JPS631176B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a socket at the end of a perforated plastic tube having multiple axial holes in the tube wall.

In plastic pipes, it has been proposed to provide a large number of axial holes in the pipe wall in order to increase the bending stiffness (EI) of the pipe without increasing the amount of material, i.e. plastic, used.

Regarding the manufacturing method of this porous plastic tube, there are many matters related to know-how, but the physical properties of the plastic tube, such as surface condition, crystalline state, and tensile strength, are comparable to ordinary plastic tubes without holes. The manufacturing technology is almost established.

Porous plastic pipes are mainly used for pipelines because of their high bending rigidity, and in these plastic pipes it is necessary to form a pipe socket at the end of the pipe.

A commonly used method for forming a pipe socket at the end of a plastic tube is to heat the end of the plastic pipe and press-fit a core for molding the socket under this heating. In addition, a socket having a groove for attaching a rubber ring is generally used, and the pipes are connected via the rubber ring.

By the way, pressure water leakage tests were conducted on the pipe joints of porous plastic pipes with sockets molded using the socket molding method described above, and the pipe joints of non-perforated plastic pipes with sockets molded using the socket molding method described above. When doing so, the former often yields slightly inferior results, even if the difference is small.

The cause of this may be the smoothness of the inner surface of the socket, but in the case of the above-mentioned socket forming method, the inner surface of the socket should be regulated by the shape of the core, so the condition of the inner surface of the socket may be the cause. It is difficult to imagine that this is the case, and in fact, as long as the inner surface of the socket is observed with the naked eye, it has sufficient smoothness. However, if the socket is cut in the middle and the cross section is observed, it can be seen that there are slight undulations on the inner and outer surfaces of the socket, as shown in FIG. 1A.

When a socket is formed at the end of a plastic pipe using the socket forming method described above, hoop stress acts in the circumferential direction of the pipe wall at the end of the plastic pipe, and the hoop stress acts on the contact interface between the core metal and the pipe wall. A balanced radial pressure acts.

FIG. 1B shows the above stress relationship when the plastic tube is a porous tube, and the tube wall portion a outside the holes is
In the hoop tress τa acting on the radial direction, due to the existence of the hole h, it is hardly related to the generation of the above-mentioned radial pressure. Therefore, the radial contact pressure Pc that balances the hoop stress τc of the tube wall portion c between the holes, and the radial contact pressure Pb that balances the hoop stress τb of the tube wall portion b inside the hole, are the hoop Stress τb, τc
should be different due to the difference in

In this way, when the end of a porous plastic tube is formed into a socket by the above-mentioned socket molding method, the contact pressure at the interface between the core metal and the pipe wall alternately differs depending on the hole spacing. This is thought to be one of the causes of the waviness of the cross section of the socket.

This wavering in the cross section of the socket occurs even in the above-mentioned forming method in which the inner surface is supposed to be regulated by a core metal, so it is more noticeable in the case of the socket forming method using the blower method, which does not have inner surface regulation. It is estimated that ripples will appear.

For the above reasons, in order to form a socket at the end of a porous plastic pipe, it is necessary to smooth the inner surface of the socket. It is also suitable for socket molding of porous plastic pipes because it is smooth like plastic pipes, and smoothness is achieved by regulating the inner surface of the core metal during socket molding (experience with plastic pipes without holes). The same molding method used for non-perforated plastic tubes is used.

The method for molding a porous plastic pipe according to the present invention is a method invented in view of the above points,
The tube end of a porous plastic tube, which has a large number of holes in the tube wall in the direction of the tube axis, is press-fitted into a socket forming mold consisting of an outer mold and an inner mold under heating, and then , a method characterized in that a pressurized fluid is forced into the pores of a porous plastic tube.

The present invention will be explained below with reference to the drawings.

In FIG. 2, reference numeral 1 indicates an inner mold for socket molding, and reference numeral 2 indicates an outer mold. 3 is a porous plastic tube.

To carry out the invention, the tip of a porous plastic tube is heated, and then the heated end is press-fitted into the gap between the molds 1 and 2 and expanded into a socket.
Thereafter, the hole at the front end 31 of the plastic tube is closed by an appropriate method, and then a pressurized medium, such as pressurized air P, is injected through the hole at the rear end 32 of the plastic tube.
Press in.

By pressurizing the air P, the hole at the end of the porous plastic tube between the molds 1 and 2 is pressurized, and the pressure (first Pb in Figure B)
is increased. Therefore, in FIG. 1B, the contact pressure Pb is increased and this contact pressure Pb is changed to the contact pressure Pc.
To the same extent as above, it is possible to prevent the aforementioned waving of the cross section of the socket, and the inner surface of the socket can be shaped into a smooth surface.

In the above, the rear end 32 of the porous plastic tube
It is also possible to close the holes in the tube and press air in through the holes in the tip 31 of the porous plastic tube.

In the present invention, as shown in FIG. 3, the inner mold 1 includes:
Press the end of the porous plastic tube, and then
The outer mold 2 is tightened, and the teeth 300 at the tip of the outer mold crush the tip of the tube end, thereby closing the hole h,
Next, it is also possible to carry out an embodiment in which the pressure medium is forced into the rear end of the porous plastic tube.

The present invention also provides a type of receiver in which the diameter of the tube end is expanded in two steps (f, S) and a rubber ring locking portion T is provided in the expanded diameter portion S of the large diameter, as shown in Fig. 4. It can also be applied when molding a spout onto the end of a perforated plastic tube.

According to the method for forming a socket for a porous plastic pipe according to the present invention, as described above, a socket having an inner surface precision equivalent to that of a non-perforated plastic pipe can be formed at the end of a porous plastic pipe, and the pipe can be joined. As with conventional non-perforated plastic pipes, excellent pressure and water leakage properties can be ensured.

[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 state of pressure generation when a socket is expanded in diameter on a porous plastic pipe, and Fig. 2 is FIGS. 3 and 4 are explanatory diagrams for illustrating the present invention, respectively, showing other embodiments of the present invention. In the figure, 1 is an inner mold for socket molding, 2 is an outer mold, 3 is a porous plastic tube, and P is press-in air.

Claims (1)

[Claims] 1. The tube end of a porous plastic tube having a large number of holes in the tube wall in the direction of the tube axis is press-fitted into a socket forming mold consisting of an outer mold and an inner mold under heating, and A method for forming a socket for a porous plastic pipe, which is characterized in that a pressurized fluid is then pressurized into the holes of the porous plastic pipe.