JPH05200844A - Blow molding apparatus - Google Patents

Abstract

PURPOSE:To uniformize the wall thickness of a molded product and to reduce the generation of flash after blow molding by detecting the position of the mold split surface part of a parison at the time of mold clamping after pre- blowing and controlling the inner pressure of the parison on the basis of the detection result. CONSTITUTION:Pre-pinches 7 are moved from the lower part of a mold 1 to the upper part thereof in such a state that a parison P is extruded into the mold 1 to a certain degree from the extrusion head 8 of an extruder 4 to grasp and close the free end part of the parison P. The pre-pinches 7 are allowed to fall in synchronous relation to the parison P at the time of the extrusion of the parison P. At the time of pre-blowing, a pressure control valve 13 is changed over to supply a pressure fluid into the parison P from a pump and subsequently closed to perform mold clamping but, at this time, the position of the parison on the mold split surface 1a of the mold 1 is detected by non- contact type position sensors 5, 6 and the pressure control valve 13 is subjected to changeover control on the basis of the detection result by a controller 14 so that width becomes a predetermined range corresponding to the interval of the mold at that time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding apparatus and a blow molding method, and more particularly to a blow molding apparatus and a blow molding method for pre-blowing.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to use a resin for various parts for automobiles, for example, but in recent years, a fuel tank, a bumper, a trunk lid, a bonnet, etc. having a hollow portion inside the above parts are molded. In order to achieve this, the use of blow molding has been studied and partly implemented.

Here, in ordinary blow molding, a cylindrical parison is extruded into a split mold opened from an extrusion head of an extruder, the mold is closed and a blow pin is inserted, and air is blown so that a predetermined internal pressure is obtained. A hollow molded article having a desired shape is obtained by bringing the parison into close contact with the inner surface of the mold. However, in the case where the molded product has a relatively complicated shape such as each of the above-mentioned parts, the usual blow molding not only makes the thickness of each part of the part uneven, but also causes many burrs. However, it is not so realistic because the quality and the yield of materials are reduced.

Therefore, the extrusion head of the above extruder is composed of a fixed die on the outer periphery and a movable core at the center which is movable in the axial direction, and the movable core is moved in the axial direction according to the shape of the molded product. , The thickness of the parison is changed and the parison is extruded into the mold to perform the parison control to make the thickness of each part uniform. Also, with the parison pushed into the mold, the free end opening of the parison is closed (pre-pinch), the mold is closed to some extent and a predetermined internal pressure is applied to the parison, and the parison is pre-aligned with the mold to some extent. The pre-blow is performed with the combined shape to reduce the occurrence of burrs. By this parison control and pre-blow, even if the shape is relatively complicated, the wall thickness can be made uniform to some extent and burr can be suppressed.

However, after the pre-blowing is performed, the opening of the parison is closed, and when the mold is closed, it is pressed by the mold and the volume of the parison is reduced. There was a problem that the parison swelled out from the uncoated portion and the wall thickness in the vicinity of the mold crack surface became thin.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and its main purpose is to provide a hollow molded product having a complicated shape with a uniform wall thickness. It is to provide a blow molding apparatus and a blow molding method that are made into a material and have less burrs.

[0007]

According to the present invention, the above-described object is to pre-blow a cylindrical parison from an extruder into an open mold, close the parison, and pressurize the inside to swell. A blow molding apparatus for closing the mold to further pressurize and swell the inside of the parison to obtain a desired hollow molded article, and means for detecting the position of the parison when the mold is closed. And a means for controlling the internal pressure of the parison on the basis of the detection result of the detection means.

[0008]

[Function] By detecting the position of the parison when closing the mold after pre-blowing and controlling the internal pressure of the parison based on the detection result, the parison has a shape that generally follows the inner surface of the mold after closing the mold and before blowing. The wall thickness will be uniform.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the structure of a blow molding apparatus to which the present invention is applied. A pair of split molds 2 and 3 each having a mold cracking surface 1a extending in a direction orthogonal to the paper surface of FIG.
A resin extruder 4 is installed on the upper part of the mold 1. Further, a pre-pinch 7 for closing and restraining the free end of the parison P is provided in the lower portion of the mold 1.

