JPH06246818A - Extrusion molding method of internal helix rib or grooved synthetic resin pipe - Google Patents

Abstract

PURPOSE:To continuously mold parisons having helix ribs or helix grooves by extrusion molding without rotating them in the peripheral direction, by setting a rotating speed of a rotating part of a core and a lead angle of recessed grooves or protruding streaks so as not to rotate a synthetic resin pipe to be continuously extruded from a mold in the peripheral direction. CONSTITUTION:In an extrusion mold 2, a plurality of recessed grooves 23c or protruding streaks which reach an end part at an outlet of a core and have a predetermined lead angle are formed on a surface of a rotating part 23 of the core at a predetermined pitch. A synthetic resin pipe having helix ribs or grooves corresponding to rotation condition of the rotating part 23 of the core and the recessed grooves 23c or the protruding streaks is molded continuously by extrusion molding on the inner face. The rotating speed of the rotating part 23 of the core and a lead angle alpha of the recessed groove 23c or the protruding streak are set so as not to rotate the synthetic resin pipe to be extruded continuously from the mold 2 in the peripheral direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for extrusion molding a synthetic resin pipe having an inner spiral rib or groove.

[0002]

2. Description of the Related Art As a method for continuously manufacturing a synthetic resin pipe with an inner spiral rib used as a drainage vertical pipe for a building, a manufacturing method as disclosed in Japanese Patent Laid-Open No. 2-78517 has been proposed. In this method, as shown in FIG. 7, a predetermined lead angle is provided on the outer periphery of a core (inner die) 102 of an extrusion molding die 101, and a recessed groove 103 that is pulled out to the tip of the core (end on the die exit side) is predetermined. The molten resin is extruded from the gap between the land (outer die) 104 and the core 102 by rotating the core 102 around the central axis while forming the pitch for each pitch, and a synthetic resin pipe in a molten state having a spiral rib on the inner surface ( Hereinafter, "parison" will be referred to as continuous extrusion molding.

[0003]

By the way, normally, the parison extruded from the mold 101 is solidified into a desired synthetic resin tube in a state where a predetermined external shape is adjusted through a forming device and a cooling tank, Although it is designed to be continuously drawn by a take-up machine, in the above extrusion molding method, the parison is also pushed out from the mold 101 while rotating in the axial direction with the rotation of the core 102.

Therefore, in the take-up machine, it is necessary to take out the synthetic resin pipe in synchronization with the extrusion speed (linear velocity) of the parison and the rotation speed in the circumferential direction so that the parison portion is not twisted or deformed. . However, in order to be able to pick up the parison in synchronization with the extrusion speed and rotation speed as described above, a special take-up machine must be prepared, which requires equipment cost and the extrusion speed at the start of molding. Since the take-up speed must be adjusted to suit both the rotation speed and the rotation speed, the workability is extremely poor.

In view of the above circumstances, the present invention has an inner surface spiral rib or grooved synthetic resin tube which can continuously extrude a parison having a spiral rib or spiral groove formed on the inner surface without rotating in the circumferential direction. It is an object of the present invention to provide an extrusion molding method.

[0006]

In order to achieve such an object, the extrusion molding method of the inner surface spiral rib or grooved synthetic resin pipe according to the present invention is such that at least the die outlet side of the core rotates about the central axis. Use an extrusion molding die in which a plurality of recessed grooves or ridges having a predetermined lead angle are formed at a predetermined pitch on the surface of the rotating portion of the core and reach the outlet side end of the core. It is an extrusion molding method of an inner surface spiral rib or a grooved synthetic resin pipe for continuously extruding a synthetic resin pipe having spiral ribs or grooves corresponding to the rotation conditions of the rotating portion of the core and the concave groove or ridge. Then, the rotational speed of the rotating portion of the core and the lead angle of the groove or protrusion are set under the condition that the synthetic resin pipe continuously extruded from the mold does not rotate in the circumferential direction.

