JP2011041973A - Method for molding water soluble mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for molding a water soluble mold, in a recycle molding method for a core, which can achieve the further improvement of productivity, concretely, can satisfy the requirements of (1) the reduction of molding time, (2) the reduction of heat cost, (3) the improvement of mold releasability or the like. <P>SOLUTION: In the method for molding a water soluble mold, kneaded casting sand obtained by adding a water-soluble inorganic salt to casting sand is blown and filled into a molding mold so as to mold a mold, after the use of the mold, it is collapsed by water contact, and the reutilization of the casting sand is made possible. The drying and curing of the mold before mold releasing is performed in such a manner that the temperature of the mold before the mold releasing is made higher than the boiling point of water under the reduced pressure, and is also made lower than the boiling point of water under the atmospheric pressure, and also in such a manner that the mold for molding is placed under the reduced pressure, thus, e.g., the water is evaporated. In this way, the mold can be dried in a short time till it reaches a dry strength at which treatable strength or above is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention blows and fills the molding sand with the water-soluble inorganic salt added to the molding sand to form a mold, and after the mold is used, it is disintegrated by water contact (water washing), The present invention relates to a method for forming a water-soluble mold that enables at least reuse of foundry sand.

  Here, a core is mainly described as an example of the mold, but the present invention can be applied to an outer mold.

  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.

In view of the above, the present inventors aim to provide a water-soluble core binder having both sufficient core strength and solubility, and a cation selected from Mg ²⁺ , Na ⁺ and Ca ²⁺ , SO ₄ ^{2 _{-, CO 3 2-, HCO 3}} -, B 4 O 7 1 or more water-soluble inorganic salt comprising a combination of anion selected from ^2- (except when only magnesium sulfate (MgSO ₄₎₎ A water-soluble core binder comprising the following was invented (Patent Document 2 below). In particular, magnesium sulfate (MgSO ₄ ) 0 to 99.9% by mass, 1 selected from sodium carbonate (Na ₂ CO ₃ ), sodium tetraborate (Na ₂ B ₄ O ₇ ), and sodium sulfate (Na ₂ SO ₄ ) It has been found that a water-soluble core binder composed of 100 to 0.1% by mass of seeds or more 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 wet sand core sand 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. "

  The core sand (slurry) in a wet sand state recovered from the slurry sand generated by the above sand removal is prepared in a process of being kneaded and used as a molding core sand. Usually, an aqueous inorganic binder solution / cast sand (Volume ratio) ≧ 1 slurry sand for molding (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; Slurry foundry sand composed of a water-soluble inorganic salt binder is placed in a slurry box connected to a cavity in a casting mold, and slurry-flowing air is blown 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. "

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

  In the core recycling molding method described in Patent Documents 1 and 2 above, further improvement in productivity, specifically 1) reduction in molding time, 2) reduction in heat cost, and 3) improvement in mold release 4) Improvement of dimensional accuracy is required.

  The present invention provides a method for molding a water-soluble mold having a novel configuration capable of 1) shortening molding time, 2) reducing thermal cost, and 3) improving mold releasability. The purpose (problem).

  In the process of diligently developing to solve the above-mentioned problems, the present inventors performed the drying treatment of the mold before mold release at a temperature higher than the water boiling point under a predetermined reduced pressure and lower than the water boiling point under atmospheric pressure. (Desirably, the casting sand is heated), the drying time can be greatly shortened and the releasability is improved. .

Casting sand containing water-soluble inorganic salt added to foundry sand is blown into a mold and filled to form a mold. After the mold is used, it can be collapsed by contact with water, allowing the foundry sand to be reused. It is said to be a water-soluble mold making method,
Drying of the mold before mold release is carried out by placing the mold for molding under reduced pressure in a state where the temperature of the mold before mold release is higher than the boiling point of water under reduced pressure and lower than the boiling point of water under atmospheric pressure. It is characterized in that it is carried out by evaporating the water until the dry strength becomes such that it can be released or handled.

