JPH0460405B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a parison extrusion method and an apparatus thereof, and more specifically, to an extrusion method and an apparatus for extruding a parison, and more specifically, by controlling the extrusion speed near the die exit of the parison, the extrusion speed can be accurately adjusted according to a set profile. The present invention relates to a parison extrusion method and an apparatus for extruding parisons that can obtain a wide change in wall thickness and can also extrude parisons with a large difference in wall thickness.

Prior Art As a parison extrusion technique, it is known to change the thickness of the parison by changing the gap between the die and the core (so-called slit) near the exit of the extrusion head when extruding the parison. It is generally called parison control (for example, JP-A-58-
(Refer to Publication No. 42437).

Problems to be Solved by the Invention With conventional parison control that changes the slits in the die and core, it has not been possible to form thick and thin portions in short portions of the same parison. In other words, even if you change the slit according to the desired wall thickness in a short period of time, adjusting the slit alone will not work.
This is because the flow of resin cannot be regulated. Generally, the flow rate per unit time is the product of the cross-sectional area of the slit and the flow rate. If the cross-sectional area is suddenly changed, the flow velocity will change, making it impossible to obtain the desired wall thickness.

Therefore, in order to correct these problems,
133562 and JP-A-56-95650 have been proposed.

However, in the former method, the pressure between the slits is detected and the slit is corrected according to the change, but in this case too, the wall thickness is regulated only by the change in the slit, so there is no sudden change like the above. It was difficult to respond to the Particularly when extruding a thin walled portion, the flow rate inevitably becomes high and swell occurs, making it impossible to obtain the desired wall thickness.

In addition, the latter attempts to fine-tune the rotational speed of the extruder by feeding back the change in wall thickness (described as a change in weight in the bulletin) to the parison each time it is extruded to achieve the desired wall thickness. However,
The object is to consider the parison as a whole and eliminate variations in weight from shot to shot, but it is not possible to control the thickness of each part of the parison as desired.
It is not possible to extrude a parison that has thick and thin sections.

Means and Effects for Solving the Problems Therefore, the manufacturing method of the present invention is a parison extrusion method in which the thickness of the parison to be extruded is controlled by changing the distance between the die exits. A parison extrusion method characterized by correcting deviations in parison wall thickness control due to changes in the distance between the die exits by increasing the parison extrusion speed and conversely slowing the parison extrusion speed in thin-walled portions of the parison. . By doing this, the thick parts of the parison can be precisely made to the desired thickness, and conversely, the thin parts can be made exactly thinner by removing the swell that conventionally occurs. It is possible to make an abrupt change from a thin section to a thick section or from a thick section to a thin section over a short longitudinal distance.

In addition, as an apparatus using this method, there is a parison having an accumulation part for storing and extruding resin, and a part for changing the relative position of the die and core mandrel in the axial direction to change the slit between the die and the core. In the extrusion device, the part that changes the slit between the die and the core has a servo cylinder that slides the core mandrel, a detector that detects the position of the core mandrel, a valve that controls the servo cylinder, and a signal that outputs a signal that controls the valve. The above-mentioned accumulation part is composed of an accumulation cylinder that extrudes resin, a detector that detects the position of the cylinder rod of the accumulation cylinder, a hydraulic drive unit that slides the accumulation cylinder rod, and a hydraulic drive. The cylinder rod consists of a valve that controls the cylinder rod and a control system that controls the valve. A parison extrusion device in which a corresponding signal is input to the control system of the part that changes the slit between the die and the core, and the control system of the storage part.

By doing this, the mechanism that controls the wall thickness of the parison by changing the slit between the die and core can be synchronized with the sliding movement of the cylinder rod of the accumulation cylinder, and the sliding speed of the cylinder rod can be controlled. By doing so, the wall thickness can be easily controlled.
Also, by using an accumulation cylinder, it is possible to react rapidly and quickly to the flow rate.