As well shown in FIG. 2 which is a side view of the blow molding apparatus shown in FIG. 1, on the side of the mold 1, in order to detect the position of the parison P on the mold cracking surface 1a, Non-contact type position sensors 5 and 6 are installed. The position sensors 5 and 6 are arranged in different directions from the parison P.
The position of the parison is detected to improve the reliability of the parison position detection. Actually, parison P
If the extruded shape is stable and the center of the mold and the center of the parison are substantially coincident with each other, the position may be detected by using only one of the left and right sensors in FIG.

The extruder 4 is provided with an extrusion head 8 which opens toward the mold 1. The extrusion head 8 includes a fixed die 9 on the outer periphery and a movable core 1 at the center that is movable in the axial direction.
And a fixed pipe 11 for controlling the internal pressure of the parison P at the center of the movable core 10.
Inward, that is, into the parison P. This pipe 11 is provided with a pressure control valve 13 via a pressure sensor 12.
It is connected to the. The pressure control valve 13 is a three-way valve, and is capable of selectively communicating the pipe 11 with the atmosphere and a pump (not shown) at a desired opening degree. Further, the pressure sensor 12 and the pressure control valve 13 are connected to the controller 14. The position sensors 5 and 6 are also connected to the controller 14, and the controller 14 opens and closes the pressure control valve 13 according to signals from the position sensors 5 and 6 and the pressure sensor 12 to control the internal pressure of the parison P. It is supposed to do.

On the other hand, the pre-pinch 7 has a pliers-shaped side surface and is closed by sandwiching the free end of the parison P. The pre-pinch 7 is movable along the pushing direction of the parison P, and guides the parison P in synchronization with the pushing of the parison P.

Next, the operating procedure of this embodiment will be described with reference to FIGS. 1, 3A to 3C, and 4 to 6.

First, as shown by the phantom line in FIG. 1, with the parison P being extruded from the extrusion head 8 of the extruder 4 into the mold 1 to some extent, the pre-pinch 7 is moved from the lower part to the upper part of the mold 1 to make the parison. It is closed by sandwiching the free end of P. Then, as shown in FIG. 3A, the parison P is extruded from the extrusion head 8 of the extruder 4 into the mold 1. At this time, the pre-pinch 7 is also lowered in synchronization with the parison P while the free end of the parison P is closed and restrained. As a result, pre-blowing, mold closing, and blowing after this can be performed with the center of the parison P and the center of the mold 1 aligned, that is, with the parison P positioned with respect to the mold 1. It is possible to prevent problems such as uneven thickness and increase in burrs due to the deviation of the center.

Next, as shown in FIG. 3B, the pressure control valve 13 is switched, connected to a pump and opened to perform pre-blowing, and the pressure control valve 13 is closed.
Then, as shown in FIG. 3C, the mold 1 is gradually closed.
At this time, as shown in FIG. 4 which is an enlarged view of the state of FIG. 3 (c) taken along line IV-IV, the parison P is formed on the inner surface of the mold 1 in particular.
Contacting with each other, the part P ′ of the parison P located on the mold-cracking surface 1a gradually swells. That is, there is a concern that the vicinity of the bulging portion will be thin.

Here, it is considered that if the peripheral length of the parison P is kept constant until the mold 1 is completely closed, the wall thickness of the parison P becomes substantially the same over the entire circumference after the mold is closed. That is, the parison P has a circular cross section, its diameter is D0, the width of the molded product is W,
If the burr is α and πD0 = 2W + α = constant, the wall thickness of the parison P after mold closing becomes substantially equal over the entire circumference. Further, it is assumed that the parison P is elliptically pressed by the molds 2 and 3 during the mold closing (FIG. 5), and its width is PH,
When the distance between the mold 2 and the mold 3 is TC, the above equation is transiently expressed during the mold closing as πD0 = πTC + 2 (PH-TC). By modifying this equation, PH = (πD0-πTC) / 2 + TC, the parison position on the mold cutting surface 1a is detected by the position sensors 5 and 6 during mold closing, and the controller 14 is based on the detection result. Width PH is the mold spacing TC at that time
The pressure control valve 13 is switched so as to be within a predetermined range according to the above, and the opening / closing control is performed by connecting to the atmosphere. That is, the pressure control valve 13 is opened so that the internal pressure becomes substantially constant as the mold 1 is closed, and the pressure control valve 13 is closed when the mold 1 is completely closed.

