JPH0441897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for blow molding a hollow body and an apparatus therefor.

Conventional technology In the conventional blow molding method, a parison is placed between the opened split molds, the molds are closed, and then fluid is blown into the parison to perform blow molding in a shape that follows the cavity of the split mold. I'm trying to get a body.

Problems to be Solved by the Invention In the conventional blow molding method described above, since the tip of the parison is pinched off using a split mold, a pinched off part is formed at the bottom of the hollow body, and cracks occur at this pinched off part. This may occur.

Also, when extruding the parison from the extrusion head, it is better to melt it at a high temperature in the extrusion head in order to extrude the parison without a weld line from the extrusion head.
If the temperature is high, there will be a problem that Paris will draw town.

Furthermore, with conventional blow molding methods, it is extremely difficult to control the wall thickness of the molded product, and there are methods such as changing the extrusion speed of the parison or changing the dimensions of the extrusion nozzle, but in both cases it is impossible to specifically measure the parts. It was almost impossible to accurately control the wall thickness because the adjustment was done by .

Means and Effects for Solving the Problems The present invention has been made in consideration of the above-mentioned problems, and it is possible to eliminate the pinch-off part at the bottom to eliminate cracks caused by this part, and the melting temperature in the extrusion head is high. It is possible to obtain a parison with no weld lines and no drawdown at all, and it is also possible to control the thickness of the molded object by changing the thickness of the parison easily and directly. In this method, a parison is extruded from an extrusion head, a mandrel is provided with the parison slidably on the axis of the extrusion head, and a mandrel is placed coaxially with the mandrel at a position opposite to this mandrel. The mandrel and the compression member are clamped with the tip of a movably provided compression member to form a closed part, and then, while extruding the molten resin, the mandrel and compression member are moved relative to the extrusion head in a direction in which the mandrel protrudes from the extrusion head. The parison is placed in close contact with the outer peripheral surface of the mandrel, and then the split mold surrounding the mandrel and the tip of the compression member is clamped, and a pressurized fluid is blown between the mandrel and the parison to obtain a hollow molded body. It's becoming like that.

In order to carry out the above molding method, the apparatus used includes an extrusion head for extruding the parison, a mandrel slidably provided at the axial center of the extrusion head,
A compression member whose distal end face faces the distal end face of the mandrel and is movable in the axial direction of the mandrel, and a split metal provided at a position surrounding the mandrel that protrudes from the extrusion head and the distal end of the compression member. It consists of a mold and a pressure blowing means for blowing pressurized fluid into the inside of the parison located on the outer peripheral surface of the mandrel. While extruding more molten resin, the mandrel and compression member are moved together in the direction of protruding from the extrusion head, and the parison is placed along the outer circumferential surface of the mandrel, and this parison is sandwiched between the split molds, and then from the inside of the parison. A hollow molded body is formed by blowing pressure fluid into it.

Example Embodiments of the present invention will be described based on the drawings.

In the figure, 1 is an extrusion head, and this extrusion head 1 includes a die 3 having a resin injection port 2, and an annular flow channel located inside the die 3 and communicating with the resin injection port 2 between the die 3 and the die 3. 4 and a mandrel 6 slidably fitted inside the core 5.
It is made up of. The annular flow path 4 has a tapered shape with a smaller diameter on the lower side, and its extrusion port 7 is directed toward the inside of the die 3. The mandrel 6 is configured to reciprocate from above the extrusion port 7 to below the extrusion head 1 over a predetermined length.

Reference numeral 8 denotes a compression member provided facing the lower end surface of the mandrel 6, and this compression member 8 is adapted to reciprocate in the vertical direction similarly to the mandrel 6 described above.

9 and 10 are left and right split molds located below the extrusion head 1, and 9a and 10a are cavities thereof. The upper edge diameter of the split molds 9 and 10 corresponds to the outer circumferential diameter of the mandrel 6, and the lower edge diameter corresponds to the outer circumferential diameter of the compression member 8.

A method for molding a hollow body according to the present invention using the apparatus having the above configuration will be described below.

The molten resin is extruded from the extrusion port 7 with the lower end of the mandrel 6 positioned above the extrusion port 7.
At this time, the annular flow path 4 has a tapered shape with a smaller diameter on the lower side, and the extrusion port 7 faces inside the die 3, so the parison 11 extruded from the extrusion port 7
are extruded toward the center of the mandrel 6, and the parisons 11 crowd together to close the lower end of the extrusion head 1 (FIG. 1).

Next, the compression member 8 is raised, and this compression member 8
The closed portion of the parison 11 is compressed between the upper end and the lower end of the mandrel 6 (FIG. 2). The compressed thickness at this time becomes a value close to the thickness of the bottom of the molded body.

Next, the mandrel 6 and the compression member 8 are lowered together (FIG. 3). At this time, the amount of molten resin supplied to the extrusion head 1 is controlled, and the molten resin is extruded from the extrusion port 7 in accordance with the descending speed of the mandrel 6 and the compression member 8, and as the mandrel 6 descends, it flows along the outer periphery of the mandrel 6. The thickness of the parison 11 thus formed is controlled.

