JP3248825B2 - Mold production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a mold by a carbon dioxide gas hardening method, and more particularly to a method for producing a mold having excellent mold strength and surface stability.

[0002]

2. Description of the Related Art Conventionally, as a method of producing a mold for curing a binder by passing a gas, a furan resin / peroxide / sulfurous acid gas curing method (Hardox method), a water-soluble phenol resin / ester gas A curing method or a water glass / carbon dioxide curing method is known. However, the Hardox method has a problem in terms of working environment because it uses sulfurous gas having a strong odor. In the water-soluble phenolic resin / ester gas curing method, since methyl formate is mainly used, there is a problem in terms of odor and flammability. Water glass /
The carbon dioxide hardening method uses carbon dioxide gas without odor, so there is no problem in terms of odor.However, since inorganic water glass is used as a binder, the disintegration of the mold after casting is reduced. However, there was a drawback that casting sand was difficult to regenerate.

For this reason, in recent years, there has been proposed a method for producing a mold by using an organic binder and passing a carbon dioxide gas having a low odor. For example, a kneading agent obtained by adding and kneading a binder obtained by adding and mixing an alkali metal salt of boric acid to a water-soluble phenol resin, filling the kneading sand obtained by adding and kneading the molding sand into a model, and then blowing carbon dioxide gas into the mold to mold. Has been proposed (JP-A-4-147743). However, when an organic binder made of a water-soluble phenol resin is used, there is a disadvantage that the strength of the obtained mold and the surface stability of the mold are low.

In order to avoid such disadvantages, it is conceivable to increase the amount of an organic binder composed of a water-soluble phenol resin to be used. For example, it is conceivable to use 1 to 4% by weight of an organic binder with respect to molding sand. However, this amount is relatively large as compared with the usual amount of 0.5 to 1.5% by weight of a self-hardening organic binder. Therefore, due to the organic binder made of a water-soluble phenol resin,
Organic decomposition gas is likely to be generated due to heat history, and gas defects may occur in the casting. In addition, a large amount of water in the binder may evaporate during pouring, causing a gas defect in the casting.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the strength of a mold obtained in a method of producing a mold using a binder containing a water-soluble phenolic resin and carbon dioxide. Together with eliminating gas defects. Another object of the present invention is to provide a mold having a satisfactory strength even when a relatively small amount of a water-soluble phenolic resin is used.

[0006]

That is, the present invention provides a kneading sand by adding a binder containing a water-soluble phenolic resin to a molding sand to obtain a kneading sand, and then filling the kneading sand into a model. After that, carbon dioxide gas is ventilated to cure the water-soluble phenolic resin to obtain a half mold, and then the half mold is kept under reduced pressure to accelerate the curing of the water-soluble phenolic resin. And a method for producing a mold.

The molding sand used in the method of manufacturing a mold according to the present invention includes quartz sand, chromite sand, zircon sand, celabe sand, olivine sand, alumina sand, mullite sand, synthetic mullite sand, etc. New sand can be used. Needless to say, as the foundry sand, those mainly composed of such recycled sand and recovered sand can also be used.

[0008] A binder containing a water-soluble phenolic resin is added to these foundry sands and kneaded. This water-soluble phenolic resin is an alkaline resol type phenolic resin, and is obtained by condensing phenols and aldehydes in the presence of an alkaline catalyst such as potassium hydroxide.

The phenols used for obtaining the water-soluble phenolic resin include phenol, cresol, 3,
5-xylenol, nonylphenol, p-tert-
Alkyl phenols such as butylphenol, isopropenylphenol and phenylphenol, polyhydric phenols such as resorcinol, catechol, hydroquinone and phloroglysin, and bisphenols such as bisphenol A, bisphenol F, bisphenol C and bisphenol E are used. Cashew nut shell liquid,
Those composed of a mixture of phenolic compounds such as lignin and tannin can also be used as phenols. One of these various phenols may be used alone, or two or more of them may be mixed and co-condensed with the aldehyde. As the aldehyde to be condensed with the phenol, formalin, paraformaldehyde, acetaldehyde, furfural, glyoxal and the like are used.

As a catalyst used for condensing phenols and aldehydes, lithium hydroxide, sodium hydroxide, potassium hydroxide and the like are used alone or as a mixture. In particular, it is preferable to use potassium hydroxide as a catalyst. The water-soluble phenolic resin obtained by condensing phenols and aldehydes is contained in the binder alone or as a mixture of two or more water-soluble phenolic resins.

