JP5912547B2 - Method for calculating volume of furnace air chamber, casting method, apparatus for calculating volume of furnace air chamber, and program for calculating volume of furnace air chamber - Google Patents

Description

  The present invention relates to a technique for obtaining a volume of an air chamber in a furnace for holding a molten metal used for casting, and a technique using the technique.

  As a low-pressure casting apparatus, a structure is known in which high-pressure air is supplied to an air chamber, which is a space above a molten metal surface in a furnace (crucible), and the molten metal is cast into a mold through stalk immersed in the molten metal. Yes. In such a low-pressure casting apparatus, it is necessary to control the amount of high-pressure air supplied so that the behavior of the molten metal in the mold is appropriate. By the way, in the low-pressure casting apparatus as described above, an inertial fluid called a molten metal is pressurized by compressible air, and therefore the actual pressure rise is delayed with respect to the commanded air pressure in the feedback control. Then, the delay is reflected in the feedback control, and an overshoot occurs in which the actual pressure becomes higher than the instructed pressure. For this reason, the air pressure fluctuates greatly, and pulsation occurs in the molten metal transported toward the mold. As a result, the surface of the molten metal undulates or the molten metal flows backward in the mold, and there is a high probability that a casting defect will occur due to a hot water boundary, unfilled, or air entrainment.

  As a low pressure casting control technique that can control the position of the molten metal surface without causing delay or overshoot with respect to the indicated value, and can make the behavior of the molten metal in the mold appropriate, Patent Literature The content of 1 is proposed.

JP 2010-227974 A

  In the technique described in Patent Document 1, the height of the molten metal surface in the stalk is predicted by calculation at a stage where a predetermined time has elapsed from a certain point in time, and the predicted molten metal surface height becomes the specified height. To control the pressure applied to the melt. In this technique, the pressure of the gas for pressurizing the molten metal is calculated based on the calculation formula. In this calculation, the value of the volume of the air chamber (the space occupied by air) in the furnace is required. .

By the way, although the inner wall of the furnace holding the molten metal is made of a refractory material, the following points have been clarified.
(1) The inner wall of the furnace is made by hand-casting a refractory material, and its internal dimensions are different from the design values, and the values are also different for each furnace.
(2) The above-mentioned refractory material constituting the inner wall of the furnace has a porous structure, and gas permeates there.
For these reasons, an error is included in the volume of the air chamber used in the above calculation, which becomes an uncertain element of the hot water surface control. In addition, the furnace has a sealed structure, but if the inside is set to a positive pressure, there is a slight gas leak, and there are individual variations and changes over time, and this is also an uncertain factor in hot water level control. It becomes.

  In such a background, an object of the present invention is to provide a technique capable of accurately grasping an effective volume and a leak amount of an air chamber of a furnace and enabling a more accurate model prediction of a molten metal surface.

  According to the first aspect of the present invention, there is provided a leak amount measuring step for measuring a leak amount of gas from the air chamber when the air chamber in the furnace is set to a predetermined pressure higher than the atmospheric pressure, and a gas having a predetermined flow rate. When the air chamber is sent to the air chamber at atmospheric pressure, the elapsed time measuring step of measuring the elapsed time until the air chamber is changed from the atmospheric pressure to the predetermined pressure, the leak amount, the measured Based on the elapsed time, the flow rate of the gas supplied to the air chamber in the elapsed time measuring step, the predetermined pressure, and the temperature of the air chamber, the volume of the air chamber is calculated using a gas equation of state. An air chamber volume calculating step, wherein the volume of the air chamber of the furnace is calculated.

  According to the first aspect of the present invention, attention is paid to the amount of gas leakage from the air chamber, and the volume of the air chamber is calculated from the amount of leakage using the gas equation of state. According to this method, the amount of gas that actually exists in the air chamber (effective value), including the amount of gas permeating into the furnace inner wall and the amount of gas present in the space in the furnace that cannot be grasped from the design drawing. ) Can be obtained with high accuracy. Here, the air chamber refers to a space that is in contact with the molten metal in the furnace and is occupied by gas in the upper part of the molten metal. The gas is used to apply pressure to the surface of the molten metal, and generally air is used, but an inert gas such as nitrogen gas may be used. Moreover, as a molten metal, molten metals, such as aluminum, an aluminum alloy, and iron, are mentioned, However, If it is the metal used by casting, it will not specifically limit.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, in the air chamber volume calculating step, the volume V of the air chamber is calculated based on the following “Equation 1”. .

