JPH0716911A - Method for stable control of discharge of multiple screw extruder - Google Patents

Abstract

PURPOSE:To stabilize a discharge amount by a method wherein a raw material feed amount to be supplied is controlled so that a filled amount of molten resin in a tip part calculated on the basis of discharge pressure of a multiple screw extruder, its extrusion capacity and a physical property of resin becomes a target value. CONSTITUTION:In a caluculation block L, a ROM is retrieved for a viscosity (mu) corresponding to a detected temperature of resin TP reading constants K1, K2 determined according to a shape of a screw from a RAM. A filled amount of the resin L1 in a tip part of a double-screw extruder is calculated according to relational formulas I, II. In the formula I, DELTAL indicates a varied amount of the resin filled amount, DELTAQ indicates an unbalanced amount in material balance, and (t) indicates time. By substituting discharge pressure P1 of the double-screw extruder for the formula II, the present filled amount L1 of resin is obtained. Then, a feed amount of a raw material is controlled so that the resin-filled amount L as a calculated result becomes constant as a target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the discharge stability of a multi-screw extruder, and more specifically, to a melter in which a multi-screw extruder is followed by a feeder such as another extruder and a gear pump connected in series. The present invention relates to a discharge stability control method for a multi-screw extruder in extrusion equipment.

[0002]

2. Description of the Related Art Conventionally, a twin-screw extruder with a vent is excellent in deaeration and dehydration ability due to its surface renewal property and vent function.
It has many advantages such as no need for pre-drying when melt-extruding resin, or promotion of chemical reaction in the extruder, and it is widely used for forming hard films. . Today, this type of twin-screw extruder is further provided with another feeder such as a single-screw extruder, a multi-screw extruder, and a gear pump through a melt line in the subsequent stage for the purpose of increasing the pressure and improving the discharge accuracy in the subsequent process. Attention has been paid to the use as a so-called tandem type melt extrusion equipment for connecting the above.

[0003]

However, in the above-described tandem type melt extrusion equipment, the balance between the raw material supply amount and the twin screw extruder discharge amount or the balance between the raw material supply amount and the gear pump discharge amount is often. There was a problem in that there were variations in discharge such as collapse, vent up, and surging. Vent-up occurs when the resin is in a molten and filled state from the extruder tip to the vent hole, and surging occurs when the extruder tip is in a molten resin depleted state. The above-mentioned discharge fluctuation is due to the fact that the movement of the material resin in the twin screw is very complicated, and even if the raw material supply amount and the discharge amount are simply set to the same amount, the imbalance of the mass balance is eliminated. Therefore, in order to improve the discharge accuracy, it is necessary to establish a discharge stability control method for a twin-screw extruder that can stably discharge the molten resin. An object of the present invention is to provide a discharge stability control method for a multi-screw extruder that can stably discharge a molten resin in consideration of the above problems of the conventional melt extrusion equipment.

[0004]

SUMMARY OF THE INVENTION The present invention is a method for controlling a multi-screw extruder in a melt-extrusion facility in which a feeder is connected in series after a multi-screw extruder. Also, the molten resin filling amount at the tip of the multi-screw extruder is calculated over time based on the discharge capacity value during operation of the multi-screw extruder and the physical properties of the resin for extrusion molding, and the calculated molten resin filling amount is the target. This is a discharge stability control method for a multi-screw extruder that controls the amount of raw material supplied to the multi-screw extruder so that the value becomes a value.

In order to control the above-mentioned resin filling amount to a target value, the resin filling amount calculated at the present time is compared with the resin filling amount calculated last time to obtain a variation amount of the resin filling amount, and the variation amount is calculated. It is preferable to determine the amount of mismatch between the raw material supply amount and the discharge amount from the above, and increase or decrease the raw material supply amount to be supplied to the multi-screw extruder according to the mismatch amount. In the present invention, the discharge pressure may be a measured value of the discharge pressure of the multi-screw extruder,
It may also be a target value.

In the present invention, the multi-screw extruder is preferably a twin-screw extruder with a vent, and in this case, the tip portion indicates the metalling zone on the downstream side of the final vent hole. In the present invention, the feeder can be composed of a gear pump, a single screw extruder, and a multi-screw extruder.

[0007]

In the present invention, the molten resin filling at the tip of the multi-screw extruder is based on the discharge pressure of the multi-screw extruder, the extrusion capability value of the multi-screw extruder, and the physical properties of the multi-screw extruder which are measured or given as target values. The amount is calculated, and the raw material supply amount supplied to the multi-screw extruder is controlled so that the calculated molten resin filling amount becomes a target value. Thereby, the discharge amount of the multi-screw extruder can be stabilized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a melt extrusion facility used to carry out the discharge stability control method of the present invention. In the figure, F is a raw material supply device, a hopper F1 for storing raw materials, and a vibrating feeder F2 provided in the hopper F1.
, And a motor F3 for driving the vibration feeder F2.

