JPH06312448A - Hollow molding method and apparatus of thermoplastic resin - Google Patents

Abstract

PURPOSE:To enhance the stability or reproducibility of molding by performing the emission and suction of a fluid with respect to a parison by a syringe and controlling the syringe according to a proper profile preset with respect to the relation between the position of a mold and the emission and suction of the fluid. CONSTITUTION:A syringe 3 is arranged to a route supplying a pre-blowing fluid to a hollow molding machine 2 from a fluid supply source 1. The fluid is supplied to the parison of the hollow molding machine 2 from the syringe 3 through piping 4. The fluid is sucked and emitted by the plunger 5 in the syringe 3 and the plunger 5 is driven by a motor 9 through a hydraulic cylinder 7. At this time, oil pressure is controlled on the basis of the fluid amt. measured by a potentiometer 12 according to a predetermined profile 13 by a control means 10. That is, a profile 13 proper with respect to the relation between the position of a mold and the emission and suction of the fluid is preset to the control means 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding method and apparatus for a thermoplastic resin using pre-blow (preliminary blow molding).

[0002]

2. Description of the Related Art In the blow molding of a thermoplastic resin, particularly in the blow molding of a hollow product having a complicated shape, parisons come into contact with each other in the process of closing the mold to cause fusion or locally blow up ratio. And the wall thickness becomes uneven, and wrinkles in the parison may cause folds in the product.

In order to avoid the above problems, preblowing (preliminary blow molding) is performed. In other words, by pre-pinch the air or other fluid inside the parison, or inject a little air or other fluid in that state in advance, and close the mold with the parison slightly inflated from the time of injection, to make the wrinkle in the parison. To prevent the fusion of the parison by the mold,
By controlling the extreme partial blow-up depending on the location, a product with a uniform wall thickness is obtained. When the amount of pre-blow is large, the thickness uniformity tends to be good with respect to the uneven shape of the product, but the parison may burst before the mold is closed, resulting in poor molding stability.

Therefore, it is important to control the amount of pre-blow fluid when the mold is closed. As a typical method for controlling the amount of pre-blow fluid, an apparatus as schematically shown in FIG. 2 is known. That is, the air or other fluid from the fluid source 1 is sent to the molding machine 2 through the blowing line 18 with the valve 15 in which the pre-blow pressure setting 16 or the pre-blow amount setting 14 is performed. At this time, another control line (16 ', 14', 15 ') in which another pre-blowing pressure or pre-blowing amount is set is provided in parallel so that the pre-blowing pressure or pre-blowing amount can be changed with time. The valve of each blow control line is opened and closed by a timer or a sequencer so that the internal fluid is controlled to reach a desired set fluid amount for each time. In FIG. 2, 17 is a fluid discharge line.

However, the adjustment of the amount of fluid for pre-blowing in the parison in the conventional technique as described above is performed by setting the set value of the fluid pressure (or flow rate) control valve and the set value of the exhaust valve pressure (or flow rate) control valve. It is difficult to secure the accuracy of adjusting the amount of fluid because it is done by the value and the opening time of those control valves, and the device becomes complicated when trying to finely control it with time or according to the process such as the mold clamping position. Not only that, but there is also the problem that it is difficult to change the set value quantitatively.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a hollow molding method for a thermoplastic resin, which enables stable molding by changing the amount of fluid in the parison during pre-blowing according to a preset profile, and It is to provide a blow molding device.

[0007]

According to the present invention, in one aspect thereof, a thermoplastic resin for supplying a fluid from a fluid supply source to a parison during pre-blowing of the parison, and then sucking the fluid from the parison while closing a mold. In the hollow molding method, the syringe provided in the path for feeding the fluid from the fluid supply source to the parison performs the fluid supply to the parison and the fluid suction from the parison, and the position of the mold and the fluid supply. And a suction-related profile are set in advance, and the hollow molding method for a thermoplastic resin is provided, characterized in that the syringe for supplying and sucking a fluid is operated in accordance with the set profile.

According to another aspect of the present invention, in a blow molding apparatus for thermoplastic resin using pre-blowing, (a) means for measuring the amount of pre-blowing fluid supplied into the parison; Control means for sending a signal for changing the amount of pre-blow fluid in the parison with time according to the set profile to the drive source of the syringe below, and (c) placed in the path for delivering fluid from the fluid supply source to the parison A syringe for containing a fluid for pre-blowing, comprising a pre-blowing device comprising a syringe that receives a signal from the control means, pushes out the fluid and supplies the fluid into the parison, and sucks the fluid from the parison. A blow molding device for a thermoplastic resin is provided.

