Heat exchanger tubes and heat exchangers with excellent brazability

Abstract

To provide a tube for a heat exchanger which prevents peeling-off and exfoliation of brazing composition coating from occurring during assembling and does not generate residue, and a heat exchanger including the tube.SOLUTION: In a tube for a heat exchanger, a plurality of plate-shaped fins having a plurality of groove parts or hole parts are arranged at prescribed interval, and the tube is composed of a tube body fit into the groove parts or the hole parts formed in each of the fins. 60 to 20,000 recesses each inscribed in a circle of 5 to 40 μm in circle-equivalent diameter are formed in an outer surface of the tube body per 1 mm2, where an area ratio of the recesses is 5 to 50%. The outer surface is coated with a brazing composition coating which is prepared by adding a binder to either of brazing powder and fluorine flux or a mixture of both.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tube for a heat exchanger having excellent brazing properties and a heat exchanger.

Background Art

[0002] In an aluminum alloy heat exchanger mainly composed of a tube, fins, and a header pipe, which is manufactured by brazing these components, a combination of an extruded tube with a Zn spray on the surface and fins made of a brazing sheet with an Al-Si alloy brazing material clad on both sides (three-layer lamination) has been widely used until now. However, in recent years, by combining an extruded tube having a brazing coating film formed on the surface, which is composed of Si powder, a Zn-containing flux, and a binder, with fins, it has become possible to globally manufacture inexpensive, high-quality, and high-performance products.

[0003] In the above-described heat exchanger, Zn contained in the flux of the brazing coating film diffuses during brazing to form a sacrificial anode layer on the tube surface, thereby suppressing the progress of corrosion occurring in the tube and preventing refrigerant leakage due to corrosion in the tube. In addition, the liquid-phase brazing formed by the reaction between the brazing coating film and the tube during brazing flows to the joint portion between the fins and the tube to form a fillet and join the two, so that high heat exchange performance can be obtained.

[0004] For example, by using the powder brazing composition and heat exchanger described in Patent Documents 1 and 2 below, selective corrosion does not occur at the brazed joint portion between the tube and the fins, and a highly reliable and industrially highly practical flat multi-hole tube (tube) and heat exchanger can be obtained.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Conventionally, when applying a powder brazing composition to a flat multi-hole tube, it is common to apply it to the front and back surfaces using a coating device such as a bar coater or a roll coater. This is because the parts in contact with the fins are the front and back surfaces of the tube, the brazing composition can be uniformly coated at the desired speed by these coating devices, and it is suitable for mass production. By the way, heat exchangers are being further miniaturized and lightened, and further measures to improve the reliability of brazed parts are required.

[0007] In a structure for joining a flat multi-hole tube and fins applied to a heat exchanger, there is known a structure in which the flat multi-hole tube is inserted into slit-shaped holes formed in the fins to position both and then brazed. In this structure, since it is necessary to insert the flat multi-hole tube into the slit-shaped holes, it is necessary to insert it while sliding the flat multi-hole tube along the inner edge of the holes. In this case, if peeling occurs in the coating film of the brazing composition, there is a risk of causing brazing failure.

[0008] An object of the present invention is to provide a heat exchanger tube that does not cause peeling or separation of the brazing composition coating film during assembly and does not cause residues after brazing and joining failures due to them, and a heat exchanger equipped with such a tube.

Means for Solving the Problems

[0009] (1) The heat exchanger tube of the present invention is a heat exchanger tube comprising a tube body that is fitted into grooves or holes formed in a plurality of plate-shaped fins each having a plurality of grooves or holes and arranged at a predetermined interval, wherein on the outer surface of the tube body, there are formed 60 to 20,000 recesses inscribed in a circle with a circle-equivalent diameter of 5 to 40 μm per 1 mm 2 and the area ratio of the recesses is 5 to 50%, and When the average value of the diameter of the concave portion is d and the height of the convex portion is h at the peripheral edge of the concave portion, the ratio of the convex portions satisfying h / d≥0.15 is formed at 30% or more. A coating film of a brazing composition obtained by adding a binder to a mixture of either one or both of brazing powder and fluoride flux is applied to the outer surface. If it is a coating film of a mixture of the brazing powder and the binder, a fluoride flux is supplied during brazing. If it is a coating film of a mixture of the fluoride flux and the binder, brazing is performed by supplying brazing filler metal during brazing. characterized in that 。

[0010] ( 2 ) The heat exchanger according to the present invention is characterized by comprising the tube described in (1) and fins joined to the tube.

