JPH0263639A - 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] TECHNICAL FIELD The present invention relates to an investment casting method.

[Prior art] Compared to the conventional sand casting method, the vanishing model casting method has the following advantages: ■ No core is required when manufacturing hollow parts, and ■ Adhesive is not mixed into the sand, making it easier to recover and collect the sand. Easy to reuse, ■Applicable to objects with complex shapes,
Because of its various advantages, its development is progressing and, for example, it is attracting attention as a casting method for engine intake manifolds.

In this investment model casting method, an investment mold made of expanded polystyrene having the same shape as the cast product to be obtained is usually housed in a casting container, the casting container is filled with casting sand, and the investment mold is placed in the casting sand. This is done by injecting molten metal through a Styrofoam sprue connected to a fugitive mold.

As a result, within the casting sand, the sprue and the fugitive mold are sequentially thermally decomposed, and these parts are replaced with the corresponding molten metal, producing the desired metal casting.

By the way, in such a casting method, for a fugitive mold having a complicated shape, the fugitive mold is divided into a plurality of models and these are bonded together with an adhesive or the like.
Boat fishing.

Then, in order to smooth the surface of the final casting, the formed fugitive mold is placed in the mold before being buried in casting sand.
Fine particles of refractory are attached to the entire surface of the fugitive type.

Specifically, a coating agent obtained by mixing refractory fine particles with an aqueous solution containing a binder, a surfactant, and an antifoaming agent is applied to the entire surface of the fugitive mold, and then dried. This allows fine refractory particles to adhere to the surface of the fugitive type.

[Problems to be Solved by the Invention] By the way, if the adhesive part of the fugitive mold formed by adhesion is incomplete or if there are minute scratches on the surface of the fugitive mold, it is difficult to apply the adhesive to the surface of the fugitive mold. The refractory particles in the mold coating do not decompose even if the fugitive mold is thermally decomposed by entering into the imperfectly bonded or scratched areas, resulting in a cast product. There is a problem that it remains inside the mold and causes casting defects.

In order to prevent such casting defects from occurring, defects such as incomplete adhesion and other flaws must be completely eliminated in the fugitive mold. In other words, it is necessary to perform the required adhesion perfectly and to manage the parts in a way that does not damage the surface of the erasable mold.

However, in the case of a model whose bonding surface is a curved surface, such as an engine intake manifold, it is extremely difficult to completely bond the model. Furthermore, since Styrofoam, which is a fugitive material, is generally soft and easily damaged, it is difficult to manage it to avoid even minute scratches.

The present invention was devised in view of such problems, and
Even if there are defects such as incomplete adhesion or scratches on the surface of the fugitive mold, refractory fine particles will not enter the defective areas during the mold coating process, preventing casting defects. The purpose is to provide a vanishing model casting method.

[Means for Solving the Problems] For this reason, the vanishing model casting method of the present invention includes a first step of applying a coating agent to the surface of the vanishing mold and then drying it, and a step of placing the vanishing mold in casting sand. In the investment model casting method, which consists of a second step of burying the investment mold, and a third step of injecting molten metal into the interior of the investment mold to replace the investment mold with the molten metal, the first step includes a binder undercoat step in which a solution containing a binder as the main component is applied to the surface of the fugitive mold, followed by a refractory fine particle adhesion step in which refractory fine particles are adhered to the surface of the fugitive mold, and after this, the surface of the fugitive mold is coated again. It consists of a binder overcoating process in which a solution containing a binder as the main component is applied.

[Function] In the above-described vanishing model casting method of the present invention, in the first step of applying a coating agent to the surface of the vanishing mold and then drying it,
First, a solution containing a binder as a main component is applied to the surface of the fugitive mold. As a result, a substantially smooth thin layer of binder undercoat is formed on the surface of the fugitive mold. Subsequently, when fine refractory particles are attached to the surface of the fugitive mold, the fine refractory particles are formed on the almost smooth outer surface of the thin layer of binder, so that the fine refractory particles will adhere to the defective parts of the fugitive mold. There is no intrusion into the area.

After this, a solution containing a binder as a main component is again applied to the surface of the fugitive mold, so that the layer of refractory fine particles is covered with a thin binder top coat layer, and the coating is coated with a thin layer of binder. Membrane strength is improved.

[Example] Hereinafter, an extinguishable model casting method as an example of the present invention will be explained with reference to the drawings. Figs. 1(a) to (d) respectively show the treatment process of the surface portion of the extinguishable mold according to this example. FIG. 2 is a front view of the evanescent die according to this embodiment, and FIGS. 3(a) to 3(d) are schematic diagrams sequentially showing the casting process of this embodiment.

The vanishing molds 1 and 2 according to this embodiment are for manufacturing an intake manifold, and as shown in FIG. 2, both are formed by joining model parts made of styrene foam. Of these, the vanishing mold 1 is made by joining model parts 1a and 1b to each other, and the vanishing mold 2 is made by joining model parts 2a and 2b to each other. Vanishing type 1 formed in this way
, 2 have air passages 1a and 1 that serve as intake ports, respectively.
b is formed inside. In addition, model part 1a.

