JP2011080121A - Extruded tube for fin tube type heat exchanger for air conditioner and refrigerant piping for heat exchange cycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extruded tube made of an aluminum alloy which has excellent strength and corrosion resistance as the tube of a heat exchanger for an air conditioner, and to provide refrigerant piping for a heat exchanger cycle having excellent strength and corrosion resistance. <P>SOLUTION: The extruded tube for a fin tube type heat exchanger for an air conditioner or refrigerant piping for a heat exchange cycle is composed of an aluminum alloy having a composition containing 0.01 to 1.2 mass% Fe, 0.01 to 1.5 mass% Mn, 0.01 to 0.3 mass% Cr and &le;0.2 mass% Si, and the balance Al with inevitable impurities. In this invention, it is preferable that the content of Cu is controlled to &le;0.05 mass%, the content of Na is controlled to &le;10 mass% and also the content of Zn is controlled to 0.1 to 1.0 mass%. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  TECHNICAL FIELD The present invention relates to a heat transfer tube incorporated in a heat exchanger, and in particular, an extruded tube for a fin tube type air conditioner heat exchanger made of aluminum alloy having excellent strength and corrosion resistance, and heat exchange suitable for being incorporated in a heat exchange cycle for an air conditioner. The present invention relates to a refrigerant pipe for a cycle.

  In recent years, air conditioners for home use and business use have been remarkably widespread, and have become indispensable for realizing comfort in daily life. The air conditioner employs a heat exchange cycle that connects the compressor, condenser, expansion valve, and evaporator with refrigerant piping and circulates the refrigerant to each device. The refrigerant is vaporized by the heat exchanger such as the condenser and evaporator. And by repeating the liquefaction, the surrounding heat is taken away by the heat of vaporization and the room is cooled.

  In these heat exchangers, pipes made of copper or copper alloy with excellent thermal conductivity and workability are used as tubes through which the refrigerant passes, and multiple thin fins made of aluminum alloy are placed in parallel around the copper pipe. An arranged fin tube type heat exchanger is used (for example, Patent Document 1). Based on FIG. 1, FIG. 2, the schematic structure of a fin tube type heat exchanger is demonstrated.

  Fig.1 (a) is a side view which shows the structure of a fin tube type heat exchanger, FIG.1 (b) is the perspective view which looked at the fin tube type heat exchanger shown in Fig.1 (a) from the hairpin tube side. is there. Fig.2 (a) is the perspective view which looked at the fin tube type heat exchanger from the U bend pipe side, FIG.2 (b) is a partially expanded view of Fig.2 (a).

  The finned tube heat exchanger shown in FIG. 1A is manufactured as follows. A heat transfer tube (tube) made of copper or a copper alloy is bent into a hairpin shape at the center to produce a U-shaped hairpin tube 2, which is made of aluminum or aluminum alloy arranged in parallel at a predetermined interval. After the hairpin tube 2 is inserted through the fin material 1, both are brought into close contact with each other and expanded by expansion. Next, a plurality of hairpin tubes 2 are formed by fitting a U-bend tube 3 that has been previously bent to the tube ends of adjacent hairpin tubes 2 and brazing the hairpin tube 2 and the U-bend tube 3 together. The U bend pipe 3 is connected.

  As the tubes constituting the hairpin tube 2 and the U-bend tube 3, copper tubes that are excellent in thermal conductivity, corrosion resistance, workability, strength, etc. are widely used. In addition, as the fin material 1, aluminum or an aluminum alloy is widely used from the viewpoint of being excellent in lightness, workability, and thermal conductivity. The fin material 1 is made thinner and higher in strength, and surface treatment is performed to improve the hydrophilicity and corrosion resistance of the surface.

  However, in recent years, heat exchangers are required to be designed not only with high performance and high functionality, but also with consideration for environmental aspects such as low resources, low energy, and low space. Furthermore, as the price of copper soars, the demand for cost reduction through the use of inexpensive members is also increasing. Therefore, in the future, in addition to higher performance and higher quality, further cost reduction, lighter weight, and improved recyclability are indispensable for heat exchangers.