In the binder, together with a water-soluble phenolic resin, boric acid compounds such as boric acid and borates, oxyanions such as aluminates such as sodium aluminate, stannates such as sodium stannate, etc. It is common to include a curing accelerator composed of a compound. That is, the curing accelerator has an effect of accelerating the curing of the water-soluble phenolic resin through the passage of carbon dioxide gas. The amount of the curing accelerator added is
About 3 to 20% by weight based on the water-soluble phenolic resin is preferable. If the amount of the curing accelerator is less than 3% by weight, there is a tendency that the curing of the water-soluble phenolic resin cannot be sufficiently promoted. Further, even if the amount of the curing accelerator exceeds 20% by weight, the degree of the curing acceleration becomes saturated, which tends to be uneconomical.

The binder may further contain the following glycols and / or ether alcohols for the purpose of improving the strength of the resulting mold. As the glycols, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, furfuryl alcohol and the like can be used. As ether alcohols, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and the like can be used. The amount of these alcohols and / or ethers used is based on the water-soluble phenolic resin.
About 1 to 20% by weight is preferable.

Further, a silane coupling agent may be contained for the purpose of improving the strength of the obtained mold.
Various conventionally known silane coupling agents can be used, and in particular, 3-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ- (2-aminoethyl) aminopropyltrimethoxysilane. Methoxysilane, N-glycidyl-N, N-bis [3-
(Trimethoxysilyl) propyl] amine and the like are preferably used. The silane coupling agent may be added to the kneading sand by being contained in the binder,
It may be directly added to the casting sand and blended in the kneading sand.

The binder described above is added and kneaded to the foundry sand to obtain a kneaded sand. After the model is filled with the kneaded sand, carbon dioxide gas is ventilated. The carbon dioxide gas may be ventilated to the filling in the model under normal pressure, or may be ventilated to the filling in the model under reduced pressure as in a molding method called a V process. The amount of carbon dioxide gas permeated is preferably at least 15 mol%, more preferably at least 30 mol%, based on the water-soluble phenolic resin in the binder.

When carbon dioxide gas is passed through the filling of the model, the curing of the water-soluble phenolic resin in the binder proceeds to some extent. Although this curing is not complete, a mold is obtained which fully retains the filled form (this mold is not the final product and is therefore referred to as a semi-mold in the present invention). What is characteristic in the present invention is that the half mold is kept under reduced pressure. In order to keep the mold under reduced pressure, the half mold may be taken out of the model and stored in a reduced pressure container, or the inside of the model may be kept under reduced pressure without removing the half mold from the model.

The degree of decompression when holding the half mold under reduced pressure is as follows:
The pressure is preferably 500 torr or less, particularly 200 torr.
rr or less, more preferably 100 torr or less. When the pressure under reduced pressure exceeds 500 torr, the curing of the water-soluble phenolic resin is not significantly accelerated, and a high-strength mold tends to be hardly obtained. Also, the time to hold the half mold under reduced pressure is
5 minutes or more is preferable, and especially 10 minutes or more is more preferable.
If the holding time is less than 5 minutes, the curing of the water-soluble phenolic resin is not significantly accelerated, and it tends to be difficult to obtain a high-strength mold. The temperature at which the half mold is kept under reduced pressure is preferably about 0 to 50 ° C. Holding temperature is 0
If it is lower than 50 ° C. or higher than 50 ° C., the curing of the water-soluble phenolic resin is not remarkably accelerated, and a high-strength mold tends to be hardly obtained.

As described above, by maintaining the half mold under reduced pressure, a mold having high strength and good surface stability can be obtained using a water-soluble phenolic resin and carbon dioxide. is there. Needless to say, the template in the present invention is used in a sense including a core.

Hereinafter, the present invention will be described in detail with reference to examples. Example 1 First, the molar ratio of formaldehyde / phenol was set to 2.
5. Formaldehyde and phenol are condensed with a molar ratio of potassium hydroxide / phenol as a catalyst of 2.0 to form a water-soluble phenolic resin (weight average molecular weight 320
0) was obtained. To this water-soluble phenolic resin, 9% by weight of sodium tetraborate decahydrate was added and mixed, and 15% by weight of diethylene glycol was added and mixed to obtain a binder aqueous solution. The solid content of this binder aqueous solution is 62% by weight.
Met.

On the other hand, Mikawa silica sand R-6 No. 10 prepared in advance
A binder aqueous solution was added and kneaded so that 3.5 parts by weight of the water-soluble phenolic resin was added to 0 parts by weight, and kneaded sand was obtained. This kneaded sand is filled into a gassing test piece model of 50 mmφ × 50 mmH, and 20 liters of carbon dioxide gas (100 mol% based on the water-soluble phenolic resin).
It was aerated to obtain a half mold. This semi-mold is 450 torr
The container was placed in a container decompressed to r and kept at 25 ° C. for 20 minutes to obtain a mold. The obtained mold was allowed to stand at 25 ° C., and the compressive strength (kg / cm ² ) of the mold was measured with time. The result was as shown in Table 1.

