TW202140167A - Method for reproducing molding sand - Google Patents

Abstract

A method for reproducing molding sand according to an embodiment of the present invention reproduces used molding sand, to a surface of which an inorganic binder is adhered. The method includes: a pulverizing step for pulverizing a sand mold used for casting, and collecting the molding sand; a water washing step for washing, after the pulverizing step, the molding sand while being stirred in water at 5 DEG C to 100 DEG C inclusive; and a heat processing step for heating, after the water washing step, the molding sand to 550 DEG C to 900 DEG C inclusive.

Description

Cast sand regeneration method

The present invention relates to a method for regenerating cast sand, in particular to a method for regenerating cast sand, which regenerates used cast sand with an inorganic binder attached to the surface.

The following process has been performed: after the regeneration process of recovering the casting sand from the sand mold used in casting and removing the adhesive attached to the surface of the casting sand, the regenerated casting sand is made and used for casting again. The adhesives used in the formation of sand molds are roughly divided into organic adhesives such as phenolic resin or furan resin, and inorganic adhesives such as sodium silicate (water glass).

Generally speaking, compared to organic binders, inorganic binders are more difficult to remove from the surface of cast sand. For example, the organic binder adhering to the surface of the casting sand can be removed by baking, but the inorganic binder cannot be removed even by baking. In addition, by polishing the casting sand after heating, the inorganic binder adhering on the surface can be removed to some extent, but in this case, the sand surface will become uneven and the sand itself will be broken. Therefore, compared with the use of organic binders, the recyclability of casting sand is poor when inorganic binders are used. Furthermore, it is difficult to chemically remove inorganic adhesives using chemicals or the like.

As a result, as a binder when forming a sand mold, it is more difficult to regenerate casting sand when an inorganic binder is used compared to an organic binder. Therefore, the applicant in this case proposed a regeneration method in Patent Document 1, which can appropriately regenerate the casting sand on which the inorganic binder has adhered to the surface. The regeneration method disclosed in Patent Document 1 includes the following steps (1) to (4). (1) The crushing step of pulverizing the recovered casting sand mold into a crushed product of casting sand. (2) The mixing step of separating the inorganic binder adhering on the surface from the casting sand by mixing and stirring the obtained pulverized product of casting sand in water at 5°C to 70°C. (3) The step of recovering the casting sand from which the inorganic binder has been separated, and heating and drying the casting sand while stirring. (4) The step of removing fine powder from the cast sand after heating and drying. [Prior Technical Literature] (Patent Document)

Patent Document 1: Japanese Patent No. 6188502

[The problem to be solved by the invention]

However, the inventors of the present case have conducted detailed investigations and found that if the regeneration method of Patent Document 1 is used to repeat the regeneration of cast sand, the amount of sand adhering to the surface of the cast product will increase, and there will be some residual sand on the surface of the cast product. Yu. In addition, for the fine and complex shapes such as the water jacket of the cylinder head, the flow path will be blocked by sand, and it will be impossible to use the knockout machine or ultrasonic wave. The problem of removing this sand by washing machine etc.

In view of the above-mentioned problems, the present invention aims to provide a method for regenerating foundry sand, in which the amount of sand adhering to the cast product will not easily increase even if the foundry sand on which the inorganic binder has been adhered on the surface is repeatedly regenerated. [Technical means used to solve the problem]

According to an embodiment of the present invention, a method for regenerating casting sand as described in the following items is provided.

[Item 1] A method for regenerating cast sand, which is a method for regenerating used cast sand with an inorganic binder attached on the surface. The method for regenerating cast sand includes: a pulverizing step, pulverizing and recycling the sand mold used in the casting Casting sand; water washing step, after the aforementioned crushing step, the aforementioned casting sand is washed while stirring in water at a temperature above 5°C and below 100°C; and, a heat treatment step, after the aforementioned water washing step, the aforementioned casting sand is heated to 550°C Above and below 900°C.

According to the casting sand regeneration method of the embodiment of the present invention, after the water washing step, it includes a heat treatment step. The heat treatment step heats the casting sand to 550°C or more and 900°C or less. The water that exists between the inorganic adhesive remaining on the surface and the crystal water contained in the inorganic adhesive (that is, dehydration). Therefore, according to the casting sand regeneration method of the embodiment of the present invention, the casting sand is regenerated, and the regenerated casting sand is used to form a sand mold, and when the sand mold is used for casting, it is possible to prevent the casting sand from being affected by moisture. Attachment of castings.

[Item 2] The casting sand regeneration method according to item 1, wherein the heat treatment step is performed while moving the casting sand.

If the heat treatment step is carried out while moving the foundry sand, it is possible to prevent the adjacent sand from being bonded to each other due to the softened inorganic binder.

[Item 3] The casting sand regeneration method according to item 1 or 2, wherein the water temperature in the water washing step is 20°C or more and 100°C or less.

