JP2015120177A - Manufacturing method of sand core used for low speed low pressure die-casting by one or more injections, sand core used for low speed low pressure die-casting by one or more injections, and die-casting method using the sand core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sand core for a low speed low pressure die casting and a die casting method, which can easily produce an undercut and/or a hollow aluminum die-casting product.SOLUTION: A manufacturing method of a sand core used for a low speed low pressure die-casting by one or more injections, comprises: a step to blend one, two or more types of particles selected from a group consisting of zircon sands, chromite sands and alumina sands, with inorganic binder (1 to 3 wt.%); and a step to mold the sand core.

Description

The present invention relates to a method for producing a sand core used in low-speed low-pressure die casting by one or more injections, a sand core used in low-speed low-pressure die casting by one or two injections, and a die casting method using the sand core. is there.

Die-casting using a collapsible sand core as a method of casting by casting high-speed and high-pressure die castings such as closed deck type automobile engine blocks and other undercut parts such as aluminum alloys and magnesium alloys. However, it is performed conventionally.

As a method for forming a collapsible sand core, it is conceivable to form an aggregate for sand core molding into a desired shape using an organic binder and coat the surface of the molded sand core with a coating solution. No satisfactory product has been obtained. As a method for forming a sand core by solidifying an aggregate for sand core modeling, a hardx method, a warm box method, a shell mold method, and a cold box method are known. As the hardx method, the technique described in Patent Document 1 is known. According to this method, the sand core is composed of a sand core molding aggregate, a furan resin, and an organic peroxide agent combination. It consists of sand and hardens with sulfurous acid gas.

In this hardx method, a sand core molding aggregate is blended with a furan-based resin and an organic peroxide that is a curing catalyst for the furan resin, and the kneaded blended sand is filled into a mold having a desired shape to form sand. In order to mold the core, sulfurous acid gas is used to harden the furan resin to mold the sand core, so sulfurous acid gas is used for sand core molding. For this reason, there is a problem that the working environment is bad.

In order to solve the problem of Patent Document 1, in Patent Document 2, a shell mold method using a phenol resin as a binder is used instead of the hardx method in which a furan resin is cured with an organic peroxide and sulfurous acid gas. Has proposed. That is, a double-coated salt M ₁ Al (SO ₄₎ composed of a resin-coated sand (RCS) coated with a phenol resin on the surface of an aggregate for sand core modeling and composed of aluminum sulfate and a sulfate of a monovalent ion such as an alkali metal or ammonium. ) ₂ [M ₁ = Na, K, Rb, Cs, NH ₄ or more] and / or double salt M ₂ SO ₄ .Al ₂ (SO ₄ consisting of aluminum sulfate and sulfate of divalent metal ion) ₃ ) [Step of adding at least one kind of M ₂ = Cu, Fe, Mg, Zn] in an amount of 0.1 to 5 wt% and coating the double salt of the above-described aluminum sulfate on the RCS; A step of forming a sand core with a salt-coated RCS, and a slurry-like coating comprising a neutral water dispersion mainly composed of a fine powder refractory on the surface of the formed sand core A step of coating a grayed solution proposes a method for producing a disintegrating sand core comprising a step of drying the sand core obtained by this coating.

Non-Patent Document 1 discloses a sand core having a two-layer structure that achieves both high strength and easy collapse removal after casting as a core that can be used for die casting that is solidified at high pressure after filling with molten metal at high speed. (Outer layer of high-strength resin-coated sand (RCS) using artificial sand (1100 N / cm ² ), low-strength RCS inner layer using recycled sand (300 N / cm ² ) , Surface coating (inside (first coating) zirconium silicate, outside (second coating) scaly natural mica), core holding method (pin holding and protrusion holding), aluminum product thickness stabilization (high molten metal) The pressure shrinks the core, the lower limit of the biscuit thickness (40 mm), the control of the lower limit thickness and the dimensional change) are introduced. As an example of ordinary die casting, casting conditions (injection speed 2.4 m) / S, casting pressure 74 MPa).

