JPH0565334B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the rotational speed of a feeder screw, which is applicable to extruders and injection machines for powder raw materials, in which a thermoplastic resin is forcibly fed into the extruder.

In extruders for thermoplastic powder resin raw materials, the amount of extrusion decreases due to poor penetration of the raw materials.
Alternatively, the problem of extrusion fluctuation is likely to occur, and in order to increase the bulk specific gravity of the raw material and increase the powder pressure at the base of the main screw, a screw-type forced feeder was installed at the extruder raw material supply hopper. A device is adopted as shown in FIG. In FIG. 1, 1 is an extruder screw, 2 is a forced feeder screw, and 3 is a drive motor.

When starting the screw of this extrusion device or changing the screw rotation speed, it is necessary to set the extruder screw rotation speed and the screw rotation speed of the forced feeder in a well-balanced manner.Currently, the current of the drive motor 3 of the forced feeder is A method of manually increasing the screw rotation speed of the force feeder according to the rotation speed of the main screw until the specified current value is reached, or determining the rotation speed of the force feeder so that the specified current value is reached, or At present, a control method is used in which the feeder screw rotation speed is always kept at a constant ratio.

That is, during steady operation, the forced feeder is always operated at a constant ratio based on the screw rotation speed of the forced feeder that matches the predetermined extruder screw rotation speed. In addition, when extruding fine powder raw materials, etc., the screw rotation speed of the forced feeder is low compared to the rotation speed of the extruder screw, and if the raw material supply state is insufficient, the powder raw material is This results in a situation where the liquid is stirred while containing air, making it easier to flow.

Once this condition is created, even if an attempt is made to increase the feed capacity by increasing the screw rotation speed of the forced feeder in this situation, the feed capacity will not increase because the powder raw materials will not be packed together. This phenomenon is due to the fact that when a fine powder raw material is stirred and contains air, it flows out between the fingers when it is held in the hand, but when the raw material is left in a stationary state for a while, it is possible to squeeze it in the hand. It is something that can be experienced.

Conversely, if the forced feeder screw rotation speed is excessively high compared to the extruder screw rotation speed,
The problem of overloading the drive motor of the forced feeder arises. Therefore, the rotation speed of the extruder screw and the rotation speed of the forced feeder must be linked to keep the powder raw material packed at the bottom of the forced feeder and the base of the extruder screw, and to prevent the drive motor of the forced feeder from overloading. There is. This delicate interlocking is necessary when starting the extruder or changing the extruder screw rotation speed, but conventional methods cannot make sufficient adjustments, which can prevent problems such as material flow conditions that make it impossible to feed and overload of the forced feeder drive motor. It will happen.

In addition, in the conventional constant ratio method, after the forced feeder rotation speed is set for a certain extruder screw rotation speed, the ratio between the two is controlled to be constant, so changes in the extruder cylinder temperature and screw temperature, When a disturbance such as a change in the height of the raw material in the hopper of the forced feeder occurs, the above-mentioned problems occur. In addition, once the raw material becomes fluid and there is a shortage of supply, it is necessary to temporarily reduce the screw rotation speed of both the extruder and the forced feeder to a low speed and restart the process to normal conditions again.

When using an extruder to extrude a mixed raw material resin containing fine powder of fillers such as charcoal and talc, whose applications are rapidly expanding recently, even if the extruder screw rotation speed and forced feeder screw rotation speed are set to predetermined values. This resulted in phenomena with poor reproducibility, such as the extrusion rate being extremely different depending on the operating route, and the extrusion rate becoming stable or unstable. Analyzing this, we found that when the extruder screw rotation speed and forced feeder rotation speed are brought to a predetermined operating condition while interlocking the extruder screw rotation speed and forced feeder rotation speed so that the resin pressure in the cylinder at the base of the extruder remains almost constant, the amount of extrusion increases. It was found that the stability was good.

