JPH02268941A - Lost foam pattern casting method - Google Patents

Abstract

PURPOSE:To prevent the development of casting defect by constituting lost foam pattern casting process of a facing agent applying stage for applying facing agent containing water glass as the essential component on the pattern surface and a successive stage for sticking refractory particles, powder or flake to the pattern surface. CONSTITUTION:The lost foam patterns 1, 2 are dipped into water solution containing the water glass as the essential component and the facing agent thin layer 6 is formed on the whole surface of the lost foam patterns 1, 2 containing unsticking part in the sticking surfaces A, B to embed recessed part on the pattern surface. Successively, refractory agent 6A is stuck on the whole surface of the pattern. As this is stuck around the facing agent thin layer 6, this does not invade in the surface defect part in the patterns 1, 2. The pattern subjected surface treatment in such way is embedded in molding sand 5 together with a sprue 3 and after that, by pouring the molten metal 7 through the sprue 3 to replace the lost foam patterns 1, 2 with the metal 7, the development of the casting defect can be prevented.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an investment casting method.

(Prior art) As is well known, the casting method called vanishing model casting method has two advantages over the conventional sand casting method: ■ It does not require a core when manufacturing hollow parts, and ■ It adheres to sand. It has various advantages, such as the ease of collecting and reusing sand because no chemicals are mixed in, and the fact that it can be applied to objects with complex shapes. is sometimes used in the construction of intake manifolds for automobile engines.

In this vanishing model casting method, a styrofoam vanishing mold having the same shape as the cast product to be obtained is usually housed in a casting container, and the molding container is filled with molding sand to cast the vanishing mold. After being buried in sand, molten metal is poured from a sprue connected to a vanishing mold.

It is carried out by injecting molten metal.

As a result, the sprue and the vanishing mold are sequentially thermally decomposed within the foundry sand, and this portion is replaced with molten metal, producing the desired cast product.

By the way, in the above-mentioned vanishing model casting method, for molds with complex shapes, it is common to divide the model into multiple models and adhere them to each other with adhesive or the like. It is said that

For this reason, in order to smooth the surface of the final cast product, fine particles of refractory are attached to the entire surface of the formed evanescent model before burying it in foundry sand. things are being done.

That is, in order to attach the fire-resistant fine particles mentioned above, a coating agent obtained by mixing fire-resistant fine particles into an aqueous solution containing a binder, a surfactant, and an antifoaming agent was applied to the entire surface of the vanishing model. After that, the fine particles are attached by drying this.

By the way, when adhering the vanishing models as described above, the adhesion may be incomplete or there may be scratches such as minute cranks on the surface of the vanishing model.

Even if the molding agent applied to the surface of the vanishing model penetrates into the imperfectly bonded or scratched areas and the vanishing model decomposes due to heat, the refractory fine particles in the coating will not decompose. There is a risk that it will remain inside the finished cast product and cause a casting defect.

In order to prevent the occurrence of such casting defects, it is necessary to completely eliminate defects such as incomplete adhesion and other flaws in the disappearing model.

That is, it is necessary to perform the desired adhesion perfectly and to manage the parts so as not to damage the surface of the vanishing model.

However, in the case of a model having a curved surface to be bonded, such as an engine intake manifold, it is often difficult to completely adhere the model due to problems such as peeling on the curved surface. In addition, the Styrofoam that is the material for the disappearing model is generally soft and easily scratched, so it is difficult to manage it to avoid even the slightest scratches.

Therefore, in order to solve this problem, after applying a solution containing a binder as the main component, refractory fine particles are attached to it, and the surface of the vanishing model is once smoothed with the binder. It has been proposed that fine refractory particles be attached to the surface of the vanishing model to suppress their intrusion into defects on the surface of the vanishing model.

(Problems to be Solved by the Invention) However, in the method for preventing casting defects as described above, as a solution containing a binder as a main component,
An organic solvent other than an aqueous solution that does not attack the vanishing model is used, and a specific example is an alcohol solution, in which about 1 to 30% of vinyl acetate resin is added as a binder. Included is used. When a solution containing such a binder as the main component is applied to the surface of the vanishing model, the same effect as filling defects such as scratches with binder can be obtained. The solution is
Due to the nature of its main components, it exhibits a bond-like shape and is in an unstable state in terms of hardness when obtaining 1 strength. Alternatively, there is a possibility that a sufficiently satisfactory result may not be obtained in terms of durability against the flow pressure of the molten metal when the molten metal is injected into the disappearing model.

Therefore, if the fixed bonding of the refractory fine particles is insufficient, durability cannot be obtained in that part.

This may cause the mold to collapse during mold filling or during pouring, leading to poor casting results.

In view of the above-mentioned problems in the conventional vanishing model casting method, an object of the present invention is to strengthen the bonds between fine particles in the refractory layer formed on the surface of the vanishing model. The object of the present invention is to provide a casting method that can eliminate casting defects due to leakage of molten metal, etc., by making the layers perfect, without causing the disappearing model to lose its shape.

