JPS5842771B2 - foundry sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to foundry sand that hardens at room temperature or by heating.

Conventionally, binders for refractory particles, which are the main components of foundry sand, are broadly classified into inorganic and organic binders.

Typical inorganic binders include water glass and bentonite, and typical organic binders include phenol resin and furan resin.

In general, molds using inorganic binders have high strength even after pouring, so their collapsibility is extremely poor.Especially when used for parts to be cast, such as cores, when the mold is broken and finished. This will be an extremely difficult task.

Although molds using organic binders have good disintegration properties,
There are many hygiene issues.

For example, the shell mold method using phenolic resin is made by filling molding sand in which refractory particles are coated with novolac-type phenolic resin and hexamethylenetetramine into a mold preheated to around 300°C and firing. However, it contains ammonia from the time of coating to the time of pouring.

Generates harmful gases such as phenol, formalin, and cyanide.

An object of the present invention is to provide foundry sand that hardens at room temperature or by heating, has high strength, has good disintegration properties after pouring, and generates less harmful gases.

As a result of intensive research to achieve the above object, the present inventors have developed a vinyl resin that is effective for increasing the strength of refractory particles at room temperature, an alkyl silicate that is effective for heat resistance, and a water-soluble coating type drying method. The present invention was achieved by discovering that the above object can be achieved by adding a fatty oil or an alkyd resin effective for water resistance, which represents the retention strength in .

In the present invention, as the first component vinyl resin added to the refractory particles, specifically, vinyl acetate resin, polyvinyl alcohol, etc., and one or two of its solvents such as alcohol, ester, water, etc. Use a solution dissolved in a mixed solvent of more than 100% of the species.

Vinyl resins have advantages such as being easily soluble in solvents and having strong adhesive strength at room temperature, but they also have the disadvantages of extremely low heat resistance and low water resistance.

In order to improve this, the second method of increasing heat resistance is
The third component, fatty oil or alkyd resin, is added to the alkyl silicate as a component to improve water resistance.

The second component alkyl silicate is methyl, ethyl,
It is a silicate ester having an alkyl group such as butyl, phenyl, octyl, or rariul.

In the present invention, alcohol is produced by hydrolyzing an alkyl silicate in the presence of an acidic catalyst.

After forming a silicic acid sol that is easily separated into water and silica, it is mixed with the vinyl resin, which can significantly increase the heat resistance of the vinyl resin.

Furthermore, after curing, the alcohol evaporates and only silica remains, so no harmful gases are generated from the alkyl silicate hydrolyzate.

However, in the case where vinyl resin as the first component and alkyl silicate as the second component are added,
When a water-soluble coating is applied and dried in an oven, the temperature in the oven becomes 140%.
At around ℃, it becomes soft and deformed.

Therefore, a third component, fatty oil or alkyd resin, is added to increase water resistance.

Fatty oils include linseed oil, soybean oil, perilla oil, fish oil, tung oil,
Use drying oils such as sunflower oil, walnut oil, castor oil, and oil.

As for fatty oils, linseed oil and tung oil have been used so far, but they must be added in large quantities, and their curing is oxidative polymerization, which is slow and can be heated to 200°C.
Had to heat it back and forth.

However, in the present invention, the alkyl silicate provides heat resistance, and the fatty oil only needs to supplement water resistance, so only a small amount is required, and heating is not an essential requirement.

Alkyd resins basically include polybasic acids such as phthalic acid, isophthalic acid, maleic acid, fumaric acid, sebacic acid, adipic acid, tartaric acid, and malic acid, and polybasic acids such as glycerin, pentaerythritol, ethylene glycol, and sorbitol. It is a polymeric ester obtained by condensation with a hydric alcohol, but it is rarely used in this state for practical purposes. Denatured or rosin.

Those modified with resins such as ester rosin and phenol resin are used.

The proportion of alkyd resin and fatty oil in this case is between 25 and 75% fatty oil content.

The solid matter of the binder composition of the present invention after removal of volatile matter consists of vinyl resin, silica precipitated from alkyl silicate, and fatty oil or alkyd resin.

