JPH0416258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a pressurizing device in a low-pressure casting machine, which is configured to fill a mold with molten metal and solidify it while pressurizing the molten metal at low pressure.

In general, a low-pressure casting machine includes a closed molten metal holding furnace that heats the molten metal and maintains it in a good molten state, and is placed on the molten metal holding furnace and communicates with the inside of the molten metal holding furnace through a cylindrical stalk. A mold and a pressurizing device that feeds high-pressure air, inert gas, etc. into the molten metal holding furnace and pressurizes the molten metal using the pressure are provided, and the molten metal in the molten metal holding furnace is pressurized by the pressurizing device. After the material is raised through a stalk and filled into the cavity of the mold, it is solidified within the cavity while maintaining a predetermined pressure.

By the way, conventionally, when pressurizing the molten metal in the molten metal holding furnace using the above-mentioned pressurizing device, the pressurization speed was set to be fast until the molten metal rose through the stalk and entered the mold, and then the molten metal was forced into the mold. When the molten metal starts to be filled, the molten metal is slowed down to prevent air entrainment, and when the molten metal is completely filled, the molten metal is slowed down again to perform feeding. (Refer to Japanese Patent Application Laid-open No. 10461/1983).

However, in this case, since the pouring speed in the second stage of filling the mold with the molten metal is constant, there is a problem in that casting defects occur frequently when the temperature of the mold or stalk is out of the appropriate range under good casting conditions. It was hot. That is, when the temperature of the mold or stalk is low, the casting speed becomes relatively slow, and a portion of the molten metal solidifies before the entire cavity of the mold is filled, resulting in poor running of the molten metal. Furthermore, when the temperature of the mold or the like is high, the casting speed becomes relatively high and the hot water flows into the gas venting hole portion of the cavity first, causing gas defects, shrinkage cavities, etc. due to poor gas venting.

Therefore, in the present invention, in the above-described low-pressure casting machine, the casting speed at the stage when the cavity of the mold is filled with molten metal is not constant, but is changed according to the temperature of the mold or stalk. The purpose of the present invention is to allow molten metal to always stably flow and fill into a cavity even if the temperature of a mold or the like is out of an appropriate range, thereby improving and maintaining casting quality in low-pressure casting.

To achieve this objective, the present invention includes a molten metal holding furnace that heats and holds molten metal, a mold that is disposed on the molten metal holding furnace and has a cavity that communicates with the inside of the molten metal holding furnace via a stalk, A low-pressure casting machine equipped with a pressurizing device that pressurizes the molten metal in the molten metal holding furnace and fills it into the cavity of the mold, a temperature detector that detects the temperature of the mold or the stalk, and an output of the temperature detector. a control device that changes and controls the pressurizing speed of the molten metal in the molten metal holding furnace in accordance with the signal so that when the temperature of the mold or stalk is low, the casting speed into the mold is fast and when the temperature is high, the casting speed is slow; It is equipped with the following. As a result, when the temperature of the mold, etc. is low and the hot water is likely to solidify, the casting speed is increased, and the hot water is circulated throughout the cavity while a part of the mold is not solidified, thereby preventing poor hot water flow. When the temperature is high and the fluidity of the molten metal is high, the pouring speed is slowed to prevent some of the molten metal from reaching the gas vent hole, thereby preventing gas defects and shrinkage cavities from occurring. .

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

Figure 1 shows the overall configuration of a low-pressure casting machine A according to the present invention, in which 1 is a closed molten metal holding furnace, in which the molten metal M for casting is constantly heated to maintain appropriate fluidity. It is something to do. A mold 2 is placed above the molten metal holding furnace 1, and the mold 2 has a cavity (not shown) formed in the same shape as the cast product inside, and the cavity extends in the vertical direction. It communicates with the molten metal M in the molten metal holding furnace 1 through a cylindrical stalk 3, and pressurizes the molten metal M in the molten metal holding furnace 1 with a pressurizing device 4, which will be described later. It is configured to be raised through the stalk 3, filled into the cavity of the mold 2, and solidified within the cavity.