The raw material (hereinafter referred to as resin) supplied from the raw material supply device F is put into the hopper of the twin-screw extruder T and extruded by receiving the thrust obtained by the rotation of the screw connected to the motor T1. It is adapted to be extruded in the direction M. The cylinder of the twin-screw extruder T is connected to a vacuum source and is provided with a first vent V1 and a second vent V2 for removing volatile components in the resin. Further, in the latter stage (downstream side) of the twin-screw extruder T,
A gear pump GP for improving pressurization and discharge accuracy is connected in series with the twin-screw extruder T via a melt line.

Also, a P1 control block C1 having a conventional structure for controlling the discharge pressure of the twin-screw extruder T, an L calculation block C3 for controlling the resin filling amount and an L control, which are the characteristic parts of this embodiment. The block C2 is composed of a microprocessor. R1 is a ROM that stores in advance the viscosity μ as a resin physical property corresponding to the resin temperature, R2
Is a RA that remembers a constant K determined from the screw shape
M and R3 are screw tachometers for detecting the screw rotation speed N, and their outputs are both L calculation block C.
Connected to 3. Further, R4 is a temperature sensor for detecting the resin temperature, R5 is a pressure gauge for detecting the discharge pressure of the twin-screw extruder T, and their outputs are all L
It is connected to the counting block C3.

Before describing the discharge stability control in the melt extrusion equipment having such a configuration, the symbols used in the description of the control operation are shown below. P1: Discharge pressure Q1: Raw material supply amount Q2: Discharge amount of twin-screw extruder Q3: Discharge amount of gear pump GP N: Screw rotation speed K1: Constant determined by screw shape K2: Constant determined by screw shape μ: Resin physical properties TP : Resin temperature The resin filling amount and other physical amount in L calculation are the following 2
It is related by a formula. ΔL = K1 ∫ΔQdt (1) P1 = K2 μLN (2) In equation (1), ΔL represents the amount of change in the resin filling amount (current resin filling amount-previous resin filling amount), and ΔQ is The material balance imbalance amount (raw material supply amount-gear pump discharge amount) is shown, and t shows time. By substituting the discharge pressure P1 of the twin-screw extruder into the above formula (2), the current resin filling amount L1
Then, the amount of change ΔL of the resin filling length L is obtained by comparing the filling amount L1 with the resin amount L0 obtained last time.
From the differential equation of the equation (1), it is possible to obtain the material balance imbalance amount in the raw material supply amount and the discharge amount.

In this embodiment, the value of P1 substituted into the above equation (1) is an actual measurement value detected by the pressure gauge R5. However, the value of P1 is not limited to this, and may be a target value of P1 control when the conventional P1 control is also used. The reason is that the control cycle (20 msec) for the P1 control is extremely short, and the output is extremely stable due to the inverter control.

FIG. 2 is a cross-sectional view of the tip cylinder of the twin-screw extruder T. Inside the cylinder, the pitch of the flight F is arranged differently toward the extruding direction M so that the space where the resin can enter along the screw S can be restricted, and the pitch is narrow near the discharge port. A disposed metering zone Z is provided. This metallic zone Z can be regarded as the "tip portion of the twin-screw extruder" in claim 1. In the figure, the resin filling amount L is the proportion of the resin in the metering zone Z. Actually, the proportion of the resin filled in the direction opposite to the extrusion direction M from the discharge port O is replaced with the length. There is.

Next, the discharge stability control operation will be described.
In FIG. 1, the microprocessor controls the twin-screw extruder T as follows. First, the discharge pressure P1 of the twin-screw extruder T detected by the pressure gauge R5, the resin temperature TP detected by the temperature sensor R4, and the rotation speed N detected by the screw tachometer R3 are given to the L calculation block C3. To be

In the L calculation block C3, the viscosity R corresponding to the detected resin temperature TP is retrieved from the ROM R1, and the constants K1 and K2 determined by the screw shape are
Read from RAM R2, and use the above relational expressions (1), (2)
The resin filling amount L at the tip of the twin-screw extruder T
1 is calculated, and by the same processing, the change amount ΔL of the resin filling amount, which is the difference from the previously calculated resin filling amount L0, is calculated.
The balance imbalance amount ΔQ (raw material supply amount-gear pump discharge amount) is calculated, and the calculated balance imbalance amount ΔQ is replaced with a control set value to perform discharge stability control of the twin-screw extruder T. That is, in the control that is processed at a cycle of 200 msec,
If the difference ΔL between the currently calculated resin filling amount L1 and the previously calculated resin filling amount L0 is calculated, then the balance imbalance amount ΔQ is calculated. If the result is, for example, a value of +, the twin screw extruder T is used. If the result is a negative value, the raw material supply amount is increased, and vice versa. At this time, since the raw materials are usually supplied to the twin-screw extruder T from a plurality of hoppers, the raw material supply amount is individually controlled according to the raw material mixing ratio in the hopper.

