KR930001489B1 - Method and apparatus for manufacturing a plastic pipe - Google Patents

Abstract

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Description

Plastic pipe manufacturing method and device

1 is a side view showing a method of manufacturing a plastic pipe according to an embodiment of the present invention.

2 is a side view of an apparatus for manufacturing a plastic pipe according to an embodiment of the present invention.

3 is a front view of the apparatus of FIG.

4 is a cross-sectional view of the device of FIG.

5 is a partial side cross-sectional view of the main part of FIG.

6 is a cross-sectional view of a plastic ribbon for one embodiment of the present invention.

7 is a cross-sectional view of a plastic ribbon according to another embodiment of the present invention.

8 is an enlarged cross-sectional view showing a spiral ridge formed on an outer surface of a plastic pipe according to an embodiment of the present invention.

9 is an enlarged cross sectional view showing a spiral ridge of a plastic pipe in which a narrow plastic ribbon is fused.

10 is an enlarged cross-sectional view of a plastic ribbon according to another embodiment of the present invention.

11A and 11B are enlarged cross sectional views showing a spiral ridge formed on an outer surface of a plastic pipe according to another embodiment of the present invention.

FIG. 12 is an enlarged cross-sectional view of the helical ridge manufactured by the method shown in FIGS. 11A and 11B.

13 to 16 are enlarged cross-sectional views of the plastic ribbon in which the slit on the ridge is sealed by various plastic ribbons.

17 is an enlarged cross sectional view showing a spiral ridge formed on an outer surface of a plastic pipe according to another embodiment of the present invention.

18 is a side view showing a method of manufacturing a plastic pipe according to another embodiment of the present invention.

Fig. 19 is an end view showing the relationship between a plastic ribbon, endless molding, a core belt, an endless second molding belt, and a narrow plastic ribbon.

20 is an end view showing the relationship between a plastic ribbon, an endless forming core belt and an endless second forming belt.

Figure 21 is a schematic diagram showing the circulation of an endless molded core belt according to another embodiment of the present invention.

22 is a cross-sectional view of an apparatus for manufacturing a plastic pipe according to another embodiment of the present invention.

Fig. 23 is an end view showing the relationship between the plastic ribbon and the endless molded core belt according to another embodiment of the present invention.

FIG. 24 is an enlarged cross sectional view showing a spiral ridge formed on an outer surface of a plastic pipe according to another embodiment of the present invention. FIG.

* Explanation of symbols for main parts of the drawings

1, 21: base 2, 22: support plate

3, 23: support rod 4, 24: central axis

5, 27: molding rules 8a, 8b: first and second movable members

9a, 9b: link rods 10, 15, 51: extruder

11: die 12: endless molded core belt

13: cutter 14: slit

16 die 18 second molding belt

25, 26: bearing 31a, 31b, 31c: first, second and third threaded portion

36: side support member 41, 42: stopper

43: slot 60, 70, 70 ': ridge-shaped deformation

61, 71: narrow side 72: middle part

62, 73: wide side A: plastic ribbon

B: narrow second plastic ribbon C: plastic pipe

D: rotatable means

The present invention relates to a method and apparatus for producing a so-called corrugated plastic pipe having a spiral ridge on its outer surface.

Corrugated plastic pipes with spiral ridges on the outside and flat inner surfaces are widely used in houses and other buildings.

In order to integrally form such corrugated plastic pipe having a spiral outer layer and a flat inner wall, various methods are used as follows.

(A) Firstly, the plastic ribbon is spirally wound in a soft state with its ends overlapped to form an inner wall, and then the molded plastic ribbon having a longitudinal ridge around the inner wall is spirally wound to form a final plastic having a spiral ridge and groove outer surface. How to give.

(B) A method of forming a plastic ribbon having a longitudinal ridge and a flat side end, and spirally winding the plastic ribbon by overlapping the side ends thereof to provide a final plastic pipe having a spiral outer side and a flat inner side at the same time.

In both methods, flat or shaped plastic ribbons are used to provide hollow ridges extending spirally on the plastic pipe outer surface. On the other hand, a molded core belt sandwiched between the upper plastic ribbon and the lower plastic ribbon may be used to provide a plastic pipe having a spiral ridge filled with the core belt. However, there is no means to remove the core after the plastic pipe is completed. Thus, this method cannot provide plastic pipes with hollow spiral ridges.