On the other hand, 4 is a pressurizing device that supplies compressed air to the upper part of the molten metal holding furnace 1 and pressurizes the molten metal M from the surface with the air pressure of the compressed air. Air tank 5 storing compressed air
The compressed air is connected to the air tank 5 through a primary air filter 6, a primary pressure reducing valve 7, a secondary air filter 8 and a secondary pressure reducing valve 9 in order, and is supplied from the air tank 5 to the upper part of the molten metal holding furnace 1. Pressure 3
The switching mechanism 10 is provided to switch the switching mechanism 10 as desired.
The switching mechanism 10 is for 1st pressurization, 2nd pressurization, and
The air passages 11 to 13 for 3rd pressurization are connected in parallel, and the air passages 11 for 1st pressurization are connected in parallel.
A manual 1st pressure reducing valve 14 that reduces the air pressure in the air passage 11, a pilot type 1st pressurization switching valve 15 that opens and closes the air passage 11, and a pilot type 1st pressurization switching valve 15 that reduces the air pressure in the air passage 11. 1st pressurizing flow valves 16 that can be changed manually are arranged in series in sequence. The 2nd pressurizing air passage 12 also includes an electric 2nd pressurizing pressure reducing valve 17 that can reduce the air pressure in the air passage 12 and change the amount of pressure reduction by a drive motor 17a. A pilot-type 2nd pressurizing switching valve 18 that opens and closes, and a 2nd pressurizing flow valve 19 that changes the flow rate of air flowing in the air passage 12 by a drive motor 19a are arranged in series.
Furthermore, the 3rd pressurizing air passage 13 has a 3rd pressurizing pressure reducing valve 20 that reduces the air pressure in the air passage 13.
and a pilot type 3rd that opens and closes the air passage 13.
A pressurizing switching valve 21 and a third pressurizing flow valve 22 that manually changes the flow rate of air flowing through the air passage 13 are arranged in series. The amount of pressure reduction by each of the pressure reducing valves 14, 17, and 20 and the amount of flow rate controlled by each of the flow rate valves 16, 19, and 22 are set to separate values, and are used for 1st pressurization, 2nd pressurization, and 3rd pressurization. Each switching valve 1
Air passages 11 to 1 having the switching valves 15, 18, 21 by opening any one of them.
By supplying compressed air in the air tank 5 into the molten metal holding furnace 1 through the molten metal holding furnace 3, the pressure increase rate for the internal molten metal M can be switched in three ways.

Further, 23 is a pressure detector for detecting the pressure inside the molten metal holding furnace 1, and 24 is a temperature detector embedded inside the mold 2 to detect the temperature thereof.
The output signals of these detectors 23 and 24 are used to control the switching of the switching valves 15, 18, and 21 of the switching mechanism 10, as well as the pressure reducing valve and flow rate valve 19 for 2nd pressurization.
is input to a control circuit 25 that controls the operation of each drive motor 17a, 19a. The control circuit 25
are each at a predetermined pressure (for example,
Two pressure setting sections 26 and 27 store the pressure as the internal pressure of the holding furnace 1 set at P ₁ and P ₂ ), and the pressure signal value from the pressure detector 23 is stored in the pressure setting sections 26 and 27 A sequence control circuit 28 that outputs a switching signal when the internal pressure of the molten metal holding furnace 1 reaches a predetermined pressure P ₁ or P ₂ in comparison with an output signal value; 15, 18, 21, and each drive motor 17 of the pressure reducing valve 17 for 2nd pressurization and the flow valve 19
a, 19a to control the pressure increase rate in the molten metal holding furnace 1;
9, and each drive motor 17 of the pressure reducing valve 17 and flow valve 19 for the 2nd pressurization is connected to the pressure increase speed control circuit 29 in response to the detection signal value from the temperature detector 24.
a, 19a to operate and control the 2nd pressurizing switching valve 18.
2nd pressurization time variable boosting speed circuit 30 that outputs a correction signal for changing the boosting speed in the 2nd pressurizing stage where the 2nd pressurizing stage is opened. As shown in FIG.
By opening each of the pressurizing switching valves 15, 18, and 19 in sequence, the pressure increase rate in the molten metal holding furnace 1 is changed in three stages, and the molten metal M in the molten metal holding furnace 1 rises in the stoke 3 during the 1st pressurization. Fast in the pressure stage,
It is slow in the 2nd pressurizing stage, which is the casting state in which the molten metal M is filled into the cavity of the mold 2.
In the 3rd pressurizing stage in which the molten metal M in the cavity is fed, the speed is controlled to be almost the same as that in the 1st pressurizing stage, and the mold 2 is heated in accordance with the output signal of the temperature sensor 24. The pressurizing speed of the molten metal M in the molten metal holding furnace 1 in the above-mentioned 2nd pressurizing stage is changed so that when the temperature is low, the casting speed of the molten metal M into the mold 2 cavity is fast, and when the temperature is high, the casting speed is slow. A control device 31 is configured to control. In FIG. 1, 32 is a stop valve that shuts off the flow of compressed air.

