JP2016064436A - Manufacturing method of casting salt core and casting salt core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a casting salt core which is suppressed in the number of kinds of raw materials, can withstand a high-pressure die-cast method, and is high in rigidity, and the casting salt core which is manufactured by the method.SOLUTION: A manufacturing method of a casting salt core includes: a melting process for heating a mixed salt which contains a first metal salt and a second metal salt to a liquidus line temperature or higher, and generating a molten salt of the first metal salt and the second metal salt; a pouring process for pouring the molten salt into a metal mold; and a molding process for molding the salt core by solidifying the molten salt in the metal mold. In the molding process, a new metal salt is generated which is different in composition from the first metal salt and the second metal salt.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a casting salt core and a casting salt core.

  The high pressure die casting method is a method in which a molten metal is injected into a mold at a high speed and a high pressure, and a metal part (for example, a cylinder head of an engine, etc.) is cast. Therefore, the core used for casting a metal part having an undercut shape is required to have a strength that can withstand high temperatures and high pressures. Moreover, since it is necessary to remove the core used for casting a metal part having an undercut shape after casting, it is also important that the core is easy to remove. For this reason, collapsible salt cores mainly composed of metal salts (also simply referred to as salts) are often used.

  Generally, a salt core does not have the strength to withstand high temperatures and high pressures. Therefore, in order to use the salt core in the high pressure die casting method, the salt core is mixed by a method such as mixing an additive such as a refractory or aggregate, or mixing several kinds of metal salts into a multi-element composition. It was necessary to improve the strength.

  As such a salt core, a salt core in which strength is increased by adding hard particles as a refractory to a mixed salt of sodium chloride, potassium chloride, and barium chloride is known (for example, Patent Document 1). ).

  In addition, by heating a plurality of salts such as sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride to form a melt in a solid-liquid coexisting state such as semi-solidified, the strength was increased by molding this melt. A method for producing a salt core is known (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2011-31276 International Publication No. 2007/135995

  However, since the refractory has a higher specific gravity than the molten salt, the salt core of Patent Document 1 may cause the refractory component to settle and separate at the time of molding, and the strength of the salt core is partially reduced significantly. There was a risk of variations. Furthermore, when the salt core is molded using the injection molding method, the refractory material becomes an injection resistance, cracks or the like occur in the salt core, and the production yield of the salt core may be deteriorated. In addition, barium chloride designated as a powerful drug is difficult to store and handle, and it is difficult to use it at actual casting sites.

  Since the salt core of Patent Document 2 also has many types of salts used as raw materials, it is necessary to store a large amount and various types of raw materials, and to appropriately manage the mixing ratio of the raw materials. Unfortunately, the manufacturing process was complicated.

  The present invention has been made in view of the above problems, and a method for producing a high-strength salt core for casting that suppresses the types of raw materials and can withstand high-pressure die casting, and a casting salt produced thereby. The purpose is to provide children.

  The present invention has been made to solve the above problems. That is, according to one aspect of the present invention, a mixed salt containing a first metal salt and a second metal salt is heated to a liquidus temperature or higher, and the first metal salt and the second metal salt are melted. A melting step, a pouring step of pouring the molten salt into a mold, and a molding step of solidifying the molten salt in the mold to form a salt core. In the molding step, the first step Provided is a method for producing a salt core for casting, in which a new metal salt having a different composition between the metal salt and the second metal salt is produced.

  In one form of the method for producing a salt core for casting according to the present invention, the first metal salt is selected from an alkali metal carbonate and a sulfate, and the second metal salt is an alkaline earth metal halide. Is preferably selected from:

  According to another aspect of the method for producing a salt core for casting according to the present invention, a second metal selected from a first metal salt selected from an alkali metal carbonate and a sulfate, and an alkaline earth metal halide. A melting step in which a mixed salt containing a metal salt is heated to form a molten salt, a casting step in which the molten salt is poured into a mold, and a molding in which the molten salt is solidified in the mold to form a salt core A method for producing a salt core for casting, wherein the mixed salt contains 10 to 40 mol% of the second metal salt and contains more of the first metal salt in terms of mole than the second metal salt.

