JPH0214144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting pressure control device for a low-pressure casting machine that controls air pressure in a heat-retaining furnace.

A low-pressure casting machine stores molten metal in a sealed heat insulating furnace, pressurizes the space above the molten metal in the heat insulating furnace, and passes through a stalk placed in the molten metal to a level above the molten metal in the heat insulating furnace. Molten metal is introduced into a mold and air pressure is maintained for a certain period of time to solidify the molten metal. In this low-pressure casting machine, the pressure that is further applied from the time when the molten metal is completely filled into the mold until it reaches the final target pressure at which the molten metal solidifies, that is, the magnitude of the feeder pressure, has a large effect on product quality. Are known. In addition, with this low-pressure casting machine, multiple castings are performed with one molten metal stored in the heat retention furnace, so as the number of castings increases, the molten metal level decreases, and the pressure of the air supplied to the heat retention furnace decreases. must be increased, and to maintain a constant feeder pressure, the final target pressure must be increased as the melt level in the furnace decreases.

Conventionally, as a method of keeping this feeder pressure constant, the final target pressure is set and programmed according to the number of castings, and according to this, the pressure is adjusted according to the drop in the level of molten metal stored in the heat retention furnace. There are known methods to increase the However, with this method,
The amount of molten metal level in the insulating furnace that decreases after one casting due to the initial level of molten metal placed in the insulating furnace before starting casting, which is not constant, and depending on the degree of slag accumulation in the insulating furnace. is not constant, so
The drawback was that it was difficult to maintain constant feeder pressure.

In addition, in order to eliminate this drawback, we measured the air pressure inside the heat retention furnace when the molten metal passed a certain point on the way from the stalk to the mold during pressurization, and the filling of the molten metal into the mold was completed at this measured value. The final pressure is the filling pressure, which is the additional pressure required to reach the top of the mold (in other words, this pressure is the pressure that the molten metal reaches from a fixed point to the top of the mold, and is a constant value determined depending on the mold) and the feeder pressure. There is a known method of controlling the pressure in a heat retention furnace so as to maintain the same pressure. In this method, it is important to detect where the molten metal level is between the stalk and the mold when pressurizing.

Methods for detecting this level include installing electrodes at detection positions between the stalk and the mold, and detecting when the molten metal passes through these electrode positions by applying electricity, or placing metal at the detection position of the stalk. A vacuum pump is connected to the thin metal tube, and the passage of the molten metal is detected by detecting the change in back pressure inside the thin metal tube due to the opening of the thin metal tube being blocked by molten metal.

However, in all of these detection methods, the detection mechanism directly comes into contact with the high-temperature molten metal, so it is necessary to consider the durability of the detection mechanism, and it is necessary to modify the stalk and mold to install this detection mechanism. There are drawbacks, including the need for maintenance of the detection mechanism.

The present invention was achieved as a result of systematic experiments and analyzes carried out by the present inventors in order to eliminate the drawbacks of the above-mentioned conventional examples.

In other words, when the present inventors observed changes in the pressure inside the heat-retaining furnace (for example, the pressure inside the header), the passage area of the molten metal changed from the stalk to the time it was filled into the mold. It has been found that an inflection point in the pressure curve, that is, an extreme value such as a minimum or maximum in the slope of the pressure curve occurs at a sudden change in the pressure curve, that is, at a point where the passage area decreases or expands.

Therefore, the inventors of the present invention found that by focusing on the inflection point of the pressure curve, it is possible to detect when the cross-sectional area between the stalk and the filling of the molten metal suddenly changes. If the final target pressure is set to the pressure when the predetermined point is reached, the filling pressure and the feeder pressure as the pressure required to complete filling of the molten metal from the predetermined point into the mold are taken into consideration.
We have achieved the present invention, which allows automatic optimal pressure control depending on the amount of molten metal in the heat-retaining furnace.

An object of the present invention is to provide a casting pressure control device for a low-pressure casting machine that always provides a homogeneous product by automatically performing optimal pressure control according to the amount of molten metal in a heat-retaining furnace.

SUMMARY OF THE INVENTION An object of the present invention is to provide a casting pressure control device for a low-pressure casting machine that detects the molten metal level without touching the high-temperature molten metal by detecting the inflection point of the pressure curve in the heat retention furnace. shall be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a casting pressure control device for a low-pressure casting machine that does not require modification of the stalk or mold and is highly durable, maintainable, and economical.

