JPS62124047A - Production of expendable pattern for casting - Google Patents

Abstract

PURPOSE:To unite a core and expendable mold by making expansion molding of an expandable thermoplastic resin packed into the mold cavity constituted by mounting a core for casting formed with flange parts at both ends into the mating parts of a pair of metallic molds for expansion molding. CONSTITUTION:The metallic molds 11, 21 having the mold surface of a semi- cylindrical curved surface corresponding to the shape of the expendable mold to be produced are attached to respective frames 10, 20 of a cope 1 and a drag 2. The molds are clamped while the core is spanned in the notched part of the cope 1 and the drag 2 and the core N is sandwiched between the upper and lower metallic molds 11 and 21. After the expandable thermoplastic resin particles from a packing device 3 are packed into the mold, the assembly is heated to obtain the expandable mold M. The expandable mold produced by such method has the excellent integrity, the defect of the product after investment casting is prevented and the yield is improved.

Description

[Detailed Description of the Invention] [Technical Field] This invention relates to a method for manufacturing an investment casting mold, and more specifically to a method for manufacturing an investment casting mold that is used in an investment casting method and is destroyed by the heat generated when molten metal is poured. It's about the method.

<Prior art> Thermoplastic resin foam molded products are used as fugitive molds used in the investment casting method described above, and these products are easy to mold, inexpensive, lightweight, and easy to handle. It has the following characteristics and is widely used.

In the case of the above-mentioned fugitive molded foam products, it is common to use one that is entirely molded in one piece, but if the shape of the fugitive mold is complex and it is difficult to mold in one piece, multiple fugitive molds are used. After dividing into parts and molding them using so-called split molds, the split molds are glued together at their mating surfaces to be used in an integrally joined state.

In particular, in the case of an extinguishable mold that is used in combination with a core during casting, if it is not made into a split mold, it may become impossible to place the core inside the extinguishable mold, or There is a problem in that the task of arranging the core is extremely difficult, and in the case of a vanishing type that is combined with a conventional core, it has generally been formed into a split mold.

However, in the case of the above-mentioned split molds, if the adhesive bonding is insufficient and there are areas with poor adhesion, the coating agent applied to the surface of the fugitive mold during casting will enter the gaps between the areas with poor adhesion, causing the cast product to deteriorate. There is a problem in that cracks appear in the mold, resulting in defective castings being manufactured. Therefore, extremely strict inspection is required for the bonded parts of split molds, but in the case of fugitive molds with complex shapes, it is difficult to completely inspect the entire bonded surface.

Particularly, as described above, in the case of a fugitive mold used in combination with a core, the inner surface of the fugitive mold adjacent to the core cannot be visually observed, making it impossible to discover poor adhesion.

Furthermore, in the case of a disappearing mold using a split mold, it takes time and effort to repeat the light foam molding for each number of split molds, and the gluing work is troublesome, and if the position of the scraping mold shifts during gluing,
There is also the problem that the shape of the cast product will be inaccurate, and when using the core described above, the core and split mold must be aligned accurately, and the split molds may not be aligned with each other or with the core. There was a problem in that adhesive bonding had to be performed, which required a great deal of time and effort.

Therefore, as an object of the present invention, among the above-mentioned fugitive molds made of foam molded products, in the fugitive molds used in combination with a core, no split molds are used at all, and the gluing work after molding is eliminated. It is an object of the present invention to develop a method for manufacturing an evanescent mold, which has excellent integrity between the core and the fugitive mold, and can accurately align the core and the evanescent mold.

<@Sei> And, as a method for achieving the above object, there is a method for manufacturing an investment mold for casting made of a foam molded product of thermoplastic resin, in which a mold is placed in the mating part of a pair of molds for foam molding. , a casting core with flanges formed at both ends is attached, and a mold cavity is formed between the mold of the mold and the flange of the core,
The mold cavity is filled with expandable thermoplastic resin particles and foam molding is performed to integrally connect the foam molded fugitive mold with the core.

<Example> Next, an example of the present invention will be described below with reference to the drawings.

Although the steps are illustrated sequentially from Fig. 1 to Fig. 4,
The illustrated embodiment exemplifies the case where a hollow annular fugitive mold (H) as shown in FIG. 4 is manufactured by molding. Next, we will explain the method of integrally joining the core (N), which has a cylindrical rod-shaped part made of a sand mold or the like, in order to form a cavity in the center of the evanescent mold (H). Regarding the structure in combination with the core (N), the shape structure shown in the drawings is not intended.