It is a flowchart including the recycling process in the molding method of the water-soluble mold (core) to which the present invention is applied. It is a schematic sectional drawing of the core molding apparatus used by this invention. It is a relationship graph figure of core sand moisture (X) and fluidization rate (Y). It is a flowchart for explanation of a sand heating and kneading process (A) and a blow filling process (B). It is a saturated vapor pressure / temperature curve diagram of water. It is a flowchart for description of a pre-drying (vacuum drying) and an extrusion mold release process. It is a flowchart for explanation of a mold release completion and a post-drying (atmospheric pressure heat drying) process. FIG. 9 of Patent Document 1 is a citation from FIG. 7 (an explanatory diagram of a core cleaning process). It is a graph which shows the relationship between the kneading sand temperature and the water | moisture-content evaporation rate in the experiment which dried the core before mold release under reduced pressure (decompression degree 63hPa).

  In the following, a preferred embodiment of the present invention will be described in the case of recycling molding of a core as shown in FIG. 1 in the method of molding a water-soluble mold (core).

  That is, the core recycle molding consists of 1) sand heating and kneading 2) blow-filling 3) pre-drying (vacuum drying; pre-release drying) 4) release → 5) post-drying (heat drying; release) After mold drying) → 6) Assembling mold → 7) Pouring → 8) Water washing (collapse of mold) → 9) Reuse work (separation / repreparation) → 1) Repeated steps of sand heating and kneading is there.

  Hereinafter, each step will be described. In the following description, “%” indicating a blending unit means “% by mass” unless otherwise specified.

  In addition, as a core molding apparatus used for this embodiment, although it does not specifically limit, For example, what is shown in FIG. 2 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. Corresponding portions of Patent Document 1 are described as necessary. 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 sand 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 7c 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.

1) Sand heating / kneading step (FIG. 4A):
4 shows the kneading tank and the kneading hopper together in the core molding apparatus of FIG. For this reason, hereinafter, the reference numerals related to the core molding apparatus refer to those in FIG.

  The composition of water-soluble core core sand (kneaded foundry sand) is made by blowing and filling kneaded foundry sand in which water-soluble inorganic salt is added to the foundry sand into the mold for molding, and the mold is used. After that, it is not particularly limited as long as it is disintegrated by washing with water (water contact) and the foundry sand can be reused.

  However, the following composition is desirable because it is excellent in blow filling and releasing properties.

  That is, when a predetermined air fluidization experiment is performed on the composition of the core sand, in the graph of the relationship between the core sand moisture (X) and the fluidization rate (Y) shown in FIG. It is assumed that a binder aqueous solution (an aqueous solution of a binder made of a water-soluble inorganic salt) in an amount capable of ensuring the necessary strength is added to the core sand moisture higher than X shown.

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 ⁻ and B ₄ O ₇ ²⁻ It is desirable to use as a main component what consists of 1 or more types of these, and has crystallization water at normal temperature. A typical example is MgSO ₄ .7H ₂ O.

  And it is desirable to set in the range of core sand moisture: 2 to 13%, and further 3 to 8%. Further, the amount of water-soluble inorganic salt (binder) added to the dry core is preferably set in a range of 1 to 6%, more preferably 1.5 to 4%.

  If the water content is too low, the fluidity is improved, but the binder addition rate contained in the molded core becomes too low 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).

As the specific water-soluble inorganic salt, magnesium sulfate (MgSO ₄ .7H ₂ O) is preferable as described above, magnesium sulfate (MgSO ₄ ) 50 to 98%, sodium carbonate (Na ₂ CO ₃ ), A mixed system of 1 to 2% selected from sodium borate (Na ₂ B ₄ O ₇ ) and sodium sulfate (Na ₂ SO ₄ ) is more preferable. Magnesium sulfate (MgSO ₄ ) 50-90%, one or more selected from 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 these water-soluble cores, the mold does not lose its shape during casting, and sand removal after casting can be easily performed with water pressure (partly changed from Patent Document 1, paragraph 0042).

  And the salt concentration of the binder aqueous 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%. To do.

  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 is added to the core sand, the amount of binder added is usually the total amount of foundry sand and binder (anhydrous equivalent), and further, inorganic fine powder is added. In this case, it is a ratio to the total amount (100%).

