JP2004322141A - Hairpin bent copper tube and hairpin bending method for copper tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-diameter hairpin bent copper tube which is suppressed of wrinkling in a hairpin bending section even if the external diameter of a copper tube is ≤10 mm ϕ and bending pitch is ≤40 mm and a hairpin bending method for the copper tube. <P>SOLUTION: In the hairpin bending section 2 of the copper tube 1, the average bending radius R<SB>0</SB>of the bending portion 2b on the side where hairpin bending is ended out of the two bending portions 2a and 2b respectively rising to an arcuate shape from the straight section of the copper tube is made larger than the average bending radius Ri of the bending portion 1a on the side where the hairpin bending is started, to suppress the wrinkling of the hairpin bending section. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hairpin bent copper pipe having a small diameter and a small center-to-center distance between substantially parallel copper pipes, and a hairpin bending method for the copper pipe.
[0002]
[Prior art]
In recent years, there has been an increasing demand for miniaturization, weight reduction, and improvement in heat transfer performance of air conditioners, etc., with the aim of reducing environmental impacts such as preventing global warming. There is a demand for improved heat exchange capacity. A typical example of the improvement of the heat exchange ability of a copper tube is an inner grooved tube. For a tube having a smooth inner surface, a plurality of spiral parallel grooves are formed on the inner surface to improve the heat exchange ability.
[0003]
In addition, as a means for improving the heat exchange capability of the copper tube, there is a method of reducing the pitch by reducing the interval between copper tubes as heat transfer tubes penetrating the heat exchange fins. This is to reduce the pitch between the copper tubes, thereby increasing the density of the heat transfer tubes and increasing the heat exchange capability of the heat exchange fins.
[0004]
FIG. 6 is a perspective view showing an example of these copper tube heat exchangers. As a copper tube used as a heat transfer tube of the heat exchanger 10, substantially parallel copper tubes 1 are hairpin bent (U-shaped bent). It is composed of a hairpin bent copper tube that is connected together by a so-called semicircular arc-shaped bent portion 2.
[0005]
It is known that such a hairpin bent copper tube is manufactured by bending a straight copper tube into a hairpin (for example, see Patent Document 1). This hairpin bending is performed, for example, by inserting a core 4 provided with a ball-head swinging mandrel 5 into a copper tube 1 by a rotary pulling bending method as shown in FIG. This is performed by bending at 180 ° with a constant center radius R 1.
[0006]
[Patent Document 1]
JP-A-2002-224756, (pages 1-2, FIG. 6)
[0007]
However, when the pitch is reduced, if the distance t (hereinafter also referred to as bending pitch) between the axial centers of the substantially parallel copper pipe straight portions of the hairpin bending copper pipe is reduced, the hairpin bending portion may be reduced during the hairpin bending process. (Bending inner part) is likely to cause shape defects such as breakage, wrinkles, and cross-sectional deformation. It is also known that this tendency increases when the copper tube is made thinner (for example, see Non-Patent Document 1). Also, comparing the same degree of bending R / D (bending center radius R 2 / wall thickness center diameter D) and the same diameter ratio (pipe wall thickness center diameter D / wall thickness t), the smaller outer diameter D 1 It is known that wrinkles are easily generated.
[0008]
[Non-patent document 1]
Copper and copper alloys, vol. 41 (2002) (pp. 54-58)
[0009]
The shape defect such as the wrinkle described above causes an appearance problem as well as a fin assembly failure. That is, the hairpin bent copper tube is assembled as a heat transfer tube by inserting a straight portion of the copper tube into a hole formed on the heat exchange fin. However, if the hairpin bending portion (bending inner portion) of the copper tube has wrinkles or cross-sectional deformation, it becomes impossible to insert heat exchange fins near the hairpin bending portion of the copper tube. In addition, when the wrinkles are large, the inner diameter of the copper tube changes, which affects the flow of the refrigerant and the heat medium passing through the inside, and adversely affects the miniaturization and weight reduction of the air conditioner and the like and the improvement of the heat transfer performance.