The blow molding method and blow molding apparatus of the present invention will be described below with reference to the accompanying drawings. Figure 1
FIG. 3 is a diagram showing an outline of the hollow molding device of the present invention, in which the arrangement of main means constituting the device is shown.

A syringe 3 is arranged in a path for supplying a fluid for pre-blowing from a supply source 1 of air or other suitable fluid to the hollow molding machine 2, and the fluid for pre-blowing is once stored in the syringe 3. It is accommodated and extruded from the syringe 3 at the time of pre-blowing, fed through the pre-blowing pipe 4 to the parison (not shown) in the hollow molding machine 2, and at the stage where the mold is closed, the fluid is discharged from the parison to the pipe 4. And is sucked into the syringe 3.

The plunger 5 pushes out the fluid contained in the syringe 3 and sucks it into the syringe. The plunger 5 is driven by known means such as hydraulic pressure, fluid pressure, electric power, magnetic force and the like. In the example shown,
The plunger 5 of the syringe 3 is hydraulically driven. That is, the driving force from the motor 9 is transmitted to the cylinder 7 via the solenoid valve and the hydraulic pipe 6,
The plunger 5 reciprocates in the syringe 3 by the operation of the hydraulic cylinder 7.

The hydraulic pressure for operating the plunger 5 of the syringe 3 is controlled by a signal from the control means 10. An appropriate profile 13 of the amount of pre-blow fluid supplied to the parison is preset in the control means 10 according to the size and shape of the molded body, and the amount of fluid in the parison is changed with time or the mold clamping position. It is configured so that it can be changed to a desired value according to the molding process of the molding machine.

As a means for measuring the amount of fluid in the parison, the plunger 5 of the syringe 3 is provided with a potentiometer 1
2 is attached. That is, the amount of fluid in the parison is detected by the position of the plunger 5. The potentiometer 12 is connected to the control means 10 and is capable of feedback control. The means for measuring the amount of fluid in the parison is not limited to the potentiometer 12 shown, as long as accurate and quick measurement is possible.

The profile 13 of the amount of the pre-blow fluid supplied to the parison can be set corresponding to the mold clamping position of the parison hollow molding machine. In this case, means for accurately and accurately detecting the mold position, for example, a potentiometer 11 is provided as shown in the figure, and this detecting means is connected to the control means 10 to feedback-control the detected mold clamping position.

The control means 10 is a means for detecting the mold clamping position 1.
1 and a potentiometer 12 for detecting the plunger position, respectively, and sends a necessary signal to the solenoid valve 8 based on a comparison between the signals from both detection means and a preset profile 13, The plunger 5 of the syringe 3 is operated via the system.

FIG. 4 shows a typical example of the profile, the horizontal axis of which is the position of the mold and the left end (0 m
m) indicates that the mold is in the open position, the right end (1000
mm) indicates that the mold is in the closed position. The vertical axis represents the position of the plunger 5 that indicates the amount of fluid in the syringe 3, and 0 mm indicates that the plunger 5 is located at the right end in the example of FIG. 1 and the maximum amount of fluid is stored in the syringe 3. Indicates that

Regarding the profile shown in FIG. 4, the pre-blow mode of the parison will be described. First, the mold is clamped from the open position (the left end of the profile) to come into contact with the parison, and the fluid to the parison is started until the parison starts to be crushed. The amount of the fluid supplied until the point a is rapidly increased (up to the point a of the profile) is predetermined depending on the size and shape of the molded body. While the mold is being closed during the transition from point a to point b, the fluid supply and suction are not performed, and the fluid amount in the parison is kept substantially constant. Therefore, when the parison is compressed by the protrusion 15 in the mold shown in FIG. 3 due to the mold clamping, the parison expands from the outer periphery of the protrusion 15 toward the recess of the mold so as to wrap the protrusion 15.

Further, as the mold clamping progresses, the optimum amount of fluid in the parison decreases (from point b to point c). The main feature of the present invention is that the suction of the fluid from the point b to the point c in FIG. 4 is performed in consideration of the shape of the molded body and in conjunction with the position of the mold until the mold is closed. Even in the case of a molded body having a complicated shape, the profile is set so that the parison follows the inner surface of the mold as much as possible. If the suction of the fluid corresponding to the position of the mold is too strong, the parison will deflate and separate from the inner surface of the mold, reducing the effect of pre-blowing.
In the case of a complicated molded body, nonuniform wall thickness occurs. vice versa,
If the fluid suction is too weak, the parison may burst.

