JPS606745B2 - Low pressure casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low pressure casting method for casting molten metal into a mold.

Conventionally, there has been a low-pressure casting machine as shown in FIG. 1 as an apparatus for casting molten metal into a mold using compressed air.

This casting machine consists of a fixed platen 1, a movable platen 2, and a vertical mold clamping device 3.
, it has a fixed mold 4 and a movable mold 5, and a stalk 7 is provided below the fixed mold 4 to reach near the bottom of the hot water tank 6. Further, the hot water tank 6 has a closed structure, and an air pressure inlet 6a is provided at the upper part of the hot water tank 6. The air pressure inlet 6a is connected to a compressed air source 11 via a throttle valve 8, a switching valve 9, and a pressure reducing valve 10. When casting, the molds 12 consisting of the movable mold 5 and the fixed mold 4 are clamped together, and compressed air is injected from the air pressure inlet 6a to increase the pressure in the upper space 13 of the hot water tank, thereby causing the rising sun 14. Cavity 1
Inject into 5.

By the way, if the injection speed is fast when injecting the molten metal into the cavity 15, the molten metal injected into the cavity 15 will entrain the gas inside the cavity 15 and generate cavities.
I can't get good quality coin products.

Therefore, in the past, the injection rate was lowered to prevent the formation of nests. For this reason, the time required for casting becomes longer, and the temperature of the mold 12 must be increased so that the face bath does not cool down during locking, which increases the cooling time after finishing casting and reduces productivity. Not only was this bad, but the solidification of the hot water was slow, resulting in a coarse material structure and reduced mechanical strength. Furthermore, in order to control the injection speed of the molten metal 14 into the cavity 15, the compressed air pressure must be determined by taking into consideration the head difference between the cavity 15 and the falling sun surface 16, and the compressed air pressure must be determined by using a pressure reducing valve 10, a throttle valve 8, etc. It took a lot of effort to finely adjust the air pressure.

In addition, in conventional low-pressure casting, the molten metal rises in the stoke 19 after each injection, and when the injection is finished and the mold is sealed, the excess molten metal flows down the stoke 19 and returns to the molten metal tank 20. Oxide was attached to the inner surface of No. 19. Therefore, there was a risk that the oxide would enter the product the next time it was injected, degrading the quality of the product. The present invention eliminates the above-mentioned drawbacks, and makes it possible to efficiently manufacture products with stable quality and high mechanical strength, which do not contain cavities or oxides, with relatively simple operations.

The present invention involves applying gas pressure to the upper surface of the molten metal in a sealed tank to push the molten metal up into the cavity of a mold that can be opened and closed through a stalk that is suspended vertically above the molten metal in the tank. In the low-pressure casting method, the molten metal in the molten metal tank is passed through the stoke to reduce the pressure in the cavity by reducing the pressure in the molten metal tank space, and then the molten metal is poured into the cavity by setting the upper space of the tundish to atmospheric pressure or pressurized state. This is a low-pressure casting method.

Next, the present invention will be explained in detail with reference to an embodiment shown in the drawings.

In the apparatus for implementing the present invention, a vacuum pump 17 is provided in addition to the compressed air source 11 in the apparatus shown in FIG.
An air circuit was formed as shown in the figure.

That is, the air port 6a of the upper part 13 of the hot water tank is connected to the first switching valve 18.
The air pressure is continuously switched to the pneumatic tank 19 and the second switching valve 20.

Then, the circuit leading to the second switching valve 20 is subsequently switched to the second switching valve 2 river trowel vacuum tank 21 or open to the atmosphere. The vacuum tank 21 is depressurized by a vacuum pump T'trowel.

Pneumatic tank 19 was connected to compressed air source 11 via pressure reducing valve 10 . In addition, 22 is a pressure switch for checking the degree of vacuum;
3 is a pressure switch for checking atmospheric pressure. In the embodiment, the vacuum tank 21 is used as a device for generating vacuum.
Although a vacuum pump was used, a cylinder-based vacuum generator, a venturi tube-based vacuum generator, or the like may be used instead. Note that the number of stalks 19 is not limited to one, and several stalks can also be used. To perform casting using the casting machine according to the present invention, first, after the mold is clamped, only the second switching valve 20 is switched to the state shown in FIG. 2.

At this time, since the upper space 13 of the hot water tank is connected to the vacuum tank 21 via the second switching valve, the pressure of the upper space 13 of the hot water tank is reduced. At this time, as the pressure in the upper space 13 of the flaw tank is reduced, the gas in the cavity 15 is removed from the stalk 7 and the molten metal 1.
Since the air bubbles 24 pass through the inside of the cavity 15 and are sucked into the upper space 13 of the wound tank and discharged, the pressure inside the cavity 15 is also reduced at the same time. At this time, the scratched surface inside the stalk 7 goes down toward the lower end of the stalk 7, but the trough 6 around the stalk 7
The inner melted surface 16 remains almost unchanged. Also, when the air in the stalk 7 is sucked downward, "stoke 7
The inner surface of the stalk 7 will be cleaned by removing oxides adhering to the inner surface. This oxide moves along with the suctioned air to the flawed surface 16 facing the upper space 13 of the hot water tank, and accumulates on the falling sun surface 16 outside the stalk 7 as a glue. Then, when the pressure inside the cavity 15 and the upper space 13 of the hot water tank are both reduced to a predetermined pressure, and the degree of vacuum is confirmed by the vacuum degree confirmation pressure switch 22, the second switching valve 20 is switched and the first switching valve is switched at the same time. 18 to make the upper space 13 of the hot water tank tangential to the pneumatic tank 19.

