Internally grooved pipe for flaring and heat exchanger equipped therewith

Abstract

To provide a pipe with an inner surface groove for flaring in which cracks are less likely to occur due to pipe expansion through flaring.SOLUTION: A pipe with an inner surface groove for flaring is a seamless pipe with a groove on an inner surface and a flared end part, where an outer diameter D is 2.0 mm or more and 5.5 mm or less, a ratio T / D of a wall thickness T and the outer diameter D is 0.057-0.005D or more and 0.075-0.005D or less, a torsion angle θ of the groove on the inner surface is 15 degrees or more and 27 degrees or less, a radius of curvature r of a tip part of a fin constituting the groove on the inner surface and the number N of the fins in a circumferential direction satisfy a specific formula, and the radius of curvature r of the tip part and the torsion angle θ satisfy a specific formula.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tube with an inner surface groove for flare processing and a heat exchanger including the same.

Background Art

[0002] Conventionally, in heat exchangers such as room air conditioners (RAC), package air conditioners (PAC), refrigerators, and water heaters, and in electronic devices such as personal computers (PC), smartphones, and game consoles, copper tubes through which a heat medium flows inside for heat exchange are incorporated.

[0003] For example, in the process of assembling a room air conditioner, first, a plurality of straight copper tubes are prepared, and each is bent at the central portion in the longitudinal direction to form a U-shaped hairpin tube. Then, each copper tube is inserted into a through-hole of an aluminum fin formed by laminating a large number of aluminum plates, and the straight tube portion of the copper tube is expanded to bring the outer surface of the straight tube portion into close contact with the inner peripheral surface of the through-hole of the aluminum fin. After that, for the tube end portions protruding from the aluminum fins in each copper tube, adjacent ones are connected with a U-shaped bend tube or a branch tube. Then, the connected copper tubes form one or more flow paths through which a heat medium flows inside. Then, the heat of the heat medium in the copper tube is transmitted to the aluminum fins, and by flowing indoor air or the like through the gaps between the aluminum plates in the aluminum fins, the temperature of the air or the like can be adjusted.

[0004] Here, expanding the straight tube portion of the copper tube to bring it into close contact with the inner peripheral surface of the through-hole of the aluminum fin is called primary expansion. Also, expanding the tube end portion of each copper tube to insert a U-shaped bend tube is called secondary expansion, and the portion subjected to secondary expansion is also called a secondary expansion portion. Furthermore, the outermost end of the secondary expansion portion is expanded. This expansion is called tertiary expansion or flare processing. Also, the portion subjected to tertiary expansion or flare processing is called a flare processing portion. The bent pipe is inserted into the secondary expanded section, passing through the flared section. A ring-shaped brazing material is then inserted into the gap between the outer surface of the bent pipe and the inner surface of the flared section. The brazing material is then heated, melted, and solidified to join the bent pipe to the end of the copper pipe. The flared section is formed to secure the gap for inserting this brazing material.

[0005] Traditionally, this type of flaring process sometimes resulted in cracks at the outer end of copper pipes. This was particularly true for copper pipes with small outer diameters, such as those with an outer diameter of 6 mm or less, where flaring could cause cracking. This was mainly because, even with small outer diameters, a certain size of gap is required for inserting the brazing material, resulting in a relatively larger expansion ratio for smaller copper pipes compared to larger ones.

[0006] In contrast, Patent Document 1 proposes a copper or copper alloy pipe for flaring, which is used to flare the end of a seamless pipe, characterized in that the outer diameter D is 2.0 to 5.5 mm, the ratio T / D of wall thickness T to outer diameter D is (0.057-0.005D) or more and (0.075-0.005D) or less, the average grain size is 30 μm or less, and the circumferential elongation is 35% or more. Patent Document 1 states that, because the wall thickness, average grain size, and elongation of such a copper or copper alloy pipe for flaring are appropriately set, it is possible to prevent cracking in the expanded portion of the flared section when flaring is performed using a small-diameter copper pipe with an outer diameter of 2.0 to 5.5 mm. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2017-20063 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention provides a pipe with internal grooves for flaring, which is less prone to cracking during expansion by flaring, and a heat exchanger equipped with the same. [Means for solving the problem]

