Inner-surface-grooved tube for flaring and heat exchanger provided with inner-surface-grooved tube for flaring

Abstract

The present invention addresses the problem of providing a pipe with a groove on the inner surface for flaring, the pipe being not susceptible to cracking due to pipe expansion by flaring. The present invention solves the above problem by a pipe with a groove on the inner surface for flaring, which is a seamless pipe having a groove on the inner surface and flaring at the ends thereof, and which has an outer diameter (D) of 2.0-5.5 mm (inclusive), a ratio (T / D) of the wall thickness (T) to the outer diameter (D) of 0.057-0.005 D (inclusive) and 0.075-0.005 D (inclusive), and a thickness (T) of the pipe with a groove on the inner surface of the pipe with a groove on the inner surface of the pipe with a groove on the inner surface of the pipe with a groove on the outer surface of the pipe with a groove on the inner surface of the pipe with a groove on the inner surface of the pipe with a groove on the inner surface. The helical angle (theta) of the grooves in the inner surface is 15-27 degrees, the radius of curvature (r) of the tip of the fins constituting the grooves in the inner surface and the number (N) of the fins in the circumferential direction satisfy a specific formula, and the radius of curvature (r) of the tip and the helical angle (theta) satisfy a specific formula.

Description

Technical Field

[0001] The present invention relates to an inner-surface grooved tube for port expansion and a heat exchanger equipped with the inner-surface grooved tube for port expansion. Background Art

[0002] Currently, heat exchangers such as window air conditioners (RACs), cabinet air conditioners (PACs), refrigerators, and water heaters, as well as electronic devices such as PCs, smartphones, and game consoles, have copper pipes built in to exchange heat by circulating heat media inside.

[0003] For example, in the process of assembling a window air conditioner, first, a plurality of straight copper tubes are prepared, and the central portions in the long-side direction are bent to form U-shaped capillaries. Then, each copper tube is inserted into the through-hole of an aluminum fin formed by stacking a plurality of aluminum plates, and the straight tube portion of the copper tube is expanded so that the outer surface of the straight tube portion and the inner circumferential surface of the through-hole of the aluminum fin are closely fitted. After that, for the tube ends protruding from the aluminum fins in each copper tube, the adjacent tube ends are connected to each other with U-shaped bends or branches. Thus, the connected copper tubes become one or more flow paths through which the heat medium flows. Moreover, by transferring the heat of the heat medium in the copper tube to the aluminum fins and allowing the indoor air to flow through the gaps between the aluminum plates in the aluminum fins, the temperature of the air, etc. can be adjusted.

[0004] Here, the expansion of the straight tube portion of the copper tube for close contact with the inner circumference of the through hole of the aluminum fin is called primary expansion. In addition, the expansion of the tube end of each copper tube for inserting the U-shaped bend is called secondary expansion, and the portion that has been expanded twice is also called the secondary expansion portion.

[0005] Furthermore, the end of the second expanded portion is expanded. This expansion is called third expansion or expansion processing. In addition, the portion that has been expanded or expanded three times is called an expansion processing portion.

[0006] The bent pipe is inserted into the secondary expanded portion through the expanded portion, and a ring-shaped brazing filler metal is inserted into the gap between the outer surface of the bent pipe and the inner surface of the expanded portion, and then the brazing filler metal is heated to melt and solidify, thereby joining the pipe end of the bent pipe and the copper pipe. The expanded portion is formed to ensure a gap for inserting the brazing filler metal.

[0007] In the past, such expansion processing may cause cracks at the end of the copper tube. In particular, when the outer diameter of the copper tube is small, for example, the outer diameter is less than 6 mm, the copper tube may crack due to the expansion processing. It is believed that the main reason is that even if the outer diameter of the copper tube is small, the gap for inserting the solder is required to be of a certain size, so the expansion rate of the copper tube with a small outer diameter is relatively large compared with the copper tube with a large outer diameter.

[0008] In contrast, Patent Document 1 proposes a copper or copper alloy tube for expansion processing in which expansion processing is performed on the tube end of a seamless tube, characterized in that the outer diameter D is 2.0 to 5.5 mm, 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 average crystal grain size is 30 μm or less, and the elongation in the circumferential direction is 35% or more. In addition, Patent Document 1 states that since the wall thickness, average crystal grain size and elongation of the seamless copper tube are appropriately set, the copper or copper alloy tube for expansion processing can prevent cracks from occurring in the expanded tube portion of the expansion processing portion when a small-diameter copper tube with an outer diameter of 2.0 to 5.5 mm is used for expansion processing.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: (Japanese) Patent Publication No. 2017-20063 Summary of the invention

[0012] Problems to be solved by the invention

[0013] The present invention provides an inner-surface grooved tube for expansion processing which is less likely to generate cracks by expansion based on the expansion processing, and a heat exchanger having the inner-surface grooved tube for expansion processing.

