JP2004181486A - Method for rebonding molding sand and method for making mold using rebonded sand - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for rebonding molding sand by controlling the rebonding degree of the sand at the simpler method than the conventional method, and a method for making a mold for casting using synthetic mullite sand rebonded in the above rebonding method, when the molding sand recovered from the mold obtained by using the synthetic mullite sand as the molding sand, a water-soluble phenolic resin as a binder and an organic ester compound as a hardening agent is thermally rebonded. <P>SOLUTION: This molding sand uses the synthetic mullite sand and the water-soluble phenolic resin is used as the binder. When the molding sand recovered from the mold obtained by hardening with the organic ester compound is rebonded with a heating-treatment, as a value for controlling the rebonding degree of the sand, a pH measured value with a JACT molding sand testing method, S-3 "the pH testing method of the molding sand" is used and this value is controlled to 9.7-10.6 so as to perform the rebonding treatment at the first step of the heating-treatment. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２４】表１より、新砂と同等かまたはそれ以上の圧縮強さを得るためには、再生砂のｐＨ値は１０．６以下であることが確認された。また、再生砂のｐＨ値が低くなるにつれて、圧縮強さが向上し、再生砂のｐＨ値が１０．５（再生条件８００℃、２０分）では、圧縮強さが新砂の場合の１．３倍、ｐＨ値が９．７（再生条件１０００℃、２０分）では１．５倍となっていた。また、低温で鋳物砂を再生するよりも高温で再生するほうが、圧縮強さの加熱時間に対する上昇の割合が大きく、短時間で鋳物砂を再生できていた。なお、比較例１および再生条件３００℃、２０分で再生した場合の鋳物砂のｐＨ値が低い原因は、鋳物砂に付着している残留有機物が多いので、遊離アルカリ分が有機物中に包まれて水に溶出してこないためと考えられる。また、鋳物砂の再生が進んでいくと、一時的に鋳物砂のｐＨ値が上昇するのは、熱により有機物の結合が切れて、遊離アルカリ分が水に溶出しやすくなるためと考えられ、さらに再生を進めると、遊離アルカリ分が残留有機物とともに大気中に飛散し水への溶出量が減少するため、鋳物砂のｐＨ値が低下していくと考えられる。
【００２５】
【発明の効果】以上説明したように、本発明の鋳物砂の再生方法は、鋳型から回収した鋳物砂を熱的に再生する際に、再生度合いの管理値として、ＪＡＣＴｐＨ試験法によるｐＨ測定値を用い、その値を９．７〜１０．６に管理することにより、より簡便な再生管理方法を提供でき、必要最小限のエネルギーで鋳物砂を再生することができる。また、この再生方法により得られた再生砂を用いた鋳型は、新砂を用いた鋳型よりも、圧縮強さが高強度となるため、鋳型に使用する粘結剤の量を削減することが可能となり、省力化につながる。また、それによって、鋳物砂に付着する残留有機物が減少し、その鋳型から回収された鋳物砂の再生に必要とされるエネルギーが減少し、さらにエネルギーの効率化を達成できる。[0001]
The present invention relates to a method for applying heat to synthetic sand obtained from a mold obtained by using synthetic mullite sand as a molding sand, a water-soluble phenol resin as a binder, and an organic ester compound as a hardener. And a method for efficiently roasting and regenerating. The present invention also relates to a method for producing a mold using the recycled molding sand.
[0002]
2. Description of the Related Art Organic room temperature mold production methods are broadly classified into gas-curable mold production methods (cold box method) and self-hardening mold production methods (no-bake method). In the self-hardening mold manufacturing method, in recent years, a method of using a water-soluble phenol resin as a binder and curing it with an organic ester to manufacture a mold is excellent in casting quality and working environment, so it is also good in the casting industry. We have a good track record. The method of manufacturing a casting using a water-soluble phenol resin as a binder is as follows. First, a water-soluble phenol resin as a binder, an organic ester compound as a hardener, and molding sand (granular refractory aggregate) are mixed in a mixer. A casting sand covered with a binder and a hardening agent is filled in a mold for mold production, cured at room temperature, and finally removed from the mold to produce a casting mold (for example, see Patent Document 1). 1).