[0009] The inventors diligently studied and conducted research to solve the above problems, and have completed the present invention. The present invention is as follows (I) to (IV). (I) A flared pipe with an internal groove that has grooves on its inner surface and is flared at its end, and is a seamless pipe, The outer diameter D is 2.0 mm or more and 5.5 mm or less. The ratio T / D of wall thickness T to outer diameter D is 0.057-0.005D or greater and 0.075-0.005D or less. The torsional angle θ of the groove on the inner surface is 15 degrees or more and 27 degrees or less. The radius of curvature r of the tip of the fin constituting the groove on the inner surface and the number of fins N in the circumferential direction satisfy the following equation (1): A pipe with an internal groove for flaring, wherein the radius of curvature r of the tip and the torsion angle θ satisfy the following equation (2). Formula (1): 0.32≦1 / (r×N)≦0.61 Formula (2): 0.04≦r×(1 / cosθ)≦0.051 (II) The flared tube with internal grooves described in (I) above, wherein the radius of curvature r of the tip and the number of fins N satisfy the following formula (1'). Formula (1´): 0.52≦1 / (r×N)≦0.61 (III) A flared pipe with an internal groove, made of copper or a copper alloy, as described in (I) or (II) above. (IV) A heat exchanger equipped with a flared tube with an internal groove for flaring as described in any of (I) to (III) above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a flared pipe with an internal groove that is less prone to cracking during expansion by flaring, and a heat exchanger equipped therewith. [Brief explanation of the drawing]

[0011] [Figure 1] FIG. 1(a) is a schematic view showing a side surface of the grooved pipe of the present invention having a straight tubular shape, FIG. 1(b) is a cross-sectional view taken along line A-A in FIG. 1(a), and FIG. 1(c) is an enlarged view of one of the eight portions (X portion) surrounded by a dotted line in FIG. 1(b). [Figure 2] FIG. 2(a) is a schematic side view showing a test piece 10 obtained by cutting out a part (a portion having a length of L in the longitudinal direction) from the grooved pipe of the present invention, and FIGS. 2(b) and 2(c) are schematic side views and schematic end views showing a state in which the test piece 10 is placed on the surface of a metal substrate 20 and a load P is applied from above. [Figure 3] FIG. 3(a) is a schematic side view showing a state in which the test piece 10 is completely crushed and two plates are overlapped due to the application of the load P, FIG. 3(b) is a schematic side view showing a state in which the two plates are separated, and FIG. 3(c) is a schematic view (schematic front view) of the lower plate (10a) viewed from above after removing the upper plate (10b) of the two plates. [Figure 4] Similar to FIG. 1(c), it is an enlarged view of one of the eight portions (X portion) surrounded by a dotted line in FIG. 1(b), and it is a diagram (schematic view) for explaining the fin height, apex angle, and fin root curvature radius R. [Figure 5] Similar to FIG. 1(c), it is an enlarged view of one of the eight portions (X portion) surrounded by a dotted line in FIG. 1(b), and it is a diagram (schematic view) for explaining the fin root curvature radius R. [Figure 6] It is a diagram showing an example of a manufacturing apparatus used for manufacturing the grooved pipe of the present invention. [Figure 7] It is a partially broken front view exemplifying a heat exchanger 60 of the present invention of a fin-and-tube type heat exchanger incorporating the grooved pipe of the present invention. [Figure 8] It is a partially enlarged view (schematic perspective view) of FIG. 7.

MODE FOR CARRYING OUT THE INVENTION

[0012] The present invention will be described. The present invention relates to a tube with an internal groove for flaring, which is a seamless tube having a groove on the inner surface and subjected to flaring at the end. The outer diameter D is 2.0 mm or more and 5.5 mm or less, the ratio T / D of the wall thickness T to the outer diameter D is 0.057 - 0.005D or more and 0.075 - 0.005D or less, the twist angle θ of the groove on the inner surface is 15 degrees or more and 27 degrees or less, the tip radius of curvature r of the fin constituting the groove on the inner surface and the number N of the fins in the circumferential direction satisfy the following formula (1), and the tip radius of curvature r and the twist angle θ satisfy the following formula (2). It is a tube with an internal groove for flaring. Formula (1): 0.32 ≤ 1 / (r×N) ≤ 0.61 Formula (2): 0.04 ≤ r×(1 / cosθ) ≤ 0.051 Such a tube with an internal groove for flaring is also referred to as the "grooved tube of the present invention" hereinafter.

