JPH0522570B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a plastic tube (hereinafter referred to as a "porous plastic tube") having a large number of holes in the tube wall in the tube axis direction.
More specifically, it relates to a method for manufacturing a porous plastic tube having a solid portion without holes in which the through holes are partially closed.

(Prior art and its problems) This type of porous plastic pipe has holes in the pipe wall, which allows for the saving of plastic material and the reduction of the pipe weight, as well as increasing the wall thickness of the pipe. This has the advantage of increasing the rigidity of the tube.

Therefore, in recent years, porous plastic pipes have been used as underground pipes.

In general, this connection between porous plastic tubes is similar to the conventional connection between solid tubes, with an enlarged socket at the end of one tube, and the socket at the end of the other tube. is inserted and connected.

However, in the case of a porous plastic tube, since there is a hole in the tube wall, this hole opens outside the tube at one end that has a socket, and is inserted into the socket of the other tube. The end opens into the tube.
Therefore, the inside and outside of the pipe communicate through this hole, causing problems such as leakage of fluid within the pipe and inflow of rainwater, groundwater, etc. into the pipe.

In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 54-99163 proposes a method of manufacturing a porous plastic tube in which the through holes communicating within the tube wall are partially closed.

However, in the above manufacturing method, the pressure inside the through hole is reduced through the through hole provided in the pin, and the inner wall is brought into close contact with the outer wall to close the through hole and form a solid part without holes. Inevitably, there will be dents in the interior walls. For this reason, when a socket is formed by expanding the diameter of the solid portion, there is a problem in that unevenness is formed on the inner surface of the socket, and sufficient watertightness cannot be ensured.

Furthermore, when the pressure inside the through hole is reduced, there is a risk that the molten resin will flow into the through hole and cause it to become clogged, and if the through hole becomes clogged, the pressure in the through hole will not be reduced and the through hole will not be completely closed. Moreover, once the through-hole becomes clogged, cleaning it is extremely troublesome.

The present invention solves this problem, and includes:
To provide a method of manufacturing a porous plastic tube with a good appearance by smoothing the inner and outer surfaces of a portion having through holes and a solid portion having no holes.

(Means for Solving the Problems) The present invention provides an annular resin passage between a die and a mandrel, and arranges a large number of pins at predetermined intervals in the circumferential direction in the resin passage. When manufacturing a plastic tube having an axial hole in the tube wall by passing molten resin through the pipe, the tip of each pin is positioned near the open end of the resin passage to form the plastic tube having the hole. Either move each pin back from the open end of the resin passage and increase the amount of molten resin extruded from the steady state, or reduce or stop the tube withdrawal speed and close the resin passage in front of the tip of each pin. is filled with molten resin to form a partially solid portion with no through holes. Next, when returning to a steady state and forming a through hole, advance the tip of each pin to near the open end of the resin passage, insert the needle into the tube wall from the outside or inside of the tube, and insert the tip. The tube wall is characterized by a small hole that faces the tip of the pin and communicates with the formed through hole.

(Function) Each pin is retracted from the open end of the resin passage and the amount of molten resin extruded is increased, or the pipe take-up speed is reduced or stopped, and the molten resin is transferred to the resin passage ahead of the tip of each pin. When filled with
A partially solid portion with no through holes is formed.

Next, when forming a through hole by positioning the tip of each pin near the open end of the resin passage, insert a needle into the tube wall from the outside or inside of the tube and insert the tip of the needle into the tip of each pin. When a small hole is drilled in the pipe wall facing the
Air flows into the through hole from the small hole.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Fig. 1 is a sectional view of a main part of the manufacturing process of a porous plastic tube showing one embodiment of the present invention, Fig. 2 is a sectional view taken along the line - - of Fig. 1, and Fig. 3 shows the manufacturing process of another embodiment. 4 is a sectional view of a porous plastic tube obtained by the present invention, and FIG. 5 is a sectional view of an essential part showing a state where the end of the porous plastic tube is enlarged in diameter and a socket is provided. It is a diagram.

First, the outline of the manufacturing apparatus of the present invention will be explained.

In the figure, reference numeral 1 denotes a die, 2 a mandrel, and 3 an annular resin passage, in which a large number of pins 4 are arranged at equal intervals over the circumferential direction.
5 is an enlarged passage connecting the extruder and the resin passage 3, and 6 is a needle.

The needles 6 are arranged on the outer periphery of the tube corresponding to the tips of the pins 4, and as shown in FIG. Fixed. This holder 7
The needle 6 is movable in the radial and axial directions of the tube, and is connected to a compressed air device (not shown) so that compressed air can be injected from the tip of the needle 6.

In the manufacturing apparatus constructed as described above, the molten resin is extruded from the extruder and is formed into a tubular shape while passing through the resin passage 3, and a through hole a is formed in the tubular wall by the pin 4. The material is then cooled and solidified while passing through a cooling device (not shown) disposed in front of this manufacturing device, and then taken off by a take-off machine.
In this manufacturing process, the extrusion amount and withdrawal speed are in a steady state, and the tip of the pin 4 advances to the vicinity of the open end of the molten resin.

Next, when forming a solid part b without holes from this steady state, the tip of the pin 4 is retreated from the state shown in FIG. 1 to the enlarged passage 5, and the amount of extrusion of the molten resin is increased; Or reduce or stop the collection speed of the collection machine. Then, the resin passage 3 in front of the tip of the pin 4 is filled with molten resin, the through hole is closed, and a tube with smooth inner and outer surfaces and no irregularities is extruded.