  To improve the performance of heat exchangers for air conditioners, and to reduce the cost and weight, and to obtain a heat exchanger that combines recyclability, the tube must be made of an aluminum alloy that is lighter and cheaper than copper. Becomes effective.

JP 2002-147981 A

However, since aluminum has a lower material strength than copper, there is a problem that local deformation occurs during hairpin processing or tube expansion, and molding defects or cracks are likely to occur. In addition, the tube is required to have high strength in order to ensure structural strength and durability as a heat exchanger. Furthermore, since the hairpin tube 2 and the U-bend tube 3 are joined by brazing, an alloy capable of brazing must be selected.
Moreover, since aluminum has inferior corrosion resistance compared to copper, it is also necessary to select an alloy having excellent corrosion resistance. Regarding the corrosion resistance, when an aluminum alloy extruded tube is manufactured by hot extrusion, there is a problem that a linear mark generally called a weld line is generated, and this weld line is preferentially corroded. The weld line indicates a portion where two or more softened metal flows merge in the mold when the softened metal is pressed into the mold.

  Furthermore, in the heat exchange cycle, the refrigerant piping that connects the heat exchanger to the compressor, expansion valve, and other equipment is also used in the same environment as the tube, so the same strength, corrosion resistance, and brazing properties as the tube are required. It has been.

  The present invention has been made in view of the above circumstances, and provides an extruded tube made of an aluminum alloy having excellent strength and corrosion resistance as a tube of a heat exchanger for an air conditioner and excellent in brazing and a refrigerant pipe for a heat exchange cycle. The purpose is that.

  At the time of manufacturing the heat exchanger, the tube is expanded by inserting a tube expansion rod that is slightly larger than the tube inner diameter into the tube, passing it through, and then expanding it from the inside to eliminate the gap between the fins. However, if the tube strength is too low, aluminum adheres to the tube expansion rod, and the pressure at the time of insertion increases remarkably, and it becomes necessary to remove the aluminum piece each time after tube expansion, which causes a decrease in productivity. . Also, if the tube strength is too high and the elongation is low, local deformation such as thinning occurs in part during tube expansion, causing cracking. Furthermore, the occurrence of cracks and thinning during molding is also a problem in the bent portion of the hairpin processing and the flared portion that becomes the joint portion with the U-bend tube.

As described above, the air conditioner tube needs to optimize the aluminum alloy components constituting the tube in order to improve formability and tube expansion. In addition, it is necessary to improve workability by optimizing mechanical properties and tempering.
Further, in order to ensure the structural strength as a heat exchanger and the durability strength when used as a heat exchanger, it is necessary to improve the strength as an aluminum alloy constituting the tube. Although it is possible to ensure strength by increasing the wall thickness, an alloy having as high a strength as possible is required because tube expandability and formability deteriorate. Since general pure aluminum has insufficient strength, it is necessary to improve the strength of an aluminum alloy containing an additive element.

  Therefore, the present inventors examined the addition of various elements such as Fe, Mn, and Si as additive elements that enhance strength and corrosion resistance. As a result, Fe and Mn are effective in improving strength and corrosion resistance, Si, which is known as an element effective in improving corrosion resistance, deteriorates brazeability and is preferably regulated. It was found that Cr is effective.

Therefore, the present invention is Fe: 0.01-1.2 mass%, Mn: 0.01-1.5 mass%, Cr: 0.01-0.3 mass%, Si: 0.2 mass% or less An extruded tube for a finned tube air conditioner heat exchanger, the balance of which is made of an aluminum alloy having a composition comprising Al and inevitable impurities.
In the extruded tube for a fin tube type air conditioner heat exchanger of the present invention, the Cu content in the aluminum alloy is preferably 0.05 mass% or less, and the Na content is preferably 10 mass ppm or less. Moreover, it is preferable that the extrusion tube for fin tube type air conditioner heat exchangers of the present invention contains Zn: 0.1 to 1.0% by mass. The inclusion of Zn is effective in improving the corrosion resistance.