[0010]
In general, it is known that the fracture at the time of bending is substantially determined by the ratio of the bending center radius R to the pipe diameter D (ε = D / 2R). Further, it is said that one cause of the shape defect such as the wrinkle occurs when the compressive stress σ applied to the copper tube material increases. The compressive stress σ is determined by the ratio of the bending center radius R to the pipe diameter D (ε = D / 2R), and the degree of occurrence of wrinkles with respect to the compressive stress σ depends on the diameter / thickness ratio D / t of the pipe. It is known.
[0011]
Therefore, as a method of preventing wrinkles and cross-sectional deformation, optimizing the D, R, and t to suppress the compressive stress σ has been performed in actual hairpin bending processes so far. In addition, a method of suppressing wrinkles by applying tension in the tube axis direction during bending is generally known, but at this time, there is a problem that a fracture is easily generated and a cross section is deformed.
[0012]
[Problems to be solved by the invention]
However, the method of suppressing breakage and wrinkles by adjusting the D 1, R 2, t and the like results in limiting the product shape. In other words, it is impossible to obtain a product with the same cross-sectional shape and a small pitch (smaller product), or a product with the same appearance (lighter product) by using a thin tube. For this reason, development of a processing method for obtaining a smaller pitch and thinner product has been desired.
[0013]
In particular, in the case of small diameter pipes, wrinkles are likely to occur when compared with the same degree of bending R / D and diameter / thickness ratio D / t, and development of such a processing method is urgently needed. In addition, high strength of the copper tube material is also being studied to achieve a product thinner, but at this time, workability is deteriorated, and it is problematic that shape defects such as breakage and wrinkles are likely to occur. . In terms of compensating for this, there is a demand for a processing method that does not easily cause fracture wrinkles.
[0014]
The present invention has been made in view of such circumstances, and its purpose is to form a hairpin bent portion even when the outer diameter of a copper tube is Φ10 mm or less and the bending pitch is 40 mm or less. An object of the present invention is to provide a small-diameter hairpin-bent copper pipe in which wrinkles are suppressed and a hairpin bending method for the copper pipe.
[0015]
[Means for Solving the Problems]
To achieve this object, the gist of the hairpin bent copper tube of the present invention is, in particular, a hairpin in which the distance between the axes of the substantially parallel copper tubes is 40 mm or less and the outer diameter of the copper tube is 10 mm or less. In a bent copper pipe, an average bending radius of any one of the two bending portions which are raised from the straight portion of the copper tube in an arc shape at the hairpin bending portion of the copper tube, and on which the hairpin bending process is finished. Is larger than the average bending radius of the other bending portion on the side where the hairpin bending process is started.
[0016]
In addition, in order to achieve the above object, the gist of the copper pin hairpin bending method of the present invention is, in particular, a copper pipe having an outer diameter of Φ10 mm or less, the distance between the axes of substantially parallel copper pipes. Is 40mm or less, a method of bending the hairpin, the method of bending the copper tube hairpin, of the two bending portions rising in an arc shape from the copper tube straight portion at the hairpin bending portion of the copper tube, The hairpin bending process is performed by setting the average bending radius of the bending portion on the side where the hairpin bending process is completed to be larger than the average bending radius of the bending portion on the side where the hairpin bending process is started.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, in a hairpin bent copper tube as shown in a front view in FIG. 1, in a hairpin bent portion 2 of a copper tube 1, there are two bent portions 2a, 2b rising from the copper tube straight portions 1a, 1b in an arc shape, respectively. The average bending radius _R0 of the bending portion 2b on the side where the hairpin bending is finished is made larger than the average bending radius Ri of the other bending portion 2a on the side where the hairpin bending is started.
[0018]
In FIG. 1, t is the distance between the axes (bending pitch) between the substantially parallel copper pipe straight portions of the hairpin bent copper pipe, and D is the outer diameter of the copper pipe. Then, the copper pipe is bent in the direction of the arrow shown in FIG. 1 (the same applies to FIG. 2 below).