If the water temperature in the water washing step is 20°C or higher, the solubility of the inorganic binder can be sufficiently improved. In addition, the preheating time in the subsequent steps can be shortened.

[Item 4] The casting sand regeneration method according to item 1 or 2, wherein the water temperature in the aforementioned washing step is 80°C or more and 100°C or less.

If the water temperature in the water washing step is 80°C or higher, the preheating time in the subsequent steps can be further shortened.

[Item 5] The casting sand regeneration method according to any one of items 1 to 4, wherein, between the water washing step and the heat treatment step, a drying step is further included in the drying step, which heats the casting sand to 100°C or higher while stirring And dry under 300°C.

A drying step may be performed between the water washing step and the heat treatment step. In this drying step, the casting sand is heated to 100°C or higher and 300°C or lower to dry while stirring. By performing the drying step, dry sand can be easily obtained, and the dry sand has a smooth surface while forming a film on the sand surface caused by the residual binder.

[Item 6] The casting sand regeneration method according to item 5, wherein, between the aforementioned water washing step and the aforementioned drying step, a dehydration step is further included, and the dehydration step separates most of the water used in the aforementioned water washing step from the aforementioned casting sand and Remove.

By performing the dehydration step between the water washing step and the drying step, the energy required for the drying step can be reduced.

[Item 7] The casting sand regeneration method according to item 6, wherein the aforementioned washing step, the aforementioned dehydrating step, and the aforementioned drying step are carried out in the same equipment.

If the water washing step, the dehydration step, and the drying step are performed in the same facility, the installation area of the entire facility required for the regeneration of cast sand can be reduced.

[Item 8] The casting sand regeneration method according to item 6, wherein the aforementioned washing step, the aforementioned dehydrating step, and the aforementioned drying step are carried out in different equipment.

If the water washing step, the dehydration step, and the drying step are performed in different equipment, the regeneration amount per unit time can be increased.

[Item 9] The method for regenerating foundry sand according to any one of items 5 to 8, wherein between the drying step and the heat treatment step, a cooling step is further included for cooling the foundry sand while ventilating.

If the cooling step is performed between the drying step and the heat treatment step, and this cooling step cools the foundry sand while ventilating, it is possible to prevent the dewing of the foundry sand.

[Item 10] The method for regenerating casting sand according to any one of items 1 to 9, wherein the aforementioned inorganic binder contains sodium silicate.

As the inorganic binder, an inorganic binder containing sodium silicate (water glass) can be suitably used.

[Item 11] The method for regenerating cast sand according to item 10, wherein the sodium silicate is represented by the general formula Na ₂ O･nSiO ₂ , wherein n is 0.5 or more and 4.0 or less.

As the sodium silicate, sodium silicate represented by the general formula Na ₂ O･nSiO ₂ (n is 0.5 or more and 4.0 or less) can be suitably used.

[Item 12] The method for regenerating cast sand according to any one of items 1 to 9, wherein the aforementioned inorganic binder is formed of an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･yM ₂ O･zH _{2 O} , Where M is Li ⁺ , K ⁺ or Na ⁺ ; in the aforementioned inorganic binder, it is added in such a way that the mass ratio of sodium-containing substance to the aforementioned alkaline silicate aqueous solution is within the range of 1:4 to 1:6 Sodium-containing material is used as a moisture absorbent; and, in the aforementioned inorganic binder, silicone oil is added as a surfactant in the form of an emulsion, and the silicone oil has a boiling point above 250°C. The content of silicone oil is 8% or more and 10% or less of the mass of the aforementioned inorganic binder.

The inorganic binder can be a water glass substrate binder formed by an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･yM ₂ O･zH ₂ O (M is Li ⁺ , K ⁺ or Na ^{+ ).} In this case, it is preferable to add a moisture absorbent to the inorganic binder. As the moisture absorbent, specifically, a sodium-containing substance can be used. The mass ratio of the sodium-containing substance to the alkaline silicate aqueous solution is preferably in the range of 1:4 to 1:6. If the mass ratio of sodium-containing substance and alkaline silicate aqueous solution is in the range of 1:4～1:6, for example, the mass ratio _{of Na 2} O to SiO _{2 in the alkaline silicate aqueous solution (Na 2} O When /SiO ₂ ) is 2.5 or more and 3.5 or less (solid content is 20% or more and 40% or less), it can prevent the early hardening of the inorganic adhesive. In addition, in this inorganic binder, in order to appropriately control the hygroscopicity, it is preferable to add a surfactant. Specifically, it is preferable to add silicone oil as a surfactant in the form of an emulsion. The silicone oil has a boiling point of 250° C. or more. It is more preferable that the content of the silicone oil in the emulsion is 8% or more and 10% of the mass of the binder. the following. [Effect of Invention]

According to an embodiment of the present invention, a method for regenerating cast sand is provided. Even if the cast sand to which the inorganic binder has been adhered on the surface is repeatedly regenerated, the amount of sand attached to the cast product will not easily increase.

