Expandable corrugated pipe and composite pipe equipped with same

Abstract

To provide: a telescopic corrugated pipe having high elasticity, scratch resistance and flatness resistance; and a composite pipe which can be reduced in a manufacturing cost.SOLUTION: In a telescopic corrugated pipe 10 which is formed of resin containing polyethylene as a main component into a bellows shape with protrusions 11 and recesses 12 alternately and continuously arranged along a pipe axial direction: the protrusion 11 has sidewalls 11a and a cylindrical short cylinder part 11b, and an average wall thickness T1 is 0.4 mm to 1.0 mm inclusive, and a width of the short cylinder parts 11b is 2.5 mm to 3.5 mm inclusive; the recess 12 is formed in a V shape with a maximum width Wg of 0.5 mm to 1.5 mm inclusive constituted of the sidewalls 11a of the two protrusions 11 neighboring each other in a pipe axial direction; a length of one pitch P between the protrusion 11 and the recess 12 is equal to or longer than 3.5 mm, and shorter than 4.5 mm; and a ratio of the maximum width Wg of the recess 12 with respect to a length of one pitch is equal to or higher than 25%. Also, a composite pipe 1 is formed of the telescopic corrugated pipe 10 and a plastic resin pipe 20.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an expansion / contraction corrugated pipe formed into a bellows shape from a resin whose main component is polyethylene, and to a composite pipe whose outer periphery is covered with the expansion / contraction corrugated pipe. [Background technology]

[0002] Flexible plastic pipes for cold and hot water supply are made of cross-linked polyethylene, polybutene, etc., and therefore have soft surfaces, so their outer peripheries are covered and protected by covering pipes. By protecting the flexible plastic pipes with covering pipes in this way, even if the flexible plastic pipes rub against the structural members of a building during plumbing work, for example, the covering pipes prevent scratches on the surfaces of the flexible plastic pipes.

[0003] Various proposals have been made regarding cladding pipes. For example, Patent Document 1 proposes a cladding pipe made of a corrugated pipe with a bellows-like shape. Here, the corrugated pipe has peaks and valleys with a semicircular cross section that are alternately arranged in the pipe axis direction, and connecting portions that connect these peaks and valleys and are approximately perpendicular to the pipe axis, and its cross section forms a corrugated shape. Such a corrugated pipe is hard even though it is thin, and can therefore protect a flexible resin pipe.

[0004] In addition to protecting the flexible plastic pipe, the corrugated pipe is also required to be stretchable in the pipe axis direction. This is because, when connecting the end of the flexible plastic pipe to a joint such as a header, water tap, or hot water tap, the end of the corrugated pipe must be shifted away from the end of the flexible plastic pipe to shrink the corrugated pipe in the axial direction and expose the end of the flexible plastic pipe. According to Patent Document 1, by making the wall thickness of the peaks of the corrugated pipe (e.g., 0.25 mm) thinner than the wall thickness of the valleys and connecting parts (e.g., 0.5 mm), elastic deformation of the peaks is facilitated, making the corrugated pipe stretchable in the pipe axis direction.

[0005] Patent Document 2 proposes a double-pipe cladding pipe including a corrugated pipe and an intermediate member interposed between the corrugated pipe and a flexible resin pipe. The corrugated pipe has short cylindrical peaks and valleys alternately arranged in the pipe axis direction, and a connecting portion connecting the peaks and valleys and substantially perpendicular to the pipe axis. The corrugated pipe is made of low-density polyethylene and has a thin wall (e.g., 0.1 to 0.4 mm thick). This allows for enhanced axial flexibility, but its low scratch resistance means it cannot protect the flexible resin pipe by itself. In other words, the cladding pipe proposed in Patent Document 2 uses the intermediate member to protect the flexible resin pipe. Furthermore, the intermediate member is made of a foaming agent, allowing the cladding pipe to retain heat. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-093547 [Patent Document 2] WO2018 / 123779 publication Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, the cladding pipe, which is made of a corrugated pipe for protecting the flexible resin pipe, is required to have the function of protecting the flexible resin pipe and flexibility in the pipe axis direction. In recent years, the cladding pipe has also been required to have a heat-retaining function (insulation function).

[0008] The corrugated pipe proposed in Patent Document 1 is made of hard polyethylene and therefore has basically high scratch resistance and is excellent in protecting the resin pipe, but has the disadvantage of being poor in elasticity in the pipe axial direction.

