JP3468607B2 - Rib forming method in rotational molding - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] FIELD OF THE INVENTION This invention relates to a hollow container 1 is manufactured by rotational molding as shown in FIG. 9, the reinforcing ribs 2 and hollow on its outer surface all around It is an object of the present invention to provide a method for forming a fixing rib 3 for fixing the container 1 (the protrusions are collectively referred to as ribs in this specification). 2. Description of the Related Art The rotary molding method will first be briefly described with reference to FIG. 10, which schematically shows an example of a rotary molding machine. The mold 4, which is a split mold, includes hollow shafts 5, 6, which are bent and connected in a crank shape.
7 is rotatably supported by a hollow shaft 5 around a rotation shaft 8. This rotating shaft 8 is composed of bevel gears 9, 10 and shaft 1.
1, driven by a drive gear 16 via sprockets 12 and 13, a chain 14 and a shaft 15 to rotate (rotate) the mold 4. The hollow shaft 7 is rotated by a drive gear 17, whereby the mold 4 supported by the hollow shaft 5 rotates (revolves) around the hollow shaft 7. 18 is the mold 4,
These are balance weights for the hollow shafts 5, 6, and the like. The mold 4, the hollow shafts 5 and 6, the balance weight 18, etc.
And rotate in the furnace. Polyethylene in the mold 4, polyphenylene sulfide, polyether ether ketone, and sealed putting powder of thermoplastic resin such as fluorine resin, rotation of the mold 4 while being heated in the furnace 19, the revolving, molten material Since the resin spreads in layers on the inner surface of the mold 4, the inside of the furnace 19 is cooled while the mold 4 rotates and revolves, the material is solidified, and the mold 4 is opened to take out the molded hollow container. When the hollow container 1 having the reinforcing ribs 2 shown in FIG. 9 is molded by a rotational molding method, for example, a deep recess is formed in the inner surface of the reinforcing ribs 2 as shown in FIG. 20 are formed. This is because the filling of the rib portion with the molten powder resin is not performed sufficiently, resulting in a hollow state. When such a concave portion 20 occurs, if the liquid in the contents deteriorates during use, even if the entire liquid is discharged to clean the inner surface of the container, the liquid contained in the concave portion 20 is not discharged. And will be soiled when new liquid is added. Also, the strength of the container near the ribs is reduced. [0005] A similar concave portion is also formed in the portion of the fixing rib 3 to weaken the strength of the container near the rib. For this reason, conventionally, as shown in FIG. 12, a nut 21 is buried in the hollow container 1 at the time of molding, and after molding, the angle member 22 is attached to the container with bolts 23, so that a complicated and costly means is taken. I was A rib forming method in rotary molding according to the present invention is characterized in that a solid rib material of the same material as that of a container previously formed into a rib shape is sandwiched by a mold, and an outer periphery is formed by a pressing member. This is a method of forming a rib by performing rotary molding while suppressing the pressure, and fusing the container body and the rib material into the same body. The solid rib material sandwiched between the two flanges provided on the mold is melted at the time of rotational molding and has a layered inner end covered with powdery resin for a container which spreads on the inner surface of the mold. The rib material itself is also melted and fused with the resin for the container to be integrated, thereby preventing the inside of the rib from becoming hollow. The molten rib material is prevented from flowing out between the flanges by the restraining member. FIG. 1 to FIG. 5 show a first embodiment of the present invention in which a reinforcing rib is formed all around the outer surface of a container. The method of this embodiment is performed as follows. First Step This step is a preparation step before heating. As shown in FIG. 1 (a cross-sectional view of a rib forming portion of a mold) and FIG.
Flanges 4a, 4 provided on the mold 4 divided by the rib forming portion
b, a solid annular rib member 2a formed of a resin of the same material as the container is sandwiched therebetween, and the outer end thereof is surrounded by an annular restraining member 24,
A bolt 25 is inserted through the flanges 4a and 4b and the holding member 24 and lightly tightened. The inner end of the rib member 2a is slightly projected into the mold, leaving a gap g between the holding member 24 and the flange 4a. [0010] The second step bolt 25 is tightened, and the holding member 2 is fixed by the flanges 4a and 4b.
3, the gaps g are eliminated and the flanges 4a, 4b and the rib material 2a are brought into close contact with each other as shown in FIG. 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 a third step described later, and also prevents the surface of the rib material 2a from melting in the third step. Is directed to the inner end of the rib material 2a . Gap g
