MXPA97000433A - Procedure for protection against external corrosion in heat exchangers based on co - Google Patents

Abstract

The process comprises coating and thermal diffusion of an Sn-based alloy with a Cu-based core, whereby a composite material formed by a Cu-based core is formed, an external surface consisting of a base-based alloy. Sn and an intermediate layer constituted by Cu-Sn alloys of variable compositions. Said formed composite material is suitable for the manufacture of fins for heat exchangers, particularly radiators for automobiles, whose combs can be welded in a furnace with oxidizing atmosphere or do not oxidize

Description

PARR PROCEDURE Lfl FRONT PROTECTION fl LR EXTERNAL CORROSION IN COPPER-BASED HEAT INTERCHANGEERS FIELD OF THE INVENTION The invention relates to a process for protecting copper-based heat exchangers against external corrosion comprising coating and diffusion Thermal insulation of a tin-based alloy on a copper-based core, thereby forming a composite material which exhibits excellent corrosion performance The invention also relates to said composite material, to fins for exchangers of heat constituted by said material and heat exchangers incorporating such fins, as well as its manufacturing process.

BACKGROUND OF THE INVENTION Heat exchangers, in particular, radiators for the cooling of engines in automobiles and agricultural and industrial machinery (thermal engines) consist of a central core, called honeycomb, formed by a set of tubes for the circulation of the coolant, and of fins, in contact with the tubes to effect the thermal exchange. The radiator is completed by tanks and collector plates that close the coolant circuit. Additionally, one steel side supports are included in order to increase its rigidity. In the case of copper radiators, the honeycomb tubes are made of brass, the fins are made of copper (Cu) and the pipe-fin connection is made by tin-based solder.

(Sn). The contribution of the Sn-based welding is made from the brass tube, which has been previously coated , / welding, mainly by immersion in a molten solder bath. Honeycomb welding can be carried out in continuous or static ovens with oxidizing environment. Normally, the honeycomb is made in two stages, first in furnace, in which the tubes are welded to the fins, and a second in which the ends of the pipes are welded to the collector plates by systems such as capillarity ^ immersion in Sn baths), Sn projection, etc. In order to achieve a correct welding between the tubes and the fins, a "flux" of welding (or stripping of the metals to be joined and protector of the welding itself during the operation) must be applied, either by immersion of the honeycomb or by projection of the flux on the honeycomb. The flux that are commonly used are those of a mineral nature that contain inorganic halides, such as zinc and ammonium chlorides, hydrochloric acid, etc., although other fluxes of a mixed nature are also used, with (organic and inorganic components such as hydrochlorides) and amine brornhydrates, hydrobromic acid, etc. In general, these products are aggressive for radiator materials and their residues cause notable corrosion, so it is necessary to perform operations of washing and drying the radiators, which leads to consumption of important energy and the production of waste water and with high concentrations of metallic ions, making it necessary to carry out a treatment.Outly, vapors containing, among other compounds, hydrochloric acid, hydrobromic acid, ammonia and ammonia compounds are released. , which are also aggressive to the environment, so operations should be carried out It is additional washing of the generated vapors, which makes the process more expensive and complicated. Another additional problem posed by current radiator manufacturing processes concerns the application of an anti-corrosion protection, since, currently, this operation is carried out, once the radiator is manufactured, by the application of an anti-corrosion paint. -corrosion by projection, with which only the outer areas of the radiator are punctured but the core of the honeycomb is not covered. Normally, the paint penetrates only about 2 mm on each side of the comb. In general, copper radiators have excellent performance in terms of thermal transfer, mechanical resistance and internal corrosion. However, resistance to external corrosion is problematic. In recent years, the requirements of protection against corrosion have increased significantly, not only in the automotive sector due, among other causes, to the increasing use of halogenated salts, such as NaCl and M Cl2, for the thawing of roads , but also other sectors where it is necessary to guarantee an effective protection against other aggressive environments, marine and industrial, fundamentally.These media cause important corrosion in pipes, fins and welds, with the consequent loss in mechanical resistance and in the thermal characteristics of the radiators, therefore, there continues to be a series of problems associated not only with the current copper radiator fabrication procedures, such as the need for - ^ «To fill a welding flux that forces to carry out operations of washing and drying of the radiators that, in turn, generate an environmental problem due to the effluents and vapors produced, as well as an important energy consumption, which complicates and makes more expensive the current manufacturing procedures for radiators, but also with the copper radiators themselves manufactured with the existing technology since these are still p > oco resistant to external corrosion. The present invention provides a solution to the problems raised.

