Sheath structure

Abstract

To provide a sheath pipe structure which can make compatible both a protection function and the elasticity of a flexible resin pipe in a pipe axial direction, has a temperature holding function, and can reduce a manufacturing cost.SOLUTION: A sheath pipe structure 2 for protecting a flexible resin pipe 1 comprises a waveform pipe 10 which is covered on the flexible resin pipe 1 not via an intermediate material. The waveform pipe 10 has an annular maximum diameter part 11 and an annular minimum diameter part 12 which use polyethylene as main raw materials, formed as moldings whose foaming magnifications are 1.05 to 4.0 times, and which are alternately arranged in the pipe axial direction, and continuous connection parts 13 for making the maximum diameter part 11 and the minimum diameter part 12 continue to each other. The maximum diameter part 11 includes a short cylinder part, and the minimum diameter part 12 does not include the short cylinder part. The continuous connection parts 13 are inclined to a pipe axis of the waveform pipe 12. A V-groove 14 is defined by the minimum diameter part 12 and the continuous connection parts 13 located at both sides of the minimum diameter part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sheath tube structure for protecting a flexible resin tube. [Background technology]

[0002] Flexible plastic pipes for cold and hot water supply are made of cross-linked polyethylene, polybutene, etc., and have a soft surface, so they are protected by a sheath pipe structure. This prevents the surface of the flexible plastic pipe from being damaged, for example, when it rubs against the building structure during plumbing work.

[0003] The sheath pipe structure disclosed in Patent Document 1 is composed of a corrugated pipe made of hard polyethylene. This corrugated pipe has peaks and valleys with a semicircular cross section that are alternately arranged in the pipe axial direction, and connecting parts that connect these peaks and valleys and are approximately perpendicular to the pipe axis, and has a corrugated cross section. The corrugated pipe is hard even though it is thin, so it can protect the flexible resin pipe.

[0004] In addition to protecting the flexible plastic pipe, the corrugated pipe is required to be stretchable in the axial direction because, when connecting the end of the flexible plastic pipe to a joint such as a header, a water tap, or a hot water tap, the end of the corrugated pipe needs to be shifted away from the end of the flexible plastic pipe to shrink it in the axial direction and expose the end of the flexible plastic pipe. In Patent Document 1, the thickness of the peaks (eg, 0.25 mm) is made thinner than the thickness of the valleys and connecting parts (eg, 0.5 mm), making it easier for the peaks to elastically deform and allowing them to expand and contract in the axial direction of the tube.

[0005] The sheath pipe structure disclosed in Patent Document 2 includes a corrugated pipe and an intermediate material interposed between the corrugated pipe and a flexible resin pipe, and has a double structure. The corrugated pipe has short cylindrical peaks and valleys alternately arranged in the pipe axis direction, and a connecting portion that connects the peaks and valleys and is 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), so that it can increase the flexibility in the pipe axis direction, but it has low scratch resistance and cannot protect the flexible resin pipe by itself. In the sheath pipe structure of Patent Document 2, the intermediate material ensures the protection function of the flexible resin pipe. In addition, the intermediate material is made of a foam material, so it also has a heat retention function. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4190923 [Patent Document 2] WO2018 / 123779 publication Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, the sheath structure for the flexible resin pipe is required to have a function of protecting the flexible resin pipe and flexibility in the axial direction of the pipe. In recent years, a heat retention function (insulation function) has also been required. The corrugated pipe of Patent Document 1 is made of hard polyethylene, so it is basically scratch-resistant and has excellent resin pipe protection function, but it has poor elasticity in the pipe axis direction. If the thickness of the crest is further reduced in an attempt to increase elasticity, it will lead to a decrease in scratch resistance. Thus, it is difficult for the corrugated pipe of Patent Document 1 to achieve both elasticity and scratch resistance. In addition, the heat retention function is also poor.

