CA1295114C - Method of manufacturing a heat-exchanger - Google Patents
Method of manufacturing a heat-exchangerInfo
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- CA1295114C CA1295114C CA000566900A CA566900A CA1295114C CA 1295114 C CA1295114 C CA 1295114C CA 000566900 A CA000566900 A CA 000566900A CA 566900 A CA566900 A CA 566900A CA 1295114 C CA1295114 C CA 1295114C
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Abstract
A METHOD OF MANUFACTURING A HEAT-EXCHANGER
ABSTRACT
A method of manufacturing a heat-exchanger with excellent pitting corrosion resistance is disclosed, wherein, in the manufacture of an aluminum heat-exchanger to be brazed under heat in a furnace having an inert gas atmosphere using fluoride flux, Zn at 430 to 620°C is fed to the furnace to melt and vaporize it and the vapor of Zn is allowed to make contact with the fin material and the tube material coated with said flux simultaneously with the brazing under heat of these aluminum components, or the fin material coated with said flux and dried, and the tube material without flux, are assembled and retained for not less that 1 minute in the vapor of Zn of a temperature lower than the melting point of said flux and higher than the temperature at which these components are heated, in the inert gas and thereafter brazing is performed at a temperature higher than the melting point of said flux. A method of concentrating Zn on the surface layer of said A1 components and a method of generating the Zn vapor for the concentration of surface Zn are also disclosed.
ABSTRACT
A method of manufacturing a heat-exchanger with excellent pitting corrosion resistance is disclosed, wherein, in the manufacture of an aluminum heat-exchanger to be brazed under heat in a furnace having an inert gas atmosphere using fluoride flux, Zn at 430 to 620°C is fed to the furnace to melt and vaporize it and the vapor of Zn is allowed to make contact with the fin material and the tube material coated with said flux simultaneously with the brazing under heat of these aluminum components, or the fin material coated with said flux and dried, and the tube material without flux, are assembled and retained for not less that 1 minute in the vapor of Zn of a temperature lower than the melting point of said flux and higher than the temperature at which these components are heated, in the inert gas and thereafter brazing is performed at a temperature higher than the melting point of said flux. A method of concentrating Zn on the surface layer of said A1 components and a method of generating the Zn vapor for the concentration of surface Zn are also disclosed.
Description
FIELD OF T~IE INVENTION
The present invention relates to a method of manufacturing aluminum heat-exchangers with excellent pitting corrosion resistance, a method of concentrating Zn on the surface layer of Al components and a method of generating the Zn vapor to form the concentrated Zn surface. In particular, the invention is applicable to the brazing of heat-exchangers for motorcars.
BACECGROUND OF THE INVENTION
Recently, in heat-exchangers for motorcars, such as cadent radiators, evaporators and condensers for air-conditioners etc., Al or Al alloys have come to be used extensively to reduce weight. In general, for the manufacture of aluminum heat-exchangers, a brazing sheet, laminated with a brazing alloy having a lower melting point than the core material, for example, ~l-Si alloy or Al-Si-Mg alloy on one or both sides of the core material comprising Al or Al alloy, has been used. This is combined with an Al component, for example, an extruded multihole tube to permit mass production by brazing.
In such aluminum heat-exchangers manufactured by heating for brazing, the following methods are used to assure pitting corrosion resistance.
(1) Chloride flux containing ZnC12 is used for heating for brazing and Zn is allowed to deposit and diffuse onto the surface of the Al components simultaneously with the brazing. The pitting corrosion of Al components is prevented through the sacrificial action of said diffused layer. This method is excellent for pitting corrosion resistance, and is utilized mainly for condensers for coolers.
The present invention relates to a method of manufacturing aluminum heat-exchangers with excellent pitting corrosion resistance, a method of concentrating Zn on the surface layer of Al components and a method of generating the Zn vapor to form the concentrated Zn surface. In particular, the invention is applicable to the brazing of heat-exchangers for motorcars.
BACECGROUND OF THE INVENTION
Recently, in heat-exchangers for motorcars, such as cadent radiators, evaporators and condensers for air-conditioners etc., Al or Al alloys have come to be used extensively to reduce weight. In general, for the manufacture of aluminum heat-exchangers, a brazing sheet, laminated with a brazing alloy having a lower melting point than the core material, for example, ~l-Si alloy or Al-Si-Mg alloy on one or both sides of the core material comprising Al or Al alloy, has been used. This is combined with an Al component, for example, an extruded multihole tube to permit mass production by brazing.
In such aluminum heat-exchangers manufactured by heating for brazing, the following methods are used to assure pitting corrosion resistance.
(1) Chloride flux containing ZnC12 is used for heating for brazing and Zn is allowed to deposit and diffuse onto the surface of the Al components simultaneously with the brazing. The pitting corrosion of Al components is prevented through the sacrificial action of said diffused layer. This method is excellent for pitting corrosion resistance, and is utilized mainly for condensers for coolers.
(2) Elements which make Al or Al alloys anodic when adding Zn, Sn, In, etc.
are added to the fin material or the filler for the brazing sheet. Through the sacrificial actlon ther-eof, the pitting corrosion of Al components forming the passageways for refrigerant etc. ls prevented. This method is utilized mainly for condensers evaporators, radiators, etc.
are added to the fin material or the filler for the brazing sheet. Through the sacrificial actlon ther-eof, the pitting corrosion of Al components forming the passageways for refrigerant etc. ls prevented. This method is utilized mainly for condensers evaporators, radiators, etc.
(3) Al-Zn alloy, Al-Zn-Mg alloy or pure Al is used as a cladding on various core materials to prevent the generatlon of pitting corrosion of the core material through the sacrificial action of the claddlng material. This method is utilized to improve the pltting corrosion resistance of tubes (seam welded tubes), headers, etc. of radiators, in particular, for the water side thereof.
(~1) To the extruded multihole tubes used for condenser tubes, a layer covered with Zn is provided beforehand by flame spray coating with Zn, zincate treatment, Zn plating, etc. Then, the diffused layer of Zn is formed by heating for brazin~ to prevent the pitting corrosion of the extruded multihole tube.
All of the conventional methods noted above to a~sure the corroslon resistance of aLuminum heat-exchangers have the followlng problems and improvements therein are earnestly desired.
In the method (1) above, post-treatment such as washing with water etc.
becomes necessary because of the occurrence of a corrosive flux residue and the production costs including the effluent treatment etc. accompanied by this becomes high. In method (2) above, there is a restriction on the range of sacrificial actlon of fin material and the application thereof does not extend all over the core of the heat-exchanger. In the method of adding Zn, Sn, In etc. to the filler of the brazing sheet, the sacrificial layer cannot be formed sufficiently due to the melting of filler and inversely, at the filler portion where the filler builds up, the sacrificial layar often extends into the core material deeply together with the diffusion of filler to thereby lower the pitting corrosion resistance. In the method (3) above, the sacrificial layer must be applisd beforehand and the application to extruded multihole tubes etc. is difficult though production is possible using a brazing sheet. Also, in the method (4) above, the surface of the Al component becomes heterogeneous through the treatment with Zn resulting in the problems such as dropping out etc. due to the bending etc.
With regard to method (1), a brazing method using nonhygroscopic and noncorrosive fluoride flux has been developed. In this method, the eutectic composition of, for example, KAlF4-K3AlF6 is used for the flux, and the brazlng is performed by heatln~ to about 600C in the furnace, where the dew point i9 controlled to be not higher than -40C and the partial pressure of 2 is controlled to be not more than 1000 ppm, and introducing the inert gas, mainly N2 ~hereinafter, thls brazing method is referred to as the NB
method). Here, washin~ aftar brazing is unnecessary.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 (A), (B) and (C) show the assembling of the core of an aluminum heat-exchanger, wherein (A) is a perspective view of the extruded tube material after bending, (;3) is a perspective view of the fin material corrugated, and (C) is a perspective view of the core assembled by pressing 3~
with jigs. Fig. 2 illustrates a continuous atmospheric furnace. Fig. 3 is a graph showing the heat pattern in the furnace when brazing in the contlnuous atmospheric furnace.
For example, when manufacturlng a condenser of alumin~ml by the ~B method, the extruded multihole tubes (hereinafter, abbreviated as tube material) (1) is formed with a bender in a serpentine shape as shown in Fig. 1 (A) and the fin material (2) corrugated as shown in Fig. 1 (B) are assembled as shown in Fig. 1 (C). After fitting the unions (3) and (3') to the inlet and outlet of the refrigerant tube material (1), respectively, they are fixed by pressing jigs (4) to maXe the core (5). Following, the degreasing of said core, fluoride type flux is coated all over it and then thls is fed to the brazing furnace to preheat and heat according to the heat pattern shown in Fig. 3 (B). Thus, the fin material and the tube material are brazed and assembled.
For the fin material, the brazing sheet (thickness: 0.16 mm) clad with JIS
4343 filler of Al-Si alloy on both sides of the core material comprising JIS
3003 ~ 1% Zn alloy, is used. However, due the the use of motorcars in areas of salt damage, the improvement in the exterior pitting corrosion resistance of said heat-exchangers has become important recently. Particularly, in the aforementioned NB method, not only the use of sacrificial fins but also the corrosion-resistant treatment of the tube material itself as noted below have become common.
(1) By submitting the tube material to the zincate treatment before brazing, Zn is allowed to deposit onto the surface of the tube material and, by the heating for brazing, Zn is allowed to diffuse into the tube material.
(2) By adding Zn to the fluoride flux, Zn is allowed to diffuse from flux into the tube material upon heating for brazing.
However, the zincate treatment before brazing brings about high cost and, at the same time, since an alkali solution is used for the zincate treatment of tube material, the invasion of the solution into the tube materia]. must be prevented, resulting in many difEiculties in the operation.
~ oreover, in the method of adding Zn to the flux, low concentrations of flux of about 10% are used satlsfactorily in the case of fluoride flux due to its strong activity contrary to the use of high concentrations of flux of the order of 50 to 6070, in the case of chloride flux. As a result, large amounts of Zn cannot be supplied and the desired amount of Zn cannot be allowed to ~35~
diffuse all over the surface.
On the other hand, a method is sho~l in Japanese Patent Publication No.
