JPH05318557A - Mold for extrusion molding of synthetic resin pipe having spiral rib provided to inner surface thereof - Google Patents

Abstract

PURPOSE:To eliminate the strain difference between the inside and outside of a pipe and to prevent the generation of distortion after piping by forming the min. diameter part having an outside diameter almost same to the circle formed by connecting the top parts of the bottoms of respective spiral grooves in a circumferential direction to a fixed core on the inlet side of a mold from a part provided with spiral grooves. CONSTITUTION:The molten resin injected into a mold 2 from an extruder is passed through the resin passage part formed by a fixed core 26 and a land 27 to be extruded from the mold 2 in a tubular form. Since a plurality of spiral grooves 28 are provided to the surface on the outlet side of the mold of the core 26, the resin is extruded while the spiral ribs corresponding to the spiral grooves 28 are formed on the inner surface of the tubular resin. The part (min. diameter passage) 26b on the inlet side (molten resin inlet side) of the mold from the part having the spiral grooves formed thereto of the core 26 has an outside diameter almost same to the circle formed by connecting the top parts of the bottoms of the spiral grooves 28 in a circumferential direction.

Description

Detailed Description of the Invention

[0001]

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

[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 of a building, a manufacturing method as disclosed in Japanese Examined Patent Publication No. 49-42670 has been proposed. In this method, as shown in FIG. 8, a thermoplastic resin tube 103 having one or two or more ridges or grooves in the length direction is continuously formed from a die (die) 102 of an extruder 101 on the inner surface of the tube. Extrude into. Then, the softened tube 103 pushed out is immediately replaced with the outer diameter former 104.
And a cooling jacket 105 provided on the outer side of the pipe 103 to cool the pipe 103 while controlling the outer diameter thereof, and then to draw it while twisting the softened portion of the pipe 103 by a take-up roll 106 that can rotate independently orthogonal to the pipe axis. I have to.

That is, the outer diameter former 104 is attached to the mold 1.
It is provided immediately after 02 to prevent expansion of the pipe 103 and to cool the jacket 10 of the outer diameter former 104.
The tube surface is rapidly cooled by 5 so that the tube surface portion is not deformed. Then, the pipe 103 is twisted and taken out, so that the inner surface side of the pipe 103 is twisted, and the ridge or the groove is formed in a spiral shape.

[0004]

However, in the above method, since the softened portion of the pipe 103 is formed by forcibly twisting it, the distortion of the outer surface of the pipe> the distortion of the inner surface of the pipe> the central portion of the pipe. There is a difference between the strain remaining on the outer surface and the inner surface of the tube, which is called strain. Therefore, deformation such as twisting is likely to occur after the piping. Further, in particular, when hot waste water flows down in the pipe, the temperature of the pipe rises and the elastic modulus decreases, so that the pipe tries to return to the state in the extrusion die, that is, the straight pipe state without ridges or grooves. ..

In other words, the spiral ribs and grooves may become smaller, and a predetermined drainage capacity may not be obtained. Therefore, in order to solve the above-mentioned problems, the present inventors continuously connect a synthetic resin pipe from an extrusion die in which spiral grooves having a cross-sectional shape corresponding to the spiral rib are provided on the outlet side surface of the core in the same number as the spiral rib. A method of extruding a synthetic resin pipe with an internal spiral rib that has a structure in which the extruded pipe is synchronized with the extrusion speed of the pipe in the axial direction of the pipe and the rotation speed in the circumferential direction of the pipe and is taken out by a rotary take-up machine. I proposed earlier.

According to this method, as shown in FIGS. 9 and 10, the molten resin 11 sent from the extruder 1 to the die 202 passes through the molten resin formed between the core 226 and the land 227. Although it passes through the part 229 and is extruded from the mold 202 as a softened tube (parison) 51 having a desired shape, since the spiral groove 228 is formed on the outlet side of the core 226, the parison 51 is made of metal. It is extruded from the mold 202 at a predetermined extrusion speed in the tube axis direction, and is extruded while rotating in the circumferential direction while the spiral rib corresponding to the spiral groove 228 is formed inside. Then, the parison 51 is immediately passed through the forming tube 3 with a cooling tank to adjust the outer diameter to be cooled and solidified to form the tube 5 having a desired shape, and then the take-out machine 4 synchronizes with the extrusion speed and the rotation speed of the tube 5. The tube 5 is continuously drawn. Also,
The pipe 5 taken by the take-up machine 4 is cut into a predetermined length by the cutting machine 6 and sent to the discharge machine 7.

