JP2898799B2 - Method for treating casting sand and method for producing sand mold for casting - 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 sand mold for casting in a self-hardening mold and a gas-curing mold and a method for treating molding sand. More specifically, the present invention relates to an improved method for treating molding sand and a method for producing a sand mold for casting used in a process of using a water-soluble phenol resin as a binder and curing it with an organic ester.

[0002]

2. Description of the Related Art As a molding method for producing a mold such as a main mold and a core using an organic binder, a self-hardening mold method, a cold box mold method, and a cloning method (shell method) are known. In particular, the organic self-hardening mold molding method has already become a general-purpose molding method in place of the inorganic type from the viewpoint of productivity, casting quality, safety and health mainly in the field of mechanical casting. On the other hand,
In order to manufacture a mold at medium and high speeds, a so-called coated sand in which a phenol resin is coated on a granular refractory is used.
The cloning method of producing a template by heat-curing d) is widely used.

[0003] However, in order to save energy during mold production, improve mold production speed, and further improve the quality of molds and castings, a cold box mold production method of curing at room temperature with a gaseous or aerosol-like material has been used as a substitute for a cloning method. Serious introduction has been attempted in the casting industry as a manufacturing method.

As a binder composition used in an organic self-hardening mold molding method and a gas-curable mold molding method, a binder composition for molding sand is prepared by using a water-soluble phenol resin as a binder and curing it with an organic ester. The products are known from JP-A-50-130627, JP-A-58-154433, JP-A-58-154434 and the like.

[0005]

The mold making method using this binder does not contain a sulfur atom in the binder, so that the tendency of sulfuration is higher than the mold making method using an acid-curable resin. However, compared to the acid-curable mold molding method, the mold strength is low, so the amount of resin required for molding is extremely large, and the amount of gas generated during pouring is small. There were drawbacks that many gas defects were likely to occur and the economic efficiency was not good. Further, the recovered sand once used for casting has a disadvantage that the strength of the mold is lower than that of the fresh sand, and the strength of the mold is further reduced as the casting and regeneration are repeated.
Therefore, in order to manufacture a sand mold for casting using the refractory granular material collected or regenerated for reuse (hereinafter, referred to as regenerated sand), the amount of resin used and the replenishment of fresh sand are required to maintain the mold strength. There is a problem that the amount must be increased, and improvement is desired.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve these problems, and as a result, have produced a sand mold for castings in which a water-soluble phenol resin is used as a binder and this is cured with an organic ester. In the method, it has been found that the strength of a mold formed using recycled sand is greatly improved by using an acid in combination with the treated sand or treating the recycled sand with an acid in advance, or by combining these methods. Thus, the present invention has been completed. That is, the present invention relates to a method for treating molding sand, which comprises adding an acid to a refractory granular material used in a method for producing a sand mold for casting in which a water-soluble phenol resin is cured with an organic ester. The present invention also relates to a method for producing a sand mold for casting, which comprises curing an aqueous phenol resin with an organic ester, wherein an acid is used.

In order to reclaim sand from a mold or a core, after removing the casting, the used mold and the core are broken up by mechanical vibration or decomposition to break up the sand, break up lumps or agglomerates, and remove the sand. to recover. Since the surface of the recovered sand contains unburned components of the binder, the sand is usually regenerated next. There are three generally accepted methods for reclaiming reclaimed sand (mechanical,
Wet or thermal), but either is acceptable.

[0008] The dissociation index pKa of the acid used in the present invention is preferably 5 or less, more preferably 3 or less. pKa is 5
If it is more than the above, the degree of neutralization of the alkali component accumulated in the sand will be low, which is not preferable. As the acid used in the present invention, either an inorganic acid or an organic acid can be used. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and the like. Organic acids include formic acid, acetic acid, oxalic acid, benzoic acid,
Carboxylic acids such as glycolic acid, sulfamic acid, xylene sulfonic acid, sulfonic acid such as toluene sulfonic acid, benzene sulfonic acid, and organic phosphoric acid esters such as methyl phosphoric acid and ethyl phosphoric acid. By using this, the mold strength of the recycled sand is improved. Further, other additives may be used to the extent that the effects of the present invention are not impaired.