[0014] Technical solutions to solve problems

[0015] The present inventors have conducted intensive studies to solve the above-mentioned problems and have completed the present invention.

[0016] The present invention relates to the following (I) to (IV).

[0017] (I) An inner grooved pipe for expansion processing, which is a seamless pipe having grooves on the inner surface and subjected to expansion processing at the end, wherein:

[0018] The outer diameter D is 2.0 mm or more and 5.5 mm or less,

[0019] The ratio T / D of the wall thickness T and the outer diameter D is 0.057-0.005D or more and 0.075-0.005D or less,

[0020] The helix angle θ of the groove on the inner surface is not less than 15 degrees and not more than 27 degrees,

[0021] The radius of curvature r of the front end 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):

[0022] The tip curvature radius r and the helix angle θ satisfy the following formula (2):

[0023] Formula (1): 0.32≤1 / (r×N)≤0.61

[0024] Formula (2): 0.04≤r×(1 / cosθ)≤0.051.

[0025] (II) The inner grooved tube for expansion processing according to (I) above, wherein:

[0026] The front end curvature radius r and the number N of the fins satisfy the following formula (1'):

[0027] Formula (1'): 0.52≤1 / (r×N)≤0.61.

[0028] (III) The inner grooved tube for expansion processing according to (I) or (II) above, wherein:

[0029] The inner grooved tube for expansion processing is made of copper or copper alloy.

[0030] (IV) A heat exchanger comprising the expanding inner grooved tube according to any one of (I) to (III) above.

[0031] Effects of the Invention

[0032] According to the present invention, it is possible to provide an inner grooved tube for expansion that is less likely to be cracked by expansion by expansion, and a heat exchanger including the inner grooved tube for expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1(a) is a schematic diagram showing the side of a straight grooved tube of the present invention, FIG1(b) is a cross section taken along line AA in FIG1(a), and FIG1(c) is an enlarged view of one of the eight locations (X portion) surrounded by dotted lines in FIG1(b).

[0034] FIG2( a ) is a schematic side view showing a test piece 10 obtained by cutting out a portion (a portion having a length L in the longitudinal direction) of a grooved tube of the present invention, and FIG2( b ) and FIG2( c ) are a schematic side view and a schematic end view 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.

[0035] FIG3(a) is a schematic side view showing a state where the test piece 10 completely collapses due to the application of a load P and the two plates overlap, FIG3(b) is a schematic side view showing a state where the two plates are cut, and FIG3(c) is a schematic diagram (schematic front view) showing a state where the upper plate (10b) of the two plates is removed and the lower plate (10a) is observed from above.

[0036] FIG4 is an enlarged view of one of the eight locations (X portion) surrounded by dotted lines in FIG1(b) similarly to FIG1(c) , and is a diagram (schematic diagram) for explaining the height, apex angle, and curvature radius R of the fin root of the fin.

[0037] FIG. 5 is an enlarged view of one (X portion) among the eight locations surrounded by dotted lines in FIG. 1( b ) similarly to FIG. 1( c ), and is a view (schematic diagram) for explaining the curvature radius R of the fin root.

[0038] FIG. 6 is a diagram showing an example of a manufacturing apparatus for manufacturing the grooved pipe of the present invention.

[0039] FIG. 7 is a partially cutaway front view illustrating a heat exchanger 60 of the present invention in which the fin-end-tube heat exchanger with grooved tubes of the present invention is incorporated.

[0040] FIG. 8 is a partial enlarged view (schematic stereoscopic view) of FIG. 7 . DETAILED DESCRIPTION

[0041] The present invention will be described.

[0042] The present invention relates to an inner grooved pipe for expansion processing, which is a seamless pipe having grooves on the inner surface and subjected to expansion processing at the end, wherein the outer diameter D is greater than 2.0 mm and less than 5.5 mm, the ratio T / D of the wall thickness T to the outer diameter D is greater than 0.057-0.005D and less than 0.075-0.005D, the helix angle θ of the groove on the inner surface is greater than 15 degrees and less than 27 degrees, the front end curvature radius 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), the front end curvature radius r and the helix angle θ satisfy the following formula (2),

[0043] Formula (1): 0.32≤1 / (r×N)≤0.61

[0044] Formula (2): 0.04≤r×(1 / cosθ)≤0.051.