In the above structure, the mold system is as follows.
The straight die method or the cross die method may be used.
The core may be of a type in which the entire core rotates around the central axis, or may be of a type in which only the portion where the groove or the ridge is formed is rotated. The number of rotations of the rotating part of the core is appropriately changed depending on the lead angle of the concave groove or the ridge, the depth of the groove or the height of the ridge, the wall thickness of the pipe to be obtained, the bore diameter, and the extrusion amount. Is set.

That is, the relationship between the rotational speed of the rotating portion of the core and the lead angle of the groove or protrusion for preventing the parison extruded from the mold from rotating in the circumferential direction is as follows:
Explaining with reference to Table 1 below, it can be obtained as follows.

[0009]

[Table 1]

For example, when the lead angle of the concave groove is formed so as to be inclined (rotated) to the right when viewed from the resin outlet of the die, as shown in Table 1, the resin always has the concave groove to the right. A constant torque is applied. Therefore, when the rotating part of the core is rotated counterclockwise to gradually increase the rotating speed, the rotating force of the rotating part of the core and the rotating force of the concave groove cancel each other out, and the relative rotation of the molten resin becomes zero. . Then, when the rotation speed of the rotating portion is further increased, the rotating force of the rotating portion exceeds the rotating force of the concave groove, and as shown in Table 1, the parison is pushed out while rotating counterclockwise.

The lead angle of the groove or protrusion is also limited by the amount of resin extruded, but is preferably 75 degrees or less. The length of the groove or the protrusion is preferably long as long as it does not disturb the flow of the resin (retention, drift, etc.).
The synthetic resin forming the tube is not particularly limited,
For example, polyvinyl chloride, post-chlorinated polyvinyl chloride,
Examples thereof include polyethylene and nylon. For example, when a pipe is extruded by the method of providing a spiral rib on the outlet side of a fixed core as described above, a synthetic resin having an apparent viscosity of 1000 poise or more is particularly preferable.

That is, when the apparent viscosity is less than 1000 poise, the molten resin is not smoothly guided to the groove, and the molten resin once entering the groove is extruded to a portion having no groove. Therefore, there is a possibility that unevenness may occur, a discontinuous rib may be formed, or a rib may be swelled on a portion of the inner surface of the tube that should be smooth, that is, a portion where the rib is not formed. Further, since the viscosity is low even after being extruded, the parison (resin in a semi-molten state) is liable to draw down, and tends to be difficult to form into a perfectly circular tube.

Incidentally, even if the resin has an apparent viscosity of less than 1000 poise, the apparent viscosity is usually 1000 poise by blending calcium carbonate or the like into the resin or utilizing chemical crosslinking with a silane coupling agent or the like. The above can be adjusted. The cross-sectional shape of the concave groove or the ridge is not particularly limited, and examples thereof include a substantially V shape, a substantially U shape, and a substantially semicircular shape. However, about 1/20 to 1/50 is preferable, and about 1/25 to 1/35 is particularly preferable.

On the other hand, the number of threads of the spiral ribs or grooves varies depending on the setting of the limit level of drainage capacity, and may be one or more, but in the case of a pipe having an inner diameter of 80 to 200 mm, it is 8 to It is preferable that the number of threads be 15 and that they be evenly arranged in the circumferential direction.

[0015]

According to the above structure, the parison is extruded linearly without rotating, while forming the spiral rib or spiral groove on the inner surface. Therefore, after the parison is shaped and cooled and solidified by the forming device and the cooling tank, the parison can be continuously drawn by using an ordinary pipe drawing machine that draws linearly only in the extrusion direction.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 shows an embodiment of an extrusion molding die used in an extrusion molding method according to the present invention. As shown in the figure, the mold 2 includes a fixed land 21, a fixed core 22, a rotary core (tip core) 23, a rotary shaft 24, and an adapter ring 25.