COMPENDIUM OF THE INVENTION Through laboratory tests analyzing external corrosion problems in copper radiators, the main mechanisms that produce corrosion in tubes and fins have been identified, which has allowed to create a new material, specifically, a composite material, suitable • »> nara manufacture fins or intercalators, which has an excellent performance against corrosion, retaining its thermal and mechanical properties, which also allows reducing the traditional thicknesses of these parts, fll same time, the composite material provides a very effective protection against the perforating corrosions that occur in the radiator honeycomb pipes as a consequence of the corrosion mechanisms that occur in copper radiators manufactured with current technology. All this guarantees the preservation of the functional characteristics of a radiator, manufactured in accordance with the teachings of the present invention, during the service, in the long term, as it has been possible to demonstrate through an extensive program of accelerated corrosion tests. . The new material provided by this invention consists of a core based on Cu, an intermediate layer consisting of Cu-Cn alloys of variable composition and an external surface formed, fundamentally, by an alloy based on Sn. This material can be obtained by means of thermal diffusion, under controlled conditions, of a coating with Sn-based alloys deposited on the Cu bae core. The use of this new material involves a series of changes in the manufacturing process of the radiators, one of which lies in the possibility of carrying out the welding of the honeycomb in atmosphere controlled furnaces. Operating under these conditions and due to the favorable welding characteristics provided by the new material, welding can be carried out without the use of any type of flux, which is impossible to achieve with current technologies. This way of making the honeycomb provides great environmental improvements since there are no gaseous effluents or water pollutants and, at the same time, significant reductions in energy consumption are obtained.Alternatively, the honeycombs built with this new material can also be soldering in a furnace with an oxidising atmosphere, although in this case a non-corrosive organic flux can be used, which does not need to be washed, with which considerable advantages are obtained compared to the current radiator manufacturing technology.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a photograph showing the perforating corrosion in a honeycomb tube, of arsenical brass CCu-Zn 70/30, As 0.03% 3m after 92 hours of salt spray test, at a scale of 20/1. In the photograph, the escape area has been indicated by an arrow. Figure 2 is a photograph showing the - 'perforating corrosion in a honeycomb tube, of areenical brass CCu-Zn 64/36, As 0.03%], after 120 hours of salt spray test, at a scale of 20/1. In the photograph, the escape area has been indicated by an arrow. Figure 3 is a photograph showing the intercrystalline corrosion and deecinication in a honeycomb tube, of arsenical brass CCu-Zn 67/33, As 0.03X3,. as well as corrosion in Sn-Pb welding, after 144 hours of testing "Saline, at a scale of 390/1 (Figure 3A) and at a scale of 325/1 (Figure 3B) Figure 4 is a photograph showing the corrosion by de-concentration in a honeycomb tube, from brass to phosphorus CCu-Zn 66/34 Pl, after 244 hours of salt spray test, on a scale of 260/1 (Figure 40), as well as perforating corrosion (intercrystalline and dezincification) in said honeycomb tube after 244 hours of test salt spray, at a scale of 260/1 (Figure 4B) Figure 5 is a photograph showing the corrosion in a fin after 144 hours of salt spray test, at a scale of 260/1 (Figure 5A), Like on a scale of 360/1 (Figure 5B), the photograph shows the connection of the honeycomb tube to the fin, and the honeycomb tube consists of arsenical brass CCu-Zn 67/33 As 0.03% »and the fin by Cu-Sn (0.1% Sn.) Figure 6 is a photograph showing the appearance of the honeycomb of a radiator incorporating fins made of an "aterial composite proportion". This invention, after 1170 hours of salt spray test (0.5 magnification C0, X5). Figure 7 shows a photograph showing an enlarged detail of Figure 6 (2X). Figure 8 is a photograph showing the appearance of the tube after 1,008 hours of salt spray test (5X). As can be seen, there are no corrosion attacks on the brass and the Sn-Pb film is preserved • "" "'base metal Figure 9 is a photograph showing the appearance of a section of the tube after 1,008 hours of salt spray test (1,000X) .The Cu-Sn alloy film can be seen on the surface of the brass, but no corrosion points are observed Figure 10 is a photograph showing the appearance of a section of a fin, made of a material provided by this invention, after 1,008 hours of salt spray test (1,000X). By means of an optical microscope examination, the Cu nucleus and Cu-Sn alloy film of approximately 1 to 2 μrn can be seen over the entire surface of the fin Figure 11 is a photograph showing the appearance of the tube-fin union afterwards. of 1,008 hours of salt spray test (100X) It can be seen that there is a slight attack of the Sn-Pb weld, but an appreciable meniscus is preserved Figure 12 is a photograph showing a detail -explained of Figure 16 (FIG. 200X). Figure 13 is a photograph showing the appearance of a comb that contains fins made of a material provided by this invention and welded from a static oven, under vacuum, under pressure of 2 and without using any type of flux.

