WO2005120805A9

WO2005120805A9 - Multilayer synthetic resin pipe having spiral ribs, and extrusion molding method and apparatus for manufacturing the same

Info

Publication number: WO2005120805A9
Application number: PCT/KR2005/001646
Authority: WO
Inventors: Hyo-Geun Nam
Original assignee: Hyo-Geun Nam
Priority date: 2004-06-08
Filing date: 2005-06-02
Publication date: 2007-03-01
Also published as: WO2005120805A1

Abstract

The present invention provides a multilayer synthetic resin pipe having spiral ribs, and an extrusion molding method and apparatus for manufacturing the same. The multilayer synthetic resin pipe (70) of the present invention includes a plurality of spiral ribs (74) and a plurality of through holes (73). The multilayer synthetic resin pipe (70) has increased strength and superior heat and noise insulation ability, considering the required amount of material. Furthermore, in the present invention, an inner layer (71) of the pipe (70) is thicker than an outer layer (72), so that the lifetime of the pipe is extended. As well, the through holes (73), defined in the inner and outer layers of the pipe, are disposed in a multilayered arrangement, so that, even if the multilayer pipe has a large diameter, spiral ribs do not buckle during a process of manufacturing the pipe.

Description

MULTILAYER SYNTHETIC RESIN PIPE HAVING SPIRAL

RIBS, AND EXTRUSION MOLDING METHOD AND

APPARATUS FOR MANUFACTURING THE SAME

Technical Field

[1] The present invention relates, in general, to multilayer synthetic resin pipes having spiral ribs and extrusion molding methods and apparatuses for manufacturing the same and, more particularly, to a multilayer synthetic resin pipe which has a plurality of spiral ribs and a plurality of through holes, and in which an inner layer of the pipe is thicker than an outer layer, and the through holes, defined by the spiral ribs, are disposed in a multilayered arrangement, so that the pipe has increased strength and superior heat and noise insulation ability, considering the required amount of material, and an extrusion molding method and apparatus for manufacturing the same.

[2]

Background Art

[3] Generally, among cylindrical synthetic resin pipes, which are made of synthetic resin, manufactured through extrusion molding processes, and used as sewage pipes, drain pipes, and pipes for covering electric/communication lines, a multilayer synthetic resin pipe means a pipe having a structure such that through holes are disposed into two or more layers of the pipe for preventing noise, and for increasing the bending strength and heat insulation ability.

[4] Typically, to manufacture such a multilayer synthetic resin pipe, first, a small rectangular pipe having a predetermined length is manufactured using soft PE material through an extrusion molding process. Thereafter, the rectangular pipe is wound around a separate pipe in a spiral shape, and molten resin is injected into a space defined between the spirally wound rectangular pipe, thus forming a large cylindrical pipe.

[5] However, in the above-mentioned multilayer pipe manufacturing method, several manufacturing stages and a large amount of raw material are required. As a result, there are problems of reduced productivity and increased manufacturing costs. Furthermore, because the multilayer pipe is manufactured by injecting molten resin into the space defined between the spirally wound rectangular pipe, a surface of the pipe may become uneven, thus deteriorating the appearance of the pipe. Moreover, when the pipe is used for a long period, cracks may occur at the junction between a layer of the pipe and the spiral portion formed by injecting the molten resin. As a result, the water tightness of the pipe is reduced, so that water leakage may occur. [6]

Disclosure of Invention Technical Problem

[7] Accordingly, the present invention has been made keeping in mind the above . problems occurring in the prior art, and an object of the present invention is to provide a multilayer synthetic resin pipe which includes a plurality of spiral ribs and a plurality of through holes, and has increased strength and superior heat and noise insulation ability, considering the required amount of material, and an extrusion molding method and apparatus for manufacturing the same. Another object of the present invention is to provide a multilayer synthetic resin pipe in which an inner layer of the pipe is thicker than an outer layer, thus extending the lifespan of the pipe, and the inner and outer layers are made of different materials so that the strengths of the inner and outer layers may differ from each other according to the intended purpose, and the through holes, defined in the inner and outer layers of the pipe, are disposed in a multilayered shape, so that, even if the multilayer pipe has a large diameter, the spiral ribs do not buckle during a process of manufacturing the pipe, and an extrusion molding method and apparatus for manufacturing the same.

[8]

Technical Solution

[9] In an aspect, the present invention provides an apparatus for manufacturing a multilayer synthetic resin pipe having spiral ribs, the pipe solving problems of cylindrical multilayer synthetic resin pipes in which both a plurality of through holes having various shapes and a plurality of ribs to define the through holes therebetween are formed in a space between layers of the pipe in longitudinal or circumferential straight lines. The apparatus includes: a rotating pipe forming unit mounted to an output end of a die of an extruding machine and rotated by a drive motor so that molten material is extruded through the rotating pipe forming unit, thus forming the spiral ribs, the rotating pipe forming unit having a spiral rib forming core provided with spiral rib forming gaps and a plurality of spiral rib forming protrusions having shapes such that at least one through hole is defined in the space between layers of the manufactured pipe, with a cooling air hole formed through each of the spiral rib forming protrusions so that air is injected through the cooling air hole at a predetermined pressure in a direction from a rear part to a front part of the spiral rib forming protrusion; and a holder threadedly fitted over the spiral rib forming core.