Advantages of the Invention

[0011] The present invention can provide a tube for a heat exchanger that does not cause peeling or separation of the brazing composition coating film during assembly and does not produce residues after brazing.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0013] Hereinafter, based on the attached drawings, an example of an embodiment of the present invention will be described in detail. Note that the drawings used in the following description may show the characteristic parts enlarged for the sake of easy understanding of the characteristics. As shown in Fig. 1(A), the heat exchanger 1 of this embodiment includes a plurality of flat tubes (tubes) 2 for passing a fluid as a heat medium, and a plurality of plate-shaped fins 3 that come into contact with the outer surfaces (front and back surfaces) of these flat tubes 2 to dissipate heat. Heat exchange is performed between the fluid as the heat medium flowing through the flat tubes 2 and the air flowing between the fins 3. Both of these flat tubes 2 and fins 3 are made of an aluminum alloy.

[0014] As illustrated in Fig. 1(B), the flat tube 2 has a flat shape with a height (thickness) smaller than the width dimension, and a plurality of inner columns (partition walls) 5 are formed at intervals in the width direction inside the tube body 4 that forms its outer periphery. The inner space of the tube body 4 is divided into a plurality of internal flow paths 6 that are parallel to each other, which is a so-called multi-hole tube. As an example, as shown in Figs. 1(A) and 1(B) showing the detailed structure, a structure with about 20 internal flow paths 6 is adopted for the flat tube 2. However, in Fig. 2(B) showing the structure of the second embodiment described later, for the sake of simplifying the figure, it is shown as a structure with 6 internal flow paths 6.

[0015] The tube body 4 that constitutes the flat tube 2 consists of planar walls 4A, 4A that are arranged parallel to each other and spaced apart, and corner walls 4B with a semi-circular cross-section that integrally connect both ends in the width direction of these planar walls 4A, 4A individually. Since 19 inner columns 5 are formed in parallel at approximately equal intervals between one corner wall 4B and the other corner wall 4B in the form shown in Fig. 1(B), the flat tube 2 shown in Fig. 1(B) has 20 internal flow paths 6 formed. Note that the flat tube 2 is integrally formed by extrusion molding of an aluminum alloy. In the flat tube 2 applied to a heat exchanger 1 of a general scale, several to several tens of internal flow paths 6 are formed. Also, the flat tube 2 has a height (total thickness) of about 1 mm to several mm and a width of about several tens of mm, and the inner columns 5 partitioning the internal flow paths 6 adopt a thin-wall structure with a wall thickness of about 0.1 to 1.5 mm.

[0016] As an example of the aluminum alloy constituting the flat tube 2, an aluminum alloy containing 0.2 to 1.5% of Mn, 0.2 to 0.5% of Si, less than 0.2% of Cu by mass%, with the balance being Al and inevitable impurities can be applied.

[0017] As an example of the aluminum alloy constituting the fin 3, an aluminum alloy containing 1.0 to 1.8% of Mn, 0.7% or less of Si, 0.3% or less of Fe, 0.5 to 2.5% of Zn by mass%, with the balance being Al and inevitable impurities can be applied.

[0018] In the flat tube 2 before brazing, a coating film 10 made of, for example, the brazing composition described below is formed on the outer surface of the flat wall 4A. The brazing composition constituting the coating film 10 is, for example, a brazing composition composed of brazing powder, flux, and binder. As the brazing powder, Si powder, Al - Si powder, Al - Si - Zn powder, etc. are used, and as the flux, 1-3 AlF 4-6 、Cs 1-3 AlF 4-6 、Cs 0.02 K 1-2 AlF 4-5 、AlF3, KF, KZnF3, K2SiF6 and other fluoride - based fluxes are used, and as the binder, an acrylic resin is used. For the brazing powder and the flux, it is preferable to use either one or a mixture of both, and a binder may be further added as necessary. As an example of the brazing composition composed of brazing powder, flux, and binder, a brazing composition containing 2 - 3 g / m 2 of brazing powder and 4 - 7.5 g / m 2 of flux, and containing 10 - 20% of binder by solid content weight based on the total amount of these can be used.

