JPS6146220B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to inorganic self-hardening molding sand using sodium silicate as a caking agent. Known methods for curing inorganic self-hardening molding sand include a reaction of added materials, or a method of curing using CO ₂ gas or the like. One type of inorganic self-hardening molding sand is exothermic self-hardening molding sand containing a heat-generating binder such as sodium silicate (water glass) and ferrosilicon (Fe-Si). This process involves mixing refractory particles such as silica sand with alloy powder containing metallic silicon and water glass appropriately diluted in water, and then producing sodium silicate through a chemical reaction accompanied by heat between caustic soda, which is a hydrolyzate of water glass, and silicon. A mold is formed by increasing the silicic acid content to firmly bond refractory particles. On the other hand, as a mold using CO ₂ gas, the required mold is formed from a mixture of refractory particles such as silica sand and sodium silicate added, and CO ₂ gas is blown into this to gel the silicic acid content in the sodium silicate. In some cases, sand particles are tightly bound together to form a mold. However, since the above two molding sands use sodium silicate as a binding agent, they have a disadvantage that the molding sand has poor disintegration properties after pouring molten metal compared to inorganic self-hardening molding sands. It is known to add graphite powder or resin powder to improve the collapsibility of molding sand, but this can only improve the collapsibility of the surface of the mold that comes into contact with the casting. It is also known to add expanded polystyrene to molding sand, but since it is not possible to make it into a powder and mix it uniformly with the molding sand, it is used in the form of blocks and placed in the mold during the molding process. Therefore, it cannot be used on the surface of the mold, and is used only inside the mold. As described above, in the conventional disintegration improving means, it is necessary to use different disintegration promoters for the mold surface and the mold inner surface. An object of the present invention is to provide an inorganic self-hardening molding sand that can improve the disintegration properties of the entire mold after pouring molten metal without using different disintegration promoters. The present invention improves the disintegration property after pouring the molten metal by adding a small amount of both wax-coated styrene powder and phenol resin powder to inorganic self-hardening molding sand. Next, examples of the present invention will be described. Example 1 Inorganic self-hardening molding sand was prepared using the blending ratios shown in Table 1. As the disintegration promoter, a mixture of wax-coated styrene foam powder and novolak phenol resin powder (30:70 weight ratio) was used. Mixed molding sand 300mm in length and width
The reactor was placed in a wooden frame with a height of 300 mm and a thermistor thermometer inserted into the center of the frame to check the reaction rate. The bonds are shown in Table 2. Also, with the same self-hardening molding sand, diameter 50mmφ, height
Prepare a 50 mm test piece, harden it, and measure the strength after a predetermined period of time, that is, 24 hours, and further
The residual coercive pressure was compared when heat treated at 1000℃. The results are shown in Figure 1. In the figure, a indicates conventional self-hardening molding sand (no additives), and b indicates the present invention (0.3 parts by weight added).

【table】

[Table] Example 2 Carbon dioxide molding sand was prepared with the blending ratio shown in Table 3. The same disintegration promoter as in Example 1 was used. Using this molding sand, a test piece with a diameter of 50 mmφ and a height of 50 mm was molded in the same manner as in Example 1, and CO ₂
It was hardened by blowing gas into it. The results are shown in Table 4. In addition, the strength of the cured test pieces after 24 hours and the residual pressure when further heat treated at 200 to 1000°C were compared. The results are shown in Figure 2. In the figure, a shows the conventional example (no additives), and b shows the one according to the present invention (0.3 parts by weight added).

【table】

[Table] From the above results, it was confirmed that the appropriate amount of the mixture of wax-coated polystyrene powder and phenol resin powder to be added is in the range of 0.1 to 0.5 parts by weight per 100 parts by weight of silica sand. Furthermore, as a result of a casting test using molten cast iron, compared to the conventional example, the ability to remove sand was significantly improved, and the collapsibility of the entire mold was improved, making it possible to reduce the number of work steps. Moreover, the cast surface of the cast product was also beautiful and the quality was improved.

[Brief explanation of the drawing]

1 and 2 are graphs showing the relationship between processing temperature and residual pressure of molding sand according to an embodiment of the present invention and conventional molding sand.

Claims (1)

[Claims] 1. Inorganic self-hardening molding sand characterized by adding wax-coated styrene foam powder and phenol resin powder to inorganic self-hardening molding sand using sodium silicate as a caking agent.