The composition of the aluminum alloy suitable for the extruded tube for the fin tube type air conditioner heat exchanger of the present invention is also suitable for the refrigerant piping for the heat exchange cycle.
Therefore, the present invention is Fe: 0.01-1.2 mass%, Mn: 0.01-1.5 mass%, Cr: 0.01-0.3 mass%, Si: 0.2 mass% or less A refrigerant pipe for a heat exchange cycle, characterized in that the balance is made of an aluminum alloy having a composition consisting of Al and inevitable impurities.
In the refrigerant pipe for heat exchange cycle of the present invention, the Cu content in the aluminum alloy is 0.05 mass% or less, the Na content is 10 mass ppm or less, and Zn is 0.1 to 0.1 mass%. It is preferable to contain 1.0 mass%.

  The extruded tube for the fin tube type air conditioner heat exchanger and the refrigerant piping for the heat exchange cycle of the present invention have excellent strength, corrosion resistance and brazing properties, and the use of this tube and this piping reduces the member cost. And weight reduction. Moreover, since it is possible to produce a heat exchanger with the same production equipment as the current copper pipe, there is no need for new equipment investment, and there is a remarkable industrial effect.

(A) is a side view which shows the structure of a fin tube type heat exchanger, (b) is the perspective view which looked at the fin tube type heat exchanger shown to Fig.1 (a) from the hairpin tube side. (A) is the perspective view which looked at the fin tube type heat exchanger from the U bend pipe side, (b) is the partially expanded view of (a). It is a refrigerant circuit diagram which shows the structure of a heat exchange cycle.

  The present invention relates to an aluminum alloy that constitutes an extruded tube for a fin tube type air conditioner heat exchanger (hereinafter sometimes simply referred to as a tube) and a refrigerant pipe for a heat exchange cycle (hereinafter sometimes simply referred to as a pipe). The composition has characteristics, and the reasons for limiting the composition defined in the present invention will be described below.

<Fe: 0.01 to 1.2% by mass>
Fe improves strength by generating Al-Fe-based or Al-Fe-Mn-based intermetallic compounds and refining the structure. Moreover, precipitation of Si is promoted, the melting point is increased, and extrudability and brazing properties are improved. Furthermore, precipitation of Mn is promoted and the extrudability is improved. Furthermore, since Fe-based crystallized substances are finely present in the material, they become a source of pitting corrosion and have an effect of suppressing the occurrence of deep pitting corrosion. In order to acquire these effects, this invention contains 0.01 mass% or more of Fe. However, when the content is increased, an excessive amount of Al-Fe intermetallic compound is formed, the corrosion resistance is reduced due to the excessive distribution of the cathode, and the bending workability and flare workability due to the formation of the Al-Mn-Fe giant intermetallic compound are reduced. Since it causes a decrease, the Fe content is set to 1.2 mass% or less. The content of Fe is preferably 0.5 to 1.0% by mass.

<Mn: 0.01 to 1.5% by mass>
Mn is dissolved in the aluminum matrix or precipitated as an Al—Mn intermetallic compound depending on the amount added, and improves the strength. Moreover, precipitation of Si is promoted to increase the melting point. Further, since the deformation resistance at high temperature is increased, it has the effect of improving the brazing property. Further, addition of Mn causes AlFe-based intermetallic compounds to precipitate as Al—Fe—Mn-based intermetallic compounds, thereby suppressing a decrease in corrosion resistance.

  In order to obtain these effects, the present invention contains 0.01% by mass or more of Mn. However, when the content increases, a large number of coarse Al—Mn intermetallic compounds are produced, and the extrudability is remarkably lowered. Moreover, if the content is increased, the tube expandability is lowered. Therefore, the present invention sets the Mn content to 1.5 mass% or less. A preferable Mn content is 0.8 to 1.4% by mass.