  In one embodiment of the method for producing a casting salt core according to the present invention, it is preferable that the difference between the liquidus temperature and the solidus temperature of the mixed salt is 24 ° C. or more.

  In one embodiment of the method for producing a salt core for casting according to the present invention, it is preferable that the alkaline earth metal is strontium.

  In one form of the method for producing a casting salt core according to the present invention, it is preferable that the heating of the mixed salt is heating to a temperature higher by 5 to 200 ° C. than a liquidus temperature of the mixed salt. is there.

  In another aspect, the present invention provides a casting salt core produced by the above-described method for producing a casting salt core.

  In one embodiment, the casting salt core according to the present invention preferably contains at least the halide of the alkali metal and the carbonate or sulfate of the alkaline earth metal.

  In one form of the casting salt core according to the present invention, it is preferable that 9 mol% or less and 29 mol% or less of a hardly soluble metal salt is contained, and the balance is a water soluble metal salt.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the high intensity | strength salt core for casting which suppresses the kind of raw material, and also endures a high pressure die-casting method, and the salt core for casting manufactured by it can be provided.

It is a figure which shows the bending strength of the test piece of Preparation Examples 1-4. It is a figure which shows the component analysis of the test pieces of Preparation Examples 1-3 and 5. It is a figure which shows the bending strength of the test piece of Preparation Examples 4 and 6. It is a figure which shows the relationship between a superheat degree and a bending strength. It is a figure which shows the relationship between mold temperature and bending strength. It is a figure which shows the relationship between the compounding quantity of strontium chloride, and bending strength.

  Below, the manufacturing method of the salt core for casting which concerns on this invention, and the salt core for casting manufactured by it are demonstrated in detail.

[Manufacturing method of salt core for casting]
The method for producing a salt core according to the present invention includes (1) a melting step in which a mixed salt containing a first metal salt and a second metal salt is heated to form a molten salt, and (2) the molten salt as a mold. And (3) a forming step of solidifying the molten salt in the mold to form a salt core. Each step will be described in detail below.

(1) Melting process In a melting process, the mixed salt containing the 1st metal salt and the 2nd metal salt which are the raw materials of the salt core for casting is heated and melted to make a molten salt. The mixed salt is preferably melted substantially completely to become a molten salt containing no solid phase. Here, “substantially completely melts” means not only when 100% of the mixed salt melts but also that at least 90%, at least 95%, or at least 98% of the mixed salt melts. In the molten salt, ions that are components of the metal salt exist in a dissociated state. In the subsequent step, when the temperature of the molten salt is lowered, ions are bonded to each other and a metal salt is newly generated. In the melting process, the salt of the raw material is substantially completely melted to form a molten salt, so that no salt remains in the solid phase that does not contribute to the reaction to generate a new salt, so that a new salt is generated. The reaction can proceed efficiently.

  The first metal salt is preferably selected from alkali metal carbonates and sulfates. The alkali metal carbonate and sulfate may be used singly or in combination of two or more. Carbonates are more preferred because they do not corrode iron. Examples of the alkali metal sulfate include sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, and cesium sulfate. Examples of the alkali metal carbonate include carbonates such as lithium carbonate, sodium carbonate, and potassium carbonate.

  The second metal salt is preferably selected from alkaline earth metal halides. The alkaline earth metal halide may be one kind alone or a combination of two or more kinds. Examples of the alkaline earth metal halide include magnesium salts such as magnesium chloride, magnesium bromide and magnesium iodide, calcium salts such as calcium chloride and calcium bromide, barium salts such as barium chloride and barium bromide, and chloride. Strontium salts such as strontium and strontium bromide can be used. The alkaline earth metal salt is particularly preferably a strontium salt from the viewpoint of improving the strength of the salt core. Furthermore, since the alkaline earth metal is a typical element, its valence does not change, and therefore a salt of a divalent cation having a small solidification shrinkage can be reliably generated. For this reason, the alkaline earth metal salt has the advantage that it is difficult to generate cracking defects on the surface of the salt core and the strength can be improved.