Sho 59-31588, wherein the vapour of Zn is blo~l onto the surface of extruded A1 material to form a layer covered with Zn, this is allowed to diffuse onto the surface of extruded Al material on heating for brazing etc., and the corrosion resistance is improved through the sacrificial effect of the surface layer. The generation of the Zn vapour in thls case is performed in such a way that the gas-introductory pipe is inserted into the melt of Zn kept at 550~, the Zn vapour is allowed to disperse into N2 gas as a carrier by supplying N2 gas in bubbles, and the ~n vapour is blown onto the surface of the Al extrusion-moulded material via the hot passage to form the layer of Zn on the surface of the extrusion-moulded Al material. The thickness of the Zn layer is determined by the extruding velocity of the extrusion-moulded material and the supply of gas.
However, with the extrusion-moulded Al material, the blowing of the Zn vapour is easy lnside the extruded material, but, on the outside, the Zn vapour tends to scatter and further, oxidation proceeds in the air.
Therefore, it is difficult to provide a uniform layer of Zn in a short time.
Moreover, with an aluminum heat-exchanger using a brazing sheet, the blowing of Zn vapour is difficult when manufacturing the brazing sheet material because the large width of the plate makes the application impossible.
Furthermore, since bubbled N2 gas is used to generate the Zn vapour, a facility for supplying N2 gas under high pressure, a furnace for retaining thé melt of Zn and pipes are needed.
As a result of extensive investigations in view of this situation, a method of manufacturing aluminum heat-exchangers wherein Zn is allowed t:o diffuse onto the surface of the Al components to be brazed simply and inexpensively by the NB brazing method to improve pitting corrosion resistance; a method of concentrating zinc on the surface layer of A1 components wherein Zn is allowed to concentrate uniformly at each portion by a simple method without affecting brazin~ in all steps including the step of preparing the material, the step of brazing, the step after brazing, etc. to provide an improvement in pitting corrosion resistance; and a method of generating Zn vapour for the concentration of a Zn coating on Al components wherein the coating with Z.n vapour and the diffusion of Zn are performed simultaneously with brazing through the efEicient ~ensration of Zn vapour are provided by the invention.
SU~MARY OF THE INVENTION
The invention provides a method of manufacturing heat-exchangers characterized in that, in the manufacture of aluminum heat-exchangers to be brazed under heat in a furnace with an inert gas atmosphere using fluoride flux, Zn is disposad at a temperature of 430 to 620C in the furnace to melt and vapourize it and the Zn vapour is allowed to contact the fin material and the tube material coated wlth said flux simultaneously while brazing under heat of these Al components to diffuse Zn.
The invention also provides a method of manufacturing heat-exchangers characterized in that, in the manufacture of heat-exchangers as described above, the fin material coated with fluoride flux and dried and the tube material without flux are assembled and retained for not less than 1 minute in Zn vapour at a temperature lower than the melting point of said flux and higher than the temperature to which these components are heated, in an inert gas and thereafter the brazing is performed at a temperature higher than the meltin~ point of the flux.
The invention also relates to a method of concentrating Zn on the surface layer of said Al components and a method of generating Zn vapour for the concentration of surface Zn, respectively.
DETAILED DESCRIPTION OF THE INVENTION
In the first method of manufacturing heat-exchangers in accordance with the invention, aEter coating the Al components for a heat-exchanger with a fluoride flux, this is heated and dried at about 200C in a preheating zone.
Then, brazing is performed by heating for several minutes at 600C (real temperature) in the brazing zone in an inert gas atmosphere. At this time, Zn is placed at a position where the temperature in the furnace becomes ll30 to 620C to melt and vapourize lt and the Al components are allowed to contact the Zn vapour generated simultaneously with the brazing under heat of the Al components to cause Zn diffusion into thc Al components.
Although the Al-Si filler melts near 577C, the diffusion of Zn proceeds from a temperature lower than this regardless of the state oE the flux (be~ore or after melting) adhered to the surface, and the diffusion of Zn into Al components occurs simultaneously with the brazing of the Al components. The Zn diffusion into the Al component depends on the generation of the Zn vapour.
The reason why Zn is dispossd at a position at a temperature of ~30 to 620C in the furnace to melt and vapourize is that the generatlon of Zn vapour is unacceptable unless above the melt temperature of Zn ~130C) and it is necessary to keep Zn above this temperature. On the other hand, in order to allow the diffusion of Zn to occur simultaneously with brazing, the upper temperature limit is 620C. Moreover, the concentration of oxygen in the inert gas atmosphere inside the furnace should be not more than 1000 ppm and the dew point hot higher than -30C. If outside of these ranges, good brazing cannot be obtained, and the generating efficiency of the Zn vapour is lowered.
~he flow rate of inert gas is suitably one tenth of the effective inner volume of the furnace per minute. If under this, the concentration of oxygen and the dew point cannot be maintained within said ranges and, if over the consumption of inert gas increases and the ~eneration of Zn vapour also increases to make the diffusion excessive leading to a lowering in the corrosion resistance.
Further, the surface area of the melt of Zn is desirably 0.05 to 2.5 cm per effective unit inner volume (litre) of furnace, thereby the generation of Zn vapour and efficient diffusion becomes efficiently possible.
Also, for uniform diffusion of Zn into the Al components, it is important to make the contact of Al components with the Zn vapour unifo~n. For this reason, appropriate agitation is desirable as well as controlled gas flow.
In the second manufacturing method of the invention, the reason why the flux is coated onto only the fin material is that, if the flux is coated beforehand onto the tube material, also, the flux acts as a barrier film and can hinder the adherence of the Zn vapour to the surface of tube material when exposed to Zn vapour to allow the Zn to diffuse into the tube material after assemb].y. Al50, the reason why the heating of these assembled components in the inert gas and exposure to the Zn vapour are practised at a temperature lower than the melting point of said flux is to avoid melting the flux coated on the fin material which would cause it to cover the surface of the tube material during the diffusion of Zn into the tube material.
Moreover, in order to allow Zn to adhere efficiently to the surface of the tube material before the melting of fluoride flux, the temperature of the Zn vapour is optimally 550 to 560C which is higher than the temperature of the tube material and lower than the melting point of flux (about 562C). If the retaining time is under 1 minute, the amount of Zn adhered ~o the sur~ace of tube material is insufficient and thus the corrosion-preventative effect i9 also unsatlsfactory. sosides~ w~en lowering said temperature of the Zn vapour, the retalning time is necessarily lengthened.
Furthermore, in order to generate the Zn vapour efficiently in the brazing furnace, the concentration of oxygen in the furnace and the dew point are desirably not more than 1000 ppm and not higher than ~30C similarly to the case of said first manufacturing method wherein the diffusion of Zn is performed simultaneously with brazing under heat. The flow rate of the inert gas per minute is optimally and economically one tenth of the volume of the furnace for the maintenance of the atmosphere in the furnace and the generation of the Zn vapour and the surface area of the Zn melt in the furnace is also effective if made 0.05 to 2.5 cm per unit volume (litre) of the furnace.
The invention provides the general method of concentrating Zn on the surface layer of Al components when heating Al or Al alloy components in the Zn vapour. In this method, the Zn vapour may be generated by heating Al or Al alloy components and Zn simultaneously in the furnace or the Zn vapour generated by heating Zn in a different apparatus may be used. The treatment temperature would be out of the question if over the melting temperature of Zn (about 420C), while the higher the temperature, the larger the surface concentration and the greater the diffusion depth. The treatment time similarly affects the diffusion pattern of Zn on the surface of components.
The atmosphere for the treatment is desirably inert gases such as N2 gas etc., but concentration of Zn is possible even in air. The pressure is sufficient if near atmosph0ric pressure, or the Zn vapour may be generated in a vacuum.
To allow Zn to diffuse when the Al or Al alloy components are being formed, they are passed through the furnaco holding vapourized Zn therein at the time of hot processing tt-olling or extrusion), or the Zn vapour may be sprayed from nozzles. The change in the surface ptoperties due to the deposition of Zn is removed and there is no restrictlon on the shape of materials. E'or example, when applying Zn when brazing the Al components, an appropriate amount of the Zn melt may be placed in the brazing furnace. Zn diffuses also onto the surface of brazing material without que.stion.
When heating Zn above the melting temperature and heating Al. or ~1 a].loy components in the Zn vapour generated, Zn diffuses from the surface to the inner portion of the Al or Al alloy components to glve a sacr~ticial effect to said components. The diffusion of Zn shows such a diffusion pattern that the surface is highest in the concentration and the pitting corrosion resistance is best. The diffusion of Zn is not affected by the flux even when brazing using fluoride flux. Also~ by carrying out the treatment of the invention at a lower temperature than the melting point of filler after the brazin~ of Al or Al alloy components, Zn can be allowed to diffuse uniformly onto the surface. This treatment may be applied to the core of -the heat-exchanger manufactured by for example vacuum-brazing. Further, by applying to Al-Mg alloy etc., the surface layer can be alloyed to Al-~g-Zn to improve the strength of the alloy.
The method of generating the vapour of Zn for the concentration of surface Zn on Al components, is applied to the NB method wherein Zn is placed in the heating furnace, N2 gas being flowed therethrough as a carrier gas; Zn and the atmosphere in the furnace are heated above 430C to melt the Zn, and the Zn vapour is generated from the Zn melt. The conditions are characterized in that, when the inner volume of the heating furnace is put as V litres, the amount of the melt of Zn, the surface area of the melt of Zn and the flow rate of N2 gas are made 1 to 10 ~/litre, 0.05 to 2.5 cm /litre and 0.05 V to V
litre~min, respectively, and the atmosphere in the heating furnace is retained so that the dew point and the concentration of oxygen become not higher than -20C and not more than 1000 ppm, respectively, in the vicinity of atmospheric pressure to allow the Zn vapour to generate from the melt of Zn.
The reason why Zn and the atmosphere in the furnace are heated above 430C
is because that, for the vapourization of Zn in the N2 atmosphere under atmospheric pressure, it is necessary to maintain Zn in a sufficiently molten state. The amount of Zn vapourized lncreases as the temperature increases, but, for the concentration of Zn on the surface of the Al components simultaneously with NB brazlng, it is desirable to maintain the temperatures of Zn and the atmosphere in the furnace at ll30 to 600C.