EXAMPLE The present invention will be explained based on the drawings. 1 is the extrusion head,
2 is an accumulator. At the center of the extrusion head 1 is a cylinder rod 7 that can be slid up and down, and at the lower end of the cylinder rod 7 is a truncated conical core 6. It has a die 5 at the lower end. A servo cylinder 3 is formed above the cylinder rod 7 so that the cylinder rod 7 can be slid up and down. Accumulator 2 has its chamber 2
It has an extruder 4 and a screw 8 that feed the melted and kneaded resin into the inside of a. Accumulator 2
has an accumulation cylinder rod 9 for changing the internal capacity of the chamber 2a, and a hydraulic cylinder 10 is formed at one end of the accumulation cylinder rod 9 to allow the accumulation cylinder rod 9 to slide. The cylinder rod 7 has a detector 11 for detecting its position, and the position of the cylinder rod 7 is input to a control system 12. A detector 17 for detecting the position of the accumulation cylinder rod 9 is provided at the rear end of the accumulation cylinder rod 9, and the position is inputted to the controller 15. The controller 15 compares the position of the accumulation cylinder rod 9 input from the detector 17 with the position of the accumulator rod 9 according to a preset desired profile, and controls the control system 1.
2, 16, and in the control systems 12, 16, the control and amplified commands are outputted to the valves 13, 13, which control the hydraulic systems of the servo cylinder 3 and the hydraulic cylinder 10.
Tell 18. Near the die exit, there is an extrusion speed detection means 20 for measuring the extrusion speed of the parison. The extrusion speed detection means 20 is composed of a marker 21 and a mark detection element 22, which attaches marks from the marker 21 at fixed time intervals, measures the mark passing time by the mark detection element 22, and sends the feedback to the controller 15. .

In addition, the extrusion speed detection means 20 can also utilize a non-contact detection means. In this way, the parison can be detected without marking it.

The manufacturing method of the present invention will be explained. The synthetic resin introduced into the extruder 4 through a raw material supply port (not shown) is supplied under pressure by the screw 8, heated and melted, and supplied into the chamber 2a and stored therein.
At this time, the storage cylinder rod 9 moves back as the water is stored. The position of the accumulation cylinder rod 9 is input to the controller 15 by a position detector 17. When the resin is stored in the chamber 2a and the storage cylinder rod 9 is retracted to a preset position, the controller 1
Control systems 16 and 12 are actuated by the signal output from 5, and valves 18 and 13 are actuated. controller 1
5, a signal is output according to a preset output profile. This signal outputs the height value of the set profile (ie, the wavy line inside the controller 15 in the figure) according to the position signal of the accumulation cylinder rod 9 (ie, the horizontal straight line inside the controller 15). In response to this signal, the valve 18 is actuated to control the hydraulic pressure sent through the pipe 19a, and the sliding speed of the accumulation cylinder rod 9 becomes faster at the position where the setting profile is high, and conversely when the setting profile is high. At a position where the value is low, the sliding speed of the accumulation cylinder rod 9 becomes slow. Furthermore, the cylinder rod 7 operates in synchronization with the movement of the valve 18. This cylinder rod 7 constantly feeds back its position to the control system 12 using a position detector 11, and sends a signal to the valve 13 while checking whether the position corresponds to the value of the setting profile of the controller 15. Activate cylinder 3. In this way, when extruding a thick part, the servo cylinder is operated to widen the gap between the die and the core slit, and the sliding speed of the accumulation cylinder rod 9 is increased to increase the extrusion speed of the synthetic resin. The higher the shear rate, the larger the diameter of the parison. This is generally called a swell. Although much research has been carried out on the mechanism of swell, it has not been clearly elucidated at present.
It is generally believed that this is due to the elastic deformation experienced during flow, and it has been found that swell actually increases as the shear rate increases.
Since the extrusion speed by the accumulator can be changed rapidly, a swell can be generated by changing the shear rate, and a thicker parison can be extruded than the thickness of the parison corresponding to the slit. When the maximum wall thickness of the parison to be determined is t _and the minimum wall thickness is t _b , the parison extrusion speed v that gives the parison the wall thickness t is as follows: (In other words, t > t _a + t _b / 2) v≧{t-t _a +t _b /2}×v _p +V _av Here, V _av is the extrusion speed during extrusion of the average wall thickness of the parison, and v _p is a constant determined by the viscosity of the resin. It is. The extrusion speed is measured by the extrusion speed detection means 20, and this value is fed back to the controller 15 to control the hydraulic cylinder 10.

