JPH08238637A - Rib forming method in rotary mold - Google Patents

Abstract

PURPOSE: To simultaneously form a rib to the outer peripheral surface of a hollow container when the container is produced by a rotary mold. CONSTITUTION: A solid rib material 2a having the same material quality as a container is preliminarily produced. The rib material 2a and the press material 24 surrounding the outer periphery thereof are firmly held between two flanges 4a, 4b of a mold 4 and the inner end of the rib material 2a is allowed to slightly protrude into the mold 4 to be exposed. In this state, the rotary molding of the container is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow container 1 manufactured by rotational molding as shown in FIG. 9, in which a reinforcing rib 2 and a fixing rib 3 for fixing the container 1 on the entire outer peripheral surface thereof.
(In this specification, these protrusions are collectively referred to as ribs)
It is intended to provide a method of forming.

[0002]

2. Description of the Related Art First, a rotational molding method will be briefly described with reference to FIG. 10 which schematically shows an example of a rotational molding machine. The mold 4 which is a split mold includes hollow shafts 5 and 6, which are bent and connected in a crank shape.
A hollow shaft 5 of the shafts 7 is rotatably supported around a rotary shaft 8. The shaft 8 is driven by the drive gear 16 via the bevel gears 9, 10, the shaft 11, the sprockets 12, 13, the chain 14, and the shaft 15 to rotate (rotate) the die 4.
The hollow shaft 7 is rotated by the drive gear 17, whereby the mold 4 supported by the hollow shaft 5 rotates (revolves) about the hollow shaft 7. 18 is a mold 4, hollow shafts 5 and 6
It is a balance weight for the like. The mold 4, the hollow shafts 5 and 6, the balance weight 18 and the like are inserted into the furnace 19 and rotate in the furnace. Powder of thermoplastic resin such as polyethylene, polyphenylene sulfide, polyether ether ketone, and fluororesin is placed in a mold and sealed, and the furnace 1
When the die is rotated and revolved while being heated in 9, the molten material resin spreads in layers on the inner surface of the die. Therefore, while rotating and revolving the die, the inside of the furnace 19 is cooled to solidify the material, Open 4 and take out the molded hollow container.

[0003]

When the container 1 having the ribs 2 shown in FIG. 9 is molded by the hollow molding method, for example, as shown in FIG.
As shown in, the deep recess 20 is formed on the inner surface of the rib 2. This is because the molten powder resin is not sufficiently filled in the rib portion, resulting in a hollow state.

When such a concave portion 20 is formed, when the liquid of the contents is deteriorated during use, the liquid contained in the concave portion 20 is not discharged even if all the liquid is discharged to clean the inner surface of the container. Will remain and will be contaminated when new liquid is added. It also weakens the strength of the container near the ribs.

Similar recesses are formed in the fixing ribs 3 to weaken the strength of the container near the ribs. Therefore, conventionally, as shown in FIG. 12, the nut 2 is attached to the container 1 during molding.
1 is embedded, and the angle member 22 is bolted 2 after molding.
A complicated and costly means such as attaching to a container in No. 3 was taken.

[0006]

According to the method of forming ribs in the rotational molding of the present invention, a solid rib material of the same material as the container formed in advance in the shape of the rib is sandwiched by the mold and the outer periphery is suppressed by the restraining material. It is a method of forming ribs by performing rotational molding in a state and fusing the container body and the rib material together.

[0007]

The solid rib material sandwiched between the two flanges provided in the mold has its inner end layer-covered with the powder resin for the container that melts during the rotational molding and spreads on the inner surface of the mold, and the rib material itself. Also melts and fuses with the resin for the container to become one, and it is possible to prevent the inside of the rib from becoming hollow. The molten rib material is prevented from flowing out between the flanges by the restraining member.

[0008]

1 to 5 show a first embodiment of the present invention in which a reinforcing rib is formed on the entire outer surface of a container. The method of this embodiment is performed as follows.

First Step This step is a preparatory step before heating. As shown in FIG. 1 (a cross-sectional view of the rib forming portion of the mold) and FIG. 2 (a view in the direction of arrow a in FIG. 1),
Flange 4a, 4 provided on the mold 4 divided at the rib forming portion
A solid ring-shaped rib member 2a made of resin of the same material as the container 1 is sandwiched between b, the outer end of the rib member 2a is surrounded by a ring-shaped holding member 24, and bolts 25 are inserted into the flanges 4a, 4b and the holding member 24. Lightly tighten. The inner end of the rib material 2a is slightly projected into the mold, and a gap g is left between the restraining material 24 and the flange 4a.

Second step: Tighten the bolt 25 and press the flange 2 with the flanges 4a and 4b.
4 is compressed, the gap g is eliminated as shown in FIG. 3, and the flanges 4a and 4b and the rib material 2a are brought into close contact with each other. This step prevents the molten resin from leaking from between the flanges 4a and 4b even if a part of the rib material 2a is melted in the third step, which will be described later. This is because the resin is directed toward the inner end of the rib material. Since the gap g is small, the gap g can be easily eliminated by the compressive deformation of the restraining member 24. The rib material 2a is thicker than the rib when finished by g.

