JP6188502B2 - Casting sand recycling process - Google Patents

Description

  The present invention relates to a method for reclaiming foundry sand.

It is publicly known that the cast sand after casting is recovered and used for casting again as the reclaimed foundry sand after performing the regeneration treatment to remove the binder adhering to the surface of the foundry sand. Heating regeneration methods and dry regeneration methods have been proposed.
However, the above-mentioned wet regeneration method requires a sewage treatment apparatus, which incurs equipment costs and increases regeneration costs. It is also necessary to dry the sand after the regeneration process. The heating regeneration method requires combustion facilities and air cooling facilities, and volatilization of exhaust gas containing dioxins is a problem. Furthermore, in the dry regeneration method, a method of removing friction between sand grains by removing centrifugal force and removing binders and the like adhering to the surface of the sand grains is widely used. However, in this method, if the regeneration efficiency is increased, the yield decreases due to sand crushing, fine graining, etc., and the power consumption per ton of recovered foundry sand also increases. In addition, it is difficult to regenerate fine-grained aggregates. Furthermore, for fire-resistant granular artificial aggregates that have recently been used frequently, the mold strength may not improve even after reclaiming. .
In view of the above circumstances, various proposals have been made for improving the method for reclaiming foundry sand. For example, a method for reclaiming recovered foundry sand having a step of contacting with water heated to 100 ° C. or higher has been proposed ( Patent Document 1).

JP 2002-178100 A

  The regeneration method described in Patent Document 1 has a high impurity removal rate and can improve casting quality and mold strength. However, since the recovered foundry sand is treated at high temperature and high pressure, from the viewpoint of operation and equipment. It is difficult to use the method industrially.

  Then, this invention is made | formed in view of the said situation, and provides the method which can recycle | recover the collect | recovered foundry sand by a simple method, without requiring special operation and equipment. For the purpose.

Castings The present inventor has conducted extensive studies to solve the above problems, which were mixed and stirred molding sand in water at a specific temperature, to separate the inorganic binder adhered to the template material sand, inorganic binder is separated The present invention was completed by finding that the sand can be regenerated by heating and drying the sand while stirring, and then removing the fine powder from the heat-dried foundry sand .
That is, the present invention
[1] A pulverization step of finely crushing the recovered foundry sand mold to obtain a pulverized product of the foundry sand,
A mixing step of separating the inorganic binder adhering to the foundry sand by mixing and stirring the obtained pulverized foundry sand in water at 5 ° C to 70 ° C;
Recovering the foundry sand from which the inorganic binder has been separated, and heating and drying while stirring the foundry sand ;
A method for reclaiming foundry sand, comprising a step of removing fine powder from the heat-dried foundry sand ,
[2 ] The method according to [ 1 ], wherein the inorganic binder is sodium silicate.
[3] The sodium silicate is the general _{formula: Na 2 O · nSiO 2 (} . N is representative of the 0.5 to 4.0) are represented by, as described in [2] method,
[4], wherein the inorganic binder, the general _{formula: xSiO 2 · yM 2 O ·} zH 2 O (M is ^Li +, ^{K +} or Na ⁺ alkali ions) of water glass base consisting of an alkali silicate aqueous solution represented by A binder containing a sodium-containing material as a hygroscopic agent is added to the binder so that a ratio of the sodium-containing material to the alkali silicate aqueous solution is 1: 4 to 1: 6. In the method described in [ 1 ], a silicone oil having a boiling point of 5 is added as a surfactant in the form of an emulsion, and the content of the silicone oil in the emulsion is 8% to 10% of the mass of the binder. is there.

The foundry sand regenerated by the method of the present invention has a bending strength comparable to or comparable to unused fresh foundry sand (also referred to herein as “new sand”) and is advantageously reused. can do. For example, in the reuse, not only a mixture of regenerated foundry sand and fresh sand but also regenerated foundry sand itself can be reused in the same manner as normal foundry sand.
In addition, since the foundry sand regenerated by the method of the present invention has little variation in bending strength, the method of the present invention can regenerate the recovered foundry sand to a foundry sand having a stable quality.
Furthermore, the method of the present invention is simpler to operate and does not require special equipment compared to the conventional recycling process in which the recovered foundry sand is treated at a high temperature and high pressure, so that the cost can be reduced. Can be environmentally friendly.