[10] In another aspect, the present invention provides an" extrusion molding method for manufacturing a multilayer synthetic resin pipe having spiral ribs, the pipe solving problems of cylindrical multilayer synthetic resin pipes in which both a plurality of through holes having various shapes and a plurality of ribs to define the through holes therebetween are formed in a space between layers of the pipe in longitudinal or circumferential straight lines. When molten synthetic resin, discharged through an output end of a die by a extruding machine, passes through a rotating pipe forming unit, the rotating pipe forming unit is rotated in a predetermined direction and at a constant speed so that spiral ribs are continuously extruded through a rear end of the rotating pipe forming unit, wherein longitudinal intervals between the spiral ribs are changed by adjusting a rotating speed of the rotating pipe forming unit.

[11] In a further aspect, the present invention provides a multilayer synthetic resin pipe, including: a plurality of ribs provided between layers of the multilayer synthetic resin pipe; and a plurality of through holes defined by the ribs.. The ribs are integrated with the multilayer synthetic resin pipe into a single body while the multilayer pipe is shaped through an extruding process, the ribs are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe and are formed in continuous spiral shapes in a longitudinal direction of the multilayer pipe, and the through holes are formed from a first end to a second end of the multilayer pipe.

[12] In yet another aspect, the present invention provides an apparatus for manufacturing a multilayer synthetic resin pipe having spiral ribs, including: first, second and third extruding machines each having a different storage tank to store therein a different kind of synthetic resin; a die coupled to the first, second and third extruding machines so that molten resin is supplied to the die, with a rotating pipe forming unit rotatably provided in the die so as to form a multilayer pipe having spiral ribs through an extrusion process; an outer diameter sizing unit to solidify the multilayer pipe extruded from the die; and driving means to generate a drive force to rotate the rotating pipe forming unit. The die includes: a hollow rotating shaft coupled to the driving means and rotatably installed in a main body of the die; the rotating pipe forming unit removably coupled to an end of the rotating shaft by a coupling bolt and rotating along with the rotating shaft; inner and outer dies provided inside and outside the rotating pipe forming unit, thus forming inner and outer layers of the multilayer pipe, respectively; first, second and third resin supply units mounted to the main body and respectively coupled to the first, second and third extruding machines to supply molten resin; and first, second and third fluid paths formed at predetermined positions in the main body to supply the molten resin from the first, second and third resin supply units into different portions of the rotating pipe forming unit. The rotating pipe forming unit includes: a plurality of spiral rib forming protrusions corresponding to through holes of the multilayer pipe to be extruded. The spiral rib forming protrusions are placed at positions closer to the outer die than to the inner die such that the inner layer of the multilayer pipe is thicker than the outer layer. [13] In still another aspect, the present invention provides a multilayer synthetic resin pipe, including: an inner layer, an outer layer and a plurality of ribs integrated together into a single body through an extruding process. The ribs are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe and are formed in spiral shapes with respect to a longitudinal direction of the multilayer pipe, and the through holes defined by the ribs are formed through the multilayer synthetic resin pipe from a first end to a second end of the pipe. The inner layer of the multilayer pipe is thicker than the outer layer.

[14] Hereinafter, a first embodiment of the present invention will be described in detail with reference to the attached drawings.

[15] FIG. 1 is a schematic view showing an apparatus for manufacturing a multilayer pipe, according to a first embodiment of the present invention. FIG. 2 is a sectional view showing an enlargement of an important part of the apparatus according to the present invention. FIG. 3 is partially broken perspective views of an outer diameter sizing unit according to the present invention. FIG.4 is a perspective view showing an enlargement of a rotating pipe forming unit according to the present invention. FIG. 5 is a perspective view of an inner diameter sizing unit according to the present invention. FIG. 6 is a broken perspective view of a multilayer synthetic resin pipe having spiral ribs according to the present invention. FIG. 7 is a perspective view showing another rotating pipe forming unit according to the present invention.

[16] The present invention provides a method for manufacturing a multilayer synthetic resin pipe which has spiral ribs and solves problems of conventional cylindrical multilayer synthetic resin pipes in which both a plurality of multilayer through holes having various shapes and a plurality of multilayer ribs to define the through holes therebetween are formed in a space between layers of the pipe in longitudinal or circumferential straight lines. To manufacture the multilayer synthetic resin pipe of the present invention having spiral ribs, when molten synthetic resin, discharged through - an output end of a die 20 by an extruding machine 10, passes through a rotating pipe forming unit 40, the rotating pipe forming unit 40 is rotated in a predetermined direction and at a constant speed. Thus, the spiral ribs are continuously extruded through the rear end of the rotating pipe forming unit.

[17] A multilayer pipe manufacturing apparatus according to the first embodiment of the present invention includes extruding machines 10 which are mounted at positions opposite the die 20 so as to supply molten resin, that is, molten synthetic resin, into the die 20, and the rotating pipe forming unit 40 which is provided in the die 20 and is forcibly rotated, so that molten material is extruded through the rotating pipe forming unit 40, thus forming the spiral ribs 74. The outer diameter sizing unit 30 is provided outside the rotating pipe forming unit 40 to support the outer surface of the pipe to be extruded. The inner diameter sizing unit 50 is provided inside the rotating pipe forming unit 40 to support the inner surface of the pipe.

