JP7171944B2 - Foundry sand regeneration method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a foundry sand reclaiming method, and more particularly to a foundry sand reclaiming method for reclaiming used foundry sand having an inorganic binder adhered to its surface.

Foundry sand is recovered from the sand mold used for casting, subjected to a reclaiming treatment to remove the binder adhering to the surface of the foundry sand, and then reused for casting as reclaimed casting sand. Binders used to form sand molds are roughly classified into organic binders such as phenol resin and furan resin, and inorganic binders such as sodium silicate (water glass).

In general, inorganic binders are more difficult to remove from the surface of foundry sand than organic binders. For example, an organic binder adhering to the surface of foundry sand can be removed by roasting, but an inorganic binder cannot be removed by roasting. In addition, the inorganic binder adhering to the surface of the foundry sand can be removed to some extent by polishing the foundry sand after heating, but in this case, the surface of the sand becomes uneven and the sand itself is crushed. . Therefore, when an inorganic binder is used, recyclability of foundry sand is worse than when an organic binder is used. Furthermore, it is difficult to chemically remove the inorganic binder using a chemical or the like.

As described above, when an inorganic binder is used as a binder for forming a sand mold, it is more difficult to reclaim foundry sand than when an organic binder is used. Therefore, the applicant of the present application has proposed in Patent Document 1 a reclaiming method capable of suitably reclaiming foundry sand having an inorganic binder adhered to its surface. The regeneration method disclosed in Patent Document 1 includes the following steps (1) to (4).
(1) A pulverizing step of pulverizing the recovered molding sand mold into pulverized molding sand.
(2) A mixing step of separating the inorganic binder adhering to the surface from the foundry sand by mixing and stirring the obtained pulverized foundry sand in water at 5°C to 70°C.
(3) A step of recovering the foundry sand from which the inorganic binder has been separated, and heat-drying the foundry sand while agitating it.
(4) A step of removing fine powder from the heat-dried foundry sand.

Japanese Patent No. 6188502

However, as a result of detailed studies by the inventors of the present application, it was found that when casting sand is repeatedly reclaimed by the reclaiming method of Patent Document 1, the amount of sand adhering to the surface of the casting increases and sand remains on the surface of the casting. It turns out that there is a risk of In addition, in a narrow and intricate shape such as the water jacket of the cylinder head, sand clogs the flow path, and there is a problem that the sand cannot be removed by a knockout machine, an ultrasonic water washing machine, or the like.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for reclaiming foundry sand in which the amount of adhering sand to a cast product is less likely to increase even if the foundry sand having an inorganic binder adhered to its surface is repeatedly reclaimed. to provide.

According to an embodiment of the present invention, there is provided a foundry sand reclamation method as described below.

[Item 1]
A method for regenerating foundry sand for reclaiming used foundry sand having an inorganic binder attached to the surface thereof, comprising:
A pulverizing step of pulverizing the sand mold used for casting to recover casting sand;
After the pulverizing step, a water washing step of washing the foundry sand in water at a temperature of 5° C. or more and 100° C. or less while stirring;
a heat treatment step of heating the foundry sand to 550° C. or more and 900° C. or less after the water washing step;
A foundry sand reclaiming method comprising:

The method for regenerating foundry sand according to the embodiment of the present invention includes a heat treatment step of heating the foundry sand to 550° C. or higher and 900° C. or lower after the water washing step. It is possible to eliminate the water present between the inorganic binder and the water of crystallization contained in the inorganic binder (that is, to make it anhydrous). Therefore, when casting is performed using a sand mold formed of foundry sand regenerated by the foundry sand regeneration method according to the embodiment of the present invention, it is possible to prevent the foundry sand from sticking to the cast product due to moisture. .

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

If the heat treatment process is carried out while moving the foundry sand, it is possible to prevent the adjoining sands from binding together due to the softened inorganic binder.