[0008] In the sheath pipe structure of Patent Document 2, the corrugated pipe has low damage resistance and is easily torn when dragged around the construction site, and the intermediate material is exposed from the torn area, damaging the appearance. In addition, if the intermediate material is repeatedly damaged by the building structure after the corrugated pipe is torn, it may not be able to protect the flexible resin pipe. In addition, there is a limit to how much flexibility can be increased due to the resistance of the intermediate material. Furthermore, the double structure of the corrugated pipe and the intermediate material increases the manufacturing cost. [Means for solving the problem]

[0009] The present invention has been made to solve the above problems, and provides a sheath tube structure that is covered over a flexible resin tube to protect the flexible resin tube, comprising: The corrugated pipe is provided with a corrugated pipe that is fitted onto the flexible resin pipe without an intermediate material, the corrugated pipe being a molded product whose main raw material is polyethylene and whose expansion ratio is 1.05 to 4.0 times, and has annular maximum diameter portions and annular minimum diameter portions arranged alternately in the pipe axial direction, and a connecting portion connecting the maximum diameter portion and the minimum diameter portion, the maximum diameter portion including a short cylindrical portion and the minimum diameter portion not including a short cylindrical portion, the connecting portion being inclined with respect to the pipe axis of the corrugated pipe, and a V-groove being defined by the minimum diameter portion and the connecting portions located on both sides of it.

[0010] According to the above-mentioned configuration, since the molded product has an expansion ratio of 1.05 to 4.0, it has excellent elasticity, can be smoothly connected to a joint of a flexible resin pipe, and has excellent heat retention. Furthermore, since the intermediate material can be omitted, the manufacturing cost can be reduced. Corrugated pipes made of foamed materials can be made thick even though their weight per unit length is small, so that cutting allowances can be secured and breakage can be avoided even if they rub against building structures made of concrete during piping installation. In addition, because the foaming ratio is 4.0 or less, deterioration of scratch resistance due to excessive foaming can be avoided. The corrugated pipe has a maximum diameter section that includes a short cylindrical section, and these short cylindrical sections are connected via a V-groove, so that the risk of the pipe getting caught on the building structure during installation can be minimized. This also improves the damage resistance.

[0011] Preferably, the corrugated pipe has an expansion ratio of 1.2 to 2.5 times. According to the above-mentioned configuration, by making the foaming ratio of the corrugated pipe 1.2 or more, it is possible to improve the elasticity and heat retention. Also, by making the foaming ratio 2.5 or less, it is possible to improve the scratch resistance.

[0012] Preferably, the thickness of the maximum diameter portion is greater than the thickness of the minimum diameter portion. According to the above-mentioned configuration, the maximum diameter part of the corrugated pipe is thickened to improve the scratch resistance of the corrugated pipe. Also, since the groove located on the radially outer side of the minimum diameter part is a V-groove, it is difficult for building structures to get into the thin-walled minimum diameter part, and the thin-walled minimum diameter part can be protected.

[0013] Preferably, the average thickness of the maximum diameter portion and the minimum diameter portion is 0.4 mm or more, which allows a sufficient cutting allowance to be secured and enhances scratch resistance. More preferably, the average thickness is 0.4 to 1.0 mm.

[0014] Preferably, the outer diameter of the maximum diameter portion is Φ (mm), and the average thickness of the maximum diameter portion is T 1 (mm), the weight per unit length (g / m) is (3.2949×Φ-26.402)×0.3 / T 1 That's all. By complying with the above conditions, scratch resistance can be reliably obtained.

[0015] Preferably, when the flexible resin pipe is bent to a minimum bending radius and the corrugated pipe is bent to a minimum bending radius, the width of the radially outer end of the V groove located inside the bent shape is Wm, and the average wall thickness of the maximum diameter portion is T. 1 Then, Wm / 2 <T 1 It is. According to the above configuration, the depth to which the piping penetrates into the V-groove of the building structure during piping work is limited, thereby further improving damage resistance.

[0016] Preferably, the distance in the tube radial direction from the outer surface of the minimum diameter portion to the center of the wall thickness of the maximum diameter portion is equal to or greater than half the width of the maximum diameter portion in the tube axial direction. According to the above-mentioned configuration, since the V-groove is deep, the air layer between the flexible resin pipe and the corrugated pipe can be thickened, and the heat insulating effect can be improved. In addition, when the corrugated pipe is molded by expanding the diameter, the minimum diameter part can be made thin, and the stretchability can be further improved.