In FIG. 1, when the plunger 5 moves to the left, the fluid in the syringe 3 is pressed into the parison, and conversely, when the plunger moves to the right, the fluid in the parison is sucked into the syringe 4. To be done. The amount of fluid in the parison can be adjusted with a syringe quickly and with high accuracy, and the accuracy of reliability is high.

Next, a specific example of blow molding will be described.

EXAMPLES Using a mold having a cross-sectional shape as shown in FIG. 3 and an apparatus as shown in FIG. 1, hollow molding was carried out according to the profile shown in FIG. 4 to evaluate molding characteristics.

Air for pre-blowing was blown from the syringe into the parison, and the speed of exhaust was changed by a flow rate control valve. 2
A combination of exhaust valves of various types was used. Slow exhaust was performed at the time when the parison touched the mold and the diameter became large so that sufficient pre-blow was applied when the mold was closed and lateral burr did not appear, and high speed exhaust was performed immediately before the closing. The weight of the hollow molded product was 12 kg, the specification was ± 0.2 kg in weight width, and the minimum wall thickness was 3 mm. For comparison, hollow molding was performed under similar conditions using a conventional hollow molding apparatus as shown in FIG.

A hollow molded article having an average wall thickness of 5 mm was molded by both the method of the present invention and the conventional method. The minimum wall thickness was 3 mm by the method of the present invention and 2 mm by the conventional method. In addition, the passing rate of molded products was not constant in the conventional method, but if pre-blowing was too effective, lateral burr was produced and it became a lightweight product of about 1 kg. The thickness was about 85% due to the lack of wall thickness, whereas it was 95% or more in the present invention.

In the conventional method, it took 2-3 days to establish the optimum molding conditions, but it was shortened to about 1 day by using the method of the present invention. Further, in an experiment in which another molding condition was once set and then returned to the molding condition again, in the present invention, the molding condition was reproduced in about 1 hour, whereas in the conventional method, it took about 1 day to adjust the flow control valve in terms of accuracy. Needed.

[0024]

EFFECTS OF THE INVENTION By hollow molding according to the present invention, as compared with the case of molding using a conventional molding machine, Shortening of molding condition setting time 2. Improved stability of molding conditions 3. Improved reproducibility of molding conditions 4. It is possible to set more detailed conditions. It has the advantage of uniform product thickness.

[Brief description of drawings]

FIG. 1 is a schematic diagram (conceptual diagram) of an apparatus of the present invention.

FIG. 2 is a schematic diagram (conceptual diagram) of a conventional apparatus.

FIG. 3 is a cross-sectional view (front view) showing an example of a mold.

FIG. 4 is a diagram showing an example of a profile used in the present invention.

[Explanation of symbols]

 1 Fluid Supply Source 2 Hollow Molding Machine 3 Syringe 4 Pre-blow Piping 5 Plunger 6 Hydraulic Piping 7 Hydraulic Cylinder 8 Solenoid Valve 9 Motor 10 Control Means 11 Potentiometer for Detecting Clamping Position 12 Plunger Position Detecting Potentiometer 13 Profile 14 Gold Mold 15 Protrusion in the mold

Claims (2)

[Claims] 1. A blow molding method for a thermoplastic resin in which a fluid is supplied from a fluid supply source to the parison during pre-blowing of the parison, and then the fluid is sucked from the parison while the mold is closed. By the syringe provided in the path for feeding, supply of fluid to the parison and suction of fluid from the parison are performed, and the profile of the relationship between the position of the mold and the supply and suction of fluid is set in advance, A hollow molding method for a thermoplastic resin, characterized in that the syringe for supplying and sucking a fluid is operated according to the set profile. 2. (a) means for measuring the amount of pre-blow fluid supplied into the parison; and (b) a signal for changing the amount of pre-blow fluid in the parison with time according to a preset profile as follows. A control means for sending to a driving source of a syringe, and (c) a syringe containing a fluid for pre-blowing arranged in a path for sending fluid from a fluid supply source to a parison, and receiving a signal from the control means. Then, the blow molding device for a thermoplastic resin is characterized by comprising a pre-blow device comprising a syringe for extruding the fluid to supply it into the parison and sucking the fluid from the parison.