JP5451587B2 - Recycling method of core and core sand - Google Patents

Description

  The present invention relates to a method for recycling molding of a core made of core sand prepared by reusing a sand-containing liquid (including sand slurry) of a water-soluble core generated by dropping core sand after casting, and Regarding core sand to be used. In particular, it relates to core sand suitable for casting light alloys such as aluminum, magnesium and zinc.

  Paragraph 0002 of Patent Document 1 relates to the core: “In precision casting technology in which a molten metal is press-fitted into a mold and rapidly solidified to produce a casting, a space is provided inside a precision casting such as a machine part. For example, the core is indispensable for the production of the inner space of the cylinder using the aluminum alloy and the cooling medium passage inside the exhaust.

  The recycling molding method of the core as described above, that is, the recycling molding method of recycling the recovered foundry sand and the water-soluble inorganic salt binder (inorganic binder) after the sand removal of the water-soluble core, In recent years, it has attracted attention from an environmental standpoint because it does not generate a large amount.

  Patent documents 1 and 2 are patent documents describing a recycling molding method using such a water-soluble core. The description relating to the water-soluble core in Patent Document 1 is cited below with some editorial changes (paragraphs 0007 to 0015). [Patent Documents 2, 3 and 4] in the following quotations correspond to Patent Documents 3, 4 and 2 in the text of the specification.

“On the other hand, by using an inorganic salt as a core binder, a water-soluble core that can reduce the amount of gas generated at the time of casting and can perform core sand removal with water after casting is considered. Similar to the water-insoluble core, the water-soluble core has a problem of how to treat a large amount of foundry sand and inorganic binder.
On the other hand, magnesium sulfate (MgSO ₄ ) is known as a water-soluble core binder. However, the magnesium sulfate (MgSO ₄ ) aqueous solution has the following drawbacks. 1) Adhesive strength is weak and core strength is not sufficient. 2) The required amount of binder increases (the amount of water also increases), the fluidity of the foundry sand deteriorates, and the blow filling property is insufficient during core molding.

Therefore, the present inventors aim to provide a water-soluble core binder having both sufficient core strength and solubility, a cation selected from Mg ²⁺ , Na ⁺ , Ca ²⁺ , SO ₄ ²⁻ , It consists of one or more water-soluble inorganic salts consisting of a combination with an anion selected from CO ₃ ²⁻ , HCO ₃ ⁻ , and B ₄ O ₇ ²⁻ (except for the case of only magnesium sulfate (MgSO ₄ )). A water-soluble core binder was invented (Patent Document 2 below). In particular, selected from magnesium sulfate (MgSO ₄ ) 0-99.9% by mass, sodium carbonate (Na ₂ CO ₃ ), sodium tetraborate (Na ₂ B ₄ O ₇ ), sodium sulfate (Na ₂ CO ₃ ). It was found that a water-soluble core binder composed of one or more of 100 to 0.1% by mass is suitable.

  Similarly, the present inventors have coated the surfaces of foundry sand particles with a water-soluble inorganic salt binder for the purpose of providing a water-soluble core having both high-temperature strength and water-solubility, which is a measure of ease of sand removal. In the water-soluble core, the water-soluble inorganic salt binder includes silica sand (silica powder), alumina, potassium titanate, silicon carbide, zircon silicate, fibrous potassium titanate, titanium oxide, zinc oxide, iron oxide, oxidation Invented a high-strength water-soluble core to which one or more inorganic fillers selected from magnesium are added (Patent Document 3 below).

  A process using a water-soluble inorganic core sand to which a known water-soluble binder is added (2 to 10% of sand in terms of moisture, hereinafter referred to as wet sand) is used to wash the core in the cast product with water (or a salt solution). . The washed sand contains a large amount of salt solution (hereinafter referred to as slurry sand). Therefore, core sand production requires a dehydration step using a centrifuge and a kneading step for fine preparation of a salt solution.

  Accordingly, the present inventors almost completely regenerate and recycle both the foundry sand and the inorganic binder after use based on the development of the water-soluble inorganic binder that can be easily removed from the sand in Patent Document 2 and Patent Document 3. In order to provide a method and make the water-soluble core more practical and environmentally friendly, the casting sand and the water-soluble inorganic salt binder are almost completely removed from the water-soluble core. For the purpose of providing a method of reusing, the supernatant liquid consisting of a water-soluble inorganic salt binder and water, which is described later, from a cast product using a water-soluble core in which the surface of the molding sand particles is coated with a water-soluble inorganic salt binder. Removing the foundry sand using water pressure, storing the removed foundry sand, a water-soluble inorganic salt binder, and a mixture of water, and a supernatant consisting of the water-soluble inorganic salt binder and water; A precipitation step of separating into a slurry consisting of a small amount of water-soluble inorganic salt binder and water, a step of dehydrating the water of the slurry to a predetermined concentration, and a step of reusing the slurry dehydrated to the predetermined concentration Invented a method of reusing foundry sand and water-soluble inorganic salt binder (Patent Document 4 below).

