JP2827267B2 - Magnesium alloy sand casting method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnesium alloy sand casting method, and more particularly to a casting method in which a flameproof effect is maintained without deteriorating a working environment.

[Conventional technology] Magnesium has a lower boiling point than aluminum or the like,
Oxidation is severe due to the high vapor pressure near the molten metal processing temperature.
For this reason, it reacts with a mold, moisture, air, etc. at the time of casting, and easily oxidizes and burns. Therefore, when casting a magnesium alloy, a flame retardant is added to the foundry sand.

Japanese Patent Application Laid-Open Nos. 56-139249 and 56-139250 are known as examples of a technique relating to a flame retardant for the foundry sand. However, adding a flame retardant to the foundry sand has a problem that harmful gas is generated from the flame retardant at the time of casting, thereby deteriorating the working environment.

Therefore, a casting method has been proposed that can prevent the combustion of a magnesium alloy without using a flame retardant (Japanese Patent Application Laid-Open No. 55-16747).

This casting method uses casting sand before pouring magnesium alloy.
This is a method in which SF ₆ (sulfur hexafluoride) gas is blown, and in this case, generation of toxic gas such as ammonia gas and SO ₂ gas is prevented.

[Problems to be Solved] However, as JP-A-55-16747, the method of blowing the SF ₆ gas into the sand mold before pouring, or worse missing gas blown during pouring, casting When the filling weight is large (when the heat capacity is large), the gas that has entered between the sand particles decomposes and disappears due to the heat of the molten metal, and the gas supply cannot keep up with the desired amount. For this reason, there has been a problem that the flameproofing effect becomes insufficient, and the molten magnesium alloy burns in the sand mold.

An object of the present invention is to provide a method for casting a magnesium alloy casting, which can maintain the flame-retardant effect at the time of casting without deteriorating the working environment, focusing on the above points.

[Means for Solving the Problems] A magnesium alloy sand casting method according to the present invention, which meets this object, is a casting method in which a magnesium alloy casting is cast using a sand mold. An inert gas is supplied into a sand mold, and the flow rate of the inert gas is controlled based on the gas concentration in the sand mold.

[Action] In such a magnesium alloy sand casting method,
Since the inert gas is continuously supplied from before the pouring to the completion of the solidification of the molten metal, the problem that the flameproofing effect is reduced even if a part of the inert gas comes out of the sand mold is solved. .

Further, since the flow rate of the inert gas is controlled based on the temperature and the gas concentration in the sand mold, a necessary amount of gas can always be supplied accurately. Therefore, the amount of gas in the sand mold does not become excessive, and conversely, does not extremely decrease, so that a stable flameproof effect can be maintained.

EXAMPLES Preferred examples of the magnesium alloy sand casting method according to the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 shows a first embodiment of the present invention. In the figure, 1
Indicates a sand mold, and the sand mold 1 includes an upper mold 3 and a lower mold 5. The upper die 3 is formed by an upper frame 6, and the lower die 5 is formed by a lower frame 7. The upper frame 5 is placed on the lower frame 7, and both are positioned at predetermined positions. The sand mold 1 has a platen 9 installed horizontally.
Is placed on top.

In the upper mold 3 and the lower mold 5 of the sand mold 1, a cavity 11 into which the molten metal is poured is formed. A runner 13 extending in a horizontal direction is located on one side of the cavity 11, and the runner 13 communicates with a sprue 15 opened at the top of the upper mold 3. On the other side of the cavity 11, a feeder 16 which is also opened at the top of the upper mold 3 is provided.
Is located.

In the upper mold 3 and the lower mold 5, a plurality of iron pipes 17 for injecting an inert gas into the sand mold are embedded. Each iron pipe 17
Is provided with a plurality of injection holes 17a having an appropriate diameter (for example, 1 to 5 mm). One end of the iron pipe 17 is closed, and the other end protrudes outward from the upper frame 6 and the lower frame 7.

Here, the arrangement of the iron pipe 17 is considered in accordance with the shape of the cavity 11. That is, when the heat capacity is large, such as in a thick portion, the iron pipe 17 is
, And a large amount of inert gas is ejected toward the thick portion. In this embodiment, the iron pipe 17 is arranged at a position about 20 to 30 mm away from the inner surface of the cavity. When the heat capacity is small, such as in a thin shape, the iron pipe 17 is arranged a little more apart than described above. In the present embodiment, in the case of a thin portion, 60 to 70 mm from the inner surface of the cavity
It is located at a distance.

A flexible tube 21 is connected to a protruding end of each iron pipe 17 protruding from the sand mold 1 via a connection fitting 19 (quick joint). Each flexible tube 21
Are connected to the external controller 23. A plurality of gas cylinders 25 filled with, for example, SF ₆ gas, CO ₂ gas, etc., are connected to the external controller 23. The external controller 23 accommodates an electromagnetic valve, a flow control valve, and the like (not shown), and each gas cylinder 25 and each flexible tube 21 are connected via these electromagnetic valves and flow control valves.

Temperature sensors 29 and 30 and a gas concentration sensor 31 are connected to the external controller 23 via a calculator 27. One temperature sensor 29 is arranged near the feeder 16, and the other temperature sensor 30 is arranged near the bottom of the gate 15. The gas concentration sensor 31 is arranged near the cavity 11 of the upper mold 3. Each of the temperature sensors 29 and 30 converts the temperature in the sand mold into an electric signal. The signal detected here is converted into an actual measured temperature by the arithmetic unit 27. Similarly, the gas concentration sensor 31 converts the gas concentration in the sand mold into an electric signal, and the signal detected here is converted by the calculator 27 into the actual measured gas concentration.