Conventional aluminum die casting is high-speed and high-pressure filling (generally, injection speed of 1 to 3 m / s, pressure of 30 to 100 MPa), and usually a metal drawing insert is used to cast an undercut shape. Is called. Some use salt cores or special coated cores, but they are expensive and not yet common. Patent Document 3 proposes a semi-molten casting method. The semi-molten method is a method in which a low-temperature semi-solid state metal is injected at low speed and low pressure, and is not a thick coating on the salt core or shell core used in general die casting, but an ordinary sand core. States that it is possible. Patent Document 2 discloses a mold made of a metal material having a product shape formed therein and a sand core obtained by molding sand into a predetermined shape and disposed in the mold. A casting apparatus having an injection means capable of injecting a semi-molten metal into the mold at a low speed and a low pressure has been proposed. Injection into the mold is possible at a speed of (m / s) and a pressure of 15 to 30 (MPa). Further, according to the embodiment of Patent Document 2, the sand core is formed into a predetermined shape by mixing a heat-resistant sand with a binder such as a resin, and the sand of this core has an AFS particle size index. In order to improve the casting surface roughness, the ceramic powder may be applied (coating) to the surface of the sand core.

Patent Document 4 proposes a spherical casting sand produced by a flame melting method, a baked mullite sand mainly composed of alumina and silica, and having an average particle diameter of 0.02 to 1 mm. Patent Document 3 discloses an inorganic binder such as clay, water glass, silica sol, sulfate, phosphate, and nitrate as a binder, or furan resin, phenol resin, furan phenol resin, urethane resin, unsaturated resin. Organic binders such as polyester resins and alkyd resins have been proposed, and a shell molding method in a thermosetting method is preferred as a particularly preferable method for producing a core. Further, a surface coating agent generally known on the surface, that is, a surface coating agent obtained by mixing refractory materials such as zircon flour, synthetic mica, colloidal silica, and binder components such as molasses and bentonite in water, lower alcohol, etc. After coating and drying to form a coating, it is also possible to form a die-casting core. In addition, the binary mixed salt of potassium sulfate blended with alumina and the die-cast product cools and solidifies (at most 2-3 seconds) before the resin core melts, and can be used at a resin melting point of about 150 ° It is also known conventionally.

In the conventional die casting technique, the injection speed is about 3 m / s and the casting pressure is 50 MPa to 100 MPa. The present inventor disclosed the injection speed in Patent Document 5, Patent Document 6, Patent Document 7, and Patent Document 8. Has proposed a die casting apparatus and a die casting method in which the casting pressure is 5 MPa to 10 MPa. That is, the present inventor provides high-quality die casting by a die casting apparatus and a die casting method in which the injection speed and casting pressure are about 1/10 of the conventional one. That is, in Patent Documents 5 to 8, while preventing solidification of the molten aluminum in the injection sleeve by the heat insulating material, each of the injection sleeves is provided at an optimum position with a single or a plurality of injection sleeves, and a high vacuum is ensured. The flow / pressurization distance per injection sleeve can be reduced, and the injection speed and molten metal pressure can be greatly reduced.

Conventionally, the reason why it was difficult to use a sand core in die casting is that (1) breakage of the sand core during high-speed and high-pressure injection, (2) penetration of molten aluminum into the sand core, (3) These include post-treatment properties of core sand, deterioration of disintegration, and (5) shrinkage defects due to delay in solidification of the sand-type contact portion and coarsening of the structure. Therefore, the above-mentioned Patent Documents 1 to 3 and Non-Patent Document 1 and the binary mixed salt of potassium sulfate mixed with alumina and the resin core are cooled and solidified before the resin core is melted (at most 2-3 seconds). In other words, it is proposed that the resin can be used at a melting point of about 150 °.