[0017] Preferably, the corrugated pipe contains up to 40% polypropylene. According to the above configuration, it is possible to improve heat retention while maintaining the flexibility of the corrugated pipe. Effect of the Invention

[0018] The sheath tube structure of the present invention can achieve both scratch resistance (protection function for the flexible resin tube) and stretchability in the axial direction of the tube, has a heat retention function (insulation function), and can reduce manufacturing costs. [Brief description of the drawings]

[0019] [Figure 1] 1 is an enlarged longitudinal sectional view showing a sheath tube structure according to a first embodiment of the present invention in a state in which it is covered with a flexible resin tube. [Diagram 2] 1 is a graph showing the relationship between the wall thickness of the peaks and the wall thickness of the valleys of a corrugated pipe obtained by diameter expansion forming. [Diagram 3] FIG. 6 is an enlarged longitudinal sectional view showing a sheath tube structure according to a second embodiment of the present invention in a state in which it is covered with a flexible resin tube. [Figure 4] FIG. 2 is a schematic diagram showing a method for a scratch resistance test. [Diagram 5] 1 is a graph showing the results of a scratch resistance test. [Figure 6] 1 is a schematic side view showing an apparatus for molding a corrugated pipe in a state in which the corrugated pipe is placed over a flexible resin pipe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] First embodiment of the present invention Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, a flexible resin pipe 1 is covered with a sheath pipe structure 2 and is arranged to be laid under the floor of a building. Hereinafter, a pipe consisting of the flexible resin pipe 1 and the sheath pipe structure 2 is referred to as a composite pipe. The flexible resin pipe 1 is made of a cross-linked polyethylene pipe, a polybutene pipe, a polyethylene pipe, a heat-resistant polyethylene pipe, a composite pipe of these resins, or a metal-reinforced composite pipe, and is used to transport water at 95°C or below.

[0021] The sheath pipe structure 2 is composed only of a corrugated pipe 10, and no intermediate material is interposed between the corrugated pipe 10 and the resin pipe 1, with only an air layer interposed therebetween. The corrugated pipe 10 is obtained by expanding the diameter of a parison made mainly of polyethylene, for example, low-density polyethylene (LDPE) having a tensile yield strength of 20 MPa or less, by blow molding or vacuum molding. The raw material contains a foaming agent, and the corrugated pipe 10 is molded at an expansion ratio of 1.05 to 4.0 times, more preferably 1.2 to 2.5 times.

[0022] The corrugated pipe 10 can be molded by adding polypropylene (PP) to the main raw material polyethylene, for example, low density polyethylene (LDPE), in the following ratio (parts by weight): LDPE:PP=100:0~60:40 More preferably, LDPE:PP=90:10~70:30. Since polypropylene has a low thermal conductivity, the inclusion of polypropylene can improve heat retention. As the polypropylene content increases, the flexibility of the corrugated pipe 10 decreases, so the polypropylene content is set to a maximum of 40%, preferably 30% or less, as described above.

[0023] The corrugated pipe 10 has annular peaks 11 (maximum diameter portions) and annular valleys 12 (minimum diameter portions) arranged alternately at equal pitch in the pipe axial direction, as well as connecting portions 13 connecting the peaks 11 and valleys 12.

[0024] The peaks 11 consist of short cylindrical sections concentric with the pipe axis. The valleys 12 do not have short cylindrical sections and consist of R sections. The connecting sections 13 are inclined with respect to a plane perpendicular to the pipe axis of the corrugated pipe 10 and have a conical shape. Each valley 12 and a pair of connecting sections 13 connected to this valley 12 define a V-groove 14. The V-grooves 14 are arranged between the peaks 11 on the radial outside of each valley 12.

[0025] In FIG. 1, the thickness of the peak portion 11 (average thickness, the same applies below) is indicated by the symbol T 1 The thickness of the valley portion 12 is indicated by T 2 The width of the peak 11 is indicated by the symbol W 1 The width of the V-groove 14 when the corrugated pipe 10 is in a straight state is indicated by the symbol Wg, and the depth of the V-groove 14 (the distance between the outer surface of the peak portion 11 and the outer surface of the valley portion 12) is indicated by the symbol D.

[0026] Thickness of mountain section 11 T 1 is the thickness T of the valley 12 2 In this case, preferably, T 1 / T 2 = 1.3 to 1.6. 1 is the thickness T of the valley 12 2 In this case, it is preferable that T 1 / T 2 =0.8~1.0. Wall thickness T 1 and thickness T 2 Regardless of the size of the thickness T of the peak 11, 1 The thickness T of the valley portion 12 is preferably 0.4 to 1.0 mm, and more preferably 0.4 to 0.7 mm. 2 is preferably 0.4 to 1.0 mm, and more preferably 0.4 to 0.7 mm.

