JP2007083284A - Core for die casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a core having such an excellent high temperature strength as to resist the injection pressure of a molten metal in a die casting method. <P>SOLUTION: The core for die casting is obtained by using a spherical molding sand manufactured by a flame-fusion method or by using a spherical molding sand having a water absorption rate of ≤0.5 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a core used for manufacturing a casting by a die casting method. More specifically, the present invention relates to a core used for producing a casting by a die casting method obtained by using spherical casting sand.

  As one type of casting method, a die casting method is known in which a molten metal is press-fitted into a precise mold to produce a high-precision casting in large quantities. Among them, when casting a product having a hollow part, a core is placed in the cavity in advance, and a molten metal is poured around the core, and after the metal is solidified, the mold is removed and the core is removed. A way to get it done.

In pressure metal casting by the die casting method, a core that is strong enough to withstand the injection pressure of the molten metal is required. Patent Document 1 discloses a casting core using spherical mullite refractory particles.
JP 7-178506 A

  However, the casting core of Patent Document 1 has a drawback that the core strength that can sufficiently withstand the injection pressure of the molten metal cannot be obtained by the die casting method.

  An object of the present invention is to provide a core excellent in hot strength that can withstand the injection pressure of molten metal in a die casting method.

  The present invention relates to a core for die casting obtained by using spheroidal molding sand produced by a flame melting method.

  Moreover, this invention relates to the core for die-casting obtained using the spherical casting sand whose water absorption is 0.5 weight% or less.

  Furthermore, the present invention relates to a method for producing a die casting mold using the die casting core of the present invention and a method for producing a casting using the die casting mold.

  ADVANTAGE OF THE INVENTION According to this invention, the core excellent in hot strength which can endure the injection pressure of a molten metal in a die-casting method can be obtained.

<Spherical casting sand>
The spherical foundry sand used for the core of the present invention is roughly composed of two aspects. A 1st aspect is the spherical foundry sand manufactured by the flame fusion method. Moreover, a 2nd aspect is the spherical foundry sand whose water absorption is 0.5 weight% or less. Hereinafter, these two may be collectively referred to as “spherical casting sand”.

  The spherical shape which is the shape of the spherical casting sand of the present invention refers to a sphericity of 0.88 or more, preferably 0.90 or more. Whether or not it is spherical can be determined by observing the foundry sand with an optical microscope, a digital scope (for example, VH-8000, manufactured by Keyence Corporation) or the like, as described in Examples below. it can.

The main component of the spherical foundry sand of the present invention is not particularly limited, and conventionally known refractories and refractory raw materials obtained by spheronization by a flame melting method are used. Among these refractories and refractory raw materials, those containing SiO ₂ as the main component, those containing Al ₂ O ₃ and SiO ₂ as the main components, MgO and SiO from the viewpoint of fire resistance and availability. Those having ₂ as a main component are preferred. Among these, those mainly containing Al ₂ O ₃ and SiO ₂ are preferable from the viewpoint of fire resistance and thermal expansion.

  Here, the “main component” means that the above components are contained in a total amount of 60% by weight or more, preferably 80% by weight or more in all components of the entire foundry sand. As the content of the main component, from the viewpoint of improving fire resistance, the total amount of these components is preferably 85 to 100% by weight, and more preferably 90 to 100% by weight, based on all components of the spherical casting sand.

Incidentally, as may be included as a component other than the main component in the spherical molding sand of the present invention, for _{example, CaO, Fe 2 O 3,} TiO 2, K 2 O, and metal oxides Na ₂ O and the like. These are derived from starting materials.

When Fe ₂ O ₃ and TiO ₂ are contained, their content is preferably 5% by weight or less. Further, the content of Fe ₂ O ₃ is more preferably 2.5% by weight or less, and further preferably 2% by weight or less. When K ₂ O and Na ₂ O are contained, the total content is preferably 3% by weight or less, more preferably 1% by weight or less.