FIG. 1 is a photograph of a bending test jig of a bending strength tester used for bending strength measurement. FIG. 2 is a schematic diagram of the bending strength measurement. FIG. 3 is a diagram showing a strength relationship between fresh sand and sand regenerated at each water temperature in bending strength measurement.

In the present invention, the recovered foundry sand mold is finely pulverized to obtain a pulverized product of the foundry sand, and the obtained pulverized product of the foundry sand is mixed and stirred in water at 5 ° C. to 70 ° C. More, a mixing step for separating the inorganic binder adhering to it, a step of recovering the foundry sand from which the inorganic binder has been separated , a step of heating and drying while stirring the foundry sand, and a step of removing fine powder from the heat-dried foundry sand In addition, the present invention relates to a method for reclaiming casting sand.

[Crushing process]
In the pulverization step of the method of the present invention, the recovered foundry sand mold is finely crushed to obtain a crushed product of foundry sand.
<Casting sand>
As the foundry sand used in the above process, refractory granular materials conventionally used for molds can be used without particular limitation, for example, silica sand, chromite sand, zircon sand, olivine sand, synthetic mullite sand. And alumina aggregate particles. These foundry sands may be used alone or in combination of two or more. Among these, alumina aggregate particles are preferable.

  Moreover, even if the foundry sand used in the above-mentioned process is founded sand that has been regenerated by using it once or a plurality of times as a foundry for casting, it is further possible to use such regenerated foundry sand and fresh sand. It may be a mixture of When the foundry sand is a mixture of regenerated foundry sand and fresh sand, the proportion of reclaimed foundry sand and fresh sand is 0.01 to 10 times the amount of fresh sand relative to the weight of the reclaimed foundry sand. Preferably, the amount is 0.1 to 10 times, more preferably 1 to 10 times.

<Crushing method>
The method for pulverizing the foundry sand mold is not particularly limited as long as the foundry sand mold can be pulverized, and a known foundry sand mold pulverizing method can be used. Examples of such a pulverization method include pulverization using a pulverizer.

[Mixing process]
In the mixing step of the method of the present invention, the obtained ground sand is mixed and stirred in water at 5 ° C. to 70 ° C., thereby separating the inorganic binder adhering to the foundry sand. <Water at a specific temperature>
The temperature of water used in the above step is usually 5 ° C. to 70 ° C., and the foundry sand regenerated by the method of the present invention has a bending strength that is comparable to or comparable to fresh sand. From the viewpoint of regenerating the recovered foundry sand into a more stable foundry sand, the temperature is preferably 10 ° C to 50 ° C, more preferably 10 ° C to 40 ° C.
The amount of water used is not particularly limited as long as the inorganic binder attached to the foundry sand can be sufficiently removed, and is 0.5 to 100 times the mass of the foundry sand, preferably 0. The amount is from 5 to 50 times, more preferably from 1 to 30 times.

<Method of stirring>
The method of stirring the pulverized foundry sand with water is not particularly limited as long as the inorganic binder attached to the foundry sand can be removed, and a known stirring method can be used. Examples of such a stirring method include stirring by a stirrer.
The stirring conditions vary depending on the type of the foundry sand and the inorganic binder adhering to the foundry sand, and thus cannot be specified unconditionally. However, the viewpoint of sufficiently removing the inorganic binder adhering to the foundry sand, and the foundry sand by stirring. From the viewpoint of preventing the particle size of the particles from becoming non-uniform, the rotational speed of the stirrer is 30 to 300 rpm, preferably 40 to 250 rpm, and more preferably 50 to 200 rpm. The stirring time is 5 minutes to 60 minutes, preferably 10 minutes to 50 minutes, and more preferably 15 minutes to 40 minutes. Stirring conditions are suitably selected from the rotation speed and stirring time of the said stirrer by the stirrer to be used.

< Inorganic binder>
By the mixing step, the non-machine binder that will be separated from the molding sand, clay, sodium silicate (water glass), silica sol, sulfates, phosphates, and nitrates. These inorganic binders may be used alone or in combination of two or more.