DETAILED DESCRIPTION OF THE INVENTION Identification of external corrosion mechanics In order to identify the possible external corrosion mechanisms that affect copper radiators, perforating corrosion in honeycomb tubes, corrosion of welds and corrosion of fins, as well as the electrochemical aspects involved, have been studied. To study the perforating corrosion in the honeycomb tubes, tests were performed on copper radiators that had experienced leaks through the honeycomb tubes after performing accelerated corrosion tests, which allowed to establish the mechanisms of the development of this type of corrosion In the pipe-welding-fin union, the aggressive action of the chemical products used in the accelerated corrosion tests 8, mainly sodium chloride in the continuous salt spray test according to NDX 41002) -develops a galvanic corrosion process based on the different potentials electrochemical of the metals that are joined by Sn welds, which produces pitting corrosion in the brass tube and ends up affecting the entire thickness of the tube (Figures 1, 2, 3A, 4A and 4B). These perforating corrosions are produced from 100 hours of salt spray test, which is clearly insufficient to meet the requirements, in terms of external protection, • bets by car manufacturers and requires technical development plans to solve this important problem presented by copper radiators. The welds also experience galvanic corrosion after accelerated external corrosion tests (Figure 3A). In the tube-welding-fin joint, the Sn welding and the brass tube are preferentially attacked because of their anodic character in front of the copper fins. Finally, outside the tube-fin area, corrosion of the copper fins also occurs due to the action of sodium chloride deposited in the salt spray test (Figure 5A and 5B). The situation, in terms of the redox potentials of the honeycomb components, can be summarized as follows: Anodic end: Sn-Pb (residual layer of the weld) Cu-Zn (honeycomb tubes) Cu-Sn (diffusion layer) in the tube) Cathodic end: Cu (fins) The potential differences between the Sn-Pb and Cu (fins) welds reach values of 300 rnV, for which strong galvanic stacks are formed that justify lae corroeionee detected in the essays.

DESCRIPTION OF THE INVENTION The procedure for protection against external corrosion in copper-based heat exchangers, especially in radiators intended to cool thermal engines, more particularly, automotive radiators, comprises the coating and thermal diffusion of a tin-based alloy on a copper-based core, which forms a composite material that has an excellent performance against corrosion.

