JPH069853B2 - Pressure control method in multi-stage extruder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multi-stage extruder used for foam molding of a resin, and particularly to a pressure control method at the time of starting the multi-stage extruder.

"Prior Art" FIG. 3 is a block diagram of a conventional multi-stage extruder. 10 is the first stage extruder. In this extruder 10, 11
Is a hopper for storing the raw material 11a. 12 is a barrel. Reference numeral 13 denotes a screw, which is mounted in the barrel 12 and is rotationally driven to convey the raw material 11 a supplied from the hopper 11 along the inner wall of the barrel 12. 14 is a motor, which drives the screw 13 to rotate. A pump 15 pumps gas into the barrel 12. Then, in the barrel 12, the raw material 1
Gas is mixed with 1a. 16 is a die, barrel 1
The raw material 11a that has been transported in 2 is mixed with gas,
It is discharged to the outside through this die 16.

20 is a second structure having the same configuration as the first-stage extruder 10.
It is the extruder of the stage. However, in the extruder 10, the raw material 11 a is supplied from the hopper 11, while the extruder 20 is supplied with the resin from the extruder 10. In the extruder 20, a screw (not shown) is rotationally driven by the motor 21, and the resin supplied from the extruder 10 is extruded and output. Then, the resin output from the extruder 20 is conveyed to the next step by the conveyor 30.

A resin pressure detector 41 outputs a detection signal corresponding to the output resin pressure in the extruder 10. 42 is a PID controller. This PID controller has a component proportional to the deviation (P; proportional operation component) in accordance with the deviation between the resin pressure indicated by the detection signal output from the resin pressure detector 41 and the resin pressure target value.
An operation signal S _{42 including} a component (I; integral action component) according to the time integration of the deviation and a component (D; differentiating action component) according to the derivative of the deviation is output. 43 is an adder, PID
The operation signal S ₄₂ output from the controller ₄₂ and the motor 2
It adds the rotational speed signal S ₂₁ of the motor output from the 1, supplied to the motor 14 as a rotation control signal S _43. Further, in this multi-stage extruder, the circuit constant (proportional element, integral) of the PID controller 42 is adjusted so that the closed loop operation including the extruder 10, the resin pressure detector 41, the PID controller 42 and the adder 43 is stabilized. Element, differential element) is adjusted.

Next, the operation of this multistage extruder will be described. In this multi-stage extruder, the extruder 10 mixes the raw material and the gas, and the extruder 20 performs extrusion molding of the resin output from the extruder 10. Since the raw material and the gas are mixed inside the extruder 10, it is necessary to control so that the output resin pressure is always constant near 100 kg / cm ² . This constant value control of the output resin pressure is performed as described below.

During normal operation, the extruder 20 moves the resin at a constant speed on the conveyor 3
Supply to 0. The motor 2 that drives the extruder 20
1 outputs the rotation speed signal S ₂₁ . On the other hand, extruder 1
The output resin pressure of 0 is detected by the resin pressure detector 41,
A detection signal corresponding to the resin pressure is output. PID controller 4
In 2, the operation signal S ₄₂ based on the deviation signal indicating the difference between this detection signal and the target resin pressure is output. Then, this operation signal S ₄₂ is transmitted to the motor 21 in the adder 43.
The addition and the rotational speed signal _{S 21,} the rotation control signal _{S 43}
Is supplied to the motor 14. As a result, the extruder 10
When the output resin pressure at is lower than the target resin pressure, the rotation speed of the motor 14 is increased, and when the output resin pressure at the extruder 10 is higher than the target resin pressure, the rotation speed of the motor 14 is decreased. In this way, in this multi-stage extruder, the extruder 10 is operated according to the speed of the extruder 20, and the output resin pressure of the extruder 10 is controlled to be always constant.