[0009] Further reducing the thickness of the crests in an attempt to increase the flexibility of the corrugated pipe would result in a decrease in scratch resistance. Therefore, with the corrugated pipe proposed in Patent Document 1, it is difficult to achieve both flexibility and scratch resistance, and the heat retention function is also poor.

[0010] Furthermore, in the cladding pipe made of the corrugated pipe proposed in Patent Document 2, when the cladding pipe is dragged at the construction site, it is easily torn due to the low scratch resistance of the corrugated pipe, and the intermediate material is exposed at the torn part, damaging the appearance. Furthermore, if the intermediate material is damaged by continued dragging after the corrugated pipe is torn, it may lead to damage to the flexible resin pipe. Furthermore, there is a limit to how much the flexibility of the corrugated pipe can be increased due to the resistance of the intermediate material. Another problem is that the cladding pipe has a double structure of the corrugated pipe and the intermediate material, which increases the manufacturing cost.

[0011] The present invention has been made in consideration of the above problems, and its object is to provide an expansion corrugated pipe having high flexibility, scratch resistance, and flattening resistance, and a composite pipe including the expansion corrugated pipe that can be manufactured at low cost. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the present invention provides an expandable corrugated pipe that coats the outer periphery of a flexible resin pipe and is formed into a bellows shape by alternately connecting convex portions that convex outward in the radial direction and concave portions that concave inward in the radial direction along the pipe axis direction using a resin whose main component is polyethylene, wherein the convex portions have a pair of side walls that are inclined with respect to the pipe axis and a cylindrical short cylindrical portion connected by the side walls, and have an average wall thickness of 0.4 mm or more and less than 1.0 mm, and a width of the short cylindrical portion of 2.5 mm or more and less than 3.5 mm, and the concave portions are formed into a V-groove shape with a maximum width of 0.5 mm or more and less than 1.5 mm by the side walls of two of the convex portions that are adjacent in the pipe axis direction, the length of one pitch between the convex portions and the concave portions that are adjacent in the pipe axis direction is 3.5 mm or more and less than 4.5 mm, and the ratio of the maximum width of the concave portions to the length of one pitch is 25% or more.

[0013] According to the above configuration, since the expansion corrugated pipe is molded from a resin whose main component is flexible polyethylene, the contractibility of the expansion corrugated pipe is enhanced, and when connecting the expansion corrugated pipe to a joint or the like of a flexible resin pipe, the end of the expansion corrugated pipe on the connecting side can be easily exposed by pressing the end of the expansion corrugated pipe in the pipe axial direction to compress it, and the flexible resin pipe can be connected to a joint or the like easily and in a short time.

[0014] Furthermore, since the average thickness of the convex portions is set to 0.4 mm or more and less than 1.0 mm, a sufficient cutting allowance can be secured for the convex portions, thereby improving the scratch resistance of the stretchable corrugated pipe.

[0015] In order to prevent flattening of an expansion corrugated pipe due to external loads and ensure high flattening resistance for the expansion corrugated pipe, it is desirable that the repeating pitch of the convex and concave portions be narrow. As a result of analysis using the finite element method, it was revealed that sufficient flattening resistance can be ensured for the expansion corrugated pipe by setting the width of the short cylindrical portion of the convex portion to be 2.5 mm or more and less than 3.5 mm, the maximum width of the concave portion to be 0.5 mm or more and less than 1.5 mm, the length of one pitch between adjacent convex and concave portions in the axial direction of the pipe to be 3.5 mm or more and less than 4.5 mm, and the ratio of the maximum width of the concave portion to the length of this one pitch to be 25% or more.

[0016] Here, the expansion corrugated pipe may have a multilayer structure. The resin constituting the expansion corrugated pipe may be foamed polyethylene with an expansion ratio of 1.05 to 4 times, or may be low-density polyethylene. The resin constituting the expansion corrugated pipe may partially contain a resin other than polyethylene.

[0017] When the expansion corrugated pipe is made of foamed polyethylene, the foamed polyethylene may be one in which the expansion ratio becomes continuously lower than that of the inner layer as it approaches the outer layer, or one in which the expansion ratio changes discontinuously from the inner layer to the outer layer.

