Method for manufacturing core

Abstract

The invention relates to a method for manufacturing a core. This core manufacturing method is provided with: a step for mixing, at a prescribed ratio, dry reclaimed sand obtained by regenerating molding sand used in the manufacturing of a core by a dry method, wet reclaimed sand obtained by regenerating the molding sand by a wet method, and fresh sand; and a step for manufacturing a core from the mixed sand. The mixing ratio is that the dry reclaimed sand accounts for 49-95 wt%, the wet reclaimed sand accounts for 1-49 wt%, and the fresh sand accounts for 1-5 wt%.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a core Background Art

[0002] In Japanese Patent Application Laid-Open No. 2018-047493, when manufacturing a core, the CS core method using an inorganic substance such as sodium silicate as a binder is used.

[0003] In the CS core method, the molding sand used in the manufacture of the core is regenerated, and the sand obtained by regeneration (regenerated sand) is reused for the manufacture of other cores. There are a dry method and a wet method as methods for regenerating the molding sand. The dry method is a method of performing heat treatment on the molding sand used in the manufacture of the core and removing the sodium silicate component remaining on the surface of the molding sand by grinding such as vibration impact. For example, an example of the dry method is disclosed in Japanese Patent Application Laid-Open No. 2017-077566. On the other hand, the wet method is a method of removing sodium silicate from the molding sand by bringing the molding sand used in the manufacture of the core into contact with a solvent such as water.

[0004] Japanese Patent Application Laid-Open No. 2020-089909 discloses a method for measuring the flexural strength of a test piece of a manufactured core. Regarding Japanese Patent Application Laid-Open No. 2020-089909, it will be used for the description of the embodiments described later. Summary of the Invention

[0005] In the technologies of Japanese Patent Application Laid-Open No. 2018-047493, Japanese Patent Application Laid-Open No. 2017-077566, and Japanese Patent Application Laid-Open No. 2020-089909, the dry method is a method of physically applying impact and friction to scrape the sodium silicate on the sand surface. Therefore, the existing method originally has a limit in removing sodium silicate. If the force of grinding is excessively increased, cracks may sometimes occur in the sand body, resulting in a decrease in strength. There are limitations, and the removal efficiency of sodium silicate is insufficient. Therefore, residual binders accumulate in the regenerated sand due to repeated sand regeneration. For example, due to the accumulation of residual binders, the binder component absorbs moisture, and when manufacturing a core using the CS core method, a part of the component dissolves in the auxiliary material, causing defects such as foam hindrance and gas defects. In addition, due to the influence of the residual binder, the strength of the core increases or decreases.

[0006] On the other hand, the wet method is a method of removing sodium silicate by bringing the molding sand into contact with a solvent such as water. Therefore, almost all of the residual binders in the regenerated sand are removed, but the strength of the core manufactured using the regenerated sand is insufficient.

[0007] That is, in the technologies of Japanese Patent Application Laid-Open No. 2018-047493 and Japanese Patent Application Laid-Open No. 2017-077566, there is a problem that it is impossible to reduce the residual binders accumulated in the regenerated sand due to repeated sand regeneration, ensure the strength of the manufactured core, and improve the quality of the core.

[0008] In view of such problems, an object of the present invention is to provide a method for manufacturing a core that can reduce the residual binder accumulated in the recycled sand due to repeated sand recycling, and can ensure the strength of the manufactured core and improve the quality of the core.

[0009] The method for manufacturing a core of the present invention includes: a step of mixing dry recycled sand, wet recycled sand, and new sand at a prescribed ratio, wherein the dry recycled sand is sand obtained by dry recycling the sand used in the manufacture of the core, and the wet recycled sand is sand obtained by wet recycling the above-mentioned sand; and a step of manufacturing a core from the mixed sand, and the mixing ratio is such that the dry recycled sand is 49 to 95% by weight, the wet recycled sand is 1 to 49% by weight, and the new sand is 1 to 5% by weight.

[0010] In addition, in the method for manufacturing a core of the present invention, the mixing ratio is such that the dry recycled sand is 69 to 95% by weight, the wet recycled sand is 1 to 30% by weight, and the new sand is 1 to 5% by weight.

