JPH0857626A - Method for controlling pressure of low pressure casting machine - Google Patents

Abstract

PURPOSE: To provide a pressure control method of a low pressure cast. ing machine which keeps the good product quality and improves the productivity. CONSTITUTION: The control unit arranges a data registration means 50 for registering a basic pressurizing curve corresponding to a used metallic mold, correcting pressure at each time of the casting and a necessary holding pressure to hold molten metal in a stoke to a prescribed height, an arithmetic means 51 for calculating an executive pressurizing curve based on casting counter value, a pressurizing curve registration means 52 for registering the executive pressurizing curve and a control means 53 for executing the pressurization of gas in a holding furnace and gas exhausting control based on the executive pressurizing curve from an outer part signal are arranged. Then, the arithmetic means 51 calculates the executive pressurizing curve A from the basic pressurizing curve and the holding pressure at the first time of casting and corrects the first time of executive pressurizing curve A based on the correcting pressure, the holding pressure and a first step of pressure rising speed of the basic pressurizing curve at the second time of casting and corrects the executive pressurizing curve of the last time based on only the correcting pressure at the third time and after.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure control method for a low pressure casting machine.

[0002]

2. Description of the Related Art Generally, in a low pressure casting machine, a molten metal is stored in a holding furnace, a gas is supplied to a space above the molten metal surface in the holding furnace according to a predetermined pressurizing curve, and the molten metal is hung vertically in the holding furnace. After pushing the molten metal into the mold through the stalk and filling it, the gas pressure is maintained for a certain period of time to solidify the molten metal to the extent that the levitation effect is not required, then the gas in the holding furnace is exhausted and The molten metal is returned to the holding furnace. However, in this method, since the molten metal head surface in the holding furnace descends as the number of castings increases, improper turning occurs if casting is performed with the same pressurizing curve. Therefore, in order to solve this problem, a method of correcting the pressure curve according to the number of castings has been proposed (for example, Japanese Patent Laid-Open No. 62-8).
1258).

Further, in order to prevent air from entering the stalk when the molten metal rises or descends in the stalk and prevents the quality of the cast product from deteriorating due to the entrainment of air into the smelt, before opening the mold. A method of holding the molten metal in the stalk at a predetermined height has been proposed (for example, Japanese Patent Laid-Open No. 5-1).
31261 gazette).

[0004]

In a low pressure casting machine,
In order to prevent improper rotation and to prevent the casting quality from deteriorating due to the inclusion of oxides in the stalk, the molten metal in the stalk from the time before the mold is opened to the time when the pressure is started is kept at a predetermined height regardless of the number of castings. Need to hold. In the conventional method, only the pressure to be applied was corrected according to the number of castings, so it was possible to maintain the molten metal in the stalk at a predetermined height from before mold opening until the start of pressing. As shown, there is a drawback that the pressure rising speeds of the first stage of the pressurizing curves after the first casting and the second casting do not match, and there is a dead time in the second stage of pressing after the first stage.

According to the present invention, when the pressure of the gas in the holding furnace is changed stepwise to fill the cavity in the mold with the molten metal, 2
In order to always match the pressurization rate of the pressurization curve after the first time with the pressurization rate of the first basic pressurization curve created so as not to cause defects, regardless of the number of castings, the switching time after the second time and The pressure is corrected and controlled, and the molten metal in the stalk is held above the stalk before the mold is opened to stabilize the product quality and to improve productivity by eliminating boost dead time. An object is to provide a pressure control method for a casting machine.

[0006]

In order to solve the above technical problems, the present invention provides a pressure control method for a low pressure casting machine, which counts the number of castings and corrects the pressurizing curve at the time of pressurization based on the counted value. , The basic pressurization curve corresponding to the mold used, the correction pressure to be corrected for each number of castings, and the holding pressure required to hold the molten metal surface in the stalk at a predetermined height are registered. In the casting of, the execution pressurizing curve is calculated by the basic pressurizing curve and the holding pressure, and in the second casting,
The first execution pressurization curve is corrected on the basis of the correction pressure, the holding pressure, and the first-stage pressurization speed of the basic pressurization curve. A pressure control method for a low-pressure casting machine is used, which is characterized in that an execution pressurization curve for each corresponding time is created by performing correction based on

Then, the calculation means performs the following calculation according to the number of castings, and creates an execution pressurization curve for each corresponding number of times. That is, in the first casting, the execution pressurization curve is calculated by using the basic pressurization curve and the holding pressure, and in the second casting, the first execution pressurization curve is calculated by the correction pressure, the holding pressure and the basic pressurization. The pressure curve is corrected based on the first stage pressure increase rate, and the third and subsequent pressures are corrected based on only the corrected pressure.