(Means for Solving the Problems) In order to achieve this object, the present invention includes a first step of applying a coating agent to the surface of a vanishing model that disappears with the molten metal and then drying it, and a step of drying the vanishing model by casting it. A vanishing model casting method comprising a second step of embedding the vanishing model in sand, and a third step of injecting the molten metal into the vanishing model to replace the vanishing model with the molten metal.

The first step includes a coating agent coating step of applying a coating agent made of an aqueous solution containing water glass as a main component to the surface of the vanishing model, and then applying fire-resistant particles or powder to the surface of the vanishing model. Alternatively, it is proposed to consist of a process of attaching a fireproofing agent to attach flakes.

(Function) According to the present invention, the coating agent applied to the surface of the vanishing model has extremely high hardness upon drying and hardening, and strongly binds the refractory particles, powder, or flakes. shall be taken as a thing.

(Embodiment) Hereinafter, details of an embodiment of the present invention will be explained with reference to FIGS. 1 to 3.

FIGS. 1A to 1C are schematic diagrams for explaining the process of treating the surface portion of a vanishing model used in the vanishing model casting method according to an embodiment of the present invention.

The vanishing model 1.2 in this example is for manufacturing an intake manifold, and as shown in Fig. 2, both model parts made of styrofoam are joined to create a shape similar to the finished product. .

Of these, the vanishing model 1 is formed by joining split molds IA and IB to each other, and the vanishing model 2 is formed by joining split molds 2A and 2B to each other, and in each of these molds, an intake port is formed. Air passages 1a and 2a are formed inside, respectively.

In addition, although the joint surfaces A and B of the split molds in the above-mentioned model are composed of curved surfaces, each joint surface is a perfect adhesive surface that is fully aligned as shown in Figure 1 (A). There is no need to do so, and when adhering, there is no problem with point adhesion without having to apply adhesion over the entire surface.

A sprue 3 made of polystyrene foam is attached to the vanishing model 1.2 as described above. In the case of this embodiment, as shown in the second figure, the disappearing models 1 and 2 are bonded to the sprue 3 while facing each other. In FIG. 2, reference numerals 3A and 3B indicate the core portions of the sprue 3, which form the runners connected from the sprue 3 to each model.

Casting is performed using the vanishing model 1.2 processed in this way, but in the casting method in this embodiment, a coating agent is applied to the surface of the vanishing model 1.2 and then dried. a second step of burying the vanishing model 1.2 in the molding sand 5 filled in the casting container 4, and pouring molten metal into the buried vanishing model 1.2. , vanishing model 1,
A third step of replacing No. 2 with molten metal is performed.

5. The feature of this embodiment is that the above-mentioned first step is replaced by (1) a coating agent application step of applying a coating agent consisting of an aqueous solution containing water glass as a main component to the surfaces of the vanishing models 1 and 2; , ■
This method consists of a refractory agent adhesion process in which refractory particles, powder, or flakes are applied to the surface of the vanishing model 1.2.

That is, in the first step, first, the vanishing model 1.2
is immersed in a silicate solution such as sodium silicate or potassium silicate, so-called an aqueous solution whose main component is water glass, and the adhesive surface A of the vanishing models 1 and 2 shown in FIG. , H, a thin layer of mold coating agent (thin layer of mold coating agent) 6 is formed on the entire surface of the vanishing model, including the unattached portions of H, as shown in FIG. 1CB).

On the other hand, the solution constituting the thin coating agent layer 6 described above is applied to the surface defects of the vanishing models 1 and 2, that is.

It penetrates into the incompletely joined surfaces of each split mold, the uneven part E, or the bead-patterned concave part C formed on the mold surface.
The recesses are filled in on the surface of the model.

Subsequently to such treatment, as shown in FIG. 1(C), a fireproofing agent 6A is applied to the entire surface of the vanishing models 1 and 2.

That is, the above-mentioned fireproof agent 6A is selected from fireproof particles, powder, or flakes. Specifically, for example, in the case of particles or powder, the size (diameter) of the particles is in the range of 5 to 1000 μm. and preferably 50 to 20
Silica (SiOz), zirconia (
Zr02) is used, and in the case of thin flakes, mica etc. are used,
Examples of fireproofing agents selected include silica and zirconia when casting iron materials, and mica with a heat-insulating space when casting aluminum-based materials. .

Since such a fireproofing agent adheres around the coating agent thin layer 6, as shown by reference numeral 6A in FIG. 1(C), the disappearing model 1.2 already filled with the coating agent It does not penetrate into the defective parts of the surface.

When we conducted an experiment on the strength of the coating agent used in the above-mentioned surface treatment, the results shown in FIG. 3 were obtained.

In other words, the experiment that yielded the results shown in Figure 3 was conducted in the fourth experiment.
As shown in the figure, a coating piece formed by mixing a coating agent and a fireproofing agent was supported in a cantilever shape, and a load W was applied to its free end to obtain the amount of deflection of the free end. It is something.

In Fig. 3, the results indicated by the symbol α are the results when no coating agent was used, and the results indicated by the symbols β, γ, and δ are the results when a general vinyl acetate resin and various fire retardants were used. These are the results when mixed individually.

