JPH06328546A - Control method for composite extrusion molding device - Google Patents

Abstract

PURPOSE:To provide a control method for sensing the pressure variation of respective sections of a composite extrusion molding device, identifying the causes of the variations and performing accurately the modification or correction in compliance with respective causes. CONSTITUTION:The pressure on the inlet side of a gear pump and the pressure P2 on the outlet side thereof is sensed and the feed quantity of a quantitative feeder 1 is controlled by the differential pressure, and also a driving motor for the gear pump 3 is so controlled as to set the pressure P2 on the inlet side of the gear pump to the preset pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extruder with a metering feeder and a gear pump, which are mainly used for direct mixing of raw material components, sufficient cooling, and molding of films and sheets which are required to have high stability. The present invention relates to a method for controlling a compound-type extrusion-molding apparatus having a core.

[0002]

2. Description of the Related Art Conventionally, in this type of apparatus, the pressure of a single-screw or twin-screw extruder configured to supply a polymer through a supply device is detected, and the detection signal is fed back to an extruder screw drive system. The rotation rate of the extruder screw is also detected, and the rotation rate detection signal is fed back to the drive system of the polymer supply apparatus to control the supply rate of the polymer (Japanese Patent Publication No. 2). -50207).

However, there are two main disturbance factors that change the state of the extrusion process in such a composite extrusion molding apparatus: characteristic change of the quantitative feeder and filter clogging.

That is, as a typical quantitative feeder, a belt type and a loss-in-weight type are used, and each is composed of a weight detecting section, a control section and a mechanical feeder. The supply amount of the feeder is designed to be kept constant by the control mechanism in the feeder system.However, the temperature drift and the time drift of the load cell used in the weight detection unit or the powder to the belt etc. The above-mentioned supply amount varies depending on the adherence of the body or the like. The characteristics of the disturbance due to the characteristic change of the quantitative feeder are not necessarily deterministic and the fluctuation period is considerably long.

On the other hand, one or more filters are always provided on the outlet side of the composite extruder. The function of this filter is to capture foreign matters such as dust, gel, carbide, and metal abrasion powder in the molten resin, and the filter will be clogged over time, increasing the resin pressure. As a result, the filling length of the tip metering portion of the extruder increases, which causes problems such as an increase in resin temperature and venting. This disturbance has features such as being deterministic and gradually increasing monotonically.

[0006]

Therefore, as described above, the inlet side pressure of the gear pump provided on the downstream side of the extruder is set as a control amount, and the feeder drive unit is controlled to control the inlet side pressure of the gear pump. In the conventional device, the production amount or the thickness of the sheet or the like is kept constant by the constant value control, and when the disturbance of the characteristic change of the quantitative feeder acts, the following phenomenon occurs.

That is, the discharge amount of the gear pump is Q (equal to the feeder supply amount Q _f in the steady process), the rotation speed of the gear pump is N, the theoretical discharge amount of the gear pump is α, the back pressure flow coefficient is β, and the material viscosity is Is μ, the inlet side pressure of the gear pump is p ₁ and the outlet side pressure is p ₂ , general characteristics of the gear pump are expressed by the following equations.

Q = αN− (p ₂ −p ₁ ) · β / μ (1) From this equation, p ₁ is p ₁ = p ₂ −μ / β · (αN−Q) (2) where When the change amount δp ₁ of the inlet pressure when the amount increases δQ _f , δp ₁ = μ / β · δQ = μ / β · δQ _f (3) In this case, p ₂ also changes depending on δQ _f , but δp ₂ is much smaller than δp ₁ and can be ignored.

However, since the back pressure flow coefficient β of the gear pump is generally very small, the inlet side pressure p ₁ of the gear pump rises considerably due to a slight fluctuation of the supply amount δQ _f . That is, the change in p ₁ can be detected with high sensitivity.

Therefore, in the above-mentioned conventional apparatus, when p ₁ rises and a control deviation occurs from the set value, the control apparatus operates to correct the material supply amount, and the production amount, sheet thickness, etc. Is kept constant.

