JPS5850861B2 - 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 boss holes in blow-molded products.

BACKGROUND ART Blow molding is conventionally known as a molding method for manufacturing resin molded products such as synthetic resins.

Blow molding, as is generally known, involves preforming a tubular or bag-like object called a parison P using plasticized material, and then drawing it into a closed mold C before cooling and solidifying it. 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 a desired product.

(See Figure 1) Now, when forming a tapping boss hole in a product by this blow molding, a forming pin 20 is provided protrudingly at a predetermined portion of the forming die C (third
(See figure A, mouth).

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

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.

First, this boxed portion will be involved in forming the boss hole, and the thinning of the part of the corner around the base of the forming pin 20 will be particularly significant due to the filling of this corner. .

That is, in the method of forming a boss hole by simply erecting a single forming pin 20, the area involved in forming the boss hole of the parison P, which is determined at the initial stage of blowing, is narrow.

It is difficult to avoid the phenomenon of thinning of the wall, which results in a situation where it is easily destroyed when screwed.

The present invention has been devised in view of the above, and its purpose is to provide a molding method suitable for forming boss holes by 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 fitted in the forming die, and parts not particularly explained follow the normal blow molding method. shall be.

Referring to the drawings, reference numeral 1 denotes a molding die, and numeral 2 denotes a substantially cylindrical molding pin protruding from a predetermined portion of the inner wall surface of the mold 1.

Reference numeral 4.4 indicates an appropriate number of auxiliary slide pins disposed near the molding pin 2, and the rear end side thereof is connected to a slide mechanism (for example, a hydraulic cylinder, etc.) not shown, so that the mold 1
It is said that it is possible to appear.

In this example, the auxiliary slide pins 4, 4 are always projected slightly lower than the forming pin 2, and are set to be retracted into the wall of the mold 1 at a predetermined speed during blow molding.

Hereinafter, a description will be given of a molding operation performed using the molding die 1 formed as described above and according to the procedure of a normal blow molding method.

1. First, a plasticized parison P is formed by heating the molding material, and the parison P is formed in the closed mold 1.
Compressed air is sent into the interior by an air supply device (not shown).

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

Here, the deformation situation of the parison P around the forming pin 2 will be explained in detail (see FIG. 2).

As the parison P progresses in expansion and deformation, the forming pins 1 and 2
It is brought into contact with the top of the auxiliary slide pin 4 after being deformed into a mountain shape with this as the top.

At this time, since the parison P is held in contact with the auxiliary slide pin 4 immediately after contacting the forming pin 2, the area surrounded by the auxiliary slide pin 4 (range S in the figure, hereinafter referred to as the effective range) ).

Almost no tensile force (stretching force) is applied to.

Then, when the parison P comes into contact with the auxiliary slide pin 4 in the opening of FIG. 2, the button is pressed and the auxiliary slide pin 4 starts to retreat.

Note that this retreat speed is slower than the deformation speed of the parison P.

As the expansion and deformation of this parison 11 and the parison P further progresses, the parison P is deformed while being attached to the top of the slide pin 4, almost following the retreat of the auxiliary slide pin 4.

First, the effective range of the parison P is deformed while being constantly raised and held by the auxiliary slide pin 4, so that almost no stretching force is applied to the effective range of the parison P, and its volume is almost maintained. The transformation will proceed in this state.

Thus, when the auxiliary slide pin 4 is inserted into the mold 1, as shown in FIG. be done.

This is because, as described above, the formation of the boss hole peripheral wall involves an effective range that maintains approximately the wall thickness at the initial stage of deformation.

After the above steps are completed and the parison P is cooled and solidified, the mold 1 is opened and the product is taken out.

The product taken out in this manner has a boss hole with high tapping strength without leaving any traces of the auxiliary slide pin 4 being removed.

button, in this example, compared to the molded pin 2, the auxiliary slide pin 4
Although the case where the protrusion height is low is illustrated, the protrusion height may be high.

Further, the backward movement of the auxiliary slide pin 4 may be performed in two stages, for example, immediately before it is immersed into the mold 1, it is stopped for a predetermined period of time, and then the backward movement is performed again. Regarding the retraction timing, it may be performed immediately before the deformation of the parison P is completed, and even in these types of collapse, the same effect as this example can be obtained.

As described in detail above, the present invention provides a method in which, 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 molding wall surface of the mold. In addition, a convex portion for guiding the parison is arranged around the boss hole near the forming pin, and the convex portion is scratched during blow molding to cause the parison to exit into the mold. It is.

In other words, the present invention secures the effective range of the parison involved in forming the boss hole by forming the convex portion particularly near the forming pin, and furthermore, the convex portion is used as the mold as the parison expands and deforms. Since the parison is immersed inward, the stretching force applied during deformation of the parison can be reduced as much as possible, and the above-mentioned effective range can be maintained in the inner thickness state.

Therefore, the peripheral wall of the boss hole to be formed has a thick wall and can sufficiently withstand screwing.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is an explanatory diagram of the blow molding method, FIG. 2 is an explanatory diagram of the main parts of the blow molding process of this example, and FIG. A2 is an explanatory diagram showing a boss hole forming method using conventional blow molding. 1, C...Forming mold, 2,20...Forming pin, 4...Auxiliary slide pin, 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 protrudingly at a predetermined position on the forming wall surface to be buttoned in a given forming mold, and a molding pin is placed in the vicinity of the forming pin. A method for forming a boss hole in a blow-molded product, characterized in that a convex portion for guiding a parison is arranged around the boss hole, and the convex portion is caused to retreat into the mold during blow molding.