[0019]
First, the mechanism by which wrinkles occur in the hairpin bending portion (bending inner portion) of the copper tube will be specifically described below. When a copper tube is subjected to a hairpin bending process such as the rotary pull bending method shown in the cross-sectional view of FIG. 4A, a portion where the bending angle of the copper tube is small and a portion where the bending angle is large in the hairpin bending portion. Inevitably occurs.
[0020]
FIGS. 2A and 2B show a portion of the hairpin bent portion where the bending angle of the copper tube is small and a portion where the bending angle is large. 2 (a) and 2 (b), in the hairpin bent portion 2 of the copper tube 1, the two bent portions rising from the copper tube straight portions 1a and 1b, respectively, are shown in accordance with the progress of the hairpin bending. ing.
[0021]
First, as shown in FIG. 2A, a bent portion 2a on the side where the hairpin bending process is started occurs in the initial to first half of the hairpin bending. The bending angle θ of the bent portion 2a is from a straight tubular 0 ° (angle before bending) to a right-angled bending angle of about 90 °, and the bending angle θ is relatively small.
[0022]
On the other hand, as shown in FIG. 2 (b), at the end or later of the bending of the hairpin, a bent portion 2b on the side where the hairpin bending process is finished is formed next to the bent portion 2a. The bending angle θ of the bent portion 2b is a bending angle from about 90 ° of the right angle to 180 ° of hairpin bending (angle at which bending is completed), and the bending angle θ is relatively large. That is, in the bending portion of the hairpin, the bending angle increases from the initial to the first half of the bending to the end to the latter of the bending.
[0023]
FIG. 3 shows the effect of the difference in the bending angle of the copper tube on the amount of strain applied to the bending inner portion 3 of the copper tube. Figure 3 shows the amount of strain in the tube axis direction (vertical axis: maximum principal strain ε) and the position φ of the specific part of the hairpin bending (horizontal axis) for the copper pin after bending the hairpin after bending the hairpin. : DEG) was obtained by FEM analysis. In the horizontal axis of FIG. , The bending start side end position is 180 DEG. And In FIG. 3, the three types of curves show the ratio R / D of R (copper tube hairpin bending center radius) to D (copper tube outer diameter). .., The square curve is 2.0.
[0024]
According to FIG. 3, in each curve, the smaller the position φ (the larger the bending angle θ, the bent portion 2b on the side where the hairpin bending process is finished), the larger the amount of strain generated in the copper pipe. On the other hand, on the side where the hairpin bending process is started (the region where the position φ is large, and the bending portion 2a where the bending angle θ is small where the hairpin bending process is started), the amount of strain generated in the bending inner portion 3 of the copper pipe is small. .
[0025]
From this, the strain amount generated in the copper pipe (including the bent inner portion 3) becomes larger in the region where the position φ is smaller, that is, in the bent portion 2b where the bending angle θ is larger and the hairpin bending process is completed. . Therefore, the bending portion 2b on the side where the hairpin bending process is completed is more likely to break or wrinkle A 2 in the bending inner portion 3. On the other hand, the bending angle θ is small in the region where the position φ is large, that is, in the bending portion 2a on the side where the hairpin bending process is started, and the amount of strain applied to the copper pipe under the influence of shear deformation can be reduced. That is, as the bending angle increases, the effect of reducing the amount of distortion decreases, and the bending portion 2b on the side where the hairpin bending process is finished is more likely to break or wrinkle in the bending inner portion 3. . Further, as can be seen from the analysis results, the influence of the shear deformation due to the difference in the bending angle of the copper pipe becomes more remarkable as the degree of bending R / D is relatively small.
[0026]
In the above-described conventional hairpin bending method, the bending center radius R 1 is fixed, and R 1 forms a constant semicircular hairpin bending portion. For this reason, from the above-described wrinkle generation mechanism, the influence of the shear deformation due to the difference in the bending angle of the copper pipe cannot be eliminated. That is, even under the condition that a molding failure such as breakage or wrinkles occurs during the hairpin bending process, the amount of strain (and stress) generated in the bending start side region is small, and there is always room for the occurrence of the molding failure. It will be molded in the state.