In the case of mainly composed of Al ₂ O ₃ and _{SiO 2, Al 2 O 3 /} SiO 2 weight ratio is preferably 1 to 15. From the viewpoint of improving fire resistance and casting sand regeneration efficiency, 1.2 to 12 is preferable, and 1.5 to 9 is more preferable. Further, when only Al ₂ O ₃ and SiO ₂ or SiO ₂ are the main components, CaO and MgO may be included as components other than the main components. In that case, from the viewpoint of improving the fire resistance of the spherical casting sand, the total content thereof is preferably 5% by weight or less.

In the case of the main component MgO and SiO _2, the weight ratio of MgO / SiO ₂ is preferably 0.1 to 10 is. From the viewpoints of easiness of spheroidization, corrosion resistance, fire resistance, and improvement in recycle efficiency of foundry sand, 0.2 to 9 is preferable, and 0.3 to 5 is more preferable.

When MgO and SiO ₂ are the main components, Al ₂ O ₃ can be included as a component other than the main components. Although this originates in a raw material, 10 weight% or less is preferable as content from a viewpoint of the corrosion-resistant improvement of a spherical casting sand.

  From the viewpoint of improving the hot strength of the core, the average particle size (mm) of the spherical casting sand of the present invention is preferably 0.02 to 1 mm, more preferably 0.05 to 0.5 mm, and further 0.05 to 0.2 mm. Further, 0.05 to 0.12 mm, particularly 0.05 to 0.10 mm is preferable. From the viewpoint of reducing the insertion of the molten metal between the sand particles, the sand particle size is preferably small.

  The AFS particle size index of the spherical casting sand of the present invention is preferably AFS 60 to 200, more preferably AFS 110 to 200, and particularly preferably AFS 110 to 170. Note that the AFS granularity index is a granularity index according to the American Foundry Society standard (AFS1106-00-S).

  The average particle diameter can be determined as follows. That is, the diameter (mm) is measured when the sphericity from the particle projection cross section of the spherical casting sand particles is 1, while the major axis diameter (mm) and the minor axis of the spherical casting sand particles are measured when the sphericity <1. The diameter (mm) is measured to determine (major axis diameter + minor axis diameter) / 2, and the average value of the average particle diameter (mm) is obtained for any 100 spherical cast sand particles. . The major axis diameter and the minor axis diameter are defined as follows. When the particle is stabilized on a plane and the projected image of the particle on the plane is sandwiched between two parallel lines, the width of the particle that minimizes the distance between the parallel lines is called the minor axis diameter. The distance when a particle is sandwiched between two parallel lines in a direction perpendicular to the line is called the major axis diameter.

In addition, the major axis diameter and minor axis diameter of the spherical casting sand particles are obtained by obtaining an image (photograph) of the particles with an optical microscope or a digital scope (for example, VH-8000 type, manufactured by Keyence Corporation). It can be obtained by analysis. The sphericity is obtained by image analysis of the obtained image to obtain the area of the particle projection cross section of the particle and the perimeter of the cross section, and then [the area of the same area as the area of the particle projection cross section (mm ² ). The circumference of the perfect circle (mm)] / [perimeter of the particle projection cross section (mm)] is calculated, and the obtained values are averaged for any of 50 spheroidal molding sand particles.

The spherical casting sand of the present invention preferably has a sphericity of 0.95 or more, more preferably 0.98 or more, and even more preferably 0.99 or more. Therefore, the spherical casting sand according to the first aspect of the present invention contains, for example, Al ₂ O ₃ and SiO ₂ as main components, and has an Al ₂ O ₃ / SiO ₂ weight ratio of 1 to 15, average grains. Spherical casting sand made by a flame melting method having a diameter of 0.02 to 0.5 mm and a sphericity of 0.95 or more is suitable.

  The spherical foundry sand according to the first aspect of the present invention is obtained by a flame melting method. Therefore, it has a structural feature of high sphericity and denseness. The structural feature greatly contributes to improvement of fluidity, mold strength, and surface smoothness of a cast product.

  Further, the water absorption rate (% by weight) of the spherical casting sand according to the present invention includes an increase in the amount of resin used due to absorption of the resin used in the production of the mold into the casting sand, an improvement in the mold strength, etc. From the viewpoint, 0.5% by weight or less is preferable, and 0.3% by weight or less is more preferable. The water absorption can be measured according to the method for measuring the water absorption of JIS A1109 fine aggregate. In addition, when RCS (resin coated sand) coated with a binder or a binder residue after casting remains, these components are removed by an appropriate method such as heat treatment (for example, 1000 ° C. or more). Measure water absorption after removal.