[18] The rotating pipe forming unit 40 includes a spiral rib forming core 41 which is provided with spiral rib forming.gaps 44 and a plurality of spiral rib forming protrusions 42 having shapes such that at least one through hole is formed in the space between layers of the manufactured pipe. The rotating pipe forming unit 40 further includes a holder 45 which is threadedly fitted over the spiral rib forming core 41. A cooling air hole 43 is formed through each of the spiral rib forming protrusions 42 so that air is injected through the cooling air hole 43 at a predetermined pressure in a direction from the rear part to the front part of the spiral rib forming protrusion 42.

[19] As shown in the drawings, the outer diameter sizing unit 30 supports the outer surface of the multilayer pipe to be shaped while the shaped multilayer pipe moves. The outer diameter sizing unit 30 has a plurality of vacuum suction holes 31 and a plurality of air circulation paths 34 for drawing the multilayer pipe using a vacuum suction force, so that the outer surface of the multilayer pipe to be extruded becomes even without being deformed. The outer diameter sizing unit 30 further has a cooling water suction hole 32 and a cooling water path 33 for cooling the multilayer pipe. The outer diameter sizing unit 30 is removably mounted to the rotating pipe forming unit 40 for easy disassembly and assembly when replacement is required or when malfunction occurs.

[20] Meanwhile, the inner diameter sizing unit 50 supports the inner surface of the multilayer pipe to be shaped. The inner diameter sizing unit 50 has a plurality of air inlets 51 through which a vacuum suction operation is executed, and a cooling water inlet and outlet 52 for the circulation of cooling water.

[21] Furthermore, a cylinder actuation rod 53, which moves forwards and backwards within a predetermined range, is axially coupled to a rear part of the inner diameter sizing unit 50, so that the inner diameter sizing unit 50 is advanced while the multilayer pipe is extruded, thus supporting the inner surface of the multilayer pipe to be extruded, thereby ensuring a smooth extrusion molding process.

[22] As such, thanks to the easily removable rotating pipe forming unit 40, the through holes 73 can be integrally formed into at least one layer in the space between the layers of the synthetic resin pipe. The shape of the through hole 73 may be selectively changed. As well, thanks to the inner diameter sizing unit 50, the inner and outer surfaces of the multilayer synthetic resin pipe to be formed through the extrusion molding process become even and smooth.

[23] In particular, the ribs 74 are formed in a spiral shape by forcibly rotating the rotating pipe forming unit 40. Here, longitudinal intervals between the spiral ribs 74 may be changed according to the rotating speed of the rotating pipe forming unit 40. That is, the spiral ribs 74 can be easily formed in a selected shape according to the intended purpose of the multilayer synthetic resin pipe.

[24] Meanwhile, in the multilayer pipe manufactured by the extrusion molding apparatus having the above-mentioned construction, the spiral ribs 74 are integrated with the multilayer pipe into a jointless single body through an extruding process. Furthermore, the spiral ribs 74 are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe and are formed in continuous spiral shapes in a longitudinal direction of the multilayer pipe. As well, the through holes 73 are continuously formed from a first end of the multilayer pipe to a second end of the pipe without being closed.

[25] Moreover, the rotating pipe forming unit 40 has a structure such that its assembly is easy. As shown in HG. 7, the spiral ribs 74 of the multilayer synthetic resin, pipe may be formed in various shapes by replacing the spiral rib forming core 41 of the rotating pipe fprming unit 40 with another. In addition, because the spiral, ribs 74 are evenly formed regardless of the direction of spiral rib forming gaps of the spiral rib forming core 41, the multilayer synthetic resin pipe having superior stiffness can be easily manufactured.

[26] Furthermore, to forcibly rotate the rotating pipe forming unit 40, the drive means 60 is coupled to the rotating pipe forming unit 40 by a belt (not shown) or a chain (not shown). It is important to rotate the rotating pipe forming unit 40 at a constant speed.

[27] Hereinafter, a second embodiment of the present invention will be explained in detail with reference to the attached drawings.

[28] FIG. 8 is a schematic view showing a multilayer pipe manufacturing apparatus according to the second embodiment of the present invention. FIG. 9 is a sectional view showing a die and a rotating pipe forming unit of the apparatus according to the second embodiment of the present invention. FIG. 10 is a sectional view showing another rotating pipe forming unit of the apparatus according to the second embodiment of the present invention. FIGS. 11, 12 and 13 are front views showing various examples of an inner die of the apparatus according to the second embodiment of the present invention. FIG. 14 is a sectional view showing an outer diameter sizing unit of the apparatus according to the second embodiment of the present invention. FIGS. 15, 16 and 17 are sectional views showing various examples of multilayer pipes manufactured by the apparatus according to the second embodiment of the present invention.

[29] As shown in FIG. 8, the multilayer pipe manufacturing apparatus according to the second embodiment of the present invention includes first, second and third extruding machines 10a, 10b and 10c, and a die 20' which shapes a multilayer pipe, on which spiral ribs are formed, through an extrusion molding process using molten resin supplied from the first, second and third extruding machines 10a, 10b and 10c. The multilayer pipe manufacturing apparatus further includes an outer diameter sizing unit 30' to cool and solidify the multilayer pipe to be extruded from the die 20', and a driving means 60' which rotates a rotating shaft, which is provided in the die 20' .

[30] In the drawings, the reference numeral 90 denotes a cooler, 100 denotes a drawing machine, 110 denotes a printer, and 120 denotes a cutting machine.