The casting pressure control device of the low-pressure casting machine of the present invention supplies pressurized air to the space above the molten metal in a sealed heat-retaining furnace in which molten metal is stored based on the output signal of the casting start/stop means. The molten metal is then pressurized, and the molten metal is guided through the stalk into a mold connected to a stalk erected in the molten metal in a heat-retaining furnace, and then kept under pressure.
In a low-pressure casting machine that exhausts pressurized air in a heat retention furnace after solidifying molten metal, an air pressure measuring means for measuring the air pressure in the heat retention furnace and an inflection point of a pressure signal from the air pressure measurement means are detected. and an inflection point detection means for detecting that the molten metal reaches a predetermined point where the cross-sectional area suddenly changes from the stalk to the time when the mold is filled, and a signal from the inflection point detection means is provided. a signal processing circuit that outputs a control signal that determines the final target pressure according to the signal processing circuit; and an air pressure control means that controls the air pressure supplied to the heat retention furnace until the final target pressure is reached according to the control signal from the signal processing circuit. The final target pressure is set and controlled according to the amount of molten metal in the heat retention furnace.

The casting pressure control device for a low-pressure casting machine of the present invention having the above-described configuration is configured to control the casting pressure at a predetermined point where the cross-sectional area suddenly changes from the inflection point of the pressure curve in the insulating furnace until the molten metal is filled from the stalk into the mold. It detects that the pressure has been reached and automatically performs optimal pressure control according to the amount of molten metal in the insulating furnace, so it has the advantage of providing a homogeneous product over multiple castings.

Furthermore, the casting pressure control device of the present invention detects the molten metal level without touching the high-temperature molten metal, so it has the advantage that the device is excellent in durability, maintainability, and economic efficiency.

Furthermore, the casting pressure control device of the present invention has the advantage that it can be applied without any modification to basic components such as the stalk and mold of a low-pressure casting machine.

Furthermore, in the casting pressure control device for a low-pressure casting machine of the present invention, the final target pressure determining means of the above-mentioned signal processing circuit has a memory that stores the pressure in the heat insulating furnace when the signal is output from the inflection point detecting means. means, pressure setting means for setting a pressure that takes into account the filling pressure and feeder pressure as the pressure required to complete filling of the molten metal from the predetermined point into the mold, the pressure signal from the storage means, and the pressure signal from the storage means; and an addition means for adding the setting signal from the pressure setting means and outputting a control signal corresponding to the final target pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings based on a casting pressure control device for a low-pressure casting machine according to an embodiment.

FIG. 1 shows a first embodiment of the present invention, in which a low-pressure casting machine includes a heat retention furnace 1 for storing molten metal 2, which is a raw material for casting, and a heat retention furnace 1 for storing molten metal 2, which is a raw material for casting, and a mold 4 for discharging the molten metal 2 in the heat retention furnace 1. It consists of a stoke 3 for pouring molten metal into the furnace 1, and an air pressure supply/exhaust device for pressurizing or depressurizing the space inside the sealed heat-retaining furnace 1. This air pressure supply/exhaust device includes an air pressure source 5, an air pressure control device 6 connected to the air pressure source 5, a header 7 connected to the air pressure control device 6, and a header 7 connected to the header 7. It consists of a pressure sensor 8 that measures the air pressure inside the header 7 and converts it into an electrical signal, an exhaust electromagnetic valve 9 connected to the header 7 to exhaust the air inside the heat retention furnace, and a signal processing circuit 13. This signal processing circuit 13 includes a timer 11 having a start switch 10 and setting a pressurization time;
A signal setting device 12 for setting pressurization conditions, and a control circuit 100 that processes signals from the pressure sensor 8, timer 11, and signal setting device 12 and sends signals to the air pressure control device 6 and the exhaust electromagnetic valve 9. It consists of

FIG. 2 shows the specific configuration of each part of the first embodiment. Accordingly, a solenoid valve 15 for intermittent supply of air pressure from the pressure reducing valve 14 to the header 7, a speed controller 16 and a check valve 1 connected between the solenoid valve 15 and the header 7.
Consists of 7. This speed controller 16 is
The check valve 17 is used to supply air to the header 7, that is, to the upper space in the heat-retaining furnace 1, at an appropriate speed, and the check valve 17 prevents air from flowing back from the header 7 to the speed controller 16. The header 7 also has the function of absorbing sudden changes in air pressure to some extent. The signal processing circuit 13 includes an amplifier circuit 18 that amplifies the pressure signal from the pressure sensor 8 and a differentiation circuit 1 that differentiates the signal from the amplifier circuit 18.
9, a differentiation circuit 20 that differentiates the signal from the differentiation circuit 19 again, an output of this differentiation circuit 20, and a power supply 2.
1 and the signal set by the volume control circuit 22, a count circuit 24 that counts the signal from the comparison circuit 23, and a signal from the amplifier circuit 18 that is sampled and held by the output of the count circuit 24. Sample and hold circuit 27, output of sample and hold circuit 27, and signal setting device 12
an adder circuit 28 that adds the outputs from the amplifier circuit 18, a comparator circuit 29 that compares the output of the amplifier circuit 18 and the output of the adder circuit 28, and a relay 3
0, a transistor 33 that drives the relay 32 with the signal from the timer 11, a transistor 34 that drives the relay 30 with the output from the count circuit 24, and a power source 35 that drives the relays 30 and 32. It consists of a power source 36 for driving the air pressure supply electromagnetic valve 15 and the exhaust electromagnetic valve 9 via the contact 30a of the relay 30 and the contact 32a of the relay 32.