[0003] In addition, molding sands used in the production of molds are also manufactured by artificially prepared molding sands for the purpose of compensating for the disadvantages of silica sand, zircon sand, chromato sand, olivine sand and the like, which have been used in many cases. And specifically, synthetic mullite sand and the like. This synthetic mullite sand is characterized by a small amount of thermal expansion, a high fire resistance, and a spherical shape (for example, see Patent Document 2). Therefore, by using a water-soluble phenol resin as a binder and manufacturing a mold using synthetic mullite sand as the casting sand, not only the casting quality and working environment are excellent, but also the refractory hardness is high and The resistance to thermal shock (for example, refer to Patent Document 2) realizes a high yield in recovering and regenerating molding sand, and makes it possible to reduce the amount of industrial waste.
[0004] Generally, there are mechanical, wet and thermal methods for regenerating the sand used for the mold. As a method for regenerating synthetic mullite sand, there is a method of performing a thermal method on sand and then performing a mechanical method (for example, see Patent Document 3). In addition, only the thermal method is a method in which the recovered sand is not pre-ground and the heat is regenerated without flowing the sand to improve efficiency and labor saving (for example, see Patent Document 4). ). As another method, there is a method of managing the degree of regeneration in the regeneration of sand, a method of calculating the amount of a binder corresponding to the lost active clay (for example, see Patent Document 5), and a method using a roasting furnace. Two or more factors (for example, Al ₂ O ₃ %, apparent density, loss on ignition, etc.) of the sand regenerated by a reclaimer after roasting the sand are measured, and a multivariate analysis method or A method of predicting the bending strength of the kneading sand by fuzzy inference and adjusting the reproduction conditions (for example, see Patent Document 6) and the like.
[0005]
[Patent Document 1] JP-A-58-154433 (pages 3 to 6)
[Patent Document 2] JP-A-5-169184 (pages 3 and 4)
[Patent Document 3] JP-A-6-154941 (page 3)
[Patent Document 4] JP-A-2000-61578 (pages 4 to 5, FIGS. 1 to 10)
[Patent Document 5] JP-A-61-150740 (pages 2-3, FIGS. 1-3)
[Patent Document 6] JP-A-6-210394 (pages 2 to 4, FIGS. 1 to 5)
[0006]
In order to regenerate synthetic mullite sand using a water-soluble phenol resin, a mechanical method, a thermal method, a method using both methods and the like are employed. However, in the mechanical method of friction and polishing, the residual organic matter adhered to the sand is strong, and the synthetic mullite sand is spherical, so that the frictional force does not act sufficiently, so that the residual organic matter can be sufficiently removed. It cannot be removed, and the strength of the mold using the recycled sand tends to decrease. In order to solve this, inefficient methods such as replenishing fresh sand or increasing the amount of adhesive have to be taken. In the thermal method, fluidized roasting and non-fluidized roasting can be mentioned.Either method is an effective method for regenerating synthetic mullite sand in order to eliminate residual organic substances adhering to sand. is there. However, since the thermal method uses a large amount of energy, there is a problem that the amount of energy used must be reduced, and various measures have been taken to solve the problem. One of the methods is to use both a thermal method and a mechanical method. However, the method of regeneration is complicated and the number of steps is long, which is not sufficient in terms of energy efficiency. Another useful method is to control the degree of sand regeneration, thereby minimizing the amount of energy used. The management method includes the method described above. From the viewpoints of efficiency, simplification, labor saving, and the like, a simpler management method is required.
[0007]
SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for heat-treating molding sand recovered from a mold obtained by using a water-soluble phenol resin as a binder and an organic ester compound as a hardener in synthetic mullite sand. The above-mentioned problem is solved by providing a method for managing the degree of regeneration by a simpler method and a method for manufacturing a casting mold using the synthetic mullite sand regenerated by the management method when regenerating the steel in a regular manner. It is possible to do.
That is, the present invention provides: When synthetic mullite sand is used as casting sand, and water-soluble phenol resin is used as a binder, and the recovered sand from the mold obtained by curing with an organic ester compound is regenerated by heat treatment, the sand is regenerated. As a value for controlling the degree, a pH measurement value according to JACT molding sand test method S-3 “pH test method for molding sand” is used, and by controlling the value to 9.7 to 10.6, heat treatment is performed in one stage. This is a method for reclaiming foundry sand, which comprises performing a reclaim treatment.