When the extruder screw rotational speed was increased to a predetermined rotational speed in advance and then the screw rotational speed of the forced feeder was increased, the extrusion amount was extremely small and the stability was poor. This phenomenon is a serious problem when adopting an actual machine, and controlling the screw rotation speed of both devices, especially the screw rotation speed of the forced feeder, is important, and the present invention has been proposed in order to effectively implement this rotation speed control. It is something.

That is, the present invention detects the powder pressure at the lower part of the forced feeder and the base of the extruder screw so as to always maintain the state of the resin in a non-flowable state, and adjusts the pressure of the forced feeder so that this remains constant. This method attempts to control the screw rotation speed, and it is difficult to measure particularly minute powder pressure. However, it is relatively easy to measure the thrust force of the forced feeder screw, or the screw thrust force detection method of the screw base of the extruder It is characterized by the detection of resin pressure at the extruder feed section, which can detect the powder pressure in an enlarged form, and is suitable for extrusion equipment with a screw-type forced feeder that forcibly feeds thermoplastic resin into the extruder. , a feeder screw rotation speed control in which the pressure of the resin raw material at the lower part of the forced feeder and the extruder screw base is detected by a sensor, and the rotation speed of the forced feeder screw is controlled so that the pressure is always constant based on the output of the sensor. The purpose is to provide a method.

Embodiments of the present invention will be described below with reference to the drawings. Figures 2 and 3 show an apparatus for implementing the method of the present invention, in which 1 is an extruder screw, 2 is a forced feeder screw, and 3 is a forced feeder screw drive motor. be. In this device, the pressure of the powder raw material at the lower part of the forced feeder and the base of the extruder screw 1 is detected, and the screw rotation speed of the forced feeder is controlled so that the pressure remains constant.

Further, a, b, c, and d indicate positions for detecting the pressure of the powder raw material for controlling the screw rotation speed of the forced feeder. Since the thrust force of the feeder screw is determined by the pressure of the supplied powder, the position a is used when the thrust force of the feeder screw is detected by, for example, a load cell. In addition, at position b, since the supply powder pressure and the resin pressure at the extruder feed section are proportional, the resin pressure at the extruder feed section can be measured using a normally used diaphragm-type strain gauge pressure gauge or a piezoelectric element pressure gauge. This is a case of detection using On the other hand, at position c, a pressure gauge is attached to the tip of the feeder screw to directly detect the pressure of the supplied powder. Further, position d is an example in which a pressure gauge is attached to the side wall of the raw material supply port to directly detect the pressure of the supplied powder.

Now, the rotation speed of the forced feeder screw 2 is controlled so that the pressure of the powder raw material detected by the positions of the detection parts a, b, c, d, etc. is always constant by a control device (not shown).

Since the present invention is configured as described above in detail, by controlling the screw rotation speed of the forced feeder so that a certain pressure of the powder material is maintained at the lower part of the forced feeder and the base of the extruder screw,
By increasing the bulk specific gravity of the powder raw material and constantly feeding a stable amount of raw material to the extruder screw, it is possible to prevent a decrease in the extrusion rate and fluctuations in the extrusion rate. In addition,
In the present invention, in addition to powder raw materials, raw materials mixed with powder and particles (pellets), crushed raw materials such as films, or raw materials mixed with this crushed raw material and pellets are fed into the main extruder using a forced feeder. Applicable to extrusion equipment.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of an extruder equipped with a conventional screw-type forced feeder, FIG. 2 is a side sectional view of the tip of the feeder screw in an apparatus for carrying out the method of the present invention, and FIG. FIG. Explanation of the main parts of the figure, 1... Extruder screw,
2...Forced feeder screw, 3...Drive motor, a, b, c, d...Powder raw material pressure detection position.

Claims (1)

[Claims] 1. In an extrusion device with a screw-type forced feeder that forcibly feeds thermoplastic resin into an extruder,
The rotation speed of the feeder screw, characterized in that the pressure of the resin raw material at the lower part of the forced feeder and the base of the extruder screw is detected by a sensor, and the rotation speed of the forced feeder screw is controlled so that the pressure is always constant based on the output of the sensor. Control method.