Among these, as the inorganic binder, sodium silicate (water glass) is preferable, and sodium silicate represented by the general formula: Na ₂ O.nSiO ₂ (n represents 0.5 to 4.0) is more preferable.
Such sodium silicate is classified according to the molar ratio of sodium oxide to silicon dioxide (value of n in the above general formula), and sodium orthosilicate [Na ₄ SiO ₄ (Na ₂ O · 0.5SiO ₂ : n = 0.5)], sodium metasilicate [Na ₂ SiO ₃ (Na ₂ O.SiO ₂ : n ² = 1)] and the like.
Examples of sodium silicate include sodium silicate No. 1 [Na ₂ Si ₂ O ₅ (Na ₂ O · 2SiO ₂ : n = 2)] and sodium silicate No. 2 [Na ₄ Si ₅ O ₁₂ (Na ₂ O · 2. 5SiO ₂ : n = 2.5)], sodium silicate 3 [Na ₂ Si ₃ O ₇ (Na ₂ O · 3SiO ₂ : n = 3)], and sodium silicate 4 [Na ₂ Si ₄ O ₉ (Na ₂ O · 4SiO ₂ : n = 4)] and the like.

As the inorganic binder, a general formula: xSiO ₂ · yM ₂ O · zH ₂ O (M is Li ⁺ ,
A water glass-based binder comprising an alkali silicate aqueous solution represented by K ⁺ or Na ⁺ alkali ions), wherein the binder contains a sodium-containing substance as a moisture absorbent, a sodium-containing substance, and the alkali silicate aqueous solution; The silicone oil having a boiling point of 250 ° C. or higher is further added to the binder as a surfactant in the form of an emulsion, and the silicone oil is contained in the emulsion. A binder whose amount is 8% to 10% of the mass of the binder is preferred.

The water glass based binder has the general _{formula, xSiO 2 · yM 2 O ·} zH 2 O (M is Li ^+, K ⁺ or Na ⁺ alkali ions) alkali silicate aqueous solution or an alkali silicate aqueous represented by It consists of a solution and additionally contains a hygroscopic agent (humidity imparting agent).

The hygroscopic agent is a sodium-containing material and has a ratio of 1: 4 to 1: 6 in the binder composed of the alkali silicate aqueous solution, that is, the ratio of the binder 4 to the hygroscopic agent 1 to the ratio of the binder 6 to the hygroscopic agent 1. Added in. As a preferred embodiment, the ratio (mass ratio) of Na ₂ O / SiO _{2 in} the aqueous alkali silicate solution or aqueous alkali silicate solution is 2.5 to 3.5 (solid content: 20% to 40%). If so, it is possible to prevent early curing under certain operating conditions. According to a preferred embodiment, it is proposed to provide a hygroscopic agent of a 30% aqueous solution of sodium-containing material.

  In order to be able to control hygroscopicity (moisture imparting property), it is preferable to use a surfactant. When a surfactant is added to the binder in the form of silicone oil having a boiling point of 250 ° C. or higher, the fluidity of the foundry sand is significantly improved. In an effective embodiment, an emulsion containing 8-10% silicone oil based on the weight of the binder is added to the binder.

The content of the inorganic binder is preferably 0.2 to 10% by mass, more preferably 0.5 to 5% by mass with respect to the foundry sand.

[Heat drying process]
In the heat drying step of the method of the present invention, the foundry sand from which the inorganic binder has been separated is recovered, and the foundry sand is heated and dried while being stirred .
Methods for drying the recovered foundry sand include hot air, drying with microwaves or superheated steam, supplying hot air to the mold to evaporate moisture, heating the mold and casting in it Examples thereof include a method of filling and hardening sand, and a method of evaporating moisture by reducing pressure after filling molding sand into a mold.
[Fine powder removal process]
In the fine powder removing step of the method of the present invention, fine powder is removed from the heat-dried foundry sand.