2. Kneading a molding sand regenerated by the method according to the above 1, a binder containing a water-soluble phenol resin, and a curing agent composed of an organic ester compound, filling the mixture into a desired mold, and curing the binder. A method for producing a mold characterized by the following. By regenerating the molding sand by the method of the present invention, the above-described problem has been solved, and a method for producing a mold using the molding sand regenerated by an extremely energy-efficient method has been established. .
The JACT is the Japan Foundry Technology Association, and the JACT foundry sand test method is a method for testing foundry sand standardized by the Japan Foundry Technology Association. In addition, the JACT molding sand test method S-3, "pH test method for molding sand" (hereinafter abbreviated as JACT pH test method) will be described. First, 20 g of a molding sand as a sample is weighed into a clean beaker having a capacity of 100 ml. 50 ml of pure water is added therein, a magnetic stirrer bar is put in, a light lid (a watch glass or the like) is closed, and the mixture is stirred with a magnetic stirrer for 30 minutes. After stirring, the mixture is allowed to stand, the temperature of the supernatant is checked, and the pH value is measured with a pH meter based on JIS Z8802 “pH measurement method”.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION The molding sand used in the present invention is synthetic mullite sand, and preferably has a mean particle size of about 50 to 600 μm. Synthetic mullite sand is a type of ceramic mainly composed of aluminosilicate, and is obtained by combining various minerals with each other, mixing and pulverizing them, turning them into a slurry state, granulating them with a spray dryer, and firing them at a high temperature.
The water-soluble phenol resin used as a binder in the present invention is an alkaline resole type phenol resin obtained by reacting phenols and aldehydes in a large amount of an aqueous solution of an alkaline substance. Examples of phenols include phenol, cresol, resorcinol, xylenol, bisphenol A, cumylphenol, nonylphenol, butylphenol, phenylphenol, ethylphenol, octylphenol, amylphenol, naphthol, bisphenol F, bisphenol C, catechol, hydroquinone, pyrogallol , Phloroglucin, lignin, bisphenol A residue, chlorophenol, dichlorophenol, and other substituted phenols. These may be used alone or in a mixture of two or more. Aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, furfural and the like. Examples of the alkaline substance include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. As the water-soluble phenolic resins obtained therefrom, those having a weight average molecular weight of preferably 500 to 5000 are preferably used, and those having a solid content of 30 to 70% by mass are preferably used.
The curing agent used in the present invention is an organic ester compound. Examples of the organic ester compound include known aromatic, aliphatic and alicyclic organic ester compounds. Specifically, for example, γ-butyrolactone, propylene carbonate, ε-caprolactone, methyl formate, ethylene glycol diacetate, ethylene glycol monoacetate, triacetin and the like, and these may be used alone or in a mixture of two or more. Is also good.
The ratio of the water-soluble phenolic resin to the molding sand is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 0.1% by mass, based on the molding sand in view of improving the curability of the mold and securing the strength. The range is preferably from 5 to 5% by mass. The ratio of the organic ester compound to the molding sand is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, based on the molding sand from the viewpoint of improving the curability of the mold and ensuring the strength. Is preferable.
The synthetic mullite sand in the mold obtained using the synthetic mullite sand, the water-soluble phenol resin and the organic ester compound is regenerated by a thermal method. In the method, first, mechanical vibrations or the like are applied to a used mold to separate the mold, break lumps and aggregates, and collect synthetic mullite sand. On the surface of the collected synthetic mullite sand (hereinafter abbreviated as collected sand), unburned components such as phenol resin remain. Next, the recovered sand is subjected to a heat treatment, preferably at a treatment temperature of 600 to 1000 ° C, particularly preferably at 800 to 1000 ° C. If the treatment temperature is lower than 600 ° C., the regeneration tends to take too much time, and the generation of dioxin and the like is also assumed. Conversely, if the processing temperature exceeds 1000 ° C., the temperature tends to be too high and the energy cost tends to be high.
As a method for controlling the degree of regeneration of the foundry sand during the regeneration of the recovered sand in the present invention, the pH value of the foundry sand is measured by the JACT pH test method, and if the value is in the range of 9.7 to 10.6. If so, the heat treatment is stopped. If the pH value of the casting sand exceeds 10.6, the regeneration of the sand is insufficient, and sufficient strength cannot be obtained when a mold is manufactured. If the pH value of the foundry sand is lower than 9.7, heating and regeneration will be performed more than necessary, and energy will be wasted.
