JPH04299103A - Method and apparatus for controlling wall thickness of parison of blow molding machine - Google Patents

Abstract

PURPOSE:To control the circumferential wall thickness of a parison at the time of blow molding with excellent conformability without generating anxiety or damage from the aspect of strength. CONSTITUTION:The plunger inserted in the cylindrical passage 18 of a die is divided circumferentially and the injection moving speeds of the divided ones are individually controlled to perform the injection of a parison. The circumferential wall thickness of the parison due to the control of swell rations in respective regions can be arbitrarily controlled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the thickness of a parison in a blow molding machine, and more particularly, a method and apparatus for controlling the thickness of a parison in a blow molding machine for partially controlling the wall thickness in the circumferential direction of the parison. Regarding.

0002

[Prior Art] A blow molding machine uses molten resin supplied from an extruder to form a cylindrical molten resin cylinder called a parison using a die having a ring-shaped resin discharge port, which is then sandwiched between molds. After that, a hollow product is formed by blowing air or other gas into the parison to cool it. Among the parison injection dies used in such blow molding machines, the die with a built-in accumulator has a mandrel inserted into the die housing to form a cylindrical resin passage, and a ring plunger inside the cylindrical passage. A hollow parison is injected from the resin discharge port opened at the lower end surface of the housing by extruding the inserted and filled molten resin under pressure by the plunger.

[0003] Such a parison injection die with a built-in accumulator is designed to change the wall thickness not only in the direction of the hanging axis of the parison but also in the circumferential direction, particularly when molding large products, in accordance with the blow ratio. Proposed. For example, in Japanese Patent Publication No. 62-5815, a part of the peripheral edge of the resin discharge port is cut out, a block that can change the die gap is attached to this, and the block is moved in the thickness direction of the parison using a cylinder or the like. A method for performing wall thickness adjustment is shown. Furthermore, as shown in Japanese Patent Application Laid-open No. 2-1583-8, a method has been proposed in which the resin temperature is given a difference in the circumferential direction by controlling the temperature of each part of the die lip at the resin discharge port, and the wall thickness is adjusted by the difference in viscosity. ing.

0004

However, in the former method, there is a problem in terms of strength due to the notch effect caused by a step formed at the die gap changing portion, and there is also a problem in that streaks remain on the parison. Furthermore, in the latter case, there is a problem that local variable control cannot be performed and effective control cannot be performed because there is no particularly quick response.

The object of the present invention is to address the above-mentioned conventional problems, and to provide a blow molding machine that can control the thickness of a parison with excellent responsiveness without worrying about strength or causing scratches. The object of the present invention is to provide a method and apparatus for controlling a parison.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a method for controlling the wall thickness of a parison in a blow molding machine according to the present invention includes inserting a ring plunger into a cylindrical passage of a parison injection die, In a method of injecting a cylindrical parison from a resin discharge port by pressurizing molten resin with the plunger, the ring plunger is divided in the circumferential direction and moved individually to control the thickness of the parison in the circumferential direction. This is what I did.

Further, the parison wall thickness control device for a blow molding machine according to the present invention includes a ring plunger inserted into a cylindrical passage of a parison injection die, and filled molten resin is pressurized by the plunger to form a resin discharge port. In an apparatus for injecting a cylindrical parison from a wafer, the ring plunger is divided in the circumferential direction, and a plunger drive mechanism is connected to each divided plunger.

[0008]

[Operation] According to the above structure, after the molten resin is filled into the cylindrical passage in the die, the hollow parison is injected from the resin discharge port by moving the ring plunger downward. The lowering operation for injection can be performed individually by dividing into two parts. Therefore, if the descending speed of the split plunger is partially increased in the cylindrical passage, the swell ratio (the ratio of the die gap to the resin wall thickness immediately after exiting the die) of the resin extruded from the resin discharge port increases. However, the wall thickness can be increased. As a result, by controlling the speed of any split plunger, the thickness of the parison in the circumferential direction can be locally changed. Since such a change in wall thickness does not directly change the gap between the resin discharge ports, the parison is not damaged or notched. Moreover, since the moving speed of the split plunger can be quickly changed by the plunger drive mechanism, the response is good and it is possible to realize not only circumferential wall thickness control but also longitudinal wall thickness control with high precision. can. Furthermore, it is also possible to correct non-uniformity in the parison discharge state when the resin discharge port has an elliptical or elliptical shape.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a method and apparatus for controlling parison wall thickness of a blow molding machine according to the present invention will be described in detail with reference to the drawings.