FIG. 6 shows a difference between the present invention and the prior art which does not include an internal pressure control means such as the pressure control valve 13 with the parison width PH on the vertical axis and the time on the horizontal axis. As is clear from this graph, in the prior art, the expansion amount increases as the mold closing progresses, the parison width rapidly expands, the thickness of the parison becomes uneven, and in the worst case, the parison bursts. However, there is no such concern in the embodiment of the present invention.

Then, a blow pin (not shown) is inserted into the parison P, and pressure is applied to bring it into close contact with the inner surface of the mold 1 (blow) to remove burrs, thereby obtaining a desired hollow molded product. Here, the smaller the predetermined range of the amount of swelling described above, the more the occurrence of burrs can be reduced.

In this embodiment, the pipe used for pre-blowing and the blow pin used for blowing are separately configured, but it goes without saying that they may be used in practice.

FIG. 7 is a view similar to FIG. 1 showing a second embodiment to which the present invention is applied. In the present embodiment, an expander 18 having a pair of L-shaped bars 19 that approach / separate from each other in the width direction of the parison P faces the lower part of the mold 1. The expander 18 can be moved in the vertical direction by a driving device (not shown). The pre-pinch 17 is fixed on the lower part of the mold 1.

In this embodiment, when the parison P is extruded as in the case of the first embodiment, the expander 18 rises to pull the parison P from the inside in the width direction as shown in the imaginary line in FIG. 7 and in FIG. By doing so, the parison P and the center of the mold 1 are synchronously lowered while the center of the parison P and the center of the mold 1 are aligned. Then, in this state, the free end of the parison P is closed by the pre-pinch 17, and pre-blowing and blowing similar to those in the first embodiment are performed. The other structure is similar to that of the first embodiment.

In each of the above-described embodiments, the pliers having a side surface shape of pliers are used, but the present invention is not limited to this, and a pair of bar-shaped members facing each other and extending in the horizontal direction are moved toward and away from each other. For example, a plurality of fan-shaped bodies facing each other may be moved closer to or separated from each other.

[0024]

As is apparent from the above description, according to the blow molding apparatus of the present invention, the parison position of the cracked surface portion of the parison is detected when the mold is closed after pre-blowing, and the parison position is detected based on the detection result. By controlling the internal pressure, the parison has a shape that generally follows the inner surface of the mold after the mold is closed and before blowing, and the wall thickness of the parison is made uniform, so that the wall thickness of the molded product is made uniform. Further, since the extruder restrains the parison and extrudes the parison into the mold, the occurrence of burrs after blowing is reduced. From the above, the effect of the present invention is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a blow molding apparatus in a first embodiment to which the present invention is applied.

FIG. 2 is a sectional view taken along line II-II in FIG.

3 (a) to 3 (c) are views similar to the main parts of FIG. 1 for explaining the operating procedure of the first embodiment.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a schematic sectional view similar to FIG. 4 for explaining the control principle of the first embodiment.

FIG. 6 is a graph showing the parison width in each step for explaining the operating procedure of the first embodiment.

FIG. 7 is a schematic diagram showing a configuration of a blow molding apparatus in a second embodiment to which the present invention is applied.

8 is a sectional view taken along line VIII-VIII in FIG.

[Explanation of symbols]

 1 type 1a type cracked surface 2, 3 split type 4 extruder 5, 6 position sensor 7 pre-pinch 8 extrusion head 9 fixed die 10 movable core 11 pipe 12 pressure sensor 13 pressure control valve 14 controller 17 pre-pinch 18 expander 19 bar

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B29C 49/42 2126-4F // B29L 22:00 4F

Claims (2)

[Claims] 1. A cylindrical parison is extruded from an extruder into an open mold, the parison is closed and pre-blowing is performed to pressurize the interior of the parison to swell, and the mold is closed to further add the interior of the parison. A blow molding device for swelling by pressing to obtain a desired hollow molded article, wherein the means for detecting the position of the parison when closing the mold, and the parison internal pressure based on the detection result of the detection means A blow molding apparatus comprising: a control unit. 2. The blow molding apparatus according to claim 1, further comprising means for restraining the parison and guiding it in the extrusion direction when the parison is extruded into the mold from the extruder.