Methods for recycling foundry 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 reconditioning foundry sand. [Background Art]

[0002] Foundry sand mixed with a binder for bonding sand particles to each other is reconditioned after use. As a method for reconditioning foundry sand, there may be mentioned a dry reclamation method in which deposits such as binder adhered to the surface of foundry sand are mechanically removed by a grinding process that applies vibration, impact or the like to the foundry sand recovered after use. However, such a dry reclamation method may result in an insufficient removal rate of deposits such as binders. In addition, in such a dry reclamation method, when an attempt is made to increase the removal rate of deposits such as binders, there may occur a decrease in yield due to crushing and atomization of sand, and a decrease in strength of a mold molded using the reconditioned foundry sand.

[0003] In contrast, a wet reclamation method has been proposed to improve the removal efficiency of deposits such as binders. As an example of the wet reclamation method, Patent Document 1 discloses a method for reconditioning recovered foundry sand, which comprises bringing recovered foundry sand into contact with water heated to 100°C or higher, preferably 150°C to 550°C. [Prior Art Document] [Patent Document]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2002-178100 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] When regenerating foundry sand using a wet regeneration method, for example, washing the foundry sand with water at a low temperature of 100°C or below reduces the removal rate of binders and other adhering substances, requiring a longer washing time. On the other hand, the regeneration method described in Patent Document 1 improves the removal rate of binders and other adhering substances by washing the foundry sand with water at a high temperature exceeding 100°C, thus shortening the washing time. However, the regeneration method described in Patent Document 1 requires special equipment such as equipment to generate high-temperature water, a pressure-resistant sealed container, and pressurizing equipment, and has the problem of consuming a very large amount of energy. Therefore, there is a need for a method that can regenerate foundry sand simply and efficiently without using special equipment.

[0006] This disclosure was made to solve such problems and aims to provide a method for recycling foundry sand that can improve the removal rate of binders and other adhering substances without using special equipment, thereby improving the quality of the casting and the strength of the mold. [Means for solving the problem]

[0007] A method for recycling foundry sand according to one embodiment includes a first washing step in which the recovered foundry sand is brought into contact with an aqueous solution containing 1% by mass or more of a binder. [Effects of the Invention]

[0008] This disclosure provides a method for recycling foundry sand that can improve the removal rate of binders and other adhering substances without using special equipment, thereby improving casting quality and mold strength. [Brief explanation of the drawing]

[0009] [Figure 1] This is a flowchart showing the method for recycling foundry sand according to Embodiment 1. [Figure 2] This graph shows the relationship between the temperature of the cleaning solution and the amount of binder remaining. [Figure 3] This graph shows the relationship between washing time and the amount of binder remaining. [Figure 4]This graph shows the relationship between the regeneration method and the amount of binder remaining. [Modes for carrying out the invention]

[0010] Embodiment 1 Embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to the embodiments described below. Also, for clarity, the following description and drawings have been simplified as appropriate.

[0011] Referring to Figure 1, the method for regenerating foundry sand according to Embodiment 1 (hereinafter also simply referred to as the "regeneration method") will be described. Figure 1 is a flowchart of the method for regenerating foundry sand according to Embodiment 1. As shown in Figure 1, the regeneration method according to this embodiment includes a first washing step of contacting the recovered foundry sand with an aqueous solution containing 1% by mass or more of a binder.

[0012] The first washing step removes binders and other deposits adhering to the surface of the recovered foundry sand, resulting in recycled foundry sand. This recycled foundry sand is foundry sand recycled by the recycling method according to this embodiment. The recycled foundry sand is reused as foundry sand when manufacturing molds.

[0013] The recovered foundry sand (hereinafter also referred to as recovered foundry sand) is, for example, recovered or surplus sand obtained by crushing (demolition) a mold that was formed using foundry sand and a water-soluble binder. The surface of the recovered foundry sand has the binder used adhering to it.

