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 metal resin composite pipe, the method comprising steps of: (a) manufacturing a metal pipe; (b) heating the metal pipe after the step (a); (c) after the step (b), forming an adhesive layer on an outer surface of the metal pipe, and forming a resin layer by extruding a polyethylene on the adhesive layer; and (d) after the step (c), cooling the resin-coated metal pipe by air-cooling and water-cooling, wherein, in the step (a), a plate stainless steel is formed into cylindrical shape with two ends thereof butted each other by plastic bending deformation process using residual stress, and then the two ends are welded to make the metal pipe, wherein a thickness of a resin layer of the resin-coated metal pipe is thicker than a thickness of the metal pipe, wherein the resin-coated metal pipe has only three layers, and the three layers consist of the metal pipe, the adhesive layer and, the resin layer, wherein the air-cooling is performed before the water-cooling, and a combination of the air-cooling and the water-cooling is performed at least one time, wherein the air-cooling is performed by blowing air to the resin-coated metal pipe, wherein the welding is performed on an upper part of the metal pipe, and the metal pipe is corrected by a correction unit between the step (a) and the step (b), wherein the correction unit comprises a first correction unit, a second correction unit placed after the first correction unit, and a third correction unit placed after the second correction unit, and the first to third correction units each have a correction groove through which the metal pipe passes, wherein the correction groove of the second correction unit is set to a higher location than the correction groove of the first correction unit, and the third correction unit is set such that the correction groove of the third correction unit is disposed at a location that is a level to or lower than the correction groove of the first correction unit.

2. The method of claim 1, wherein the air-cooling is performed by an air-cooling unit, and the air-cooling unit comprises a cooling tank through which the resin-coated metal pipe passes, a plurality of air supply pipes installed in the cooling tank and which has a plurality of air jet holes, and a compressor which supplies compressed air to the air supply pipes.

3. The method of claim 2, wherein the water-cooling is performed by moving the resin-coated metal pipe while immersed in cooling water or by spraying the cooling water to the resin-coated metal pipe.

4. The method of claim 3, wherein the water-cooling is performed by an water-cooling unit which sprays the cooling water, and the water-cooling unit comprises an cooling tank having an inlet on one sidewall and an outlet on the other sidewall, transfer rollers mounted in the cooling tank, and coolant pipes having a plurality of water supply nozzles which sprays the cooling water to the resin-coated metal pipe.

5. The method of claim 2, wherein the air supply pipes have a ring shape, the air supply pipes are installed at a predetermined interval, and the air jet holes are formed on an inner circumferential surface of the air supply pipes, wherein the air jet holes spray air to the resin-coated metal pipe while the resin-coated metal pipe passes through the air supply pipes.

6. The method of claim 1, wherein the thickness of the metal pipe is within a range of 5% to 20% of the thickness of the resin layer.

7. The method of claim 6, wherein the resin-coated metal pipe is manufactured as a straight pipe in the step (d), the resin-coated metal pipe is wound in a ring shape without deformation to a circular cross section of the metal pipe and the resin-coated metal pipe after the step (d), and the resin-coated metal pipe has a property of going back to a straight pipe without deformation to the circular cross section of the metal pipe and the resin-coated metal pipe after the winding.

8. The method of claim 7, wherein a diameter of the ring shape is 20 times to 50 times greater than an outer diameter of the resin-coated metal pipe.

9. The method of claim 7, wherein the step (c) is performed by extruding an adhesive resin of the adhesive layer and the resin in a sequential order while the metal pipe passes through a coating mold unit, the coating mold unit comprises an inner dice, an inner die lip disposed at a rear of the inner dice, an outer die lip disposed at a rear of the inner die lip, and an outer dice surrounding the outer die lip, the metal pipe is coated while passing through the inner dice, the inner die lip, and the outer die lip in a sequential order, an inner diameter of the outer dice is equal to an outer diameter of the resin-coated metal pipe or less than the outer diameter of the resin-coated metal pipe by 1 mm or less, and the extrusion is performed by extruding polyethylene resin under a pressure of 88 kg/cm2 to 96 kg/cm2 being applied to the polyethylene resin.

10. The method of claim 9, wherein the inner die lip includes a slope surface formed inside the inner die lip, the slope surface extends to a tip of the inner die lip, and the tip is pointed, wherein the tip and a metal ring installed in the inner dice guide sliding of the metal pipe together.