In FIG. 1 and FIG. 2, reference numerals 19, 2
0, 21, 22, 23, 24 are provided with inflection point detection means a ₁ (to avoid difficulty in viewing, a ₁
etc. are not shown, and the same applies hereinafter) are denoted by reference numerals 12, 27,
The final target pressure determining means _a2 is represented by the component 28, and the signal processing circuit A is represented by the inflection point detecting means _a1 and the final target pressure determining means _a2 .
0, 11, 36, 32, 33, 35, 29, 3
It is assumed that the components designated by 0, 31, 34, and 35 constitute the air pressure control means B, and the components designated by the symbols 7, 8, and 18 constitute the air pressure measuring means C, respectively.

FIG. 3 shows the configuration of the pressure sensor 8, which includes a metal case 4 having an opening 39 for introducing pressure.
An insulating substrate 41 with a hole in the center is placed inside the O.
A hole in the center of the insulating substrate serves as a pressure receiving chamber, and a silicon diaphragm 43 is bonded to the substrate 41 so that the sensing portion is in contact with the pressure receiving chamber. Four diffusion-type strain gauges are arranged at the center and periphery of the sensitive part of the silicon diaphragm 43, and these four strain gauges constitute a bridge.Also, electrodes are erected on the insulating substrate 41, and the strain gauges and leads are arranged. The lid 4 of the metal case 40 is connected with a wire.
It is also connected to electrode No. 4, and a voltage is applied to the bridge from a power source 45, and the voltage change is taken out to the outside. The pressure sensor 8 is attached to the header 7 so that the pressure receiving chamber of the pressure sensor 8 is connected to the internal space of the header 7 through an opening 39 and is isolated from external atmospheric pressure.

Next, the operation of the first embodiment will be explained. First, casting is started by closing the start switch 10 of the timer 11. This start switch 10
When the timer 11 closes, the timer 11 switches the low-level signal that had been output until then to a high level, turns on the transistor 33, and puts the count circuit 24 into a counting start state. This transistor 33
When conducts, the contact 32a of the relay 32 closes,
A current flows from the power source 36 to the exhaust electromagnetic valve 9 to close the exhaust electromagnetic valve 9. Since the sample hold circuit 27 is in the reset state, a 0 level voltage is output to the adder circuit 28. When the count circuit 24 is placed in the counting start state, it outputs a high level signal, turns the transistor 34 on, and closes the contact 30 of the relay 30.
Close a. Contacts 30a, 3 of relays 30, 32
2a is closed, the electromagnetic valve 15 is connected to the power source 36.
A current flows through the solenoid valve 15 to open the solenoid valve 15, and the air whose pressure is reduced by the pressure reducing valve 14 from the air pressure source 5 is supplied to the speed controller 16 and the check valve 1.
7. The air is supplied to the upper space of the heat-retaining furnace 1 through the header 7, the air pressure is increased, and casting is started.

Since the air pressure in the upper space of the heating furnace 1 is equal to the internal pressure of the header 7, this pressure is detected by the pressure sensor 8.
is measured, converted into an electrical signal, and input to the amplifier circuit 18. The pressure signal amplified by this amplifier circuit 18 is input to a differentiating circuit 19, a differentiating circuit 20, and a comparing circuit 23. As shown in FIG. 4a, as the pressure in the space inside the heat retention furnace 1 increases, the molten metal 2 rises in the stoke 3 from level A just before pressurization in the heat retention furnace 1, and when it reaches level B. ,
The cross-sectional area of the molten metal head (the top of the molten metal that is being filled) expands rapidly. Molten metal head is level C
, the cross-sectional area of the molten metal head is rapidly narrowed. When the molten metal passes through a portion where the cross-sectional area of the molten metal passage changes suddenly, a so-called inflection point occurs, which is a point where the slope of the pressure signal curve becomes maximum or minimum. In this embodiment, an inflection point corresponding to the minimum value of the pressure gradient, which occurs in a portion where the cross-sectional area is narrowed, is targeted. This point of inflection occurs when the molten metal head passes through the constriction of the mold 4. The molten metal head that has passed through the constriction section C-D enters the product space between levels D and E, and when it reaches level E, the filling of the molten metal into the mold 4 is completed. When the molten metal head reaches level E, the cross-sectional area suddenly becomes zero, and a significant inflection point appears on the pressure curve. Depending on the shape of the product, there may be a point where the cross-sectional area changes abruptly between level D and level E, and several inflection points may occur on the pressure curve.