The applicant in this case studied in detail the mechanism of sand adhesion on the surface of the casting product, and found that the adhesion of sand is caused by the moisture existing between the inorganic binder (residual binder) attached to the surface of the casting sand and the sand. Crystal water contained in the residual adhesive. The present invention is based on the above findings. Hereinafter, the mechanism of sand adhesion and the casting sand regeneration method according to the embodiment of the present invention will be explained.

[The mechanism of sand adhering to the surface of the casting] If the regeneration method of Patent Document 1 is used to repeat the regeneration of the cast sand 20 times or more, the phenomenon that the sand adheres to the surface of the cast product made of aluminum alloy may occur.

Observing the sand attached to the surface of the casting product and the interface between the sand and the surface of the casting product, it was found that a white substance was attached to the surface of the sand. This white substance was identified by the X-ray diffraction method, and it was confirmed that the monohydrate containing sodium carbonate was the main component.

In addition, using a scanning electron microscope (SEM) to observe the interface between the sand and the surface of the casting product, it was found that a film such as an adhesive exists. Using energy dispersive X-ray analysis (EDS) for qualitative analysis of this film, silicon (Si) and oxygen (O) are detected, and the composition of the film is similar to that of the inorganic adhesive.

If only the reclaimed sand is put into a stainless steel cup and heated to 740°C, the reclaimed sand will be combined with each other in the cup. If the heated reclaimed sand is observed, it is known that the residual adhesive layer on the surface of the reclaimed sand will soften and generate bubbles (blister) at about 600°C. If it is further heated to 740°C, it will be smoothed. In addition, through gas analysis, it was determined that the gas discharged from the bubbles was water, hydrogen, carbon monoxide, and carbon dioxide.

Based on these facts, it is speculated that the adhesion of sand occurs by the following mechanism. First, on the surface of the sand mold contacting the molten metal, the binder component is heated to over 600°C to soften, and the residual moisture between the sand and the residual binder, and the crystal water contained in the residual binder will be combined with the softened The components of the binder react and the water vitrifies. Then, the water vitrified adhesive will absorb the carbon dioxide generated between the sand and the residual adhesive and the carbon dioxide in the sand mold to gel (at this time, sodium carbonate will be generated). It is thought that afterwards, in a state of being attached to the aluminum alloy, the adhesive will harden, and as a result, sand will attach to the surface of the cast product.

In this way, the adhesion of sand is presumed to be caused by the water existing between the inorganic binder (residual binder) attached to the surface of the casting sand and the sand, and the crystal water contained in the residual binder.

[Method of Regenerating Cast Sand] While referring to Fig. 1, a method for regenerating casting sand according to an embodiment of the present invention will be described. Figure 1 is a flow chart showing one aspect of a casting sand regeneration method according to an embodiment of the present invention. According to the casting sand regeneration method of the embodiment of the present invention, it is a method of regenerating the used casting sand to which the inorganic binder has been attached to the surface.

＜Cast sand＞ As the casting sand, various known refractory granular materials can be used without particular limitation. For example, quartz sand, chromite sand, zircon sand, olivine sand, synthetic mullite sand, and alumina-based aggregate particles can be used. These granular materials may be used alone or in combination of two or more kinds. Among the granular materials exemplified here, alumina-based aggregate particles are preferred from the viewpoint of filling properties to the forming mold and the collapse of the sand mold after casting.

Casting sand can be new sand, reclaimed sand regenerated once or several times, or a mixture of new sand and reclaimed sand. In the case of using a mixture, the quality of new sand is, for example, 0.01 times or more and 10 times or less, preferably 0.1 times or more and 10 times or less, and more preferably 1 time or more and 10 times or less the quality of reclaimed sand.

＜Inorganic Binder＞ As the inorganic binder for forming the sand mold, for example, sodium silicate (water glass), clay, silica sol, sulfate, phosphate, and nitrate can be used. The inorganic binders exemplified here can be used alone, or two or more of them can be used in combination.

Among the exemplified inorganic binders, sodium silicate is preferred, and sodium silicate represented by the general formula Na ₂ O･nSiO ₂ (n is 0.5 or more and 4.0 or less) is more preferred. This type of sodium silicate is classified by the molar ratio of sodium oxide to silicon dioxide (the value of n in the above general formula). Specifically, sodium orthosilicate can be cited [ Na ₄ SiO ₄ (Na ₂ O･0.5SiO ₂ :n=0.5)], sodium metasilicate [Na ₂ SiO ₃ (Na ₂ O･SiO ₂ :n=1)], etc. In addition, as sodium silicate, sodium silicate No. 1 [Na ₂ Si ₂ O ₅ (Na ₂ O･ ₂ SiO ₂ :n=2)], sodium silicate No. 2 [Na ₄ Si ₅ O ₁₂ (Na ₂ O･2.5SiO ₂ :n=2.5)], sodium silicate No. 3 [Na ₂ Si ₃ O ₇ (Na ₂ O･3SiO ₂ :n=3)], and sodium silicate No. 4 [Na ₂ Si ₄ O ₉ (Na ₂ O･4SiO ₂ :n=4)] and so on.

