The force of the capillary action is the same as the wicking of paint in between the bristles of a brush, or in induction brazing the wicking of the braze alloy between the two surfaces of the joint.
Higher temperature silver alloys typically have a higher percentage of copper. Even higher melting alloys are made of nickel and other metals and are popular in the aerospace industry.
However, when these metals are mixed in particular ratios the combination typically melts at a temperature that is much lower than the alloying metals. The mixture is called a Eutectic.
The holding device should also not become a heat sink, robbing the heat from the actual parts being heated. In some applications the fixture is what is heated because the parts are so small that it is impractical to heat them directly.
The purpose of the flux is to provide a shield to the joint area so that the metal surfaces being heated do not oxidize.
The strength of the braze joint is obtained from the lap joint area between the parts being joined, however the appearance of a good braze fillet may act as a simple quality control check for the brazing process.
alloy flows towards the heat source, pulling it away from the joint. A few brazing applications can benefit from the use of a braze stop-off compound.
Voids in braze joints are undesirable. They are also unpredictable and result in quality problems. They reduce the strength of the brazed parts. Often leaks in the braze joints are a result of the voids in the braze joints. The following are common practices for the elimination of voids in braze joints.
- Inadequate time at the brazing temperature for the braze alloy to flow and wick around due to capillary action, some processes require a soak at temperature to allow for the braze to flow.
A number of applications, especially in the aerospace and automotive markets, require temperatures in the vicinity of 2000 °F (1093 °C). Generic fluxes do not work at these elevated temperatures.
In order to protect the oxidation of the metal at these elevated temperatures, vacuum or other inert gas environments are needed. Typical inert gasses include cracked ammonia, nitrogen or argon. Other gasses may also be used for specialized applications.