What factor mainly determines the strength of a brazed copper tube joint?

The strength of a brazed copper tube joint is primarily influenced by the proper clearance between the tube and fitting. This clearance is crucial because it affects the ability of the filler metal to flow into the joint during the brazing process. A good fit ensures that there's enough gap for the filler metal to penetrate effectively while also preventing excessive gaps that could weaken the joint. If the clearance is too tight, the filler metal may not be able to flow into the joint properly, leading to insufficient bonding and strength. On the other hand, if the clearance is too large, it can lead to weakened areas in the joint where the filler metal does not adequately fill the gap.

While the type of filler metal, the heat application method, and the cooling rate all play important roles in the brazing process and can influence joint strength, they are secondary to the significance of achieving the appropriate clearance for ensuring optimal joint integrity.