JPH0134719B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to vacuum brazing of assembled structures. BACKGROUND OF THE INVENTION Brazing of assembled structures made of oxidizing materials, such as aluminum heat exchangers, is usually carried out by vacuum brazing. Vacuum brazing is performed by placing the brazed assembled structure temporarily fixed with a jig in a vacuum furnace equipped with a radiant screen, and heating the entire structure to the brazing temperature using radiant heat from a heat source. However,
Heating by radiant heat requires a considerable amount of time for the entire structure to reach the brazing temperature; When the soldering base material, the tube plate 2, and the corrugated fin 3 are stacked one after another to form a so-called laminated structure, the thermal conductivity in the Z direction, that is, in the vertical direction, as shown in the thermal conductivity data in Table 1. Zλ is extremely small compared to the thermal conductivities Xλ and Yλ in the X and Y directions on both sides, and therefore a considerable temperature difference occurs between the surface layer and the center of the core 1.

[Table] Additionally, the temporary fixing jigs (not shown) for tightening core 1 from above and below are usually made of stainless steel, which has a higher radiation absorption rate than aluminum cores. Only the part that comes into contact with the jig is heated particularly rapidly and exposed to brazing temperature for a long time. As a result, the brazed part (fillet) between the tube plate 2 and the fin 3 in this part becomes thinner, which reduces the pressure resistance. There were problems such as causing insufficient strength. For this reason, conventional vacuum brazing involves applying black-gray paint to the outer surface of this type of brazed structure, or roughening the outer surface of the structure by mechanical or chemical treatment. Various measures have been taken to reduce the reflective ability of the surface of structures and increase the absorption rate of radiant heat.
None of them were effective enough to solve the above-mentioned problems. In view of these circumstances, the present inventor conducted various experiments and research on methods for increasing the radiant heat absorption rate of vacuum brazing structures, and found that Na0.1 to 0.4
%, Al0.1~0.5%, Si8.0~30%, Mn5.0~20%,
It has been found that a volatile paint containing 7.0 to 28% Fe and 1.2 to 4.7% Cu has an excellent effect of dramatically increasing the radiant heat absorption rate of structures. Then, when the volatile paint was applied to the entire outer surface of the core 1 for the plate-fin type heat exchanger except for the jig fastening part and vacuum heating was performed, the temperature remained until the entire core reached the brazing temperature. Not only was the time required for heating significantly reduced, but the entire core could be heated almost uniformly, and no brazing defects due to uneven heat were observed. Regarding this, even if the volatile paint described above is applied only to the outer surface of the core 1 other than both end surfaces on the passage side, that is, the surface of the side bar 4 and the end surface of the tube plate 2, almost the same effect as described above can be obtained. did it. Further, no influence of volatile components on brazing properties was observed at all. That is, in the present invention, Na0.1-0.4%, Al0.1-0.5%,
Si8.0~30%, Mn5.0~20%, Fe7.0~28%, Cu1.2
The gist is a vacuum brazing method for assembled structures, which is characterized by applying a paint containing up to 4.7%, with the remainder consisting essentially of volatile components, and heating it to a brazing temperature in a vacuum furnace. Table 2 shows the radiant heat absorption rate of the side bar 4 subjected to the method according to the present invention in comparison with the radiant heat absorption rate of the untreated side bar and the side bar whose surface was finished with sandpaper.