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

[0015] In the first washing step, the recovered foundry sand is washed with an aqueous solution. The aqueous solution is prepared by dissolving a binder of the same type as the binder attached to the foundry sand in water. The concentration of the aqueous solution is 1% by mass or more, 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 contacting the recovered foundry sand with an aqueous solution containing 1% by mass or more of a binder, the binder adhering to the recovered foundry sand easily dissolves in the aqueous solution and is effectively removed from the recovered foundry sand. Therefore, according to this embodiment, it is possible to provide a method for regenerating foundry sand that can improve the removal rate of adhering substances such as binders without using special equipment, thereby improving the quality of the casting and the strength of the mold.

[0017] In the first cleaning step, the method for bringing the recovered foundry sand into contact with the aqueous solution can be one in which the recovered foundry sand is immersed in the aqueous solution placed in a cleaning tank. By using the method of immersing the recovered foundry sand in the aqueous solution in combination with physical forces such as ultrasound, liquid jets, and oscillations, a high cleaning effect can be obtained, thereby increasing the removal rate of adhering substances such as binders. The method for bringing the recovered foundry sand into contact with the aqueous solution is not limited to the method of immersing the recovered foundry sand in the aqueous solution as described above. The method for bringing the recovered foundry sand into contact with the aqueous solution can also be one in which the aqueous solution is applied to the recovered foundry sand by showering, spraying, etc.

[0018] Furthermore, the temperature of the aqueous solution may be 100°C or lower. When the aqueous solution is within such a temperature range, no special equipment such as facilities for generating high-temperature aqueous solution, pressure-tight sealed containers, or pressurization equipment is required, so that costs can be reduced and energy consumption can also be suppressed. Here, Figure 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 Figure 2 illustrates the relationship between the temperature of the cleaning liquid and the residual amount of the binder when reclaimed foundry sand is regenerated by bringing the recovered foundry sand into contact with a cleaning liquid having a temperature ranging from normal temperature to 120°C. In the graph shown in Figure 2, the horizontal axis represents the temperature (°C) of the cleaning liquid, and the vertical axis represents the residual amount (%) of the binder. The cleaning liquid is an aqueous solution containing 1% by mass of the binder or water containing no 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 into a solution obtained by immersing the foundry sand in a solution capable of dissolving the binder (for example, an acid).

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

[0020] Furthermore, the time for bringing the recovered foundry sand into contact with the aqueous solution (cleaning time) may be 1 to 10 minutes. Setting the cleaning time to 1 to 10 minutes can shorten the time required for regenerating the foundry sand and efficiently remove deposits such as binders adhering to the recovered foundry sand.

[0021] Here, Figure 3 is a graph showing the relationship between cleaning time and the residual amount of binder. The graph shown in Figure 3 illustrates the relationship between cleaning time and the residual amount of binder when reclaimed foundry sand is produced by bringing recovered foundry sand into contact with a cleaning solution at 120°C for 0 to 30 minutes. In the graph shown in Figure 3, the horizontal axis represents cleaning time (min.), and the vertical axis represents the residual amount of binder (%). The cleaning solution is water.

[0022] Figure 3 shows that when the cleaning time is "no cleaning", the residual binder content of the unrecovered foundry sand that has not been brought into contact with the cleaning solution before regeneration is 1.882 mass%. Figure 3 also shows that when the cleaning time is 0 minute, the residual binder content of the reclaimed foundry sand obtained after instantaneously bringing the recovered foundry sand into contact with the cleaning solution is 1.653 mass%. As shown in Figure 3, when the cleaning time is up to 10 minutes, the longer the cleaning time, the lower the residual amount of binder remaining in the reclaimed foundry sand. When the cleaning time is 10 minutes, the residual amount of binder decreases to 0.500 mass%. Furthermore, when the cleaning time exceeds 10 minutes and reaches 30 minutes, the residual amount of binder remaining in the reclaimed foundry sand is 0.867 mass%, which is increased compared with the case where the cleaning time is 10 minutes.

[0023] The regeneration method according to the present embodiment may optionally include a second cleaning step of bringing rinse water into contact with the foundry sand obtained after the first cleaning step. Through the second cleaning step, reclaimed foundry sand is obtained, in which deposits such as binder adhering to the surface of the foundry sand cleaned in the first cleaning step (hereinafter also referred to as cleaned foundry sand) are removed.

