JPS63295058A - Production of heat exchanger made of aluminum - Google Patents

Abstract

PURPOSE:To easily produce a heat exchanger made of aluminum having excellent pitting corrosion resistance at a low cost by subjecting an Al member coated with a fluoride flux to soldering under heating and melting Zn to evaporate in a furnace in which an inert gaseous atmosphere is maintained. CONSTITUTION:The fluoride flux is coated on the Al member and after the flux is dried by heating at about 200 deg.C, the flux is heated and held to and at about 600 deg.C and is thereby soldered in the furnace in which the inert gaseous atmosphere of N2 or the like is maintained. The Zn is disposed in the position of 430-620 deg.C in the furnace and is melted to evaporate. The concn. of the oxygen in the furnace is preferably maintained at<=1000ppm, the dew point at <=-30 deg.C, the flow rate of the inert gas at 0.1-1 times the volume of the furnace per minute, and the surface area of the molten Zn at 0.05-2.5cm<2> per unit volume l of the furnace at this time. The evaporated Zn vapor is brought into the Al member simultaneously with the soldering of the Al member by heating, by which the Al member is subjected to the Zn diffusion treatment. The pitting corrosion resistance of the resulted heat exchanger made of Al is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing an aluminum heat exchanger by brazing, and in particular improves pitting corrosion resistance.

(Prior art) Aluminum heat exchangers have traditionally been manufactured by brazing using a chloride flux containing ZnCJ!2, and this method provides excellent pitting corrosion resistance due to Zn diffusion from the flux. However, since corrosive flux is left behind, it is necessary to wash and remove it after brazing, which poses problems in wastewater treatment, etc.

In recent years, a brazing method using a fluoride-based non-hygroscopic and non-corrosive chloride-based flux has been developed and is now widely used in the manufacture of aluminum heat exchangers. This method can be applied to fluxes, for example /M! A eutectic structure of 3AfF6 is used for F4-, an inert gas, mainly N2 is introduced, and the dew point is -40.
Brazing is carried out by heating to about 600° C. in a furnace controlled at a temperature below 0.degree. For example, condensers are made by combining and brazing an extruded multi-hole tube with corrugated fin material.
Al on both sides of the core material made of S 3003 + 1% Zn alloy
-5; A plating sheet (thickness: 0.16 m) made of JIS 4343 alloy as a brazing material is used.

However, since automobiles drive in salt-affected areas, improving the external pitting corrosion resistance of aluminum heat exchangers has become an important issue, and in particular, brazing using the above-mentioned non-hygroscopic, non-corrosive flux is based on the NB method (hereinafter referred to as NB method). In addition to the use of sacrificial fins, the following anti-corrosion treatment is applied to the tube material itself.

(1) Before brazing, Zn is deposited on the tube surface by subjecting the Al member to zincate treatment, and during brazing, Zn is diffused by heating.

(2) Zn is added to the flux, and during brazing, Zn is diffused from the flux into the Al member by heating.

[Problem that the invention seeks to solve]

The zincate treatment before waxing is expensive, and since an alkaline solution is used to etch the tube material, there are many operational difficulties, such as preventing the solution from entering the tube.

The method of adding Zn to the flux uses a high concentration flux of 50 to 60%, which results in good diffusion, whereas the method of using chloride-based flux uses a high concentration flux of 50 to 60%.
In this method, the activity of fluoride is strong, and since a low concentration flux of about 10% is used, Zn cannot be sufficiently diffused.

[Means for solving problems]

In view of this, as a result of various studies, the present invention has developed a method for producing an aluminum heat exchanger that improves pitting corrosion resistance by diffusing Zn on the surface of the Al member to be brazed using a simple and low-cost NB brazing method. This is an Al. In the manufacture of aluminum heat exchangers, parts are heated and brazed in a filter in an inert gas atmosphere. This method is characterized in that Zn diffusion treatment is carried out by bringing Zn vapor into contact with the Al member.

That is, in the present invention, a fluoride flux is coated on an Al member for a heat exchanger, and then heated and dried at about 200° C. in a preheating zone. Next, in the brazing zone in an inert gas atmosphere,
When performing brazing by heating to ℃ for several minutes (actual temperature), Zn was placed at a position where the temperature inside the furnace was 430 to 620 ℃ to melt and evaporate, and Al members were generated at the same time as the Al members were heated and brazed. Zn diffusion treatment is performed by contacting with Zn vapor.

[For production]

AZ-St brazing filler metal melts at around 577°C, but zn
The diffusion of the flux depends on the state of the flux attached to the surface (before and after melting).
Irrespective of this, the process proceeds from the lower temperature side, and the Zn diffusion treatment of the Al member is performed at the same time as the brazing of the Al member.

The state of Zn diffusion depends on the state of Zn vapor generation.

However, placing Zn at a temperature of 430 to 620°C in the furnace to melt and evaporate it is impossible to generate Zn vapor unless it is above the melting temperature of 7N (430°C), and it is necessary to maintain Zn above this temperature. There is a need to. On the other hand, at the same time as brazing
The upper limit temperature for performing n diffusion treatment is 620°C. In addition, the oxygen concentration in the inert gas atmosphere inside the furnace was set to 1100.
The reason for setting the dew point below OpD and below -30°C is that good brazing cannot be obtained unless it is within this range, and Zn
This is because the steam generation efficiency decreases.