In order to produce the sand mold for castings of the present invention by a self-hardening mold method, 0.0001 to 10 parts by weight, preferably 0.001 to 3 parts by weight, of acid is added to 100 parts by weight of recycled sand, and water-soluble phenol as a binder is used. 0.4 to 15 parts by weight of resin, preferably 0.6 to
5 parts by weight, and 0.05 to 9 parts by weight of an organic ester, preferably
0.1 to 5 parts by weight is kneaded by a known method, and a mold can be manufactured by utilizing the conventional self-hardening mold manufacturing process as it is. Further, in order to produce the sand mold for castings of the present invention by a gas hardening method, an acid is used in an amount of 0.0001 to 100 parts by weight of recycled sand.
10 parts by weight, preferably 0.001 to 3 parts by weight, and 0.4 to 15 parts by weight of a water-soluble phenol resin as a binder are added to the model by hand-mixing or blowing using pressurized air. Then, gaseous or aerosol-like organic ester is blown and cured by blowing 0.05 to 9 parts by weight,
Make a mold. The foundry sand obtained by the treatment method of the present invention is obtained by kneading 10001 parts by weight of recycled sand with 0.0001 to 10 parts by weight, preferably 0.001 to 3 parts by weight of acid. The kneading method is not particularly limited as long as the regenerated sand and the acid are uniformly mixed. A well-known method can be applied to the production of a sand mold for casting by a self-hardening method or a gas curing method using a water-soluble phenol resin using the treated sand.

As the organic ester used in the present invention, a lactone or an organic ester derived from a monohydric or polyhydric alcohol having 1 to 10 carbon atoms and an organic carboxylic acid having 1 to 10 carbon atoms alone or in a mixture is used. However, γ-butyrolactone, propionlactone, ε-caprolactone, ethyl formate, ethylene glycol diacetate, ethylene glycol monoacetate, triacetin, and the like are preferable in the self-hardening molding method, and methyl formate is preferable in the gas-curing molding method.

The water-soluble phenolic resin used in the present invention is a resin curable with an organic ester, and includes phenols including phenol, cresol, resorcinol, 3,5-xylenol, bisphenol A, and other substituted phenols. Phenolic resins obtained by reacting these mixtures with aldehydes such as, for example, formaldehyde, acetaldehyde, furfural aldehyde and mixtures thereof are mentioned. Suitable alkaline substances used for the condensation of these phenolic resins are sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof, with potassium hydroxide being preferred. Further, a compound such as a silane coupling agent may be added for the purpose of further improving the mold strength. As the refractory granular material, inorganic refractory particulates such as chromite sand, zircon sand, and olivine sand are used in addition to silica sand having quartz as a main component, but are not particularly limited.

[0012]

The mechanism by which the mold strength is remarkably improved by using the acid based on the present invention with the regenerated sand using the water-soluble phenolic resin is as follows. It is presumed that as a result of the neutralization by the acid and the restoration of the reactivity between the sand and the binder, the mold strength is improved.

[0013]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Example 1 The mold strength in the self-hardening mold making method was evaluated. That is,
An aqueous solution of acid whose acid value (KOHmg / g) has been adjusted to 250 per 100 parts by weight of reclaimed sand whose sand type is Fremantle sand
1.5 parts by weight of a water-soluble phenol resin (solid content 49%, weight average molecular weight 2300) containing 0.3 parts by weight, 0.375 parts by weight of triacetin and 0.5% by weight (based on the resin) of γ-aminopropyltriethoxysilane The mixture
The test piece was filled into a test piece model of 50 mmφ × 50 mmh, and the withstand pressure after 24 hours was measured. Table 1 shows the results.

<Adjustment method of reclaimed sand> Recycled sand was prepared by adding triacetin to 0.375 with respect to 100 parts by weight of fresh mantle sand.
Parts by weight and γ-aminopropyltriethoxysilane 0.5
Using a mold molded from a mixture obtained by adding and mixing 1.5 parts by weight of a water-soluble phenol resin (solid content: 49%, weight-average molecular weight: 2,300) containing 0.1% by weight (based on the resin), FC-25 was used.
(S / M = 3.5) An equivalent product was cast, the collected sand was crushed, and reclaimed (A regeneration, 2 passes) using an M-type rotary reclaimer manufactured by Nippon Casting Co., Ltd. The reclaimed sand obtained by repeating the above steps five times was used as reclaimed sand for testing.

