JP2007296566A - Core for casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new core for casting capable of obtaining high pressure resistance, regarding a core for casting made of a salt formed of a molten salt composed of Na<SP>+</SP>, K<SP>+</SP>, Cl<SP>-</SP>, CO<SB>3</SB><SP>2-</SP>, in the range of a composition where K<SP>+</SP>is higher than Na<SP>+</SP>and CO<SB>3</SB><SP>2-</SP>is lower than Cl<SP>-</SP>. <P>SOLUTION: A salt core 2 is first composed of potassium and sodium as cations and chlorine and carbonic acid as anions. Additionally, in the salt core 2, the mol component ratio of the potassium ions in all the cations, XK<SP>+</SP>(=[K<SP>+</SP>]/([Na<SP>+</SP>]+[K<SP>+</SP>])×100) is controlled to 60 to 70 mol%, and, the mol component ratio of the carbonic acid ions in all the anions, YCO<SB>3</SB><SP>2-</SP>([CO<SB>3</SB><SP>2-</SP>]/([CO<SB>3</SB><SP>2-</SP>]+[Cl<SP>-</SP>])×100) is controlled to 30 to 40 mol%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a casting core having water solubility.

  For example, casting of aluminum die casting or the like is a technique for casting a structure having a desired shape by injecting a molten aluminum alloy into a mold at the speed of light and high pressure, as is well known. In such casting, for example, a core is used when a casting having a hollow structure such as a water jacket for water cooling such as a cylinder block of an internal combustion engine is formed. The core used in such a case is susceptible to a large impact due to collision of the molten metal injected at high speed from the gate, and the casting pressure is large until the solidification is completed, so that the core can withstand high pressures and high temperatures. Required. In addition, the core is removed from the casting after casting. However, in the case of a casting having a complicated internal structure, it is removed when a sand core hardened with a general phenol range is used. It is not easy. On the other hand, there are water-soluble salt cores that can be removed by dissolving with high-temperature water or the like (see Patent Documents 1, 2, and 3).

The salt core as described above uses a composite salt composed of sodium carbonate (Na ₂ CO ₃ ), potassium chloride (KCl), sodium chloride (NaCl), etc., and is molded by melting them to provide high pressure strength. In addition, the workability and stability in casting are improved.

Japanese Patent Laid-Open No. 48-039696 JP 50-136225 A JP-A-52-010803

By the way, the above-described salt core formed from a molten salt composed of sodium ions (Na ⁺ ), potassium ions (K ⁺ ), chlorine ions (Cl ⁻ ), and carbonate ions (CO ₃ ²⁻ ) that has been conventionally used. Then, only when the ratio of these compositions is within a specific range, a high pressure strength is obtained. However, in the range of conventional compositions, many melting points are 700 ° C. or higher and are not suitable for melt molding. Some compositions have a high melting point at a melting point of 700 ° C. or lower, but all have a composition with more sodium ions than potassium ions and a composition with more carbonate ions than chlorine ions. For example, in a composition having a large amount of CO ₃ ²⁻ , the alkalinity of the aqueous solution dissolved when removing the salt core becomes stronger, and the corrosion of the casting becomes a problem. This corrosion problem can be solved by neutralizing with hydrochloric acid, but in a composition with a large amount of CO ₃ ^2- , the amount of hydrochloric acid used is proportionally increased. That is, the conventional technique has a problem that the range of the composition that can easily obtain a high pressure strength applicable to casting of aluminum die casting or the like is not so wide.

The present invention has been made to solve the above-described problems, and is an aqueous solution composed of a salt (molten salt) formed from a molten salt composed of Na ⁺ , K ⁺ , Cl ⁻ , and CO ₃ ^2−. An object of the present invention is to provide a new casting core capable of obtaining high pressure strength in a composition range in which K ⁺ is greater than Na ^{+ and} CO ₃ ²⁻ is less than Cl ^−. To do.

  The casting core according to the present invention is formed of a molten salt consisting only of potassium ions, sodium ions, chlorine ions, and carbonate ions, and the molar component ratio of potassium ions in all cations is 60 to 70 mol%, The molar component ratio of carbonate ions in all anions is 30 to 40 mol%.

