MXPA99006938A - Heat exchanger core based on aluminum and process for producing the same - Google Patents

Abstract

Mediante el uso de un tubo intercambiador de calor que no requiere adhesión previa de Zn y una aleta sin revestimiento de una composición de soldadura fuerte, se provee un núcleo intercambiador de calor que tiene resistencia a la corrosión y capacidad de soldadura fuerte comparable o mayor a sus contrapartes convencionales;aplicada sobre una superficie externa de un tubo aplanado extruido como un tubo intercambiador de calor, se encuentra una composición de soldadura fuerte, derivada de la mezcla de silicio y fundente de tipo flúor, y se prepara una aleta formada con un material basado en aluminio que contiene zinc;entonces, el tubo aplanado extruido y la aleta se calientan a una temperatura determinada para que los mismos queden soldados entre sí, y entonces una capa de difusión mixta de silicio y zinc queda sobre la superficie externa del tubo aplanado extruido.

Description

PROCEDURE FOR THE PRODUCTION OF AN ALUMINUM-BASED HEAT EXCHANGER CORE FIELD OF THE INVENTION This invention relates to a heat exchanger core based on aluminum and also to the process for manufacturing the same. More specifically, the invention relates to an aluminum-based heat exchanger core, wherein, for example, a flattened aluminum-based heat exchanger tube and an aluminum-based fin are welded together by the use of a brazing composition. In addition, the invention relates to a process for the production of said heat exchange core.

BACKGROUND OF THE INVENTION In general, a particular aluminum-based heat exchanger has been widely used, which is constructed with a heat exchanger tube formed of aluminum or an aluminum alloy (hereinafter referred to as an aluminum-based heat exchanger) and a fin based on aluminum welded together. In addition, and to achieve greater efficiency in heat exchange, an extruded flat tube has been used as a heat exchanger tube; extruded flattened tube that is derived from an aluminum-based extruded figure.

In order for the resulting heat exchanger to be corrosion proof (corrosion resistant), zinc (Zn) has generally been made to adhere to the flat heat exchanger tube on the outer surface, after the diffusion of Zn on the outer surface of said flat tube during brazing with heat, and of the subsequent formation of a Zn diffusion layer thereon. In addition, the fin has been prepared from a welding foil chosen from the materials coated with a brazing material containing Zn, mainly from a brazing composition. As a similar example, US-A-4 831 701 discloses a method in which a fin based on aluminum coated on the surface with a brazing composition derived from the Al-Si alloy and flux coated with Zn are applied and weld with flat heat exchanger tube. However, the use of such a strong brazing sheet in the preparation of the fin is expensive in comparison with a fin preform material without the coating of a brazing material. In addition, due to the coating of the surface with a brazing material, the brazing sheet causes a rapid abrasion of a fin working roll, therefore said work roll needs to be polished frequently. As an additional problem, there tend to be edges or burrs in the operation of a grid or the like with the final quality deterioration of the finished heat exchanger core. In addition, by the method of US-A-4 831 701, the coating flux process with Zn is _ ______________________ ¡¡¡^^ responsible for the increase in the steps of the procedure and, therefore, the increase in the cost of production and material. In order to improve the corrosion resistance of the flat heat exchanger tube, a method has been used in which the zinc (Zn) becomes adherent prior to an external surface of said flat tube, as well as by a galvanizing method or a spray coating Zn, and then a Zn diffusion layer is formed during brazing so that the flat tube can avoid corrosion by an electrode shield. However, this method has the problem that the adhesion of Zn is quite tedious and laborious. On the other hand, a method is known in which a fin preform material without brazing material coating is employed, and in which an Al-Si powder alloy derived from aluminum (Al) and silicon (Yes) ) is applied and soldered with a flat heat exchanger tube. Said known method requires that the Al-Si powder alloy be applied in a fairly considerable amount and therefore offers disadvantages relative to cost and assembly. By another known methodA flat heat exchanger tube is prepared from an electrically welded tube coated with a brazing material. For example, the patent JP59086899 describes a method in which an aluminum-based heat-exchange tube coated on the surface with a brazing composition derived from the Al-Si alloy, and wherein the aluminum-based fin is employed, is employed. Contains Zn applied and welded with the tube flat heat exchanger. However, in the latter method an insert is required that will be discarded internally of said tube when it has multiple channels; and this is responsible for the increase in the steps of the procedure, and therefore the increase in the cost of production and the cost of the material.

