JP3361202B2 - Plastic hollow molding method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molding apparatus for blowing a compressed air into a parison housed in a mold to obtain a desired product along the inner surface of the mold.

[0002]

2. Description of the Related Art In a conventional blow molding machine, as shown in FIG. 9, a die is inserted from a extrusion head 2 between a pair of blow molding dies 1 (1a, 1b) which are vertically divided and are opposed to each other. The plastic parison 3 softened through is pushed downward by a predetermined amount, and then the blow nozzle 4 is raised to seal the lower side of the parison 3 with the pre-pinch device 5, and while blowing the pre-blow air into the parison 3 from the extrusion head 2 side, After moving the molds 1a and 1b inward in the horizontal direction and completing the mold clamping (see FIG. 10), high pressure air is blown into the parison 3 through the blow nozzle 4 to make the mold 1
Blow molding of a hollow body having an outer shape that models the inner shape (cavity) of

By the way, according to the conventional hollow molding apparatus,
Since the distance between the extrusion head 2 and the mold 1 is constant, the parison 3 in the mold is likely to change due to the upper part of the parison 3 being cut or stretched during the mold clamping. In the case of No. 3, air inside leaks easily into two flat plates when the die 1 is clamped (see FIGS. 10 and 11).
When the cavity shape is a round shape or a deep shape such as a square shape, when high pressure air is blown into the parison 3 and then blow molding is performed, the direction perpendicular to the mold split surface (see FIG. 10).
Since the distance to the mold surface is large, the elongation rate becomes large as shown by the phantom line, and in the parallel direction (see FIG. 11), the distance to the mold surface is small and the elongation rate becomes small, resulting in a large molded body. Uneven thickness occurs.

In such a conventional blow molding machine, even when the upper part of the parison 3 is not cut and air leakage does not occur, the elongation at the time of blow molding is parallel to the direction perpendicular to the mold split surface of the mold. The rates are different, and especially in the vicinity where the parison is sandwiched between the molds, there is uneven thickness, such as thick wall near the molding surface and thin wall away from the molding surface. In order to prevent such uneven thickness, there is also a method of performing wall thickness correction for correcting uneven thickness in advance with a parison controller, but this is not sufficient and it is very expensive.

Further, as shown in FIGS. 12 and 13, in the case of blow molding a hollow double wall molded product having a shape such as a cooler box using the core mold 11a and the cavity mold 11b, the parison 3 is used. In particular, the side of the core mold 11a is pulled and largely drawn into the mold 11, so that the upper part is cut or cut more than in the case shown in FIGS. 9 and 10.
A portion (arrow a) drawn into the core is stretched and a large uneven thickness is likely to occur. Further, the upper part of the cavity mold 11b is also easily cut. When the upper part of the parison 3 is cut and the air inside leaks, the bulging of the parison 3 due to pre-blow air becomes insufficient, and the parison on the core mold 11a side and the cavity mold 11b side stick to each other at the lower part (arrow b), forming Is very difficult to do, or defective products are created.

Further, as shown in FIGS. 14 and 15,
When molding a bottle 22 having a dented bottom, the problem of uneven thickness in a direction parallel to the mold splitting surface of the bottle molding die 21 (21a, 21b) and a direction perpendicular thereto is the same as described above. In addition to the occurrence, the bottle 22 is pushed up when the mold is opened (at the same time, the blow nozzle 23 is allowed to escape upward), and at this time, the mouth portion (arrow c) of the bottle 22 is easily scratched and may be damaged when it is thin.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the above-mentioned conventional hollow molding apparatus, and has less uneven thickness of the molded body, and the parison is cut or stretched badly during mold clamping. It is an object of the present invention to obtain a hollow molding device which is not easily scratched at the mouth when molding a hollow body such as a bottle having a dented bottom.

[0008]

The hollow molding method according to the present invention is a method of extruding a parison downward through a die, and blowing a pre-blow air into the parison to clamp a pair of vertically-molded hollow molding dies. In the blow molding method for plastics, in which the parison is sandwiched, and subsequently, high-pressure air is blown into the parison to blow-mold the plastic, the pair of blow molding dies are made relatively close to the extrusion head. It is characterized in that the upper part of the parison is pulled into the hollow molding mold while preventing the lower part of the parison from sliding down from the hollow molding mold in the mold clamping process. When the hollow molding die approaches the extrusion head, the hollow molding die side may rise or the extrusion head side may descend.

Further, the blow molding apparatus according to the present invention comprises an extrusion head for pushing a parison downward through a die, a pair of vertically divided molds located below the extrusion head, and a parison at the time of clamping. In a plastic hollow molding apparatus equipped with pre-blowing means for blowing air into the inside, the pair of hollow molding dies clamps while relatively approaching the extrusion head, or clamping while relatively approaching the extrusion head. It is characterized in that the molds are opened while moving away from each other, and preferably, a pre-pinch device for sealing the lower part of the parison is provided at a lower position of the pair of hollow molding molds, and when the mold is clamped, the pair of hollow molding molds is formed. In addition, it is characterized in that it is relatively close to the extrusion head. When the hollow molding die approaches or moves away from the extrusion head, the hollow molding die side may move up or down, or the extrusion head side may move down or up.