The mutual bonding surface A of 1b and the mutual bonding surface B of model parts 2a and 2b are formed of curved surfaces, but each bonding surface A, B
It is not necessary that the bonding surfaces are perfectly aligned over the entire surface [see FIG. 1(a)], and each bond does not need to be bonded completely, and there is no problem with point bonding.

A sprue 3 made of expanded polystyrene is attached to such evanescent molds 1 and 2. Here, as shown in Figure 2,
Erasable molds 1 and 2 are placed opposite each other and both are bonded to sprues 3, respectively. Note that the symbols 3a and 3b in FIG. 2 indicate the sprue 3.
This is the core part of the sprue 3 provided to connect the evanescent molds 1 and 2.

Casting is carried out using the vanishing molds 1 and 2 processed in this way, and this vanishing model casting method includes the first step of applying a mold coating agent to the surface of the vanishing mold 1゜2 and then drying it; A second step of embedding the evanescent molds 1 and 2 in casting sand 5, and
and a third step of injecting the molten metal 7 into the inside of the molten metal 7 to replace the vanishing molds 1 and 2 with the molten metal 7.

In this casting method, the first step consists of three steps:
In other words, ■ a binder undercoating process in which a solution containing a binder as the main component is applied to the surfaces of fugitive molds 1 and 2;
(1) A refractory fine particle adhesion step in which refractory fine particles are adhered to the surface of the refractory mold 1, and (2) a binder overcoating step in which a solution containing a binder as the main component is again applied to the surfaces of the fugitive molds 1 and 2.

Therefore, in the first step, first, the fugitive molds 1 and 2 are immersed in a solution containing a binder as the main component, and the adhesive surface A of the fugitive mold 1°2 is
, A thin layer of binder (thin layer of binder undercoat) 9 is applied to the entire surface of the fugitive molds 1 and 2, including the unbonded parts of B [see Figure 1 (a)].
a [see FIG. 1(b)].

The solution mainly composed of binder used at this time is dissipative type 1,
Examples of this solution include an aqueous solution or an alcohol solution. In the case of an aqueous solution,
It is an aqueous solution containing a binder, a surfactant, and an antifoaming agent. Among these, starch, vinyl acetate, carboxymethylcellulose (CMC), etc. can be used as the binder, and cationic, anionic or Amphoteric surfactants can be used, and commonly used antifoaming agents such as alcoholic antifoaming agents or silicones can be used as antifoaming agents.

Further, in the case of an alcohol solution, for example, one containing about 1 to 30% of vinyl acetate resin as a binder in alcohol can be mentioned, and in this case, a surfactant and an antifoaming agent are not necessary.

The thin layer 9a of the binder formed at this time is the fugitive type 1, 2.
Defects on the surface (that is, incomplete adhesion on the bonding surfaces A and B of fugitive molds 1 and 2, scratches E on the surfaces of fugitive molds 1 and 2, and bead patterns formed on the surfaces of fugitive molds 1 and 2) It penetrates into the inside of the recess C etc.) and smoothly covers the surfaces of the vanishing molds 1 and 2.

Subsequently, refractory fine particles 10 are applied to the entire surface of the fugitive molds 1 and 2.
Attach. [See Figure 1(C).

Examples of the refractory fine particles 10 used at this time include silica (Sin2) and zirconia (ZrO□).

Alternatively, fine particles such as mica may be mentioned. In the case of forging iron materials, silica or zirconia are usually used, but in the case of forging aluminum-based materials, fine particles of mica with a heat-insulating space are suitable.

Since the refractory fine particles 10 adhere around the thin layer 9a of the binder, the refractory fine particles 10 will not penetrate into defects on the surface of the fugitive molds 1 and 2 that are already filled with binder. do not have.

After this, a solution containing a binder as a main component is again applied to the entire surface of the fugitive molds 1 and 2, and a thin layer of binder ( Thin layer of binder topcoat)
Form 9b. The solution mainly composed of a binder used at this time is an organic solvent that does not attack the dissipative types 1 and 2, such as an aqueous solution or an alcohol solution, as described above.

As a result, the refractory fine particles 10 are coated with a thin layer of binder i.
9b, the fixing properties of the refractory fine particles 10 are greatly improved.
And the strength of the coating film formed by the thin topcoat layer 9b of binder is improved.

After the surface treatment is applied to the evanescent molds 1 and 2 in the first step in this way, in the subsequent second step, the evanescent molds 1 and 2 are treated as shown in FIGS. 3(a) and 3(b). , and are buried in the casting sand together with the sprue 3.

That is, first, as shown in FIG. 3(a), the fugitive molds 1 and 2 are placed in a desired posture in a container 4 containing unmixed casting sand 5 with an appropriate amount of binder added to the lower part. Then, the container 4 is further filled with casting sand (casting sand to which no binder has been added or mixed) 5, and as shown in FIG. Bury it. The casting sand 5 is filled while the container 4 is vibrated by the vibration device 6. As a result, the passage spaces 1a and 2a of the fugitive molds 1 and 2 are also filled with casting sand 5. At the same time, the bonding force between each particle of the casting sand 5 is also strengthened.