  The inorganic fine powder is considered to improve the core strength by filling the gaps between the particles of the foundry sand, and is preferably added. For example, kaolin and talc can be used.

  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 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.

  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.

2) Blow filling process (Fig. 4 (B))
The kneaded core sand prepared as described above is filled as follows (see FIG. 2).

  A predetermined amount of the kneaded core sand is fed into the hopper 2 through its own feed pipe 1b by its own weight drop. In this state, when the filling air A1 is blown through the air blowing on / off valve 3, the core sand S is filled into the cavity 8 in the casting mold 7 through the sand filling on / off valve 6. After the filling of the core sand S, the filling air A1 is exhausted by the filling air exhaust valve 4.

  Here, the casting sand before kneading or the kneading core sand S has a temperature higher than the boiling point of water under reduced pressure when the core mold (molding mold) 7 before release is placed under reduced pressure, and There is no particular limitation as long as it has a temperature below the boiling point of water at atmospheric pressure (100 ° C.). For example, the temperature is usually 20 ° C. or higher, preferably 30 ° C., more preferably 40 ° C. higher than the boiling point of water under reduced pressure. Therefore, for example, when the degree of vacuum is 63 hPa (boiling point: about 37 ° C.), assuming that the average temperature drop by the kneading / filling process is 3 ° C., it is 60 ° C. or higher, preferably 70 ° C. or higher, more preferably 80 ° C. or higher. . The upper limit is less than the boiling point of water under atmospheric pressure (100 ° C), preferably less than 95 ° C. The relationship between the degree of vacuum and the boiling point can be obtained from a saturated vapor pressure / temperature curve diagram as shown in FIG.

  Usually, the foundry sand is heated. As a heating aspect, the aspect which heats with a drying furnace or a heating furnace by a shelf, or inserts a sheathed heater and can heat is considered.

  The core sand S filled in the cavity 8 is compressed by the filling pressure of the filling air A1, and at the same time exhausted and dehydrated from the main vent 9 and the sub vent (see FIG. 2). The amount of dehydration at this time is usually several percent.

3.4) Pre-drying (vacuum drying), mold release process (Figs. 6 and 7)
The molded core (mold) 12 before demolding thus dehydrated is continuously transported to the decompression chamber 11 together with the core mold 7 and dried under reduced pressure. It has been confirmed that when the water content of the kneaded sand at this time is dehydrated (dried) to an evaporation rate of about 75% or more, preferably about 80% or more, the strength is such that it can be extruded and handled. In addition, when the mold is small (1350 cc), the dehydration time is 10 seconds to 2 minutes, and it has been confirmed that the mold can be dried beyond the strength that can be handled after mold release (see Experimental Examples). In addition, when a casting_mold | template is large (for example, 10L or more), it is thought that drying time becomes long and several minutes-10 minutes are needed.

  The degree of vacuum (degree of vacuum) at this time is appropriately selected from the range of 32 hPa (water boiling point 25 ° C.) to 699 hPa (water boiling point 90 ° C.), preferably 56 hPa (water boiling point 35 ° C.) to 199 hPa (water boiling point 60 C.), and more desirably in the range of 74 hPa (water boiling point 40 ° C.) to 123 hPa (water boiling point 50 ° C.).

  When the degree of vacuum (degree of vacuum) is high, the vacuum chamber is required to have high sealing performance, but the water boiling point corresponding to the degree of vacuum can be lowered and the drying efficiency can be improved (drying can be performed in a shorter time). On the other hand, if the degree of vacuum is low, the vacuum chamber 11 is not required to have high sealing performance, but the water boiling point corresponding to the degree of vacuum is relatively high, and drying and heat efficiency cannot be expected for a short time.

  The core 12 is released (taken out) as follows.

  Open the core mold (molding mold) 7. At this time, the core 12 is detached from the upper mold 7b, but remains in contact with the lower mold 7b. Next, as shown in the drawing, the core 12 is partially extruded on the lower mold 7b. Then, this partially extruded state is maintained for 2 minutes or longer (usually 2 to 3 minutes). As a result, it has been confirmed that the strength of the core 12 is further increased. The reason is estimated as follows.