Third step A powdery thermoplastic resin as a container material is put into the mold 4, and the mold is heated and rotated in a furnace to melt the powdered container material.
As shown in FIG. 4, the melted thermoplastic resin 26 of the container material spreads in layers on the inner surface of the mold 4, and covers the end portion of the rib material 2a slightly protruding into the mold. The surface portion of the rib material 2a also slightly melts.

Fourth Step As the heating progresses, the inner end portion and part of the side surface of the rib material 2a are melted, and as shown in FIG. To do. At this time, the rib material 2a whose upper and lower surfaces are melted causes the melted portion to flow toward the inner end portion of the rib material due to the compressive stress generated in the second step, thereby strengthening the fusion of the container material resin and the rib material. Most of the rib material 2a does not flow but is in a softened state.

Fifth Step: Heating by the furnace is stopped, and the mold is cooled while rotating. As shown in FIG. 5, the rib material 2a is solidified while being integrally bonded to the container wall, and the container having the rib is hollow-molded.

In the above-mentioned embodiment, the inner end of the rib material 2a is slightly projected into the mold because the vicinity of the inner end is also melted by heating and a recess is formed due to shrinkage during cooling.
This is to make up for this. Therefore, the physical properties of the rib material,
The degree of protrusion is determined in consideration of the heating temperature, the shape and size of the rib, and the like. That is, if the end surface of the rib material 2a is aligned with the inner surface of the mold, the rib material also partially melts during heating,
This is because the shrinkage of the rib material becomes larger than that of only the container wall during cooling, resulting in a shallow recess 20a as shown in FIG.

One of the molding conditions in this embodiment is as shown in the following table.

[0016]

[Table 1]

Since the gap g is to prevent the inner end of the rib material from being recessed during solidification, the amount of protrusion of the inner end of the rib material, which is provided for the same purpose, is adjusted to adjust the gap g. It can be omitted.

In order to form the container fixing rib according to the present invention, as in the second embodiment shown in FIG. 7 (a sectional view similar to FIG. 3) and FIG. This is done by dividing the bottom plate 4c of No. 4 and forming a groove portion 27 that tightly holds the fixing rib member 2b and the holding member 24a in a part of the flange 4d provided for connecting the bottom plate 4c.

[0019]

EFFECTS OF THE INVENTION (1) Since ribs are simultaneously formed during rotational molding of a hollow container, container molding can be performed efficiently.

(2) No recess is formed at the inner end of the rib.

(3) Since the concave portion is not formed, when the deteriorated content liquid is discharged, the liquid does not remain and the new liquid is not contaminated.

(4) The recess prevents the strength of the inner end of the rib from being impaired.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a die rib material sandwiching portion showing an embodiment of the present invention.

FIG. 2 is a view on arrow a of FIG.

FIG. 3 is a sectional view of the flange portion of FIG. 1 showing a first step of this embodiment.

FIG. 4 is a sectional view of the same portion showing a second step.

FIG. 5 is a sectional view of the same portion showing the third step.

FIG. 6 is a cross-sectional view similar to FIG. 5, showing shallow recesses in the rib portion formed when the rib material is not projected inward.

7 is a cross-sectional view similar to FIG. 3 for forming a fixing rib.

FIG. 8 is a view on arrow b of FIG.

FIG. 9 is a perspective view of a hollow container having a rib.

FIG. 10 is a cross-sectional view illustrating the configuration of a rotary molding machine.

11 is a cross-sectional view taken along the line AA of FIG. 9 showing a concave portion formed in a rib portion formed by a conventional method.

FIG. 12 is a sectional view taken along line BB in FIG. 9 showing a conventional example for forming a container fixing rib.

[Explanation of symbols]

 1 Hollow Container 2 Reinforcing Ribs 2a, 2b Rib Material 3 Fixing Ribs 4 Molds 4a, 4b Flange 4c Bottom Plate 4d Flange 5, 6, 7 Hollow Shaft 8 Rotating Shaft 9, 10 Bevel Gear 11 Shaft 12, 13 Sprocket 14 Chain 15 shafts 16 and 17 drive gears 18 balance weights 19 furnaces 20 and 20a recesses 21 nuts 22 angle materials 23 bolts 24 and 24a restraining materials 25 bolts 26 thermoplastic resin 27 container material groove g gap

Claims (1)

[Claims] 1. A method of forming ribs on the outer surface of a container at the same time as molding the container by putting the powdered thermoplastic resin in a mold and rotating and revolving the mold in a furnace to mold a hollow container by rotational molding. Then, a solid rib material made of resin of the same material as that of the container is sandwiched between two flanges provided in advance in the mold with part of the inner end protruding into the mold, and the outer periphery of the rib material is A method for forming ribs in rotational molding, which is characterized in that it is held by a holding member that is tightly held by the two flanges.