JPH1157981A - Pressure reducing suction casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously realize the improvement of pressure reducing responsiveness and the accurate adjustment of pressure reducing degree. SOLUTION: An adjusting valve 21 for reducing pressure, continuously changing the opening degree according to an inputted analog signal 61a, is interposed in a pressure reducing passage 91 connected with a chamber 1 at the one end and reaching a vacuum pump 4 at the other end. A PID control part 61 of a sequncer device 6 selectively outputs a feedback arithmetic output based on the negative pressure in the chamber 1 and a forced operational output to the adjusting valve 21 for reducing pressure as an analog signal 61a. In the case of necessitating he change of the pressure reducing degree in a short time, the PID control part 61 outputs the forced operational output to the adjusting valve 21 for reducing pressure as the analog signal 61a. In the case of necessitating the adjustment of the accurate pressure reducing degree, the PID control part 61 outputs the feedback arithmetic output to the adjusting valve 21 for reducing pressure as the analog signal 61a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum suction casting apparatus, and more particularly to an improvement in a vacuum exhaust system.

[0002]

2. Description of the Related Art A vacuum suction casting apparatus performs a precision casting by placing a mold in a depressurized chamber and sucking a molten metal into a cavity. In this type of vacuum suction casting apparatus, a pressure reducing path leading to a negative pressure source and a return pressure path leading to a positive pressure source, each having a control valve interposed therebetween, are connected to the chamber, and the opening of both control valves is adjusted appropriately. In some cases, the degree of pressure reduction in the chamber is made to accurately follow a predetermined pattern by adjusting the pressure.

[0003] By the way, it is necessary to change the decompression pattern according to the target casting. In particular, when manufacturing a thin casting, it is necessary to finish the decompression treatment in a few seconds in order to prevent poor running of the molten metal. It is necessary to quickly change the degree of reduced pressure in the chamber according to the reduced pressure pattern. In order to change the degree of pressure reduction in a short time, the response of the control valve is required, and conventionally, for example, as disclosed in JP-A-62-3861 and JP-A-8-300136, It has been practiced to provide a plurality of solenoid valves in parallel in the middle of a pressure return path and selectively open them to change the flow path area with good responsiveness.

[0004]

However, the one disclosed in the above publication, in which the flow passage area is changed by an electromagnetic valve, is as follows.
Although the responsiveness is excellent, the change in the flow path area is stepwise and discontinuous. is there.

An object of the present invention is to provide a reduced-pressure suction casting apparatus which achieves both improvement of the reduced-pressure response and precise adjustment of the reduced-pressure degree.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, one end is connected to a pressure reducing passage (91) which is connected to the chamber (1) and the other end is connected to a negative pressure source (4). A pressure reducing control valve (21) whose opening is continuously changed according to the degree change signal (61a) is provided, and a negative pressure in the chamber (1) is supplied to the pressure reducing control valve (21). A valve control means (6) for selectively outputting a feedback calculation output based on the above and a forced operation output as an opening degree change signal (61a) is provided.

In the first invention, when it is necessary to change the degree of pressure reduction in a short time, the valve control means outputs a forced operation output to the pressure reducing control valve as an opening degree change signal.
Since the forced operation output is not delayed by the feedback loop, the pressure reducing control valve quickly reaches a desired opening degree, and the pressure reducing degree in the chamber is quickly changed. On the other hand, when precise pressure reduction adjustment is required, the valve control means outputs a feedback calculation output to the pressure reduction control valve as an opening change signal. As a result, the opening of the pressure reduction control valve is changed based on the negative pressure in the chamber so that the pressure is accurately matched with the target pressure reduction degree.

In the second aspect of the present invention, the speed increasing bypass valve (32) is provided in parallel with the pressure reducing control valve (21), and the valve control means (6) is forcibly applied to the pressure reducing control valve (21). It is set so that a signal for opening the speed increasing bypass valve (32) is issued for an appropriate time while the operation output is output as the opening change signal (61a).

In the second aspect of the invention, by outputting the forced operation output as an opening change signal, the pressure reducing control valve is quickly changed to a desired opening. At this time, if the speed-up bypass valve is opened as required, the exhaust in the chamber further proceeds, the degree of pressure reduction is rapidly changed to a higher direction, and the pressure reduction response is further improved.