In addition, the inorganic binder can be a binder of a water glass substrate formed by an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･yM ₂ O･zH ₂ O (M is Li ⁺ , K ⁺ or Na ^{+ ).} In this case, it is preferable to add a moisture absorbent (or humidifying agent) to the inorganic binder. As the moisture absorbent, specifically, a sodium-containing substance can be used. The mass ratio of the sodium-containing substance to the alkaline silicate aqueous solution is preferably in the range of 1:4 to 1:6. If the mass ratio of sodium-containing substance and alkaline silicate aqueous solution is in the range of 1:4～1:6, for example, the mass ratio _{of Na 2} O to SiO _{2 in the alkaline silicate aqueous solution (Na 2} O When /SiO ₂ ) is 2.5 or more and 3.5 or less (solid content is 20% or more and 40% or less), it can prevent the early hardening of the inorganic adhesive. In addition, in this inorganic binder, in order to appropriately control hygroscopicity (humidification), it is preferable to add a surfactant. Specifically, it is preferable to add silicone oil as a surfactant in the form of an emulsion. The silicone oil has a boiling point of 250° C. or more. It is more preferable that the content of the silicone oil in the emulsion is 8% or more and 10% of the mass of the binder. the following.

When forming the sand mold, the addition amount of the inorganic binder relative to the cast sand is preferably 0.2% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less.

<Crushing step> First, the sand mold used for casting is crushed and the casting sand is recovered (crushing step s1). The method of crushing the sand mold is not particularly limited, and various known crushing methods can be used. For example, it can be pulverized by a pulverizer. When the sand mold is a sand core, the sand is shaken out by a sand cleaner or the like, and then granulated using a sand fresher or the like.

＜Washing step＞ Subsequently, the casting sand is washed while stirring in water at 5°C or higher and 100°C or lower (water washing step s2). Thereby, the inorganic binder adhering to the surface of the casting sand can be dissolved in water and removed to some extent. The amount of water used is not particularly limited as long as it can remove the inorganic binder adhering to the casting sand to some extent. For example, it is 0.5 times or more and 100 times or less relative to the mass of the casting sand, preferably 0.5 times the amount The amount is greater than or equal to 50 times or less, and more preferably the amount is greater than or equal to 30 times.

As a stirring method, as long as the inorganic binder adhering to the casting sand can be removed to some extent, a well-known stirring method can be used without a restriction|limiting in particular. For example, it can stir suitably by a stirrer (mixer). The rotation speed of the mixer is, for example, 30 rpm or more and 300 rpm or less, preferably 40 rpm or more, from the viewpoint of sufficiently removing the inorganic binder adhering to the casting sand, and from the viewpoint of preventing the particle size of the casting sand from becoming uneven by stirring. And 250 rpm or less, more preferably 50 rpm or more and 200 rpm or less. In addition, the stirring time is, for example, 5 minutes or more and 60 minutes or less, preferably 10 minutes or more and 50 minutes or less, and more preferably 15 minutes or more and 40 minutes or less. The rotation speed and the stirring time during stirring by the stirrer can be appropriately set from the above-mentioned range according to the specifications of the stirrer, the types of casting sand and the inorganic binder, and the like.

＜Dehydration step＞ Next, most of the water used in the water washing step s2 is separated and removed from the casting sand (dehydration step s3). As a dehydration method, as long as the majority of water can be separated and removed from the casting sand, a known dehydration method can be used without particular limitation.

For example, a container is prepared that has a drain port provided with a metal mesh or the like so that sand does not flow out, and an air introduction hole for introducing compressed air, and the drain port and the air introduction hole can be hermetically sealed. In this container, water-washed sand containing water is added, and compressed air (for example, 0.2 MPa or less) is introduced into the container from the air introduction hole while the sand is still, so as to force out the sand originally held in the container. The water is easily dehydrated.

＜Drying step＞ Subsequently, while stirring, the casting sand is heated to 100° C. or higher and 300° C. or lower and dried (drying step s4). By subjecting the dehydrated sand to hot air, microwaves, superheated steam, etc. while stirring, the sand can be dried. Thereby, it is possible to obtain dry sand which has a spherical smooth surface while forming a film on the surface of the sand caused by the residual binder.