[0013] The present invention also relates to a heat exchanger including the grooved tube of the present invention. Such a heat exchanger is also referred to as the "heat exchanger of the present invention" hereinafter.

[0014] <The grooved tube of the present invention> The grooved tube of the present invention will be described. The grooved tube of the present invention is a tube with an internal groove for flaring, which is a seamless tube having a groove on the inner surface and subjected to flaring at the end. Note that the grooved tube of the present invention may be before or after the flaring process. The grooved tube of the present invention included in the heat exchanger of the present invention is usually after the flaring process.

[0015] The shape of the grooved tube of the present invention is not particularly limited, and it may be a straight tube, a state where a straight tube is wound in a coil shape, or a U-shaped (hairpin tube) formed by bending a straight tube. Also, the cross-sectional shape is not particularly limited, and the cross-section in a direction perpendicular to the longitudinal direction of the tube may be an ellipse, a triangle, a quadrilateral, or other polygons, but a circular shape is preferred.

[0016] The material of the grooved pipe of the present invention is not particularly limited, but it is preferably made of copper or a copper alloy. Examples of copper or copper alloys include C1220 (phosphorus-deoxidized copper), C1201 (low-phosphorus-deoxidized copper), C1020 (oxygen-free copper), C5010, C1862, and C1565 (high-strength copper), as specified in JIS H 3300.

[0017] The grooved pipe of the present invention has grooves on its inner surface. The grooves on the inner surface of the grooved pipe of the present invention will be explained with reference to Figure 1. Figure 1(a) is a schematic diagram showing a side view of the grooved pipe of the present invention when it is straight and has a circular cross-section. In Figure 1(a), the central axis of the grooved pipe of the present invention is indicated as ω. Figure 1(b) is a cross-section along line AA in Figure 1(a), representing a cross-section perpendicular to the longitudinal direction of the pipe (parallel to the central axis ω) (a schematic cross-sectional view). In Figure 1(b), the eight locations enclosed by dotted rectangles indicate the locations where the outer diameter D, wall thickness T, and fin tip radius of curvature r are measured using the method described later. These locations are arranged at approximately equal intervals (approximately 45-degree intervals) in the circumferential direction in the cross-section shown in Figure 1(b). As will be described later, these values ​​in the grooved pipe of the present invention represent the simple average of the measurement results at these eight locations. Figure 1(c) is a magnified view of one of the eight areas (area X) enclosed by the dotted line in Figure 1(b).

[0018] [Outer diameter D] In the grooved pipe of the present invention, the outer diameter D is 2.0 mm or more and 5.5 mm or less, and preferably 3.5 mm or more and 5.0 mm or less. The outer diameter D is measured at eight locations enclosed by dotted lines in Figure 1(b). In other words, in Figure 1(b), these eight locations consist of four pairs of opposite locations with respect to the central axis ω. After obtaining four outer diameter measurements at these eight locations (four pairs) that are approximately uniform in the circumferential direction, the simple average of these four measurements is taken as the outer diameter D of the grooved pipe according to the present invention. The outer diameter is measured using a digital caliper.

[0019] Traditionally, copper tubes with an outer diameter of 7 to 9.52 mm were mainly used for flaring. However, in recent years, there has been a demand for smaller diameters to reduce the weight and improve the performance of heat transfer tubes. Furthermore, in order to reduce the global warming potential, the heat transfer medium (refrigerant, etc.) flowing through the tubes is being switched to R32, but since R32 is slightly flammable, there is a need to reduce the amount used, and smaller diameters are also desired to achieve this. Since the outer diameter D of the grooved pipe of the present invention is within the range described above, it satisfies the recent demand for smaller diameters.

[0020] [Thickness T] In the grooved pipe of the present invention, the ratio of outer diameter D to wall thickness T (T / D) is preferably 0.057-0.005D or more and 0.075-0.005D or less, and preferably 0.059-0.005D or more and 0.071-0.005D or less.

[0021] The wall thickness T is preferably 0.09 to 0.27 mm, more preferably 0.13 to 0.25 mm, even more preferably 0.17 to 0.23 mm, and even more preferably 0.18 to 0.21 mm. In recent years, due to factors such as the soaring price of copper, there has been a demand for lightweight grooved tubes used in heat exchangers and the like, while still satisfying the required pressure resistance. The grooved tube of the present invention has the aforementioned outer diameter D and wall thickness T, and thus satisfies this demand.

