JPH07308752A - Method for removing low melting metal core - Google Patents

Abstract

PURPOSE:To easily remove a low melting metal core without receiving any restriction in the position and shape of the low melting metal core in a cast product by immersing the cast product contg. the low melting metal core into a salt bath in which nitrates are melted by heating, thereby dissolving away the low melting metal core. CONSTITUTION:The liquid salt bath 3 is prepd. by putting a mixture composed of sodium nitrate and potassium nitrate into a dissolving away vessel B and melting the mixture by heating. The temp. of the salt bath 3 of the nitrates is set higher by plus 50 deg.C than the m.p. of the low melting metal core 1 to be eluted. The cast product A contg. the low melting metal core 1 is directly heated by the salt bath 3 of the nitrates and simultaneously the low melting metal core 1 in the cast product A is heated by coming partly into direct contact with the nitrates 3 when the cast product A is immersed into the nitrates 3. Consequently, the low melting metal core 1 in the cast product A is rapidly dissolved and is eluted from the core taking-out part 2 of the cast product A into the dissolving away vessel B and is thus removed from the cast product A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a removing method for removing a low melting metal core inside a cast product cast using a low melting metal core.

[0002]

2. Description of the Related Art Conventionally, when removing a low melting point metal core from a casting product containing a low melting point metal core, the casting product is conventionally placed in a hot blast stove or immersed in a heat transfer oil tank, or at a high frequency. By using a heating coil, the low melting point metal core inside is dissolved and removed.

However, when a hot-air stove is used, the core material that has been eluted falls everywhere in the furnace and its recoverability is poor, and when a heat-medium oil tank is used, harmful gas is generated during use. Not only is it generated, it takes time and effort to remove the heat transfer oil adhering to the cast product, which deteriorates productivity, and when using a high frequency heating coil, there are many restrictions due to the position and shape of the core material, There was such a problem.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is not restricted by the position or shape of the low melting point metal core inside the cast product. It is intended to provide a method for removing a low-melting point metal core, which enables easy removal of the low-melting point metal core and easy recovery of the removed low-melting point metal core.

[0005]

The method for removing a low-melting-point metal core according to the present invention, which achieves the above objects, is a casting product containing a low-melting-point metal core in a salt bath prepared by heating and melting a nitrate. It is characterized in that the low melting point metal core is dissolved and removed by immersing in, and the nitrate is composed of sodium nitrate and potassium nitrate.

[0006]

Embodiments of the present invention will be described below with reference to the schematic drawings. In the figure, A indicates a casting product containing the low-melting-point metal core 1, and a core take-out portion 2 for removing the low-melting-point metal core 1 inside is formed in a part thereof.

As the low melting point metal core 1 to which the present invention is applied, a low melting point metal such as lead, tin, zinc alloy, antimony alloy or the like or a desired shape thereof is used as in the conventional case. Is formed.

Further, as the casting product A cast using the low melting point metal core 1, a product cast by a conventionally known casting method such as a die casting casting product or a low pressure casting product can be used. .

As the nitrate used in the present invention, one or a mixture of two or more selected from sodium nitrate, potassium nitrate, sodium nitrite, potassium nitrite and the like is used. From the viewpoint of safety and handling, sodium nitrate and potassium nitrate are used. It is preferred to use a mixture of When used, the nitrate is heated and melted to form a liquid salt bath 3.

At this time, since the temperature of the salt bath suitable for use can be obtained by the mixing ratio of sodium nitrate and potassium nitrate, the mixing ratio of sodium nitrate and potassium nitrate is adjusted according to the target low melting metal core 1. . In particular,
Sodium nitrate is 55-60% and potassium nitrate is 40%.
When mixed at a ratio of ~ 45%, the temperature of the salt bath could be stabilized in the range of 330 to 550 ° C.

The dissolution removal tank B for accommodating the salt bath 3 of nitrate is composed of a well-known electric furnace 4 and an iron pot 5.

Then, a mixture of sodium nitrate (55-60%) and potassium nitrate (40-45%) is placed in the dissolution removal tank B and heated and melted to form a liquid salt bath 3, and the salt of the nitrate salt is added. The temperature of the bath 3 is set higher by about 50 ° C. than the melting point of the low melting point metal core 1 to be eluted.