[0045] Hereinafter, such an inner-surface grooved pipe for expansion processing is also referred to as a "grooved pipe of the present invention".

[0046] Furthermore, the present invention relates to a heat exchanger including the grooved tube of the present invention.

[0047] Such a heat exchanger will also be referred to as "the heat exchanger of the present invention" hereinafter.

[0048] <Grooved tube of the present invention>

[0049] The grooved pipe of the present invention will be described.

[0050] The grooved pipe of the present invention is a seamless pipe having grooves on the inner surface and subjected to expansion processing at the end, that is, an inner grooved pipe for expansion processing.

[0051] It should be noted that the grooved tube of the present invention may be a grooved tube before or after the expansion process. The grooved tube of the present invention provided in the heat exchanger of the present invention is usually a grooved tube after the expansion process.

[0052] The shape of the grooved tube of the present invention is not particularly limited, and may be a straight tube, a straight tube wound in a spiral, or a straight tube bent into a U-shape (capillary tube).

[0053] The cross-sectional shape is not particularly limited either, and the cross-sectional shape of the tube in a direction perpendicular to the longitudinal direction may be an ellipse, triangle, quadrilateral, or other polygon, but is preferably a circle.

[0054] The material of the grooved pipe of the present invention is not particularly limited, but is preferably made of copper or a copper alloy.

[0055] 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) specified in JIS H 3300.

[0056] The grooved pipe of the present invention has grooves on its inner surface.

[0057] The grooves on the inner surface of the grooved pipe of the present invention will be described with reference to FIG. 1 .

[0058] Fig. 1(a) is a schematic diagram showing a side view of a grooved pipe of the present invention in a straight pipe shape with a circular cross section. In Fig. 1(a), the central axis of the grooved pipe of the present invention is represented by ω.

[0059] FIG. 1(b) is a cross section along the line AA in FIG. 1(a), and is a diagram (schematic cross-sectional view) showing a cross section of the tube in a direction perpendicular to the long side direction (direction parallel to the central axis ω). Here, the eight locations surrounded by a dotted rectangle in FIG. 1(b) represent locations where the outer diameter D, the wall thickness T, and the radius of curvature r of the fin tip are measured according to the method described later, and these locations are arranged at approximately equal intervals (approximately 45 degree intervals) along the circumferential direction in the cross section shown in FIG. 1(b). As described later, these values ​​in the grooved tube of the present invention refer to the simple average values ​​of the measurement results of these eight locations.

[0060] FIG1(c) is an enlarged view of one of the eight locations enclosed by dotted lines in FIG1(b) (X portion).

[0061] [Outer diameter D]

[0062] 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.

[0063] The outer diameter D is measured at eight locations surrounded by dotted lines in FIG1(b). That is, in FIG1(b), these eight locations are composed of four pairs facing each other with the point representing the central axis ω as a symmetrical point, and after obtaining four measured values ​​of the outer diameter at eight locations (four pairs) that are approximately equal in the circumferential direction, these four measured values ​​are simply averaged, and the average value is set as the outer diameter D of the grooved tube of the present invention.

[0064] In addition, the outer diameter was measured using a digital caliper.

[0065] At present, copper tubes with an outer diameter of 7 to 9.52 mm are mainly used as copper tubes for flaring. However, in recent years, in order to achieve lightweight and improved performance of heat transfer tubes, it is required to reduce the diameter. In addition, in order to reduce the global warming coefficient, the heat medium (refrigerant, etc.) flowing in the tube is switching to R32, but because R32 is slightly flammable, it is sought to reduce the amount used. In order to achieve the above goals, it is also required to reduce the diameter.

[0066] Since the outer diameter D of the grooved pipe of the present invention is within the above-mentioned range, it meets the recent demand for smaller diameters.

[0067] [Wall thickness T]

[0068] In the grooved pipe of the present invention, the ratio (T / D) of the outer diameter D to the wall thickness T is 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.

[0069] The wall thickness T is preferably 0.09 to 0.27 mm, more preferably 0.13 to 0.25 mm, more preferably 0.17 to 0.23 mm, and further preferably 0.18 to 0.21 mm.

[0070] In view of the recent rise in copper prices, internally grooved tubes used in heat exchangers are required to be lightweight while satisfying compressive strength. The grooved tube of the present invention has the above-mentioned outer diameter D and wall thickness T to meet such requirements.

[0071] The method for measuring the wall thickness T will be described.

