CA1221280A - Method for manufacture of heat exchanger with aluminum material - Google Patents
Method for manufacture of heat exchanger with aluminum materialInfo
- Publication number
- CA1221280A CA1221280A CA000464338A CA464338A CA1221280A CA 1221280 A CA1221280 A CA 1221280A CA 000464338 A CA000464338 A CA 000464338A CA 464338 A CA464338 A CA 464338A CA 1221280 A CA1221280 A CA 1221280A
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- Prior art keywords
- aluminum material
- heat exchanger
- zinc
- tube
- liquid passing
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A method for the manufacture of a heat exchanger with aluminum material, characterized by the steps of causing precipitation of 0.5 to 20 g/m2 of zinc on the surface of at least the liquid passing tube or members making up said liquid passing tube, of a heat exchanger fabricated of aluminum material, then applying to the surface flux formed of a mixture of potassium tetrafluoro-aluminate with potassium hexafluoroaluminate, and brazing said heat exchanger by the use of brazing filler of an aluminumsilicon alloy having a lower melting point than said aluminum material at a temperature of about 580° to about 620°C.
A method for the manufacture of a heat exchanger with aluminum material, characterized by the steps of causing precipitation of 0.5 to 20 g/m2 of zinc on the surface of at least the liquid passing tube or members making up said liquid passing tube, of a heat exchanger fabricated of aluminum material, then applying to the surface flux formed of a mixture of potassium tetrafluoro-aluminate with potassium hexafluoroaluminate, and brazing said heat exchanger by the use of brazing filler of an aluminumsilicon alloy having a lower melting point than said aluminum material at a temperature of about 580° to about 620°C.
Description
1~:2~
METHOD FOR MANUFACTURE OF HEAT EXCHAN OER
WITH ALUMINUM M~TERIAL
FIELD OF INVENTION AND PRIOR ART
This invention relates to a method for the manufacture of a heat exchanger with aluminum material.
More particularly, this invention relates to a method for the manufacture of a heat exchanger with aluminum material excellent in resestance to corrosion.
Recently, heat exchangers such as radiators for automobiles, evaporators for car coolers and condensers for car coolers have been advancing toward preponderant use of aluminum material for reduction in weight. The condenser for a car cooler, for example, is manufactured by fabricat-ing both the tube and the heat transfer fins with aluminum material clad with brazing filler or fabricating one of them with aluminum material clad with brazing filler and the other simply with aluminum material, tying the fabricated components as with jigs, and brazing them with a corrosive flux in an oven.
Heretofore, in the manufacture of a heat exchanger with aluminum material by the brazing process with a flux, it has been customary for the component parts fabricated of aluminum material to be coated with flux consisting of an alkaline earth metal salt containing zinc chloride and an alkali metal salt and then brazed by the use of a brazing filler of Al-Si alloy (Si content 5 to 12%) at a temperature below the melting point of aluminum material (about 580 to 6~0 C). By the brazing, the component parts are joined and, at the same time, the zinc is precipitated to the surface of '~ ~
~2;~8~
the aluminum material (3ZnC12 + 2Al > 3Zn + 2AlC13) and diffused toward the center of the aluminum material because of the heat of brazing. The zinc-diffused layer exhibits the effect of a sacrificial anode, which goes to improve the resistance of brazed heat exchanger to corrosion.
When this process is adopted, however, since the flux to be used possesses high hygroscopicity, the brazed heat exchanger must be immediately washed with hot water, pickled with nitric acid, washed with cold water, etc. to a sufficient extent. These treatments add greatly to the complexity of process. The zinc chloride contained in the flux is utilized for incorporating the zinc-diffused layer in the aluminum material. In any structure of the heat exchanger's complexity, it is difficult to apply this flux uniformly on its entire surface. Thus, the amount of zinc diffused in the aluminum material is heavily dispersed. The heat exchanger, therefore, locally fails to manifest the effect of a sacrificial anode in resisting corrosion and suffers development of pinholes in the wall.