  On the other hand, the water absorption of the spherical casting sand according to the second aspect of the present invention is 0.5% by weight or less. From the viewpoint of suppressing increase in the amount of resin used due to absorption of the resin used in the production of the mold into the molding sand and improving the mold strength, it is preferably 0.3% by weight or less, and 0.1% by weight or less. Is more preferable.

  In addition, the water absorption rate of spherical cast sand is usually lower when the sand is prepared by a flame melting method and the same sphericity as compared with sand prepared by a firing method other than the method.

The main components of the spherical molding sand of the second aspect of the present invention are the same as the spherical molding sand of the first aspect, and particularly Al ₂ O ₃ and SiO ₂ are the main components from the viewpoint of fire resistance and thermal expansion. The Al ₂ O ₃ / SiO ₂ weight ratio is preferably 1-15.

  On the other hand, when the sphericity of the spherical casting sand of the present invention is 0.98 or more, the spherical casting sand is preferably contained in a mixture with a known casting sand having low fluidity such as silica sand in an amount of 50% by volume or more. In this case, the foundry sand made of the mixture can sufficiently exhibit the desired effect of the present invention. That is, if the spherical foundry sand of the present invention is gradually added to the known foundry sand as described above, the desired effect of the present invention will be exhibited depending on the amount added, but the cast comprising the above mixture. The effect becomes remarkable when 50% by volume or more of the spherical cast sand of the present invention having the predetermined sphericity is contained in the sand. In addition, as content of the spherical foundry sand of this invention whose sphericity is 0.98 or more in the foundry sand which consists of the said mixture, More preferably, it is 60 volume% or more, More preferably, it is 80 volume% or more. Accordingly, as the spherical casting sand of the present invention, one having a sphericity of 0.98 or more is particularly suitable because of its excellent utility. Further, since the foundry sand containing 50% by volume or more of the spherical foundry sand can exhibit the same effect as the spherical foundry sand of the present invention, such foundry sand is also included in the present invention.

  As described above, the spherical foundry sand according to the first aspect of the present invention is manufactured by the flame melting method. On the other hand, the spherical foundry sand according to the second aspect of the present invention can be produced by a known method such as a method of granulating and sintering, an electromelting atomizing method, etc. It is preferable to manufacture by the flame melting method similarly to the spherical casting sand of the first aspect. Therefore, in the following, an example of a method for producing the spherical casting sand of the present invention by the flame melting method will be described.

  The spheroidal sand of the present invention is produced, for example, by a flame melting method as disclosed in JP-A-2004-202577.

That is, for example, refractory powder particles having an average particle diameter of 0.05 to 2 mm are used as a starting material, and the powder particles are dispersed in a carrier gas such as oxygen and melted into a sphere to form a sphere. Occurs flame propane, butane, methane, natural liquefied gas, LPG, heavy oil, kerosene, gas oil, and that is generated by burning the fuel oxygen pulverized coal etc., ionizes the N ₂ inert gas or the like used Plasma jet flames can be used.

  The spheroidal foundry sand of the present invention preferably has a fire resistance of SK17 (1480 ° C.) or higher, low thermal expansion, a fire resistance of 1800 ° C. or higher, more preferably SK37 (1825 ° C.) or higher. Although an upper limit is not specifically limited, SK42 (2000 degreeC) or less is preferable. This fire resistance is measured according to the Seegel cone method based on JIS R 2204.

 By using the spherical casting sand of the present invention, a core excellent in hot strength that can withstand the injection pressure of the molten metal in the die casting method can be obtained. The die casting method is a method for manufacturing a casting by pressing a molten or semi-molten alloy into a mold with a force larger than atmospheric pressure. In particular, in the present invention, medium-pressure casting (pressing pressure of 1 to 50 MPa) and high-pressure casting (pressing pressure of 50 MPa or more), which are difficult to use general sand cores, are mentioned.