According to the present invention, by a molar ratio of components potassium ions in the total cations and 60～70Mol%, a molar component ratio of carbonate ions in the total anions was 30~40mol%, Na ^+, K ⁺ In a water-soluble core composed of a salt (molten salt) formed from a molten salt composed of, Cl ⁻ , CO ₃ ²⁻ , in a composition range where K ⁺ is greater than Na ⁺ and CO ₃ ²⁻ is less than Cl ⁻ . It is possible to provide a new water-soluble casting core capable of obtaining a high pressure strength.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the usage form of the casting core according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a perspective view of a cylinder block in the case of casting using a casting core according to the present invention, which is drawn in a partially broken state. In FIG. 1, what is shown by the code | symbol 1 is an engine cylinder block which consists of an aluminum alloy cast using the salt core 2 as a casting core which concerns on this invention. The cylinder block 1 is a part of a water-cooled four-cycle four-cylinder engine for a motorcycle, and is formed into a predetermined shape by a die casting method.

  A cylinder block 1 shown in FIG. 1 is integrally formed with a cylinder body 4 having four cylinder bores 3 and cylinder bores 3 and an upper crankcase 5 extending downward from the lower end of the cylinder body 4. The upper crankcase 5 has a lower crankcase (not shown) attached to a lower end portion, and a crankshaft (not shown) is rotatably supported through a bearing together with the lower crankcase.

  The cylinder body 4 is of a so-called closed deck type, and a water jacket 6 is formed inside using a salt core 2. The water jacket 6 includes a cooling water passage forming portion 7, a cooling water inlet 8, a main cooling water passage 9, and a communication passage 10. The cooling water passage forming portion 7 projects from one side of the cylinder body 4 and extends in the direction in which the cylinder bores 3 are arranged. Further, the cooling water port 8 is formed in the cooling water passage forming portion 7. The main cooling water passage 9 communicates with a cooling water distribution passage (not shown) formed inside the cooling water passage forming portion 7 and is formed so as to cover the periphery of all the cylinder bores 3. Further, the communication passage 10 extends upward from the main cooling water passage 9 in FIG. 1 and opens to a mating surface 4 a with a cylinder head (not shown) at the upper end of the cylinder body 4.

  The above-described water jacket 6 supplies the cooling water flowing from the cooling water inlet 8 to the main cooling water passage 9 around the cylinder bore through the cooling water distribution passage, and further supplies this cooling water from the main cooling water passage 9 to the communication passage 10. It is comprised so that it may guide to the cooling water path in a cylinder head (not shown) through. By forming the water jacket 6 in this way, the cylinder body 4 has a ceiling wall of the cylinder body 4 except that the communication path 10 of the water jacket 6 is opened at the upper mating surface 4a to which the cylinder head is connected. It will be covered with (wall which forms the mating surface 4a), and becomes a closed deck type structure.

  The salt core 2 for forming the water jacket 6 is formed in a shape in which each part of the water jacket 6 is integrally connected. In FIG. 1, the cylinder body 4 is drawn in a partially broken state so that the shape of the salt core 2 (the shape of the water jacket 6) can be easily understood.

  The salt core 2 according to this embodiment is formed to have the shape of the water jacket 6 by die casting using a plurality of salts such as sodium carbonate, sodium chloride, and potassium chloride. The components of the salt core 2 will be described in detail below. The salt core 2 can be formed by other casting methods such as a gravity casting method in addition to the die casting method. In the formation of the salt core 2 by the die casting method, first, a molten metal is made by heating and melting a mixture composed of a plurality of salts described later. Next, the molten metal is injected into a salt core mold under high pressure to be solidified, and is taken out from the mold after solidification.

  As shown in FIG. 1, the salt core 2 includes a passage forming portion 2a that forms a cooling water inlet 8 and a cooling water distribution passage, an annular portion 2b that surrounds the four cylinder bores 3, and an annular portion. A plurality of convex portions 2c protruding upward from 2b are formed integrally. The communication path 10 of the water jacket 6 is formed by these convex portions 2c. As is well known in the art, the salt core 2 is supported at a predetermined position in a mold (not shown) by a skirting board (not shown) at the time of casting, and is heated by hot water or steam after casting. Dissolve and remove.

  In order to remove the salt core 2 after casting, it can be performed by immersing the cylinder block 1 in a dissolution tank (not shown) in which a solution composed of hydrochloric acid and warm water is stored. By immersing the cylinder block 1 in the solution, the passage forming portion 2a in the salt core 2 and the convex portion 2c exposed on the mating surface 4a come into contact with the solution and dissolve. This dissolved portion gradually expands and finally all the sites are dissolved. In such a core removal step, hot water or steam may be sprayed with pressure from the hole in order to promote dissolution of the salt core 2 remaining in the water jacket 6. The salt core 2 can also insert a baseboard instead of the convex part 2c in the site | part in which the convex part 2c is formed.