[0027] As will be described later, the flexible plastic pipe 1 and the corrugated pipe 10 are bent together during piping work. The flexible plastic pipe 1 has a minimum bending radius that allows it to be used for a long time without buckling or other abnormalities. The minimum bending radius of the corrugated pipe 10 can be set to be approximately equal to or slightly smaller than the minimum bending radius of the flexible plastic pipe 1. When the corrugated pipe 10 is bent at the minimum bending radius, the adjacent peaks 11 approach each other on the inside of the bent shape as shown by the imaginary lines in Figure 1, so that the width of the V-groove 14 becomes narrower than Wg, becoming Wm. The ratio of this narrowed groove width Wm to the wall thickness T of the peaks 11 is 1 has the following relationship: Wm / 2 <T 1 (1)

[0028] Thickness experiment Width W of the crest 11 of the corrugated pipe 10 1 A mold was prepared with a diameter of 3.14 mm, width Wg of the V-groove 14 of 1.256 mm, depth D of the V-groove 14 of 0.95 mm, and outer diameter R of the R part of the valley portion 12 of 0.5 mm, and a corrugated tube was obtained by blow molding from parisons with different thicknesses and low-density polyethylene, polypropylene, and microcapsule compounding ratios (weight ratio). Note that the microcapsules are formed by encapsulating a volatile expansion agent (foaming agent) as a core agent in a shell made of polymer.

[0029] The experimental results are shown in Table 1 below. [Table 1]

[0030] Table 1 can be represented graphically as shown in Figure 2. The above experimental results show that if blow molding is performed using a parison with a thickness such that the thickness of the valley portion 12 is 0.35 mm or more, the thickness of the peak portion 11 can be made larger than that of the valley portion 12 without being greatly affected by the blending ratio of low-density polyethylene and propylene. Changing the foaming ratio by changing the blending ratio of the microcapsules did not have a significant effect. The corrugated pipe 10 also has similar results when vacuum molded.

[0031] The difference in thickness between the peaks 11 and valleys 12 is due to the cross-sectional shape of the corrugated pipe 10, i.e., the shape of the mold. That is, the mold has a cylindrical main molding surface corresponding to the peaks 11, and an annular molding protrusion protruding radially inward from the main molding surface corresponding to the V-groove 14. Both sides of the molding protrusion are inclined. When the amount of resin in the parison is equal to or greater than a predetermined amount, a part of the resin located at the tip of the molding protrusion flows radially outward along both sides of the molding protrusion and reaches the cylindrical main molding surface. As a result, the valleys 12 formed at the tip of the molding protrusion have a smaller amount of resin and are thin-walled, while the peaks 11 formed at the main molding surface have a larger amount of resin and are thick-walled.

[0032] Performance of the sheath structure The performance of the sheath tube structure 2 having the above configuration will be described below. (1) Scratch resistance When a composite pipe consisting of a flexible resin pipe 1 and a sheath pipe structure 2 is laid under the floor of a building, the peaks 11 of the corrugated pipe 10 rub against the building structure (for example, a sleeve penetrating the partition foundation of a detached house). In this case, the peaks 11 of the corrugated pipe 10 are short cylindrical in shape, and the peaks 11 of these short cylindrical parts are connected via the V-groove 14, so that the risk of getting caught on the building structure can be minimized. 1 is thicker than the valley portion 12, being 0.4 mm or more, so it is difficult to tear even if it is scratched. Even if it is scratched shallowly or worn down, other materials such as intermediate materials are not exposed, and the appearance is not impaired. 2 Even though the V-groove 14 is thin, it does not rub directly against the building structure and is not damaged. Also, since the width of the V-groove 14 narrows toward the inside in the radial direction, even if the building structure enters the V-groove 14, it is difficult for the structure to reach the valley portion 12, and the thin valley portion 12 is protected.

[0033] (2) Elasticity in the axial direction The corrugated pipe 10 is made primarily of polyethylene, for example, low-density polyethylene (LDPE) with a tensile yield strength of 20 MPa or less, and is a molded product with an expansion ratio of 1.05 to 4.0 times, so that sufficient flexibility can be ensured even if the peaks 11 are thick, and because the valleys 12 are thin-walled, it has excellent elasticity in the axial direction. Therefore, when connecting the flexible resin pipe 1 to a joint, the end of the corrugated pipe 10 can be easily shifted in the axial direction to expose the flexible resin pipe 1, and the connection work can be performed smoothly. Furthermore, since there is no intermediate material between the corrugated pipe 10 and the flexible resin pipe 1, even if the corrugated pipe 10 is repeatedly expanded and contracted, or even if it is dragged during construction and stretched once, there is no problem that the intermediate material gets caught and makes it difficult to expand and contract.