[Item 3]
3. The method for regenerating foundry sand according to item 1 or 2, wherein the water temperature in the water washing step is 20° C. or higher and 100° C. or lower.

When the water temperature in the water washing step is 20°C or higher, the solubility of the inorganic binder can be sufficiently increased. Also, the preheating time in the subsequent steps can be shortened.

[Item 4]
3. The method for regenerating foundry sand according to item 1 or 2, wherein the water temperature in the water washing step is 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.

[Item 5]
5. The foundry sand regeneration according to any one of items 1 to 4, further comprising a drying step of drying the foundry sand by heating it to 100° C. or more and 300° C. or less while stirring it, between the water washing step and the heat treatment step. Method.

Between the washing step and the heat treatment step, a drying step may be performed in which the foundry sand is heated to 100° C. or higher and 300° C. or lower while being stirred to dry it. By carrying out the drying process, it is possible to easily obtain dry sand having a smooth surface while forming a film of residual binder on the sand surface.

[Item 6]
6. The method for regenerating foundry sand according to item 5, further comprising, between the water washing step and the drying step, a dehydration step of separating and removing most of the water used in the water washing step from the foundry sand.

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

[Item 7]
7. The method for reclaiming foundry sand according to item 6, wherein the water washing process, the dewatering process, and the drying process are performed in the same equipment.

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

[Item 8]
7. The method for reclaiming foundry sand according to item 6, wherein the water washing step, the dewatering step, and the drying step are performed in different facilities.

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

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

If the cooling step of cooling the casting sand while ventilating is performed between the drying step and the heat treatment step, dew condensation on the casting sand can be prevented.

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

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

[Item 11]
11. The method for regenerating foundry sand according to item 10, wherein the sodium silicate is represented by the general formula: _{Na2O.nSiO2 (} where n is 0.5 or more and 4.0 or less).

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

[Item 12]
The inorganic binder is formed from an aqueous alkali silicate solution represented by the general formula: xSiO ₂ ·yM _{2 O ·zH 2 O} (M is Li ⁺ , K ⁺ or Na ⁺ ),
A sodium-containing material is added to the inorganic binder as a moisture absorbent so that the mass ratio of the sodium-containing material to the alkali silicate aqueous solution is in the range of 1:4 to 1:6,
Silicone oil having a boiling point of 250° C. or higher is added to the inorganic binder in the form of an emulsion as a surfactant, and the content of the silicone oil in the emulsion is 8% or more of the mass of the inorganic binder. % or less.

The inorganic binder is a water glass-based binder formed from an alkali silicate aqueous solution represented by the general formula: xSiO ₂ .yM ₂ O.zH ₂ O (M is Li ⁺ , K ⁺ or Na ⁺ ). good too. In that case, it is preferable that a moisture absorbent is added to the inorganic binder. As the hygroscopic agent, specifically, a sodium-containing material can be used. The mass ratio of the sodium-containing material to the aqueous alkali silicate solution is preferably within the range of 1:4 to 1:6. If the mass ratio of the sodium-containing substance to the aqueous alkali silicate solution is within the range of 1:4 to 1:6, for example, the mass ratio of Na ₂ O to SiO ₂ in the aqueous alkali silicate solution (Na ₂ O/SiO ₂ ) is 2.5 or more and 3.5 or less (the solid content is 20% or more and 40% or less), it is possible to prevent the inorganic binder from prematurely curing. Further, it is preferable that a surfactant is added to the inorganic binder in order to suitably control the hygroscopicity. Specifically, it is preferable that silicone oil having a boiling point of 250° C. or higher is added as a surfactant in the form of an emulsion, and the silicone oil content in the emulsion is 8% or more and 10% or less of the mass of the binder. It is more preferable to have

According to an embodiment of the present invention, there is provided a method for reclaiming foundry sand in which the amount of adhering sand to a cast product is less likely to increase even when reclaimed foundry sand having an inorganic binder adhered to its surface is repeated.