The weight percentage of the solids is, assuming that the entire solids after removing the volatile matter of the binder composition is 100%, the vinyl resin is 30 to 60 φ, the silica content precipitated from the alkyl silicate is 20 to 50%, Fatty oil or alkyd resin 1
Good results have been obtained in the range of 0 to 30%, as will be described later.

In addition, when silica sand is used as the refractory particles, the weight ratio of the foundry sand to the solid matter after removing the volatile matter of the binder composition is 0.3 to 1.2 parts by weight of vinyl resin per 100 parts by weight of silica sand. part, silica content precipitated from alkyl silicate 0.2
~1.0 parts by weight, fatty oil or alkyd resin 0.0
As will be described later, good results have been obtained when the amount is 5 to 1.0 parts by weight.

The curing reaction of foundry sand in the present invention is completed by removing the vinyl resin solvent and the volatile components of the alkyl silicate hydrolyzate and oxidatively polymerizing the fatty oil or alkyd resin.

As a method, it is effective to remove the volatile components of the vinyl resin solvent, alkyl silicate, and hydrolyzed solution by flowing air through the foundry sand, and heated air further accelerates the removal.

Oxidative polymerization of fatty oils or alkyd resins is generally promoted in a heated atmosphere.

As mentioned above, the common feature of the two curing methods of supplying heated air and exposing to a heated atmosphere is heating, and it is most desirable for the method of curing foundry sand of the present invention to flow heated air.

However, the present invention does not limit the curing method, and curing can be performed by leaving at room temperature or in a heating oven, although it takes a longer time than the above-mentioned method.

In addition, the time required for oxidative polymerization of fatty oil or alkyd resin depends on the solvent of vinyl resin, alkyl silicate,
Since curing time is longer than that required by removing the volatile matter from the hydrolyzed liquid, in the present invention, as a method of shortening the curing time, a naphthenic acid metal soap, which is a catalyst for curing fatty oil or alkyd resin, is added to fatty oil or alkyd resin in advance. Alternatively, it can be adjusted by mixing it with an alkyd resin and heating it to advance polymerization halfway, or by adding it during kneading of foundry sand.

The metals in the naphthenic acid metal soap include copper, cobalt, lead, manganese, and zinc, and the weight ratio with respect to 100 parts by weight of fatty oil or alkyd resin is 0 when added to the fatty oil or alkyd resin in advance. ．．
1 to 1 part by weight, 1 to 5 parts by weight when added during kneading of foundry sand
Good results are obtained with 0 parts by weight.

A mold made of the above-mentioned foundry sand has sufficient strength, good water resistance, almost no harmful gases generated during molding and casting, and has good disintegration properties afterward.

Examples of the present invention will be described below.

In addition, the implementation procedure for the coating mold test results is as follows:
A dry standard bending test piece with a length of 5 mm and a length of 170 mm was prepared.
A commercially available water-soluble coating mold was immersed in a solution diluted to 50 Baumé for 10 seconds, and then dried in an oven at 130°C, and those that did not deform or break during drying were evaluated as good.

Further, the transverse rupture strength was measured using the dry standard transverse rupture test piece at room temperature.

The basic components of the binder used in this experiment are shown in Tables 1 to 4.
Shown below.

Table 1 shows the blending composition of the vinyl resin solution, Table 2 shows the alkyl silicate hydrolyzed solution, Table 3 shows the fatty oil, and Table 4 shows the blending composition of the alkyd resin.

Table 5 shows experimental examples using fatty oil as the third precept of the present invention, and Table 6 shows experimental examples using alkyd resin.

As shown in Tables 5 and 6, all test pieces using the components specified in the present invention were coated with a water-soluble coating and heated at 130°C.
Even when it was dried in an oven*, it did not deform or break during drying, and its transverse rupture strength was 25 kg/cr? That's all for now.

*3 A low-linearity composite mixture mainly consisting of tetra-hexamers with an effective silica content of about 40 or more.

*4 Concentrated hydrochloric acid diluted 20 times with water.

*5 Silica content that precipitates from alkyl silicate hydrolyzate.

*6 The code g is fatty acid modified type, the code is It is a resin-modified alkyd resin.

Since it is a commercially available product, the detailed composition is not available. not clear.

Claims (1)

[Claims] 1. Foundry sand made by impregnating refractory particles with vinyl resin, alkyl silicate, and fatty oil or alkyd resin.