[0018] Furthermore, a plurality of holding protrusions that hold the flexible resin pipe concentrically may be provided protruding radially inward from the inner surface of the expandable corrugated pipe, and by adopting such a configuration, an insulating air layer can be stably formed between the expandable corrugated pipe and the flexible resin pipe.

[0019] The present invention is also characterized in that a composite pipe is formed from the expansion / contraction corrugated pipe configured as described above and a flexible resin pipe arranged approximately concentrically inside the expansion / contraction corrugated pipe, wherein the average value of the radial gap formed between the inner peripheral portion of the expansion / contraction corrugated pipe and the outer peripheral portion of the flexible resin pipe is set to 4 mm or more.

[0020] According to the composite pipe of the present invention, there is no intermediate material between the stretchable corrugated pipe and the flexible resin pipe, and a radial gap of 4 mm or more is formed between them, and this radial gap forms an insulating air layer, which improves the heat retention of the flexible resin pipe and keeps the temperature change of the fluid flowing through the flexible resin pipe small. Furthermore, because the composite pipe does not have an intermediate material, its structure is simplified and manufacturing is easy, thereby keeping the manufacturing cost of the composite pipe low.

[0021] However, as described above, the composite pipe according to the present invention has no intermediate material between the expansion / contraction corrugated pipe and the flexible resin pipe, and a radial gap (insulating air layer) of 4 mm or more is formed between them, so that when the expansion / contraction corrugated pipe is subjected to an external load, it deforms radially, and the expansion / contraction pipe is prone to flattening. As a result of an analysis using the finite element method regarding this point, it was found that a shorter repeat pitch of the convex and concave portions of the expansion / contraction corrugated pipe is more effective in terms of flattening resistance.

[0022] In addition, the analysis showed that by setting the specifications of the convex and concave portions of the telescopic corrugated pipe (average thickness of the convex portion, width of the short cylindrical portion, maximum width of the concave portion, length of one pitch between the convex and concave portions, and ratio of the maximum width of the concave portion to this length of one pitch) as described above, the telescopic corrugated pipe can be given high flattening resistance, flexibility, and scratch resistance. [Effects of the Invention]

[0023] According to the present invention, it is possible to obtain an expansion corrugated pipe that can ensure high expansion, contraction resistance, and flattening resistance, and a composite pipe that includes the expansion corrugated pipe and that can be manufactured at low cost. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a side cross-sectional view of a composite pipe end portion according to the present invention, cut in half. [Figure 2] FIG. 2 is a side cross-sectional view of a half-section of the end portion of the elastic corrugated pipe according to the present invention. [Figure 3] FIG. 3 is an enlarged detailed view of part A in FIG. 2. [Figure 4] 1 is a side cross-sectional view of a part cut in half showing a state in which the elastic corrugated pipe is compressed to expose the end of the flexible resin pipe in the composite pipe according to the present invention. FIG. [Figure 5] FIG. 4 is a partial cutaway side view of a composite pipe according to another embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view taken along line BB in FIG. 5. [Figure 7] FIG. 1 is a perspective view showing a method for testing the scratch resistance of a composite pipe. [Figure 8] FIG. 10 is a table showing the concave-convex models and flattening strength ratios of various stretchable corrugated pipes. [Figure 9] This figure shows in tabular form the analysis results of the specifications and flattening loads of various types of elastic corrugated pipes. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0026] FIG. 1 is a cross-sectional side view of a composite pipe end portion according to the present invention, in which the composite pipe 1 shown is composed of a round pipe-shaped flexible resin pipe 20 and a bellows-shaped elastic corrugated pipe 10 that covers the outer periphery of the flexible resin pipe 20 to protect it.

[0027] The flexible resin pipe 20 is made of cross-linked polyethylene, polybutene, polyethylene, heat-resistant polyethylene, or a composite resin of these, or a metal-reinforced composite resin, and is used to transport water at a temperature of 95°C or less.

[0028] The stretchable corrugated pipe 10 is obtained by expanding the diameter of a parison made primarily of a resin containing polyethylene, for example, low-density polyethylene (LDPE) having a tensile yield strength of 20 MPa or less, by blow molding or vacuum molding. In this case, an appropriate color masterbatch or the like may be added as an additive to the low-density polyethylene (LDPE), which is the polyethylene that is the main component, as needed, before molding.