On the other hand, assuming that the supply amount Q _{f of the} feeder is constant, when the filter is clogged, the outlet side pressure of the gear pump first rises by δp ₂ . However, since Q _f is constant, the differential pressure Δp (= p ₂ −p
₁ ) does not change. Accordingly, since the inlet pressure p ₁ also same amount rises outlet pressure p _2, the p ₁ + .delta.p _2,
There is a control deviation from the set value.

Therefore, in the control system of the above conventional apparatus,
Determines that "the deviation is caused by variations in the feeder supply quantity Q _f", the operation that reduces the Q _f is executed.
Therefore, as the filter is clogged, the extrusion amount or sheet thickness is gradually reduced.

That is, in the above-mentioned conventional apparatus, there is a problem that the production amount and the sheet thickness are reduced due to the disturbance of filter clogging.

In view of such a point, the present invention detects the change in pressure of each part of the composite extrusion molding apparatus, identifies the cause of the change, and executes an appropriate correction or correction operation according to each cause. Aim to get a way.

[0015]

A first invention of the present application is to provide a quantitative feeder for quantitatively controlling raw materials to feed an extruder, an extruder to which raw materials are fed from the quantitative feeder, and an extrusion side of the extruder. In a method for controlling a composite extrusion molding apparatus having a gear pump connected to a gear pump and a filter provided on at least one of an inlet side and an outlet side of the gear pump, a pressure P ₁ on an inlet side and a pressure P ₂ on an outlet side of the gear pump are provided. Is detected, and the supply amount of the quantitative feeder is controlled based on the differential pressure, and the drive motor of the gear pump is controlled so that the inlet side pressure P ₁ of the gear pump becomes a preset pressure.

A second aspect of the invention is a quantitative feeder for quantitatively controlling the raw material to feed the extruder, an extruder to which the raw material is fed from the quantitative feeder, a gear pump connected to the extrusion side of the extruder, and a gear pump. In the method of controlling the composite extrusion molding apparatus having a filter provided on at least one of the inlet side and the outlet side, the inlet side pressure P ₁ and the outlet side pressure P ₂ of the gear pump are detected, and based on the differential pressure thereof, In addition to controlling the supply amount of the quantitative feeder, the extrusion pressure P ₀ of the extruder is detected, and the drive motor of the gear pump is controlled so that the pressure becomes a preset pressure.

Further, a third aspect of the present invention is connected to the fixed amount feeder for supplying the raw material to the extruder under quantitative control, the first extruder supplied with the raw material from the fixed amount feeder, and the first extruder. A method for controlling a composite extrusion molding apparatus, comprising: a second extruder; a gear pump connected to an extrusion side of the second extruder; and a filter provided on at least one of an inlet side and an outlet side of the gear pump. Detecting the inlet side pressure P ₁ and the outlet side pressure P ₂ of the gear pump, controlling the supply amount of the quantitative feeder based on the differential pressure, and detecting the extrusion side pressure P ₀ of the first extruder. The drive motor of the second extruder is controlled so that the pressure becomes a preset pressure.

[0018]

The pressure p ₁ on the inlet side of the gear pump changes depending on two disturbance factors as described above. Therefore, first p
We must identify the change factor of ₁ . Then, it is possible to discriminate whether the cause of the change in the pressure p _{1 on} the inlet side of the gear pump is the fluctuation in the supply amount due to the change in the characteristic of the constant amount feeder or the clogging of the filter by examining the differential pressure Δp before and after the gear pump.

That is, the fluctuation of the supply amount of the quantitative feeder is
It always appears as a change in the differential pressure Δp before and after the gear pump.

From the equation (1), this Δp is Δp = p ₂ −p ₁ = μ / β · (2N−Q _f ) (4) ∴δ (Δp) = − μ / β · δQ _f (5) -Μ / β in the equation is the sensitivity coefficient (λ) when the supply amount fluctuation δQ _f of the quantitative feeder is detected by the change amount δ (Δp) of the differential pressure, and this λ is a very high value as described above. With.

