Method for recycling casting sand

Abstract

To provide a method for recycling casting sand, capable of improving casting quality and mold strength by increasing a removal rate of adhesion materials such as binder, without using a special apparatus.SOLUTION: A method for recycling casting sand has a first washing step of bringing recovered casting sand into contact with an aqueous solution containing 1 mass% or more of binder. A temperature of the aqueous solution can be 100°C or lower. The time to bring the casting sand into contact with the aqueous solution can be from 1 to 10 minutes. The method of recycling the casting sand may have a second washing step of bringing water into contact with the casting sand obtained after the first washing step. A temperature of the water can be 100°C or lower.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for recycling foundry sand.

Background Art

[0002] Foundry sand mixed with a binder for sticking sand together is recycled after use. As a method for recycling foundry sand, a dry recycling method is exemplified in which an abrasive treatment such as vibration or impact is applied to the used foundry sand to mechanically remove deposits such as binders adhering to the surface of the foundry sand. However, in such a dry recycling method, the removal rate of deposits such as binders may be insufficient. Further, in such a dry recycling method, when trying to increase the removal rate of deposits such as binders, a decrease in yield due to crushing or granulation of sand may occur, or a decrease in the strength of a mold formed using the recycled foundry sand may occur.

[0003] On the other hand, in order to improve the removal efficiency of deposits such as binders, a wet recycling method has been proposed. As an example of the wet recycling method, Patent Document 1 discloses a method for recycling recovered foundry sand by bringing the recovered foundry sand into contact with water heated to 100°C or higher, preferably 150°C to 550°C.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When regenerating foundry sand by a wet regeneration method, if the foundry sand is washed with water at a low temperature of 100°C or lower, for example, the removal rate of deposits such as binders decreases, so it is necessary to extend the washing time. On the other hand, in the regeneration method described in Patent Document 1, by washing the foundry sand with water at a high temperature exceeding 100°C, the removal rate of deposits such as binders is improved, so the washing time can be shortened. However, in the regeneration method described in Patent Document 1, there is a problem that special equipment such as equipment for generating high-temperature water, pressure-resistant closed containers, and equipment for pressurizing is required, and the energy consumption is also very large. Therefore, there is a need for a method that can regenerate foundry sand simply and efficiently without using special equipment.

[0006] The present disclosure has been made to solve such problems, and an object thereof is to provide a method for regenerating foundry sand that can increase the removal rate of deposits such as binders without using special equipment and improve the quality of castings and the strength of molds.

Means for Solving the Problems

[0007] The method for regenerating foundry sand according to an embodiment includes a first washing step of bringing an aqueous solution containing 1% by mass or more of a binder into contact with the recovered foundry sand.

Effects of the Invention

[0008] According to the present disclosure, it is possible to provide a method for regenerating foundry sand that can increase the removal rate of deposits such as binders without using special equipment and improve the quality of castings and the strength of molds.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] Embodiment 1 Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate.

[0011] Referring to FIG. 1, a method for regenerating foundry sand according to Embodiment 1 (hereinafter, also simply referred to as “regeneration method”) will be described. FIG. 1 is a flowchart showing the method for regenerating foundry sand according to Embodiment 1. As shown in FIG. 1, the regeneration method according to the present embodiment has a first washing step of bringing an aqueous solution containing 1% by mass or more of a binder into contact with the recovered foundry sand.

[0012] By the first washing step, regenerated foundry sand from which deposits such as the binder adhering to the surface of the recovered foundry sand have been removed is obtained. The regenerated foundry sand is foundry sand regenerated by the regeneration method according to the present embodiment. The regenerated foundry sand is reused as foundry sand when manufacturing a mold.

[0013] The recovered foundry sand (hereinafter, also referred to as recovered foundry sand) is, for example, recovered sand or surplus sand obtained by crushing (breaking the mold) a mold molded using foundry sand and a water-soluble binder. The used binder adheres to the surface of the recovered foundry sand.

[0014] Examples of the foundry sand include silica sand, zircon sand, chromite sand, synthetic mullite sand, etc. Examples of the binder include inorganic binders such as water glass. The binder may contain additives such as solid metal oxides, salts, carbohydrates, surfactants, coupling agents, lubricants, mold release agents, etc. as necessary.

[0015] In the first washing step, the recovered casting sand is washed with an aqueous solution. The aqueous solution is prepared by dissolving a binder of the same type as the binder adhering to the casting sand in water. The concentration of the aqueous solution is 1% by mass or more, and preferably 1% by mass or more and 5% by mass or less. Here, the concentration of the aqueous solution is the mass ratio of the binder to water.

[0016] By bringing the recovered casting sand into contact with an aqueous solution containing 1% by mass or more of the binder, the binder adhering to the recovered casting sand is easily dissolved in the aqueous solution and effectively removed from the recovered casting sand. Therefore, according to the present embodiment, it is possible to provide a method for regenerating casting sand that can increase the removal rate of deposits such as binders without using special equipment and improve the quality of castings and the strength of molds.

