem that the mold could not be produced. Even when the foundry sand regenerated according to Patent Document 3 was mixed with the foundry sand used for the first time by several percent, the mold of the cold box did not harden. Therefore, manufacturing and recycling of molds using cold boxes and manufacturing and recycling of molds using inorganic binders must be strictly separated to prevent foundry sand contamination, which increases costs. It was.

  The present invention has been made in view of such points, and the object of the present invention is to provide a simple and highly productive recycling method for producing recycled foundry sand using an inorganic binder that can be used in the cold box method. It is to provide.

  The method for reclaiming foundry sand according to the present invention is a method for reclaiming foundry sand used in a mold, and crushing a mold made of foundry sand covered with a binder mainly composed of water glass to obtain a crushed piece. And a polishing step of polishing the foundry sand by adding an acid solution to the crushed pieces. In the polishing step, the alkaline component of the water glass is neutralized by the acid solution, and at least a part of the binder mainly composed of the water glass covering the foundry sand is scraped off to regenerate the foundry sand.

  The amount of the acid contained in the acid solution is preferably an amount capable of neutralizing the alkali component contained in the binder covering the foundry sand. As a result, the reclaimed foundry sand becomes neutral.

  In the polishing step, it is preferable that water contained in the acid solution is evaporated and discharged, and a salt generated by neutralization is discharged by a dust collector. Thereby, salt is discharged | emitted with a dust collector with the binder shaved off in the grinding | polishing process.

  It is preferable to include a classification step for classifying the foundry sand after the polishing step. The reclaimed foundry sand is classified into only suitable sizes as foundry sand.

  The polishing apparatus of the present invention is a polishing apparatus that polishes foundry sand covered with a binder mainly composed of water glass, and has an amount capable of neutralizing an alkali component contained in the binder covering the foundry sand. It has the structure provided with the acid solution addition part which adds an acid solution to the said foundry sand. When this apparatus is used, neutralization of the alkali component is also reliably performed at the same time when polishing is performed.

  The acid solution adding section is preferably a spraying device for spreading the acid solution on the foundry sand. With this configuration, the acid solution is dispersed almost uniformly throughout the foundry sand.

  In the present invention, since an acid solution is added and neutralized in the polishing step, the reclaimed foundry sand becomes neutral and can be used in a cold box, and as a method for reclaiming foundry sand for an inorganic binder. However, the heat treatment step is unnecessary, the processing time can be shortened, and the cost can be reduced.

It is a typical figure of the polish device concerning an embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

(Embodiment)
The recycling method of the present embodiment is to mold a mold using a molding material mixture for molding, in which a binder mainly composed of water glass is mixed with foundry sand, and after the mold is used for casting, the mold is recycled. This is a method for producing recycled foundry sand.

  As the foundry sand, various conventionally used foundry sands can be used. For example, silica sand or zircon sand can be used. Fibrous refractory molding materials such as chamotte fiber are also suitable. Other suitable foundry sands are, for example, olivine, chrome ore sand and vermiculite.

As the water glass, a conventional water glass that has already been used as a binder in a molding material mixture can be used. These water glasses contain dissolved sodium or potassium silicate and can be prepared by dissolving glassy potassium and sodium silicate in water. The water glass preferably has a SiO ₂ / M ₂ O ratio in the range of 1.6 to 4.0, in particular 2.0 to 3.5, where M represents sodium and / or potassium. The water glass preferably has a solid content in the range of 30 to 60% by weight. The solid content is relative to the amount of SiO ₂ and M ₂ O present in the water glass. The water glass binder may contain other components in addition to the water glass having a binding action. However, it is preferred to use pure water glass as the binder. The water glass solids content preferably consists of more than 80% by weight of alkali silicate, more preferably at least 90% by weight, particularly preferably at least 95% by weight and even at least 98% by weight. If the binder contains a phosphate, the proportion is calculated as P ₂ O ₅ and is preferably less than 10% by weight, more preferably less than 5% by weight and even less than 2% by weight, based on the water glass solids. It is.

