JPS5973169A - Control device for low pressure casting - Google Patents

Abstract

PURPOSE:To eliminate instantaneously the difference between the pressure in a hermetic furnace and a set pressure by providing a mechanism for discharging the gas pressing the surface of the molten metal in the furnace to the outside of the furnace in addition to a mechanism for adjusting the introducing flow rate of said gas and controlling both in accordance with the command from an arithmetic device. CONSTITUTION:A deviation between the set value of the pressure in a holding furnace 1 from an arithmetic device and the detected value of the pressure in the furnace from a pressure gauge 9 is determined with a comparator in a casting device which feeds carrier gas into the furnace to increase the pressure in the furnace and feeds a molten metal 3 into the cavity 5 in a casting mold 4. A motor 15 is driven according to the deviation and a flow rate regulating valve 14 is operated to eliminate the deviation value, whereby the pressure in the furnace adaptive to an elapsed time is accomplished. On the other hand, the controlled pressure in the furnace is inputted to the arithmetic device which feeds an operation command, when said pressure exceeds a set pressure, to a solenoid valve 17 to discharge the gas in the furnace through a stop valve 16 thereby controlling the pressure in the furnace in conjunction with the operation of the valve 14. The pressure in the furnace is thus extremely quickly regulated to the set pressure and the molten metal speed is precisely controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for a low-pressure casting apparatus used for casting aluminum and the like, and particularly to a device for controlling gas pressure in a molten aluminum holding furnace.

[Technical background of the invention]

The supply of molten aluminum (hereinafter referred to as "molten metal") to a mold cavity by a low-pressure casting device is carried out using a device as shown in FIG.

A holding furnace 1 contains a molten metal 3, which is hermetically sealed with a lid 2. By pumping a carrier gas such as air into this holding furnace 1 and increasing the gas pressure in the furnace (hereinafter referred to as ``furnace pressure''), the molten metal is formed inside the mold 4 through 3 molten metals and 6 torches. It is configured to feed into the cavity 5 and fill it. The carrier gas is transferred to pressure reducing valve 7.
The pressure is reduced to an appropriate level and then introduced into the holding furnace 1 via a valve 8. The gas pressure inside the holding furnace 1 is also measured by the pressure side 9. When the molten metal 3 is supplied to the cavity 5 with such a structure, the amount of gas fed into the holding furnace 1 is constant, and therefore the increase in the furnace pressure is also constant.
It remains almost constant.

However, it is generally necessary to change the rate of increase in furnace pressure depending on the shape and size of the mold. This is because the rising speed of the molten metal in the cavity 5 varies depending on the horizontal cross-sectional area of the cavity 5 when the furnace pressure increases to a certain degree. If the cross-sectional area is large, the top speed of the molten metal will be low; if the speed is lower than the required speed, the temperature of the molten metal will drop and surface oxidation will occur, causing defects such as wrinkles and oxide entrainment. On the other hand, if the cross-sectional area becomes smaller and the speed exceeds the required speed, the flow of the molten metal may stagnate, and a jet of molten metal (tin rush) may occur due to one phase. When these phenomena occur, many defects such as oxides, pinholes, blowholes, and specie are generated. In addition, when there is a large amount of hot water in the furnace, the volume of the gas to be brought in is small9, and the pressure at the start of gas feeding is likely to rise rapidly.

As a result, the molten metal 3 splashes, causing the defects described above. In either case, there are problems with the quality, reliability, and economy of the casting. Therefore, when manufacturing castings using the low-pressure casting method, adjusting the molten metal speed and furnace pressure is an important issue in obtaining excellent castings, especially when casting large castings weighing several tens of kg or more. Its importance becomes even more important.

[Problems with background technology]

Conventionally, when casting a simple shape, an operator had to adjust the furnace pressure.

As shown in FIG. 1, for example, about 1
．． 41 (g/crd) of the carrier gas is transferred to the pressure gauge 9 using the valve 8.
The operator makes the adjustments himself while looking at the However, this adjustment method has the disadvantage that it cannot be applied to castings other than simple shapes because the work is complicated and the IAJ accuracy is poor.

One way to solve this problem is to automatically control the pressure inside the furnace. FIG. 2 is a configuration diagram of an adjustment mechanism showing an example thereof.

