JPH06170933A - Hollow molding machine using hollow part molding blow pin - Google Patents

Abstract

PURPOSE:To facilitate a stopping accuracy of mold closing and a centering accuracy of a mold by forming a pre-blow air passage at a core disposed at a center of a die, and movably inserting a high pressure blow pin in the passage coaxially with the passage. CONSTITUTION:A parison 22 formed of thermoplastic resin as a base material is vertically extruded from a slit 20 of a die 10 and suspended between a male mold 24 and a female mold 26 heated to a predetermined temperature. Then, after a lower end of the parison 22 is pinched by a pinch unit to a bag state, pre-blow air of low pressure is introduced from a pre-blow air passage 30 into the parison 22. Then, after the molds are clamped, high pressure blow air is charged into the parison 22 from a high pressure blow pin 28 movably inserted into the passage 30 coaxially with the passage 30 into the parison 22 closed at upper, lower sides and periphery by both the molds 24, 26 thereby to complete a molded form of a final shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molding machine having a blow molding blow pin for injecting a fluid into a parison in the hollow molding.

[0002]

2. Description of the Related Art Conventionally, hollow resin moldings such as resin fuel tanks for automobiles and resin door panels for office equipment have been manufactured by a hollow molding method. In this hollow molding, a cylindrical parison of thermoplastic resin is made by an extrusion method or an injection method, and the parison is sandwiched between molds and gas such as pressurized air is blown into the core metal through a blow pin attached to the core metal. This is a method in which a hollow product is molded by expanding and shaping it until it comes into close contact with the cavity, and then cooling.

FIG. 3 shows a mounting cross section of a conventional blow pin. In the conventional blow pin 3, a screw is engraved on the upper and lower sides of an air passage hole 6 formed in a core metal 5, and the air passage hole is formed at the lowermost end of a lower attachment 2 which is screwed with the screw. It is provided in communication with. On the other hand, a switching valve 4 for pre-blowing air and high-pressure blowing air, which is connected to the upper attachment 1 and is located upstream of the air, is provided.
The parison can be expanded and brought into close contact with the mold cavity by appropriately switching.

[0004]

However, such a blow molding machine has the following problems. That is, when the parison is drooped between the two dies facing each other, and the hollow mold is repeatedly sandwiched on the mold clamping line by closing both dies, the parison is fixed to the lowermost end of the lower attachment 2. The blow pin 3 is deformed due to the original relative position of the blow pin 3 and the two dies due to the difference in mold closing speed between the dies and the blow pin 3 having the blow air hole downward. Or it may have been damaged. Furthermore, even in the case of a mold clamping unit that controls left and right simultaneously, there was a problem that it was difficult to center the center lines of both molds.

It is an object of the present invention to provide a blow molding blow pin which is not deformed or damaged even if the relative positions with respect to both molds are slightly deviated from the above conventional problems.

[0006]

In order to solve such a problem, in a blow molding machine having blow blow pins for blow molding according to the present invention, a parison is held in a mold and a die above the mold is provided. In a hollow molding machine having a blow molding blow pin that blows a pressurized fluid into the parison through a blow pin provided on a cored bar located at the center to mold a hollow product, the cored bar is punched in the axial direction. The pre-blow air passage is provided, and the upper end portion is fixed in the pre-blow air passage, the lower end portion is a free end, and the high pressure blow pin is provided in a loosely fitted state.

[0007]

[Operation] The parison is hung from the parison die, the tip is pinched by the pinch device, and then hung down to the position where it is interposed between the molds again. At this position, the lower part of the parison is pinched to the bottom, and pre-blow air is blown in to inflate it slightly. Next, the parison is sandwiched between both molds, and high-pressure blow air is introduced from the pre-blow air passage through the high-pressure blow pin. At this time, since the high-pressure blow pin has flexibility, the displacement due to the relative position of the high-pressure blow pin and both molds and damage during repeated mold closing / clamping even when it is difficult to center the center lines of both molds And deformation can be prevented.

[0008]

EXAMPLE An example of a hollow molding machine having a blow molding blow pin according to the present invention will be described in detail below.
FIG. 1 is an explanatory view showing a molding process of a hollow molded article according to the present invention, and FIG. 2 is an enlarged sectional view of a main part of a blow air blowing section showing an embodiment of the present invention.

In FIG. 1, the die 10 includes a die housing 12 whose outer peripheral surface is formed in a square shape and whose inner peripheral surface is formed in a circular shape. The inner peripheral surface of the die housing 12 is not shown. A mandrel and a core metal 16 composed of a core 14 are fitted to each other, and the die housing 12
An annular resin passage 18 is provided between the resin passage 18 and the inner peripheral surface of the die, and the resin passage 18 has a slit 20 serving as a resin discharge port at the lower end of the die 10.
The molten resin inside is extruded through the slit 20 to the outside of the die 10 main body to form a parison 22.

On the other hand, below the die 10, there are provided a male die 24 and a female die 26 which are located on a machine head (not shown) and are moved forward and backward by a mold clamping cylinder (not shown). The parison 22 is configured to be clamped and opened by means of the pair of left and right male dies 24 and female dies 26 provided with respect to the center line of the parison 22. It is configured to be typed into.