The following matters can be cited as problems of conventional reuse technology (core sand is wet sand).
1) A dehydration step and a kneading step for producing core sand in a wet sand state from slurry sand are required.
2) Although the salt solution (water | moisture content) in sand can be prepared almost by control of the centrifugal effect, the dehydration process is difficult in accuracy.
3) Dehydrated sand requires a structure such as a hopper to prevent natural drying during storage, which complicates equipment.
4) In order to produce the core salt of the target salt solution (moisture), a kneading step with measurements such as the amount of salt solution (water) in the sand of dehydrated sand and the control of the amount of sand is required.
The reason why these problems occur is that there is a large difference in composition between slurry sand after sand removal (sand-containing liquid) and core sand (wet sand). For example, in the weight ratio of sand / salt solution, slurry sand is significantly different from 1 / 0.3 to 50, whereas wet sand is significantly different from 1 / 0.03 to 0.10. "

  In addition, wet sand core sand (wet sand) recovered from the slurry sand generated by the sand removal is prepared in a process of being kneaded and used as molding core sand. Usually, an aqueous inorganic binder solution / casting Sand (volume ratio) ≧ 1 is used for molding slurry sand (Patent Document 1, Claim 4 etc.).

  For this reason, Patent Document 1 proposes a recycling method (core recycling method) of foundry sand and water-soluble inorganic salt binder having the following configuration (claim 1).

  “Recovering slurry foundry sand composed of foundry sand and a water-soluble inorganic salt binder from a cast product using a water-soluble core in which the surface of the foundry sand particles is coated with a water-soluble inorganic salt binder; A step of placing slurry-like foundry sand composed of a water-soluble inorganic salt binder into a slurry box connected to a cavity in a casting mold, and blowing slurry-flowing air into the slurry-like foundry sand in the slurry box to obtain slurry-like foundry sand. Including a step of fluidizing, a step of filling the fluidized slurry-like foundry sand into a cavity in a mold as a new core sand, and a step of drying the core sand filled in the cavity. And a method for reusing the foundry sand and water-soluble inorganic salt binder. "

  For reference, FIGS. 1 (A) and 1 (B) show a flowchart of the core recycling method of Patent Document 1. FIG.

  In the core recycling molding method described in Patent Documents 1 and 2 above, further improvement of productivity, specifically 1) reduction of molding time, 2) reduction of heat cost, 3) improvement of dimensional accuracy, 4) Improvements in releasability and the like have been demanded.

  Therefore, the present inventors previously proposed a novel core recycle molding method having the following configuration, which can solve the above-mentioned problems, in cooperation with other inventors (Patent Document 5).

Using a core sand in which an aqueous solution of a binder composed of a water-soluble inorganic salt (hereinafter referred to as “binder aqueous solution”) is added to foundry sand, a water-soluble core (hereinafter referred to as “core”) is molded into an aerator. And
In a molding method in which the sand-containing liquid generated by sand removal of the core after casting with the core is recycled as a raw material for the core sand,
In the graph of the relationship between the core sand moisture (X) and the fluidization rate (Y) when a predetermined air fluidization experiment is performed on the composition of the core sand, the core from X where Y is a minimum value. A sand water content is low, and an aqueous binder solution in an amount capable of ensuring the required strength is added.

  The above core recycle molding method can be expressed as concrete invention specific items as follows.

Using core sand to which an aqueous binder solution has been added, the core is made into an aerator,
After casting using the core, in the molding method for recycling the sand-containing liquid generated by the sand removal of the core as a raw material for the core sand,
As the water-soluble inorganic salt, a cation selected from Mg ²⁺ , Na ⁺ and Ca ²⁺ , and an anion selected from SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , and B ₄ O ₇ ²⁻ And using a combination of one or more of
The core sand moisture is set in the range of 2 to 13% by mass, and the binder addition amount in the dry core is set in the range of 1 to 6% by mass.

  The use of the core molding method of the present invention defined by the above-described invention specific matters can achieve the following effects and solve the above problems.

  That is, the following actions and effects can be achieved by using a core sand having a low water content without using a slurry sand (high water content) foundry sand (hereinafter referred to as “slurry sand”). .

  1) For core curing, heating of the core mold and blowing of hot air into the cavity after filling become unnecessary. In the case of slurry sand, it is necessary to remove the water in the core by evaporation. However, in the present invention, the core curing only requires the dehydration time by the filling pressure. Therefore;

    ・ Molding cycle time can be shortened. For example, in the case of conventional slurry sand, the curing time is 4 to 13 minutes (total heat evaporation after dehydration), whereas in the case of the core sand (wet sand) of the present invention, it is only 2 to 3 minutes.