[0034] (3) Heat retention The corrugated pipe 10 is foam-molded, and therefore has excellent insulation and heat retention properties. In addition, the valleys 12 close to the flexible resin pipe 1 are narrow, while the peaks 13 far from the flexible resin pipe 1 are wide, allowing for an increased air space. By making the valleys 12 thin-walled, the air space between the flexible resin pipe 1 and the corrugated pipe 1 can be increased. As a result, heat retention can be further improved. In addition, due to the shapes of the valleys 12 and peaks 13 described above, it is less likely to get caught on corners at the construction site. (4) Manufacturing costs Since the sheath pipe structure 2 does not require an intermediate material between the corrugated pipe 10 and the flexible resin pipe 1, the manufacturing cost can be reduced.

[0035] Foaming ratio (1.05~4.0) As described above, since the foaming ratio of the corrugated pipe 10 is 1.05 or more, the elasticity and heat retention can be secured. Furthermore, by making the foaming ratio 1.2 or more, the thermal conductivity can be sufficiently reduced, and the elasticity and heat retention can be further improved. When the expansion ratio is 4.0 or less, scratch resistance can be ensured, but when it exceeds 4.0, scratch resistance decreases. When the expansion ratio is 2.5 or less, scratch resistance can be further improved.

[0036] Thickness of the peak (0.4~1.0mm) Thickness of mountain section 11 T 1 Since the thickness is 0.4 mm or more, it will not break even if it rubs against the building structure and is scratched shallowly. 1 If the thickness is less than 0.4 mm, the scratch resistance decreases. 1 The reason why the wall thickness T is set to 1.0 mm or less is to suppress an increase in the outer diameter of the corrugated pipe 10 and save material. 1 shall be 0.7 mm or less.

[0037] Regarding the thickness of the valley part (0.4 to 1.0 mm) Thickness T of valley 12 2 The thickness T is set to 0.4 mm or more in order to obtain strength. 2 The reason why the thickness T is set to 1.0 mm or less is to increase the clearance with the flexible resin pipe 1 to improve the heat insulation and to save materials. 2 shall be 0.7 mm or less.

[0038] Regarding formula (1) The meaning of the above formula (1) will be explained. Usually, many pipes are passed through a sleeve that penetrates a partition foundation. When the last pipe is passed through, the flexible plastic pipe 1 is pulled while bent at the minimum bending radius, and there is a possibility that the corrugated pipe 10 hits the corner of the sleeve. Even in such a worst-case situation, if the above formula (1) is satisfied, it is possible to reliably prevent the corrugated pipe 10 from being damaged and broken. That is, when the corrugated pipe 10 is at the minimum bending radius as described above, if the corner of the sleeve that forms a right angle on its cross section bites into the V-groove 14 that has narrowed to the groove width Wm, the maximum depth of the bite of this corner is half the groove width Wm. Therefore, the bite depth (Wm / 2) of the corner of this sleeve into the V-groove 14 is set to the thickness T of the ridge portion 11. 1 By making it smaller, it is possible to reliably prevent the corrugated tube 10 from breaking.

[0039] Second embodiment of the present invention 3 shows a second embodiment of the present invention. Since the basic structure of this embodiment is similar to that of the first embodiment, the components in the figure are given the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be omitted.

[0040] In the second embodiment, the distance Dx in the tube diameter direction from the outer surface of the valley portion 12 to the center of the wall thickness of the ridge portion 11 is set to be equal to the width W 1 This is more than half of the formula below. Da≧W 1 / twenty two) According to the above configuration, the V-groove 14 is deep, so the air layer between the flexible resin pipe 1 and the corrugated pipe 10 can be thickened, and the heat insulating effect can be improved. Also, during molding by expanding the diameter, the amount of resin flowing from the valley portion 12 to the peak portion 11 increases, making it easier to create a thickness difference. In other words, the valley portion 12 can be made thin, and the stretchability can be improved.

