JPH0773789B2 - Preparation method of heat exchanger with excellent pitting corrosion resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an Al heat exchanger having excellent pitting corrosion resistance.

[Conventional technology]

Conventional fluoride-based non-corrosive flux (eg KAlF ₄ -K
₃ AlF ₆ eutectic composition) is used for brazing an Al heat exchanger, which is usually performed by introducing an inert gas such as N ₂ and having a dew point of −40 ° C.
And oxygen partial pressure is about 600 ℃ in a furnace controlled to 1000ppm or less.
It was carried out by heating (hereinafter, such brazing method is referred to as NB method).

For example, in the case of an Al heat exchanger condenser, in the NB method, an extruded multi-hole pipe (hereinafter abbreviated as a tube material) bender-processed into a large S-shaped shape as shown in Fig. 1 (a).
(1) and a fin material (2) obtained by corrugating a brazing sheet in which a brazing material of an Al-Si alloy is clad on both sides of the core material as shown in FIG. 1 (b). After assembling as shown in the figure, after attaching the unions (3) and (3 ') to the refrigerant inlet and outlet of the tube material (1), they are fixed by the holding jig (4) to form the core (5), and after cleaning the core Fluoride-based flux is applied to the entire surface, and then it is fed into a brazing furnace and residual heat / heating is performed according to the temperature distribution curve shown in Fig. 3 (B) to braze and integrate the fin material and tube material. To do.

Since automobiles equipped with the Al heat exchanger manufactured as described above have come to run in a salt damage area, improvement of external pitting corrosion resistance of the heat exchanger has become an important issue in recent years. Therefore, in the NB method, not only the use of sacrificial fins but also the following anticorrosion treatment of the tube material itself has been performed.

(1) By subjecting the tube material to a zincate treatment before brazing, Zn is deposited on the surface of the tube material, and Zn is diffused into the tube material by heating for brazing.

(2) Zn is added to the fluoride-based flux to diffuse Zn into the tube material from the flux during brazing and heating.

According to the conventional method, flux brazing using a chloride-based flux containing ZnCl ₂ diffuses Zn from the flux, so it has an excellent anticorrosion effect, but it is necessary to clean and remove corrosive flux residues. Is improved by using a fluoride-based flux.

[Problems to be solved by the invention]

However, the zincate treatment before brazing is costly, and since an alkaline solution is used to etch the tube material, it is necessary to prevent the solution from entering the inside of the tube, and there are many operational difficulties.

As for the method of adding Zn to the flux, a high concentration flux of 50 to 60% is used in the case of chloride type flux, whereas a high activity is itself in the case of fluoride type flux, so it is as low as about 10%. Since the concentration flux is sufficient, a large amount of Zn cannot be supplied, and a desired amount of Zn cannot be diffused over the entire surface.

[Means for solving problems]

The present invention is a result of various studies in view of this, a simple and at low cost to develop a manufacturing method with improved pitting corrosion resistance of the heat exchanger by the NB method, the tube forming the refrigerant passage of the Al heat exchanger Tube in which a flux is applied after the fluoride flux is applied and a flux is not applied in the production of a heat exchanger in which a fin material subjected to corrugated processing is assembled and brazed using a fluoride flux in an inert gas And the material is assembled and held in Zn vapor at a temperature lower than the melting point of the flux in an inert gas and higher than the temperature at which these members are heated for 1 minute or more, and then at a temperature higher than the melting point of the flux. It is characterized by brazing.

[Work]

In this way, applying the flux only to the fin material means that the flux is already applied to the tube material when it is exposed to Zn vapor and diffused into the tube material after being assembled with the tube material. , Because the flux acts as a protective film and prevents Zn vapor from adhering to the surface of the tube material. Furthermore, when these assembly members are heated in an inert gas and exposed to Zn vapor, the melting point is lower than the above-mentioned flux. The temperature is also used to prevent the flux applied to the fin material from melting and coating the surface of the tube material during the Zn diffusion treatment to the tube material.

In order to efficiently attach Zn from the Zn vapor to the tube surface before melting the fluoride flux, the temperature of the Zn vapor is higher than the heating temperature of the tube material and the melting point of the flux (about 562
550-560 ° C, which is lower than the
If it is less than a minute, the amount of Zn adhering to the tube surface is not sufficient,
Therefore, the anticorrosion effect is also insufficient. When the temperature of the Zn vapor is lowered, it is necessary to lengthen the holding time accordingly.

Furthermore, in order to efficiently generate Zn vapor in the brazing furnace, the oxygen concentration in the furnace should be 1000ppm or less and the dew point should be -30 ° C or less, and the flow rate of the inert gas per minute is effective in the furnace. 0.1 to 1 times the internal volume is optimal and economical for maintaining the atmosphere in the furnace and generating Zn vapor, and the surface area of the molten Zn in the furnace is 0.05 to ^2.5 cm ² per unit effective internal volume (liter) of the furnace. Is effective.

〔Example〕

 The present invention will be described based on examples.