With the method that this invention eliminates the mechanism of corrosion by perforating points that are produced in honeycomb tubes (brass) manufactured according to procedures of the state of the art and corrosions in the welds and in the fins are significantly reduced. All these corrosion processes lead to a great decrease in the functional characteristics of the heat exchangers and particularly in the radiators of automobiles, since although the perforating corrosion in the honeycomb tubes makes the radiator useless, it causes corrosion in the fins and in the welds cause noticeable losses in the thermal and mechanical characteristics of the radiator. To solve the problem raised, the invention provides a method for the protection of heat exchangers comprising the formation of a new composite material, suitable for the manufacture of ^ Letae for heat exchange interchanges, consisting of a Cu-based core, an external surface consisting of an Sn-based alloy and an intermediate layer consisting of Cu-Sn alloys of variable composition, obtained by coating and thermal diffusion , under controlled conditions, of a Sn-based alloy deposited on the Cu-based core. Accordingly, this invention provides a method for protection against external corrosion in copper-based heat exchangers characterized in that a) a coating is applied with an Sn-based alloy on a Cu-based core; and b) the Cu-based core coated with the Sn-based alloy is subjected to a suitable thermal treatment, under controlled conditions, aimed at causing the thermal diffusion of said alloy in said Cu-based core, in case said Thermal diffusion has not taken place in a similar way to the application of the coating, which forms a composite material that is constituted by a core based on Cu, by an external surface consisting of an alloy based on Sn and a intermediate layer made up of Cu-Sn alloys, of variable compositions, which guarantee a total adhesion and the continuity of the different layers of the composite material. The term "Cu-based nucleus" refers to a Material constituted mainly and fundamentally by Cu which, optionally, can be weakly alloyed with one or more metals, selected from the group formed by, for example, Te, ttg, Sn, Cd, Cr, Ag, Pb, In, Be , Zr, Pe, P, Al and Ni, which, as a whole, may be present in a concentration of less than 0.2% by weight. These elements added to the Cu are intended to increase the thermal resistance of the Cu so that its mechanical properties are maintained after the thermal cycles of welding of the honeycomb. At the same time, these elements make it possible to guarantee the highest possible thermal conductivity values in order to achieve the most adequate performance of the radiator. The Cu-based core, capable of being coated by the Sn-based alloy, can be in the form of Cu bands, Cu fins for heat intercarriers and honeycombs for heat exchangers formed by brass tubes and Cu fins. . The term "Sn-based alloys" includes pure Sn and any Sn alloy with other metals. In particular, the preferred Sn-based alloys used to prepare the composite material of this invention comprise: a) Sn-Pb binary alloys, in any proportion, preferably in a proportion between 1% and 99% in Sn and 99% and 1% in Pb; b) Sn-Pb alloys with addition of other elements, such as Sb, Og, Cu, Zn, Bi, Cd, In, Ni, Pb, in the following proportions: Sn: from 0.5 to 99% Sb: from 0 , 01 to 7% Og: from 0.01 to 5% Cu: from 0.01 to 2% Zn: from 0.01 to 1% Bi: from 0.01 to 2% Cd: from 0.01 to 5% In: from 0.01 to 5% Ni: from 0.01 to 1% Pb: from 0.5 to 99% c) Sn-Sb alloys, in a proportion comprised between 93% and 99.5% in Sn and 7% and 0.5% in Sb; d) Sn-Ag alloys, in a proportion comprised between 95% and 99% in Sn and 5% and 1% in Ag; e) Sn-Zn alloys, in a proportion comprised between 97% and 99% in Sn and 3% and 1% in Zn; and f) Pure Sn, with a minimum Sn percentage of 99%. These Sn-based alloys have an anodic electrochemical potential against the Cu-based core, which allows an effective protection of the Cu against the aggression caused in natural or artificial media that contain, among other compounds, inorganic chlorides, nitrogenous compounds and oxides. of sulfur, which significantly increases life -from the fin of the radiator and allows to reduce radiator thicknesses and weights, by achieving an adequate conservation of the mechanical and thermal properties of the fins. To obtain an affective protection against external corrosion, the composite material formed must have a minimum thickness of 1 miera (μm). In this ecription, it is considered that said mirror is determined by the eurone of the middle layer member, constituted by the alloys - "" "e Cu-Sn of variable composition, and the thickness of the external surface, constituted by the Sn-based alloy. Because the protection against corrosion increases with the thickness of the coating, to obtain a certain The thickness of the intermediate layer and the outermost surface should be between 1 μm and 1/5 of the total thickness of the composite material, including the thickness of the core. In practice, it has been observed that a total thickness between 2 and 4 μm provides good results.The fabrication of the composite material comprises the coating of the Cu-based core with an Sn-based alloy and the thermal diffusion of said alloy deposited on the Cu-based core. The applied deposit of said Sn-based alloy on the Cu-based core can be performed by various procedures. , the coating The core can be made by immersing said core with Cu, continuously, in a bath of an alloy based on Sn melted, the coating layer being regulated by means of a jet of air, an inert gas, water or lamination. In this case, the thermal diffusion of the alloy occurs simultaneously with the core coating. In another alternative, said coating can be carried out by projecting the molten Sn-based alloy, either by wave or by drop, onto the Cu-based core. In this case, the thermal diffusion of the alloy also occurs simultaneously with the coating of the core with said alloy. In another alternative procedure, the coating can be carried out by depositing a metal powder comprising pure Sn or the Sn-based alloy, or from pulp containing a metal powder comprising pure Sn or the Sn-bae alloy, on the Cu-based core, followed by a heat treatment at a temperature equal to or higher than 300 ° C for the thermal diffusion of the alloy to the Cu-based core to take place. Additionally, the core coating based on Cu with the Sn-based alloy can be made by electro-deposition of pure Sn or Sn-based alloys on the Cu-based core, followed by thermal diffusion at a temperature equal to or greater than 100 ° C. Sn-based alloy It can be applied on a Cu-based core in the form of a strip and with the proper thickness for the manufacture of fins for heat exchangers, or alternatively, it can have a thickness greater than that necessary for the manufacture of such fins, in which case, it is possible to carry out a step of rolling the composite material once formed until obtaining the adequate thickness for the manufacture of fins. Additionally, the Sn-based alloy can be applied over the fins constructed from uncoated Cu bands and also over a conventional honeycomb constructed with brass tubes and Cu fins. The coating of the Cu based core with the Sn bae alloy can be total or partial. In the latter case, the partial coating can be carried out, preferably, by electrolytic deposition of pure Sn or of the Sn-based alloy, or by casting the molten Sn-based alloy, or by depositing either a metal powder containing Pure Sn or the Sn-based alloy, or from paetas containing a metallic powder comprising pure Sn or the Sn-based alloy, over the area of the Cu-based core to be coated, followed by thermal diffusion at a temperature equal to or greater than 300 ° C. When the Sn-based alloy is applied on the honeycomb, the coating can be applied either on the entire honeycomb or on its external surfaces. Because corrosion is most important on the external surfaces of the -s >; > a the coating can be applied in a way that only affects the outer areas of the comb and not the central core of the comb. In a particular embodiment of this invention, the composite material may not be present throughout the width of the fins, not being able to cover the front and rear surfaces of the comb in sun to a depth of 1/3 of the width of the comb. In this case, the partial coating can be carried out on the surfaces to be covered, preferably by "^ pure electrolytic positing of Sn or of the Sn-based alloy, either by projection of the molten Sn or of the molten Sn-based alloy, or by depositing either a pure Sn-containing metallic powder or the base alloy of Sn, or of pulps containing a metallic powder comprising pure Sn or the Sn bae alloy, on the surface of the honeycomb to be covered, followed by thermal dif- fusion at a temperature of 300 ° C or more. in front of the corrosion of the fins themselves, in the whole of the honeycomb a great -> l increase in its resistance to corrosion, with the new material a balance is achieved in the electrochemical potentials of the metals that make up the honeycomb, thus avoiding the galvanic mechanism that produces the perforating corrosion points in the tubes and a rapid deterioration of the welding menisci By using the procedure provided by this invention it is avoided the mechanism that affects, short - '• loop, to the functionality of the radiator, and, instead, there is a slow attack of the Sn alloys that have an anodic nature compared to the constituent materials of the tubes and fins. The results obtained when performing comparative tests of accelerated corrosion Cniebla salina continuo. Standard NFX 410023 between conventional Cu radiators and Cu radiators to which the protection treatment proposed by this invention has been applied or which "" The tcorporan aletae made with said composite material, show that the perforating corrosion are produced in a period of time about 10 times greater in the radiators of Cu treated with the process of the invention than in conventional Cu radiators, ie , uncoated (see Examples 1 and 2). Also, it is very interesting to observe how the mechanical reheating and the thermal efficiency of the radiator treated with the protection method proposed by this invention is preserved after the corrosion tests, which indicates the scarce attack on the tubes. , fins and meniscus welding. Tests conducted have shown that, after 1,000 hours of salt spray test, the thermal efficiency of the treated radiators is reduced by only 10%. All this guarantees the functionality of the radiator treated with this protection procedure, in service , in aggressive environmental conditions, for long term. "With respect to the manufacture of heat exchangers that incorporate parts manufactured with the composite material provided by this invention, and in particular, in the operation of welding the honeycomb, said composite material allows to use both an oxidant atmosphere furnace as a controlled non-oxidizing atmosphere furnace When said welding is carried out in an oxidizing atmosphere furnace, the conditions of honeycomb eelibility, These materials are much more favorable, since said composite material, thanks to its intermediate layer based on Cu-Sn alloys and its external surface at Sn's surface, has a much improved weldability. The use of solder flux consisting of organic acids, amines and resin, without inorganic components, makes the welding process much smoother and is eliminated. of washing and drying the combs.