For example, Patent Document 2 shows an example in which die-casting with a sand core becomes possible by applying a strong surface coating to a two-layer sand mold core having a special surface-high speed and internal-low speed. However, in reality, the production of special sand cores and the discharge of cores after casting are expensive, and the application to special parts remains.

On the other hand, in Patent Document 3, a special low-speed low-pressure casting method called a semi-molten casting method is required for a normal sand core (molded into a predetermined shape by mixing a heat-resistant sand with a resin binder). According to the method, casting is possible by surface coating. However, it is presumed that the core used in gravity casting or air low pressure casting cannot be used as it is. The reason is that the casting pressure in the gravity casting method or the like is up to about 0.5 MPa and the filling speed is about 0.1 m / s, whereas in the general semi-molten casting method, the filling pressure is 15 to 30 MPa. It is estimated that the pressure and speed are much higher than the gravity casting method and the like, and the damage to the sand core due to the flow resistance of the semi-solidified slurry is increased. Therefore, it is estimated that it is necessary to limit the target product and further reinforce the core. In addition, Patent Documents 1 to 4 and Non-Patent Document 1 and a binary mixed salt of potassium sulfate blended with alumina, and the die-cast product to cool and solidify before the resin core melts (at most 2-3 seconds), It is also difficult to combine that the melting point of the resin can be used at about 150 °.

Japanese Patent Publication No. 64-9898 JP-A-6-106294 JP2013-052421A JP 2007-83284 A Japanese Patent No. 4810706 Japanese Patent No. 5327605 JP 2012-148319 A JP2013-132644A

“Development of high-speed and high-pressure die casting technology using double-layer sand cores”, “SOKEIZAI”, Vol. 23, 2012)

Problems to be solved are (1) about twice as high as usual (the anti-deposition force is about 800 N), and within the casting time (about 10 seconds depending on the product size) has heat resistance, That is, sufficient strength can be maintained. (2) The molten aluminum does not easily enter between the sand particles, and the casting surface of the product is good. Avoiding a strong surface coating (however, surface coating is unavoidable at locations where the molten metal collides). (3) If gas is generated during casting and filling, gas bubbles are generated and defects in the product are generated, so that the exhaust gas can be reduced as much as possible and discharged out of the mold. (4) Sand discharge after casting is fast. (5) The core portion is rapidly solidified. This is because if the solidification of the core portion is slow, the directional solidification and the casting cycle are adversely affected, and the generation of the solidified layer is delayed, which adversely affects the casting surface of (2) above. In short, the problem to be solved is to provide a sand core capable of easily obtaining an undercut or hollow aluminum die-cast product in low-temperature and low-pressure die casting, and a die casting method using the sand core. .

The manufacturing method of the sand core used in the low-speed and low-pressure die casting by one or more injections according to the first aspect of the present invention is one or more selected from the group consisting of zircon sand, chromite sand, and alumina sand. It comprises a step of kneading and preparing particles and an inorganic binder (1 to 3% by weight) and a molding step for producing a sand core.

The inorganic binder is preferably sodium silicate.

Moreover, it is preferable that the molded sand core has a partial coating containing zircon flour.

Moreover, in the said molding process, it is preferable to shape | mold with a cooling metal.

The core for thin large die casting according to the second aspect of the present invention comprises one or more particles selected from the group consisting of zircon sand, chromite sand, and alumina sand, and an inorganic binder (1 to 3 weights). %).

The inorganic binder is preferably sodium silicate.

Moreover, it is preferable that the core sand made into the spherical particles has a partial coating containing zircon flour.

A third aspect of the present invention is an aluminum die casting method using the core of claim 1,
The step of inserting the core according to claim 1 together with the heat insulating material between the upper mold and the lower mold, the step of closely attaching the heat insulating material to the inner walls of the plurality of injection sleeves in the lower mold, the heat insulating material A step of pouring the molten metal, a step of closing and clamping the upper mold, a step of injecting the molten metal, a step of solidifying the hot water, a step of raising the upper mold after solidification of the hot water, and the product together with the core It is characterized by comprising a step of extruding from a mold.