OBJECTS OF THE INVENTION
It is, therefore, an object of an aspect of this in-vention to provide a novel method for the manufacture of a heat exchanger using aluminum material.
An object of an aspect of this invention is to provide a method for the manufacture of a heat exchanger with aluminum material excellent in resistance to corrosion.
BRIEF DESCRIPTION OF INVENTION
The objects described above are attained by a method for the manufacture of a heat exchanger with aluminum material, characterized by the steps of causing precipita-
METHOD FOR MANUFACTURE OF HEAT EXCHAN OER
WITH ALUMINUM M~TERIAL
FIELD OF INVENTION AND PRIOR ART
This invention relates to a method for the manufacture of a heat exchanger with aluminum material.
More particularly, this invention relates to a method for the manufacture of a heat exchanger with aluminum material excellent in resestance to corrosion.
Recently, heat exchangers such as radiators for automobiles, evaporators for car coolers and condensers for car coolers have been advancing toward preponderant use of aluminum material for reduction in weight. The condenser for a car cooler, for example, is manufactured by fabricat-ing both the tube and the heat transfer fins with aluminum material clad with brazing filler or fabricating one of them with aluminum material clad with brazing filler and the other simply with aluminum material, tying the fabricated components as with jigs, and brazing them with a corrosive flux in an oven.
Heretofore, in the manufacture of a heat exchanger with aluminum material by the brazing process with a flux, it has been customary for the component parts fabricated of aluminum material to be coated with flux consisting of an alkaline earth metal salt containing zinc chloride and an alkali metal salt and then brazed by the use of a brazing filler of Al-Si alloy (Si content 5 to 12%) at a temperature below the melting point of aluminum material (about 580 to 6~0 C). By the brazing, the component parts are joined and, at the same time, the zinc is precipitated to the surface of '~ ~
~2;~8~
the aluminum material (3ZnC12 + 2Al > 3Zn + 2AlC13) and diffused toward the center of the aluminum material because of the heat of brazing. The zinc-diffused layer exhibits the effect of a sacrificial anode, which goes to improve the resistance of brazed heat exchanger to corrosion.
When this process is adopted, however, since the flux to be used possesses high hygroscopicity, the brazed heat exchanger must be immediately washed with hot water, pickled with nitric acid, washed with cold water, etc. to a sufficient extent. These treatments add greatly to the complexity of process. The zinc chloride contained in the flux is utilized for incorporating the zinc-diffused layer in the aluminum material. In any structure of the heat exchanger's complexity, it is difficult to apply this flux uniformly on its entire surface. Thus, the amount of zinc diffused in the aluminum material is heavily dispersed. The heat exchanger, therefore, locally fails to manifest the effect of a sacrificial anode in resisting corrosion and suffers development of pinholes in the wall.
OBJECTS OF THE INVENTION
It is, therefore, an object of an aspect of this in-vention to provide a novel method for the manufacture of a heat exchanger using aluminum material.
An object of an aspect of this invention is to provide a method for the manufacture of a heat exchanger with aluminum material excellent in resistance to corrosion.
BRIEF DESCRIPTION OF INVENTION
The objects described above are attained by a method for the manufacture of a heat exchanger with aluminum material, characterized by the steps of causing precipita-
-2-2~3~
tion of zinc in an amount of 0.5 to 20 gjm2 on the surface of at least a liquid passing tube or members making up the liquid passing tube, of the heat exchanger formed of aluminum material, subsequently applying on the surface a flux formed of a mixture of potassium tetrafluoroaluminate (KAlF4) with potassium hexafluoroaluminate tK3AlF6), and brazing the heat exchanger by the use of brazing filler formed of an aluminum-silicon alloy having a lower melting point than the aluminum material at a tempera-ture of about 580 to about 620 C.
BRIEF DESCRIPTION OF T~E DRAWINGS
Fig. 1 is a sectional view of a superposition type heat exchager;
Fig. 2 is a perspective view of a serpentine type heat exchanger;
Fig. 3 is a graph showing the data of a test for resistance to corrosion conduc-ted on a heat exchanger manufactured by the method of this invention and a heat exchanger manufactured by the conventional method: and Fig. 4 is a graph showing relation between amount of precipitated zinc and zinc concentration in surface layer.