First, to explain the mold for foam molding shown in Fig. 1, (1) is the upper mold, (2) is the lower mold, and the upper mold (1) is the lower mold.
And the lower mold (2) has each frame (1o) (
20), a mold (m(21)) is attached which has a semi-cylindrical curved mold surface corresponding to the shape of the evanescent mold to be manufactured.

Then, in a state where the upper mold (1) and the lower mold (2) are clamped, the upper and lower molds (11N21) match, and a cylindrical mold cavity space is formed between them.

Note that (3) is a filling device, which is attached to the upper mold (1) and fills the mold cavities with expandable thermoplastic resin particles.

In addition, the mold (11N21) has a steam hole, a heating mechanism using steam, etc., and a cooling mould.
Although various mechanisms similar to those of a normal foam molding apparatus are installed, such as a mechanism for taking out a foam molded product, detailed illustrations and explanations are omitted.

Using the above-mentioned mold, as shown in Fig. 2, in the notches (12) (22) of the upper mold (1) and lower mold (2),
Pass the core (N) and place the upper and lower molds (11) (21).
The mold is clamped with the core (N) sandwiched between the two.

The structure of this core (N) is that a rod-shaped part (50) for forming a hollow part in the disappearing type (H) is formed in the center, and a disc-shaped part is formed at both ends of the rod-shaped part (50). The flange part (
51), and furthermore, a stepped portion (52) is formed on the inner edge of the flange portion (51) over the entire circumference.

Therefore, when the core fN) is placed on the mating surfaces of the upper and lower molds (11) and (21), the flange portion (51) of the core (N) is located within the mold (11) +21). Both ends of the cylindrical mold surface are closed, and a mold cavity (4) is formed in the part surrounded by the inner surface of the flange part (51) and the molds (11) and (21). Center the rod-shaped part (50 mm) of the core (N).
) will pass through. In addition, the step part (52) of the flange part (51) engages with the corner part of the mold (11021),
The core (N) is positioned with respect to the mold (11) [21]. In addition, the flange part (51
), the parts exposed to the outside of the molds (11) and (21), that is, the mold cavity (4), are the fixing parts for fixing the core (N) to the molding sand during casting, and the so-called baseboards. It acts as.

In this state, the mold cavity (4) formed between the molds (11) and (21) is filled with foamable thermoplastic resin particles from the filling device (3), and then heated with steam or the like. Then, usual foam molding is carried out to form an extinguishable mold (14) consisting of a foam molded product, as shown in FIG.

After molding the foam molded product (+4), it goes through the usual cooling process, mold opening and ejecting process, and collects the fugitive mold (H) and core (N), resulting in a circular shape as shown in Figure 4. A tubular vanishing mold (H) and a rod-shaped core (
This means that it is possible to manufacture a product in which the parts (N) and (N) are integrally joined.

If this fugitive mold (14) and core (N) are buried in molding sand as they are and normal investment casting is carried out, the fugitive mold [8] consisting of a foam molded product will absorb heat during casting. By melting and disappearing, a cast product corresponding to the shape of the vanishing mold (H) can be manufactured, and a cavity corresponding to the shape of the core (N) can be formed in the center of the cast product.

Among the methods for manufacturing evanescent type explained above, evanescent type (H)
As the expandable thermoplastic resin particles for molding, those made of various thermoplastic resins such as polystyrene, polyethylene, etc., which are similar to those used for manufacturing fugitive molds made of ordinary foam molded products, can be used.

In addition to the shape of the vanishing mold 04), in addition to relatively simple shapes such as the circular tubular shape shown in the figure, it can also be manufactured with more complex uneven shapes, etc., and corresponds to the shape of the vanishing mold (H). The molds (11) (21) constituting the mold cavity (4)
) may be formed into an appropriate shape.

In addition, as the core (N), a core made of a normal sand mold can be used, but if it is made of a material that does not cause deformation or quality deterioration due to heating or cooling during foam molding, a conventional suitable core can be used. You can use materials made from the following materials.

