Influence of brazing quality in vacuum brazing furnace

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In the vacuum brazing furnace, in addition to the vacuum brazing parameters which have a serious impact on the quality of brazing joints, the following important factors also have a greater impact on the quality of brazing.

1. Leakage rate of brazing furnace
The leakage rate of the vacuum brazing furnace is one of the important factors affecting the quality of brazing joints. When the leakage rate of the brazing furnace is too large, it does not meet the allowable leakage rate or the vacuum brazing furnace leaks, it will cause the oxidation of the weldment. Therefore, it is very important to control the leakage rate of the brazing furnace below the allowable leakage rate (usually less than 10 ~ 6Pa·m3/S).

In addition, many domestic vacuum equipment manufacturers also use the back rise rate of the control equipment, that is, the pressure rise rate in the furnace after the main valve of the vacuum system is closed is usually not allowed to exceed the standard of 0～75Pa/h to ensure that the furnace should have the qualified leakage rate.

2.The purity of working gas　
In vacuum brazing, argon or nitrogen is usually used as the working gas. On the one hand, they are used as a forced cooling gas, and on the other hand, they are used as a protective gas for brazing materials with high evaporation pressure (such as copper or copper alloy). . In order to reduce the oxygen content in the gas, the purity of the gas is required to be as high as possible. This is because even if the oxygen content is extremely small at high temperatures, it will oxidize the component and cause it to change color.

3. Cleanliness of work parts
The surface cleanliness of the parts before brazing should not only be carried out in accordance with the requirements of the degreasing and cleaning process, but also after cleaning and degreasing, the parts should be prevented from being contaminated again. This is because the filler and the elbow of the furnace will usually be re-contaminated during assembly. Parts, so wear clean cotton gloves when touching the parts to prevent the parts from being contaminated again due to hand contact. In addition, it is strictly forbidden to hit with an aluminum hammer during assembly to avoid low melting point metal contamination on the brazing surface.

At the same time, attention should be paid to the contamination of the parts by the vacuum brazing furnace. When the furnace with the copper-based brazing material has just been dried, the furnace wall will be more or less contaminated with copper (when the pressure in the furnace is adjusted with micro-argon, the copper brazing material is very Less volatilization, but it is impossible to completely avoid it), if there is more or less copper contamination (when the pressure in the furnace is adjusted with micro-argon, the copper solder rarely volatilizes, but it is impossible to completely avoid it), if When the nickel-based material parts are then brazed, it may cause the copper to dissolve the nickel. Therefore, the empty furnace should be vacuum cleaned to make the low melting point alloy that contaminates the furnace wall volatilize again and be pumped out.

4. The size of the gap during assembly
Vacuum brazing furnace joint gap size can directly determine the compactness and strength of the brazing seam. If the gap is too large, it can weaken the capillary action, make it difficult to fill the brazing filler metal, and weaken the alloying effect, resulting in poor mechanical properties of the joint. Especially for joints with open ends, the surface tension of the liquid solder and the part is less than the gravity of the solder, and the liquid solder cannot maintain its quality, resulting in the failure of brazing. If the gap is too small, it will hinder the filling of the solder, and it is difficult to form a joint with good penetration rate. The surface tension of the liquid solder and the part is less than the gravity of the solder, and the liquid solder cannot maintain its quality, which leads to the failure of brazing. If the gap is too small, it will hinder the filling of the solder, and it is not easy to form a joint with good penetration rate. However, under the premise of not affecting the filling of the solder, the smaller the brazing gap, the better. In this way, the alloying effect of the solder is stronger, which is conducive to diffusion, and there are fewer metal compounds. More importantly, the solder in the narrow gap is limited by the surrounding high-strength brazing metal when it is plastically deformed by the force, and the joint is formed The complex stress is reduced, and the joint strength is greatly improved as a result.

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