Using the mold left for 24 hours, 143
FC-25 at 0 ° C (S / M = 3.5, unit weight 110kg)
Was cast, and the presence or absence of gas defects on the obtained casting surface was visually observed. The results were as shown in Table 1.

[0021]

[Table 1]

Example 2 A mold was produced in the same manner as in Example 1 except that the holding pressure of the half mold was changed to 150 torr. Then, the compressive strength of the mold and gas defects on the casting surface were measured in the same manner as in Example 1. The results were as shown in Table 1.

Example 3 Example 1 except that the holding pressure of the half mold was set to 80 torr.
A mold was produced in the same manner as described above. Then, the compressive strength of the mold and gas defects on the casting surface were measured in the same manner as in Example 1. The results were as shown in Table 1.

Example 4 A mold was produced in the same manner as in Example 1 except that the holding pressure of the half mold was changed to 550 torr. Then, the compressive strength of the mold and gas defects on the casting surface were measured in the same manner as in Example 1. The results were as shown in Table 1.

Example 5 A mold was produced in the same manner as in Example 1 except that the amount of the water-soluble phenolic resin added was 1.5 parts by weight, and the holding pressure of the half mold was 150 torr. Then, the compressive strength of the mold and gas defects on the casting surface were measured in the same manner as in Example 1. The results were as shown in Table 1.

COMPARATIVE EXAMPLE 1 A half mold was placed under atmospheric pressure at 25 ° C. and 60% without being placed under reduced pressure.
A mold was produced in the same manner as in Example 1 except that the mold was left in an open system under an atmosphere of RH. Then, the compressive strength of the mold and gas defects on the casting surface were measured in the same manner as in Example 1.
The results were as shown in Table 1.

As is clear from the comparison between the molds obtained by the methods according to Examples 1 to 4 and the mold obtained by the method according to Comparative Example 1, the methods according to Examples 1 to 4 It can be seen that the compressive strength of the obtained mold is higher by treating the half mold under reduced pressure as compared with the method according to Comparative Example 1 in which the mold is left alone. Also, comparing Example 5 with Comparative Example 1, it was found that the holding pressure was set to 200 torr or less, so that half
It can be seen that equivalent mold strength can be obtained with the following resin amounts.

[0028]

The method for producing a mold according to the present invention comprises filling a kneaded sand of molding sand and a water-soluble phenolic resin into a model, aerating carbon dioxide gas, and holding the half mold under reduced pressure. It is. Then, the hardening of the water-soluble phenolic resin is more remarkable than in the case where the half mold is not held under the reduced pressure and is simply left in the air atmosphere. The reason why the curing of the water-soluble phenolic resin easily proceeds when the semi-mold is held under reduced pressure is as follows.
Although it is not clear, by treating under reduced pressure, it is because water and the like that easily inhibit curing are removed,
Alternatively, it is presumed that the decompression promotes dehydration condensation of the water-soluble phenolic resin.

[0029]

According to the method of manufacturing a mold according to the present invention, a mold having significantly improved strength can be obtained while using a water-soluble phenolic resin and carbon dioxide. In addition, when obtaining a mold having satisfactory strength, the amount of water-soluble phenolic resin used can be reduced. Furthermore,
Gas defects caused by water contained in the water-soluble phenolic resin and gas defects caused by the decomposition of the water-soluble phenolic resin can be prevented, and a sound casting with few gas defects can be obtained. It works. Furthermore,
When the amount of the water-soluble phenolic resin used is small, the amount of resin adhering to the molding sand also decreases, and when regenerating the molding sand after use, the number of steps in the regeneration process can be reduced, and the recycled sand can be economically used. It also has the effect of being able to obtain.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B22C 1/00-9/30

Claims (3)

(57) [Claims] A kneading sand is obtained by adding and kneading a binder containing a water-soluble phenolic resin to casting sand to obtain a kneading sand. After filling the kneading sand in a model, carbon dioxide gas is passed through the kneading sand to form a kneading sand. A method for producing a mold, comprising curing a water-soluble phenolic resin to obtain a half-mold, and then maintaining the half-mold under reduced pressure to promote curing of the water-soluble phenol-based resin. 2. The method according to claim 1, wherein the half mold is maintained under a pressure of 500 torr or less. 3. The method according to claim 1, wherein the half mold is maintained under a pressure of 200 torr or less.