[0041] <Conditions for weight per unit length of corrugated pipe to ensure scratch resistance> In order to determine the conditions for the weight per unit length of the corrugated pipe to ensure scratch resistance, a scratch resistance test was conducted using a composite pipe A consisting of a flexible resin pipe 1 similar to that of the first embodiment and a sheath pipe structure 2 (corrugated pipe 10) as shown in Figure 4. The composite pipe A was passed through one of the holes 50a in the concrete block 50, rubbed against the upper edge of the hole 50a, and pulled up with a force of 15 kgf while checking with a hand scale 51. After this, the appearance of the composite pipe A was visually checked, and if no tears were found in the corrugated pipe, it was deemed to have passed, and if tears were found, it was deemed to have failed.

[0042] The composite pipes A to be tested are broadly divided into the following three types. (A) Composite pipe using corrugated pipe made of foamed resin (ridge thickness 0.5 mm) (B) Composite pipe using corrugated pipe made of foamed resin (ridge thickness 0.4 mm) (C) Composite pipe using non-foamed corrugated pipe (ridge thickness 0.3 mm) More specifically, the corrugated pipes (A) and (B) described above are according to the present invention, and their raw material is a mixture of 80% polyethylene (M1820 manufactured by Asahi Kasei Corporation) and 20% polypropylene (EX6000 manufactured by Japan Polypropylene Corporation) as main materials, with 1 to 8.5 parts of foaming agent (MB5885 manufactured by Sankyo Kasei Co., Ltd.) (corresponding to a foaming ratio of 1.16 to 2.20 times) mixed with respect to the main materials. The corrugated pipe (C) above was a test subject for comparison and was made of non-foamed high-density polyethylene (B470, manufactured by Asahi Kasei Corporation).

[0043] For the corrugated pipe (A) above (with foaming, ridge thickness 0.5 mm), a scratch resistance test was carried out by changing the weight per unit length of the corrugated pipe for each different outer diameter (ridge outer diameter). Table 2 below shows some of the test results. [Table 2]

[0044] As shown in Table 2, when the test was performed with an outer diameter of 28.1 mm, samples with a weight per unit length of 39.7 (g / m) or more passed, and samples with a weight less than this passed. Similarly, as shown in sample group 2, when the test was performed with an outer diameter of 30.0 mm, samples with a weight per unit length of 43.5 (g / m) or more passed, and samples with a weight less than this failed. Similarly, as shown in sample group 3, when the test was performed with an outer diameter of 30.5 mm, samples with a weight per unit length of 44.5 (g / m) or more passed, and samples with a weight less than this failed.

[0045] When further tests were conducted for different outer diameters with a wall thickness of 0.5 mm, it was found that the lower limit of the weight per unit length of an acceptable product had a linear relationship with the outer diameter, as shown by line A in Figure 5.

[0046] In Figure 5, an example of the test results is shown, with passed products indicated by black circles and failed products indicated by crosses. In simple terms, a product with an outer diameter of 28.1 mm and a weight per unit length of 42.5 g / m (expansion ratio 2.2 times) passes. A product with an outer diameter of 30.0 mm and a weight per unit length of 48.0 g / m (expansion ratio 2.2 times) passes. A product with an outer diameter of 30.5 mm and a weight per unit length of 42.5 g / m fails, but a product with 48.5 g / m (expansion ratio 1.6 times) passes.

[0047] Similarly, for the corrugated pipe (B) (with foaming, ridge wall thickness 0.4 mm), a scratch resistance test was conducted by changing the weight per unit length of the corrugated pipe for each different outer diameter (ridge outer diameter). Table 2 above shows the test results for sample group 4 with an outer diameter of 30.9 mm (foaming ratio 1.4 times). In this case, the weight per unit length was 56.6 g / m or more and passed. When further testing was conducted for each different outer diameter, it was found that the lower limit of the weight per unit length of a passing product had a linear relationship with the outer diameter, as shown by line B in Figure 5.

[0048] Similarly, for the corrugated pipe (C) (non-foamed, crest thickness 0.3 mm), a scratch resistance test was conducted by changing the weight per unit length of the corrugated pipe for each different outer diameter. That is, when tests were conducted for outer diameters of 19.0 mm, 23.5 mm, 29.0 mm, and 35.0 mm, the lower limit values ​​of the weight per unit length of the acceptable products were 36.0 g / m, 50.0 g / m, 68.0 g / m, and 88.0 g, respectively (see the open circles in Figure 5). It was found that the lower limit value of the weight per unit length of the acceptable products has a linear relationship with the outer diameter, as shown by line C in Figure 5.