[0022] This section explains how to measure wall thickness T. First, the eight locations enclosed by dotted lines in Figure 1(b) are magnified 10 times using a laser microscope (e.g., Keyence VK-8500) to obtain images or photographs as shown in Figure 1(c). Next, at each of the eight locations shown in Figure 1(c), the wall thickness at which it is thinnest in the radial direction centered on the central axis ω is measured. The value obtained by simply averaging the measured values ​​at the eight locations is defined as the wall thickness T of the grooved pipe of the present invention.

[0023] [Tip radius of curvature r] The radius of curvature r at the tip of the fins constituting the grooves on the inner surface of the grooved tube of the present invention is preferably 0.030 to 0.045 mm, and when heat transfer performance is taken into consideration, it is preferably 0.030 to 0.040 mm. Furthermore, when productivity is a priority, it is more preferably 0.036 to 0.040 mm.

[0024] The method for measuring the radius of curvature r at the tip of the fin will be explained using Figures 1(b) and 1(c). First, the eight areas enclosed by dotted lines in Figure 1(b) were magnified 10 times using a laser microscope (for example, Keyence VK-8500) to obtain images or photographs as shown in Figure 1(c). Next, in an image or photograph as shown in Figure 1(c), draw a curve Y that is tangent to the tops of the three fins: the fin 1 to be measured and the two adjacent fins 1a and 1b. This curve Y usually roughly coincides with the circumference of a circle centered at ω, as shown in Figure 1(b). Next, the groove bottom 3a between the fin 1 to be measured and the adjacent fin 1a is identified, and similarly, the groove bottom 3b between the fin 1 to be measured and the adjacent fin 1b is identified, and then a straight line W, which is tangent to both of these, is drawn. Next, in Figure 1(c), the point on the contour of fin 1 where the length of the line perpendicular to line W, connecting the contour of fin 1 to a point on line W, is longest is defined as vertex V. Vertex V usually coincides approximately with the point of tangency between the contour of fin 1 and curve Y. Then, a line perpendicular to line W is drawn from vertex V of fin 1. Next, identify the point that bisects the perpendicular line drawn from vertex V to line W, draw a line through this point parallel to line W, and let the points where this line intersects the contour of fin 1 be 5a and 5b. Then, let Za be the tangent line passing through point 5a and touching the contour of fin 1, and similarly, let Zb be the tangent line passing through point 5b and touching the contour of fin 1. Next, draw a circle that passes through vertex V and is tangent to tangents Za and Zb on the outer perimeter of vertex V. The radius of the circle drawn in this way is defined as the radius of curvature r at the tip of the fin.

[0025] [Number of fins N] The number of fins N constituting the grooves on the inner surface of the grooved tube of the present invention is preferably 36 to 69, and more preferably 37 to 52.

[0026] The number N of fins constituting the grooves on the inner surface of the grooved tube of the present invention is measured in a cross-section as shown in Figure 1(b). That is, the number N of fins present in the circumferential direction is measured visually in a cross-section perpendicular to the longitudinal direction of the tube (the direction parallel to the central axis ω).

[0027] [Twist angle θ] The twist angle θ of the grooves on the inner surface of the grooved pipe of the present invention is 15 degrees or more and 27 degrees or less, and preferably 20 degrees or more and 27 degrees or less. If the torsional angle θ is too large, the pressure loss of the heat transfer medium (refrigerant, etc.) flowing through the pipe will increase, potentially leading to increased power consumption of the compressor in air conditioning units. In that case, the coefficient of performance (COP) of the equipment will decrease. Furthermore, there is a risk of fin collapse during the primary pipe expansion. If the torsional angle θ is too small, cracks are more likely to occur during the expansion process caused by flaring. Furthermore, the heat transfer coefficient within the pipe may decrease, potentially reducing heat exchange performance.

[0028] The method for measuring the torsional angle θ will be explained using Figures 2 and 3. Figure 2(a) is a schematic side view showing a test piece 10 cut from a grooved pipe of the present invention (a portion with a length L in the longitudinal direction). Figures 2(b) and 2(c) are schematic side and end views showing the test piece 10 placed on the surface of a metal substrate 20 with a load P applied from above. Figure 3(a) is a schematic side view showing the test piece 10 completely crushed by the applied load P, resulting in a state where two plates are stacked on top of each other. Figure 3(b) is a schematic side view showing the two plates separated. Figure 3(c) shows a schematic view (Schematic Front View) of the lower plate (10a) viewed from above after the upper plate (10b) of the two plates has been removed.