According to the sand core used in the low-speed and low-pressure die casting by one or more injections of the present invention, an aluminum die-cast product having an undercut and a hollow portion (H) can be easily obtained in the die casting. In addition, according to the aluminum die casting method using the sand core used in the low-speed low-pressure die casting by one or more injections of the present invention, (a) inserting a plurality of heat insulating materials, (b) pouring a plurality of hot waters, (c) gold It is possible to provide an efficient process in which mold clamping, (d) vacuum, (e) removal, (f) air blow, (g) mold release agent application, and (h) multiple sleeve lubricant application can be performed simultaneously in multiple ways. A high-quality die-cast product can be provided.

It is explanatory drawing which shows an example of schematic shape of the thin large sized die-cast product applied to this invention. It is a schematic explanatory drawing which shows arrangement | positioning of the metal mold | die extraction core to the metal mold | die of the conventional die-casting apparatus. It is a schematic explanatory drawing which shows arrangement | positioning of the sand core to the metal mold | die of the die-casting apparatus which concerns on one Embodiment of this invention. It is a graph which shows the relationship of the molten metal pressure with respect to the time concerning a die-cast injection output. It is explanatory drawing which shows the example of application to the die-casting method of a core in one Embodiment of this invention.

The thin large aluminum die-cast product is, for example, 800 mm × 600 mm × 3 mm thick, and has a shape having a hollow portion on the left side of FIG. Referring to FIGS. 3 and 5, according to the present embodiment, for example, three electric servo plungers (PL) are installed, and a heat insulating material (C) is installed on the sleeve (SL). Injection at 1 m / s molten metal pressure of 5 MPa is performed. In cores (shell mold method, cold box method, etc.) bonded with organic binders, such as those used in gravity casting and low pressure casting (pneumatic push-up method), the moment when the molten aluminum and sand core come into contact with each other. A large amount of reaction gas is generated, causing casting defects. Therefore, an inorganic binder is employed in the core (1) of the present embodiment. As such an inorganic binder, for example, sodium silicate is employed. As a result, gas generation during casting is reduced by orders of magnitude. However, it is preferable to vacuum-suck through the baseboard part (2) because there is some moisture and air expansion. In addition, since the heat absorption is greatly different between the sand core and the mold, the occurrence of shrinkage cavities and the delay of the casting cycle become problems due to the solidification delay of the sand mold contact portion. Therefore, as the material of the sand core, a material having high heat absorption performance, for example, zircon sand, chromite sand, or alumina sand is preferably employed. In addition, when spherical sand is used, the amount of binder added can be greatly reduced. For example, in the conventional sand shape, the addition amount of the inorganic binder was 2.5%, but in the sand shape (spherical shape) of the present embodiment, the addition amount of the inorganic binder may be 1.5%. Disintegration after gas generation and casting is improved.

Therefore, the sand core used in the low-speed low-pressure die casting by one or more injections according to the present embodiment is one or more particles selected from the group consisting of zircon sand, chromite sand, and alumina sand, and inorganic particles. And a binder (1 to 3% by weight). The shape of the particles may be either spherical or non-spherical, but when the spherical shape is adopted, there is an advantage that the amount of the inorganic binder can be reduced (for example, 1 to 2% by weight). Moreover, although the sand core used in the low-speed and low-pressure die casting of the present embodiment has been described as being used in the low-speed and low-pressure die casting by a plurality of injections, it can be applied to the low-speed and low-pressure die casting by one injection. Moreover, in this embodiment, since it has a shape that is round and close to a true sphere, has excellent crush resistance, excellent disintegration properties, high fire resistance, etc., the ESPAR ( (Registered trademark) is preferably employed, but the present invention is not limited to this.