As described above, as the molten metal head rises, the pressure signal from the pressure sensor 8 increases while producing an inflection point as shown in FIG. 4a. The output of this pressure sensor 8 is differentiated by a differentiation circuit 19, and as shown in FIG. 4b, it is differentiated in accordance with the curve of FIG. 4a.
Further, the output of the differentiating circuit 19 is differentiated again by the differentiating circuit 20 as shown in FIG. 4c, and changes in accordance with FIG. 4b. The output of this differentiating circuit 20 is input to a comparison circuit 23 and compared with a signal set by a volume control circuit 22 . The signal set by the volume 22 is set slightly higher than the 0 level of the differential value in consideration of noise fluctuations near the 0 level of the output of the differentiating circuit 20. Therefore, the comparison circuit 23 receives the signal from the differentiating circuit 20 from the volume 22.
Count circuit 2 outputs a high level signal when the value is higher than the value set in , and a low level signal when it is lower than the value set in .
Output to 4. This count circuit 24 enters a count start state by a signal from the timer 11,
The number of times the output of the comparator circuit 23 switches from a low level to a high level is counted, and when this count reaches 2 times, the signal that was at a high level until then is switched to a low level signal and the sample hold circuit 27 and transistor 34. The transistor 34 becomes non-conductive when this low level signal is input, and the moment this low level signal is input to the sample hold circuit 27,
The output of the amplifier circuit is held in the sample and hold circuit 27. That is, as is clear from FIG. 4a, a signal corresponding to the air pressure _P1 in the space inside the heat retention furnace 1 at the first inflection point appears in the output of the amplifier circuit 18. This signal is held in the sample hold circuit 27. At this time, the molten metal head has passed through the first constriction between the stalk 3 and the mold 4, and the pressure value corresponds to around P ₁ , which corresponds to the first inflection point on the pressure curve in Figure 4a. The signal is held in the sample and hold circuit 27. That is, during pouring, the air pressure _P1 in the space inside the heat retention furnace 1 at the time when the molten metal head reaches the first constriction part is converted into an electrical signal and held. This held signal is input to the adder circuit 28, and a signal preset by the power supply 37 and the volume controller 38 is input to the other input of the adder circuit 28. The signal set by this regulator 38 indicates the pressure required to fill the molten metal from the first constriction part to the top of the mold, which are both fixed values determined by the mold shape, that is, the filling pressure and the feeder pressure. The adding circuit ₂₈ outputs a signal corresponding to the final target pressure setting value P ₁ +ΔP ₁ to the comparison circuit 29.

Now, in the count circuit 24, if the number of counts is 1+N times, a signal corresponding to the pressure value P _N corresponding to the Nth inflection point is held in the sample hold circuit 27. At this time, the volume is 38
The preset signal is the pressure required to fill the top of the mold from the Nth constriction part with molten metal, that is, the pressure corresponding to the pressure value ΔP _N , which is the sum of the filling pressure and the feeder pressure. It is a value. That is, addition circuit 2
The output final target pressure setting value of 8 is P _N +ΔP _N ,
If the Nth inflection point occurs when the molten metal reaches the top of the mold, ΔP _N will be only the riser pressure.

The comparison circuit 29 compares the signal from the adder circuit 28 and the signal from the amplifier circuit 18 .
When the signal from the adder circuit 28 is lower than the signal from the adder circuit 28, it outputs a high level signal and the transistor 31
is turned on and the valve 15 is opened. Further, a signal corresponding to the pressure inside the heat-retaining furnace 1 always appears at the output of the amplifier circuit 18, and the adder circuit 28
Since _a signal corresponding to the final target pressure (P ₁ + ΔP ₁ ) appears in the output of ₁ ), the valve 15 is closed, and when the pressure inside the heating furnace 1 becomes smaller than the final target pressure (P ₁ + ΔP ₁ ), the valve 15 is opened, and the pressure inside the heating furnace 1 is set to the final target pressure. Maintain the pressure at (P ₁ + ΔP ₁ ).