<Die-cast core>
The core for die casting of the present invention can be produced by the following curing method using the above spherical foundry sand and the binder for binding them. As the binder, inorganic binders such as inorganic salts such as clay, water glass, silica sol, sulfate, phosphate, nitrate, or furan resin, phenol resin, furan phenol resin, urethane resin, unsaturated polyester resin, alkyd resin, etc. The organic binder is preferably used. As the curing method, a conventionally known curing method such as a self-curing method, a thermal curing method, a gas curing method or the like is used. As a particularly preferable method for producing a core, a shell mold method in a thermosetting method is preferable, and a resin-coated sand obtained by coating the above spherical cast sand with a phenolic resin such as a novolak resin or a resole resin is used in a heated mold. This can be done by filling and curing. The content of these binders is preferably selected in the range of 0.2 to 10% by weight, more preferably 0.5 to 5% by weight with respect to the foundry sand. It is also possible to use regenerated spheroidal foundry sand as spheroidal foundry sand.

  Although the core for die casting of the present invention can be used as it is, a surface coating agent generally known on the surface, that is, a refractory such as zircon flour, synthetic mica, colloidal silica, and a binder such as molasses and bentonite. After forming a coating by applying and drying a surface coating agent obtained by mixing the components in water, lower alcohol or the like, it is also possible to form a die-casting core. Regarding the core coating method, a first coating layer made of olivine powder, scaly graphite powder, and a binder is formed on the surface of the sand core, and a second coating layer made of barculite powder and a binder is formed thereon. After impregnating a resin for reinforcing the core (Japanese Patent Laid-Open No. 280944), a prevention coating mold made of zircon fine powder is applied, and a mold release mold containing mica is applied An example (Japanese Patent Laid-Open No. 8-132178) is known.

  In the core of the present invention, it is preferable to use a sand casting casting composition containing a refractory aggregate having a sphericity of 0.88 to 1.00, a binder, and a solvent. In other words, the core of the present invention is preferably formed with a coating mold using such a sand casting casting composition. Specifically, a spherical aggregate having a sphericity of 0.88 to 1.00 to obtain silica-alumina, silica, mullite, obsidian and the like in a flame melting method, a binder such as saccharide, and a solvent such as water and methanol By applying the coating composition for sand mold casting containing the composition to the core of the present invention, the spherical aggregate of the coating mold is densely filled between the mold sand grains, so that a high aim prevention effect can be obtained. Further, from the viewpoint of preventing cracks due to coating film deformation during heating, the coating type spherical aggregate is preferably a low thermal expansion material, and for example, a material such as fused silica, silica alumina, mullite is preferable. Refer to JP-A-2005-224815 for such a mold casting composition for sand casting.

<Casting manufacturing method>
The manufacturing method of the casting of the present invention can be performed by a die casting method using the core of the present invention. Specifically, a die used in die casting is composed of at least two parts so that a cast casting can be taken out. After the core of the present invention is set in the die, it is melted or semi-molten. It can be carried out by press-fitting a metal at about 1 to 100 MPa, opening the mold after solidifying the metal, and taking out the casting. The die casting method can produce a large amount of castings by repeating the above cycle. Suitable casting metals in the die casting method include aluminum alloys, zinc alloys, magnesium alloys, copper alloys, and iron. The core of the present invention has excellent hot strength compared to the conventional core, so that the core can be made thinner and thinner, and is particularly suitable for the production of precision automotive castings. It is.

<Manufacture of foundry sand>
In the casting sands of Table 1, the inventive products 1 to 3 and the calcination method mullite sands 1 to 3 are respectively obtained by the following methods.

(1) Invention products 1-3
96% by weight of Al ₂ O ₃ and SiO ₂ in total, Al ₂ O ₃ / SiO ₂ weight ratio is 2.7, moisture content is 0% by weight, average particle size is 0.21 mm, major axis diameter / A flame in which a mullite powder having a minor axis diameter ratio of 1.5 is used as a starting material, oxygen is used as a carrier gas, and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1 (volume ratio) Into a spherical casting sand (invention product 1 in Table 1). Only the fine particles of the resulting spherical casting sand were collected and designated as products 2 and 3 of the present invention.

