Methods for manufacturing metal-resin composite pipe that can be easily wound into ring shape

Abstract

The present invention may manufacture a composite pipe by forming an adhesive layer and a resin layer on an outer surface of a metal pipe, and although the composite pipe is wound in a ring shape after the composite pipe is manufactured, a circular cross sectional shape may be maintained without deformation, and after the composite pipe is straightened for the purpose of construction, separation or buckling may be prevented, resulting in excellent transportability and constructability of a product.

Claims

1. A method of manufacturing a three-layer metal resin composite pipe for transport, the method comprising the steps of: (a) manufacturing a straight metal pipe (30) only using thin plate stainless steel; (b) coating the metal pipe (30) by forming an adhesive layer (40) on an outer surface of the metal pipe (30) and by forming a resin layer (50) by extruding a polyethylene resin on the adhesive layer (40), wherein the metal pipe (30) forms a first layer, the adhesive layer (40) forms a second layer and, the resin layer (50) forms a third layer of the three-layer metal resin composite pipe (100); and (c) winding the metal resin composite pipe (100) in a helix shape having a diameter (u) in a range from 20 times to 50 times of an outer diameter (G) of the metal resin composite pipe (100) and of which a number of turns is at least 5, wherein the helix shape is capable to be maintained without an external force, wherein a thickness (p) of the straight metal pipe (30) is within a range of 5% to 20% of a thickness (q) of the resin layer (50), wherein a circular cross section of the metal pipe (30) and the metal resin composite pipe (100) is maintained without deformation regardless the metal resin composite pipe (100) is wound in the step (c) or straightened back.

2. The method of claim 1, wherein the step (b) is performed by extruding the adhesive resin and the polyethylene resin in a sequential order while the metal pipe (30) passes through a coating mold unit (200), the coating mold unit (200) comprises an inner dice (210), an inner die lip (230) disposed at a rear of the inner dice (210), an outer die lip (250) disposed at a rear of the inner die lip (230), and an outer dice (270) surrounding the outer die lip (250), the metal pipe (30) is coated while passing through the inner dice (210), the inner die lip (230), and the outer die lip (250) in a sequential order, and an inner diameter (D1) of the outer dice (270) is less than the outer diameter (G) of the composite pipe (100) by 1 mm or less, and the extrusion is performed by extruding the polyethylene resin under a pressure of 88 kg/cm.sup.2 to 96 kg/cm.sup.2 being applied to the polyethylene resin.

3. The method of claim 2, wherein the inner die lip (230) includes a slope surface (232) formed inside, and the slope surface (232) extends to a tip (233) of the inner die lip (230), and the tip (233) is pointed, wherein the tip (233) and a metal ring (211) installed in the inner dice (210) guide the sliding of the metal pipe (30) together.

4. The method of claim 3, wherein an inner diameter (D3) at the tip (233) is greater than an outer diameter of the metal pipe (30) by 0.1 mm to 0.2 mm.

5. The method of claim 4, wherein an inner diameter (D2) of the outer die lip (250) is larger than the inner diameter (D3), and a difference between the inner diameter (D2) and the inner diameter (D3) makes a space for the extrusion of the adhesive resin, wherein the inner diameter (D1) of the outer dice (270) is larger than the inner diameter (D2), and a difference between the inner diameter (D1) and the inner diameter (D2) makes a space for the extrusion of the polyethylene resin.

6. The method of claim 1, wherein a strip (9) fixes the wound composite pipe (100) in the helix shape.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view illustrating a metal resin composite pipe according to prior art.

(2) FIG. 2 is a cross sectional view taken along a line II-II in FIG. 1.

(3) FIG. 3 is a cross sectional view illustrating a coating mold unit used to manufacture the metal resin composite pipe according to prior art.

(4) FIG. 4 is a perspective view illustrating a metal resin composite pipe wound in a ring shape manufactured according to a preferred embodiment of the present invention.

(5) FIG. 5 is a cross sectional view of the metal resin composite pipe of FIG. 4.

(6) FIG. 6 is a cross sectional view illustrating a main configuration of a coating mold unit used to manufacture the metal resin composite pipe according to the present invention.

REFERENCE SYMBOLS

(7) 1, 30: metal pipe

(8) 5, 50: resin layer

(9) 40: adhesive layer

(10) 1, 100: metal resin composite pipe

(11) 20, 200: coating mold unit

(12) 21, 210: inner dice

(13) 23, 230: inner die lip

(14) 25, 250: outer die lip

(15) 27, 270: outer dice

(16) 24a, 231: adhesive resin injection hole

(17) 25a, 251: resin injection hole

(18) D1: inner diameter of the outer dice

(19) p: thickness of the metal pipe

(20) q: thickness of the resin layer

Mode for Carrying Out the Invention

(21) Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings. Prior to the description, the terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

(22) The present invention relates to methods for manufacturing a metal resin composite pipe, and is characterized in that the composite pipe may be wound in a ring shape, for example, in a shape of a roll, and the composite pipe having excellent density and surface quality may be manufactured without undergoing a sizing process. Accordingly, the following description is provided based on these characteristics. For a detailed description of a configuration of a general metal resin composite pipe and a manufacturing method thereof, reference may be made to Korean Patent No. 10-1094185 etc., the disclosure of which is incorporated herein in the condition of understanding a configuration of a general metal resin composite pipe and a manufacturing method thereof.