<Cr: 0.01 to 0.3% by mass>
Cr has the effect of increasing the melting point of the alloy to improve brazing properties and improving deformation resistance at high temperatures, and contributes to securing rigidity during brazing.
However, when the Cr content is less than 0.01% by mass, the effect of increasing the melting point and improving the brazing property is insufficient. On the other hand, when it contains exceeding 0.3 mass%, extrudability will fall. Therefore, the Cr content is set to 0.01 to 0.3% by mass. The preferable Cr content is 0.1 to 0.2% by mass.

<Si: 0.2 mass% or less>
Si is an element that dissolves in an aluminum matrix and improves strength and corrosion resistance, but lowers the melting point, and thus lowers extrudability and brazing. In the present invention, Cr is added as described above in order to improve the brazing property by increasing the melting point, but in order to sufficiently obtain the effect of improving the brazing property by Cr, an element that lowers the melting point of the alloy. It is necessary to regulate the Si content. Therefore, in the present invention, the Si content is 0.2 mass% or less. The preferable content of Si is 0.15% by mass or less, and the more preferable content is 0.1% by mass or less.

<Cu: 0.05% by mass or less>
As the content of Cu increases, the corrosion rate of the tube increases and the corrosion resistance decreases. Therefore, the present invention preferably regulates the Cu content as low as 0.05% by mass or less. A more preferable Cu content is 0.02 mass% or less.

<Zn: 0.1 to 1.0% by mass>
Zn is an effective element for improving corrosion resistance. However, if the content is less than 0.1% by mass, the effect of improving corrosion resistance is insufficient. On the other hand, when it contains exceeding 1.0 mass%, corrosion resistance will deteriorate. Therefore, when Zn which is an arbitrary element is contained, Zn: 0.1 to 1.0% by mass is preferable, and Zn: 0.1 to 0.7% by mass is more preferable.

<Na: 10 mass ppm or less>
When Na exceeds 10 ppm by mass, the high-temperature workability decreases, and cracks occur during hot extrusion. Therefore, Na is preferably 10 ppm by mass or less.

  In addition to the above elements, the tubes and pipes of the present invention are each added with 0.3 mass% or less of Zr, Ti, V, Sr, Bi as trace addition elements in order to improve strength, formability, and corrosion resistance. You can also

  The aluminum alloy constituting the tube and piping of the present invention can have a melting point of 640 ° C. or higher by adjusting the content of each element so as to be within the composition range of the present invention. When the melting point is lower than 640 ° C., the brazing property is lowered. Therefore, the melting point is preferably 640 ° C. or higher.

  The manufacturing method of the tube and piping of this invention should just follow a conventional method. That is, the aluminum alloy billet is manufactured by a semi-continuous casting method and hot extrusion is performed. In order to improve the extrudability, it is preferable to perform a homogenization treatment of the billet. In addition, it can be considered that the process of heating a billet before hot extrusion serves as a homogenization process.

  The tube of the present invention does not affect the corrosion resistance in any shape. Specifically, a tube having a groove on the inner surface is usually used for improving heat exchange performance, but the inner surface shape is not limited. The outer diameter (diameter) of the tube is appropriately selected from the range of 5 to 12 mm. In order to increase the corrosion resistance of the tube, the present invention allows the surface of the tube outer surface to be subjected to a surface treatment such as a Zn diffusion layer.

<Heat exchanger>
The heat exchanger for an air conditioner using the tube of the present invention is manufactured in substantially the same process as when a copper tube is used as the tube.
That is, a U-shaped hairpin tube 2 is produced by bending the tube into a hairpin shape at the center, and the hairpin tube 2 is attached to the fin material 1 made of aluminum or aluminum alloy arranged in parallel at a predetermined interval. Insert. After that, the two are closely fixed by expanding the tube, and an aluminum alloy U-bend tube 3 that has been previously bent is fitted to the tube end of the adjacent hairpin tube 2, and the hairpin tube 2 and the U-bend tube 3 are connected to each other. A plurality of hairpin tubes 2 are connected to the U-bend tube 3 by brazing using an aluminum alloy brazing material to form a heat exchanger. The brazing is preferably a torch brazing.

