JPH10272539A - Manufacture of core made of low melting point metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a bag-shaped hollow lost core by pressurizing the molten metal of low melting point in a holding furnace so as to be elevated in a nozzle, filling the molten metal in a cavity of a die arranged on an upper part of the nozzle, stopping the pressurization when only the molten metal at a wall surface part in the cavity is solidified, and introducing the gas from the upper part of the nozzle. SOLUTION: A die 7 is closed, a piston rod 10 of a cylinder 9 is contracted to closely attach an upper end part of a nozzle 4 to a gate 12 of a die 7. The inside of a holding furnace 1 is pressurized with the compressed gas, and the molten metal 2 is pushed up into a die cavity 14 so as to be filled. Pressurization is kept for the prescribed time, only the molten metal 2 in contact with the die 7 is solidified to release the pressurization. The piston rod 10 is expanded to release the tight attachment of the upper end part of the nozzle 4 to the gate 12. The atmospheric air enters through the clearance between the two, and the unsolidified molten metal 2 in the die cavity 14 is returned into the holding furnace 1. When the cooling is completed, the die 7 is opened and a hollow product is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low-melting metal core used for molding plastic.

[0002]

2. Description of the Related Art A plastic product may have a hollow portion or an undercut shape in terms of function or integration of components. It is generally difficult to integrally mold a plastic product having such a shape, and various attempts have been made in molding. One of them is to use a lost core. This makes a core of a low melting point alloy with the same internal shape as the hollow part and the undercut part of the product, that is, a lost core, set it in a mold for plastic molding, mold plastic around the core, Later, the lost core is eluted to obtain a product having a predetermined shape. This lost core is often made by casting with an alloy made of Bi, Sn, Pb or the like. However, when an attempt is made to produce a large plastic product, the lost core becomes large and the weight becomes very heavy, which makes it difficult to handle and takes a long time to elute.

[0003] The present applicant has proposed in Japanese Patent Application Laid-Open
A method for producing a low-melting metal core as disclosed in Japanese Patent No. 38761 was developed. The method aims to reduce the weight by hollowing the lost core, and more specifically,
With the loose piece with a built-in heater fitted and inserted into the ceiling of the mold, the molten metal of the low melting point metal in the holding furnace is pushed up to the cavity of the mold via the stalk, and casting is performed. While maintaining the predetermined time, the unsolidified molten metal is left in the central portion to cancel the push-up casting of the molten metal, and the loose piece is extracted from the ceiling of the mold to return the unsolidified molten metal to the holding furnace.

However, the above method is suitable for casting a cylindrical lost core having both ends opened. However, when casting a bag-shaped product having only one end opened, pressurization is required during the solidification of the molten metal. Even when it is released, the outer periphery of the lost core is solidified, so it is difficult for air to enter the stalk from the outside (gap between molds), and it is difficult for unsolidified metal to return to the holding furnace, and the return timing is not constant. . For this reason, there was a problem that a stable hollow product was not obtained. If it does not become a stable hollow product, the wall thickness of the lost core will not be constant and it will not be able to withstand the molding pressure when molding plastic,
There is a problem that the elution conditions after molding are not constant and automation is difficult to achieve.

[Problems to be solved by the invention]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for casting a stable hollow product even when casting a bag-shaped lost core having only one end opened. The purpose is.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the present invention pressurizes a molten metal of a low-melting point metal in a holding furnace, raises the molten metal in a stalk, and fills the cavity of a mold disposed on the stalk with a metal. The method is characterized in that the pressurization is stopped when only the molten metal on the inner wall surface of the cavity solidifies, and at the same time, gas is introduced into the stalk from above the stalk.

