JP2747367B2 - Mold or core manufacturing method - Google Patents

Description

The present invention relates to a method for producing a mold or a core.

Specifically, by molding molding sand and a specific organic binder, and then hardening by passing carbon dioxide gas through, the mold or medium is excellent in mold strength and surface stability and has little moisture absorption deterioration. A method of manufacturing a child.

2. Description of the Related Art As a method of manufacturing a mold or a core using a gas-curable binder, a method of mixing an inorganic binder such as water glass with molding sand and molding the same with carbon dioxide gas (carbonate) is used. Gas curing method), a method of mixing a mixture of benzylic ether type phenolic resin and polyisocyanate in molding sand, curing the molded product with an amine gas (isocure method), and a method of molding a mixture of a furan resin and peroxide into molding sand. Method of hardening mixed and molded products with sulfurous acid gas (Hardox method)
Etc. are known. However, the carbon dioxide gas hardening method using an inorganic binder has a poor disintegration property of a mold after casting,
There are problems such as an increase in the number of finishing steps, the recoverability of sand, and environmental destruction caused by waste sand. On the other hand, the ISOCURE method and the HARDOX method using an organic binder have better mold disintegration and sand recovery than the carbon dioxide curing method using an inorganic binder, but have a toxic gas. Not only is not preferable from the viewpoint of working environment hygiene, but also there is a problem that a gas component, a soot defect, a vaning defect, and the like are liable to occur in the casting because the binder component contains nitrogen.

Therefore, in recent years, attempts have been made to cure with low-toxic carbon dioxide using an organic binder. For example, a method in which carbon dioxide gas is passed through a mixture of molding sand and an aqueous solution of alkaline phenol formaldehyde resin, or a mixture of a binding agent and molding sand in which an alkali metal salt of boric acid is further added to the aqueous solution of alkaline phenol formaldehyde resin. Methods for ventilating carbon dioxide gas have been proposed, but all have the problem that the strength of the casting is low, the surface stability is inferior, and the moisture absorption deteriorates under high humidity.

Problem to be Solved by the Invention The present invention provides a method capable of producing a mold or a core having excellent mold strength and surface stability and less deterioration due to moisture absorption using an organic binder and carbon dioxide gas. The purpose is to do.

Means for Solving the Problems The present invention relates to molding sand, the following components (a) to (c): (a) 60 to 96% by weight of an aqueous solution of an alkaline phenol formaldehyde resin (b) 3 to 20% by weight of an alkali metal salt of boric acid % (C) a mixture containing a glycol ether and / or a binder containing 1 to 20% by weight of furfuryl alcohol, followed by molding and then curing by passing carbon dioxide gas through. A method for producing the same.

 Hereinafter, the present invention will be described in detail.

Examples of the alkali metal of the aqueous alkaline phenol formaldehyde resin solution used in the present invention include lithium, sodium, potassium and the like. The molar ratio of phenol to alkali metal is phenol: alkali metal = 1.0: 0.
It is 4 to 1.0: 2.5, preferably 1.0: 1.0 to 1.0: 2.0. If the molar ratio is less than 1.0: 0.4, the water solubility of the resin will be poor, and if it is greater than 1.0: 2.5, only insufficient strength will be obtained. One or more alkali metals may be contained in the reaction system, or may be added after the completion of the reaction. The molar ratio of phenol to formaldehyde is from 1.0: 1.0 to
1.0: 3.0, preferably 1.0: 1.2 to 1.0: 2.5. If the molar ratio is less than 1.0: 1.0, the obtained strength is insufficient,
On the other hand, when the molar ratio is larger than 1.0: 3.0, not only does the viscosity of the resin become high, but also the working environment deteriorates due to the pungent odor of formaldehyde.

Alkaline phenol formaldehyde resin, 30 ~
Prepare a 70% by weight aqueous solution. If the resin content is less than 30% by weight, the moisture content is too large and the strength of the mold or the core is not sufficiently developed, and if the resin content is more than 70% by weight, the viscosity of the resin becomes high and there is a problem in handling. .

The blending amount of the aqueous alkaline phenol formaldehyde resin solution with respect to the total amount of the binder is 60 to 96% by weight, preferably 75 to 90% by weight. If the amount is less than 60% by weight, the strength immediately after carbon dioxide gas ventilation is insufficient, and 96% by weight.
If it is larger, the effect of improving the mold strength is small.

Examples of the alkali metal salt of boric acid used in the present invention include sodium borate and potassium borate.

An alkali metal salt of boric acid is used after being added to and dissolved in an aqueous solution of an alkaline phenol formaldehyde resin.

The compounding amount of the alkali metal salt of boric acid with respect to the total amount of the binder is 3 to 20% by weight, preferably 5 to 15% by weight. If the compounding amount is less than 3% by weight, the strength immediately after aeration of carbon dioxide gas is insufficient and it is not practical, and if it is more than 20% by weight, not only the viscosity of the resin increases but also the obtained strength decreases.