As an actual industrial control method, a correlation between a processing time at a heat treatment temperature actually performed in advance and a pH value measured by a JACT pH test method of the molding sand regenerated under the processing conditions is obtained. To determine. After the heat regeneration conditions were determined, the recovered sand was actually regenerated under these conditions, and in order to confirm the degree of regeneration, the pH value was measured by the JACT pH test method to confirm that there was no problem as sand for mold production. Used as molding sand for mold production.
The regenerated synthetic mullite sand (hereinafter abbreviated as regenerated sand) obtained as described above is used again as molding sand for producing a mold. That is, molding sand obtained by adding only a desired amount of unused synthetic mullite sand (hereinafter, abbreviated as “new sand”) to recycled sand alone or recycled sand, a water-soluble phenol resin, and an organic ester compound are mixed. And a molding sand covered with a curing agent is filled into a desired mold, and the water-soluble phenol resin is cured to obtain a mold.
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Further, all percentages and parts in the following description indicate mass% or parts by mass.
【Example】
[Example of pretreatment] (Creation of original sand for recycled sand)
Chem Rez 6016 (manufactured by Hodogaya Ashland Co., Ltd., organic ester-based curing agent for water-soluble phenolic resin) 0.4 part per 100 parts of Cerabeads # 500 (manufactured by ITOCHU CERATECH CORPORATION, synthetic mullite sand), Chem Rez 630 LV (manufactured by Hodogaya Ashland Co., Ltd., water-soluble phenol resin) (2.0 parts) was kneaded with a Shinagawa mixer. Using the kneaded sand, a mold for a step cone vaning test having a mold weight of 45 kg and a casting weight of 10 kg was molded, FC250 ordinary cast iron was cast at 1350 ° C., the mold was separated, and synthetic mullite sand was recovered. Further, the collected massive mold sand was pulverized with a crusher, and the massive sand was removed with a 10-mesh sieve. The recovered sand obtained by repeating the operations from molding to casting of the mold, pulverization of the mold, crusher pulverization of the mold five times was used as the original sand of the reclaimed sand and subjected to the following tests.
[0019]
[Example 1]
Using a propane gas burner, the obtained raw sand was heated and regenerated at a temperature of 300 ° C. to 1000 ° C. for 20 minutes at each temperature as shown in Table 1. After the heat regeneration treatment, each regenerated sand was allowed to stand in a constant temperature and humidity room at 20 ° C. and 60% RH for 24 hours. Thereafter, 0.4 part of Chem Rez 6016 (manufactured by Hodogaya Ashland Co., Ltd., an organic ester-based curing agent for a water-soluble phenol resin) and 100 parts of Chem Rez 630 LV (manufactured by Hodogaya Ashland Co.) , A water-soluble phenol resin) was kneaded with a Shinagawa mixer, and the kneaded product was filled in a mold strength test model having a diameter of 50 mm and a height of 50 mm to obtain a test mold. After leaving the mold for 24 hours, its compressive strength was measured. Further, a sample (weight W ₀ ) obtained by removing the free moisture of the regenerated sand obtained by heating and regenerating at each temperature was subjected to the JACT molding sand test method S-2 based on the “Ignition loss on ignition of molding sand” method. Ignition was performed at about 1000 ° C. for about 1 hour, and the weight (W ₁ ) after cooling to room temperature in a desiccator was measured, and the ignition loss was calculated and shown in Table 1. The ignition loss is a numerical value calculated by the formula [(W ₀ −W ₁ ) / W ₀ ] × 100 (%), and a smaller value indicates higher regeneration efficiency. Further, based on the JACT pH test method, 20 g of the reclaimed sand was weighed into a plastic container, and 50 ml of purified water was added to the sand, followed by stirring for 30 minutes, and the component eluted from the sand into the purified water was determined as the pH value of the sand. It was measured. Table 1 shows the results.