＜Cooling step＞ Next, while ventilating, the casting sand is cooled to a predetermined temperature (for example, 60° C.) (cooling step s5). Cooling can be performed by subjecting the casting sand to, for example, cold air.

＜Heat treatment steps＞ After that, the casting sand is heated to 550° C. or higher and 900° C. or lower (heat treatment step s6). The heat treatment is not particularly limited as long as it can heat the casting sand to 550°C or more and 900°C or less. For example, if a kiln is used as an apparatus for performing heat treatment, it is possible to heat the casting sand to 550°C or higher and 900°C or lower while moving the casting sand. The heat treatment time can be set appropriately. For example, an electron microscope can be used to confirm the surface of the heat-treated sand, and the heat treatment time can be set so that the surface becomes an appropriate state. Alternatively, the heat-treated sand may be poured into water, and the heat treatment time may be set so that the concentration of the eluted sodium ions becomes an appropriate one.

Figure 2 shows an example of the kiln used in the heat treatment step s6. The kiln (rotary kiln) 10 shown in Figure 2 includes: a main body (kiln body) 11, a spiral blade (feeder) 12 provided in the main body 11, and heating the inside of the main body 11 The burner 13. One end of the main body portion 11 is provided with an introduction port 11a for introducing the processed object 1 (herein casting sand) into the main body portion 11, and at the other end is provided for discharging the processed object 1 from the main body portion 11 to the outside之出口11b. The kiln 10 is an apparatus which heat-treats the to-be-processed object introduced from the inlet 11a while rotating the spiral blade 12, and transfers the obtained heat-treated object, and discharges it from a discharge port. By using this type of kiln 10, the casting sand can be heat-treated while being moved. In addition, Fig. 2 illustrates a configuration in which the object 1 is directly exposed to the flame of the burner 13, but the kiln 10 is not limited to this configuration.

＜Mixed steps＞ Subsequently, a predetermined amount (for example, 5 mass %) of new sand is added to and mixed with the heat-treated casting sand (mixing step s7). The mixing step s7 is performed in order to adjust the particle size and supplement the loss part.

＜Kneading step＞ Thereafter, a binder (inorganic binder) is further added and kneaded to obtain knead sand (knead step s8). If implemented in this way, it is possible to regenerate the used cast sand with the inorganic adhesive attached to the surface.

As described above, the casting sand regeneration method according to the embodiment of the present invention includes a heat treatment step s6 after the water washing step s2. The heat treatment step s6 heats the casting sand to a temperature above 550°C and below 900°C. Step s6 can eliminate the water existing between the cast sand and the inorganic binder remaining on the surface and the crystal water contained in the inorganic binder (that is, dehydration, in other words, minimize the water content). Therefore, the casting sand is regenerated by the casting sand regeneration method according to the embodiment of the present invention, and the regenerated casting sand is used to form a sand mold, and when the sand mold is used for casting, it is possible to prevent the casting sand from being affected by moisture. Attachment of castings.

If the casting sand is moved (for example, stirring, vibrating, etc.) while performing the heat treatment step, it is possible to prevent the softened inorganic binder from causing adjacent sands to bond to each other. It is preferable to keep moving the casting sand until the casting sand becomes less than 550°C.

The water temperature in the water washing step is preferably 20°C or more and 100°C or less. If the water temperature is 20°C or higher, the solubility of the inorganic binder can be sufficiently improved. In addition, the preheating time in the subsequent steps can be shortened.

The water temperature in the water washing step is more preferably 80°C or higher and 100°C or lower. If the water temperature in the water washing step is 80°C or higher, the preheating time in the subsequent steps can be further shortened.

As shown in the example, by performing the drying step s4 between the water washing step s2 and the heat treatment step s6, in this drying step s4, the casting sand is heated to 100°C or higher and 300°C or lower to dry while stirring, and dry sand can be easily obtained , The dry sand has a smooth surface while forming a film on the sand surface caused by the residual adhesive.

In addition, as long as the coating film caused by the residual adhesive can be appropriately formed on the sand surface in the heat treatment step s6, since the heat treatment step s6 essentially doubles as the drying step s4, as shown in Fig. 3, the drying step can be omitted s4 (and cooling step s5). For example, if the above-mentioned kiln 10 etc. can be used and the cast sand can be heat-treated while stirring in the heat-treatment step s6, the heat-treatment step s6 can substantially serve as the drying step s4.

In addition, by performing the dehydration step s3 between the water washing step s2 and the drying step s4, the energy required for the drying step s4 can be reduced.

The washing step s2, the dehydration step s3 and the drying step s4 can be carried out in the same equipment or in different equipment. If the water washing step s2, the dehydration step s3, and the drying step s4 are performed in the same facility, the installation area of the entire facility required for the regeneration of cast sand can be reduced. If the water washing step s2, the dehydration step s3, and the drying step s4 are performed in different equipment, the regeneration amount per unit time can be increased.