FIGS. 1 and 2 are cross-sectional views of a parison injection die 10 equipped with a parison thickness control device according to a first embodiment. This die 10 is for injecting parisons corresponding to large products, and has a die housing 12 made of a rectangular block, and a through hole 14 with an approximately oval cross section is bored along the vertical center line of the die housing 12. has been done. The through-hole 14 is opened at the lower end surface of the housing 12 with its inner diameter gradually decreasing from the middle thereof to the lower end surface of the housing 12.

A through hole 14 is provided in the housing 12.
A mandrel 16 formed with a smaller diameter is inserted, and a cylindrical passage 18 is formed between the outer circumferential surface of the mandrel 16 and the inner circumferential surface of the through-hole 14 . A flange 20 having a diameter larger than the outer diameter of the main body is provided at the upper end of the mandrel 16, and this flange 20 is connected to the die housing 1.
The opening of the through-hole 14 is sealed by being engaged with and attached to an engagement step 22 formed on the upper surface of the through-hole 14 . In addition, the lower part of the mandrel 16 is formed with a narrowed tip in accordance with the reduced diameter part of the through-hole 14, but the tip of the mandrel 16 is particularly
Parison control mandrel 2 that can be accessed from 6
6 is installed. A die lip 29 is integrally provided at the tip of the parison control mandrel 26, facing the opening of the through hole 14 and forming an oval ring-shaped resin discharge port 28 between it and the opening of the through hole 14. . Therefore, by changing the amount of movement in and out of the parison control mandrel 26, the die gap t can be changed arbitrarily.

Changing the die gap t is made possible by driving a control cylinder 30 installed on the support plate 24 holding the die housing 12, and thus connecting the control cylinder 30 and the parison control mandrel 26. A rod 32 is passed through the mandrel 16.

Further, in order to flow the molten resin from the extruder into the cylindrical passage 18, a supply passage 34 connected to the extruder is bored in the center of the mandrel 26, and this supply passage 34 is connected to the extruder at the lower part of the mandrel 26. The inlet 36 is branched left and right, and an inlet 36 is opened in the cylindrical passage 18 .

Such a die has a die structure with a built-in accumulator, and therefore a ring plunger 40 is slidably inserted into the cylindrical passage 18. This ring plunger 40 pressurizes and extrudes the resin filled into the cylindrical passage 18 through the resin inlet 36 from the resin discharge port 28 by moving downward, thereby injecting a hollow parison.

Here, a parison thickness control device is incorporated into the parison injection die 10 as follows. That is, the ring plunger 40 has an oval cross section to fit the cylindrical passage 18, but in the embodiment, this is divided into four parts in the circumferential direction, as shown in FIG.
As shown in the figure, a pair of semicircular split ring plungers 40A,
40C and a pair of flat plate split ring plungers 40B, 4
0D. Further, an L-shaped step groove 42 is formed at each dividing and joining edge. They are closely engaged with each other so that they can move vertically within the cylindrical passage 18 while sliding at the joints. The divided ring plungers 40A to 40D are movable independently, and therefore a drive mechanism is connected to each of the divided ring plungers 40A to 40D. This is composed of hydraulic cylinders 44A to 44D arranged around the control cylinder 30 for adjusting the die gap described above, and drive rods 46A to 46D, which are extended and contracted by the cylinders 44A to 44D, are connected to each split ring plunger. 40A~40
It is connected to the upper end surface of D. Plunger drive cylinder 4
4A to 44D are support frames 4 for the control cylinder 30
8, and is installed on a pedestal 50 attached to this. As a result of the plunger drive cylinders 44A to 44D installed on the pedestal 50 being arranged so as not to interfere with the control cylinder 30 side, if the cylinder expansion/contraction axis direction and the sliding direction line of each split ring plunger 40A to 40D do not match, Drive rods 46A-4 as shown
Attach by bending 6D in the middle.

