Method for manufacturing bend resin pipe

Abstract

To provide a method for manufacturing a bend resin pipe, capable of efficiently manufacturing a three-dimensionally bent bend resin pipe.SOLUTION: In a method for manufacturing a bend resin pipe, an uncrosslinked resin pipe is heated to a softening temperature or above and a melting point or below, bent into a three-dimensional shape, and then crosslinked. During a shaping process, an original pipe 1' is held in grooves 11, 21, 31 of shaping molds 10, 20, 30 for maintaining a bent shape. The molds 10, 20, 30 each have the grooves 11, 21, 31 extending in an L-shape. There is a gap of 30 mm or more between the molds 10, 20 and between the molds 20, 30. The pipe is then removed from the shaping mold and placed in a crosslinking mold for crosslinking.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a resin (synthetic resin) pipe having a bent portion, and in particular to a method for manufacturing a three-dimensionally bent resin pipe. More specifically, the present invention relates to a method for manufacturing a bent resin pipe, which includes a step of bending a straight resin pipe before cross-linking, and a step of cross-linking the resin pipe thereafter. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known a method for bending a polyolefin resin pipe, in which a polyolefin resin pipe is heated and bent.

[0003] One example of a conventional method for bending polyolefin-based resin pipes is a method in which a polyolefin-based resin pipe that serves as the original pipe is heated to a temperature at which it can be deformed, the resin pipe is bent using a mold with a cavity that matches the desired bending shape of the resin pipe, the resin pipe is cooled inside the mold, and the mold is opened to remove the resin pipe bent to the desired bending angle (Patent Document 1).

[0004] However, such a method for bending a polyolefin resin pipe has a problem in that the pipe will unbend over time due to residual stress after bending.

[0005] There is also a known method of manufacturing a curved resin pipe by crosslinking a resin pipe and then bending it. However, in this method, when the manufactured curved resin pipe is heated by passing hot water through it, the shape memory effect of the resin generates a force that returns the curved resin pipe to its crosslinked shape (straight pipe), and the curved resin pipe is deformed from the intended shape back to a shape close to the straight pipe.

[0006] Patent Document 2 describes a method for manufacturing a curved resin pipe in which an uncrosslinked (including slightly crosslinked) resin pipe is heated to above its softening temperature and below its melting point, bent using a shaping mold, and then crosslinked, and the pipe is held in place by a crosslinking mold to maintain the bent shape during the crosslinking process.

[0007] The bent resin pipe manufactured by this method is cross-linked after bending, and the shape is maintained by the mold during the cross-linking process. Therefore, even if heat is applied to the bent resin pipe by passing hot water through it, the shape memory effect causes almost no force to return it to a straight pipe, and the bent shape is maintained.

[0008] When the crosslinking treatment is performed by heating, the residual stress generated during bending is eliminated or alleviated by heating, which also improves the shape retention of the bent resin pipe. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 11-300821 [Patent Document 2] JP 2017-87623 A Summary of the Invention [Problem to be solved by the invention]

[0010] The manufacturing method of the curved resin pipe of Patent Document 2 is for manufacturing a curved resin pipe that is curved in two dimensions, but cannot manufacture a curved resin pipe that is curved in three dimensions. In addition, when manufacturing a pipe that is curved in three dimensions, it is necessary to manufacture it using a mold with a large cubic or rectangular pipe groove, and it is expected that the cost of the shaping mold will increase.

[0011] An object of the present invention is to provide a method for manufacturing a bent resin pipe, which can efficiently manufacture a bent resin pipe that is bent three-dimensionally. [Means for solving the problem]

[0012] The method for manufacturing a curved resin pipe of the present invention involves heating an uncrosslinked resin pipe above its softening temperature and below its melting point, bending it three-dimensionally in a shaping mold, and then crosslinking the pipe, and is characterized in that the pipe is held in a groove in the crosslinking mold to maintain the bent shape during the crosslinking process.

[0013] In one embodiment of the present invention, the mold comprises a plurality of planar shaping molds arranged at intervals from each other.

[0014] In one aspect of the present invention, the shaping molds each have the grooves extending in two dimensions.