When all or part of the cast product A containing the low-melting-point metal core 1 is immersed in the salt bath 3 of nitrate, the cast product A is directly heated by the salt bath 3 of nitrate. At the same time, the low melting point metal core 1 inside the cast product A
Is heated in direct contact with the nitrate salt bath 3. As a result, the low-melting-point metal core 1 inside the cast product A is rapidly melted, and the melt removal tank B is removed from the core take-out part 2 of the cast product A.
It melts in and is removed from the cast product A. The low-melting-point metal core melted out in the dissolution removal tank B does not dissolve in the salt bath 3 and naturally falls to the bottom of the dissolution removal tank B by its own weight.

When the cast product A is put into the dissolution removal tank B, as shown in the drawing, a nitrate salt is suspended in a state in which the core take-out portion 2 of the cast product A is on the lower side and is suspended by a suspender 6. Bath 3
It is preferable to immerse in. Then, casting product A
The low-melting-point metal core 1 that has melted out of the molten metal is prevented from settling and accumulating at the bottom of the dissolution removal tank B and reattaching to the cast product A.

After a lapse of a predetermined time, the casting product A is pulled up from the dissolution removing tank B and the casting product A is washed with water. The remnants of the melting point metal core 1 as well as the coating agent and the like are peeled off and discharged from the core take-out section 2.

[0016]

INDUSTRIAL APPLICABILITY According to the present invention, a casting product containing a low melting metal core is thus immersed in a salt bath of nitrate to dissolve and remove the low melting metal core inside the casting product. Therefore, the following effects are achieved.

The low melting point metal core inside the cast product can be eluted in a short time. That is, since the cast product and the low melting point metal core are in direct contact with a high temperature (400 ° C. to 550 ° C.) salt bath, heat conduction is improved, and as a result, the low melting point metal core inside the cast product is eluted in a short time. It can be done. By the way, when an elution experiment of a low-melting-point metal core was conducted using the same casting product, it took 1 minute by the method of the present invention and 25 minutes by a hot-air stove to elute the low-melting-point metal core inside. It was impossible with the medium oil (it did not melt because the melting point of the low-melting metal core used was high), and with the high-frequency heating coil, it was 2 and a half minutes.

The low-melting-point metal core dissolved and removed from the inside of the cast product does not mix and mix with the salt bath of nitrate and settles and accumulates at the bottom of the melt-removal tank, so that it does not adhere to the cast product again. At the same time, it can be easily recovered.

The nitrate adhering to the cast product can be easily removed by washing with water together with the remains of the low-melting metal core remaining inside the cast product, a coating agent, etc., and post-treatment becomes easy.

When a mixture of sodium nitrate and potassium nitrate is used as the nitrate, it is easy to handle, does not volatilize harmful gases, etc., and can be safely operated without special equipment.

Since the immersion time in the salt bath can be shortened, thermal adverse effects on the cast product (such as swelling and decrease in hardness) can be reduced.

The elution residue of the low melting point metal core into the casting product is very small. That is, the heat of the salt bath is constantly transferred to the low-melting metal core, and the low-melting metal core inside the cast product can be efficiently eluted. Since it does not settle to the bottom of the alloy and redeposit on the cast product, the elution residue of the low-melting-point metal core becomes very small. By the way, when the elution residue test of the low melting point metal core was performed using the same casting product, the elution residual amount of the low melting point metal core was 3% in the method of the present invention, 8% in the hot stove, It was impossible with oil (not eluted due to the high melting point of the low-melting metal core used), and 10% with the high-frequency heating coil.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating a method according to the present invention.

[Explanation of symbols]

 A: Cast product B: Melt removal tank 1: Low melting point metal core 2: Core removal part 3: Salt bath 4: Electric furnace 5: Iron pot 6: Hanging tool

Claims (2)

[Claims] 1. A method for removing a low melting point metal core from a casting product containing a low melting point metal core, wherein the casting product is immersed in a salt bath prepared by heating and melting a nitrate salt. A method for removing a low-melting metal core, characterized in that the low-melting metal core is dissolved and removed. 2. The method for removing a low-melting metal core according to claim 1, wherein the nitrate comprises sodium nitrate and potassium nitrate.