[Problems to be Solved by the Invention] The conventional multistage extruder described above has a problem that it is difficult to smoothly raise the output resin pressure of the extruder 10 to the target resin pressure at the time of starting. FIG. 4 shows the output resin pressure P of the extruder 10 in the multi-stage extruder shown in FIG.
It is a figure which shows the rising of. When the extruder 10 is started at time t ₁ , the output resin pressure P at this time is detected by the resin pressure detector 41. Here, since the output resin pressure P is very low at the time of starting, a large deviation from the target value is detected, and the motor 14 is rotated at a high speed according to this deviation. As a result, in the rising characteristic of the output resin pressure P, there is a possibility that overshooting may occur as shown by the curve B ₁ a. As a countermeasure against this, the PID controller 4
There is also a method of suppressing the overshoot amount of the output resin pressure P by adjusting 2 to suppress the proportional operation component in the operation signal S ₄₂ , but if the suppression is excessive, it rises to the target value as shown by the curve B ₁ b. The time required to do this will be significantly longer. Further, since the rising characteristic of the output resin pressure P varies depending on conditions such as temperature and resin state,
Adjustment is difficult. As described above, the conventional multi-stage extruder has a problem that it is difficult to adjust the rise of the output resin pressure at the time of starting, and if the adjustment is poor, it takes a lot of time for the output resin pressure to converge to the target value. It was Further, as described above, when the operation in a state where the output resin pressure P is unstable at the time of starting becomes long, there is a problem that a large amount of starting waste is generated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pressure control method in a multi-stage extruder capable of smoothly raising the output resin pressure to a target value at the time of starting.

"Means for Solving the Problem" The present invention relates to a first extruder that mixes a gas with a resin raw material and outputs the gas, and a second extruder that extrudes a resin supplied from the first extruder. In the pressure control method for a multi-stage extruder having: (a) detecting an initial value of the output resin pressure at the time of starting the first extruder, and (b) a final target of the output resin pressure in the first extruder. Calculating a pressure difference between the pressure value and the initial value, and (c) calculating the step value by equally dividing the pressure difference so that a step value equal to or less than a predetermined value is obtained. The output resin pressure of the first extruder is increased by setting a value obtained by adding the step value to the current output resin pressure in the extruder as a target pressure value, and (e) the output resin pressure of the first extruder is When the target pressure value reaches a predetermined range, the step value is set to the target pressure value. What was example as a new target pressure value, repeating the boosting of the first extruder output resin pressure,
It is characterized in that it can be raised to the final target value.

[Operation] According to the above method, in the first extruder, the target pressure value is sequentially increased little by little at the step value equal to or less than the predetermined value every time the current output resin pressure reaches the predetermined range of the target pressure value. In this way, the target pressure value increases little by little, and the boost control according to the target pressure value is performed each time, so the output resin pressure of the first extruder rises smoothly without generating an overshoot amount.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a multi-stage extruder to which a pressure control method according to an embodiment of the present invention is applied. In this figure, the parts corresponding to those in FIG. 3 described above are designated by the same reference numerals, and the description thereof will be omitted.

This multi-stage extruder is a PID in the multi-stage extruder shown in FIG.
Adjusting device 42 includes A / D converter 44, CPU 45, D / A
The configuration is replaced with the converter 46.

Next, the operation of this multistage extruder will be described. FIG. 2 shows the rising characteristics of the output resin pressure of the extruder 10 at the start of the multi-stage extruder, where A ₂ is the target value of the output resin pressure and B ₂ is the detected value of the output resin pressure. First, in this multistage extruder, when an unillustrated start button is pressed, the resin pressure detector 41 detects the initial value P ₀ of the output resin pressure of the extruder 10. And the resin pressure detector 4
A detection signal is output from 1, which is converted into a digital signal by the A / D converter and supplied to the CPU 45. CP
In U45, the step value Δ that satisfies the following conditions (1) and (2) from the final target value P ₁₀₀ of the output resin pressure and the initial value P _0:
Pa is calculated.