Next, the reason why the amount of Zn ls 1 to 10 g/litre, of volume when the volume of the furnace used for the generation of vapour is V litres is that, if the amount of Zn melt is under 1 g/litre, the inslde of the furnace is not filled up with Zn vapour and the contact of Zn vapour with the Al components becomes insufficient resulting ln inappropriated diffusion of ;7n, and, if over 10 g/litra, an excessive diffusion pattern i9 realized on vapour treatment of the Al components with Zn together with the Zn vapour saturation. Also, the reason why the surface area of the Zn melt is 0.05 to 2.5 cm2/litre is because that, if under 0.05 cm2/litre, the inside of the furnace cannot be filled with Zn vapour and, if over 2.~ cm2/litre, the consumption of Zn vapour becomes extreme and the efficiency of the continuous generation of Zn vapour.
Further, the reason whey the flow rate of the N2 gas is 0.05V to V
litres/min is because that, if under 0 05V litres/min, the vapourization of Zn is insufficient and, if over lV litre/min, the consumption of Zn becomes excessive. A flow rate of N2 at the time of NB brazing would be out oE the question even if allowed to flow in amounts of 30 to 60 m /hr or so (when using a continuous furnace with an inner volume of about 2000 litres). From this fact, the Zn vapour can be generated by placing the melt of Zn in the NB
brazing furnace as well as by generation in a different furnace. Moreover, the reasons why the atmosphere in the heating furnace is made so that the dew point and the concentration of oxygen are not higher than 20C and not more than 1000 ppm, respectiveLy, in the vicinity of atmospheric pressure are for the prevention of oxidation of the surface of the Zn melt and for the efficient generation of Zn vapour. For N2 gas, liquid N2 is vapourized for use. Taking the u~e of N2 gas even in NB brazing into consideration, the use of N2 gas is most sultable. Since the conditions for the atmosphere necessary for NB brazing are that the dew polnt is below -30C and the concentration of oxygen is below 1000 ppm. even in the case where Zn is placed in the N~ brazing furnace, Zn can be vapourized without oxidation.
By keeping the conditions as described above while allowing the Zn vapour to generate from the Zn melt, the efficient diffusion of Zn onto the surface of Al components becomes possible. Besi.des, in order to remove the initial oxidation film from the Zn melt, it is effective to melt the Zn metal in the atmospheric furnace after acid pickling. ~oreover, the mechanical removal of the film from the surface of the Zn melt ln the heating furnace is also effective for the enhancement of the generation rate of the vapour of Zn.
~l2~
Example 1 through 9 and Comparative example 1 through 4 Employin~ a continuous atmospherlc furnace with a length of 9 m, a muffle of 300 tntn, a height of 100 mm and a volume of 270 litres and a drying furnace,the brazing of a condenser core with an outer slze of 70 x 200 mm was carried out. For the tube (1), four-hole extrusion-moulded materlal with a thicXness of 5 mm and a width of 22 mm which comprises JIS 1050 alloy and which is shown in Fig. 1 (A) was used and bent. Moreover, for the fin (2), a brazinO sheet cladded with JIS 4343 alloy as a filler onto both sides of core material comprisin~ JIS 3003 alloy (thickness of plate : 0.16 mm, cladding ratio with filler : 10%) was used and corrugated (Fig. 1 (B)). The tube (1) and fin (2) were disposed so that fin (2) was interposed between portions of tube (1) as shown in Fig. 1 (C) and fixed with jigs. After degreasin~, fluoride flux at a concentration of 5 wt. % was coated on it and the moisture was removed in the dryin~ furnace of 200C. The assembly then was placed in the contlnuous atmospheric furnace for brazing.
The continuous atmospheric furnace consists of a preheating zone, a brazing zone and a cooling zone. The preheatin~ zone was kept at 350C, the brazin~ zone was kept at 550C and 600C, and the cooling zone was cooled to 300C or so by a water-cooling jacket structure. Through the furnace, N2 gas was fed. In this way with the retention times in the furnace, and in the brazing zone, 20 and 15 minutes, respectively, and placing a vessel with a surface area of 10 to 800 cm , in which the molten Zn was accommodated, at a brazing zone position kept at 550C, the diffusion of Zn was performed simultaneously with brazing under a flow rate of N2 gas of 20 to 350 litres/min. Using these cores, the diffusion of Zn was examin~d and, at the same time, CASS test was conducted for 500 hours. The results are shown in Table 1.
The diffusion of Zn was shown by the average value determined at five points for each core with X-ray micro-analyser ~EP~A). Moreover, in the CASS
test, after removing the corrosion products, maximum depth of pit was determined by a microscope.
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rj , i ~9!1 , , , _ As evident from Table 1, in those cases involving the method of the invention, No. 1 through 9, the diffusion patterns of ~n with a concentration of surface Zn of 2.1 to 9.5% and a depth of diffusion of Zn oE 110 to 106 ~m, were formed on the surfaces of the tube, and, in the corrosion test according to CASS, too, excellent pitting corrosion resistance was recognized.
Whereas, in the case of comparative method No. 1, the concentration of surface Zn was low and the pitting corrosion resistance was poor because of the small surface area of the melt of Zn and, in the case of comparative method No. 2, the dew point was high and the brazing of fin material was partially insufficient. Moreover, since the surface area of the melt of Zn is large in comparative method No. 3 and the flow rate of N2 is high in comparative method No. 4, it was seen in all cases that the concentration of surface Zn was high, the diffusion was deep, and the deep pitting corrosi~n was generated.
Example 10 through 17 and Comparative example 5 through 9 The fin material (2) was made by corrugating a brazing sheet with a plate thic~ness of 0.16 mm which was coated with a filler of JIS 4343 alloy (6.8-8.2% Si-Al alloy) onto both sides of a core material of JIS 3003 alloy (0.05 -0.270 Cu-1.0-1.570 Mn-A1 alloy) in a coating ratio of 10%. This was dipped into a solution of a 5% concentration of fluoridc flux after washing with solvent, and then dried in a drying furnace at 200C to coat the flux onto the surface. Said fin material (2) and the four-hole tube material (1) with a wall thickness of 0.8 mm, a width of 22 mm and a thickness of 5 mm, which was obtained by extruding JIS 1050 alloy (~1 : above 99.5%) and thereafter processed with a bender and washed with solvent, were pressed with pressing jigs (4) as in Fig. 1 (C) to use for the brazing sample as a core (5) not fitted with unions. Such a core was submitted to the brazing tcst using the NB method in the furnace as below.
As shown in Fig. 2, an endless mesh belt (7) running through the muffle (6) with a width of 300 mm, a height of 100 mm and a length of 9 m (effective inner volume: 270 litres) is furnished, and the preheating zone (8) which preheats the core (5) resting on the belt (7) and transferred by said belt (7); the brazing zone (9) brazing said core (5) and the coollng zone (10) cooling the brazed article, are provided in the continuous atmospheric furnace ~5~ ~
(11). Through the muffle t6) of said furnace tll), N~ ~as amounting to 30 liters/min was fed, the inside of braxing zone t9) was established at 600~C, and the vessel of Zn tl2) with a surface area of 50 cm containing the melt of Zn was placed in the preheating zone t8)-In such a continuous atmospheric furnace, the preheating temperature andthe preheating time in the preheating zone for the di~fusion of the vapour of Zn onto the tube of said core were varied as shown in Table 2, and said core was brazed according to the heat pattern showing the real temperature in the furnace as shown by tA) in Fig. 3. Then, the concentration of surface Zn and the depth of the diffusion of Zn into the tube material of the core obtained under those various conditions were determined at five points respectively.
These results are noted in Table 2. Besides, the dew point and the concentration of oxygen in the atmosphere inside the furnace upon brazing were -35C and 100 ppm, respectively. Further, of the cores thus obtained, GASS
tests for 500 hours were conducted and the maximum depth of pit at that time was determined by microscope. The results are also noted in Table 2.
Moreover, for comparison of the cores manufactured by the method, wherein, after coating said core with flux all over, this was brazed at 600C according to the heat pattern in the furnace shown by tB) in Fig. 3, placing the Zn melt in the preheatin~ zone in the continuous atmospheric furnace aforementioned, and similar tests were carried out, the results of which are noted in Table 2.
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i i i ' ' i i i;;;
'v, ll l ll l ll l ll l l l ~, ~ l ~ . l l l ~, '' '.' ' ' ' ' l ll l l ~o _ o ' o ' o ' ' o ' o ' o ' o o ' o ' o ' o ' -E r~" r~ , ~, o, ~, _ o~ " ~c" u~i, s ~ 3, _ ' _ ' _ ' ' ~ ' _ ' _ ' _ lll l ll i i-, li'i i, i,, i'-i~- ll l I ll ll ll l l l l l r ~, ~ ~ ' ~ r_ ' I ' ' c~.
Ci C~ J 3 _i I ,.', I _i I --', I ,-'i I ,.', I ,; I ,; o 1 1 1 1 o C ~''' i I I i l l l ll l ll l ~i -- i,,, ,,_, i i i i i -,,,, i,,, C~ r.,'~i'''_,'~,'u~,'_',,~,'_ ol'~
cl E; E ¦ , ~ , , , , l l l ll _ ,' ,' , , , I i i , . I_ , . ., ~o~ ll l l ll ll l ll l ll l l o O O I ~ O I ' I ' ' O I o I U~
;,,,;, ~
:2: O ~ " ~ i U~i i ~D i 1~ i cci, O'i , ,1 1 _ I ,i I ,1 1 _ I _ I ,~1, _ . .c i -- I I ,, - -- ~ ' I I . _1 _ a ~ ~ ~3.~': ': ,: ':
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As evldent from Table 2, with the cores according to the method of the invention No. 10 throu~h 17, the concentration of surface Zn was as high as l to 270 and the depth of diffusion was also about 100 ~Im showin~ good diffusion patterns. Further, even directly under the fin, that is, on the surface of the tube material at the brazed portion, similar diffusion patterns were recognized. Moreover, the depth of pit by CASS test was ssen to be excellent. On the other hand, in the cases of comparatlve method No. 5 wherein the preheating time is under 1 minute and comparative method No. 6 through 8 wherein the preheating temperature is higher than the melt temperature of flux, good diffusion patterns could not be obtained and further the depth of the pit was also seen to be two to three times as deep as in the case of the invention. Moreover, in the case of comparative method No. 9 wherein, after coating with flux, brazing was made passing through the Zn vapour, the concentration of diffused Zn was low and the corrosion-resistant effect was markedly poor. From this, it can be seen that the flux on the surface of the tube supresses the adherence of Zn.