  When the second metal salt is melted, it dissociates into an alkaline earth metal cation and a halogen ion. When the alkaline earth metal cation is cooled, it binds to a carbonate or sulfate derived from the first metal salt. Produces sparingly soluble salts. This hardly soluble salt plays a role as a refractory in the salt core after production, and contributes to an improvement in the strength of the salt core. Therefore, by using an alkaline earth metal halide as the second metal salt, sufficient strength can be achieved without mixing a separate refractory into the mixed salt. Here, the sparingly soluble salt is a salt whose amount dissolved in 100 g of water (25 ° C.) is less than 1 g.

  The mixed salt is preferably prepared so that the blending ratio of the second metal is 10 to 40 mol% and the blending ratio of the first metal salt is larger than the blending ratio of the second metal salt in terms of mole. The mixing ratio of the first metal salt in the mixed salt preferably occupies the entire amount other than the second metal and constitutes the balance. By setting the blending ratio of the first metal salt and the second metal salt in the above range, a salt core excellent in strength can be produced. Further, the core can be given good disintegrability and can be easily removed.

  Furthermore, the blending ratio of the first metal salt and the second metal salt is more preferably 90:10 to 80:20. When the mixing ratio of the first metal salt and the second metal salt is within this range, the temperature range of the solid-liquid coexistence region of the molten salt obtained by melting the mixed salt may have a width of 24 ° C. or more. it can. The temperature range of the solid-liquid coexistence region of the molten salt corresponds to the difference between the liquidus temperature and the solidus temperature, and here indicates a value when the atmospheric pressure (1 atm) is constant. When the temperature range of the solid-liquid coexistence zone of the molten salt is 24 ° C. or higher, the temperature of the molten salt poured into the mold decreases, and when it changes from liquid to solid, it slowly solidifies in the mold. Therefore, the components do not vary and the strength of the salt core can be improved. On the other hand, if the temperature range in which the molten salt is in a solid-liquid coexistence state is narrow, the salt may crystallize all at once in the mold. The strength may decrease.

  The heating temperature of the mixed salt is preferably 5 to 200 ° C. higher than the liquidus temperature of the mixed salt. Here, the temperature difference from the liquidus temperature of the mixed salt to the heating temperature is also referred to as “degree of superheat”. By setting the superheat degree to the liquidus temperature of the mixed salt to 5 ° C or higher, the temperature of the molten salt is unlikely to drop to the salt formation temperature during the pouring process into the mold. do not do. Therefore, there is an advantage that there is no possibility of variations in strength because variations in components and variations in the amount of pouring do not occur due to salt precipitation. Furthermore, increase in the viscosity of the molten salt due to a temperature drop until pouring can be suppressed, and release of the molten salt as vapor can be suppressed when the molten salt is held in the furnace. Moreover, since the superheat degree with respect to the liquidus temperature of the mixed salt is 200 ° C. or less, the molten salt is less likely to evaporate, and the component variation due to the preferential evaporation of the specific salt does not occur. There is an advantage that there is no risk of occurrence.

(2) Casting process In the casting process, the molten salt prepared in the melting process is poured into a mold. The molten salt can be poured into the mold by any method as long as the object of the present invention is achieved. For example, the molten salt can be poured by a method using the gravity of the molten metal (gravity casting method). In addition, a high strength salt core can be obtained without mixing refractory and other additives that may cause injection resistance into the molten salt, so the molten salt is pressed into the mold at high pressure (high pressure die casting method) ) Can also be used, and the production efficiency of the salt core itself can be increased.

