JPS5913937B2 - frozen mold - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a freezing mold that freezes water constituting the mold at a cold temperature in a casting mold, and fixes sand grains with the generated ice to harden the entire mold. Naturally, it is necessary to expose the mold to an atmosphere below the freezing point, and to obtain this atmosphere, liquid gas such as liquid nitrogen is usually used as a refrigerant.

The main components in the mold are foundry sand as aggregate and several percent water.

Considering the technology of casting, it is desirable that the moisture content be as small as possible, but from the viewpoint of mold strength after freezing, 2 to 4% is required.

According to the inventor's experiments, it is known that when the moisture content in the mold is 3%, the mold strength is 10 to 20 kg/ffl, which is considered to be an acceptable limit for a mold.

On the other hand, it is conventionally known to add a small amount of bentonite to the mold as an auxiliary additive in order to facilitate molding.

The added bentonite can be used as a binder to easily solidify the molding process in the same way as a normal green mold, and to obtain a frozen mold by exposing the mold to a refrigerant atmosphere after removing the frame. That's why.

As a result of detailed research into the behavior of bentonite in frozen molds, the present inventors have found that addition of bentonite in an amount of 2 to 6 percent causes shrinkage of the mold during freezing.

For example, add 3 parts of moisture and 2 to 6 parts of bentonite to 100 parts of sand, and add 50 mm according to the foundry sand test method.
φ×5011! Make a standard test piece of m, and
When cooled to 00°C, the diameter was 0.09 mm when 2 parts of bentonite was added, and 0.07 mm when 4 parts of bentonite was added.
mm.

It was revealed that when 6 parts of bentonite was added, there was a shrinkage deformation of 0.18 mrn.

When measuring in exactly the same way with 4 parts of water,
For each amount of bentonite added, 0.13 h,
A shrinkage of 0.123 m to 0.145 mm was observed.

As a result of intensive research into materials suitable as auxiliary additives that have the same purpose as bentonite, that is, caking action, and on the other hand exhibit small expansion and contraction deformations during freezing, the inventors discovered that they have the same chemical composition as foundry sand. It has been found that the addition of a certain ultrafine silica powder is suitable for such purposes.

That is, by adding several percent of silica (silicic acid) powder with a particle size of 1 μm or less, molding becomes extremely easy.

In other words, the silica fine powder is significantly thickened by a small amount of water.

A specific example is described below.

When 3 parts of water and 4.6 parts of fine silica powder were added to 100 parts of sand, the amount of deformation of a standard test piece during the cooling process was measured, and the results shown in Table 1 were obtained.

In Table 1, the negative sign for the amount of deformation (, m) means shrinkage, but it can be seen that the amount of deformation is very small compared to the case of bentonite described above.

Table 2 shows 4 parts of water and 2 parts of silica powder per 100 parts of sand.
This figure shows the results of measuring the amount of deformation of a standard test piece during the cooling process of a molded article to which 6 parts of 100% of the standard test piece was added.

As shown in the results in Table 2, even when the water content is 4 parts, it is known that the amount of deformation is very small compared to the case where bentonite is added.

As described above in the specific examples, it is clear that the dimensional accuracy of the frozen mold is improved by using fine silica powder as an auxiliary binder.

Silica that can be used for this purpose includes fine silica powder generated during the production of ferrosilicon or naturally amorphous silica powder as so-called soluble silicic acid powder.

Since the addition of these silica fine powders to the mold has exactly the same chemical composition as the foundry sand, it is clear that, unlike the case of adding bentonite, there is no change in the quality of the foundry sand, particularly the chemical composition, and this is advantageous.

Claims (1)

[Claims] 1. Freeze by adding 2 to 6 parts by weight of silica fine powder of 1 micron or less to the iron sand, which is the aggregate, to foundry sand consisting of 2 to 4 parts of water per 100 parts of iron sand. Frozen molds are designed to prevent deformation caused by mold expansion and contraction during work.