At the time of drying under reduced pressure, MgSO ₄ .7H ₂ O, which is the main component of the binder, is in a state where all or part of the crystal water has been removed (monohydrate). In addition, from saturated aqueous solution, magnesium sulfate (MgSO ₄ ) is precipitated as heptahydrate at 1.8-48.1 ° C (room temperature), hexahydrate at 48.1-67.5 ° C, and monohydrate from 67.5 ° C or higher. (Oki et al. "Chemical Dictionary 1st edition" Tokyo Chemical Doujin).

By leaving the core 12 in the atmosphere, the magnesium sulfate (MgSO ₄ ), which is a binder component, hydrates and returns to the hexahydrate or heptahydrate, thereby expanding and solidifying the core. Increase.

  Then, the core 12 is detached from the lower mold 7b using an extrusion pin or the like to complete the mold release of the core 12 (left side in FIG. 7). 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.

5) Post-drying (heat drying: drying after mold release) step (FIG. 7)
The released core 12 is processed into a core product through a post-drying step as in the conventional case. In the drying method, post-drying is performed by microwave heating (FIG. 7A) or hot air heating (FIG. 7B). The post-drying does not need to be performed at a high temperature of 200 ° C. × 1 h as in the prior art, and it has been confirmed that a treatment at 100 ° C. or higher, for example, 150 ° C. × 1-2 minutes is sufficient. The purpose of this drying treatment is to blow off the extra adhering water that does not contribute to the increase in core strength other than crystal water (coordination water, anion water). However, it is considered that drying at room temperature (standing) is sufficient with short-time heat drying or although it takes some time.

6 ・ 7 ・ 8) Assembly, pouring, water washing process (see Fig. 1)
And after casting using the said core, sand removal of a core is performed using a washing | cleaning liquid.

  For example, as shown in FIG. 8, the core 12 in the casting 14 is circulated through the cleaning liquid 13 so that the crystal 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 less (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 liquid tank 15 is composed of foundry sand 16 and a diluted binder aqueous solution 17.

  Then, the foundry sand 16 is separated from the binder aqueous solution 17 through a sedimentation separation operation and an overflow separation operation. The aqueous binder solution 17 from which the foundry sand 16 has been separated is appropriately heated and concentrated (dehydrated) and reused as an added aqueous binder solution to the foundry sand.

  In addition, like patent document 1, the supernatant liquid (binder aqueous solution which does not contain sand) after sedimentation operation can be repeatedly circulated and used as the cleaning liquid 13.

  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 obtained 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, casting sand and aqueous binder solution can be used in core molding from the sand-containing liquid generated by core sand removal, and the molding time can be shortened. In addition to the above, it can be made environmentally friendly.

  Hereinafter, based on the Example of this invention, it demonstrates further in detail.

The aqueous binder solution was prepared by mixing equal amounts (1/1) of the added water and the binder (2MgSO ₄ .7H ₂ O / Na ₂ SO ₄ ). At this time, the mass composition ratio is 2MgSO ₄ .7H ₂ O / Na ₂ SO ₄ ≈2 × 246 / 142≈0.776 / 0.224≈3.64, 2MgSO ₄ / Na ₂ SO ₄ ≈2 × 120 / 142≈0.628 / 0.372≈ 1.69. Further, 2MgSO ₄ / Na ₂ SO ₄ mass composition ratio, a substantial amount for the apparent weight of the _{binder, 2MgSO 4 · Na 2 SO 4} /2 (MgSO 4 · 7H 2 O) · Na 2 SO 4 ≒ (2 × 120 + 142) / (2 × 246 + 142) ≈0.602 times, and the crystallization water content is about 0.4 times. The total amount of water in the aqueous binder solution is approximately 0.7 times the aqueous binder solution = (1.0 + 0.4) /2.0.

Note that the salt concentration (2MgSO ₄ · Na ₂ SO ₄ ) of the aqueous binder solution in the example of the present invention is 50% × 0.602≈about 30.1% because the apparent binder concentration is 50%. 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 the core was molded.