[0015] In one embodiment of the invention, at least one of the shaping molds has the groove extending in an L-shape.

[0016] In one embodiment of the present invention, the spacing between the shaping dies is 30 to 500 mm, and the multiple shaping dies on a plane are arranged so that the linear grooves overlap on their respective extension lines, that is, the linear parts of the processed pipes are arranged so as to cross the gaps between the shaping dies. The shaping dies are constructed three-dimensionally by combining them with wood or metal frames at positions that do not interfere with pipe insertion. Effect of the Invention

[0017] According to the present invention, a resin pipe that is bent in three dimensions can be efficiently manufactured. [Brief description of the drawings]

[0018] [Figure 1] 2 is an oblique view of a shaping mold used in a manufacturing method of a curved resin pipe according to an embodiment of the present invention. FIG. [Diagram 2] 2 is a perspective view showing a method for manufacturing a resin pipe using the shaping mold of FIG. 1. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described.

[0020] In the manufacturing method of the curved resin pipe of the present invention, an uncrosslinked (including slightly crosslinked) straight resin pipe (original pipe) is heated and bent three-dimensionally in a shaping mold, and then held in a crosslinking mold for crosslinking treatment.

[0021] Suitable uncrosslinked resins for use in the resin pipe include polyethylene, polypropylene, polybutene, and copolymers of these olefins, each having a crosslinking degree of 10% or less, particularly about 0.01 to 5%, as well as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-propylene-diene elastomers, with polyethylene being particularly preferred.

[0022] The inner diameter of the uncrosslinked original pipe is preferably about 4 to 20 mm, particularly about 8 to 16 mm. The wall thickness of the original pipe is preferably about 1 to 4 mm, particularly about 1.6 to 3 mm. The wall thickness of the original pipe is preferably 100 to 200%, particularly 100 to 160%, of the wall thickness after bending. This is because the wall thickness on the outside (stretched side) of the bent part is reduced by bending.

[0023] This original pipe is heated to a temperature above the softening temperature and below the melting point of the resin, and is then bent.

[0024] 3 to 5 are perspective views, plan views and front views showing an example of the shape of a curved resin pipe after bending and crosslinking. This curved resin pipe 1 has a short pipe section 3, a first long pipe section 2 extending from one end side of the short pipe section 3, a second long pipe section 4 extending from the other end side of the short pipe section 3, and a vertical pipe section 5 rising from the tip side of the second long pipe section 4 in the extending direction.

[0025] The short tube section 3 and the second long tube section 4 are located in one plane (XY plane), and the intersection angle between the two tubes is 90°. The vertical tube section 5 extends in the Z direction perpendicular to the XY plane or approximately in the Z direction. The intersection angle of the vertical tube section 5 with respect to the XY plane is 90°.

[0026] The first long tubular portion 2 extends in a diagonal direction with respect to the XY plane. The intersection angle θ (FIG. 5) between the first long tubular portion 2 and the XY plane is 20°. The intersection angle between the first long tubular portion 2 and the short tubular portion 3 is 90°.

[0027] The length of the first long tube section 2 is approximately twice the length of the short tube section 3. The length of the second long tube section 4 is approximately three times the length of the short tube section 3. The length of the vertical tube section 5 is approximately 0.5 times the length of the short tube section 3.

[0028] The connecting portion between the short pipe section 3 and the first long pipe section 2 and the second long pipe section 4, and the connecting portion between the second long pipe section 4 and the vertical pipe section 5 are curved bent sections 6, 7, and 8. The radius of curvature of the bent sections 6 and 7 is approximately 40 mm, and the radius of curvature of the bent section 8 is approximately 20 mm.

[0029] This bent resin pipe 1 is suitable for being placed inside the casing of a heat pump heat source device or a water heater equipped with a gas-fired boiler, but its use is not limited to this.

