Inorganic coated sand

Abstract

This invention provides a method for producing inorganic coated sand that suppresses variations in the strength of inorganic cores. [Solution] A dry inorganic coated sand, wherein foundry sand is coated with sodium silicate, and then an additive is added and coated with a binder mixture of sodium silicate and caustic soda.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing inorganic-coated sand.

Background Art

[0002] Conventionally, various methods for manufacturing inorganic-coated sand have been proposed. For example, a manufacturing method is disclosed in which foundry sand and the metasilicate hydrate are mixed at a temperature equal to or higher than the melting point of the metasilicate hydrate. (See, for example, Japanese Patent No. 7372766).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] Inorganic cores generate less gas during pouring than organic cores, so they have fewer gas defects and no strange odors, making the working environment good and attracting attention in recent years. However, especially when using recycled sand, the strength of inorganic cores may vary greatly, and a simpler method for stabilizing the strength is required to solve this problem.

[0005] That is, an object of the present invention is to provide a method for manufacturing inorganic-coated sand that suppresses variations in the strength of inorganic cores. Means for Solving the Problems

[0006] This is achieved by a method for manufacturing inorganic-coated sand in which foundry sand is coated with sodium silicate, and then an additive is added and a binder obtained by mixing sodium silicate and caustic soda is coated. Effects of the Invention

[0007] According to the present invention, particularly in the case of silica sand and recycled sand, the surface condition of the sand differs slightly from one sand to another, which causes variations in the strength of inorganic cores made using these materials. However, by coating the foundry sand with sodium silicate in the initial operation, the sand surface is kept in a constant state, making it possible to suppress variations in the strength of inorganic cores. [Modes for carrying out the invention]

[0008] The embodiments of the present invention will be described in detail below. The following description of preferred embodiments is essentially illustrative and is not intended to limit the present invention, its applications, or its uses.

[0009] (Embodiment) In this embodiment, inorganic coated sand is prepared by coating recycled silica sand with sodium silicate, then adding additives and coating it with a binder mixture of sodium silicate and caustic soda. Test specimens are then prepared using this inorganic coated sand, and their flexural strength is measured.

[0010] For foundry sand, silica sand or artificial sand can be used. Examples include flatteny sand and mullite sand.

[0011] For sodium silicate, a molar ratio in the range of 1.6 to 4.5 can be used.

[0012] As additives, those selected from the group consisting of metakaolin, magnesium hydroxide, calcium hydroxide, magnesium oxide, aluminum oxide, and spinel can be used. These additives can also be used by adding them to the binder. [Examples]

[0013] In this example, recycled silica sand was used as the foundry sand. Sodium silicate RC with a molar ratio of 2.1 was used. 48% caustic soda was used. Metakaolin was used as an additive. 0.5 parts of sodium silicate RC was added to 100 parts of the above foundry sand and kneaded to coat the entire sand with sodium silicate RC. Next, 1.0 part of metakaolin was added and kneaded, and then 7 parts of a binder mixture of sodium silicate RC and 48% caustic soda were added and kneaded for 10 minutes to obtain dry inorganic coated sand. Using this inorganic coated sand, a test specimen of 22.4 mm × 22.4 mm × 180 mm was prepared and its flexural strength was measured. [Examples]

[0014] Three lots of recycled silica sand from different recycling dates were prepared, designated as Recycled Sand 1, Recycled Sand 2, and Recycled Sand 3. 0.5 parts of sodium silicate RC were coated onto 100 parts of each recycled sand, followed by the addition and mixing of 1.0 part of metakaolin. Then, 7.0 parts of a binder mixture of sodium silicate RC and 48% caustic soda were added and mixed for 10 minutes to obtain dry inorganic coated sand. These inorganic coated sands were blown into a mold heated to 250°C and heated for 90 seconds to obtain 22.4 mm × 22.4 mm × 180 mm test specimens for flexural strength, and the flexural strength of each test specimen was measured.

[0015] (Comparative Example 1) The same recycled sand as in Example 1 was used, and the same procedures and measurements were performed as in Example 1, except that the initial step of coating the recycled sand with 0.5 parts sodium silicate RC was omitted.

[0016] (Evaluation method) 1.Folding strength The flexural strength was measured using the test specimens prepared in Example 1 and Comparative Example 1. The test method used was the three-point bending test.

[0017] (evaluation) Table 1 shows the results for flexural strength in Example 1 and Comparative Example 1. [Table 1]

[0018] (comprehensive evaluation) In Example 1 of the present invention, the flexural strength was measured consistently without variation in all recycled sand, demonstrating that good results could be obtained using a simple method of coating foundry sand with sodium silicate.

Claims

1. A dry inorganic coated sand, wherein foundry sand is coated with sodium silicate, and then an additive is added and coated with a binder mixture of sodium silicate and caustic soda.

2. The method according to claim 1, characterized in that the additive is selected from the group consisting of metakaolin, magnesium hydroxide, calcium hydroxide, magnesium oxide, aluminum oxide, and spinel.

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