[0007] Therefore, the mold 20 is dripped in a state without twisting the parison 51 as in the prior art.
It is excellent that it is possible to obtain a synthetic resin pipe 5 with an inner surface spiral rib in which a spiral rib is formed on the inner surface at the same time as being extruded from No. 2 and there is no distortion inside and outside the tube 5, and a plurality of spiral ribs are formed on the inner surface Is. However, in the method as described above, the spiral ribs are formed on the inner surface of the pipe by the number of spiral grooves. However, the cross-sectional shape of the molded inner-surface spiral ribs is the same as the cross-sectional shape of the spiral groove provided on the core. Therefore, the shape of the spiral groove must be designed in advance in anticipation of deformation, and the present invention in which the design of the mold was troublesome, in view of such circumstances, deformation such as twisting occurs after piping. It is also possible to manufacture a synthetic resin pipe with an inner spiral rib that does not impair the drainage capacity semi-permanently because the spiral rib does not become smaller due to the effect of hot waste water flowing inside, etc. It is an object of the present invention to provide an extrusion molding die capable of forming a spiral rib having substantially the same cross-sectional shape as the spiral groove provided in the.

[0008]

In order to achieve such an object, the extrusion molding die according to the present invention has a spiral groove having a cross-sectional shape corresponding to the spiral rib on the surface of the fixed core on the die exit side. A die for extrusion molding of a plurality of synthetic resin pipes with spiral ribs on the inner surface, wherein the fixed core has a top portion at the bottom of each spiral groove on the die inlet side from the portion where the spiral groove is provided. A minimum diameter portion having an outer diameter substantially the same as the circle formed by connecting in the circumferential direction is formed.

In the above structure, the spiral groove is not particularly limited, but it is preferable to form the spiral groove so that the spiral groove gradually becomes deeper toward the outlet side of the core. Further, the pitch of the spiral groove largely depends on the extrusion speed in the tube axis direction and the melt viscosity of the resin. Therefore, when the extruder has a high plasticizing ability and a high extrusion speed, the pitch of the spiral groove may be reduced.

Incidentally, when it is desired to set the pitch of the spiral groove to 100, it is preferable to set the spiral pitch of the spiral groove to about 35 to 65. Then, the pitch of the spiral groove may be made closer to 35 as the extruder has a higher plasticizing ability and a higher extrusion speed. The cross-sectional shape of the spiral groove is
Although not particularly limited, examples thereof include a substantially V shape, a substantially U shape, and a substantially semicircular shape, and the depth thereof may be appropriate, but it is preferably about 1/20 to 1/50 with respect to the inner diameter of the pipe. / 2
About 5 to 1/35 is particularly preferable.

On the other hand, the number of threads of the spiral groove depends 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 1
It is preferable that the number of threads is five, and they are evenly arranged in the circumferential direction. Further, the synthetic resin constituting the pipe that can be formed by using this mold is not particularly limited, for example,
Examples thereof include polyvinyl chloride, post-chlorinated polyvinyl chloride, polyethylene, nylon, and the like, and 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 spiral groove,
The molten resin once entering the spiral groove may be extruded to the part without the groove. Therefore, there is a possibility that unevenness may occur in a portion of the inner surface of the tube which should be originally smooth, that is, a portion where no rib is formed, a discontinuous rib may be formed, or a rib may be swelled. 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 by utilizing chemical crosslinking with a silane coupling agent or the like. It can be adjusted to the above.