[0029] Furthermore, foamed polyethylene having an expansion ratio of 1.05 to 4 times, preferably 1.2 to 2.5 times, may be used as the raw material of the resin constituting the expansion corrugated pipe 10. The expansion corrugated pipe 10 may have a multi-layer structure, and when foamed polyethylene is used as its material, the foamed polyethylene may be one in which the expansion ratio continuously decreases from that of the inner layer toward the outer layer, or one in which the expansion ratio changes discontinuously from the inner layer to the outer layer. Furthermore, the expansion corrugated pipe may partially contain resins other than polyethylene, for example, polyolefins such as polybutene and polypropylene, and vinyl chloride, either alone or in combination.

[0030] In this specification, the "main component" of a resin refers to the component that is contained in the largest amount by mass in a mixture.

[0031] Next, the details of the configuration of the stretchable corrugated pipe 10 according to the present invention will be described below with reference to FIGS.

[0032] Fig. 2 is a half-section side cross-sectional view of a stretchable corrugated pipe end portion according to the present invention, and Fig. 3 is an enlarged detailed view of part A in Fig. 2. The stretchable corrugated pipe 10 shown in the figure is formed in a bellows shape by alternately connecting annular convex portions 11 that are convex outward in the radial direction and annular groove-like concave portions 12 that are concave inward in the radial direction along the pipe axis (left-right direction in Figs. 2 and 3). Here, as shown in detail in Fig. 3, each convex portion 11 has a pair of side walls 11a inclined with respect to the pipe axis S and a cylindrical short cylindrical portion 11b that is coaxial with the pipe axis S and connected by the side walls 11a. The cross section of the convex portion 11 is trapezoidal, the width of which narrows radially outward. Furthermore, the concave portion 12 formed between adjacent convex portions 11 is defined by one side wall 11a of the two adjacent convex portions 11 and a cylindrical short cylindrical portion 12a that is coaxial with the pipe axis S and connects the inner ends of these side walls 11a. The cross section of the concave portion 12 is a V-groove shape that narrows radially inward.

[0033] Each of the protrusions 11 has an average wall thickness T1 of 0.4 mm or more and less than 1.0 mm (0.5 mm in this embodiment (see FIG. 3)), and a width W1 of the short cylindrical portion 11b of 2.5 mm or more and less than 3.5 mm (3.0 mm in this embodiment (see FIG. 3)). Each of the recesses 12 has a maximum width Wg of 0.5 mm or more and less than 1.5 mm (1.3 mm in this embodiment (see FIG. 3)). The length P of one pitch between adjacent protrusions 11 and recesses 12 in the tube axis direction is set to 3.5 mm or more and less than 4.5 mm (4.3 mm in this embodiment), and the ratio Wg / P of the maximum width Wg of the recesses 12 to the length P of one pitch is set to Wg / P-=25% or more (1.3 / 4.3=30.2% in this embodiment). In this embodiment, as shown in FIG. 3, the thickness T2 of the short tube portion 12a defining the recess 12 is set to T2=0.58 mm, and the depth H of the recess 12 (half the difference between the inner diameter of the end tube portion 11b of the protrusion 11 and the outer diameter of the short tube portion 12a of the recess 12) is set to H=1.5 mm.

[0034] The expandable corrugated pipe 10 configured as described above is made of a flexible resin whose main component is polyethylene, which enhances its expandability, and when connecting the flexible resin pipe 20 to a joint or the like, the end of the contractible corrugated pipe 10 can be easily exposed by pressing and compressing the end of the contractible corrugated pipe 10 in the pipe axial direction (to the right in FIG. 4) as shown in Fig. 4. This allows the flexible resin pipe 20 to be connected to a joint or the like easily and in a short time.

[0035] In reality, when a pressing force is applied to the expandable corrugated pipe 10 in the pipe axis direction, the expandable corrugated pipe 10 contracts in the pressing direction (pipe axis direction), and when the pressing force is released, the expandable corrugated pipe 10 tries to return to its original length by its own elastic restoring force, but does not fully return to its original length. However, this contractible corrugated pipe 10 has enough flexibility that it can be pulled in the opposite direction to the pressing direction and returned to its original length.