Next, to explain the operation of the above embodiment,
At the start of operation, the switching valves 15, 18, and 21 of the switching mechanism 10 of the pressurizing device 4 are closed, and the pressure inside the molten metal holding furnace 1 is maintained at the same level as atmospheric pressure, and the molten metal M inside and outside the stalk 3 is kept closed. The surfaces are kept at the same height.

When the mold 2 is set in this state, the switching mechanism 10 is first activated by the control circuit 25.
Only the 1st pressurization switching valve 15 opens and the air tank 5
The inside and the inside of the molten metal holding furnace 1 are the 1st pressurizing air passage 11
The compressed air in the air tank 5 communicates with the
The pressure is reduced by the pressure reducing valve 14 of the first pressurizing air passage 11, and the molten metal is supplied into the holding furnace 1 while the flow rate is controlled by the flow valve 16. As a result, the molten metal M in the holding furnace 1 is pressed from its surface to perform the first pressurization, and the molten metal M rises within the stalk 3 due to this first pressurization.

Next, the pressure inside the molten metal holding furnace 1 is controlled by the control circuit 2.
When the pressure rises to the lower set pressure _P1 stored in one of the pressure setting units 26 of 5, the pressure detector 23 detects this and outputs a detection signal, and the sequence control circuit receives this detection signal. 28, the 1st pressurization switching valve 15 is closed, and the 2nd pressurization switching valve 18 is opened instead, and the air tank 5 is closed.
The compressed air inside is reduced in pressure by a pressure reducing valve 17 for second pressurization, and is supplied into the molten metal holding furnace 1 through an air passage 12 for second pressurization while its flow rate is controlled by a flow valve 19. As a result, the molten metal M in the holding furnace 1 is continuously pressurized at a speed slower than the pressurization speed in the first pressurization, and the second pressurization is performed.
Due to the pressurization, the molten metal M in the stalk 3 further rises and is forced into the cavity of the mold 2,
That is, casting into the mold 2 is performed.

At that time, the temperature sensor 2 embedded in the mold 2
4 detects the temperature of the mold 2 and outputs a detection signal;
In response to this detection signal, the 2nd pressurization variable pressure increase speed circuit 30 of the control circuit 25 drives each drive motor 17a, 1 of the pressure reducing valve 17 and flow rate valve 19 for the 2nd pressurization.
By controlling the operation of 9a, the casting speed is changed according to the temperature of the mold 2. That is, mold 2
When the temperature of the mold 2 is low, the pouring speed increases as shown by the broken line in Figure 3, and the molten metal M quickly circulates within the mold 2 cavity, and when the temperature of the mold 2 is high, the casting speed increases as shown by the solid line in the same figure. As the filling speed becomes slower, the molten metal M begins to slowly rotate inside the cavity. Therefore, when the casting speed is kept constant, there may be poor running due to partial solidification of the molten metal M at low mold temperatures, and gas defects or shrinkage cavities due to blockage of the gas vent holes of the molten metal M at high mold temperatures. The occurrence of defects can be reliably suppressed.