1 is a flow chart showing one aspect of a foundry sand reclamation method according to an embodiment of the present invention. FIG. 4 is a diagram showing the kiln 10 used in the heat treatment step s6; 4 is a flow chart showing another aspect of the foundry sand reclamation method according to the embodiment of the present invention. 4 is a graph showing the amount of sand adhering to the surface of castings for Examples, Comparative Examples, and Reference Examples.

The inventors of the present application have studied in detail the mechanism by which sand adheres to the surface of castings, and have found that the adhesion of sand is caused by moisture and water existing between the sand and the inorganic binder (residual binder) adhered to the surface of the casting sand. , was found to be caused by water of crystallization contained in the residual binder. The present invention has been made based on the above findings. The mechanism of sand adhesion and the molding sand reclamation method according to the embodiment of the present invention will be described below.

[Mechanism of adhesion of sand to casting surface]
When the casting sand was reclaimed 20 times or more by the reclaiming method of Patent Document 1, a phenomenon occurred in which the sand adhered to the surface of the casting made of aluminum alloy.

Observation of the sand adhering to the surface of the casting and the interface between the sand and the surface of the casting revealed that a white substance adhered to the surface of the sand. As a result of identification by X-ray diffraction, this white substance was identified to contain sodium carbonate monohydrate as a main component.

Further, when the interface between the sand and the surface of the casting was observed by SEM (Scanning Electron Microscope), it was found that an adhesive-like film was present. When this film was qualitatively analyzed by EDS (energy dispersive X-ray spectroscopy), silicon (Si) and oxygen (O) were detected, and it was found that the components of the film were similar to those of the inorganic binder.

When only reclaimed sand was placed in a cup made of stainless steel and heated to 740° C., a phenomenon was observed in which the reclaimed sands bonded together in the cup. When the heated reclaimed sand was observed, it was found that the residual binder layer on the surface layer of the reclaimed sand softened at about 600°C to generate blisters, and was smoothed when further heated to 740°C. Also, gas analysis identified that the gases discharged from the blister were water, hydrogen, carbon monoxide, and carbon dioxide.

From these facts, it is presumed that adhesion of sand occurs by the following mechanism. First, on the surface of the sand mold that touches the molten metal, the binder component is heated to 600° C. or higher and softened, and the water remaining between the sand and the residual binder and the water of crystallization contained in the residual binder combine with the softened binder component. It reacts to form water glass. Then, the water-vitrified binder absorbs carbon dioxide generated between the sand and the residual binder and carbon dioxide in the sand mold and gels (sodium carbonate is produced at this time). It is believed that the sand then adheres to the surface of the casting due to hardening of the binder while adhering to the aluminum alloy.

Thus, it is presumed that the adhesion of sand is caused by water present between the inorganic binder (residual binder) adhering to the surface of the foundry sand and the sand, and water of crystallization contained in the residual binder.

[Casting sand regeneration method]
A molding sand reclamation method according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flow chart showing one mode of a foundry sand reclamation method according to an embodiment of the present invention. A method for regenerating foundry sand according to an embodiment of the present invention is a method for reclaiming used foundry sand having an inorganic binder adhered to its surface.

<Casting sand>
As the foundry sand, various known refractory granular materials can be used without particular limitation. For example, silica sand, chromite sand, zircon sand, olivine sand, synthetic mullite sand and alumina-based aggregate particles can be used. These particulate materials may be used alone, or two or more of them may be used in combination. Among the granular materials exemplified here, alumina-based aggregate particles are preferable from the viewpoints of fillability into a mold and sand mold collapsibility after casting.

The foundry sand may be new sand, reclaimed sand that has been reclaimed once or multiple times, or a mixture of new sand and reclaimed sand. When a mixture is used, the mass of new sand is, for example, 0.01 to 10 times, preferably 0.1 to 10 times, more preferably 1 to 10 times the mass of reclaimed sand. be.