  The molding material mixture for mold making according to the present embodiment preferably contains a particulate metal oxide selected from the group consisting of silicon dioxide, aluminum oxide, titanium oxide and zinc oxide in a predetermined ratio. . The average major particle size of the particulate metal oxide may preferably be between 0.10 μm and 1 μm. However, due to the aggregation of the main particles, the particle size of the metal oxide is preferably less than 300 μm, in particular less than 200 μm, in particular less than 100 μm. According to one embodiment, the particle size is greater than 5 μm, according to another embodiment, greater than 10 μm, and according to another embodiment, greater than 15 μm. The average particle size is preferably in the range of 5 to 90 μm, particularly preferably in the range of 10 to 80 μm, particularly preferably in the range of 15 to 50 μm. The particle size can be determined, for example, by sieve analysis. It is particularly preferred if the residue on the sieve having a mesh size of 63 μm is less than 10% by weight, preferably less than 8% by weight.

  Particular preference is given to using silicon dioxide as the particulate metal oxide, in which case synthetically produced amorphous silicon dioxide is particularly preferred.

  Particulate silicon dioxide cannot be considered equivalent to foundry sand. For example, when silica sand is used as a refractory basic molding material (casting sand), the silica sand cannot satisfy the function of particulate silicon dioxide. Silica sand has a very clear reflectivity in the X-ray diffraction pattern, while amorphous silicon dioxide has low crystallinity and therefore a fairly broad reflectivity.

  It is preferred to use silicic acid precipitates or pyrogenic silicic acid as fine particle silicon dioxide. Accordingly, these silicic acids may be used in a mixture as well. The silicic acid precipitate is obtained by reacting an aqueous alkali silicate solution with a mineral acid. The resulting precipitate is then separated, dried and ground. The term exothermic silica refers to silica obtained by coagulation from a gas phase at high temperatures. Exothermic silica can be produced in an electric arc furnace, for example, by flame hydrolysis of silicon tetrachloride or by reducing silica sand with coke or anthracite that forms silicon monoxide gas and then oxidizes to silicon dioxide. Exothermic silica produced by the electric arc furnace process can still contain carbon. Precipitated silica and pyrogenic silica are equally suitable for the molding mixture of the present invention. These silicas are hereinafter referred to as “synthetic amorphous silicon dioxide”.

Exothermic silicic acid is characterized by a very large specific surface area. Accordingly, it is preferred that the particulate silicon dioxide has a specific surface area of greater than 10 m ² / g, and according to another embodiment, greater than 15 m ² / g. According to one embodiment, the particulate silicon dioxide has a specific surface area of less than 40 m ² / g and according to another embodiment less than 30 m ² / g. The specific surface area can be determined by nitrogen adsorption according to DIN 66131.

According to one embodiment, the amorphous, uncompressed particulate silicon dioxide has a bulk density of greater than 100 m ³ / kg and according to another embodiment greater than 150 m ³ / kg. According to one embodiment, the amorphous, uncompressed particulate silicon dioxide has a bulk density of less than 500 m ² / g and according to another embodiment a bulk density of less than 400 m ² / g.

  As a binder, strong alkaline water glass can react with silanol groups present on the surface of the synthetic amorphous silicon dioxide, and due to moisture evaporation, between the silicon dioxide and the solid water glass at that time It is assumed that the strong bond is formed.

  The molding material mixture for mold making of this embodiment preferably contains a surface active substance. The surface-active substance is a substance that can form a monomolecular layer on the water surface, that is, can form a film, for example. Furthermore, the surface active substance reduces the surface tension of water. Suitable surface active materials include, for example, silicone oil.

  As the surface active substance, a surfactant is particularly preferable. Surfactants contain a hydrophilic part and a hydrophobic part, the property of which is balanced, for example in the aqueous phase, so that the surfactant can form micelles or accumulate at the interface. .