    ・ The dimensional accuracy of the core is improved. This is because, like slurry sand, after the filling and dehydration, it is not necessary to heat and evaporate the water, and the mold can be formed only by dehydration at normal temperature by the filling pressure.

    -There is no need to arrange heating means such as an oil heater in the core mold, and the core structure is simplified (only a vent hole is required). Furthermore, the hot air blowing means is unnecessary, and the mechanism of the molding apparatus is simplified.

    -Rust is less likely to occur in the molding equipment. This is because the molding apparatus is not exposed to scattered salt water or salt vapor generated during dehydration and heating for core curing. As a result, it is not necessary to manufacture a molding apparatus including a core mold with a corrosion-resistant metal such as stainless steel.

  2) When filling the core sand, the release agent applied to the cavity surface of the core mold is not washed away. This is because the moisture content of the core sand is low. Therefore, it is not necessary to use a special release agent (for example, oil-based F-Si) as the release agent, and it is not necessary to apply the release agent thickly every time the casting sand is filled. The amount is small, and it is not necessary to apply a release agent for each core molding.

  3) At the time of heat curing, an excessive binder layer is not formed on the surface side of the core as in the prior art. For this reason, mold release resistance does not increase. In addition, a large amount of a special release agent is not mixed in the sand-containing liquid during sand removal, and the recycling of the binder aqueous solution in the spilled sand-containing liquid is facilitated. Furthermore, as a result of the reduction in mold release resistance, it is not necessary to add a filler or a wetting agent to the core sand composition in order to ensure the strength of the core.

  Note that, in Patent Document 2, paragraph 0032, lines 4 to 2 below, “The slurry dehydrated to a predetermined concentration by the dehydrator is a wet sand state containing a predetermined solution (a kneaded sand state). ), It is sent to the next molding machine as it is, and is reused. "From the description of Fig. 1 (A), etc., it is necessary to again knead for molding, Similarly to Patent Document 1 (Claim 4), it is understood that the core is filled in a slurry state with a binder aqueous solution / sand volume ratio of 1.0 or more.

JP 2007-152368 A JP 2005-138141 A Japanese Patent Laying-Open No. 2005-066664 JP 2005-059081 A JP 2010-234388 A

  In recent years, there has been a demand for further increase in the strength (bending strength) of the core.

  However, in the above-described core recycling molding method, it is necessary to increase the amount of binder aqueous solution added in order to obtain strength. When the addition amount of the binder aqueous solution is increased, the blowing flow at the time of filling the core sand mold is reduced (see FIG. 3). Therefore, when the mold is complicated (for example, an automobile engine, a cylinder head, a water jacket, etc.), a core (mold) defect due to poor filling is likely to occur. Therefore, there has been a limit in increasing the bending strength (mold strength) of the core by increasing the amount of the binder aqueous solution added.

  It is an object of the present invention to achieve further increase in core strength in the core recycling molding method.

  The present inventors have found that the above object (problem) can be solved if a specific inorganic fine powder is added in the method described in Patent Document 5, and the core recycling method described below is applied. I came up with it.

Using a core sand in which an aqueous solution of a binder composed of a water-soluble inorganic salt (hereinafter referred to as “binder aqueous solution”) is added to foundry sand, a water-soluble core (hereinafter referred to as “core”) is formed by an aerator. And
In a molding method in which the sand-containing liquid generated by sand removal of the core after casting with the core is recycled as a raw material for the core sand,
In the graph of the relationship between the core sand moisture (X) and the fluidization rate (Y) when a predetermined air fluidization experiment is performed on the composition of the core sand, the core from X where Y is a minimum value. In the recycling molding method of the core in which the sand water is low and the binder aqueous solution in an amount capable of ensuring the required strength is added together with the inorganic fine powder,
The inorganic fine powder is made of a non-water-absorbing inorganic substance, has a melting point of 700 ° C. or higher, Mohs hardness: 5 or higher, particle size: median diameter ratio of the core sand: 1/400 to 1/10 times, and addition thereof The amount is set in the range of 0.05 to 0.9 times the binder.