[0072] First, the eight locations surrounded by the dotted lines in FIG. 1(b) are magnified 10 times using a laser microscope (e.g., VK-8500 manufactured by KEYENCE), and an image or photograph shown in FIG. 1(c) is obtained. Next, the thinnest wall thickness in the radial direction centered on the central axis ω is measured at each of the eight locations shown in FIG. 1(c). The value obtained by simply averaging the measured values ​​at the eight locations is set as the wall thickness T of the grooved tube of the present invention.

[0073] [Front end curvature radius r]

[0074] The curvature radius r of the tip of the fin constituting the groove on the inner surface of the grooved tube of the present invention is preferably 0.030 to 0.045 mm, preferably 0.030 to 0.040 mm if thermal conductivity is considered, and more preferably 0.036 to 0.040 mm if productivity is emphasized.

[0075] A method for measuring the curvature radius r of the tip portion of the fin will be described using FIG. 1( b ) and FIG. 1 ( c ).

[0076] First, the eight locations enclosed by the dotted lines in FIG. 1( b ) are magnified 10 times using a laser microscope (eg, VK-8500 manufactured by KEYENCE), to obtain an image or photograph as shown in FIG. 1( c ).

[0077] Next, in the image or photograph shown in Fig. 1(c), a curve Y is drawn that touches the tops of the three fins, the fin 1 to be measured and the two fins 1a and 1b next to it. The curve Y generally overlaps the circumference of the circle centered on ω shown in Fig. 1(b).

[0078] Next, the groove bottom 3a between the fin 1 to be measured and the fin 1a existing next to it is identified, and similarly the groove bottom 3b between the fin 1 to be measured and the fin 1b existing next to it is identified, and then a straight line W that is a tangent line connecting both is drawn.

[0079] Next, in FIG. 1( c ), the point on the contour of the fin 1 where the length of the line connecting the contour of the fin 1 and the point on the straight line W is the longest is the vertex V. The top V generally coincides with the point where the contour of the fin 1 and the curve Y meet. Then, a line perpendicular to the straight line W is drawn from the vertex V of the fin 1.

[0080] Next, a point perpendicularly bisecting the line W from the vertex V is identified, and a line parallel to the line W is drawn through the point, and the points where the line intersects with the outline of the fin 1 are designated as 5a and 5b. Furthermore, a tangent line passing through the point 5a and connecting with the outline of the fin 1 is designated as Za, and similarly, a tangent line passing through the point 5b and connecting with the outline of the fin 1 is designated as Zb.

[0081] Next, a circle passing through the vertex V and in contact with the tangent line Za and the tangent line Zb is drawn on the outer peripheral side of the vertex V.

[0082] The radius of the circle thus drawn is defined as the curvature radius r of the tip portion of the fin.

[0083] [Number of fins N]

[0084] The number N of fins constituting the grooves on the inner surface of the grooved tube of the present invention is preferably 36 to 69, more preferably 37 to 52.

[0085] 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 Fig. 1(b). That is, the number N of fins existing in the circumferential direction is visually measured in a cross section perpendicular to the longitudinal direction (direction parallel to the central axis ω) of the tube.

[0086] [Helix angle θ]

[0087] The helix angle θ of the grooves included in the inner surface of the grooved pipe of the present invention is 15 degrees or more and 27 degrees or less, preferably 20 degrees or more and 27 degrees or less.

[0088] If the helix angle θ is too large, the pressure loss of the heat medium (refrigerant, etc.) flowing through the tube will increase, which may increase the power of the compressor in the air conditioning unit, etc. In this case, the coefficient of performance (COP) of the equipment will decrease. In addition, fin distortion may occur during the primary expansion.

[0089] If the helix angle θ is too small, cracks are likely to occur during the pipe expansion by the flaring process. In addition, the heat transfer coefficient in the pipe is reduced, which may reduce the heat exchange performance.

[0090] The method of measuring the helix angle θ will be described using FIG. 2 and FIG. 3 .

[0091] FIG2(a) is a schematic side view showing a test piece 10 in which a portion (a portion of length L in the longitudinal direction) is cut out of the grooved tube of the present invention. In addition, FIG2(b) and FIG2(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. In addition, FIG3(a) is a schematic side view showing a state in which the test piece 10 is completely collapsed by the application of the load P and the two plates are overlapped, FIG3(b) is a schematic side view showing a state in which the two plates are cut, and FIG3(c) is a schematic diagram (schematic front view) showing a state in which the upper plate (10b) of the two plates is removed and the lower plate (10a) is observed from above.

[0092] First, as shown in Fig. 2(a), a part is cut out from the grooved tube of the present invention to obtain a test piece 10. Specifically, the test piece 10 is cut out so that the length L in the longitudinal direction becomes 15 to 30 mm.