In addition, by attaching the core (N) to the molds (11) and (21),
For reliable positioning, as in the illustrated embodiment, a stepped portion (52) is formed on the flange portion (51) and the mold (11
) (21), the core (N) can be easily and reliably positioned.
If the core (N) and the dissipating mold (H) are temporarily fixed in a certain position, positioning means consisting of a fitting structure, an engagement structure, etc., can be set as appropriate depending on the overall shape and arrangement combination of the core (N) and the extinguishable mold (H). Can be adopted.

In addition, the overall shape of the core (N) and the shape of the flange part (51) are adjusted according to the shape of the disappearing mold (H) to be manufactured.
It can be changed as appropriate, and when using a core (N) with a complex shape, the core (N) can be changed as shown in Figures 5 and 6.
N) may be divided into a plurality of parts and then assembled and used as a single unit. In this case, even if there are gaps or cavities inside the core (N), they will not be exposed to the outside when attached to the molds (11) and (21), so the disappearing mold (H) There is no effect on foam molding or casting operations. In addition, in the modified example shown in FIG. 6, the flange portion (5
As for 1), we use an asymmetrical type on the left and right,
Between the mold (11) (21) and the flange part (51),
There is no problem as long as the mold cavity (4) can be configured reliably.

Next, the foam molding process of the fugitive mold (14) is carried out in the same process as the foam molding of ordinary various foam molded products, but in particular, in the heating process using steam, first the steam chamber of the mold is After supplying steam with the drain valve open to perform so-called preheating, the drain valve is closed and the pressure in the steam chamber is increased to about 0.7 to 1.21 tQ-J.
After that, the steam is stopped, the drain valve is closed, the pressure in the steam chamber is lowered to about 0.2 to 0.5 kg4, and the pressure in the steam chamber is increased again. After repeating steam heating or pressure increase several times, By stopping the cooling process and performing the cooling process using cooling water, steam heating can be performed efficiently even when the surface of the steam supply to the mold cavity (4) is reduced due to the installation of the core (N). , foam molding can be performed well.

<Effects> According to the manufacturing method of the present invention configured as described above, when manufacturing the fugitive mold (H) by foam molding, the core (N) is installed in the cavity (4j) of the mold in advance. Then, at the same time as the foam molding of the fugitive mold (U), the fugitive mold (H) and the core (N
), so in order to attach the core, as with conventional evanescent molds, the evanescent mold is molded into multiple split molds (1) and the core is sandwiched inside. This method has the following advantages compared to the method of gluing the split molds together and joining them together.

First, as a foam molded product that forms an extinguishable mold (H), there is no need to mold and manufacture multiple split molds, and the entire mold is molded in one foam molding, so molding efficiency is high, and molding equipment such as molds The molding cost is also low.

Next, since there is no need to adhesively bond the split molds, there is no need for adhesive, and there is no need for work time or work costs for the work of adhesion. Since the produced fugitive mold (H) has no adhesive surface at all, the generation of defective cast products caused by poor adhesion of the split molds, which was a big problem in the past, can be completely eliminated. It is also possible to save the effort of inspecting the bonded parts each time after manufacturing the mold (H).

Furthermore, since the fugitive mold (H) and the core (N) are integrally bonded together at the same time as the foam molding, there is no need to worry about creating gaps or cavities between them, compared to using adhesive. hand,
It has a much better integrity, and when cast, it is a fugitive type (
There is also no possibility that molten metal will flow between H) and the core (N) and cause defects in the casting. Moreover, with conventional split molds, the space for installing the core (N) must be accurately formed in the split mold, and the outer shape of the core (N) must also be formed accurately. However, with the method of this invention, even if there is an error in the outer shape of the core (N), it does not affect the integrity of the core (N) with the disappearing mold (14) at all.

Next, the placement of the core (N) with respect to the extinguishable mold (H) can be reliably set by the mounting position of the core (N) with respect to the mold H) (21), and once the split mold has been manufactured, the core (N) While adjusting the mating position with the core (N), the gap between the surfaces to be bonded can be eliminated, and the placement of the core (N) with respect to the fugitive mold (14) becomes extremely accurate.

