WO2004068055A1

WO2004068055A1 - Heat exchanger and process for fabricating same

Info

Publication number: WO2004068055A1
Application number: PCT/JP2004/000712
Authority: WO
Inventors: Yoshinori Nakata
Original assignee: Showa Denko K.K.
Priority date: 2003-01-27
Filing date: 2004-01-27
Publication date: 2004-08-12
Also published as: AU2004207223A1

Abstract

A heat exchanger (1) which comprises a plurality of flat hollow bodies (2) arranged in parallel, and an aluminum fin (3) disposed between each pair of adjacent flat hollow bodies (2) and brazed thereto. The flat hollow body (2) is made from two plates (6) of an aluminum clad material comprising an aluminum core and a cladding of Al-Si brazing material covering at least one outer surface of the core, by brazing peripheral edges of the two plates to each other. The core of the clad material is made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities. A line graph representing variations in potential relative to the depth of a surface layer portion of an outer surface of the flat hollow body (2) from the outermost surface thereof to a depth of 100 νm has a potential gradient of at least 0.25 mV at points on the line of the graph. The heat exchanger can be fabricated easily at a low cost and has satisfactory resistance to pitting corrosion.

Description

DESCRIPTION

HEAT EXCHANGER AND PROCESS FOR FABRICATING SAME

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111 (a) claiming the benefit pursuant to 35 U.S.C. §119 (e) (1) of the filing date of Provisional Application No. 60/449,876 filed February 27, 2003 pursuant to 35 U.S.C. §111 (b) .

TECHNICAL FIELD

The present invention relates to heat exchangers and a process for fabricating the same, and more particularly to heat exchanges for use as condensers or evaporators for motor vehicle air conditioners wherein a chlorofluorocarbon refrigerant is used, gas coolers or evaporators formotor vehicle air conditioners wherein C0₂ refrigerant is used, motor vehicle oil coolers and motor vehicle radiators, and also to a process for producing the exchanger. The term "aluminum" as used herein and in the appended claims includes aluminum alloys in addition to pure aluminum.

Furthermore, the term "potential" as used herein and in the appended claims refers to a potential as measured in a

5 wt. % NaCl aqueous solution having a pH of 3 using a saturated calomel electrode. BACKGROUND ART

Evaporators for use in motor vehicle air conditioners wherein a chlorofluorocarbon refrigerant is used include those of the layered type which are widely known. Such layered evaporators comprise a plurality of flat hollow bodies arranged in parallel and brazed to and communicating with one another each at at least one of upper and lower ends thereof, and a corrugated aluminum fin disposed between each pair of adjacent flat hollow bodies and brazed thereto . The refrigerant flowing into the evaporator through a fluid inlet flows through fluid passage portions of all the flat hollow bodies and is run off through a fluid outlet. The flat hollow body is made from two plates of aluminum brazing sheet which has an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing the peripheral edges of the two plates to each other. Between the two plates, the hollow body has a bulging refrigerant channel (fluid passage portion) and bulging tank portions communicating with the refrigerant channel. The adjacent flat hollow bodies in each pair are brazed to and communicate with each other (see, for example, the publications of JP-A No. 1997-264635 and JP-A No. 2001-324293) . With this evaporator, the two plates of aluminum brazing sheet are brazed to each other for forming each flat hollow body simultaneously with the brazing of the corrugated fin to the hollow body by the vacuum brazing method.

The aluminum brazing sheets already known for use in making the flat hollow body include one comprising a core which is made from an alloy containing at least 0.3 mass % to less than 0.6 mass % of Mn, over 0.6 mass % to up to 1.0 mass % of Cu, less than 0.1 mass % of Si, up to 0.3 mass % of Fe and 0.06 to 0.35 mass % of Ti, and the balance aluminum and inevitable impurities, and a cladding made of an Al-Si alloy brazing material having a limited Ca content of up to 0.006 mass % (see, for example, the publication of JP-A No. 2000-135588) . With the evaporator flat hollow body disclosed in the publications of JP-A No. 1997-264635 and JP-A No. 2001-324293, the surface of the hollow body is conventionally subjected to a chromate treatment so as to give improved corrosion resistance. However, the treatment requires cumbersome work. Furthermore, Cr⁶⁺ is harmful and necessitates a troublesome waste liquid treatment. The evaporator therefore has the problem of being cumbersome to fabricate. Moreover, use of Cr⁶⁺ is to be prohibited in the near future in Europe.