[0027]
In contrast, as in the present invention, by increasing the average bending radius _R0 of the copper tube bending portion 2b having a large copper tube bending angle θ, which is the end to late stage of the hairpin bending shown in FIG. The amount of strain applied to the copper tube during bending can be averaged in the bending circumferential direction. That is, by increasing the bending radius on the bending end side where molding defects such as breaks and wrinkles are likely to occur, molding defects can be avoided. Then, the bending pitch can be reduced by reducing the bending radius on the bending start side having a margin for forming.
[0028]
As a guide for increasing the average bending radius _R0 of the copper pipe bending portion 2b, the average bending radius Ri of the side where the hairpin bending is started (the region where φ is large) is compared with the average bending radius Rave of the entire bending portion. And the average bending radius Ro on the bending end side (the area where φ is small) is equal to or less than (Rave. ≧ Ro + Ri), and Ri <Ro is selected.
As a result, as will be described later, it is possible to make it difficult to cause shape defects such as breakage and wrinkles during hairpin bending without affecting media distribution and heat exchange capacity, etc. If it occurs, it is possible to reduce the degree. In particular, the effect is remarkable under the condition that the outer diameter D 1 of the copper tube in which wrinkling is liable to occur is 10 mm or less and the bending pitch t is 40 mm or less, the high-strength copper tube with poor workability, and the inner grooved tube.
[0029]
Hereinafter, specific embodiments of the present invention will be described.
First, as a premise, in the present invention, the bending center radius R 1 is constant at the hairpin bending portion, for example, as shown in FIG. It does not become a semi-circular shape (arc shape). That is, as shown in FIG. 1, in the hairpin bending portion 2 of the copper tube of the present invention, the average bending radius _R0 of the copper tube bending portion 2b at the end or late stage of the hairpin bending is large, and the hairpin bending process is started. The mean bending radius Ri of the copper tube bending portion 2a on the side is small, that is, a distorted semicircular shape (arc shape).
[0030]
Thus, like the copper pipe of the present invention, even if it has a hairpin bent portion having a different average bending radius, there is no sudden change in shape, and there is no effect on the flow of the refrigerant or the heat medium passing through the inside. In air conditioners and the like, there is no adverse effect on miniaturization, weight reduction, and improvement in heat transfer performance. On the contrary, by suppressing the generation of wrinkles, the effect of eliminating the adverse effect on the flow of the refrigerant and the heat medium passing through the inside of the copper tube is eliminated. . Further, since breakage and wrinkles are less likely to occur than in the conventional bending method, bending can be performed at a smaller pitch, thereby reducing the size and weight of the product.
[0031]
In this respect, when wrinkles occur at the hairpin bending portion of a conventional copper tube with a constant bending center radius R 1, the change in the inner diameter of the copper tube due to the wrinkles rather affects the flow of the refrigerant and the heat medium passing through the inside. There is. This effect is large even for a pipe with a smooth inner surface, but is greater for a pipe with an inner groove provided with a plurality of spiral parallel grooves on the inner surface. An adverse effect on improvement is inevitable.
[0032]
In the present invention, the extent to which the average bending radius _R0 of the copper tube bending portion 2b shown in FIG. 1 is larger than the average bending radius Ri of the copper tube bending portion 2a depends on the conventional shape from the design shape of the hairpin bending portion. The bending center radius R 1 is used as a base, and the lower limit is selected from the minimum value that can suppress breakage and wrinkles generated in the bending inner portion 3 of the copper tube bending portion 2b during bending.
[0033]
However, if the average bending radius _R0 of the copper tube bending portion 2b is too much larger than the average bending radius Ri of the copper tube bending portion 2a, it becomes difficult to insert the fins to the vicinity of the bent portion. Occurs. For this reason, it is desirable to select the upper limit of Ro within a range that does not affect this.
[0034]
On the other hand, the average bending radius Ri of the copper pipe bending portion 2a is determined by the conventional uniform bending center radius Rave. And the average bending radius _R0 of the copper tube bending portion 2b.