[0017] In the first washing step, as the method of bringing the aqueous solution into contact with the recovered casting sand, a method of immersing the recovered casting sand in the aqueous solution placed in a washing tank can be adopted. In the method of immersing the recovered casting sand in the aqueous solution, a high washing effect can be obtained by using physical forces such as ultrasonic waves, in-liquid jets, and rocking in combination, so that the removal rate of deposits such as binders can be increased. The method of bringing the aqueous solution into contact with the recovered casting sand is not limited to the method of immersing the recovered casting sand in the aqueous solution as described above. As the method of bringing the aqueous solution into contact with the recovered casting sand, the aqueous solution may be applied to the recovered casting sand by a shower, a spray, or the like for contact.

[0018] Also, the temperature of the aqueous solution can be 100°C or lower. Since the aqueous solution is in such a temperature range, special equipment such as equipment for generating a high-temperature aqueous solution, a pressure-resistant sealed container, and equipment for pressurization are not required, so the cost can be reduced and the energy consumption can also be suppressed. Here, FIG. 2 is a graph showing the relationship between the temperature of the cleaning liquid and the residual amount of the binder. The graph shown in FIG. 2 shows the relationship between the temperature of the cleaning liquid and the residual amount of the binder when the recycled casting sand is regenerated by contacting it with a cleaning liquid having a temperature from normal temperature to 120°C. The horizontal axis of the graph shown in FIG. 2 indicates the temperature (°C) of the cleaning liquid, and the vertical axis indicates the residual amount (%) of the binder. The cleaning liquid is an aqueous solution containing 1% by mass of the binder or water not containing the binder. The residual amount of the binder is the ratio of the mass of the binder to the mass of the granular material. The residual amount of the binder can be determined from the amount of the binder eluted in the solution by immersing the casting sand in a solution (for example, an acid) capable of dissolving the binder.

[0019] As shown in FIG. 2, when water is used as the cleaning liquid, the casting sand cleaned with water having a temperature of 100°C or lower (normal temperature, 50°C, 70°C) has a residual amount of the binder of 0.28 to 0.93% by mass. The casting sand cleaned with water having a temperature of 100°C or higher (100°C, 120°C) has a residual amount of the binder of 0.13 to 0.18% by mass. When an aqueous solution is used as the cleaning liquid, the casting sand cleaned with an aqueous solution having a temperature of 100°C or higher (100°C, 120°C) has a residual amount of the binder of 0.22 to 0.37% by mass. And the casting sand cleaned with an aqueous solution having a temperature of 100°C or lower (normal temperature, 50°C, 70°C) has a residual amount of the binder of 0.23 to 0.72% by mass. Therefore, the present regeneration method using an aqueous solution as the cleaning liquid has a higher removal rate of the binder in the low-temperature region where the temperature is 100°C or lower compared to the method using water as the cleaning liquid.

[0020] Also, the time (cleaning time) for contacting the recycled casting sand with the aqueous solution can be 1 to 10 minutes. Since the cleaning time is 1 to 10 minutes, the time required for regenerating the casting sand can be shortened, and deposits such as the binder attached to the recycled casting sand can be efficiently removed.

[0021] Here, FIG. 3 is a graph showing the relationship between the cleaning time and the residual amount of the binder. The graph shown in FIG. 3 shows the relationship between the cleaning time and the residual amount of the binder when the recycled casting sand is regenerated by bringing it into contact with a cleaning liquid at a temperature of 120° C. for 0 to 30 minutes. The horizontal axis of the graph shown in FIG. 3 indicates the cleaning time (min.), and the vertical axis indicates the residual amount of the binder (%). The cleaning liquid is water.

[0022] FIG. 3 shows that when the cleaning time is "no cleaning", the residual amount of the binder in the recycled casting sand before regeneration that has not been brought into contact with the cleaning liquid is 1.882% by mass. Further, FIG. 3 shows that when the cleaning time is 0 minute, the residual amount of the binder in the regenerated casting sand obtained after instantaneously bringing the cleaning liquid into contact with the recycled casting sand is 1.653% by mass. As shown in FIG. 3, until the cleaning time reaches 10 minutes, the longer the cleaning time, the lower the residual amount of the binder remaining in the regenerated casting sand, and when the cleaning time is 10 minutes, the residual amount of the binder decreases to 0.500% by mass. Further, when the cleaning time exceeds 10 minutes and is 30 minutes, the residual amount of the binder remaining in the regenerated casting sand becomes 0.867% by mass, which is an increase compared to the case where the cleaning time is 10 minutes.

[0023] The regeneration method according to this embodiment may have a second cleaning step of bringing rinsing water into contact with the casting sand obtained after the first cleaning step. By the second cleaning step, a regenerated casting sand is obtained in which deposits such as the binder adhering to the surface of the casting sand (hereinafter also referred to as cleaned casting sand) cleaned in the first cleaning step are removed.