[0010] The symbols in parentheses of the above means indicate the correspondence with the concrete means described in the embodiments described later.

[0011]

FIG. 1 shows a piping and wiring system diagram of a vacuum suction casting apparatus. In the figure, the solid line is a piping system, and the broken line is a wiring system. In the figure, a decompression tube 91 is connected to a chamber 1 for accommodating a mold.
To the vacuum pump 4 as a negative pressure source. The deceleration adjusting valve 21 is connected in parallel with the speed increasing bypass valve 32.
Is connected. Further, between the pressure-reducing shut-off valve 31 and the vacuum pump 4, a pressure-reducing pipe 91 branches off from the pressure-reducing pipe 91 to reach the booster tank 5, and the pressure-reducing pipe 92 is provided with a speed-up shut-off valve 33. I have. The capacity of the booster tank 5 is set such that a sufficient pumping speed can be obtained while rapid depressurization is required in the depressurizing process described later.

At a position upstream of the pressure reducing control valve 21, the pressure reducing pipe 9
An air pressure recovery pipe 93 branches from 1 and is open to the atmosphere via an air pressure reduction control valve 22 provided on the way. At the above position, Ar
Ar gas is supplied by branching the pressure recovery pipe 94 and opening the Ar shut-off valve 34 provided therein.

A sequencer device 6 is provided, and its PI
Analog output signal 61 as an opening change signal of D control unit 61
a, the opening degree of the pressure reducing control valve 21 is continuously changed, and the analog output signal 62 a of the ratio bias (RB) section 62 provided at the subsequent stage of the PID control section 61 opens the air return pressure controlling valve 22. The degree is changed continuously. As a result, as shown in FIG. 2, while the output signal 61a of the PID control unit 61 changes between 0% and 100%,
The opening degree of the pressure-reducing control valve 21 and the air return-pressure control valve 22 is continuously changed so that they are not simultaneously opened in principle.

A detection signal 11a corresponding to the degree of pressure reduction in the chamber is fed back from the pressure transmitter 11 provided in the chamber 1 to the PID controller 61. In addition, PID
The control unit 61 outputs, as the signal 61a, a result obtained by performing a comparison operation between the target pressure reduction degree and the fed back detection signal 11a of the pressure transmitter 11, as well as a feedforward forced operation output as the signal 61a. It can be output to the pressure reducing control valve 21.

An input touch panel 7 is connected to the sequencer device 6, and a pressure reduction pattern for each target casting is set. Specifically, the pressure reduction pattern is a target pressure reduction degree given to the PID control unit 61 and its duration, each constant of the PID control unit 61 at this time, and the value of the forced operation output and its duration when PID control is not performed. Time and pressure reducing shut-off valve 3
1, the opening / closing timing of the speed increasing bypass valve 32, the speed increasing shutoff valve 33, the Ar shutoff valve 34, and the like. The set pressure reduction pattern for each target casting is hard copied by the printer 71 and stored in the IC card by the memory card recorder 72. The sequencer device 6 is provided with information on a target casting or the like from a central process computer (pro computer) 8, and based on the information, a pressure reduction pattern is selected.
A decompression process in the chamber 1 is performed as will be described later.

FIG. 3 shows a time chart of the decompression process under the selected decompression pattern. In this decompression process, the degree of decompression ((1) in FIG. 3) increases in a substantially S-shaped curve from the processing start point (S point in the figure), and ends in the processing (E in the figure).
At point), the pressure is restored and the pressure returns to atmospheric pressure. Prior to the start of the process, the pressure reducing control valve 21 is opened to a predetermined opening (for example, 30%) by a forced operation output from the PID control unit 61 (FIG. 3 (2)). 33 is opened (FIG. 3 (5)), and the booster tank 5 is reduced to a predetermined negative pressure.