[0035]
The reason why the bending radius Ri of the copper pipe bending portion 2a and the bending radius _R0 of the copper pipe bending portion 2b are each averaged is that Ri and _R0 are constant over each portion in the arc direction of each bending portion. It is not necessary to take the value of That is, over the respective arc portions of the respective bent portions, Ri and R ₀ are appropriately changed within the allowable range in which the effects of the present invention of Ri and R ₀ are exhibited due to the bending process and the shape design. This is because you may.
[0036]
The above description has mainly been directed to a copper tube having an outer diameter of Φ10 mm or less for a copper tube and a hairpin bent copper tube having a distance between axes of approximately parallel copper tubes of 40 mm or less. Therefore, the present invention can exert the same effect and can be applied to a copper tube having a large outer diameter of the copper tube or a large distance between the axial centers of the substantially parallel copper tubes. However, in such a copper tube, the demand for light weight and small size required for the product is small, and the conventional technology (adjustment of D 1, R 2, and t) can often be sufficiently satisfied. Few.
[0037]
The copper pipe to which the present invention is applied is mainly a direct pipe, an inner grooved pipe, an outer grooved pipe, an inner and outer grooved pipe, etc., which are generally used for refrigerators and air conditioner pipes. For this reason, in the present invention, the manufacturing process of the copper tube itself is the same as the normal manufacturing method of these copper tubes. That is, first, pure copper such as phosphorous deoxidized copper is melted and cast, and then a raw tube is formed by hot extrusion. This extruded raw tube, including the intermediate annealing, cold rolling of a reducer or the like, drawing, drawing, stretching, etc., are subjected to cold working appropriately combined, etc., to form a copper tube, finish annealing and product copper tube. I do. In the case of a copper tube with a groove on the inner or outer surface, after the above-mentioned cold working or during the cold working, intermediate annealing (including partial annealing) is performed again if necessary, and then the inner or outer surface is processed. A groove is machined, and then finish annealing is performed to obtain a product copper tube. The form of the product copper tube may be a coil shape or a tubular shape.
[0038]
The copper tube material used for the hairpin bent copper tube of the present invention has high yield strength, high workability, and high heat conduction. Is done. In other words, it is not necessary to apply a special copper alloy in the present invention. For example, examples of pure copper include oxygen-free copper, tough pitch copper, and deoxidized copper. However, among them, phosphorus deoxidized copper, which is widely used for piping of refrigerators and air conditioners, is preferable as a copper tube material. As phosphorous deoxidized copper, the chemical components are specified in the JIS standard of copper-brought products, and the phosphorous deoxidized copper 1A class of C1201 (P: 0.004 to 0.015% by mass, Cu: 99.90% by mass or more) ), 1220 phosphorous deoxidized copper 1B species (P: 0.015 to 0.040% by mass, Cu: 99.90% by mass or more), 1221 phosphorous deoxidized copper 2 species (P: 0.004 to 0. 040% by mass, Cu: 99.75% by mass or more). These phosphorus deoxidized copper are appropriately selected and used in accordance with the grade of the small-diameter product copper tube.
[0039]
Next, a method for bending a copper tube of the present invention with a hairpin will be described below. As a prerequisite bending machine, as shown schematically in FIG. 4 (a), an initial state of copper pipe bending, a drawbender generally used for this kind of application is used. It is preferable to use a mandrel that has. This bending method by the draw bender is usually called a rotary drawing bending method. Then, in order to maintain the cross-sectional shape of the tube, a mandrel such as a shell type, a swing type, or a knife type is inserted into the tube, and the bending (bending) die 6, the gripping (clamp) die 7, and the feeding (feeding) are performed. ) The copper tube 1 is bent in cooperation with the die 8. At this time, the tube material moves in the direction of the arrow in the figure following the bending process.
[0040]
Specifically, as shown in FIG. 4A, a core (mandrel) 4 provided with a ball-head swinging mandrel 5 is inserted into a copper tube 1, and then the copper tube is clamped by a clamp die 7. After clamping 1, the bending die 6 is rotated, and the copper tube 1 is bent along this rotation. In FIG. 4A, θ is a bending angle, R is a bending center radius (bending inner radius), D is an outer diameter of the copper tube 1, 2 is a hairpin bending portion of the copper tube 1, 1a and 1b are copper tube straight portions. , Respectively.