Ｐ：空気室の圧力、Ｇ_In：空気室への気体の流入量、G_Leak：空気室からの気体のリーク量
Ｖ：空気室の体積、Ｔ：空気室の温度、Ｒ：気体定数

P: pressure of the air chamber, G _In : amount of gas flowing into the air chamber, G _Leak : amount of gas leakage from the air chamber V: volume of the air chamber, T: temperature of the air chamber, R: gas constant

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the air chamber volume calculation step is performed before and after casting using the furnace. According to the third aspect of the present invention, even if a change occurs in the volume of the air chamber due to casting, that is, even if a change with time occurs in the volume, the change of the air chamber is taken into account after taking in the change. Volume can be obtained. The number of castings between the first air chamber volume calculating step and the second air chamber volume calculating step adjacent on the time axis is usually a plurality of times, but the number is not limited.

  According to a fourth aspect of the present invention, based on the volume of the air chamber of the furnace calculated by the invention according to any one of the first to third aspects, the pressure increase due to the gas flowing into the air chamber and As a result of the molten metal being pushed down in the air chamber by the gas flowing into the air chamber, a pressure decrease due to an increase in the volume of the air chamber and a pressure decrease caused by a leak from the air chamber are calculated. A pressure change calculating step, and a molten metal surface position calculating step of calculating the height position of the molten metal sent from the furnace via the stalk based on the calculation result in the pressure change calculating step. This is a characteristic casting method.

  According to the invention described in claim 4, since the calculation is performed using the accurate volume of the air chamber and further taking into account the gas leak from the air chamber, the calculation accuracy of the position of the hot water surface in the stalk is further improved. Can be high.

  The invention according to claim 5 is the invention according to claim 4, wherein the pressure change calculation step is performed based on the following “Equation 2”, and the molten metal surface position calculation step is based on the following “Equation 3”. It is characterized by being performed.

P_１：空気室の予測ガス圧力、Ｐ：空気室の実測ガス圧力、Ｖ：空気室の体積、Ｒ：気体定数
Ｔ：空気室の温度、Ｇ：空気室に流入するガス流量、G_Leak：空気室からのガスリーク量

P ₁ : Predicted gas pressure in the air chamber, P: Actual gas pressure in the air chamber, V: Volume of the air chamber, R: Gas constant T: Temperature of the air chamber, G: Gas flow rate flowing into the air chamber, G _Leak : Gas leakage from the air chamber

P_１：空気室の予測ガス圧力、Ｓ：ストーク内部の水平断面積、P_i：溶湯の湯面にかかる背圧
m_A：ストーク内部の溶湯の質量、ｇ：重力加速度、h_１：送り出された溶湯の湯面の高さ
μ（ｈ）：溶湯の粘性係数

P ₁ : Predicted gas pressure in the air chamber, S: Horizontal cross-sectional area inside the stalk, P _i : Back pressure applied to the molten metal surface
m _A : Mass of molten metal inside stalk, g: Gravitational acceleration, h ₁ : Height of molten metal surface sent out μ (h): Viscosity coefficient of molten metal

  According to a sixth aspect of the present invention, there is provided a leak amount measuring means for measuring a leak amount of gas from the air chamber when the air chamber in the furnace is set to a predetermined pressure higher than atmospheric pressure, and a gas having a predetermined flow rate. , An elapsed time measuring means for measuring an elapsed time until the air chamber is changed from atmospheric pressure to the predetermined pressure, and the amount of leakage is measured. Air chamber volume calculating means for calculating the volume of the air chamber using a gas equation of state based on the elapsed time, the predetermined flow rate of the gas, the predetermined pressure, and the temperature of the air chamber. This is a device for calculating the volume of the air chamber of the furnace.

The invention according to claim 7 is a program that is read and executed by a computer, and is a program that is read and executed by a computer. The CPU causes the air pressure in the furnace to be a predetermined pressure P higher than atmospheric pressure. It said air upon way kept, and the leakage amount measuring step of measuring the leakage amount G _leak of gas from said air chamber by measuring the inflow of air into the air chamber, after the measurement of the leakage quantity in A control step for controlling the proportional valve so that the chamber is returned to atmospheric pressure and air is introduced into the air chamber at a flow rate G _In greater than the leak amount G _Leak until the pressure P is _{reached, and} a gas having a predetermined flow rate G _In When the air chamber is sent to the air chamber at atmospheric pressure, the calculation of the above-mentioned “Equation 1” is performed within the range of the elapsed time from the atmospheric pressure to the predetermined pressure P. Volume of A program for calculating the volume of the air chamber of the furnace, characterized in that to execute the air chamber volume calculation step of calculating a.