When the pressure-reducing shut-off valve 31 is opened at the start of the pressure-reducing process (FIG. 3 (4)), the gas is exhausted from the chamber 1 to the booster tank 5 via the pressure-reducing control valve 21. In the present decompression process, the opening degree of the decompression control valve 21 is temporarily reduced (for example, 10 degrees) immediately after the start of the decompression process in order to realize an S-shaped curve of the decompression degree change.
%), And thereafter the opening degree is increased (for example, 25%).
When the pressure-reducing control valve 21 once squeezed is opened again, the speed-up bypass valve 32 is simultaneously opened (FIG. 3).
(6)) The reduced pressure response is improved. The processing time required during this time (time T1 in FIG. 3) is a few seconds.

Thereafter, the opening control of the pressure-reducing control valve 21 is controlled by P
The control is switched to the ID control, and during this time, the speed increasing cutoff valve 33 is continuously opened. Since the booster tank 5 maintains a sufficient exhaust capacity, the pressure-reducing control valve 21 is placed in a feedback-controlled state without being fully opened,
In this state, the degree of decompression in the chamber 1 is reduced for a sufficiently short time T2.
(Approximately 1.5 seconds) to reach the target value P1. After the elapse of time T2, the pressure reduction target value is switched to P2, and the pressure reduction control valve 2
The opening of 1 is adjusted under the PID control, and the degree of pressure reduction in the chamber reaches the target value P2 (time T3 in FIG. 3).

The speed increasing shut-off valve 33 is closed after a lapse of time T2. This is because the negative pressure in the booster tank 1 having a limited capacity is reduced during the processing during the time T2, and the booster tank 1 no longer contributes to an increase in the exhaust capacity. This is because if it is kept connected, the load on the vacuum pump 4 is increased. Thus, only when the negative pressure is high and the exhaust capacity is sufficient, the speed-up shut-off valve 33 is opened to communicate the booster tank 5 with the chamber 1, so that the capacity of the booster tank 5 is minimized. And the size can be avoided.

During the time T4 after the elapse of the time T3, the degree of pressure reduction in the chamber 1 is maintained at the target value P2. In order to avoid overshoot of the decompression degree at the beginning of time T4, PID
The controlled pressure-reducing control valve 21 is once in a fully closed state. During this time, the air return-pressure control valve 22 is opened and air is introduced into the chamber 1. Thereafter, the negative pressure in the chamber 1 is accurately maintained at the predetermined value P2 by adjusting the opening of the pressure reducing control valve 21 by PID control.

After the elapse of the time T4 and the completion of the decompression process, the decompression shutoff valve 31 is closed, the Ar shutoff valve 34 is opened (not shown), and the pressure in the chamber 1 is restored. At this time, the speed increasing bypass valve 32 is also opened, and the pressure inside the pressure reducing pipe 91 leading to the pressure reducing cutoff valve 31 is also restored. On the other hand, the speed increasing cutoff valve 33 is opened, and the evacuation of the booster tank 5 by the vacuum pump 4 is started.

[0022]

As described above, according to the vacuum suction casting apparatus of the present invention, it is possible to achieve both improvement of the reduced pressure response and precise adjustment of the reduced pressure degree.

[Brief description of the drawings]

FIG. 1 is a piping / wiring system diagram of a vacuum suction casting apparatus.

FIG. 2 is a graph showing a relationship between an output value of a PID control unit and a control valve opening degree.

FIG. 3 is a time chart at the time of a decompression treatment by a decompression suction casting apparatus.

[Description of Signs] 1 ... chamber, 21 ... pressure reducing control valve, 32 ... speed increasing bypass valve, 33 ... speed increasing shutoff valve, 4 ... vacuum pump (negative pressure source), 6 ... sequencer device (valve control means) ), 61a: analog output signal (opening change signal), 91: pressure reducing tube.

Claims (2)

[Claims] A pressure reducing control valve whose one end is connected to a chamber and the other end of which is connected to a negative pressure source is provided with a pressure reducing control valve whose opening is continuously changed in response to an opening changing signal. A pressure control means for selectively outputting a feedback calculation output based on the negative pressure in the chamber and a forced operation output to the pressure reducing control valve as the opening degree change signal. Suction casting equipment. 2. A speed increasing bypass valve is provided in parallel with said pressure reducing control valve, and said valve control means is adapted to output a forced operation output to said pressure reducing control valve as said opening change signal. 2. The vacuum suction casting apparatus according to claim 1, wherein a signal for opening the speed-up bypass valve is issued for an appropriate time.