DETAILED DESCRIPTION OF THE INVENTION
The expression "heat exchanger manufactued by the method of this invention" embraces radiators for automo-biles, evaporators for car coolers, condensers for car coolers, car heaters, etc., which each comprise a tube and heat tranfer fins and, in radiators, further comprise a seat plate, a reinforcement, etc. All these components are formed of aluminum material.
~2~
The laminate type heat exchanger illustrated in Fig. 1, for example, is a typical evaporator in an automo-bile air conditioner. This evaporator 1 is consturcted by superposing a multiplicity of tube units 5 each formed by joining two tray-shaped plates (pieces) 2 around their peripheral flanges 3 after the manner oE a cream puff to embrace therein coolant passages 4 and setting corrugated fins 7 in place in the spaces 6 separating the depressed walls of the tube units 5. The coolant which enters the evaporator 1 through an inlet side conduit 8, flows through the tube units 5, and departs from the evaporator 1 through an outlet side conduit 9, therefore, exchanges heat with the air flowing on the fins 7.
The serpentine type heat exchanger has an appearance as illustrated in Fig. 2. This evaporator 11 is constructed by zigzagging a flattened tube 14 incorporating therein a multiplicity of holes 13 for passing coolant and nipping corrugated fins 15 between the adjacent webs of the zigzagged tube 14. The coolant which enters the evaporator 11 through an inlet side conduit 16, flows through the interior of the tube 15, and departs from the evaporator 11 through an outlet side conduit 17, therefore, exchanges heat with the air flowing along the fins 15.
All the components of the evaporator are formed of aluminum material.
In the method of this invention, the components made of aluminum material, particularly the liquid passing tube or the members forming the liquid passing tube, are caused to precipitate zinc on the surface in an amount of 0.5 to 2Q g/m2, preferably 5 to 15 g/m2. If the amount of zinc thus precipitated is less than 0.5 g/m2, the treated surface fails to manifest the effect of a sacrificial anode sufficiently and offers satisfactory resistance to corrosion after the brazing. If the amount of zinc precipitated exceeds 20 g/m2, the cost is increased without any further improvement in resistance to corrosion., Besides, the zinc concentration is so high as to accelerate the elution of the zinc-diffusd layer and impair the effect of a sacrificial anode.
The precipitation of zinc to the surface of aluminum material can be effected by a chemical plating method, an electroplating method and the like. A uniform zinc coating is formed on the surface of aluminum material by immersing this aluminum material in a treating liquid such as, for example, a zinc salt bath containing 50 to 500 g/liter, preferably 200 to 400 g/liter, oE sodium hydroxide, to 100 g/liter, preferably 20 to 80 g/liter, of zinc oxide, and the balance of water at a temperature of not more than 60 C, preferably in the range of 20 to 50C, for 0.5 to 10 minutes, preferably 0.5 to 5 minutes.
The aluminum material to be used for liquid passing tube as well as fins are, for example, are aluminum materials rated as 1050, 1070, I100, 1200, 3003, 3004, 3005, 3200, 5005, 6951, etc.
The brazing filler to be used during the course of brazing is an aluminum-silicon alloy (having a silicon content of about 4.5 to about 13.5%) having a lower melting point than the aluminum material to be used. Concrete examples are aluminum maerials rated as 4034 (silicon content 4.5 to 6.0%), 4045 (silicon content 9.0 to 11.0%), 4343 (silicon content 6.8 -to 8.2%), 4047 (silicon content 11.0 to 13.0%), etc. By reason of workability, such brazing filler is used as deposited in the form of clad on at least one of the members of aluminum material to be joined.
The flux to be used in the method of this inven-tion is a mixture of potassium tetrafluoroaluminate (KAlF4) with potassium hexafluoroaluminate (K3AlF6), both complexes of potassium fluoride (KF) and aluminum fluoride (AlF3).