Japanese Patent Laid-Open No. 51-37969 describes a method for producing a corrugated plastic pipe using a flat plastic ribbon attached to the bottom of a molded core belt and a flat plastic ribbon wound on a core belt. A molded core belt and a flat plastic ribbon are spirally wound around the core cylinder to form a corrugated plastic pipe. After solidifying, the core belt and inner ribbon are removed from the final plastic pipe to provide a corrugated pipe having a helical surface both inside and outside. However, this method has the drawback that the plastic pipe thus produced cannot have a flat inner surface.

On the other hand, one of the prior arts for an apparatus for producing a plastic pipe of such a structure includes a plurality of rotatable forming rolls disposed on a virtual cylindrical surface, one end of which is supported by a cantilevered support base and operatively connected to the drive means. Each rotatable forming roll is slightly inclined with respect to the axis on the virtual cylindrical surface. The extruder is located near the rotatable forming roll, and the extruded resin ribbon is fed to the forming roll and spirally wound around the forming roll with its side ends overlapped. When all the forming rolls rotate in the same direction at the same time, the plastic ribbon is continuously conveyed toward the tip of the rotatable forming roll with its side ends overlapping into the tubular body. Since the plastic ribbon is still sufficiently hot on the rotatable forming roll, some overlapping plastic ribbon is perfectly formed into a plastic pipe that is continuously drawn off the tip of the rotatable forming roll.

However, in the above conventional method and apparatus, it is difficult to form the spiral ridge on the plastic pipe outer surface without deforming the helical ridge when the spiral ridge is also hollow. This is because the plastic ribbons to be molded to the plastic pipe are in a soft state, that is, when they overlap each other, the adjacent plastic ribbons can fuse. The use of molded core belts avoids this deformation of the helical ridge, but suffers from the drawback that plastic pipes comprising molded core belts are very heavy and not easy to bend.

It is therefore another object of the present invention to provide a method for producing such corrugated plastic pipes.

Another object of the present invention is to provide an apparatus for manufacturing such corrugated plastic pipes.

In view of the above, the present inventors use a molded core belt to form such corrugated plastic pipes in a precisely shaped spiral ridge, and cut the final spiral ridge to remove the core belt, It was found that it could be produced by closing with a plastic ribbon.

Thus, a plastic pipe having a helical ridge and a flat inner surface on the outer surface according to the present invention has at least one ridge-shaped deformation portion extending in the longitudinal direction and provided with a longitudinal slit and a flat extending both sides of the ridge deformation portion. Consisting of a spirally wound plastic ribbon comprising a portion, at least adjacent plastic ribbons being fused to each other in the flat portion such that the fused flat portion provides the flat inner surface covering the bottom of the spiral ridge, and the longitudinal slits are in the spiral ridge. It is characterized in that it is sealed with a second plastic ribbon fused to.

According to the present invention, a plastic pipe manufacturing method having a spiral ridge on the outer surface and a flat inner surface consists of the following steps.

(A) feeding the plastic ribbon in a soft state onto a plurality of rotating forming rolls arranged in a circle such that the plastic ribbon is spirally wound around the forming roll while partially overlapping to fuse with each other; (b) the molding Spirally wound the endless molded core belt around the forming roll in such a manner that the endless forming core belt is sandwiched between the plastic ribbon already wrapped around the roll and the newly supplied plastic ribbon. (C) providing a slit extending along the helical ridge to the helical ridge to remove the endless molded core belt therefrom after the plastic ribbons are fused together and sufficiently cooled. And (d) attaching said second plastic ribbon to said spiral ridge. A second plastic ribbon in a spiral around the ridge in order to combined by winding a soft state, the method which closes the said slit.

According to the present invention, an apparatus for producing a plastic pipe having a spiral ridge on the outer surface and a flat inner surface has the following configuration.

(A) a plurality of rotatable forming rolls arranged in a circular manner, and (b) first means positioned near the rear end of the rotatable forming roll for supplying the plastic ribbon softly to the rotatable forming roll; (C) a portion thereof around the rotatable forming roll in such a manner that the endless forming core belt is sandwiched between the plastic ribbon already wrapped around the rotatable forming roll and the newly supplied plastic ribbon from the first means. To provide an endless molded core belt wound up to provide a helical ridge to the final plastic pipe, and (d) to provide a slit extending along the helical ridge to the helical ridge to remove the endless molded core belt from the helical ridge. (2) second means provided downstream of said cutter to provide a second plastic ribbon fused to said spiral ridge to seal said slit.