The thickness control of the parison constructed as described above is performed as follows. When molding a large product, when a deep drawing part exists in the center of both male and female molds, an oblong flat parison 52 is injected, and as shown in FIG. 4, a parison flat plate part facing the deep drawing part is injected. 52F has a large blow ratio, so its wall thickness needs to be relatively thicker than the arcuate portions 52T at both ends. Further, the arcuate portions at both left and right ends of the parison correspond to the joints of the mold, and therefore burrs occur. Since it is desirable to suppress the occurrence of burrs from the viewpoint of improving yield, it is also necessary to control the thickness of the parison in the arcuate portion to be thin, and to make the other portions relatively thick. In this case, since the ring plunger 40 is divided in the circumferential direction as described above, when injecting the parison, the pair of flat plate divided ring plungers 40B, 40
Increase the descending speed of D, and use the semicircular split ring plunger 40.
Adjust the control to slow down the descent speed of A and 40C. This can be easily achieved by controlling the amount of pressure oil supplied to the hydraulic cylinders 44A to 44D connected to the respective split ring plungers 40A to 40D. It can be realized by this valve control.

In the parison injection die 10, by increasing the descending speed of the plunger 40, the thickness of the parison 52 can be increased due to the shear rate dependence of the swell characteristic of the resin, and as a result, as shown in FIG. Furthermore, it is possible to inject a parison 52 in which the flat plate portion 52F is thick and the circular arc portion 52T is thin. In this case, the required wall thickness dimensions of each part of the parison 52 are set at the mold design stage, and the relationship between the descending speed of the plunger 40 and the swell ratio is determined based on experience, including factors such as the type of resin material and resin temperature. It can be found by the following rules. Therefore, the resin used and the cylindrical passage 1
The relationship between the plunger descending speed and the swell ratio is determined in advance according to the temperature of the resin supplied to the plunger 8, and the descending speed of each divided plunger 40A to 40D is set based on this relationship so that it matches this set value. It controls. At this time, since the resin temperature is a major variable factor that affects parison wall thickness control during actual operation, the resin temperature is monitored and the descending speed of each divided plunger 40A to 40D is adjusted according to temperature changes and circumferential temperature distribution. may be individually controlled by feedback.

A flow chart of such parison wall thickness control is shown in FIG. First, the relationship between the swell ratio at the resin discharge port 28 and the descending speed of the ring plunger 40 or the die gap is calculated (step 100). This is determined based on factors such as the die gap, the resin used, and the set resin temperature. At the same time, set the wall thickness of each part in the parison injection direction, which is determined by the molded product shape (step 1).
10). When locally changing the parison thickness,
Calculate the swell ratio from the wall thickness and die gap value,
The plunger descending speed calculated in step 100 is determined so as to satisfy the swell ratio of the die gap control, and the hydraulic cylinder 4 of each split ring plunger 40A to 40D is
Output settings are made to the servo valve controllers 4A to 44D (step 120). After such processing is completed,
On the valve controller side, the position of the plunger 40 is detected (step 130), and the plunger is driven for injection (step 140). During this injection, it is monitored whether the descending speed of the plunger 40 is within a permissible range (step 150), and if it is out of the range, feedback control is performed by the valve controller to adjust the descending speed to an appropriate value. We also monitor the resin temperature.
If the resin temperature is out of the allowable range and has become low, the process returns to step 100 and the plunger descending speed is reset (step 160), and if the resin temperature is within the appropriate temperature range, injection is continued (step 170). Such processing is performed for each divided ring plunger 40A to 40D.
Have them do it every time.

In the example shown in FIG. 4(2), the cylindrical passage 18 inside the die is made cylindrical, the plunger 40 is inserted as a two-part structure, and the cylindrical parison 54 is injected. It is. This is because when a product with a convex cross section is molded, the part of the parison facing the convex part is deep drawn, so this part is made into a thick parison 54F. In such a case as well, the descending speed of the divided plunger corresponding to the thick portion 54F is controlled to be faster than the speed of the other divided plungers.