[0036] As mentioned above, by constructing the contractible corrugated pipe 10 from foamed polyethylene, which has low thermal conductivity, the thermal insulation and heat retention properties of the expansion corrugated pipe 10 are improved, thereby minimizing temperature changes in the fluid flowing through the flexible resin pipe 20. Furthermore, foamed polyethylene has high sound absorption properties, so it can absorb, for example, water hammer noise. In particular, by constructing the resin from foamed polyethylene with an expansion ratio of 1.05 to 4, the apparent elastic modulus of the resin decreases, making the resin more flexible for the same thickness. Although foaming reduces the resin's scratch resistance, the average wall thickness T1 of the convex portions 11 of the expansion corrugated pipe 10 is set to T1-- = 0.4 mm or more and less than 1.0 mm as shown in Figure 3 . This ensures a sufficient cutting allowance when the expansion corrugated pipe 10 is scratched, preventing damage such as breakage and deterioration of the appearance of the expansion corrugated pipe 10.

[0037] Furthermore, when foamed polyethylene is used as the resin constituting the expansion corrugated pipe 10, the expansion ratio may be made continuously lower than that of the inner layer as it approaches the outer layer, as described above, or the expansion ratio may be made to change discontinuously from the inner layer to the outer layer. By doing so, the expansion corrugated pipe 10 is expected to have an advantage in terms of scratch resistance.

[0038] Furthermore, the stretchable corrugated pipe 10 may have a multi-layer structure, for example, with a surface layer made of high-density polyethylene (HDPE), a middle layer made of low-density polyethylene (LDPE), and an olefin-based elastomer only in the inner surface layer that comes into contact with the flexible resin pipe 20. As long as the resin is mainly made of polyethylene, a resin other than polyethylene may be used. In addition, as described above, the stretchable corrugated pipe 10 may partially contain a resin other than polyethylene, for example, polyolefins such as polybutene and polypropylene, vinyl chloride, etc., either alone or in combination.

[0039] In the composite pipe 1 shown in Figure 1, whose outer periphery is protected by the expandable corrugated pipe 10 configured as described above, the average value of the radial gap δ formed between the inner periphery of the expandable corrugated pipe 10 and the outer periphery of the flexible resin pipe 20 may be set to 4 mm or more.

[0040] 1, there is no intermediate material between the stretchable corrugated pipe 10 and the flexible resin pipe 20, and a radial gap of 4 mm or more is formed between them, and this radial gap δ forms an insulating air layer, which improves the heat retention of the flexible resin pipe 20 and keeps small temperature changes in the fluid flowing through the flexible resin pipe 20. Furthermore, because the composite pipe 1 does not have an intermediate material, its structure is simplified and its manufacturing is easy, and the manufacturing cost of the composite pipe 1 can be kept low.

[0041] 5 and 6 show a composite pipe 1' according to another embodiment of the present invention.

[0042] 5 is a side view of a broken portion of a composite pipe according to another embodiment of the present invention, and Fig. 6 is a cross-sectional view taken along line BB in Fig. 5. In the illustrated composite pipe 1', a plurality of holding projections 13' for concentrically holding the flexible plastic pipe 20 are integrally provided at regular intervals in the axial direction of the pipe and protrude radially inward from the inner peripheral surface of the stretchable corrugated pipe 10'. Note that in this embodiment, four holding projections 13' are provided protruding from the inner peripheral surface of the stretchable corrugated pipe 10' at equal angular pitches (90° pitches) in the circumferential direction, but the number of these holding projections 13' can be any number as long as it is plural, but three or more is preferable in consideration of their function.

[0043] In the above-mentioned composite pipe 1', if a configuration is adopted in which the flexible plastic pipe 20' is concentrically held by a plurality of holding protrusions 13' protruding from the inner peripheral surface of the expansion / contraction corrugated pipe 10' as described above, a certain insulating air layer can be formed between the flexible plastic pipe 20' and the expansion / contraction corrugated pipe 10', thereby ensuring high thermal insulation and heat retention for the composite pipe 1'. In addition, depending on the shape of the holding protrusions 13' and the orientation of the holding protrusions 13' at the site, it is expected that the flattening resistance of the expansion / contraction corrugated pipe 10' can be reinforced.

[0044] 1, as mentioned above, there is no intermediate material between the expansion / contraction corrugated pipe 10 and the flexible resin pipe 20, and a radial gap (insulating air layer) δ of 4 mm or more is formed between them, so when the expansion / contraction corrugated pipe 10, which is the covering pipe, is subjected to an external load, the expansion / contraction corrugated pipe 10 is easily deformed in the radial direction and prone to flattening. Regarding this point, an analysis was carried out using the finite element method, and it was found that a short length of the repeat pitch P of the convex portions 11 and concave portions 12 of the expansion / contraction corrugated pipe 10 is effective for flattening resistance.