(2) calcination method mullite sand 1-3
Powder particles in which aluminum hydroxide and kaolin are mixed so that the weight ratio of Al ₂ O ₃ / SiO ₂ is 2.7 and are made spherical using a spray dryer (96% by weight in total amount of Al ₂ O ₃ and SiO ₂₎ Containing) was fired in an electric furnace at 1500 ° C. for 1 hour to obtain spherical cast sand (calcined mullite sand 1 in Table 1). Only the fine particles of the obtained spherical cast sand were collected and used as the calcination method mullite sand 2 and sand 3.

Examples 1-4 and Comparative Examples 1-3
(1) Production of RCS The foundry sand obtained above was used as the foundry sand. Their chemical composition and the like are shown in Table 1. In Table 1, calcined mullite sand corresponds to conventional spherical casting sand. The water absorption is measured according to the method for measuring the water absorption of JIS A1109 fine aggregate.

  RCS was manufactured using the foundry sand of Table 1. Specifically, after casting sand was heated at 150 ° C., 1 part by weight of phenol resin was added to 100 parts by weight of foundry sand and kneaded. Next, the temperature is lowered to 105 ° C., and at this temperature, 0.15 parts by weight of a hexamethylenetetramine aqueous solution (curing agent) (concentration of 18% by weight) in terms of solid content is added to 100 parts by weight of the resin and kneaded. Kneading while blowing cold air. Further, RCS was obtained by adding 0.05 parts by weight of calcium stearate (lubricant) to 100 parts by weight of foundry sand and kneading to improve fluidity.

  Example 4 was the same as Example 1 except that the RCS of Example 1 was molded by the shell method to obtain a mold, and then subjected to roasting treatment at 1000 ° C. for 30 minutes as roasted recycled sand. What was made into RCS by the method of was used.

(2) Evaluation 1. Hot strength measurement Using the RCS produced above, a test piece having a diameter of 11 mm and a height of 21 mm was molded by firing at 250 ° C. for 90 seconds and used for measurement. The measurement was performed using a high-temperature compressive strength tester (PHT type) manufactured by George Fisher in a nitrogen atmosphere. The results are shown in Table 2.

2. Thermal expansion coefficient test Using the RCS produced above, a test piece having a diameter of 30 mm and a height of 50 mm was molded by firing at 250 ° C. for 90 seconds and used for measurement. The measurement was performed by placing the test piece in a 1000 ° C. furnace and measuring the dimensional change until 600 seconds later, and using the maximum value as a coefficient of thermal expansion compared to the initial dimension (25 ° C.). The results are shown in Table 2.

  As shown in Table 2, Examples 1 to 4 using the foundry sands 1 to 3 of the present invention can not only obtain high room temperature mold strength with a small amount of binder, but also are exposed to a high-pressure molten metal flow. Even at a temperature, a high mold strength can be maintained and the molten metal pressure can be withstood. A smaller sand particle size can prevent the high-pressure molten metal from being inserted between sand particles, but conventionally known sand has a lower mold strength and hot strength when the particle size is smaller. With the foundry sand of the present invention, higher mold strength and hot strength can be obtained even when the average particle size is small. This effect of the present invention is a unique effect as compared with conventionally known sand, and from this, not only can the core be prevented from breaking or deforming at a high melt pressure in the die casting method, Can be prevented.

Claims (6)

A core for die casting obtained by using spherical casting sand produced by a flame melting method. A core for die casting obtained by using spherical casting sand having a water absorption of 0.5% by weight or less. The spherical molding sand, and also contains Al ₂ O ₃ and SiO ₂ as the main component, Al ₂ O ₃ / SiO ₂ weight ratio of 1 to 15 claim 1 or 2 for die-casting core according. The core for die casting according to any one of claims 1 to 3, wherein an average particle diameter of the spherical casting sand is 0.02 to 1 mm. The core for die casting according to any one of claims 1 to 4, wherein the spherical casting sand has an AFS particle size index of AFS 60 to 200. It is a manufacturing method of the casting performed by the die-casting method, Comprising: The manufacturing method of the casting using the core for die-casting in any one of Claims 1-5.