[0019] In the coating film 10, if the amount of the brazing powder is less than 2 g / m 2 , brazing defects are likely to occur, and if the amount of the brazing powder is 6 g / m 2In an amount exceeding this, the coating film is liable to remain unreacted. In the coating film 10, when the amount of the flux is less than 4 g / m 2 it becomes unreacted and liable to be difficult to solder. When the amount of the flux is more than 20 g / m 2 an additional process for removing residues is required. In the coating film 10, when the amount of the binder is less than 10%, the hardness of the coating film tends to be small, and when the amount of the binder exceeds 20%, the coating film is liable to remain unreacted with the tube.

[0020] The coating amount of the coating film 10 is preferably in the range of 6 to 33 g / m 2 . In the case of this embodiment, the coating film 10 may be applied over the entire outer surface of the flat tube 2, but in order to correspond to the fitting structure shown in FIG. 1, except for the other end portion in the width direction that does not contact the fin 3, the coating film 10 may be applied to the portion from one end portion in the width direction that contacts the fin 3 to the flat surface. The method of applying the soldering composition is not particularly limited in this embodiment, and it can be carried out by an appropriate method such as a spray method, a shower method, a flow coater method, a roll coater method, a brush coating method, a dipping method, an electrostatic coating method, etc. When the coating amount of the coating film 10 is less than 6 g / m 2 a sufficient fin fillet cannot be formed. When the coating amount exceeds 33 g / m 2 the coating film is liable to remain unreacted and may cause soldering defects. If it is in the range of 6 to 33 g / m 2 it is the range of the necessary amount to realize the above-mentioned coating film hardness, and it is the optimal range in which the flat tube 2 and the fin 3 can be surely soldered.

[0021] On the other hand, the fin 3 is formed in a rectangular plate shape and a plurality of them are arranged in parallel to each other at a certain interval. A plurality of groove portions 7 for inserting the flat tube 2 in the width direction are formed at a predetermined interval along the longitudinal direction of the side portion on one side thereof. Further, on both side edges of each groove portion 7, piece-shaped rising portions 8 that rise perpendicularly to the fin 3 are integrally formed. The flat tube 2 and the fins 3 are assembled by fitting and fixing the flat tube 2 into each groove 7 along the width direction as shown by the arrow in Fig. 1(A) from one side of the plurality of fins 3 arranged at regular intervals. In the case of this structure, the flat tube 2 has a portion from one end in the width direction to the flat surface accommodated in the groove 7, the other end in the width direction is arranged at the opening of the groove 7, and the rising portion 8 of the groove 7 is in contact with the flat surface of the flat tube 2 (the surface of the coating film 10 applied to the surface wall 4A). And a portion from one end in the width direction of the flat tube 2 to the flat surface is fixed to the fins 3 by brazing described below.

[0022] In the flat tube 2 according to the present embodiment, a plurality of fine recesses described below are formed on the outer surfaces of the flat walls 4A, 4A on which the coating film 10 is applied. The recesses are recesses inscribed in a circle with an equivalent circle diameter of 5 to 40 μm, and 60 to 20,000 recesses are formed per 1 mm. 2 The shape in plan view may be any shape such as a triangle, a quadrilateral, a pentagon, or a polygon having more corners, or an arbitrary shape such as a grit shape or a pockmarked shape. As shown in Fig. 3, which shows an electron microscope (SEM) image of the recesses obtained in the examples described later, recesses with various shapes in plan view are formed.