Further, the target value of the resin filling amount L should be appropriately changed depending on the resin used, and the raw material supply amount should be controlled so that the resin filling amount L as a calculation result is constant at the target value. For example, the discharge amount of the twin-screw extruder T can be stabilized. Next, a comparison between the discharge pressure control method of this example and the conventional extrusion method is shown below.

[0017]

[Table 1]

As is clear from the above comparison table, in this embodiment, vent up and surging did not occur. Therefore, continuous operation of the twin-screw extruder becomes possible. Further, the unevenness of the vertical thickness of the product film is significantly improved as compared with the conventional example. The IV value indicating deterioration of the resin is decreasing. Since no human intervention is required, labor can be saved. The multi-screw extruder used in the discharge stability control method of the present invention is a twin-screw extruder in the above embodiment, but a three-screw or more extruder can also be applied. Further, although the ejection stabilization control of the present invention is realized by software using a microcomputer, it may be realized by using a dedicated hardware circuit that performs those functions.

[0019]

As is apparent from the above description, according to the discharge stability control method for a multi-screw extruder of the present invention, a tandem type melting system in which another feeder is connected to the latter stage of the multi-screw extruder In the extrusion equipment, the molten resin can be stably discharged from the multi-screw extruder. Further, according to the present invention,
There is no need to manually adjust the raw material supply rate. Furthermore, since the balance of the material balance is maintained, the stability of the discharge pressure control can be greatly improved, and as a result, the physical properties of the extruded molten resin become uniform.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a twin-screw extruder used for discharge stability control according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a tip portion of the twin-screw extruder shown in FIG.

[Explanation of symbols]

 F Raw material supply device T Twin screw extruder GP Gear pump P1 Pressure gauge TP Resin thermometer V1 1st vent V2 2nd vent

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[Procedure amendment]

[Submission date] June 23, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

Also, a P1 control block C1 having a conventional structure for controlling the discharge pressure of the twin-screw extruder T, an L calculation block C3 for controlling the resin filling amount and an L control, which are the characteristic parts of this embodiment. The block C2 is composed of a microprocessor. R1 is a ROM that stores in advance the viscosity μ as a resin physical property corresponding to the resin temperature, R2
Is a RA that remembers a constant K determined from the screw shape
M and R3 are screw tachometers for detecting the screw rotation speed N, and their outputs are both L calculation block C.
Connected to 3. Further, R4 is a temperature sensor for detecting the resin temperature, R5 is a pressure gauge for detecting the discharge pressure of the twin-screw extruder T, and their outputs are all L
It is connected to a calculation block C3.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

In the L calculation block C3, the viscosity R corresponding to the detected resin temperature TP is retrieved from the ROM R1, and the constants K1 and K2 determined by the screw shape are
Read from RAM R2, and use the above relational expressions (1), (2)
The resin filling amount L at the tip of the twin-screw extruder T
1 is calculated, and by the same processing, the change amount ΔL of the resin filling amount, which is the difference from the previously calculated resin filling amount L0, is calculated.
The balance imbalance amount ΔQ (raw material supply amount-gear pump discharge amount) is calculated, and the calculated balance imbalance amount ΔQ is replaced with a control set value to perform discharge stability control of the twin-screw extruder T. That is, in the control that is processed in a cycle of 10 seconds , the difference ΔL between the resin filling amount L1 calculated at the present time and the resin filling amount L0 calculated last time is calculated, and then the balance imbalance amount ΔQ is calculated. If the value is, the amount of raw material supplied to the twin-screw extruder T is reduced, and vice versa.
If the result is a negative value, the raw material supply amount is increased. At this time, since the raw materials are normally supplied to the twin-screw extruder T from a plurality of hoppers, the raw material supply amount is individually controlled according to the raw material mixing ratio in the hopper.

Claims (5)

[Claims] 1. A method for controlling a multi-screw extruder in a melt-extrusion equipment, in which a feeder is connected in series after a multi-screw extruder, the discharge pressure of the multi-screw extruder, and the multi-screw extruder. The molten resin filling amount in the tip portion of the multi-screw extruder is calculated over time based on the discharge capacity value during operation and the physical properties of the extrusion molding resin so that the calculated molten resin filling amount becomes a target value. A method for controlling discharge stability of a multi-screw extruder, which comprises controlling a feed amount of a raw material supplied to the multi-screw extruder. 2. The molten resin filling amount calculated this time is compared with the molten resin filling amount calculated last time to obtain a variation amount of the resin filling amount, and the raw material supply amount and the discharge amount are calculated from the variation amount. The ejection stability control method according to claim 1, wherein a non-coincidence amount is obtained, and the raw material supply amount is controlled according to the non-coincidence amount. 3. The discharge pressure is a measured value or a target value of the discharge pressure of the multi-screw extruder.
The discharge stability control method described. 4. The stable discharge according to claim 1, wherein the multi-screw extruder is a twin-screw extruder with a vent, and the tip portion is a metalling zone on the downstream side of the final vent hole. Control method. 5. The discharge stability control method according to claim 1, wherein the feeder includes a gear pump, a single-screw extruder, and a multi-screw extruder.