DETAILED DESCRIPTION OF THE INVENTION The present invention was made and completed considering the aforementioned situation. It is an object of the invention to provide a core heat exchanger, which results from the use of a heat exchanger tube that does not require a pre-bonding of Zn, and a fin preform material without a brazing composition coating and that it presents resistance to corrosion and brazing capacity comparable or greater than those of the conventional equivalent. Another object of the invention is to provide a process for the production of said heat exchanger core. To achieve the aforementioned objectives, the invention cited in claim 1 is directed to an aluminum-based heat exchanger core in which an aluminum-based heat exchanger tube and an aluminum-based fin are welded together by use of a brazing composition, characterized in that a mixed diffusion layer composed of a mixture of silicon and zinc is formed on an external surface of the heat exchanger tube and the fin is formed _________ by a material based on aluminum containing zinc, which is used for the formation of a part of the mixed diffusion layer. In addition, the invention mentioned in claim 3 is directed to a process for the production of an aluminum-based heat exchanger core, in which an aluminum-based heat exchanger tube and an aluminum-based fin are welded together by the use of a brazing composition, further characterized in that the process comprises the application of a brazing composition derived from a mixture of silicon and fluoro-type flux on the external surface of the heat-exchanging tube; the preparation of the fin formed of a material containing zinc based on aluminum; and subsequently heating the heat exchanger tube and the fin at a certain temperature, whereby the exchanger tube and the fin are welded together; and also the formation of a mixed diffusion layer of silicon and zinc on an external surface of the heat exchanger tube. In this example, in the mixed diffusion layer composed of silicon and zinc and located on the surface of the heat exchanger, the maximum concentration is on the scale of 0.5 - 1.5% depending on the silicon, and 0.4 - 3.0% depending on the of zinc. In the present invention, the mentioned heat exchanger tube can have an optional shape, as long as it is based on aluminum. Preferably, said tube may be an extruded flattened tube based on aluminum and may have a plurality of passages for the supply of a heating means. In addition and preferably, the concentration of zinc in the fin described above can be in the 1-5% scale (claim 2). According to the present invention, a mixture of silicon and fluoro-type flux is used as a brazing composition with the result that the heat exchanger tube does not need to previously adhere Zn to it, and for convenience a preform material containing Zn to form the fin without the coating of a brazing composition. Part of the resulting fin is melted with the aid of a brazing composition during welding, whereby the zinc contained in the fin diffuses on an external surface of the heat exchanger tube to form a mixed diffusion layer thereon. that results from silicon and zinc. Accordingly, a zinc diffusion layer can be formed on an external surface of the heat exchanger tube without first needing a zinc adhesion relative to this latter tube. This allows a heat exchanger core to be easily made with excellent corrosion resistance and weldability. Also, conveniently, the fin does not need to be coated with a brazing composition, and therefore ensures easy formation and also avoids burrs or edges with the final production of a high quality heat exchanger core. In addition, improved productivity is achieved with cost savings. _________________ BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates, in perspective, the important parts of a form of a heat exchanger having assembled therein in the heat exchanger core according to the present invention. Figure 2 is a perspective view showing each of the extruded flattened tubes and a corrugated fin according to the embodiment of the invention. Figure 3 is a cross-sectional view showing the manner in which the brazing composition is applied on an extruded flattened tube according to the invention. Figure 4 is a cross-sectional view, partially elongated, of the manner in which a heat exchanger tube and a fin are strongly welded together according to the invention. In these figures, the reference number 4 refers to an extruded flattened tube (a heat exchanger tube), 5 to a corrugated fin, 6 to a heat exchanger core, 7 to a brazing composition and 8 to a layer of diffusion of Si and Zn.