This pressure P ₁ corresponds to the pressure inside the heat retention furnace 1 when the molten metal passes through the first constriction part, so this P ₁
By adding ΔP ₁ to the final holding pressure in the heat retention furnace 1, the temperature in the heat retention furnace 1 at the start of pressurization
Even if the level of molten metal in the mold fluctuates, the pressure applied to the feeder after the molten metal is completely filled into the mold remains constant.

In order to carry out the above operations within a certain period of time, the timer 11 outputs a low level signal after a certain period of pressurization, so the transistor 33 becomes non-conductive, the valve 15 closes, and the valve 9
Since it is opened, the inside of the heat retention furnace 1 is exhausted,
At the same time, the sample hold circuit 27 and the count circuit 24 are reset.

As described above, in the first embodiment, in order to keep the feeder pressure constant, compared to the conventional method of increasing the final target pressure according to a program, the stalk and gold during pressurization are Since the final target pressure is set and maintained based on the pressure value at the time when it passes a certain fixed point inside the mold, the feeder pressure is much more accurate than before, and it is possible to set and maintain the final target pressure based on the pressure value at the time it passes a certain fixed point in the mold. The effect remains constant even when casting is performed many times during filling.

Furthermore, in the conventional example, a detection mechanism that directly contacts the molten metal is used to detect when the molten metal head passes a fixed point. The molten metal head can be detected simply by attaching a sensor to the casting machine to measure the pressure in the space above the molten metal in the insulating furnace, and the modification of conventional equipment to install the pressure sensor is much easier than modifying the stalk or mold. Therefore, it is much more economical, and since the detector does not come into contact with high-temperature molten metal, it has excellent durability and maintainability. Furthermore, the air pressure supply circuit system can have fewer parts than conventional control devices, and is superior in terms of economy, maintainability, durability, and reliability. Furthermore, since the final target pressure is under feedback control, it is always constant according to the first embodiment even if the supply pressure or leakage amount fluctuates, and the pressure sensor for controlling this final target pressure is Since it also serves as a sensor for detecting the molten metal level, only one sensor is required, making the configuration extremely simple. Furthermore, while pressurizing the heat-retaining furnace, it is possible to display the pressurizing status to a remote worker, which has the advantage of making it easier to discover pressure abnormalities during pressurization.

FIG. 5 shows a second embodiment of the present invention, and parts with the same reference numerals as in FIG. A solenoid valve 25 is provided in parallel to connect air to the bypass pipe, and a relay 26 is provided to supply current to the solenoid valve 25. In the final target pressure state, the solenoid valve 15 remains closed and the valve connected to the bypass pipe is connected to the bypass pipe. The pressure is maintained at a set pressure by turning the electromagnetic valve 25 on and off.

Next, the operation of the second embodiment will be explained. First, the electromagnetic valve 25 connected to the bypass pipe is connected to the relay 2
The electromagnetic valve 15 connected to the main pipe is driven by the relay 32 and the contact 3 of the relay 32.
2a and the contact 30a of the relay 30,
Also, the relay 30 is a transistor 34 or a contact 3
0b and transistor 31.

As in the case of the first embodiment, the start switch 1
When 0 is closed, timer 11 is activated and relay 32 is activated. At this time, the transistor 34 has already
is on, the relays 26 and 30 are turned on, the exhaust electromagnetic valve 9 is closed, the electromagnetic valves 15 and 25 are opened, and pressurization is started. When this pressurization is started, similarly to the first embodiment, the pressure sensor 8, amplifier circuit 18, differentiation circuits 19, 20, comparison circuit 23, count circuit 24, and sample hold circuit 27 detect An inflection point pressure P ₁ of the temporal change in pressure within 1 is detected and held in the sample hold circuit 27 . At the same time as this inflection point pressure P ₁ is held, the transistor 34 is turned off, but a signal corresponding to P ₁ +ΔP ₁ is output to the output of the adder circuit 28.
In addition, this output is compared with the output of the amplification circuit 18 corresponding to the pressure inside the heat retention furnace 1 in the comparison circuit 29. At this point, the pressure inside the heat retention furnace has not reached P ₁ +ΔP ₁ , so the comparison circuit 29 output the level,
Transistor 31 becomes conductive and relay 3
0 and 26 are left in the on state. Note that the transistor 34 will not become conductive again until the pressurization is finished and the timer 11 is activated. Here, when the pressure inside the heat insulating furnace 1 reaches P ₁ +ΔP ₁ , the output of the comparison circuit 29 becomes a low level and the transistor 31 becomes non-conductive, so that the relays 26, 3
0 is off, contacts 26a, 30a, 30b are opened, and valves 15, 25 are closed. When the pressure inside the insulating furnace 1 drops below P ₁ +ΔP ₁ , the comparator circuit 29 outputs a high-level signal, makes the transistor 31 conductive, and turns on the relay 26, but the relay 3
Since the 0 contact 30b is open, this relay 30 is not turned on, the valve 15 remains closed, and only the valve 25 in the bypass piping is opened. In the subsequent operation, the pressure inside the heat insulating furnace 1 is P ₁
When +∆P ₁ is exceeded, the valve 25 closes and the insulating furnace 1
When the pressure inside the furnace 1 drops below P ₁ +ΔP ₁ , the valve 25 opens and the final target pressure inside the heat retention furnace 1 is maintained at P ₁ +ΔP ₁ . During this time, the valve 15 in the main pipe remains closed.

