JPH0796236B2 - Rotational molding and molds used in rotational molding - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid container having a relatively large volume such as a tank truck,
The present invention relates to a rotational molding method of a hollow resin molding having a protrusion such as a flange on the outer periphery, and a mold used in the rotational molding method.

[0002]

2. Description of the Related Art A rotational molding method is known as a method for molding a hollow resin molded body such as a liquid container having a large volume. The rotational molding method is a method in which a powdered resin is put in a mold, the mold is rotated and heated, the molten resin is attached to the inner wall of the mold, and the resin is cooled to solidify the resin to obtain a molded body.

FIG. 3 shows an example of a container of a resin molded body manufactured by the rotational molding method. This container 1 has a flange portion 5 protruding from the container body 3 to the outer periphery. The flange portion 5 is provided with a bolt hole 14a for screwing with another component (not shown) such as a lid. Conventionally,
Such a container was formed by a split mold 2.4 as shown in FIG. One of the split molds 2 and 4 is a cylindrical concave mold corresponding to the main body 3 and the flange portion 5 of the container 1, and the other mold 4 is a flat mold corresponding to the upper surface of the container 1. . A bolt 15 and a nut 16 can fix between the cylindrical concave mold 2 and the flat plate mold 4. Further, the rod body 14 penetrates between the cylindrical concave mold 2 and the flat plate mold 4 at a position corresponding to the bolt hole 14 a of the flange portion 5 of the container 1.

The split molds 2 and 4 are broken and opened, and thermoplastic resin powder, for example, polyethylene or polypropylene powder is put therein and then closed. Split mold containing resin powder 2.
4 is heated vertically and horizontally (see the rotation arrow in FIG. 4). As a heating method, there are a method of directly heating with a burner and a method of providing a heating chamber and raising the temperature of the entire chamber with hot air. The split mold 2 in which the molten resin 19 is heated by it
* Gradually adhere to the inner surface of 4. A concave portion 21 (corresponding to the flange portion 5) formed between the cylindrical concave mold 2 which is one of the split molds 2 and 4 and the flat plate-shaped mold 4 which is the other mold.
Then, the resin 20 is laminated. When the melting and adhesion are finished, the heating is stopped and cooled, the split molds 2 and 4 are opened, and the resin molding inside is taken out. This resin molded body is hollow and the outer periphery is closed, and the container 1 shown in FIG. 3 is completed by opening the opening as a container by machining.

[0005]

In the container 1 molded by the conventional method using the conventional split mold described above, the flange portion 5 is used.
Cavities 6 were often formed inside the. In particular, it tends to occur around the bolt holes 14a. Therefore, there is a problem that liquid leakage occurs from the bolt hole 14a through the cavity 6. In addition, when the residue in the container 1 is washed, there are problems that it is easy to leave an unwashed residue inside the cavity 6 and the compression strength of the flange portion 5 is weak.

The present invention has been made in order to solve the above-mentioned problems, and is a rotational molding method in which a hollow resin molding having a protrusion on its outer periphery can be molded without leaving a cavity in the protrusion, and its rotation. It is intended to provide a mold used in a molding method.

[0007]

The rotational molding method of the present invention made to achieve the above object will be described below with reference to FIG. 1 which corresponds to an embodiment.

As shown in the figure, the rotational molding method of the present invention is
Put the resin material into the split mold 7.8,
In the rotational molding method, in which the resin is heated to rotate and the molten resin is adhered to the inner wall thereof, and then the resin is cooled to solidify to obtain a hollow resin molded body, a resin molded body having a protrusion on the outer periphery is molded. At this time, after the resin 19 melted as described above is adhered and before cooling, the protrusions retained in the concave portion 21 at the meeting position between the one mold 7 and the other mold 8 of the split molds 7 and 8. Split mold 7 for molten resin 20 corresponding to
· 8 is compressed from either type of characterized by degassing.

Similarly, as shown in FIG. 1, the mold used in the rotational molding method of the present invention rotates while heating the resin material charged inside, and cools and solidifies the molten resin adhering to the inner wall to form a hollow. Split mold 7 for obtaining resin molded products
8 is characterized in that one mold of the split molds 7 and 8 is slidably fitted to the other mold at a position corresponding to the outer peripheral projection of the resin molded body.

[0010]

[Function] The split molds 7 and 8 are split and opened, and the resin material is put into the interior and then closed. When the split molds 7 and 8 containing the resin powder are heated while being rotated in the vertical and horizontal directions, the molten resin 19 is gradually attached to the inner surface of the split molds 7 and 8 and laminated. The molten resin 20 is also laminated on the concave portion 21 (corresponding to the protrusion on the outer periphery, for example, corresponding to the flange portion 5 in FIG. 3) at the position where the one mold 7 and the other mold 8 of the split molds 7 and 8 meet. go. Here, the concave portion 21 is formed by the mold 8.
The molten resin 20 staying at is compressed. The bubbles in the molten resin 20 in the recess 21 are pushed out by the compression. After that, heating is terminated and cooled, the split molds 7 and 8 are opened, and the resin molding 1 (see FIG. 3) inside is taken out.

Thus, the molten resin 20 in the recess 21 is formed by the mold 8.
Since the air bubbles are extruded by compressing the
There is no cavity in the protrusion (for example, the flange portion 5 in FIG. 3) on the outer periphery of the.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. The embodiment shown here is the container 1 shown in FIG.
Is an example of molding by using a mold to which the present invention is applied by a rotational molding method to which the present invention is applied. Since the structure of the container 1 has already been described, the description thereof will be omitted.

