JPS6234451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mold coating agent applied to the surface of a core set in a mold for casting, for example, at relatively low pressure.

(Prior art) Since cylinder blocks, cylinder heads, intake manifolds, etc. for automobiles have complex shapes, when casting these, a sand core such as a shell mold or cold box is set in a mold. After casting, the core is collapsed to obtain products with complex shapes. When casting using a core, there is a risk that the core may be crushed by the pressure of the molten metal, so casting is generally performed at a relatively low pressure.

By the way, since the core is made of silica sand hardened with a binder, its surface is rougher than the surface of the mold, and if it is set as is, the casting surface of the product will be rough. Therefore, conventionally, a mold coating agent made by dissolving refractory powder or the like in an organic binder is applied to the surface of the core and dried to form a film, and then the core is set in a mold.

(Problems to be Solved by the Invention) However, in the case of coatings formed using conventional mold coating agents, the resin constituting the binder evaporates due to the heat of the molten metal during casting and generates gas. This causes casting defects such as cavities, cannot sufficiently prevent the insertion of molten metal, has weak adhesion to the surface of the core, and has problems such as seizure to the surface of the product.

(Means for Solving the Problems) In order to solve the above problems, the core coating agent according to the present invention consists of a synthetic mica aqueous solution containing a surfactant and a scale-like refractory powder such as natural phlogopite. Mix the
The viscosity was set to 150 to 300 cp.

(Example) Examples of the present invention will be described below with reference to the accompanying drawings.

First, a method for molding a core by applying a mold coating agent according to the present invention will be described.

To mold the core, silica sand, zircon sand, chromite sand, high alumina sand, or the like is used as aggregate, and an organic binder such as phenolic resin is mixed with the aggregate, and the mixture is placed in a mold and fired. In this way, the resistance force is 35Kg/cm ² to 60Kg/
Obtain a sand core of cm ² .

Next, a mold coating agent according to the present invention is applied to the surface of the core and dried to form a coating layer to make the core surface smooth.

To obtain the above-mentioned mold coating agent, a scaly refractory is mixed into a synthetic mica (containing sodium, fluorine, 4-silicon or lithium, fluorine, 4-silicon) aqueous solution to which a surfactant has been added to form a slurry. Get it.

Here, the scale-like refractory is preferably one that has a weak affinity with molten metal and has excellent mold releasability,
For example, phlogopite (KMg ₃ (Si ₃ Al) O ₁₀ (OH) ₂ ),
Examples include sericite and flaky graphite.

Then, as described above, a slurry type coating agent is applied to the core surface and dried at 100°C or higher to form a coating layer, and the thickness of this coating layer is 0.05 to 0.2 mm. It is preferable to reduce the thickness of the coating layer to 0.05mm.
If it is less than 0.2 mm, sufficient pressure resistance cannot be exhibited, and if the thickness of the coating layer is thicker than 0.2 mm, the product precision after casting cannot be maintained. In order to obtain a coating layer having a thickness within the above range, the viscosity of the slurry coating agent must be 150 to 300 cp (centipoise). Figure 1 also shows the viscosity of the slurry and the solvent (water) for synthetic mica and flaky refractory.
As is clear from this figure, in order to set the viscosity of the slurry coating agent to 150 to 300 cp, the total weight ratio of synthetic mica and scale-like refractory to the solvent must be 70-150% against
The condition is that

Figure 2 is a 250x micrograph showing the particle structure of the core surface before forming the coating layer.
Figure 3 is a 250x micrograph showing the grain structure of the core surface after the coating layer has been formed. As is clear from these figures, the core surface has large pores before the coating layer is formed, but after the coating layer is formed, the synthetic mica and the scaly refractory are It adheres to the surface of the sand core in a layered manner, completely covering the pores between the sand cores and creating a smooth surface.

Therefore, there is no penetration of molten metal into the core surface.
Furthermore, the synthetic mica that constitutes the slurry coating exhibits fluidity when it comes into contact with water, and this water solubility provides excellent adhesion, so that the coating layer firmly adheres to the core surface. On the other hand, scale refractories such as phlogopite have a weak affinity with molten metal, so they exhibit excellent mold releasability.
Furthermore, the coating layer adhering to the product surface after release from the mold exhibits fluidity when in contact with water, so it can be easily removed, and therefore no restrictions are imposed on the core shape.

Next, specific experimental examples will be given to further clarify the effects of the present invention. Here, Experimental Example 1 concerns a casting core for a cylinder head for an automobile, and Experimental Example 2 concerns a casting core for an automobile intake manifold.