After a certain pressurization time has elapsed, the output of the timer 11 becomes a low level, so the transistor 33 is turned off, the valves 15 and 25 are closed, and the valve 9 is opened, and the air in the heat retention furnace 1 is exhausted. At the same time, the sample hold circuit 27 and the count circuit 24 are reset.

Generally, in low-pressure casting, it is necessary to supply a large amount of air to increase the pressure until the final target pressure is reached within a predetermined time from the start of pressurization, but when the final target pressure is reached, The pressure can be maintained by supplying enough air to compensate for the leakage from inside the insulating furnace. This may be air at a smaller flow rate than during pressurization. In the second embodiment, air is supplied through a large-capacity main pipe and a large-capacity valve 15 during pressurization, and when the final target pressure is maintained, a small-capacity bypass pipe and a small-capacity valve 25 are turned on and off. The system attempts to supply an amount of air equivalent to the amount of leakage.

In the above first embodiment, the large capacity required during pressurization uses a valve as it is, and is repeatedly turned on and off in order to maintain the final target pressure state. If the leakage is large, the number of on/off cycles will increase, but
In general, large-capacity valves have low durability against frequent turning on and off, poor response, and large overshoot. However, in the second embodiment, only a small-capacity electromagnetic valve is turned on and off, and this small-capacity valve is generally durable and responsive to high-frequency on and off operations. Therefore, according to the second embodiment, the durability of the device is increased, the amount of overshoot is reduced, and better pressure control is achieved.

In FIG. 5, symbols 9, 14, 15, 16,
17, 25, 10, 11, 32, 33, 35, 2
9, 31, 26, 35, 34, 30, 35, 36
The pneumatic pressure control means B is composed of the constituent parts represented by , and the other parts are the same as those shown in FIGS. 1 and 2.

Fig. 6 shows a third embodiment of the present invention. Parts with the same symbols as in Fig. 2 indicate the same parts, but in this embodiment, the air pressure is set by turning on and off the valve Instead of maintaining the air pressure at the same pressure, a motor drives the pressure reducing valve to continuously control the air pressure. A power supply 48 for giving an initial setting value to the circuit 47 and a signal setting circuit consisting of a volumetric volume 49 are added to the first embodiment, and the comparison circuit 29 of the first embodiment is
and the transistor 31 are removed, the relay 30 is changed to a contact switching type relay 50, and the relay 30 connected to the valve 15 is removed. Also, the addition circuit 28
The output of is connected to the contact 50b of the relay 50, and the transistor 34 drives the relay 50. The motor control circuit 47 has two inputs, one of which is a reference input, and the contacts 50a and 50 of the relay 50.
b, and the other input is a feedback input, which is connected to the amplifier circuit 18, and rotates the motor 46 in the forward or reverse direction according to the difference between these two inputs.
The output pressure of the pressure reducing valve 14 is adjusted so that the pressure inside the heat retention furnace becomes the reference input.