[0007]

Embodiment 1 Hereinafter, a first embodiment of the present invention shown in the drawings will be described. FIG. 1 is a longitudinal sectional view of a main part of a low-pressure casting apparatus for implementing a method for producing a low-melting metal core according to the present invention.
In the figure, reference numeral 1 denotes a closed holding furnace.
The molten metal 2 is maintained at a constant temperature by a temperature detecting means (not shown) and a heater 3 whose temperature is controlled by a control device. Reference numeral 4 denotes a stalk. The lower part of the stalk 4 is immersed in the molten metal 2 in the holding furnace 1 and the upper part thereof penetrates the holding furnace 1 and protrudes upward. A mold 7 composed of an upper mold 5 and a lower mold 6 is mounted on the die base 8 above the stalk 4 and is arranged on the die base 8.
Is supported by an upwardly directed cylinder 9, and can be moved up and down by an expansion and contraction operation of a piston rod 10 of the cylinder 9.

The upper end of the stalk 4 relatively rises in a through hole 11 penetrated through the center of the die base 8 so as to be in pressure communication with the gate 12 of the mold 7. The pressing force between them is adjusted by the expansion and contraction operation of the piston rod 10 of the cylinder 9.
In the holding furnace 1, a piping 1
3, compressed air is supplied, and the compressed air pressurizes the inside of the furnace 1 to push up the molten metal 2 through the stalk 4 into the cavity 14 of the mold 7.

In the apparatus constructed as described above, the mold 7 is closed by a mold opening / closing mechanism (not shown), and then the piston rod 10 of the cylinder 9 is contracted and the upper end of the stalk 4 and the gate of the mold 7 are opened. 12 are crimped. Next, the inside of the furnace 1 is pressurized with a compressed gas by a control device (not shown),
The molten metal 2 is pushed up and filled into the mold cavity 14. After the pressurization is maintained for a predetermined time, the pressurization is released and the piston rod 10 of the cylinder 9 is extended to release the pressure contact between the upper end of the stalk 4 and the gate 12 of the mold 7. And the unsolidified metal 2 in the mold cavity 14 and the stalk 4 returns to the holding furnace 1 due to the atmospheric pressure. When the product is sufficiently cooled in the mold 7, the mold 7 is opened and the product is taken out.

Using the above apparatus, low melting point metal 2 (Sn)
43 wt% -Bi 57 wt% alloy: mp 138
C.) in the holding furnace 1 at 180 ° C., pressurizing the inside of the furnace 1 with compressed air, filling the mold 7 having a mold temperature of 50 ° C. and pressurizing for 30 seconds, then releasing the pressing force The pressure bonding between the Stoke 4 and the gate 12 of the mold 7 was released, and the unsolidified low melting point alloy was returned into the furnace 1. When the molten metal 2 is filled in the entire cavity 14 and solidified, the weight becomes 10 kg. In the method of the present invention, a hollow lost core having a very small variation in weight of 7.2 ± 0.2 kg was obtained. When a plastic product was molded with the obtained lost core, it could be molded stably without any problem of deformation.

[0011]

Embodiment 2 FIG. 2 shows another low-pressure casting apparatus for realizing a casting method according to the present invention. The apparatus supports the holding furnace 1 with an upwardly directed cylinder 15, and allows the holding furnace 1 to be moved up and down by an extension operation of a piston rod 16 of the cylinder 15, so that the pressing force between the upper end of the stalk 4 and the gate 12 of the mold 7 is increased. The apparatus is the same as that of the first embodiment except that it can be increased or decreased. Except for reducing the pressure between the upper end of the stalk 4 and the gate 12 of the mold 7 until the pressurization in the holding furnace 1 is released by using the device, the unsolidified metal does not leak. When the product was cast in the same manner as in Example No. 1, 7.2 ± 0.
A hollow lost core with a very small variation in weight of 25 kg was obtained.