  The mold is preferably heated in advance before pouring the molten salt. The preheating temperature of the mold is preferably 100 to 250 ° C, more preferably 200 to 250 ° C, and particularly preferably 250 ° C. If the mold temperature is 20 ° C (room temperature), a salt core that satisfies the strength level that can withstand high-pressure die casting can be manufactured. However, when the molten salt is poured by preheating to 100 ° C or higher. The molten salt is not rapidly cooled. For this reason, possibility that a crack will occur due to rapid cooling of the molten salt can be reduced. Furthermore, the intensity | strength of a salt core can be raised more as the preheating temperature of a metal mold | die is 200 degreeC or more. Further, by setting the preheating temperature of the mold to 250 ° C. or less, the molten salt solidified in the mold is less likely to stick to the mold, and the molded body of the salt core can be easily released.

(3) Molding step In the molding step, the molten salt poured is cooled in a mold and solidified to mold a salt core. Cooling is performed by natural cooling or slow cooling using a heat insulating material.

  In the above (2) casting step and (3) molding step, the temperature of the molten salt gradually decreases. As the temperature of the molten salt decreases, the ions constituting the first metal salt and the second metal salt existed in a dissociated state, but are bonded to each other to form a metal salt and precipitate. At this time, at least a part of the cation and the anion constituting the first metal salt and the second metal salt are combined with a partner different from that before melting to form a salt. Thus, another new metal having a composition different from that of the first metal salt and the second metal salt by recombination of the cation and the anion constituting the first metal salt and the second metal salt. Salt is also produced. Examples of the new metal salt include a metal salt composed of a cation of a first metal salt and an anion of a second metal salt, that is, an alkali metal halide, a cation of the second metal salt, and a first metal. Metal salts composed of salt anions, ie, alkaline earth metal carbonates or sulfates, first metal salt cations and second metal cations and first metal anions Examples include, but are not limited to, salts. Metal salts also include those in the form of hydrates. In this way, a metal salt is newly generated from the ions constituting the first metal salt and the second metal salt, and a ternary system or more multi-component system including a metal salt of a type larger than the type of the metal salt of the raw material is used. A salt core can be produced. For this reason, the strength of the salt core can be increased, the types of metal salts of the raw material can be reduced, and the manageability and manufacturing workability of the raw material can be improved.

  Furthermore, newly produced alkaline earth metal carbonates and sulfates are generally insoluble or hardly soluble in water and have a high melting point. For this reason, when the alkaline earth metal carbonate and sulfate are contained in the salt core, they serve as a refractory and can improve the strength of the salt core. Therefore, in the production method according to the present invention, a separate refractory does not have to be mixed with the raw material in order to achieve a sufficient salt core strength. In the conventional production method, refractory components having a high specific gravity may settle and separate in the molten salt, and the strength of the salt core may partially decrease significantly, resulting in a variation in strength. Since the refractory is not an essential component in the production method according to the invention, there is no such fear.

  In addition, since alkaline earth metal carbonate has the property of thermally decomposing to generate carbon dioxide and oxide, when alkaline earth metal carbonate is blended in the raw material, the oxide is decomposed by heat in the melting step. There is a possibility of generating. Alkaline earth metal oxides react with water and carbon dioxide in the air, so if contained in the salt core, there is a risk of deterioration of the storage stability of the salt core, such as causing cracks. However, in the production method according to the present invention, an alkaline earth metal carbonate can be produced during the production process. For this reason, even if it does not mix | blend alkaline-earth metal carbonate with a raw material, alkaline-earth metal carbonate can be contained in the salt core after manufacture, and it can contribute to the improvement of intensity | strength. Moreover, by not containing alkaline earth metal carbonate in the raw material, the content of alkaline earth metal oxide in the salt core after production can be suppressed to a small amount, resulting from the alkaline earth metal oxide. Deterioration of the storage stability of the salt core can be avoided.