<Inorganic binder>
As inorganic binders for sand mold formation, for example, sodium silicate (water glass), clay, silica sol, sulfates, phosphates and nitrates can be used. The inorganic binders exemplified here may be used alone, or two or more of them may be used in combination.

Among the exemplified inorganic binders, sodium silicate is preferable, and sodium silicate represented by the general formula: Na ₂ O.nSiO ₂ (where n is 0.5 or more and 4.0 or less) is more preferable. Such sodium silicates are classified according to the molar ratio of sodium oxide to silicon _{dioxide (} value of _n in the above general formula). 5SiO ₂ : n=0.5)], sodium metasilicate [Na ₂ SiO ₃ (Na ₂ O.SiO ₂ : n=1)], and the like. Examples of sodium silicate include sodium silicate No. 1 [Na ₂ Si ₂ O ₅ (Na ₂ O.2SiO ₂ : n=2)] and 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)].

The inorganic binder is a water glass-based binder formed from an alkali silicate aqueous solution represented by the general formula: xSiO ₂ .yM ₂ O.zH ₂ O (M is Li ⁺ , K ⁺ or Na ⁺ ). There may be. In that case, it is preferable that a hygroscopic agent (or moisturizing agent) is added to the inorganic binder. As the hygroscopic agent, specifically, a sodium-containing material can be used. The mass ratio of the sodium-containing material to the aqueous alkali silicate solution is preferably within the range of 1:4 to 1:6. If the mass ratio of the sodium-containing substance to the aqueous alkali silicate solution is within the range of 1:4 to 1:6, for example, the mass ratio of Na ₂ O to SiO ₂ in the aqueous alkali silicate solution (Na ₂ O/SiO ₂ ) is 2.5 or more and 3.5 or less (the solid content is 20% or more and 40% or less), it is possible to prevent the inorganic binder from prematurely curing. Further, it is preferable that a surfactant is added to the inorganic binder in order to suitably control the hygroscopicity (humidity imparting property). Specifically, it is preferable that silicone oil having a boiling point of 250° C. or higher is added as a surfactant in the form of an emulsion, and the silicone oil content in the emulsion is 8% or more and 10% or less of the mass of the binder. It is more preferable to have

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

<Pulverization process>
First, a sand mold used for casting is pulverized to collect molding sand (pulverization step s1). There is no particular limitation on the method of pulverizing the sand mold, and various known pulverizing methods can be used. For example, pulverization can be performed with a pulverizer. When the sand mold is a core, the sand is removed by a knockout machine or the like, and then finely granulated using a sand fresher or the like.

<Washing process>
Next, the foundry sand is washed with stirring in water at a temperature of 5° C. to 100° C. (washing step s2). As a result, the inorganic binder adhering to the surface of the foundry sand can be dissolved in water and removed to some extent. The amount of water to be used is not particularly limited as long as the inorganic binder attached to the molding sand can be removed to some extent. is 0.5 to 50 times the amount, more preferably 1 to 30 times the amount.

The stirring method is not particularly limited as long as the inorganic binder adhering to the foundry sand can be removed to some extent, and known stirring methods can be used. For example, stirring can be suitably performed with a stirrer (mixer). The rotation speed of the stirrer is, for example, 30 rpm or more and 300 rpm or less, preferably 40 rpm, from the viewpoint of sufficiently removing the inorganic binder adhering to the molding sand and from the viewpoint of preventing the grain size of the molding sand from becoming uneven due to stirring. 250 rpm or more, more preferably 50 rpm or more and 200 rpm or less. 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, more preferably 15 minutes or more and 40 minutes or less. The number of revolutions and the stirring time during stirring by the stirrer can be appropriately set within the above ranges according to the specifications of the stirrer, the types of the foundry sand and the inorganic binder, and the like.

<Dehydration process>
Subsequently, most of the water used in the water washing step s2 is separated and removed from the foundry sand (dehydration step s3). The dehydration method is not particularly limited as long as most of the water can be separated and removed from the foundry sand, and any known dehydration method can be used.