It is also likely that pitting corrosion resistance can not be expected of the flat hollow body made from the aluminum brazing sheet disclosed in the publication of JP-A No.

2000-135588, unless the body is subjected to the chromate treatment.

An object of the present invention is to overcome the above problem and to provide a heat exchanger which has satisfactory resistance to pitting corrosion and which can be fabricated easily at a lost cost, and a process for fabricating the same.

DISCLOSURE OF THE INVENTION The present invention provides a heat exchanger which comprises a plurality of flat hollow bodies arranged in parallel and each having a fluid passage portion, and an aluminum fin disposed between each pair of adjacent flat hollow bodies and brazed thereto and wherein a refrigerant flowing thereinto through a fluid inlet flows through the fluid passage portions of all the flat hollow bodies and is run off through a fluid outlet, each of the flat hollowbodies beingmade froman aluminum clad material having an aluminum core and a cladding of Al-Si alloy brazing material covering at least an outer surface of the core, the core of the clad material being made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities, a line graph representing variations in the potential of a surface layer portion of an outer surface of the flat hollow body from the outermost surface thereof to a depth of 100 μ, m relative to the depth having a potential gradient of at least 0.25 mV at points on the line of the graph. With the heat exchanger of the present invention, each of the flat hollow bodies is made from an aluminum clad material having an aluminum core and a cladding of Al-Si alloy brazing material covering at least the outer surface of the core, and the core of the clad material is made of an alloy containing 0.4 to 1.5mass % of Cu andthebalanceAl and inevitable impurities . A line graph representing variations in the potential of a surface layer portion of the outer surface of the flat hollow body from the outermost surface thereof to a depth of 100 jum relative to the depth has a potential gradient of at least 0.25 mV at points on the line of the graph. Accordingly, the flat hollow body can be prevented from pitting although the body is not subjected to the chromate treatment. Moreover, the heat exchanger can be fabricated by a process including making each flat hollow body from the aluminum clad material described and brazing a fin to each pair of adjacent flat hollow bodies, with a temperature of at least 550° C maintained for the brazing for 5 to 45 minutes, and is therefore easy and inexpensive to fabricate.

With the heat exchanger of the present invention, the flat hollow body may be made from two plates of an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing peripheral edges of the two plates to each other, the flat hollow body having between the two plates a bulging fluid passage portion and a tank portion communicating with the fluid passage portion.

The flat hollow body to be used may comprise an aluminum clad tube which is made from a hollow billet and which has an aluminum core and a cladding of Al-Si alloy brazing material covering at least the outer surface of the core . Alternatively, the flat hollow body may be made by forming a plate of an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core. The flat hollow body is not limited to these examples.

With the heat exchanger of the present invention, the core of the aluminum clad material forming the flat hollow body may further contain 0.4 to 1.5 mass % of Mn. The core of the aluminum clad material forming the flat hollow body may further contain 0.06 to 0.35 mass % of Ti. The core of the aluminum clad material forming the flat hollow body may contain up to 0.4 mass % of Si as an inevitable impurities. The core of the aluminum clad material forming the flat hollow bodymay containup to 0.3mass % of Fe as an inevitable impurities . The core of the aluminum clad material forming the flat hollow bodymaycontainup to 0.4 mass % ofMgas an inevitable impurities . In these cases, the flat hollow body is given further improved resistance to pitting corrosion.

The present invention provides a vehicle having an air conditioner comprising a compressor, a condenser and an evaporator and adapted for use with a chlorofluorocarbon refrigerant, the evaporator comprising the heat exchanger described above.