[Salt core for casting]
The salt core produced by the production method according to the present invention contains a metal salt newly generated from the ions constituting the first metal salt and the second metal salt, and is a ternary or higher multicomponent system. The salt core. The salt core contains, for example, an alkali metal halide and an alkaline earth metal carbonate or sulfate in addition to the first metal salt and / or the second metal salt. The salt core preferably contains at least an alkali metal halide and an alkaline earth metal carbonate or sulfate. The alkaline earth metal carbonate is preferably strontium carbonate from the viewpoint of improving the strength of the salt core. The alkaline earth metal sulfate is preferably cesium sulfate. The alkali metal halide is preferably sodium chloride.

  The content of the alkaline earth metal carbonate or alkaline earth metal sulfate in the salt core is preferably 9 to 29 mol%, and the remainder is preferably a water-soluble metal salt. As the water-soluble metal salt, an alkali metal halide or an alkali metal carbonate is preferable. Alkaline earth metal carbonate or alkaline earth metal sulfate, which is hardly soluble, works as a refractory. Therefore, by setting the content to 9 to 29 mol%, an improved strength can be obtained even if no separate refractory is contained. For example, a bending strength of 15 MPa or more, preferably 25 MPa or more can be realized. Since this strength is strong enough to withstand the high pressure die casting method, the salt core according to the present invention can be applied to casting by the high pressure die casting method. Furthermore, if the content of the hardly soluble salt is 50 mol% or less, the disintegration property of the salt core is not affected, but the content of the alkaline earth metal carbonate or alkaline earth metal sulfate is 9 to 9%. 29 mol%, and the remainder is composed of water-soluble alkali metal halide or alkali metal carbonate, or both, so the salt core is disintegrating and can be easily removed .

[Study of metal salt compounds for salt cores 1]
(Preparation of test piece)
A mixed salt obtained by weighing and mixing the first metal salt (carbonate) and the second metal salt shown in Table 1 so that the ratio of the first metal salt: second metal salt = 80 mol%: 20 mol% was melted. The mixture was placed in an aluminum-plated SUS316L crucible and stirred, and then placed in an electric furnace and heated at 720 ° C. to prepare a molten salt. The molten salt was poured into a mold heated in advance to 250 ° C. by gravity to obtain bending test pieces of Production Examples 1 to 4. The bending test specimen was molded so that the specimen width w≈0.01 m (= 10 mm) and the specimen thickness t≈0.011 m (= 11 mm). The length of the test piece was set to a length that can be supported by two support points placed at intervals of 50 mm in a three-point bending test described later, that is, 90 mm.

(3-point bending test)
A three-point bending test was performed using a bending test piece, and the bending force was measured. In the three-point bending test, an autograph AG-250KNX (manufactured by Shimadzu Corporation) was used, and the test piece was placed on two fulcrums arranged at a distance of 50 mm between the fulcrums and placed on the upper surface of the test piece in the center between the fulcrums. The load was applied, the test was terminated when the test piece was broken, the load at that time (maximum load) was recorded, and the bending strength was calculated from the following formula. The measurement was performed at room temperature. The measurement results are shown in Table 1 and FIG.

σ = 3PL / 2wt ²

(Σ: bending strength (N / m ² ), P: maximum load (N), L: distance between fulcrums (m), w: test piece width (m), t: test piece thickness (m))

  As shown in Table 1 and FIG. 1, it was confirmed that all the test pieces of Production Examples 1 to 4 had a bending strength of 15 MPa or more. Therefore, it turned out that all the test pieces of Preparation Examples 1 to 4 have a strength enough to withstand the high-pressure die casting method.

(Component analysis)
The bending test piece was made into powder and component analysis was performed using a powder X-ray crystal structure analysis (XRD) apparatus SmartLab manufactured by Rigaku. The result of component analysis is shown in FIG. 2A shows the component analysis results of Production Example 1, FIG. 2B shows the Production Example 2, FIG. 2C shows the Production Example 3, and FIG. Here, Production Example 5 is a production example using a mixed salt having the same composition as in Production Example 4, and a test piece was obtained in the same manner as in Production Example 4 except that a molten salt was produced by heating at 650 ° C. Is.