<Heat exchange cycle>
The tube and piping of the present invention are used as an extruded tube for heat exchanger and refrigerant piping in a heat exchange cycle. The outline of the cooling process in the heat exchange cycle will be described with reference to FIG.

  FIG. 3 is a refrigerant circuit diagram showing the configuration of the heat exchange cycle. In the refrigerant circuit 10 shown in FIG. 3, the refrigerant compressed by the compressor 11 is discharged to the refrigerant pipe 12a in a gas-liquid mixed phase state, and flows into the condenser 13 through the refrigerant pipe 12a. The refrigerant that has passed through the tube (not shown) of the condenser 13 while radiating heat and has been liquefied flows into the expansion valve 14 via the refrigerant pipe 12b. The refrigerant flowing into the expansion valve 14 is injected from a minute nozzle hole of the expansion valve 14 and flows into a tube (not shown) of the evaporator 15 through the refrigerant pipe 12c, and absorbs heat from the room air to evaporate (vaporize). To do. As a result, the room air is cooled. The refrigerant evaporated in the evaporator 15 flows into the compressor 11 through the refrigerant pipe 12d, is compressed in the compressor 11, and becomes a gas-liquid mixed phase state again. In the case of heating, the refrigerant flows in the opposite direction.

  As described above, the heat exchange cycle is formed by circulating the refrigerant through a refrigerant pipe through a heat exchanger such as a condenser and an evaporator, and a device such as a compressor and an expansion valve. The tube of the present invention is suitable for heat exchangers such as a condenser and an evaporator because it has excellent strength and corrosion resistance and is excellent in brazing. Moreover, the aluminum alloy which has the composition range of this invention which has a suitable performance as a tube for heat exchangers is suitable also for refrigerant | coolant piping used in the environment similar to a tube.

  In the heat exchange cycle, it is preferable to combine the heat exchanger provided with the tube of the present invention as a heat exchanger such as a condenser and an evaporator, and the pipe of the present invention, but the heat exchanger using other than the tube of the present invention And the pipe of the present invention may be combined, or a heat exchanger provided with the tube of the present invention and a pipe other than the present invention may be combined.

Using billets prepared using aluminum alloys having the compositions shown in Tables 1 and 2 (the balances in Tables 1 and 2 are Al and inevitable impurities), in accordance with conventional methods, after homogenization treatment, hot extrusion is performed, and the outer diameter A round tube (tube) having a diameter of 7 mm, an inner diameter of 6 mm, and a thickness of 0.5 mm was produced.
After hot extrusion, the tube surface was observed for roughness, and the extrudability was evaluated according to the following criteria.
Extrudability: No roughness; ○ Minor roughness; △ Extreme roughness; ×

Using hot-extruded tubes, hairpin bending, tube expansion test, flare processing for joining with U-bend, and brazing with a torch, tube shape change and occurrence of cracks Evaluation was performed. Moreover, the corrosion resistance of the tube was evaluated. The results are shown in Tables 3 and 4. The conditions for hairpin bending, tube expansion test and flare processing, and the criteria for each evaluation are as follows.
Further, the melting point was measured, and the results are shown in Tables 3 and 4.