With the mandrel 6 and compression member 8 lowered to a predetermined position, the split molds 9 and 10 are tightened (fourth
figure).

Then, pressure fluid is blown into the parison 11 through a fluid blowing channel (not shown) provided in the mandrel 6 to perform blow molding (FIG. 5).

In the above molding method, the lower end of the parison 11 may be closed naturally by extrusion from the extrusion port 7 at the initial stage of extrusion of the parison 11 shown in FIG. The mandrels 6 and the compression member 8 may be positioned opposite each other, and the molten resin may be extruded into the space between the mandrel 6 and the compression member 8 to close the space. Other closure means may also be used.

The inner surface of the bottom of the molded body is molded at the lower end of the mandrel 6, but by chamfering the outer periphery of the lower end of the mandrel 6, the amount of resin for the bottom corner of the molded body increases. Thinning of the corners during blow molding is prevented.

The lower edge portions of the split molds 9, 10 abut against the outer peripheral surface of the upper edge of the compression member 8, and the cavities 9a,
By making the bottom of 10a substantially coincide with the upper end of compression member 8, the parison 11 is not cut off at the bottom of the molded body, and therefore no pinch-off portion occurs in this portion.

The upper edge portions of the split molds 9 and 10 come into contact with the outer periphery of the mandrel 6, whereby the parison 11 is pinched off, and a wide-mouthed molded body whose opening diameter is the diameter of the mandrel 6 is obtained.

Since the bottom of the molded body is compression-molded between the end faces of both the mandrel 6 and the compression member 8, projections and recesses can be formed on the inner and outer surfaces of the bottom by appropriately shaping the end faces of the mandrel 6 and the compression member 8. .

Since the parison 11 is extruded along the outer circumference of the mandrel 6 and together with the mandrel 6, no drawdown occurs. In addition, by cooling or heating the inside of the parison 11 using the mandrel 6 during extrusion of the parison 11, the temperature of the parison 11 after extrusion can be controlled not only from the outside surface of the parison 11 cooled by the split mold but also by the conventional control. The inner surface of the parison 11 that could not be controlled is also controlled.

Furthermore, by changing the diameter of the mandrel 6 in the axial direction and controlling the downward movement speed of this mandrel 6 and the supply speed of the molten resin, it is possible to change the wall thickness of the parison 11 in accordance with the change in the diameter of the mandrel 6. can.

Effects of the Invention According to the present invention, it is possible to eliminate the pinch-off portion at the bottom of the molded article, and therefore, it is possible to eliminate cracks in the bottom due to the pinch-off portion. In addition, no drawdown occurs in the parison 11 extruded from the extrusion head 1, so that the melting temperature inside the extrusion head 1 can be increased, and an ideal parison 11 without weld lines can be obtained. I can do it. Furthermore, the thickness of the parison 11 can be easily and directly changed by controlling the extrusion speed of the parison 11 and the relative movement speed of the mandrel 6, or by changing the shape of the mandrel 6. This makes it possible to control the wall thickness of the molded body extremely easily.

Further, according to the present invention, the inner and outer surfaces of the bottom of the molded body can be molded using a mold, and the shape of this portion can be molded into a desired shape. Further, the temperature of the parison 11 can be easily controlled from the inside by the mandrel 6, and the temperature can be adjusted to match the molding conditions, such as making the wall thickness uniform by cooling, for example.

[Brief explanation of drawings]

1 to 5 are cross-sectional views showing the steps of the method of the present invention, and FIG. 6 is a cross-sectional view of the molding apparatus. 1 is an extrusion head, 6 is a mandrel, 8 is a compression member,
9 and 10 are split molds, and 11 is a parison.

Claims (1)

[Claims] 1 A parison 11 is extruded from an extrusion head, and a mandrel 6 is provided with the parison 11 slidably provided on the axis of the extrusion head 1, and a mandrel 6 is provided coaxially with the mandrel 6 at a position facing the mandrel 6. A closed part is formed by clamping the movable compression member 8 with the tip thereof, and then, while extruding the molten resin, the mandrel 6 and the compression member 8 are moved against the extrusion head 1, and the mandrel 6 protrudes from the extrusion head. The parison 11 is placed in close contact with the outer peripheral surface of the mandrel 6 by relatively moving in the direction, and then the split molds 9 and 10 surrounding the mandrel 6 and the tip of the compression member 8 are clamped, and pressure is applied to the inside of the parison 11. A method for blow molding a hollow body, characterized by blowing fluid into it. 2. An extrusion head 1 for extruding the parison 11, and a mandrel 6 slidably provided at the axial center of the extrusion head 1.
and a compression member 8 whose distal end face faces the distal end face of the mandrel 6 and is movable in the axial direction of the mandrel 6, and a compression member 8 that protrudes from the extrusion head and surrounds the distal end of the mandrel 6 and the compression member 8. A blow molding apparatus for a hollow body, characterized in that it is comprised of split molds 9 and 10 provided at positions to do so, and pressure blowing means for blowing pressurized fluid into the inside of a parison 11 located on the outer peripheral surface of a mandrel 6.