FIG. 2 is a citation diagram from FIG. 1 of Patent Document 1 in the recycling molding method of the core. FIG. 7 is a citation diagram of Patent Document 1 and FIG. 6 (a graph showing a relationship between a binder aqueous solution (salt solution) / sand volume ratio and a fluidization rate). It is the graph which showed the relationship between the use range of the core sand water | moisture content in the example of this invention, and a prior art example, and core intensity | strength (post-drying bending strength). It is the schematic of the core molding apparatus used by this invention. FIG. 9 is a citation diagram from Patent Document 1 and FIG. FIG. 9 is a citation diagram from FIG. 8 (a graph showing the relationship between concentration and specific gravity when the MgSO ₄ / Na ₂ SO ₄ ratio is constant (1.64)). FIG. 10 is a quoted drawing from FIG. 9 (also a graph showing the relationship between concentration and sugar content). It is a graph which shows the result of the bending strength experiment at the time of changing the binder addition rate in a reference example. Bonding in each case of a reference example in which inorganic fine powder is not added, Example 1 in which the alumina fine powder of the present invention (0.3 times the binder) is added, and a comparative example in which bentonite fine powder is added (0.3 times the binder) It is a graph which shows the experimental result of agent content rate and bending strength. It is a graph which shows the experimental result which measured the binder content rate and the bending strength in each case of the reference example which does not add inorganic fine powder, and Example 2 which added the alumina fine powder of this invention (vs. binder 0.1 time). is there. It is a graph which shows the experimental result which measured the binder content rate and the bending strength in each case of the reference example which does not add inorganic fine powder, and Example 2 which added the alumina fine powder of this invention (vs. binder 0.5 time). is there.

  Hereinafter, embodiments of the present invention will be described. In the following description, “form for carrying out the invention” in Patent Document 5 is cited except for the characteristic part of the present invention. “%” Indicating a blending unit means “% by mass” unless otherwise specified.

  Although it does not specifically limit as a core molding apparatus used for this embodiment, For example, what is shown in FIG. 4 can be used. The present invention is basically an improved invention using Patent Document 1 as a conventional example, and many of the descriptions from Patent Document 1 are cited with appropriate modifications. In addition, since the description regarding the "flowing air" and the "filling air" in Patent Document 1 is considered to be reversed, the correction is cited as such.

  The core molding apparatus includes a core sand kneading tank 1, a core sand hopper 2, and a core mold 7. The core sand kneading tank 1 is provided with a kneading stirrer 1a inside, and at the bottom thereof is provided with a core hopper 2 and a core sand feed pipe 1b. The core sand hopper 2 includes a sand filling on-off valve 6 connected to the sand filling port 7a of the core mold 7, and a filling air blow for blowing the filling air A1 into the core sand S in the core sand hopper 2. And a filling air exhaust valve 4 for exhausting the filling air. Further, the core mold 7 has a cavity 8 inside and a main vent (exhaust vent) 9 for exhausting the inside of the cavity 8. 7 has a large number of ventilating and dewatering holes (sub vents: not shown) communicating with the surface. The main vent 9 has a slit structure smaller than the core sand particles so that the filled sand is not discharged from the cavity 8, and the ventilation / dehydration hole has a small diameter that prevents the core sand particles from passing through or clogging. Yes.

  Next, a method for recycle molding the core of the present invention using the above molding apparatus will be described.

  In the core molding method of the present embodiment, when the composition of the core sand is subjected to a predetermined air fluidization experiment, the relationship between the core sand moisture (X) and the fluidization rate (Y) Assuming that the core sand moisture is higher than X indicating the minimum value, and an amount of a binder aqueous solution (an aqueous solution of a binder made of a water-soluble inorganic salt) is added to the foundry sand to ensure the required strength. Features.

As the water-soluble inorganic salt, a cation selected from Mg ²⁺ , Na ⁺ and Ca ²⁺ and an anion selected from SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , and B ₄ O ₇ ²⁻ Use one or more of the combination. And it is desirable to set in the range of core sand moisture: 2 to 13%, and further 3 to 8%. Moreover, it is desirable to set in the range which becomes binder addition amount in a dry core: 1-6%, Furthermore, 1.5-4%.

  If the amount of the binder aqueous solution is too small, the fluidity is improved, but the binder addition rate contained in the molded core is too small, and it is difficult to ensure the core strength (bending strength). If the ratio of the aqueous binder solution is excessive, it is difficult to ensure practical fluidity and it is difficult to obtain the effects of the present invention (such as shortening of the molding cycle).

Specific examples of the water-soluble inorganic salt include magnesium sulfate (MgSO ₄ ), magnesium sulfate (MgSO ₄ ) 50 to 98%, sodium carbonate (Na ₂ CO ₃ ), sodium tetraborate (Na ₂ B _4). A mixed system of 1 to 2 to 50% selected from O ₇ ) and sodium sulfate (Na ₂ SO ₄ ) is more preferable. One or more selected from magnesium sulfate (MgSO ₄ ) 50 to 90%, sodium carbonate (Na ₂ CO ₃ ), sodium tetraborate (Na ₂ B ₄ O ₇ ), sodium sulfate (Na ₂ SO ₄ ) 10 More preferred is a mixed system consisting of ˜50%. By using a water-soluble core having such a composition, the mold does not lose its shape during casting, and sand removal after casting can be easily performed with water pressure (see paragraph 0042 of Patent Document 1).