[0045] Specifically, it was found that by setting the specifications of the convex portions 11 and concave portions 12 of the telescopic corrugated pipe 10 (average wall thickness T1 of the convex portions 11, width W1 of the short cylindrical portions 11b, maximum width Wg of the concave portions, length of one pitch P between the convex portions 11 and the concave portions 12, and ratio Wg / P of the maximum width Wg of the concave portions 12 to the length of this one pitch P) as shown in Figure 3, the telescopic corrugated pipe 10 can be made to have high flattening resistance, flexibility, and scratch resistance.

[0046] [Test and analysis results] Here, we will explain the various tests (flexibility test, scratch resistance test, and flattening resistance test) conducted on various composite pipes and elastic corrugated pipes, as well as the analysis results on flattening resistance.

[0047] The stretchable corrugated pipe 10 according to the present invention used in the test was obtained by vacuum molding a parison made of low-density polyethylene (LDPE) and an inorganic foaming agent using a mold with a width W1 of the convex portion 11 of 3.103 mm, a maximum width Wg of the concave portion 12 of 1.293 mm, a depth of the concave portion 12 of 2.195 mm, and a diameter R of the outer surface of the R portion of the concave portion 12 of 0.5 mm. The inorganic foaming agent was sodium bicarbonate (NaHCO3).

[0048] (Stretchability test) The flexibility test was conducted on the stretchable corrugated pipe of the present invention and the conventional stretchable corrugated pipes 1 and 2, and the specifications (outer diameter, thickness and material of the convex portion) and test results of these stretchable corrugated pipes are shown in Table 1.

[0049] [Table 1] The shrinkage test was conducted using a special jig on a composite pipe covered with the three types of stretchable corrugated pipe shown in Table 1, and a compression testing machine to measure the load (50 mm shrinkage load) required to shrink a 200 mm long stretchable corrugated pipe by 50 mm. The results are shown in Table 1.

[0050] As shown in Table 1, the 50mm contraction loads of the conventional expandable corrugated pipes 1 and 2 are 67N and 44N, respectively, whereas the 500mm contraction load of the contractible corrugated pipe of the present invention is a small value of 31N, demonstrating that the contractible corrugated pipe of the present invention has high contractibility.

[0051] (Scratch resistance test) The scratch resistance test was conducted on a composite pipe 1 consisting of a contracted corrugated pipe 10 according to the present invention (having the same specifications as those shown in Table 1) and a flexible resin pipe 20 made of cross-linked polyethylene (PEX) using the method shown in Figure 7.

[0052] 7 is a perspective view showing the scratch resistance test method, and as shown in the figure, the scratch resistance test was performed by passing a composite pipe 1 through one hole 100a in a fixed concrete block 100, rubbing the surface of the composite pipe 1 against the upper edge of the hole 100a, and then visually checking the appearance of the composite pipe 1 (the appearance of the thermal insulation protection part) when the composite pipe 1 was pulled up with a force of 15 kgf while checking with a hand balance 50. If no breaks or holes were formed, the result was rated as ◯ (good), and if holes were formed, the result was rated as × (unacceptable). The results are shown in Table 2.

[0053] [Table 2] As shown in Table 2, it has been demonstrated that the expansion corrugated pipe 10 according to the present invention and the composite pipe 1 coated therewith exhibit high scratch resistance. This is due to the fact that the average thickness of the convex portions 11 of the expansion corrugated pipe 10 according to the present invention is set to 0.4 mm or more.

[0054] (Flatness resistance test and analysis) Assuming that the compressive force when the allowable flattening ratio of the expansion corrugated pipe 10 is 10% is 7 kg / m (63 N / m), verification was carried out using a compression tester, and the load required to flatten the expansion corrugated pipe 10 with an outer diameter of 30.5 mm by 10% was found to be 351 N / m to 501 N / m. This value is at least five times the assumed load (63 N / m), and therefore it has been confirmed that the expansion corrugated pipe 10 according to the present invention has a sufficiently high resistance to flattening.