[31] The first, second and third extruding machines 10a, 10b and 10c each has a different storage tank which stores therein a different kind of molten synthetic resin.

[32] As shown in FIG. 9, the die 20' includes first, second and third resin supply units

22, 23 and 24 which are respectively coupled to the first, second and third extruding machines 10a, 10b and 10c and are supplied with molten resin. The die 20' further includes a rotating pipe forming unit 40' which shapes a multilayer pipe, on which spiral ribs are formed, using the molten resin to be supplied from the first, second and third resin supply units 22, 23 and 24. The die 20' further includes inner and outer dies 28 and 29 which are provided inside and outside the rotating pipe forming unit 40', thus supporting inner and outer layers of the multilayer pipe to be extruded, respectively. The die 20' further includes a rotating shaft 47 which is rotated by the driving means 60', thus forcibly rotating the rotating pipe forming unit 40'.

[33] The first, second and third resin supply units 22, 23 and 24 are mounted at predetermined positions to a main body 21 of the die 20'. Here, the first resin supply unit 22 is coupled to the first extruding machine 10a and is supplied with molten resin from the first extruding machine 10a. The second resin supply unit 23 is coupled to the second extruding machine 10b and is supplied with molten resin from the second extruding machine 10b. The third resin supply unit 24 is coupled to the third extruding machine 10c and is supplied with molten resin from the third extruding machine 10c. The molten resin, supplied into the first, second and third resin supply units 22, 23 and 24, is supplied into the rotating pipe forming unit 40' through different fluid paths.

[34] In detail, the molten resin, which is supplied from the first resin supply unit 22, moves into the rotating pipe forming unit 40' through a first fluid path 25, which is formed in the main body 21. Here, the first fluid path 25 is formed such that the molten resin moves along a circumferential outer portion of the rotating pipe forming unit 40', that is, along the outer die 29' . Thus, the molten resin, supplied from the first extruding machine 10, forms an outer layer 72 of a multilayer pipe 70.

[35] The molten resin, which is supplied from the second resin supply unit 23, moves into the rotating pipe forming unit 40' through a second fluid path 26, which is formed in the main body 21. Here, the second fluid path 26 is formed such that the molten resin moves along a circumferential inner portion of the rotating pipe forming unit 40', that is, along the inner die 28. Thus, the molten resin, supplied from the second extruding machine 10b, forms an inner layer 71 of the multilayer pipe 70.

[36] Furthermore, the molten resin, which is supplied from the third resin supply unit 24, moves into the rotating pipe forming unit 40' through a third fluid path 27, which is formed in the main body 21. Here, the third fluid path 27 is formed such that the molten resin moves between the first and second fluid paths 25 and 26. Thus, the molten resin, supplied from the third extruding machine 10c, forms spiral ribs 74 of the multilayer pipe 70.

[37] As such, different kinds of molten resins, which are supplied from the first, second and third extruding machines 10a, 10b and 10c, respectively form the outer layer, the inner layer and spiral ribs of the multilayer pipe. Therefore, in the present invention, the outer layer, the inner layer and the spiral ribs of the multilayer pipe may be made of different materials and colors. Furthermore, of the first, second and third extruding machines 10a, 10b and 10c, only a desired extruding machine may be selectively operated while manufacturing a multilayer pipe. Moreover, if the amount of molten resin supplied from the desired extruding machine is increased, the part of the multilayer pipe formed by the desired extruding machine may become thicker.

[38] Meanwhile, the rotating pipe forming unit 40' is removably coupled to a first end of the rotating shaft 47, which is placed through the main body 21 of the die 20' , so that the rotating pipe forming unit 40' is forcibly rotated by the rotation of the rotating shaft 47. Here, the rotating shaft 47 is coupled at a second end thereof to the driving means 60' so that the rotating shaft 47 is rotated by power generated by the driving means 60' . The driving means 60' is not shown in detail, but a typical motor may be used as the driving means 60' . Furthermore, the motor and the rotating shaft may be coupled to each other by a belt or chain so that the rotating shaft is rotated by the motor at a constant speed.

[39] The rotating pipe forming unit 40', which is coupled to and rotated by the rotating shaft 47, includes a spiral rib forming core 41 ' which forms through holes in the multilayer pipe to be shaped. The spiral rib forming core 41' has a plurality of spiral rib forming protrusions 42' which correspond to the through holes to be formed in the multilayer pipe 70 and are arranged in a circular shape. A cooling air hole 43', through which air is supplied to cool molten resin to be extruded, is formed through each spiral rib forming protrusion 42'. Furthermore, the cooling air holes 43' communicate with the interior of the hollow rotating shaft 47, so that cooling air is supplied to the cooling air holes 43' from a blower 80 which is coupled to the rotating shaft 47 by an air supply pipe 81.

[40] Furthermore, a stop plate 46 is coupled to a front end of the inner die 28, which is fastened to the front end of the rotating pipe forming unit 40' , by locking bolts, so that a user can adjust the amount of cooling air supplied into the cooling air holes 43' . IQ other words, if the locking bolts are tightened such that the stop plate 46 comes into close contact with the inner die 28, all of the cooling air is supplied into the cooling air holes 43' from the rotating shaft 47. If there is a gap between the stop plate 46 and the front end of the inner die 28, only some of the cooling air is supplied into the cooling air holes 43'.