The present invention provides a process for fabricating a heat exchanger which comprises a plurality of flat hollow bodies arranged in parallel and each having a fluid passage portion, and an aluminum fin disposed between each pair of adjacent flat hollow bodies and brazed thereto and wherein a refrigerant flowing thereinto through a fluid inlet flows through the fluid passage portions of all the flat hollow bodies and is run off through a fluid outlet, the process being characterized in that the process includes making each of the flat hollow bodies from an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering at least an outer surface of the core, the core being made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities, and brazing the fin to the pair of flat hollow bodies by maintaining a temperature of at least 550° C for 5 to 45 minutes.

The heat exchanger described above can be fabricated relatively easily and inexpensively by the process of the invention.

In the heat exchanger fabricatingprocess of the invention, it is desirable that the fin and the pair of flat hollow bodies be quenched to 400° C at a cooling rate of at least 50° C/min after heating for the brazing.

The heat exchange fabricating process of the invention may include making the flat hollow body from two plates of an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing peripheral edges of the two plates to each other, and the plates are brazed for making the flat hollow body simultaneously with the brazing of the fin. The brazing may be effected by vacuum brazing. With the heat exchanger fabricating process of the invention, the core of the aluminum clad material forming the flat hollow body may further contain 0.4 to 1.5 mass % of Mn. The core of the aluminum clad material forming the flat hollow body may further contain 0.06 to 0.35 mass % of Ti. The core of the aluminum clad material forming the flat hollow bodymay containup to 0.4 mass % of Si as an inevitable impurities . The core of the aluminum clad material forming the flat hollow bodymay contain up to 0.3mass % of Fe as an inevitable impurities . The core of the aluminum clad material forming the flat hollow body contains up to 0.4 mass % of Mg as an inevitable impurities .

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view partly exploded and showing a layered evaporator embodying the invention. FIG. 2 is a line graph representing variationβ q- the potential of a surface layer portion of the outer surface of each of flat hollow bodies of the evaporator shown in FIG. 1 from the outermost surface thereof to a depth of 100 μm relative to the depth. FIG. 3 is a graph showing a heating pattern in Examples and Comparative Example.

BEST MODE OF CARRYING OUT THE INVENTION An embodiment of the invention will be described below with reference to the drawings.

FIG. 1 shows a layered evaporator embodying the present invention.

With reference to FIG. 1, the layered evaporator 1 is for use in vehicles, such as motor vehicles equipped with a motor air conditioner (refrigeration cycle) wherein a chlorofluorocarbon refrigerant is used and which has a compressor, condenser and evaporator, the evaporator being adapted for use in the refrigeration cycle. The evaporator 1 comprises a plurality of flat hollow bodies 2 arranged in parallel and brazed to and communicating with one another each at the upper end thereof, and a corrugatedaluminumfin 3 disposed between each pair of adjacent flat hollow bodies 2 and brazed thereto. The refrigerant flowing into the evaporator through a fluid inlet 4 flows through all the flat hollow bodies 2 and is run off through a fluid outlet 5.

The flat hollow body 2 is made from two plates 6 of aluminum brazing sheet (clad material) which has an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing the peripheral edges of the two plates 6 to each other. Between the two plates, the hollow body has a generally U-shaped bulging refrigerant channel 7 (fluid passage portion) and bulging tank portions 8 communicating with respective opposite ends of the refrigerant channel 7. The core of the aluminum brazing sheet making the plates is made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities. FIG. 2 shows a line graph representing variations in the potential of a surface layer portion X of each of the inner and outer surfaces of the flat hollow body 2 from the outermost surface thereof to a depth of 100 m relative to the depth. The line graph has a potential gradient of at least 0.25 mV at points on the line of the graph.

