JP3323277B2 - Control method of compound extrusion molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a twin-screw extruder with a fixed-quantity feeder, which is mainly used for direct mixing of raw material components, sufficient cooling, and molding of films and sheets, etc., which require high stability. And a method for controlling a compound extrusion molding apparatus having a gear pump as 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 which supplies a polymer via a feeder is detected, and the detection signal is fed back to an extruder screw drive system. In addition, the rotation speed of the extruder screw is also detected, and the rotation speed detection signal is fed back to the drive system of the polymer supply device to control the supply amount of the polymer (Japanese Patent Publication No. Hei. -50207).

However, in such a composite extrusion molding apparatus, two main factors of disturbance that change the state of the extrusion process are considered to be a change in the characteristics of a quantitative feeder and clogging of a filter.

In other words, a belt type and a loss-in-weight type are used as typical quantitative feeders, each of which is composed of a weight detecting unit, a control unit, and a mechanical feeder. The feeder feed rate is designed to be kept constant by a control mechanism in the feeder system.However, temperature drift or aging drift of a load cell or the like used in the weight detection unit, or powder to a belt or the like, may occur. The supply amount fluctuates due to attachment of the body and the like. The characteristic of the disturbance due to the characteristic change of the quantitative feeder is not always deterministic and the fluctuation period is considerably long.

[0005] On the other hand, at least one filter is always provided at the outlet side of the compound extruder. The function of this filter is to catch foreign substances such as dust, gel, carbide, and metal abrasion powder in the molten resin, and the filter is clogged with time and increases the resin pressure. As a result, the filling length of the tip measuring section of the twin-screw extruder increases, and thus troubles such as an increase in resin temperature and vent up occur. This disturbance is characterized by being deterministic and gradually increasing monotonically.

[0006]

Therefore, as described above, the feeder drive unit is controlled using the pressure on the inlet side of the gear pump provided downstream of the twin-screw extruder as a control amount, and the inlet side of the gear pump is controlled. In a conventional apparatus in which the production amount or the thickness of a sheet or the like is kept constant by controlling the pressure at a constant value, the following phenomenon occurs when a disturbance such as a change in the characteristic of a fixed-quantity feeder acts.

Namely, (equal to the feeder supply quantity Q _f in stationary process) the discharge rate of the gear pump Q, the rotation speed of the gear pump of N, theoretical discharge amount of the gear pump alpha, the same back pressure flow coefficient beta, the viscosity of the material Is μ, the pressure on the inlet side of the gear pump is p ₁ , and the pressure on the outlet side is p ₂ , the 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 expressed as p ₁ = p ₂ −μ / β · (αN−Q) (2) When the change amount δp ₁ of the inlet side pressure when the amount increases by δQ _f is obtained, δp ₁ = μ / β · δQ = μ / β · δQ _f (3) In this case, in fact can be but p ₂ also changes by .delta.Q _f is ignored because .delta.p ₂ is very small compared to .delta.p _1.

[0009] Thus, since the back pressure flow coefficient of the gear pump β generally very small, inlet pressure p ₁ of the gear pump by a small supply amount fluctuation .delta.Q _f is considerably increased. That is, a change in p ₁ can be detected with high sensitivity.

[0010] Therefore, the above-described conventional apparatus, when the p ₁ is the control deviation occurs between the elevated setting value, the control device is carried out supply of modifications働Ra-out material, production and sheet thickness and the like Is kept constant.

Meanwhile, if the supply amount Q _f the feeder is assumed to be constant, the clogging in the filter progresses, firstly, the outlet side pressure of the gear pump .delta.p ₂ rises. But since Q _f is constant, before and after the gear pump 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,
A control deviation occurs with the set value.

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

That is, in the above-mentioned conventional apparatus, there is a problem that a disturbance such as filter clogging causes a reduction in production amount and sheet thickness.

In view of the foregoing, the present invention detects a change in the pressure of each part of the compound extrusion molding apparatus, identifies the cause of the change, and performs a control capable of executing an accurate correction or correction operation according to each cause. The aim is to get the method.