[Table] As shown in Table 2, the radiant heat absorption rate of the sidebar according to the present invention is 0.661 higher than that of the sidebar treated with conventional sandpaper, which is a dramatic improvement. I understand. The above-mentioned radiant heat absorption coefficient was calculated by measuring the diffuse reflectance and vertical reflectance of each sidebar subjected to the above-mentioned treatment in advance, and using the measured values using the following equations. ε＝∫ ^∞ / ₀ (1−σ ₁・λ−σ ₂・λ)Eb・λdλ／∫ ^∞
/ ₀ Eb・λdλ… Eb・λ = 3.218×10 ⁸ /λ5 1/exp(1.439×10 ⁴ /λT)−1
... Kcal/m ² hμm However, ε: Absorption rate σ: Reflectance T: Temperature (300°K) E: Radiance λ: Wavelength b: Black body 1: Diffusion component 2: Vertical component Next, examples will be described. . After assembling the core 1 for the plate-fin heat exchanger (700W x 550H x 1150L) shown in Fig. 1 and fixing it with a jig, Na0.1-0.4% was added according to the method of the present invention.
Al0.1~0.5%, Si8.0~30%, Mn5.0~20%,
A paint containing 7.0 to 28% Fe and 1.2 to 4.7% Cu, with the remainder substantially consisting of volatile components, was applied to the entire outer surface of the core 1 except for the jig fastening area. In this case, the paint was appropriately diluted with thinner and coated three to five times at room temperature to form a coating film of about 10 to 20 microns. Additionally, the opening of the core was masked to prevent paint from adhering to it. After air drying for about 24 hours, the core was placed in a vacuum furnace and subjected to a vacuum rapid heating and cooling test. As a comparative example, an untreated plate-fin heat exchanger core (700W x
550H x 1150L) was subjected to the same vacuum rapid heating and cooling test as above. As a result, the entire core is heated to a predetermined brazing temperature of 550
The time required to heat the core to ℃ was 5.0 hours as shown in Figure 2 for the untreated core without coating, while the time required for heating it to ℃ was 5.0 hours as shown in Figure 3 for the core coated with paint according to the method of the present invention. As you can see, it took 3.6 hours, which was a reduction of 1.4 hours. Furthermore, when looking at the temperature difference in the vertical direction (Z direction) at the center of the core between the - point 〇 in the middle row and the - point △ in the bottom row, the maximum temperature difference is the second largest in the untreated core without coating. As shown in the figure, the temperature was 148°C, whereas in the case of the coated core according to the method of the present invention, the temperature decreased to 121°C as shown in Fig. 3. Similarly, if we look at the temperature difference in the vertical direction at the corner of the outer surface of the core, that is, the jig fastening part, between the - point x on the top row and the - point □ on the middle row, the maximum temperature difference is
In the untreated core with no paint applied, the temperature was 112°C as shown in Figure 2, while in the core coated with paint according to the method of the present invention, the temperature decreased to 59°C as shown in Figure 3. As explained above, according to the present invention, the efficiency of radiation heating in vacuum brazing is significantly improved, so the brazed structure can be heated uniformly in a short time, and brazing defects can be avoided. Excellent effects such as no occurrence of

[Brief explanation of drawings]

Figure 1 is a perspective view of a core for a plate-fin heat exchanger shown to explain the implementation procedure of the method of the present invention, and Figure 2 is a vacuum rapid heating and cooling of an untreated core that is not coated with paint according to the method of the present invention. FIG. 3 is a temperature graph of each part of the core showing the results of a vacuum rapid heating and cooling test on a core coated with the paint according to the method of the present invention. 1: core, 2: tube plate, 3: fin, 4: side bar.

Claims (1)

[Scope of Claims] 1. Na0.1 to 0.4%, Al0.1 to 0.5%, Si8 on the entire outer surface excluding the outer side surface part or the temporary fixing part of the assembly structure for vacuum brazing temporarily fixed with a jig. .0~30%,
A paint containing 5.0 to 20% Mn, 7.0 to 28% Fe, and 1.2 to 4.7% Cu, with the remainder essentially volatile components, is applied and heated in a vacuum furnace to brazing temperature in a short time. A method for vacuum brazing an assembled structure, characterized by: 2. The outer surface of the vacuum brazing assembly structure temporarily fixed with a jig was coated with Na0.1-0.4%, Al0.1-0.5%, Si8.0.
~30%, Mn5.0~20%, Fe7.0~28%, Cu1.2~
The assembly structure is characterized in that the assembly structure is heated uniformly by partially painting only the outer surface other than both end surfaces on the passage side with a paint containing 4.7% and the remainder substantially consisting of volatile components. How to vacuum braze things.