Additionally, the honeycomb can be made in a controlled non-oxidising atmosphere, so that the welding operation is carried out without any flux, which greatly simplifies the heat exchanger manufacturing process since the installations of the heat exchanger are eliminated. Fluxing, washing and drying. With the use of this technology, significant energy savings are obtained and gaseous and aqueous effluents are eliminated, thus presenting a very favorable environmental impact. Also, this technology also contemplates the possibility of welding the ends of the tubes to the collector plates in the same welding operation of the tubes to the fins. For it, it is enough to apply locally a Sn-based solder, without flux or including a very weak, non-corrosive organic flux, which does not produce any environmental problem. This is possible due to the favorable conditions of the non-oxidizing controlled atmosphere of the furnace, Among the non-corrosive organic fluxes there may be mentioned the alcoholic dissolution of rosin, without activating or activated with organic acids or amines, for example, rosin: ieopropanol (10:90), rosin-glutamic acid: ieopropanol (10: 2: 88) or rosin: dibutylamine hydrochloride-dimethylamine hydrochloride: isopropanol (10: 2: 4: 84). current manufacturing of heat exchangers that require the / realization of the honeycomb in two stages, a great simplification in the manufacture and a reduction of energy costs is achieved, as well as a very important improvement in the productivity. object of the present invention, it »constitutes a process for the manufacture of heat exchangers to copper bath, especially radiators for cooling of thermal engines, and more Automobile radiators, in which the fins are composed or coated totally or partially, by the composite material provided by this invention, which includes a step of welding the tubes to said fins, which may be carried out: a) in a continuous furnace or static oxidant atmosphere, through the use of a non-corrosive organic welding flux that does not need washing, consisting of organic acids, amines and resin, and inorganic components; or alternatively, b) in a controlled atmosphere non-oxidizing furnace, without the incorporation of any type of flux. In this case, such furnaces can be either vacuum furnaces, continuous or static furnaces or furnaces of inert, continuous or static atmosphere, with the presence of inert gases, such as N2, CO2, and other inert gases, and absence of O2 and H2O . Another object of this invention is constituted by fins for heat exchangers, especially suitable for use in the manufacture of radiators for the cooling of thermal engines, such as radiators for automobiles, essentially constituted by the composite material provided by this invention. Said fins can be manufactured by coating and thermal diffusion of an Sn-based alloy on a Cu-based core in the form of a strip and with the thickness suitable for the manufacture of the fins, or alternatively, it can have a thickness greater than that necessary for the manufacture of such fins, in which case, a step of rolling the composite material once formed to obtain the proper thickness for the manufacture of fins can be carried out. In a particular embodiment, such fins are manufactured from a Cu-based core, in the shape of a fin and with the appropriate thickness, on which a coating with a Sn-coated alloy is applied over the whole? the surface of the fin or on outer strips of said fins, by means of the application of sheets, threads or strands preformed of Sn alloys, or by means of electro deposition of pure Sn or of the Sn-based alloy, or by means of projection of the alloy based on molten Sn, or by depositing either a metallic powder containing pure Sn or an Sn-based alloy, or from pads containing a metal powder comprising either pure Sn or an Sn-based alloy, followed by of thermal diffusion at a temperature equal to or greater than 300 * C Alternatively, the coating of said fin, consisting of a core based on Cu, can be carried out by immersion in a molten bath of an alloy based on Sn, by projection of the Sn pure molten or of the Sn-based alloy, by wave or cascade, of the Cu-based core or of the surface strip to be coated, with simultaneous thermal diffusion to the coating. Another additional object of this invention is constituted A copper heat exchanger, such as a radiator intended to cool a heat engine, more particularly a radiator for automobiles, which contains fins manufactured wholly or partially with the composite material obtained by the process of this invention. Finally, the invention also provides a method for depositing Sn-based alloys on the honeycomb of a copper bake heat exchanger, manufactured by the technology belonging to the state of the art, that is, formed by brass tubes. and copper fins, characterized in that said alloy is applied on the honeycomb so as to cover mainly the external fringes of the fins, by electro-deposition, applied on both sides of the honeycomb, either pure or of alloys based on Sn, or by projection either of a metallic powder containing pure Sn or an Sn-based alloy, or of pastes containing a metal powder comprising pure Sn or an alloy based on Sn, followed by thermal diffusion at a temperature equal to or greater than 300 ° C. The following examples serve to illustrate the invention, and should not be considered as limiting the scope thereof.