Next, the structure of the blow molding blow pin according to the present invention will be described. A pre-blow air passage 30 is bored in the core metal 16 in the same direction as the axis of the die 10, and a high-pressure blow pin 28 forming a high-pressure blow air passage coaxial with the pre-blow air passage 30 is provided in the center of the pre-blow air passage 30. It is arranged in a fitted state.
While slightly deviating from the stopping accuracy (generally ± 0.2 to 0.3 mm or less) at the mold clamping limit of both the molds 24 and 26,
As shown by the chain double-dashed line in FIG. 2, even if the mold is repeatedly clamped due to this displacement, the pre-blow air passage 30 and the high pressure blow pin 28 are loosely fitted to each other, so that the high pressure blow pin 28 is not easily damaged. Has become.

A blow air block 32 for distributing blow air passages is mounted on the core metal 16 by bolts or the like on the core metal 16, and the high pressure blow pin 28 has a blow air block 32 in which an air inlet is formed. Is connected to a high-pressure compressed air source of, for example, 5 to 7 kg / cm ² . Similarly, the pre-blow air passage 30 is also configured so that the air from the high pressure compressed air source can be decompressed and supplied to the low pressure air of, for example, ² to 3 kg / cm ² through the blow air block 32.

The operation of the blow molding machine having the blow molding blow pin configured as described above will be described.

First, the left and right male molds 2 under the mold open state.
4 and the female mold 26, a parison 22 made of a thermoplastic resin such as polyethylene or polypropylene as a base material is extruded downward from the slit 20 of the die 10, and the parison 22 is heated to a predetermined temperature. It is provided between the mold 24 and the female mold 26. The extruding of the molten resin from the extruder to the die 10 is temporarily stopped with the tip of the parison 22 hanging from the lower ends of the molds 24 and 26 to a position below. In this state, the lower end of the parison 22 is pinched by a pinch device (not shown) to form a bag, and at the same time, a low pressure of ² to 3 kg / cm ² is applied from the preblow air supply source to the bottomed parison 22 through the preblow air passage 30. Pre-blow air is introduced (Fig. 1 (1)).

Then, by supplying pressure oil to the mold clamping cylinder, the parison 22 is sandwiched between the male mold 24 and the female mold 26, and the top and bottom or the periphery of the parison 22 are sealed.
This tube-shaped parison 22 is sandwiched between the two molds 24 and 26 about the high-pressure blow pin 28, and the two molds 2
Stopping accuracy at the mold closing limit by 4, 26 (for example, ± 0.2 ~
0.3 mm or less is desirable) is important,
If the stopping accuracy is low, there is a risk that the conventional blow pin fixed to the lower portion of the core 14 may be damaged. Therefore, in the present invention, the high pressure blow pin 28 as shown in FIG.
A gap is provided between the pre-blowing air passage 30 and the pre-blowing air passage 30. For example, a slight difference in mold closing speed between the two molds 24 and 26 may occur. The high pressure blow pin 28 is not damaged.

Following this blockage, the supply of the pre-blow air is stopped, and at the same time, a high pressure of 5 to 7 kg / cm ² is applied from the high pressure blow air supply source through the high pressure blow pin 28 into the parison 22 blocked by both molds 24 and 26. High-pressure blow air is introduced (Fig. 1 (2)). Thereafter, the male mold 24 and the female mold 26 are cooled to cool both molds 24, 26.
When the mold is opened, a desired hollow molded product can be obtained.

[0017]

As is apparent from the above description, in the blow molding machine having the blow molding blow pin according to the present invention, the parison is held in the mold, and the parison is provided in the center of the die above the mold. In a hollow molding machine having a blow molding blow pin for injecting a pressurized fluid into the parison through a blow pin provided on a positioned core metal to form a hollow product, the hollow core is bored in the axial direction of the core metal. The pre-blow air passage and the upper end in this pre-blow air passage are fixed, the lower end is a free end, and the high-pressure blow pin is arranged in a loosely fitted state. The stopping accuracy and the centering accuracy of the mold can be tolerated lower, and deformation and damage of the high-pressure blow pin can be prevented.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a molding process of a hollow molded product.

FIG. 2 is an enlarged cross-sectional view of a main part of a blow air blowing section showing an embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of a conventional blow air blowing section.

[Explanation of symbols]

 10 dies 12 dies housing 14 core 16 core metal 18 resin passage 20 slit 22 parison 24 male die 26 female die 28 high pressure blow pin 30 pre-blow air passage 32 blow air block

Claims (1)

[Claims] 1. A hollow product is obtained by holding a parison in a mold and blowing a pressurized fluid into the parison through a blow pin provided in a core metal located in the center of the die above the mold. In a hollow molding machine having a blow molding blow pin for molding, a pre-blow air passage bored in the axial direction of the core metal and an upper end in the pre-blow air passage are fixed and a lower end is made a free end, A blow molding machine having blow molding blow pins, wherein high pressure blow pins are arranged in a fitted state.