JPH06234153A - Blow molding method - Google Patents

Abstract

PURPOSE:To cool and solidify a molded product early and uniformly by blowing cooling liquid together with compressed air in the atomized state when a parison clamped between a couple of molds is expanded by blowing the compressed air into the parison through a blow pin. CONSTITUTION:When a valve 13 is opened by a blow start command for compressed air to a parison P in the state that the parison P ejected from an accumulator 2 is clamped between a couple of molds 4 and 5, a valve 31 for feeding cooling water is also opened simultaneously or just a little later. Compressed air from a compressed air feed passage 25 of a blow pin 21 and cooling water from a cooling water feed passage 26 are blown into the parison P respectively by the arrangement, and the cooling water is atomized by the discharge pressure of the compressed air and filled all over inside the parison P in the atomized state. In the expansion process of parison P through the cooling process of a molded product, therefore, cooling is accelerated from the inner peripheral face side of the molded product to shorten the cooling and solidifying 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 method for molding a hollow molded product, and more particularly to a method for efficiently cooling a molded product.

[0002]

2. Description of the Related Art The most common conventional blow molding method is shown in FIG. As shown in FIG. 3, the molding material at around 200 ° C. which has been plasticized (melted) by the screw type extruder 1 is temporarily stored in the accumulator 2 and then injected by the cylinder 3 in a tubular shape called a parison P. Then
The parison P is sandwiched by a pair of molds 4 and 5. Then, the compressed air stored in the surge tank 8 is blown into the parison P by the blow pin 7 which is inserted into the parison P at the pinch-off part 6, and the parison P is expanded by the pressure and pressed against the inner surfaces of the molds 4 and 5. . On the other hand,
Under the above pressure-holding condition, cooling water is passed through the cooling water passages 9 of the molds 4 and 5 to accelerate the cooling and solidification of the molded product, and then the molds 4 and 5 are opened to take out the molded product. 1
Reference numeral 5 is a pressure control unit of the cylinder 3.

Here, the blow pin 7 has a composite cylindrical structure having a compressed air supply passage 10, a compressed air return passage 11 and a cooling water chamber 12 as shown in FIG. 4, and is also shown in FIG. As described above, the compressed air in the surge tank 8 is blown into the parison (molded product) P through the valve 13 and the compressed air supply passage 10 and then again into the surge tank 8 through the compressed air return passage 11 and the check valve 14. Will be returned. Further, in the blow pin 7, cooling water is circulated between the cooling water chamber 12 and a cooling water tank (not shown) equipped with cooling means such as a heat exchanger, like the molds 4 and 5. The blow pin 7 is constantly cooled by.

[0004]

However, in the conventional blow molding method as described above, the heat exchange of the cooling water in the cooling water passage 9 from the outer peripheral surface side of the molded product in contact with the molds 4 and 5 is performed. Since the cooling is performed by the action, the inner peripheral surface side is not always sufficiently cooled as compared with the outer peripheral surface side of the molded product, so that the molded product is distorted after being taken out from the molds 4 and 5, so that stable molding is achieved. The product shape cannot be obtained.

Further, in the method of cooling from the outer peripheral surface side of the molded product as described above, the cooling cycle is inevitably long, so that the molding cycle time becomes long and the productivity cannot be improved.

The present invention has been made in view of the above problems, and provides a blow molding method capable of uniformly cooling the inner peripheral surface side of a molded product and shortening the cooling time. The purpose is to

[0007]

According to the present invention, when a compressed air is blown into a parison sandwiched between a pair of molds by a blow pin inserted into the parison to expand the parison, the compressed air and the parison are compressed together with the compressed air. The cooling liquid is blown into the parison in a spray form, and the molded product is cooled by the latent heat of vaporization of the cooling liquid in parallel with the cooling of the molded product by the cooling means on the die side.

[0008]

According to this method, the molded product in the mold is cooled from the outer peripheral surface side, and at the same time, is also cooled from the inner peripheral surface side. The temperature difference between the two becomes small, and the entire molded product can be cooled uniformly.

[0009]

1 and 2 are views showing an embodiment of the present invention, in which the same parts as those of the conventional example shown in FIGS.

That is, in this embodiment, the blow pin 21
At the same time that compressed air is blown into the parison P from the blow pin 21, the cooling water is blown into the parison P from the blow pin 21 at the same time. It is different from the one.