[0008]

In the present invention, when the start signal is input, the arithmetic means controls the first casting by using the basic pressurizing curve and the holding pressure corresponding to the mold used in the data registering means. The means creates an execution pressurization curve output for each unit operation time and stores it in the pressurization curve registration means.

Next, when the pressurization start signal is input, the control means pressurizes the molten metal surface in the holding furnace according to the execution pressurization curve stored in the pressurization curve registration means, and the molten metal is passed through the stoke. To fill the mold cavity. Then, if the molten metal is solidified to a degree that does not require the feeder effect, the pressurizing gas is exhausted, and if the gas pressure in the holding furnace reaches the holding pressure for holding the molten metal in the stalk at a predetermined height. , Maintain its pressure.

In the second casting, when the start signal is input, the calculating means receives the start signal from the first execution pressurizing curve stored in the pressurizing curve registering means, and the inclination A01 of the first stage (FIG. 2).
The reference pressure is calculated, and the holding pressure and the correction pressure registered in the data registration means and the slope A01 are used to calculate a second execution pressurization curve output by the control means for each unit operation time, and pressurization is performed. Store in the curve registration means.

When the pressurization start signal is input, the control means pressurizes the molten metal surface in the holding furnace in accordance with the execution pressurization curve stored in the pressurization curve registration means, as in the first casting.
The molten metal is filled into the mold cavity through the stalk.
Then, if the molten metal is solidified to a degree that does not require the feeder effect, the pressurizing gas is exhausted, and if the gas pressure in the holding furnace reaches the holding pressure for holding the molten metal in the stalk at a predetermined height. , Maintain its pressure.

In the third and subsequent castings, when the start signal is input, the calculation means calculates the holding pressure and the correction pressure registered in the data registration means from the previous execution pressurization curve stored in the pressurization curve registration means. Using the control means, a second execution pressurization curve output by the control means for each unit operation time is calculated and stored in the pressurization curve registration means.

When the pressurization start signal is input, the control means pressurizes the molten metal surface in the holding furnace according to the execution pressurization curve stored in the pressurization curve registration means, as in the previous casting, and melts the molten metal. Is charged into the mold cavity through the stalk. Then, if the molten metal is solidified to a degree that does not require the feeder effect, the pressurizing gas is exhausted, and if the gas pressure in the holding furnace reaches the holding pressure for holding the molten metal in the stalk at a predetermined height. , Maintain its pressure.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is a holding furnace for storing molten metal, and the upper part is closed by a platen 11. Then, a pouring hole 14 is formed in the central portion of the platen 11 and a stalk 12 is vertically provided, and the mold 1 is placed on the platen 11.
Set 3. The compressed air source 20 includes a filter 21,
Mist separator 22, primary pressure reducing valve 23, solenoid on-off valve 2
4, the power pressure reducing valve 8 and the electromagnetic opening / closing valve 25 are connected in this order to the air supply hole 15 provided in the platen 11. The electropneumatic proportional valve 7 is connected to the conduit 30 via a branch pipe 31,
The electropneumatic proportional valve 7 is connected to the pilot portion of the power pressure reducing valve 8 via the conduit 32. From the conduit 33, the electromagnetic on-off valve 28 is connected via a branch pipe 34, and the exhaust valve cylinders 26a, 27a are connected via conduits 38a, 38b. Conduits 38a, 3
In the middle of 8b, exhaust cylinder valve cylinders 26a, 27
In order to perform speed control of a, the flow rate adjusting valves 29a, 29b
Connect. The exhaust valve 26b is connected to the exhaust hole 16 of the platen 11 via a conduit 35, and the exhaust valve 27b is connected to a conduit 36 via a branch pipe 37. At the tip of the conduit 35, pressure sensors 5 and 6 for measuring the pressure inside the holding furnace are connected. The electropneumatic proportional valve 7 is electrically connected to the pressure controller 1 via the amplifier 9 and the D / A converter 2, and the pressure sensors 5 and 6 are electrically connected to the pressurization controller 1 via the A / D converter 3. The on-off valves 24, 25, 28 are also electrically connected to the pressurization controller 1. Further, the pressurizing controller 1 is connected to a display 4 for monitoring the stored pressurizing curve and the actual pressurizing curve.