The case where the parison is thick has been described above, but next, the case where the parison is thin will be described.
Swell also occurs due to a change in the cross-sectional area of the slit at the same flow rate. Even if the flow velocity was kept constant, the thickness of the parison could not be suppressed due to the smaller slit, which was an obstacle to rapidly reducing the thickness of the parison. Examples include preventing swell from occurring or even going further to prevent reverse swell (extruding a parison smaller than the slit shape formed by the die and core).
is formed. The parison extrusion speed v at this time is given by v≦V _av + (t−t _a +t _b /2)×vp (that is, when t<t _a +t _b /2).

When such extrusion is performed, swell can be obtained in thick-walled areas that require swell, and conversely, swell can be suppressed or reversed in thin-walled areas where wall thickness control has been inhibited due to swell. A special effect of thinning can be expected.

Effects of the Invention According to the method of the present invention, the extrusion speed near the die exit is controlled such that the extrusion speed of the parison is increased in the thick portion of the parison, and conversely, the extrusion speed of the parison is decreased in the thin portion of the parison. Not only can the weight of the parison as a whole be made uniform for each shot, but also it is possible to cope with variations in wall thickness caused by changes in extrusion speed due to changes in the slit. Furthermore, it has become possible to extrude particularly thick and thin parts accurately.

According to the apparatus of the present invention, since extrusion is performed using an accumulation cylinder rod, it is possible to rapidly change or control the extrusion speed. Changes in the flow velocity of the synthetic resin due to changes in the slits between the die and core can be improved in synchronization with changes in the slits, making it possible to change the thickness of the parison accurately and in a short time.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG. 2 is a partial sectional view of a parison obtained by the present invention. 1... Extrusion head, 2... Accumulator, 3
... Servo cylinder, 5 ... Die, 6 ... Core, 7 ... Cylinder rod, 9 ... Acquisition cylinder rod, 10 ... Hydraulic cylinder, 1
1, 17... position detector, 12, 16... control system, 13, 18... valve, 15... controller, 20... extrusion speed detection means.

Claims (1)

[Claims] 1. A method for extruding a parison in which the wall thickness of the extruded parison is controlled by changing the distance between the die exits,
By increasing the extrusion speed of the parison in the thick part of the parison and slowing down the extrusion speed of the parison in the thin part of the parison, the deviation in the control of the thickness of the parison due to the change in the distance between the die exits is corrected. A parison extrusion method characterized by: 2. A parison extrusion device having an accumulation part for storing and extruding resin, and a part for changing the relative position of the die and core mandrel in the axial direction to change the slit between the die and the core. The part that changes the slit of the core mandrel is composed of a servo cylinder that slides the core mandrel, a detector that detects the position of the core mandrel, a valve that controls the servo cylinder, and a control system that outputs a signal that controls the valve, and The above accumulation part includes an accumulation cylinder that extrudes resin, a detector that detects the position of the cylinder rod of the accumulation cylinder, a hydraulic drive unit that slides the accumulation cylinder rod, a valve that controls the hydraulic drive unit, and this valve. The controller provides a preset profile according to the signal from the detector that detects the position of the accumulation cylinder rod, and the controller sends a signal corresponding to the profile to the die and core. A parison extrusion device characterized by input to a control system for a part that changes the slit and a control system for an accumulation part.