[0093] Next, as shown in Fig. 2(b) and Fig. 2(c), the test piece 10 is placed on the surface of the metal substrate 20, and a load P is applied to the test piece 10 from above. Here, the load P is about 0.14 to 0.20 kN.

[0094] Here, the metal substrate 20 only needs to have a hardness sufficient to prevent the test piece 10 from being dented when the load P is applied to the test piece 10 , and may be, for example, a plate made of stainless steel.

[0095] When the load P is applied to the test piece 10 as described above, the test piece 10 completely collapses, and the two plates ( 10 a , 10 b ) overlap as shown in FIG3( a ). Thereafter, as shown in FIG3( b ), the two plates are cut.

[0096] Here, in the state shown in Fig. 3(a), the two plates (10a and 10b) may be connected at both ends (both ends in a direction parallel to the main surface of the substrate 20 in Fig. 3(a)). In this case, the two plates can be cut by grinding the connected portion with sandpaper or the like.

[0097] Thus, grooves formed (transferred) by pressing the fins of the upper plate 10b appear on the fins 15 of the lower plate 10a. If the grooves are connected by a straight line, the straight line (the straight line indicated by a dotted line in FIG. 3(c)) indicates the position where the fins 16 of the upper plate 10b exist when the two plates (10a, 10b) are overlapped as shown in FIG. 3(a).

[0098] Then, the angle formed by the fins 15 and 16 is measured and defined as 2θ. In addition, the value obtained by dividing 2θ by 2 is defined as the helix angle (θ).

[0099] [Formula 1]

[0100] In the grooved tube of the present invention, the radius of curvature r of the front end of the fin and the number N of the fins in the circumferential direction satisfy the following formula (1):

[0101] Formula (1): 0.32≤1 / (r×N)≤0.61.

[0102] They preferably further satisfy the following formula (1'),

[0103] Formula (1'): 0.52≤1 / (r×N)≤0.61.

[0104] If the above formula (1) is satisfied, cracks are less likely to occur during pipe expansion by the expansion process.

[0105] If equation (1') is satisfied, this trend becomes more significant.

[0106] As shown in FIG. 1(b) and FIG. 1(c), in the cross section of the slotted tube of the present invention in the direction perpendicular to the long side direction (the direction parallel to the central axis ω), portions where the slots exist and portions where the fins exist are alternately presented in the circumferential direction. Here, the latter portion is set as (i) slot bottom wall thickness portion + fin, and the former portion is set as (ii) slot bottom wall thickness portion. Here, during the expansion process, the material elongation of portion (i) is smaller than that of portion (ii). That is, portion (ii) is stretched more. Therefore, in order to suppress the fracture at portion (ii), it is necessary to widen the width of portion (ii) (the slot bottom width shown in FIG. 4 described later). If the number of fins N is reduced or the radius of curvature r of the front end of the fin is reduced to satisfy the above formula (1), the width of portion (ii) can be widened, and cracks during the expansion process can be suppressed.

[0107] In addition, by increasing the number of fins N or increasing the radius of curvature r of the front end of the fin, when the ratio of the groove bottom width to the fin height (groove bottom width / fin height) is below a certain value, there is a tendency for the slot plug to be easily damaged during the manufacturing process. If the slot plug is damaged, the formation of the fin at the damaged part is incomplete, or the damaged part becomes a resistance, and the slotted tube breaks. In other words, it cannot be commercialized. As long as the number of fins N and the radius of curvature r of the front end of the fin are determined in a manner that satisfies the above formula (1), the slot plug is not easily damaged during the manufacturing process.

[0108] In addition, if the curvature radius r of the front end of the fin is too large or the number of fins N is too large, the unit mass of the inner grooved tube becomes heavier, resulting in an increase in cost. In addition, if the curvature radius r of the front end of the fin is too large, the surface area of ​​the inner grooved tube that contributes to the heat conduction effect is reduced, resulting in a decrease in heat conduction performance. As long as the number of fins N and the curvature radius r of the front end of the fin are determined in a manner that satisfies the above formula (1), this problem is unlikely to occur.

[0109] [Formula 2]

[0110] In the grooved tube of the present invention, the curvature radius r and the helix angle θ of the front end of the fin satisfy the following formula (2):

[0111] Formula (2): 0.04≤r×(1 / cosθ)≤0.051.

[0112] Here, cosθ represents the distance between an arbitrary fin and an adjacent fin in the inner grooved tube in the longitudinal direction of the tube (a direction parallel to the central axis ω).