With the core of the aluminum brazing sheet making the plate 6, Cu is an element required to make the potential gradient not smaller than 0.25 mV to thereby give the flat hollow body 2 improved resistance to pitting corrosion. If the Cu content is less than 0.4 mass %, the above potential can not be made at least 0.25 mV, whereas if the content is over 1.5 mass %, the core material itself exhibits impaired corrosion resistance . Accordingly, the Cu content of the core should be 0.4 to 1.5 mass %. Furthermore, the line graph representing variations in the potential of the surface layer portion of the outer surface of the flat hollow body 2 from the outermost surface thereof to a depth of 100 μ relative to the depth should have a potential gradient not smaller than 0.25 mV at points on the line of the graph because if the potential gradient is less than 0.25 mV, satisfactory resistance to pitting corrosion is not available. Preferably, the potential gradient is at least 0.30 mV. The core of the aluminum brazing sheet making the plate 6 may further contain 0.4 to 1.5 mass % of Mn. The presence of Mn in the core affords f rther improved resistance to pitting corrosion, whereas if the content is less than 0.4 mass %, satisfactory pitting corrosion resistance is not available. When the content is in excess of 1.5 mass %, the core exhibits an excessive strength to entail the likelihood that the clad material will not be formed into the hollow body smoothly. When the core contains Mn, it is therefore desirable that the content thereof be 0.4 to 1.5 mass %. The core of the aluminum brazing sheet making the plate 6 may further contain 0.06 to 0.35 mass % of Ti. The presence of Ti in the core produces a stratifying effect to give further improved pitting corrosion resistance, whereas if the content is less than 0.06 mass %, it is impossible to produce improved resistance to pitting corrosion. If the Mn content is in excess of 0.35 mass %, the material is difficult to produce. Accordingly, whenpresent in the core, Ti is containedpreferably in an amount of 0.06 to 0.35 mass %.

The amount of Si to be present as an inevitable impurity in the core of the aluminum brazing sheet making the plate 6 is preferably up to 0.4 mass % because if the Si content is in excess of 0.4 mass %, impaired resistance to pitting corrosion is likely to result. The amount of Fe to be present as an inevitable impurity in the core of the aluminum brazing sheet making the plate

6 is preferably up to 0.3 mass % because if the Fe content is in excess of 0.3 mass %, impaired resistance to pitting corrosion is likely to result.

The amount of Mg to be present as an inevitable impurity in the core of the aluminum brazing sheet making the plate 6 is preferably up to 0.4 mass % because if the Mg content is in excess of 0.4 mass %, impaired resistance to pitting corrosion is likely to result.

The layered evaporator 1 is fabricated in the following manner .

A plurality of plates 6 of the aluminum brazing sheet described above are prepared, and combinations of plates 6 each comprising two plates 6 are arranged in parallel, with a corrugated fin 3 disposed between each pair of adjacent combinations. The resulting arrangement is heated to braze the two plates 6 of each combination to each other, form a flat hollow body, braze the upper end portions of each pair of adjacent flat hollow bodies to each other and braze the corrugated fin 3 to the adjacent flat follow bodies 2. For the brazing, the arrangement is held heated at a temperature of at least 550° C for 5 to 45 minutes. The heating temperature for brazing is limited to a temperature of at least 550° C because we have found that the period of time during which the arrangement is held heated at the temperature of at least 550° C exerts a great influence on the potential gradient of the points on the line graph representing variations in the potential of the surface layer portion of the outer surface of the brazed flat hollow body 2 from the outermost surface thereof to a depth of 100 μm relative to the depth. The upper limit of the heating temperature is about 600° C. Further the period of time for holding the temperature of at least 550° C for brazing is limited to 5 to 45 minutes because if the period is less than 5 minutes, the arrangement is difficult to braze, whereas if the period is in excess of 45 minutes, it is impossible to make the potential gradient not smaller than 0.25 mV after brazing and to obtain satisfactory resistance to pitting corrosion. Preferably, the heating time is 15 to 30 minutes.

It is desirable that the assembly resulting from brazing by heating be quenched to 400° C at a cooling rate of at least 50° C/min because if the cooling rate is lower than 50° C/min, the brazing operation is likely to result in impaired resistance to pitting corrosion. Preferably, the cooling rate is at least 100° C/min.