[0023] The depth of the recesses is about 5 to 40 μm, and 60 to 20,000 recesses are formed per 1 mm on the outer surface of the flat wall 4A, and the area ratio of the recesses (area of the recesses / field area) is 5 to 50%. 2 When these fine recesses are formed on the outer surface of the flat wall 4A of the flat tube 2, an anchor effect is exerted on the coating film applied thereon, improving the adhesion of the coating film. When the equivalent circle diameter of the recesses is less than 5 μm, the effect of improving the coating film adhesion is poor, and when it exceeds 40 μm, the number of recesses is small, so the adhesion of the coating film becomes a problem. When the number of recesses per 1 mm is less than 60, the anchor effect on the coating film 10 is insufficient, and coating film peeling is likely to become a problem during the assembly of the heat exchanger. 1mm 2 When the number of recesses per 1 mm is less than 60, the anchor effect on the coating film 10 is insufficient, and coating film peeling is likely to become a problem during the assembly of the heat exchanger. 2When the number of recesses per hit exceeds 60 to 20,000, the flow of Al-Si solder is hindered, resulting in an increase in soldering joint defects. When the area ratio of the recesses is less than 5%, the anchor effect on the coating film 10 is insufficient, and coating film peeling is likely to become a problem during the assembly of the heat exchanger. When the area ratio of the recesses exceeds 50%, the flow of Al-Si solder is hindered, resulting in an increase in soldering joint defects. Furthermore, it is preferable that convex portions are formed on the peripheral edges of the recesses. When the average value of the diameter of the recesses is d and the height of the convex portions is h, if the ratio of the convex portions with h / d ≥ 0.15 is 30% or more, the adhesion of the coating film can be made stronger. As a method of forming the recesses on the surface of the tube 2, any of mechanical, physical, electrochemical, and chemical treatment methods may be selected. Specifically, shot blasting, polishing, plasma, laser, anodizing, wet etching, etc. can be used. For example, in the method of mechanically imparting unevenness, any mesh number such as a polishing sheet can be used, attached to the roll of a rolling mill, and pressed against the tube 2 with an appropriate load to form unevenness. Also, by selecting the number of presses and the way of passing through the roll, it is possible to vary the size and number of the recesses.

[0024] After fitting the flat tube 2 coated with the coating film 10 into the groove portion 7 of the fin 3 as shown by the arrow in FIG. 1, the whole is put into a heating furnace and heated to melt the coating film 10 on the surface of the flat tube 2, and then cooled and solidified to form a fillet, which is a melt-solidified product of the coating film, at the contact portion between the fin 3 and the flat tube 2, and the flat tube 2 and the fin 3 can be soldered to form the heat exchanger 1.

[0025] In the above-mentioned assembly work, the flat tube 2 is fitted into the groove portion 7 of the fin 3 while being rubbed against both side edges of the groove portion 7 of the fin 3, and there is a possibility that the rising portions 8 formed on both side edges of the groove portion 7 of the fin 3 may scrape off a part of the coating film 10 applied on the surface of the flat tube 2. However, in this embodiment, since a plurality of the above-mentioned recesses are provided on the outer surface of the flat tube 2 coated with the coating film 10, the coating film 10 is prevented from peeling off by the anchor effect of the plurality of recesses. Even if the flat tube 2 is fitted along the groove portion 7 of the fin 3 while generating a certain amount of friction, the amount of the coating film scraped off by the rising portion 8 during fitting can be reduced, and a sufficient amount of the coating film 10 necessary for brazing can be left on the surface of the flat tube 2.

[0026] That is, if the coating film 10 is fixed to the outer surface of the flat tube 2 by a plurality of concave portions, even if the flat tube 2 slides with a certain degree of low friction with respect to the groove portion 7 during fitting, the ratio of the coating film 10 being scraped off can be reduced. In addition, the brazing composition scraped off from the surface of the flat tube 2 adheres to the surface near the side edge of the groove portion 7 of the fin 3. When heated during brazing, it melts and flows between the fin 3 and the flat tube 2 to merge with the surrounding brazing material, forming a fillet. When the gap between the fin 3 and the flat tube 2 is small, it also penetrates into the gap. Therefore, the brazing composition remaining on the surface of the flat tube 2 can surely braze the fin 3 and the flat tube 2 without causing fillet shortage.

[0027] During brazing, heat to an appropriate temperature in an appropriate atmosphere such as an inert atmosphere to melt the coating film 10. This increases the activity of the flux, and the components in the flux diffuse to the surfaces of the flat tube 2 and the fin 3, breaking the oxide film and promoting wetting. The heating temperature for brazing is, as described above, equal to or higher than the melting point of the coating film 10. However, in the case of the brazing composition having the above-described composition, it can be heated in the range of 580 to 610 °C, held for about 1 to 10 minutes, and then cooled.