Then, in the subsequent third step, FIG. 3(C).

As shown in (d), molten metal (for example, molten aluminum alloy) 7 is injected into the inside of the fugitive mold 1.degree. 2 through the sprue 3, and the molten metal 7 replaces the fugitive molds 1 and 2.

In other words, when the molten metal 7 is injected into the dissipating molds 1 and 2 through the sprue 3, the high-temperature molten metal 7 thermally decomposes the sprue 3 and disappears, as shown in FIG. 3(c). Type 1, 2
and gradually thermally decomposes the vanishing type 1゜2. Then, this thermally decomposed part, that is, the space where the sprue 3 and the extinguishable molds 1 and 2 were, is replaced with molten metal 7, and when this molten metal 7 is cooled to a predetermined temperature, a desired metal casting product (i.e., 2 engine intake manifold) 8
a, 8b are manufactured.

The vanishing model casting method as an embodiment of the present invention is configured as described above, and in particular, the binder undercoat is applied in the first step of applying a coating agent to the entire surface of the vanishing molds 1 and 2 and then drying it. The treatment prevents the refractory fine particles 10 from penetrating into defects on the surface of the fugitive molds 1.2, and the refractory fine particles 10 adhere only to the surfaces of the fugitive molds 1 and 2. Therefore, the refractory fine particles 10 do not remain inside the completed metal castings 8a, 8b, and casting defects are prevented from occurring.

In addition, due to the binder overcoat treatment formed in the first step,
Since the refractory fine particles 10 are coated, a thin layer of binder 9a
The strength of the coating film composed of the refractory fine particles 10 and the thin layer 9b of the binder is improved, and the surfaces of the metal castings 8a and 8b can be formed more smoothly.

The strength of this coating film can be adjusted as appropriate by adjusting the thickness of the thin layer 9b of the binder.

When applying a top coat with a solution containing a binder as the main component, care must be taken to ensure that the binder for the top coat does not dissolve the thin layer of binder undercoat. It is conceivable to set the solution to be made of a material different from that used for the undercoat.

Further, the solution containing the binder as a main component is not limited to an aqueous solution or an alcohol solution, and may be any other organic solvent as long as it satisfies the condition that it does not attack the dissipative types 1 and 2.

[Effects of the Invention] As detailed above, according to the vanishing model casting method of the present invention, the first step is to apply a coating agent to the surface of the vanishing mold and then dry it, and to apply the vanishing mold to casting sand. In an extinguishable model casting method, which includes a second step of embedding in the extinguishable mold, and a third step of injecting molten metal into the inside of the extinguishable mold to replace the extinguishable mold with the molten metal,
The first step is a binder undercoating step in which a solution containing a binder as a main component is applied to the surface of the fugitive mold, and then a refractory fine particle adhesion step in which refractory fine particles are attached to the surface of the fugitive mold. This process consists of a binder overcoat process in which a solution containing a binder is applied again to the surface of the fugitive mold, so that no refractory fine particles remain inside the cast product and the casting process is completed. This has the effect of preventing the occurrence of defects, and also has the effect of making the surface of the cast product smoother because the strength of the coating film is improved by the overcoating of the binder.

[Brief explanation of the drawing]

Figures 1 to 3 show the investment model casting method as an embodiment of the present invention, and Figures 1 (a) to 3 (d) respectively show the treatment process of the surface portion of the investment model according to this embodiment. A schematic sectional view, FIG. 2 is a front view of the vanishing type according to this embodiment, and FIG.
Figures (a) to (d) are schematic diagrams sequentially showing the casting process of this example. 1.2-vanishing type, 1 a, 1 b, 2 a,
2 b - model part, 3... sprue, 3a, 3b...
- Core part of sprue 3, 4... Container, 5... Casting sand (casting sand to which no binder has been added and mixed), 6... - Vibration device, 7
- Molten metal (e.g. molten aluminum alloy) 8a, 8
b - metal castings (i.e. intake manifolds of two engines), 9a, 9b - thin layer of binder, 10... - refractory particles, A, B - joint surfaces, C - fugitive mold 1 , a bead-patterned recess formed on the surface of 2, D... joint surface A. Incomplete adhesion in B, E. - Surface scratches on the vanishing type 1°2.

Claims (1)

[Claims] The first step is to apply a coating agent to the surface of the fugitive mold and then dry it, the second step is to embed the fugitive mold in casting sand, and the second step is to inject molten metal into the inside of the fugitive mold. In the fugitive model casting method, the first step includes a binder undercoating step of applying a solution containing a binder as a main component to the surface of the fugitive mold, and The process consists of a refractory fine particle adhesion step in which fine refractory particles are attached to the surface of the fugitive mold, and a binder overcoating step in which a solution containing a binder as the main component is applied again to the surface of the fugitive mold. Disappearance model casting method.