JPH02268942A - Lost foam pattern casting method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 casting 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. This is done by burying the mold in sand and injecting molten metal through a sprue connected to the vanishing mold. 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 disappearing models as described above, if the adhesion is incomplete or there are scratches such as minute cracks on the surface of the disappearing model, the coating agent applied to the surface of the disappearing model may be damaged. Even if the disappearing model is thermally decomposed by penetrating into the imperfectly bonded or scratched parts, the refractory fine particles in this coating will not decompose and will remain inside the finished cast product. Otherwise, there is a risk of 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 with a curved surface to be bonded, such as an engine intake manifold, it is often difficult to completely adhere it due to problems such as peeling on the curved surface. Styrofoam, which 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 prevent the fine particles from entering 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 strength. or.

A new problem may arise in that a sufficiently satisfactory result cannot be obtained in terms of durability against the flow pressure of the molten metal when it is injected into the vanishing model. Therefore, in order to solve the above-mentioned problems, instead of the above-mentioned binder,
Proposals have been made to strengthen the bond between refractory fine particles using a binder containing water glass as a main component.

However, when the binder material is changed in this way, it takes a long time to dry the water glass, which lengthens the production time of the disappearing model, and also , if the binder is applied to the vertical surface of the model.

Until it dries and hardens, dripping may occur, and as a result, there is a risk that a new problem will occur in that it will not be possible to obtain a sufficient amount of refractory fine particles to form a refractory layer on that surface. .

Therefore, if the thickness of the refractory layer obtained from the refractory fine particles is not the specified thickness, the durability in that area will not be obtained, and the shape will collapse during pouring or the mold will collapse during pouring. There is a risk of collapse, and the cause of the casting defect will remain unresolved.

In view of the above-mentioned problems with the conventional vanishing #X type casting method, an object of the present invention is to shorten the manufacturing time of a vanishing model, and also to prevent leakage of molten metal and eliminate casting defects. It's about getting.

(Means for Solving the Problems) In order to achieve this object, the present invention provides 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, and In the vanishing model casting method, which comprises a second step of embedding in sand, and a third step of injecting the molten metal into the inside of the vanishing model to replace the vanishing model with the molten metal, the first step includes the above-mentioned A coating agent application 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 a fire-resistant agent that adheres fire-resistant particles, powder, or flakes to the surface of the vanishing model. The present invention proposes that the fireproofing agent be composed of a mixture of fine particles made of calcium silicon, ferrosilicon, etc. that harden by reaction with the water glass.

(Function) According to the present invention, the fireproofing agent that adheres to the surface of the vanishing model is
By having the property of causing reaction hardening with water glass when mixed with this, the time required to complete drying is shortened.

(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 the 10% molds IA and IB to each other, and the vanishing model 2 is formed by joining the 10% molds 2A and 2B to each other. 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.

In the case of this embodiment, in which a sprue 3 made of styrofoam is attached to the vanishing models 1 and 2 as described above, the vanishing models 1 and 2 are placed facing each other and adhered to the sprue 3, as shown in the second figure. It is. In FIG. 2, reference numerals 3A and 3B indicate branch portions of the sprue 3 that serve as runners connected from the sprue 3 to each model.

Casting is performed using the vanishing models 1 and 2 processed in this way, but in the casting method in this example, a coating agent is applied to the surfaces of the vanishing models 1 and 2, and then this is dried. a second step of burying the vanishing model 1.2 in molding sand 5 filled in a 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.

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 made of an aqueous solution containing water glass as a main component to the surface of the vanishing model 1.2; ,■
It consists of a fire-retardant adhesion process in which fire-resistant particles, powder, or flakes are attached to the surface of the vanishing model 1.2, and the above-mentioned fire-resistant particles, powder, or flakes contain a component that hardens by reaction with water glass. The reason lies in the fact that the materials are mixed together.

That is, in the first step, first, the vanishing models 1 and 2 are
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 bonding surface A of the vanishing model 1.2 shown in FIG. 1(A) is prepared. 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 unbonded portions of , B, as shown in FIG. 1CB).

On the other hand, the solution constituting the thin coating agent layer 6 described above is applied to the defective parts of the surface of the vanishing model 1.2, that is, the imperfectly joined surfaces and uneven parts E of each split mold, or the beads formed on the mold surface. It penetrates into the interior of the concave portions C of the pattern, etc., and fills the concave portions 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 fireproofing agent 6A is selected from fireproof particles, powder, or flakes. Specifically, for example, in the case of one particle or powder, the size (diameter) of the particle is in the range of 5 to 1000 μm. and preferably 50 to 20
Silica (SiO, ) and zirconia (ZrO□) set at 0 ILm are used, and in the case of thin flakes, mica, etc. are used. Examples of selecting these refractory agents include: 1. Usually, in the case of iron casting, Silica and zirconia are now being selected, and in the case of casting aluminum-based materials, mica with a heat-insulating space is being selected.