[0012]

Third Embodiment FIG. 3 shows another low-pressure casting apparatus for realizing the casting method according to the present invention. The apparatus fixes both the holding furnace 1 and the mold 7, completely seals the connection between the upper end of the stalk 4 and the gate 12 of the mold 7, and installs a gas introduction valve 17 above the stalk 4. Atmosphere is introduced into the Stoke 4 via the valve 17. Using this apparatus, low melting point metal 2 (Sn4
(3wt% -Bi 57wt% alloy: melting point 138 ° C)
Is held in a holding furnace 1 at 180 ° C., the inside of the furnace 1 is pressurized with compressed air, filled into a mold 7 having a mold temperature of 50 ° C., pressurized for 30 seconds, and then the pressure is released and the stalk 4 is released. The upper gas introduction valve 17 was opened, the atmosphere was introduced into the Stoke 4, and the unsolidified low melting point alloy 2 was returned into the furnace 1. As a result, a lost core similar to that of Example 1 was obtained. In the present embodiment, the gas introducing valve 17 is mounted on the upper part of the stalk 4. However, the gas introducing valve 17 may be mounted on the gate 12 side of the mold 7 as long as the effects of the present invention are not hindered.

[0013]

[Comparative Example] For comparison, an apparatus in which both the holding furnace and the mold are fixed, the connection between the upper end of the stalk and the gate of the mold is completely airtight, and a gas introduction valve is not attached to the stalk. When cast, the weight is 7.5 ± 0.8k
A hollow lost core having a large variation with g was obtained. When a plastic product was injection-molded with the lost core, a light-weight product was partially thinned, and could not withstand the pressure of the injection molding and was deformed, resulting in a defective product.

[0014]

As is clear from the above description, the present invention provides a method for controlling the pressure between the upper end of the stalk and the gate of the mold, or providing a gas introduction valve in the stalk, and thereby providing air in the stalk. And the unsolidified metal is returned to the holding furnace at a predetermined timing. According to the present invention, a stable hollow product can be obtained even when a bag-shaped lost core having only one end opened is cast, plastic molding is stabilized, and the dissolution can be easily automated. In this embodiment, the casting is performed by low-pressure casting. However, as long as the effects of the present invention are not impaired, not only low-pressure casting but also suction casting, pressure casting using a plunger, or a combination thereof may be used. In the embodiment of the present invention, the atmosphere is used as the introduced gas, but an inert gas such as argon or nitrogen may be used. Thereby, oxidation of the unsolidified metal inside the stalk is suppressed, and the surface shape of the product is improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a low-pressure casting apparatus for carrying out a method of the present invention.

FIG. 2 is a longitudinal sectional view of a main part of another low-pressure casting apparatus for carrying out the method of the present invention.

FIG. 3 is a longitudinal sectional view of a main part of still another low-pressure casting apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Holding furnace 2 Molten metal 4 Stoke 7 Mold 12 Gate 17 Gas introduction valve

Claims (4)

[Claims] 1. A low melting point metal melt (2) stored in a holding furnace (1) is pressurized to rise in a stalk (4).
A method for producing a low-melting-point metal core, in which the molten metal 2 is filled in a cavity 14 of a mold 7 disposed at an upper portion and molded, wherein the cavity of the molten metal 2 filled in the cavity 14 of the mold 7 is 14. A method for producing a low-melting metal core, wherein the pressurization is stopped when only the molten metal 2 on the inner wall portion solidifies, and a gas is introduced into the stalk 4 from above the stalk 4 at the same time. 2. The gas is introduced into the stalk 4 by lifting the mold 7 and releasing the pressure between the gate 12 of the mold 7 and the upper end of the stalk 4. The method for producing a low melting point metal core according to claim 1. 3. The gas is introduced into the stalk 4 by lowering the holding furnace 1 to release the pressure contact between the gate 12 of the mold 7 and the upper end of the stalk 4. The method for producing a low melting point metal core according to claim 1. 4. The production of a low melting point metal core according to claim 1, wherein the gas is introduced into said stalk 4 via a gas introduction valve 17 provided in said stalk 4. Method.