JPH0144135B2 - - 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 produced by colliding and mixing at least two 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 provides a method for inputting a target value of the gas mixture rate or a limit value larger than the target value into a control device as a depressurization start setting value, and then The mixing rate is measured, and if the actual value of the gas mixing rate is larger than the depressurization start setting value, the pressure in the liquid tank is reduced to promote release of the gas mixed in the liquid. This is how it was done.

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

Reference numeral 1 in FIG. 1 denotes a raw solution tank (liquid 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 made of piping for circulating the liquid in the stock solution tank 1 are connected to the stock solution tank 1.
A stirring blade rotated by a motor (not shown) is provided inside. 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. β
The end is connected to one end of a circulation cylinder 6 having high wear resistance. The other end of the circulation cylinder 6 is connected to the β end of the second three-way switching valve 5, and a piston 7a that slides inside the circulation cylinder 6 is provided at one end of the piston rod 7. . 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 piston inside the circulation cylinder 6 to move. 7a is configured to reciprocate from side to side. Further, the γ end of the second three-way switching valve 5 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, so that the gas The other end of the blowing device 10 is connected to the stock solution tank 1 via a check 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 stock solution tank 1 is connected to the stock solution tank 1 via a tank internal pressure control mechanism 25 that controls the pressure inside the stock solution tank 1.

A computing device 26 is electrically connected to the encoder 14 and pressure sensor 15 to constitute a gas entrainment rate detection device 27, and based on the measurement data obtained by the encoder 14 and pressure sensor 15 when measuring the gas entrainment rate. Accordingly, the arithmetic unit 26 calculates the gas mixture rate of the liquid.

The arithmetic device 26 is electrically connected to a gas mixing rate control device 28. This gas mixing rate control device 28 calculates the output value (actual value of the gas mixing rate) x a of the arithmetic unit 26 x the target value of the gas mixing rate input in advance from the input device 29 .
b, the gas blowing amount control valve 22
Alternatively, a command signal is output to the tank internal pressure control mechanism 25.

As is well known, a measuring cylinder 30 and a mixing head 31 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 31 and 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. Also, 32
is a pressure gauge that detects the pressure inside the stock solution tank 1.

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 26, and the actual measurement value x a of the gas mixture rate is calculated.

The measured value xa of the gas mixing rate is as follows: (1) The gas state equation (PV=constant) holds true even when the gas is mixed in the 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 V _P : 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 where the pressure reaches the first pressure condition P ₁ Distance cm from b to point c where the pressure reaches the second pressure condition P ₂ (l = l ₂ − l ₁ ) D: Diameter of cylinder 6 cm Xa: Volume ratio of liquid and gas under atmospheric pressure (gas Mixing rate), then Xa=πD ² lP ₁ P ₂ / (N ₁ + N ₂ ) where N=4.132 (V ₀ +Vp−πD ² l ₁ /4) (P ₂ − P ₁ ) N ₂ = πD 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 26 is compared in the gas mixture rate control device 28 with the target value Xb, which is input in advance to the gas mixture rate control device 28 by the input device 29. Ru.

When the actual value Xa and the target value Xb are equal, the gas mixing rate control device 28 controls the pressure in the stock solution tank 1 to normal with the gas injection amount control valve 22 closed and the tank internal pressure control mechanism 25. (for example, 5 Kg/cm ² G), switch the switching valves 4, 5, and 9, and reciprocate the piston 7a in the circulation cylinder 6, so that the liquid in the stock solution tank 1 is Circulate through the liquid channel 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 28,
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 28. 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 pressure inside the stock solution tank 1 is set to normal pressure (5 kg/cm ² G in the example) by the tank internal pressure control mechanism 25.
is held in Then, when it comes time to measure the next gas entrainment rate, the liquid circulation is stopped.