[0030] As described above, when the bent resin pipe manufactured by bending and cross-linking is heated by passing hot water of 90°C or higher through the pipe, the angles of the bent portions 6, 7, and 8 tend to increase due to the shape memory effect resulting from the cross-linking of the resin constituting the original pipe. Therefore, in this embodiment, the pipe is bent deeply so that the intersection angle is smaller than the target angle. By doing so, when the intersection angle increases due to the shape memory effect, the bent resin pipe 1 becomes a curved resin pipe 1 having a target shape with an intersection angle that is approximately the target angle.

[0031] When bending the pipe, a core material is inserted into the pipe to prevent buckling. A synthetic resin rope is suitable as the core material. The rope may be inserted directly into the substantially straight pipe, or a wire may be attached to the end of the rope, which may then be passed through the pipe and pulled to insert the rope into the pipe.

[0032] The diameter of this rope is preferably about 70 to 95%, particularly 80 to 90% of the inner diameter of the pipe. A synthetic resin rope hardly shrinks in diameter even when compressed radially inside a pipe, and buckling of the pipe during bending is prevented. In addition, since a synthetic resin rope bends flexibly, it bends freely following the bending of the pipe. In addition, since the contact area of ​​this rope with the inner peripheral surface of the pipe is smaller than that of a rod or tube, it can be easily pulled out of the pipe by pulling after bending the pipe.

[0033] In particular, when a rope made of nylon, fluororesin, polyester resin, polyethylene, polypropylene or the like is used as the synthetic resin rope, friction with the inner circumferential surface of the pipe is small, and the rope can be pulled out smoothly.

[0034] To bend the pipe (original pipe) with the core material inserted, a heating means such as an oven is used to heat the pipe (original pipe) to a temperature above the softening temperature and below the melting point of the resin, and the pipe is placed in a bending mold (molds 10, 20, and 30 shown in the figure) and bent. The pipe is then cooled by leaving it to cool to below the softening temperature, for example to about 40°C, and then removed from the mold. Then, a crosslinking process is performed.

[0035] To carry out this crosslinking treatment, it is preferable to mount the bent pipe (original pipe 1') in a crosslinking mold as shown in Figures 1 to 5 of JP2017-87623A and heat it to carry out the crosslinking treatment.

[0036] In one embodiment, the shaping mold 10 is L-shaped and has a long portion 10a and a short portion 10b connected to one end of the long portion 10a. The mold 10 is provided with a groove 11 for inserting an original pipe. The groove 11 is L-shaped and includes a long groove 11a extending in the longitudinal direction of the long portion 10a and a short groove 11b provided in the short portion 10b and connected to the long groove 11a. The long groove 11a faces the end face of the long portion 10a at the tip end in the extension direction. The short groove 11b faces the end face of the short portion 10b at the tip end in the extension direction.

[0037] The shaping mold 20 is L-shaped and has a long portion 20a and a short portion 20b connected to one end of the long portion 20a. The mold 20 is provided with a groove 21 for inserting an original pipe. The groove 21 is L-shaped and includes a long groove 21a extending in the longitudinal direction of the long portion 20a and a short groove 21b provided in the short portion 20b and connected to the long groove 21a. The long groove 21a faces the tip surface on the opposite side of the short portion 20b. The short groove 21b faces the end surface on the tip side in the extension direction of the short portion 20b.

[0038] The shaping mold 30 is L-shaped and has a long portion 30a and a short portion 30b connected to one end of the long portion 30a. The mold 30 is provided with a groove 31 for inserting an original pipe. The groove 31 is L-shaped and includes a long groove 31a extending in the longitudinal direction of the long portion 30a and a short groove 31b provided in the short portion 30b and connected to the long groove 31a. The short groove 31b faces the end face of the short portion 30b on the tip side in the extension direction.

[0039] As described above, each of the grooves 11, 21, and 31 is L-shaped and extends in a two-dimensional direction.

[0040] The shaping molds 10, 20, 30 are arranged so that the grooves 11, 21, 31 of the shaping molds 10, 20, 30 are positioned along the curved resin pipe 1 of the desired shape, and are held by a mold holding member (not shown). In the molds 10, 20, the grooves 11, 21 are positioned on the upper surface, and the short grooves 11b, 21b are positioned on a straight line. In the mold 30, the groove 31 is positioned on the side surface, the long groove 31a extends in the vertical direction, and the short groove 31b is positioned on a straight line with the long groove 21a of the mold 20.