  ADVANTAGE OF THE INVENTION According to this invention, the effective volume and leak amount of the air chamber of a furnace are grasped | ascertained correctly, and the technique which enables the more accurate model prediction of the hot_water | molten_metal surface is provided.

It is a conceptual diagram which shows an example of the low pressure casting apparatus using invention. It is a block diagram of the volume calculation apparatus of an air chamber. It is a flowchart which shows an example of the process which calculates | requires the volume of an air chamber. It is a time chart for demonstrating the model prediction control of embodiment. It is a time chart for demonstrating the model prediction control of embodiment. It is a time chart which shows the state which advanced 1 step from the state shown in FIG. It is a time chart which shows the state advanced 1 step from the state shown in FIG. It is a time chart which shows the state which advanced 1 step from the state shown in FIG. It is a time chart which shows the state advanced 1 step from the state shown in FIG.

  Hereinafter, an embodiment of the present invention will be described.

(System configuration)
FIG. 1 shows a low pressure casting apparatus 10 utilizing the present invention. The low pressure casting apparatus 10 includes a furnace 11 and peripheral devices associated therewith. First, the low-pressure casting apparatus 10 includes a furnace (crucible) 11. On the furnace 11, a lower mold 12 and an upper mold 13 that can be approached and separated in the vertical direction with respect to the lower mold 12 are arranged. A mold cavity 14 is formed by the lower mold 12 and the upper mold 13. .

  At the top of the furnace 11, a stalk 15 having a hollow pipe structure with the axis line directed in the vertical direction is disposed so as to pass through, and the upper end portion of the stalk 15 passes through the lower mold 12 and faces the cavity 14. A pipe 16 connected to an air compressor (not shown) is connected to the upper part of the side wall of the heating furnace 11 via a proportional valve (flow rate adjusting valve) 17 and is an upper space of the molten metal M held inside, Air is allowed to flow into the upper space A, which is an example of an air chamber. The furnace 11 is provided with a pressure sensor (pressure detection means) 18 for detecting the pressure in the upper space A of the molten metal M. In this low pressure casting apparatus 10, by increasing the pressure (in-furnace pressure) of the upper space A of the molten metal M in the furnace 11, the molten metal M in the furnace 11 is sent to the stalk 15, and the molten metal rises in the stalk 15. Then, the molten metal is filled in the cavity 14.

  The low pressure casting apparatus 10 includes a control unit 20 and a model prediction controller 21. The control unit 20 controls the operation of the low-pressure casting apparatus 10 and outputs a molten steel surface position instruction signal that instructs the model prediction controller 21 of the molten metal surface position of the molten metal M. Based on the pressure information input from the pressure sensor 18, the model prediction controller 21 predicts the molten metal surface position and the furnace pressure from the present to several steps (for example, three steps) ahead, and the predicted molten metal surface position and instruction. The proportional valve 17 is controlled so that the predicted hot water surface position is approximated to the instructed hot water surface position. The proportional valve 17 includes a flow rate detection sensor 19 that detects the flow rate of the passing gas, and the detection result is input to the model prediction controller 21.

  The system shown in FIG. 1 includes an air chamber volume calculation device 30. The volume calculation device 30 of the air chamber has a function as a computer, and includes a CPU, a data storage device such as a semiconductor memory and a hard disk device, and various interfaces. FIG. 2 shows a block diagram of the air chamber volume calculation device 30. The air chamber volume calculation device 30 includes a gas leak amount measurement unit 31, an elapsed time measurement unit 32, a gas inflow as functional units configured in software (of course, some may include dedicated hardware). It has a quantity measuring unit 33, an air chamber pressure measuring unit 34, an air chamber temperature measuring unit 35, an air chamber volume calculating unit 36, and a control signal output unit 37.

  The gas leak amount measuring unit 31 calculates the amount of air leak from the upper space A based on the output of the flow rate detection sensor 19. The elapsed time measurement unit 32 measures the inflow time of air when the air is caused to flow into the upper space A using the pipe 16. The gas inflow measuring unit 33 measures the inflow of air flowing from the pipe 16 into the upper space A based on the output of the flow rate detection sensor 19. The air chamber pressure measuring unit 34 measures the pressure in the upper space A that is an air chamber. The pressure in the air chamber A is measured based on the output of the pressure sensor 18 or the height position of the hot water surface in the stalk 15. The air chamber temperature measurement unit 35 measures the temperature of the upper space A. The air chamber volume calculation unit 36 calculates the effective volume of the upper space A that cannot be obtained from the design drawing by a method described later. The control signal output unit 37 generates a control signal for the proportional valve 19 and others necessary for executing the process of FIG. 3 described later, and outputs it.

(Calculation of volume of upper space A)
As described above, the volume of the upper space A, which is the air chamber of the furnace 11, cannot be accurately determined from the design information of the furnace, and the value fluctuates with the passage of time of use of the furnace 11. The upper space A is sealed and sealed, but may be used at a high temperature, and air leaks from the upper space A. Here, P is the pressure of the upper space A, G _{In is} the amount of air flowing into the upper space A, G _{Leak is} the amount of air leakage from the upper space A, V is the volume of the upper space A, and the temperature of the upper space A is Is T (temperature of air contained in the upper space A), and R is a gas constant, the following equation 4 is obtained from the gas equation of state. G _In and G _Leak are masses (mass flow rate) of the moved air.

Ｐ：上部空間Ａの圧力、G_In：上部空間Ａへの気体の流入量、G_Leak：上部空間Ａからの気体のリーク量、Ｖ：上部空間Ａの体積、Ｔ：上部空間Ａの温度、Ｒ：気体定数

P: pressure of the upper space A, G _In : amount of gas flowing into the upper space A, G _Leak : amount of gas leakage from the upper space A, V: volume of the upper space A, T: temperature of the upper space A, R: Gas constant

Here, the pressure in the upper space A is calculated from the position of the molten metal surface in the stalk 15 (may be measured by the pressure sensor 18). G _In is measured by the gas inflow measuring unit 33. Here, G _Leak is obtained by a method described later, and V is calculated from “ _Equation 4”.

FIG. 3 shows an example of a procedure for obtaining V. The program for executing the processing shown in FIG. 3 is stored in the storage unit of the air chamber volume calculation device 30 in FIG. 1, and is read out to an appropriate storage area so that the air chamber volume calculation device 30 And executed. The program may be stored in a suitable storage medium and provided from there.

When the processing of FIG. 3 is started (step S301), first, a leak amount (G _Leak ) of gas (in this case, air) from the upper space A is measured. The procedure for obtaining G _Leak will be described below. First, it is assumed that the upper space A exists in a state where a predetermined molten metal is put in the furnace 11. Here, the amount of the molten metal put into the furnace 11 is set to a value close to a state in which casting is actually performed.

  Next, a control signal is sent from the volume calculation unit 20 of the air chamber to the proportional valve 7 so that air flows into the upper space A from the pipe 16 connected to an air compressor (not shown). At this time, the proportional valve 17 is operated so as to keep the pressure of the upper space A at a specific positive pressure P (for example, atmospheric pressure +11 kP). Here, the proportional valve 17 is operated so as to keep the position of the hot water surface in the stalk 15 constant based on the relationship between the position of the hot water surface in the stalk 15 and the pressure in the upper space A, which has been obtained in advance. The pressure in the upper space A is set to a specific positive pressure state (step S302).

Then, the inflow amount G1 of air into the upper space A at this time is measured by the gas inflow amount measuring unit 33 (step S303). If there is no leak in the upper space A, no gas flows into the upper space A under a constant pressure condition. Accordingly, the flow rate G1 of the air flowing into the upper space A in a state where the pressure is constant becomes the leak amount G _Leak generated in the upper space A. In this way, the value of G _Leak is obtained (step S304).

Once G _Leak is obtained, the pressure in the upper space A is once returned to atmospheric pressure. Then, the proportional valve 17 is controlled to allow air to flow into the upper space A at a constant flow rate G _In from the pipe 16 connected to an air compressor (not shown) (step S305). The value of G _In is measured by the gas inflow measuring unit 33, and the flow rate of G _In is selected so that the condition of G _In > G _Leak is _satisfied . Then, an elapsed time Δt until the specific positive pressure P (for example, air chamber atmospheric pressure +11 kP) used when the pressure in the upper space A is obtained in the previous leak amount G _Leak is calculated in the elapsed time measuring unit 32. Measurement is performed (step S306). Here, the pressure P in the upper space A is obtained from the height of the hot water surface in the stalk 15. This process is performed in the air chamber pressure measurement unit 34. The pressure value P at this time is the value of P in “Equation 4”. Then, during the period of Δt, the integration of G _In and G _Leak in “ _Equation 4” is executed in the range of Δt, and the integration value is calculated. Further, the temperature T of the air in the upper space A is measured by a temperature sensor (not shown) (step S307). This process is performed in the air chamber temperature measurement unit 35.

  Thus, values other than V in “Equation 4” are obtained. Then, the calculation of V based on “Equation 4” is performed in the air chamber volume calculation unit 36 (step S308), and the process ends (step S309). The value of V obtained in step S308 is an effective value including an error in internal dimensions that cannot be obtained from the design drawing and the amount of air that permeates the inner wall of the furnace 11.

(High precision pressurization control)
In the following, the effective volume V of the upper space A obtained by the procedure of FIG. 4 is used to appropriately control the behavior of the molten metal in the mold without causing a delay or overshoot with respect to the position of the indicated molten metal surface. An example of the method of performing will be described.

  In this example, the model prediction controller 21 predicts the molten metal surface position and the furnace pressure from the present three steps ahead based on the pressure information input from the pressure sensor 18, and is also instructed as the predicted molten metal surface position. The proportional valve 17 is controlled so that the predicted hot water surface position approximates the instructed hot water surface position.

  First, an outline of calculation in model prediction will be described. Here, the height of the molten metal surface in the stalk 15 at the time when a predetermined time has elapsed from the present time is predicted by the following “Equation 4” and “Equation 5”.

P_１：上部空間Ａの予測ガス圧力、Ｓ：ストーク内部の水平断面積、P_i：溶湯の湯面にかかる背圧
ｍ_A：ストーク内部の溶湯の質量、ｇ：重力加速度、P_１：予測ガス圧力
ｈ_１：送り出された溶湯の湯面の高さ、μ（ｈ）：溶湯の粘性係数

P ₁ : Predicted gas pressure in the upper space A, S: Horizontal cross-sectional area inside the stalk, P _i : Back pressure applied to the molten metal surface m _A : Mass of the molten metal inside the stalk, g: Gravitational acceleration, P ₁ : Predicted Gas pressure h ₁ : Height of molten metal surface sent out, μ (h): Viscosity coefficient of molten metal

P_１：上部空間Ａの予測ガス圧力、Ｐ：上部空間Ａの実測ガス圧力、Ｖ：上部空間Ａの体積
Ｒ：気体定数、Ｔ：上部空間Ａ内の温度、Ｇ：上部空間Ａに流入するガス流量
G_Leak：上部空間Ａからのガスリーク量

P ₁ : Predicted gas pressure in the upper space A, P: Actual gas pressure in the upper space A, V: Volume of the upper space A R: Gas constant, T: Temperature in the upper space A, G: Inflow into the upper space A Gas flow rate
G _Leak : Gas leakage from the upper space A

  Here, G is proportional to the opening degree of the flow rate adjusting valve. However, depending on the type of the electromagnetic flow rate adjusting valve, the channel is not opened until the operating voltage exceeds the lower threshold value. After opening, there is a thing whose flow rate changes linearly with respect to the operating voltage. Also, with such a flow rate adjustment valve, even when the flow rate adjustment valve is throttled from the fully open state, the flow path is not throttled until the operating voltage falls below the upper threshold, and the flow control valve is operated after the flow path starts to be throttled. The flow rate varies linearly with voltage. Therefore, when the flow rate is obtained from the operation voltage, it is necessary to consider the operation hysteresis as described above.

  Here, the first term on the right side of “Equation 6” is a pressure increase due to the gas flowing into the furnace 11, and the second term is a result of the molten metal being pushed down in the upper space A by the gas flowing into the furnace 11, This is a pressure decrease due to an increase in the volume of the upper space A. The third term is a pressure decrease caused by a leak from the upper space A.

  The gas pressure P after t seconds from the current time t1 can be obtained by integrating “Equation 6” from t1 to (t1 + t). In this case, the gas temperature T can be kept constant, and the gas flow rate G is preset as that at time (t1 + t). The gas volume V at time (t1 + t) can be obtained by adding Ah1 to the gas volume at time t1 (which has already been obtained).

Back pressure P _i in the "Number 5" can be atmospheric pressure. Further, the mass mA of the molten metal in the stalk is obtained at the time t1, and has already been obtained in the past calculation. Further, the viscosity coefficient μ (h) is known from the material and temperature of the molten metal. Then, when these values and the gas pressure P ₁ obtained by “Equation 6” are substituted into “Equation 5” and integration is performed twice, the height h _{1 of} the molten metal surface at the time (t1 + t) of the delivered molten metal. Is required. In this case, when the time (t1 + t) greater than the height the height h ₁ is designated by the calculated water surface in lowers the operating voltage of the flow control valve, Stoke by lowering the pressure in the upper space A 15 Control is performed so that the position of the hot water surface in the inside is lowered. On the other hand, when the height h ₁ of the hot water surface at time (t1 + t) is lower than the specified height, the operating voltage of the flow control valve is increased and the pressure in the upper space A is raised to increase the temperature of the hot water surface in the stalk 15. Control so that the position is raised. Such control by performing, can be brought close to the height specified the actual height h ₁ of the molten steel surface at the time (t1 + t). Incidentally, of decrease of the operation voltage may be proportional to the difference between the height and the specified height h ₁ of the molten metal surface.

  By the method described above, it is possible to suppress the undulation of the molten metal surface in the stalk 15 (variation in the position of the molten metal surface). Hereinafter, this model prediction control will be described in detail with reference to FIGS. In the example shown below, the prediction is made up to 3 steps ahead from the present, but the number of steps ahead can be determined as appropriate, and is not limited to the following example.

  FIG. 4 is a timing chart for explaining the model predictive control, and the horizontal axis indicates the time at each step in which the model predictive control is performed. In FIG. 4, the interval of one step is indicated by a scale of 0.1. The current time is indicated by time t, and information indicating the hot water surface position is input from the controller 20 to the model prediction controller 21 at this time t.

  When the information that supports the position of the molten metal surface is input, the model prediction controller 21 increases the operating voltage for the proportional valve 17 to activate the proportional valve 17 as shown in FIG. Since the proportional valve 17 has an operation hysteresis, the flow path starts to open from time (t + 1), and air starts to flow from time (t + 1). Further, the model prediction controller 21 substitutes the in-furnace pressure input from the pressure sensor 18 at the time of the current time t into the above-mentioned “Equation 6”, and the time (t + 1), time (t + 2), time (t + 3) Is obtained, and the obtained predicted furnace pressure is substituted into “Equation 5”, and the predicted hot water in the stalk 15 at time (t + 1), time (t + 2), and time (t + 3) is obtained. Get the surface position. In FIG. 4, for convenience of explanation, the predicted furnace pressure and the predicted molten metal surface position are shown up to the future time from the time (t + 3), but actually the prediction up to the time (t + 3) is shown. But not. This also applies to the drawings subsequent to FIG.

  FIG. 6 shows a state that proceeds from the state shown in FIG. 5 to the next step (1.1). The model prediction controller 21 calculates the time (t + 1), the time (t + 2), and the time (t + 3) from the in-furnace pressure input from the pressure sensor 18 at the time of the current time t and the above-described “Equation 6” and “Equation 5”. The predicted hot water surface position at the time of is obtained. In the prediction by the model prediction controller 21, the furnace pressure starts to increase from the middle of the current time t and time (t + 1), and as a result, the surface of the molten metal M in the heating furnace 11 is pushed, and a little at time (t + 1). The molten metal M is pushed into the stalk 15 from the front, and the molten metal level in the stalk 15 starts to rise. In this expected state, the predicted hot water surface position is significantly lower than the indicated hot water surface position. Therefore, the model prediction controller 21 maintains the operation voltage applied to the proportional valve 17 and promotes the rise of the molten metal level in the stalk 15.

  FIG. 7 shows a state that proceeds from the state shown in FIG. 6 to the next step (1.2). Also in this case, the model prediction controller 21 calculates the time (t + 1), the time (t + 2), the in-furnace pressure input from the pressure sensor 18 at the time of the current time t, and the above-mentioned “Equation 6” and “Equation 5”. The predicted hot water surface position at time (t + 3) is obtained. At this time, in the prediction by the model prediction controller 21, since the predicted hot water surface position is close to the indicated hot water surface position at time (t + 2), it is necessary to lower the operation voltage applied to the proportional valve 17 at time (t + 1). At time t, the control voltage is maintained.

  FIG. 8 shows a state that proceeds from the state shown in FIG. 7 to the next step (1.3). In this state, the model prediction controller 21 determines the time (t + 1), the time (t + 2), the furnace pressure inputted from the pressure sensor 18 at the time of the current time t, and the above-mentioned “Equation 4” and “Equation 3”. The predicted hot water surface position at time (t + 3) is obtained. In the prediction of the model prediction controller 21 in this state, the predicted hot water surface position is close to the indicated hot water surface position at time (t + 1), so that the hot water surface in the stalk 15 is lowered at time t, which is the timing one step before. The operating voltage applied to the proportional valve 17 is lowered.

  In other words, in the situation shown in FIG. 8, at the time t before the time (t + 1) when the predicted hot water surface position approaches the indicated hot water surface position, the proportional valve 17 is throttled early to reduce the pressure in the upper space A early. Then, an operation for lowering the hot water level in the stalk 15 is performed. When the pressure in the upper space A is changed, a change in the hot water level in the stalk 15 appears at a timing slightly delayed due to the compressibility of the air and the inertia of the molten metal. In consideration of the above timing delay, the pressure change is applied at a slightly earlier timing so that the actual position of the hot water surface in the stalk 15 is close to the position indicated at time (t + 1). .

  FIG. 9 shows a state that proceeds from the state shown in FIG. 8 to the next step (1.4). Even in this state, the model prediction controller 21 determines the time (t + 1) and the time (t + 2) from the in-furnace pressure input from the pressure sensor 18 at the time of the current time t and the above-mentioned “Equation 6” and “Equation 5”. The predicted hot water surface position at time (t + 3) is obtained. In the prediction of the model prediction controller 21, after the time t, the predicted molten metal surface position approximates the indicated molten metal surface position, but due to the inertia of the molten metal, the molten metal surface height position does not become a constant value and fluctuates up and down. . For example, in this case, the predicted hot water surface position is slightly lower than the indicated hot water surface position at time (t + 2). Therefore, the model prediction controller 21 slightly increases the operation voltage of the proportional valve 17 at time t, and slightly increases the pressure in the upper space A to raise the position of the hot water surface in the stalk 15 at a timing slightly earlier than time (t + 2). increase. In this manner, the predicted hot water position after time (t + 3) is indicated by dynamically controlling the pressure in the upper space A in small increments in correspondence with the predicted hot water position in the stalk 15. The hot water surface is brought close to the surface, and the position of the hot water surface in the stalk 15 is stabilized in the vicinity of the designated position.

  By the model predictive control as described above, the position of the molten metal surface of the molten metal M in the stalk 15 can be stabilized. Then, by stabilizing the position of the molten metal surface, the rising speed of the molten metal surface in the stalk 15 can be increased, and the casting time can be shortened. Further, since the stable state is substantially maintained even when the molten metal is filled in the cavity 14, it is possible to suppress the occurrence of delay and overshoot as in PID control, and the occurrence of molten metal pulsation and the resulting hot water boundary. It is possible to prevent the occurrence of unfilling or air entrainment.

  By the way, if the operating voltage of the proportional valve 17 is kept constant even after the molten metal has passed through the stalk 15, the rise rate of the molten metal surface fluctuates when the horizontal cross-sectional area greatly changes in the gate or the cavity 14. It is assumed that the hot water surface is disturbed. In this case, the model prediction controller 21 stores the horizontal cross-sectional area information of the stalk 15 and the cavity 14 and corrects the operation voltage using this as a disturbance.

  Specifically, when the horizontal cross-sectional area of the stalk 15 is A and the horizontal cross-sectional area of the gate or cavity 14 is S, the operation voltage is multiplied by S / A for correction. As a result, the rising speed of the hot water surface in the pouring gate and the cavity 14 becomes constant, and the hot water surface is prevented from being disturbed.

(V recalculation process)
The effective volume V of the upper space A changes according to the use of the furnace 11 due to a change in the material of the inner wall of the furnace 11 or the like. Further, the leak amount also changes due to deterioration of the packing or the like. Therefore, in the process of repeating the casting, the accuracy of the predicted gas pressure P ₁ of the calculation result by "6" is reduced. Therefore, by performing the process shown in FIG. 3 again at an appropriate timing, the accuracy of the value of V can be ensured over a long period of time, and the accuracy of the calculation result of “Equation 6” can be maintained. The timing of performing the process of FIG. 3 again is a method of counting the number of castings, a method of performing when the cumulative value of the number of castings reaches a specified value, a method of performing when the furnace has been used for a certain cumulative time, etc. Is mentioned. It is effective to set a program so that this process is automatically performed. Of course, the timing for performing the processing of FIG. 3 can be determined by the operation of the operator.

(Superiority)
According to the techniques exemplified above, the effective volume V of the upper space A can be obtained in consideration of the gas permeation into the furnace inner wall and the volume of the irregular portion. Therefore, “Equation 5” and “Equation 6” The accuracy of the control shown in FIGS. If, as the value and V, the use of the value of the design value, since there is included a large error, the error value of P ₁ obtained by "6" increases, is calculated by the "Number 5" The predicted value of the height position of the hot water surface in the stalk 15 also includes a large error. And the precision of control shown in Drawing 5-Drawing 9 also falls, and the effect which prevents generation | occurrence | production of the pulsation of the molten metal in low-pressure casting, and the hot water boundary and unfilling resulting from it, or entrainment of air, etc. falls.

In addition, in the calculation of P ₁ using “Equation 6”, the influence of the leak to the outside in the upper space A is taken in. Compared to the case of performing the calculation without taking in the influence of this leak, The prediction accuracy of P _{1 and} the accuracy of the predicted position of the molten metal surface in the stalk 15 calculated from “Equation 5” are improved. This also improves the accuracy of the control shown in FIGS. 5 to 9 and enhances the effect of preventing the occurrence of molten metal pulsation and the occurrence of molten metal boundary, unfilled, or air entrainment in low pressure casting. Contribute to.

  The present invention can be used in casting techniques.

  DESCRIPTION OF SYMBOLS 10 ... Low pressure casting apparatus, 11 ... Furnace, 12 ... Lower mold, 13 ... Upper mold, 14 ... Cavity, 15 ... Stoke, 16 ... Pipe, A ... Upper space (space above the molten metal in the furnace), M ... Molten metal .

Claims (7)

A leak amount measuring step of measuring a leak amount of gas from the air chamber when the air chamber in the furnace is set to a predetermined pressure higher than the atmospheric pressure;
An elapsed time measuring step of measuring an elapsed time required for the air chamber to change from atmospheric pressure to the predetermined pressure when a gas having a predetermined flow rate is sent to the air chamber at atmospheric pressure;
Based on the amount of leak, the measured elapsed time, the flow rate of the gas supplied to the air chamber in the elapsed time measuring step, the predetermined pressure, and the temperature of the air chamber, using a gas equation of state An air chamber volume calculating step for calculating the volume of the air chamber. A method for calculating the volume of the air chamber of the furnace. The method of calculating the volume of the air chamber of the furnace according to claim 1, wherein, in the air chamber volume calculating step, the volume V of the air chamber is calculated based on the following "Equation 1".

P: pressure of the air chamber, G _In : amount of gas flowing into the air chamber, G _Leak : amount of gas leakage from the air chamber V: volume of the air chamber, T: temperature of the air chamber, R: gas constant
  The method for calculating the volume of the air chamber of the furnace according to claim 1, wherein the air chamber volume calculating step is performed before and after casting using the furnace. Based on the volume of the air chamber of the furnace calculated by the invention according to any one of claims 1 to 3, the pressure increase due to the gas flowing into the air chamber and the gas flowing into the air chamber As a result of the molten metal being pushed down in the air chamber, a pressure change calculation step for calculating a pressure decrease due to an increase in the volume of the air chamber and a pressure decrease caused by a leak from the air chamber;
And a molten metal surface position calculating step of calculating the height position of the molten metal surface fed from the furnace via the stalk based on the calculation result in the pressure change component calculating step. The pressure change calculation step is performed based on the following “Equation 2”,
The casting method according to claim 4, wherein the molten metal surface position calculating step is performed based on the following “Equation 3”.

P ₁ : Predicted gas pressure in the air chamber, P: Actual gas pressure in the air chamber, V: Volume of the air chamber, R: Gas constant T: Temperature of the air chamber, G: Gas flow rate flowing into the air chamber, G _Leak : Gas leakage from the air chamber

P ₁ : Predicted gas pressure in the air chamber, S: Horizontal cross-sectional area inside the stalk, P _i : Back pressure applied to the molten metal surface, m _A : Mass of molten metal inside the stalk, g: Gravitational acceleration, h ₁ : Delivery Molten metal surface height μ (h): Melt viscosity coefficient
A leak amount measuring means for measuring a leak amount of gas from the air chamber when the air chamber in the furnace is set to a predetermined pressure higher than the atmospheric pressure;
An elapsed time measuring means for measuring an elapsed time required for the air chamber to change from atmospheric pressure to the predetermined pressure when a gas having a predetermined flow rate is sent to the air chamber at atmospheric pressure;
An air chamber that calculates the volume of the air chamber using a gas equation of state based on the leak amount, the measured elapsed time, the predetermined flow rate of the gas, the predetermined pressure, and the temperature of the air chamber A device for calculating the volume of the air chamber of the furnace. A program that is read and executed by a computer,
CPU
When the air pressure in the furnace is kept at a predetermined pressure P higher than the atmospheric pressure, the amount of air leakage G _Leak from the air chamber is measured by measuring the amount of air flowing into the air chamber. A leak amount measuring step ;
A control step of controlling the proportional valve so that the air chamber is returned to atmospheric pressure after the leakage amount is measured and air is allowed to flow into the air chamber at the flow rate G _In higher than the leakage amount G _Leak until the pressure P is reached. ,
When a gas having a predetermined flow rate G _In is sent to the air chamber that is set to atmospheric pressure, the following “Equation 4” is satisfied within the range of elapsed time that the air chamber takes from atmospheric pressure to the predetermined pressure P. An air chamber volume calculating step for calculating and calculating a volume V of the air chamber;
Program for calculating the volume of the air chamber of the furnace, characterized in that for the execution.

T: temperature of air chamber, R: gas constant

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