11. The method of claim 10, wherein an inner diameter at the tip is greater than an outer diameter of the metal pipe by 0.1 mm to 0.2 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view illustrating a metal resin composite pipe according to the present invention.

(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 of FIG. 1.

(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 of FIG. 5.

(7) FIG. 7 is a flowchart showing a method for manufacturing a metal resin composite pipe according to the present invention.

(8) FIG. 8 is a front view showing the apparatus for manufacturing a metal resin composite pipe.

(9) FIG. 9 is a front view of a correction unit provided in the apparatus shown in FIG. 8.

(10) FIG. 10 is a side view of the first correction unit of FIG. 9.

(11) FIG. 11 is a diagram showing an example of a water-cooling unit of the apparatus shown in FIG. 8.

(12) FIG. 12 is a diagram showing another example of a water-cooling unit of the apparatus.

(13) FIG. 13 is a diagram showing an air-cooling unit of the apparatus.

REFERENCE SYMBOLS

(14) 1, 30: metal pipe 5, 50: resin layer 40: adhesive layer 10, 100: metal resin composite pipe 20, 200: coating mold unit 21, 210: inner dice 23, 230: inner die lip 25, 250: outer die lip 27, 270: outer dice 24a, 231: adhesive resin injection hole 25a, 251: resin injection hole 120: welding unit 300: correction unit 310: the first correction unit 320: the second correction unit 330: the third correction unit 400: drawing unit 500: preheating unit 700, 700: water-cooling unit 700b: air-cooling unit D1: inner diameter of the outer dice p: thickness of the metal pipe q: thickness of the resin layer

MODE FOR CARRYING OUT THE INVENTION

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) 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.

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

(21) 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.

(22) 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.

(23) 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.

(24) 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.

(25) 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.

(26) 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.

(27) 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.

(28) Then, the manufacturing methods for the metal resin composite pipe 100 is described with referenced to FIGS. 6 to 13.

(29) First, a pipe forming unit (not shown) forms thin plate stainless steel into cylindrical shape with two ends thereof butted (joined) each other by plastic deformation process using residual stress, and then a welding unit 120 welds the two ends to make the metal pipe 30 (S1 step).

(30) The welded part is mostly the upper part of the metal pipe 30, and when the welded part is cooled, shrinkage occurs, causing the metal pipe 30 to bend upward. Accordingly, the method includes the step S2b in which the metal pipe 30 passes through the correction unit 300 to correct the metal pipe 30 to achieve roundness, and correct straightness to maintain horizon.

(31) As shown in FIGS. 910, the correction unit 300 includes first to third correction units 310, 320, 330. Of course, it is obvious that the number of correction units 300 installed may be increased or reduced when necessary. Since the first to third correction units 310, 320, 330 have the same configuration, only the first correction units 310 is explained below.

(32) The first correction units 310 includes first and second rollers 311, 312 having recess grooves 301, 302 formed on the outer surface thereof, correction groove 313 formed as roundness by recess grooves 301, 302 and, a gap adjustment means to adjust the gap between the first and second rollers 311, 312.

(33) The first to third correction units 310, 320, 330 are sequentially arranged along the moving direction of the metal pipe 30. The correction groove 313 of the second correction unit 320 is set to be disposed at a higher location than the correction groove 313 of the first correction unit 310 so that the metal pipe 30 primarily corrected by the first correction unit 310 to have roundness but upwardly bent is corrected to horizontal state while passing through the correction groove 313 of the second correction unit 320.

(34) The third correction unit 330 is set such that the correction groove 313 thereof is disposed at a location that is level to or slightly lower than the correction groove 313 of the first correction unit 310, so that roundness correction and horizon correction are performed again for the metal pipe 30 having corrected to horizontal state by the correction unit 320, thereby having more accurate roundness and straightness.

(35) Meanwhile, the gap adjustment means adjusts the gap between the first and second rollers 311, 312. As shown in FIGS. 9 and 10, the gap adjustment means includes a plurality of guide rods 361, first and second beds 331, 341 having the first and second rollers 311, 312 mounted thereon respectively and coupled to the guide rods 361, lift rods 391 screw coupled to the first and second beds 331, 341 respectively.

(36) By rotating the lift rods 391 with a tool such as a spanner, the first and second beds 331, 341 are lifted up or down, and then the gap between the second roller 312 and the first roller 311 is adjusted.