  The salt concentration of the aqueous binder solution at this time is saturated or close to the concentration from the viewpoint of securing the core strength, for example, in the case of the magnesium sulfate system, usually 20 to 35%, preferably 25 to 32%. .

  The binder addition amount (content ratio) is usually 1 to 6%, preferably 1.5 to 4% in the dry core. In the present invention, since no reinforcing filler (different from the inorganic fine powder in the present invention) is added to the core sand, the above binder addition amount is usually the total amount of foundry sand and binder (anhydrous conversion). Furthermore, when adding inorganic fine powder, it becomes the ratio with respect to the total amount (100%) added.

  The amount of the binder added is lower than the conventional “4-7%” (paragraph 0043 of Patent Document 1), and the amount of the binder used can be reduced. There is no sticking to the child mold. Therefore, a special release agent is not used and a small amount is sufficient, and the release resistance is small. Therefore, the core required at the time of mold release is not required to have a large strength, and the addition of a filler to the core sand is not necessary.

  Conventionally known sand can be used as the foundry sand used in the present invention. Specifically, it is preferable to use one made of SiC, alumina, mullite, silica, zircon or the like. These have excellent strength and low thermal expansion coefficient and are relatively easily available, and can produce a water-soluble core excellent in strength, dimensional accuracy, and the like.

  And in this invention (this embodiment), it has the biggest characteristic in adding the following specific inorganic fine powder.

  The inorganic fine powder used in the present invention is made of a non-water-absorbing inorganic substance that satisfies the following requirements. The inorganic fine powder is made of a non-water-absorbing inorganic substance. If it is water-absorbing, it will tend to aggregate when added to the binder aqueous solution, and will not uniformly penetrate between the core sand particle gaps. It is difficult to obtain an increase stably. Conversely, it leads to a decrease in strength (see FIG. 10). A water-absorbing material has a low Mohs hardness. For example, bentonite and kaolin, both of which are in the category of clay, have a Mohs hardness of 1, and talc having some water absorption also has a Mohs hardness of 1.

  1) Melting point: 700 ° C. or higher, desirably 800 ° C. or higher. This is because the core of the present invention is mainly scheduled for aluminum alloy casting, and therefore it is necessary to set the melting point of aluminum to a molten metal temperature higher than about 660 ° C. (for example, 700 ° C. or higher).

2) Mohs hardness: 5 or more, preferably 6 or more, more preferably 7 or more. Since the foundry sand is mainly composed of silica sand (SiO ₂ ), when it penetrates into the gap between the foundry sands, the sand sand with the Mohs hardness (quartz: 7) or more contributes to the increase in core strength. It is estimated to be.

  3) Core sand particle size (median diameter) ratio, 1/400 to 1/10 times, preferably 1/200 to 1/20 times, more preferably 1.5 / 200 to 5/200 times.

  When the average particle diameter (median diameter) of the core sand is 0.2 mm (200 μm), for example, the particle diameter is 0.5 to 20 μm, desirably 1 to 10 μm, and more desirably 1.5 to 5 μm. .

  If the particle size is too large, it is presumed that the inorganic fine powder does not enter between the particle gaps of the core sand and hardly contributes to an increase in the strength of the core. Even if the particle size is small, the strength is increased, but advanced dust countermeasure equipment is required.

As the inorganic fine powder (inorganic material) that satisfies the above requirements, those similar to the following foundry sand can be suitably used. Write the melting point and Mohs hardness in parentheses. This is because these can be reused even if they are mixed into foundry sand.
Alumina (2054 ° C, 9), silica (1703 ° C, 7), magnetite (1538 ° C, 5.5-6.5),

  And the addition amount of the alumina fine powder satisfying the above requirements is in the range of 0.05 to 0.9 times the binder ratio, desirably 0.1 to 0.45 times, more desirably 0.25 to 0.35 times. Set. Outside the above range, it is difficult to obtain an effect of increasing the core strength in proportion to the amount of binder (binding aqueous solution) added.

  Patent Document 5 suggests that the addition of inorganic fine powder may increase the core strength. That is, in paragraph 0052, it is considered that “inorganic fine powder fills gaps between particles of foundry sand and improves core strength, so it is preferably added, and kaolin and talc are preferably exemplified”. is there.

  However, when the present inventors conducted a confirmation experiment, those having low Mohs hardness such as kaolin (clay) and talc described above do not increase the strength of the core of the water-absorbing inorganic fine powder, but instead decrease. (See FIG. 10).

  Further, Patent Document 3 describes that alumina or silica is added as an inorganic filler (aggregate) to increase the strength (paragraphs 0024 and 0025). However, the molding method which is the premise of Patent Document 3 is different from that of the present invention, and the inorganic filler is added as an aggregate and is different from the inorganic fine powder in the present invention (Patent Document 5, Paragraph 0085 Table 1 Conventional Example) reference).