Referring to FIG. 1, the apparatus of the present invention extends from a base 1, a support plate 2, a plurality of support rods 3 securing the support plate 2 to the base 1, and a base 1. And a central shaft 4 rotatably supported by the base 1 and the support plate 2 via a bearing.

First actuating means comprising a first movable member 8a which is screwed onto the central shaft 4 and a plurality of first link rods 9a pivotally connected to the first movable member 8a on the central shaft 4. This is mounted movable. The first link rod 9a extends radially from the first movable member 8a at equal intervals. Similarly, the second actuating means comprising the second movable member 8b is screwed on the central shaft 4 and the link rod 9b is pivotally connected to the second movable member 8b and radially equidistant therefrom. Extends. The direction of the screw is opposite to the direction between the first movable member 8a and the second movable member 8b. When the central shaft 4 rotates, the first and second movable members 8a and 8b are opposite to each other. You should know that you can go to.

The apparatus comprises a plurality of rotatable forming rolls 5 pivotally connected to the link rods 9a, 9b at both ends. Therefore, the cylindrical shell formed by the forming roll 5 can be expanded and contracted by the rotation of the central axis 4.

An extruder 10 having a die 11 with a slit orifice is arranged near the rear end of the forming roll 5 to feed it a flat plastic ribbon A. However, it should be appreciated that the extruder die 11 may have an orifice capable of providing a plastic ribbon with one or more longitudinal ridged deformations. The plastic ribbon A is here wound spirally around the forming roll 5 so that the side edges thereof overlap each other. The spiral winding of the plastic ribbon A causes the shaping | molding roll 5 to incline a little as mentioned below.

The endless forming core belt 5 is sandwiched between the plastic ribbon already wrapped around the forming roll and the plastic ribbon newly supplied from the extruder 10. The plastic ribbon A just released from the extruder 10 is sufficiently flexible because it is still hot. Thus, it is easily deformed along the forming core belt 12 to provide a ridged deformation. This flexible state of the plastic ribbon is hereinafter simply referred to as the "light state". Instead of the extruder 10, a heater that can heat and flex the plastic ribbon may be used.

The plastic ribbon A comprising the forming core belt 12 thus moves towards the tip of the forming roll 5 so that the side edges overlap and fuse together while spirally winding around the forming roll. The forming core belt 12 is also spirally wound around the forming roll 5 in the spiral ridge of the final plastic pipe C. FIG. After several revolutions, the spirally wound and fused plastic ribbon A is sufficiently cooled and solidified.

The cutter 13 is provided near the forming roll 5 to cut the helical ridge of the final plastic pipe C after it is sufficiently solidified. Since the helical ridge is firmly supported by the molded core belt 12 accommodated therein, it can be easily cut without deformation. After cutting, the forming core belt 12 is returned from its helical ridge through the slit 14 formed by the cutter 13 to its original position which is taken out by the upper and lower plastic ribbons.

A second extruder 15 with a small flat die 16 is arranged near the forming roll downstream of the cutter 13 and likewise has a second plastic ribbon B in a soft state on the helical ridge of the plastic pipe C. To supply. The second plastic ribbon B has a width capable of sufficiently covering the slit 14. Since the upper surface of the helical ridge is relatively narrow, the second plastic ribbon B can be made narrow. The second plastic ribbon B, which is still hot when reaching the helical ridge, is easily melt attached to the helical ridge to close the slit. This makes it possible to continuously produce corrugated plastic pipes having hollow spiral ridges on the outer surface and flat inner surfaces.

The apparatus for producing such corrugated plastic pipes according to a preferred embodiment of the present invention will be described in detail below.

2 to 4, the plastic pipe manufacturing apparatus includes a base 21 and a support plate 22, a plurality of support rods 23 for fixing the support plate 22 to the base 21, and a base ( A central shaft 24 extending from 21 and rotatably supported by the base 21 and the support plate 22 via bearings 25 and 26.

According to this embodiment, as shown in FIG. 3, six radial slots 43 are provided on the support plate 22 extending circumferentially at equal intervals from the vicinity of the bearing 26 to the periphery of the support plate 21. have. The support plate 22 is further provided with side support members 36 having six support blades extending laterally from the support plate 22 and protruding radially at equal intervals in the circumferential direction therefrom.