For example, a container is prepared which has a drain port provided with a wire mesh or the like to prevent sand from flowing out, an air introduction hole for introducing compressed air, and which can be sealed except for the drain port and the air introduction hole. Sand containing washed water is placed in this container, and compressed air (e.g., 0.2 MPa or less) is introduced into the container through the air introduction hole while the sand is still. dehydration can be easily performed by expelling the

<Drying process>
Next, the foundry sand is dried by heating to 100° C. or higher and 300° C. or lower while being stirred (drying step s4). While stirring the sand after dehydration, it can be dried by applying hot air, microwaves, superheated steam, or the like to the sand. As a result, it is possible to obtain dry sand having a spherical smooth surface while forming a film of the residual binder component on the sand surface.

<Cooling process>
Subsequently, the molding sand is cooled to a predetermined temperature (eg, 60° C.) while being ventilated (cooling step s5). Cooling can be achieved by blowing cold air onto the foundry sand, for example.

<Heat treatment process>
Thereafter, the foundry sand is heated to 550° C. or more and 900° C. or less (heat treatment step s6). The heat treatment is not particularly limited as long as the molding sand can be heated to 550°C or higher and 900°C or lower. For example, if a kiln is used as an apparatus for heat treatment, the foundry sand can be heated to 550° C. or higher and 900° C. or lower while being moved. The heat treatment time is appropriately set. For example, the surface of sand after heat treatment may be checked with an electron microscope, and the heat treatment time may be set so that the surface is in an appropriate state. Alternatively, the heat-treated sand may be put into water, and the heat treatment time may be set so that the dissolved sodium ion concentration is appropriate.

FIG. 2 shows an example of a kiln used in the heat treatment step s6. A kiln (rotary kiln) 10 shown in FIG. An introduction port 11a is provided at one end of the barrel 11 for introducing the object 1 to be treated (foundry sand in this case) into the barrel 11, and the other end is provided with the object 1 to be treated. An outlet 11b is provided for discharging from the outside. The kiln 10 is a device that heat-treats the material to be processed 1 introduced from the introduction port 11a while rotating the helical blades 12, transfers the obtained heat-processed material, and discharges it from the discharge port. By using such a kiln 10, heat treatment can be performed while moving the foundry sand. Although FIG. 2 illustrates a configuration in which the workpiece 1 is directly exposed to the flame of the burner 13, the kiln 10 is not limited to such a configuration.

<Mixing process>
Next, a predetermined amount (for example, 5% by mass) of new sand is added to and mixed with the heat-treated foundry sand (mixing step s7). The mixing step s7 is performed for the purpose of adjusting the particle size and replenishing the depleted amount.

<Kneading process>
Thereafter, a binder (inorganic binder) is further added and kneaded to obtain kneaded sand (kneading step s8). In this manner, used foundry sand with an inorganic binder adhered to its surface can be reclaimed.

As described above, the method for regenerating foundry sand according to the embodiment of the present invention includes the heat treatment step s6 of heating the foundry sand to 550° C. or higher and 900° C. or lower after the water washing step s2. Water present between the sand and the inorganic binder remaining on its surface and water of crystallization contained in the inorganic binder can be eliminated (that is, dehydrated, in other words minimized). Therefore, when casting is performed using a sand mold formed of foundry sand regenerated by the foundry sand regeneration method according to the embodiment of the present invention, it is possible to prevent the foundry sand from sticking to the cast product due to moisture. .

If the heat treatment process is performed while moving (for example, stirring or vibrating) the foundry sand, the softened inorganic binder can prevent the adjacent sands from binding to each other. It is preferred to keep the foundry sand moving until the foundry sand is below 550°C.