  The core sand S composed of the foundry sand and the binder aqueous solution (salt solution) is put into the core sand kneading tank 1 and kneaded and stirred. Thereafter, a predetermined amount of the kneaded core sand is fed into the hopper 2 through its own weight drop through the feed pipe 1b. When the filling air A1 is blown in this state, the core sand S is filled into the cavity 8 in the casting mold 7 via the sand filling on-off valve 6. The filling air A1 is exhausted by the filling air exhaust valve 4.

  The core sand S filled in the cavity 8 is compressed by the filling pressure of the filling air A1, and simultaneously exhausted and dehydrated from the main vent 9 and the sub vent. The amount of dehydration at this time is usually several percent.

  The molded core thus dehydrated is released from the core mold using an extrusion pin or the like. The mold release resistance of the mold release process is low, and the mold release is possible with the core fastening force only after the dehydration process. The reason is presumed to be because no excess binder is used.

  Then, the released core is made into a core product through a drying (sintering) step as in the conventional case (see FIG. 1). Drying conditions are, for example, room temperature air drying × 10 min, 200 ° C. × 1 h (in an electric furnace).

  And after casting using the said core, sand removal of a core is performed using a washing | cleaning liquid.

  The sand removal will be described with reference to FIG. 5 (see Patent Document 1, paragraph 0053).

  The core 12 of the cast product 11 is circulated through the cleaning liquid 13 so that the crystalline salt of the core 12 is melted and washed away. The cleaning liquid 13 may be a salt solution from fresh water to a saturation concentration of the binder or lower (34.3%), for example, 28%. The crystalline salt can be melted and washed away. The sand to be washed away and the binder aqueous solution (salt solution) are stored in the liquid tank 15. The inside of the liquid tank 15 is composed of foundry sand 16 and excess binder aqueous solution 17.

  Then, the foundry sand 16 is settled and separated. In addition, like patent document 1, a supernatant liquid (binder aqueous solution which does not contain sand) can be repeatedly circulated and used as the cleaning liquid 13. The aqueous binder solution is usually concentrated and reused as a binder as described below. Moreover, in the sedimentation separation of the foundry sand, there is a difference in the sedimentation time between the foundry sand and the fine powder, which can be used to separate the foundry sand and the fine powder.

  The supernatant liquid can be used as an aqueous binder solution added to foundry sand by overflow separation or the like, and further heating and concentrating (dehydrating) as appropriate (Patent Document 2, Claim 1, etc.).

  Since the binder in the core 12 to be washed away is dissolved in the cleaning liquid 13, the salt concentration of the aqueous binder solution in the liquid tank changes approximately proportionally according to the number of processed products. If the said salt concentration is below solubility (saturation concentration), it can be used as a washing | cleaning liquid. In addition, when the binder is contained in the solubility or higher, crystals are formed and precipitated. However, the binder is dissolved by heating and stirring so that the solubility is lower than the solubility, so that it can be used as a cleaning liquid. However, in order to eliminate the need for the operation, it is desirable that the binder concentration is not more than the solubility at room temperature (factory temperature).

  The separated foundry sand (wet sand) and binder aqueous solution (concentrated as appropriate) are mixed at a set mixing ratio to prepare regenerated core sand.

  The regenerated core sand is prepared by utilizing the fact that the concentration of the water-soluble inorganic salt, the sugar content and the specific gravity are approximately proportional if the composition of the binder aqueous solution is constant. That is, the mixing ratio of the foundry sand (wet sand) and the binder aqueous solution can be easily determined by measuring the sugar content of the foundry sand adhesion binder aqueous solution and measuring the specific gravity of the binder aqueous solution.

  Then, the core is formed using the regenerated core sand. In this way, the core can be recycled.

  In this way, it is possible to use casting sand and a binder aqueous solution from the sand-containing liquid generated by the sand removal of the core in the core molding, and the molding time can be shortened. While being able to be, it can be excellent in environmental performance.

  Embodiments of the present invention will be described below together with reference examples with reference to the drawings. In addition, the part which concerns on a reference example quotes the item of <Example> in patent document 5 with an edit change.

The aqueous binder solution was prepared by mixing the added water and the binder (MgSO ₄ .7H ₂ O / Na ₂ SO ₄ (mass ratio) ≈77 / 23 = 1.64) in the same amount (1/1).

FIGS. 6 and 7 are graphs showing the relationship between the binder aqueous solution concentration, the sugar content, and the specific gravity in MgSO ₄ / Na ₂ SO ₄ = 62/38 = 1.64, respectively. 6 and 7 are the same as Patent Document 1 and FIGS. 8 and 9 (MgSO ₄ / Na ₂ SO ₄ = 17.4 / 10.6 = 1.64).

