JPH06122038A - Vacuum molding process - Google Patents

Abstract

PURPOSE:To provide a vacuum molding process capable of manufacturing a casting cavity by forming a perfect film on a pattern in a simple process even for the pattern having thick and sharp parts. CONSTITUTION:Liquid resin for forming a film is coated on the surface of a pattern 23 and dried to form a non-permeable film 30 on the surface of the pattern 23, and a flask 33 is loaded on the film, and the refractory material powder 44 is packed in the flask. After the inside space of the flask 33 is evacuated, the porous pattern 23 is separated to make a casting cavity. In manufacturing the casting cavity where the non-permeable film 30 is coated on the surface of the pattern 23, the refractory material powder 44 is packed in the flask 33 loaded on the periphery of the film, the packed part is wrapped with the non-permeable film 45, the part where the refractory material is packed within the flask 33 is evacuated, and the part is separated from the pattern 23, the non-permeable film 30 to be coated on the surface of the pattern 23 is formed by coating the adhesive composed of the adhesive resin and drying it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduced pressure molding method for forming a casting cavity by utilizing a reduced pressure.

[0002]

2. Description of the Related Art A conventional casting mold manufacturing method is shown in FIG.
There is a vacuum molding method as shown in FIG. The outline of the method is described below. In producing the mold, first, as shown in FIG. 1, a porous model 1 having pores 2 at various places on the surface and communicating with a cavity 3 inside is prepared. Then, the plastic film 4 is held above the model 1, and the film is heated by the heater 5 to descend, the cavity 3 under the model is decompressed, and the plastic film 4 is placed on the surface of the model 1. To suck. Since the plastic film 4 is increased in plasticity by heating, as shown in FIG. 2, the model 1 is attached to the surface of the model 1 so as to wrap it by the suction force due to the above-mentioned decompression, and is cooled along the model surface by cooling. Form a breathable membrane.

On the periphery of the model 1 is the film 4
2 is placed in a state of being molded, and dry sand 9 as a refractory powder is filled on the molded film in the upper frame 6 as a refractory powder. The upper frame 6 is provided with a hollow portion 7 inside and a suction pipe 8 located at an inner side surrounded by the upper frame 6 and having an end communicating with the hollow portion 7. The suction pipe 8 sucks the air in the upper frame 6 by depressurizing the hollow portion 7, but is wound with a fine wire mesh so as not to suck the sand 9 during the suction.

After the sand 9 is densely filled in the upper frame 6 by vibration or the like to smooth the surface, as shown in FIG. 3, the non-breathable backside film 10 is placed on the upper frame 6 and the sand 9 filled therein.
And wrap the sand 9 with a non-permeable membrane. Then, the hollow portion 7 of the upper frame is decompressed, and the portion of the frame filled with the dry sand 9 is decompressed through the suction pipe 8. As a result, a vacuum-packed sand mold is formed, and the upper mold is completed by removing it together with the upper frame 6 from the model 1. A lower mold is manufactured in the same manner, and a cavity for casting is formed by combining the upper and lower molds 11 and 12 as shown in FIG.

The above conventional reduced-pressure molding method is an excellent molding method that does not require a binder or the like in addition to the sand 9 in the molding process, and can easily remove sand even in the mold releasing process after casting. is there. Furthermore, since the flow of molten metal is good, even complicated shapes can be manufactured with good yield. However, in the process of sticking the film 4 onto the model 1, the film 4 must be heated in order to impart plasticity to the film 4, and the heating of the film 4 is uneven, or the film 4 is extremely heated. When there is a sharp edge portion, the film 4 may be partially stretched and torn or cut at a corner portion. Furthermore, when the thickness of the model 1 is partially increased, the film 4 may not be fully extended and may be damaged, and there is a limit to the change in the thickness of the model. Further, the film sticking process is often difficult to automate, and usually requires manual work. Therefore, the application field of the vacuum molding method up to now has been limited to the case where the plane has a complicated shape such as a window frame for sash, a gate, or a manhole cover.

[0006]

The technical object of the present invention is to provide a non-breathable film to be formed on a model for the above-mentioned vacuum molding, even when the model is partially thick or has an acute angle portion. By simple means that can be easily automated,
Moreover, it is to be possible to form a complete and substantially uniform film on a model with as few steps as possible.

[0007]

A first vacuum molding method of the present invention for solving the above-mentioned problems is a frame in which a non-breathable film is attached to the surface of a model and placed on the periphery of the film. After filling the inside with refractory powder and encapsulating it with a non-breathable film, depressurizing the refractory-filled part in the frame, and then releasing from the model to produce a casting cavity. In the above, the non-breathable film adhered to the surface of the model is formed by applying an adhesive agent made of an adhesive resin to the surface of the model and drying the film.