[0055] Here, we will explain the results of analyzing the flattening resistance of six types of expansion corrugated pipes (No. 1 to No. 6) with convex and concave portions of various specifications shown in Figures 8 and 9. Specifically, the pushing force (33% flattening load) at which the flattening ratio of each type of expansion corrugated pipe becomes 33% was calculated using the finite element method. The results are shown in Figures 8 and 9. Below, we will explain each of the six types of expansion corrugated pipes (No. 1 to No. 6).

[0056] 1) No.1 Telescopic Corrugated Pipe: The No. 1 expansion corrugated pipe is an ideal form according to this embodiment, and the specifications of the convex and concave portions are the same as those shown in Fig. 3. As a result of the analysis, the load at an aspect ratio of 33% (one pitch of convex and concave portions) and the load at an aspect ratio of 33% (converted to 100 mm) for this No. 1 expansion corrugated pipe are 19.67 N and 457.52 N, respectively, as shown in Fig. 9.

[0057] 2) No.2 telescopic corrugated pipe: The No. 2 telescopic corrugated pipe is thicker than the No. 1 ideal form. Analysis results show that the load at a flattening ratio of 33% (1 uneven pitch) and the load at a flattening ratio of 33% (equivalent to 100 mm) for this No. 2 telescopic corrugated pipe are 36.37 N and 845.82 N, respectively, as shown in Figure 9. These values ​​are 185% of the value for the No. 1 telescopic corrugated pipe, which is 100%. In this telescopic corrugated pipe, thickening is effective in improving flattening resistance, but it has the problem of increasing the expansion and contraction load. The expansion and contraction load should usually be set within a range that does not pose a problem in construction (for example, 60 N or less), and the wall thickness should be set to 0.4 mm to 1.0 mm.

[0058] 3) No.3 telescopic corrugated pipe: The width of the convex portion (convex width) of the No. 3 expansion corrugated pipe is larger than that of the No. 1 ideal configuration. Analysis results show that the load (one pitch of convex / concave) at a flattening ratio of 33% and the load (converted to 100 mm) at a flattening ratio of 33% for this No. 3 expansion corrugated pipe are 21.33 N and 367.78 N, respectively, as shown in Figure 9. These values ​​are 80% of the value for the No. 1 expansion corrugated pipe, which is 100%. In this expansion corrugated pipe, if the side wall thickness per unit length is small, the flattening resistance decreases. In practical terms, it is desirable to make one pitch of convex / concave as short as possible. To ensure that the convex portion does not collapse even if the wall thickness is 1 mm, it is desirable to set the center width of the convex portion to 3 mm.

[0059] 4) No.4 telescopic corrugated pipe: The width of the recesses (recess width) of the No. 4 expansion corrugated pipe is larger than that of the No. 1 ideal form. Analysis results show that the load (one recess pitch) at a flattening ratio of 33% and the load (converted to 100 mm) at a flattening ratio of 33% for this No. 3 expansion corrugated pipe are 23.63 N and 429.64 N, respectively, as shown in Figure 9. These values ​​are 94% of the value for the No. 1 expansion corrugated pipe, which is 100%. In this expansion corrugated pipe, if the side wall thickness per unit length is small, the flattening resistance decreases. A large recess width reduces the flattening resistance to a smaller extent than a large convex width, but in any case, it is desirable for one recess pitch to be as short as possible in practice.

[0060] 5) No.5 telescopic corrugated pipe: The width of the convex and concave portions (convex + concave width) of the No. 5 telescopic corrugated pipe is smaller than that of the No. 1 ideal configuration. Analysis revealed that the load (one convex / concave pitch) at a flattening ratio of 33% and the load (converted to 100 mm) at a flattening ratio of 33% for this No. 5 telescopic corrugated pipe were 12.73 N and 592.29 N, respectively, as shown in Figure 9. These values ​​are 129% of the value for the No. 1 telescopic corrugated pipe, which is 100%. This telescopic corrugated pipe has a large number of side walls per unit length, which improves its flattening resistance. However, if the convex portions are narrow, resin will fill the convex portions, increasing the expansion resistance. Therefore, a convex width that allows for a margin equivalent to the wall thickness is required.