FIG. 4 shows the structure of the pressure controller 1. The pressurizing controller 1 includes a basic pressurizing curve corresponding to a die used and a correction pressure ΔPS (FIG. 2) for correcting each casting number.
(Refer to FIG. 2), the data registration means 50 for registering the holding pressure ΔPH (see FIG. 2) necessary to hold the molten metal surface in the stalk at a predetermined height, and the casting number counter 54 for counting the number of castings. Then, by the start command 61, an execution pressurization curve is calculated from the basic pressurization curve of the data registration means 50 based on the casting counter value of the casting number counter 54, and the execution pressurization curve is stored in the pressurization curve registration means 52. Based on the execution pressurization curve in the pressurization curve registration means 52 by the arithmetic means 51 to register and the pressurization start signal 62 externally input after the mold is closed after the start command 61 is input, the inside of the holding furnace A control means 53 for controlling pressurization and exhaust of gas and outputting a pressurization end signal 63 to the outside upon completion of pressurization to open the mold by an external device (not shown), and a basic pressurization curve. And execution pressurization curve Display the actual pressurization curve 4
It is composed of a pressurizing curve display means 55 for outputting to.
The casting number counter 54 is reset by the reset command 60. The pressure controller 1 may be a microcomputer, programmable controller, personal computer, or the like.

Next, the operation of the pressure controller 1 will be described with reference to FIGS. 1 and 2. First, a predetermined amount of molten metal is supplied to the holding furnace 10, and the set pressure of the primary pressure reducing valve 23 is set to the maximum pressure applied to the holding furnace 10. When the apparatus is started, the pressurization controller 1 operates the electromagnetic opening / closing valve 24 to send air to the electropneumatic proportional valve 7 and the power pressure reducing valve 8. By the closing confirmation signal of the mold 13,
By operating the electromagnetic opening / closing valve 28, the exhaust cylinders 26a, 27a are operated, the exhaust valves 26b, 27b are closed, and the electromagnetic opening / closing valve 25 is operated to hold the holding furnace 10.
Make the space above the surface of the inner bath pressurized. Pressure sensor 5,
The pressure of the molten metal surface space 17 in the holding furnace 10 is detected by 6 and this pressure signal is input to the pressurization controller 1 via the A / D converter 3. By inputting this pressure signal, the pressurization controller 1 calculates the required pressurizing force to the space above the molten metal surface inside the holding furnace 10 based on the registered basic pressurization curve, and the calculation result is used as the D / A converter 2 And output to the electropneumatic proportional valve 7 via the amplifier 9. Here, the reason why two pressure sensors 5 and 6 are provided is to detect an abnormality of one of the pressure sensors by comparing and calculating the pressure values of the two.

FIG. 2 shows an example of the execution pressurization curve created by the arithmetic means 51 and registered in the pressurization curve registration means 52.
After the mold 13 is closed and the pressurization start signal output from an external device (not shown) is input, the molten metal upper space 1 of the holding furnace 10
7 shows the time change of the pressure applied to 7. In the first casting, the pressurization curve A is created based on the basic pressurization curve and the holding pressure ΔPH, and pressurization control is performed. The molten metal level in the stalk 12 before pressurization is the same as the molten metal level of the holding furnace 10. In the first stage (in the figure), the molten metal level in the stalk 12 is raised above the stalk 12. In the second stage (in the figure), the mold 13 is filled with molten metal. Third
The feeder pressure is applied in the step (in the figure), and the pressure is maintained and solidified in the fourth step (in the figure) until the effect of the feeder is unnecessary. At the fifth stage (in the figure), the electromagnetic opening / closing valve 25 is turned off to shut off the pressurization into the holding furnace 10, and
The electromagnetic on-off valve 28 is turned off, and the compressed air in the molten metal upper space 17 in the holding furnace 10 is exhausted from the exhaust valves 26b and 27b. At the sixth stage (in the figure), when the pressure of the space above the molten metal in the holding furnace 10 reaches the molten metal holding pressure ΔPH in the stalk,
The electromagnetic opening / closing valve 25 is turned on, the electromagnetic opening / closing valve 28 is turned on, and the electropneumatic proportional valve 7 is controlled so as to follow the pressurizing pattern. The above is the operation of the first casting cycle.