[0041]
Here, like the hairpin bending portion of the copper tube of the present invention, the average bending radius _R0 of the copper tube bending portion 2b which is the end or late stage of the hairpin bending is large, and the copper tube bending on the side where the hairpin bending process is started. In order to reduce the average bending radius Ri of the portion 2a, a bending die as shown in FIG. 4B is used. That is, as shown in FIG. 4B, the innermost shape of the bending die 6 is represented by an arc-shaped involute curve, and the average bending radius Ri on the bending start side and the average bending radius on the bending end side. and _{R 0} is _set as R 0> Ri (design) to. As shown in FIG. 4 (b), the bending radius of the innermost shape of the bending die can be set to an angle from the bending center within the allowable range of _R0 and Ri described above, without using constant values of _R0 and Ri. The bending radius may be changed continuously according to the conditions, or a different bending radius may be formed stepwise.
[0042]
In the bending method according to the present invention, as shown in FIG. 4A, a copper pipe is formed by using the bending die as shown in FIG. After clamping 1, the bending die 6 is rotated. At this time, in order to keep the contact state between the bending dies 6 in which the innermost shapes Ri and _R0 are changed and the copper tube 1 constant, as shown in FIG. The center needs to be eccentric or moved by changing the position of the feed die.
[0043]
At this time, the center of rotation of the bending die 6 may be moved mechanically in accordance with the change between Ri and _R0 set on the bending die, or the pressure or sense applied to the bending die may be detected. These may be controlled to be constant. Conversely, while the center of rotation of the bending die 6 is fixed, the position of the feed die holding the pipe and the position of the mandrel may be moved. For these, a suitable method is selected depending on the device and space restrictions.
[0044]
Further, even if different Ri and _R0 are not set for such a bending die, after bending at a constant angle with a bending die having an average bending radius _R0 on the bending end side, an average bending radius on the bending start side is used. The bending of the hairpin with another bending die having Ri ( _R0 > Ri) may be performed to obtain a bent copper tube having a different average bending radius of the present invention.
[0045]
In addition, the size of the mandrel (core) 4, the clearance C between the mandrel 4 and the copper tube 1, and the position of the mandrel also affect the occurrence of wrinkles and cross-sectional deformation after bending. As in the prior art, the condition of the mandrel where wrinkles and cross-sectional deformation do not occur is set.
[0046]
【Example】
The results of comparison of the wrinkle generation state inside the bend of the hairpin bent portion between the present invention example and the conventional example in which the hairpin bent portion has the same bending radius R by FEM analysis will be described below with reference to FIG. I do. FIG. 5 shows a bent portion of a copper tube hairpin bent by FEM analysis. FIG. 5A shows a hairpin bent portion of the present invention, and FIG. 5B shows a conventional hairpin bent portion. 5 (a) and 5 (b) show the upper and lower portions of the copper tube (the bent portion 2b where the hairpin bending process is finished, and the other bent portion 2a where the hairpin bending process is started). It is the reverse of FIG.
[0047]
As is clear from the comparison between the FEM analysis results of FIG. 5A and FIG. 5B, in the hairpin bent portion of the example of the present invention in FIG. Almost no wrinkles A occurred inside the bending (surface) of the copper tube. On the other hand, in the hairpin bending portion of the conventional example in FIG. 5B, a large number of wrinkles A are generated inside the bending (surface) of the copper tube.
[0048]
As a condition of the FEM analysis, a bending method using a draw bender shown in FIG. 4A is used. In the present invention, as shown in FIG. The average bending radius Ri on the bending start side was set to a constant 8.5 mm, the average bending radius _R0 on the bending end side was set to a constant 10.0 mm, and _R0 > Ri. On the other hand, the same bending radius R 1 of the conventional example was fixed at 9.25 mm. The prerequisite copper tube condition is a copper tube made of the above-mentioned C1201 phosphorous deoxidized copper 1A type, having a wall thickness of 0.2 mm, an outer diameter D of φ7 mm of φ10 mm or less, and a bending pitch t of 32 mm of 40 mm or less. The clearance C between the mandrel 4 and the copper tube 1 was 0.1 mm.