[41] The spiral rib forming protrusions 42' are placed at positions closer to the outer die

29, which will be explained later herein, than to the inner die so that the inner layer 71 of the multilayer pipe 70 is formed thicker than the outer layer 72.

[42] Furthermore, as shown in FIG. 10, the rotating pipe forming unit 40' may have a cross-sectional shape such that a plurality of spiral rib forming protrusions 42' and 42a' is disposed in two or more layers. Typically, as the size of the multilayer pipe is increased, the thickness of the layers of the multilayer pipe is increased. Furthermore, the height of each rib 74, formed between the through holes, should be increased. Therefore, in the case of a large multilayer pipe, when the rotating pipe forming unit 40' is rotated to form the multilayer pipe, the ribs 74 may buckle. However, the rotating pipe forming unit 40' of FIG. 10 can prevent this phenomenon from occurring.

[43] In detail, the plurality of second spiral rib forming protrusions 42a' is arranged in a circular shape outside the plurality of first spiral rib forming protrusions 42', which is arranged in a circular shape, with gaps between the first and second spiral rib forming protrusions 42' and 42a'. The rotating pipe forming unit 40' having the above- mentioned construction can shape a multilayer pipe 70 having a structure in which first and second through holes 73 and 73' are disposed in a layered shape. Here, the rotating pipe forming unit 40' may be constructed, such that the spiral rib forming protrusions 42' and 42a' are disposed in two, three or more layers, depending on the diameter of the pipe 70.

[44] Furthermore, the first and second spiral rib forming protrusions 42' and 42a' , which are respectively placed at inside and outside positions, may be aligned on the same radial lines or, alternatively, may be alternately arranged.

[45] Meanwhile, the inner and outer dies 28 and 29 are provided at inside and outside positions of the rotating pipe forming unit 40' so as to shape inner and outer layers of the multilayer pipe to be formed through the extrusion molding process. Here, the outer die 29 is mounted to the main body 21 of the die, and the inner die 28 is fastened to the rotating pipe forming unit 40' and is rotated along with the rotating pipe forming unit 40'.

[46] As shown in FIG. 11, a plurality of grooves 28a is formed on a circumferential outer surface of the inner die 28 so as to shape a plurality of assistant ribs 75 on an inner surface of the multilayer pipe 70. The grooves 28a are placed at positions aligned with spaces between the spiral rib forming protrusions 42' of the rotating pipe forming unit 40'. Thus, the plurality of assistant ribs 75, which extend from the spiral ribs 74, is formed on the inner surface of the multilayer pipe 70 when the multilayer pipe 70 is extruded.

[47] The assistant ribs 75, which protrude inwards from the multilayer pipe 70, cause fluid flowing through the interior of the multilayer pipe 70 to become turbulent so as to generate air bubbles, thus having an effect of purification of the fluid.

[48] Alternatively, as shown in FIG. 12, second grooves 28a may be formed at positions aligned with the spiral rib forming protrusions 42', but are not formed at positions aligned with spaces between the spiral rib forming protrusions 42'. The second grooves 28a, which are formed at positions aligned with the spiral rib forming protrusions 42', serve to prevent spiral ribs 74 of a multilayer pipe 70 to be manufactured from protruding inwards from the inner surface of the multilayer pipe 70 due to the difference between contraction rates of the through holes 73 and the spiral ribs 74. That is, an additional amount of molten resin corresponding to the difference between contraction rates of the through holes 73 and the spiral ribs 74 is supplied to the second grooves 28a around which the through holes 73 are formed, thus manufacturing the multilayer pipe 70 having planar inner surface.

[49] As a further .alternative, as shown in FIG. 13, a plurality of protrusions 28b may be formed on an outer surface of the inner die 28, thus manufacturing a multilayer pipe 70 having the planar inner surface. Here, the protrusions 28b are disposed at predetermined positions aligned with spaces between the spiral rib forming protrusions 42' of the rotating pipe forming unit 40. That is, the protrusions 28b reduce the amount of molten resin to be supplied to form the spiral ribs 74 by the amount of molten resin corresponding to the difference between contraction rates of the through holes 73 and the spiral ribs 74. Thus, a multilayer pipe 70 having a planar inner surface can be manufactured.

[50] As such, in the present invention, a multilayer pipe having assistant ribs 75 or having a planar inner surface may be manufactured by changing the positions of the grooves 28a which are formed on the outer surface of the inner die 28.

[51] As shown in FIG. 14, the outer diameter sizing unit 30' is reduced in diameter from an inlet to an outlet. The outer diameter sizing unit 30' includes a passage 35, through which a multilayer pipe to be manufactured passes, and a plurality of vacuum suction holes 31' which are provided along a circumferential outer surface of the passage 35 so as to evenly draw the outer surface of the multilayer pipe 70 to be extruded, so that the outer surface of the multilayer pipe becomes even and smooth without being deformed. The outer diameter sizing unit 30' further includes a plurality of cooling water suction holes 32' which are provided along the outer surface of the passage 35 to spray water onto the outer surface of the multilayer pipe 70 to be extruded, so that the multilayer pipe 70 is cooled and smoothly drawn by the vacuum suction holes 31'.