Experimental example 1 100 parts of JIS No. 7 silica sand (AFS110) as aggregate,
A water jacket core weighing 1.4 kg was molded using shell sand containing 3 parts of phenol resin as an organic binder and 0.1 part of calcium stearate as a wetting agent. The molding conditions were a mold temperature of 300°C, a firing time of 40 seconds, and a blowing pressure of 2.5 kg/cm ² . Next, prepare 9.8 kg of a 15% aqueous solution of synthetic mica (containing sodium, fluorine, and 4 silicones) thoroughly mixed and stirred, add 10 kg of water, and 5% aqueous solution of sodium dialkyl sulfone succinate as a wetting agent. 0.4Kg, 12Kg of phlogopite (KMg ₃ (Si ₃ Al) O ₁₀ (OH) ₂ ) with an average particle size of 3μ, and antifoaming agent
0.02Kg was mixed and stirred for a day and night to prepare a slurry-like coating agent with a viscosity of 150 cp, the core was immersed in this coating agent for 1 to 2 seconds, and after being left in the air for 60 seconds,
The core was immersed again in the same solution for 1 to 2 seconds, and then the core was left to dry at 170° C. for 20 minutes to form a coating layer.

The core obtained as above was set in a mold, and aluminum alloy (AC4B) was cast at a pressure of 0.3 kg/cm ² .
Low-pressure casting (LPDC) was performed at a pouring temperature of 700℃.

After casting, the sprue is cut and the JIS standard Te (500℃
After treatment (water cooling for 4 hours, air cooling at 200°C for 6 hours), sand was removed from the core using a normal core knock act machine.

As a result, there was no breakage or deformation of the core, and 100% of the core sand had fallen off.

Furthermore, after washing with tap water at a water pressure of 2 kg/m ² , a smooth product with excellent dimensional accuracy was obtained.

Fig. 4A shows the results of measuring the surface roughness of the cast product obtained by the above Experimental Example 1, and Fig. 4B shows the result of measuring the surface roughness of the cast product obtained by the conventional method. As is clear from these figures, the surface roughness formed by the core coated with the coating agent of the present invention is around 15S, compared to the conventional one of around 40S. It can be seen that this is a significant improvement compared to the previous one.

Experimental Example 2 Shell sand having the same formulation and molding conditions as in Experimental Example 1 was used to mold an intake manifold casting core weighing 3.2 kg.

Next, prepare 20 kg of a 15% aqueous solution of synthetic mica (including sodium, fluorine, and 4 silicones) thoroughly mixed and stirred, add 10 kg of water and 25 kg of scaly Al metal powder, and further moisten. A 5% aqueous solution of sodium dialkyl sulfone succinate (0.8 kg) and an antifoaming agent (0.1 kg) were added thereto and mixed and stirred for one day to prepare a slurry-like coating agent with a viscosity of 200 cp. The core was immersed in this mold coating agent under the same conditions as in Example 1 to form a coating layer.

The core obtained as above was set in a mold, and aluminum alloy (AC2B) was cast at a pressure of 0.2 kg/cm ² .
Low-pressure casting (LPDC) was performed at a pouring temperature of 700℃.

After casting, the sprue is cut to meet JIS standard T ₆ (500℃
After treatment (water cooling x 4 hours, air cooling at 170°C x 4 hours), sand was removed from the core using a normal core knock act machine.

FIGS. 5A and 5B show the measurement results of the surface roughness of the core part of the casting product according to the present invention and the measurement results of the conventional product. These figures show that with the coating of the present invention, the surface roughness has decreased from 54S to 10~10.
This is a significant improvement of 15S, indicating that the present invention is highly effective.

In addition, similar good results were obtained even when sericite and scaly graphite were added instead of the phlogopite and aluminum metal powder.Furthermore, the mold coating agent according to the present invention is applicable only to cores for low-pressure casting. It can also be applied to cores for general sand casting and gravity casting.

(Effects of the Invention) As is clear from the above explanation, if a coating layer is formed on the surface of a casting core using the mold coating agent according to the present invention, the pores on the surface of the core can be completely covered in a layered manner. This makes the surface of the core smooth and prevents molten metal from penetrating. Furthermore, since the mold coating agent according to the present invention contains synthetic mica, it has excellent adhesion to the core surface, but on the other hand, the mold coating agent contains scale-like refractories that have a weak affinity with molten metal. Since the coating layer does not contain an organic binder, it does not generate gas due to the heat of the molten metal, and it is possible to obtain a product without casting defects such as blowholes.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the blending ratio of synthetic mica and scaly refractory and the viscosity of the coating agent, Fig. 2 is a micrograph showing the particle structure of the core surface before forming the coating layer; Fig. 3 is a micrograph showing the particle structure of the core surface after the coating layer has been formed, Fig. 4A is a graph showing the surface roughness of the surface of the cast product obtained in Experimental Example 1, Fig. 4 B is a graph showing the surface roughness of the casting product surface obtained by the conventional method, FIG. 5A is a graph showing the surface roughness of the casting product surface obtained by Experimental Example 2, and FIG. 5B is a graph showing the surface roughness of a cast product surface obtained by a conventional method.

Claims (1)

[Claims] 1. A mold coating agent applied to the surface of a sand core set in a metal, which is a slurry of a synthetic mica aqueous solution containing a surfactant and a scale-like refractory powder mixed therein. A coating agent for a core, characterized in that the slurry has a viscosity of 150 to 300 cp. 2. The core according to claim 1, wherein the scale-like refractory powder is natural mica such as natural phlogopite (KMg ₃ (Si ₃ Al) 0 ₁₀ (OH) ₂ ). Coating agent.