As described above, according to this embodiment, the dice 10
The ring plunger 40 inserted into the cylindrical passage 18 of the cylindrical passage 18 to pressurize and inject the filled resin is divided in the circumferential direction, and the descending speed is changed and controlled for each divided plunger 40A to 40D. By directly controlling the swell ratio at each part of the resin discharge port 28 facing the resin discharge port 40D, the parison wall thickness can be arbitrarily adjusted in the circumferential direction.

In particular, in this embodiment, since the gap between the resin discharge ports 28 is not locally adjusted, the thickness change portion of the parison changes smoothly, and no cuts or streaks occur. The descending speed of the divided plungers 40A to 40D can be quickly changed by the hydraulic cylinders 44A to 44D, and wall thickness control with excellent responsiveness can be performed, which has the advantage of being applicable to drawdown suppression control. be. As a result of the wall thickness control in the above embodiment, the difference in the amount of resin at the divided portions (the amount of resin injected at the thicker portion increases) can be corrected by changing the measured values of the respective dividing plungers 40A to 40D. This can be easily handled by adjusting the rising ends of the plungers 40A to 40D.

In the above embodiment, an example was shown in which the resin supply passage 34 to the cylindrical passage 18 was formed in the mandrel 16.
It goes without saying that the present invention can also be applied to a die formed in the die housing 12 as shown in FIG. Since the other configurations are the same as those of the embodiment shown in FIGS. 1 and 2, the same reference numerals are given to the same structural members and the explanation thereof will be omitted.

In the above embodiment, an example of controlling the thickness of the parison in the circumferential direction was shown, but the divided ring plunger 40
In the above-mentioned die 10 equipped with the above-mentioned die 10, it is also possible to control the length of the parison. That is, the parison length is corrected by the extrusion speed of each of the divided plungers 40A to 40D. This allows the length of the parison to be detected by a photoelectric sensor, magnetic sensor, ultrasonic sensor, or the like arranged along the direction in which the parison hangs down. This may be arranged under each of the divided plungers 40A to 40D to detect the partial length of the parison extruded by each of the divided plungers 40A to 40D. If it is detected that the length of the parison at each part is shorter than a predetermined value, the extrusion speed of the plungers 40A to 40D corresponding to this part is slowed down to partially reduce the parison wall thickness, and the hanging speed is increased. Adjust by doing. Conversely, if it is determined that the length of the parison is partially long, the corresponding plunger 4
By selecting 0A to 40D, the extrusion speed is increased, the parison wall thickness is increased, and the hanging speed is partially decreased. This makes it possible to control the parison length so that the lower end of the parison is uniform over the entire circumference.

Flowcharts of such parison length control are shown in FIGS. 8 and 9. In the example shown in FIG. 8, the parison length is controlled by replacing the parison length with the time from the start of injection to the time when the sensor detects the lower end of the parison. That is, when there is an injection start command (step 200), measurement is started (step 210), and counting is continued until the photoelectric sensor detects the lower end of the parison (step 220). The measurement ends when the photoelectric sensor detects the bottom edge of the parison (
Step 230), and define the parison length as t=t1 (Step 240). Compare this with the length of the previous shot (t=t0), and the length of the previous shot will be t
When 1 is small, it can be determined that the parison is long, so
A command to increase the injection speed of the corresponding plungers 40A to 40D is output (step 260). Conversely, when t1 is large, it can be determined that the parison has become short, so in such a case, a command to slow down the injection speed is output (step 2).
70). By increasing the injection speed, the swell ratio can be increased and the wall thickness can be increased; by decreasing the injection speed, the swell ratio can be decreased and the wall thickness can be decreased, and the parison length can be controlled by controlling the thickness. The injection speed is reset as described above, and a command to start the next injection is issued (step 280). In step 250, t1=t0
If so, it is sufficient to directly proceed to the start of the next injection.