[52] As such, because water is sprayed onto the outer surface of the multilayer pipe 70 which enters the outer diameter sizing unit 30' , a film which fills up a gap between the multilayer pipe 70 and vacuum suction holes 31' is formed, thus enhancing the vacuum suction force of the vacuum suction holes 31 ' .

[53] Preferably, the cooling water suction holes 32' spray tepid water having a temperature ranging from approximately 30° to approximately 55° so as to prevent the multilayer pipe to be shaped from being deformed due to rapid temperature change.

[54] In the multilayer synthetic resin pipe manufacturing apparatus having the above- mentioned construction, molten resins are supplied from the first, second and third extruding machines 10a, 10b and 10c to the rotating pipe forming unit 40' through the first, second and third resin supply units 22, 23 and 24 and the first, second and third fluid paths 26, 26 and 27, respectively. At this time, the rotating pipe forming unit 40' is rotated by the rotating shaft 47 at a constant speed, thus continuously shaping the spiral ribs 74 by which the inner layer 71 and the outer layer 72 of the multilayer pipe to be manufactured are connected to each other.

[55] Meanwhile, as shown in FIG. 15, in the multilayer pipe 70 manufactured by the above-mentioned apparatus, the inner layer 71, the outer layer 72 and the spiral ribs 74 are integrally formed into a jointless single body. The spiral ribs 74 are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe 70 and are formed in continuously spiral shapes in a longitudinal direction of the multilayer pipe 70. The plurality of through holes 73, Which are defined by the spiral ribs 74, are formed from a first end to a second end of the multilayer pipe 70 without being closed. The inner layer 71 of the multilayer pipe 70 is thicker than the outer layer . 72. Furthermore, the inner layer 71, the outer layer 72 and the spiral ribs 74 are made of different materials or colors according to the kinds of molten resin to be supplied from the first, second and third extruding machines 10a, 10b and 10c.

[56] Meanwhile, when extruding a multilayer pipe, the multilayer pipe may have a plurality of assistant ribs 75 on the inner surface thereof or, alternatively, may have a planar inner surface, depending on the shape of the inner die 28. Thus, the user can selectively manufacture such multilayer pipes.

[57] As such, the multilayer pipe 70 may be manufactured such that the outer layer 71 and the inner layer 72 are made of different materials or colors by supplying different kinds of molten resins into the first, second and third extruding machines 10a, 10b and 10c. For example, because the possibility of abrasion to the outer layer and the spiral ribs is relatively low, they may be made of inexpensive resin. Because the possibility of abrasion to the inner layer of the multilayer pipe is relatively high, it may be made of synthetic resin having superior abrasion resistance. Then, the multilayer pipe having superior properties can be manufactured at reduced cost.

[58] Meanwhile, as shown in FIGS. 16 and 17, the multilayer pipe 70 may have a structure in which a plurality of first and second through holes 73 and 73' are partitioned by a partition layer into at least two layers. Furthermore, the first and second through holes 73 and 73', which are disposed in a multilayered shape, are alternately arranged based on the partition layer 76. As such, the multilayer pipe 70 may be manufactured in various cross-sectional shapes. Such a change in the cross-sectional shape is realized by changing the rotating pipe forming unit 40' .

[59] The multilayer pipe 70 having the above-mentioned construction is used for various purposes, for example, a water or sewage pipe, a gas pipe, an electrical wiring pipe, etc. In the multilayer pipe having the multilayered cross-section, the outermost through holes, which are placed adjacent to the outer layer of the multilayer pipe, serve to protect the multilayer pipe, thus enhancing the durability of the multilayer pipe.

[60] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[61]

Advantageous Effects

[62] As described above, the present invention can manufacture a multilayer synthetic resin pipe, which is integrally formed into a single body, and in which inner and outer layers of the pipe maintain even and smooth shapes. In addition, spiral ribs are integrally shaped with the inner and outer layers. Consequently, the present invention provides a multilayer synthetic resin pipe having superior quality at a relatively reduced cost. Furthermore, the inner layer of the multilayer pipe is thicker than the outer layer, and the inner and outer layers may be made of different materials and colors. Therefore, the present invention can manufacture a multilayer pipe having superior properties at reduced cost, and the multilayer pipe may be used for a sewage pipe. Moreover, in the present invention, through holes are disposed in a multilayered arrangement. Therefore, even in the case of a large pipe, the present invention prevents the spiral ribs from buckling when manufacturing a large pipe, and can increase the strength of the multilayer pipe.

[63]

Brief Description of the Drawings

[64] FIG. 1 is a schematic view showing an apparatus for manufacturing a multilayer pipe, according to a first embodiment of the present invention;

[65] FIG. 2 is a sectional view showing an enlargement of an important part of the apparatus according to the present invention; [66] FIG. 3 is partially broken perspective views of an outer diameter sizing unit according to the present invention; [67] FIG. 4 is a perspective view showing an enlargement of a rotating pipe forming unit according to the present invention; [68] FTG. 5 is a perspective view of an inner diameter sizing unit according to the present invention; [69] FIG. 6 is a broken perspective view of a multilayer synthetic resin pipe having spiral ribs according to the present invention; [70] FIG. 7 is a perspective view showing another rotating pipe forming unit according to the present invention; [71] FIG. 8 is a schematic view showing a multilayer pipe manufacturing apparatus according to the second embodiment of the present invention; [72] FIG. 9 is a sectional view showing a die and a rotating pipe forming unit of the apparatus according to the second embodiment of the present invention; [73] FIG. 10 is a sectional view showing another rotating pipe forming unit of the apparatus according to the second embodiment of the present invention; [74] FIGS. 11, 12 and 13 are front views showing various examples of an inner die of the apparatus according to the second embodiment of the present invention; [75] FIG. 14 is a sectional view showing an outer diameter sizing unit of the apparatus according to the second embodiment of the present invention; and [76] FIGS. 15, 16 and 17 are sectional views showing various examples of a multilayer pipe manufactured by the apparatus according to the second embodiment of the present invention. [77]