[0041] In this deployed state, the tip surface of the short portion 10b of the mold 10 faces the tip surface of the short portion 20b of the mold 20, with a gap of about 40 mm between them. Also, the tip surface of the long portion 20a of the mold 20 faces the tip surface of the short portion 30b of the mold 30, with a gap of about 70 mm between them.

[0042] 2, the bent original pipe 1' is fitted into the grooves 11, 21, 31 of the shaping dies 10, 20, 30 thus arranged. Since there are the above-mentioned intervals between the dies 10, 20 and between the dies 20, 30, the original pipe can be fitted into the grooves 11, 21, 31 smoothly.

[0043] The original pipe 1' thus attached to the shaping molds 10, 20, and 30 in the state shown in FIG. 2 is removed from the mold after cooling, and placed back into a crosslinking mold as shown in FIGS. 1 to 5 of JP 2017-87623 A, and then moved into a crosslinking tank (not shown). Steam is supplied into the crosslinking tank and the temperature is kept at 90 to 110°C, preferably 95 to 100°C, for 3 hours or more, preferably 3 to 12 hours, to thermally crosslink the resin that constitutes the pipe 1. The degree of crosslinking after the crosslinking process is preferably 40 to 100%, and more preferably about 60 to 100%.

[0044] After a predetermined time has elapsed, the pipe 1 is removed from the crosslinking tank.

[0045] During this cross-linking process, the pipe 1 is heated, so that the residual stress generated in the pipe 1 by the bending process disappears or is alleviated.

[0046] The pipe 1 taken out together with the crosslinking mold from the crosslinking tank is cooled to 40° C. or less, for example, 35 to 15° C., by standing to cool, etc. Then, the pipe 1 is removed from the crosslinking mold (demolding). The curved resin pipe taken out of the crosslinking mold after cooling has the three-dimensional shape shown in FIGS. 3 to 5.

[0047] This manufacturing method uses three shaping molds 10, 20, and 30. Each mold 10, 20, and 30 has a two-dimensional L-shape, so the structure is simple and the mold cost is low. In addition, there is a gap of 30 mm or more between the molds 10 and 20 and between the molds 20 and 30, so that the pipes can be easily attached and detached.

[0048] In this manner, a cross-linked, three-dimensionally shaped curved resin pipe can be smoothly manufactured.

[0049] The above embodiment is one example of the present invention, and the present invention may have other embodiments, specifically, the number of bends, the bend angle, the length of the straight portion, the number of mold combinations, etc. may be values ​​other than the examples. That is, in the present invention, the curved resin pipe may have a three-dimensional shape other than that shown in the drawings, and for example, the number of bends may be four or more. [Explanation of symbols]

[0050] 1. Bent plastic pipe 1' Original pipe 2 1st long pipe section 3 Short pipe section 4 2nd long pipe section 5 Vertical pipe section 6,7,8 Bends 10,20,30 Shaping type 11,21,31, groove

Claims

1. A method for manufacturing a bent resin pipe, comprising heating an uncrosslinked resin pipe above its softening temperature and below its melting point, bending it in three dimensions, and then crosslinking the pipe, characterized in that the three-dimensional bending is performed by combining multiple planar shaping molds.

2. The method for manufacturing a curved plastic pipe according to claim 1, wherein the shaping mold is a plurality of planar shaping molds arranged with a gap between them and such that the straight grooves into which the plastic pipes are inserted overlap in the same straight line on an extension line.

3. A method for manufacturing a curved plastic pipe as claimed in claim 2, wherein each of the shaping dies has a groove extending in a two-dimensional direction, and at least two of the shaping dies have a groove extending in an L-shape on the same plane.

4. The method for manufacturing a curved resin pipe according to claim 2, wherein the shaping dies are assembled in a three-dimensional manner at a position that does not interfere with the insertion of the resin pipe.

5. The method for manufacturing a curved resin pipe according to any one of claims 2 to 4, wherein the distance between the shaping dies is 30 to 500 mm.

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