  In addition, if hydrochloric acid is used in the step of removing the salt core 2 from the casting, the carbon dioxide gas foams, so that the stirring action by this foaming is obtained, and the dissolution can be effectively promoted. Moreover, since the salt core 2 contains potassium carbonate or sodium carbonate, it will exhibit alkalinity when dissolved in water. Thus, in an alkaline state, there exists a problem that the aluminum which is a casting melt | dissolves. This problem can also be neutralized by adding hydrochloric acid, so that the adverse effect of alkali on the molded product can be reduced.

Next, the salt core 2 will be described. The salt core 2 in the present embodiment is first composed of potassium and sodium as cations and chlorine and carbonic acid as anions. In addition, the salt core 2 has a molar component ratio XK ⁺ (= [K ⁺ ] / ([Na ⁺ ] + [K ⁺ ]) × 100) of potassium ions in all cations to 60 to 70 mol%. The molar component ratio YCO ₃ ²⁻ ([CO ₃ ²⁻ ] / ([CO ₃ ²⁻ ] + [Cl ⁻ ]) × 100) of carbonate ions in all anions is 30 to 40 mol%. .

  For example, sodium carbonate, sodium chloride, and potassium chloride may be mixed so as to achieve the above composition, and the salt core 2 may be produced by the above-described die casting method. Alternatively, potassium carbonate, sodium chloride, and potassium chloride may be mixed and the salt core 2 may be produced by the above-described die casting method. Alternatively, the salt core 2 may be produced by mixing sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride and using the above-described die casting method. The salt core 2 is formed only of potassium, sodium, chlorine, and carbonic acid, and does not contain reinforcing ceramics or other reinforcing agents.

The structure of the salt core 2 described above has been found as a result of detailed examination of the results of experiments conducted by the inventors as will be described later, and has a bending strength that can be used for die casting methods such as aluminum alloys. It has a value that can be obtained. According to the inventors' experiment, as shown in Table 1 and Table 2 below and FIG. 2 and FIG. 3, XK ⁺ is set to 60 to 70 mol% in the range of the composition having more potassium ions than sodium ions, and YCO ₃ ^A high core strength is obtained with a salt core in which ^2- is 30 to 40 mol%. On the other hand, high bending strength is not obtained with salt cores having compositions outside this range. The concentration of each ion is measured by an analysis method established in the general rules for ion chromatograph analysis of JIS standard K0127.

FIG. 4 shows the relationship between the cation ratio of potassium ions and the cation ratio of carbonate ions and the melting temperature (liquidus temperature) (phase diagram of Na—K—Cl—CO ₃ system). Each of the compositions shown in Table 1 is shown in correspondence with the sample number. Further, in FIG. ^{4, K + 0mol%, CO} 3 2- 0mol% of the liquidus temperature of NaCl _{^{when, Na + 0mol%, CO 3}} 2- 0mol% of the liquidus temperature of the KCl in the case, K _{^{+ 0mol%, Cl - Na 2}} CO 3 of the liquidus temperature of the case of ^{0mol%, Na + 0mol%,} Cl - liquidus temperature of the of K ₂ CO ₃ when the 0 mol% is also shown. In FIG. 4, a eutectic line is indicated by a bold line.

As is clear from FIG. 4, Samples 1-1, 1-2, 1-3, 1-4, and 1-5 in which high bending strength is obtained have XK ⁺ of 60 to 70 mol%, there YCO ₃ ^2-to 30～40Mol% and the region. In contrast, Samples 2-1, 2-2, 2-3, 2-4, and 2-5, which do not have a high bending strength, have XK ⁺ of 60 to 70 mol%, and YCO ₃ ^2- Is outside the region of 30 to 40 mol%. Moreover, it turns out that said area | region exists between the liquidus line 600 degreeC and the liquidus line 650 degreeC.

Therefore, the salt core in the present embodiment does not melt even when used for casting an aluminum alloy having a melting point of about 580 ° C. Further, since the salt core in the present embodiment has a composition in which CO ₃ ²⁻ is less than Cl ⁻ , there is little CO ₃ ²⁻ which causes strong alkalinity in the step of removing the salt core, For example, corrosion of the casting can be suppressed, and the amount of hydrochloric acid required for neutralization can be reduced. Further, the melting point does not exceed 700 ° C., and melt molding is easy.

