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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Factors Affecting The Quality of Vacuum Brazing

Generally speaking, the brazing quality is not only related to the process parameters, but the following factors in production practice have a greater impact on the brazing quality.

1. Leakage Rate of Equipment

When the equipment leaks, the parts will oxidize. When the leakage rate is much lower than the pumping speed, the equipment can still obtain the vacuum required by the process, but the brazed parts are not in a high-purity atmosphere, but in a vacuum atmosphere that is constantly impacted by air. When a small amount of air enters the vacuum The chamber is immediately pumped away, and the brazing cycle in the furnace is in a dynamic equilibrium process where a little gas is pumped away. .

It can be seen that the leakage of the equipment has a great influence on the brazing and the brazing joints, and even the base material is oxidized. If you only pay attention to the vacuum indicated on the instrument without considering the air leakage, the quality of the brazing cannot be guaranteed. Therefore, it is necessary to regularly check the leakage rate of the equipment.

2. The Purity of the Gas

When high-purity argon or nitrogen is used in vacuum brazing, on the one hand it is used as a forced cooling medium, on the other hand, when using brazing materials with high vapor pressure (such as copper or aluminum alloy, etc.), as a shielding gas, the higher the purity, the better , The oxygen content should be as small as possible, because trace oxygen will also cause discoloration or oxidation of parts at high temperatures. The impure gas will also bring many adverse effects to the process, and at the same time it will bring certain harm to the heating elements of the vacuum furnace, thereby shortening the life of the equipment.

3. Cleanliness of Parts

The surface cleanliness of the parts before brazing is very important. In addition to the strict implementation of oil removal and cleaning procedures, special attention must be paid to not re-contamination after cleaning. When assembling, filling the brazing filler metal and installing the furnace, you must wear clean cotton gloves when touching the parts, because the sweat contains salt lactic acid, which seriously pollutes titanium alloys and nickel-based alloys. In addition, it is strictly forbidden to hit with an aluminum hammer during assembly to avoid the low melting point metal pollution caused by the brazing surface. At the same time, it should be noted that the contamination of the parts of the furnace is just over the copper-based brazing furnace, the furnace wall is more or less There will be copper contamination (when the pressure in the furnace is adjusted with micro-argon, the copper solder is rarely volatilized, but it is impossible to completely avoid it). If the nickel-based material parts are then brazed, it may cause copper to nickel fusion Therefore, the empty furnace should be cleaned up straight to make the low melting point alloy contaminating the furnace wall volatilize again and be pumped away.

4. Assembly Clearance

The size of the joint gap directly determines the density and strength of brazing. If the space is too large, the capillary action is weakened, the filler is difficult to fill, and the alloying effect is weakened, resulting in poor mechanical properties of the joint.

Especially for joints with open ends, the surface tension of the liquid solder and the parts is less than the gravity of the solder, and the liquid solder cannot hold its weight, resulting in the failure of brazing. If the indirect image is too small, it will hinder the filling of the solder, and it is not easy to form a joint with a good penetration rate. Under the premise of not affecting the filler filling, the smaller the brazing gap, the better. In this way, the alloying effect of the solder is stronger, which is conducive to less diffusion of metal compounds. More importantly, when the solder in a narrow gap undergoes plastic deformation under force, it is limited by the surrounding high-strength brazing metal, and the joint is formed The complex stress results in a greatly improved joint strength. In actual production, the machining accuracy of the joints is guaranteed during the yard, and there is generally no re-inspection.