The 10 reduced pressure sources are actuated using a driving device, such as a ZZ motor 11. The operating amount is determined by the output from the comparator 12, and its output needle is determined by the difference between the furnace internal pressure output by the comparator 12 and the set pressure output from the set value storage output device 13. By using a number of mechanisms like this, it is possible to automatically control the furnace pressure and obtain a molten metal speed suitable for the casting shape. However, even with this method, the relationship between the furnace pressure and the set pressure is There is a difference between them.

In Fig. 3, the furnace internal pressure is controlled using the mechanism shown in Fig. 2.

It is a characteristic diagram showing the set pressure and the control state time of the furnace internal pressure on the horizontal axis. The set pressure is shown by a solid line, and the actual pressure inside the furnace is shown by a broken line. A difference between the set pressure and the measured value of the furnace internal pressure occurs at the start of feeding the carrier gas or when the amount of gas fed suddenly decreases. In such a case, the furnace internal pressure becomes higher than the set value, and the furnace waits for the set pressure to rise with the gas supply stopped. When the set pressure reaches the furnace pressure, gas supply starts again, but the valve that had been closed suddenly closes, causing a sudden inflow of gas, causing the furnace pressure to drop below the set pressure again. becomes. Although the difference between the furnace internal pressure and the set pressure gradually decreases, the phenomenon described above will be repeated several times. This phenomenon is influenced by the response speed of the operated valve, the dimensional tolerances of the valve parts, the transition from the closed state to the open state of the valve, etc. When the cavity 5 is filled with the molten metal 3 in such a state, the molten metal 3 rises in the cavity 5 in a stepwise manner. Therefore, as described above, this causes defects such as oxides and hot water wrinkles, which impairs the quality of the H product.

[Object of the Invention] An object of the present invention is to provide a control device for a low-pressure casting furnace that instantly eliminates the difference between the furnace internal pressure and the set pressure.

[Summary of the invention]

In order to achieve the above object, the present invention provides a low-pressure casting apparatus equipped with a mechanism for filling a cavity in a mold with bath water by pressing the surface of the molten metal in the closed holding furnace with gas. an in-furnace gas supply device that introduces gas for pressing the molten metal surface into the furnace; a gas pressure detection means in the holding furnace; and a preset gas pressure value in the holding furnace and an output value of the detection means. Based on the deviation from )q11! Dedicated gas bit shortage control 1 - flow Nil %Q control valve from the in-furnace gas supply device to extinguish the gas pressure value 7 at which the output value of the detection means is within the set value.
When the temperature exceeds the temperature, a few words are placed in the holding furnace so that the gas in the holding furnace is discharged to the outside of the furnace and the discharge is stopped when the output value of the detection means and the set gas pressure value become equal. Gino et al. 7+ is characterized in that it includes a discharge device, and an arithmetic device that sets a gas pressure value in the holding furnace and sends an operation command signal to the discharge device.

[Embodiments of the invention]

The present invention will be described in detail below based on embodiments.

FIG. 4 is a schematic diagram showing an embodiment of the present invention. In the following drawings, the same parts as shown in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

The flow rate of the carrier gas introduced into the holding furnace 1 is controlled by a variable flow rate regulating valve 14 driven by a servo motor 15. Additionally, the holding furnace l is equipped with an on-off valve 16 for discharging gas within the furnace. The on-off valve 16 is configured to be opened and closed by an electromagnetic valve 17 operated by an operation command signal from an arithmetic unit, which will be described later.

FIG. 5 is a block diagram showing the configuration of the control device. A microcomputer 18 is used as an arithmetic device to send an operation command signal to the on-off valve 16 that has set the furnace pressure.
is used. The microcomputer 18 stores the optimal furnace internal pressure, which is determined by the conditions of the cavity 5 and the holding furnace 1, the temperature of the melt 3, etc., as a set value, and outputs this value every moment.

Since the output of this microcomputer 18 is generally output as a digital signal, it is
The signal is converted into an analog signal and input to the comparator 2J.

On the other hand, the pressure inside the holding furnace 1 due to the gas is detected by the pressure gauge 9, and the pressure inside the holding furnace 1 is detected by the pressure transducer 2tJ.
It is converted into air volume and input to the comparator 2J.

Comparator 2] shows the difference in the input range between the D/A converter 19 and the pressure transducer side, and calculates the deviation it fire height - days? By outputting the signal to the variable flow rate regulating valve 14 via the motor 15, the valve of the variable flow rate regulating valve 14 is adjusted so as to eliminate the deviation M:. The internal pressure in the holding furnace 1 is converted into a digital signal by the A/D converter 22 and fed back to the microcomputer 18. On the other hand, from the microcomputer 18, the %i1 magnetic valve magnet 17 which drives the on-off valve 16
An operation command signal is outputted via the contact output device 23.