[0061] 6) No.6 telescopic corrugated pipe: The width of the convex and concave portions (convex + concave width) of the No. 6 telescopic corrugated pipe is larger than that of the No. 1 ideal form. As a result of the analysis, the load (one pitch of convex and concave portions) at a flattening ratio of 33% and the load (converted to 100 mm) at a flattening ratio of 33% for this No. 6 telescopic corrugated pipe were 24.18 N and 374.87 N, respectively, as shown in Figure 9. These values ​​are 82% of the value for the No. 1 telescopic corrugated pipe, which is 100%. In this telescopic corrugated pipe, the number of side walls per unit length is small, which reduces the flattening resistance. The load capacity of this telescopic corrugated pipe is slightly higher than that of the No. 3 telescopic corrugated pipe, which is thought to be due to the analytical conditions set, but in any case, it is desirable for one pitch of convex and concave portions to be as short as possible in practical use.

[0062] As is clear from the above explanation, according to the present invention, it is possible to obtain an expandable corrugated pipe having high flexibility, scratch resistance, and flattening resistance, and a composite pipe that can be manufactured at low costs.

[0063] 1 to 4, for convenience, the shape of the recess 12 is shown to be trapezoidal in cross section, but it is actually preferable that the short cylindrical portion 12a be replaced by an R-shaped portion, and the cross section of the recess 12 be U-shaped (see FIG. 5). In this case, it is preferable that the thickness of the R-shaped portion is thicker than the thickness of the protrusion 11.

[0064] Furthermore, the present invention is not limited to the application of the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0065] 1,1' composite pipe 10,10' telescopic corrugated tube 11 Convex part 11a Side wall of the convex part 11b Short cylindrical part of the convex part 12 recess 12a Cylindrical end portion of recess 13' retaining projection 20,20' flexible resin pipe P: Pitch between convex and concave parts T1 Average thickness of the convex part T2 Recessed portion thickness W1 Width of the short cylindrical part of the convex part wg Maximum width of recess δ Radial gap between the elastic corrugated pipe and the flexible resin pipe

Claims

1. The outer periphery of a flexible resin pipe is covered, and the pipe is formed into a bellows shape by alternately connecting convex portions that are convex on the radially outward side and concave portions that are concave on the radially inward side along the pipe axis direction using a resin whose main component is low-density polyethylene or foamed polyethylene with an expansion ratio of 1.05 to 4 times. the convex portion has a pair of side walls inclined with respect to the tube axis and a cylindrical short cylindrical portion connected by the side walls, the average wall thickness being 0.4 mm or more and less than 1.0 mm, and the width of the short cylindrical portion being 2.5 mm or more and less than 3.5 mm, the recess is formed by the side walls of two of the protrusions adjacent to each other in the tube axis direction into a V-groove shape having a maximum width of 0.5 mm or more and less than 1.5 mm, An expansion corrugated pipe characterized in that the length of one pitch between the convex portion and the concave portion adjacent in the pipe axis direction is 3.5 mm or more and less than 4.5 mm, and the ratio of the maximum width of the concave portion to this length of one pitch is 25% or more.

2. 2. The expansion corrugated pipe according to claim 1, characterized in that it has a multi-layer structure.

3. An expandable corrugated pipe as described in claim 1, characterized in that the main component of the resin that forms the expandable corrugated pipe is the foamed polyethylene, and the foamed polyethylene has a foaming ratio that becomes continuously lower than that of the inner layer as it approaches the outer layer.

4. An expandable corrugated pipe as described in claim 1, characterized in that the main component of the resin that forms the expandable corrugated pipe is the foamed polyethylene, and the foamed polyethylene has a foaming ratio that changes discontinuously from the inner layer to the outer layer.

5. An expandable corrugated pipe as described in any one of claims 1 to 4, characterized in that the resin used to form the expandable corrugated pipe contains a resin other than polyethylene in part.

6. The stretchable corrugated pipe according to any one of claims 1 to 5, characterized in that a plurality of holding protrusions for holding the flexible resin pipe concentrically are provided protruding radially inward from the inner peripheral surface.

7. A composite pipe comprising the expansion and contraction corrugated pipe according to any one of claims 1 to 6 and the flexible resin pipe arranged approximately concentrically inside the expansion and contraction corrugated pipe.

8. 8. The composite pipe according to claim 7, wherein a radial gap having an average value of 4 mm or more is formed between the inner peripheral portion of the stretchable corrugated pipe and the outer peripheral portion of the flexible resin pipe.

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