[0049]
Therefore, from the result of this FEM analysis, even if the outer diameter D of the copper tube is Φ10 mm or less and the bending pitch t is 40 mm or less, the present invention is generated inside the bending portion of the hairpin bending portion of the copper tube. It can be seen that wrinkling can be suppressed and bending can be performed without breaking the copper tube.
[0050]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, even if the outer diameter of a copper pipe is 10 mm or less and bending pitch is 40 mm or less, the small diameter hairpin bending copper pipe which suppressed the wrinkle of the hairpin bending part, and the hairpin bending process of the copper pipe We can provide a method. Further, in the hairpin bent copper tube of the present invention, although the hairpin bent portion has a different average bending radius, there is no change in the inner diameter of the copper tube, and there is no influence on the flow of the refrigerant or the heat medium passing through the inside, and In such cases, there is no adverse effect on miniaturization, weight reduction, and improvement in heat transfer performance. And, on the contrary, the suppression of the generation of wrinkles in the bent portion of the hairpin eliminates the adverse effect on the flow of the refrigerant and the heat medium passing through the inside of the copper tube, so that in an air conditioner or the like, miniaturization, weight reduction, and improvement in heat transfer performance can be achieved. The benefits are great.
[Brief description of the drawings]
FIG. 1 is a front view showing an example of a hairpin bent copper tube of the present invention.
FIGS. 2A and 2B are front views showing a state of a bent portion at the time of hairpin bending of a copper tube, wherein FIG. 2A shows an initial stage of bending and FIG. 2B shows an end of bending.
FIG. 3 is an explanatory diagram showing a relationship between a bending angle of a copper tube at the time of a hairpin bending process and an amount of strain applied to a bending inner portion of the copper tube.
FIGS. 4A and 4B schematically show bending of a copper tube by a draw bender according to the present invention. FIG. 4A is a cross-sectional view showing an initial state of bending, and FIG. is there.
5A and 5B are explanatory diagrams showing a hairpin bent copper tube analyzed by FEM, FIG. 5A showing an example of the present invention, and FIG. 5B showing an example of a conventional example.
FIG. 6 is a perspective view showing a general heat exchanger using a hairpin bent copper tube.
[Explanation of symbols]
1: Copper pipe 2: Hairpin bent part, 1a, 1b: Copper pipe straight part,
2a: a bent portion on which hairpin bending is started,
2b: a bent portion on the side where the hairpin bending process is finished,
R ₀ : average bending radius of bending portion 2b, Ri: average bending radius of bending portion 2a,
3: Inside the bend,

Claims (6)

At the hairpin bending part of the copper pipe, the average bending radius of one of the two bending parts that rises from the straight part of the copper pipe in an arc shape on the side where the hairpin bending processing ends is the hairpin bending processing. A hairpin-bent copper tube having a larger bending radius than the average bending radius of the other bending portion on the side to be bent. The hairpin bent copper tube according to claim 1, wherein the distance between the axes of the substantially parallel copper tubes is 40mm or less, and the outer diameter of the copper tube is 10mm or less. The hairpin bent copper pipe according to claim 1 or 2, wherein the copper pipe is a high-strength copper pipe having a proof stress of 100 MPa or more. A method of bending a copper tube by a hairpin, wherein an average bending of a bending portion on a side where the hairpin bending process is completed is included in two bending portions rising in an arc shape from a straight portion of the copper tube in a hairpin bending portion of the copper tube. A hairpin bending method for a copper pipe, wherein the radius is larger than an average bending radius of a bending portion on a side where hairpin bending is started, and the hairpin bending is performed. 5. The copper tube hairpin bending method according to claim 4, wherein the distance between the axes of the substantially parallel copper tubes is 40 mm or less, and the outer diameter of the copper tubes is 10 mm or less. The method according to claim 4 or 5, wherein the copper pipe is a high-strength copper pipe having a proof stress of 100 MPa or more.

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