(23) FIG. 4 is a perspective view illustrating a metal resin composite pipe wound in a ring shape manufactured according to a preferred embodiment of the present invention. FIG. 5 is a cross sectional view of the metal resin composite pipe.

(24) Referring to FIGS. 4 and 5, the metal resin composite pipe 100 may include a metal pipe 30, an adhesive layer 40 formed on an outer surface of the metal pipe 30, and a resin layer 50.

(25) The metal pipe 30 may have a direct contact with a fluid flowing therethrough. Preferably, the metal pipe 30 may be made from a good corrosion resistant metal such as, for example, stainless steel.

(26) The metal pipe 30 may be formed of a thin plate, and the thin plate may be thinner than the resin layer 50.

(27) The applicant discovered through long-term experience and research that if a thickness ratio p/q of the metal pipe 30 and the resin layer 50 has a certain range, the composite pipe 100 may be easy to wind in a ring shape, for example, in a shape of a roll, and a property change of the metal pipe 30 may be prevented.

(28) Specifically, according to the study of the applicant, in a case in which a thickness p of the metal pipe 30 is within a range of 5% to 20% of a thickness q of the resin layer 50, when the composite pipe 100 is wound in a ring shape, roundness of the cross section of the metal pipe 30 can be maintained and plasticity may be maintained so that a circular shape can be maintained and deformation of the metal pipe 30 can be prevented. In this instance, when the composite pipe 100 is wound in a ring shape, a diameter u of the ring shape may be preferably greater about 20 times to about 50 times than an outer diameter G of the composite pipe 100.

(29) Meanwhile, the term roundness used herein refers to a shape of a circle in a mathematical sense or a shape analogous or similar thereto, other than a crushed circle, for example, an oval. A reference numeral 9 is a strip used to fix the wound composite pipe 100 in a ring shape.

(30) When the thickness ratio p/q is less than 5%, plasticity may not be maintained due to elasticity or resilience of the resin layer 50 and consequently, the ring shape, for example, the shape of the roll, may not be maintained. When the thickness ratio p/q exceeds 20%, the resin layer 50 may fail to prevent deformation of the metal pipe 30, circularly winding and straightening may be difficult, properties of the metal pipe 30 may be liable to change, and economic efficiency may be reduced.

(31) The adhesive layer 40 may be made from an adhesive resin and may allow a strong adhesion of the resin layer 50 to the metal pipe 30. The adhesive resin may include a general adhesive resin.

(32) The resin layer 50 may be extruded on the adhesive layer 40 to coat the metal pipe 30. The resin layer 50 may be formed to have a thickness greater than the thickness p of the metal pipe 30. The resin layer 50 may be made from a resin, and the resin may include polyethylene and the like.

(33) The adhesive resin and the resin may be extruded to form the adhesive layer 40 and the resin layer 50 while the metal pipe 30 passes through a coating mold unit.

(34) As shown in FIG. 6, the coating mold unit 200 may include an inner dice 210, an inner die lip 230 disposed at the rear of the inner dice 210, an outer die lip 250 disposed at the rear of the inner die lip 230, and an outer dice 270 surrounding the outer die lip 250.

(35) The metal pipe 30 (not shown in FIG. 6) may pass through the inner dice 210, the inner die lip 230, and the outer die lip 250 in a sequential order. That is, the metal pipe 30 may move inside the coating mold unit 200 in a direction of an arrow.

(36) An inner diameter D4 of the inner dice 210 may be greater than a maximum possible outer diameter of the metal pipe 30 in the coating mold unit 200.

(37) The inner die lip 230 may include a slope surface 232 formed inside, and an inner diameter D3 at a tip 233 of the slop surface 232 may be greater than an outer diameter of the metal pipe 30 by 0.1 mm to 0.2 mm. The tip 233 may guide the sliding of the metal pipe 30 together with a metal ring 211.

(38) Meanwhile, the inner die lip 230, the outer die lip 250, the outer dice 270, and the metal ring 211 may be detachably installed, and may be properly replaced in consideration of the outer diameter of the metal pipe 30 to guide the sliding of the metal pipe 30 and to allow proper extrusion.