ΔPa = (P ₁₀₀ −P ₀ ) / n (1) (n is a natural number) ΔPa ≦ 20 kg / cm ² (2) Then, as the target pressure value Pt, Pt = P ₀ ΔPa ...... (3) is set. The CPU 45 then determines the target pressure value P
The digital signal corresponding to the deviation between t and the resin pressure P at the present time (however, P = P ₀ at this time) is D / A.
It is supplied to the converter 46, and the D / A converter 46 outputs it as the operation signal S ₄₆ to the adder 43. Then, in the adder 43, the operation signal S ₄₆ and the rotation speed signal S ₂₁ from the motor 21 are added, and the rotation control signal S ₄₃
Is supplied to the motor 14. As a result, the motor 14
Is started, and the output resin pressure P of the extruder 10 gradually increases accordingly.

On the other hand, the output resin pressure P of the extruder 10 is detected by the resin pressure detector 41 in parallel with the rotation control of the motor 14, and the detection signal is supplied to the CPU 45 via the A / D converter 44. Then, the CPU 45 determines that the output resin pressure P of the extruder 10 is ΔPb (≦ 5 kg / c with respect to the target pressure value Pt.
It is determined whether or not the pressure value within m ² ) has been reached, and when the determination result is “Yes”, a new pressure target value Pt is set according to the following equation.

Pt = Pt + ΔPa (3) Then, the CPU 45 determines the D / A converter 46 based on the deviation between the new target pressure value and the current output resin pressure.
The operation signal S ₄₆ is output via the to increase the rotation speed of the motor 14. As a result, the output resin pressure P of the extruder 10 further increases.

Hereinafter, similarly, when the output resin pressure P of the extruder 10 is sufficiently close to the target pressure value Pt, the target pressure value is updated, and the extruder 10 is pressure-controlled. In this way, the output resin pressure P smoothly rises as shown by the curve B ₂ and is increased to the final target value P ₁₀₀ .

Further, during normal operation of this multi-stage extruder, when the detected resin pressure deviates from the target value, the CPU 45 outputs a digital signal corresponding to the deviation, which is D /
The A converter 46 converts the operation signal S ₄₆ and outputs the operation signal S ₄₆ . Then, according to the operation signal S ₄₆ , the motor 1
4 is rotationally controlled, and the output resin pressure P is controlled so as to maintain a target value.

As described above, according to the present invention, when the extruder is started, the target value of the resin pressure is set according to the output resin pressure, and the output resin pressure is gradually increased. The output resin pressure can be smoothly increased to the target value.

[Brief description of drawings]

FIG. 1 is a block diagram of a multistage extruder to which a pressure control method according to an embodiment of the present invention is applied, FIG. 2 is a diagram showing rise of output resin pressure in the same embodiment, and FIG. 3 is a conventional multistage extruder. FIG. 4 is a diagram showing the rise of output resin pressure in the multistage extruder of FIG. 45 ... CPU, 44 ... A / D converter, 46 ... D /
A converter, 41 ... Resin pressure detector, 10 ... First stage extruder, 20 ... Second stage extruder.

Claims (1)

[Claims] 1. A pressure control in a multi-stage extruder having a first extruder for mixing a resin raw material with gas and outputting the mixture, and a second extruder for extruding a resin supplied from the first extruder. In the method, (a) the initial value of the output resin pressure at the time of starting the first extruder is detected, and (b) the pressure between the final target value and the initial value of the output resin pressure in the first extruder. The difference is calculated, and (c) the pressure difference is equally divided so as to obtain a step value equal to or less than a predetermined value, and the step value is calculated, and (d) the current output resin pressure in the first extruder is calculated. The output resin pressure of the first extruder is increased by setting a value obtained by adding the step value as a target pressure value, and (e) the output resin pressure of the first extruder is within a predetermined range of the target pressure value. When it reaches, the new target pressure value is calculated by adding the step value to the target pressure value. To repeat the step-up of the first extruder output resin pressure,
A pressure control method in a multi-stage extruder, wherein the pressure is raised to the final target value.