[0028] According to the structure of the coating film 10 of the present embodiment, even if the flat tube 2 is fitted into the groove portion 7 of the fin 3 for brazing and the coating film 10 on the surface is rubbed against the peripheral portion of the groove portion 7 of the fin 3, the amount of the coating film 10 scraped off is small. For this reason, brazing can be performed while leaving a sufficient amount of the coating film 10 at the brazed portion, so that good brazing is achieved and a fillet of a sufficient size can be formed between the flat tube 2 and the fin 3.

[0029] Figure 2 shows a second embodiment of the heat exchanger according to the present invention. The heat exchanger 11 of this embodiment includes a plurality of flat tubes 12 through which a fluid as a heat medium passes, a large number of fins 13 that are in contact with the outer surface of the flat tubes 12 and dissipate heat by fitting the flat tubes 12 in a skewered state, a header tube 14 that connects the flat tubes 12, a supply tube 15 that supplies the fluid to the flat tubes 12 through the header tube 14, and a recovery tube 16 that recovers the fluid that has passed through the flat tubes 12. These flat tubes 12, fins 13, header tube 14, supply tube 15, and recovery tube 16 are all made of an aluminum alloy.

[0030] Also, the flat tube 12 has the same flat shape as the flat tube 2 in FIG. 1, with a height (thickness) smaller than the width dimension. By being bent in the middle of the length direction, a U-shaped bent tube portion 18 is formed between the straight tube portions 17, and each end of the straight tube portion 17 is connected to the header tube 14. The header tube 14 has an internally divided structure, and the supply tube 15 and the recovery tube 16 are connected to both ends of the header tube 14. As a result, each flat tube 12 is sequentially connected via the inside of the header tube 14 from the supply tube 15 to the recovery tube 16, and the flow path is formed in a meandering shape. The flat tube 12 is made of the same aluminum alloy tube as the tube body 4 of the first embodiment, but the description is omitted because the tube structure is equivalent.

[0031] On the other hand, the fins 13 are arranged parallel to each other at regular intervals, and a plurality of hole portions 19 for partially fitting the flat tubes 12 are formed. Also, a burring process is performed on the peripheral edge of the hole portion 19, and as shown in FIG. 2(C), a rising portion 20 formed by vertically rising the peripheral edge of the hole portion 19 is integrally formed. Then, the flat tube 12 and the fins 13 are arranged such that the straight tube portions 17 of the flat tube 12 are fitted into the hole portions 19 of the fins 13 so as to skewer the fins 13 arranged at regular intervals, and the fins 13 are fixed by brazing at the portions of the straight tube portions 17.

[0032] When assembling and brazing the heat exchanger 11 of this form, it is necessary to fit and assemble the straight pipe portion 17 of the flat pipe 12 into the hole portion 19 of the fin 13 at the stage of assembly before brazing. For this reason, when applying a coating film of a brazing composition to the straight pipe portion 17, there is a risk that the coating film will be peeled off by the fitting. Therefore, as in the case of the previous first embodiment, a plurality of fine recesses are formed, and the coating film 10 is applied to the outer surface on which these recesses are formed.

[0033] Insert the straight pipe portion 17 of the flat pipe 12 into the hole portion 19 of the fin and fit the fins 13 one by one. Alternatively, a plurality of fins 13 can be arranged in advance and the flat pipe 12 can be inserted. At this time, as shown in Fig. 2(C), it is inserted so that the rising portion 20 of the fin 13 faces the rear in the insertion direction. Then, a large number of fins 13 are sequentially fitted, and by bringing the surface of the rear fin 13 into contact with the rising portion 20 of the front fin 13, each fin 13 is arranged at a certain interval corresponding to the length of the rising portion 20. After fitting a large number of fins 13 to the flat pipe 12 in this way, the whole is put into a heating furnace and heated to melt the brazing composition on the surface of the flat pipe 12, and then cooled and solidified to integrate the fin 13 and the flat pipe 12.

[0034] In the above-mentioned assembly work, the fin 13 is fitted while rubbing the surface of the straight pipe portion 17 of the flat pipe 12, and the fin 13 tries to scrape off a part of the coating film 10 applied to the surface of the flat pipe 12. However, since the coating film 10 is fixed by the plurality of recesses, the amount of the coating film 10 scraped off is small, and a sufficient amount of brazing composition necessary for the brazed portion remains. For this reason, a good fillet can be formed at the brazed portion, and as in the case of the heat exchanger 1 of the first embodiment, the fin 13 and the flat pipe 12 can be brazed with good strength.