(37) The metal pipe 30 corrected by the correction unit 300 is drawn continuously by the drawing unit 400 to move to the next process. Meanwhile, the drawing unit 400 may be also further installed at the rear of the cooling unit to draw the finally cooled metal resin composite pipe.

(38) As shown in FIG. 8, the drawing unit 400 includes upper and lower caterpillars and a drive motor (not shown) to drive the upper and lower caterpillars.

(39) The metal pipe 30 having passed the drawing unit 400 is heated by a preheating unit 500 for efficient coating (step S2c). The preheating unit 500 generates heat using a heating coil etc., and has a common configuration.

(40) The preheated metal pipe 30 is coated with synthetic resin by the coating mold unit 200 (S3 step).

(41) 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.

(42) 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.

(43) 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.

(44) 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.

(45) 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.

(46) The outer die lip 250 may have an inner diameter D2 greater than an inner diameter D3. An inner diameter difference D2D3 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.

(47) 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 D1D2 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.

(48) 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.

(49) 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.

(50) 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.

(51) 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.

(52) 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.

(53) 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.

(54) 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.

(55) The composite pipe 100 manufactured by the processes explained above is cooled. Although a water-cooling unit is disclosed in FIG. 8, an air-cooling or a water-cooling after an air-cooling or repetitions of a water-cooling after an air-cooling is also preferred (S4).

(56) The water-cooling unit 700 immerses the composite pipe 100 in the cooling tank 710 to cool it. As shown in FIG. 11, the water-cooling unit 700 includes the cooling tank 710 having a predefined storage space, an inlet 701 on one sidewall and an outlet 702 on the other sidewall, and in which a transfer roller 703 is mounted on a cover 709 and a cooling water is stored; and a debubbling device 720 formed in the inlet 701.

(57) When the composite pipe 100 is immersed in the water, the composite pipe 100 floats due to the buoyancy, and the transfer roller 703 supports and presses down the composite pipe 100 to prevent floating.

(58) The debubbling device 720 is configured to remove bubbles generated on the outer surface of the composite pipe 100 while introducing the composite pipe 100 into the cooling tank 710, and includes a barrier 721 that is attached to the inlet 701 and has a through-hole through which the composite pipe 100 passes at the center part and has an elastic property, and foam resin 722 that is placed apart from the barrier 721 and has a through-hole through which the composite pipe 100 passes at the center part.

(59) Accordingly, when the composite pipe 100 is introduced into the cooling tank 710 through the through-hole of the barrier 721, bubbles on the outer surface may be cleared off and removed by the foam resin 722.

(60) Preferably, the barrier 721 is heat resistant rubber having heat resistance, and the foam resin 722 is a heat resistant sponge.

(61) Meanwhile, as shown in FIG. 12, another embodiment of the water-cooling unit 700 uses a showering process in which cooling is performed by spraying water.

(62) That is, water-cooling unit 700 includes a cooling tank 710 having an inlet 701 on one sidewall, an outlet 702 on the other sidewall, and a transfer roller 703 mounted therein; and a coolant pipe 724 installed in the cooling tank 710 and having a plurality of water supply nozzles 725.

(63) A barrier 721 is attached to the inlet 701 and the outlet 702. Accordingly, the composite pipe 100 introduced into the cooling tank 710 may be cooled by showering of water from the water supply nozzles 725 placed on upper, lower, left and right sides around it while it is moving along the transfer roller 703.

(64) The air-cooling unit performs cooling by spraying air of room temperature or low temperature to the composite pipe 100. As shown in FIG. 13, the air-cooling unit 700b includes a cooling tank 710 in which the composite pipe 100 is received, a plurality of air supply pipes 724b installed in the cooling tank 710 and having a plurality of air jet holes 725b on the inner circumferential surface, and a compressor 705 which supplies air to the air supply pipe 724b.

(65) The air supply pipe 724b is in the shape of a ring with a through-hole formed therein, and the composite pipe 100 may pass through the through-hole.

(66) Of course, it is noted that the air supply pipe 724b is not necessarily limited to a ring shape, and various modifications may be made if the shape has a through-hole through which the composite pipe 100 passes.

(67) While the composite pipe 100 passes through the air supply pipe 724b, a spray of air having high pressure generated from the compressor 705 is blown from the air jet holes 725b to cool the composite pipe 100.

(68) After passing through the cooling process, the composite pipe 100 is cut to a predetermined length by a cutter to manufacture a finished product.