Representative examples of glycol ethers used in the present invention include diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol. Glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,
Examples thereof include diethylene glycol / monopropyl ether, diethylene glycol / monobutyl ether, propylene glycol / monomethyl ether, and dipropylene glycol / monomethyl ether.

The amount of the glycol ethers and / or furfuryl alcohol is 1 to 20% by weight based on the total amount of the binder.
Preferably it is 3 to 15% by weight. If the amount is less than 1% by weight, the effect of improving the strength and the surface stability of the mold is small. If the amount is more than 20% by weight, the effects of the strength and the surface stability of the mold are reduced, and it is not economical.

Examples of the molding sand used in the present invention include silica sand, olivine sand, chromite sand, zircon sand and the like.

In the present invention, a mold or a core can be manufactured by mixing the molding sand and the binder to form a desired shape, and then passing carbon dioxide gas therethrough.

A silane coupling agent may be added to the binder of the present invention in order to improve the binding between the alkaline phenol formaldehyde resin and the foundry sand. Preferred silane coupling agents include γ-aminopropyltriethoxysilane and γ- (2-aminoethyl) aminopropyltrimethoxysilane.

The amount of the binder added to 100 parts by weight of molding sand is 0.4
To 10 parts by weight, preferably 0.8 to 5 parts by weight.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Examples 1 to 5 and Comparative Example 1 A four-necked flask equipped with a thermometer, a stirrer, and a cooler was charged with 94 g of phenol, and 101 g of 50% potassium hydroxide and 65.2 g of 92% paraformaldehyde were added thereto while stirring. Slowly added. Next, this solution was heated to 90 ° C. and reacted at 90 ° C. for 3 hours to obtain an alkali phenol formaldehyde resin.

Next, after the reaction was completed, 50% potassium hydroxide 12
3.4 g, borax 30 g and γ-aminopropyltriethoxysilane 1.9 g were added to obtain an alkali phenol formaldehyde resin solution.

<Preparation of Binder> 10% by weight of various glycol ethers or furfuryl alcohol shown in Table 1 was added to and mixed with the above-mentioned alkali phenol formaldehyde resin solution to prepare a binder.

<Performance evaluation> Silica sand (trade name "Mikawa No. 6 sand", manufactured by Mikawa silica stone Co., Ltd.)
35 g of the above binder was added to 1 kg and kneaded for 1 minute. The kneaded sand was molded into a test wooden mold (50φ × 50 hmm, 6 pieces), and then cured by passing carbon dioxide gas at a flow rate of 20 / min for 60 seconds.

Using the obtained cured test pieces, the compressive strength and surface stability were measured immediately after ventilation and after standing for 24 hours in an atmosphere of 20 ° C.-60% RH and 20 ° C.-100% RH. The results are shown in Table 1.

The compressive strength was measured with an Amsler compression tester.

The surface stability was measured using a standard 50φ × 50hmm test piece
It was shaken for 60 seconds on a sieve of μm and calculated by the following equation.

Examples 6 to 12 <Preparation of Binder> For the same alkali phenol formaldehyde resin solution as used in Examples 1 to 5 and Comparative Example 1, Table-
As shown in FIG. 2, diethylene glycol / monobutyl ether and furfuryl alcohol were added to and mixed in 2.5 to 15% by weight to prepare a binder.

<Performance Evaluation> The performance evaluation was performed in the same manner as in the methods of Examples 1 to 5. Table 2 shows the results.

Examples 13 to 15 <Preparation of Binder> For the same alkali phenol formaldehyde resin solution as used in Examples 1 to 5 and Comparative Example 1, Table-
5% by weight of various glycol ethers shown in No. 3 were added and mixed to prepare a binder.

<Performance evaluation> Silica sand (trade name "Mikawa No. 6 sand", manufactured by Mikawa silica stone Co., Ltd.)
35 g of the above binder was added to 1 kg and kneaded for 1 minute. This kneaded sand was molded into a test wooden mold (50φ × 50 hmm, 6 pieces), and then cured by passing carbon dioxide gas at a pressure of 2.0 kg / cm ^{2 at} a flow rate of 20 / min for 60 seconds.

Immediately after aeration and 20 ° C-60% using the obtained cured test piece
The compressive strength after standing for 24 hours in an RH atmosphere was measured. The results are shown in Table-3.

According to the method of the present invention, it is possible to produce a mold or a core having excellent mold strength and surface stability and less deterioration due to moisture absorption.

Further, since the present invention hardens the mold with low-toxic carbon dioxide gas, it does not require a toxic gas unlike the conventional isocure method or the Hardox method. Since the binder containing no component is used, the quality of the casting is improved.

Claims (1)

(57) [Claims] 1. Foundry sand and the following components (a) to (c): (a) 60 to 96% by weight of an aqueous solution of an alkaline phenol formaldehyde resin (b) 3 to 20% by weight of an alkali metal salt of boric acid (c) Glycol ether And / or a binder containing 1 to 20% by weight of furfuryl alcohol, followed by molding and curing by passing carbon dioxide gas through.