[0113] When the helix angle θ is small and the value of cosθ is large, the distance between any fin and the adjacent fin in the long-side direction of the tube is large. When the expansion process is performed, the thinnest (ii) groove bottom wall thickness portion must withstand the expansion process cracks. In addition, the tensile strength in the tube circumferential direction is lowest in the (ii) groove bottom wall thickness portion. Therefore, the larger the distance between any fin and the adjacent fin in the long-side direction of the tube, the easier it is for the (ii) groove bottom wall thickness portion to generate expansion process cracks.

[0114] On the other hand, when the helix angle θ is large and cosθ is small, the interval between any fin and the adjacent fin in the long side direction of the tube is small, so the (ii) groove bottom wall thickness portion becomes narrower. In this case, when the tool for expanding is inserted, as the insertion proceeds, before the expansion cracks occur in the (ii) groove bottom wall thickness portion, the tool reaches the (i) groove bottom wall thickness portion + fin. That is, the (ii) groove bottom wall thickness portion is supported by the fin before it breaks, and the expansion cracks can be suppressed.

[0115] If the value of r×(1 / cosθ) is too large, the thermal conductivity tends to be lowered, and the productivity tends to be lowered.

[0116] From this viewpoint, the grooved pipe of the present invention that satisfies the above-mentioned formula (2) is less likely to be cracked by pipe expansion by the expansion process.

[0117] [Inner area]

[0118] The surface area of ​​the inner surface of the grooved tube of the present invention is the inner area (mm 2 ) preferably 94~335mm 2 , more preferably 243 to 255 mm 2 .

[0119] This is because, if the inner area is within this range, the thermal conductivity is excellent and it is less likely to cause cracks during expansion processing. If the inner area is too large, there is a tendency that rolling processing is difficult.

[0120] The inner area is calculated based on the outer diameter D, wall thickness T, helix angle θ, fin tip curvature radius r, number of fins N, and fin height, vertex angle, and fin root curvature radius measured as described above.

[0121] Here, the height and the top angle of the fin refer to the length and the angle shown in Fig. 4. In addition, the radius of curvature R of the fin root refers to the radius R of the circle in contact with the portion shown in Fig. 4. It should be noted that Fig. 4 is an enlarged view of one of the eight locations (X portion) surrounded by dotted lines in Fig. 1 (b), similarly to Fig. 1 (c).

[0122] The height of the fin is a value obtained by subtracting the distance between the central axis ω and the apex V of the fin and the wall thickness T from 1 / 2D, which is half of the outer diameter D in the cross section shown in FIG. 1( c ).

[0123] In addition, the vertex angle refers to the angle formed by the tangent line Za and the tangent line Zb shown in FIG. 1( c ).

[0124] A method for measuring the fin root curvature radius R will be described using FIG. 5 .

[0125] Fig. 5 is an enlarged view (schematic diagram) of one of the eight locations (X portion) surrounded by dotted lines in Fig. 1(b) similarly to Fig. 1(c) . Note that in Fig. 5 and Fig. 1(c) , the same reference numerals are used to denote the same locations.

[0126] First, let point Q be the point of contact between the straight line W described with reference to FIG. 1( c ) and the contour of the fin 1 .

[0127] Next, the intersection point of the tangent line Za and the straight line W is defined as point O. Then, a circle in contact with the outline of the fin 1 is drawn with point O as the center, and the point of contact between the circle and the outline of the fin 1 is defined as point S.

[0128] Next, a circle passing through point Q is drawn with point O as the center, and a point P is defined as a point on the side of fin 1 close to 5 a among the intersections of the circle and tangent line Za.

[0129] Next, a circle passing through the three points of point P, point Q, and point S is drawn, and the radius of the circle is defined as the "fin root curvature radius R".

[0130] The grooved pipe of the present invention is less likely to crack due to pipe expansion by the expansion process.

[0131] <Manufacturing method>

[0132] The method for producing the grooved pipe of the present invention is not particularly limited. The grooved pipe of the present invention can be produced using, for example, a production apparatus shown in FIG. 6 .

[0133] The production apparatus shown in FIG. 6 will be described.

[0134] FIG. 6 is a schematic cross-sectional view of a manufacturing apparatus 30 capable of manufacturing the grooved pipe of the present invention.

[0135] The manufacturing device 30 has a retaining plug 32 inserted into the inside of the mother tube 31. Here, the retaining plug 32 has a truncated cone shape and is inserted so that the side with a smaller diameter is on the downstream side in the direction in which the mother tube 31 is pulled out.

