The Influence of Vacuum Brazing Heating Rate on Brazing Quality

Heat exchanger (also called heat exchanger or heat exchange equipment) is a device used to transfer heat from hot fluid to cold fluid to meet the specified process requirements. It is an industrial application of convective heat transfer.

When the heating rate is fast, the surface color of the parts is dark, and the flatness is poor. The comparative experiment found that the staged heating effect is better. During heating, the activity of aluminum is enhanced, and small amount of air can oxidize it. At the same time, the gas is expanded by heating,When the heating rate is reduced , and the hot air can be extracted as much as possible; the heating rate is fast, and the other ad-versing effect is that the parts are easy to get deformed.

Relying on radiation heat transfer, rapid heating leads to uneven temperature, which is resulting in thermal stress or releasing stress in different regions and deforming. It is necessary to raise the temperature quickly when it is close to the brazing temperature. The heating rate is slow, and the residence time in the solid-liquid line temperature range of the solder is long. In the condition of vacuum , the low melting point components of the solder and the components with high vapor pressure volatilize seriously, and the melting point of the remaining solder components increases and remains solid state does not melt and cannot be brazed. This is the same situation that occurs when the brazing tool has a large heat capacity. As for the flatness of the parts, rapid heating at this stage is also allowed.

The stress has been released at 500 ℃, the recrystallization temperature of aluminum alloy is lower than 500 ℃, and the plasticity of aluminum alloy is good above 500 ℃, and the thermal stress is easily released. In the brazing experiment of the simulated test piece, the temperature is kept at 400 ℃ for 30 minutes and then quickly heated to 600 ℃ for 25 minutes, which is better than the brazing effect directly raised to 600 ℃. The result of further experiment is that a part brazed only at 450 ℃ for 30 min, and then 10 ℃·min -1 raised to 620 ℃ . then the workpieces all be fully qualified.

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