  After preparing core sand so that the total moisture is about 2%, that is, binder aqueous solution addition amount 3.10% (binding agent addition amount 1.55%, moisture: 1.55 + 1.55 × 0.4 = 2.17%), FIG. Using a molding apparatus as shown in FIG.

  At this time, the raw material sand used was preheated at intervals of 10 ° C. in the range of 60 to 90 ° C.

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, the core mold was introduced for 2 minutes into a vacuum chamber adjusted to a degree of vacuum (63 hPa: relative pressure −0.095 MPa, corresponding water boiling point: about 42.5 ° C.). Then, the dry core was released.

  And about each sample, the water | moisture-content evaporation rate (R) was calculated | required about the following formula, respectively.

R = 100 × (Test piece weight after drying−Test piece weight before drying)
/ Test piece weight before drying x Binder aqueous solution addition rate x 0.70
FIG. 9 showing the result shows that the strength that can be handled after mold release is sufficiently obtained when the water evaporation rate is close to 75%, and the dryness is 25 ° C. (difference between the casting sand preheating temperature and the water boiling point corresponding to the pressure reduction degree) In the case of sand temperature: 70 ° C, water boiling point corresponding to the degree of vacuum: 42.5 ° C), it was confirmed that the drying time under reduced pressure and 60 seconds were sufficient. Therefore, if it is 30 ° C. or higher, the drying time may be much shorter than 60 seconds (for example, within 30 seconds), and even in the case of 15 ° C., it is estimated that the drying time may be 60 seconds or more.

  It has been confirmed that the molding cycle can be remarkably shortened according to the present invention, and energy for molding can be significantly saved.

1: Kneading tank 2: Core sand hopper 3: Filling air blowing valve 4: Filling air exhaust valve 7: Core mold 7a: Core mold upper mold 7b: Core mold lower mold 8: Cavity 11: Decompression chamber S: Core sand

Claims (10)

Kneaded foundry sand with water-soluble inorganic salt added to the foundry sand is blown and filled into a mold for molding to mold the mold. After the mold has been used, it can be destroyed by contact with water, allowing the foundry sand to be reused. A method for forming a water-soluble mold,
Drying of the mold before mold release (pre-drying) is carried out by placing the mold for molding under reduced pressure, with the temperature of the mold before mold release being higher than the boiling point of water under reduced pressure and lower than the boiling point of water under atmospheric pressure. And then evaporating the water until it has a dry strength that is higher than the extrudable or handleable strength.   The method for forming a water-soluble mold according to claim 1, wherein the temperature of the foundry sand or the kneaded foundry sand before filling is set to a temperature higher than the boiling point of the sewage under reduced pressure.   The method for forming a water-soluble mold according to claim 2, wherein the boiling point of water under reduced pressure is set to 25 to 90 ° C.   4. The method for forming a water-soluble mold according to claim 3, wherein the temperature difference between the temperature of the mold before mold release and the boiling point of the sewage under reduced pressure is set to 20 ° C. or more.   5. The water-soluble mold according to claim 1, wherein after the mold is opened and the state where the mold is partially extruded is maintained for 2 minutes or longer, the mold release is completed. Molding method.   6. The method for forming a water-soluble mold according to claim 5, wherein the mold after completion of the mold release is further post-dried by heating under atmospheric pressure.   The method for molding a water-soluble mold according to claim 6, wherein microwave heating or hot air heating is selected as the heating under atmospheric pressure.   The method for forming a water-soluble mold according to any one of claims 1 to 7, wherein an evaporation rate of the water evaporation is 75 mass% or more. 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 ⁻ , and B ₄ O ₇ ²⁻ And having a crystal water at room temperature,
The kneading foundry sand moisture is set in a range of 2 to 13% by mass, and the binder addition amount in the dry core is set in a range of 1 to 6% by mass. A method for forming a water-soluble mold according to claim 1. The method for forming a water-soluble mold according to claim 9, wherein the salt concentration (anhydride conversion) of the aqueous binder solution is 20 to 35% by mass.

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