Troubleshooting Common Brazing Issues
Brazing is a straightforward process when the right principles are followed. However, sometimes issues arise that prevent a successful joint. The following guide provides practical solutions to common brazing problems, helping ensure a strong and reliable bond.
Brazing Issues
When the Brazing Alloy Doesn't Flow into the Joint Despite Melting
- Uneven Heating:If the alloy forms a fillet but doesn’t flow into the joint, the inside of the joint may not be reaching brazing temperature. Always heat the tube first to conduct heat inside the fitting, ensuring uniform heating.
- Flux Breakdown:Excessive heat can cause flux to become saturated with oxides, preventing the alloy from flowing properly. Use a softer flame and/or apply a heavier layer of flux. For prolonged heating or stainless steel applications, consider using Harris Stay-Silv® black flux.
When the Brazing Alloy Forms Beads Instead of Wetting the Surface
- Improper Heating:The base metals might not be reaching the correct brazing temperature, while the torch flame prematurely melts the filler alloy. Adjust the heating technique to ensure even distribution.
- Surface Contamination: If the base metals are not properly cleaned, oxidation and dirt can prevent the alloy from adhering. Always clean the surfaces thoroughly before brazing.
When the Brazing Alloy Flows Away from the Joint Instead of Into It
- Incorrect Heat Distribution:Ensure that the fitting is heated adequately and that the torch flame is directed toward the fitting to draw the filler metal into the joint.
When the Filler Metal Cracks After Solidification
- Dissimilar Metal Expansion:When brazing different metals, the varying expansion rates may put stress on the filler metal as it cools. This is common in copper-to-steel joints, where copper expands and contracts more than steel. A steel-into-copper assembly may help alleviate this issue.
- Phosphide Formation:Using a phosphorus-containing alloy on steel or other ferrous metals can create brittle phosphide compounds, leading to cracks. Use non-phosphorus alloys when brazing ferrous metals.
- Excessive Joint Clearance:A joint gap that is too wide can cause cracking due to stress or vibration. Maintain a clearance of .002” - .006” at brazing temperature, depending on the alloy used.
- Rapid Cooling:If the joint is quenched too quickly, cracks may develop. Allow the joint to cool gradually before cleaning off flux residue.
When the Joint Leaks During Service
- Uneven Heating:If the joint is not heated uniformly, the filler metal may not fully penetrate, resulting in weak or incomplete bonding. Proper heating techniques must be reviewed and followed.
- Overheating:Excessive heat can cause elements like phosphorus and zinc to volatilize, weakening the filler metal.
- Torch Flame Issues:An incorrect flame setting can lead to carbon deposition or excessive oxidation, affecting joint integrity.
By addressing these potential problems with the right techniques, brazing reliability can be significantly improved, ensuring durable and high-quality joints.
Joint Leaks During Service
