JPS61135449A - Manufacture of sprue of vacuum casting mold - Google Patents

Abstract

PURPOSE:To prevent the intrusion of sand into a product part in the stage of casting in a vacuum casting mold which consists of silica sand for molding coated with a plastic film by forming the cavity for the sprue prior to charging of the silica sand in the stage of forming separately the cup and bar of the sprue. CONSTITUTION:The sprue bar 21 is formed integrally with the pattern 22 and after the film is formed, the sprue cup 21' enveloped by the film is lowered to be brought into tight contact with the bar 21. A heater 30 is contained in the cup 21' to melt-cut the tightly adhered film and at the same time to weld the films at the outside circumferential part to each other. A molding flask is set and the silica sand for molding is put into the flask and is molded, then the cup 21' is raised and a top surface film is put on. The inside of the flask is then sucked to a negative pressure. The sprue cavity is thus formed prior to putting of the silica sand for molding into the flask in the above-mentioned manner, by which the danger for the intrusion of the sand to the mating faces 20 of the film is eliminated and therefore the intrusion of the sand into the product part is obviated.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in casting manufacturing technology.

There is a depressurization method for making molds for foundries, and it has been put into practical use in recent years.One of these methods is to cover silica sand for molds with a plastic film, and to create molds by sucking up the silica sand inside with a vacuum pump. There is a molding method to make it.

This mold has a high mold hardness due to the pressure difference inside the mold, and if the pressure difference can be maintained by the ventilation holes that can supply outside air to the product cavity during casting, even if the film is burnt out, it will remain healthy and have a beautiful appearance. It has the characteristic of being able to be cast.

[Conventional technology]

Conventionally, in castings using this method, as shown in Figure 1, the sprue part 1 is made separately from the model 2, and when the upper mold is made, it is fitted into the model 2 via pins etc. and molded integrally with the film 5. .

Then, after setting the casting flask 4, silica sand 5 for molding is put into the casting flask 4.
is vibrated, and after molding, a film 6 is covered on the upper surface, and the inside of the mold is suctioned with a vacuum pump. Next, the suction on the suction box 7 side is stopped and the model 2 is separated from the mold. The sprue part 1 has a cup O (there is a cup O), so when releasing the mold, it separates from the model 2 and enters the mold.
Then, the film 6' on the upper surface is cut by melting, and the sprue is pulled out upward.

However, with this method, each time the upper mold is manufactured, the film must be cut, the sprue removed, and then set again, making the movements complicated on high-speed lines and not easy to automate. For this reason, a method has been adopted in which the sprue part is formed into a cup and a rod separately.

The method is disclosed in Patent Publication No. 56-71554,
As shown in the figure, the sprue rod 11 is joined to the model 12, and after integral molding, a casting flask is set. Then, after lowering the sprue cup N' so that it comes into close contact with the sprue rod 11, pour in the silica sand for the mold, and then put the sprue cup 11' back up with vibration to increase the filling rate. This method involves covering the mold with a film and creating negative suction pressure inside the mold.

As a result, the sprue cavity is located at the mating surface 10 of the cup and rod.
The films overlap and stick together.

In this composite image, the inside of the bus is melted with heat so as to leave the surrounding area intact.
Sometimes molten metal is cast directly into the mold.

[Problem that the invention seeks to solve]

If the sprue cup and the sprue rod are separately film-molded as described above, automatic molding becomes easier than when they are integrally molded.

However, the problem here is that there is a risk that sand may enter the cup-rod mating area 10 and be caught in the product cavity during casting.

[Means and Embodiments for Solving the Problems] The present invention attempts to improve the problem in order to prevent the entrainment of sand.

An example thereof is shown in FIG. After the sprue rod 21 is integrated with the model 22 to form a film, the sprue cup 21' wrapped in the film is lowered and brought into close contact with the sprue rod 21.

A heater 50 is built into the sprue cup H', and at the same time melts and cuts the films that are in close contact with each other, it also welds the external films together. Next, after setting the casting flask, pour in silica sand for molding, raise the hot water cup after molding, cover the top with a film, and apply negative suction pressure. By forming the sprue cavity before introducing the silica sand for casting, there is no risk of sand getting mixed into the film mating surface 20, so that it will not get caught up in the product section.

The burnt residue of the fused film is removed from the sprue cup 21.
It is sufficient to discharge the liquid through the internal gap through a suction medium (not shown).

〔Effect of the invention〕

With the above-mentioned measures, it is possible to obtain excellent castings without entrainment of sand when manufacturing castings using the vacuum molding method.

[Brief explanation of drawings]

Figures 1, 2, and 5 are all schematic cross-sectional views during molding, with Figure 1 being an example of integral molding of the sprue part, Figure 2 being an example of molding the sprue cup and sprue rod separately, and Figure 5. The figure shows an example of the present invention in which the sprue cup and sprue rod are separately molded. 1: sprue part, 2, 12, 22: model, 5.15: film, 4: casting flask, 5: silica sand for mold, 6, 6#, 16:
Top film, 7: Suction box, 8: Suction pipe, 1
0.20: Film mating surface, 11.21: Sprue rod,
11', 21': sprue cup, 50: handle. 2nd rA

Claims (1)

[Claims] When molding the sprue cup and sprue rod separately in the upper mold of the vacuum molding mold, the outside of which is covered with a plastic film and a casting flask, and the inside of which is kept under negative pressure, the mold surface on which the sprue rod is placed is first heated. Next, the sprue cup covered with the film is lowered onto the sprue rod, and the upper and lower films in contact are cut by heat, and at the same time, the periphery is welded to the thickness of the sprue rod. A sprue manufacturing method for a vacuum mold mold, which is characterized in that a cavity is formed, then silica sand for molding is poured in, and a negative pressure is applied to obtain a mold.