Besides, even when the core coated wLth flux onto the fin alone is brazed by raising the temperature continuously as (B) in Fig. 3 or even when the generation sources of Zn are arranged at several points in the furnace kept at a temperature lower than the melting point of flux (about 562C), similar effects to the invention can be obtained.
Example 18 A condenser tube (outer siæe: 5 x 22 mm, b holes, wall thLckness: 0.8 mm) for the air-conditioners of motorcars, which comprises JIS 1050 (pure Al with a purity of above 99.5 wt.%), was extruded at 500C, retained immediately thereafter for 1 minute at 600C in the atmospheric furnace Oe N2 with the melt of Zn therein to treat the tube with Zn vapour and processed with a bender. On the other hand, a brazing sheet with a thickness of 0.16 mm and a width of 22 mm, which was coated with lOqo of a filler equivalent to JIS 4343 not both sides of the core material of Al alloy equivalent to JIS 3003, was corrugated in a height of 20 mm to form the fin. This was assembled wLth said tube having been bent and washed. Then, the noncorrosive fluoride flux, which hitherto was said to have poor pit corrosion resistance was coated at a 3qO
concentration and, after drying, bra~ing was performed for 3 minutes at 600C
~3s~
in N2 gas to manufacture the condens~r.
On this, the CASS test (720 hours) was conducted to dete~nine the maximum depth of pitting corrosion generated on the tube and compared with that generated on the brazed article with flux, which hitherto has excellent pitting corrosion resistance, that is a tube material of a condenser was assembled with the bent tube without treating with Zn vapour and, after brazing for 3 minutes at 600~C in the air with chloride flux containing ZnCl2, the residue of flux was removed by washing with hot water, acid pickling and washing with water. As a result, only shallow corrosions below 0.2 mm were generated in each case and the one given the treatment of the invention showed equal corrosion resistance to that of the brazed article with flux, which is known to have excellent pitting corrosion resistance.
Example 19 Using the fin material similar to Example 18 and the tube not treated with Zn vapour, brazing was performed for 3 minutes at 600C in zir with a chloride type flux containing no ZnC12. This was retained for 10 minutes st 500C in the atmospheric furnace of N2 containing the Zn melt therein to treat with Zn vapour and a diffuse layer of Zn was formed all over the condenser. On this, the CASS test (720 hours) was conducted similarly to Example 18 and the maximum depth of pitting corrosion generated on the tube material was determined to compare with that of a brazed article with chloride flux containing ZnC12, which has excellent pitting corrosion resistance. The brazed article showed a depth of pitting corrosion of 0.15 mm, whereas one given the treatment of the invention showed a depth of pltting corrosion as shallow as 0.08 mm and the pitting corrosion resistance was excellent.
Example 20 A brazing sheet (plate thickness: 0.~ mm, coating ratio: 10%) coated with filler equivalent to JIS 4343 on one side of the core matarial equivalent to JIS 3003 was converted to a tube (outer size: thickness 2.5 mm, width 13 mm) in which the core material comprlsing JIS 3003 faced inslde (water si.dQ) by seam welding. Also, a brazing sheet (thicXness: 1.6 mm) coated with brazing material in a coating ratio of 7% WclS processed to make a headcr (by boring for inserting the tube, providing a flange for attaching the resin tanlc and providing pawls etc. for caullcing). On the other hand, a fin material (plate thickness: 0.1 mm, width 16 mm) equivalent to JIS 3003 was corrugated to a height of 10 mm to form the fin. Said tube, header and fin were assembled, coated with noncorrosive fluoride flux at 5% concentration and, after drying, heated for brazing for 3 minutes at 600C in the atmosphere of N2. Successively, the vapour of Zn generated by melting Zn under heat at 500C in a different furnace was introduced to the brazing furnace without lowering the temperature, making the N2 gas a carrier and treatment with the Zn vapour was performed simultaneously with brazing to manufactura the radiator.
Next, a brazing sheet (plate thicXness: 0.4 mm) coated with a filler equivalent to JIS 4343 on one side of the core material equivalent to JIS 3003 (cladding ratio: 1070) and with a skin material equivalent to JIS 7072, excellent in corrosion resistance, onto the other side (cladding ratio: 10~) was converted to a tube (outer size: thickness 2.5 mm, width 13 mm) in w~ich the core material comprising JIS 7072 faced inside (water side), ~y seam welding. Also, a brazing sheet with a thickness of 1.6 mm coated similarly with skin material equivalent to JIS 7072 and fi.ller equivalent to JIS 43~l3 was processed to make a header. Furthermore, a fin material (thicXness: 0.1 mm, width: 16 mm) equivalent to JIS 3003 was corrugated to a height of 10 mtn to manufacture the fin. This tube, header and fin were assembled and bra~ed as described above. At this time, one set was treated with Zn vapour simultaneously with bra~ing and the other set was not trsated with ~n vapour.
To three sets of radiators thus manufactured, tanks made of resin were attached respectively and the corrosion test was conducted by allowing a corrosive solution of 10 ppm of Cu in tap water, to circulate internally. The test was conducted for 3 months making 8 hours at 80C and 16 hours at room temperature as 1 cycle. The flow velocity of corrosive solution was 40 litres/min. AFter completion of the test, the maximum depth of pitting corrosion of the tube material of the radiator given the treatment of the invention was 0.07 mm i.n either case, whereas, with one not given the treatment (which used the skin materlal equivalent to JIS 7072 which is excellent in corrosion resistance), the maximum depth of pitting corrosion was 0.15 mm. From this, it can be seen that pitting corrosion resistance is improved remarkably by treating with Zn vapour.
Example 21 through 31 and Comparative example 10 through 16 An Al plate with a thickness of 1 mm, a width of 50 mm and a length of 100 mm was brazed in an NB brazing furnace and, at the same time, the treatment of concentrating Zn on the surface of the Al plate was carried out. For the NB
brazing furnace, a muffle type furnace wlth a height of 400 ~n, a width of 600 mm, a length of 2000 mm and a volume of 480 litres provided the preheating chamber and the heating chamber therein was used. ~he Al p:Late was coated with fluoride noncorrosive flux at 5% concentration. Ten sheets of these plates were hung down together from a jig and fed to the drying furnace heated to 200C to evaporate the moisture. These were placed in the preheating chamber heated to 550C in the NB brazing furnace. After being retained for 5 minutes, they were transferred to the heating chamber heated to 600C and retained for 15 minutes, whereupon brazing for 3 minutes at a real temperature of 600C was performed. After heating, they were taken out rapidly into the air via the preheating chamber and allowed to cool.
Into the heating chamber of the NB brazing furnace, 240 litres~min of N2 gas were introduced via the preheating chamber and the atmosphere inside the furnace was kept so that the dew point and the concentration of oxygen were at -35C and 100 ppm, respectively. On the other hand, Zn was placed in a generating furnace for Zn vapour, with a height of 200 mm, a width of 300 tnm, a length of 500 mm and a volume of 30 litres, and melted at 500C, Iceeping the atmosphere inside the furnace so that the dew point, and the concentration of oxygen, stayed at -40 to -30C and 100 to 300 ppm, respectively, by flowing N2 gas through the furnace to allow the Zn vapour to generate. The Zn vapour generated in this way, was introduced into the preheating chamber of the NB brazing furnace via a pipe kept at 550C and the Zn concentrating treatment was performed on the surface of the Al plate simultaneously with NB
brazing. At this time, the behaviour of Zn (surface concentration and depth of diffusion) on the surface of Al, when varying the flow rate of N2, the amount of Zn tnelt and the surface area of the Zn melt in the Zn vapour generating furnace was examined by means of EPMA analysis. The results are shown in Table 3.
Besldes, the EP~A analysls was conducted by measuring at five points for each of 10 sheets of Al plates and determining the average value of the 50 points.
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As evident from Table 3, in the case of generatlon of Zn vapour in accordance with the method of the invention, No. 21 through 31, dlffusion patterns of Zn such that the concentration of surface Zn was 2 to 10~ a~d the depth of diffusion was lOO,um or so, were shown. From this, lt can be seen that the pitting corrosion resistance equal to that of a flux-brazed artlcle excellent in corrosion resistance is obtained.
On the contrary, in tha case of comparative methods outsi.de of the conditions prescribed by the invention, Zn diffusion patterns excellent in pitting corrosion resistance could not be obtained, or there arose the problem that the consumption of zn became high because of the deep diffusion of ~n.
For example, in the case of comparative methods No. 10, 12, 14 and 16, sufficient Zn vapour did not generate, failing to show diffusion patterns of Zn excellent in pitting corrosion resistance. ~oreover, in the case of comparative methods No. 11, 13 and 15, the generation of Zn vapour was remarkable and diffusion was deep resulting in problems of high consumption of Zn, deep pitting corrosion, etc.
Example 32 through 35 The NB brazing was performed similarly to Example 21. At that time, Zn was placed in the preheating chamber (height: 40mm, width: 600 mm~ length: 900 mm, volume: 216 litres) to melt and vapourize and the Zn concentrating treatment was given to the surface of an Al plate simultaneously with the preheating of the Al plate in the preheating chamber. Then, the diffuslon of Zn was examined similarly to Example 21. As a result, in all cases of the method of the invention, No. 32 through 35, excellent diffusion patterns of Zn were obtained as shown in Table 4.
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Example 36 and 37 The NB brazing was performed similarly to Example 21. AT that time, Zn was placed in the heating chamber (height: 400 mm, wldth: 600 mm, length: 1100 mm, volume: 246 litres) to melt and vapourize and the ~n coneentrating treatment was given to the surface of the Al plate simultsneously with he NB
braæing of AL plate in the heating chamber. Then, the diffusion of Zn was examined as in Example 21. As a resul.t, in all cases of the method of the invention, No. 36 and 37, excellent diffusion patterns of Zn were obtained as shown in Table 5.
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As described, in accordance with the invention, when brazing a heat-exchanger requiring pitting corrosion resistance, with noncorrosive flux, a Zn diffusion pattern excellent in pitting corrosion resistance can be formed on the Al components simultaneously with brazinz, thereby the process can be shortened remarkably compared with the zincate treatment befora the brazlng, and thus manufacturing costs can be reducsd. Moreover, by treating with Zn vapour without coating flux onto the tube material and yet at a temperature lower than that at which the flux flows, it is possible to prevent the flux film from suppressing the adherence of Zn. Therefore, such a way has been disclaimed utilizable not only for condenser cores and evaporator cores using extruded multihole tubes for the tube material, but also for drawn-cup evaporators using brazing sheets for the tube material, radiators using seam welded Al tube, and the like to~ether with the improvement in pitting corrosion resistance.