The central shaft 24 has a first screw portion 31a at its tip, a second screw portion 31b near the support plate 22 that is the same as the first screw portion 31a, and these first and second screw portions 31a and 31b. Has a third screw portion 31c near the support plate 22 opposite to (). The first screw portion 31a and the second screw portion 31b have the same spiral direction, and the third screw portion 31c has a spiral in the opposite direction to the first and second screw portions 31a and 31b.

A first movable member 31a having a screw inner wall for screwing the first screw portion 31a onto the first screw portion 31a and a plurality of first link rods 35a pivotably connected to the first movable member 32a. The first operating means including a) is installed to be movable. The first link bar 35a extends at regular intervals in the radial direction from the first movable member 32a. Similarly, the second actuating means is pivotally connected to the second movable member 32b screwed onto the second screw portion 31b and the second movable member 32b, and extends therefrom at equal intervals in the radial direction. Link rods 35b. The third actuating means is pivotally connected to the third movable member 32c screwed to the third screw portion 31c and the third movable member 32c, and six link rods 35c extending radially at equal intervals therefrom. ).

The apparatus for manufacturing a plastic pipe according to the present embodiment includes a plurality of (six) rotatable forming rolls 27, the leading end of each of the rotatable forming rolls 27 passing through a first bearing 28 at the leading end thereof. It is pivotally supported by one of the first link rods 35a, and the rear end of each of the rotatable forming rolls 27 is pivotally supported by the second and third link rods 35b and 35c, respectively. It is connected flexibly by flexible link means as described in the following.

Each flexible link means comprises a single shaft 37b connected to the roll body 27a of each of the forming rolls 27 rotatable via the universal joint 30 and a link rod connected to the single shaft 27b via the universal joint 44. And a shaft 47 connected to the link rod 46 via the universal joint 45 and rotatably supported by a bearing provided on the front wall 21a and the rear wall 21b of the base 21. ). The short axis 27b is rotatably supported by the second bearing 29 slidably accommodated in the radial slot 43 of the support plate 22. The 2nd bearing 29 is supported by the 2nd link rod 35b and the 3rd link rod 35c at both sides with respect to the support plate 22 so that it can coat | cover.

In this embodiment, the tubular body 37 is fixed to the side support plate 36 so as to surround the central axis 24. The tubular body 37 is fixed to the flange 38a of the inner tube member 38 surrounding the central shaft 24 with a small clearance for allowing the central shaft 24 to rotate freely in the inner tube member 38. The flange 37a is provided at its distal end. The inner tube member 38 is provided with a spline axially extending on its outer surface, and the outer tube member 39 fixed to the first movable member 32a has a spline of the inner tube member 38 on its inner surface. Combinable axial splines are provided. Due to this structure, the first movable member 32a can move back and forth along the central axis 24 without rotating by the rotation of the central axis 24. In addition, by changing the angular position of the inner tube member 38 or the outer tube member 39 around the axis of the central shaft 24, the direction of each of the rotatable forming rolls 27 is changed to that of the central shaft 24. Can be adjusted along the axis. Suitably, the rotatable forming roll 27 is slightly inclined on the outer skin formed as shown in FIG. The angle adjustment of the first movable member 32a may be achieved by changing the angular position of the inner tube member 38 with respect to the tubular body 37.

The side support plate 36 has a stopper 42 for adjusting the leftward movement of the second movable member 32b around the central axis 24. Similarly, the side support plate 40 fixed to the support plate 22 has a stopper 41 for adjusting the rightward movement of the third movable member 32c around the central axis 24. Due to the stoppers 41 and 42, the minimum radius of the shell formed by the rotatable forming roll 27 is determined.

The central shaft 24 is fixedly installed with a gear 33 that can be operatively coupled to a timing belt 34 connected to a drive means (not shown). Through the timing belt 34 and the gear 33, the central shaft 24 is rotated independently of the rotatable forming roll 27.

As clearly shown in FIG. 4, each shaft 47 has a small gear 48 meshed with a standby gear 50 fixed to an axis rotatably supported by the base 21 via a bearing 49. The fault is installed, and the shaft is connected to the drive means (M). Since each small gear 48 meshes with the atmospheric gear 50, it rotates simultaneously in the same direction as the rotatable shaping | molding roll 27. As shown in FIG.

