JP3541168B2 - Core with coating layer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a core with a coating layer which is suitably used in high-pressure casting such as die casting.
[0002]
[Prior art]
In high-pressure casting such as die casting, it is known to use a core with a coating layer provided with a coating layer on the surface of a core substrate made of sand in order to prevent the molten metal from being aimed at the core. .
[0003]
[Problems to be solved by the invention]
Conventionally, sand having an average particle diameter of about 250 to 270 μm is generally used as sand for a core substrate. Then, in forming the coating layer formed on the surface of the core substrate, in order to prevent filling of the coating particles from the gap between the sand particles constituting the core substrate to the deep portion of the core substrate, First, a coating lower layer made of relatively coarse particles is formed, and then a coating upper layer made of fine particles is formed on the surface of the coating lower layer.
However, such a mold layer composed of a plurality of layers requires a large number of steps for manufacturing, and since the mold layer is thick, the amount of deformation due to pressure during casting is large, and the size of the casting is large. There was a problem that the accuracy was reduced.
[0004]
Further, as shown in FIG. 5, Japanese Patent Application Laid-Open No. 7-100585 includes refractory particles 911 having a particle size of 1 to 10 μm and refractory fine particles 912 having a particle size of 0.1 to 1 μm. A collapsible core 9 having a coating layer (surface layer) 91 that can be formed by a coating / drying process is disclosed.
However, according to the collapsible core 9, even if it is possible to prevent the intrusion into the core substrate 92 of the molten metal 3, it is not possible to prevent the intrusion into the coating layer 91, and a fine aim 3a is generated. Further, when the refractory particles 911 and the refractory fine particles 912 are not uniformly mixed, as shown in FIG. 6, the molten metal 3 enters the core base 92 from that location to generate a large aim 3a. There is also a risk.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a coating that can be formed by a single coating and drying process and that has a coating mold layer that prevents the intrusion of molten metal even when used in high-pressure casting, and that provides a cast with good dimensional accuracy. An object of the present invention is to provide a core with a mold layer.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the core with a coating layer of the present invention includes a core substrate made of sand having an average particle size of 20 to 300 μm, and an average particle size of 0.1 to 0.1 formed on the surface of the core substrate. A mold layer made of refractory particles of 0.5 μm, wherein the mold layer penetrates from the surface of the core substrate to a depth of 50 to 200 μm, and penetrates into the core of the mold layer. The thickness excluding the portion is 50 to 300 μm, and the thickness is larger than the penetration depth from the surface of the core substrate .
[0007]
The coating layer is formed by applying a coating slurry on the surface of the core substrate, and the coating slurry contains 2 to 5 parts by weight of water with respect to 5 to 8 parts by weight of the refractory particles, Is preferably 3700 to 4000 cps.
[0008]
Hereinafter, the present invention will be described in detail.
The "core substrate" used in the present invention comprises sand and usually an organic binder. As the organic binder, a conventionally known resin such as a vinyl resin, a cellulose resin, and a phenol resin can be used. The average particle diameter of the sand constituting the core substrate is 20 to 300 μm, preferably 100 to 200 μm, and more preferably 125 to 175 μm. If the average particle diameter of the sand exceeds 300 μm, the coating slurry will penetrate deep into the core substrate, making it difficult to control the thickness and permeability of the coating layer. On the other hand, when the average particle diameter of the sand is less than 20 μm, the core disintegration is reduced.
[0009]
The "refractory particles" constituting the coating layer are preferably made of a material having a large specific heat, such as alumina or zircon, and 90% or more (more preferably 95% or more) of the entire refractory particles used are alumina particles. Preferably, there is. The average particle size of the refractory particles is 0.1 to 0.5 μm, preferably 0.2 to 0.4 μm. If the average particle diameter of the refractory particles exceeds 0.5 μm, it is not possible to sufficiently prevent the molten metal from penetrating into the coating layer. On the other hand, if the average particle size of the refractory particles is less than 0.1 μm, the coating slurry will penetrate deep into the core substrate, making it difficult to control the thickness and permeability of the coating layer. Also, it is difficult to obtain refractory particles having an average particle diameter of less than 0.1 μm.
[0010]
As shown in FIG. 1, this "coating layer" has penetrated to a depth of 50 to 200 [ mu] m (more preferably 50 to 100 [ mu] m) from the surface of the core substrate. If the penetration depth is too small, the mold layer falls into the core substrate from between the sand particles constituting the core substrate due to the pressure during casting, and the mold layer may be damaged. On the other hand, if the penetration depth is too large, many refractory particles are required to form the coating layer, and the core disintegration is reduced.