[0015]

Means for Solving the Problems A first invention of the present application is a quantitative feeder for supplying a raw material to a twin-screw extruder under quantitative control, a twin-screw extruder for supplying a raw material from the quantitative feeder,
In a control method of a compound extrusion molding apparatus having a gear pump connected to the extrusion side of the twin-screw extruder and a filter provided on at least one of an inlet side and an outlet side of the gear pump, an inlet pressure P of the gear pump is provided. ₁ and detects the outlet pressure P _2, and controls the supply amount of the quantitative feeder based on the differential pressure, gear pump inlet pressure P
Characterized in _{that one} or outlet pressure P ₂ controls the drive motor of the gear pump so that a set pressure which is set in advance.

According to a second aspect of the present invention, there is provided a fixed-quantity feeder for supplying a raw material to a twin-screw extruder while performing quantitative control, a twin-screw extruder for supplying a raw material from the fixed-quantity feeder, and a connection to an extrusion side of the twin-screw extruder. in been gear pump and control method of a composite type extruder having a filter provided in at least one of the inlet and outlet sides of the gear pump, to detect the inlet pressure P ₁ and the outlet pressure P ₂ of the gear pump controls the supply amount of the quantitative feeder on the basis of the pressure difference, to detect the extrusion side pressure P ₀ of the twin-screw extruder, the pressure controls the drive motor of the gear pump so that a set pressure which is set in advance It is characterized by the following.

According to a third aspect of the present invention, there is provided a fixed-quantity feeder for supplying a raw material to a twin-screw extruder under quantitative control, a twin-screw extruder for supplying a raw material from the fixed-quantity feeder, and connected to the twin-screw extruder. A single-screw extruder, a gear pump connected to the extrusion side of the single-screw extruder, and a control method for a composite extrusion molding apparatus having a filter provided on at least one of an inlet side and an outlet side of the gear pump; detecting the inlet pressure P ₁ and the outlet pressure P ₂ of the gear pump, to control the supply amount of the quantitative feeder on the basis of the pressure difference,
Wherein detecting the extrusion side pressure P ₀ of the twin-screw extruder, and controls the drive motor of the single-screw extruder so that the set pressure of the pressure is set in advance.

[0018]

[Action] gear pump inlet pressure p ₁ varies by two disturbance factor as described above. Therefore, first this p
We need to identify _one of the variables. Then, the gear pump inlet pressure changes cause p ₁ Do supply amount fluctuation caused by the characteristic change of the quantitative feeder, identification of how clogging of the filter is possible by examining the differential pressure Δp of about gear pump.

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

From equation (1), Δp is given by Δp = p ₂ −p ₁ = μ / β · (2N−Q _f ) (4) ∴δ (Δp) = − μ / β · δQ _f (5) formula - [mu] / beta is, the sensitivity coefficient when detected by the supply amount fluctuation .delta.Q _f quantitative feeder variation in the differential pressure δ (Δp) (λ), a very high value as the lambda is 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 fixed-quantity feeder by the differential pressure Δp, it is possible to cope with disturbance due to a change in the characteristic of the fixed-quantity feeder, and to supply a 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 the outlet-side pressure p _{2 of the} gear pump or the extrusion-side pressure p ₀ of the twin-screw extruder corresponding to the inlet-side pressure of the gear pump increases, the cause of this increase is It can be determined that the filter is clogged, and by controlling the rotation speed of the gear pump by any of these signals, the influence of the filter clogging can be eliminated.

Further, even if the change in the supply amount of the feeder and the clogging of the filter occur simultaneously, the differential pressure Δp before and after the gear pump reacts only to the change in the supply amount of the feeder. Therefore, based on the differential pressure Δp, it can be divided into a component due to a change in the supply amount of the feeder and a component due to clogging of the filter.

According to the third aspect of the present invention, by controlling the drive motor of the single-screw extruder so that the pressure on the extruding side of the twin-screw extruder is controlled according to the same principle as that of the first invention, the filter filter The effects of clogging can be eliminated.

[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. The raw material supplied from a fixed-quantity feeder 1 to a twin-screw extruder 2 is heated and melted while being kneaded by the twin-screw extruder 2. The raw material continuously fed from the twin-screw extruder 2 is measured by a fixed amount at a time, supplied to the die 5 through the filter 4, and discharged from the die 5 at a constant rate.