Further, the sacrificial layer of Zn, which improves remarkably the pitting corrosion resistance of Al or Al alloy components with simple facility, can be formed easily and, at the same time, the generation of the Zn vapour has been ~ade easy to permit the diffusion of Zn simultaneously with brazing in NB brazing usin~ fluoride noncorrosive flux. Therefore, the invention exerts an extremely remarkable effect, industrially.
(~1) To the extruded multihole tubes used for condenser tubes, a layer covered with Zn is provided beforehand by flame spray coating with Zn, zincate treatment, Zn plating, etc. Then, the diffused layer of Zn is formed by heating for brazin~ to prevent the pitting corrosion of the extruded multihole tube.
All of the conventional methods noted above to a~sure the corroslon resistance of aLuminum heat-exchangers have the followlng problems and improvements therein are earnestly desired.
In the method (1) above, post-treatment such as washing with water etc.
becomes necessary because of the occurrence of a corrosive flux residue and the production costs including the effluent treatment etc. accompanied by this becomes high. In method (2) above, there is a restriction on the range of sacrificial actlon of fin material and the application thereof does not extend all over the core of the heat-exchanger. In the method of adding Zn, Sn, In etc. to the filler of the brazing sheet, the sacrificial layer cannot be formed sufficiently due to the melting of filler and inversely, at the filler portion where the filler builds up, the sacrificial layar often extends into the core material deeply together with the diffusion of filler to thereby lower the pitting corrosion resistance. In the method (3) above, the sacrificial layer must be applisd beforehand and the application to extruded multihole tubes etc. is difficult though production is possible using a brazing sheet. Also, in the method (4) above, the surface of the Al component becomes heterogeneous through the treatment with Zn resulting in the problems such as dropping out etc. due to the bending etc.
With regard to method (1), a brazing method using nonhygroscopic and noncorrosive fluoride flux has been developed. In this method, the eutectic composition of, for example, KAlF4-K3AlF6 is used for the flux, and the brazlng is performed by heatln~ to about 600C in the furnace, where the dew point i9 controlled to be not higher than -40C and the partial pressure of 2 is controlled to be not more than 1000 ppm, and introducing the inert gas, mainly N2 ~hereinafter, thls brazing method is referred to as the NB
method). Here, washin~ aftar brazing is unnecessary.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 (A), (B) and (C) show the assembling of the core of an aluminum heat-exchanger, wherein (A) is a perspective view of the extruded tube material after bending, (;3) is a perspective view of the fin material corrugated, and (C) is a perspective view of the core assembled by pressing 3~
with jigs. Fig. 2 illustrates a continuous atmospheric furnace. Fig. 3 is a graph showing the heat pattern in the furnace when brazing in the contlnuous atmospheric furnace.
For example, when manufacturlng a condenser of alumin~ml by the ~B method, the extruded multihole tubes (hereinafter, abbreviated as tube material) (1) is formed with a bender in a serpentine shape as shown in Fig. 1 (A) and the fin material (2) corrugated as shown in Fig. 1 (B) are assembled as shown in Fig. 1 (C). After fitting the unions (3) and (3') to the inlet and outlet of the refrigerant tube material (1), respectively, they are fixed by pressing jigs (4) to maXe the core (5). Following, the degreasing of said core, fluoride type flux is coated all over it and then thls is fed to the brazing furnace to preheat and heat according to the heat pattern shown in Fig. 3 (B). Thus, the fin material and the tube material are brazed and assembled.
For the fin material, the brazing sheet (thickness: 0.16 mm) clad with JIS
4343 filler of Al-Si alloy on both sides of the core material comprising JIS
3003 ~ 1% Zn alloy, is used. However, due the the use of motorcars in areas of salt damage, the improvement in the exterior pitting corrosion resistance of said heat-exchangers has become important recently. Particularly, in the aforementioned NB method, not only the use of sacrificial fins but also the corrosion-resistant treatment of the tube material itself as noted below have become common.
(1) By submitting the tube material to the zincate treatment before brazing, Zn is allowed to deposit onto the surface of the tube material and, by the heating for brazing, Zn is allowed to diffuse into the tube material.
(2) By adding Zn to the fluoride flux, Zn is allowed to diffuse from flux into the tube material upon heating for brazing.
However, the zincate treatment before brazing brings about high cost and, at the same time, since an alkali solution is used for the zincate treatment of tube material, the invasion of the solution into the tube materia]. must be prevented, resulting in many difEiculties in the operation.
~ oreover, in the method of adding Zn to the flux, low concentrations of flux of about 10% are used satlsfactorily in the case of fluoride flux due to its strong activity contrary to the use of high concentrations of flux of the order of 50 to 6070, in the case of chloride flux. As a result, large amounts of Zn cannot be supplied and the desired amount of Zn cannot be allowed to ~35~
diffuse all over the surface.
On the other hand, a method is sho~l in Japanese Patent Publication No.
Sho 59-31588, wherein the vapour of Zn is blo~l onto the surface of extruded A1 material to form a layer covered with Zn, this is allowed to diffuse onto the surface of extruded Al material on heating for brazing etc., and the corrosion resistance is improved through the sacrificial effect of the surface layer. The generation of the Zn vapour in thls case is performed in such a way that the gas-introductory pipe is inserted into the melt of Zn kept at 550~, the Zn vapour is allowed to disperse into N2 gas as a carrier by supplying N2 gas in bubbles, and the ~n vapour is blown onto the surface of the Al extrusion-moulded material via the hot passage to form the layer of Zn on the surface of the extrusion-moulded Al material. The thickness of the Zn layer is determined by the extruding velocity of the extrusion-moulded material and the supply of gas.
However, with the extrusion-moulded Al material, the blowing of the Zn vapour is easy lnside the extruded material, but, on the outside, the Zn vapour tends to scatter and further, oxidation proceeds in the air.
Therefore, it is difficult to provide a uniform layer of Zn in a short time.
Moreover, with an aluminum heat-exchanger using a brazing sheet, the blowing of Zn vapour is difficult when manufacturing the brazing sheet material because the large width of the plate makes the application impossible.
Furthermore, since bubbled N2 gas is used to generate the Zn vapour, a facility for supplying N2 gas under high pressure, a furnace for retaining thé melt of Zn and pipes are needed.
As a result of extensive investigations in view of this situation, a method of manufacturing aluminum heat-exchangers wherein Zn is allowed t:o diffuse onto the surface of the Al components to be brazed simply and inexpensively by the NB brazing method to improve pitting corrosion resistance; a method of concentrating zinc on the surface layer of A1 components wherein Zn is allowed to concentrate uniformly at each portion by a simple method without affecting brazin~ in all steps including the step of preparing the material, the step of brazing, the step after brazing, etc. to provide an improvement in pitting corrosion resistance; and a method of generating Zn vapour for the concentration of a Zn coating on Al components wherein the coating with Z.n vapour and the diffusion of Zn are performed simultaneously with brazing through the efEicient ~ensration of Zn vapour are provided by the invention.
SU~MARY OF THE INVENTION
The invention provides a method of manufacturing heat-exchangers characterized in that, in the manufacture of aluminum heat-exchangers to be brazed under heat in a furnace with an inert gas atmosphere using fluoride flux, Zn is disposad at a temperature of 430 to 620C in the furnace to melt and vapourize it and the Zn vapour is allowed to contact the fin material and the tube material coated wlth said flux simultaneously while brazing under heat of these Al components to diffuse Zn.
The invention also provides a method of manufacturing heat-exchangers characterized in that, in the manufacture of heat-exchangers as described above, the fin material coated with fluoride flux and dried and the tube material without flux are assembled and retained for not less than 1 minute in Zn vapour at a temperature lower than the melting point of said flux and higher than the temperature to which these components are heated, in an inert gas and thereafter the brazing is performed at a temperature higher than the meltin~ point of the flux.
The invention also relates to a method of concentrating Zn on the surface layer of said Al components and a method of generating Zn vapour for the concentration of surface Zn, respectively.
DETAILED DESCRIPTION OF THE INVENTION
In the first method of manufacturing heat-exchangers in accordance with the invention, aEter coating the Al components for a heat-exchanger with a fluoride flux, this is heated and dried at about 200C in a preheating zone.
Then, brazing is performed by heating for several minutes at 600C (real temperature) in the brazing zone in an inert gas atmosphere. At this time, Zn is placed at a position where the temperature in the furnace becomes ll30 to 620C to melt and vapourize lt and the Al components are allowed to contact the Zn vapour generated simultaneously with the brazing under heat of the Al components to cause Zn diffusion into thc Al components.
Although the Al-Si filler melts near 577C, the diffusion of Zn proceeds from a temperature lower than this regardless of the state oE the flux (be~ore or after melting) adhered to the surface, and the diffusion of Zn into Al components occurs simultaneously with the brazing of the Al components. The Zn diffusion into the Al component depends on the generation of the Zn vapour.
The reason why Zn is dispossd at a position at a temperature of ~30 to 620C in the furnace to melt and vapourize is that the generatlon of Zn vapour is unacceptable unless above the melt temperature of Zn ~130C) and it is necessary to keep Zn above this temperature. On the other hand, in order to allow the diffusion of Zn to occur simultaneously with brazing, the upper temperature limit is 620C. Moreover, the concentration of oxygen in the inert gas atmosphere inside the furnace should be not more than 1000 ppm and the dew point hot higher than -30C. If outside of these ranges, good brazing cannot be obtained, and the generating efficiency of the Zn vapour is lowered.
~he flow rate of inert gas is suitably one tenth of the effective inner volume of the furnace per minute. If under this, the concentration of oxygen and the dew point cannot be maintained within said ranges and, if over the consumption of inert gas increases and the ~eneration of Zn vapour also increases to make the diffusion excessive leading to a lowering in the corrosion resistance.
Further, the surface area of the melt of Zn is desirably 0.05 to 2.5 cm per effective unit inner volume (litre) of furnace, thereby the generation of Zn vapour and efficient diffusion becomes efficiently possible.
Also, for uniform diffusion of Zn into the Al components, it is important to make the contact of Al components with the Zn vapour unifo~n. For this reason, appropriate agitation is desirable as well as controlled gas flow.