Normally, this flux is used in the form of aqueous slurry.
This mixture is obtained by dissolving AlF3 and KF in respective amounts constituting an accurate ratio, cooling the resultant dissolved mixture, pulverizing the cooled substance to a suitable particle diameter, and suspending the produced powder in water to afford a dilute slurry.
Generally, this particle diameter is below 100 mesh, desirably below 150 mesh, and more desirably below 200 mesh.
The preparation of the aforementioned mixture can otherwise be effected by preparing KAlF4 and K3AlF6 separatel~ and mixing the complexes in a prescribed ratio. The method for the preparation of KAlF4 is disclosed in Brosset Z. Anorg.
Algem. Chemie, 239, 301-304 (1938).
A typical method for the preparation of the flux comprises adding 2 parts of water to 1 part of the pulveriz-ed mixture of complexes thereby producing a dilute slurry and optionally adding a small amount of surfactant. The relative ratio of KF and AlF3 to be used in the preparation of the flux is desired to be such that the resultant mixture will acquire a melting point as close to the eutectic as possible. The flux to be used in this invention, therfore, substantially constists of a mixture of K3AlF6 and KAlF4 in ~,2~i2~C3i respective amounts such that the KE/~lF3 (weight) ratio will range from 40 : 60 to 50 : 50. The flux contains virtually no unaltered KF.
The members fabricated of aluminum material which has undergone the treatment for surface precipitation of zinc and which optionally has been clad with brazing filler such as the tube produced for use in the condenser of a car cooler by fabricating a tube of aluminum material and treating the tube for surface precipitation of zinc and the heat transfer fins fabricated, similarly for the condenser of aluminum material having brazing filler deposited in the form of clad on either or both of the surfaces, are tied in .J a prescribed structure, optionally with the aid of a jig, then coated with the aforementioned flux in an application ratio of 0.5 to 50 g/m2, preferably 2 to 10 g/m2, placed in an oven, and brazed therein at a temperature below the melting point, desirably at a temperature in the range of about 580 to about 620 C, and preferably in the range of 590 to 610 C. In this case, the site of brazing is desired to be enveloped with a non-oxidative atmosphere of nitrogen or argon, for example. The pressure falls in the range of Torr to 20 Torrs above the atmospheric pressure, preferably in the rclnge of atmospheric pressure + 20 Torrs.
~ w, the method of this invention will be described more specifically below with reference to working examples.
Example 1 A tube 1.0 mm in wall thickness was fabricated of aluminum material 1050. This tube was immersed in a zinc salt bath formed of an aqueous solution of 356 g of sodium z~
hydroxide (NaOH) per liter and 60 g of zinc oxide (ZnO) per liter at a temperature of 20 C for 5 minutes to effect precipitation of zinc at a rate of 12 g/m2 on the surface of the tube. This tube was washed with water, and dried.
Separately, heat transfer fins were fabricated of aluminum foil of 3003 having aluminum material of 4343 deposited in the form of clad on both surfaces thereof. The dried tube and the heat transfer fins were assembled with the aid of a jig~ The assembly was coated with an aquieous slurry of a finely pulverized (less than 200 mesh) mixture of potassium tetrafluoroaluminate and potassium hexafluoroaluminate [KF/AlF3 (weight) ratio 45 : 55] at an application rate of 5 g/m2 (as solids). The assembly was then placed in an oven and heated therein under a blanket of nitorgen gas at 600C
under atmospheric pressure to effect brazing. Consequetly, there was obtained a condenser.
The tube of the condenser thus producd was tested for internal diffusion of zinc with an X-ray microanalyzer.
The results were as shown in Table 1. The test was conduct-ed on a total of five points randomly selected.