EXAMPLE 1 Bands of Cu-Sn (0.1% Sn) of 0.042 mm of thickness were continuously coated with an Sn Pb alloy (15% Sn + 85% Pb), in a cast year and with a coating thickness of 2 μ /expensive. With the material obtained, fins were manufactured for radiators of automobiles and radiators were mounted including such fins. The honeycomb was made in a continuous furnace, with an oxidizing atmosphere, using an organic flux. The thermal diffusion was achieved by the coating of the band with the molten Sn alloy. ^ A continuous salt spray test was carried out, according to the NFX 41002 standard, with 5% NaCl at 35 ° C. After 1,170 hours the radiator did not show any type of perforating corrosion, neither in the tubes nor in the fins, only a slight euperficial attack was observed in the coating of lae aletae (Figures 6 and 7), while in the copper radiators manufactured With the current technology, that is, with the protective treatment proposed by this invention, when carrying out the same test of the salt spray, corroeionee perforantee were taken in tubes and fins between 100 and 200 hours of < . trial session.

EXAMPLE 2 Bands of Cu-Cd (0.2% Cd) of 0.04 mm thickness were coated, continuously, with an Sn-Pb alloy (25% Sn + 75% Pb) melted, by immersion in a molten bath, and with a coating thickness of 4 μm / face. With the material obtained They fabricated fins for automobile radiators and mounted radiators including such fins. The honeycomb was made in a continuous furnace, with an oxidizing atmosphere, using an organic flux. The thermal diffusion was achieved by the coating of the band in the molten Sn alloy. A continuous salt spray CMORM NFX 410023. test was carried out, with 5% NaCl at 35 ° C, for 1,008 hours.

After that time, only a slight attack was observed The coating of the fins, the radiator retained its mechanical resistance perfectly and there was no point of perforating corrosion in the fin or in the tubes, only the menisci of the Sn-based solder were weakly attacked. Figures 8, 9, 10, 11 and 12) Figures 8 to 12, by comparison with Figures 1 to 5 that correspond to radiators built with the technology belonging to the prior art, submitted to a salt spray test in short-term tests (less than 244 hours) and in which very intense corrosion has occurred, show the greater resistance to external corrosion of the copper radiators treated with the protective process of the present invention.

EXAMPLE 3 Fins were manufactured from a Cu band coated with an Sn-Pb alloy (60/40), by • electrolysis in aqueous phase. After electrodeposing, a thermal diffusion treatment was carried out at 300 ° C for 30 seconds. Subsequently, radiators including the fins described above were built. The honeycomb welding was carried out in a static vacuum oven. The radiators were subjected to a continuous acetic salt fog test, containing CuCl-2 - CASS TEST - according to • ASTM B 368. Examined the radiator, no significant corrosion was observed in the tubes or in the fins or weld connections.

EXAMPLE 4 A radiating honeycomb containing fins manufactured using a composite material provided by this invention was produced from a film of Sn-Cu and Sn alloys of 3 um total thickness. The welding was carried out in a static oven, under vacuum and under a nitrogen pressure of 40 mbar. No type of flux was used. Upon examining the honeycomb solder, it was observed that the honeycomb was perfectly welded and had a clean, shiny and completely oxide-free appearance (Figure 13).