Next, the operation of this embodiment will be explained. First, the first
Similarly to the embodiment, when the start switch 10 is closed, the timer 11 is activated, the relay 32 is activated, the valve 15 is opened, the valve 9 is closed, and pressurization is started. At this time, the reference input of the motor control circuit 47 receives the signal set by the volume control 49 and the power supply 48 via the contact 50a of the relay 50, so that the pressure inside the heat retention furnace 1 reaches the initial setting pressure. rise towards Here, the initial setting pressure set by the volume 49 and the power supply 48 may be set to a pressure sufficiently higher than the pressure P ₁ at the expected inflection point position. After this pressurization starts, similarly to the first embodiment, the amplifier circuit 18, the differentiating circuits 19 and 20,
The comparison circuit 23, the count circuit 24, and the sample hold circuit 27 detect the pressure _P1 at the inflection point position on the pressure change curve in the heat retention furnace 1,
A signal corresponding to the pressure P ₁ is held in the sample hold circuit 27 and inputted to one input of the adder circuit 28 . The other input of the adder circuit 28 is supplied with the pressure set by the volume controller 38 and the power supply 37 to fill the molten metal from the first constriction part to the top of the mold, that is, the filling pressure and the feeder pressure. Since a signal corresponding to the pressure value ΔP ₁ is input, the addition circuit 28 outputs a signal corresponding to P ₁ +ΔP ₁ to the relay contact 50b. Count circuit 2
4 switches the output from a low level to a high level at the same time as detecting _P1 , so the transistor 34 connected to this count circuit 24 is turned on at the same time, the relay 50 is driven, and the motor control circuit 47 is switched on.
The reference input of the motor control circuit 47 is switched from the initial setting pressure to a signal corresponding to P ₁ +ΔP ₁ .
Since the pressure inside the warming furnace 1 is always inputted to the feedback input of the motor control circuit 47 from the amplifier circuit 18, the pressure inside the warming furnace 1 is P ₁ +ΔP ₁
The motor 46 and the pressure reducing valve 14 work so that the pressure inside the heat retention furnace 1 is maintained at P ₁ +ΔP ₁ , and the feeder pressure is P ₁
remains constant even if changes. Simultaneously with the end of pressurization, the exhaust valve 9 opens, the electromagnetic valve 15 closes, and the reference input of the motor control circuit 47 is connected to the initial setting circuit to be in a reset state.

As described above, according to this embodiment, the valve 15
Since the valve does not have to be repeatedly turned on and off frequently, the life of the valve is significantly improved and the durability of the device is increased.

In addition, in FIG. 6, symbols 9, 14, 15,
16, 17, 46, 10, 11, 32, 33, 3
5, 36, 47, 50, 34, 35, 48, 49
The pneumatic pressure control means B is composed of the constituent parts represented by , and the other parts are the same as those in FIGS. 1 and 2.

FIG. 7 shows a fourth embodiment of the present invention.
Parts with the same symbols as in FIG. 5 indicate the same parts, and in the second embodiment, bypass piping is used to turn on,
However, in this embodiment, continuous control is performed using bypass piping, and the pressure reducing valve 51 that operates according to the pilot pressure is replaced with the pressure reducing valve 14 and the solenoid valve 25 in the bypass piping of the second embodiment. In addition, the bypass piping outlet is connected between the speed controller 16 and the check valve 17 in the main piping. Further, a voltage-pneumatic converter 52 is connected to generate the pilot pressure P _i of the pressure reducing valve 51 according to the output voltage of the adder circuit 28, and the relay 26
A contact 30c is added to the relay 30, and an electromagnetic valve 25 is connected to this so that the contact 30c opens when the relay 30 is on and closes when the relay 30 is off.

Next, the operation of this embodiment will be explained. As in the first embodiment, by closing the switch 10, the timer 11 is activated and pressurization is started. Also, the pressure sensor 8, the amplifier circuit 18, and the differential circuits 19 and 2
0, the comparator circuit 23, and the count circuit 24 detect an inflection point on the pressure curve, and at the same time as this inflection point is detected, the pressure value _P1 at that point is held in the sample hold circuit 27. .
At this time, similarly to the second implementation column, the transistor 34
becomes non-conductive, but at the same time the transistor 31 becomes non-conductive.
becomes conductive, the relay 30 remains on, and the electromagnetic valve 25 remains closed. When the pressure inside the heat insulating furnace 1 exceeds P ₁ +ΔP ₁ , the output of the comparison circuit 29 becomes a low level and the transistor 3
1 becomes non-conductive, the electromagnetic valve 15 closes,
The electromagnetic valve 25 is opened and air pressure is supplied from the bypass circuit. After this, relay contact 30b
is opened, so even if the transistor 31 becomes conductive, the relay 30 is not turned on, and in the final target pressure holding state, air is continuously supplied into the heat retention furnace 1 from the bypass circuit. At this time, the voltage-pneumatic converter 52 is connected to the adding circuit 28.
A voltage corresponding to P ₁ + ΔP ₁ is input, and P ₁ +
A pilot pressure of ΔP ₁ is applied to the pressure reducing valve 51.
The output pressure of this pressure reducing valve 51 is set to be P _i +ΔP _i with respect to the pilot pressure P _i , taking into account the pressure drop ΔP _i from the pressure reducing valve 51 to the space inside the heat retention furnace 1. By doing this, the pressure in the space inside the heat-retaining furnace 1 is maintained at approximately P ₁ +ΔP ₁ .

When the set pressurization time has passed, the timer 11 becomes low level, the transistor 33 becomes non-conductive, the relay 32 opens, and the electromagnetic valve 1
5 and 25 are closed and the electromagnetic valve 9 is opened to end pressurization, the sample hold circuit 27 and the count circuit 24 are reset.