In the method of this invention, flange portions (51) are formed at both ends of the core (N), in particular, the core (fN),
Since a mold cavity (4) is formed between this flange part (51) and the molds (11) and (21), the outer surface of the ejectable mold (N) consisting of a foamed molded product is good. If this is done, it is not necessary to finish the inner surface of the adjacent part between the vanishing mold (H) and the rod-shaped part (50) of the core (N) so precisely. In other words, when it comes into contact with the prayer sand during casting,
The shape of the cast product is composed of the outer peripheral surface of the fugitive mold (H), the rod-shaped part (50) and the 7 flange part (5) of the core (N).
1), even if there is a slight filling defect or melting defect on the inner surface of the fugitive mold () I), it will not affect the quality of the cast product at all. Therefore, the process control and working conditions for foam molding are relatively loose and simple, which is effective for increasing manufacturing efficiency.

Further, the flange portion (51) is a manufactured vanishing type (
Protect the side edges of H) to prevent the evanescent type (H) from being transported and stored.
It is possible to prevent part of the disappearing mold (H) from being chipped or deformed.

Furthermore, the flange part (51) on the core (N) side
), the mold (11) (
21) The shape of the side is simple, and the mold (11) (21)
It also has the effect of making manufacturing easier and reducing molding costs.

As mentioned above, the vanishing type (
H) can be manufactured much more efficiently and at a lower cost than conventional split molds, and the integrity and rough alignment of the core (N) and evanescent mold (H) are also extremely good. It can produce products with excellent usability and other excellent effects.

Specific Example> In order to demonstrate the effects of the invention described above, a specific dissipative type (H) was manufactured.

The molding equipment used for manufacturing was the same as that of the illustrated example, and the extinguishable mold (H) to be manufactured had an outer diameter of 90 m.
For the one with n+φ and length 5QOTIII11, the outer diameter of the rod-shaped part (50) is 50n as a sand mold core (N).
A vanishing type (H
) was manufactured with a flange portion (51) of the same shape. Therefore, the molds (11) and (21) are designed so that mold cavities (4) corresponding to the above shapes can be constructed.

After filling the mold cavity (4) of the above-described molding device with expandable polystyrene resin particles having an expansion ratio of 50 times from the filling device (3), heating was performed using steam.

As a specific steam heating process, first, with the drain valve of the mold open, steam is supplied for 5 seconds, then the drain valve is closed, and the pressure in the steam chamber inside the mold becomes 1.0 kg, J. Adjust as follows, supply steam for 15 seconds, then open the drain valve once to lower the pressure inside the steam chamber to 0.8 k (IJ), then close the drain valve again to reduce the pressure inside the steam chamber to 1.8 k (IJ).
After setting the pressure to 0 kg and J and holding it for 15 seconds, repeating the above pressure increase and decrease three times, the heating process was completed.

Then, with the steam valve closed and the drain valve opened, cooling water at a pressure of 3 kq4 was supplied for 30 seconds to perform a cold working process, and after draining, the molded extinguishable mold (14) and core ( N) was taken out.

As a result, a product with good integrity between the fugitive die (M) and the core (N), a smooth surface of the fugitive die f14), and an accurate finished shape was obtained. When performing normal investment casting using (N),
A good cast product could be manufactured, and the excellent effects of this invention could be demonstrated.

Furthermore, using the modified example core (N) shown in FIG.
When an evanescent mold (H) was produced using the same process as above, there were no 11>a particles in the cavity inside the core (N), but the finish as an evanescent mold (H) was completely different. The results of casting were also good.

[Brief explanation of drawings]

The figures show embodiments of this invention, and are shown in Figures 1 to 3.
4 is a front view of the manufactured vanishing type, and FIGS. 5 and 6 are sectional views of different modifications. (1)... Upper mold, (11)... Mold,
(2)・・・Lower mold, (21)・・・Mold,
(3)...Filling device, (4)...Mold cavity,
(H)...Disappearing type, (N)... Core,
(5o)... Rod-shaped part, (51)... Flange part, (52)... Step part.

Claims (1)

[Claims] 1. Castings made of foamed thermoplastic resin products 1. A method for manufacturing an extinguishable mold, the method comprising: At both ends of the mold matching part of the paired foam molding molds, A casting core with a flange formed on the Attach the mold and the flange of the core. A mold cavity is formed between the mold cavities, and a foaming material is Filled with thermoplastic resin particles and foam molded This foam molded by doing Integrating the vanishing mold and the core described above A method for producing an expendable mold for casting, characterized by: 2. As a core, there are steps on the flanges at both ends. This step is connected to the mold. Then, position the mold and core. Casting according to claim 1 above Manufacturing method for evanescent molds.