After the solid portion b has been molded to a predetermined length in this manner, the steady state is returned to mold the plastic tube having the through hole a.

In this manufacturing process, the pin 4 is advanced together with the tube passing through the resin passage 3 until the tip of the pin 4 is substantially flush with the open end of the resin passage 3.
Therefore, each holder 7 is moved from the outer circumferential side of the tube toward the center, the tip of the needle 6 is brought to face the tip of the pin 4, and compressed air is injected from the tip. Although this injection of compressed air is not necessarily necessary, when the compressed air is injected from the tip of the needle 6, the molten resin at the tip of the pin 4 is removed, and communication between the molded through hole a and the atmosphere is ensured. becomes.

When a small hole communicating with the atmosphere is formed at the tip of the pin 4, air flows smoothly into the through hole a.
Since there is no vacuum inside, dents do not occur on the inner and outer surfaces of the tube.

Incidentally, the above-mentioned piercing by the needle 6 and injection of compressed air are carried out instantaneously at the same time as the extrusion amount of molten resin or the take-up speed of the take-up machine is restored to the original state and the steady state operation is resumed. Since the tube is pushed out and moves a little, it is preferable to move the holder 7 in the direction of taking the tube along with this movement.

In the present invention, the forming of a portion with holes a and a solid portion b without holes is repeatedly performed at predetermined intervals, thereby forming a porous plastic tube A as shown in the cross-sectional view in FIG. can get. The length L1 of the part with the through hole a and the length L2 of the solid part b without holes can be set as appropriate depending on the intended use of the pipe, but as shown in Fig. When providing the opening B, it is preferable to make the length L2 of the solid portion b match the length of the socket, and cut the pipe A with the cutting machine C at the small hole portion behind the solid portion b.

FIG. 3 is a partial sectional view showing another embodiment of the present invention, in which the die 1 can be moved in the axial direction.

When manufacturing a porous plastic tube using this manufacturing apparatus, when molding the solid part b without holes, the amount of extrusion of the molten resin is increased as in the previous example, or the take-up speed of the take-off machine is decreased. , or stop the resin passage 3 in front of the tip of the pin 4.
is filled with molten resin.

After forming the solid part b of a predetermined length in this way, the steady state is restored, the die 1 is moved back, and the tip of the pin 4 is placed almost flush with the opening end of the resin passage 3 between the die 1 and the mandrel 2. place it in the first place. Therefore, the holder 7 is moved toward the center of the tube so that the tip of the needle 6 faces the tip of the pin 4, a small hole is made in the tube wall, and then the holder 7 is moved back. Then, air flows into the through hole a, and a tube with no irregularities on the inner and outer surfaces is continuously formed as in the previous embodiment.

In the above embodiments, the small hole was provided in the outer wall of the tube, but the needle 6 and holder 7 may be provided inside the tube to form a small hole in the inner wall of the tube. .

(Effects of the Invention) As detailed above, the present invention fills the resin passage in front of the tip of the pin with molten resin when molding a partially hole-free solid part, so that the inner and outer surfaces of the tube are smooth. becomes. In addition, when returning to a steady state and molding a part with a through hole, a small hole is made in the tube wall and air is allowed to flow into the through hole, so the inside of the through hole is not in a vacuum state and the inner and outer surfaces are A smooth porous plastic tube with good appearance can be obtained.

Therefore, when a socket is formed by enlarging the diameter of the solid part of the porous plastic tube obtained by the present invention, the inside and outside surfaces of the socket are smooth, and not only does it have a good appearance, but it also has extremely high watertightness. can get.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a main part of the manufacturing process of a porous plastic tube showing one embodiment of the present invention, Fig. 2 is a sectional view taken along the line - - of Fig. 1, and Fig. 3 shows the manufacturing process of another embodiment. 4 is a sectional view of a porous plastic tube obtained by the present invention, and FIG. 5 is a sectional view of an essential part showing a state where the end of the porous plastic tube is enlarged in diameter and a socket is provided. It is a diagram. A... Porous plastic pipe, a... Through hole, b...
...Full part, 1...Die, 2...Mandrel, 3
...Resin passage, 4...Pin, 5...Enlarged passage, 6
...Needle, 7...Holder.

Claims (1)

[Claims] 1 An annular resin passage is provided between the die and the mandrel, a large number of pins are arranged in the resin passage at predetermined intervals in the circumferential direction, and the molten resin is passed through the resin passage to form an axis within the tube wall. In manufacturing a plastic tube having a through hole in the direction, the tip of each pin is positioned near the open end of the resin passage and a plastic tube having a through hole is molded. Retract from the open end and increase the amount of molten resin extruded, or reduce or stop the pipe take-up speed to fill the resin passage ahead of the tip of each pin with the molten resin to partially penetrate the hole. After forming a solid part with no cracks, the tip of each pin is advanced to near the open end of the resin channel when returning to a steady state and forming a through hole, and the needle is inserted into the tube wall from the outside or inside of the tube. A method for manufacturing a porous plastic tube, characterized in that a small hole is bored in the tube wall so that the tip thereof faces the tip of the pin and communicates with the through hole to be formed.