In addition, the flow rate of inert gas is 0.1 to 1 of the filtration volume per minute.
The reason why the oxygen concentration of the gas was doubled was 11,000 pp or less.
This is to maintain the dew point below -30°C and to promote the generation of Zn vapor. Below the lower limit, it is not possible to maintain the oxygen concentration and dew point within the above range, and when the upper limit is exceeded, inert gas consumption increases. This is because the corrosion resistance increases, and the generation of Zn vapor also increases, resulting in excessive diffusion and deterioration of corrosion resistance.

Furthermore, the surface area of the Zn molten metal is 0 per unit volume (1) of the filter.
．． The reason why the range is 05 to 2.5 crA is that this range is good for generating Zn vapor and performing efficient diffusion treatment.

In order to uniformly diffuse Zn into the Al member, it is important to make the contact between the Al member and the Zn vapor uniform, and it is desirable to use not only gas flow but also appropriate stirring.

〔Example〕

Length 9m, pine full frontage 300 rrvn, height 110
0n.

Using a continuous atmosphere furnace and a drying furnace with a capacity of 2701, the external dimension is 7.
The capacitor core of 0x200 rrun was brazed. A 4-hole extruded material made of JIS 1050 alloy and having a thickness of 5# and a width of 22# as shown in FIG. 1 was used as the tube, and this was bent. In addition, JIS 434 is used for the fins.
A plating sheet made of JIS 3003 alloy with 3 alloys as a brazing material and a core material made of gold with cladding on both sides (plate thickness 0.16 m, brazing material cladding ratio 10%) was used and corrugated. As shown in Fig. 2, the fin (1) is placed between the tube (2), fixed with a jig, degreased (U5wt%m degree fluoride flux is applied), and heated at 200℃. Moisture was removed in a drying oven.This was placed in a continuous atmosphere oven and brazed.

The continuous atmosphere furnace consists of a preheating section, a brazing section, and a cooling section.The preheating section is maintained at 35℃, the brazing section is maintained at 550℃ and 600℃, and the cooling section has a water-cooled jacket structure that allows cooling to about 300℃. N2 gas was flowed into the furnace. In this way, the temperature was maintained in the furnace for 20 minutes, and the brazed area was maintained for 15 minutes, and the surface area was 10 to 800 ℃ in the 55°C maintained area of the brazed area.
A container containing molten Zn was placed in a CNI container, and a Zn diffusion treatment was performed simultaneously with brazing using a N2 gas flow of 120 to 3501/min. Regarding these, the Zn diffusion situation was investigated and a Cath test was conducted for 500 hours.

The results are shown in Table 1.

The Zn diffusion status was analyzed at five points in each core using EPMA.
The average value is shown. In addition, in the CASS test, after removing corrosion products, the maximum pitting depth was determined using the depth of focus method.

As is clear from Table 1, all of the methods Nα1 to Nα9 of the present invention have a surface ZnC degree of 2.1 to 9.5% and a Zn diffusion depth of 11%.
A Zn diffusion pattern of 0 to 160 μm is formed on the tube surface, and exhibits excellent pitting corrosion resistance in a corrosion resistance test using a CASS test.

On the other hand, in the comparative method NQIO, which has different conditions, the surface Z n 4 degree was low due to the small surface area of the Zn molten metal, resulting in poor pitting corrosion resistance, and in the comparative method Nα11, the dew point was high and the brazing of the fin material was partially insufficient. . In addition, the comparative method Nα12 is Zn
Since the molten metal surface area is large and the comparative method Nα13 has a large N2 flow m, the surface 7n concentration is high and the diffusion depth is deep.
It can be seen that deep pitting corrosion occurs.

[Effects of the Invention] As described above, according to the present invention, in brazing using non-corrosive flux, a Zn diffusion pattern with good pitting corrosion resistance can be easily formed in an Al member at the same time as brazing. , brazing compared to the previous zincating treatment,
It has significant industrial effects such as significantly fewer work steps and reduced manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a duplex used in the example, and FIG. 2 is an explanatory view showing an example of the capacitor core used in the example. 1, Fin 2, Tube Procedure Amendment M Import) Passed away on January 25, 1986, Commissioner of the Patent Office l''\11 Obetao 1, Indication of the case. 1988 Patent Application No. 132660 2 Name of the invention Method for manufacturing an aluminum heat exchanger 3 Name of the person making the amendment Furukawa Aluminum Industry Co., Ltd. 4 Agent 5 Detailed description of the invention in the specification to be amended column

Claims (2)

[Claims] (1) In the manufacture of aluminum heat exchangers in which aluminum parts coated with fluoride flux are heated and brazed in a filter in an inert gas atmosphere, a Z
A method for manufacturing an aluminum heat exchanger, characterized in that Zn is diffused by disposing Zn vapor and melting and evaporating the Al member, and simultaneously bringing Zn vapor into contact with the Al member at the same time as heating and brazing the Al member. (2) The oxygen concentration in the filter is 1000 ppm or less, the dew point is -30°C or less, the flow rate of inert gas is 0.1 to 1 times the filter volume per minute, and the surface area of the molten Zn is the unit volume of the filter (l).
The method for manufacturing an aluminum heat exchanger according to claim 1, wherein the thickness is 0.05 to 2.5 cm^2.