[0011] In addition, in the method for manufacturing a core of the present invention, the mixing ratio is such that the dry recycled sand is 79 to 95% by weight, the wet recycled sand is 1 to 20% by weight, and the new sand is 1 to 5% by weight.

[0012] According to the present invention, a method for manufacturing a core that can reduce the residual binder accumulated in the recycled sand due to repeated sand recycling, and can ensure the strength of the manufactured core and improve the quality of the core can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the drawings, wherein the same reference numerals denote the same elements.

[0014] Figure 1 is a flowchart showing an example of the method for manufacturing a core according to the first embodiment.

[0015] Figure 2 is a graph showing the test results of the flexural strength measurement of test pieces of cores manufactured at different mixing ratios by the method for manufacturing a core according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment

[0017] Use Figure 1 The method for manufacturing a core according to the first embodiment will be described.

[0018] Figure 1 is a flowchart showing an example of the method for manufacturing a core according to the first embodiment.

[0019] As Figure 1 shown, first, in S101, dry recycled sand, wet recycled sand, and new sand are mixed in a kneader at a specified ratio.

[0020] Dry recycled sand is sand obtained by dry-method recycling of the sand used in the manufacture of cores. In the dry recycled sand, the residual binder (residual sodium silicate) is greater than 0 wt% and 4 wt% or less. In addition, wet recycled sand is sand obtained by wet-method recycling of the sand used in the manufacture of cores. In the wet recycled sand, the residual binder is less than 1 wt%. In addition, new sand is not sand obtained by recycling the sand used in the manufacture of cores, but new sand, for example, sand mainly composed of alumina. New sand is sand mixed to fill the amount of sand lost in the following core manufacturing process.

[0021] The mixing ratio is preferably 49 - 95 wt% dry recycled sand, 1 - 49 wt% wet recycled sand, and 1 - 5 wt% new sand. In addition, the mixing ratio is more preferably 69 - 95 wt% dry recycled sand, 1 - 30 wt% wet recycled sand, and 1 - 5 wt% new sand. In addition, the mixing ratio is more preferably 79 - 95 wt% dry recycled sand, 1 - 20 wt% wet recycled sand, and 1 - 5 wt% new sand.

[0022] In addition, the above dry method is a method of removing the sodium silicate component remaining on the surface of the sand used in the manufacture of cores by heat-treating and grinding the sand. Specifically, the dry method is disclosed in JP-A-2017-077566. For example, in the dry method, the sand used in the manufacture of cores is crushed into granular bodies. The granular bodies are heated at a temperature of 300°C to 550°C. The heated granular bodies collide with each other, and sodium silicate peels off from the sand. Air is blown onto the mixture of the peeled-off sodium silicate and the sand, and the sand is separated and recovered from the mixture as dry recycled sand using the specific gravity difference between sodium silicate and the sand.

[0023] In addition, the above wet method is a method of removing sodium silicate from the sand by bringing dry recycled sand or the sand used in the manufacture of cores into contact with a solvent containing water. For example, in the wet method, first, mass-produced dry recycled sand with a residual binder of 1 - 4 wt% is prepared. 1500 g of this dry recycled sand and 2000 g of water are charged into an autoclave, and the sand is washed at 120°C for 5 minutes. After that, the washed sand (hereinafter referred to as washed sand) is dewatered. Then, 1500 g of the washed sand is rinsed with 2000 g of water and recovered as wet recycled sand.

[0024] Note that after S101, the sand obtained by mixing dry recycled sand, wet recycled sand, and new sand at a specified ratio can be stored in a tank. In addition, when the sand previously mixed is stored in the tank, S101 may not be performed in the method for manufacturing the present core.

[0025] Next, in S102, the mixed sand (hereinafter referred to as the mixed sand) is kneaded in a kneading kettle. In this kneading, 2 kg of the mixed sand, 0.65 AI% (active ingredient (Active ingredient)%) of sodium silicate, 0.03 AI% of a surfactant, and 3.2% by weight of water are added to the kneading kettle, and kneading is performed for 300 seconds.