[0014]

According to the above construction, the molten resin injected from the extruder into the mold is the resin formed by the fixed core (hereinafter referred to as "core") 26 and the land 27 as shown in FIG. Although it is extruded from the mold in a tubular shape through the passing portion 29, the spiral groove 28 is provided on the surface of the core 26 on the mold outlet side, and thus the spiral groove 28 is provided.
While being rotated along the spiral, the spiral rib corresponding to the spiral groove 28 is formed on the inner surface and is extruded.

Moreover, the (a) portion (minimum diameter portion) on the die inlet side (molten resin inlet side) of the (c) portion of the core 26 where the spiral groove 28 is formed is the top of the bottom of each spiral groove 28. The outer diameter is almost the same as the circle formed by connecting in the circumferential direction, and the molten resin flowing on the core surface in the part (a) of FIG. Compressed in the direction of the tube axis and extends in the direction of the tube axis (especially the die outlet direction). Due to this deformation, a large amount of elastic energy is accumulated in the resin. Next, when it reaches the portion (c), as shown in FIG. 2, the molten resin B in the portion corresponding to the groove has a wider flow-down cross section corresponding to the groove, so that it elastically recovers and is deformed all at once toward the groove top ( Bulge). Moreover, when the molten resins A and C on both sides of the molten resin B reach the portion (C), they are deformed toward the molten resin B side in order to release the accumulated elastic energy, and the molten resin B is further moved to the groove top side. Push in. Therefore, the parison (a tubular body in a molten state) is extruded from the mold while forming spiral ribs having substantially the same cross-sectional shape as the spiral groove on the inner surface.

[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. As shown in FIGS. 3 to 5, the mold 2 is composed of a breaker plate 21, an adapter 22, a rear portion 23, a topede 24, a bridge 25, a core 26, and a land 27.

The clearance of the molten resin passage portion formed between the core 26 and the land 27 is gradually narrower in the extrusion direction than the bridge 25, and the tip of the core 26 has a core parallel portion (core portion). Tip) 26a
Is provided. The core 26 is a core parallel portion 26a.
12 spiral grooves 28 having a V-shaped cross section are formed on the surface of the core at equal intervals. Except for the spiral groove 28, the core parallel portion 2 is formed.
6a has a substantially equal diameter over the entire length. The gap between the land 27 and the core parallel portion 26a is parallel to the tube axis (center line of the mold 2).

As shown in FIG. 6, the spiral groove 28 is an incomplete groove having a shallow groove starting end portion (extruder side) 28c and a complete groove 28d having a constant depth from the middle. There is. Further, the core 26 has a minimum diameter portion 26b formed slightly closer to the die inlet side than the portion where the spiral groove 28 of the core parallel portion 26a is formed. A large diameter portion 26c is provided in a ring shape between the core parallel portion 26a and the minimum diameter portion 26b.

The minimum diameter portion 26b has substantially the same diameter as the circle connecting the bottom apex portions 28a of the spiral grooves 28 in the circumferential direction.
That is, if the mold 2 of this embodiment is used, the mold 2 of FIG.
Similarly to 02, the molten resin 11 sent from the extruder 1 to the mold 2 passes through the molten resin passage portion 29 formed between the core 26 and the land 27, and spiral ribs are formed on the inner surface from the mold 2. The formed parison 51 is pushed out from the mold 2 in a running state while rotating in the circumferential direction. Moreover, since the minimum diameter portion 26b is provided closer to the die inlet side than the spiral groove 28, the molten resin is densely filled in the spiral groove 28, and a spiral rib having substantially the same cross-sectional shape as the spiral groove 28 is formed on the inner surface. To be done. Then, as in the case of using the mold 202 of FIG. 9, the extruded parison 51 is synchronized with the extrusion speed and the rotation speed and taken by a rotary take-off machine, so that the parison 5 in the softened state is twisted as in the conventional case. An inner spiral ribbed tube can be obtained without kinking.

Incidentally, a diagram in which 12 spiral grooves 28 having a V-shaped cross section (width 5 mm, depth 3 mm) are provided on the circumference of the core parallel portion (length 75 mm, clearance with fixed land 2 mm) every 30 degrees around the circumference. When a hard PVC inner surface spiral rib tube with an inner diameter of 100 mm was molded using a mold of the same shape as 3, the ribs of the inner spiral rib tube had a height of 2.6 mm, a spiral pitch of 1600 mm, and a rib cross-sectional shape of spiral. The V shape was substantially the same as that of the groove 28.