In the second manufacturing method of the invention, the reason why the flux is coated onto only the fin material is that, if the flux is coated beforehand onto the tube material, also, the flux acts as a barrier film and can hinder the adherence of the Zn vapour to the surface of tube material when exposed to Zn vapour to allow the Zn to diffuse into the tube material after assemb].y. Al50, the reason why the heating of these assembled components in the inert gas and exposure to the Zn vapour are practised at a temperature lower than the melting point of said flux is to avoid melting the flux coated on the fin material which would cause it to cover the surface of the tube material during the diffusion of Zn into the tube material.
Moreover, in order to allow Zn to adhere efficiently to the surface of the tube material before the melting of fluoride flux, the temperature of the Zn vapour is optimally 550 to 560C which is higher than the temperature of the tube material and lower than the melting point of flux (about 562C). If the retaining time is under 1 minute, the amount of Zn adhered ~o the sur~ace of tube material is insufficient and thus the corrosion-preventative effect i9 also unsatlsfactory. sosides~ w~en lowering said temperature of the Zn vapour, the retalning time is necessarily lengthened.
Furthermore, in order to generate the Zn vapour efficiently in the brazing furnace, the concentration of oxygen in the furnace and the dew point are desirably not more than 1000 ppm and not higher than ~30C similarly to the case of said first manufacturing method wherein the diffusion of Zn is performed simultaneously with brazing under heat. The flow rate of the inert gas per minute is optimally and economically one tenth of the volume of the furnace for the maintenance of the atmosphere in the furnace and the generation of the Zn vapour and the surface area of the Zn melt in the furnace is also effective if made 0.05 to 2.5 cm per unit volume (litre) of the furnace.
The invention provides the general method of concentrating Zn on the surface layer of Al components when heating Al or Al alloy components in the Zn vapour. In this method, the Zn vapour may be generated by heating Al or Al alloy components and Zn simultaneously in the furnace or the Zn vapour generated by heating Zn in a different apparatus may be used. The treatment temperature would be out of the question if over the melting temperature of Zn (about 420C), while the higher the temperature, the larger the surface concentration and the greater the diffusion depth. The treatment time similarly affects the diffusion pattern of Zn on the surface of components.
The atmosphere for the treatment is desirably inert gases such as N2 gas etc., but concentration of Zn is possible even in air. The pressure is sufficient if near atmosph0ric pressure, or the Zn vapour may be generated in a vacuum.
To allow Zn to diffuse when the Al or Al alloy components are being formed, they are passed through the furnaco holding vapourized Zn therein at the time of hot processing tt-olling or extrusion), or the Zn vapour may be sprayed from nozzles. The change in the surface ptoperties due to the deposition of Zn is removed and there is no restrictlon on the shape of materials. E'or example, when applying Zn when brazing the Al components, an appropriate amount of the Zn melt may be placed in the brazing furnace. Zn diffuses also onto the surface of brazing material without que.stion.
When heating Zn above the melting temperature and heating Al. or ~1 a].loy components in the Zn vapour generated, Zn diffuses from the surface to the inner portion of the Al or Al alloy components to glve a sacr~ticial effect to said components. The diffusion of Zn shows such a diffusion pattern that the surface is highest in the concentration and the pitting corrosion resistance is best. The diffusion of Zn is not affected by the flux even when brazing using fluoride flux. Also~ by carrying out the treatment of the invention at a lower temperature than the melting point of filler after the brazin~ of Al or Al alloy components, Zn can be allowed to diffuse uniformly onto the surface. This treatment may be applied to the core of -the heat-exchanger manufactured by for example vacuum-brazing. Further, by applying to Al-Mg alloy etc., the surface layer can be alloyed to Al-~g-Zn to improve the strength of the alloy.
The method of generating the vapour of Zn for the concentration of surface Zn on Al components, is applied to the NB method wherein Zn is placed in the heating furnace, N2 gas being flowed therethrough as a carrier gas; Zn and the atmosphere in the furnace are heated above 430C to melt the Zn, and the Zn vapour is generated from the Zn melt. The conditions are characterized in that, when the inner volume of the heating furnace is put as V litres, the amount of the melt of Zn, the surface area of the melt of Zn and the flow rate of N2 gas are made 1 to 10 ~/litre, 0.05 to 2.5 cm /litre and 0.05 V to V
litre~min, respectively, and the atmosphere in the heating furnace is retained so that the dew point and the concentration of oxygen become not higher than -20C and not more than 1000 ppm, respectively, in the vicinity of atmospheric pressure to allow the Zn vapour to generate from the melt of Zn.
The reason why Zn and the atmosphere in the furnace are heated above 430C
is because that, for the vapourization of Zn in the N2 atmosphere under atmospheric pressure, it is necessary to maintain Zn in a sufficiently molten state. The amount of Zn vapourized lncreases as the temperature increases, but, for the concentration of Zn on the surface of the Al components simultaneously with NB brazlng, it is desirable to maintain the temperatures of Zn and the atmosphere in the furnace at ll30 to 600C.
Next, the reason why the amount of Zn ls 1 to 10 g/litre, of volume when the volume of the furnace used for the generation of vapour is V litres is that, if the amount of Zn melt is under 1 g/litre, the inslde of the furnace is not filled up with Zn vapour and the contact of Zn vapour with the Al components becomes insufficient resulting ln inappropriated diffusion of ;7n, and, if over 10 g/litra, an excessive diffusion pattern i9 realized on vapour treatment of the Al components with Zn together with the Zn vapour saturation. Also, the reason why the surface area of the Zn melt is 0.05 to 2.5 cm2/litre is because that, if under 0.05 cm2/litre, the inside of the furnace cannot be filled with Zn vapour and, if over 2.~ cm2/litre, the consumption of Zn vapour becomes extreme and the efficiency of the continuous generation of Zn vapour.
Further, the reason whey the flow rate of the N2 gas is 0.05V to V
litres/min is because that, if under 0 05V litres/min, the vapourization of Zn is insufficient and, if over lV litre/min, the consumption of Zn becomes excessive. A flow rate of N2 at the time of NB brazing would be out oE the question even if allowed to flow in amounts of 30 to 60 m /hr or so (when using a continuous furnace with an inner volume of about 2000 litres). From this fact, the Zn vapour can be generated by placing the melt of Zn in the NB
brazing furnace as well as by generation in a different furnace. Moreover, the reasons why the atmosphere in the heating furnace is made so that the dew point and the concentration of oxygen are not higher than 20C and not more than 1000 ppm, respectiveLy, in the vicinity of atmospheric pressure are for the prevention of oxidation of the surface of the Zn melt and for the efficient generation of Zn vapour. For N2 gas, liquid N2 is vapourized for use. Taking the u~e of N2 gas even in NB brazing into consideration, the use of N2 gas is most sultable. Since the conditions for the atmosphere necessary for NB brazing are that the dew polnt is below -30C and the concentration of oxygen is below 1000 ppm. even in the case where Zn is placed in the N~ brazing furnace, Zn can be vapourized without oxidation.
By keeping the conditions as described above while allowing the Zn vapour to generate from the Zn melt, the efficient diffusion of Zn onto the surface of Al components becomes possible. Besi.des, in order to remove the initial oxidation film from the Zn melt, it is effective to melt the Zn metal in the atmospheric furnace after acid pickling. ~oreover, the mechanical removal of the film from the surface of the Zn melt ln the heating furnace is also effective for the enhancement of the generation rate of the vapour of Zn.
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Example 1 through 9 and Comparative example 1 through 4 Employin~ a continuous atmospherlc furnace with a length of 9 m, a muffle of 300 tntn, a height of 100 mm and a volume of 270 litres and a drying furnace,the brazing of a condenser core with an outer slze of 70 x 200 mm was carried out. For the tube (1), four-hole extrusion-moulded materlal with a thicXness of 5 mm and a width of 22 mm which comprises JIS 1050 alloy and which is shown in Fig. 1 (A) was used and bent. Moreover, for the fin (2), a brazinO sheet cladded with JIS 4343 alloy as a filler onto both sides of core material comprisin~ JIS 3003 alloy (thickness of plate : 0.16 mm, cladding ratio with filler : 10%) was used and corrugated (Fig. 1 (B)). The tube (1) and fin (2) were disposed so that fin (2) was interposed between portions of tube (1) as shown in Fig. 1 (C) and fixed with jigs. After degreasin~, fluoride flux at a concentration of 5 wt. % was coated on it and the moisture was removed in the dryin~ furnace of 200C. The assembly then was placed in the contlnuous atmospheric furnace for brazing.
The continuous atmospheric furnace consists of a preheating zone, a brazing zone and a cooling zone. The preheatin~ zone was kept at 350C, the brazin~ zone was kept at 550C and 600C, and the cooling zone was cooled to 300C or so by a water-cooling jacket structure. Through the furnace, N2 gas was fed. In this way with the retention times in the furnace, and in the brazing zone, 20 and 15 minutes, respectively, and placing a vessel with a surface area of 10 to 800 cm , in which the molten Zn was accommodated, at a brazing zone position kept at 550C, the diffusion of Zn was performed simultaneously with brazing under a flow rate of N2 gas of 20 to 350 litres/min. Using these cores, the diffusion of Zn was examin~d and, at the same time, CASS test was conducted for 500 hours. The results are shown in Table 1.
The diffusion of Zn was shown by the average value determined at five points for each core with X-ray micro-analyser ~EP~A). Moreover, in the CASS
test, after removing the corrosion products, maximum depth of pit was determined by a microscope.
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rj , i ~9!1 , , , _ As evident from Table 1, in those cases involving the method of the invention, No. 1 through 9, the diffusion patterns of ~n with a concentration of surface Zn of 2.1 to 9.5% and a depth of diffusion of Zn oE 110 to 106 ~m, were formed on the surfaces of the tube, and, in the corrosion test according to CASS, too, excellent pitting corrosion resistance was recognized.
Whereas, in the case of comparative method No. 1, the concentration of surface Zn was low and the pitting corrosion resistance was poor because of the small surface area of the melt of Zn and, in the case of comparative method No. 2, the dew point was high and the brazing of fin material was partially insufficient. Moreover, since the surface area of the melt of Zn is large in comparative method No. 3 and the flow rate of N2 is high in comparative method No. 4, it was seen in all cases that the concentration of surface Zn was high, the diffusion was deep, and the deep pitting corrosi~n was generated.