[0026] Next, in S103, the kneaded mixed sand (hereinafter referred to as the kneaded sand) is filled into a mold. The filling into the mold is performed under the conditions of a pressing pressure of 0.35 MPa and a pressing time of 30 seconds. The mold temperature of the mold is set to 260 °C by an electric heater or the like.

[0027] Next, in S104, the kneaded sand filled into the mold is fired. The firing is performed under the conditions of a mold temperature of 260 °C and a firing time of 60 seconds in the mold.

[0028] Next, use Figure 2 The verification results of the appropriate mixing ratios of the dry recycled sand, wet recycled sand, and new sand in the method for manufacturing the core of the first embodiment will be described.

[0029] Figure 2 It is a graph showing the test results of the measurement of the flexural strength of the test pieces of the cores manufactured at different mixing ratios by the method for manufacturing the core of the first embodiment. The horizontal axis of the graph represents the mixing ratio of each test piece. The vertical axis of the graph represents the measurement results of the flexural strength [kgf / cm 2 of each test piece.

[0030] The mixing ratios of the respective test pieces are, starting from the left side of the figure, 100% by weight of new sand, 100% by weight of dry recycled sand, 100% by weight of wet recycled sand, 95% by weight of dry recycled sand and 5% by weight of new sand, 1% by weight of new sand and 1% by weight of wet recycled sand (98% by weight of dry recycled sand), 1% by weight of new sand and 4% by weight of wet recycled sand (95% by weight of dry recycled sand), 1% by weight of new sand and 6% by weight of wet recycled sand (93% by weight of dry recycled sand), 1% by weight of new sand and 12% by weight of wet recycled sand (87% by weight of dry recycled sand), 1% by weight of new sand and 20% by weight of wet recycled sand (79% by weight of dry recycled sand), 1% by weight of new sand and 30% by weight of wet recycled sand (69% by weight of dry recycled sand), and 1% by weight of new sand and 49% by weight of wet recycled sand (50% by weight of dry recycled sand). The mixed sand of 5% by weight of the above new sand and 95% by weight of dry recycled sand is also referred to as the current sand, which represents the recycled sand used in the manufacture of the currently used cores.

[0031] The test method for measuring the flexural strength was disclosed in Japanese Unexamined Patent Application Publication No. 2020-089909. Here, the flexural strength is a value representing the strength against bending. Regarding the flexural strength, each test piece was set on a mold flexural strength testing machine, and the measurement was performed using this mold flexural strength testing machine.

[0032] The evaluation of the flexural strength of each test piece is as follows. If the flexural strength is 20.0 to 50.0 [kgf / cm 2 , the test piece of the core is "good". If the flexural strength is further 31.0 [kgf / cm 2 or more, the test piece of the core is "excellent". When the flexural strength is further above the 95% line of the current sand ( Figure 2 shown by the single dotted line), the test piece of the core is "optimal". Regarding this threshold value, since it can be said that the flexural strengths are equivalent when the strength is ±5% based on 5% by weight of new sand and 95% by weight of dry recycled sand (current sand), the line of 95% when the flexural strength of the current sand is set to 100% is set.

[0033] For the test pieces of 1% by weight of new sand and 1% by weight of wet recycled sand, 1% by weight of new sand and 4% by weight of wet recycled sand, 1% by weight of new sand and 6% by weight of wet recycled sand, 1% by weight of new sand and 12% by weight of wet recycled sand, 1% by weight of new sand and 20% by weight of wet recycled sand, 1% by weight of new sand and 30% by weight of wet recycled sand, and 1% by weight of new sand and 49% by weight of wet recycled sand, the flexural strength is 20.0 to 50.0 [kgf / cm 2, so the evaluation of the flexural strength is "good". Therefore, it is verified that cores manufactured with a mixing ratio of 1% by weight of new sand and 1-49% by weight of wet recycled sand can be expected to have flexural strength.