Claims (46)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A procedure for the protection against external corrode in copper baee heat exchanger that includes the coating and thermal diffusion of an alloy with Sn on a core based on Cu, with which "it forms a composite material constituted by a core based on Cu, an external surface constituted by an alloy based on Sn and an intermediate layer constituted by Cu-Sn alloy of variable components, characterized in that said alloys based on Sn comprise: a) alloy binariae Sn-Pb, in any proportion, preferably, in a proportion comprised between 1% and 99% in Sn and 99% and 1% in Pb; b) Sn-Pb alloys with the addition of other elements, such as >, Cu, Zn, Bi, Cd, In, Ni, Pb, in the following proportions: Sn: from 0.5 to 99% Sb: from 0.01 to 7% Ag: from 0.01 to 5% Cu from 0.01 to 2% Zn: from 0.01 to 1% Bi: from 0.01 to 2% Cd; from 0.01 to 5% In: from 0.01 to 5% Ni: from 0.01 at 1% Pb: from 0.0 5 to 99% c) Sn-Sb alloys, in a proportion comprised between 93% and 99.5% in Sn and 7% and 0.5% in Sb; d) Sn-Ag alloys, in a proportion comprised between 95% and 99% in Sn and 5% and 1% in Ag; e) Sn-Zn alloys, in a proportion comprised between 97% and 99% in Sn and 3% and 1% in Zn; and f) Pure Sn, with a minimum Sn percentage of 99%.
2. 2. Method according to claim 1, characterized in that the composite material formed has a minimum thickness, considered co or the sum of the thickness of the intermediate layer and the thickness of the external surface, of 1 miera (μm).
3. 3. Method according to claim 2, characterized in that the thickness of the composite material formed is comprised between 1 μm and 1/5 of the total thickness of the composite material, including the core thickness based on Cu.
4. 4. Method according to claim 2, characterized in that the thickness of the composite material formed is comprised between 2 and 4 μ.
5. 5. Process according to claim 1, This process is carried out by depositing or applying said Sn-based alloy onto the Cu-based core by immersing said core in a bath of a molten Sn-based alloy 6. Process according to claim 5, characterized in that the coating layer with said? ned alloy is regulated by means of an air jet, an inert gas, water or lamination 7. Process according to claim 5, characterized in that the thermal diffusion of the 8. Process according to claim 5, characterized in that the coating of the Cu-based core with the Sn-based alloy is carried out by projecting the Sn-based alloy fused, by wave or by cascade, on the core based on Cu. 9. Process according to claim 8, characterized in that the thermal diffusion of the alloy based on Sn is produced simultaneously to the coating of the Cu-based core with the Sn-based alloy. 10. Method according to claim 5, characterized in that the coating of the Cu-based core with the Sn-based alloy is carried out by deposition either of a pure Sn-containing metallic powder or an Sn-based alloy, or of pastes containing a metallic powder that ignites pure Sn or an Sn-based alloy on the Cu-based core. 11. Method according to claim 10, characterized in that the thermal diffusion of the Sn-based alloy on the Cu-based core is carried out by heating at a temperature equal to or greater than 300 ° C. 12. Process according to claim 5 , characterized in that the coating of the Cu-based core with the Sn-based alloy is carried out by electro deposition of either pure Sn or Sn-based alloys on the .. Cu-based core. 13. Process according to claim 12, characterized in that the thermal diffusion of the Sn-based alloy on the Cu-based core is carried out by heating at a temperature equal to or greater than 300 ° C. 14. Process according to claim 1, characterized in that the core based on What to coat is a copper fin for heat exchangers. 15. Method according to claim 14, characterized in that the coating with the Sn-based alloy applied to said copper fin is partial. 16. Method according to claim 15, characterized in that the partial coating and the thermal diffusion of the Sn-based alloy is carried out by pure Sn electrolytic deposition or Sn-based alloy, or by projection of the base alloy. of molten Sn, or by "" "positing either a metallic powder containing pure Sn or the baee alloy of sn, or of pastes containing a pure Sn-containing metallic powder or the Sn-based alloy, on The zone of the Cu-based core to be coated, followed by thermal diffusion at a temperature equal to or greater than 300 ° C. 17. Process according to claim 1, characterized in that the Cu-based core to be coated is a honeycomb constructed with 18. Brass tubes and copper fins, suitable for heat exchangers 18. Method according to claim 17, characterized in that the coating with the Sn-based alloy applied to said honeycomb is partial, and is applied over the The front and rear surfaces of the honeycomb, in a depth of up to 1/3 of the width of the honeycomb. 19. Process according to claim 18, characterized in that the partial coating of the honeycomb with the Sn-based alloy and its thermal diffusion is carried out locally on the surfaces of the honeycomb to be covered, by means of electrolytic deposition either of pure Sn or of the Sn alloy, either by pure Sn or either Sn-based alloy casting, or by depositing either a pure Sn-containing metallic powder or Sn baee alloy, or paste containing a metal powder which comprises pure Sn or the Sn-based alloy, followed by differed? thermal at a temperature equal to or greater than 300 ° C. 20. A process for the manufacture of copper-based heat exchangers, including a stage for welding the tubes to the fins, characterized in that the fins are composed, totally or partially, of a composite material constituted by a core base of Cu, an external surface constituted by an alloy based on Sn and an intermediate layer constituted by Cu-Sn alloys of variable compositions, and said welding is carried out in a furnace with an oxidizing atmosphere or with a non-oxidising controlled atmosphere. 21. Process according to claim 20, . characterized because the welding is done in a continuous or static furnace with an oxidizing atmosphere. 22. Method according to claim 21, characterized in that the welding is carried out with the incorporation of a non-corrosive organic welding flux that does not need washing. 23. Method according to claim 22, characterized in that said welding flux is constituted? OG organic acids, amines and resin, without inorganic components. 24. Method according to claim 20, characterized in that the welding is carried out in a controlled atmosphere non-oxidizing furnace, without the incorporation of any type of flux. 25. Method according to claim 24, characterized in that the welding is carried out in a continuous or static furnace. 