The external controller 23 switches between the gas cylinders 25 and adjusts the gas flow rate based on a command from the calculator 27. That is, the calculator 27 determines the most appropriate gas flow rate from the gas concentration measured by each sensor and the temperature of the mold, and based on this, the external controller
By operating each solenoid valve in 23, an appropriate amount of gas is blown into the sand mold.

In this embodiment, the type of inert gas used before pouring and after pouring is different, and before pouring, SF ₆ gas or S
O ₂ gas is used, and after pouring, CO ₂ gas or N ₂ gas is used.

Next, the magnesium alloy sand casting method will be described.

First, before the magnesium alloy is poured, the flexible tube 21 is connected to each iron pipe 17 via the connection fitting 19. At this point flexible tube 21 from cylinder 25
The inert gas (SF ₆ gas or SO ₂ gas) G is supplied to the iron pipe 17 in the sand mold 1 through the
, An inert gas G is jetted into the molding sand.

Next, when the molten metal is poured from the gate 15, the temperature sensor
The temperature at the bottom of the gate 15 is detected by 30 and the arithmetic unit 27 is activated by this detection signal. And each sensor 3
The flow rate of the inert gas G supplied into the sand mold 1 is controlled based on the temperature and the gas concentration in the sand mold 1 measured by 0 and 31. In this state, the inert gas jetted into the molding sand is appropriately distributed to the thick and thin portions of the cavity 11. During casting, the gas concentration in the sand mold is constantly measured by the gas concentration sensor 31, and the measured value is calculated by the calculation gas.
27, the supply amount of the inert gas G is always maintained at a desired value. Therefore, the stable fire prevention effect is maintained, and the combustion of the molten metal in the sand mold 1 is prevented.

When pouring is completed, the solenoid valve in the external controller 23 is switched by a command from the calculator 27, and the inert gas supplied into the mold 1 is changed from SF ₆ gas or SO ₂ gas to CO ₂ gas or N ₂ gas. Switch to gas. Also in this case, the flow rate of the supplied inert gas G is controlled based on the temperature and gas concentration in the mold measured by each sensor. This flow control is performed until the molten metal is completely solidified.

In this way, from before the pouring of the magnesium alloy to the completion of solidification, an appropriate amount of inert gas is continuously supplied to the thick portion and the thin portion of the cavity 11,
An extremely high flame retardant effect is maintained as compared with the conventional method.

In the present invention, since it is not necessary to add a flame retardant to the molding sand, the generation of gas by the flame retardant during pouring is also eliminated,
Generation of casting defects due to entrainment of gas is prevented.

Second Embodiment FIG. 2 shows a second embodiment of the present invention. The second embodiment is different from the first embodiment in the flow of the inert gas in the thick portion and the arrangement position of the temperature sensor. Other parts are the same as those in the first embodiment. By giving the same reference numerals as in the example, the description of the multiplied part will be omitted, and only different parts will be described.

In FIG. 2, the temperature sensor 29 is disposed near the thick portion 41 located below the hot water 16 and constantly measures the temperature near the thick portion 41. A gas injection hole 43 having a small diameter is formed between the iron pipe 17 and the lower part of the feeder 16 in the lower die 5. This gas injection hole 43 is made of iron pipe
17 and the diameter is set, for example, to 1 mm or less. In this embodiment, only one gas injection hole 43 is shown, but a plurality of gas injection holes 43 may be provided depending on the thickness of the thick portion.

In the case of such a sand mold, a part of the inert gas supplied to the iron pipe 17 is jetted from the jet holes 17a toward the gas jet holes 43. Therefore, the molten metal in the thick portion 41 is cooled by the inert gas G, and solidification is promoted. As a result, directional solidification in which the position of the solidification end portion of the molten metal gradually moves toward the gate 15 is obtained, and the occurrence of sink marks is prevented.

By appropriately providing the gas injection holes 43 in the sand mold 1, the cooling effect can be further enhanced, and the solidification time of the molten metal can be shortened.

[Effects of the Invention] As described above, when the magnesium alloy sand casting method according to the present invention is used, an inert gas is supplied into the sand mold from before the pouring of the magnesium alloy to the completion of solidification, and the inert gas is supplied. Since the flow rate is controlled based on the temperature and the gas concentration in the sand mold, it is possible to maintain the fire prevention effect at the time of casting without deteriorating the working environment, and the combustion of the molten metal in the mold It can be reliably prevented. As a result, the safety of the casting operation can be improved.

Further, since it is not necessary to add a flame retardant to the molding sand, generation of gas by the flame retardant is prevented, and casting defects due to entrainment of gas can be prevented.

Further, the solidification of the thick portion can be promoted by the cooling effect due to the supply of the inert gas into the sand mold.
Therefore, directional solidification can be obtained, and the casting cycle can be shortened by shortening the solidification time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a casting apparatus used in a magnesium alloy sand casting method according to a first embodiment of the present invention, and FIG. 2 is a casting apparatus used in a magnesium alloy sand casting method according to a second embodiment of the present invention. FIG. 1 ... Sand mold 11 ... Cavity 15 ... Gap 16 ... Golder 17 ... Iron pipe 23 ... External controller 25 ... Gas cylinder 27 ... Calculators 29 and 30 ... Temperature sensor 31 ... Gas concentration sensor 43 …… Gas injection hole G …… Inert gas

Claims (1)

(57) [Claims] In a casting method for casting a magnesium alloy casting using a sand mold, an inert gas is supplied into the sand mold from before the pouring of the magnesium alloy until solidification is completed,
A sand casting method for a magnesium alloy, wherein a flow rate of the inert gas is controlled based on a temperature and a gas concentration in the sand mold.