In this way, the layered evaporator 1 is fabricated. The layered evaporator 1 thus embodied provides a refrigeration cycle wherein a chlorofluorocarbon refrigerant is used, along with a compressor and a condenser, for use as a vehicle air conditioner in a vehicle, e.g., in a motor vehicle. Alternatively, the heat exchanger obtained is used as the condenser of the refrigeration cycle. Further alternatively, the heat exchanger is installed in a motor vehicle as an oil cooler or a radiator.

The heat exchanger of the invention may be installed in vehicles, such as motor vehicles, equipped with an air conditioner which has a compressor, gas cooler, intermediate heat exchanger, expansion valve and evaporator and wherein a C0₂ refrigerant is used, for use as the gas cooler or evaporator of the air conditioner.

According to the foregoing embodiment, the flat hollow body 2 is made from two plates 6 of the brazing sheet described above by brazing the plates to each other, whereas the material for making the hollow body is not limited only to the sheet. The flat hollow body may comprise an aluminum clad tube having a core in the form of a flat tube made from an alloy containing 0.4 to 1.5 mass % of Cu, and the balance Al and' inevitable impurities, and a cladding of Al-Si alloy brazing material covering at least the outer peripheral surface of the core having inner and outer peripheral surfaces. This clad tube may be made by forming the brazing sheet into a flat tube and brazing opposite edge portions of the tube to each other. Alternatively, the clad tube may be formed by extruding a hollow billet which comprises a hollow body provided by the above core and having a cast Al-Si alloy brazing material at least around the outer of the inner and outer peripheral surfaces of the hollow body. The clad tube may be formed f om an extruded tube containing 0.4 to 1.5 mass % of Cu, and the balance Al and inevitable impurities, by immersing the tube in a molten Al-Si alloy brazing material to thereby cover at least the outer of the inner and outer peripheral surfaces of the tube with the brazing material. Furthermore, the flat hollow body is not limited to these examples. The present invention will be described below in detail with reference to Examples and Comparative Example. Examples 1-11 and Comparative Example 1

Rectangular aluminum brazing sheets were prepared which comprise a core made from one of the four kinds of alloys shown in Table 1 and having a thickness of 0.4 mm, and cladding of JIS A4004 covering each of opposite surfaces of the core. Each sheet had a cladding ratio of 15%. A recessed portion is formed by press work in the entire portion of each aluminum brazing sheet except at a peripheral edge portion thereof. [Table 1]

Subsequently two aluminum brazing sheets of the same kind were fitted together in combination, with the recessed portions facing toward each other andthe peripheral edge portions thereof in contact with each other. The combination was heated to 550° C in a vacuum heating furnace, thereafter further heated to 600° C, and quenched to 400° C at a cooling rate of at least 100° C/min, whereby the two sheets were brazed to each other to obtain a flat hollow body. The same procedure as above was repeated by holding combinations of sheets heated at a temperature of at least 550° C for brazing for varying periods of time T .

A line graph was determined which represented variations in the potential of surface layer portions of the inner and outer surfaces of each flat hollow body, each from the outermost surface to a depth of 100 μm, relative to the depth. The line graphs had a potential gradient of at least 0.25 mV at points on the line of each graph in Examples 1 to 11, whereas the graph of Comparative Example 1 had a potential gradient of less than 0.25 mV at points on the line of the graph. Table 2 shows the average of the potential gradients at the points on each of the lines for Examples 1 to 11 and Comparative Example 1.

The flat hollow bodies were further subjected to a SWAAT 960-hr test and checked for the resulting corrosion. Table 2 shows the maximum corrosion depth in each of the flat hollow bodies tested.

[Table 2 ]

INDUSTRIAL APPLICABILITY

The heat exchanger of the present invention is suitable for use as the evaporator or condenser of motor vehicle air conditioners adapted, for example, for use with a chlorofluorocarbon refrigerant .

