JPS6015417B2 - Coated sand composition for light alloy casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coated sand whose surface is coated with a resin to be used as a casting mold, and particularly to a coated sand composition for light alloy casting.

For example, the cores used when casting products with complex internal structures, such as engine cylinder heads, must maintain sufficient strength to withstand the pressure of the hot metal during pouring, and be resistant to collapse after pouring. Must be in good condition.

Therefore, foundry sand called coated sand has conventionally been used as this type of core. This is made by coating the surface of foundry sand with a phenol resin or the like used as a sticky agent. However, although conventional coated sand shows relatively good disintegration properties when cast iron has a high mirroring temperature, it has poor disintegration properties when cast with metals with low rusting temperatures such as aluminum and aluminum alloys. It was not sufficient and had the disadvantage that it took time to remove sand after casting, especially to eject the core.

To address this situation, for example, there is an invention related to "shell mold mold material for casting light alloy" disclosed in Japanese Patent Application Laid-Open No. 57-149043. This is based on 100 parts by weight of foundry sand, 0.3 to 7 parts by weight of phenolic resin, and 0.001 to 7 parts by weight of Br-containing organic compound that splits Br or Br compounds by heating.
This method is characterized by coating the foundry sand with a composition consisting of 7 parts by weight, and has improved disintegration properties at low temperatures by adding a bromine-containing organic compound. However, in the mold material according to the present invention, the bromine-containing organic compound itself decomposes at low temperatures (300 to 40,000 ℃), and the decomposition products become sticky and deposit on the mold, so the shell core cannot be separated. There are disadvantages in that it makes molding difficult and the dimensions of the core set vary. A coated sand composition using zinc chloride as an additive has also been proposed, but this has the disadvantage that the chlorine in the additive has a strong oxidizing effect and tends to corrode the mold. The present invention addresses the above-mentioned conventional problems and uses a brominated inorganic compound such as zinc bromide as a disintegrant for coated sand.

The purpose of this is to realize a coated sand composition that has good disintegration properties at low temperatures and is suitable for use in light alloy castings without causing tar generation or corrosion of molds. That is, the coated sand composition according to the present invention contains 1 part of phenolic resin for every 10 parts of refractory particles such as silica sand.
~3 parts, and at least one kind of brominated inorganic compound such as zinc bromide is added and mixed in a ratio of 0.01 to 1.0 parts.

With such a composition, it is possible to obtain a coated sand that has good disintegrability at low temperatures and is suitable for light alloy castings, which does not cause mold formation or mold corrosion. It should be noted that if the amount of the brominated inorganic compound is less than 0.01 part, there is no effect of improving the disintegration property, and if it is more than 1.0 part, the strength will be greatly reduced, which is a practical problem. Preferably 0.05-0
．． There are 5 parts. Next, the present invention will be explained based on examples.

Example 1 In an experimental speed maller, 10k9*silica sand heated to 150°C was placed, and 2 kg of solid novolac type phenolic resin was added.
After adding 0.00 g of sand and kneading 4 top sand, hardened water consisting of 30 g of hexamethylenetetramine and 150 g of water was added,
Thereafter, a disintegrant consisting of the following amounts of zinc bromide and 50 parts water was added.

After the lumps were loosened, 10 pieces of calcium stearate were added, and after the first acid, the mixture was divided into stripes and cooled to obtain coated sand. The coated sand thus obtained exhibited the properties listed in Table 1, depending on the zinc bromide additive.

As comparative examples, there are cases in which no additives are used (Comparative Example 1), cases in which 0.2% of bromine-containing organic compounds are added to silica sand (Comparative Examples 2 and 3), and cases in which 0.2% of bromine-containing inorganic compounds are added to silica sand.
．． The results for the cases where 2% was added (Comparative Examples 4 and 5) are shown at the same time.

Table 1 As a result, when zinc bromide was used, the disintegration properties were significantly improved, and there was no generation of large amounts of gunk, unlike when bromine-containing organic compounds were added, and mold molding was better than that of chlorine-containing inorganic compounds. It was found that the rust was slight.

In addition, each item in Table 1 was measured by the following test method or measurement method.

Fusion point: JACT test method C-1 Transverse rupture strength: Supporting both ends of a 1'4" x 1" x 2" test piece (fired between 6 tops of sand at a mold temperature of 250°C),
Value obtained by dividing the load when the test piece breaks by applying a load to its center by the cross-sectional area of the test piece Pend: JACT test method SM-3 Collapse property: Cylindrical mold A (700 ×70)
, Test core C (500 x 50) is set in lower mold B (150 x 20 circles set in the center of the flat plate), and 700q○ of aluminum D is poured into it.

After cooling for 30 minutes, the aluminum casting was taken out from the mold frame and hit with an air hammer at 3 kg' of air pressure through 9 inkstone sands, and the weight of the collapsed material that came out of the 150 holes was measured. It was calculated using the following formula.

(Weight of collapsible material/150) x 100 Amount of crab generated: Test piece 2 used in the above transverse rupture strength measurement
Wrap the aluminum foil in a single layer of aluminum foil of known weight, and add 700
The aluminum foil was placed in an electric furnace set at a temperature of 0.00, heated for 9 minutes, and left to cool.**The amount of tar adhering to the aluminum foil was weighed, and this was taken as the amount of tar generated.

Mold rust: After leaving the lower mold B of the above disintegration test in the air for 24 hours, the surface of the ordinary iron round birch (150) in the center was observed with a loupe with a magnification of 3M, and the degree of occurrence of bells was determined. saw.

Example As a result of adding a brominated inorganic compound other than zinc brobromide as a disintegrant, coated sand with the performance shown in Table 2 was obtained.

Here, the ratio of brominated inorganic compound to silica sand is 0.2
%, and the method for producing the coated sand and the method for measuring the effect are the same as in Example 1. In Table 2, the performance of coated sand using zinc bromide (0.2% of silica sand) as described in Example 1 is rewritten for comparison. . Table 2 As a result, it was found that calcium bromide, like zinc bromide, had excellent disintegration properties, and also produced less gunk and rust.

However, compared to zinc bromide or calcium bromide,
It was found that rust occurred frequently when ammonium bromide and aluminum bromide were used, and that disintegration was low when potassium bromide and sodium bromide were used. As described above, according to the present invention, the coated sand composition has good disintegration properties at low temperatures, and has little generation of mold and metal corrosion, and is therefore optimal for use in light alloy castings such as engine cylinder heads. is obtained.

[Brief explanation of drawings]

The drawing is a schematic diagram of the apparatus used to confirm collapsibility.

Claims (1)

[Claims] 1. 1 to 3 parts by weight of a phenol resin and 0.01 to 1.0 parts by weight of a brominated inorganic compound per 100 parts by weight of refractory particles such as silica sand.
A coated sand composition for light alloy casting, characterized in that it is mixed in a proportion of 0 parts by weight. 2. The coated sand composition for light alloy casting according to claim 1, wherein the brominated inorganic compound is zinc bromide.