Example 10 through 17 and Comparative example 5 through 9 The fin material (2) was made by corrugating a brazing sheet with a plate thic~ness of 0.16 mm which was coated with a filler of JIS 4343 alloy (6.8-8.2% Si-Al alloy) onto both sides of a core material of JIS 3003 alloy (0.05 -0.270 Cu-1.0-1.570 Mn-A1 alloy) in a coating ratio of 10%. This was dipped into a solution of a 5% concentration of fluoridc flux after washing with solvent, and then dried in a drying furnace at 200C to coat the flux onto the surface. Said fin material (2) and the four-hole tube material (1) with a wall thickness of 0.8 mm, a width of 22 mm and a thickness of 5 mm, which was obtained by extruding JIS 1050 alloy (~1 : above 99.5%) and thereafter processed with a bender and washed with solvent, were pressed with pressing jigs (4) as in Fig. 1 (C) to use for the brazing sample as a core (5) not fitted with unions. Such a core was submitted to the brazing tcst using the NB method in the furnace as below.
As shown in Fig. 2, an endless mesh belt (7) running through the muffle (6) with a width of 300 mm, a height of 100 mm and a length of 9 m (effective inner volume: 270 litres) is furnished, and the preheating zone (8) which preheats the core (5) resting on the belt (7) and transferred by said belt (7); the brazing zone (9) brazing said core (5) and the coollng zone (10) cooling the brazed article, are provided in the continuous atmospheric furnace ~5~ ~
(11). Through the muffle t6) of said furnace tll), N~ ~as amounting to 30 liters/min was fed, the inside of braxing zone t9) was established at 600~C, and the vessel of Zn tl2) with a surface area of 50 cm containing the melt of Zn was placed in the preheating zone t8)-In such a continuous atmospheric furnace, the preheating temperature andthe preheating time in the preheating zone for the di~fusion of the vapour of Zn onto the tube of said core were varied as shown in Table 2, and said core was brazed according to the heat pattern showing the real temperature in the furnace as shown by tA) in Fig. 3. Then, the concentration of surface Zn and the depth of the diffusion of Zn into the tube material of the core obtained under those various conditions were determined at five points respectively.
These results are noted in Table 2. Besides, the dew point and the concentration of oxygen in the atmosphere inside the furnace upon brazing were -35C and 100 ppm, respectively. Further, of the cores thus obtained, GASS
tests for 500 hours were conducted and the maximum depth of pit at that time was determined by microscope. The results are also noted in Table 2.
Moreover, for comparison of the cores manufactured by the method, wherein, after coating said core with flux all over, this was brazed at 600C according to the heat pattern in the furnace shown by tB) in Fig. 3, placing the Zn melt in the preheatin~ zone in the continuous atmospheric furnace aforementioned, and similar tests were carried out, the results of which are noted in Table 2.
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As evldent from Table 2, with the cores according to the method of the invention No. 10 throu~h 17, the concentration of surface Zn was as high as l to 270 and the depth of diffusion was also about 100 ~Im showin~ good diffusion patterns. Further, even directly under the fin, that is, on the surface of the tube material at the brazed portion, similar diffusion patterns were recognized. Moreover, the depth of pit by CASS test was ssen to be excellent. On the other hand, in the cases of comparatlve method No. 5 wherein the preheating time is under 1 minute and comparative method No. 6 through 8 wherein the preheating temperature is higher than the melt temperature of flux, good diffusion patterns could not be obtained and further the depth of the pit was also seen to be two to three times as deep as in the case of the invention. Moreover, in the case of comparative method No. 9 wherein, after coating with flux, brazing was made passing through the Zn vapour, the concentration of diffused Zn was low and the corrosion-resistant effect was markedly poor. From this, it can be seen that the flux on the surface of the tube supresses the adherence of Zn.
Besides, even when the core coated wLth flux onto the fin alone is brazed by raising the temperature continuously as (B) in Fig. 3 or even when the generation sources of Zn are arranged at several points in the furnace kept at a temperature lower than the melting point of flux (about 562C), similar effects to the invention can be obtained.
Example 18 A condenser tube (outer siæe: 5 x 22 mm, b holes, wall thLckness: 0.8 mm) for the air-conditioners of motorcars, which comprises JIS 1050 (pure Al with a purity of above 99.5 wt.%), was extruded at 500C, retained immediately thereafter for 1 minute at 600C in the atmospheric furnace Oe N2 with the melt of Zn therein to treat the tube with Zn vapour and processed with a bender. On the other hand, a brazing sheet with a thickness of 0.16 mm and a width of 22 mm, which was coated with lOqo of a filler equivalent to JIS 4343 not both sides of the core material of Al alloy equivalent to JIS 3003, was corrugated in a height of 20 mm to form the fin. This was assembled wLth said tube having been bent and washed. Then, the noncorrosive fluoride flux, which hitherto was said to have poor pit corrosion resistance was coated at a 3qO
concentration and, after drying, bra~ing was performed for 3 minutes at 600C
~3s~
in N2 gas to manufacture the condens~r.
On this, the CASS test (720 hours) was conducted to dete~nine the maximum depth of pitting corrosion generated on the tube and compared with that generated on the brazed article with flux, which hitherto has excellent pitting corrosion resistance, that is a tube material of a condenser was assembled with the bent tube without treating with Zn vapour and, after brazing for 3 minutes at 600~C in the air with chloride flux containing ZnCl2, the residue of flux was removed by washing with hot water, acid pickling and washing with water. As a result, only shallow corrosions below 0.2 mm were generated in each case and the one given the treatment of the invention showed equal corrosion resistance to that of the brazed article with flux, which is known to have excellent pitting corrosion resistance.
Example 19 Using the fin material similar to Example 18 and the tube not treated with Zn vapour, brazing was performed for 3 minutes at 600C in zir with a chloride type flux containing no ZnC12. This was retained for 10 minutes st 500C in the atmospheric furnace of N2 containing the Zn melt therein to treat with Zn vapour and a diffuse layer of Zn was formed all over the condenser. On this, the CASS test (720 hours) was conducted similarly to Example 18 and the maximum depth of pitting corrosion generated on the tube material was determined to compare with that of a brazed article with chloride flux containing ZnC12, which has excellent pitting corrosion resistance. The brazed article showed a depth of pitting corrosion of 0.15 mm, whereas one given the treatment of the invention showed a depth of pltting corrosion as shallow as 0.08 mm and the pitting corrosion resistance was excellent.
Example 20 A brazing sheet (plate thickness: 0.~ mm, coating ratio: 10%) coated with filler equivalent to JIS 4343 on one side of the core matarial equivalent to JIS 3003 was converted to a tube (outer size: thickness 2.5 mm, width 13 mm) in which the core material comprlsing JIS 3003 faced inslde (water si.dQ) by seam welding. Also, a brazing sheet (thicXness: 1.6 mm) coated with brazing material in a coating ratio of 7% WclS processed to make a headcr (by boring for inserting the tube, providing a flange for attaching the resin tanlc and providing pawls etc. for caullcing). On the other hand, a fin material (plate thickness: 0.1 mm, width 16 mm) equivalent to JIS 3003 was corrugated to a height of 10 mm to form the fin. Said tube, header and fin were assembled, coated with noncorrosive fluoride flux at 5% concentration and, after drying, heated for brazing for 3 minutes at 600C in the atmosphere of N2. Successively, the vapour of Zn generated by melting Zn under heat at 500C in a different furnace was introduced to the brazing furnace without lowering the temperature, making the N2 gas a carrier and treatment with the Zn vapour was performed simultaneously with brazing to manufactura the radiator.
Next, a brazing sheet (plate thicXness: 0.4 mm) coated with a filler equivalent to JIS 4343 on one side of the core material equivalent to JIS 3003 (cladding ratio: 1070) and with a skin material equivalent to JIS 7072, excellent in corrosion resistance, onto the other side (cladding ratio: 10~) was converted to a tube (outer size: thickness 2.5 mm, width 13 mm) in w~ich the core material comprising JIS 7072 faced inside (water side), ~y seam welding. Also, a brazing sheet with a thickness of 1.6 mm coated similarly with skin material equivalent to JIS 7072 and fi.ller equivalent to JIS 43~l3 was processed to make a header. Furthermore, a fin material (thicXness: 0.1 mm, width: 16 mm) equivalent to JIS 3003 was corrugated to a height of 10 mtn to manufacture the fin. This tube, header and fin were assembled and bra~ed as described above. At this time, one set was treated with Zn vapour simultaneously with bra~ing and the other set was not trsated with ~n vapour.
To three sets of radiators thus manufactured, tanks made of resin were attached respectively and the corrosion test was conducted by allowing a corrosive solution of 10 ppm of Cu in tap water, to circulate internally. The test was conducted for 3 months making 8 hours at 80C and 16 hours at room temperature as 1 cycle. The flow velocity of corrosive solution was 40 litres/min. AFter completion of the test, the maximum depth of pitting corrosion of the tube material of the radiator given the treatment of the invention was 0.07 mm i.n either case, whereas, with one not given the treatment (which used the skin materlal equivalent to JIS 7072 which is excellent in corrosion resistance), the maximum depth of pitting corrosion was 0.15 mm. From this, it can be seen that pitting corrosion resistance is improved remarkably by treating with Zn vapour.
Example 21 through 31 and Comparative example 10 through 16 An Al plate with a thickness of 1 mm, a width of 50 mm and a length of 100 mm was brazed in an NB brazing furnace and, at the same time, the treatment of concentrating Zn on the surface of the Al plate was carried out. For the NB
brazing furnace, a muffle type furnace wlth a height of 400 ~n, a width of 600 mm, a length of 2000 mm and a volume of 480 litres provided the preheating chamber and the heating chamber therein was used. ~he Al p:Late was coated with fluoride noncorrosive flux at 5% concentration. Ten sheets of these plates were hung down together from a jig and fed to the drying furnace heated to 200C to evaporate the moisture. These were placed in the preheating chamber heated to 550C in the NB brazing furnace. After being retained for 5 minutes, they were transferred to the heating chamber heated to 600C and retained for 15 minutes, whereupon brazing for 3 minutes at a real temperature of 600C was performed. After heating, they were taken out rapidly into the air via the preheating chamber and allowed to cool.