  In principle, all classes of surfactants can be used. In addition to anionic surfactants, nonionic, cationic and amphoteric surfactants are also suitable. For illustrative purposes, nonionic surfactants include, for example, ethoxylated or propoxylated long chain alcohols, amines or acids such as fatty alcohol ethoxylates, alkylphenol ethoxylates, fatty amine ethoxylates, fatty acid ethoxylates, corresponding Propoxylates, or even sugar surfactants such as fatty alcohol polyglycosides. The fatty alcohol preferably contains 8 to 20 carbon atoms. Suitable cationic surfactants include alkyl ammonium compounds and imidazolinium compounds.

  Anionic surfactants are particularly preferred as the surfactant. The anionic surfactant preferably contains a sulfate group, a sulfonate group, a phosphate group or a carboxylate group as a polar hydrophilic group, and a sulfate group and a phosphate group are particularly preferable. When an anionic surfactant containing a sulfate group is used, it is particularly preferable to use a sulfuric monoester. When phosphate groups are used as polar anionic surfactant groups, orthophosphoric acid monoesters and diesters are particularly preferred.

  Properties common to the surfactants used in this embodiment are that the nonpolar hydrophobic moiety preferably has 6 carbon atoms, particularly preferably an alkyl group or aryl group having 8 to 20 carbon atoms. And / or preferably an aralkyl group. The hydrophobic part may have both a linear structure and a branched structure. Mixtures of various surfactants can also be used.

  In the molding material mixture for mold making according to this embodiment, the pure surface active substance is contained in a ratio of 0.001 to 1% by weight, particularly 0.01 to 0.5% by weight, based on the weight of the foundry sand. It is preferable that Such surface active substances are widely marketed in 20% to 80% solutions. In this case, an aqueous solution of a surface active substance is preferred.

  In principle, the surface-active substance can be added to the molding material mixture as a separate component or even via a solid phase component, for example in the form dissolved in a binder. It is particularly preferred that the surface active substance is dissolved in the binder.

  In the present embodiment, at least a part of the foundry sand for molding the foundry may contain regenerated foundry sand. That is, the used casting mold to which the regeneration method according to the present embodiment is applied may include reclaimed foundry sand as a part of the raw material. Regenerated foundry sand is foundry sand that has been used at least once to produce the mold and then readjusted so that it can be returned to the process of producing the mold. The readjustment may be performed by an arbitrary method, but it is preferable to perform reproduction by a reproduction method according to the present embodiment described later. Alternatively, for example, the used foundry sand may be mechanically regenerated, in which case binder residues or decomposition products remaining on the used foundry sand after casting are removed by rubbing. In this regard, the sand may be shaken vigorously so that, for example, the sand particles collide with surrounding sand particles and the binder residue is struck by impact. The binder residue can then be separated from the reclaimed foundry sand by sieving and removing.

  In this embodiment, at least one carbohydrate may be added to the molding material mixture. By adding carbohydrate to the molding material mixture, it is possible to produce an inorganic binder-based mold that retains high strength not only immediately after manufacture but also after prolonged storage. In addition, the metal casting produces a cast with very good surface quality and requires little post-treatment on the surface of the cast product after demolding. High molecular oligosaccharides, as well as polysaccharides, can be used as carbohydrates as well as monosaccharides or disaccharides.

  The molding material mixture preferably comprises a phosphate-containing compound, especially when producing molds having very thin portions. In this connection, either organic phosphorus compounds or inorganic phosphorus compounds can be used. It is further preferred that phosphorus in the phosphorus-containing compound is preferably present in oxidation state V to avoid any undesirable side reactions during metal casting. By adding a phosphorus-containing compound, the stability of the template can be further enhanced. This is particularly important because when molten metal encounters an aspect during casting, the high metal static pressure generated thereby has a strong erosive action and can cause deformation of the thin part of the mold, in particular. is there.