Then, while the inside of the cavity 15 is in a reduced pressure state, the upper space 13 of the flaw tank becomes a pressurized state, and due to this pressure difference, the molten metal 14 in the hot water tank 6 rapidly flows into the cavity 15. Since the inside is in a reduced pressure state, there is very little residual gas in the cavity 15, and even if the molten metal suddenly flows into the cavity 15, gas will not be drawn into the molten metal as in the past, and there will be no gas left inside the sengo product. No cavities are generated.After pouring the molten metal into the cavity 15 as described above, cooling is performed for an appropriate period of time, and the first switching valve 1
8, the upper space 13 of the wound tank is opened to the atmosphere via the second switching valve 20, and the inside of the wound tank is brought to atmospheric pressure.

After confirming that the inside of the wound tank has reached atmospheric pressure using the atmospheric pressure confirmation pressure switch 23, the movable mold 5 is opened and the coin-filled product is taken out from the cavity 15. Note that, unlike the above-described embodiment, the upper space 13 of the hot water tank after being depressurized is simply made to communicate with the atmosphere via the first and second switching valves 18, 20, and due to this sudden communication with the atmosphere. It is also possible to cast the molten metal 14 in the flaw tank 6 into the cavity 15 by the action of atmospheric pressure.

When the head difference between the cavity 15 and the surface 16 of the molten metal in the tank 6 is relatively small, when the specific gravity of the molten metal is small, or due to the shape of the cavity, even if the pressure difference between the inside of the cavity and the upper space of the tank is small, If possible, this method is effective when it is sufficient to reduce the pressure in the cavity and the upper space of the bath, then bring the upper space of the bath to atmospheric pressure, and then draw up the molten metal by reducing the pressure inside the cavity. As described above, the present invention applies gas pressure to the upper surface of the flaw in the flaw in the flawed tank with a sealed structure, thereby allowing the inside of the cavity of the mold to be opened and closed via the stalk that is permanently suspended within the flaw in the flaw in the flawed tank. In the low-pressure casting method, in which casting is performed by pushing up the rising sun, the pressure inside the cavity is reduced by reducing the pressure in the molten metal tank space, through which the molten metal in the tundish tank passes through the stoke, and then the upper space of the tundish tank is set at atmospheric pressure or pressurized to release the molten metal. Since the molten metal is cast into the cavity, the molten metal can be flowed into the cavity after most of the air in the cavity 15 has been exhausted.

Therefore, it is possible to eliminate the drawback that the setting sun entrains the air in the cavity and causes nests in the product. In this way, since the casting is performed with very little residual gas in the cavity, the inflow speed of the molten metal can be increased.

Furthermore, since casting can be performed instantaneously, even if the mold temperature is somewhat low, the filling of the cavity can be completed before the molten metal cools down, and there is no need to maintain the mold temperature at a high temperature. Therefore, the cooling time after casting can be shortened and productivity can be increased. In addition, since casting can be performed instantaneously and cooling solidification can be performed in a short time, the metal structure has various advantages such as the ability to obtain a high-quality product with a dense metal structure and high strength.
In addition, in the present invention, the air in the cavity and the air in the stalk are drawn below the stalk, and these air forms bubbles from the lower end of the stalk and moves toward the scratched surface in the bath. Oxide adhering to the inner surface of the stalk is also carried away at the same time.

Therefore, the oxide adhering to the inner surface of the stalk is not rolled into the product, and a high-quality product can be easily obtained. In addition, in the case of the present invention, the lower end of the stalk, which is suitable for the cavity, is always deep in the molten metal, so when the air inside the cavity or stalk is vacuumed, the inner surface of the cavity or stalk is removed. If there are any oxides or metal powders left on the stalk, these metal powders will be absorbed into the falling sun when the vacuum is drawn, where they will be melted due to the heat of the molten metal, and they will also be deposited on the inner surface of the stalk. The oxides move with the sucked air to the molten surface facing the upper space of the hot water tank, and accumulate on the surface of the molten metal outside the stalk as a glue, causing oxides and metal powder to be carried toward the vacuum tank and vacuum pump. Therefore, the vacuum pump always works well without any problems.

In addition, the mold of the present invention consists of a fixed mold and a movable mold, there is a split mating surface between both molds, and there is a slight gap between the mold and the extrusion pin. Therefore, even if the inside of the cavity is not completely vacuumed and a small amount of air remains, the remaining air can be extracted from the extremely narrow gap around the split mating surface of the mold or the ejector pin during casting. Air escapes.

Therefore, it is easy to obtain mirror-embedded products with no cavities or mirror-embedded products with extremely few cavities.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a secondary low-pressure casting machine, and FIG. 2 is a longitudinal sectional view showing one embodiment of the apparatus used for carrying out the present invention. 4...Fixed mold, 5...Movable mold, 6...
Kizutan, 7... Stoke, 9, 18, 20...
...Switching valve, 11...Compressed air source, 12...
... Mold, 13... Space above the water tank, 14...
・Molten metal, 15...Cavity, 17...Vacuum pump, 19...Pneumatic tank, 21...
...Vacuum tank. Figure 1 Figure 2

Claims (1)

[Claims] 1 A low-pressure casting method in which gas pressure is applied to the top surface of the molten metal in a sealed tank, pushing the molten metal up into the cavity of a mold that can be opened and closed via a stalk that is suspended vertically above the molten metal in the tank. In the casting method, by reducing the pressure in the tundish space, the pressure in the cavity is reduced through the molten metal in the tundish and the stoke, and then the molten metal is poured into the cavity with the upper space of the tundish set at atmospheric pressure or pressurized. Low pressure casting method.