The water temperature in the water washing step is preferably 20°C or higher and 100°C or lower. When the water temperature is 20°C or higher, the solubility of the inorganic binder can be sufficiently increased. Also, 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 exemplified, between the water washing step s2 and the heat treatment step s6, the casting sand is heated to 100° C. or higher and 300° C. or lower while being stirred to dry it, thereby forming a film of residual binder on the sand surface. A dry sand having a smooth surface can be easily obtained while forming a

If a film of the residual binder can be suitably formed on the surface of the sand in the heat treatment step s6, then the heat treatment step s6 substantially doubles as the drying step s4, so that the drying step s4 (and the cooling Step s5) may be omitted. For example, if the kiln 10 or the like described above can be used to perform heat treatment while stirring the foundry sand in the heat treatment step s6, the heat treatment step s6 can substantially serve as the drying step s4.

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

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

If the high-temperature sand immediately after the drying step s4 is put into the hopper as it is and cooled to room temperature, the hot air between the hopper and the sand grains cools down and condensation may occur. Blocking occurs when the moisture generated by this condensation reacts with the residual binder on the surface of the sand. If the cooling step s5 of cooling the casting sand while ventilating is performed between the drying step s4 and the heat treatment step s6, dew condensation on the casting sand can be prevented. Therefore, it is possible to prevent the above-described blocking from occurring.

[Verification results of the effect of preventing sand adhesion]
EXAMPLES The result of actually reclaiming foundry sand using the method for reclaiming foundry sand according to the embodiment of the present invention and verifying the effect of preventing adhesion of sand will be described.

<Example>
Recycled foundry sand of Examples was obtained in the following manner.

・Pulverization process Pieces of the sand mold (core) collected after the sand removal process are put into a sand fresher equipped with a screen with a gap of 2 to 4 mm. turned into Foundry sand passed through a wire mesh with an opening size of 850 μm was recovered.

Water washing process 250 kg of foundry sand and 250 kg of water were put into a mixer manufactured by Enshu Tekko, and washed by rotating the impeller at 61 rpm for 20 minutes.

・Dehydration process On the bottom of the mixer described above, a drainage port configured to prevent sand from flowing out with a wire mesh filter was provided, and the valves were closed to seal everything other than the air introduction hole for introducing compressed air and the drainage port. After washing with water, the impeller was stopped, the valves other than the air introduction hole were closed, the drain valve was opened, and compressed air of 0.2 MPa was introduced into the mixer through the air introduction hole. Dehydration was carried out to a moisture content of 5-10% by introducing compressed air for 20 minutes.

・Drying process Open the valves of the exhaust port and the hot air blowing port in the mixer described above, blow hot air of 300 ° C from the hot air blowing port, rotate the impeller of the mixer at 81 rpm, and exhaust from the exhaust port to make a spherical smooth A dry sand with a smooth surface was obtained.

- Cooling process In the mixer described above, after the drying process, the heater of the hot air generator was turned off, the rotation of the impeller was lowered to 27 rpm, stirring was continued until the temperature reached about 60 ° C., and the mixture was discharged to the hopper.

- Heat treatment step The casting sand after the drying step was placed in a rotary kiln manufactured by Enshu Iron Works Co., Ltd., heated at 750°C for 10 minutes, cooled to 500°C, and then the casting sand was recovered.

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

<Reference example>
New sand was prepared as a reference example.

<Amount of sand adhering>
Using the examples, comparative examples, and reference examples prepared as described above, sand molds (cores) were formed, and cast products made of aluminum alloy were produced using these molds. Then, the amount of sand adhering to the surface of the casting was verified.

・Core molding 0.2% by mass of caustic soda, 1.0% by mass of sodium silicate, and 0.6% by mass of nanosilica suspension are added to and kneaded with respect to the foundry sand of Examples, Comparative Examples, and Reference Examples, and then molded. It was filled into a mold, dehydrated and hardened, and taken out to obtain a core.

・Cylinder heads were cast by gravity casting using casting cores. Aluminum alloy AC4B was used as the material of the cylinder head.

- Remove sand The obtained cylinder head was attached to a knockout machine made by Yomer Co., Ltd. and subjected to impact and rocking for 30 seconds.

