KR800000495B1 - Binder compositions - Google Patents

Abstract

Alkali metal silicate binder composition, useful for manufg. mold and core, was manufd. by mixing stabilized, starch-hydrolysate having 5>=dextrose equivalent wt. and aq. soln. of alkali metal silicate. The wt. ratio of solid materials in binder compsn. was 20-49.5 parts alkali metal silicate against 0.4-35 parts stabilized starch hydrolysate.

Description

Adhesive composition

The present invention relates to alkali metal silicate adhesive compositions for use in the manufacture of casting molds and shims.

It is common to use a water-soluble alkali metal silicate solution, in particular sodium silicate solution, as an adhesive to the sand for casting molds. This solution usually contains 40-50% by weight of sodium silicate having a SiO ₂ : Na ₂ O ratio of 2.0: 1 to 3.0: 1. In some processes, the sodium silicate solution is mixed with sand, where the resulting mixture is formed into a mold or shim. Next, carbon dioxide is blown through the mold or shim, and a bonded mold or shim is formed by a chemical reaction between sodium silicate and carbon trioxide. In another process, as a so-called hardener, for example, a mixture of diacetin and triatine is mixed with sodium silicate and sand, formed into a mold or shim, and left to cure upon chemical reaction between the hardener and sodium silicate. .

The drawback of the two processes is that they are very difficult to disintegrate or remove from the cast metal after casting and the mold has solidified.

This is particularly disadvantageous when molds and shims are used to produce castings from metals that are cast at high temperatures, such as steel casting, in the case of shims with complex shapes. Therefore, in the past, there have been various proposals for adding a so-called disintegrant to a mixture of sand and sodium silicate, which helps the sand mold or shim separate or collapse after casting.

Examples of disintegrants which have been used include coal dust and carbohydrates which are cellulosic substances such as starch derivatives such as wood flour, starch and starch hydrolysates, and sugars such as sucrose and dextrose.

If a disintegrant is used, it is advantageous to dissolve it or mix it in the sodium silicate solution. This is because the rapid homogenization of the sand-adhesive mixture simplifies the seam or mold manufacturing process and makes it easier to automate.

However, if the disintegrant must be incorporated in the sodium silicate solution, it is desirable that the solution remain stable during storage, preferably three months or longer. Unfortunately any hydrocarbon material that has been used as a disintegrant, i.e., reducing sugars, such as glucose, reacts with strong alkaline sodium silicates and converts them to black insoluble products. At the same time the solution increases in viscosity and eventually solidifies due to the consumption of sodium hydroxide, thus increasing the ratio of silica to sodium hydroxide in sodium silicate.

Non-reducing sugars, such as sucrose, form a stable solution when added to sodium silicate solution as an effective disintegrant. However, molds or shims made of sand bonded with silicate containing sucrose have hygroscopic properties and therefore have additional disadvantages. Thus, if these molds or shims are stored in a particularly humid atmosphere they are less likely to break and become brittle.

Stable adhesive solutions that give sand molds or shims good disintegration and do not lose strength during storage can be prepared by mixing with alkali metal silicate solutions and stabilized starch hydrolysates having a dextrose equivalent of 5 or less. Found.

According to the present invention, there is provided an adhesive composition composed of an alkali metal silicate solution and a starch hydrolyzate having less than 5 equivalents of dextrose.

According to the present invention there is provided a method for producing an adhered indented material such as a mold or a seam, which method comprises a mixture consisting of particulate matter, a water-soluble alkali metal silicate and starch hydrolyzate having a dextrose equivalent of 5 or less. It consists of the process of shape | molding to a desired shape, and the process of hardening this mixture.

Dextrose equivalent is defined as the reducing power, ie the reducing sugar content of the starch hydrolyzate, expressed as D-gluose on a dry basis.

Indeed, the lower the dextrose equivalent of the starch hydrolyzate, the longer the stable residual alkali metal silicate solution containing the starch hydrolyzate. It is therefore preferred that the starch hydrolyzate has a dextrose equivalent weight of 2 or less, more preferably 0.5 or less.

By selective oxidation or hydrogenation with urea or urea derivatives, suitable starch hydrolysates can be prepared from high dextrose equivalent starch hydrolysates.

The preferred method is hydrogenation with a catalyst with hydrogen.

The dextrose equivalent weight of the starch hydrolyzate before the hydrogenation reaction is preferably 5-75, more preferably 10-40.

The dextrose equivalent of the starch hydrolyzate after hydrogenation is reduced to 5 or less, preferably 2 or less, more preferably 0.5 or less. Stabilized starch hydrolyzate can be readily handled in the form of a water-soluble syrup, which generally contains 40-70% by weight of starch hydrolyzate.

Preferred alkali metal silicates are sodium silicates. The SiO ₂ : Na ₂ O ratio of sodium silicate can vary widely, for example 2: 1-3.5: 1, but sodium silicate having a ratio of 2.0: 1-2.5: 1 is preferred. Because a high proportion of alkali metal silicate is chemically reactive, the adhesive composition containing it has a shorter shelf life.

Although the composition of the adhesive solution varies widely, it is generally prepared by mixing 1-50% by weight of starch hydrolysis with syrup and 50-99% by weight of sodium silicate solution.

Preferred compositions contain 10-30% by weight starch hydrolysis syrup and 70-90% by weight sodium silicate solution.