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

[0025] In the second cleaning step, the method for bringing the cleaning sand into contact with the cleaning sand is to immerse the cleaning sand in rinsing water placed in a rinsing tank. By using the method of immersing the cleaning sand in rinsing water in combination with physical forces such as ultrasound, liquid jets, and oscillations, a high rinsing effect can be obtained, thereby increasing the removal rate of adhering substances such as binders. The method of bringing the cleaning sand into contact with the rinsing water is not limited to the method of immersing the cleaning sand in rinsing water as described above. Alternatively, the rinsing water may be applied to the cleaning sand by a shower, spray, or the like.

[0026] Here, Figure 4 is a graph showing the relationship between the regeneration method and the amount of binder remaining. In the graph shown in Figure 4, the horizontal axis represents the temperature of the aqueous solution (°C), and the vertical axis represents the amount of binder remaining (%). In the graph shown in Figure 4, "No Rinse" shows the relationship between the temperature of the aqueous solution and the amount of binder remaining when the foundry sand is regenerated by contacting the recovered foundry sand with an aqueous solution at a temperature of room temperature to 120°C. In other words, "No Rinse" shows the relationship between the temperature of the aqueous solution and the amount of binder remaining when the second washing step is omitted and only the first washing step is performed. In the graph shown in Figure 4, "With Rinse" shows the relationship between the temperature of the aqueous solution and the amount of binder remaining when the foundry sand is regenerated by contacting the washed foundry sand with rinse water at room temperature. In other words, "With Rinse" shows the relationship between the temperature of the aqueous solution and the amount of binder remaining when the second washing step is performed after the first washing step.

[0027] As shown in Figure 4, in a regeneration method that includes a first washing step, the foundry sand washed with an aqueous solution at room temperature to 120°C (washed foundry sand) has a binder residue of 0.70 to 1.45 mass%. On the other hand, in a regeneration method that includes a second washing step after the first washing step, the foundry sand rinsed with rinse water at room temperature after the first washing step (regenerated foundry sand) has a binder residue of 0.22 to 0.72 mass%. Therefore, the second washing step can further improve the removal rate of binders and other adhering substances, thereby further improving the casting quality and mold strength.

[0028] The rinse water temperature may be 100°C or lower. Because the rinse water is within this temperature range, it does not require special equipment such as equipment to generate high-temperature rinse water, pressure-resistant sealed containers, or pressurizing equipment, thus reducing costs and energy consumption. From the viewpoint of improving the removal rate of binders and other deposits, the rinse water temperature is preferably between 5 and 90°C.

[0029] Furthermore, the regeneration method according to this embodiment may include a moisture removal step after the first or second washing step to remove moisture from the regenerated foundry sand. For example, separation means such as filtration or centrifugal separation can be used to remove moisture from the regenerated foundry sand. Furthermore, the regeneration method according to this embodiment may include a drying step after the first or second washing step to dry the regenerated foundry sand. For example, drying means such as natural drying or heat drying can be used to dry the regenerated foundry sand.

[0030] The regeneration method according to this embodiment allows for the simple and efficient regeneration of foundry sand without the need for special equipment, compared to methods that use water at temperatures exceeding 100°C. Furthermore, the foundry sand regenerated by this embodiment can provide castings with superior casting quality and molds with superior mold strength.

[0031] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its spirit.

Claims

1. The process includes a first washing step in which the recovered foundry sand is brought into contact with an aqueous solution containing 1% by mass or more of a binder. A method for regenerating foundry sand, wherein the time for which the foundry sand is in contact with the aqueous solution is 1 to 10 minutes.

2. The method for regenerating foundry sand according to claim 1, wherein the temperature of the aqueous solution is 100°C or less.

3. A method for regenerating foundry sand according to claim 1, further comprising a second washing step of bringing the foundry sand obtained after the first washing step into contact with water.

4. The method for regenerating foundry sand according to claim 3, wherein the temperature of the water is 100°C or less.

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