[0011]
The thickness of the entire coating layer (including the portion penetrating into the core) is preferably from 60 to 500 μm, more preferably from 75 to 300 μm, and still more preferably from 100 to 250 μm. If the coating layer is too thick, the deformation of the core with the coating layer due to the pressure of the molten metal increases, and the dimensional accuracy of the casting decreases. Further, when the coating slurry applied to the surface of the core substrate is dried by heating, cracks are easily generated in the coating layer, and the molten metal may penetrate into the core substrate from the cracks. On the other hand, if the mold wash layer is too thin, the strength of the mold wash layer may be insufficient to prevent intrusion of the molten metal.
The thickness excluding the penetration portion of the core of the mold wash layer, 50 to 300 [mu] m der is, more preferably 50 to 250 [mu] m, more preferably from 75～200Myuemu. Further, the thickness is larger than the penetration depth from the surface of the core substrate.
The thickness of the entire coating layer and the thickness of the coating layer permeating the core substrate can be measured, for example, by observing the core cross section after the formation of the coating layer.
[0012]
The method of forming the coating layer on the surface of the core substrate is not particularly limited, but it is usually preferable to apply a coating slurry to the surface of the core substrate. The coating slurry is usually prepared by dispersing and dissolving the refractory particles and an organic binder in a solvent (preferably water). As the organic binder, a conventionally known resin such as a vinyl resin, a cellulose resin, and a phenol resin can be used. The method of applying the coating slurry is not particularly limited, and for example, a dipping method in which the core substrate is immersed in the coating slurry can be suitably used. In order to form the above-mentioned coating layer having a preferable thickness by the dipping method, the coating slurry is used in an amount of 2 to 5 parts by weight of water (more preferably 6 to 7 parts by weight) with respect to 5 to 8 parts by weight of the refractory particles. (2.5 to 4 parts by weight of water with respect to 0.5 part by weight), and the viscosity of the coating slurry at room temperature is preferably 3700 to 4000 cps (3.7 to 4.0 Pa · s). . The viscosity of the coating slurry is more preferably 3750 to 3850 cps (3.75 to 3.85 Pa · s), and the most preferred viscosity is 3800 cps (3.8 Pa · s).
[0013]
The core with a coating layer of the present invention is suitable as a core used for high-pressure casting at a casting pressure of 20 MPa or more (more preferably, 50 MPa or more, and the upper limit is not particularly limited, but is usually 200 MPa or less).
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to experimental examples.
(Experimental example 1)
The core 1 with a coating layer shown in FIG. 1 was produced, and its performance was evaluated.
(1) Production of Core Substrate As the sand particles 121 constituting the core substrate 12, spherical mullite particles having an average particle diameter of 150 μm were used. This sand, 1.5% by weight of phenol resin (organic binder) 122 with respect to the sand, 15% by weight of hexamethylenetetramine (added as a 30% by weight aqueous solution) with respect to the phenol resin, and The mixture was mixed with 0.1% by weight of calcium stearate to prepare sand for shell molding, and this was heated and baked at 250 ° C. for 2 minutes to produce a core substrate 12 having a thickness of 10 mm.
[0015]
(2) Preparation of Coating Slurry and Formation of Coating Layer Alumina particles having an average particle size of 0.5 μm were used as the refractory particles 111 constituting the coating layer 11. 10 parts by weight of the alumina particles, 0.03 parts by weight of cellulose as binder (0.3% by weight based on the alumina particles), and 4 parts by weight of water were mixed to obtain an alumina particle concentration of 71% by weight and a viscosity of 3700 at room temperature. A coating slurry of ~ 4000 cps was prepared.
The core substrate 12 prepared in the above step (1) is immersed in the coating slurry for 2 seconds, and then dried at 130 ° C. for 20 minutes to form a 325 μm-thick coating layer 11. An attached core 1 was obtained. In addition, 175 μm of the thickness of the coating layer 11 has penetrated into the core substrate 12.
[0016]
(3) Die casting test Using the obtained core 1 with a coating layer, a die casting test was performed under the following die casting conditions.
[Die casting conditions]
Applicable equipment: 800T horizontal die casting machine Melt composition: ADC10
Melt temperature: 650 ° C
Casting pressure: 60MPa
Injection speed: 0.5 m / sec Mold temperature: 150 ° C
After cooling and solidifying the molten metal in the device and removing the mold, vibration is applied to the casting and the core with a coating layer using an air hammer, and the vibration causes the core with the coating layer to collapse and cast. I got something. No core with a coating layer remained in the obtained casting.
When the surface of the obtained casting was observed with a 400-fold optical microscope, no aiming layer was observed as shown in FIG. That is, as shown in FIG. 1, the molten metal 3 was prevented from entering the coating layer 11 during casting.
[0017]
(Experimental example 2)
A coating slurry having a viscosity of 3700 to 4000 cps was prepared in the same composition as in Experimental Example 1 except that various alumina particles having different average particle diameters were used as the refractory particles. Using these coating slurry, a 325 μm-thick coating layer was formed on the surface of the core substrate prepared in the step (1) of Experimental Example 1 by the same method as in Experimental Example 1. An attached core was produced.
