JPS5843169B2 - Resin coated sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to resin-coated sand, in which the surface of refractory particles is coated with two layers of vinyl resin and thermosetting resin in that order, thereby forming a shell mold with excellent disintegration properties after casting. This relates to resin-coated sand for legal use.

The shell molding method is a type of precision casting method invented in Germany during the Second War, and initially a mixture of sand and powdered resin was used as the molding material.

In this mixture, sand and resin have different specific gravity, so when the mixture is blown into the core box using compressed air, the two will separate and the resin concentration will increase abnormally, especially on the surface of the core that contacts the core box. Therefore, not only was it not easy to release the core from the core box, but gas defects often occurred in the cast product.

Resin-coated sand, in which the surface of sand particles is coated with resin, has these defects removed.

Resin-coated sand has fluidity comparable to or exceeding that of refractory particles before being coated with resin, and can be easily molded into hollow cores and thin shell molds or shell cores.

Shell molds and shell cores made of resin-coated sand are significantly stronger than shell molds and shell cores made of sand powder and resin mixtures, so the ratio of resin to sand added can be reduced by almost half by weight. be able to.

If a metal or alloy with a high melting point, such as copper alloy, cast iron, or steel, is cast into a shell mold or shell core made of resin-coated sand, the resin will thermally decompose and subsequently burn, causing the shell mold or shell core to It has excellent disintegration properties.

However, when casting low melting point metals or alloys such as aluminum alloys using shell molds or shell cores, the resin hardly thermally decomposes or burns, so the core has particularly poor collapsibility, resulting in problems such as 'sand firing'. It is common practice to heat products containing a core at around 500 DEG C. for several hours, which is a bottleneck in efforts to save labor and energy.

Various inventions have been made to improve the collapsibility of shell molds, especially shell cores, after casting when casting alloys with low melting points such as aluminum alloys.

For example, a method has been proposed in which inorganic salts such as potassium permanganate and potassium nitrate are added to resin-coated sand as combustion improvers, but since the combustion improvers are in powder form, the strength of the shell mold and shell core is reduced. However, the disintegration properties after casting have not been improved to the point where the sand baking process is abolished.

It is said that collapsibility can be improved by reducing the amount of resin coated on the refractory particles and conversely increasing the amount of hexamine added to the resin, but sand baking cannot be abolished even with this method.

The present inventors investigated various methods to improve the disintegration after casting when casting low melting point metals or alloys such as aluminum alloys using a shell core made of resin coated sand, and as a result, they were satisfied. We obtained a new resin-coated sand.

The object of the present invention is to have fluidity comparable to that of ordinary resin coated sand, have stronger strength after shell molding than ordinary shell molds made of resin coated sand, and have low melting point materials such as aluminum alloys. An object of the present invention is to provide resin-coated sand with excellent collapsibility after casting metal or alloy.

The resin-coated sand according to the present invention is characterized in that the surface of the refractory particles is first coated with a vinyl resin, and then further coated with a thermosetting resin.

Vinyl resins used in the present invention include polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals,
such as polystyrene.

The thermosetting resin used in the present invention is not particularly limited and may be any thermosetting resin commonly used in the production of resin coated sand.

The refractory particles used in the present invention are ordinary refractories for molds, such as silica sand, olivine sand, chromite sand, zircon sand, fused silica grains, and alumina grains.

The coating of the refractory particles with the vinyl resin can be carried out by a hot process, a semi-hot process, or a cold process, as in the case of ordinary resin-coated sand.

The coating amount of vinyl resin is 0.1 to 3.0% by weight,
Preferably it is 0.3 to 1.5%.

The reason why the lower limit of the coating amount is set to 0.1% by weight is that if the coating amount is less than this, no effect of improving the collapsibility after casting will be observed even if the coating is applied at all costs.

The reason for setting the upper limit of the coating amount to 3% by weight is that increasing the coating amount beyond this will not only increase the material cost and not improve the collapsibility commensurately, but also cause gas defects to occur in the cast product. Because you will see it.

The refractory particles whose surfaces are coated with a vinyl resin can be coated with a thermosetting resin by a hot process, a semi-hot process, or a cold process, as in the case of ordinary resin-coated sand.

The surface of the refractory particles is first coated with vinyl resin,
Molding of shell molds and shell cores using the resin-coated sand of the present invention, which is further coated with a thermosetting resin, can be carried out in exactly the same manner as when using ordinary resin-coated sand.

Shell molds and shell cores formed in this way, especially shell cores, are not easily disintegrated even when metals or alloys with low melting points such as aluminum alloys are cast, as the vinyl resin thermally decomposes and vaporizes. Very good.

Preferred embodiments will be described in detail below.

Example 1 The surface of 100 parts by weight of silica sand was coated with 1 part by weight of polyvinyl alcohol in a cold process, and after the solvent was completely evaporated, the surface was further coated with 2.5 parts by weight of phenol resin in a cold process. Then, the solvent was completely evaporated to produce resin coated sand.

A shell mold transverse rupture strength test piece (o 10 m 1 x 60 mm) was molded using the resin coated sand, and the test piece was placed in a gas mold as core 1. Aluminum alloy (AC2B) was then cast into the mold. A casting 2 shown in the figure was cast.

After the casting had cooled to room temperature, a core disintegration test was conducted using the method shown in FIG.

In other words, from the height of 450 mm from the casting, 3 to 9
The weight 3 was allowed to fall freely, the core sand was dropped by impact, and the degree of collapsibility was expressed by the number of times the weight 3 was dropped until the core sand was completely removed.

The method for producing the resin coated sand and the results obtained are shown in Table 1.

Example 2 In Example 1, the surface of 100 parts by weight of silica sand was coated with 1 part by weight of polyvinyl alcohol by a cold process, and after the solvent was completely evaporated, the surface was further coated with 2.5 parts by weight of phenol. Resin-coated sand was produced by coating with resin in a cold process and completely evaporating the solvent. In this Example 2, the second layer was coated with 1.5 parts by weight of phenol resin in a cold process, and the solvent was completely evaporated to produce resin coated sand.

A disintegration test was conducted on the resin coated sand in exactly the same manner as in Example 1.

The method of manufacturing the resin coated sand and the results obtained are shown in Table 2.

As mentioned above, in the resin coated sand of the present invention, the surface of the refractory particles is first uniformly coated with a vinyl resin with a low thermal decomposition temperature. The vinyl resin easily thermally decomposes even when in contact with other materials, giving it excellent disintegrability, facilitating post-processing after casting work, and providing industrial benefits such as the ability to obtain castings with beautiful casting surfaces. It's a huge amount.

[Brief explanation of the drawing]

FIG. 1 shows a cast test piece, and FIG. 2 shows a collapsibility test method.

Claims (1)

[Claims] 1. A resin-coated sand characterized in that the surface of refractory particles is first coated with a vinyl resin, and then further coated with a thermosetting resin.