Next, before starting the second casting, the first-stage inclination B01 of the second-time pressing curve is made equal to the first-step inclination A01 of the first-time pressing curve. Inflection point B
1 at time TB1 and pressure PB1 at inflection point A1 at time T
It is calculated by the following formula based on A1 and pressure PA1. TB1 = TA1 + Δt −−−−−−−−−−−−−−−−−−− (1) Δt = (ΔPS−ΔPH) / A01 −−−−−−−−−−−− −− (2) PB1 = PA1 + ΔPS −−−−−−−−−−−−−−−−−− (3) Δt: correction time ΔPS: correction pressure ΔPH: melt holding pressure in stalk A01 Slope at the first stage of the first pressurization curve Similarly, for the inflection points B2 to B5, the correction time Δt and the correction pressure ΔPS are based on the inflection points A2 to A5 of the first pressurization curve A. The pressure curve B is created by correcting The slope of the second pressurization curve B thus obtained is the same as that of the first pressurization curve A at all stages. Therefore, it is possible to obtain a cast product of the same quality as that cast by the pressurization curve A.

Before starting the third casting, the pressure curve C is prepared by correcting only ΔPS based on the second pressure curve B. That is, the time TC1 of the inflection point C1 of the third pressurization curve C to be obtained and the pressure PC1 are the second pressurization curve B
It can be expressed as follows using the time TB1 of the inflection point B1 and the pressure PB1. TC1 = TB1 −−−−−−−−−−−−−−−−−−− (4) PC1 = PB1 + ΔPS −−−−−−−−−−−−−−− (5) Inflection Similarly, the points C2 to C5 can be obtained by correcting only the correction pressure ΔPS to the pressure with reference to the inflection points B2 to B5 of the second pressurization curve B. The slope of each step of the third pressurization curve C thus obtained is
The same as the second pressurization curve B at all stages,
A cast product of the same quality as that cast by the pressurization curve B can be obtained.

After the fourth casting, the same correction is performed before the third casting, and the same inclination is obtained in all stages, so that castings of the same quality can be cast. Further, the end of casting is when the molten metal in the holding furnace 10 is exhausted or when the expected number of castings is completed. As the former detection method, the amount of residual molten metal in the holding furnace 10 is detected by a sensor. Or, since the amount of molten metal required for one casting is known in advance, the amount of molten metal supplied to the holding furnace 10 should be controlled so that the molten metal per casting is calculated from the amount of molten metal remaining in the holding furnace 10 each time casting is performed. It is possible to determine the end of casting by subtracting the amount. The latter can be judged by counting the number of castings with a counter or the like.

[0022]

As described above, according to the present invention, regardless of the number of castings, the slope of the pressurizing curve becomes the same in all cycles, and casting with reproducibility becomes possible. Further, not only improper rotation and casting failure due to oxide entrainment can be prevented, but also the cycle time can be shortened.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an execution pressurization curve according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining correction of a pressurizing curve in a conventional technique.

FIG. 4 is a view for explaining internal means of the pressure controller according to the embodiment of the present invention.

[Explanation of symbols]

 1 Pressure Controller 2 D / A Converter 3 A / D Converter 5 Pressure Sensor 6 Pressure Sensor 7 Electropneumatic Proportional Valve 9 Amplifier 10 Holding Furnace 12 Stoke 13 Mold 17 Space above Water 50 Data Registering Means 51 Computing Means 52 Pressurization curve registration means 53 Control means 54 Casting frequency counter

Claims (1)

[Claims] 1. A pressure control method for a low-pressure casting machine, which counts the number of castings and corrects the pressurizing curve at the time of pressurization based on the count value. The correction pressure to be corrected for each time and the holding pressure necessary to hold the molten metal surface in the stalk at a predetermined height are registered, and in the first casting, the basic pressurization curve and the holding pressure are used to perform pressurization. A curve is calculated and created, and in the second casting,
The first execution pressurization curve is corrected on the basis of the correction pressure, the holding pressure, and the first-stage pressurization speed of the basic pressurization curve. A pressure control method for a low-pressure casting machine, characterized in that an execution pressurization curve for each corresponding time is created by performing correction based on the above.