[0029] First, as shown in Figure 2(a), a portion is cut from the grooved pipe of the present invention to obtain a test piece 10. Specifically, it is cut so that its longitudinal length L is 15 to 30 mm. Next, as shown in Figures 2(b) and 2(c), the test specimen 10 is placed on the surface of the metal substrate 20, and a load P is applied to the test specimen 10 from above. Here, the load P is approximately 0.14 to 0.20 kN. Here, the metal substrate 20 only needs to have enough hardness to prevent it from denting when a load P is applied to the test piece 10, and may be, for example, a plate made of stainless steel.

[0030] As described above, when a load P is applied to the test specimen 10, the test specimen 10 collapses completely, resulting in a state where two plates (10a, 10b) are stacked on top of each other, as shown in Figure 3(a). Then, as shown in Figure 3(b), the two plates are separated. In the state shown in Figure 3(a), the two plates (10a and 10b) may be connected at both ends (both ends in the direction parallel to the main surface of the substrate 20 in Figure 3(a)). In such cases, the two plates can be separated by polishing the connected portion with sandpaper or the like. This results in grooves being formed (transferred) by the fins on the upper plate 10b being pressed against the fins 15 on the lower plate 10a. If these grooves are connected by a straight line, that line (represented by a dotted line in Figure 3(c)) represents the position where the fins 16 on the upper plate 10b were located when the two plates (10a, 10b) were overlapping as shown in Figure 3(a). Then, the angle between fin 15 and fin 16 is measured and defined as 2θ. The value obtained by dividing this by 2 is defined as the torsional angle (θ).

[0031] [Formula 1] In the grooved tube of the present invention, the radius of curvature r at the tip of the fin and the number of fins N in the circumferential direction satisfy the following equation (1). Formula (1): 0.32≦1 / (r×N)≦0.61

[0032] These are preferably also satisfied by the following equation (1'). Formula (1´): 0.52≦1 / (r×N)≦0.61

[0033] When equation (1) is satisfied, cracks are less likely to occur due to pipe expansion by flaring. This tendency becomes even more pronounced when equation (1') is satisfied.

[0034] As shown in Figures 1(b) and 1(c), in the cross-section of the grooved pipe of the present invention in a direction perpendicular to the longitudinal direction (direction parallel to the central axis ω), portions with grooves and portions with fins alternate in the circumferential direction. Here, the latter portion is referred to as (i) groove bottom wall thickness portion + fins, and the former portion as (ii) groove bottom wall thickness portion. When flaring is performed, the amount of material elongation in portion (i) is smaller than in portion (ii). In other words, portion (ii) is stretched more. Therefore, in order to suppress fracture in portion (ii), it is necessary to widen the width of portion (ii) (groove bottom width shown in Figure 4, which will be described later). By reducing the number of fins N or reducing the radius of curvature r of the fin tip so as to satisfy the above equation (1), it is possible to widen the width of portion (ii), and cracking during flaring can be suppressed.

[0035] Furthermore, if the number of fins N increases or the radius of curvature r at the tip of the fins increases, and the ratio of the groove bottom width to the fin height (groove bottom width / fin height) falls below a certain value, the grooved plug tends to break easily during the manufacturing process. When a grooved plug breaks, the formation of the fins at the broken point becomes incomplete, or the broken point becomes a resistance, causing the grooved pipe to rupture. In other words, the product cannot be manufactured. By determining the number of fins N and the radius of curvature r at the tip of the fins to satisfy the above equation (1), the breakage of grooved plugs during the manufacturing process becomes less likely.

[0036] Furthermore, if the radius of curvature r at the tip of the fin is made too large, or if the number of fins N is made too large, the unit mass of the grooved tube becomes heavier, leading to increased costs. Also, if the radius of curvature r at the tip of the fin is made too large, the surface area of ​​the grooved tube that contributes to the heat transfer effect decreases, leading to a decrease in heat transfer performance. By determining the number of fins N and the radius of curvature r at the tip of the fin so as to satisfy equation (1) above, these problems are less likely to occur.