As described above, according to the fourth embodiment, since the valve is not turned on and off frequently, the life of the valve is improved, and the cost is lower than that of the third embodiment, which uses a motor and a motor control circuit. It has the advantage of being cheaper and having improved reliability.

In addition, in FIG. 7, symbols 9, 14, 15,
16, 17, 25, 51, 52, 10, 11, 3
6, 32, 33, 35, 29, 31, 30, 3
Components denoted by 4 and 35 constitute the air pressure control means B, and the other parts are the same as in FIGS. 1 and 2.

As explained above, according to the present invention, the pressure of the air sent into the insulating furnace is measured and the pressure of this air is controlled, so the sensor does not come into direct contact with the molten metal. It has the advantage of increased durability and reliability, and fewer parts than conventional controls.

In the first embodiment described above, as a representative example, the inflection point is detected from point C in FIG. 4 and the pressure is controlled, but the present invention is not limited to this, and In the mold shown in Fig. 4, is the time when the filling in the mold is completed, that is, point E in Fig. 4, and in actual implementation, the maximum and minimum values that occur between the stalk and the filling of the mold are It is sufficient to select and use a convenient one among a large number of inflection points.

As for the pressure sensor as a pressure detection means, we have described a semiconductor pressure sensor, but as long as it can measure the pressure inside the heat insulating furnace or the pressure inside the header 7, it is possible to use a resistance wire strain gauge or a Bourdon tube. It is possible to use either a type that uses a differential transformer or a type that uses a differential transformer.

The signal processing circuit may be constructed of other circuit elements having similar functions other than those shown in the first embodiment, and furthermore, the signal processing circuit may be constructed using, for example, a microcomputer. .
In other words, if a microcomputer is used in the signal processing circuit, changing the condition settings for detecting the position of an inflection point (maximum or minimum point of the slope of the curve) on a pressure curve can be easily done by simply changing the program. is possible, and it is easy to find the optimal conditions. In addition, by changing the shape from the stalk to the top of the mold, even if the appearance of inflection points on the pressure curve (location and number of inflection points) changes, programs can be exchanged without changing the circuit. With this, it is possible to detect a predetermined inflection point position. Furthermore, it has the advantage of increasing reliability and control accuracy.

In addition to the four embodiments described above, the air pressure control means can be modified in various ways as needed.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG.
The figure is a configuration diagram of the first embodiment of the present invention, and FIG.
4 is a sectional view of the pressure sensor, FIG. 4 is an operation waveform diagram of each part of FIG. 2, FIG. 5 is a configuration diagram of the second embodiment of the present invention, and FIG. 6 is a diagram of the third embodiment of the present invention. Diagram,
FIG. 7 is a configuration diagram of a fourth embodiment of the present invention. 1... Heat retention furnace, 2... Molten metal, 3... Stoke,
4... Mold, 5... Air pressure source, 6... Air pressure control device, 7... Header, 8... Pressure sensor,
9... Solenoid valve for exhaust, 10... Start switch, 11... Timer, 12... Signal setting device, 1
3...Signal processing circuit.

Claims (1)

[Claims] 1. Pressurized air is supplied and pressurized to the space above the molten metal in a sealed heat insulating furnace in which molten metal is stored, based on the output signal of the casting start/stop means. In the low-pressure casting machine, the molten metal is guided through a mold connected to a stalk set up in the molten metal and then held under pressure to solidify the molten metal, and then the pressurized air in the heat retention furnace is exhausted. an air pressure measuring means for measuring the air pressure in the heat retention furnace; and detecting an inflection point of the pressure signal from the air pressure measuring means, whereby the cross-sectional area of the molten metal changes suddenly from the stalk to the time when the mold is filled. an inflection point detection means for detecting that a predetermined point has been reached; a pressure required for the stalk to reach the predetermined point according to a signal from the inflection point detection means; a signal processing circuit having a final target pressure determining means for outputting a control signal for determining a final target pressure based on the filling pressure and feeder pressure required until the final target pressure is reached; A low-pressure casting machine comprising: an air pressure control means for controlling the air pressure supplied to the heat retention furnace until the final target pressure is reached; pressure control device. 2. The final target pressure determining means of the signal processing circuit includes:
a memory means for storing the pressure in the heat insulating furnace at the time when the signal is output from the inflection point detection means, and an estimate of the pressure required to complete filling of the molten metal into the mold from the predetermined point and the riser pressure. pressure setting means for setting the pressure, and addition means for adding the pressure signal from the storage means and the setting signal from the pressure setting means and outputting a control signal corresponding to the final target pressure. A casting pressure control device for a low pressure casting machine according to claim 1.