Each use test machine and test machine conditions in the examples are as follows.
[1] Washing machine: Takemura Tech Co., Ltd. PM-1.5
[2] Blower: HJF-300 manufactured by TRUSCO NAKAYAMA
[3] Fine powder removing machine: Nippon Casting Co., Ltd. HSM1115
[4] Kneading machine: MG-150, manufactured by Daiwa Koki Co., Ltd.
[5] Molding machine: JNC-5 manufactured by Naniwa Seisakusho Co., Ltd.
Molding conditions
Mold temperature: 150 ° C
Blow pressure: 0.25 MPa
Blow time: 3 seconds
Gassing temperature: 100 ° C
Gassing pressure: 0.15 MPa
Gasing time: 7 seconds [6] Dryer: JM-17C made by Haier
[7] Anti-bending force tester: SC-200D-B manufactured by Takachiho Seiki Co., Ltd.
Bending test measurement conditions
Compression speed: 5 [mm / min] ± 5 [%] (return speed approximately 50 [mm / min])
Compression plate interval: Max. 55 [mm]
Sample stage material: S45C
Bending test jig: span 50 [mm], 3-point bending test jig

[Example 1]
10 kg of ESPAL [registered trademark] # 60 (manufactured by Yamakawa Sangyo Co., Ltd., alumina-based spherical aggregate) (hot sand: non-heated sand = about 7: about 3) and 5 ° C. 10 L of water was put into a water washer and stirred for 20 minutes (60 rpm). After washing with water, Espar [registered trademark] # 60 and water were separated, and Espar [registered trademark] # 60 was put into a mortar mixer, and while stirring, a duct was connected to a portable blower and air was sent from the top to dry. Next, the dried ESPAR [registered trademark] # 60 was put into a fine powder remover , and the ESPAR [registered trademark] # 60 (heatless sand) was regenerated and the fine powder was removed for 20 minutes.
1 kg of regenerated ESPAL [registered trademark] # 60 is placed in a kneader, and while moving the kneader, 0.1% of caustic soda 32% is added to 1 kg of ESPAL [registered trademark] # 60 and kneaded for 60 seconds. (Rotational speed: 185 rpm). Next, 1.1% sodium silicate was added and kneaded for 40 seconds (rotation speed: 185 rpm). Finally, 0.8% of fumed silica was added and kneaded for 40 seconds (rotation speed: 185 rpm). A sample [length 10 mm × width 100 mm × thickness 10 mm] was formed by using the molding machine with Espearl [registered trademark] # 60 to which the binder [trade name: AWB40 (manufactured by Minerco)] was adhered by the kneading. Then, the sample was put in a dryer and dried at 200 W for 30 seconds.

[Example 2]
A sample was prepared by performing the same operation as in Example 1 except that 10 ° C. water was used instead of 5 ° C. water.

[Example 3]
A sample was prepared in the same manner as in Example 1 except that 20 ° C. water was used instead of 5 ° C. water.

[Example 4]
A sample was prepared in the same manner as in Example 1 except that 30 ° C. water was used instead of 5 ° C. water.

[Example 5]
A sample was prepared in the same manner as in Example 1 except that 40 ° C. water was used instead of 5 ° C. water.

[Example 6]
A sample was prepared in the same manner as in Example 1 except that 50 ° C. water was used instead of 5 ° C. water.

[Example 7]
A sample was prepared in the same manner as in Example 1 except that 60 ° C. water was used instead of 5 ° C. water.

[Example 8]
A sample was prepared by performing the same operation as in Example 1 except that 70 ° C. water was used instead of 5 ° C. water.

[Comparative Example 1]
A sample was prepared in the same manner as in Example 1 except that 0 ° C. water was used instead of 5 ° C. water.

[Comparative Example 2]
A sample was prepared in the same manner as in Example 1 except that 3 ° C. water was used instead of 5 ° C. water.

[Comparative Example 3]
A sample was prepared in the same manner as in Example 1 except that 100 ° C. water was used instead of 5 ° C. water.

[Reference example]
Add 1 kg of new Espearl [registered trademark] # 60 to the kneader, and move the kneader to add 0.1% of caustic soda 32% to 1 kg of Esper [registered trademark] # 60 and knead for 60 seconds (rotation speed) 185 rpm). Next, 1.1% sodium silicate was added and kneaded for 40 seconds (rotation speed: 185 rpm). Finally, 0.8% of fumed silica was added and kneaded for 40 seconds (rotation speed: 185 rpm). A sample [length 10 mm × width 100 mm × thickness 10 mm] was formed by using a molding machine with Espearl [registered trademark] # 60 to which a binder [trade name: AWB40 (manufactured by Minerco)] was adhered by kneading. Then, the sample was put in a dryer and dried at 200 W for 30 seconds.

