Why use process boxes in vacuum brazing

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Vacuum brazing uses a vacuum atmosphere without using flux, and realizes the connection of various easy-to-solder or difficult-to-solder materials at high temperatures. The resulting brazed joints have high quality and beautiful shapes. It is very suitable for vacuum brazing of precision parts and has been used more and more in industrial production. The vacuum degree or atmosphere in the vacuum brazing furnace has a great influence on the quality of brazing. In order to ensure the quality of brazing, it is very important to control the atmosphere in the vacuum brazing furnace. The Craft Box is a simple and effective way to temporarily control the brazing atmosphere. During conventional brazing, we put the assembled parts and fixtures directly on the platform in the vacuum brazing furnace, then close the furnace door, vacuumize and heat.

When using the process box, put the assembled parts and fixtures into the box, then put the box with the parts on the platform of the vacuum brazing furnace, then close the furnace door, vacuumize and heat to complete the brazing.

Craft boxes are ideal for the following situations:

1 The vacuum brazing furnace is polluted, but there is an urgent need for brazing

In normal production, the long-term use of the vacuum furnace will inevitably pollute the inner furnace to a certain extent, resulting in worse and worse internal vacuum. Therefore, vacuum brazing furnaces need to arrange regular cleaning and maintenance. If there is a product that needs to be brazed urgently at this time, in order to cooperate with the plan of an important customer, direct brazing may lead to substandard brazing quality and cannot meet the needs of customers. With the process box, as the vacuum is carried out, the vacuum inside the box is higher and higher until it meets the brazing requirements. The box effectively blocks the pollution outside the box in the furnace and maintains the vacuum inside the box, thereby providing the necessary conditions for successful brazing.

2 There are volatile elements in the base metal or solder under vacuum brazing conditions

Because vacuum brazing furnaces are relatively expensive, in many factories or processing plants, a vacuum brazing furnace needs to braze many different materials. If there is element volatilization in the brazing of a certain product, the brazing furnace will be polluted. Then the subsequent brazing of other products may not be possible, and the furnace needs to be shut down for cleaning before continuing. This can lead to blocked production plans, or reduced efficiency. For example, use OKNA Cu110 to braze stainless steel, the brazing temperature is 1120°C, and the vacuum degree is 3×10^-2Pa. Under this vacuum degree, the volatilization temperature of the solder is about 1027°C, and at a brazing temperature of 1120°C, OKNA Cu110 will volatilize to a certain extent, and the volatilized elements are deposited on the furnace wall. Under certain conditions, after reheating, the deposited elements volatilize into the atmosphere again, contaminating the subsequent brazing parts.

For such a situation, the stainless steel parts brazed with OKNA Cu110 can be put into the process box, and the volatilized elements are confined in the process box and deposited on the inner wall of the box after cooling, without polluting the vacuum brazing furnace wall.

3 Aluminum alloy vacuum brazing

In “flux-free brazing of aluminum alloy—vacuum brazing”, we introduced that it is impossible to remove the oxide film on the surface of aluminum alloy by relying on vacuum atmosphere alone. Instead, it is necessary to place magnesium in the vacuum brazing furnace and rely on vacuum The magnesium vapor formed under it is used to remove the oxide film and realize brazing. Putting the aluminum alloy parts into the process box and forming magnesium vapor in the process box can give full play to the role of magnesium vapor and reduce the requirement for the vacuum degree of the brazing furnace.

Craft box production and requirements

The material of the craft box is generally recommended to use titanium alloy or stainless steel. You can choose a piece of foil and bend it into a box shape, as shown in the figure below.

The following points should be paid attention to when using the craft box:

The titanium alloy or stainless steel foil bent into the craft box should be as thin as possible;

The foil used to make the box should be kept clean to prevent contamination or oxidation during storage;

Clean gloves should be worn when making boxes and placing workpieces.

Learn More:
Ceramic-To-Metal Vacuum Brazing Services

Flux-free Vacuum Brazing of Aluminum Alloys

The Key Steps for Daily Maintenance of Vacuum Brazing Furnaces