Incidentally, the salt concentration in the reference examples, examples of the present invention is about 30.3% the _{(MgSO 4: 11.5%: 18.8} %, Na 2 SO 4). The specific gravity of the aqueous binder solution at that time is 1.33.

  The casting sand having an apparent specific gravity of 1.73, a true sand specific gravity of 2.7, and a porosity of 35.93% was used.

  Using the binder aqueous solution, core sand was prepared as follows, and each experiment of each item described below was performed.

  In addition, the binder addition rate is in the range of 1 to 10% of the apparent addition concentration of the binder (the range of 0.6 to 6% of the actual addition concentration), and core sand (1% and 6% except for 1% and 6%) in principle 2 After the preparation, core molding was performed using a molding apparatus as shown in FIG.

As a core mold, a water jacket core (cavity capacity (filling volume of core sand): 1350 cc, cavity area: 1400 cm ² , minimum gap: 3 mm) is used. 5 mL of the agent was applied. In addition, the core type was set to room temperature without heating.

  The charging air pressure was set to the first stage: 200 kPa × 5 seconds and the second stage: 400 kPa × 5 seconds. After the filling, it was dried by flowing normal temperature filling air (200 kPa) for about 2 minutes.

  Then, the dry core was released. The release resistance at this time was small, and it was confirmed that the release was basically possible by the fastening force between the sand particles of the core obtained by dehydration by the filling pressure.

[Fluidization rate experiment]
In the above molding, the weight of each core after molding was measured, and the ratio between the weight and the conventional good product weight (filling rate 100%) was determined as the fluidization rate.

  The model characteristics of the measurement results are as shown in FIG. 3, and it was confirmed that the fluidization rate of the core sand was improved when the apparent moisture was 8% or less (substantially moisture 11%) or less.

[Core bending strength test]
Furthermore, in order to confirm the bending strength when casting using each core, each core after mold release is dried under the condition of dry air (200 kPa) × 10 minutes and then 200 ° C. in an electric furnace. Sintering was performed under conditions of × 1 h, and the bending strength was measured (test specimen cross section: 30 × 10 mm, distance between fulcrums: 5 cm).

  From FIG. 8 showing the result, it is only necessary to add an aqueous binder solution so that the binder addition amount (substantial concentration) in the dry core is 1 to 6%, preferably 1.5 to 4%. I understand. The actual concentration “1.5 to 4%” in the foundry sand only coincides with the lower limit of the desirable concentration “4 to 7%” described in paragraphs 0043 and 0027 of the conventional patent document 1. Is completely out of place.

  Table 1 summarizes the specifications from filling to mold release in the above reference example together with the specifications in the conventional example.

  It can be seen that the molding cycle of the present invention can be remarkably shortened, and the energy for molding can be significantly saved.

  Next, in the composition of the above reference example, inorganic fine powder (alumina fine powder: median diameter 2 μm) was prepared by adding each amount of a binder ratio of 0.1, 0.3 and 0.5 times. A few aqueous binder solutions were prepared. An inorganic fine powder (bentonite fine powder: median diameter: 2 μm) added with a binder ratio of 0.3 times was used as a control example. The thing without an inorganic fine powder was made into the reference example.

  And, in the range of 2.1 to 3.5%, the core sand is prepared at intervals of 0.2% in the same manner as in the reference example. , Made core molding. The minimum and maximum concentrations in Example 1 and the reference example were 10 samples and 6 samples, respectively. For the intermediate concentration, the number of samples was basically 2 or 1 (part of the control and reference examples).

  The above-mentioned bending strength test was performed on each sample obtained by core molding. The results are shown in FIGS.

  From these results, it can be seen that the bending strength (core strength) is significantly increased. However, even if the addition ratio of the binder is small or large, it increases when the concentration of the binder added to the core sand is low (less than about 3%), but when it exceeds about 3%, the core strength does not increase. I can ask you.

  In addition, about Example 1 (Al addition 30%) and a reference example (no fine powder addition), about each case of mold release resistance, salt (binder) content rate 2.1%, 2.5%, and 3.0% (N = 30), releasability was observed. In Example 1, none of the release defects (release failure: mold breakage) occurred in all, whereas in the reference example, release defects occurred with a probability of about 40%. The reason is estimated that in the case of the reference example, the mold strength (bending strength) is relatively lower than that of Example 1, and it is difficult to stably mold the mold strength against the mold release resistance. Note that the higher the salt content, the higher the mold strength, but the mold is more likely to stick to the mold and the mold release resistance increases. It is estimated that is likely to occur.