[0010]

In the blow molding method and apparatus of the present invention, the blow molding die is clamped while approaching the extrusion head, so that the upper part of the parison is pulled and severely stretched during the mold clamping process. There is nothing to do.

In the above hollow molding method and apparatus (if the extrusion head is fixed above and the hollow molding die rises), in the process of clamping the hollow molding die while raising it, The lower part of the parison expanded by the pre-blow air is pulled up together with the hollow molding die, and the upper part of the parison is drawn into the cavity of the hollow molding mold by the action of gravity and the expansion of the parison.

This operation will be specifically described with reference to FIGS. A pair of vertically-formed hollow molding dies 31 (31a, 31b) is arranged below the extrusion head 2, and pre-blow air is blown into the parison 3 from the extrusion head 2 at the time of mold clamping. , 31b move inward in the horizontal direction while keeping the mold splitting surfaces in parallel, and at the same time ascend toward the extrusion head 2, the mold splitting surfaces of the hollow molding dies 31a and 31b come into contact with the parison 3. When starting (see FIG. 2), the part of the parison 3 inside the hollow molding die 31 swells with pre-blow air,
The part (arrow d) that is in contact with the mold cutting surface is pressed and dents.

Therefore, the lower part of the parison 3 is caught by the hollow molding die 31 at the position of the arrow d, and is pulled up together with the hollow molding die 31 without slipping off from there.
The upper part of the parison 3 gradually slides into the cavity of the hollow molding die 31 during the mold clamping process due to the pulling force and the action of gravity due to the bulging of the inside of the hollow molding die 31 (FIG. 2). (Fig. 4). A guide surface 32 is formed at the upper part of the split surface of the hollow molding die 31 so that the parison 3 can be smoothly slid therein.

Parison 3 in the cavity at the end of mold clamping
4, as shown in FIG. 4, is in a state of swelling in a drop shape in a direction perpendicular to the mold dividing plane XX (plane perpendicular to the paper surface), and then high pressure air is blown into the parison 3. When blow molding, the difference in the distance to the mold surface is small in the direction (see FIG. 5) parallel to the direction (see FIG. 4) perpendicular to the split surface XX of the hollow molding die 31, and the elongation is There is little difference between the two directions, and as a result, uneven thickness of the molded body is reduced.

The parison 3 is largely swollen in the direction perpendicular to the mold cutting surface XX, but is not particularly swollen in the direction parallel to the mold cutting surface XX as shown in FIG. The reason is that the direction perpendicular to the molding surface XX of the parison 3 comes into quick contact with the hollow forming mold 31 and is pulled up together with the hollow forming mold 31, but the horizontal direction is the hollow forming mold 31. Three
This is because the contact with 1 is slow and can be raised only slightly or not at all. Therefore, in FIG. 5, the left and right sides of the parison 3 (the direction parallel to the mold cutting surface XX) are lowered and the center (the mold cutting surface X- The direction perpendicular to X) is raised.

Further, in the blow molding apparatus of the present invention,
When the pre-pinch device is provided, the lower part of the parison can be pre-pinched to prevent leakage of pre-blow air, and the lower part of the parison can be supported during mold clamping to reliably raise the parison as the hollow molding die rises. Like The pre-pinch device may be attached, for example, to the lower part of the hollow forming mold and moved up and down together with the hollow forming mold, or below the hollow forming mold and separately from the hollow forming mold. It may be installed so that it can move up and down and move up and down in synchronization with the hollow molding die.

The hollow molding die may be set so as to rise at an angle of approximately 15 ° to 30 ° with respect to the horizontal plane with respect to the extrusion head, but it is not particularly limited to this as long as it has an intended function. is not. Further, the operation of the present invention has been described so far by assuming that the extrusion head is fixed at the upper side and the side of the hollow molding die rises, but the same applies when the hollow molding die is fixed and the side of the extrusion head descends. Is.

Also, when the present invention is applied to a hollow molding device equipped with a core mold 51a and a cavity mold 51b (see FIG. 6), the parison 3 is naturally drawn into the mold cavity, so The meat becomes smaller, and the parison 3 will not be stretched or cut by the mold 51 when the mold is clamped. Furthermore, since the parison 3 is not pulled, it is easy for the parison 3 to follow the mold surface by the pressure of the pre-blowing air, and the parison does not stick to each other during mold clamping.

Further, when the hollow molding device of the present invention is applied to molding a hollow body such as a bottle having a dented bottom, uneven thickness is reduced, and when the hollow molding die is lowered to open the bottle, the bottle is opened. Since it cannot be pushed up, it is possible to prevent the mouth of the bottle from being scratched.