The adhesive composition in use is generally mixed with sand in a ratio of 2-10 parts by weight of the adhesive composition with respect to 100 parts by weight of sand.

The mixture is cured by feeding carbon dioxide or by combining chemical curing agents such as esters of polyhydric alcohols in a known manner.

The following examples illustrate the invention.

Example 1

An adhesive composition was prepared having the following weight composition.

Sodium silicate aqueous solution (SiO ₂ : Na ₂ O 2.2: 1, sodium silicate content 46.4% by weight) 80%

Hydrogenated starch hydrolyzate syrup (dextrose equivalent 0.005: starch hydrolyzate content 65% by weight) 20%

3.5 parts by weight of the adhesive composition were mixed with 100 parts by weight of silica sand (AFS powder figure 44). The sand-adhesive mixture was then used to prepare a cylindrical shim of standard AFS 50 mm height x 50 mm diameter.

The shim was then passed through carbon dioxide at a flow rate of 5.5 L / min at 25 ° C. for several hours at a line pressure of 0.35 kg / cm 2.

The compressive strength of the prepared shim was measured.

(a) for samples immediately after gas passage (ie within 10 seconds)

(b) for specimens stored for 24 hours in a relatively dry laboratory atmosphere,

(c) For samples stored for 24 hours in a humid atmosphere (25-27 ° C, 90% relative humidity)

The obtained results were prepared in the table as follows.

These tests were repeated by replacing 20% by weight aqueous solution of sucrose containing 65% by weight sucrose with syrup for hydrogenated starch hydrolysis. The obtained results are shown in the following table.

As can be seen from these results, the sand bound with the adhesive composition containing the starch hydrolyzate showed similar results to the sand containing sodium silicate solution and sucrose depending on the strength of the shim prepared immediately after the passage of gas. However, it can be seen that the adhesive composition of the present invention is remarkably excellent even when the shim is stored in either of a relatively dry atmosphere or a humid atmosphere.

In fact, it is thought that the gas passage time of about 120 seconds is excessive compared to a small seam like a standard AFS sample.

This is because excessive gas passage and reduced compressive strength will be caused.

The effect of excess gas passage is generally most pronounced in shims stored in a dry or relatively dry atmosphere, where the sand mixtures containing starch hydrolyzate are found to be a It is less susceptible to excessive gas passage than sand mixtures containing rose.

Example 2

An adhesive composition having the following weight composition was prepared.

Sodium silicate aqueous solution (SiO ₂ : Na ₂ O 2.4: 1, sodium silicate content 46.0 wt%) 70%

Hydrogenated starch hydrolyzate syrup (dextrose equivalent 0.003: starch hydrolyzate content 65% by weight) 30%

The composition was divided into three samples. One sample was tested immediately (a), the other sample was tested after 2 months of storage (b), and the other sample was tested after 3.5 months of storage (c).

According to the procedure described in Example (1), a sand-adhesive mixture and a standard AFS shim were prepared and the compressive strength of the shim was measured immediately after gas passage.

The following results were obtained.

Test results showed that the adhesive composition of the present invention only slightly degraded during storage.

Example 3

Example 2 An unstored sample of adhesive composition was used to evaluate the disintegration of sand adhered to the composition.

The sand core was prepared and passed through the gas as described in Example 1, and then the gas passage time required for obtaining a mold core compressive strength of about 7 kg / cm 2 on a test basis was calculated (about 25 seconds).

During this period, gas was passed through a number of shims up to an intensity of about 7 kg / cm 2. This shim was then stored in the laboratory for 24 hours, then heated in a furnace in the range 200-1200 ° C. for 5 minutes and then cooled to room temperature.

The compressive strength of the shim was measured and the following results were obtained.

Temperature compressive strength (kg / cm ² )

200 61.2

400 12.3

600 2.5

800 0.6

1000 0

1200 0

These results indicate that starch hydrolyzate is an effective disintegrant.

Example 4

Aqueous sodium silicate solution (SiO ₂ : Na ₂ O ratio of 2.4: 1, 46 wt% solids) was mixed with 43 parts (weight) of hydrogenated starch hydrolyzate syrup (65 wt% solids).

This syrup was obtained by catalytic hydrogenation of a starch hydrolyzate with a DE of 30 and a DE of 0.01.

3.5 parts of this premixed composition were mixed with 100 parts of sand (50-55 in AFS powder) used to make the mold and shim. (AFS = American Foundrymans Society)

The sand composition is poured into a standard AFS 50mm × 50mm test sample and passed through carbon dioxide (25 ° C, 0.35kg / ㎠ linear pressure: 5.5l / min flow rate) for 30 seconds to provide an instantaneous compressive strength of 9.9kg / l. It became.

Immediately after gas passage, identically prepared specimens were exposed to wet conditions (25 ° C., 90% relative humidity) for 72 hours. After the treatment, the compressive strength was measured to be 10.6 kg / cm 2, which shows excellent stability under such conditions.

The premixed adhesive composition appeared substantially stable over three months in view of its adhesiveness.

Claims (1)

Molded starch hydrolysate having an dextrose equivalent of 5 or less, and an aqueous solution of alkali metal silicate is essentially included and the solids weight ratio of the components is 0.4-35 parts of stabilized starch hydrolyzate to 20-49.5 parts of alkali metal silicate and Adhesive composition used for the production of shims.