DETAILED DESCRIPTION OF THE INVENTION With reference to the appended drawings, the present invention is described below with respect to several of its modalities. ?? ------ ¡--_____- _______ t (_______ ii ________ ¡l_ n & Figure 1 is a perspective view showing the important parts of a form of a heat exchanger that has assembled therein the core exchanger of heat according to the invention The said heat exchanger is constructed with a pair of collector tubes 3 placed in an opposite space position, and has an inlet for the heating means 1 or an outlet for the heating means 2, a plurality of extruded flat tubes 4 serving as heat exchange tubes: the extruded flattened tubes are arranged parallel to each other and are communicated with the collecting tubes 3, and the fins, such as the corrugated fins 5 interposed between the tubes flattened extruded 4. In the heat exchanger thus assembled, the collector tubes 3 and the extruded flattened tubes 4 are formed by an extruded aluminum-based form. The corrugated fins 5 are formed with an aluminum-based plate material flexed into alternate depressions and ridges or in a corrugated configuration. The collector tubes 3, the extruded flattened tubes 4 and the corrugated fins 5 are completely brazed together by the use of a brazing composition (a brazing material), so that a heat exchanger is produced. In that case, a heat exchanger core 6 made with the extruded flattened tubes 4 and the corrugated fins 5 are formed by the extruded aluminum-based flattened tubes (for example, JIS A1050), which are not treated in advance with the adhesion of zinc (Zn) and corrugated fins 5 are formed by a plate material containing Zn based on aluminum without the coating of a brazing material. As a brazing material, a mixture of powdered silicon (Si) and a fluoro-powder-type flux or a mixture of powdered Si powder Zn and fluoro-powder flux has been commonly used. Here, the fluoro-type flux can be, for example, a composition of KA1F4, K2A1F5. H20 or K3AIF6. This kind of fluoro-type flux is preferable, since it is different from chloride and immune to corrosion of aluminum. The Si ratio with the flux (% by weight) is set to Yes: flux = 1: 2. In order to produce the said heat exchanger core 6, a first step of the process lies in the preparation, as shown in Figure 2 , of the extruded flattened tubes 4, based on aluminum, and having defined therein a plurality of passages for the passage of a heating means, and having flexed the corrugated fins 5 with an undulated arrangement and containing Zn. Up to this point, the corrugated fins 5 are derived from the bending of a plate material d on aluminum containing Zn (JIS A3N03, for example), in corrugated form with the use of a work roll. In said example, the work roll is less susceptible to abrasion than in the case of a brazing sheet coated with a brazing material. Another advantage is that no edges or burrs are formed even when working and mounting a grid or something similar on the fins. This contributes to improve the quality of the fins. A brazing composition 7 is then applied on a surface of the extruded flattened tube 4, as shown in Figure 3, by the use of a binder, such as, for example, a thermoplastic acrylic resin or the like. The application of this brazing composition to the extruded flattened tube 4 can be effected, for example, by the spray coating of a mixed suspension of the binder and the brazing composition, or by immersion of the extruded flattened tube 4 in a mixed suspension. of the binder and the brazing composition, and then removing the tube vertically from the suspension to remove excess suspension therefrom. Next, the extruded flat tube 4, which is also charged with the brazing composition, and the corrugated fins containing Zn 5 are incorporated and fixed to each other by the use of an unillustrated tool, or are fixed together by the joint with the collector tubes 3. By subsequent heating to a predetermined temperature or higher than 590 ° C, for example in a heating furnace or the like, the brazing composition is caused to melt to completely weld the tube together flattened extruded 4 and the corrugated fins 5. During the welding operation, part of the corrugated fin 5 is melted by the action of the brazing composition with the consequence that the Zn contained in the corrugated fin 5 is diffused by the outer surface of the extruded flattened tube 4, cooperating at the end with Si contained in the brazing composition in the formation of a diffusion layer 8 of Si and Zn on the outer surface of the flattened tube 4. The extruded flattened tube 4 and the corrugated fins 5 are furthermore held in a complete connection relationship with each other with a concave connection 9 of an Al-Si-Zn alloy interposed therebetween. With the diffusion layer 8 of Si and Zn formed on the outer surface of the extruded flattened tube 4, the resulting heat exchanger core 6 is resistant to corrosion. Next, an explanation is given regarding the experiments carried out to evaluate the brazing capacity and the corrosion resistance of the heat exchanger core according to the present invention, in comparison with those of the aluminum-d heat exchanger core of the prior art. ® initial materials extruded flattened tubes (1) material: JIS A1050: JIS A1050 + Zn arc spray coating (target amount of Zn 8 g / m2): NE alloy (modified A1050 alloy) (composition: 0.18% Fe, 0.4% Cu, 0.02% Zn and 0.04% Zr) (2) shape: external measurement (width x wall thickness) = 19.2 mm x 1.93 mm (wall thickness of one side only: 0.4 mm) »fins (1) material: preform material (JIS A3N03 + content of Zn 0 - 4.0%): brazing foil (A4343 + 1.0% Zn / 3N03 + 1.5% _-_ ------ ________ i Zn / A4343 + 1.0% Zn) (2) shape: (width x wall thickness) = 21.1 mm x? .1 mm brazing compositions (1) Si powder + Fluorine type flux powder + binder Total amount of adhesion: 16 g / m2 ® brazing conditions current operating conditions: under nitrogen atmosphere (amount of nitrogen: 40 heating rate: 30 ° C per minute) comparative examples 1 and 2 and examples 1-4 in which the mentioned extruded flattened tube 4 was fixed by welding with a fin preform material (with a Zn content of 0-4.0%) by using the composition of brazing mentioned, and also with respect to the comparative methods of brazing 1 and 2 (current brazing), the details of which are shown in Table 1, a joining portion between the extruded flattened tube 4 and the fin was cut and checked. The results of brazing capacity were obtained as they appear in table 2. A deeper evaluation of the resistance of the finished welded product against corrosion was carried out using the CASS test (JIS H8681). The results appear in table 2. In addition, the extruded flattened tube 4 was observed crosswise by means of an X-ray microanalyzer (XMA) to verify the diffusion states of Zn and Si. The results appear in table 2. TABLE 1 ^ Hg TABLE 2 Zn content of 1.2% - 4.0% and of an extruded aluminum-based flattened tube without pre-bonding of Zn, which were welded together by the use of a brazing composition composed of a mixture of Si powder and flux of type fluorine, can provide brazing capacity and corrosion resistance, similar to or greater than those of the heat exchanger core practiced in the art today. Although not expressly shown in the experimental results mentioned above, the content of Zn in the material of the fin less than 1% achieves a diffusion concentration of the Zn surface less than 0.4%, which therefore results in an insufficient anodic action in the diffusion layer of Zn. On the contrary, the high content of Zn greater than 5% makes the fin material very corrosive, with the consequence that the finished heat exchanger implies a short service life and also that, at high temperatures, the fin The resultant reduces the force in the material itself, and therefore tends to bend when welding. Therefore, in the case where Zn is present at a content of 1.0% - 5.0% in the material of the fin, the brazing capacity and the corrosion resistance are achieved at said magnitudes when they are equivalent to or greater than the of the current heat exchanger core. Although not demonstrated in the previous experimental results, it has also been discovered from this series of experimental results that the larger the amount of Zn that is added, the Zn diffusion layer can be formed at a higher concentration and therefore much greater resistance to corrosion can be expected; and since the diffusion layer of Si corresponds to a possible cavity induced by corrosion at the end of an extruded flattened tube, greater resistance to corrosion can be achieved than in an extruded flattened tube without Si diffusion layer.