As shown in FIGS. 2 to 4, the fixed core 22 is provided with a flange 22b and an oilless bearing 22c with the main body 22a interposed therebetween, and the rotary shaft 24 is inserted along the central axis of the main body 22a. A hole 22d is provided. In addition, on the surface of the main body 22a,
e is formed. As shown in FIGS. 1, 5 and 6, the rotary core 23 is composed of a main body 23a and an oilless bear rig 23b provided on the end surface of the main body 23a on the fixed core 22 side.

A plurality of (eight in the figure) concave grooves 23c are formed on the peripheral surface of the main body 23a, and an insertion hole 23d for the rotary shaft 24 is provided along the central axis. The groove 23c is gradually deepened from the inlet side of the molten resin, and when it reaches a certain depth, the groove 23c is provided in parallel to the outlet of the mold 2, and a predetermined lead angle α is set with respect to the rotation axis. Have

The fixed core 22 and the rotary core 23 are inserted into the through holes 22d and 23d through the rotary shaft 24, and the nut 27 is tightened onto the rotary shaft 24.
The two oilless bearings 22c and 23c facing each other are sandwiched firmly between the rotation stopper 26 and slidably pressed against each other. The rotating shaft 24 is fixed to the fixed core 22.
As shown in FIG. 1, the insertion hole 22d is rotatably supported by oilless bearings 22f, 22f, 22f, and a key (not shown) is driven into a key groove 23e of the rotary core 23. The rotary core 23 and the rotary core 23 rotate together.

Therefore, when the rotary shaft 24 connected to a continuously variable transmission device (not shown) via the chain 81 rotates, only the rotary core 23 smoothly rotates as the rotary shaft 24 rotates. To do. In addition, the fixed core 22 and the rotating core 23 form the oilless bearing 22.
Since they are pressed against each other via c and 23c, the molten resin does not enter the gap or the like. Of course, when the driving device is stopped, the rotating core 23 also stops rotating.

As shown in FIG. 1, the fixed land 21 surrounds the fixed core 22 and the rotary core 23 from the outside, and the extruder 1 is provided between the fixed land 22 and the stepped-down portion 22e of the fixed core 22 and the outer peripheral surface of the rotary core 23. The flow path (resin passage portion) 29 of the molten resin extruded from the flange 22 is formed.
It is bolted to b and integrated with the fixed core 22.

The adapter ring 25 is provided on the side of the fixed land 21 as shown in FIG. 1, and is an injection port for injecting the molten resin extruded from the extruder (not shown) into the mold 2. Has become. The materials of the oil bearings 22c, 22f, 23c include metals, alloys, ceramics, etc., and the tube molding temperature (usually 160 to 300).
℃), rotation speed, wear resistance, etc. can be taken into consideration.

That is, in this mold 2, the molten resin sent from the extruder to the mold 2 has a step-down portion 22e and a fixed land 22e provided on the surface of the main body 22a of the fixed core 22, as shown in FIG. 21 and the first resin passage portion 29 formed between
After passing through a and then through a second resin passage portion 29b formed between the rotary core 23 and the fixed land 21, it becomes a parison and is pushed out of the mold 2. Moreover, due to the rotation of the rotary core 23 and the action of the concave groove 23c, the rotary core 23 is extruded while forming the spiral rib on the inner surface of the parison.

In the mold 2, the second resin passage portion 2
Before the molten resin enters 9b, it is necessary to adjust the speed of the molten resin to the tube axis (extrusion direction) at a constant rate. That is, if the speed cannot be adjusted as described above, the molten resin causes a high speed and a slow speed in the circumferential direction of the pipe in the second resin passage portion 29b, and the formed inner surface spiral ribbed pipe bends in a certain direction. The product value is reduced. Therefore, in this mold 2, the stepped portion 22e is provided with an island-shaped portion 22g, and the molten resin 11 sent from the extruder into the mold 2 is filled with the island-shaped portion 22g as shown by an arrow in FIGS. By detouring, it is possible to immediately push out at a constant speed in the pipe axis direction.