[0020]
[Example 2]
The raw sand obtained in the pretreatment example was heated and regenerated using propane gas burners at temperatures of 500 ° C. and 600 ° C. for 10 minutes, 20 minutes and 30 minutes as shown in Table 1. After the heat regeneration treatment, each regenerated sand was allowed to stand in a constant temperature and humidity room at 20 ° C. and 60% RH for 24 hours. Using the regenerated sand subjected to the heat regeneration treatment, a mold was manufactured in the same manner as in Example 1, and the compressive strength of the mold was measured. Further, the ignition loss and pH value of the recycled sand were measured in the same manner as in Example 1. The results are shown in Table 1.
[0021]
[Comparative Example 1]
In the examples, a mold was produced in the same manner as in the example 1 except that the raw sand before regeneration obtained in the pretreatment example was used for the production of the mold, and the compressive strength of the mold was measured. Further, the ignition loss and pH value of the recycled sand were measured in the same manner as in Example 1. The results are shown in Table 1.
[0022]
[Comparative Example 2]
In the example, a mold was produced in the same manner as in Example 1 except that fresh sand was used for producing the mold instead of the heat-treated regenerated sand, and the compressive strength of the mold was measured. Further, the ignition loss and the pH value of the recycled sand were measured in the same manner as in Example 1. The results are shown in Table 1.
[0023]
[Table 1]

From Table 1, it was confirmed that the pH value of the regenerated sand was 10.6 or less in order to obtain a compressive strength equal to or higher than that of the fresh sand. Further, as the pH value of the reclaimed sand decreases, the compressive strength increases, and when the pH value of the reclaimed sand is 10.5 (regeneration condition: 800 ° C., 20 minutes), the compressive strength is 1.3 in the case of the fresh sand. When the pH value was 9.7 (regeneration conditions: 1000 ° C., 20 minutes), the value was 1.5 times. In addition, when the molding sand is regenerated at a high temperature, the rate of increase in the compressive strength with respect to the heating time is greater than when the molding sand is regenerated at a low temperature, and the molding sand can be regenerated in a short time. The reason for the low pH value of the molding sand in the case of Comparative Example 1 and the regeneration under the regeneration conditions of 300 ° C. for 20 minutes is that the amount of the residual organic matter adhering to the molding sand is large, so that the free alkali is wrapped in the organic matter. Is not eluted in water. In addition, as the regeneration of molding sand progresses, the reason that the pH value of the molding sand temporarily rises is considered to be that the bond of the organic matter is cut by heat and the free alkali component is easily eluted into water, When the regeneration is further promoted, it is considered that the pH value of the foundry sand decreases because the free alkali is scattered into the air together with the residual organic matter and the amount of elution into water decreases.
[0025]
As described above, in the method for reclaiming molding sand of the present invention, when the molding sand recovered from the mold is thermally regenerated, the measured value of the pH measured by the JACT pH test method is used as the management value of the degree of regeneration. By controlling the value in the range of 9.7 to 10.6 using, a more simple regeneration management method can be provided, and the molding sand can be recycled with a minimum necessary energy. In addition, since the mold using recycled sand obtained by this recycling method has higher compressive strength than the mold using fresh sand, it is possible to reduce the amount of binder used in the mold. It leads to labor saving. This also reduces the amount of residual organic matter adhering to the foundry sand, reduces the energy required to regenerate the foundry sand recovered from the mold, and achieves more efficient energy.

Claims (4)

When synthetic mullite sand is used as the molding sand, and the water-soluble phenol resin is used as a binder, and the molding sand recovered from the mold obtained by curing with the organic ester compound is regenerated by a heat treatment, As a value for controlling the degree of regeneration, a pH value measured by the JACT molding sand test method S-3 “pH measurement method for foundry sand” is used, and the value is controlled to 9.7 to 10.6 to perform one stage of heat treatment. A method for reclaiming foundry sand, wherein the method comprises reclaiming. The method of claim 1, wherein the temperature of the recovered molding sand is 600 to 1000C. The method according to claim 1, wherein the temperature of the recovered molding sand is from 800 to 1000C. The foundry sand, a water-soluble phenol resin, and an organic ester compound are kneaded with the foundry sand regenerated by any one of the above-mentioned claims 1 to 3, and the foundry sand and the foundry sand coated with a curing agent are mixed with a desired amount. A method for producing a mold, comprising filling a mold and curing a water-soluble phenol resin to obtain a mold.