Example

[0035] An aluminum alloy ingot with a composition containing 0.3% Mn, 0.35% Si, and 0.1% Cu by mass, with the balance being Al and unavoidable impurities, was homogenized and then extruded to produce flat extruded tubes with a height (thickness) of 1 mm, an outer wall thickness of 0.25 mm, an inner column thickness (partition wall thickness) of 0.25 mm, a hole width (internal flow path width) of 0.7 mm, a hole height (internal flow path height) of 0.5 mm, and 12 holes (internal flow paths). On the front and back surfaces of each flat tube (tube), abrasive sheets of #120, #240, #400, #600, #1200, and #1500 were used, and any one of them was attached to the roll of a rolling mill, and rolling was performed up to 1 to 30 times with a reduction rate of 2 to 5% to impart unevenness to the tube. Among them, some were polished again on the surface to adjust the height of the convex part.

[0036] <Average value of the inscribed circle diameter (d: μm), number of recesses (number / mm 2 )), area ratio (%)> The average value d of the diameter of the circle inscribed by the recesses on the tube surface, the number of recesses, and the area ratio were determined using SEM (scanning electron microscope) images and calculated by binary processing of the images. Fig. 3 shows an SEM image of the tube surface of Example 19 shown in Table 1 described later, and Fig. 4 shows an SEM image of Comparative Example 4 shown in Table 1.

[0037] <Height of the convex part (h: μm), depth of the recess (μm)> The recesses and convex parts formed on the tube surface were determined by observation using a laser microscope on the tube surface. The height h of the convex part at the periphery of the opening of the recess was determined by observation with a laser microscope by measuring the unevenness of an arbitrarily 500 μm length × 10 cross-sections parallel to the rolling direction. When the depth of the recess was 5 to 40 μm and the ratio of the convex parts with h / d ≧ 0.15 to the number of recesses in the cross-sectional view was 30% or more, it was judged that there were convex parts.

[0038] Fig. 5 shows, as an example, the laser microscope observation results in Example 12 shown in Table 1 described later. The method for determining the ratio of convex portions where h / d ≥ 0.15 is as follows: In the region of the circled numerical value 1 in Fig. 5, since no concave portion is shown, it is a region where neither concave nor convex portions are counted. In the region of the circled numerical value 2, the number of concave portions is counted, but since the convexity is low, it is a region where convex portions are not counted. In the region of the circled numerical value 3, h / d = 4.0 / 21.2 = 0.19, and both concave and convex portions are counted. In the region of the circled numerical value 4, h / d = 2.8 / 21.2 = 0.13, the number of concave portions is counted, but since the value of h / d is 0.15 or less, convex portions are not counted. In the region of the circled numerical value 5, the number of concave portions is counted, but since the convexity is low, convex portions are not counted. In the region of the circled numerical value 6, h / d = 8.2 / 21.2 = 0.39, and both the number of concave and convex portions are counted. In the region of the circled numerical value 7, the number of concave portions is counted, but since the convexity is low, convex portions are not counted. In Example 12, the regions of the circled numerical values 2 to 7 were counted as the number of concave portions, and the regions of the circled numerical values 3 and 7 were determined to have convex portions. In Example 12, the ratio of convex portions (number of convex portions / number of concave portions) was calculated by measuring the unevenness of an arbitrarily selected 500 μm length × 10 cross-sections parallel to the rolling direction.

[0039] <Pencil scratch hardness> The pencil scratch hardness was measured according to the method of JIS K5600-5-4:1999. It was evaluated as ◎ for 2H or higher, ○ for H or higher, and × for lower than that. <Evaluation of poor joint after soldering> For the poor joint after soldering, it was evaluated as ○ when 90% or more of the joint part was normal, and × when it was 90% or less. That the soldering of the joint part is normal means that the tube and the fin are well joined via a fillet. On the other hand, the unjoined part between the tube and the fin was judged as a poor joint location, and it was judged by the ratio of the length of the poor joint location to the joint location. <Residue> For the residue due to unreacted coating film on the tube, it was evaluated as ○ when the area ratio was 10% or less, and × when it was 10% or more. Thereafter, 3 g / m 2 Si solder powder, 6 g / m 2A coating film composed of a brazing composition with a flux amount (KZnF3 amount) and a binder amount of 15% was applied at a coating amount of 10 g / m 2 to produce a tube with a coating film.