Is small, the gap g can be easily eliminated by compressive deformation of the holding member 24. The rib material 2a is made thicker by g than the rib at the time of completion. Third Step A powdered thermoplastic resin as a container material is charged into the mold 4, and the mold 4 is heated and rotated in a furnace to melt the powdered container material. As shown in FIG. 4, the molten thermoplastic resin 2
Numeral 6 spreads in a layer form on the inner surface of the mold 4 and also covers the end of the rib material 2a slightly projecting into the mold 4 . The surface of the rib material 2a also slightly melts. As the heating in the fourth step proceeds, the inner end and part of the side surface of the rib material 2a are melted, and as shown in FIG. 5, the thermoplastic resin 26 of the container material and the inner end of the rib material 2a Melt and mix. At this time, the rib material 2a whose upper and lower surfaces are melted causes the melted portion to flow toward the inner end of the rib material by the compressive stress generated in the second step, thereby strengthening the fusion between the resin material for the container and the rib material. Most of the rib material 2a does not flow but is in a softened state. The heating in the fifth step furnace is stopped, and the mold 4 is cooled while rotating. The rib material 2a is solidified while being connected to the container wall as shown in FIG. 5, and a container having ribs is hollow-molded. In the above embodiment, the reason why the inner end of the rib material 2a is slightly projected into the mold 4 is that the vicinity of the inner end is melted by heating and a concave portion is formed by shrinkage upon cooling. This is to make up for this. Therefore, the degree of protrusion is determined in consideration of the physical properties of the rib material, the heating temperature, the shape and dimensions of the rib, and the like. That is, the end face of the rib material 2a is
4 , the rib material is partially melted during heating, and the rib material shrinks more during cooling than the container wall alone, resulting in a shallow recess 20a as shown in FIG. is there. One of the molding conditions in this embodiment is as shown in the following table. [Table 1] Since the gap g is for preventing the inner end of the rib material from being dented at the time of solidification, the gap g is adjusted by adjusting the protrusion amount of the inner end of the rib material provided for the same purpose. It can be omitted. In order to form the container fixing rib according to the present invention, as shown in FIG. 7 (a sectional view similar to FIG. 3) and FIG. The bottom plate 4c of FIG. 4 is divided, and a fixing rib 2b and a groove 27 for tightly holding the holding member 24a are formed in a part of a flange 4d provided for connecting the bottom plate 4c. (1) Since the ribs are formed simultaneously during the rotational molding of the hollow container, the container can be molded efficiently. (2) No recess is formed at the inner end of the rib. (3) Since the concave portion is not formed, the liquid does not remain when the deteriorated content liquid is discharged and the new liquid is not contaminated. (4) The strength of the inner end of the rib is prevented from being impaired due to the recess.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a mold rib holding portion according to an embodiment of the present invention. FIG. 2 is a view taken in the direction of arrow a in FIG. 1; FIG. 3 is a sectional view of the flange portion of FIG. 1 showing a first step of the 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 a third step. FIG. 6 is a sectional view similar to FIG. 5, showing a shallow concave portion of a rib portion formed when the rib material is not projected inward; FIG. 7 is a sectional view similar to FIG. 3 for forming a fixing rib; FIG. 8 is a view taken in the direction of the arrow b in FIG. 7; FIG. 9 is a perspective view of a hollow container having a rib. FIG. 10 is a sectional view illustrating the configuration of a rotary molding machine. FIG. 11 is a 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 cross-sectional view taken along the line BB of FIG. 9 showing a conventional example for forming a container fixing rib. [Description of Signs] 1 hollow container 2 reinforcing ribs 2a, 2b rib material 3 fixing rib 4 mold 4a, 4b flange 4c bottom plate 4d flanges 5, 6, 7 hollow shaft 8 rotating shaft 9, 10 bevel gear 11 shaft 12 , 13 Sprocket 14 Chain 15 Shaft 16, 17 Drive gear 18 Balance weight 19 Furnace 20, 20 a Recess 21 Nut 22 Angle material 23 Bolt 24, 24 a Holding material 25 Bolt 26 Thermoplastic resin of container material 27 Groove g Gap

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 41/00-41/52

Claims (1)

(57) [Claims] [Claim 1] The powder thermoplastic resin is put into a mold, and the mold is rotated and revolved in a furnace to form a hollow container. A method of forming ribs on an outer surface, wherein a solid rib material formed of resin of the same material as a container is protruded into two flanges provided in advance in a mold, and a part of an inner end is projected into the mold. A rib forming method in rotary molding, characterized in that the outer periphery of the rib material is held down by a holding member tightly held between the two flanges.