[78] <Description of the elements in the drawings>

[79] (10): extruding machine (10a): first extruding machine

[80] (10b): second extruding machine

[81] (10c): third extruding machine

[82] (20)(20'):dies (21): main body

[83] (22): first resin supply unit

[84] (23): second resin supply unit

[85] ' (24): third resin supply unit

[86] (25): first fluid path (26): second fluid path

[87] (27): third fluid path (28): inner die

[88] (28a): groove (28b): protrusion

[89] (29): outer die

[90] (30)(30^!): outer diameter sizing units [91] (31): vacuum suction hole {32): cooling water suction hole

[92] (33): cooling water path (34): air circulation path

[93] (35): passage (40)(40')'- rotating pipe forming unit

[94] (41): spiral rib forming core

[95] (42)(42'): spiral rib forming protrusions

[96] (43): cooling air hole

[97] (44): spiral rib forming gap (45): holder

[98] (46): stop plate (47): rotating shaft

[99] (50): inner diameter sizing unit

[100] (51): air inlet (52): cooling water inlet and outlet

[101] (53): cylinder actuation rod (60): driving means

[102] (70): multilayer synthetic resin pipe

[103] (71): inner layer (72): outer layer

[104] (73),(73^!): through holes (74): spiral ribs

[105] (75): assistant ribs (76): partition layer

[106] (80): blower (81): supply pipe

Claims

[1] An apparatus for manufacturing a multilayer synthetic resin pipe having spiral ribs, the pipe solving problems of cylindrical multilayer synthetic resin pipes in which both a plurality of through holes having various shapes and a plurality of ribs to define the through holes therebetween are formed in a space between layers of the pipe in longitudinal or circumferential straight lines, the apparatus comprising: a rotating pipe forming unit (40) mounted to an output end of a die (20) of an extruding machine (10) and rotated by a drive motor (60) so that molten material is extruded through the rotating pipe forming unit, thus forming the spiral ribs (74), the rotating pipe forming unit comprising: a spiral rib forming core (41) provided with spiral rib forming gaps (44) and a plurality of spiral rib forming protrusions (42) having shapes such that at least one through hole is defined in the space between layers of the manufactured pipe, with a cooling air hole (43) formed through each of the spiral rib forming protrusions (42) so that air is injected through the cooling air hole (43) at a predetermined pressure in a direction from a rear part to a front part of the spiral rib forming protrusion (42); and a holder (45) threadedly fitted over the spiral rib forming core (41).

[2] An extrusion molding method for manufacturing a multilayer synthetic resin pipe having spiral ribs, the pipe solving problems of cylindrical multilayer synthetic resin pipes in which both a plurality of through holes having various shapes and a plurality of ribs to define the through holes therebetween are formed in a space between layers of the pipe in longitudinal or circumferential straight lines, wherein when molten synthetic resin, discharged through an output end of a die (20) by a extruding machine (10), passes_. through a rotating pipe forming unit (40), the rotating pipe forming unit (40) is rotated in a predetermined direction and at a constant speed so that spiral ribs (74) are continuously extruded through a rear end of the rotating pipe forming unit, wherein longitudinal intervals between the spiral ribs (74) are changed by adjusting a rotating speed of the rotating pipe forming unit (40).

[3] A multilayer synthetic resin pipe, comprising: a plurality of ribs provided between layers of the multilayer synthetic resin pipe; and a plurality of through, holes defined by the ribs, wherein the ribs are integrated with the multilayer synthetic resin pipe into a single body while the multilayer pipe is shaped through an extruding process, the ribs (74) are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe and are formed in continuous spiral shapes in a longitudinal direction of the multilayer pipe, and the through holes (73) are formed from a first end to a second end of the multilayer pipe.

[4] An apparatus for manufacturing a multilayer synthetic resin pipe having spiral ribs, comprising: first, second and third extruding machines (10a, 10b and 10c) each having a different storage tank to store therein a different kind of synthetic resin; a die (20') coupled to the first, second and third extruding machines (10a, 10b and 10c) so that molten resin is supplied to the die (20'), with a rotating pipe forming unit (40') rotatably provided in the die (20') so as to form a multilayer pipe having spiral ribs through an extrusion process; an outer diameter sizing unit (30') to solidify the multilayer pipe extruded from the die (20'); and driving means (60') to generate a drive force to rotate the rotating pipe forming unit (40^s), wherein the die (20') comprises: a hollow rotating shaft (47) coupled to the driving means (60') and rotatably installed in a main body (21) of the die (20'); the rotating pipe forming unit (40') removably coupled to an end of the rotating shaft (47) by a coupling bolt and rotating along with the rotating shaft (47); inner and outer dies (28 and 29) provided inside and outside the rotating pipe forming unit (40'), thus forming inner and outer layers of the multilayer pipe, respectively; first, second and third resin supply units (22, 23 and 24) mounted to the main body and respectively coupled to the first, second and third extruding machines (10a, 10b and 10c) to supply molten resin; and first, second and third fluid paths (25, 26 and 27) formed at predetermined positions in the main body (21) to supply the molten resin from the first, second and third resin supply units (22, 23 and 24) into different portions of the rotating pipe forming unit (40'), and the rotating pipe forming unit (40^s) comprises: a plurality of spiral rib forming protrusions (42') corresponding to through holes of the multilayer pipe to be extruded, the spiral rib forming protrusions (42') being placed at positions closer to the outer die (29) than to the inner die such that the inner layer of the multilayer pipe is thicker than the outer layer.