[0037] [Formula 2] In the grooved tube of the present invention, the radius of curvature r at the tip of the fin and the torsional angle θ satisfy the following equation (2). Formula (2): 0.04≦r×(1 / cosθ)≦0.051

[0038] Twist When the angle θ is small and the value of cosθ is large, the distance between any fin and its adjacent fins in the longitudinal direction of the pipe is large. When flaring is performed, the thinnest part, the groove bottom section mentioned above, must withstand flaring cracks, and the tensile strength in the circumferential direction of the pipe is lowest at the groove bottom section. Therefore, the larger the distance between any fin and its adjacent fins in the longitudinal direction of the pipe, the more likely flaring cracks are to occur at the groove bottom section. On the other hand, when the torsional angle θ is large and cosθ is small, the distance between any fin and the adjacent fin in the longitudinal direction of the pipe is small, so (ii) the groove bottom wall thickness becomes narrower. In this case, when inserting the tool for flaring, as it progresses, the tool reaches (i) the groove bottom wall thickness + fin before (ii) flare expansion crack occurs in the groove bottom wall thickness. In other words, (ii) the groove bottom wall thickness is supported by the fin before it breaks, thus suppressing flare crack. Furthermore, if the value of r × (1 / cosθ) is too large, the heat transfer performance tends to decrease, and productivity also tends to decrease. From this perspective, the grooved pipe of the present invention that satisfies formula (2) above is less prone to cracking when expanded by flaring.

[0041] The method for measuring the radius of curvature R at the base of the fin will be explained using Figure 5. Figure 5, like Figure 1(c), is an enlarged view (schematic diagram) of one of the eight areas (area X) enclosed by the dotted line in Figure 1(b). Note that the same parts are denoted by the same reference numerals in both Figure 5 and Figure 1(c). First, let Q be the point of tangency between the straight line W, as explained using Figure 1(c), and the contour of fin 1. Next, let O be the intersection point of the tangent line Za and the line W. Then, draw a circle centered at point O that is tangent to the contour of fin 1, and let S be the point of tangency between this circle and the contour of fin 1. Next, draw a circle centered at point O and passing through point Q. Let point P be the point where this circle intersects with the tangent line Za, the point closest to 5a of fin 1. Then, draw a circle passing through points P, Q, and S, and define the radius of that circle as the "fin root radius of curvature R".

[0042] The grooved pipe of this invention is less prone to cracking when expanded by flaring.

[0043] <Manufacturing method> The method for manufacturing the grooved pipe of the present invention is not particularly limited. The grooved pipe of the present invention can be manufactured, for example, using the manufacturing apparatus shown in Figure 6. The manufacturing apparatus shown in Figure 6 will be described below. Figure 6 is a schematic cross-sectional view of a manufacturing apparatus 30 capable of producing grooved pipes according to the present invention. The manufacturing apparatus 30 has a retaining plug 32 that is inserted into the raw tube 31. The retaining plug 32 is frustoconical in shape, and is inserted so that the smaller diameter side is on the downstream side when the raw tube 31 is pulled out. Furthermore, a retaining die 33 is located on the outer circumference of the retaining plug 32, and the retaining plug 32 and the retaining die 33 are positioned to sandwich the raw pipe 31 from the inside and the outside. The raw pipe 31 is reduced in diameter by being sandwiched between the retaining plug 32 and the retaining die 33. A grooved plug 35 is connected to the retaining plug 32 via a rod-shaped plug shaft 34. A groove of the shape to be formed on the inner surface of the raw tube 31 is formed on the outer surface of the grooved plug 35. The grooved plug 35 can rotate freely around the plug shaft 34. The grooved plug 35 has multiple rolling balls 36 on its outer circumference, and the raw tube 31 is sandwiched between the grooved plug 35 and the rolling balls 36 from the inside and outside. The rolling balls 36 are arranged to revolve and rotate around the tube axis (same as the central axis ω) of the raw tube 31 in the circumferential direction of the tube. The rolling balls 36 are also held by a processing ring 40. Each rolling ball 36 can rotate on its own axis, and each rolling ball 36 can rotate planetarily within the processing ring 40 while in contact with the outer surface of the raw tube 31. The grooved plug 35 and the rolling balls 36 constitute the rolling section 37. Furthermore, a shaping die (not shown) is provided on the downstream side of the rolling section 37 in the direction of extraction of the raw tube 31, which has grooves formed on its inner surface, to reduce the outer diameter of the raw tube 31 to a predetermined dimension.