[0049] From the lines A, B, and C in Figure 5, it was found that the lower limit of the weight per unit length of the acceptable product has little correlation with the expansion ratio and is smaller as the wall thickness increases. More specifically, it was found that the lower limit of the weight per unit length of the acceptable product is inversely proportional to the wall thickness.

[0050] The straight line C in Figure 5 can be expressed mathematically as follows. Y'=(3.2949×Φ-26.402) ···(3) Here, Y' is the lower limit of the weight per unit length of an acceptable product when a non-foamed corrugated pipe (ridge thickness 0.3 mm) is used, and Φ is the outer diameter of the corrugated pipe.

[0051] The weight per unit length Y (g / m) of the accepted product when using a foamed corrugated pipe is calculated by adding the thickness of 0.3 mm and the thickness of T 1 The reciprocal of the ratio (0.3 / T 1 ) as a coefficient. See the formula below. Y≧(3.2949×Φ-26.402)×0.3 / T 1 (4)

[0052] <Method of forming corrugated pipe> Next, we will verify whether a composite pipe with a corrugated pipe that satisfies formula (4) can be manufactured at low cost using the corrugated pipe molding method described below. Simply put, this method is a method of forming a corrugated pipe by extruding a resin material into a tubular shape so as to enclose a flexible resin pipe, and then expanding the diameter. The method will be described in detail below.

[0053] 6 shows a manufacturing apparatus 100 for the composite pipe A. The manufacturing apparatus 100 includes a foaming resin supply section 110, an extrusion nozzle 120, and a corrugated pipe forming section . The foaming resin supplying section 110 includes a hopper for receiving the resin that is the raw material for the corrugated pipe 3, a heater for heating and melting the resin, a foaming agent adding section, and a cylinder and screw for kneading and extruding the resin and foaming agent. The raw resin before being fed into the hopper may contain a foaming agent. The foaming resin supplying section 110 may be disposed vertically as shown in the figure, or horizontally.

[0054] The extrusion nozzle 120 has a circular passage opening through which the flexible resin tube 1 passes, and an annular extrusion opening formed so as to surround this passage opening. The corrugated pipe forming section 130 (corrugator) is disposed downstream in the extrusion direction of the extrusion nozzle 120 (right side in FIG. 6). The corrugated pipe forming section 130 is equipped with two upper and lower elliptical annular tracks 131, 132, and a large number of split dies 133, 134 that are aligned along the annular tracks 131, 132, respectively, and circulate as indicated by the arrows. The axis of the extrusion nozzle 120 passes between the two annular tracks 131, 132.

[0055] In the figure, split dies 133 and 134 are joined near the extrusion nozzle 120 to form a cylindrical die pair, and their molding surfaces can mold ridges and valleys at multiple pitches. In the molding surfaces of each of the split dies 133 and 134, a suction port (not shown) is formed in the molding portion for molding the ridges.

[0056] The composite pipe A is manufactured as follows. The flexible resin tube 1 is prepared in advance by molding and hardening it, obtaining it, etc. This flexible resin tube 1 is passed through a passage port 121 of the extrusion nozzle 120, and is sent out from the extrusion nozzle 120 to the corrugated pipe forming section 130 at a constant speed, and is sent between split dies 133 and 134 arranged on circulation tracks 131 and 132 and moving at the same speed.

[0057] In the foaming resin supply section 110, the resin is heated and melted, and a foaming agent is added in a predetermined mixing ratio so that the resin is foamed at a predetermined expansion ratio.Then, the resin is supplied to the extrusion nozzle 120 and extruded from the annular extrusion port of the extrusion nozzle 120 toward the corrugated pipe molding section 130 at the same speed as the flexible resin pipe 1.

[0058] Due to the high pressure inside the extrusion nozzle 120, the resin has not yet started to foam. Because the pressure applied to the resin by extrusion decreases, foaming starts after the resin is extruded about 100 mm. The resin extruded in a tubular shape is expanded in diameter by the vacuum from the suction ports of the split dies 133, 134, and reaches the molding surfaces of the split dies 133, 134 to be molded into the corrugated pipe 3. The corrugated pipe 3 foams as it passes through the corrugated pipe molding section 130, and its thickness increases.

[0059] The above molding method can significantly reduce the manufacturing cost of the composite pipe compared to molding a corrugated pipe separately and then covering it with a flexible resin pipe. However, since the resin is discharged upstream of the overlapping portion of the split dies 133, 134, if the discharge amount is increased, the resin will expand in diameter due to the die swell or ballast effect and get caught in the split dies 133, 134, causing resin clogging. Therefore, there is a limit to the weight per unit length of the corrugated pipe.