  In this connection, the phosphorus-containing compound is preferably present in the form of phosphate or phosphorus oxide. The phosphate may be an alkali or alkaline earth metal phosphate, with the sodium salt being particularly preferred. In principle, ammonium phosphates or phosphates of other metal ions can be used. However, alkali or alkaline earth metal phosphates that are considered preferred are readily available and are available in any amount and at low cost.

  When the phosphorus-containing compound is added to the molding material mixture in the form of phosphorus oxide, the phosphorus oxide is preferably phosphorus pentoxide. However, phosphorus trioxide and phosphorus tetroxide can also be used.

A preferred ratio of phosphorus-containing compound to foundry sand is between 0.05 and 1.0% by weight. When the proportion is less than 0.05% by weight, no significant effect on the dimensional stability of the mold is observed. When the proportion of phosphate exceeds 1.0% by weight, the thermal stability of the mold decreases rapidly. The proportion of the phosphorus-containing compound is preferably selected in the range between 0.10 and 0.5% by weight. Phosphorus-containing _compounds, when calculated as P 2 _{O 5,} preferably contains phosphorus between 0.5 to 90 wt%. When using the inorganic phosphorus compound, _they, when calculated as P 2 _{O 5,} preferably contains 40 to 90 wt%, in particular 50 to 80% by weight of phosphorus. When using the organic phosphorus compound, _they, when calculated as P 2 _{O 5,} preferably contains a phosphorus 0.5 to 30 wt%, especially 1 to 20 wt%.

  Binders, ie water glass and particulate metal oxides, in particular synthetic amorphous silicon dioxide, and surface-active substances are preferably present in the molding material mixture in a proportion of less than 20% by weight, in particular less than 15% by weight. Exists. The percentage of binder then refers to the solid component of the binder. When using large amounts of foundry sand, such as silica sand, the binder is preferably present in a proportion of less than 10% by weight, preferably less than 8% by weight, particularly preferably less than 5% by weight. When using low density foundry sand, such as hollow microspheres, the proportion of binder increases correspondingly. In order to ensure the agglomeration of the particles in the foundry sand, the proportion of binder is chosen to be more than 1% by weight or even more than 1.5% by weight.

  The particulate metal oxide, in particular synthetic amorphous silicon dioxide, is preferably 2 to 80% by weight, more preferably 3 to 60% by weight, in particular based on the weight of the binder, based on the weight of the binder. Preferably it is present in a proportion of 4 to 50% by weight.

  In the present embodiment, the method for forming the mold is not particularly limited, and a known method and various other methods can be adopted. For example, the above-described binder (bonding) mainly composed of water glass on the above-described foundry sand. A mixing step of mixing the agent), a heating step in which the molding sand mixed with the binder is filled in the cavity of the molding die and heated by the molding die, and a take-out step of taking out the binder mixed casting sand that has hardened from the cavity The included methods may be employed.

  When producing the molding material mixture in the mixing step described above, it is preferable to first place the foundry sand in a mixing vessel, and then add the solid component (s) of the binder and mix with the foundry sand. The mixing time is selected so that the foundry sand and the solid binder component are intimately mixed. The mixing time depends on the amount of molding material mixture to be produced and the mixing equipment used. The mixing time is preferably selected between 1 and 5 minutes. The liquid component of the binder is then added, preferably while still stirring the mixture, and then the mixture is continued to mix until the foundry sand particles are uniformly coated with the binder layer. Again, the mixing time depends on the amount of molding material mixture to be produced and the mixing equipment used. The mixing time is preferably selected between 1 and 5 minutes. The term liquid component refers to both a mixture of various liquid components and the entirety of all individual liquid components, where these lasts can also be added individually. Similarly, the term solid component refers to both a mixture of the above solid components, individually or together, and the entirety of all individual solid components, the last of these being either together or alternating with the molding material mixture. May be added at

  Alternatively, the liquid component of the binder can be added first to the foundry sand and then to the solid component. As a further alternative, 0.05-0.3% water, based on the weight of the foundry sand, is first added to the foundry sand, followed by the solid and liquid components of the binder. In this way, a surprisingly clear effect on the processing time of the molding compound mixture can be realized. We assume that the dehydrating action of the solid binder component is thus reduced, thereby delaying the curing process.