The operation of the thus configured control device will now be described.

Dry gas (for example, dry air) with a manual pressure of 6 kg/i is reduced in pressure by the pressure reducing valve 7 to 1>1.4 kgA-rI and reaches the variable flow rate 1iIA1 regulating valve 14. Here, the microcomputer 18 transmits the set pressure adapted to the elapsed time to the D/A converter 19y! It is output to the comparator 21 via l-. The comparator 21 measures the deviation from the electrical quantity from the pressure gauge 19, and by outputting this deviation to the servo motor 15, the variable flow rate regulating valve 14 is operated. Since the furnace internal pressure is configured to be foot-checked to the microcomputer 8 via the A/D converter 22, the above-mentioned deviation is eliminated and the furnace internal pressure is adjusted in accordance with the elapsed time. It will be.

However, the variable flow rate regulating valve 14 is slow! 1, so if the pressure inside the furnace exceeds the set pressure, this device operates as follows. The furnace internal pressure is input to the microcomputer 18 via the A/D converter 22 and is constantly compared with the set pressure, so if the furnace internal pressure exceeds the set pressure, the contact output device 23 An operation command signal is sent to the solenoid valve 17 through the solenoid valve 17, and the on-off valve 16 is opened and the gas in the furnace is discharged. Therefore, the furnace pressure instantly decreases and approaches the set pressure. Even when the on-off valve 16 is operated in this way, the furnace internal pressure is controlled by the variable flow rate adjustment valve 14, and when the furnace internal pressure reaches the set pressure, the on-off valve 16 closes. , the exhaust of gas inside the furnace will stop.

Conventional control devices do not have such a discharge device, so adjustment of the furnace internal pressure and set pressure is done using a variable flow adjustment valve (14).Therefore, it takes a long time for the two to match. There was a case. However, since the present invention is provided with a discharge device, even if a difference occurs between the furnace internal pressure and the set pressure, it operates so that this difference is instantly eliminated.

〔Effect of the invention〕

As described above in detail based on the embodiments, in this invention, in addition to the KWM regulating mechanism for the flow of the gas introduced into the furnace, a discharge device for discharging the gas introduced into the furnace outside the furnace is provided, so that both can be controlled. Since the furnace is configured to be controlled based on commands from the device, there is an advantage that the pressure inside the furnace can be adjusted to the set pressure extremely quickly.

However, the use of this method has the excellent effect of stably supplying high-quality products with very few defects.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a conventional device, Fig. 2 is an example of a conventional in-furnace controller 11, and Fig. 3 is a diagram showing an example of the side of the conventional furnace internal pressure controller. Characteristic diagram showing control status,
FIGS. 4 and 5 show an embodiment of the present invention.
), FIG. 4 is a schematic configuration diagram thereof, and FIG. 5 is a block diagram thereof. l... Holding furnace, 3... Molten metal, 4... Mold, 5...
・Cavity, 9...Pressure gauge, 12...Comparator, 1
4... Variable flow area regulating valve, 16... Opening/closing valve, 17.
...Solenoid valve, 18...Microcomputer, n...
・Contact output device. Applicant's agent Kiyoshi Inomata Cause 3 Figure 4

Claims (1)

[Claims] A machine for filling the cavity in the mold with the molten metal by pressing the surface of the molten metal in the closed holding furnace with the introduced gas! / A low-pressure casting apparatus equipped with: an in-furnace gas supply device for introducing gas for pressing the molten metal level into the holding furnace; a means for detecting the gas pressure in the holding furnace; a flow rate regulating valve that controls an inlet gas flow area of an in-furnace gas supply device in an nIJ recording furnace to eliminate the deviation based on a deviation between a gas pressure value in the furnace and an output value of the detection means;
When the output value of the detection means exceeds the set gas pressure value, the gas in the holding furnace is discharged to the outside of the furnace, and the output value of the detection means and the set gas pressure (g+I) are a discharge device attached to the holding furnace so as to stop discharge when the pressure becomes equal; a calculation device that sets the gas pressure value in the holding furnace and sends an operation command signal to the discharge device; A low-pressure casting control device with the following features.