The fire retardant 6A is mixed with fine particles 6B such as calcium silicon or ferrosilicon which have the property of reacting with water glass to harden the fire retardant.
It is deposited on the mold coating thin layer 6 with a thickness of 1.0+a.

By the way, the process of attaching the fire retardant 6A to the coating agent thin layer 6 made of the above-mentioned solution containing water glass as a main component is as follows.
Normally, in the process of manufacturing a heat-generating self-hardening mold (a process called the N process), raw sand, water glass, and ferrosilicon are simultaneously mixed, and from the time when this mixing is completed, a predetermined period of time, e.g. 20 Unlike the process of pouring into a mold and curing it within minutes, a thin layer 6 of a mold coating agent made of a solution mainly composed of water glass is coated with a fire retardant 6A and a reaction hardening agent mixed therein. This is a process in which the reaction between water glass and calcium silicon or ferrosilicon starts from the moment they come into contact with the fine particles 6B, and in order to cause this reaction to harden, an ambient temperature of about 60°C is set. There is.

Therefore, by setting such a process, it is possible to select the timing for starting one reaction. For example, after performing the process of forming the coating agent thin layer 6 on a large number of disappearing models,
Next, if the reaction curing of this mold coating agent is carried out continuously, it becomes possible to carry out assembly operations in each process. In addition, as shown in FIG. 1(C), the above-mentioned fireproofing agent 6A adheres around the coating agent thin layer 6, so that the surface of the vanishing model 1.2 that is already filled with the coating agent. It does not penetrate into defective parts.

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

That is, FIG. 3 shows the second step, and first, as shown in FIG. 3(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
The vanishing model 1.2 is set in a predetermined position in the container 4, and the molding sand 5, which has not been mixed with a mold coating agent, is filled into the container 4, as shown in FIG. 3(B). In, Disappearance Model 1
．． 2 is completely buried in the foundry sand. Furthermore, this foundry sand 5
The filling 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. 3(B) is completed,
A third step shown in FIG. 3(C) and FIG. 3(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 model 1.2 through the sprue 3, and the vanishing models 1 and 2 are replaced with this molten metal. do.

In other words, when molten metal is injected into the vanishing models l and 2 through the sprue 3, the high-temperature molten metal 7 thermally decomposes the sprue 3 and forms the vanishing model. 1 and 2, and gradually thermally decomposes the disappeared model 1.2.

Then, this thermally decomposed part, that is, the space where the sprue 3 and the disappearing models 1 and 2 existed, is replaced with the molten metal 7, and the desired metal casting product 1 is produced.In this embodiment, the intake manifolds 8A and 8B of the engine are manufactured. be done.

(Effects of the Invention) As is clear from the description of the embodiments, according to the present invention, in the step of applying a mold coating agent to the surface of the vanishing model when the vanishing model is placed in the molding sand. By using a coating agent made of an aqueous solution containing water glass as a main component to bond the fireproofing agent, and by mixing fine particles that can be hardened by reaction with this coating agent with the fireproofing agent, one heat release is achieved. It is possible to accelerate curing through hardness and shorten the time it takes to dry and harden. This eliminates the dripping phenomenon that tends to occur during drying and hardening, and suppresses fluctuations in the thickness of the fireproof layer. This prevents the mold layer from deteriorating due to a decrease in the strength of the refractory layer, thereby preventing the occurrence of casting defects.

[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 a casting diagram according to the embodiment of the present invention. FIG. 2 is a model diagram for explaining the method. 1.2... Vanishing model, 3... Sprue, 4... Casting container, 5... Foundry sand, 6... Thin layer of mold coating agent, 6A...
Fireproofing agent, 6B: Fine particles that can be mixed with a fireproofing agent and hardened by reaction with water glass.

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. a coating agent application process of applying a coating agent consisting of a coating agent, and a fireproofing agent adhesion process of attaching fire-resistant particles, powder, or flakes to the surface of the vanishing model; , or the flakes are made of calcium silicon or ferrosilicon,
A vanishing model casting method characterized in that the above-mentioned water glass is mixed with fine particles that harden through reaction.