In the second vacuum molding method of the present invention, in the vacuum molding for manufacturing the above-mentioned casting cavity, the non-air-permeable film adhered to the surface of the model, the low-viscosity resin and the refractory fine powder are used. The mixed pressure-sensitive adhesive is applied to the surface of the model and formed by drying it. Furthermore, the third vacuum molding method of the present invention is the same vacuum molding, in which the surface of the model is coated. The non-air-permeable film is formed by applying a photocurable resin to the surface of the model while irradiating it with ultraviolet rays and rapidly curing it.

According to the above-described reduced-pressure molding method, the surface of the model is coated with a pressure-sensitive adhesive made of an adhesive resin or the like and dried to form an impermeable film, so that the model is partially thickened. ,
Or even if it has an acute angle part, a non-breathable film can be formed on the model as a complete and almost uniform film by a simple means that can be easily automated, and with as few steps as possible. It is possible to easily manufacture a large casting cavity. Also, when applying a resin for forming a non-breathable film on a porous model,
There is a case where the resin does not form the film by soaking into the model, but the above method also addresses such a problem, without using a resin that has a high viscosity to prevent soaking and is difficult to spray and apply. , Which has a low viscosity and is capable of preventing penetration.

The method of the present invention will be described more specifically with reference to FIGS. 5 to 7. In any of the first to third vacuum molding methods, first, as shown in FIG. A closed box-shaped jig 21 having a through hole 22 and an open top is prepared. The model 23 made of a porous material, which is the original form of the casting, is placed on the jig 21. The material of the porous model is metal, plastics, artificial wood, etc.
Various materials can be used, but it is necessary that the back surface of the model has air permeability, and it is desirable that the holes are fine and uniformly dispersed. The breathability of this model facilitates the release of the non-breathable film at the time of die-cutting described later. In addition, on the model 23, a runner 25 and, if necessary, a riser 26 or a riser is set up. Further, a resin collar 27 is fitted on the rise 26 or the upper part of the riser.

Next, the non-breathable film 3 is formed on the entire surface of the model 23.
Although a resin or the like for forming 0 is applied, in the first vacuum molding method described above, an adhesive resin is used as the spray gun 31.
Spray coating or brush coating. Then, the non-breathable film 30 is formed by drying the coating film. Examples of the adhesive resin include polystyrene dissolved in toluene, acrylic dissolved in acetone, and silicone resin to which an appropriate curing accelerator is added.

When these resins are applied onto the porous model 23, the resin may soak into the model and the film may not be formed. In this case, it is necessary to prepare a resin with high viscosity so that it does not soak into the model,
If the viscosity is high, spray coating is difficult. To cope with such a problem, the inventors of the present invention use a resin having a low viscosity, and a finely mixed refractory powder made of ceramics such as alumina, and well agitated the resin, so that the resin inside the model is It has been confirmed that it can prevent the soaking in.

In the second reduced-pressure molding method, the pressure-sensitive adhesive obtained by mixing refractory fine powder with such a low-viscosity resin is applied to the surface of the model 23 and dried to dry the non-permeable film 30.
Is characterized in that As the low-viscosity resin, used is polystyrene dissolved in toluene, acrylic dissolved in acetone, or silicone resin added with an appropriate curing accelerator, which is suitable for use in the first vacuum molding method. However, by increasing the amount of these solvents, the viscosity is lowered so that spray coating is possible. Also, the film 3 molded with this resin
Since 0 also serves as a coating material during casting, it has been confirmed that the skin of the casting is extremely beautiful. The resin may be overcoated if necessary.

In order to prevent the resin from soaking into the inside of the porous model 23, the third vacuum forging method is also effective. In this case, a photo-curable resin is used in place of the above resin, which is applied by spraying or brushing while irradiating with ultraviolet rays to rapidly cure. As a result, the film 30 can be formed without allowing the resin to soak into the model 23.

After forming the film 30, the film 3 is formed as shown in FIG.
The frame 33 is placed on 0. The frame 33 is provided with a sand inlet 34 on its upper surface, and holes are formed in the rising 35, the sprue 36, and the like. Further, a hollow portion 37 communicating with the suction port 38 on the side surface is provided inside, and a suction pipe 39 having a wire mesh whose end communicates with the hollow portion 37 is provided in the inner space surrounded by the frame 33. On the other hand, on the runner 25, a film 3 made of a porous material is used on the surface of the model, like the model.
The sprue 36 having a membrane integrated with 0 is placed. A resin-made collar 42 is fitted to the sprue 36 similarly to the collar 27, and the collars 27 and 42 are arranged so as to be located in the holes provided on the upper surface of the frame 33.

Next, dry sand 44 of refractory powder is added to the sand inlet 3
4 to fill the inside of the frame 33. At this time, while applying vibration to the frame 33, the dry sand 44 is completely filled up to the height of the brims 27, 42, and thereafter, as shown in FIG. The back film 45 is attached to the opening of the. The back film 45 is overlapped with the collar at a portion where the collar is provided, such as a sprue or a feeder. Then, suction is performed from the suction port 38 of the frame 33, and the suction pipe 3
The dry sand filling portion in the frame is depressurized through 9 to solidify the dry sand into a vacuum packed state. After that, the mold solidified in the vacuum packed state is released from the model 23 as shown in FIG. 7 to obtain a casting cavity.