  Next, the molding material mixture is formed into a desired shape in the first half of the heating step. For this approach, conventional methods are used. For example, the molding material mixture may be injected into the mold cavity with the aid of compressed air on a core injection molding machine.

  Subsequently, the molding material mixture is cured by heating in order to evaporate the water present in the binder as a second half of the heating process. Heating is performed in the mold cavity. That is, the molding die is heated to a predetermined temperature, whereby the molding material mixture is heated and cured. The mold can be completely cured by setting the mold for molding to 100 ° C. or more and 200 ° C. or less and holding and heating the molding material mixture in the cavity for 30 seconds or more and 60 seconds or less. Alternatively, the mold may be cured by blowing hot air into the cavity.

  Next, a metal part is manufactured by casting using the mold thus prepared. The casting method is not particularly limited.

  The casting mold is regenerated to become foundry sand. The regeneration method in the present embodiment includes a crushing step for crushing the mold to obtain a crushed piece, and a polishing step for polishing the foundry sand by adding an acid solution to the crushed piece.

In Patent Document 3, heat treatment is performed at a temperature of at least 200 ° C. in order to recycle the foundry sand using the above-mentioned inorganic binder mainly composed of water glass. By this heat treatment, SiOH groups in the water glass in the binder are dehydrated and converted to SiO ₂ to prevent water absorption and suppress elution of Na ⁺ , thereby reducing the acid consumption. Thereby, it is said that it can be reduced to an acid consumption amount necessary for producing a mold again by using an inorganic binder mainly composed of water glass for recycled casting sand. However, for use in the cold box method, the acid consumption must be further reduced to neutrality. In this case, in order to make it neutral by heat treatment, it is necessary to further increase the temperature or to increase the processing time, which increases the process time and greatly increases the cost. In this embodiment, the surface of the foundry sand that has been regenerated by reducing the amount of acid consumption without performing heat treatment is made neutral so that both inorganic and organic binders can be used. The cost is reduced because no heat treatment is performed.

  In the crushing process of this embodiment, the mold is crushed into small crushed pieces so that polishing can be performed in a short time in the polishing process. The crushed pieces introduced into the polishing step are preferably about several mm or less. In order to perform polishing in a short time, it is preferable that the crushed pieces have a size close to one grain of foundry sand, but in order to reduce the size of the crushed pieces in the crushing process. Considering both the time and the time for polishing the crushed pieces in the polishing step, it is preferable that the size is within the above-mentioned size range of the crushed pieces. In addition, crushing is performed in several steps, and the crushing pieces may be made smaller in order.

  In the polishing step, the crushed pieces are put into the polishing apparatus 1 shown in FIG. In the polishing step, first, the crushing pieces are crushed by the rotor 3 where the crushed pieces rotate, and the binder mainly composed of water glass covering the surface of the foundry sand 8 is scraped off. In the process, the acid solution is added to the foundry sand 8 by spraying from the nozzle 7 of the acid solution adding section. The amount of the binder can be calculated from the weight of the crushed pieces put into the polishing apparatus 1, and the amount of alkali in the binder can also be calculated. Accordingly, an acid solution in an amount capable of neutralizing the alkali is added to the foundry sand 8. Since the amount of the acid solution is determined according to the weight of the crushed pieces, the spraying device (acid solution addition unit) provided in the polishing apparatus 1 calculates and sprays the necessary amount of acid solution according to the weight of the crushed pieces. The polishing is performed by collision / rubbing between the foundry sands, or by collision / rubbing between the polishing member and the foundry sand.

