JPS5850860B2 - Boss hole forming method for blow molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a boss hole in a blow-molded product, and more particularly to a method for increasing the thickness of the peripheral wall of a boss hole.

BACKGROUND ART Conventionally, a hollow molding method called blow molding has been known as a method for manufacturing resin molded products such as synthetic resins.

As is generally well known, in blow molding, a tubular or bag-like object called a parison P is pre-molded with a plasticized material, and before it is cooled and solidified, it is molded in a closed mold C. , compressed air is blown into the inside of the parison P by the air supply device AS, and the parison P is pressed against the wall surface of the mold C to obtain the desired product (first step).
(see figure).

Now, when forming a tapping boss hole in a product by this blow molding, a forming pin 20 is provided to protrude from a predetermined portion of the forming die C.

(See FIG. 4) However, according to this method, thin-walled areas may occur on the peripheral wall of the boss hole after molding, especially on the wall on the base side of the hole (section A in the figure).

This is due to the following reason.

When the parison P is expanded by blowing, it first comes into contact with the top of the forming pin 20.

Thereafter, the parison P is rapidly deformed to follow the outer wall of the forming pin 20, and is subjected to a tensile force in the direction directly below (to the left in the figure), so that the parison P becomes thinner than the hem side portion.

In other words, this thinned portion will be involved in forming the boss hole, and the corner portion of the base periphery of the forming pin 20 will be particularly thinned to a great extent in order to fill this corner.

That is, in the method of forming a boss hole by simply erecting the forming pin 20, the range involved in forming the boss hole of the parison P determined at the initial stage of blowing is narrow, so it is difficult to avoid the thin wall phenomenon. This resulted in a situation where the screws were easily destroyed when screwed on.

The present invention has been devised in view of the above, and its purpose is to provide a molding method suitable for forming a boss hole while suppressing the occurrence of the thin-wall phenomenon.

Hereinafter, one embodiment of the present invention will be described according to the drawings. The drawings are enlarged views showing the vicinity of the forming pin in the forming die, and parts not particularly explained follow the usual blow molding method.

In the drawings, reference numeral 1 denotes a molding die, and a guide hole 2 is provided through the wall surface of the mold, into which a sleeve pin 5 (described later) can be inserted at a portion where a large boss is to be formed.

The bottom side of the guide hole 2 (on the outer wall side of the mold 1) is formed to have a slightly larger diameter and is a threaded hole, and a forming pin 3 for forming a boss hole is erected on the surface side of the hole. For installation, the disc 4 is screwed together.

The molding pin 3 is formed into a substantially cylindrical shape, and its tip is chamfered into a hemispherical shape, and is formed so as to protrude from the inner wall surface of the mold 1 by a predetermined height.

5 is a sleeve pin formed in a cylindrical shape, and the sleeve pin 5 is fitted onto the molded pin 3 in a substantially tight state;
Moreover, its outer wall is formed so as to be able to abut along the wall surface of the guide hole 2.

Further, two bushing rods 6 shown in the figure are connected to the lower end periphery of the sleeve pin 5.

Each bushing rod 6 passes through both slide holes 7, 7 formed through the disk 4, and is fastened to a plate 9 attached to the rond end of the hydraulic cylinder 8, respectively.

Although the hydraulic cylinder 8 is normally in an extended state and holds the sleeve pin 5 in an exposed state, it is contracted at a set speed during blow molding, so that the sleeve pin 5 is slid downward in the figure along the guide hole 2 and can be inserted into the mold 1.

Note that the sleeve pin 5 is always set at a slightly lower height than the protruding height of the forming pin 3, and its stroke is adjusted so that its top is substantially flush with the inner wall surface of the mold 1 when retracted.

Next, a blow molding procedure will be explained using the molding die 1 having the above configuration.

First, a plasticized parison P is formed by heating a molding material, and compressed air is sent into the parison P inside the closed mold 1.

As a result, the parison P is strained and expanded by a substantially uniform internal pressure, and is pressed against the inner wall surface of the mold 1, thereby being deformed to follow the wall surface.