Table 1 and FIG. 4 show the results of measuring the amount of sand adhering to the surface of castings for the examples, comparative examples, and reference examples.

From Table 1 and FIG. 4, it can be seen that the amount of adhering sand is significantly increased in the comparative example compared to the reference example (fresh sand). On the other hand, it can be seen that in the example, the amount of adhered sand is almost the same as in the reference example. Further, in the example, the collapsibility of the sand mold (core) was as good as in the reference example. Thus, according to the embodiment of the present invention, it was confirmed that the amount of sand adhering to the cast product was comparable to that of new sand.

As described above, the foundry sand reclaiming method according to the embodiment of the present invention is a foundry sand reclaiming method for reclaiming used foundry sand 1 having an inorganic binder adhered to its surface, and the sand mold used for casting is pulverized. a crushing step s1 for recovering the foundry sand 1 by means of the crushing step s1; after the crushing step s1, a washing step s2 for washing the foundry sand 1 in water at a temperature of 5° C. or higher and 100° C. or lower while stirring; and after the washing step s2, the and a heat treatment step s6 of heating the foundry sand 1 to 550° C. or more and 900° C. or less.

The method for regenerating the foundry sand according to the embodiment of the present invention includes the heat treatment step s6 of heating the foundry sand 1 to 550° C. or higher and 900° C. or lower after the water washing step s2. It is possible to eliminate water present between the surface and the inorganic binder remaining on the surface and water of crystallization contained in the inorganic binder (that is, dehydration). Therefore, when casting is performed using a sand mold formed of the foundry sand 1 regenerated by the foundry sand regeneration method according to the embodiment of the present invention, it is necessary to prevent the foundry sand 1 from sticking to the cast product due to moisture. can be done.

In one embodiment, the heat treatment step s6 is performed while the foundry sand 1 is being moved.

If the heat treatment step s6 is performed while moving the foundry sand 1, it is possible to prevent adjacent sands from being bonded together by the softened inorganic binder.

In one embodiment, the water temperature in the water washing step s2 is 20°C or higher and 100°C or lower.

When the water temperature in the water washing step s2 is 20°C or higher, the solubility of the inorganic binder can be sufficiently increased. Also, the preheating time in the subsequent steps can be shortened.

In one embodiment, the water temperature in the water washing step s2 is 80°C or higher and 100°C or lower.

When 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 method for regenerating foundry sand includes a drying step s4 in which the foundry sand 1 is dried by being heated to 100° C. or higher and 300° C. or lower while being stirred, between the water washing step s2 and the heat treatment step s6. Including further.

Between the water washing step s2 and the heat treatment step s6, a drying step s4 may be performed in which the foundry sand 1 is heated to 100° C. or higher and 300° C. or lower while stirring to dry. By performing the drying step s4, it is possible to easily obtain dry sand having a smooth surface while forming a film of residual binder on the sand surface.

In one embodiment, the foundry sand regeneration method includes a dehydration step of separating and removing most of the water used in the water washing step s2 from the foundry sand 1 between the water washing step s2 and the drying step s4. s3 is further included.

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 washing step s2, the dehydration step s3, and the drying step s4 are performed in the same facility.

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

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

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

In one embodiment, the molding sand regeneration method further includes a cooling step s5 of cooling the molding sand 1 with ventilation between the drying step s4 and the heat treatment step s6.

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

In one embodiment, the inorganic binder contains sodium silicate.

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

In one embodiment, the 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, one represented by the general formula: Na ₂ O.nSiO ₂ (where n is 0.5 or more and 4.0 or less) can be preferably used.