The results obtained when the mold coating agent made of an aqueous solution containing water glass as a main component used in this example and the fire retardant were mixed are shown by symbols i, ζ, and η. In the experimental results according to this example, the results indicated by the symbol E are those obtained when the content ratio of water glass and water is 1:1 and silica sand is mixed therein, and the results indicated by the symbol ζ are those obtained by mixing silica sand. , is the result when the content ratio of water glass and water is 2:1 and mica is mixed therein, and the result indicated by the symbol η is the result when the content ratio of water glass and water is 2:1, This is the result when silica sand is mixed with this.

As is clear from the above-mentioned results, the mold coating used in this example has significantly improved strength compared to the commonly used mold coating whose main component is a binder. Therefore, the fire retardant 6A combined with such a coating agent
This means that the mechanical strength when bonded is increased, which increases the strength against deformation when the vanishing model 1.2 is inserted into the mold, and the strength against the flow pressure of molten metal during pouring. It is said to be in a satisfactory condition, and it is possible to obtain a condition that does not cause any change in the size of the ventilation space in the biryushan, so that the flow of 788 during pouring is smooth, and the styrofoam generated at that time is reduced. entrainment of gas,
So-called stagnation can be prevented.

The disappearing models 1 and 2 that have undergone the surface treatment as described above are buried together with the sprue 3 in the foundry sand 5 in a second step that is subsequently carried out.

That is, FIG. 5 shows the second step. First, as shown in FIG. 5(A), an appropriate amount of molding agent was added to the lower part of the molding sand 5 and unmixed molding sand 5 was stored therein. Casting container 4
Inside, the vanishing model 1.2 is set in a predetermined posture, and the inside of the container 4 is filled with molding sand 5 which has not been mixed with a mold coating agent.

As shown in FIG. 5(B), the disappearing model 1.2 is completely buried in molding sand. Note that this filling of the molding sand 5 is performed while applying vibration by a vibration device (not shown), so as to densify the space between the molding sands.

Therefore, by filling the molding sand 5 in this way, it is possible to promote the densification of the sands as described above, and also to completely fill the passage spaces 1a and IB in the disappearing model 1.2 with the molding sand. becomes.

When the process shown in FIG. 5(B) is completed,
The third step shown in FIG. 5(C) and FIG. 5(D) is performed.

That is, in the third step, molten metal of an aluminum alloy, for example, so-called molten metal 7 is injected into the vanishing models 1 and 2 through the sprue 3, and the vanishing models 1 and 2 are replaced with this molten metal. do.

In other words, when the molten metal is injected into the vanishing model 1.2 through the sprue 3, as shown in FIG. 1 and 2, and gradually thermally decomposes the disappeared models 1 and 2.

The pyrolyzed portion, that is, the space in which the sprue 3 and the melt 1.2 were present, is replaced by the molten metal 7, and the desired metal casting, in this example, the intake manifolds 8A and 8B of the engine, is formed. Manufactured.

(Effects of the Invention) As is clear from the description of the embodiments, according to the present invention, in the process of applying a mold coating agent to the surface of the disappearing model when the disappearing model is placed in the molding sand. By using a coating agent made of an aqueous solution containing water glass as the main component to bind the fireproofing agent, it became possible to significantly increase the hardness of the coating agent after drying and hardening. , it is possible to improve the strength against deformation of the lost model when it is buried in foundry sand, and the durability against flow pressure during pouring, and the size of the ventilation space between the fireproofing agents can also be changed. This prevents such things from happening, allowing the molten metal to flow more smoothly during pouring.

It also prevents the accumulation of gas generated from within the vanishing model, which maintains the refractory layer in the vanishing model in an almost perfect state, preventing casting defects and increasing the casting speed. You can obtain the law.

[Brief explanation of drawings]

Fig. 1 is a model diagram for explaining the processing process for the vanishing model used in the embodiment of the present invention, Fig. 2 is a model diagram for explaining an example of the vanishing model, and Fig. 3 is the same as shown in Fig. 1. A diagram showing the results of comparing the strength of the mixture of mold coating agent and fireproofing agent obtained by the treatment with the strength of the mixture obtained by conventional mold treatment. Figure 4 shows the strength comparison shown in Figure 3. Model diagram for explaining the structure for obtaining results, Part 5
The figure is a model diagram for explaining a casting method according to an embodiment of the present invention. 1.2... Vanishing model, 3... Sprue, 4... Casting container, 5... Foundry sand, 6... Thin layer of mold coating agent, 6A...
・Fire retardant. (A) Figure (B) (C)

Claims (1)

[Claims] A first step of applying a coating agent to the surface of a disappearing model that disappears with the molten metal and then drying it, a second step of burying the disappearing model in foundry sand, and a second step of burying the disappearing model in foundry sand; In the vanishing model casting method, which includes a third step of injecting the molten metal into the interior and replacing the vanishing model with the molten metal, the first step includes coating the surface of the vanishing model with an aqueous solution containing water glass as a main component. Disappearance characterized by comprising a coating agent application step of applying a coating agent consisting of the following: a refractory agent adhesion step of adhering refractory particles, powder, or flakes to the surface of the vanishing model. Model casting method.