[0044] Next, a method for manufacturing the grooved pipe of the present invention using such a manufacturing apparatus will be described. First, the raw tube 31 is reduced in diameter using a retaining plug 32 and a retaining die 33. Next, the diameter-reduced raw tube 31 is further reduced in diameter by pressing the outside of the raw tube 31 with a planetary-rotating rolling ball 36, while simultaneously pressing the inner surface of the raw tube 31 against the grooved plug 35. As a result, the grooves of the grooved plug 35 are transferred to the inner surface of the raw tube 31, and spirally extending fins 39 are formed. At this time, the grooved plug 35 rotates due to the fins 39 it has formed on the inner surface of the raw tube 31. Furthermore, the grooved plug 35 is connected to the retaining plug 32 via the plug shaft 34. The retaining plug 32 remains in place on the inner circumference side of the retaining die 33 due to the frictional force from the withdrawal of the raw tube 31 and the resistance force from the retaining die 33, and therefore the grooved plug 35 also remains in place on the inner circumference side of the rolled ball 36. Next, the raw tube 31, which has passed through the rolling section 37 and has grooves formed on its inner surface, is further reduced in diameter by a shaping die (not shown) to become the grooved tube of the present invention. The internally grooved pipes, formed through this rolling process, are typically wound into coils. These coils are then annealed and shipped to air conditioner manufacturers and other suppliers.

[0045] <Heat exchanger of the present invention> The heat exchanger of the present invention will be described. The heat exchanger of the present invention is not particularly limited as long as it is equipped with the grooved tube of the present invention. For example, Figure 7 is a partially cutaway front view illustrating the heat exchanger 60 of the present invention, a fin-and-tube type heat exchanger incorporating the grooved tube of the present invention, and Figure 8 is a partially enlarged view (schematic perspective view) thereof. As shown in Figures 7 and 8, in the heat exchanger 60 of the present invention, the grooved pipe 52 of the present invention is processed into a hairpin pipe. It has a plurality of parallel stacked aluminum fins 50 and the grooved pipe 52 of the present invention, and the grooved pipe 52 of the present invention is inserted into each of the plurality of holes provided in the aluminum fins 50, and is fixed after being temporarily expanded. Furthermore, a return bend pipe 54 is interposed between two grooved pipes 52 of the present invention to connect the two grooved pipes 52 of the present invention, and the grooved pipe 52 of the present invention is a flow path with a long distance over which the heat transfer medium flows. Although a smooth pipe is usually used for the return bend pipe 54, the grooved pipe of the present invention may also be processed into a return bend pipe and used. Air or the like flows between the aluminum fins 50, and heat exchange takes place between the heat transfer medium and the air or the like by flowing the heat transfer medium, such as a fluorocarbon refrigerant, inside the grooved pipe 52 of the present invention. [Examples]

[0046] The present invention will be described with reference to examples. The present invention is not limited to the embodiments described below.

[0047] Flared pipes with internal grooves for flaring were manufactured according to Examples 1 to 7 and Comparative Examples 1 to 8, which possess the characteristics shown in Table 1. All are seamless copper pipes made of C1020 (oxygen-free copper as specified in JIS H 3300).

[0048] The outer diameter D, wall thickness T, fin tip radius of curvature r, and number of fins N for each internally grooved pipe for flaring shown in Table 1 are values ​​obtained by measuring the ring-shaped cross-section obtained by cutting each internally grooved pipe for flaring perpendicular to its pipe axis, using the method described above. Also, the inner area (mm²) 2 The values ​​for ) were also obtained by measuring and calculating using the method described above. Furthermore, the torsional angle (θ) in Table 1 is also a value obtained by measuring using the method described above.

[0049] Each of the internally grooved pipes for flaring according to Examples 1 to 7 and Comparative Examples 1 to 8 was subjected to a flaring test. The expansion test is a test in which the end of each internally grooved pipe for flaring is gradually expanded using a flaring tool with a cone angle of 60 degrees until a flaring crack occurs. Five internally grooved tubes for flaring were prepared for each type of flaring, and their ends were gradually widened using the flaring tool. The outer diameter at which flaring cracks occurred was determined in the same way as when measuring the outer diameter D described above. Specifically, the outer diameter at which flaring cracks occurred (the outer diameter of the widened outer end) was measured at eight approximately equal points (four pairs) in the circumferential direction using a digital caliper, and the value obtained by simply averaging these four measurements was determined. Then, the outer diameters (simple average values) of the five identical internally grooved tubes for flaring were further simply averaged, and the resulting value was defined as the widened outer diameter D' of that internally grooved tube for flaring.

