JPH0233464B2 - IMONOZUNASOSEIBUTSU - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a foundry sand composition used for manufacturing foundry casting molds, and in particular can easily destroy molds that are no longer needed after casting. The present invention relates to a foundry sand composition.

Prior Art When manufacturing molds for casting, a binder or binder whose main component is a thermosetting resin (for example, phenol resin, urea resin, furan-based binding resin, etc.) is added to the foundry sand as the material. It is common to use a mixture of glue and a binder whose main component is polyvinyl alcohol. This is to impart moldability to the foundry sand and to facilitate the destruction of the mold after casting in order to take out the cast product from the mold. A mold made by mixing foundry sand with the organic binder described above is used for castings with high casting temperatures, such as cast iron castings (1300
When applied to production at temperatures up to 1400°C), the organic binder is completely thermally decomposed and the mechanical strength of the mold is significantly reduced. As a result, the mold can be easily destroyed with a small external force. However, when applied to the manufacture of castings where the casting temperature is relatively low (650 to 750°C), such as aluminum casting, the outer mold of the mold can be destroyed by vibration or other relatively small external forces. However, the core cannot be easily destroyed. This is because oxygen is not supplied to the core because it is surrounded by molten metal, and the organic binder is not sufficiently decomposed and carbonized, resulting in insufficient reduction in the mechanical strength of the core. For this reason, it is usually 400 to 500℃.
An extra step was required to reduce the mechanical strength of the core by performing so-called sand firing for 4 to 10 hours at a temperature of .

For these reasons, various attempts have been made to create cores that are easily broken after casting. For example, a method that uses potassium nitrate or sodium nitrate in combination with a phenolic resin binder and thermally decomposes these substances at the casting temperature to generate oxygen to help the combustion of the phenolic resin, and a method that uses modified phenolic resin instead of phenolic resin. or the Ashyland method using isocyanate. However, none of these methods achieves sufficient effects and has not yet been put into practical use.

Furthermore, there is also a method of using an inorganic substance such as water glass or hydraulic cement instead of the above-mentioned organic binder. Such inorganic binders have the advantage of not emitting bad odor or toxic gas during casting operations, but have the disadvantage that they are less likely to destroy the mold after casting.

OBJECT OF THE INVENTION Accordingly, an object of the present invention is to provide a mold for casting a cast product, particularly a foundry sand with improved breakability of the core.

Composition of the Invention As a result of extensive research in line with the above objectives, the present inventor has discovered that the present inventors have developed a composition comprising 1.0 to 30.0 weight percent of an inorganic destructive agent mixed with foundry sand. The present invention was completed based on the discovery that molds made using various binders can be easily destroyed by immersing them in water or spraying them with water after casting.

In the present invention, the inorganic destructive agent refers to the formation and growth of hydrate crystals associated with hydration reactions, resulting in
It refers to a chemical that contains as a main compound an inorganic compound that causes sufficient expansion pressure to cause the destruction of brittle materials such as concrete, and is already in practical use as a cement expansion agent in the field of cement concrete. . For the purposes of the present invention, (i) calcium sulfoaluminate (3CaO.
3Al ₂ O ₃ CaSO ₄ (hereinafter abbreviated as C ₃ A ₃ CaSo ₄ )
−Free lime−Free anhydrous gypsum system, (ii) Calcium aluminoferrite (4CaO・
Al ₂ O ₃・Fe ₂ O ₃・hereinafter abbreviated as C ₄ AF) - free lime - free magnesia system, (iii) Alizto (3CaO ・SiO ₂ with a small amount of Al ₂ O ₃ ,
Solid solution of Fe ₂ O ₃ , MgO, etc.) - Free lime -
Inorganic crushing agents of the free anhydrous gypsum type are preferably used.

If the mixing ratio of the inorganic destructive agent exceeds 30.0% by weight, the transverse rupture strength of the manufactured mold will decrease and there is a risk that the mold will break during handling or casting operations (normally, the transverse rupture strength of the mold is 30.0 kg/ ^cm2 ). ). Moreover, if it is less than 1.0 weight percent, a sufficient destructive effect cannot be obtained.

Examples Hereinafter, the present invention will be explained based on examples. Commercially available foundry sand used for manufacturing mold cores is mixed with an inorganic destructive agent whose particle size is adjusted (to match the particle size and particle size distribution with that of the foundry sand) (addition amount: 1.0, 10.0 , 20.0, 30.0%) to prepare various foundry sand compositions. For each 100 parts by weight of these compositions, 3 parts by weight of liquid phenolic resin was added to 80 parts by weight.
The composition was coated while heated to a temperature of 300°C or above, then packed into a mold with internal dimensions of 10 x 10 x 60 mm, and heated at 300°C.
It was kept in an electric furnace kept at a temperature of 3 minutes to harden it. At the same time, for comparison, molding sand containing no inorganic destructive agent was molded and hardened using the same method.

The test piece obtained by demolding is immersed in water for a predetermined period of time, then taken out, placed in a 4-mesh sieve of a rotorp type sieving machine used in the particle size testing method specified in JIS-Z-2602, and placed in a saucer underneath. The sample was screened for 5 minutes, and the amount of disintegration of the test piece at this time was measured. The results of this test are shown in Figures 1A-C and 2A-C. In these figures, Figure 1 relates to data for foundry sand with sample code X-1, which will be described later, Figure 2 relates to data on molding sand with sample code Data for times 2 hours, 5 hours and 21 hours are presented. Further, the "amount of collapse" in the figure is expressed as the ratio (weight percent) of the fallen objects to the receiving tray with respect to the weight of the test piece.

[Foundry sand]

(a) Sample code X-1: Nippon Steel Corporation J-30 coated sand (b) Sample code X-2: Tochiyu Co., Ltd. RP-20N-
Coated sand [Inorganic destructive agent] (a) Sample code S-1: C ₃ A ₃ CaSO ₄ 40%,
_CaSO4 30%, CaO30%, fineness Blaine value 1050
cm ² /g (b) Sample code S-2: CaO90%, C ₄ AF7%,
MgO1%, _C3S2 %, fineness Blaine value ^1050cm2 /
g (c) Sample code S-3: CaO90%, C ₄ AF7%,
MgO1%, _C3S2 %, fineness Blaine value ^1250cm2 /
g (d) Sample code S-4: CaO90%, C ₄ AF7%,
MgO1%, _C3S2 %, fineness Blaine value ^1550cm2 /
g (E) Sample code S-5: CaO60%, _C3S30 %,
CaSO ₄ 10%, Blaine fineness value 1550 cm ² /g Effects of the Invention From the graphs in Figures 1 and 2, it can be seen that the mold made from the foundry sand composition according to the present invention can resist a small external force by simply immersing it in water. It turns out that it can be easily destroyed.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs showing the relationship between the content of an inorganic destructive agent in a foundry sand composition and the amount of disintegration when a molded article made from this composition is treated in water.

Claims (1)

[Claims] 1. A foundry sand composition comprising foundry sand mixed with 1.0 to 30.0% by weight of an inorganic destructive agent. 2. The foundry sand composition according to claim 1, wherein the inorganic destructive agent comprises calcium sulfoaluminate, free lime, and free anhydrous plaster. 3. The foundry sand composition according to claim 1, wherein the inorganic destructive agent comprises calcium aluminoferrite, free lime, and free magnesia. 4. The foundry sand composition according to claim 1, wherein the inorganic destructive agent comprises Aritz, free lime, and free anhydrous gypsum.