The extruder 51 with the die 52 is located at the rear or near the base of the rotatable forming roll 27, and the extruded plastic base “A” is fed to the forming roll 27 as in FIG. 1. It winds continuously around the rotatable forming roll 27 so that the side edge part may overlap.

With the above-described apparatus, a plastic pipe manufacturing method will be described below.

First, in order to obtain the desired radius of the sheath formed by the rotatable forming roll 27, the central axis 24 is rotated in the left or right direction by first, second and second distances along the central axis 24 by a desired distance. The third movable members 32a, 32b, and 32c are moved. Since the first screw portion 31a and the second screw portion 31b have the same spiral direction and the third screw portion 31c has the opposite helical direction, the first movable member 32a and the second movable member 32b. ) Is moved in the same direction while the third movable member 32c is moved in the opposite direction. Since the rotatable forming roll 27 is supported by the first, second and third movable members 32a, 32b, 32c via the pivotally movable link rods 35a, 35b, 35c, the rotatable forming The radial positions of the roll 27 are changed by moving the movable members 32a, 32b, 32c in the axial direction. In other words, the radius of the shell formed by the rotatable forming roll 27 is adjusted by rotating the central axis 24, so that the plastic pipe to be molded can have the desired diameter.

In this position, each rotatable forming roll 27 is simultaneously rotated in the same direction via each flexible link means operatively connected to the motor M. As shown in FIG. The plastic ribbon “A” extracted from the extruder 51 through the die 52 with the desired inclination with respect to the axis of the central axis 24 is fed onto the rotatable forming roll 27. The rotational speed of the rotatable forming roll 27 and the inclination and feed rate of the plastic ribbon "A" are adjusted so that the plastic ribbon "A" is wound around the rotatable forming roll 27 with side edges overlapped at a desired angle. Since the plastic ribbon "A" is still hot at the time of overlap, the partially overlapped plastic ribbon is integrally molded into a plastic pipe which is continuously drawn out from the leading end of the rotatable forming roll 27.

Next, when plastic pipes of various diameters are desired, the central shaft 24 is rotated so that the rotatable forming roll 27 can have a shell of the desired diameter via the actuating means. Likewise, changing the radius of the outer shell of the rotatable forming roll 27 can be easily performed by simply rotating the central axis 24.

In the apparatus, it should be noted that while the circular arrangement of the rotatable forming rolls 27 is variable, the rotatable forming rolls 27 need not be as variable as in conventional apparatus for the purposes of the present invention. .

FIG. 5 shows in detail how the plastic pipe is produced by the apparatus of FIG. 1 according to the invention. As described in connection with FIG. 1, the plastic ribbon A is partially overlapped and spirally wound, and the molded core belt 12 is sandwiched between the overlaps of the plastic ribbon A, thereby having a spiral ridge. Provide the final plastic pipe. In order to ensure the molding of the spiral ridge of the correct shape, the second forming belt 18 is wound around the plastic pipe C for a pair of turns. In this embodiment, the second linear belt 18 is endless, so a guide roll (not shown) is used to circulate it. However, it should be noted that more than one independent second forming belt 18 may be used for the same purpose. In this case, the second forming belt 18 is pulled downwards by weight or some other means. In some cases, the second forming belt 18 is received in a groove between adjacent spiral ridges formed on the outer surface of the plastic pipe C. Therefore, the second forming belt 18 should have a cross section that is comparable to the cross section of the endless forming core belt 12. If the forming core belt 12 has a trapezoidal cross section, the second forming belt 18 should also have a trapezoidal cross section.

As in FIG. 1, the cutter 13 provides a helical ridge of plastic pipe C with a slit 14 extending along the helical ridge. This slit 14 makes it possible to remove the molded core belt 12 from the helical ridge of the plastic pipe C. Since the helical ridge of the plastic pipe C is cut after it has completely cooled and solidified, the helical ridge can maintain its original shape even after removing the forming core belt 12 through the slit 14. Finally, the narrow second plastic ribbon B fed from the extruder 15 is wound around the helical ridge. Since the narrow plastic ribbon B is still hot and flexible when it reaches the helical ridge, it is easily fused to the helical ridge to seal the slit 14.