A sand core with high heat absorption alone may not prevent the solidification delay. For this reason, if the cooling metal is integrally formed during core molding (see FIG. 3), solidification is promoted during die casting, and penetration of shrinkage nests and aluminum sand particles can be prevented. In this case, aluminum is preferable as the material of the cooling metal. The reason is that trouble does not occur even if the return material is mixed during post-processing.

As described above, the sand of this embodiment is preferably a sand core material having high heat absorption performance, such as zircon sand, chromite sand, and alumina sand, but is not limited thereto. If the artificial heat-insulating sand, zircon sand, mullite sand or the like having high heat absorption is used, small articles and thin-walled articles can be suitably cast. Also, the coating on the core surface is unnecessary in most cases. However, especially when it is necessary to improve the casting surface, a heat-resistant coating should be applied to the part where the molten metal collides with the core surface. Is also possible.

In FIG. 5, the mold (M) is opened and closed by an electric servo located on the side, and the mold (M) is clamped with a half nut type and then clamped with a half nut (HN) by hydraulic drive. It is a method to do. It is sufficient that the hydraulic clamping is about 1/10 of the conventional capacity. In the present invention, in this embodiment, since the injection pressure is very low as described above, there is an advantage that the clamping force can be greatly reduced, the equipment can be simplified, and a larger die-cast part can be cast. .

The die casting method of this embodiment will be described.
Step (I): Insert the core into the upper mold (M1), and simultaneously insert the heat insulating material (C) into the lower mold (M2). The heat insulating material (C) is charged into the three injection sleeves (SL), and at the same time, the core (1) is charged into the cavity (CV) in the upper mold (M1). The number of injection sleeves (SL) is not limited to three, and may be two, or four or five or more. The cylindrical heat insulating material holding cylinder stops vacuum suction and conversely pressurizes air. By the air pressurization, the heat insulating material is brought into close contact with the inner wall of the injection sleeve (SL).

Step (II): When the charging of the heat insulating material (C) into the injection sleeve (SL) is completed, the heat insulating material (C) in close contact with the inner wall of the injection sleeve (SL) charged with the heat insulating material (C) ), And a clean molten metal with almost no temperature drop is held in the injection sleeve (SL).

Step (III): The upper mold (M1) is closed and the mold is clamped. In order to vacuum and hold the inside of the mold (M), in this embodiment, as shown in FIGS. 1 and 2, a vacuum chamber (on the back side of the upper mold into which the extrusion plate (P) is inserted is provided. VC) and vacuum suction from the gap between the chill vent (V) and the push pin (PP) is performed. In the method of the present embodiment, since the solidification does not proceed due to the thin film heat insulating material (C) in the injection sleeve (SL), the vacuum suction time can be made sufficiently long (for example, about 10 seconds), and a small capacity There is an advantage that a high degree of vacuum can be obtained only by vacuum suction from the gap between the chill vent (V) and the push pin (PP). That is, by the vacuum structure (VC) that houses the extrusion plate (P), the suction structure from the small clearance of the small volume chill vent (V) and the extrusion pin (PP), and other sealable structures Can easily achieve and maintain a high degree of vacuum.

Step (IV): After confirming the degree of vacuum in the mold, injection from the three injection sleeves (SL) is performed. For these, a speed (for example, 0.1 m / s) and pressure (molten metal pressure of 5 to 10 MPa) of about 1/10 that of conventional die casting are sufficient. That is, it is because a clean molten metal without a temperature drop is possible by short-distance flow and pressurization from each injection sleeve (SL).

Process (V): solidify hot water

Step (VI): After completion of solidification, the upper mold (M1) is raised.

Step (VII): The product and the core (1) are extruded from the mold (M1).