FIG. 1 is a sectional view showing a state in the middle of molding by the rotational molding method of the present invention. Split mold used 7
Reference numeral 8 denotes a cylindrical concave mold 7 corresponding to the main body 3 and the flange portion 5 of the container 1, and a sliding disk 8 slidably fitted therein.
have. The sliding disk 8 includes a screw rod 10 and a guide rod 18.
Is connected to the frame 9. Threaded rod 10 having one end in the center of the upper surface of Suridoenban 8 is pivotally supported is screwed into hard 9, the upper end is connected to the handle 11. A guide rod 18 planted in the sliding disk 8 penetrates the frame 9, and the guide ring 18 sandwiches the frame 9 so that the sliding disk 8 slides at a distance to slide the stop ring. 12 and stop ring 13
Is installed. The cylindrical concave mold 7 is fixed to the frame 9 with bolts 15 and nuts 16, and the cylindrical concave mold 7 and the sliding disk 8 (the split molds 7 and 8) fitted therein form a cavity space. There is.

The nut 16 is removed from the bolt 15, the sliding disk 8 is removed from the cylindrical concave mold 7, and a calculated amount of resin powder raw material Neozex 2540R (made by Mitsui Nisseki Polymer Co., Ltd.) is put therein. Fit the sliding disk 8 and tighten the bolt 15 and nut 16. At this time, the sliding disk 8 is retracted by the screw rod 10 until the stop ring 13 hits the frame 9 (state of FIG. 1), and a recess formed between the cylindrical concave mold 7 and the sliding disk 8 is formed. 21 (corresponding to the flange portion 5 of the container 1) has a dimension A of 4
It is 0 mm. Rotate the split molds 7 and 8 containing resin powder in the cavity space vertically and horizontally (see the rotation arrow in Fig. 1).
While heating, the mold surface temperature is heated to 200 ° C. for 30 minutes by direct flame of propane gas (not shown). As a result, the molten resin 19 gradually adheres to the inner surfaces of the split molds 7 and 8. The resin 20 is also laminated on the concave portion 21 (corresponding to the flange portion 5). The rotation and heating are terminated when the melt adhesion is completed.

Before cooling, the handle 11 is rotated and the sliding disk 8 is advanced by the screw rod 10 until the stop ring 12 hits the frame 9, and the recess dimension A (40) before sliding is obtained.
mm) from the position B (2)
4 mm). The sliding distance is 16 mm.
As the sliding disk 8 advances, the molten resin 20 staying in the recess 21 is compressed, and the bubbles mixed in the molten resin 20 in the recess 21 are pushed out. Then, it is naturally cooled for 30 minutes, further cooled with water spray at 30 ° C. for 6 minutes, the nut 16 is removed, and the sliding disk 8 together with the frame 9 is removed from the cylindrical concave mold 7 to take out the resin molded body. . This resin molded body is hollow and the outer periphery is closed, and the container 1 shown in FIG. 3 is completed by opening the opening as a container by machining.

In the container 1 obtained in the above-mentioned embodiment, the wall thickness of the flange portion 5 was 24 mm, and there was no cavity around the bolt hole 14a. In the embodiment, the molten resin 20 of the flange portion 5 is 1 / 1.6 when molded.
Compressed to 7. This compression ratio is 1 / 1.5 to 1/2
The degree is preferred.

[0017]

As described above in detail, the hollow container formed by the rotational molding method of the present invention and the split mold thereof and having a protrusion such as a flange on the outer periphery does not leave a cavity in the flange. Therefore, there is no deformation of the flange, there is no liquid leakage from the bolt hole in the flange, the inside of the container can be completely cleaned, and the wall thickness of only the protrusion such as the flange is The strength can be improved by making the thickness of the container main body 2 to 3 times.

[Brief description of drawings]

FIG. 1 is a sectional view showing a state in the middle of a molding process according to an embodiment of a rotational molding method to which the present invention is applied.

FIG. 2 is a cross-sectional view showing another state of the molding process according to the embodiment.

FIG. 3 is an external perspective view of a container molded by a rotational molding method.

FIG. 4 is a schematic view showing a state in the middle of molding by a conventional rotational molding method.

[Explanation of symbols]

1 is a container, 2 and 7 are cylindrical concave type, 3 is a container body, 4 is a flat plate type, 5 is a flange part, 6 is a cavity, 8 is a sliding disk, 9
Is a frame, 10 is a threaded rod, 11 is a handle, 12 and 13 are stop rings, 14 is a rod, 14a is a bolt hole,
5 is a bolt, 16 is a nut, 18 is a guide rod, 19 is a molten resin of the container body, 20 is a molten resin of the flange portion, 21 is a concave portion, A is the inner size of the concave portion before sliding, B is after sliding. It is the inner size of the recess.

Claims (2)

[Claims] 1. A resin material is put into a split mold, the split mold is heated while being rotated, and molten resin is adhered to the inner wall of the split mold, followed by cooling to solidify the resin to form a hollow resin molded body. In the rotational molding method to obtain, when molding a resin molded body having a protrusion on the outer periphery, after the molten resin is adhered as described above and before cooling, the association of one mold of the split mold with the other mold. rotational molding of projecting to the molten resin corresponding to the raised portion, characterized in that degassing is compressed from one type of該割Ri type remaining in the recess at the position. 2. A rotation molding split mold for rotating a resin material charged inside while rotating to solidify a molten resin adhering to an inner wall thereof to obtain a hollow resin molded body, the outer periphery of the resin molded body. A mold used in a rotational molding method, wherein one mold of a split mold is slidably fitted to the other mold at a position corresponding to a protrusion.