JIS 3003 alloy (0.05-0.2% Cu-1.0-1.5% Mn-Al alloy) core material with JIS 4343 alloy (6.8-8.2% Si-Al alloy) brazing filler metal clad at a clad rate of 10% 0.16 mm
The brazing sheet of 1 was corrugated to produce a fin material, which was washed with a material, immersed in a 5% concentration solution of a fluoride-based flux, and then dried through a drying oven at 200 ° C. to apply the flux to the surface. The fin material and JIS 1050 alloy (Al 99.5% or more) are extruded and a 4-hole tube material with a wall thickness of 0.8 mm, a width of 22 mm and a thickness of 5 mm is bender processed and solvent-cleaned. It was held by the holding jig (4) as shown in (c) and used as the core (5) without the union attached to the brazed sample. A brazing test was conducted on such a core by the NB method in a furnace as shown below.

As shown in FIG. 2, an endless mesh belt (7) running in a muffle (6) (effective internal volume 270) having a width of 300 mm, a height of 100 mm and a length of 9 m is provided, and the belt (7) is provided. The preheating zone (8) for preheating the core (5) placed on the belt (7) and conveyed by the belt (7) from the front in the traveling direction of, and the brazing zone (for brazing the core (5) ( 9) 30 / min N ₂ gas is flowed into the muffle (6) of the continuous atmosphere furnace (11) provided with the cooling zone (10) for cooling the brazed product, and the brazing zone (9) is 600 Zn with a surface area of 50 cm ² set to ℃
The molten Zn was placed in the container (12) and placed in the preheating zone (8).

Zn in the above core tube in a continuous atmosphere furnace like this
The preheating temperature and the preheating time in the preheating zone for performing the vapor diffusion treatment are changed as shown in Table 1, and the core is brazed according to the in-furnace temperature distribution curve shown in FIG. Surface of core tube material obtained under each condition
The Zn concentration and the Zn diffusion depth were measured at 5 points with an X-ray microanalyzer, and the results are also shown in Table 1. The dew point of the furnace atmosphere during brazing is -35 ° C and the oxygen concentration is 10
It was 0 ppm. Further, the obtained core was subjected to a cast test for 500 hours, the maximum pit depth at that time was determined by the depth of focus method, and the results are also shown in Table 1.

Further, for comparison, after applying the flux to the whole surface of the core, the molten Zn is placed in the preheating zone in the continuous atmosphere furnace and brazing is performed at 600 ° C. according to the temperature distribution curve in the furnace shown in FIG. 3B. Similar tests were conducted on the cores manufactured by the method, and the results are also shown in Table 1.

As is clear from Table 1, the core according to the method of the present invention has a surface Zn
A good diffusion pattern having a high concentration of 1 to 2% and a diffusion depth of about 100 μm was obtained, and a similar diffusion pattern was observed immediately below the fins, that is, even on the surface of the tube material in the brazed portion. Also, it is found that the pit depth by the cass test is good. On the other hand, the comparative method No. 9 in which the preheating time is less than 1 minute and the comparative methods No. 10 to No. 12 in which the preheating temperature is higher than the flux melting temperature do not give a good diffusion pattern, and the pit depth is also the value of the method of the present invention. It can be seen that it is 2-3 times larger than the case. Comparative method No. 13 in which flux is applied to the entire surface and then brazed through Zn vapor is diffusion Z
It is clear that the concentration of n is small and the anticorrosion effect is greatly inferior, and the flux on the tube surface suppresses the adhesion of Zn.

In addition, even when the core coated with the flux only on the fins is continuously heated and brazed as shown in FIG. 3 (B), the temperature inside the furnace is kept below the melting point (about 562 ° C.) of the flux. The same effects as those of the method of the present invention can be obtained by arranging Zn generating sources at several places.

〔The invention's effect〕

As described above, according to the present invention, by performing non-corrosive flux brazing of a heat exchanger that requires pitting corrosion resistance without performing flux application to the tube material and performing Zn vapor treatment at the temperature before the flux flows. It is possible to prevent the effect of suppressing the Zn adhesion of the flux film, improving the pitting corrosion resistance,
Furthermore, it can be used not only for condenser cores and evaporator cores that use extruded multi-hole tubes for tube materials, but also for drone cup evaporators that use brazing sheets for tube materials and radiators that use electric resistance welded tubes (brazing sheets). It has a remarkable effect.

[Brief description of drawings]

1 (a), (b) and (c) show the assembly of the core of the Al heat exchanger. (A) is a perspective view of the extruded tube material that has been bender processed, and (b) is the corrugated fin material. A perspective view, (C) is a perspective view of a core assembled by pressing with a jig, FIG. 2 is an external view showing a continuous atmosphere furnace, and FIG. 3 is a temperature distribution curve in the furnace when brazing in a continuous atmosphere furnace It is a graph which shows. 1 …… Extruded multi-hole tube (tube material) 2 …… Fin material 3,3 ′ …… Union 4 …… Holding jig 5 …… Core 6 …… Muffle 7 …… Endless mesh belt 8 …… Preheating zone 9… … Brazing zone 10 …… Cooling zone 11 …… Continuous atmosphere furnace 12 …… Zn container

Claims (1)

[Claims] 1. A method of manufacturing a heat exchanger in which a tube material forming a refrigerant passage of an Al heat exchanger and a corrugated fin material are assembled and brazed with a fluoride flux in an inert gas. Assembling a fin material that has been dried after applying a fluoride-based flux and a tube material that is not applied with a flux, and a Zn temperature that is lower than the melting point of the flux in an inert gas and that is higher than the temperature at which these members are heated. A method for producing a heat exchanger having excellent pitting corrosion resistance, which comprises holding in steam for 1 minute or more and then brazing at a temperature higher than the melting point of the flux.