Furthermore, as a result of comparing the measured value Xa of the gas mixing rate with the target value Xb in the gas mixing rate control device 28, if the measured value Xa is larger than the target value Xb, the gas mixing rate control device 28 Since a command signal is output to the internal pressure control mechanism 25, the tank internal pressure control mechanism 25 discharges the gas in the stock solution tank 1 and maintains the internal pressure of the stock solution tank 1 at a certain constant value (for example, 2 kg/cm ² G). lower. This results in
The gas contained in the liquid in the stock solution tank 1 as minute bubbles expands its volume, so the buoyancy force exerted on the bubbles from the liquid increases (for example, if the absolute pressure in the stock solution tank 1 becomes 1/2) , the bubble volume is 2
(the buoyancy force exerted on the bubble is doubled), and the bubble rises rapidly and is expelled from the liquid to the outside.
Therefore, the rate of gas contamination in the liquid is reduced. Also,
The liquid in the stock solution tank 1 is circulated through the liquid flow path 2 by operating the piston 7a in the circulation cylinder 6 and the switching valves 4, 5, and 9 together with this pressure reduction control inside the stock solution tank 1. . Then, depending on the gas mixture rate and measurement results, it is determined whether to return to the original pressure (5 kg/cm ² G), although the pressure remains low. The pressure reduction control inside the stock solution tank 1 is performed for a certain period of time from when the gas mixture rate control device 28 determines that the measured value Xa of the gas mixture rate exceeds the target value Xb, and then the tank internal pressure is reduced. In some cases, it may be useful to use the control mechanism 25 to return the pressure in the stock solution tank 1 to its original state (5 kg/cm ² G) in order to prevent the mixing rate from decreasing too much.

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 34 is provided in the liquid flow path 2. In the second embodiment, liquid always flows through the liquid circulation pump 33,
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 by the gas mixing rate detection device 34, the actual measured value Xa of the gas mixing rate is sent to the gas mixing rate control device 28 and compared with the target value Xb input from the input device 29. be done. Based on the comparison result, the same control as in the first embodiment is carried out, that is, when the actual measurement 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 Xb, the tank internal pressure control mechanism 25 performs pressure reduction control within the stock solution tank 1 to lower the pressure inside the stock solution tank 1 and release the gas contained in the liquid.

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-mentioned stock solution tank pressure reduction control may be performed. In this case, the gas mixture rate will not drop too much due to excessive depressurization in the stock solution tank 1, and the fluctuations in the gas mixture rate can be suppressed to a smaller value based on the target value Xb, resulting in a more stable can be controlled. Furthermore, instead of the gas injection amount control valve 22, an electromagnetic on-off valve may be used to perform on-off control to control the amount of gas mixed into the liquid.

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 depressurization start setting value, the gas mixture of the liquid in the hydraulic tank is prevented. measure the rate,
Since the pressure in the liquid tank is reduced when the measured value of the gas mixture rate is larger than the depressurization start setting value, the pressure in the liquid tank decreases to reduce the amount of gas contained in the liquid. As the volume of the microscopic bubbles (gas) expands, the buoyancy of the bubbles from the liquid increases, and the gas in the liquid is quickly and smoothly released from the liquid to the outside, reducing the gas contamination rate of the liquid. can be lowered. 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. Furthermore, since this method limits the time for reducing the pressure in the liquid tank, it has excellent effects such as preventing the mixing rate from decreasing too much.

[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 (liquid tank), 27... Gas mixing rate detection device, 28... Gas mixing rate control device, 34... Gas mixing rate detection device, Xa... Actual value, Xb... Target value, Xc ...Limit value.

Claims (1)

[Claims] 1. After inputting a target value of the gas mixture rate or a limit value larger than the target value into the control device as a depressurization start setting value, the gas mixture rate in the liquid tank is detected. When the measured value obtained by the gas mixing rate detection device is larger than the depressurization start setting value, the pressure in the liquid tank is reduced to release the gas mixed in the liquid. A method for controlling the amount of gas mixed into a liquid, characterized in that: 2. The method according to claim 1, wherein the pressure in the liquid tank is lowered for a predetermined set time when the actual value obtained by the gas mixing rate detection device is larger than the set value for starting pressure reduction. A method for controlling the amount of gas mixed into a liquid.