Table 1 Zinc concentration in Depth of diffusion Point of test surface layer (% by wei~ht) of zinc (~m) 1 4.9 80 2 4.5 85
tion of zinc in an amount of 0.5 to 20 gjm2 on the surface of at least a liquid passing tube or members making up the liquid passing tube, of the heat exchanger formed of aluminum material, subsequently applying on the surface a flux formed of a mixture of potassium tetrafluoroaluminate (KAlF4) with potassium hexafluoroaluminate tK3AlF6), and brazing the heat exchanger by the use of brazing filler formed of an aluminum-silicon alloy having a lower melting point than the aluminum material at a tempera-ture of about 580 to about 620 C.
BRIEF DESCRIPTION OF T~E DRAWINGS
Fig. 1 is a sectional view of a superposition type heat exchager;
Fig. 2 is a perspective view of a serpentine type heat exchanger;
Fig. 3 is a graph showing the data of a test for resistance to corrosion conduc-ted on a heat exchanger manufactured by the method of this invention and a heat exchanger manufactured by the conventional method: and Fig. 4 is a graph showing relation between amount of precipitated zinc and zinc concentration in surface layer.
DETAILED DESCRIPTION OF THE INVENTION
The expression "heat exchanger manufactued by the method of this invention" embraces radiators for automo-biles, evaporators for car coolers, condensers for car coolers, car heaters, etc., which each comprise a tube and heat tranfer fins and, in radiators, further comprise a seat plate, a reinforcement, etc. All these components are formed of aluminum material.
~2~
The laminate type heat exchanger illustrated in Fig. 1, for example, is a typical evaporator in an automo-bile air conditioner. This evaporator 1 is consturcted by superposing a multiplicity of tube units 5 each formed by joining two tray-shaped plates (pieces) 2 around their peripheral flanges 3 after the manner oE a cream puff to embrace therein coolant passages 4 and setting corrugated fins 7 in place in the spaces 6 separating the depressed walls of the tube units 5. The coolant which enters the evaporator 1 through an inlet side conduit 8, flows through the tube units 5, and departs from the evaporator 1 through an outlet side conduit 9, therefore, exchanges heat with the air flowing on the fins 7.
The serpentine type heat exchanger has an appearance as illustrated in Fig. 2. This evaporator 11 is constructed by zigzagging a flattened tube 14 incorporating therein a multiplicity of holes 13 for passing coolant and nipping corrugated fins 15 between the adjacent webs of the zigzagged tube 14. The coolant which enters the evaporator 11 through an inlet side conduit 16, flows through the interior of the tube 15, and departs from the evaporator 11 through an outlet side conduit 17, therefore, exchanges heat with the air flowing along the fins 15.
All the components of the evaporator are formed of aluminum material.
In the method of this invention, the components made of aluminum material, particularly the liquid passing tube or the members forming the liquid passing tube, are caused to precipitate zinc on the surface in an amount of 0.5 to 2Q g/m2, preferably 5 to 15 g/m2. If the amount of zinc thus precipitated is less than 0.5 g/m2, the treated surface fails to manifest the effect of a sacrificial anode sufficiently and offers satisfactory resistance to corrosion after the brazing. If the amount of zinc precipitated exceeds 20 g/m2, the cost is increased without any further improvement in resistance to corrosion., Besides, the zinc concentration is so high as to accelerate the elution of the zinc-diffusd layer and impair the effect of a sacrificial anode.
The precipitation of zinc to the surface of aluminum material can be effected by a chemical plating method, an electroplating method and the like. A uniform zinc coating is formed on the surface of aluminum material by immersing this aluminum material in a treating liquid such as, for example, a zinc salt bath containing 50 to 500 g/liter, preferably 200 to 400 g/liter, oE sodium hydroxide, to 100 g/liter, preferably 20 to 80 g/liter, of zinc oxide, and the balance of water at a temperature of not more than 60 C, preferably in the range of 20 to 50C, for 0.5 to 10 minutes, preferably 0.5 to 5 minutes.
The aluminum material to be used for liquid passing tube as well as fins are, for example, are aluminum materials rated as 1050, 1070, I100, 1200, 3003, 3004, 3005, 3200, 5005, 6951, etc.