FIG. 6 shows a cross section of the plastic ribbon A formed in the plastic pipe C manufactured by the method shown in FIG. This plastic ribbon A has a ridge-shaped deformation 60, a narrow side 61 and a wide side 62. Since the ridge-shaped deformation portion 60 has a trapezoidal cross section, it has an upper wall 63 to be cut. In addition, since the plastic pipe molded from the plastic ribbon A must have a flat inner surface, the plastic ribbon A has a part of the narrow side 61 and the wide side 62 formed from the molded plastic ribbon A (already formed). It must overlap spirally in such a way as to be fused to the wide side 62 of the roll wound around the roll. In this sense, narrow side 61 may be referred to as "front side" and wide side 62 as "rear side".

FIG. 7 shows a plastic ribbon A with notches 64 on the top wall 63 of the ridge shaped deformation 60. Except that, it is exactly the same as the plastic ribbon A of FIG.

FIG. 8 schematically shows the calculation of the spiral ridge from the plastic ribbon A shown in FIG. As described above, part of the narrow (front) side portion 61 and the wide (rear) side portion 62 of the plastic ribbon Z is fused to the wide (back) side portion 62 of the preceding plastic ribbon A, A plurality of second forming belts 18 are received in a spiral groove defined by the spiral ridges. The helical ridge is then provided with a slit 14 by the cutter 13 to remove the endless forming core belt 12. The hollow helical ridge thus produced is covered with a narrow plastic ribbon B fused therein, whereby the slit 4 is completely sealed.

9 shows in detail a typical example of a spiral ridge covered with a narrow plastic ribbon (B). Since the narrow plastic ribbon B is fused to the upper wall 63 of the helical ridge, the slit 14 is filled with a part of the narrow plastic ribbon B as clearly shown in FIG.

FIG. 10 shows another example of the plastic ribbon A formed from the plastic pipe C. As shown in FIG. In this embodiment, the plastic ribbon A has two ridged deformable portions 70 and 70 ', a narrow side portion 71, a wide side portion 73 and an intermediate portion 72. 11a and 11b show in detail the calculation of the helical ridges in the plastic ribbon A of FIG. Ridge deformable portion 70 covers the bottom disposed ridged deformable portion 70 'of the preceding plastic ribbon A already wound around the forming roll, the middle portion 72 and the wide side of the plastic ribbon A. 73 is fused to the wide side 73 of the preceding plastic ribbon A. FIG. In addition, the narrow side 71 of the plastic ribbon A is fused to the middle portion 72 of the preceding plastic ribbon. Thus, the plastic ribbon A is successively overlapped and fused to form a plastic pipe C having a single spiral ridge. The grooves defined in the helical ridges are filled with a second forming belt, which cooperates with the forming core belt 12 to form a spiral ridge of the correct shape. Of course, the second forming belt 18 may be a single endless forming belt wound around the plastic pipe C or may be separate belts each pulled downward by a weight. After being sufficiently cooled and solidified, the helical ridge is cut by the cutter 13 to provide a slit 14 that allows removal of the molded core belt 12 contained therein. Finally, the slit 14 of the helical ridge is closed by a narrow plastic ribbon B fused to the helical ridge. This completed helical ridge is hollow as indicated by reference numeral 75 in FIGS. 11B and 12.

13 to 16 show plastic ribbons A coated with various narrow plastic ribbons B to seal their slits. In some cases, it is important to completely cover the slit with a narrow plastic ribbon (B).

17 illustrates another example of a spiral ridge having a circular cross section. In this embodiment, an endless shaped core belt 12 'of semicircular cross section was used. By this endless molded core belt 12 ', the spiral ridge can be produced in the same manner as described above.

18 shows another example of a device according to the invention. This device itself is essentially the same as the device of FIGS. In this apparatus, the endless forming core belt 112 and the second endless forming belt 113 are wound around the forming roll 27 via guide rolls 122 and 124, respectively.

An example of the circulation of the endless forming core belt 112 and the second endless forming belt 113 is shown in FIG. 19. In this embodiment, both the endless forming core belt 112 and the second forming belt 113 are wound around the forming roll 27 and circulated through the guide rolls 122 and 124, respectively. 20 shows another example of circulation of the second forming belt 113, where the second forming belt 113 is circulated through the pulley 125 pulled downward by the weight 126.

