JPS6057424B2 - Manufacturing method of microwave heat-curable foundry sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing foundry sand used when molding molds using microwaves.

The applicant first irradiates the mold material with microwaves,
We are proposing a method of forming molds using self-heating of the mold material.

The microwave heat-curable foundry sand used in this mold making method requires a dielectric material that absorbs microwaves and generates heat, and molding sand made by coating the sand grain surface with a dielectric material such as graphite and a resin binder is used. This has already been proposed by the applicant. Conventionally, the method for manufacturing such microwave heat-curable foundry sand has been to coat the surface of the sand grains with an organic resin in advance, then heat the resin to 350 to 450°C to carbonize the resin, and then scrub the sand grains. The surface is coated with a dielectric material layer made of carbide,
After the sand has been pretreated in this manner, the sand is further coated with a thermosetting resin by a general shell coating method (dry mix coat, cold coat, semi-hot coat, dry hot coat), etc.

That is, the above conventional method consists of a first process of carbide coating (including a scrubbing process) and a second process of thermosetting resin coating. Foundry sand coated with a curable resin is obtained. However, the conventional method described above requires a large number of steps, which is disadvantageous in terms of energy saving and economic efficiency.Furthermore, the scrubbing process generates dust, which requires a separate dust collector and worsens the working environment. There were some issues that needed to be improved.

The present invention was made in view of the above circumstances, and its purpose is to uniformly apply a dielectric material and a resin binder to the surface of sand grains in a short time and in a single process without causing pollution problems such as dust. An object of the present invention is to provide a method for producing microwave heat-curable foundry sand that can be coated.

According to the research conducted by the present inventors, by adding a water-soluble graphite dispersion (liquid) after coating the sand grain surface with resin during the general shell coating method (dry hot coating method), sand grain surface The present invention was completed based on the discovery that microwave-heated 5-hardenable foundry sand coated with a resin binder and a dielectric material (graphite) uniformly and with sufficient strength can be obtained in a single process.

In other words, the method for producing foundry sand that can be hardened by microwave heating of the present invention involves sequentially adding resin and a water-soluble graphite dispersion to heated sand grains while mixing the sand, thereby applying resin and dielectric material to the surface of the sand grains. By using a water-soluble graphite dispersion (liquid) instead of the usual water cooling after resin coating in the dry hot coating method, dielectric material (graphite) can be added to the coating resin at the same time as cooling. It is something to do. To explain the method of the present invention in detail, a resin is added while mixing refractory sand grains heated to a high temperature (for example, about 150° C.).

The resin then melts and coats the surface of the sand grains. Next, after a predetermined period of time, water-soluble graphite dispersion (liquid)
When added, the graphite is mixed into the coating resin, the graphite becomes embedded in the resin coated on the surface of the sand grains, and is cooled at the same time. After that, it is air-cooled and mixed sand is stopped to obtain foundry sand. Note that the foundry sand after adding the water-soluble graphite dispersion is in the form of granules, and can be formed into granules by continuing to mix the sand or mechanically crushing it, but the coated resin and inducer substance may be peeled off. Therefore, it is preferable to accelerate the disintegration of the granular foundry sand by adding a lubricant such as calcium stearate as a disintegrant after air cooling. The sand mixing method and the blending ratio of each component vary depending on the type of sand mixing machine (rotation speed, batch amount, etc.) and mold hardening speed, so it is only necessary to set appropriate conditions for use.

An example of the combination of each component is as follows. Silica sand (new sand) 100%. resin
3% hexamethylenetetramine 1.5%
/resin water 1.5%
Graphite dispersion (graphite solid content is 0.4%)
Sea urchin adjustment) Calcium stearate
As the appropriate amount of graphite dispersion, a liquid in which graphite is dispersed in a solvent such as water or alcohol can be used, but in the present invention, instead of cooling with water as usual in the dry hot coating method, the graphite dispersion is added at the same time. In order to also perform cooling 1,
Preferably, graphite is dispersed in water.

As such graphite dispersion water, there is, for example, Carhohite #407 manufactured by Nippon Graphite Industries Co., Ltd. (solid content 20.8%, moisture 79.2%, viscosity 0.35 Boaz, specific gravity 1.07). As the refractory sand grains, in addition to the above-mentioned silica sand, zircon sand, alumina sand, mullite, or even recycled sand recovered and recycled after casting can be used.

Although sand grains to which carbide is attached can also be used, the present invention is more effective with fresh sand. As a resin,
Various resins such as phenol resin and furan resin can be used.

However, the curing behavior of the resin differs slightly depending on the type of resin, for example, thermosetting and thermoplastic. For example, in the case of thermosetting, the addition of a resin coats the heated sand grain surface and begins to harden, while in the case of thermoplastic, the addition of a water-soluble graphite dispersion causes it to harden simultaneously with cooling. Start. Furthermore, depending on the type of resin, hexamethylenetetramine may be added as a curing accelerator as necessary when adding the water-soluble graphite dispersion.

As described above, the method for producing microwave heat-curable foundry sand of the present invention involves sequentially adding a resin and a water-soluble graphite dispersion to the surface of the sand grains while mixing the heated sand grains. Because it coats a dielectric material, there is no pre-process of carbide coating as in conventional methods.
Coating of resin and dielectric material can be done with one heating, which saves energy and reduces the number of man-hours, making it economical. Furthermore, since a water-soluble graphite dispersion is used as the carbide coating, less dust is generated, making the working environment much better than in conventional methods. Furthermore, with the method of the present invention, the surface of the sand grains can be uniformly coated with resin and dielectric material, and because the sand has good fluidity, blow molding (
Suitable for mechanical molding). Next, examples will be shown.

Example: Heat silica sand to 150°C, and mix it with sand for about 5 to 1
[Phase] Afterwards, phenolic resin is added at a rate of 3 parts per 10 parts of silica sand, and then 4 parts after the addition, 1.5 parts per 10 parts of silica sand is added to the resin.
% hexamethylenetetramine and silica sand per 10%.
5 parts of graphite water (manufactured by Nippon Graphite Industries, Carbohite #407
) and water (graphite solids content 0.4%) was added and then air cooled.

Claims (1)

[Claims] 1. Production of microwave heat-curable foundry sand characterized by coating the surface of sand grains with a resin and a dielectric substance by sequentially adding a resin and a water-soluble graphite dispersion while mixing heated sand grains. Law.