Claims

CLAIMS 1. A heat exchanger which comprises a plurality of flat hollow bodies arranged in parallel and each having a fluid passage portion, and an aluminum fin disposed between each pair of adjacent flat hollow bodies and brazed thereto and wherein a refrigerant flowing thereinto through a fluid inlet flows through the fluid passage portions of all the flat hollow bodies and is run off through a fluid outlet, each of the flat hollow bodies being made from an aluminum clad material having an aluminum core and a cladding of Al-Si alloy brazing material covering at least an outer surface of the core, the core of the clad material being made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities, a line graph representing variations in potential relative to the depth of a surface layer portion of an outer surface of the flat hollow body from the outermost surface thereof to a depth of 100 μm having a potential gradient of at least 0.25 mV at points on the line of the graph.

2. A heat exchanger according to claim 1 wherein the flat hollow body is made from two plates of an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing peripheral edges of the two plates to each other, the flat hollow body having between the two plates a bulging fluid passage portion and a tank portion communicating with the fluid passage portion.

3. A heat exchanger according to claim 1 wherein the core of the aluminum clad material forming the flat hollow body further contains 0.4 to 1.5 mass % of Mn.

4. A heat exchanger according to claim 1 wherein the core of the aluminum clad material forming the flat hollow body further contains 0.06 to 0.35 mass % of Ti.

5. A heat exchanger according to claim 1 wherein the core of the aluminum clad material forming the flat hollow body contains up to 0.4 mass % of Si as an inevitable impurities.

6. A heat exchanger according to claim 1 wherein the core of the aluminum clad material forming the flat hollow body contains up to 0.3 mass % of Fe as an inevitable impurities.

7. A heat exchanger according to claim 1 wherein the core of the aluminum clad material forming the flat hollow body contains up to 0.4 mass % of Mg as an inevitable impurities.

8. A vehicle having an air conditioner comprising a compressor, a condenser and an evaporator and adapted for use with a chlorofluorocarbon refrigerant, the evaporator comprising a heat exchanger according to any one of claims 1 to 7.

9. A process for fabricating a heat exchanger which comprises a plurality of flat hollow bodies arranged in parallel and each having a fluid passage portion, and an aluminum fin disposed between each pair of adjacent flat hollow bodies and brazed thereto and wherein a refrigerant flowing thereinto through a fluid inlet flows through the fluid passage portions of all the flat hollow bodies and is run off through a fluid outlet, the process being characterized in that the process includes making each of the flat hollow bodies from an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering at least an outer surface of the core, the core being made of an alloy containing 0.4 to 1.5 mass % of Cu and the balance Al and inevitable impurities, and brazing the fin to the pair of flat hollow bodies by maintaining a temperature of at least 550° C for 5 to 45 minutes.

10. A process for fabricating a heat exchanger according to claim 9 wherein the fin and the pair of flat hollow bodies are quenched to 400° C at a cooling rate of at least 50° C/min after heating for the brazing.

11. A process for fabricating a heat exchanger according to claim 9 which includes making the flat hollow body from two plates of an aluminum clad material having an aluminum core and a cladding of Al-Si brazing material covering opposite surfaces of the core, by brazing peripheral edges of the two plates to each other, and the plates are brazed for making the flat hollow body simultaneously with the brazing of the fin.

12. A process for fabricating a heat exchanger according to claim 9 wherein the brazing is effected by vacuum brazing.

13. A process for fabricating a heat exchanger according to claim 9 wherein the core of the aluminum clad material forming the flat hollow body further contains 0.4 to 1.5 mass % of Mn.

14. A process for fabricating a heat exchanger according to claim 9 wherein the core of the aluminum clad material forming the flat hollow body further contains 0.06 to 0.35 mass % of Ti .

15. A process for fabricating a heat exchanger according to claim 9 wherein the core of the aluminum cladmaterial forming the flat hollow body contains up to 0.4 mass % of Si as an inevitable impurities.

16. A process for fabricating a heat exchanger according to claim 9 wherein the core of the aluminum clad material forming the flat hollow body contains up to 0.3 mass % of Fe as an inevitable impurities.

17. A process for fabricating a heat exchanger according to claim 9 wherein the core of the aluminum cladmaterial forming the flat hollow body contains up to 0.4 mass % of Mg as an inevitable impurities .