  Although the kind of acid is not particularly limited, an inorganic acid such as phosphoric acid, sulfuric acid, and hydrochloric acid, or an organic acid such as citric acid can be used in consideration of cost and safety. Since the pH of foundry sand that can be used in the cold box method is 6.5 to 8.0, the amount of the acid solution is adjusted so that the pH becomes 6.5 to 8.0 by neutralization. The acid solution is preferably added to the foundry sand by spraying such as a shower so that the acid solution is uniformly added to the foundry sand. The concentration of the acid is not particularly limited, but is preferably determined in consideration of the uniformity of spraying, cost, safety, process stability, and the like.

  In the polishing process, scraped binder dust and salt dust generated by neutralization are scattered in the air, and frictional heat and neutralization heat are generated to evaporate the water in the acid solution. 9 is discharged out of the polishing apparatus 1 by a dust collector. Thus, when the polishing step is completed, most of the binder and salt are removed from the foundry sand, and a dried foundry sand is obtained.

  When the polishing process is completed, the foundry sand 8 is discharged from the discharge port 11. At this time, if the inclined plate 12 is provided at the bottom of the polishing apparatus 1, the discharging is performed smoothly. And it is preferable to classify the discharged foundry sand. Classification is performed using a commercially available classifier to remove sand particles of 600 μm or more and 53 μm or less. As a result, the casting sand becomes uniform in size, and sufficient strength can be obtained when it is used as a mold by reuse.

  When the above regeneration is completed, the regenerated casting sand is reused to produce a mold. At this time, the mold may be produced using an inorganic binder, or the mold may be produced by a cold box method using an organic binder. If the foundry sand regenerated by the regenerating method according to the present embodiment is used, a mold having sufficient strength can be produced regardless of whether an inorganic binder or an organic binder is used.

(Experiment)
Silica sand (this is referred to as unused sand) is used as foundry sand, and binder HC2000 (manufactured by ASK Chemicals Japan Co., Ltd.) is 2.0% by mass with respect to the foundry sand, and promoter TC5000 (manufactured by ASK Chemicals Japan Co., Ltd.) is used. 1.3% by mass was added to the foundry sand and kneaded for several minutes with a mixer to obtain a molding material mixture. A combination of HC2000 and TC5000 is a binder mainly composed of water glass.

  10 kg of the prepared molding material mixture was filled in the cavity of the molding die. After blowing hot air of 50 to 100 ° C. into the filling for 20 to 60 seconds, the mold was heated at 110 ° C. for 60 seconds to produce a mold.

  Using this mold, aluminum was cast at a casting temperature of 740 ° C. at an S / M ratio of 7/4. After casting and taking out the cast product, the mold was crushed with a hammer into pieces (crushed pieces) having a diameter of 5 mm or less. Of these crushed pieces, the one that has been crushed to the state of one grain of sand is called foundry sand.

  The crushed pieces were put into a hybrid sand master (manufactured by Nippon Casting Co., Ltd.), which is a polishing apparatus, and polished for 60 minutes at a rotational speed of 2000 rpm. During polishing, the generated dust was sucked and removed by a dust collector. The sand after polishing is referred to as (casting + polishing) sand.

  (Casting + Polishing) Sand was thrown into a 3-1DC furnace and spread, and baked at 400 ° C. for 3 hours in a stationary state. The sand after roasting is called (casting + polishing + roasting) sand.

  On the other hand, 20 g of cast sand that was not polished and roasted was placed in a mortar, and 0.706 g of 85% phosphoric acid solution was added to the cast sand and polished using a pestle. That is, the amount of acid required to neutralize the amount of alkali component of water glass covering the casting sand is calculated to be 3% by mass of phosphoric acid with respect to the casting sand. The amount of phosphoric acid was added because it was known by calculation. The sand after this polishing is called (casting + acid addition / polishing) sand.

  Table 1 shows the characteristics of the above sands.