[0015]

[Table 1]

* 1: From the Handbook of Science II, 2nd revised edition (edited by The Chemical Society of Japan) * 2: J. Horyna, Collection Czech. Chem. Commun., 24, 195
6,2637 (1959); From 27,1324 (1961) * 3: GEKBranch and M. Calvin, The Theory of Organi
c Chemistry, PrenticeHall, Englewood Cliffs, NJ, 194
5, p.207. Example 2 The mold strength in the self-hardening mold making method was evaluated. That is,
An aqueous solution of an acid whose acid value (KOHmg / g) was adjusted to 250 with respect to a mixture of 80 parts by weight of reclaimed sand and 20 parts by weight of fresh sand in which the kind of sand was Fremantle sand was as shown in Table 2, and triacetin was 0.3 part
75 parts by weight and γ-aminopropyltriethoxysilane 0.
A mixture prepared by adding and mixing 1.5 parts by weight of a water-soluble phenol resin (solid content: 49%, weight average molecular weight: 2300) containing 5% by weight (based on resin) is filled in a test piece model of 50 mmφ × 50 mmh for 48 hours. The post-compression pressure was measured. The method for adjusting the reclaimed sand is the same as in the first embodiment. Table 2 shows the results.

[0017]

[Table 2]

Example 3 0.5 part by weight of an aqueous solution of an acid whose acid value (KOH mg / g) was adjusted to 250 was added to 100 parts by weight of reclaimed sand whose type of sand was Mikawa No. 5 silica sand, and kneaded. The mold strength in the self-hardening mold making method was evaluated using sand left in a constant temperature room of 24% RH for 24 hours. The evaluation of the mold strength was performed using the recycled sand
0.375 parts by weight of triacetin and γ-
Water-soluble phenolic resin containing 0.5% by weight (based on resin) of aminopropyltriethoxysilane (solid content 49%)
%, Weight average molecular weight 2300), and the mixture was kneaded and filled in a 50 mmφ × 50 mmh test piece model.
The anti-pressure after 24 hours was measured. The method for adjusting the reclaimed sand is the same as in the first embodiment. Table 3 shows the results.

[0019]

[Table 3]

Example 4 The strength of a mold in a gas-curable mold molding method was evaluated. That is, with respect to 100 parts by weight of reclaimed sand whose type of sand is Mikawa No. 6 silica sand, 0.4 parts by weight of an aqueous solution of an acid whose acid value (KOH mg / g) shown in Table 4 was adjusted to 250, and γ-glycidoxypropyl Water-soluble phenol resin containing 0.5% by weight (based on resin) of trimethoxysilane (solid content 49%, weight average molecular weight 23
00) was added and kneaded with 2.5 parts by weight of a mixture of 50 mmφ × 50 mmh
Was filled in a test piece model for gas curing. 3.0 parts by weight of gaseous and aerosol methyl formate were injected into this model, and the withstand pressure after 24 hours was measured. Table 4 shows the results.

[0021]

[Table 4]

[0022]

As is apparent from the above embodiment, when a mold is produced using recycled sand, according to the method of the present invention, a mold having a higher strength than a mold obtained by a conventional production method is used. Is obtained. As a result, the amount of the binder used can be reduced, so that the collection and regeneration of the molding sand is facilitated, and at the same time, the amount of gas generated from the casting mold during casting can be reduced. Casting can be manufactured, which is practically useful. In addition, the use of the acid of the present invention makes it possible to extend the pot life during the production of the mold, which makes the production of the mold practically easy.

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Claims (6)

(57) [Claims] 1. A method for treating molding sand, which comprises adding an acid to a refractory granular material used in a method for producing a sand mold for molding in which a water-soluble phenol resin is cured with an organic ester. 2. The method according to claim 1, wherein the main component of the refractory granular material is recovered sand or recycled sand for reuse. 3. The method for treating molding sand according to claim 1, wherein the acid used has an acid dissociation index pKa of 5.0 or less. 4. A method for producing a sand mold for casting, comprising curing a water-soluble phenol resin with an organic ester, wherein an acid is used together with the refractory granular material. 5. The method for producing a sand mold for casting according to claim 4, wherein the main component of the refractory granular material is recovered sand or recycled sand for reuse. 6. The method for producing a sand mold for casting according to claim 4, wherein the acid used has an acid dissociation index pKa of 5.0 or less.