Into the heating chamber of the NB brazing furnace, 240 litres~min of N2 gas were introduced via the preheating chamber and the atmosphere inside the furnace was kept so that the dew point and the concentration of oxygen were at -35C and 100 ppm, respectively. On the other hand, Zn was placed in a generating furnace for Zn vapour, with a height of 200 mm, a width of 300 tnm, a length of 500 mm and a volume of 30 litres, and melted at 500C, Iceeping the atmosphere inside the furnace so that the dew point, and the concentration of oxygen, stayed at -40 to -30C and 100 to 300 ppm, respectively, by flowing N2 gas through the furnace to allow the Zn vapour to generate. The Zn vapour generated in this way, was introduced into the preheating chamber of the NB brazing furnace via a pipe kept at 550C and the Zn concentrating treatment was performed on the surface of the Al plate simultaneously with NB
brazing. At this time, the behaviour of Zn (surface concentration and depth of diffusion) on the surface of Al, when varying the flow rate of N2, the amount of Zn tnelt and the surface area of the Zn melt in the Zn vapour generating furnace was examined by means of EPMA analysis. The results are shown in Table 3.
Besldes, the EP~A analysls was conducted by measuring at five points for each of 10 sheets of Al plates and determining the average value of the 50 points.
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As evident from Table 3, in the case of generatlon of Zn vapour in accordance with the method of the invention, No. 21 through 31, dlffusion patterns of Zn such that the concentration of surface Zn was 2 to 10~ a~d the depth of diffusion was lOO,um or so, were shown. From this, lt can be seen that the pitting corrosion resistance equal to that of a flux-brazed artlcle excellent in corrosion resistance is obtained.
On the contrary, in tha case of comparative methods outsi.de of the conditions prescribed by the invention, Zn diffusion patterns excellent in pitting corrosion resistance could not be obtained, or there arose the problem that the consumption of zn became high because of the deep diffusion of ~n.
For example, in the case of comparative methods No. 10, 12, 14 and 16, sufficient Zn vapour did not generate, failing to show diffusion patterns of Zn excellent in pitting corrosion resistance. ~oreover, in the case of comparative methods No. 11, 13 and 15, the generation of Zn vapour was remarkable and diffusion was deep resulting in problems of high consumption of Zn, deep pitting corrosion, etc.
Example 32 through 35 The NB brazing was performed similarly to Example 21. At that time, Zn was placed in the preheating chamber (height: 40mm, width: 600 mm~ length: 900 mm, volume: 216 litres) to melt and vapourize and the Zn concentrating treatment was given to the surface of an Al plate simultaneously with the preheating of the Al plate in the preheating chamber. Then, the diffuslon of Zn was examined similarly to Example 21. As a result, in all cases of the method of the invention, No. 32 through 35, excellent diffusion patterns of Zn were obtained as shown in Table 4.
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Example 36 and 37 The NB brazing was performed similarly to Example 21. AT that time, Zn was placed in the heating chamber (height: 400 mm, wldth: 600 mm, length: 1100 mm, volume: 246 litres) to melt and vapourize and the ~n coneentrating treatment was given to the surface of the Al plate simultsneously with he NB
braæing of AL plate in the heating chamber. Then, the diffusion of Zn was examined as in Example 21. As a resul.t, in all cases of the method of the invention, No. 36 and 37, excellent diffusion patterns of Zn were obtained as shown in Table 5.
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As described, in accordance with the invention, when brazing a heat-exchanger requiring pitting corrosion resistance, with noncorrosive flux, a Zn diffusion pattern excellent in pitting corrosion resistance can be formed on the Al components simultaneously with brazinz, thereby the process can be shortened remarkably compared with the zincate treatment befora the brazlng, and thus manufacturing costs can be reducsd. Moreover, by treating with Zn vapour without coating flux onto the tube material and yet at a temperature lower than that at which the flux flows, it is possible to prevent the flux film from suppressing the adherence of Zn. Therefore, such a way has been disclaimed utilizable not only for condenser cores and evaporator cores using extruded multihole tubes for the tube material, but also for drawn-cup evaporators using brazing sheets for the tube material, radiators using seam welded Al tube, and the like to~ether with the improvement in pitting corrosion resistance.
Further, the sacrificial layer of Zn, which improves remarkably the pitting corrosion resistance of Al or Al alloy components with simple facility, can be formed easily and, at the same time, the generation of the Zn vapour has been ~ade easy to permit the diffusion of Zn simultaneously with brazing in NB brazing usin~ fluoride noncorrosive flux. Therefore, the invention exerts an extremely remarkable effect, industrially.
Claims (7)
1. A method of manufacturing a heat-exchanger characterized in that, during the manufacture of an aluminum heat-exchanger by brazing under heat in a furnace having an inert gas atmosphere using fluoride flux, Zn is disposed at a temperature of 430 to 620°C in the furnace to melt and vaporize it, and the Zn vapour is allowed to contact with the heat-exchanger coated with said flux simultaneously with the brazing under heat of these A1 components, to diffuse Zn.
2. The method of manufacturing a heat-exchanger according to claim 1, characterized in that, in the manufacture of said aluminum heat-exchanger, its fin material coated with fluoride flux and dried and the tube material without flux are assembled and retained for not less than 1 minute in the Zn vapour at a temperature lower than the melting point of said flux and higher than the temperature at which these components are heated, in the inert gas and thereafter brazing is performed at a temperature higher than the melting point of flux.
3. The method of manufacturing a heat-exchanger according to either of claims 1 or 2, wherein the concentration of oxygen in the furnace is not more than 1000 ppm, the dew point is not higher than -30°C, the flow rate of inert gas is one tenth of the volume of the furnace per minute, and the surface area of the melt of Zn is 0.05 to 2.5 cm2 per unit volume (litre) of the furnace.
4. A method of concentrating zinc on the surface layer of an A1 component comprising heating the A1 or A1 alloy component in the presence of vaporized Zn.
5. A method of manufacturing a heat-exchanger comprising:
brazing aluminum components of the heat exchanger together using fluoride flux in a heated furnace having an inert gas atmosphere;
melting and vaporizing Zn in the furnace at a temperature of from 430° to620°C;
controlling the concentration of oxygen in the furnace to be not more than 1000 ppm;
controlling the dew point in the furnace to be not more than -30°C;
flowing inert gas through the furnace at a rate of one tenth of the volume of the furnace per minute; and sizing the surface area of the molten Zn being vaporized to be 0.05 to 2.5 cm2 per unit volume (liter) of the furnace.
brazing aluminum components of the heat exchanger together using fluoride flux in a heated furnace having an inert gas atmosphere;
melting and vaporizing Zn in the furnace at a temperature of from 430° to620°C;
controlling the concentration of oxygen in the furnace to be not more than 1000 ppm;
controlling the dew point in the furnace to be not more than -30°C;
flowing inert gas through the furnace at a rate of one tenth of the volume of the furnace per minute; and sizing the surface area of the molten Zn being vaporized to be 0.05 to 2.5 cm2 per unit volume (liter) of the furnace.
6. The method according to claim 5, wherein said components include fin material and tube material, further comprising:
prior to brazing, coating said fin material with the fluoride flux;
drying the coated fin material;
assembling the coated fin material with uncoated tube material;
heating the assembled fin material and tube material for not less than one minute in the presence of vaporized Zn in the inert gas at a temperature lower than a melting point of the fluoride flux and in the range of 430° to 620°C;
and thereafter performing said brazing and said simultaneous contacting at a temperature higher than said melting point of the fluoride flux.
prior to brazing, coating said fin material with the fluoride flux;
drying the coated fin material;
assembling the coated fin material with uncoated tube material;
heating the assembled fin material and tube material for not less than one minute in the presence of vaporized Zn in the inert gas at a temperature lower than a melting point of the fluoride flux and in the range of 430° to 620°C;
and thereafter performing said brazing and said simultaneous contacting at a temperature higher than said melting point of the fluoride flux.
7. Method of generating vaporized Zn for concentration of surface Zn on A1 components comprising melting and vaporizing Zn in a furnace having an inner volume V liters at a temperature greater than 430°C;
flowing N2 through the furnace at a rate of 0.05 V to 1.0 V liters/min.;
providing Zn in the furnace to be vaporized in the amount of 1 to 10 g/liter;
sizing the surface area of the molten Zn to be 0.05 to 2.5 cm2/liter;
controlling the concentration of oxygen in the furnace to be not more than 1000 ppm; and controlling the dew point in the furnace to be not more than -20°C.
flowing N2 through the furnace at a rate of 0.05 V to 1.0 V liters/min.;
providing Zn in the furnace to be vaporized in the amount of 1 to 10 g/liter;
sizing the surface area of the molten Zn to be 0.05 to 2.5 cm2/liter;
controlling the concentration of oxygen in the furnace to be not more than 1000 ppm; and controlling the dew point in the furnace to be not more than -20°C.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13266087A JPH0736950B2 (en) | 1987-05-28 | 1987-05-28 | Manufacturing method of aluminum heat exchanger |
| JP62-132660 | 1987-05-28 | ||
| JP62146501A JPH0830259B2 (en) | 1987-06-12 | 1987-06-12 | Method for generating Zn vapor for surface Zn concentration of Al member |
| JP62-146501 | 1987-06-12 | ||
| JP62-221574 | 1987-09-04 | ||
| JP22157487A JPH0773789B2 (en) | 1987-09-04 | 1987-09-04 | Preparation method of heat exchanger with excellent pitting corrosion resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1295114C true CA1295114C (en) | 1992-02-04 |
Family
ID=27316547
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000566900A Expired - Fee Related CA1295114C (en) | 1987-05-28 | 1988-05-16 | Method of manufacturing a heat-exchanger |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1295114C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009026988A1 (en) * | 2007-08-24 | 2009-03-05 | Modine Manufacturing Company | Installation and process for soldering |
| CN116984845A (en) * | 2023-09-27 | 2023-11-03 | 山东三源铝业有限公司 | Manufacturing method of intercooler anti-penetration main sheet |
-
1988
- 1988-05-16 CA CA000566900A patent/CA1295114C/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009026988A1 (en) * | 2007-08-24 | 2009-03-05 | Modine Manufacturing Company | Installation and process for soldering |
| US8313688B2 (en) | 2007-08-24 | 2012-11-20 | Modine Manufacturing Company | Method for in-line heat exchanger tube brazing |
| CN116984845A (en) * | 2023-09-27 | 2023-11-03 | 山东三源铝业有限公司 | Manufacturing method of intercooler anti-penetration main sheet |
| CN116984845B (en) * | 2023-09-27 | 2023-12-26 | 山东三源铝业有限公司 | Manufacturing method of intercooler anti-penetration main sheet |
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