  The method for measuring the characteristics of sand is as follows. The acid consumption was measured using JACT Test Method S-4 “Testing Method for Acid Consumption of Foundry Sand” of Japan Foundry Association. The hydrogen ion index (pH) was measured using JACT test method S-3 “pH test method of foundry sand” of Japan Foundry Association. The packing density was measured by using JACT test method S-10 “casting sand filling property (bulk specific gravity) test method” of Japan Foundry Association. The particle size was measured using JACT test method S-1 “casting sand particle size test method” of Japan Foundry Association. The conditions (standard) for using casting sand using a binder mainly composed of water glass as a mold are that the acid consumption is less than 10 ml / 50 g, the packing density is more than 1.55 g / cc, and the particle size is 55 to 61. It is. On the other hand, the conditions (standards) for using the casting sand used in the cold box method as a mold are pH 6.5 to 8.0, packing density over 1.55 g / cc, and particle size 55 to 61.

  Since the cast sand is covered with a binder mainly composed of water glass, the acid consumption is large and the pH is strong alkaline exceeding 11. Furthermore, the packing density is smaller than that of unused sand, and it can be seen that the shape of the sand is greatly deviated from the spherical shape due to the coating of the binder. The particle size is 53.4, which is smaller than the standard.

  By polishing this using a hybrid sand master, the (consumed + polished) sand has an acid consumption of slightly less than 60% of that of the cast sand, but the pH is 10.54 and the degree of pH decrease is small. Both acid consumption and pH are values outside the standard for recycling. On the other hand, polishing increases the packing density and the particle size, both of which are within the standards for reuse.

  When further roasting is performed, dehydration reaction of water glass occurs by heating, acid consumption becomes less than 10 ml / 50 g, and conditions for acid consumption for using casting sand using a binder mainly composed of water glass as a mold However, the pH is 10.47, which does not satisfy the pH condition for using the casting sand used in the cold box method as a mold.

  On the other hand, the (casting + acid addition / polishing) sand has a pH of 6.91, which satisfies the conditions for using the casting sand used in the cold box method as a mold together with the packing density and particle size. Moreover, the conditions for using the casting sand which uses the binder which mainly consists of water glass for a casting_mold | template are also satisfy | filled.

  If an acid solution spraying device is attached to the hybrid sand master so that the acid solution is sprayed on the crushed pieces during polishing, the pH is in the range of 6.5 to 8.0 after polishing (casting + Acid addition and polishing) sand can be obtained. As shown in FIG. 1, the acid solution spraying apparatus includes a container 4 for storing an acid solution separately from the main body of the polishing apparatus (hybrid sand master) 1 and a pump for sending the acid solution from the container 4 to the main body of the polishing apparatus 1. 5 and the delivery pipe 6 and a nozzle 7 for spraying the acid solution from above the foundry sand 8 in the polishing apparatus 1 may be used. Since the total amount of the acid solution to be sprayed is obtained in advance by calculation, the spray amount of the acid solution may be adjusted by the flow rate control unit 10 having a flow meter and a timer.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

1 Polishing device 7 Nozzle 8 Foundry sand

Claims (6)

A method for reclaiming foundry sand used in a mold,
Crushing a mold made of foundry sand covered with a binder mainly composed of water glass to obtain a crushed piece;
And a polishing step of polishing the foundry sand by adding an acid solution to the crushed pieces.   The method for reclaiming foundry sand according to claim 1, wherein the amount of acid contained in the acid solution is an amount capable of neutralizing an alkali component contained in the binder covering the foundry sand.   The method for reclaiming foundry sand according to claim 1 or 2, wherein, in the polishing step, water contained in the acid solution is evaporated and discharged, and a salt generated by neutralization is discharged by a dust collector.   The method for reclaiming foundry sand according to any one of claims 1 to 3, further comprising a classification step of classifying the foundry sand after the polishing step. A polishing apparatus for polishing foundry sand covered with a binder mainly composed of water glass,
A polishing apparatus comprising an acid solution addition unit that adds an acid solution in an amount capable of neutralizing an alkali component contained in the binder covering the foundry sand to the foundry sand.   The polishing apparatus according to claim 5, wherein the acid solution addition unit is a spraying device for spreading the acid solution on the foundry sand.

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