Therefore, the supply amount fluctuation δQ _f can be detected with high accuracy by the differential pressure Δp before and after the gear pump. Therefore, by controlling the supply amount of the quantitative feeder by this differential pressure Δp, it is possible to cope with the disturbance due to the characteristic change of the quantitative feeder and supply the predetermined amount of raw material.

On the other hand, if the feeder supply amount does not change, the differential pressure Δp before and after the gear pump is constant. Therefore, if Δp is constant and the inlet side pressure p ₁ or outlet side pressure p _{2 of the} gear pump or the extruder side pressure p ₀ of the twin-screw extruder corresponding to the inlet side pressure of the gear pump rises, the cause of this rise is It can be determined that the filter is clogged, and the influence of the filter clogging can be eliminated by controlling the rotation speed of the gear pump with any of these signals.

Further, even if the feeder supply amount variation and the filter clogging occur simultaneously, the differential pressure Δp before and after the gear pump reacts only to the feeder supply amount variation. Therefore, based on this differential pressure Δp, it is possible to divide into a component due to the fluctuation of the supply amount of the feeder and a component due to the clogging of the filter.

According to the third aspect of the invention, the drive motor of the second extruder is controlled so that the pressure on the extrusion side of the first extruder becomes a set pressure according to the same principle as the first invention. This makes it possible to eliminate the effect of filter clogging.

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an apparatus for carrying out the method of the present invention, in which the raw material supplied from the fixed amount feeder 1 to the twin-screw extruder 2 is heated and melted while being kneaded by the twin-screw extruder 2. Is fed to the gear pump 3, where the raw material continuously conveyed from the twin-screw extruder 2 is weighed by a fixed amount, supplied to the die 5 through the filter 4, and discharged quantitatively from the die 5.

Pressure detectors 6 and 7 are provided on the inlet side and the outlet side of the gear pump 3, respectively. The pressure p on the inlet side of the gear pump detected by the pressure detectors 6 and 7 is p.
The signals of ₁ and the pressure p ₂ on the outlet side are compared and calculated by the differential pressure calculator 8, the differential pressure is compared with the set value of the differential pressure setter 10 by the comparator 9, and the deviation signal is input to the control unit 11. Then, the operation amount is calculated and the correction amount of the set value of the feeder supply amount is calculated. Then, this new set value is output to the setting controller 12, whereby a control signal is input to the drive unit 13 of the fixed quantity feeder 1 to control the raw material supply charge by the fixed quantity feeder 1.

On the other hand, the pressure signal from the pressure detector 7 for detecting the pressure on the outlet side of the gear pump 3 is also sent to the comparator 14, where it is compared with the set value from the pressure setter 15, and the deviation signal is controlled. The correction amount of the set value of the rotation speed of the gear pump is input to the section 16, and this new setting signal is sent to the drive motor 1 of the gear pump 3 via the setting controller 17.
8, and the rotation speed of the gear pump 3 is controlled.

Therefore, the constant quantity feeder 1 is controlled by the differential pressure Δp between the inlet side pressure and the outlet side pressure of the gear pump, and the disturbance due to the characteristic change of the constant quantity feeder is corrected and the pressure fluctuation at the outlet side of the gear pump is adjusted. By controlling the rotation speed of the gear pump, the effect of filter clogging is corrected.

By the way, the operation order of both control loops when both the disturbances act simultaneously is important. Although it is possible to identify the magnitudes of both disturbances by calculation and perform simultaneous operations, mutual interference causes a complicated operation method. In addition, both disturbances have a long period as described above,
In particular, considering that the clogging of the filter has the property of increasing monotonically, it is judged that it is not necessary to operate it immediately.

Therefore, in this embodiment, the following sequential operation method is adopted. That is, the supply amount fluctuation of the still feeder is checked by the differential pressure Δp before and after the gear pump. At this time, if there is a deviation in Δp, the feeder supply amount is corrected by issuing a correction command for the set value of the feeder supply amount.