In one embodiment, the inorganic binder is formed from an alkali silicate aqueous solution represented by the general formula: xSiO ₂ ·yM _{2 O ·zH 2 O} (M is Li ⁺ , K ⁺ or Na ⁺ ), A sodium-containing material is added as a moisture absorbent to the inorganic binder so that the mass ratio of the sodium-containing material to the alkali silicate aqueous solution is in the range of 1:4 to 1:6. Furthermore, silicone oil having a boiling point of 250° C. or higher is added as a surfactant in the form of an emulsion, and 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 is a water glass-based binder formed from an alkali silicate aqueous solution represented by the general formula: xSiO ₂ .yM ₂ O.zH ₂ O (M is Li ⁺ , K ⁺ or Na ⁺ ). good too. In that case, it is preferable that a moisture absorbent is added to the inorganic binder. As the hygroscopic agent, specifically, a sodium-containing material can be used. The mass ratio of the sodium-containing material to the aqueous alkali silicate solution is preferably within the range of 1:4 to 1:6. If the mass ratio of the sodium-containing substance to the aqueous alkali silicate solution is within the range of 1:4 to 1:6, for example, the mass ratio of Na ₂ O to SiO ₂ in the aqueous alkali silicate solution (Na ₂ O/SiO ₂ ) is 2.5 or more and 3.5 or less (the solid content is 20% or more and 40% or less), it is possible to prevent the inorganic binder from prematurely curing. Further, it is preferable that a surfactant is added to the inorganic binder in order to suitably control the hygroscopicity. Specifically, it is preferable that silicone oil having a boiling point of 250° C. or higher is added as a surfactant in the form of an emulsion, and the silicone oil content in the emulsion is 8% or more and 10% or less of the mass of the binder. It is more preferable to have

According to an embodiment of the present invention, there is provided a method for reclaiming foundry sand in which the amount of adhering sand to a cast product is less likely to increase even when reclaimed foundry sand having an inorganic binder adhered to its surface is repeated.

1 Object to be treated (foundry sand)
10 Kiln 11 Rotating Body 11a Inlet 11b Outlet 12 Burner

Claims (9)

A method for regenerating foundry sand for reclaiming used foundry sand having an inorganic binder attached to the surface thereof, comprising:
A pulverizing step of pulverizing the sand mold used for casting to recover casting sand;
a water washing step of washing the foundry sand in water at a temperature of 80 ° C. or higher and 100° C. or lower after the pulverizing step while stirring;
a heat treatment step of heating the foundry sand to 550° C. or more and 900° C. or less after the water washing step;
A foundry sand reclaiming method comprising: 2. The method of regenerating foundry sand according to claim 1, wherein said heat treatment step is performed while moving said foundry sand. 3. The method of reclaiming foundry sand according to claim 1, further comprising a drying step of drying the foundry sand by heating it to 100[deg.] C. or more and 300[deg.] C. or less while stirring, between said water washing step and said heat treatment step. 4. The method of reclaiming foundry sand according to claim 3 , wherein said water washing step and said drying step are performed in the same facility. 4. The method of reclaiming foundry sand according to claim 3 , wherein said water washing step and said drying step are performed in different facilities. 6. The method of reclaiming foundry sand according to any one of claims 3 to 5 , further comprising a cooling step of cooling said foundry sand while ventilating between said drying step and said heat treatment step. 7. The method for reclaiming foundry sand according to any one of claims 1 to 6 , wherein the inorganic binder contains sodium silicate. 8. The method for regenerating molding sand according to claim 7 , wherein the sodium silicate is represented by the general formula: _{Na2O.nSiO2 (} where n is 0.5 or more and 4.0 or less). The inorganic binder is formed from an aqueous alkali silicate solution represented by the general formula: xSiO ₂ ·yM _{2 O ·zH 2 O} (M is Li ⁺ , K ⁺ or Na ⁺ ),
A sodium-containing material is added to the inorganic binder as a moisture absorbent so that the mass ratio of the sodium-containing material to the alkali silicate aqueous solution is in the range of 1:4 to 1:6,
Silicone oil having a boiling point of 250° C. or higher is added to the inorganic binder in the form of an emulsion as a surfactant, and the content of the silicone oil in the emulsion is 8% or more of the mass of the inorganic binder. % or less.

Images