From FIG. 2, in the test pieces of Production Examples 1 to 3 and 5, new metal salts other than the first metal salt (carbonate) and the second metal salt of the raw material are generated and have a multi-component composition. confirmed. In particular, a poorly soluble salt (carbonate) (SrCO ₃ or CaCO ₃ ) composed of an anion (carbonate ion) of the first metal salt (carbonate) and a divalent cation of the second metal salt is generated. It was confirmed. These poorly soluble salts (carbonates) are considered to be aggregates and improve the strength of the test piece. It was also confirmed that water-soluble salts (KCl, LiCl, NaCl) composed of a cation of the first metal salt (carbonate) and an anion of the second metal salt were also generated. From this, it was confirmed that the test pieces of Production Examples 1 to 3 and 5 had disintegration properties.

In the following experiment, using the composition of Preparation Example 4 (preparation example using Na ₂ CO ₃ and SrCl ₂ ), which had the highest bending strength and confirmed that a new carbonate was formed by XRD analysis. And determine the detailed conditions.

[Study of metal salt compounds for salt cores 2]
Na ₂ CO ₃ , NaCl, and SrCO ₃ are mixed with Na ₂ CO ₃ : NaCl: SrCO ₃ = 50 so as to have the same composition as that of the metal salt of the test piece of Preparation Example 5 shown in FIG. A test piece of Preparation Example 6 was molded by the same procedure as Preparation Examples 1 to 4, except that a mixed salt mixed at a ratio of 33:17 (mol%) was used.
The bending strength of the test piece of Production Example 6 was measured by a three-point bending test in the same manner as in Production Examples 1 to 4. As shown in Table 2, it was confirmed that the test piece of Preparation Example 6 had a bending strength of 25.4 MPa and had sufficient strength to apply the high-pressure die casting method.

  From the results of component analysis and bending strength measurement, it was estimated that it is important to contain a hardly soluble salt, for example, a carbonate such as strontium carbonate, in order to increase the strength of the salt core.

  Further, as shown in FIG. 3, when the production example 4 and the production example 6 are compared, both of the bending strengths are as high as the same, but the test piece of the production example 4 is the same as that of the production example 6. It had a slightly higher bending strength than the test piece. In Production Example 6, strontium carbonate, which is a poorly soluble salt, may be thermally decomposed when heated to a molten salt, whereas in Production Example 4, strontium carbonate is generated during the production process. It is presumed that it cannot be thermally decomposed. Thus, since the manufacture example 4 contains more sparingly soluble strontium carbonate than the manufacture example 6, it is thought that intensity | strength is higher. Furthermore, Production Example 4 can produce a ternary salt core using salts of two kinds of raw materials, and thus has an advantage that the manageability of the raw materials can be improved.

[Examination of superheat of molten metal]
Test pieces of Production Examples 7 to 11 were produced in the same manner as in Production Example 4 except that the heating temperature when heating the mixed salt to form a molten salt was changed to the temperature shown in Table 3. Here, the superheat degree in Table 3 represents the temperature difference from the liquidus temperature of the mixed salt having a specific mixing ratio to the heating temperature. That is, since the liquidus temperature of the mixed salt obtained by mixing sodium carbonate and strontium chloride at 80 mol%: 20 mol% is 646 ° C., it represents a temperature difference from 646 ° C. to the heating temperature.

  The bending strength of the test pieces of Production Examples 7 to 11 was measured by the three-point bending test. The results are shown in Table 3 and FIG. As shown in Table 3, the specimens of Production Examples 7 to 11 have a bending strength of 15 MPa or more, and thus it was confirmed that the test pieces satisfy the standard that can be used for high-pressure die casting. From FIG. 4, it was confirmed that if the degree of superheat is between 5 and 205 ° C., a high bending strength is maintained. In particular, it was shown that the bending strength is high when the degree of superheat is 5 to 20 ° C.