26. Method according to claim 24, characterized in that the welding is carried out in an inert, continuous or eetatic atmosphere furnace, with the preemption of inert gases, and the absence of O2 and H20. 27. Method according to any of claims 20 to 26, characterized in that said manufactured heat exchanger is a radiator designed to cool down thermal engines, particularly a radiator for automobiles. 28. Composite material characterized in that said Sn-based alloys comprise: a) Sn-Pb binary alloys, in any proportion, preferably, in a proportion comprised between 1% and 99% in Sn and 99% and 1%. in Pb; b) Sn-Pb alloys with addition of other elements, such as Sbrn Og, Cu, Zn, Bi, Cd, In, Ni, Pb, in the following proportions: Sn: from 0.5 to 99% Sb: from 0 , 01 to 7% Ag: from 0.01 to 5% Cu; from 0.01 to 2% Zn: from 0.01 to 1% Bi: from 0.01 to 2% Cd; from 0.01 to 5% In: from 0.01 to 5% Ni: from 0.01 to 1% Pb: from 0.05 to 99% c) Sn-Sb alloys, in a proportion between 93% and 99.5% in? n and 7% and 0.5% in Sb; d) Sn-Ag alloys, in a proportion comprised between 95% and 99% in Sn and 5% and 1% in Ag; e) Sn-Zn alloys, in a "Voporción comprised between 97% and 99% in Sn and 3% and 1% in Zn; and f) Sn pure, with a minimum percentage of Sn of 99%. - Material according to claim 28 characterized in that it has a minimum thickness, considered as the sum of the thickness of the intermediate layer and the thickness of the external surface, of 1 miera (μm) 30.- Material according to claim 29, characterized in that it has a thickness comprised between 1 μm and 1/5 of the total thickness of the composite material, including the thickness of the core based on Cu. 31. - Material according to claim 29, characterized in that it has a thickness comprised between 2 and 4 μrn. 32. Material according to claim 28, characterized in that the deposit or application of said Sn-based alloy on the Cu-based core is carried out by immersion of said core in a bath of an alloy based on Sn melted, the coating layer being regulated by means of -a jet of air, an inert gas, water or lamination, and the thermal diffusion of the Sn-based alloy occurs simultaneously to the coating of the Cu-based core with said alloy. 33.- Material according to claim 28, characterized in that the deposit or application of said Sn-coated alloy on the Cu bae core is carried out by projection of the molten Sn-based alloy, by wave or by This is based on the Cu-based core, and the thermal diffusion of the Sn-based alloy occurs simultaneously with the coating of the Cu-based core with said Sn-based alloy. 34. Material according to claim 28, characterized in that the deposit or application of said Sn-based alloy on the Cu-based core is carried out by depositing either a pure Sn-containing metallic powder or a Baee-Sn alloy, or of paetae containing a metallic powder comprising pure Sn or a bae alloy of n, on the Cu-based core and the thermal diffusion of the Sn-based alloy on the Cu-based core is carried out by heating to a temperature equal to or greater than 300C. 35.- Material according to claim 28, characterized in that the deposit or application of said Sn-based alloy on the Cu-based core is performed by electrodepoeating either pure Sn or Sn bae alloys on the Cu based core, and thermal diffusion of the alloy. Sn-based on the Cu-based core is carried out by heating at a temperature equal to or higher than 300C. 36.- Material according to claim 28, characterized in that the Cu-based core is in the form of a strip, with a thickness equal to or greater than that necessary for the manufacture of fins for heat exchangers. 37.- Material according to claim 28, characterized in that the coating of the core based on Cu »n the alloy based on Sn is total. 38.- Material according to claim 28, characterized in that the coating of the Cu-based core with the Sn-based alloy is partial. 39. Material according to claim 38, characterized in that the partial coating of the Cu-based core with the Sn-based alloy and its thermal diffusion is carried out locally by means of electrolytic deposition of either pure Sn or Sn alloy, or projection of the molten Sn-based alloy, or deposit either of a metallic powder containing the Sn-based alloy, or of pastes containing a metallic powder comprising the Sn-based alloy, on the core area based on Cu to be coated, followed by thermal diffusion at a temperature equal to or greater than 300 ° C. 40.- Material according to claim 28, characterized in that it is suitable for the manufacture of fins for heat exchangers, especially for radiators intended to cool thermal engines, particularly automobile radiators. 41. A fin for a copper-based heat exchanger, characterized in that it is constituted by a composite material according to one of claims 28 to 40. 42. A flap according to claim 41, characterized in that it is obtainable by coating a Bae core of Cu by means of the application of lane, preformed strands of Sn alloys, or by electro-deposition of pure Sn or Sn alloy, or by projection of the Sn-based alloy melting, or depositing a metallic powder containing pure Sn or an Sn-based alloy, or from a pulp containing a pure Sn-containing metallic powder or an Sn-based alloy, on the Cu-based core or the strip Surface to be coated, followed by thermal diffusion at a temperature equal to or greater than 300 ° C. 43. - Fin according to claim 41, characterized in that the coating of the Cu-based core is carried out by immersion in a bath Sn-based alloy, wave or cascade, of the Cu-based core or the surface strip to be coated, with thermal diffusion simultaneous to the coating. 44.- Fin according to any of the claims 42 or 43, characterized in that the Cu-based core is in the form of a strip of thickness equal to or greater than that suitable for the manufacture of fins. 45.- Flap according to claim 41, characterized in that it is suitable for use in the manufacture of radiators intended for the cooling of thermal engines, particularly radiators for automobiles. 46.- A method for depositing Sn-based alloys on the honeycomb of a copper-based heat exchanger, formed by brass tubes and copper fins, characterized in that said alloy is applied on the honeycomb covering mainly the external fringes of the fins, by electro-deposition, applied on the honeycomb's doe carae, either pure Sn or of Sn baee alloys, or by projection either of a pure Sn-containing metallic powder or an alloy based on Sn, or else from pastes containing a metal powder comprising pure Sn or an alloy with Sn bae, followed by thermal diffusion at a temperature equal to or greater than 300 ° C.