  Next, measurement of the bending strength will be described. For the measurement of the bending strength, a prismatic test piece having a predetermined size is prepared, a load is applied to the test piece, and the bending load is obtained from the maximum load required for the fracture. First, preparation of a test piece will be described. A rod-shaped test piece 501 as shown in FIG. 5 is formed using a predetermined mold. The used mold is made of chrome molybdenum steel such as SCM440H, for example. Although FIG. 5 also shows the portion 502 of the hot water used for filling the mold with the molten metal, the portion 502 is cut out in the measurement of the bending strength. 5A is a side view, FIG. 5B is a cross-sectional view at the position bb in FIG. 5A, and the dimensions shown in the drawing are design values in the mold. .

  As shown in FIG. 6, the bending strength of the rod-shaped test piece 501 manufactured as described above is measured by first supporting two supports arranged at a distance of 50 mm at the center of the test piece 501. The test piece 501 is supported by the part 601. In a state of being supported in this manner, a load is applied to the test piece 501 by two load portions 602 having an interval of 10 mm at an intermediate location between the two support portions 601. The load applied to the test piece 501 was gradually increased, and the load when the test piece 501 was broken was defined as the bending load shown in Table 1.

Here, the bending strength σ (MPa) can be obtained from the bending load P according to the formula “σ = 3LP / BH ² ”. In the above formula, H represents the length in the load direction in the cross section of the test piece, B represents the length perpendicular to the load direction in the cross section of the test piece, and L represents a load portion to which a load is applied from the support portion 601 serving as a fulcrum. The interval is up to 602. By the way, since the test piece 501 is formed by pouring into the above-mentioned mold, there are hot water wrinkles and sinkholes and it is difficult to accurately measure the dimensions. For this reason, the bending strength is calculated by approximating that the cross-section of the test piece is rectangular, and H≈20 mm, B≈18 mm, and L = 20 mm. By making this approximation, the strength is estimated to be 0 to 20% lower than the actual strength. For example, a test piece fractured at a bending load of 1200 N is an ideal test piece having a bending strength of 10 MPa. It can be considered stronger.

Hereinafter, the molar component ratio XK ⁺ (= [K ⁺ ] / ([Na ⁺ ] + [K ⁺ ]) × 100) of potassium ions in all cations is set to 60 to 70 mol%, and carbonate ions in all anions. In the composition range in which the molar component ratio of YCO ₃ ²⁻ ([CO ₃ ²⁻ ] / ([CO ₃ ²⁻ ] + [Cl ⁻ ]) × 100) is 30 to 40 mol%, high pressure strength can be obtained. Think about it.

From FIG. 4, since the components of Sample Nos. 1-1 to 1-5 are located on the chloride side from the eutectic line, the primary crystals are all solid solution K _x Na _1-x Cl (x = 0 to ₁ ) of chloride. ). Usually, the ratio of potassium and sodium in the primary crystal varies depending on the initial composition of the mixed salt, but this ratio is thought to have a large effect on the strength. In the components of Sample Nos. 1-1 to 1-5, the primary crystal total solid solution K _x Na _1-x Cl (x = 0 to 1) is almost pure potassium chloride with x≈0.9 to 1. KCl. Since the primary crystal of potassium chloride is a stable phase, no phase transformation occurs in the temperature range from room temperature to the liquidus. For this reason, it is considered that a high strength salt core can be obtained by melt-molding the mixed salt of this component. On the other hand, except for the components of sample numbers 1-1 to 1-5, the primary crystal total solid solution K _x Na _1-x Cl (x = 0 to 1) is x≈0.1 to 0.9. Often. In this case, the primary crystal is not stable and is embrittled by two-phase separation, and the strength is considered to decrease.

It is a perspective view of a cylinder block at the time of casting using the core for casting concerning the present invention. It is a graph which shows the bending strength of a bending test piece. It is a graph which shows the bending strength of a bending test piece. It is a characteristic view (state diagram) which shows the relationship between the cation ratio of potassium ion, the cation ratio of carbonate ion, and liquidus temperature. It is a block diagram which shows the state of the test piece used for bending strength measurement. It is explanatory drawing for demonstrating bending strength measurement.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cylinder block, 2 ... Salt core, 2a ... Passage formation part, 2b ... Annular part, 2c ... Convex part, 3 ... Cylinder bore, 4 ... Cylinder body, 4a ... Matching surface, 5 ... Upper crankcase, 6 ... Water Jacket: 7 ... Cooling water passage forming portion, 8 ... Cooling water inlet, 9 ... Main cooling water passage, 10 ... Communication passage.

Claims (1)

Formed by molten salt consisting only of potassium ion, sodium ion, chlorine ion, and carbonate ion,
A casting core, wherein the molar component ratio of potassium ions in all cations is 60 to 70 mol%, and the molar component ratio of carbonate ions in all anions is 30 to 40 mol%.