[0040] Regarding the presence or absence of poor bonding after brazing and residues of the coating film, as shown in Fig. 1(B), a flat tube with a coating film was used, and three stages of fins were assembled as shown in Fig. 1(A) to construct a heat exchanger test piece. This test piece was subjected to brazing heat treatment in a heating furnace in a nitrogen gas atmosphere under the conditions of a heating rate of 100 °C / min, holding at 600 °C for 3 minutes, and a cooling rate of -70 °C / min. After that, a tube with some fins removed was produced to check the brazed joint state.

[0041] [Table 1]

[0042] [Table 2]

[0043] As shown by the results of the examples shown in Table 1, on the outer surface of the tube body, there are 60 to 20,000 recesses inscribed in a circle with an equivalent diameter of 5 to 40 μm per 1 mm 2 It can be seen that a tube with such a structure can provide a tube that does not cause coating film peeling when assembled into a heat exchanger. Also, it can be seen that such a tube can provide a tube that does not cause brazing defects or residues after being assembled into a heat exchanger and brazed. Furthermore, it can be seen that when the ratio of convex portions with h / d ≧ 0.15 to the number of recesses in the cross-sectional view is 30% or more and there are convex portions at the peripheral edges of the recesses, the adhesion is higher.

[0044] As shown by the results of the comparative examples shown in Table 1 and Table 2, on the outer surface of the tube body, there are 5 to 40 μm equivalent diameter circles inscribed with recesses of 1 mm 2In the comparative examples having 60 to 20,000 formed per hit and having recesses such as a planar polygonal shape inscribed in a circle with a diameter of less than 5 μm or a pockmarked shape, the pencil scratch hardness was insufficient, and in some comparative examples, brazing joint failure or residues occurred. In the comparative examples having recesses such as a planar polygonal shape inscribed in a circle with a diameter exceeding 40 μm or a pockmarked shape, the pencil scratch hardness was insufficient, or brazing joint failure or residues occurred. Even for the recesses within the aforementioned desirable size range, in the comparative examples where the number of recesses was not within the range of 60 to 20,000, the pencil scratch hardness was insufficient, or brazing joint failure or residues occurred. Further, even when having recesses with the desirable size and number, in the comparative examples where the area ratio of the recesses was not within the above range, the pencil scratch hardness was insufficient, or brazing joint failure or residues occurred. Therefore, it can be understood that a tube body having recesses with a size inscribed in a circle having a diameter within the above range and having the number and area ratio of the recesses within the above range can provide a tube that does not cause brazing joint failure or residues after being assembled into a heat exchanger and brazed.

Explanation of Signs

[0045] 1... Heat exchanger, 2... Flat tube (tube), 3... Fin, 4... Tube body, 4A... Surface wall, 7... Groove portion, 10... Coating film, 11... Heat exchanger, 12... Flat tube (tube), 13... Fin, 19... Hole portion.

Claims

1. A tube for a heat exchanger applied to a heat exchanger in which a plurality of plate-shaped fins each having a plurality of grooves or holes are arranged at a predetermined interval and which includes a tube body fitted into the grooves or holes formed in each fin, and the fins and the tube body are brazed, wherein On the outer surface of the tube body, there are 60 to 20,000 recesses inscribed in a circle with an equivalent diameter of 5 to 40 μm per 1 mm, and the area ratio of the recesses is 5 to 50%, and ２ at the same time, when the average value of the diameter of the recess is d and the height of the protrusion is h at the peripheral edge of the recess, a ratio of the protrusions satisfying h / d≥0.15 is formed at 30% or more, a coating film of a brazing composition obtained by adding a binder to either one or both of brazing powder and a fluoride flux is applied to the outer surface, and when it is a coating film of a mixture of the brazing powder and the binder, the fluoride flux is supplied during brazing, and when it is a coating film of a mixture of the fluoride flux and the binder, the brazing material is supplied during brazing to perform brazing. A tube for a heat exchanger characterized by this.

2. A heat exchanger, comprising the tube for a heat exchanger according to claim 1 and fins joined to the tube for a heat exchanger.

Images