Here, the deformation situation of the parison P around the forming pin 3 will be explained in detail (see FIG. 3).

As the parison P progresses in expansion and deformation, the forming pin 3 first
The sleeve pin 5 is immediately abutted against the top of the sleeve pin 5 and attached thereto.

In the following description, the range where the parison P covers the upper surface of the sleeve pin 5 (range S shown in the figure) will be referred to as the effective range.

Thereafter, as the expansion and deformation progresses further, the parison P is transformed into a yamabushi shape with the effective range at the top.

During this deformation, since the parison P is attached to the top periphery of the sleeve pin 5, it is possible to resist the stretching force on the foot side of the parison P, and therefore the thickness in the effective range is maintained as much as possible. will be done.

Now, in the state shown in FIG. 3, the hydraulic cylinder 8 is operated to move the sleeve pin 5 backward.

However, this retraction speed is equal to or slightly lower than the deformation speed of the parison P.

When this backward movement is started, the parison P is deformed to follow this movement.

During this time, as mentioned above, the parison P is connected to the sleeve pin 5.
Since it remains attached to the top of the forming pin 3, the boss hole wall is gradually formed around the forming pin 3 in the parison P in the above range while ensuring the above effective range.

When the sleeve pin 5 is inserted into the mold 1 in this manner, the peripheral wall around the forming pin 3 is formed to have the desired thickness, as shown in FIG. 3-2.

Then, after the parison P is cooled and solidified, the mold 1 is opened and the molded product is taken out, thereby obtaining a product having boss holes with high tapping strength.

In other words, according to the method of this example, the effective range of the parison involved in forming the boss hole can be continuously secured during the blowing process, so thinning due to outward stretching can be avoided as much as possible.
Therefore, the peripheral wall of the boss hole is formed with increased thickness compared to the conventional means.

In addition, in this example, the case where the protrusion height of the sleeve pin 5 is lower than the protrusion height of the molded pin 3 was illustrated, but the case where it is high conversely may be sufficient.

Further, the backward movement of the sleeve pin 5 may be performed in two stages, for example, the sleeve pin 5 may be stopped for a predetermined period of time immediately before it is immersed into the mold 1, and then the backward movement may be performed again.

Furthermore, the timing to start retracting the sleeve pin 5 is not limited to this example, and may be performed after the parison P completes deformation around the sleeve pin 5. effect can be obtained.

As described in detail above, in the method of the present invention, when forming a boss hole in a molded product by blow molding, a forming pin for forming the boss hole is protruded in advance at a predetermined position on the forming wall surface of the mold. In addition, a sleeve pin is provided around the molding pin, and the gist is to sink the sleeve pin into the mold during blow molding.

That is, in the method of the present invention, by providing the sleeve pin around the forming pin, it is possible to secure an effective range involved in forming the peripheral wall of the boss hole, and furthermore, the sleeve pin can be used to prevent odor during blow molding. Since the blower is recessed inward, the above-mentioned effective range can be continuously ensured during the blowing process, so the peripheral wall of the boss hole to be formed can be formed thick.

Therefore, the boss hole after molding can sufficiently withstand screwing.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is an explanatory diagram explaining the blow molding method, Fig. 2 is a schematic sectional view showing an enlarged view of the periphery of the forming pin, and Fig. 3 is an illustration. 2 is an explanatory diagram showing the boss hole forming process, and FIG. 4 is an explanatory diagram showing the conventional boss hole forming situation. 1, C...Forming mold, 3,20...Forming pin, 5...Sleeve pin, 8...
Hydraulic cylinder, P...Parison.

Claims (1)

[Claims] 1. When forming a boss hole in a molded product by blow molding, a forming pin for forming the boss hole is provided in advance at a predetermined position on the forming wall surface of the molding die, and a sleeve pin is placed around the forming pin. A method for forming a boss hole in a blow molded product, characterized in that the sleeve pin is provided in advance and is immersed into the mold during blow molding.