Next, after the above operation, when the differential pressure Δp falls within the allowable range, the pressure p ₂ is checked, and if there is a deviation in these pressures, a gear pump speed correction command is issued. When this operation is executed, the set value of the differential pressure Δp before and after the gear pump must be updated without fail. This renewal timing is performed when the pressure of each part becomes stable after the above operation is performed, and new set values are measured in a stable state by measuring p ₁ and p ₂ , and the differential pressure (p ₂ −p _{2
Use the} value calculated in ₁ ).

The control flow of the above control method is shown in FIG.

FIG. 3 shows another embodiment of the present invention, in which a filter 20 is provided between the twin-screw extruder 2 and the gear pump 3, and the upstream side of the filter 20, that is, the twin-screw extruder 2 is shown. A pressure detector 21 is provided on the discharge side.

The pressure p ₀ on the extrusion side of the twin-screw extruder 2 detected by the pressure detector 21 is the pressure setter 22.
Is compared with the set value, the deviation signal is input to the control unit 23, and the output signal from the control unit 23 is set by the setting controller 17.
Is input to the drive motor 18 of the gear pump 3 via the control unit to control the rotation speed of the gear pump 3. Others are the same as those shown in FIG.

Therefore, also in this embodiment, the pressure difference between the front and rear of the gear pump 3 is detected, the supply amount of the constant amount feeder is controlled according to the pressure difference, and the pressure on the discharge side of the twin-screw extruder rises. In this case, the rotation speed of the gear pump is controlled and the effect of filter clogging is corrected.

By the way, in each of the above-described embodiments, the gear pump, which is originally desired to be operated at a constant speed as the reference device, is shifted to cope with the clogging of the filter. However, when the speed of the gear pump is changed, the set value of the differential pressure Δp before and after the gear pump related to the control of the constant quantity feeder must be updated each time based on the following equation.

Δp = μ / β (αN−Q) (6) For this reason, it is necessary to coordinate the operation sequence and the like between the two control systems of the quantitative feeder control system and the gear pump control system.

On the other hand, in order to keep the degree of kneading, temperature, or volatility of the resin within the allowable range and prevent venting up in the extruder, the filling length x of the tip measuring part of the extruder is kept constant. I have to keep it.

FIG. 4 is a view showing another embodiment capable of achieving the above-mentioned object. A single-screw extruder (second extruder) is provided on the downstream side of the twin-screw extruder (first extruder) 2. Extruder) 25,
The filter 26 and the gear pump 3 are sequentially arranged.

A pressure detector 21 is provided on the extrusion side of the twin-screw extruder 2, and the extrusion-side pressure of the twin-screw extruder detected by the pressure detector 21 corresponds to the set pressure of the pressure setter 22. The deviations are compared, and the deviation is input to the control unit to calculate the manipulated variable. This operation signal is sent to the setting controller 27 of the single-screw extruder drive motor to update the set speed. The control signal from the setting controller 27 drives the drive motor 2
The rotation of the single screw extruder 25 is controlled, and the rotation speed of the single screw extruder 25 is controlled.

On the other hand, the control method of the quantitative feeder 1 is exactly the same as that of FIG.

By the way, a simple means for detecting the filling length x of the tip measuring portion of the twin-screw extruder 2 is to measure the screw tip pressure p ₀ of the extruder. This p ₀
Is expressed as follows, and p ₀ is proportional to x.

P ₀ = μα ₁ N ₁ x / β ₁ · (1-Q / α ₁ N ₁ ) (7) where α ₁ is the thrust flow coefficient of the twin-screw extruder and β ₁ is the same back pressure flow coefficient. , N ₁ are the same number of revolutions.

Therefore, x can be kept constant by controlling p ₀ to a constant value.

On the other hand, in FIG. 4, when the filter 4 is clogged, the outlet side pressure p _{2 of the} gear pump 3 increases by δp '. However, the gear pump 3 equal to the feeder supply amount Q _f
Since the flow rate Q of the pump is constant, the differential pressure Δ before and after the gear pump 3
p (= p ₂ −p ₁ ) does not change. That is, the pressure on the inlet side of the gear pump also rises by δp '. If the filter 26 is clogged, the head pressure of the single-screw extruder increases by δp ″. However, if the flow rate and the screw speed are constant, the differential pressure between the inlet and the outlet of the single-screw extruder does not change as in the case of the gear pump. The inlet pressure p ₀ also rises by the same amount δp ″. After all, the amount of increase δp ₀ of the extrusion side pressure of the twin-screw extruder becomes δp ′ + δp ″.