According to this embodiment, the length of the parison portion corresponding to each of the divided ring plungers 40A to 40D can be detected and controlled so that the length is uniform over the entire circumference, so that the length of the parison can be controlled so that the length is uniform over the entire circumference. It is possible to prevent the lower end from being uneven, thereby improving the yield.

The example shown in FIG. 9 is a flowchart of a method of controlling the time from when the photoelectric sensor detects the lower end of the parison until the completion of injection is defined by replacing it with the length of the parison. That is, after the injection start command (step 300), the process waits until the photoelectric sensor detects the lower end of the parison (
Step 310), measurement is started when the photoelectric sensor detects the lower end of the parison (Step 320). and,
When the injection completion signal is output from the injection machine (step 330), the measurement is finished (step 340), and the parison length is defined as t=t1 based on the measurement time (step 350). This is the length of the previous shot (t=
t0) (step 360), and if t1 is smaller than the previous shot, it can be determined that the parison is longer, so a command to increase the injection speed of the corresponding plungers 40A to 40D is output (step 370). Conversely, when t1 is large, it can be determined that the parison has become shorter, so
In such a case, a command to slow down the injection speed is output (step 380). By increasing the injection speed, the swell ratio can be increased and the wall thickness can be increased; by decreasing the injection speed, the swell ratio can be decreased and the wall thickness can be decreased, and the parison length can be controlled by controlling the thickness. The injection speed is reset as described above, and a command to start the next injection is issued (step 390). In step 250, t
If 1=t0, it is sufficient to directly proceed to the start of the next injection.

In these parison length controls, the die gap may be adjusted at the same time as the injection speed of the splitting plunger 40 is controlled. In this gap adjustment, when the rate of change of the die gap is α, it is desirable that the injection speed be the square root of the rate of change.

As described above, according to this embodiment, the swell ratio can be controlled by changing the extrusion speed of the divided plungers 40 individually, thereby making it possible to control the length of the parison to be uniform over the entire circumference, thereby improving the yield. Benefits that can be achieved are obtained.

[0029]

[Effects of the Invention] As explained above, according to the present invention,
The plunger inserted into the cylindrical passage of the die is divided in the circumferential direction, and the injection movement speed is individually controlled to perform parison injection, and the circumferential wall thickness can be arbitrarily adjusted by controlling the swell ratio at each part. This makes it possible to control the thickness of the parison with excellent responsiveness without worrying about strength or the possibility of scratches, and it is also possible to correct uneven parison discharge from elliptical and oblong dies. This excellent effect can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram of a parison injection die equipped with a parison wall thickness control device for a blow molding machine according to an embodiment.

FIG. 2 is a longitudinal cross-sectional view of FIG. 1;

FIG. 3 is a schematic diagram of a parison wall thickness control device of a blow molding machine.

FIG. 4 is a cross-sectional view of a parison with controlled wall thickness.

FIG. 5 is a flowchart of parison wall thickness control of the blow molding machine.

FIG. 6 is a sectional view of a modified example of the die provided with the parison wall thickness control device of the blow molding machine according to the embodiment.

FIG. 7 is a longitudinal cross-sectional view of FIG. 6;

FIG. 8 is a flowchart of parison length control.

FIG. 9 is a flowchart showing another embodiment of parison length control.

[Explanation of symbols]

Claims (2)

[Claims] 1. A method in which a ring plunger is inserted into a cylindrical passage of a parison injection die, and a filled molten resin is pressurized by the plunger to inject a cylindrical parison from a resin discharge port. A method for controlling the wall thickness of a parison in a blow molding machine, characterized in that the wall thickness of the parison in the circumferential direction is controlled by dividing the parison in different directions and moving the parison individually. 2. An apparatus for inserting a ring plunger into a cylindrical passage of a parison injection die, and injecting a cylindrical parison from a resin discharge port by pressurizing filled molten resin by the plunger, wherein the ring plunger is inserted into a cylindrical passage. A parison wall thickness control device for a blow molding machine, characterized in that the parison is divided into two directions, and a plunger drive mechanism is connected to each divided plunger.