More specifically, as shown in FIG. 2, the blow pin 21 includes an outer pin 22 in which the cooling water chamber 12 is formed, an inner pin 23 arranged concentrically on the inner circumference of the outer pin 22, and an inner pin 23. The center pin 24 and the center pin 24 form a composite cylindrical structure. These pins 22, 2
The compressed air supply passage 25,
The cooling water supply passage 26 and the compressed air return passage 27 are formed, and the discharge port 28 at the tip of the inner pin 23 forming the cooling water supply passage 26 is locally reduced in diameter to have a small diameter. Has become.

Then, as shown in FIG. 1, the compressed air in the surge tank 8 is blown out from the compressed air supply passage 25 through the valve 13 as in the conventional case, and conversely, the return side from the inside of the parison P. The compressed air to be returned to the surge tank 8 from the compressed air return passage 27 through the check valve 14 and the condenser 29.

On the other hand, the cooling water supply passage 26 has a cooling water chamber 12 for cooling the blow pin 21 itself.
Cooling water is supplied from the cooling water tank 30 via the valve 31 separately from the cooling water supply system.
Then, the cooling water supply passage 26 (inner pin 23)
The cooling water atomized by the discharge pressure of the compressed air from the compressed air supply passage 25 is jetted from the discharge port 28 at the tip of the.

Therefore, according to the structure of the above embodiment,
When the parison P injected from the accumulator 2 is sandwiched between the pair of molds 4 and 5, and the valve 13 is opened by the compressed air blowing start command to the parison P, at the same time or slightly from this. The valve 31 for supplying the cooling water opens later.

By the opening operation of the valves 13 and 31, the compressed air is blown into the parison P from the compressed air supply passage 25 of the blow pin 21, and at the same time, the inside of the parison P is fed from the cooling water supply passage 26. The cooling water is blown out against.

At this time, the cooling water blown from the discharge port 28 at the tip of the cooling water supply passage 26 is atomized by the discharge pressure of the compressed air discharged from the compressed air supply passage 25, and is compressed together with the compressed air into a parison ( The inside of the molded product P will be filled evenly.

On the other hand, since the parison P expanded by blowing the compressed air still has a sufficient amount of heat, the cooling water blown into the parison P together with the compressed air is inside the parison P. Evaporate. Then, the gas that has become saturated vapor by the compressed air and the cooling water is guided from the compressed air return passage 27 of the blow pin 21 to the condenser 29 via the check valve 14 and condensed there.
The condensed water is returned to the cooling water tank 30 and
The compressed air is returned to the surge tank 8.

In the process of cooling the molded product due to the expansion of the parison P due to the blowing of compressed air, not only the cooling progresses from the outer peripheral surface side of the molded product which is in close contact with the molds 4 and 5, but also the compression is performed. Since the latent heat of vaporization of the cooling water blown into the parison P together with the air accelerates the cooling from the inner peripheral surface side of the molded product, the surface temperature difference between the inner and outer peripheral surfaces of the molded product quickly becomes small. The time required for cooling and solidifying the molded product can be remarkably short.

[0019]

As described above, according to the present invention, when the parison is expanded, the cooling liquid is sprayed into the parison together with the compressed air, and the molded product is cooled by the cooling means on the die side. In parallel, the molded product (parison) is also cooled from the inner peripheral surface side by the latent heat of vaporization of the cooling liquid, so that the molded product can be molded more quickly than the conventional method in which it is cooled from the outer peripheral surface side. Since the surface temperature difference between the inner and outer peripheral surfaces of the product can be reduced and the molded product can be cooled and solidified evenly at an early stage, shape defects due to distortion etc. after taking out the molded product from the mold can occur. As a result, the molding quality can be improved and stabilized.

Further, as described above, the cooling and solidification of the molded product is promoted, so that the cooling time can be shortened as compared with the conventional case, and the shortening of the molding cycle time improves the productivity.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of the blow pin shown in FIG.
(A) is the plane explanatory view, (B) is sectional explanatory drawing.

FIG. 3 is a structural explanatory view showing a general example of a conventional blow molding method.

FIG. 4 is an enlarged view of a main part of the blow pin shown in FIG.
(A) is the plane explanatory view, (B) is sectional explanatory drawing.

[Explanation of symbols]

 4, 5 ... Mold 9 ... Cooling water passage 21 ... Blow pin 25 ... Compressed air supply passage 26 ... Cooling water supply passage 27 ... Compressed air return passage 29 ... Condenser 30 ... Cooling water tank P ... Parison

Claims (1)

[Claims] 1. When a parison sandwiched between a pair of molds is blown with compressed air by a blow pin inserted into the parison to expand the parison, a cooling liquid is sprayed into the parison together with the compressed air. Blow molding method, characterized in that the molded product is cooled by the latent heat of vaporization of the cooling liquid in parallel with cooling the molded product by the cooling means on the die side.