With respect to these cores with a coating layer, two kinds of casting pressures of 60 MPa and 20 MPa were used, and the other points were cast under the same die casting conditions as in Experimental Example 1. The surface of the obtained casting was observed under an optical microscope of 400 times to check for the presence of a target layer, and when the target layer was present, its thickness was measured. The thickness of the aiming layer corresponds to the permeation distance of the molten metal from the surface of the coating layer to the inside of the core with coating. FIG. 3 shows the obtained results as a relationship between the average particle diameter of the alumina particles constituting the coating layer and the permeation distance of the molten metal. When alumina particles having an average particle diameter of 2 μm or less at a casting pressure of 20 MPa and alumina particles having an average particle diameter of 0.5 μm or less at a casting pressure of 60 MPa were used, the permeation of the molten metal into the coating layer could be prevented.
[0018]
(Experimental example 3)
Relationship between Thickness of Coating Layer and Deformation Rate of Mold A plurality of types of coating slurries having different viscosities were prepared by increasing or decreasing the amount of water added from the composition of the coating slurry of Experimental Example 1. These coating slurries were applied to the surface of the core substrate having a thickness of 10 mm used in Experimental Example 1 in the same manner as in Experimental Example 1. Thus, a core with a coating layer having a coating layer of various thicknesses was obtained according to the viscosity of the coating slurry.
The core with the coating layer was subjected to a die casting test under the same conditions as in Experimental Example 1 to measure the linear shrinkage, and the deformation rate of the core with the coating layer was obtained. The results are shown in FIG. 4 as a relationship between the thickness of the mold layer and the deformation rate of the core with the mold layer. When the thickness of the coating layer is 300 μm or less, the deformation rate of the core with the coating layer is 6% or less, and it can be seen that a casting with good dimensional accuracy can be obtained. In addition, about 6% of this deformation rate is a deformation caused by shrinkage of the core substrate. That is, when the thickness of the mold wash layer is 300 μm or less, the shrinkage due to the mold wash layer becomes negligibly small.
[0019]
In the above embodiment, the core with a coating layer of the present invention was used for high-pressure casting, but the core with a coating layer of the present invention may be used for other casting methods, for example, low-pressure casting, gravity casting, and the like. Can be.
[0020]
【The invention's effect】
Since the core with a coating layer of the present invention has a coating layer made of refractory particles having a smaller average particle diameter than the conventional one, when used in high pressure casting or the like, not only the core substrate but also the coating mold is used. Intrusion of the molten metal into the layer can also be prevented. Therefore, according to the core with a coating layer of the present invention, it is possible to obtain a casting having a good surface state without any aim. This coating layer can be formed by a single coating and drying process using a coating slurry, so that productivity is good, and a conventional coating layer composed of a coating lower layer composed of coarse particles and a coating upper layer composed of fine particles. Can reduce the shrinkage deformation of the mold layer during casting. Thereby, according to the core with a coating layer of the present invention, a cast with good dimensional accuracy can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a core with a coating layer manufactured in Experimental Example 1.
FIG. 2 is a diagram obtained by observing the surface of a casting obtained in Experimental Example 1 with an optical microscope.
FIG. 3 is a characteristic diagram showing a relationship between an average particle diameter of alumina particles forming a coating layer and a molten metal permeation distance in Experimental Example 2.
FIG. 4 is a characteristic diagram showing the relationship between the thickness of a mold wash layer and the deformation rate of a core with a mold wash layer during casting in Experimental Example 3.
FIG. 5 is a schematic sectional view showing a conventional core with a coating layer.
FIG. 6 is a schematic sectional view showing a conventional core with a coating layer.
[Explanation of symbols]
Reference Signs List 1 core with coating layer 11 coating layer 111 refractory particles 12 core substrate 121 sand particles (sand)
3 Melt 3a Aiming 9 Collapsible core 91 Coating layer 92 Core substrate

Claims (2)

A core substrate made of sand having an average particle size of 20 to 300 μm, and a coating layer formed of refractory particles having an average particle size of 0.1 to 0.5 μm formed on the surface of the core substrate,
The coating layer has penetrated from the surface of the core substrate to a depth of 50 to 200 μm, and the thickness of the coating layer excluding the portion penetrating into the core is 50 to 300 μm. A core having a coating layer, wherein the core has a depth greater than a penetration depth from the surface of the core substrate . The coating layer is formed by applying a coating slurry on the surface of the core substrate, and the coating slurry contains 2 to 5 parts by weight of water with respect to 5 to 8 parts by weight of the refractory particles, 2. The core with a coating layer according to claim 1 , wherein the viscosity is 3700 to 4000 cps .

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