[0020]

EXAMPLE FIG. 7 and FIG. 8 show a hollow molding die 5
In this embodiment, a parallel link mechanism is used as the mold clamping mechanism of No. 1, and the mold plate 52 of the hollow molding mold 51 is a mold plate stay 53.
One end of each of the mold clamping stay 54 and the link 55 is rotatably connected to the mold plate stay 53, and the other ends thereof are rotatably connected to the frame 56. Template stay 5
3, the mold clamping stay 54, and the link 55 constitute a kind of parallel link mechanism, and the hydraulic cylinder 57 swings the mold clamping stay 54 around the shaft 58 to move the mold plate 52 in the arrow direction or in the reverse direction. The hollow mold 51 is rotated in the direction to clamp or open the hollow mold 51. Reference numeral 59 is a tuning gear for tuning the left and right parallel link mechanisms.

Using such a hollow molding device, the inner volume 8 having a substantially square cross section with a dented bottom and a rounded even part
A 30 cc bottle was molded. In the conventional blow molding device, the wall thickness of the bottom corner portion of the bottle is 2.0 mm at the position of the molding surface and 0.9 mm in the direction perpendicular to the molding surface,
Although the mouth portion of the bottle was scratched, the hollow molding apparatuses of the examples had the same weights of 1.8 mm and 1.3 mm, respectively, and the uneven thickness was small, and the mouth portion was scratched. There wasn't.

Also, a hollow double-walled container was molded by using such a hollow molding device, but the uneven thickness was smaller than in the conventional case,
The parison did not stick when the mold was clamped.

[0023]

According to the present invention, the parison is naturally drawn into the mold cavity by the action of gravity or the like, and the parison is not cut or stretched during mold clamping.
Further, it is possible to obtain a hollow molded body with less uneven thickness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining the operation of the hollow molding apparatus of the present invention, before the hollow mold is clamped.

FIG. 2 is a sectional view of the same during mold clamping.

FIG. 3 is a cross-sectional view of the same process during mold clamping.

FIG. 4 is a sectional view of the same when the mold clamping is completed.

FIG. 5 is a sectional view of the mold splitting surface when the mold clamping is completed.

FIG. 6 is a cross-sectional view for explaining the operation of the hollow molding apparatus of the present invention, which is a process of clamping the hollow molding die.

FIG. 7 is a front view of an embodiment of a mold clamping mechanism of a hollow molding die.

FIG. 8 is a side view of the same.

FIG. 9 is a cross-sectional view of a hollow molding die of a conventional hollow molding apparatus before being clamped.

FIG. 10 is a sectional view of the same when the mold clamping is completed.

FIG. 11 is a sectional view of the mold splitting surface when the mold clamping is completed.

FIG. 12 is a cross-sectional view of a hollow molding die portion of a conventional hollow molding device before mold clamping.

FIG. 13 is likewise a cross-sectional view during mold clamping.

FIG. 14 is a cross-sectional view after blow molding of a portion of a bottle molding die of a conventional hollow molding device.

FIG. 15 is a sectional view of the mold during opening.

[Explanation of symbols]

1, 11, 21, 31, 41, 51 Hollow mold 2 extrusion head 3 parison 4 blow nozzle 5 Pre-pinch device

Claims (4)

(57) [Claims] 1. A parison is extruded downward through a die, and a pair of vertically-molded hollow molding dies are clamped by blowing a pre-blow air into the interior of the parison to sandwich the parison, and then the interior of the parison. In a plastic hollow molding method in which high-pressure air is blown into the mold, the pair of hollow molding dies are clamped while being relatively close to the extrusion head, and in the mold clamping process, the lower part of the parison is hollow. A hollow molding method for plastics, characterized in that the upper part of the parison is drawn into the hollow molding die while preventing the parison from slipping off. 2. An extrusion head for extruding a parison downward through a die, a pair of hollow molding dies positioned below the extrusion head and divided vertically, and a pre-blowing means for blowing air into the parison during mold clamping. A plastic hollow molding apparatus, characterized in that the pair of hollow molding dies clamp the mold while relatively approaching the extrusion head. 3. An extrusion head for extruding a parison downward through a die, a pair of hollow molding dies positioned below the extrusion head and divided vertically, and a pre-blowing means for blowing air into the parison during mold clamping. A plastic hollow molding apparatus, characterized in that the pair of hollow molding dies clamp the mold while relatively approaching the extrusion head, and open the mold while relatively moving away from the extrusion head. 4. A pre-pinch device for sealing the lower part of the parison is provided below the pair of hollow molding dies, and the pre-pinch device is provided relative to the extrusion head together with the pair of hollow molding dies during mold clamping. The plastic hollow molding apparatus according to claim 2 or 3, wherein the plastic hollow molding apparatus is close to each other.