Then, the extrusion side pressure signal of the twin-screw extruder 2 is compared with the set value as described above, and the manipulated variable is calculated by the deviation signal. This calculation formula is appropriately proportional / integral or the following formula.

ΔN ₂ = −β ₂ / μα ₂ · δp ₀ (8) where δN _{2 is the} speed increase amount of the single-screw extruder, α _{2 is} the thrust flow coefficient of the extruder, and β _{2 is the} same backflow. It is a coefficient.

An operation signal based on the above calculation result is sent to the setting controller 27 of the drive motor 28 of the single screw extruder to increase the set speed. As a result, the inlet pressure of the single-screw extruder, that is, the screw tip pressure p ₀ of the twin-screw extruder is always kept constant, and the filling length x can be kept constant.

[0050]

As described above, according to the present invention, the supply amount of the constant amount feeder is controlled by the differential pressure between the inlet side pressure and the outlet side pressure of the gear pump, and the inlet side pressure of the gear pump and the extruder side pressure of the extruder are controlled. Since the drive motor of the gear pump or the drive motor of the second extruder is controlled by the above, the influence of filter clogging can be eliminated and the feed amount of the feeder can be controlled to be constant. It is possible to always maintain a high precision and a constant level, and to keep the degree of kneading, temperature or devolatilization of the resin within an allowable range and prevent venting up in the extruder.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the method of the present invention.

FIG. 2 is a diagram showing a control flow of the present invention.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram showing still another embodiment of the present invention.

[Explanation of symbols]

 1 Quantitative Feeder 2 2 Screw Extruder 3 Gear Pump 4 Filter 5 Die 6,7,21 Pressure Detector 11,16 Control Unit 12,17,27 Setting Controller 25 Single Screw Extruder

Claims (3)

[Claims] 1. A quantitative feeder for quantitatively controlling the raw material to feed the extruder, an extruder to which the raw material is fed from the quantitative feeder, a gear pump connected to the extrusion side of the extruder, an inlet side of the gear pump, and In a method of controlling a composite extrusion molding apparatus having a filter provided on at least one of outlet sides, a pressure P ₁ on an inlet side and a pressure P ₂ on an outlet side of the gear pump are detected, and a quantitative feeder based on the differential pressure thereof. Is controlled and the drive motor of the gear pump is controlled so that the inlet pressure P ₁ of the gear pump becomes a preset pressure. 2. A quantitative feeder for quantitatively controlling the raw material to feed the extruder, an extruder to which the raw material is fed from the quantitative feeder, a gear pump connected to the extrusion side of the extruder, an inlet side of the gear pump, and In a method for controlling a composite extrusion molding apparatus having a filter provided on at least one of outlet sides, an inlet side pressure P ₁ and an outlet side pressure P ₂ of the gear pump are detected, and a constant amount feeder pressure is detected based on the differential pressure. Controlling the supply amount, detecting the extrusion pressure P ₀ of the extruder, and controlling the drive motor of the gear pump so that the pressure becomes a preset pressure, control of the composite extrusion molding apparatus Method. 3. A quantitative feeder for quantitatively controlling the raw material to feed the extruder, a first extruder to which the raw material is fed from the quantitative feeder, and a second extruder connected to the first extruder. And a gear pump connected to the extrusion side of the second extruder, and a filter provided on at least one of the inlet side and the outlet side of the gear pump, the inlet of the gear pump The side pressure P ₁ and the outlet side pressure P ₂ are detected, the supply amount of the quantitative feeder is controlled based on the differential pressure, and the extrusion side pressure P ₀ of the first extruder is detected and the pressures are set in advance. A method for controlling a composite extrusion-molding apparatus, characterized in that the drive motor of the second extruder is controlled so as to achieve the set pressure.