Hairpin bending: Hairpin bending (curvature radius 8mm) is performed using the above-mentioned aluminum tube pipe bender with the same manufacturing method as copper tube.
Normal; ○ Surface roughness; △ Crack generation; ×
Tube expansion test: Tube expansion was performed by changing the size of the expansion rod so that the expansion rate (change in tube outer diameter) was constant at 5%.
Expanded tube load 40N or more; x (seizure occurrence) Expanded tube load less than 40N;
Flare processing: Processed with a flare processing dimension of 9 mm and observed whether cracks occurred in the U-bend tube insertion part
Normal; ○ Partially cracked; △ All cracked; ×
Torch brazing: brazing a brazing material composition containing Al-Si alloy powder with a torch and observing the joining condition of the brazing material
Normal: ○ The tube is deformed or melted and cannot be joined; ×
Tube corrosion resistance: 20 days exposure with SWATT (ASTM G85 standard)
Pitting corrosion less than 1/4 of the wall thickness; ◎ Pitting corrosion less than 1/4 or less than 1/2 the wall thickness;
Pitting corrosion of 1/2 or more of wall thickness; Δ Generation of through holes; ×
Melting point: 640 ° C. or higher; ○ <640 ° C .; ×

Next, using the prepared hairpin tube, a heat exchanger was manufactured by combining with a fin material made of JIS 1050 alloy and having a plate thickness of 0.1 mm, a pressure resistance test was performed, and a breaking pressure was evaluated. The evaluation criteria are as follows. The results are shown in Tables 3 and 4.
Breaking pressure: less than 12 MPa; x 12 to less than 14 MPa; Δ 14 MPa or more;

From Tables 3 and 4, the following was found.
When Fe, Mn, Cr, and Si are included within the scope of the present invention, the fracture pressure, extrudability, tube formability, corrosion resistance, and torch brazing properties during the pressure test are excellent.
On the other hand, if Fe is less than the range of the present invention, tube formability (hairpin bending, flare processing) and fracture pressure are inferior. If Fe is more than the range of the present invention, tube formability (hairpin bending, tube expansion). Flare processing) and corrosion resistance are inferior.

When Mn is not included or Mn is included but is less than the range of the present invention, the fracture pressure is inferior. When there is more Mn than the range of this invention, extrudability and tube moldability (tube pipe expandability) will be inferior.
When Cr is not included or when Cr is included but less than the range of the present invention, the torch brazing property is inferior, and when Cr is more than the range of the present invention, the extrudability is inferior.
When there is more Si than the range of this invention, melting | fusing point will fall and torch brazing property will be inferior.
Moreover, when there is more Cu than the range of this invention, extrudability and corrosion resistance are a little inferior, and when there is more Na than the range of this invention, extrudability is a little inferior.

Furthermore, Zn is effective in improving the corrosion resistance, but when the content exceeds 1.0 mass% and becomes 1.2 mass%, the corrosion resistance is slightly inferior.
Furthermore, when the melting point is less than 640 ° C., the torch brazing property is inferior.

DESCRIPTION OF SYMBOLS 1 ... Fin material, 2 ... Hairpin pipe, 3 ... U bend pipe 10 ... Refrigerant circuit, 11 ... Compressor, 12a, 12b, 12c, 12d ... Refrigerant piping, 13 ... Condenser, 14 ... Expansion valve, 15 ... Evaporator

Claims (5)

  Fe: 0.01-1.2 mass%, Mn: 0.01-1.5 mass%, Cr: 0.01-0.3 mass%, Si: 0.2 mass% or less, the balance being Al and inevitable An extruded tube for a fin tube type air conditioner heat exchanger, characterized in that it is made of an aluminum alloy having a composition comprising impurities.   The extruded tube for a finned tube air conditioner heat exchanger according to claim 1, wherein the content of Cu in the aluminum alloy is 0.05% by mass or less.   The extruded tube for a finned-tube air conditioner heat exchanger according to claim 1 or 2, wherein the content of Na in the aluminum alloy is 10 mass ppm or less.   The extruded tube for a finned-tube air conditioner heat exchanger according to any one of claims 1 to 3, wherein the aluminum alloy contains Zn: 0.1 to 1.0 mass%.   A refrigerant pipe for a heat exchange cycle, comprising an aluminum alloy having the composition according to any one of claims 1 to 4.

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