[0050] Then, the performance of the internally grooved pipe for flaring was evaluated based on the relationship between the obtained outer diameter D' and the outer diameter D before widening. Specifically, if D'-D≧2 was not satisfied, it was considered a failure (×), and if D'-D≧2 was satisfied, it was considered a pass (〇). Furthermore, among those who passed, if D'-D≧2.32 was also satisfied, it was judged as particularly good (◎).

[0051] Here, I will explain the basis for considering D'-D≧2 as a passing condition. The wire diameter of a ring brazing rod is typically φ1.4 mm. This is because, when fitting a U-shaped vent pipe into a flared pipe with an internal groove for flaring with an outer diameter D of φ5.00 mm, the flared section needs to be expanded by about 1.0 mm on each side, which corresponds to about 72% of the wire diameter of the ring brazing rod, i.e., to an outer diameter of 7.0 mm, in order to prevent brazing leakage.

[0052] [Table 1] [Explanation of Symbols]

[0053] 1, 1a, 1b Fins 3a, 3b groove bottom Points 5a and 5b 10, 10a, 10b test specimens 15 Fins on the test specimen (plate) 10a 16 Fins on the test specimen (plate) 10b 20 circuit boards 30 Manufacturing equipment 31 Raw Tube 32 Retaining plug 33 Holding Dice 34 Plug shaft 35 Grooved Plug 36 Rolled Balls 37 Rolling section 39 Fins 40 processed rings 50 Aluminum Fins 52 Grooved pipe of the present invention 54 Return bend pipe 60 Heat exchanger of the present invention

Claims

1. A flared pipe with an internal groove, which is a seamless pipe having grooves on its inner surface and flared ends, The outer diameter D is 3.5 mm or more and 5.5 mm or less. The ratio T / D of wall thickness T to outer diameter D satisfies 0.057-0.005D or more and 0.075-0.005D or less. The aforementioned wall thickness T is 0.17 to 0.25 mm. The torsional angle θ of the groove on the inner surface is 15 degrees or more and 27 degrees or less. The radius of curvature r of the tip of the fin constituting the groove on the inner surface and the number N of the fins in the circumferential direction satisfy the following equation (1): The radius of curvature r of the tip and the torsion angle θ satisfy the following equation (2): The radius of curvature r of the tip portion is 0.042 to 0.045 mm. The number of fins N is 37 to 52. A flared pipe with internal grooves, made of C1220 (phosphorus-deoxidized copper), C1201 (low-phosphorus-deoxidized copper), or C1020 (oxygen-free copper) as specified in JIS H 3300. Formula (1): 0.500≦1 / (r×N)≦0.61 Formula (2): 0.046≦r×(1 / cosθ)≦0.051

2. A flared pipe with an internal groove, which is a seamless pipe having grooves on its inner surface and flared ends, The outer diameter D is 3.5 mm or more and 5.5 mm or less. The ratio T / D of wall thickness T to outer diameter D satisfies 0.057-0.005D or more and 0.075-0.005D or less. The aforementioned wall thickness T is 0.17 to 0.25 mm. The torsional angle θ of the groove on the inner surface is 15 degrees or more and 27 degrees or less. The radius of curvature r of the tip of the fin that constitutes the groove on the inner surface and the number N of the fins in the circumferential direction satisfy the following equation (1'), The radius of curvature r of the tip and the torsion angle θ satisfy the following equation (2'), The radius of curvature r of the tip portion is 0.036 to 0.045 mm. The number of fins N is 37 to 52. A flared pipe with internal grooves, made of C1220 (phosphorus-deoxidized copper), C1201 (low-phosphorus-deoxidized copper), or C1020 (oxygen-free copper) as specified in JIS H 3300. Formula (1'): 0.52≦1 / (r×N)≦0.61 Formula (2'): 0.04≦r×(1 / cosθ)≦0.051

3. A heat exchanger comprising a flared tube with internal grooves according to claim 1 or 2.

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