[5] . The multilayer synthetic resin pipe manufacturing apparatus according to claim 4, wherein the spiral rib forming protrusions (42') of the rotating pipe forming unit (40') comprise: at least two spiral rib forming protrusions (42', 42a') spaced apart from each other and having a layered cross-sectional structure, such that at least two through holes of the multilayer pipe to be extruded are formed in a mul- tilayered arrangement.

[6] The multilayer synthetic resin pipe manufacturing apparatus according to claim 4 or 5, further comprising: a cooling air hole (43') formed through each spiral rib forming protrusion of the rotating pipe forming unit (40') and communicating with the hollow rotating shaft (47); an air supply pipe (81) mounted to a first end of the rotating shaft (47) to inject cooling air supplied from a blower,(80); and a stop plate (46) coupled to the inner die (28), which is fastened to the rotating pipe forming unit (40') mounted to a second end of the rotating shaft (47), by locking bolts, so that the amount of cooling air supplied into the cooling air holes (43') is adjusted according to a coupling state of the stop plate (46).

[7] The multilayer synthetic resin pipe manufacturing apparatus according to claim

6, wherein the inner die (28) is fastened to the rotating pipe forming unit (40') such that the inner die (28) is rotated along with the rotating pipe forming unit (40'), and the inner die (28) comprises a plurality of grooves (28a) on an outer surface thereof at predetermined positions aligned with spaces between the spiral rib forming protrusions (42'), so that a plurality of assistant ribs (75) is formed on an inner surface of a multilayer pipe when the multilayer pipe is extruded by the multilayer synthetic resin pipe manufacturing apparatus.

[8] The multilayer synthetic resin pipe manufacturing apparatus according to claim

6, wherein the inner die (28) is fastened to the rotating pipe forming unit (40') such that the inner die (28) is rotated along with the rotating pipe forming unit (40'), and the inner die (28) comprises a plurality of grooves (28a) on an outer surface thereof at predetermined positions aligned with the spiral rib forming protrusions (42'), thus extruding a multilayer pipe having a planar inner surface.

[9] The multilayer synthetic resin pipe manufacturing apparatus according to claim

6, wherein the inner die (28) is fastened to the rotating pipe forming unit (40') such that the inner die (28) is rotated along with the rotating pipe forming unit (40'), and the inner die (28) comprises a plurality of protrusions (28b) on an outer surface thereof at predetermined positions aligned with spaces between the spiral rib forming protrusions (42'), thus extruding a multilayer pipe having a planar inner surface.

[10] The multilayer synthetic resin pipe manufacturing apparatus according to claim

4, wherein the outer diameter sizing unit (30') supports an outer surface of the multilayer pipe to be extruded, and comprises: a plurality of vacuum suction holes (31') to draw the outer surface of the multilayer pipe using a vacuum suction force, so that the outer surface of the multilayer pipe becomes even without being deformed; and a plurality of cooling water suction holes (32') spraying water onto the outer surface of the multilayer pipe so that the multilayer pipe is smoothly drawn by the vacuum suction holes (31'). [11] A multilayer synthetic resin pipe, comprising: an inner layer (71), an outer layer

(72) and a plurality of ribs (74) integrated together into a single body through an extruding process, wherein the ribs (74) are spaced apart from each other at regular intervals in a circumferential direction of the multilayer pipe and are formed in spiral shapes with respect to a longitudinal direction of the multilayer pipe, and the through holes (73) defined by the ribs (74) are formed through the multilayer synthetic resin pipe from a first end to a second end of the pipe, wherein the inner layer (71) of the multilayer pipe is thicker than the outer layer (70).

[12] The multilayer synthetic resin pipe according to claim 11, wherein the through holes (73) have multilayered structures in that through holes (73, 73') are partitioned by a partition layer (76) into at least two layers.

[13] The multilayer synthetic resin pipe according to claim 12, wherein the through holes (73, 73'), which are formed in a multilayered arrangement, are alternately arranged on opposite sides of the partition layer (76).

[14] The multilayer synthetic resin pipe according to any one of claims 11 through 13, further comprising: a plurality of assistant ribs (75) protruding inwards from an inner surface of the multilayer pipe at predetermined positions aligned with the spiral ribs (74), each of the assistant ribs (75) being formed in the same spiral shape as the spiral ribs (74), so that the assistant ribs (75) cause fluid flowing through an interior of the multilayer pipe to be turbulent so as to generate air bubbles, thus purifying the fluid.

[15] The multilayer synthetic resin pipe according to claim 14, wherein the inner layer

(71), the outer layer (72) and the spiral ribs (74) are made of different materials or colors.