In this embodiment, when the electric servo is used to inject at a constant speed (for example, 0.2 m / s), as shown in FIG. 4, a so-called surge pressure is generated upon completion of filling, for example, far exceeding 10 MPa. Such a pressure will be generated. Therefore, the electric servo is controlled so that the surge pressure is generated and the molten metal pressure is controlled, for example, to 10 MPa or less so that an excessive force is not applied to the sand core and damage deformation or “aim” does not occur. It is necessary to perform control of the above. For example, it is necessary to perform control so as to decelerate immediately before completion of filling and prevent surge pressure. This control of the present embodiment takes advantage of the good controllability of the electric servo, and such control is difficult in conventional hydraulic control of die casting.

As shown in FIG. 2, when die-casting is performed with a conventional plunger-type die-casting device, high speed and high pressure (for example, plunger speed 3 to 5 m / s, molten metal pressure 50 to 100 MPa), vacuum valve, etc. It is necessary to add the mechanism. Therefore, a large die casting machine (for example, a large machine with a clamping force of 4000 tons, a large mold) is required. Furthermore, when casting at such a high speed and high pressure, the sand core breaks or deforms, or the molten aluminum enters the inside of the sand core, resulting in a so-called “aim” defect, which is not possible to manufacture. Is possible. Therefore, developments such as strengthening special metal cores, molten salt cores and sand cores and applying special coatings on the surface have been carried out, but this is not a situation where mass production is possible from the viewpoint of productivity. Therefore, although the die pulling insert shown in FIG. 2 is usually used, since a draft is required, a predetermined shape cannot be obtained, and the shape becomes extra and cannot be reduced in weight. In addition, it becomes difficult to vacuum seal the die insert. According to the die casting method using the sand core used in the low-speed low-pressure die casting by one or more injections according to the present invention, (a) inserting a plurality of heat insulating materials, (b) pouring a plurality of hot waters, (c) clamping a mold , (D) vacuum, (e) removal, (f) air blow, (g) mold release agent application, (h) a plurality of sleeve lubricant application can be provided at the same time in an efficient process, In addition, high quality die casting products can be provided. Moreover, according to the die-casting apparatus of the present invention, it is possible to provide a very simple configuration and thus to provide a high-quality die-cast product.

DESCRIPTION OF SYMBOLS 1 Core 2 Cooling metal 3 Skirting board C Thermal insulation material CL Hydraulic clamp M type M1 Upper type M2 Lower type P Extrusion board PL Plunger PP Extrusion pin V Chill vent VC Vacuum cavity

Claims (8)

A step of preparing kneading one or more kinds of particles selected from the group consisting of zircon sand, chromite sand and alumina sand and an inorganic binder (1 to 3% by weight), and molding for producing a sand mold core A process for producing a sand core used in low-speed low-pressure die casting by one or more injections, characterized by comprising a step. The method for producing a sand core used in low-speed low-pressure die casting by one or more injections, wherein the inorganic binder is sodium silicate. The method for producing a sand core for use in low-speed low-pressure die casting by one or more injections according to claim 1 or 2, wherein the molded sand core has a partial coating containing zircon flour. . 4. The method for producing a sand core for use in low-speed and low-pressure die casting by one or more injections according to claim 1, wherein the molding is performed together with a cooling metal. In the same manner as in claims 1 to 4, it comprises one or more particles selected from the group consisting of modified zircon sand, chromite sand, and alumina sand, and an inorganic binder (1 to 3% by weight). The core for thin large die castings. The core for thin-walled large die casting according to claim 5, wherein the inorganic binder is sodium silicate. The core for thin-walled large die-casting according to claim 5 or 6, wherein the core sand made into spherical particles has a partial coating containing zircon flour. An aluminum die casting method using the core of claim 1,
The step of inserting the core according to claim 1 together with the heat insulating material between the upper mold and the lower mold, the step of closely attaching the heat insulating material to the inner walls of the plurality of injection sleeves in the lower mold, the heat insulating material A step of pouring the molten metal, a step of closing and clamping the upper mold, a step of injecting the molten metal, a step of solidifying the hot water, a step of raising the upper mold after solidification of the hot water, and the product together with the core An aluminum die casting method comprising a step of extruding from a mold.