In addition, if the high-temperature sand immediately after the completion of the drying step s4 is directly put into the hopper and cooled to normal temperature, the hot air between the hopper and the sand grains will become cold and cause condensation. If the moisture generated by this condensation reacts with the residual binder on the surface of the sand, clogging will occur. If the cooling step s5 is performed between the drying step s4 and the heat treatment step s6, and this cooling step s5 cools the casting sand while ventilating, the dew condensation of the casting sand can be prevented. Therefore, it is possible to prevent the occurrence of the above-mentioned clogging.

[Verification result of the effect of preventing sand adhesion] It is explained that the casting sand regeneration method according to the embodiment of the present invention is used to actually regenerate the casting sand, and the effect of preventing sand adhesion is verified.

<Example> The reclaimed casting sand of the example was obtained as follows.

‧Smashing steps Put the fragments (fragments) of the sand mold (sand core) recovered after the sand falling step into a sand regenerating machine equipped with a screen with a gap of 2 to 4 mm and apply vibrations, whereby the fragments will run in with each other. Fine-grained. The casting sand that has passed through a metal mesh with a mesh size of 850 μm is recovered.

‧Washing steps After putting 250 kg of casting sand and 250 kg of water into a mixer made by Enshu Iron Works, an impeller (impeller) was rotated at 61 rpm for 20 minutes to wash with water.

‧Dehydration step On the bottom surface of the mixer, a drain port made of a metal mesh filter so that sand does not flow out is installed, and it is made to be sealed by closing the valve (valve) except for the air introduction hole for introducing the compressed air and the drain port. state. After washing with water, after stopping the impeller, the valve other than the air introduction hole is closed and the valve of the drain port is opened, and compressed air of 0.2 MPa is introduced into the mixer from the air introduction hole. By introducing compressed air for 20 minutes, dehydration is performed until the moisture content becomes 5-10%.

‧Drying step Open the valve of the exhaust port and the hot air blowing inlet in the above-mentioned mixer, while blowing in hot air at 300°C from the hot air blowing inlet, while rotating the impeller of the mixer at 81 rpm to exhaust air from the exhaust port, it is possible to obtain Spherical dry sand with a smooth surface.

‧Cooling steps In the above-mentioned mixer, after the drying step, the heater of the hot air generator is turned off and the air blowing operation is switched, and the rotation of the impeller is reduced to 27 rpm and stirring is continued until it reaches about 60°C, and then discharged to the hopper.

‧Heat treatment steps The casting sand after the drying step was put into a rotary kiln manufactured by Enshu Iron Works and heated at 750°C for 10 minutes, then cooled to 500°C, and then the casting sand was recovered.

＜Comparative example＞ The casting sand regenerated by the regeneration method of Patent Document 1 is prepared. Specifically, except that the heat treatment step was not performed, the casting sand was regenerated in the same manner as in the examples.

＜Reference example＞ As a reference example, prepare fresh sand.

＜Sand adhesion amount＞ The casting sand of the Examples, Comparative Examples, and Reference Examples prepared as described above was used to mold sand molds (sand cores), and these were used to produce cast products made of aluminum alloys. Then, the amount of sand adhering to the surface of the cast product was verified.

‧Sand core modeling For the casting sand of the Examples, Comparative Examples, and Reference Examples, 0.2% by mass of sodium hydroxide, 1.0% by mass of sodium silicate, and 0.6% by mass of nanosilica suspension were added and kneaded, and then filled in the forming mold, and dehydrated and hardened. Take it out to get the sand core.

‧Casting Use sand core to cast cylinder head by gravity casting. As the material of the cylinder head, aluminum alloy AC4B (specification) is used.

‧Sand The obtained cylinder head was installed in a sand cleaning machine manufactured by YOMAR Co., Ltd., and shock and shaking were applied for 30 seconds.

For the Examples, Comparative Examples, and Reference Examples, the results of measuring the amount of sand attached to the surface of the cast product (the amount of sand attached) are shown in Table 1 and Figure 3.

[Table 1]

From Table 1 and Figure 3, it can be seen that, compared to the reference example (new sand), the adhesion amount of sand is greatly increased in the comparative example. It can also be seen that in comparison with this, in the examples, the adhesion amount of sand is approximately the same as in the reference example. In addition, in the examples, the collapsibility of the sand mold (sand core) was also good as in the reference example. In this way, it was confirmed that according to the embodiment of the present invention, the amount of sand adhering to the cast product is not worse than that of new sand (that is, the amount of sand adhering is also less).

As described above, the casting sand regeneration method according to the embodiment of the present invention is a casting sand regeneration method that regenerates used cast sand 1 with an inorganic binder attached to the surface, and the cast sand regeneration method includes: a crushing step s1, pulverize the sand mold used for casting and recover the foundry sand 1; water washing step s2, after the aforementioned pulverization step s1, wash the aforementioned foundry sand 1 in water at a temperature above 5°C and below 100°C while stirring; and, heat treatment In step s6, after the water washing step s2, the casting sand 1 is heated to a temperature above 550°C and below 900°C.

