Process Parameters of Vacuum Brazing Heating and Cooling

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Vacuum brazing furnace degree of vacuum , operating pressure, brazing heating rate, holding time and temperature stability, temperature, holding time, cooling rate, temperature and so has a direct impact on the vacuum brazing process.

1. Cold Vacuum Degree The Choice of Cold Vacuum Degree Mainly Depends on the Type of Substrate

2. Work Pressure

The brazing material will release a large amount of gas, resulting in continuous changes in the cold state, but at the brazing temperature of the vacuum brazing furnace, the vacuum brazing furnace is required to basically return to the cold vacuum state. But there are exceptions. For example, the vapor pressure of copper in copper-based solder is 1 Pa at 940 degrees, so the working pressure is not allowed to be lower than 1 Pa. For this reason, high-purity nitrogen and argon can be passed into the furnace to maintain the working pressure in the furnace.

3. Heating Rate During Brazing

The heating rate of the substrate should be able to ensure that the released gas is pumped away, and the element should be heated uniformly to reduce or prevent deformation of the element due to the stress caused by sudden heating. The main factors that should be considered when determining the heating rate of the vacuum brazing furnace are the material, shape, structure and size of the component. For copper and copper alloys, heating should be performed at a faster rate between 250°C and 500°C. For heat-resistant alloys or austenitic stainless steels, rapid heating is required in the danger temperature zone where carbides are precipitated. For components with complex shapes and large assembly prestress, they should be heated slowly. For thicker parts, the heating speed should not be too fast.

4. Type of Solder and Crystallization Temperature Range

If it is pure metal solder, the heating speed can be faster; the alloy solder should be heated faster within the melting temperature range to avoid solder segregation and increase the liquidus temperature; when using cream solder, the heating speed should be slower below 500C , So as to avoid the violent volatilization of the bonding agent and cause the solder splash. However, no matter what kind of solder is used, the heating rate of the vacuum brazing furnace should not be too fast within the range of 50~100°C below the solidus temperature of the solder to ensure that the internal and external temperatures are basically the same when the solder is melted. Capillary action. Have a good time. When brazing thin-walled weldments in a vacuum brazing furnace,

5. Stable Temperature and Holding Time

Stable temperature and holding time means that when the vacuum brazing furnace is brazing, it is heated to a temperature close to the solidus of the solder and the heating is suspended. Keep it at this temperature for a certain period of time. The purpose is to reduce the temperature gradient of the module and make the temperature of each part of the module uniform. When brazing parts with poor thermal conductivity such as stainless steel and heat-resistant alloys in a vacuum brazing furnace, if the temperature of the vacuum brazing furnace is heated from normal temperature to the brazing temperature, a large temperature difference will occur in each component. The size of this temperature difference is related to the type, structure and wall thickness of the component material. At this time, the outer layer of solder melts and flows along the high temperature zone; however, due to the low temperature at the joint, the solder cannot be filled well.

6. The Cooling Rate of the Vacuum Brazing Furnace

When the solder is in a liquid state, do not ventilate or turn on the fan to cool it down.

In order to meet the heat treatment requirements of the base material, such as 1Crl8Ni9, in order to prevent the precipitation of carbides at the grain boundary, the cooling rate should be accelerated, and the fan should be forced to cool.

For long and complex parts, the cooling rate should be slow.

7. The Temperature of the Vacuum Brazing Furnace

Generally, the furnace temperature of stainless steel and heat-resistant alloy is lower than 150°C; aluminum and aluminum alloy is lower than 300°C; carbon steel and alloy structural steel are lower than 100°C.