If the resin film 30 and the model 23 are in close contact with each other at the time of this mold release, a vacuum is created between the surfaces of the film 30 and the model 23, and not only the mold release is possible but also the film 30 may be damaged. Furthermore, the film 30 shrinks when the resin is dried, and the model 2
If it sticks to 3, it cannot be released. Therefore, a porous model 23 having air permeability is used, and the through hole 2 of the jig 21 is used at the time of mold release.
The mold is released while supplying pressurized air from 2. When pressurized air is supplied, the air passes through the fine pores of the porous model 23 and pushes the membrane 30 from the back side, so that the mold can be easily released. Of course, when the resin is applied onto the porous model 23, the release material may be applied in advance. In the same manner as the above steps, the lower mold is also pressure-reduced, and the upper and lower molds are overlapped with each other to manufacture the casting cavity.

As described above, since the resin is applied and then dried to form the film, the film can be completely and evenly formed on the entire surface of the model even if the model is partially thick or has an acute angle portion. Further, unlike the conventional example, since there is no step of heating and sucking the film, the film can be easily formed and can be easily automated.

[0019]

EXAMPLE An example of the vacuum molding method of the present invention will be described below. The model used is porous artificial wood, 40x40x
It is a 50 mm rectangular parallelepiped. As the adhesive resin, polystyrene was dissolved in toluene, and alumina fine powder having a particle size of 1 μm or less was added thereto and sufficiently stirred, and then sprayed onto the surface of the model. The coating thickness after drying is 0.1 to 0.2 m
It was m. Further, as a device for manufacturing the casting cavity, a device substantially similar to that described in FIGS. 5 to 7 was used.

The dry sand used is No. 6 silica sand. Tsuba is
It was made of polystyrene having a thickness of 0.3 mm, and the back film was also made of polystyrene. The vacuum degree of the applied vacuum molding is 300 to 400 Torr, and if the vacuum degree is higher than this, there is a risk that the coating film will be damaged. Further, since the coating film adheres to the model and cannot be released at the time of mold release, a positive pressure of 0.1 kg / cm ² was applied from the cavity of the jig to separate the model surface from the coating film, and then the mold was released. When a cast iron molten metal was cast using this mold, a casting having an extremely clean skin was obtained.

[0021]

As described above, in the method of the present invention, the non-breathable film is formed on the model by applying the resin for film formation and drying, so that the model is partially thick, or Even if it has a sharp angle, it can be formed as a complete and almost uniform film on a model by a simple means that can be easily automated, and with as few steps as possible, and a highly reliable film is obtained overall. be able to.

[Brief description of drawings]

FIG. 1 is a cross-sectional view shown for explaining a mode of forming a film on a model in a conventional example.

FIG. 2 is a cross-sectional view showing a state where the upper frame is filled with dry sand subsequent to the formation of the film according to FIG.

FIG. 3 is a cross-sectional view showing a vacuum packed state of the dry sand.

FIG. 4 is a cross-sectional view of the manufactured upper and lower molds.

FIG. 5 is a cross-sectional view showing an aspect of forming a film on a model in the method of the present invention.

6 is a cross-sectional view showing the filling state of dry sand into the frame following the formation of the film according to FIG.

FIG. 7 is a cross-sectional view showing a released state of a molded die.

[Explanation of symbols]

 23 model, 30 non-breathable membrane, 33 frame, 44 refractory powder, 45 non-breathable membrane.

Claims (3)

[Claims] 1. A non-breathable film is adhered to the surface of a model, refractory powder is filled in a frame placed on the periphery of the model, and the frame is covered with the non-breathable film. After depressurizing the refractory-filled part in the mold, in a depressurization molding for releasing the mold from the above model to manufacture a casting cavity, a non-air-permeable film adhered to the surface of the model is formed by a pressure-sensitive adhesive made of an adhesive resin. Is applied to the surface of a model and is then dried to form a reduced-pressure molding method. 2. A non-breathable film is adhered to the surface of the model, refractory powder is filled in a frame placed on the periphery of the model, and the refractory powder is covered with the non-breathable film, and then the frame is formed. After depressurizing the refractory-filled part in the mold, in the depressurization molding for releasing the mold from the model to manufacture the casting cavity, the non-breathable film adhered to the surface of the model is a low-viscosity resin with refractory fine powder. Apply the mixed adhesive to the surface of the model,
A reduced-pressure molding method characterized by forming by drying it. 3. A non-breathable film is adhered to the surface of the model, refractory powder is filled in a frame placed on the periphery of the model, and the frame is covered with the non-breathable film, and then the frame is formed. After depressurizing the refractory-filled part in the mold, in a depressurization molding for releasing the mold from the above model to manufacture a cavity for casting, a non-air-permeable film adhered to the surface of the above model is irradiated with a photocurable resin by ultraviolet rays. Meanwhile, the reduced-pressure molding method is characterized in that it is formed by applying it to the surface of the model and rapidly curing it.