The brazing filler to be used during the course of brazing is an aluminum-silicon alloy (having a silicon content of about 4.5 to about 13.5%) having a lower melting point than the aluminum material to be used. Concrete examples are aluminum maerials rated as 4034 (silicon content 4.5 to 6.0%), 4045 (silicon content 9.0 to 11.0%), 4343 (silicon content 6.8 -to 8.2%), 4047 (silicon content 11.0 to 13.0%), etc. By reason of workability, such brazing filler is used as deposited in the form of clad on at least one of the members of aluminum material to be joined.
The flux to be used in the method of this inven-tion is a mixture of potassium tetrafluoroaluminate (KAlF4) with potassium hexafluoroaluminate (K3AlF6), both complexes of potassium fluoride (KF) and aluminum fluoride (AlF3).
Normally, this flux is used in the form of aqueous slurry.
This mixture is obtained by dissolving AlF3 and KF in respective amounts constituting an accurate ratio, cooling the resultant dissolved mixture, pulverizing the cooled substance to a suitable particle diameter, and suspending the produced powder in water to afford a dilute slurry.
Generally, this particle diameter is below 100 mesh, desirably below 150 mesh, and more desirably below 200 mesh.
The preparation of the aforementioned mixture can otherwise be effected by preparing KAlF4 and K3AlF6 separatel~ and mixing the complexes in a prescribed ratio. The method for the preparation of KAlF4 is disclosed in Brosset Z. Anorg.
Algem. Chemie, 239, 301-304 (1938).
A typical method for the preparation of the flux comprises adding 2 parts of water to 1 part of the pulveriz-ed mixture of complexes thereby producing a dilute slurry and optionally adding a small amount of surfactant. The relative ratio of KF and AlF3 to be used in the preparation of the flux is desired to be such that the resultant mixture will acquire a melting point as close to the eutectic as possible. The flux to be used in this invention, therfore, substantially constists of a mixture of K3AlF6 and KAlF4 in ~,2~i2~C3i respective amounts such that the KE/~lF3 (weight) ratio will range from 40 : 60 to 50 : 50. The flux contains virtually no unaltered KF.
The members fabricated of aluminum material which has undergone the treatment for surface precipitation of zinc and which optionally has been clad with brazing filler such as the tube produced for use in the condenser of a car cooler by fabricating a tube of aluminum material and treating the tube for surface precipitation of zinc and the heat transfer fins fabricated, similarly for the condenser of aluminum material having brazing filler deposited in the form of clad on either or both of the surfaces, are tied in .J a prescribed structure, optionally with the aid of a jig, then coated with the aforementioned flux in an application ratio of 0.5 to 50 g/m2, preferably 2 to 10 g/m2, placed in an oven, and brazed therein at a temperature below the melting point, desirably at a temperature in the range of about 580 to about 620 C, and preferably in the range of 590 to 610 C. In this case, the site of brazing is desired to be enveloped with a non-oxidative atmosphere of nitrogen or argon, for example. The pressure falls in the range of Torr to 20 Torrs above the atmospheric pressure, preferably in the rclnge of atmospheric pressure + 20 Torrs.
~ w, the method of this invention will be described more specifically below with reference to working examples.
Example 1 A tube 1.0 mm in wall thickness was fabricated of aluminum material 1050. This tube was immersed in a zinc salt bath formed of an aqueous solution of 356 g of sodium z~
hydroxide (NaOH) per liter and 60 g of zinc oxide (ZnO) per liter at a temperature of 20 C for 5 minutes to effect precipitation of zinc at a rate of 12 g/m2 on the surface of the tube. This tube was washed with water, and dried.
Separately, heat transfer fins were fabricated of aluminum foil of 3003 having aluminum material of 4343 deposited in the form of clad on both surfaces thereof. The dried tube and the heat transfer fins were assembled with the aid of a jig~ The assembly was coated with an aquieous slurry of a finely pulverized (less than 200 mesh) mixture of potassium tetrafluoroaluminate and potassium hexafluoroaluminate [KF/AlF3 (weight) ratio 45 : 55] at an application rate of 5 g/m2 (as solids). The assembly was then placed in an oven and heated therein under a blanket of nitorgen gas at 600C
under atmospheric pressure to effect brazing. Consequetly, there was obtained a condenser.