1: Kneading tank 2: Core sand hopper 3: Filling air blowing valve 4: Filling air exhaust valve 7: Core type 8: Cavity S: Core sand

Claims (8)

Using a core sand in which an aqueous solution of a binder composed of a water-soluble inorganic salt (hereinafter referred to as “binder aqueous solution”) is added to foundry sand, a water-soluble core (hereinafter referred to as “core”) is formed by an aerator. And
In a molding method in which the sand-containing liquid generated by sand removal of the core after casting with the core is recycled as a raw material for the core sand,
In the graph of the relationship between the core sand moisture (X) and the fluidization rate (Y) when a predetermined air fluidization experiment is performed on the composition of the core sand, the core from X where Y is a minimum value. In the recycling molding method of the core in which the sand water is low and the binder aqueous solution in an amount capable of ensuring the required strength is added together with the inorganic fine powder,
The inorganic fine powder is made of a non-water-absorbing inorganic substance, melting point: 700 ° C. or more, Mohs hardness: 5 or more, particle size: median diameter ratio of the core sand is 1/400 to 1/10 times, A method for recycle molding a core, characterized in that the addition amount is set in the range of 0.05 to 0.9 times the binder. Using a core sand in which an aqueous solution of a binder composed of a water-soluble inorganic salt (hereinafter referred to as “binder aqueous solution”) is added to foundry sand, a water-soluble core (hereinafter referred to as “core”) is formed by an aerator. And
After casting using the core, in the molding method for recycling the sand-containing liquid generated by the sand removal of the core as a raw material for the core sand,
As the water-soluble inorganic salt, a cation selected from Mg ²⁺ , Na ⁺ and Ca ²⁺ , and an anion selected from SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , and B ₄ O ₇ ²⁻ And using a combination of one or more of
Core sand moisture: set in the range of 2 to 13% by mass, binder in the dry core: set in the range of 1 to 6% by mass, and further, fine inorganic powder for the purpose of increasing the strength of the core In the recycling molding method for cores,
The inorganic fine powder is made of a non-water-absorbing inorganic substance, melting point: 700 ° C. or more, Mohs hardness: 5 or more, particle size: 1/400 to 1/10 times the median diameter of the core sand, A method for recycle molding a core, wherein the addition amount is set in the range of 0.05 to 0.9 times the binder.   The said inorganic fine powder is melting | fusing point: 800 degreeC or more, Mohs hardness: 7 or more, a particle size: 1 / 200-1 / 20 of the median diameter of the said core sand, The Claim 1 or 2 characterized by the above-mentioned. Recycle molding method for cores.   The core recycling method according to claim 2, wherein a salt concentration (anhydride conversion) of the binder aqueous solution is 20 to 35 mass%. In any one of Claims 1-4,
1) a sand removal step for generating the sand-containing liquid;
2) a recovery step of recovering the hydrous casting sand and the aqueous binder solution from the sand-containing liquid;
3) a binder aqueous solution regeneration step for concentrating (dehydrating) the recovered binder aqueous solution;
4) A core sand regeneration step of preparing a reclaimed core sand having the same composition as the core sand using the hydrated casting sand and the regenerated binder aqueous solution;
5) a molding process for forming an aerator of the core using the regenerated core sand;
A method for recycle molding a core, wherein the core prepared through each of the steps is cast and then returned to the sand removal step of 1). A core sand used in the core recycling molding method, in which a binder aqueous solution (binder aqueous solution) made of a water-soluble inorganic salt is added to foundry sand,
In the case where a predetermined air fluidization experiment is performed, in the graph of the relationship between the core sand moisture (X) and the fluidization rate (Y), the core sand moisture is lower than X where Y is a minimum value, and In core sand in which an aqueous binder solution in an amount that can ensure the required strength is added together with inorganic fine powder,
The inorganic fine powder is made of a non-water-absorbing inorganic substance, melting point: 700 ° C. or more, Mohs hardness: 5 or more, particle size: 1/400 to 1/10 times the median diameter of the core sand, Core sand characterized in that the addition amount is set in the range of 0.05 to 0.6 times the binder. A core sand used in the core recycling molding method, in which an aqueous solution (a binder aqueous solution) of a water-soluble inorganic salt is added to foundry sand,
The water-soluble inorganic salt is a cation selected from Mg ²⁺ , Na ⁺ and Ca ²⁺ , and an anion selected from SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ²⁻ , and B ₄ O ₇ ^2−. And using a combination of one or more of
In the core sand moisture: set in the range of 2 to 13% by mass, the binder in the dry core: set in the range of 1 to 6% by mass, and further added with inorganic fine powder ,
The inorganic fine powder is made of a non-water-absorbing inorganic substance, melting point: 700 ° C. or more, Mohs hardness: 5 or more, particle size: 1/400 to 1/10 times the median diameter of the core sand, The core sand is characterized in that the addition amount is set in the range of 0.05 to 0.6 times the binder.   The core sand according to claim 7, wherein the concentration of the aqueous binder solution is set in a range of 20 to 35%.

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