On the other hand, 12 spiral grooves 28 having a V-shaped cross section (width 5 mm, depth 3 mm) are provided in the circumference of the core parallel portion (length 75 mm, clearance with fixed land 2 mm) at intervals of 30 degrees in FIG. When a hard PVC inner surface spiral rib tube with an inner diameter of 100 mm was molded using a mold of the same shape, the resulting spiral rib tube had a rib height of 1.4 mm, a spiral pitch of 1600 mm, and a rib cross-sectional shape of It had a semi-circular shape with a radius of 1.4 mm.

The extrusion molding die for the synthetic resin pipe with the inner surface spiral rib according to the present invention is not limited to the above embodiment. For example, in the above embodiment, the large diameter portion 26c is formed in a ring shape between the core parallel portion 26a and the minimum diameter portion 26b, but the large diameter portion 26c may be omitted as shown in FIG. ..

[0023]

EFFECT OF THE INVENTION Since the extrusion molding die for the synthetic resin pipe with the inner surface spiral rib according to the present invention is constructed as described above, the parison extruded through the die is a tube shaft at a predetermined extrusion speed. In addition to being extruded in the direction, the spiral rib corresponding to the spiral groove is formed inside and extruded while rotating in the circumferential direction. Then, if this parison is continuously drawn in synchronization with the extrusion speed and the rotation speed by a take-up machine, the inner spiral rib tube can be obtained without applying a load such as twisting to the parison portion.

Therefore, in the obtained synthetic resin pipe with the inner surface spiral rib, a large strain does not remain, and there is no difference in the strain between the inside and outside of the pipe, which causes deformation such as twisting after the pipe or flows inside. The spiral rib does not become smaller due to the effect of hot water drainage. That is, if this synthetic resin pipe is used as a vertical pipe for drainage of buildings such as middle- and high-rise buildings, the ability to effectively reduce the downflow rate of drainage and ensure sufficient ventilation in the center of the pipe is impaired semipermanently. Never.

Moreover, it is possible to form a spiral rib having a cross-sectional shape substantially the same as the cross-sectional shape of the spiral groove, which facilitates the design of the mold.

[Brief description of drawings]

FIG. 1 is a transverse cross-sectional view of a resin passage portion schematically illustrating movement of resin in the resin passage portion.

FIG. 2 is a vertical cross-sectional view of a resin passage portion for schematically explaining the movement of resin in a spiral groove portion.

FIG. 3 is a cross-sectional view showing an example of an extrusion molding die according to the present invention.

FIG. 4 is a half cross-sectional view of the core of the mold of FIG.

5 is a view taken in the direction of the arrow X in FIG.

FIG. 6 is a cross-sectional view showing the shape of a spiral groove portion.

FIG. 7 is a cross-sectional view of a resin passage portion of a mold of another embodiment.

FIG. 8 is an explanatory view showing a known method for manufacturing a synthetic resin pipe with an inner spiral rib.

FIG. 9 is a cross-sectional view showing a mold of a prior art example.

FIG. 10 is a perspective view showing an example of a synthetic resin pipe manufacturing apparatus used for carrying out the method for manufacturing a synthetic resin pipe with an inner spiral rib.

[Explanation of symbols]

 2 mold 5 synthetic resin pipe 26 core 28 spiral groove 26b minimum diameter part 28a bottom top part

Claims (1)

[Claims] 1. A mold for extrusion molding of a synthetic resin pipe with an inner surface spiral rib, wherein a plurality of spiral grooves having a cross-sectional shape corresponding to the spiral rib are provided on the surface of the fixed core on the mold outlet side, wherein the fixed core. Is that a minimum diameter part having substantially the same outer diameter as a circle formed by connecting the tops of the bottoms of the spiral grooves in the circumferential direction is formed on the die inlet side of the portion where the spiral grooves are provided. A die for extrusion molding.