INDUSTRIAL APPLICABILITY As described and shown above, the present invention allows a mixture of silicone and fluoro-type flux to be used as a brazing composition, so that a heat exchanger tube does not require prior adhesion of Zn, and can be used a fin preform material containing Zn, but not coated with a brazing composition, in the formation of a fin. In this way, part of the flap melts when subjected to the action of the brazing composition, so that the zinc contained in the fin diffuses on an outer surface of the heat exchanger tube, and therefore functions as in the formation of a diffusion layer composed of a mixture of silicon and zinc on said external surface. Accordingly, a zinc diffusion layer can be formed on an outer surface of the heat exchanger tube without the need for prior zinc adhesion relative to the previous tube. This in turn allows a heat exchanger core to be easily coded with high corrosion resistance and high brazing capacity. Another advantage ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ fc ^^ g || ß & ^ i * gi ^ ^ ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ high quality heat.

As an additional advantage, high productivity is feasible with cost savings. i r i i - ___? i__r_? m-i_ "," a > A * a g & ^^ j ^ & ^ j ^

Claims (2)

NOVELTY OF THE INVENTION CLAIMS

1. A process for the production of a heat exchanger core 6 based on aluminum, in which an aluminum-based extruded flattened heat exchanger tube 4 and an aluminum-based fin 5 are welded together by the composition of a braze 7 , characterized in that said heat exchange tube is not pretreated with zinc adhesion, and the method comprises the application, on the external surface of said heat exchanger tube, of a brazing composition derived from the mixture of silicon and Fluorine type flux; the preparation of said fin formed of an aluminum-based material containing zinc; and subsequently heating the aforementioned heat exchanger tube and fin to a certain temperature, and then welding said heat exchanger tube and fin together, and also to forming, on the outer surface of said tube heat exchanger , a mixed diffusion layer 8 of silicon and zinc, in which the zinc contained in said fin cooperates with the silicon of the aforementioned brazing composition during the brazing operation in the formation of said mixed diffusion layer.

2. A process for the production of the aluminum-based heat exchanger core according to claim 1, ISmma ^^^ t í? further characterized in that the concentration of zinc in said fin is in the range of 1 to 5%.