Next, the embodiment will be described more specifically. (Example 1) Using a mold of the same type as the above-mentioned mold 2,
Under the following molding conditions, a synthetic resin pipe with an inner surface spiral rib made of polyvinyl chloride having a bore of 100 A, a wall thickness of the portion other than the ribs of 3 mm, and a spiral pitch of 560 mm was molded, and the parison was rotated in the circumferential direction. Instead, it was extruded linearly in the tube axis direction.

Therefore, molding could be performed without using a special rotary type take-up machine. Molding conditions Groove depth of rotary core: 6 mm Lead angle of groove: 26 ° (to the right toward the extrusion direction) Extrusion rate: 50 kg / h Rotational core speed: 1 rpm

(Embodiment 2) Using a mold of the same type as the above-mentioned mold 2, under the following molding conditions, the diameter of the pipe is 100 A, the thickness of the pipe other than the rib is 2 mm, and the spiral pitch is 370 mm. When a synthetic resin pipe with an inner spiral rib made of vinyl chloride was molded, the parison was extruded linearly in the axial direction of the pipe without rotating in the circumferential direction.

Therefore, molding could be performed without using a special rotary type take-up machine. Molding conditions Groove depth of rotating core: 3 mm Lead angle of groove: 45 ° (right direction toward extrusion direction) Extrusion amount: 50 kg / h Rotating core rotation speed: 0.7 rpm

(Comparative Example 1) The rotating core rotation speed is 1.5 rpm.
Molding was carried out under the same molding conditions as in Example 1 except that the parison was extruded while rotating in the circumferential direction. Therefore, the synthetic resin pipe was pulled in the axial direction while rotating in the circumferential direction as well. Unless a special take-up machine was used, the parison portion was distorted due to distortion such as twisting, and the molding was not successful.

The extrusion molding method according to the present invention is not limited to the above embodiments. In the above embodiment, the core is composed of the fixed core and the rotating core, but a mold having a structure in which the entire core rotates like the mold 101 shown in FIG. 6 may be used. .

[0031]

Since the extrusion molding method of the inner surface spiral rib or grooved synthetic resin pipe according to the present invention is constituted as described above, the pipe shaft which is usually used when the synthetic resin pipe is extruded. A desired internal spiral rib or grooved synthetic resin pipe can be continuously manufactured using a take-out machine capable of taking out the pipe which has been extruded linearly in the direction.

Therefore, the facility cost and the production cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a metal mold used for carrying out a method for manufacturing a synthetic resin pipe with an internal spiral rib according to the present invention.

FIG. 2 is a side view of a fixed core of the mold shown in FIG.

FIG. 3 is a view on arrow B in FIG.

FIG. 4 is a view in the direction of arrow C in FIG.

5 is a side view of the rotary core of the mold of FIG. 1. FIG.

FIG. 6 is a view in the direction of the arrow D in FIG.

FIG. 7 is a cross-sectional view of a known mold.

[Explanation of symbols]

 2 Mold 23 Rotating core (rotating part of core) 23c Recessed groove α Lead angle

Claims (1)

[Claims] 1. At least a die outlet side of a core is rotatable about a central axis, and a plurality of recessed grooves or ridges having a predetermined lead angle are formed on a surface of a rotating portion of the core to reach an end portion on an outlet side of the core. Using an extrusion molding die formed at a predetermined pitch, continuously extruding a synthetic resin pipe on the inner surface of which spiral ribs or grooves corresponding to the rotation conditions of the rotating portion of the core and concave grooves or ridges are formed. An extrusion molding method of a synthetic resin pipe with an inner spiral rib or a groove to be molded, wherein the rotational speed of the rotating portion of the core and the concave are provided under the condition that the synthetic resin pipe continuously extruded from the mold does not rotate in the circumferential direction. An extrusion molding method of an inner surface spiral rib or a grooved synthetic resin pipe, characterized in that a lead angle of the groove or the ridge is set.