Pressure detectors 6 and 7 are provided on the inlet side and the outlet side of the gear pump 3, respectively, and the pressure p on the gear pump inlet side detected by the two pressure detectors 6 and 7 is provided.
₁ and the signal of the pressure p ₂ at the outlet side is comparison operation at a differential pressure calculator 8, the pressure difference is compared with a set value of the differential pressure setting unit 10 by the comparator 9, an input the deviation signal to the control unit 11 Then, the operation amount calculation is performed, and the correction amount of the set value of the feeder supply amount is calculated. Then, the 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, and the raw material feed rate by the fixed quantity feeder 1 is controlled.

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 calculated and input to the section 16, and the new setting signal is transmitted to the drive motor 1 of the gear pump 3 via the setting controller 17.
8 to control the rotation speed of the gear pump 3.

Thus, the fixed-quantity feeder 1 is controlled by the differential pressure Δp between the pressure on the inlet side and the pressure on the outlet side of the gear pump, and the disturbance due to the change in the characteristics of the fixed-quantity feeder is corrected. By controlling the rotation speed of the gear pump, the effects of filter clogging are corrected.

The order of operation of both control loops when both disturbances act simultaneously is important. It is possible to identify the magnitude of both disturbances by calculation and perform simultaneous operations, but the operation method becomes complicated due to mutual interference. In addition, both disturbances have a long period as described above,
In particular, it is determined that it is not necessary to operate the filter in a hurry in view of the fact that the clogging of the filter monotonically increases.

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

Next, after the above operation execution, Once in the pressure difference Δp within the allowable range, examines the pressure p _2, issues a correction instruction of the gear pump speed if there is deviation in these pressures. When this operation is performed, the set value of the differential pressure Δp before and after the gear pump must be updated. This updating is performed when the pressure of each part is stabilized after the above-described operation is performed. The new set value is obtained by actually measuring p ₁ and p ₂ in a stable state, and calculating the differential pressure (p ₂ −p
₁ ) The calculated value.

FIG. 2 shows a control flow of the above control method.

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 filter 20 is located upstream of the filter 20, that is, of the twin-screw extruder 2. A pressure detector 21 is provided on the discharge side.

The extrusion-side pressure p ₀ of the twin-screw extruder 2 detected by the pressure detector 21 is used as a pressure setting device 22.
, And the deviation signal is input to the control unit 23, and the output signal from the control unit 23 is output to the setting controller 17.
Is input to the drive motor 18 of the gear pump 3 via the control unit, thereby controlling 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 before and after the gear pump 3 is detected, the supply amount of the fixed 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 to correct the influence of the filter clogging.

By the way, in each of the above embodiments, the gear pump, which is originally desirably operated at a constant speed as a reference unit, is shifted to cope with clogging of the filter. However, when the gear pump is shifted, the set value of the differential pressure Δp before and after the gear pump related to the control of the fixed amount 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 order and the like between the two control systems, the control system of the fixed quantity feeder and the control system of the gear pump.

On the other hand, in order to keep the kneading degree, temperature or devolatilization of the resin within allowable ranges and to prevent venting up in the extruder, the filling length x of the extruder tip measuring section must be kept constant. Must be kept.

FIG. 4 shows another embodiment in which the above object can be achieved. A single screw extruder (second extruder) is provided downstream of a twin screw extruder (first extruder) 2. Extruder) 25,
The filter 26 and the gear pump 3 are sequentially provided.

A pressure detector 21 is provided on the extrusion side of the twin-screw extruder 2. The extrusion-side pressure of the twin-screw extruder detected by the pressure detector 21 is equal to the set pressure of the pressure setter 22. The differences are compared, and the deviation is input to the control unit to perform the operation amount calculation. The operation signal is sent to the setting controller 27 of the drive motor for the single-screw extruder to update the set speed.
8 is controlled, and the rotation speed of the single screw extruder 25 is controlled.

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

A simple means for detecting the filling length x of the tip measuring section 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 propulsion flow coefficient of the twin-screw extruder, and β ₁ is the back pressure flow coefficient , N ₁ is the same rotational speed.

