Metal fusion bonding – Process – Plural joints
Reexamination Certificate
1999-07-13
2001-02-27
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S182000, C228S214000, C228S193000
Reexamination Certificate
active
06193140
ABSTRACT:
TECHNICAL FIELD
This invention relates to a heat exchanger core based on aluminum and also to a process for producing the same. More particularly, the invention relates to a heat exchanger core based on aluminum in which an aluminum-based flattened heat exchanger tube, for example, and an aluminum-based fin are held in brazed relation to each other by the use of a brazing composition. The invention further relates to a process for the production of such heat exchanger core.
BACKGROUND ART
In general, a certain heat exchanger based on aluminum has been widely used which is constructed with a heat exchanger tube formed of aluminum or an aluminum alloy (hereafter referred to as being based on aluminum) and an aluminum-based fin brazed with each other. Further and to gain improved heat exchange efficiency, an extruded flattened tube has been employed as a heat exchanger tube, which extruded flattened tube is derived from an extruded shape based on aluminum.
For the resultant heat exchanger to be proof to corrosion (resistant to corrosion), zinc (Zn) has generally been caused to adhere to the flat heat exchanger tube on its outer surface, followed by diffusion of Zn over the outer surface of such flat tube during brazing with heat and by subsequent formation of a Zn diffusion layer thereover. Additionally, the fin has been prepared from a brazing sheet chosen from among those materials clad with a Zn-containing brazing material, namely of a brazing composition. As a like instance, U.S. Pat. No. 4,831,701 discloses a method in which an aluminum-based fin clad on its surface with a brazing composition derived from Al—Si alloy and flux coated with Zn are applied to and brazed with the flat heat exchanger tube.
Such a brazing sheet for use in fin preparation, however, is costly as compared to a blank fin material not clad with a brazing material. Moreover, because of the cladding on its surface with a brazing material, the brazing sheet leads to rapid abrasion of a fin working roll, thus needing frequent polishing of such working roll. As a further problem, flashes or burrs tend to take place when in working of a louver or the like with eventual quality deterioration of the finished heat exchanger core. Furthermore, by the method of U.S. Pat. No. 4,831,701, process of coating flux with Zn is responsible for increased process step and hence for added production cost and material cost.
In order to improve the corrosion resistance of the flat heat exchanger tube, a method has been employed in which zinc (Zn) is made adherent in advance to an outer surface of such flat tube as by a zincate method or a spray coating of Zn, and a Zn diffusion layer is then formed in the course of brazing so that the flat tube is prevented against corrosion by electrode shielding. However, this method leaves the problem that Zn adhesion is rather tedious and time-consuming.
On the other hand, a method is known in which a blank fin material not clad with a brazing material is put to use and in which a powdered Al—Si alloy derived from aluminum (Al) and silicon (Si) is applied to and brazed with a flat heat exchanger tube. Such known method needs for the powdered Al—Si alloy to be coated in a markedly large amount and hence poses those drawbacks related to cost and assembly. By another known method, a flat heat exchanger tube is prepared from an electrically welded tube clad with a brazing material. For example, JP59086899 discloses a method in which an aluminum-based heat exchanger tube clad on its surface with a brazing composition derived from Al—Si alloy is put to use and in which aluminum-based fin containing Zn applied to and brazed with the flat heat exchanger tube. In this and last method, however, an insert is required to be disposed internally of such tube when rendered multi-channel, and this is responsible for increased process step and hence for added production cost and material cost.
SUMMARY OF THE INVENTION
The present invention has been made and completed with the aforementioned situation in view. One object of the invention is to provide a heat exchanger core which results from use of a heat exchanger tube not needed for adhesion of Zn in advance and a blank fin material not clad with a brazing composition and which exhibits corrosion resistance and brazing capability comparable to or higher than those of the conventional equivalent. Another object of the invention is to provide a process for the production of such heat exchanger core.
To achieve the above noted objects, the invention is directed to a heat exchanger core based on aluminum wherein an aluminum-based heat exchanger tube and an aluminum-based fin are held in brazed relation to each other by the use of a brazing composition, characterized in that a mixed diffusion layer composed of a mixture of silicon and zinc is formed on an outer surface of the heat exchanger tube, and the fin is formed by an aluminum-based material containing zinc, which zinc is used for formation of a part of the mixed diffusion layer.
Furthermore, the invention is directed to a process for the production of a heat exchanger core based on aluminum wherein an aluminum-based heat exchanger tube and an aluminum-based fin are held in brazed relation to each other by the use of a brazing composition, characterized in that the process comprises applying on to an outer surface of the heat exchanger tube a brazing composition derived from a mixture of silicon and fluorine type flux, preparing the fin formed of an aluminum-based zinc-containing material, and subsequently heating the heat exchanger tube and the fin at a given temperature, thereby bringing the exchanger tube and the fin into brazed relation to each other and also forming on an outer surface of the heat exchanger tube a mixed diffusion layer of silicon and zinc. In such instance, in the mixed diffusion layer composed of silicon and zinc and located on the heat exchanger surface, the maximum concentration is in the range of 0.5-1.5% in terms of silicon and of 0.4-3.0% in terms of zinc.
In the present invention, the above heat exchanger tube may be of an optional shape so long as it is based on aluminum. Preferably, such tube may be an extruded flattened tube based on aluminum and provided with a plurality of passages for supply of a heating medium. Besides and desirably, the concentration of zinc in the above described fin may be in the range of 1-5%.
According to the present invention, a mixture of silicon and fluorine type flux is employed as a brazing composition with the result that the heat exchanger tube is not required for Zn to previously adhere thereto, and a blank fin-forming Zn-containing material not clad with a brazing composition may be used to advantage. Part of the resulting fin is molten with the aid of a brazing composition during brazing, whereby the zinc contained in the fin is diffused over an outer surface of the heat exchanger tube so as to form thereover a mixed diffusion layer resulting from silicon and zinc.
Consequently, a zinc diffusion layer can be formed on an outer surface of the heat exchanger tube without zinc adhesion previously needed relative to the latter tube. This permits a heat exchanger core to be easily feasible with excellent corrosion resistance and brazing capability. Also advantageously, the fin does not need to be clad with a brazing composition and hence ensures easy formation and moreover avoids flashes or burres with ultimate production of a heat exchanger core of high quality. Improved productivity is further attainable with saved cost.
REFERENCES:
patent: 4831701 (1989-05-01), Yutaka
patent: 5148862 (1992-09-01), Hashiura et al.
patent: 32 06 298 A1 (1983-07-01), None
Patent Abstract of Japan, vol. 8, No. 197 (M-324), Sep. 11, 1984, publication number JP59086899.
Patent Abstract of Japan, vol. 017, No. 059 (M-1363), Feb. 5, 1993 in the English Abstract of JP 04 270058.
Ogasawara Meitoku
Oki Yoshito
Suzuki Toshihiro
Tanaka Tsunehiko
Alcan International Limited
Elve M. Alexandra
Heslin & Rothenberg, P.C.
Ryan Patrick
LandOfFree
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