According to the casting sand regeneration method of the embodiment of the present invention, after the water washing step s2, it includes a heat treatment step s6. The heat treatment step s6 heats the casting sand 1 to a temperature above 550°C and below 900°C. Therefore, by this heat treatment step s6, It can eliminate the water existing between the cast sand 1 and the inorganic binder remaining on the surface and the crystal water contained in the inorganic binder (that is, dehydration). Therefore, according to the casting sand regeneration method of the embodiment of the present invention, the casting sand 1 is regenerated, and the regenerated casting sand 1 is used to form a sand mold, and when the sand mold is used for casting, it is possible to prevent the casting from being caused by moisture. The attachment of sand 1 to the casting.

In one embodiment, the heat treatment step s6 is performed while moving the casting sand.

If the heat treatment step s6 is performed while the casting sand 1 is moved, it is possible to prevent adjacent sands from being bonded to each other due to the softened inorganic binder.

In one embodiment, the water temperature in the aforementioned water washing step s2 is 20°C or more and 100°C or less.

If the water temperature in the water washing step s2 is 20°C or higher, the solubility of the inorganic binder can be sufficiently improved. In addition, the preheating time in the subsequent steps can be shortened.

In one embodiment, the water temperature in the aforementioned water washing step s2 is 80°C or more and 100°C or less.

If the water temperature in the water washing step s2 is 80°C or higher, the preheating time in the subsequent steps can be further shortened.

In one embodiment, the aforementioned casting sand regeneration method further includes a drying step s4 between the aforementioned water washing step s2 and the aforementioned heat treatment step s6. The drying step s4 heats the aforementioned casting sand 1 to 100°C or higher while stirring. Dry below 300°C.

A drying step s4 may be performed between the water washing step s2 and the heat treatment step s6. In this drying step s4, the casting sand 1 is heated to 100°C or higher and 300°C or lower to dry while stirring. By performing the drying step s4, dry sand can be easily obtained, and the dry sand has a smooth surface while forming a film on the sand surface caused by the residual binder.

In one embodiment, the aforementioned casting sand regeneration method further includes a dehydration step s3 between the aforementioned water washing step s2 and the aforementioned drying step s4. The dehydration step s3 removes most of the water used in the aforementioned water washing step s2 from The aforementioned casting sand 1 is separated and removed.

By performing the dehydration step s3 between the water washing step s2 and the drying step s4, the energy required for the drying step s4 can be reduced.

In one embodiment, the aforementioned water washing step s2, the aforementioned dehydration step s3, and the aforementioned drying step s4 are performed in the same equipment.

If the water washing step s2, the dehydration step s3, and the drying step s4 are performed in the same facility, the installation area of the entire facility required for the regeneration of the cast sand 1 can be reduced.

In one embodiment, the aforementioned water washing step s2, the aforementioned dehydration step s3, and the aforementioned drying step s4 are performed in different equipment.

If the water washing step s2, the dehydration step s3, and the drying step s4 are performed in different equipment, the regeneration amount per unit time can be increased.

In one embodiment, the aforementioned casting sand regeneration method further includes a cooling step s5 between the aforementioned drying step s4 and the aforementioned heat treatment step s6, and the cooling step s5 cools the aforementioned casting sand 1 while ventilating.

If the cooling step s5 is performed between the drying step s4 and the heat treatment step s6, and this cooling step s5 cools the casting sand 1 while ventilating, the condensation of the casting sand 1 can be prevented.

In one embodiment, the aforementioned inorganic binder includes sodium silicate.

As the inorganic binder, an inorganic binder containing sodium silicate (water glass) can be suitably used.

In one embodiment, the aforementioned sodium silicate is represented by the general formula Na ₂ O･nSiO ₂ , where n is 0.5 or more and 4.0 or less.

As the sodium silicate, sodium silicate represented by the general formula Na ₂ O･nSiO ₂ (n is 0.5 or more and 4.0 or less) can be suitably used.

In one embodiment, the aforementioned inorganic binder is formed from an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･yM ₂ O･zH ₂ ^{O, where M is Li +} , K ⁺ or Na ⁺ , in the aforementioned inorganic binding In the agent, a sodium-containing substance is added as a moisture absorbent such that the mass ratio of the sodium-containing substance to the aforementioned alkaline silicate aqueous solution is in the range of 1:4 to 1:6. In the aforementioned inorganic binder, further In the form of an emulsion, silicone oil is added as a surfactant. The silicone oil has a boiling point of 250° C. or more. The content of the silicone oil in the emulsion is 8% or more and 10% or less of the mass of the inorganic binder.

