JP3517902B2 - Discharge stability control method for multi-screw extruder - Google Patents

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-mentioned 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 used. 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. If, over time to calculate the molten resin filled amount in the multi-screw extruder tip portion based on the physical properties of the discharge capacity value and extrusion molding the resin during the operation of the multi-screw extruder, the resin filled calculated at the present time
Compare the amount with the previously calculated amount of resin filling
The fluctuation amount is calculated, and the fluctuation of the raw material supply amount and discharge amount
Calculate the matching amount and supply to the multi-screw extruder according to the mismatching amount
A method for controlling the discharge stability of a multi-screw extruder that controls the amount of raw material supplied .

In the present invention, the discharge pressure may be a measured value of the discharge pressure of the multi-screw extruder or 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 raw material storage, a vibration feeder F2 provided in the hopper F1,
It is mainly composed of 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 provided with a first vent V1 and a second vent V2, which are connected to a vacuum source and remove volatile components in the resin. Further, in the subsequent stage (downstream side) of the twin-screw extruder T, a gear pump GP for improving the 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, which is a characteristic part of this embodiment, and an L control. The block C2 is composed of a microprocessor. R1 is a ROM that stores in advance a viscosity μ as a resin physical property corresponding to the resin temperature, R2 is a RAM that stores a constant K determined from the screw shape,
R3 is a screw tachometer for detecting the screw rotation speed N, and their outputs are all connected to the L calculation block C3. 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 both connected to the L calculation 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 : The resin filling amount and other physical amounts in the calculation of the resin temperature L are the following 2
It is related by a formula. ΔL = K1∫ΔQdt (1) P1 = K2μLN (2) In formula (1), ΔL represents the amount of change in the resin filling amount (current resin filling amount-previous resin filling amount), and ΔQ is the substance. Balance imbalance (raw material supply-
Gear pump discharge amount), and t indicates time. The current resin filling amount L1 is obtained by substituting the discharge pressure P1 of the twin-screw extruder into the above formula (2), and the filling amount L1 is compared with the previously obtained resin amount L0 to obtain the resin filling length. The change amount ΔL of L is calculated, and from the differential equation of equation (1),
It is possible to obtain the material balance imbalance amount in the raw material supply amount and the discharge amount.

The value of P1 substituted into the above equation (1) in this embodiment is an actual measurement value detected from 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 ROM R1 is searched for the viscosity μ corresponding to the detected resin temperature TP, and the constants K1, K2 determined by the screw shape are
Read from RAM R2, and fill resin amount L1 at the tip of twin-screw extruder T according to the above relational expressions (1) and (2).
Is calculated, and the amount of change ΔL in the resin filling amount, which is the difference from the previously calculated resin filling amount L0, is calculated by the same process, and the balance imbalance amount ΔQ (raw material supply amount−gear pump discharge amount) is calculated and calculated. The balance unbalance amount ΔQ is replaced with the control set value to perform the discharge stability control of the twin-screw extruder T. That is, in the control that is processed at the 200 msec cycle ,
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 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.

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 first vent V2 second vent

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 47/00-47/96

Claims (4)

(57) [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 of and the physical properties of the extrusion molding resin, and the molten resin filling amount calculated at the present time is
The amount of change in the resin filling amount compared to the molten resin filling amount
From the fluctuation amount of the raw material supply amount and the discharge amount
Calculate the amount of inconsistency, and supply the raw material according to the amount of inconsistency.
Ejection stabilization control method of a multi-screw extruder and controlling the. 2. The discharge pressure is the discharge pressure of a multi-screw extruder.
The measured value or the target value of
The discharge stability control method described. 3. The multi-screw extruder is a twin-screw extruder with a vent.
And the tip portion is located downstream of the final vent hole.
The discharge stability control method according to claim 1, wherein the method is a metering zone . 4. The feeder is a gear pump, a single screw extruder.
Stability control method according to claim 1, characterized in that it comprises a machine and a multi-screw extruder .