The tube of the condenser thus producd was tested for internal diffusion of zinc with an X-ray microanalyzer.
The results were as shown in Table 1. The test was conduct-ed on a total of five points randomly selected.
Table 1 Zinc concentration in Depth of diffusion Point of test surface layer (% by wei~ht) of zinc (~m) 1 4.9 80 2 4.5 85
3 4.5 80
4 4.4 80 4.5 85 The tube of this condenser was subjected to the ~2~2~3~
C~SS test (JIS El-~681) Eor 12nO hours. The results were as indicated by the curve A in Fig. 3.
Example 2 The procedure of Example 1 was repeated, with that the amount of æinc precipitated was changed to 5 g/m2, to produce a condenser. When the -tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curve A in Fig~ 3.
Example 3 The procedure of Example 1 was repeated, except that the amount of zinc precipitated was changed to 15 g/m2, to produce a condenser. When the tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curbe A in Fig. 3.
Example 4 The procedure of Example 1 was repeated, with that the amount of æinc precipitated was changed to 0.5 g/m2, to produce a condenser. When the tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curve B in Fig. 3.
Example 5 The procedures of Example 1 were repeated, with that the amounts of zinc precipitated were varied from 5 g/m2 to 20 g/m2 using 3 g/m2 of flux at a temperature of 600 C under atmospheric pressure, to produce a condenser. The relation between amount of precipitated zinc and zinc concentration in surface layer is as shown in Fig. 4.
Control A condenser was produced by following the procedure of Example 1, except that the treatment for zinc _g_ precipitation was omitted. The tube of this condenser was subjected to the same test as in Example 1. The results were as indicated by Curve B Fig. 3. It is noted from the data that the tube .sustained through holes.
As described above, the method of this invention for the manuEacture of a heat exchanger with aluminum material comprises causing precipitation of 0.5 to 20 g/m2 of zinc on the surface of at least the liquid passing tube or members making up the liquid passing tube, of the heat exchanger fabricated of aluminum material, then applying on the surface the flux, a mixture of potassium tetrafluoro-aluminate with potassium hexafluoroaluminate, and brazing the assembled heat exchanger by the use of brazing filler of an aluminum-silicon alloy having a lower melting point than the aluminum material at a temperature of about 580 to about 620 C. The zinc initially precipitated on the surface of the aluminum material, therefore, is diffused from the surface toward the center of the aluminum material by virtue of the heat of brazing and distributed therein at a certain concentration gradient. At this time, the zinc content in the surface zone of the aluminum material falls in the range of 0.2 to 10% by weight as shown in Fig. 4 and the depth of zinc diffusion falls in the ragne of 30 to 200 ~m. Owing to the effect of a sacrificial anode manifested by the zinc uniformly diffusd in the surface zone, therfore7 the hea-t exchanger of aluminum material is rendered resistant to corrosion at least in the liquid passing tube. Thus, the heat exchanger enjoys notably enhanced resistance to corrosion. Further, since the aforementioned flux is minimally soluble in water and not hygroscopic, it is incapable of corroding the aluminum material. The flux remaining on the surface, therefore, is not required to be removed at the cost of time and labor.
C~SS test (JIS El-~681) Eor 12nO hours. The results were as indicated by the curve A in Fig. 3.
Example 2 The procedure of Example 1 was repeated, with that the amount of æinc precipitated was changed to 5 g/m2, to produce a condenser. When the -tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curve A in Fig~ 3.
Example 3 The procedure of Example 1 was repeated, except that the amount of zinc precipitated was changed to 15 g/m2, to produce a condenser. When the tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curbe A in Fig. 3.
Example 4 The procedure of Example 1 was repeated, with that the amount of æinc precipitated was changed to 0.5 g/m2, to produce a condenser. When the tube of this condenser was subjected to the same test as involved in Example 1, the results were as indicated by the curve B in Fig. 3.