The inorganic binder can be a water glass substrate binder formed by an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･yM ₂ O･zH ₂ O (M is Li ⁺ , K ⁺ or Na ^{+ ).} In this case, it is preferable to add a moisture absorbent to the inorganic binder. As the moisture absorbent, specifically, a sodium-containing substance can be used. The mass ratio of the sodium-containing substance to the alkaline silicate aqueous solution is preferably in the range of 1:4 to 1:6. If the mass ratio of sodium-containing substance and alkaline silicate aqueous solution is in the range of 1:4～1:6, for example, the mass ratio _{of Na 2} O to SiO _{2 in the alkaline silicate aqueous solution (Na 2} O When /SiO ₂ ) is 2.5 or more and 3.5 or less (solid content is 20% or more and 40% or less), it can prevent the early hardening of the inorganic adhesive. In addition, in this inorganic binder, in order to appropriately control the hygroscopicity, it is preferable to add a surfactant. Specifically, it is preferable to add silicone oil as a surfactant in the form of an emulsion. The silicone oil has a boiling point of 250° C. or more. It is more preferable that the content of the silicone oil in the emulsion is 8% or more and 10% of the mass of the binder. the following. [Industrial Utilization]

According to an embodiment of the present invention, a method for regenerating cast sand is provided. Even if the cast sand to which the inorganic binder has been adhered on the surface is repeatedly regenerated, the amount of sand attached to the cast product will not easily increase.

1: Casting sand (object to be processed) 10: Kiln 11: Main body 11a: inlet 11b: Outlet 12: Spiral wing (feeder) 13: Burner s1～s8: steps

Figure 1 is a flow chart showing one aspect of the casting sand regeneration method according to the embodiment of the present invention. Fig. 2 is a diagram showing the kiln 10 used in the heat treatment step s6. Figure 3 is a flowchart showing another aspect of the casting sand regeneration method according to the embodiment of the present invention. Fig. 4 is a graph showing the amount of sand adhering to the surface of a cast product for Examples, Comparative Examples, and Reference Examples.

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s1~s8: steps

Claims (12)

A method for regenerating cast sand, which is a method for regenerating cast sand after use with an inorganic binder attached to the surface. The method for regenerating cast sand includes: In the crushing step, the sand mold used in casting is crushed and the casting sand is recovered; In the water washing step, after the aforementioned crushing step, the aforementioned foundry sand is washed while stirring in water at a temperature above 5°C and below 100°C; and, In the heat treatment step, after the water washing step, the casting sand is heated to 550°C or more and 900°C or less. The casting sand regeneration method according to claim 1, wherein the heat treatment step is performed while moving the casting sand. The casting sand regeneration method according to claim 1 or 2, wherein the water temperature in the water washing step is 20°C or more and 100°C or less. The casting sand regeneration method according to claim 1 or 2, wherein the water temperature in the water washing step is 80°C or more and 100°C or less. The casting sand regeneration method according to any one of claims 1 to 4, wherein, between the water washing step and the heat treatment step, a drying step is further included in the drying step, which heats the casting sand to 100°C while stirring Above and below 300°C and dry. The method for regenerating casting sand according to claim 5, wherein between the water washing step and the drying step, a dehydration step is further included, and the dehydration step separates most of the water used in the water washing step from the casting sand And removal. The casting sand regeneration method according to claim 6, wherein the water washing step, the dehydration step, and the drying step are performed in the same equipment. The casting sand regeneration method according to claim 6, wherein the water washing step, the dehydration step, and the drying step are performed in different equipment. The casting sand regeneration method according to any one of claims 5 to 8, wherein, between the drying step and the heat treatment step, a cooling step is further included in the cooling step to cool the casting sand while ventilating. The method for regenerating foundry sand according to any one of claims 1 to 9, wherein the inorganic binder contains sodium silicate. The method for regenerating foundry sand according to claim 10, wherein the sodium silicate is represented by the general formula Na ₂ O･nSiO ₂ , wherein n is 0.5 or more and 4.0 or less. The method for regenerating foundry sand according to any one of claims 1 to 9, wherein the aforementioned inorganic binder is formed from an alkaline silicate aqueous solution represented _{by the general formula xSiO 2} ･M ₂ O･zH _{2 O, wherein M} Li ⁺ , K ⁺ or Na ⁺ ; In the aforementioned inorganic binder, sodium-containing substance is added so that the mass ratio of the sodium-containing substance to the aforementioned alkaline silicate aqueous solution is in the range of 1:4 to 1:6 As a moisture absorbent; and, in the aforementioned inorganic binder, silicone oil is further added as a surfactant in the form of an emulsion, the silicone oil has a boiling point of 250°C or more, and the content of the silicone oil in the aforementioned emulsion is the quality of the aforementioned inorganic binder Above 8% and below 10%.

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