JPS6350180B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for socket molding a porous plastic tube.

In order to increase the bending rigidity of plastic pipes without increasing the amount of pipe material used, that is, plastic, it is known to provide a large number of holes in the pipe axis direction in the pipe wall of the plastic pipe. .

In order to use this porous plastic pipe for a pipe such as a sewage pipe, it is necessary to form a socket at one end of the pipe for joining the plastic pipe.

Traditionally, plastic pipes (hereinafter referred to as
Various methods are known for forming sockets into plastic pipes (referred to as non-perforated plastic pipes), but one method is to press-fit a socket molding core into the end of a non-perforated plastic pipe under heat. There are known methods for doing so.

However, when a socket is formed on the above-mentioned porous plastic pipe by this method, the following problems arise which are not observed in the case of non-perforated plastic pipes.

First, (1) the occurrence of small wave-like irregularities as shown in FIG. 1A on the inner and outer surfaces of the socket is unavoidable. This unevenness is caused by the hoop stress τa acting on the tube wall A' in the hole portion and the tube wall B' between the holes when the tube end is expanded in diameter during socket molding, as shown in FIG. 1B. The contact pressure between the core and the inner surface of the tube end, Pa,
This is thought to be due to the fact that Pb accumulates differently depending on the hole spacing.

Next, (2) the strength of the socket changes in the circumferential direction, and there is a disadvantage that the strength of the socket in the circumferential direction cannot be guaranteed uniformly. In other words, when a plastic body undergoes flow deformation, the direction of orientation of the plastic crystals changes, and the strength also changes accordingly. There are considerable differences in the degree of flow of the wall material, resulting in the strength of the socket being different from one circumferential hole spacing to another.

The present invention provides a method for molding a socket into a porous plastic tube without the above problems (1) and (2). Foaming material is put into the hole, and then the end of the plastic tube is heated, and the inside and outside of the socket forming mold, which is made up of an inner mold and an outer mold, where the thickness of the space becomes thinner toward the tip, is formed. This method is characterized by press-fitting between molds and molding into a socket.

Hereinafter, the present invention will be described with reference to one embodiment.

In FIGS. 2A to 2C, 1 is a porous plastic pipe (for example, a vinyl chloride pipe), and the pipe wall is provided with many holes h in the pipe axis direction, as shown in FIG. ing.

Reference numeral 2 denotes a socket molding die, which is composed of an inner die 21 and an outer die 22. Although any suitable inner mold 21 can be used, the one shown in the drawing allows the segment members 212 to expand and contract in diameter by moving the tapered member 211 in the axial direction.

The thickness of the gap between the inner mold 21 and the outer mold 22, that is, the space for molding the socket, is made thinner toward the tip. The thickness of the gap at A is T, the thickness of the gap at the pocket B is 0.75 to 0.85T, and the thickness of the gap at the tip C including the packing locking part _C1 is 0.6 to 0.7T. There is.

To carry out the invention, the pores of the porous plastic tube end 10 are first filled with foam material 3, such as foamed polyurethane, as shown in FIG. 2B.
In this case, it may be filled with foamed polyurethane that has been foamed in advance, or foamed polyurethane may be injected,
This may then be foamed. Further, the filling length of the foam material is at least the length equivalent to the end of the tube formed into the socket.

As described above, the porous plastic tube end 1
After filling the foam material 3 into the holes h, h... of 0, the end of the plastic tube is heated, and the end of the heated tube is inserted into the inner and outer molds of the socket mold 2, as shown in FIG. 2C. Press fit into the gap between 21 and 22.

By this press-fitting, the foamed material 3 is compressed, and the air bubbles in the foamed material are compressed to generate pressure, and as shown in _FIG .
12 on the inner surface of the outer mold 22 and the outer surface of the inner mold 21. Therefore, this pressure _P1 varies depending on the degree of foaming of the foam material before compression, and depending on the setting of this degree of foaming, the pressure Pa in FIG.
Pb can be made equal to Pb, and it is possible to prevent the aforementioned small wave-like unevenness of the socket due to the difference between the pressure Pa and Pb.

The pressures Pa and Pb in FIG. 4 differ depending on the diameter expansion ratio of the pipe end, and increase as the diameter expansion ratio increases. Therefore, in FIG. 2C, the socket part A,
Depending on B and C, there is a difference, even if only slightly, in the pressures, and it is advantageous for the pressures to vary in accordance with this difference. However, in the above embodiment, the thickness of the space in the socket molding die is made different depending on the socket parts A, B, and C, as shown in FIG. 2C. The compressibility of the foamed material differs in the order of C, B, and A, and the above pressure Pa can be suppressed.
The above pressure Pa can be increased according to this degree of suppression,
It's advantageous.

Furthermore, in the present invention, since the end of the porous plastic tube is molded with the pores filled with foamed urethane, the flow deformation during molding is less severe than when the pores are unfilled. It can be stopped.
Therefore, the aforementioned decrease in strength of the socket can be sufficiently reduced.

According to the present invention, the foamed material can be compressed to have a porosity of almost zero at the socket tip C, and the pores of the porous pipe can be watertightly closed at the pipe socket.
Therefore, there is no need to separately perform special treatment to cut off communication between the inside of the porous pipe and the outside.

The present invention is also applicable to an oval-shaped porous plastic pipe, as shown in FIG. It can also be applied to molding. Furthermore, as shown in FIG. 6, the present invention can also be applied to the case of molding into a socket in which a rubber ring mounting groove _C0 is provided in one step of enlarged diameter portion _B0 .

As described above, according to the present invention, a socket can be formed at the end of a porous plastic pipe without the above-mentioned disadvantages (1) and (2), and it is extremely useful for molding the socket of a porous plastic pipe. .

[Brief explanation of the drawing]

Fig. 1A is an explanatory diagram showing the unevenness in a conventional socket of a porous plastic pipe, Fig. 1B is an explanatory diagram showing the pressure state generated when expanding the diameter of the socket in a porous plastic pipe, and Fig. 2A , FIG. 2B and FIG. 2C are explanatory diagrams for showing the present invention, FIG. 3 is a sectional view of FIG. 2A, and FIG. 4 shows the pressure state generated during socket molding according to the present invention. The explanatory drawings, FIG. 5A and FIG. 5B are cross-sectional explanatory views showing another example of a porous plastic pipe to which the present invention is applied, and FIG. 6 is an explanatory view showing another embodiment of the present invention. . In the figure, 1 is a porous plastic tube, h, h
... is a hole, 10 is an end of a porous plastic tube, 2 is a socket mold, 21 is an inner mold, 22 is an outer mold, and 3 is a foamed material.

Claims (1)

[Claims] 1. A foamed material is put into the hole at the end of a plastic tube that has a hole in the tube axis direction in the tube wall, and then the end of the plastic tube is heated so that the thickness of the space becomes thinner toward the tip. A method for molding a porous plastic pipe into a socket by press-fitting between the inner and outer molds of a socket-forming mold consisting of an inner mold and an outer mold.