[0034] In addition, for specimens of 1% by weight of new sand and 1% by weight of wet recycled sand, specimens of 1% by weight of new sand and 4% by weight of wet recycled sand, specimens of 1% by weight of new sand and 6% by weight of wet recycled sand, specimens of 1% by weight of new sand and 12% by weight of wet recycled sand, specimens of 1% by weight of new sand and 20% by weight of wet recycled sand, and specimens of 1% by weight of new sand and 30% by weight of wet recycled sand, the flexural strength is further 31.0 [kgf / cm 2 or more, so the evaluation of the flexural strength is "excellent". Therefore, it is verified that cores manufactured with a mixing ratio of 1% by weight of new sand and 1-30% by weight of wet recycled sand can be more expected to have flexural strength.

[0035] In addition, for specimens of 1% by weight of new sand and 1% by weight of wet recycled sand, specimens of 1% by weight of new sand and 4% by weight of wet recycled sand, specimens of 1% by weight of new sand and 6% by weight of wet recycled sand, specimens of 1% by weight of new sand and 12% by weight of wet recycled sand, and specimens of 1% by weight of new sand and 20% by weight of wet recycled sand, the flexural strength is further above the 95% by weight line of the current sand ( Figure 2 shown by the single dotted line), so the evaluation of the flexural strength is "optimal". Therefore, it is verified that cores manufactured with a mixing ratio of 1% by weight of new sand and 1-20% by weight of wet recycled sand can be more expected to have flexural strength.

[0036] As described above, in the method for manufacturing a core of the first embodiment, dry recycled sand, wet recycled sand, and new sand are mixed at a specified ratio, and a core is manufactured from the mixed sand. The mixing ratio is preferably 49-95% by weight of dry recycled sand, 1-49% by weight of wet recycled sand, and 1-5% by weight of new sand. In addition, the mixing ratio is more preferably 69-95% by weight of dry recycled sand, 1-30% by weight of wet recycled sand, and 1-5% by weight of new sand. In addition, the mixing ratio is more preferably 79-95% by weight of dry recycled sand, 1-20% by weight of wet recycled sand, and 1-5% by weight of new sand.

[0037] Here, when only dry recycled sand is used for manufacturing the core, residual binders accumulate in the recycled sand due to repeated sand recycling. On the other hand, when only wet recycled sand is used for manufacturing the core, almost all of the residual binders in the recycled sand are removed, but the strength of the core manufactured using this recycled sand is insufficient.

[0038] In the method for manufacturing a core of the first embodiment, dry recycled sand is mixed in addition to wet recycled sand, and the mixing ratio is set as described above, whereby the strength of the manufactured core can be ensured. Further, in this method for manufacturing a core, the residual binder accumulated in the recycled sand due to repeated sand recycling can be reduced (in other words, in repeated sand recycling, the amount of binder in the recycled sand can be made close to constant). Therefore, in this method for manufacturing a core, by reducing the residual binder accumulated in the recycled sand due to repeated sand recycling, the possibility of defects such as foaming hindrance and gas defects caused by the accumulation of the residual binder can be reduced. Further, the possibility of an increase or decrease in the strength of the core due to the influence of the residual binder can be reduced. Further, this method for manufacturing a core can improve the quality of the core. In this method for manufacturing a core, for example, wrinkles and clogging defects of the core are reduced, so that the surface of the rough material (e.g., engine) becomes beautiful. Further, the core can withstand the pressure of the aluminum melt, so that swelling defects of the rough material are reduced.

[0039] It should be noted that the present invention is not limited to the above embodiments and can be appropriately modified without departing from the gist.

Claims

1. A method for manufacturing a core, comprising: a step of mixing dry regenerated sand obtained by dry-regenerated sand used in manufacturing the core, wet regenerated sand obtained by wet-regenerated sand, and new sand at a predetermined ratio; and The step of manufacturing a core from the mixed sand, The mixing ratio is 49 to 95% by weight of the dry regenerated sand, 1 to 49% by weight of the wet regenerated sand, and 1 to 5% by weight of the new sand.

2. The method for manufacturing a core according to claim 1, wherein: The mixing ratio is 69 to 95% by weight of the dry regenerated sand, 1 to 30% by weight of the wet regenerated sand, and 1 to 5% by weight of the new sand.

3. The method for manufacturing a core according to claim 2, wherein: The mixing ratio is 79 to 95% by weight of the dry regenerated sand, 1 to 20% by weight of the wet regenerated sand, and 1 to 5% by weight of the new sand.

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