[Examination of mold temperature]
Test pieces of Production Examples 12 to 17 were produced in the same procedure as in Example 4 except that the mold temperature was previously heated to the temperature shown in Table 4. The bending strength of the test pieces of Production Examples 12 to 17 was measured by the above three-point bending test. The results are shown in Table 4 and FIG.

  As Table 4 shows, since the bending strength was 15 Mpa or more, it has confirmed that the test piece of Preparation Examples 12-15 was satisfy | filling the level which can be used for a high voltage | pressure die-cast. From FIG. 5, it was found that the bending strength is improved when the mold temperature is raised. However, in Production Examples 16 and 17, the test piece stuck to the mold and could not be released. For this reason, it was considered that the mold temperature is preferably 250 ° C. or lower. In addition, if the mold temperature is 20 degrees (normal temperature) or higher, a test piece that satisfies the bending strength level that can be used for high-pressure die casting can be manufactured. Since the possibility that the molten salt was rapidly cooled to cause cracking could be reduced, it was considered more preferable.

[Examination of mixing ratio 1]
Test pieces of Preparation Examples 18 to 20 according to the same procedure as in Example 4 except that the first metal salt (Na ₂ CO ₃ ) and the second metal salt (SrCl ₂ ) were mixed at the mixing ratio shown in Table 5. Was made. In the manufacturing process, after pouring the molten salt into the mold, the temperature of the thermocouple provided in the hot metal part (molten pool part provided at the upper part of the mold) was measured, and this temperature change was plotted with time. Read the liquid phase temperature (temperature when all raw materials are liquid) and solid phase temperature (temperature when all raw materials are solid) from the graph, and the difference between them is the solid-liquid coexistence zone (raw materials are solid and liquid) Temperature range at the time of the mixed state). Moreover, the bending strength of the test pieces of Production Examples 18 to 20 was measured by the three-point bending test. These results are shown in Table 5.

As shown in Table 5, the test pieces of Production Examples 18 and 19 exhibited a high bending strength of about 30 MPa. This is presumed that, in Production Examples 18 and 19, the temperature range of the solid-liquid coexistence region is 24 ° C. or higher, and the molten metal slowly solidifies in the mold, so that the components of the test piece are less likely to vary. Is done. On the other hand, in the test piece of Production Example 20, the solid phase temperature could not be measured, and there was almost no solid-liquid coexistence region. In addition, in the manufacturing example 20, the bending strength was very low. This is because there is almost no solid-liquid coexistence zone, so when the temperature of the molten salt poured into the mold decreases, the state immediately changes from the liquid phase to the solid phase, and the eutectic structure crystallizes all at once. Then, it is considered that there is a high possibility that the components of the test piece will vary, and this will contribute to a decrease in the bending strength. From this result, it was shown that the temperature range of the solid-liquid coexistence region of the molten salt varies depending on the mixing ratio of Na ₂ CO ₃ and SrCl ₂ and may affect the bending strength of the test piece. Therefore, in order to increase the bending strength, it was considered necessary to adjust the mixing ratio of Na ₂ CO ₃ and SrCl ₂ to an appropriate range.
It was also confirmed that the test piece of Production Example 19 had a low liquidus temperature and a solidus temperature. Therefore, it is considered that the salt mixing ratio in Production Example 19 gives the salt core the characteristics of high bending strength and low melting point, and can improve the safety of the salt core and simplify the equipment.

[Examination of mixing ratio 2]
Test pieces of Preparation Examples 21 to 27 in the same procedure as in Example 4 except that the first metal salt (Na ₂ CO ₃ ) and the second metal salt (SrCl ₂ ) were mixed at the mixing ratio shown in Table 6. Was made. The bending strength of the test pieces of Production Examples 21 to 27 was measured by the three-point bending test. The results are shown in Table 6.