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 pressure p _{2 of the} gear pump 3 increases by δp ′. However, the gear pump 3 is equal to the feeder supply quantity Q _f
Is constant, the differential pressure Δ across the gear pump 3
p (= p ₂ −p ₁ ) does not change. That is, the pressure on the gear pump inlet side also increases by δp ′. When 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, as in the case of the gear pump, the differential pressure between the inlet and the outlet of the single-screw extruder does not change. The inlet pressure p ₀ also increases by the same amount δp ″. Eventually, the increase amount 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 operation amount is calculated based on the deviation signal. This arithmetic expression is appropriately proportional / integral or the following expression.

ΔN ₂ = −β ₂ / μα ₂ · δp ₀ (8) where, δN ₂ : speed increase amount of the single screw extruder, α ₂ : propulsion flow coefficient of the extruder, β ₂ : back flow 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, thus the screw tip pressure p ₀ of the biaxial extruder is kept constant, it is possible to maintain full length x constant.

[0050]

As described above, according to the present invention, the feed rate of the fixed-quantity 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 extrusion side pressure of the extruder. Control the drive motor of the gear pump or the drive motor of the second extruder, so that the feeder supply amount can be controlled to be constant by eliminating the effects of filter clogging and the like, and the production amount or sheet thickness can be reduced. It can always be kept at a high precision and constant, and the kneading degree, temperature or devolatilization of the resin can be kept within allowable ranges, and vent up in the extruder can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one 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]

 DESCRIPTION OF SYMBOLS 1 Fixed-quantity feeder 2 Twin-screw extruder 3 Gear pump 4 Filter 5 Die 6, 7, 21 Pressure detector 11, 16 Control part 12, 17, 27 Setting controller 25 Single-screw extruder

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-39354 (JP, A) JP-A-52-151354 (JP, A) JP-A-2-120023 (JP, A) JP-A-58-1983 183210 (JP, A) JP-A-59-5044 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 47/00-47/96

Claims (3)

(57) [Claims] 1. A quantitative feeder for supplying a raw material to a twin-screw extruder under quantitative control, and a raw material supplied from the quantitative feeder.
The method for controlling a compound extrusion molding apparatus, comprising: a shaft extruder; a gear pump connected to an extrusion side of the twin-screw extruder; and a filter provided on at least one of an inlet side and an outlet side of the gear pump. Inlet pressure P
₁ and detects the outlet pressure P _2, and controls the supply amount of the quantitative feeder on the basis of the pressure difference, so that the set pressure of the inlet-side pressure P ₁ or outlet pressure P ₂ is set in advance of the gear pump A method for controlling a compound extrusion molding device, comprising controlling a drive motor of a gear pump. 2. A quantitative feeder for supplying a raw material to a twin-screw extruder under quantitative control, and a raw material supplied from the quantitative feeder.
The method for controlling a compound extrusion molding apparatus, comprising: a shaft extruder; a gear pump connected to an extrusion side of the twin-screw extruder; and a filter provided on at least one of an inlet side and an outlet side of the gear pump. Inlet pressure P
₁ and detects the outlet pressure P _2, and controls the supply amount of the quantitative feeder on the basis of the pressure difference, to detect the extrusion side pressure P ₀ of the twin-screw extruder, the set pressure of the pressure preset A method for controlling a compound extrusion molding device, characterized by controlling a drive motor of a gear pump. 3. A quantitative feeder for supplying a raw material to a twin-screw extruder under quantitative control, and a raw material supplied from the quantitative feeder.
A single-screw extruder, a single-screw extruder connected to the twin-screw extruder, a gear pump connected to the extrusion side of the single-screw extruder, and a filter provided on at least one of the inlet side and the outlet side of the gear pump a method of controlling a composite type extruder having bets, detects the inlet pressure P ₁ and the outlet pressure P ₂ of the gear pump, to control the supply amount of the quantitative feeder on the basis of the pressure difference, the two-axis detecting the extrusion side pressure P ₀ of the extruder, and controls the drive motor of the single-screw extruder so that the set pressure of the pressure is preset, the control method of a composite type extruder.