FIG. 21 schematically illustrates another example of circulation of the endless molded core belt 250. In this example, the apparatus of the present invention has a rotatable means (D) located near the plastic pipe (C) wound around the forming roll, and the endless forming core belt 250 is a forming roll, rotatable means (D) and It is surrounded by the guide roll 251 and circulated. In particular, the endless forming core belt 250 is fed to the forming rolls in such a way as to be sandwiched between the preceding plastic ribbon A already wound around the forming roll and the newly supplied plastic ribbon A, and overlapped and fused together. It is wound around the forming roll by a number of turns toward the leading end of the forming roll while being sandwiched between the upper and lower plastic ribbon portions. The endless shaped core belt 250 is then spirally wound around the pivotable means C by a number of turns in the opposite direction, ie towards the rear end of the pivotable means C. Then, the roller is finally returned to the forming roll through the lower roll 251.

FIG. 22 shows a specific example of a device in which the endless molded core belt 250 is to be circulated in the manner shown in FIG. The apparatus for producing a plastic pipe body is substantially the same as that shown in FIGS. 2 to 4, with some minimal differences. The apparatus comprises a polymerization shaft 204 rotatably supported by a base 201, first, second and third movable members 212a, 212b and 212c, and first, second and third movable members. A forming roll 207 pivotally supported by link rods 215a, 215b, 215c and link bars 215a, 215b, 215c pivotally connected to 212a, 212b, and 212c, respectively, and a universal joint 223 The gears are connected to rods 210 connected to the forming rolls 207 through a single rod 210 and a universal joint 224, and connected to the rods 210 through a universal joint 225. Link rod 226 is connected through. Pivotally supported on the second central shaft 230 rotatably supported by the base 201, the first and second movable members 231a and 231b, and the first and second movable members 231a and 231b, respectively. Rotatable means (D) consisting of link rods 232a and 232b connected to each other and a rotatable roll 233 pivotally supported by link rods 232a and 232b at both ends thereof, the base in parallel with the forming roll 207. 201 is mounted. The first and second movable members 231a and 231b rotate the second central shaft 230 in the same manner as the first and third movable members 212a and 212c, so that the second central shaft ( 230).

The endless forming core belt 250 circulates between the forming roll 207 and the rotatable roll 233. This shape ensures smooth circulation of the endless molded core belt 250. Incidentally, the second forming belt 260 can also be similarly circulated.

Figure 23 shows another example of producing a plastic pipe according to the present invention. In this example, the endless forming core belt 312 passes through the die 311 of the extruder 310 such that the plastic ribbon A extracted from the extruder 310 has an endless forming core belt 312 fitted therein. Passing by The plastic ribbon A produced by this method of FIG. 23 is formed of a plastic pipe as shown in FIG. The plastic ribbon A has a ridge containing an endless molded core belt 12 ″ so that the sides of adjacent plastic ribbons overlap and fuse together. After completing the helical ridge on the outer surface of the plastic pipe C, cutting the helical ridge with the cutter 13, removing the endless molded core belt 12 '' there, and then sealing the slit 14 ''. Fusing the narrow plastic ribbon B to the helical ridge can be carried out in the same manner as described above.

The plastic ribbons (A) and narrow plastic ribbons (B) used in the present invention may be made of various thermoplastic resins such as, for example, polyethylene, polypropylene and other polyolefins, polyvinyl chloride and the like. The plastic ribbon A and the narrow plastic ribbon B may be made of the same material, but the plastic ribbon A may be made of a soft resin and the narrow plastic ribbon B may be made of a relatively hard resin.

For the endless molded core belt, it can be made of various materials such as, for example, hard rubber, synthetic resin, leather and the like. It may also be made of a material, for example aluminum, as long as it consists of a separating belt block attached to the endless flexible support member. In addition, depending on which spiral ridge is required, it may have various cross sections, for example, trapezoidal or semicircular cross sections.

As described above, the helical ridge of the plastic pipe according to the present invention first forms the helical ridge with an endless molded core belt, cuts the helical ridge to remove the molded core belt through the slit, and then narrows the slit of the helical ridge. Since it is formed by sealing with a plastic ribbon, it can form a hollow without deformation. Thus, the plastic pipe of the present invention has a spiral ridge of the correct shape on the outer surface. It also has a flat inner surface. In this regard, although the accompanying drawings show a relatively non-uniform inner plastic pipe, this is to emphasize the relationship of adjacent plastic ribbons in the plastic pipe of the present invention, and the spiral winding operation when the plastic ribbons are sufficiently soft. It should be noted that since they are deformed by the forming rolls at the time, their inner surfaces are substantially flat.