[0136] The retaining plug 32 is provided with a retaining die 33 at the outer peripheral side thereof, and the retaining plug 32 and the retaining die 33 clamp the tube 31 from the inside and outside. The tube 31 is clamped by the retaining plug 32 and the retaining die 33 and the diameter is reduced.

[0137] A grooved plug 35 is connected to the retaining plug 32 via a rod-shaped plug shaft 34. A groove having a shape to be formed on the inner peripheral surface of the tube 31 is formed on the outer peripheral surface of the grooved plug 35. The grooved plug 35 is rotatable about the plug shaft 34 as an axis.

[0138] Then, a plurality of rolling balls 36 are provided at the position on the outer peripheral side of the grooved plug 35, and the tube 31 is clamped from the inside and outside by the grooved plug 35 and the rolling balls 36. The rolling balls 36 are arranged to be able to revolve and rotate in the tube circumferential direction around the tube axis (which is the same as the central axis ω) of the tube 31. In addition, the rolling balls 36 are held by the processing ring 40. Each rolling ball 36 can rotate on its own axis, and each rolling ball 36 can perform planetary rotation in the processing ring 40 while being in contact with the outer surface of the tube 31. The grooved plug 35 and the rolling balls 36 constitute a rolling section 37. In addition, a shaping die (not shown) for reducing the outer diameter of the tube 31 having grooves formed on the inner surface to a predetermined size is provided on the downstream side of the tube 31 in the drawing direction in the rolling section 37.

[0139] Next, a method for producing the grooved pipe of the present invention using such a production apparatus will be described.

[0140] First, the tube blank 31 is subjected to a diameter-reducing process by the retaining plug 32 and the retaining die 33 .

[0141] Next, the tube 31 that has been subjected to the diameter reduction process is pressed by the rolling balls 36 that planetarily rotate on the outside of the tube 31 to reduce the diameter, and at the same time, the inner surface of the tube 31 is pressed against the grooved plug 35. As a result, the grooves of the grooved plug 35 are transferred to the inner surface of the tube 31 to form the fins 39 extending in a spiral shape. At this time, the grooved plug 35 is rotated by the fins 39 directly formed on the inner surface of the tube 31.

[0142] In addition, the grooved plug 35 is connected to the retaining plug 32 via the plug shaft 34. The retaining plug 32 stays at the inner side of the retaining die 33 due to the friction force generated by the drawing of the tube blank 31 and the resistance from the retaining die 33. Therefore, the grooved plug 35 also stays at the inner side of the rolling ball 36.

[0143] Next, the pipe blank 31 having grooves formed on the inner surface thereof having passed through the rolling section 37 is further reduced in diameter by a shaping die (not shown) to become the grooved pipe of the present invention.

[0144] The internally grooved pipe thus rolled is usually wound into a coiled product, which is then annealed and shipped to an air conditioner manufacturer or the like.

[0145] <Heat Exchanger of the Present Invention>

[0146] The heat exchanger of the present invention will be described.

[0147] The heat exchanger of the present invention is not particularly limited as long as it is a heat exchanger including the grooved tubes of the present invention.

[0148] For example, FIG. 7 is a partially cutaway front view of a heat exchanger 60 of the present invention in which the fin-end-tube heat exchanger with grooved tubes of the present invention is incorporated, and FIG. 8 is a partially enlarged view thereof (schematic perspective view).

[0149] As shown in FIG. 7 and FIG. 8, in the heat exchanger 60 of the present invention, the grooved tube 52 of the present invention is processed into a capillary tube. Moreover, the plurality of aluminum fins 50 and the grooved tube 52 of the present invention are stacked in parallel, and the grooved tube 52 of the present invention is respectively inserted into the plurality of holes provided in the aluminum fins 50, and is fixed by expanding the tube once. In addition, the return bend tube 54 is interposed between the two grooved tubes 52 of the present invention, and the two grooved tubes 52 of the present invention are connected to each other, and the grooved tube 52 of the present invention becomes a flow path with a long distance for the heat medium to flow. It should be noted that the return bend tube 54 usually uses a smooth tube, but the grooved tube of the present invention can also be processed into a return bend tube for use. By allowing air or the like to flow between the aluminum fins 50, the heat medium such as Freon-based refrigerant flows to the inside of the grooved tube 52 of the present invention, and heat exchange is performed between the heat medium and the air or the like.

[0150] Example

[0151] The present invention will be described below with reference to Examples. The present invention is not limited to the following Examples.

[0152] Internally grooved tubes for expansion processing of Examples 1 to 7 and Comparative Examples 1 to 8 having the configurations shown in Table 1 were produced. All of them were seamless copper tubes made of C1020 (oxygen-free copper specified in JIS H 3300).