[0060] Using the above molding method, the relationship between the weight per unit length and resin clogging was obtained by experiment. In this experiment, a resin raw material of 100% non-foamed polyethylene was used, but the same results should be obtained with the foamed resin of the present invention. This is because the foamed resin is not foamed at the position where the split molds 133 and 134 overlap.

[0061] As a result of the experiment, it was confirmed that when the outer diameter of the corrugated pipe is 30.5 mm, the upper limit of the weight per unit length at which resin clogging does not occur stably is 60 g / m. Returning to Figure 5, in the case of a non-foamed corrugated pipe with an outer diameter of 30.5 mm, the weight per unit length that passes the test from the standpoint of scratch resistance is 75.1 g / m or more (see line C in Figure 5). Therefore, in the case of a non-foamed resin corrugated pipe, if one tries to satisfy the scratch resistance requirement, the above molding method will cause resin clogging, and therefore the above molding method cannot be used.

[0062] In contrast, for the corrugated pipe made of foamed resin of the present invention, when the outer diameter is 30.5 mm and the crest thickness is 0.5 mm, the weight per unit length must be 44.5 g / m or more to satisfy the scratch resistance, and even when the outer diameter is 30.5 mm and the crest thickness is 0.4 mm, the weight must be 56 g / m or more to satisfy the scratch resistance. These values ​​are smaller than the upper limit of 60 g / m to avoid resin clogging, so the above molding method can be used.

[0063] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. The outer surface of the valley (the bottom surface of the V-groove) may have substantially no R portion. In this case, in the cross-sectional shape of the V-groove, both side surfaces remain approximately straight and intersect at the bottom. [Industrial Applicability]

[0064] The present invention is applicable to a sheath pipe structure that protects flexible resin pipes for supplying cold or hot water. [Explanation of symbols]

[0065] 1 Flexible resin pipe 2. Sheath structure 10 wave tube 11 Mountain section (maximum diameter section) 12 Valley (smallest diameter) 13 Connection part 14 V groove

Claims

1. A sheath tube structure that is placed over a flexible resin tube to protect the flexible resin tube, a corrugated pipe that is covered with the flexible resin pipe without an intermediate material and is exposed to the outside; The corrugated pipe is a molded product made mainly of polyethylene and has an expansion ratio of 1.05 to 4.0 times, and has annular maximum diameter portions and annular minimum diameter portions alternately arranged in the pipe axial direction, and a connecting portion connecting the maximum diameter portion and the minimum diameter portion, the maximum diameter portion includes a short cylindrical portion, the minimum diameter portion does not include a short cylindrical portion, the connecting portion is inclined with respect to a pipe axis of the corrugated pipe, and a V-groove is defined by the minimum diameter portion and the connecting portions located on both sides thereof, A sheath tube structure, characterized in that the wall thickness of the maximum diameter portion is greater than the wall thickness of the minimum diameter portion.

2. The sheath tube structure according to claim 1, characterized in that the corrugated tube has a foaming ratio of 1.2 to 2.5 times.

3. A sheath tube structure as described in claim 1 or 2, characterized in that the thickness of the connecting portion gradually decreases from the maximum diameter portion to the minimum diameter portion.

4. The sheath tube structure according to any one of claims 1 to 3, characterized in that, when the outer diameter of the maximum diameter portion is Φ (mm) and the average thickness of the maximum diameter portion is T1 (mm), the weight per unit length (g / m) is (3.2949 x Φ-26.402) x 0.3 / T1 or more.

5. When the flexible resin pipe is bent to a minimum bending radius and the corrugated pipe is bent to a minimum bending radius, the width of the radial outer end of the V-groove located inside the bent shape is Wm, and the average wall thickness of the maximum diameter portion is T1, Wm / 2<T1. The sheath tube structure according to any one of claims 1 to 3.

6. The sheath tube structure according to any one of claims 1 to 3, characterized in that the distance in the tube diameter direction from the outer surface of the minimum diameter portion to the center of the wall thickness of the maximum diameter portion is equal to or greater than half the width in the tube axial direction of the maximum diameter portion.

7. The sheath tube structure according to any one of claims 1 to 6, characterized in that the corrugated tube contains 40% or less of polypropylene.

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