Although the present invention has been described with reference to the accompanying drawings, it is to be understood that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims (9)

Plastic ribbons A in soft state on a plurality of rotationally forming rolls 5; 27; 207; 307 arranged in a circle so that the plastic ribbons are spirally wound around the forming rolls, partially overlapping to be fused together. A method of manufacturing a plastic pipe (c) having a spiral ridge on the outer surface and a flat inner surface, the method comprising the steps of: (a) between the plastic ribbon already wrapped around the forming roll and the newly supplied plastic ribbon; Spirally winding the endless forming core belts 12; 112; 250; 312 around the forming rolls in such a way that a forming core belt is fitted, providing a helical ridge to the final plastic pipe; After the ribbons are fused with each other and sufficiently cooled, the spiral ridge is cut to remove the endless formed core belt from it. Providing a ridge with slits 14, 14 ′, 14 ″ extending along the helical ridge, and (c) around the helical ridge to fuse the second plastic ribbon B to the helical ridge. And winding the second plastic ribbon in a soft state to close the slit. 2. The second forming belt (18; 113) according to claim 1, wherein the second forming belt (18; 113) is accommodated in the spiral groove between adjacent ridges of the plastic pipe to form a spiral ridge of the correct shape in cooperation with the endless forming core belt. 260; 313) spirally winding the plastic pipe manufacturing method comprising a. 2. The apparatus of claim 1, further comprising: at least one second forming belt (18; 113; 260) in each spiral groove between adjacent ridges of the plastic pipe to cooperate with the endless forming core belt to form a correctly shaped spiral ridge; Positioning 313) and pulling it downwards. A plurality of rotatable forming rolls 5; 27; 207; 307 arranged in a circle, and located near the rear end of the rotatable forming roll for feeding the plastic ribbon A softly to the rotatable forming roll. Apparatus for producing a plastic pipe (c) having a spiral inner ridge and a flat inner surface, the first means (10; 15; 310) comprising: (a) a plastic ribbon already wound around the rotatable forming roll And a portion thereof is wound around the rotatable forming roll in such a manner as to sandwich the endless forming core belt between the first ribbon and the newly supplied plastic ribbon, thereby providing a spiral ridge to the final plastic pipe. Endless molded core belts (12; 112; 250; 312) and (b) spiral ridges on spiral ridges to remove the endless formed core belts from the spiral ridges; A cutter 13 for providing a slit 14; 14 '; 14' 'that extends along, and (c) a second plastic ribbon B that is fused to the spiral ridge to seal the slit 14. Apparatus for producing a plastic pipe, characterized in that it comprises a second means (15) provided downstream of the cutter (13) to provide. 5. The apparatus of claim 4, wherein the endless formed core belt is provided on its upper surface with a longitudinal groove adapted to receive the cutter during the cutting operation of the helical ridge. 5. The method of claim 4, further comprising a rotatable means and a guide roll positioned near the rotatable forming roll, wherein the endless forming core belt is first wound around the rotatable forming roll and then wound around the rotatable means. Apparatus for producing a plastic pipe characterized in that they are circulated in such a manner as to return to the rotatable forming roll via a guide roll. 6. The endless forming core belt (250) according to claim 5, wherein the rotatable means comprises a plurality of second rotatable rolls (233) arranged in a circle and extending in the same direction as the rotatable forming roll (207). ) Is wound around the rotatable forming roll by a plurality of turns from near the rear end of the rotatable forming roll toward its tip, and wound around the second rotatable roll by a plurality of turns in the opposite direction, An apparatus for producing a plastic pipe, characterized by returning to the rotatable forming roll via the guide roll. 5. A second forming belt (18) spirally wound around a final plastic pipe containing said acid free forming core belt in said spiral ridge, in order to form a spiral ridge of the correct shape in cooperation with said endless forming core belt. 113; 260; 313). 5. The belt of claim 4, wherein at least one second forming belt (18; 113; 260; 313) accommodated in each helical groove between adjacent ridges of the plastic pipe to accurately form a spiral ridge in cooperation with the endless forming core belt. Apparatus for producing a plastic pipe, characterized in that it also comprises a).