From the results shown in Table 6, the test pieces manufactured by mixing in the range of Na ₂ CO ₃ : SrCl ₂ = 90: 10 to 60:40 as in Production Examples 21 to 24 have a bending strength of 15 MPa or more. Therefore, it was confirmed that the level that can be used for high-pressure die casting was satisfied. It was shown that when the mixture was mixed with Na ₂ CO ₃ : SrCl ₂ = 100: 0 as in Production Example 25, a hardly soluble carbonate that works as an aggregate was not generated, so that the bending strength was reduced. In addition, when mixed at Na ₂ CO ₃ : SrCl ₂ = 50: 50 or 30:70 as in Preparation Examples 26 and 27, that is, the bending strength of the test pieces manufactured with a high mixing ratio of strontium chloride is The level that can be used for high pressure die casting was not met (reason is unknown). From these results, it was found that increasing the compounding amount of Na ₂ CO ₃ in terms of moles compared to SrCl ₂ helps to increase the bending strength.

Moreover, the component ratio of the test pieces of Preparation Examples 21 to 27 was measured. For measurement of the component ratio, a powder X-ray crystal structure analysis (XRD) apparatus SmartLab manufactured by Rigaku was used. Table 7 shows the measurement results. From the results of Table 7, the test pieces containing ₉ to 29 mol% of SrCO ₃ as in Production Examples 21 to 24 have a bending strength of 15 MPa or more, and therefore satisfy the level that can be used for high pressure die casting. It could be confirmed. It was shown that the test piece containing 100 mol% of Na ₂ CO ₃ as in Production Example 25 does not produce a poorly soluble carbonate that works as an aggregate, so that the bending strength is low. The bending strength of the test piece containing 67 mol% of SrCO ₃ as in Production Example 26 and the test piece containing SrCl ₂ as in Production Example 27 did not satisfy the level that can be used for high-pressure die casting (the reason is unknown). ).

Claims (9)

A melting step in which a mixed salt containing a first metal salt and a second metal salt is heated to a liquidus temperature or higher, and the first metal salt and the second metal salt are made into a molten salt;
A pouring step of pouring the molten salt into a mold;
Forming a salt core by solidifying the molten salt in the mold, and in the forming step, the first metal salt and the second metal salt have different compositions. A method for producing a salt core for casting in which salt is produced.   The method for producing a salt core for casting according to claim 1, wherein the first metal salt is selected from an alkali metal carbonate and a sulfate, and the second metal salt is selected from an alkaline earth metal halide. A melting step of heating a mixed salt containing a first metal salt selected from alkali metal carbonates and sulfates and a second metal salt selected from alkaline earth metal halides to form a molten salt;
A pouring step of pouring the molten salt into a mold;
Forming a salt core by solidifying the molten salt in the mold, wherein the mixed salt contains 10 to 40 mol% of the second metal salt, and the first metal salt is the second metal salt The manufacturing method of the salt core for casting which contains more by mol conversion than.   The method for manufacturing a salt core for casting according to any one of claims 1 to 3, wherein the heating of the mixed salt is heating to a temperature higher by 5 to 200 ° C than a liquidus temperature of the mixed salt.   The method for producing a salt core for casting according to any one of claims 2 to 4, wherein the alkaline earth metal is strontium.   The method for producing a salt core for casting according to any one of claims 1 to 5, wherein a difference between a liquidus temperature and a solidus temperature of the mixed salt is 24 ° C or higher.   The salt core for casting manufactured by the manufacturing method in any one of Claims 1-6.   The casting salt core according to claim 7, wherein the casting salt core contains at least the halide of the alkali metal and the carbonate or sulfate of the alkaline earth metal.   The casting salt core according to claim 7 or 8, wherein the casting salt core contains 9 mol% or less and 29 mol% or less of a hardly soluble metal salt, and the balance is a water-soluble metal salt.

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