[0024] In the second cleaning step, the cleaned casting sand is rinsed with rinsing water. The rinsing water used in the second cleaning step is water that does not contain a binder. By bringing the rinsing water into contact with the cleaned casting sand, the binder remaining on the surface of the cleaned casting sand is removed from the cleaned casting sand.

[0025] In the second cleaning step, as the method of bringing the aqueous solution into contact with the cleaned foundry sand, a method of immersing the cleaned foundry sand in the rinse water placed in a rinse tank can be adopted. In the method of immersing the cleaned foundry sand in the rinse water, a high rinsing effect can be obtained by using physical forces such as ultrasonic waves, in-liquid jets, and rocking in combination, so that the removal rate of deposits such as binders can be increased. The method of bringing the rinse water into contact with the cleaned foundry sand is not limited to the method of immersing the cleaned foundry sand in the rinse water as described above. The method of bringing the rinse water into contact with the cleaned foundry sand may be to apply the rinse water to the cleaned foundry sand by means of a shower, a spray, etc. and bring them into contact.

[0026] Here, FIG. 4 is a graph showing the relationship between the regeneration method and the residual amount of the binder. The horizontal axis of the graph shown in FIG. 4 indicates the temperature (° C.) of the aqueous solution, and the vertical axis indicates the residual amount (%) of the binder. In the graph shown in FIG. 4, "without rinsing" shows the relationship between the temperature of the aqueous solution and the residual amount of the binder when the foundry sand is regenerated by bringing an aqueous solution with a temperature of normal temperature to 120° C. into contact with the recovered foundry sand. That is, "without rinsing" shows the relationship between the temperature of the aqueous solution and the residual amount of the binder when only the first cleaning step is carried out by omitting the second cleaning step. In the graph shown in FIG. 4, "with rinsing" shows the relationship between the temperature of the aqueous solution and the residual amount of the binder when the foundry sand is regenerated by bringing rinsing water with a temperature of normal temperature into contact with the cleaned foundry sand. That is, "with rinsing" shows the relationship between the temperature of the aqueous solution and the residual amount of the binder when the second cleaning step is carried out after the first cleaning step.

[0027] As shown in FIG. 4, in the case of a regeneration method having a first cleaning step, the foundry sand (cleaned foundry sand) cleaned with an aqueous solution having a temperature of normal temperature to 120° C. has a residual amount of the binder of 0.70 to 1.45% by mass. On the other hand, in the case of a regeneration method having a second cleaning step after the first cleaning step, the foundry sand (regenerated foundry sand) rinsed with rinsing water having a temperature of normal temperature after the first cleaning step has a residual amount of the binder of 0.22 to 0.72% by mass. Therefore, due to the second cleaning step, the removal rate of deposits such as binders can be further increased, so that the quality of the cast product and the mold strength can also be further improved.

[0028] The temperature of the rinse water can be 100°C or lower. Since the rinse water is in such a temperature range, special equipment such as equipment for generating high-temperature rinse water, pressure-resistant closed containers, and equipment for pressurizing is not required, so the cost can be reduced and the energy consumption can also be suppressed. From the viewpoint of increasing the removal rate of deposits such as binders, the temperature of the rinse water is preferably 5 to 90°C.

[0029] Furthermore, the regeneration method according to the present embodiment may have a water removal step of removing moisture from the regenerated casting sand after the first washing step or after the second washing step. As a method for removing moisture from the regenerated casting sand, for example, separation means such as filtration and centrifugation can be used. Furthermore, the regeneration method according to the present embodiment may have a drying step of drying the regenerated casting sand after the first washing step or after the second washing step. As means for drying the regenerated casting sand, for example, drying means such as natural drying and heat drying can be used.

[0030] According to the regeneration method according to the present embodiment, compared with a method of regenerating casting sand using water at a high temperature exceeding 100°C, the casting sand can be regenerated simply and efficiently without using special equipment. In addition, the casting sand regenerated by the regeneration method according to the present embodiment can provide a casting excellent in casting quality and a mold excellent in mold strength.

[0031] Note that the present disclosure is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist.

Claims

**Claim 1** A method for regenerating foundry sand, comprising a first washing step of bringing an aqueous solution containing 1% by mass or more of a binder into contact with the recovered foundry sand. **Claim 2** The method for regenerating foundry sand according to claim 1, wherein the temperature of the aqueous solution is 100°C or lower. **Claim 3** The method for regenerating foundry sand according to claim 1, wherein the time for bringing the aqueous solution into contact with the foundry sand is 1 to 10 minutes. **Claim 4** The method for regenerating foundry sand according to claim 1, further comprising a second washing step of bringing water into contact with the foundry sand obtained after the first washing step. **Claim 5** The method for regenerating foundry sand according to claim 4, wherein the temperature of the water is 100°C or lower.

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