Example 5 The procedures of Example 1 were repeated, with that the amounts of zinc precipitated were varied from 5 g/m2 to 20 g/m2 using 3 g/m2 of flux at a temperature of 600 C under atmospheric pressure, to produce a condenser. The relation between amount of precipitated zinc and zinc concentration in surface layer is as shown in Fig. 4.
Control A condenser was produced by following the procedure of Example 1, except that the treatment for zinc _g_ precipitation was omitted. The tube of this condenser was subjected to the same test as in Example 1. The results were as indicated by Curve B Fig. 3. It is noted from the data that the tube .sustained through holes.
As described above, the method of this invention for the manuEacture of a heat exchanger with aluminum material comprises causing precipitation of 0.5 to 20 g/m2 of zinc on the surface of at least the liquid passing tube or members making up the liquid passing tube, of the heat exchanger fabricated of aluminum material, then applying on the surface the flux, a mixture of potassium tetrafluoro-aluminate with potassium hexafluoroaluminate, and brazing the assembled heat exchanger by the use of brazing filler of an aluminum-silicon alloy having a lower melting point than the aluminum material at a temperature of about 580 to about 620 C. The zinc initially precipitated on the surface of the aluminum material, therefore, is diffused from the surface toward the center of the aluminum material by virtue of the heat of brazing and distributed therein at a certain concentration gradient. At this time, the zinc content in the surface zone of the aluminum material falls in the range of 0.2 to 10% by weight as shown in Fig. 4 and the depth of zinc diffusion falls in the ragne of 30 to 200 ~m. Owing to the effect of a sacrificial anode manifested by the zinc uniformly diffusd in the surface zone, therfore7 the hea-t exchanger of aluminum material is rendered resistant to corrosion at least in the liquid passing tube. Thus, the heat exchanger enjoys notably enhanced resistance to corrosion. Further, since the aforementioned flux is minimally soluble in water and not hygroscopic, it is incapable of corroding the aluminum material. The flux remaining on the surface, therefore, is not required to be removed at the cost of time and labor.
Claims (5)
1. A method for the manufacture of a heat exchanger with aluminum material, characterized by the steps of causing precipitation of 0.5 to 20 g/m2 of zinc on the surface of at least the liquid passing tube or members making up said liquid passing tube, of a heat exchanger fabricated of aluminum material, then applying to the surface flux formed of a mixture of potassium tetrafluoro-aluminate with potassium hexafluoroaluminate, and brazing said heat exchanger by the use of brazing filler of an aluminumsilicon alloy having a lower melting point than said aluminum material at a temperature of about 580 ° to about 620°C.
2. A method according to Claim 1, wherein the amount of zinc to be precipitated is in the range of 5 to 15 g/m2.
3. A method according to Claim 1, wherein the amount of said flux to be applied is in the range of 0.5 to 50 g/m2.
4. A method according to Claim 1, wherein the brazing is carried out under a pressure of 10-2 Torr to 20 Torr above the atmospheric pressure.
5. A method according to Claim 1, wherein the zinc is precipitated on the surface of the liquid passing tube or members making up said liquid passing tube and fins are set between the liquid passing tube.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000464338A CA1221280A (en) | 1984-09-28 | 1984-09-28 | Method for manufacture of heat exchanger with aluminum material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000464338A CA1221280A (en) | 1984-09-28 | 1984-09-28 | Method for manufacture of heat exchanger with aluminum material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1221280A true CA1221280A (en) | 1987-05-05 |
Family
ID=4128805
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000464338A Expired CA1221280A (en) | 1984-09-28 | 1984-09-28 | Method for manufacture of heat exchanger with aluminum material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1221280A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4955525A (en) * | 1986-04-25 | 1990-09-11 | Mitsubishi Aluminum Co., Ltd. | Heat exchanger and method of producing same |
-
1984
- 1984-09-28 CA CA000464338A patent/CA1221280A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4955525A (en) * | 1986-04-25 | 1990-09-11 | Mitsubishi Aluminum Co., Ltd. | Heat exchanger and method of producing same |
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