[0153] The outer diameter D, wall thickness T, curvature radius r of the tip of the fin, and number of fins N of each of the inner grooved tubes for expansion shown in Table 1 are the values ​​measured by the above method in the annular cross section obtained by cutting each inner grooved tube for expansion in a direction perpendicular to its tube axis. In addition, the inner area (mm 2 ) is also the value measured and calculated by the above method.

[0154] In addition, the helix angle (θ) in Table 1 is also a value measured by the above-mentioned method.

[0155] The internally grooved tubes for expansion processing of Examples 1 to 7 and Comparative Examples 1 to 8 were respectively subjected to elongation tests.

[0156] The ductility test is a test in which the end of each inner grooved tube for flaring is gradually stretched using a flaring tool with a cone angle of 60 degrees until flaring cracks are generated.

[0157] Five of each of the inner grooved tubes for expansion processing are prepared, and their ends are gradually extended using the above-mentioned expansion processing tool, and the outer diameter when the expansion processing crack occurs is obtained by the same method as the case of measuring the above-mentioned outer diameter D. That is, using a digital caliper, the outer diameter when the expansion processing crack occurs (the outer diameter of the end portion after expansion) is measured at eight locations (four pairs) roughly equal in the circumferential direction, and the value is obtained as the value obtained by simply averaging these four measured values. Then, the outer diameters (simple average value) of the five identical inner grooved tubes for expansion processing are further simply averaged, and the obtained value is used as the outer diameter D' of the inner grooved tube for expansion processing after extension.

[0158] Then, the performance of the internally grooved pipe for expansion was evaluated based on the relationship between the obtained outer diameter D' and the outer diameter D before expansion.

[0159] Specifically, the case where D'-D ≥ 2 was not satisfied was judged as unqualified (×), and the case where D'-D ≥ 2 was satisfied was judged as qualified (○). Among the qualified cases, the case where D'-D ≥ 2.32 was further satisfied was judged as particularly good (◎).

[0160] Here, the basis for determining that D′-D ≥ 2 is acceptable is described.

[0161] The wire diameter of the annular solder is usually φ1.4mm. This is because when the U-shaped ventilation pipe is fitted into the inner grooved pipe with an outer diameter of φ5.00mm for expansion processing, in order to prevent the solder from leaking, the expansion processing part needs to be expanded to about 1.0mm on one side, which is about 72% of the wire diameter of the annular solder, that is, the outer diameter is 7.0mm.

[0162]

Table 1

[0163]

[0164] Description of Reference Numerals

[0165] 1, 1a, 1b fin

[0166] 3a, 3b groove bottom

[0167] Points 5a, 5b

[0168] 10, 10a, 10b test pieces

[0169] 15 The fins of the test piece (plate) 10a

[0170] 16 The fins of the test piece (plate) 10b

[0171] 20 substrate

[0172] 30 Manufacturing equipment

[0173] 31 tube blank

[0174] 32 Keep plug

[0175] 33 Keep the mold

[0176] 34 Plug shaft

[0177] 35 Slotted plug

[0178] 36 Rolling Ball

[0179] 37 Rolling Department

[0180] 39 fins

[0181] 40 machining ring

[0182] 50 Aluminum fin

[0183] 52 The grooved tube of the present invention

[0184] 54 return bend

[0185] 60 Heat exchanger of the present invention

[0186] This application claims the benefit of priority based on Japanese patent application No. 2022-107073, filed on July 1, 2022, the disclosure of which is incorporated herein in its entirety.

Claims

1. An inner grooved pipe for expansion processing, which is a seamless pipe having grooves on the inner surface and expansion processing is performed on the end, characterized in that: 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 and the outer diameter D is 0.057-0.005D or more and 0.075-0.005D or less, The helix angle θ of the groove on the inner surface is not less than 15 degrees and not more than 27 degrees, The radius of curvature r of the front end 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): The tip curvature radius r and the helix angle θ satisfy the following formula (2): Formula (1): 0.32≤1 / (r×N)≤0.61 Formula (2): 0.04≤r×(1 / cosθ)≤0.

051.

2. The inner grooved tube for expansion processing according to claim 1, characterized in that: The front end curvature radius r and the number N of the fins satisfy the following formula (1'): Formula (1'): 0.52≤1 / (r×N)≤0.

61.

3. The inner grooved tube for expansion processing according to claim 1 or 2, characterized in that: The inner grooved tube for expansion processing is made of copper or copper alloy. 4 . A heat exchanger comprising the expanding inner grooved tube according to claim 1 .

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