(39) The outer die lip 250 may have an inner diameter D2 greater than an inner diameter D3. An inner diameter difference D2-D3 may allow a space for extrusion of an adhesive resin. The adhesive resin (not shown) may be extruded on the outer surface of the metal pipe 30 through an adhesive resin injection hole 231 formed between the inner die lip 230 and the outer die lip 250.

(40) The outer dice 270 may surround the outer die lip 250, and may have an inner diameter D1 greater than the inner diameter D2. An inner diameter difference D1-D2 may allow a space for extrusion of a resin. The resin (not shown) may be extruded through a resin injection hole 251 formed between the outer die lip 250 and the outer dice 270.

(41) Meanwhile, as described in the foregoing, when manufacturing a resin pipe, extrusion is performed with an outer diameter of a resin pipe being greater than a desired outer diameter by 2 mm to 5 mm, and the outer diameter is reduced through a sizing process during the cooling to meet the density and surface requirements.

(42) However, because the metal resin composite pipe 100 includes the metal pipe 30 embedded therein, the sizing process may be infeasible, resulting in a low surface quality of the composite pipe 100. When the outer diameter of the resin layer 50 is greater than the inner diameter D1 of the outer dice 270, an excessive resin of the resin layer 50 may flow back. When the outer diameter of the resin layer 50 is less than the inner diameter D1 of the outer dice 270, an outer surface of the resin layer 50 may fail to contact an inner surface of the outer dice 270, leading to an improper density of the resin layer 50, and the absence of a surface polishing effect may contribute to a rough surface, resulting in a low surface quality.

(43) To solve these problems, the present invention may set the inner diameter D1 of the outer dice 270 to be equal to an outer diameter G of a resulting composite pipe(a composite pipe intended to manufacture) or to be less than the outer diameter G of the resulting composite pipe(the composite pipe intended to manufacture) by 1.0 mm or less. Also, when extruding, the present invention may apply to the resin a pressure in a range of 88 kg/cm.sup.2 to 96 kg/cm.sup.2 that is higher by about 10% to about 20% than a pressure of about 80 kg/cm.sup.2 used in a general case.

(44) Accordingly, when the resin is extruded under the conditions of the inner diameter D1 of the outer dice 270 equal to the outer diameter of the resulting composite pipe(the composite pipe intended to manufacture) or less than the outer diameter of the resulting composite pipe by 1 mm or less and the increased pressure, the resin may be expanded after the composite pipe is discharged from the outer dice 270 so that the resin layer 50 greater than the inner diameter D1 of the outer dice 270 may be obtained. Also, the resin layer 50 formed through this process may have a proper density and a high surface quality. That is, a product having a quality as good as a product obtained through a sizing process may be obtained without passing through a sizing process.

(45) As described in the foregoing, because the metal pipe 30 passes through the inner dice 210 and the inner die lip 230, a gap between the tip 233 of the slope surface 232 and the metal pipe 30 may be important in ensuring roundness of the resin layer 50 of the resulting composite pipe 100 by forming the resin layer 50 uniformly. When the gap is excessively great, the resin layer 50 may have a non-uniform thickness, and preferably, the inner diameter D3 at the tip 233 may be greater than the outer diameter of the metal pipe 30 by 0.1 mm to 0.2 mm.

(46) Hereinafter, a method of manufacturing the metal resin composite pipe 100 is described. The following description includes an extrusion process only in the manufacturing process of the metal resin composite pipe 100. Certain processes before and after the extrusion process, for example, a metal pipe manufacturing process, a cooling process, and the like, are well known in the art and disclosed in Korean Patent No. 10-1094185 etc., and thus a detailed description is omitted herein.

(47) After the metal pipe 30 is manufactured, the metal pipe 30 may be inserted in the coating mold unit 200. When the metal pipe 30 is inserted in the inner dice 210 and makes a movement, the movement of the metal pipe 30 may be guided by the metal ring 211 and the tip 233. The adhesive resin may be extruded from the adhesive resin injection hole 231 and applied to the outer surface of the metal pipe 30, and subsequently, the resin may be extruded from the resin injection hole 251. In this instance, the resin may be extruded under a pressure of 88 kg/cm.sup.2 to 96 kg/cm.sup.2 that is higher than a general extrusion pressure of about 80 kg/cm.sup.2 by 10% to 20%. Meanwhile, because the inner diameter D1 is equal to an outer diameter of a resulting composite pipe(composite pipe intended to manufacture) or less than the outer diameter of the resulting composite pipe by 1 mm or less, the resin layer 50 may be expanded after the composite pipe is discharged from the outer dice 270 and a composite pipe having a desired outer diameter may be manufactured by the expansion. The composite pipe 100 manufactured through this process may have advantages of a proper density and a good surface quality of the resin layer 50 without passing through a sizing process.