[Bending strength measurement]
The sample produced in the reference example was allowed to stand for 15 minutes, and the temperature of the sample was brought to room temperature. The sample was then heated in the microwave and left for 5 minutes. Then, the sample was set on the bending test jig 2 of the bending strength tester 1, and the bending strength was measured by applying a load from the top of the sample 3 to the center of the sample with the indenter 4 (see FIG. 2).
Moreover, the bending strength was measured in the same manner for each sample produced in Examples 1 to 11 and Comparative Examples 1 to 3. The measurement results are shown in Tables 1 to 13 below and FIG.

From the results shown in Tables 1 to 9, Table 13, and FIG. 3, in the mixing step of the method for reclaiming foundry sand according to the present invention, ESPAR [registered trademark] with a binder [trade name: AWB40 (manufactured by Minerco)] adhered thereto. When # 60 is mixed and stirred in water at 5 ° C. to 70 ° C., the regenerated ESPAL [registered trademark] # 60 is equivalent to or comparable to ESPAL [registered trademark] # 60 (reference example) which is fresh sand. The bending strength was shown. On the other hand, from the results of Table 1, Table 10 to Table 13 and FIG. 3, it was found that ESPAL [registered trademark] # 60 to which the binder [trade name: AWB40 (manufactured by Minerco)] was attached was 0 ° C. (comparison) In the case of mixing and stirring in water of Example 1) and 3 ° C. (Comparative Example 2) and 100 ° C. (Comparative Example 3) in which the water temperature exceeds 70 ° C., the regenerated ESPAL [registered trademark] # 60 is ESPAL which is fresh sand. Bending strength was inferior to [registered trademark] # 60 (reference example).
Further, from Table 13, since the measured value width of the bending strength of the samples prepared in Examples 1 to 8 is smaller than the measured value width of the bending strength of the samples prepared in Comparative Examples 1 to 3, The variation in strength was small and the quality of the reclaimed foundry sand was stable. On the other hand, since the measurement value width of the bending strength of the samples produced in Comparative Examples 1 to 3 was large, the variation in bending strength was large, and the quality of the reclaimed foundry sand was unstable.
From the above results, the foundry sand regenerated by the method of the present invention has a bending strength comparable to or comparable to that of fresh sand, and the method of the present invention is a foundry sand that has a stable quality compared to the used foundry sand. It is clear that it can be played back.

1 Bending test machine 2 Bending test jig 3 Sample 4 Indenter 5 Sample base material: S45C

Claims (4)

Crushing the collected foundry sand mold into finely crushed cast sand,
A mixing step of separating the inorganic binder adhering to the foundry sand by mixing and stirring the obtained pulverized foundry sand in water at 5 ° C to 70 ° C;
Recovering the foundry sand from which the inorganic binder has been separated, and heating and drying while stirring the foundry sand ;
A method for reclaiming foundry sand, comprising a step of removing fine powder from the heat-dried foundry sand. The method according to claim 1 , wherein the inorganic binder is sodium silicate. The method according to claim 2 , wherein the sodium silicate is represented by a general formula: Na ₂ O.nSiO ₂ (n represents 0.5 to 4.0). Wherein the inorganic binder, the general _{formula: xSiO 2 · yM 2 O ·} zH 2 O (M is ^Li +, ^{K +} or Na ⁺ in alkaline ions) was with water glass based binder comprising an alkali silicate aqueous solution represented by In addition, a sodium-containing material as a moisture absorbent is added to the binder so that the ratio of the sodium-containing material and the aqueous alkali silicate solution is 1: 4 to 1: 6, and the binder further has a boiling point of 250 ° C. or higher. how silicone oil is added in the form of an emulsion as a surfactant, the content of silicone oil in the emulsion is 8% to 10% by weight of the binder, of claim 1 having a.