After such pouring, when the pressure inside the molten metal holding furnace 1 rises to the higher set pressure _P2 stored in the other pressure setting section 27 of the control circuit 25, the sequence control circuit 28 The 2nd pressurization switching valve 18 is closed, and the 3rd pressurization switching valve 21 is opened instead, and the compressed air in the air tank 5 is switched to the 3rd
The molten metal is supplied into the molten metal holding furnace 1 through the 3rd pressurizing air passage 13 while being pressurized by a pressure reducing valve 20 and having its flow rate controlled by a flow rate valve 22 . As a result, the molten metal M is subsequently pressurized at approximately the same speed as the above-mentioned 1st pressurization, and the 3rd pressurization is performed, and this 3rd pressurization causes the molten metal M to enter the cavity of the mold 2. The molten metal M is pressed in even more forcefully, that is, so-called feeding is performed to reinforce the solidification shrinkage of the molten metal M that has already been filled.

After that, when the molten metal M in the mold 2 cavity is completely solidified after a certain period of time has passed in the feeder state, the 3rd pressurizing switching valve 21 is closed and the compressed air in the molten metal holding furnace 1 is Switching valve 15,1
As the molten metal M in the stalk 3 slowly flows out from the holding furnace 1 and the pressure in the holding furnace 1 decreases, the molten metal M in the stoke 3
falls and returns to its original state. Further, the molten metal M solidified within the mold 2 is taken out from the mold 2 as a cast product. With the above, one cycle of casting is completed, and the same operations as described above are repeated thereafter.

In the above embodiment, the molten metal M in the molten metal holding furnace 1
Although the invention was applied to a low-pressure casting machine A that pressurizes the molten metal using the air pressure of compressed air, the present invention is also applicable to a low-pressure casting machine that pressurizes the molten metal using the gas pressure of an inert gas. It goes without saying that you can.

Further, in the above embodiment, the casting speed was changed according to the temperature of the mold 2, but the casting speed was changed according to the temperature of the stalk 3 or the intermediate portion between the stalk 3 and the mold 2. However, the same effects as those of the above embodiment can be achieved.

As explained above, according to the present invention, there is provided a molten metal holding furnace, a mold whose cavity communicates with the inside of the molten metal holding furnace through a stalk, and a pressurized inside of the molten metal holding furnace to transfer the molten metal into the cavity of the mold. In a low-pressure casting machine equipped with a pressurizing device for filling, the temperature of the mold or stalk is detected and the casting speed is changed and controlled according to the detected temperature. It maintains stable fluidity and ensures good running conditions, thereby reliably preventing mold defects such as poor running water and gas defects during low-pressure casting, contributing to improved quality of cast products. It has the excellent effect of being able to

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a general schematic explanatory diagram, FIG. 2 is a detailed explanatory diagram of the control device, and FIG.
The figure is an explanatory diagram illustrating a pressure increase pattern of molten metal. A...Low pressure casting machine, 1... Molten metal holding furnace, 2...
Mold, 3... Stoke, 4... Pressure device, 10...
...Switching mechanism, 17...2nd pressure reducing valve, 17a
...Drive motor, 19...2nd pressurization flow valve, 1
9a... Drive motor, 24... Temperature detector, 25
... Control circuit, 30 ... 2nd pressure increase rate variable circuit during pressurization, 31 ... Control device, M ... Molten metal.

Claims (1)

[Claims] 1. A molten metal holding furnace that heats and holds the molten metal, a mold that is placed on the molten metal holding furnace and has a cavity that communicates with the inside of the molten metal holding furnace via a stalk, and a mold that pressurizes the molten metal in the molten metal holding furnace. In a low-pressure casting machine equipped with a pressurizing device for filling the cavity, a temperature detector detects the temperature of the mold or stalk, and according to the output signal of the temperature detector,
and a control device that changes and controls the pressurizing speed of the molten metal in the molten metal holding furnace so that the casting speed into the mold is fast when the temperature of the mold or stalk is low, and slow when the temperature is high. A pressurizing device for a low-pressure casting machine featuring: