JPH0144136B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the amount of gas entrained in a liquid, such as a plastic liquid component.

In reaction injection molding, in which molded products are manufactured by collision-mixing at least two types of plastic liquid components that react with each other, the purpose of this is to make the foam structure inside the molded product denser, improve physical properties and appearance, and increase product value. , air is mixed into the plastic liquid component as fine bubbles. When air (gas) is mixed into the plastic liquid component (liquid), it is necessary to control the gas mixing rate to match a predetermined target value in order to maintain the quality of the molded product at a high level. is necessary.

By the way, the conventional method for controlling the gas mixture rate is to measure the gas mixture rate in the liquid, compare the measured value with the target value, and if the actual value is smaller than the target value, add gas to the liquid. If the measured value is larger than the target value, the gas in the liquid is naturally released and the gas mixture in the liquid is stopped until the rate of gas mixture in the liquid decreases and becomes smaller than the target value. That's what I do.

However, in the conventional method as mentioned above,
Once the gas mixture rate exceeds the target value, it takes time for the gas mixture rate to decrease to the target value (control response is poor), and it is difficult to maintain the gas mixture rate at a constant target value (optimal value). The problem is that it is difficult.

The present invention was made in view of the above circumstances, and
The purpose of this is to quickly and reliably reduce the gas mixture rate when it exceeds the target value, to ensure good control response, and to stably maintain the gas mixture rate at the target value. An object of the present invention is to provide a method for controlling the amount of gas mixed into a liquid.

In order to achieve this object, the present invention inputs a target value of the gas mixture rate or a limit value larger than the target value into the control device as a liquid introduction start setting value, and then controls the liquid in the main tank. The gas mixture rate is measured, and if the actual value of the gas mixture rate is greater than the liquid introduction start setting value, the liquid with a lower gas mixture rate than the liquid in the main tank stored in the sub tank is added to the main tank. It was designed to be introduced in

A first embodiment of the present invention will be described below based on the drawings.

Reference numeral 1 in FIG. 1 is a stock solution tank (main tank) that accommodates a plastic liquid component (liquid) of a high-pressure reaction molding apparatus. Both ends 2a and 2b of a liquid flow path 2 consisting of piping for circulating the liquid in the stock solution tank 1 are connected to the stock solution tank 1, and inside the stock solution tank 1 is connected a liquid flow path 2 which is rotated by a motor (not shown). A stirring blade is provided. The stock solution tank 1 is connected to the α ends of the first and second three-way switching valves 4 and 5, respectively, via the first switching valve 3, which is normally open. The β end is connected to one end of a circulation cylinder 6 having high wear resistance. In addition, the other end of the circulation cylinder 6 is
A piston 7a is provided at one end of the piston rod 7 and is connected to the β end of the second and third type switching valve 5 and slides within the circulation cylinder 6. A piston 7b that slides within an actuator 8 is provided at the other end of the piston rod 7, and a hydraulic circuit (not shown) connected to both ends of the actuator 8 causes the circulation cylinder 6 to
The inner piston 7a is configured to reciprocate from side to side. Furthermore, the second and third type switching valve 5
The γ end of the gas blowing device 10 is connected to the γ end of the first three-way switching valve 4 and one end of the gas blowing device 10 via the second switching valve 9, and the other end of the gas blowing device 10 is connected to a non-return valve. It is connected to the stock solution tank 1 via a valve 11 and a third switching valve 12 which is normally open.

The piston rod 7 has a hook-shaped probe 13.
An encoder (position detecting means) 14 for measuring the position of the piston 7a is provided on a rack 13a formed on one side of the probe 13.
The pinions 14a are engaged with each other. Also,
A pressure sensor (pressure detection means) 15 is provided on the other end side of the circulation cylinder 6 to detect the internal pressure. Then, each time it is time to measure the gas mixing rate, the second and third method switching valves 5 and the second switching valve 9
In the step of pressurizing the liquid by the rotation operation in one direction and the pressurization operation of the liquid on the piston head side in the circulation cylinder 6 by the piston 7a, the encoder 14 and the pressure sensor 15 are connected to the circulation cylinder 6, respectively. 6 and the position information of the piston 7a at that time, and during periods other than when measuring the gas mixture rate, the first and second three-way switching valves 4 and 5 are turned to the other one. The liquid in the stock solution tank 1 is circulated through the liquid flow path 2 by the dynamic operation and the reciprocating movement of the piston 7a.

Further, a gas supply source 17 is connected to the gas blowing device 10 through a pipe 16, and a gas pressure control valve 18, a gas pressure gauge 19, a gas pressure control valve 18, a gas pressure gauge 19, a gas pressure Flow rate adjustment valve 2
0, a gas flow meter 21, a gas injection amount control valve 22, and a gas check valve 23 are provided. Furthermore, the piping 16 between the gas pressure control valve 18 and the gas pressure gauge 19
A pipe 24 branched from the sub-tank 25 is connected to the sub-tank 25 via a tank internal pressure control mechanism 26 that controls the pressure within the sub-tank 25, and is also connected to the main tank 1 via a pressure control valve 42. .

The sub-tank 25 is provided with a pressure gauge 27 for detecting internal pressure. Also, sub tank 2
5 contains a liquid that is the same as the liquid in the stock solution tank 1 and has a low gas contamination rate. Further, the sub tank 25 is connected to the stock solution tank 1 via a charging pipe 28 and a return pipe 29, and the charging pipe 28 includes a charging pump 30 and a charging control valve 3.
1 and the return pipe 29 are each provided with a return valve 32.

A computing device 33 is electrically connected to the encoder 14 and pressure sensor 15 to constitute a gas entrainment rate detection device 34, and based on measurement data obtained by the encoder 14 and pressure sensor 15 when measuring the gas entrainment rate. The arithmetic unit 33 calculates the gas mixture rate of the liquid.

The arithmetic device 33 is electrically connected to a gas mixing rate control device 35. This gas mixture rate control device 35 is configured such that the output value (actual measurement value of the gas mixture rate) Xa of the arithmetic unit 33 is a target value of the gas mixture rate inputted in advance from the input device 36.
The above gas injection amount control valve 2
2, a command signal is output to the input control valve 31, the return valve 32, and the tank internal pressure control mechanism 26.

As is well known, a measuring cylinder 37 and a mixing head 38 are connected to the stock solution tank 1, and the plastic liquid component supplied from the stock solution tank 1 is sent to the mixing head 38, and then sent to another measuring cylinder (not shown). The plastic liquid component is mixed with other plastic liquid components sent from other companies, and molded products are obtained by the reaction of both liquid components. In the figure, 41 is a pressure gauge provided in the main tank 11.

Next, using the device configured as above,
A method for controlling the amount of gas mixed into a liquid according to the present invention will be explained.

When the operation starts, first, the gas mixture rate in the liquid is measured. That is, the α end and the β end of the second and third type switching valve 5 are communicated with each other, and the second switching valve 9
In the closed state, the piston 7a in the circulation cylinder 6 is moved from the right to the left to draw liquid into the circulation cylinder 6 from the other end (see FIG. 2A). Next, in order to reduce the pressure of the liquid in the circulation cylinder 6, the β end and the γ end of the second three-way switching valve 5 are communicated with each other, and while the liquid does not flow in from the α end, the pressure inside the circulation cylinder 6 is reduced. further move the piston 7a to the left (see FIG. 2B). Subsequently, the piston 7a in the circulation cylinder 6 is moved to the right to begin compressing the liquid. Then, the pressure sensor 15 detects that the preset first pressure (low pressure) _P1 has been reached, and the piston stroke _l1 at that point is read by the encoder 14 (see FIG. 2C). Further, the pressure sensor 15 detects when a preset second pressure (high pressure) P ₂ is reached, and the encoder 14 reads the piston stroke l ₂ at that point. These measurement data P ₁ , P ₂ , l ₁ , l ₂ are sent to the arithmetic unit 33, and the actual measurement value Xa of the gas mixing rate is calculated.

The measured value Xa of the gas mixing rate is as follows: (1) The gas state equation (PV=constant) also holds true in the state of mixing with liquid.

(2) Liquids are incompressible.

and Pa: Atmospheric pressure (1.033Kg/cm ² ) P ₁ : First pressure condition Kg/cm ² (absolute pressure) P ₂ : Second pressure condition Kg/cm ² (absolute pressure) V ₀ : Circulation cylinder 6 volume cm ³ Vf: Total volume of liquid and gas in the circulation cylinder 6 under the first pressure condition P ₁ cm ³ Vs: Total volume of liquid and gas in the circulation cylinder 6 under the second pressure condition P ₂ Volume cm ³ Vp: Pipe internal volume cm ³ l ₁ : Distance from encoder 14 origin a to point b where the pressure reaches the first pressure condition P ₁ cm l: Point b where the pressure reaches the first pressure condition P ₁ Distance cm from the point c where the pressure reaches the second pressure condition P ₂ (l = l ₂ − _{l 1} ) D: Diameter of the circulation cylinder 6 cm Xa: Volume ratio of liquid and gas under atmospheric pressure ( _Then ^, _{_ _ _ _ _} ^_ _{_ _ _ _} ² lP ₂ (P ₁ −1.033).

In this way, the actual measurement value Xa of the gas mixture rate determined by the arithmetic device 33 is compared in the gas mixture rate control device 35 with the target value Xb, which is input in advance to the gas mixture rate control device 35 by the input device 36. Ru.

Then, when the actual measurement value Xa and the target value Xb are equal, the gas mixing rate control device 35 closes the gas injection amount control valve 22 and
With the switch closed, switch each switching valve 4, 5, 9,
By reciprocating the piston 7a in the circulation cylinder 6, the liquid in the stock solution tank 1 is circulated through the liquid flow path 2.

To explain this liquid circulation control in detail, first, when the piston 7a in the circulation cylinder 6 retreats and moves to the leftmost position in FIG.
The first three-way switching valve 4 switches between its α end and β end.
At the same time, the second three-way switching valve 5 is switched, and its β and γ ends are in communication, and the first, second, and third switching valves 3, 9, and 12 are in the open state, respectively. be made into Then, the piston 7 in the actuator 8 is activated by operating a hydraulic circuit (not shown).
When b is moved forward to the right in FIG. The liquid flows out into the flow path 2 through the β end, the γ end of the second three-way switching valve 5, and the second switching valve 9, and the α end of the first three-way switching valve 4 flows into the circulation cylinder 6. , the liquid is allowed to flow in from one end of the circulation cylinder 6 through the β end. Therefore, the liquid in the stock solution tank 1 is sucked into the circulation cylinder 6 in the order of the first switching valve 3, the first three-way switching valve 4, the second three-way switching valve 5, the second switching valve 9, and the gas. The liquid is fed under pressure in this order through the blowing device 10, the check valve 11, and the third switching valve 12, and then returns to the stock solution tank 1.

Next, the piston 7a in the circulation cylinder 6
moves to the rightmost position in FIG. In other words, its α end and β end communicate with each other. Then, when the hydraulic circuit is switched and the piston 7b in the actuator 8 is moved back to the left in FIG. 1, the piston 7a in the circulation cylinder 6 moves to the left in conjunction with this, so The liquid in the circulation cylinder 6 flows out into the liquid flow path 2 from one end of the circulation cylinder 6 through the β and γ ends of the first three-way switching valve 4. α of 23-way switching valve 5
Liquid is made to flow in from the other end of the circulation cylinder 6 through the end and the β end. Therefore, the liquid in the stock solution tank 1 is sucked into the circulation cylinder 6 in the order of the first switching valve 3, the second three-way switching valve 5, and the first three-way switching valve 4, the gas blowing device 10, and the check valve. The liquid is pumped through the valve 11 and the third switching valve 12 in that order and returns to the stock solution tank 1.

Further, in the gas mixing rate control device 35,
As a result of comparing the measured value Xa of the gas mixing rate with the target value Xb, if the measured value Xa is smaller than the target value Xb, the gas injection amount control valve 22 is controlled by the command signal output from the gas mixing rate control device 35. The opening degree of the gas supply source 17 is controlled, and the gas sent from the gas supply source 17 is mixed into the liquid in the liquid flow path 2 by the gas blowing device 10, and the piston 7a in the circulation cylinder 6 and each switching The liquid is circulated between the liquid flow path 2 and the stock solution tank 1 by means of valves 4, 5, and 9. At this time, the input control valve 31 and the return valve 32 are closed, and the auxiliary tank 25 is not in communication with the stock solution tank 1. Then, when it comes time to measure the next gas entrainment rate, the liquid circulation is stopped.

Further, in the gas mixing rate control device 35, as a result of comparing the measured value Xa of the gas mixing rate with the target value Xb, if the measured value Xa is larger than the target value Xb, the gas mixing rate control device 35 control valve 3
Since a command signal to open 1 is output, the liquid in the sub tank 25 (liquid with a gas mixture rate lower than that of the liquid in the stock solution tank 1 or a liquid with a gas mixture rate of 0) is transferred to the input pipe 28, the input pump 30, and the input control. valve 31
By opening the return valve 32, the liquid in the stock solution tank 1 is returned to the sub tank 25 through the return pipe 29 and the return valve 32. Therefore, the liquid mixing rate in the stock solution tank 1 decreases, and the gas mixing rate of the liquid in the sub tank 25 increases. In addition to this liquid introduction control, by operating the piston 7a in the circulation cylinder 6 and the switching valves 4, 5, and 9, the liquid in the stock solution tank 1 is circulated through the liquid flow path 2. Then, based on the measurement results of the gas mixing rate,
It is determined whether to continue introducing the liquid from the sub tank 25 or to stop it.

On the other hand, since the gas mixture rate of the liquid in the sub tank 25 increases, the gas mixture rate control device 35 outputs a command signal to the tank internal pressure control mechanism 26 while the valves 31 and 32 are closed. The pressure inside the tank 25 is reduced. That is, the tank internal pressure control mechanism 26 discharges the gas in the sub tank 25 to reduce the pressure in the sub tank 25 from, for example, 5 Kg/cm ² G (same as the main tank pressure) to 0 Kg/cm ² G. As a result, the gas contained in the liquid in the sub-tank 25 as fine bubbles expands its volume, so the buoyant force that the bubbles receive from the liquid increases, and the bubbles rise rapidly and are released from the liquid to the outside. be done. Therefore, the gas mixture rate of the liquid in the sub tank 25 is reduced. In this way, when the sub tank 25 is not communicating with the main tank 1, air bubbles in the sub tank 25 are discharged.

In this way, the pressure inside the sub tank 25 is controlled by the tank internal pressure control mechanism 26, and the pressure inside the sub tank 25 is controlled.
The gas mixture rate of the liquid in the liquid tank 5 is maintained at a value smaller than the target value Xb of the gas mixture rate of the fluid in the stock solution tank 1.

In addition, when introducing the liquid from the auxiliary tank 25 to the stock solution tank 1, the actual measured value Xa of the gas mixture rate is the target value.
The introduction may be stopped after a certain amount has been introduced from the time when it is determined that Xb has been exceeded, and the state within the stock solution tank 1 may be stabilized.

Next, a second embodiment of the present invention will be described based on FIG. In this second embodiment, whereas the first embodiment shown in FIG.
The difference is that a gas mixing rate detection device 40 is provided in the liquid flow path 2. In the second embodiment, liquid always flows through the liquid circulation pump 39,
Detection of the contamination rate is also carried out every moment. Note that the other configurations are the same as those of the first embodiment, so the same reference numerals are given and the explanation will be omitted.

When the gas mixing rate of the liquid is measured in the gas mixing rate detection device 40, the actual measured value Xa of the gas mixing rate is sent to the gas mixing rate control device 35 and compared with the target value Xb input from the input device 36. be done. Based on this comparison result, the same control as in the first embodiment is carried out, that is, when the measured value Xa is equal to the target value Xb, the gas injection is stopped and the liquid in the stock solution tank 1 is If the measured value Xa is smaller than the target value Gas mixing control is performed to mix gas A into the circulating fluid in the flow path 2, and the actual measured value is
When Xa is larger than the target value The liquid introduction control is performed to return the liquid to the inside of 25.

In each of the above embodiments, the actual measured value Xa of the gas mixture rate was compared with the target value Xb, but in addition to the target value Xb, a limit value Xc larger than the target value Xb is set, a) Actual value Xa < target value Xb,
Perform the above gas mixture control, and (b) perform gas mixture stop control when target value Xb≦actual value Xa≦limit value Xc,
(c) When the limit value Xc<actual value Xa, the above liquid introduction control may be performed. In this case, the gas mixture rate does not drop too much due to too much liquid being introduced from the sub tank 25, and the fluctuations in the gas mixture rate can be suppressed to a smaller value with respect to the target value Xb, making it possible to Stable control can be performed. Further, instead of the gas injection amount control valve 22, the amount of gas mixed into the liquid may be controlled by performing on-off control using an electromagnetic on-off valve.

As explained above, in the present invention, after inputting the target value of the gas mixture rate or a limit value larger than the target value into the restriction device as the liquid introduction start setting value, the gas mixture of the liquid in the main tank is prevented. If the actual value of the gas mixture rate is greater than the liquid introduction start setting value, a liquid with a lower gas mixture rate than the liquid in the main tank stored in the sub tank is introduced into the main tank. Therefore, by introducing the liquid in the sub-tank into the main tank, it is possible to reduce the gas contamination rate of the liquid in the main tank. Therefore, even if the gas mixture rate of the liquid becomes larger than the target value, it can be quickly lowered to match the target value, and the control response is extremely good, and the gas mixture rate can be stably maintained at a constant value. and can easily keep the liquid homogeneous. In addition, since the system is designed to reduce the gas contamination rate of the liquid in the sub tank, even if the liquid in the main tank returns to the sub tank and the gas contamination rate of the liquid in the sub tank increases, it will be quickly removed. It is possible to keep the rate of gas contamination of the liquid in the sub tank low by lowering it to . Furthermore, since this method limits the amount of liquid introduced from the sub-tank into the main tank to a predetermined set amount, after the liquid is introduced from the sub-tank, the state inside the main tank is stabilized. Therefore, the following control can be carried out, and the gas mixture rate can be controlled more stably, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing the apparatus used in the first embodiment of the method for controlling the amount of gas mixed in a liquid according to the present invention, and FIG. 2 is a schematic diagram showing the apparatus used in the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing the procedure for measuring the gas mixing rate, and FIG. 3 is a schematic configuration diagram showing the apparatus used in the second embodiment of the present invention. 1... Raw solution tank (main tank), 25... Sub-tank, 34... Gas mixing rate detection device, 35... Gas mixing rate control device, 40... Gas mixing rate detection device, Xa... Actual measurement value, Xb ...Target value, Xc...Limit value.

Claims (1)

[Claims] 1. After inputting the target value of the gas mixture rate or a limit value larger than the target value into the control device as the liquid introduction start setting value, the gas mixture rate in the main tank is set as the gas mixture rate. If the actual value obtained by the gas mixing rate detection device is larger than the liquid introduction start setting value, the liquid contained in the sub tank is of the same quality as the liquid in the main tank and has a higher gas content than the liquid. A method for controlling the amount of gas mixed into a liquid, characterized by introducing a liquid with a small mixing rate into the main tank. 2. A method for controlling the amount of gas mixed into a liquid according to claim 1, which comprises reducing the gas mixing rate of the liquid in the sub-tank. 3. Claim No. 3, characterized in that a predetermined set amount of liquid is introduced from the sub tank into the main tank when the actual measurement value obtained by the gas mixing rate detection device is larger than the set value for starting liquid introduction. A method for controlling the amount of gas mixed into a liquid according to item 1 or 2.