Silbraze Product Shot




Brazing - Problems & Remedies

SYMPTOM CAUSE ACTION
Failure of filler metal to wet both surfaces Surface dirt or contamination
Unsatisfactory fluxing
Improve cleaning procedures
Apply sufficient flux of correct grade
Failure of filler metal to wet one surface 1.One component contaminated

2.Unsatisfactory heating pattern

3.Preform only in contact with one side of the joint
1.Check cleaning procedure

2.Apply heat to the heavier part

3.Ensure that capillary gap is bridged at melting point by adjusting tolerance to give spring-fit.
Failure of filler metal to flow smoothly (Joint is rough and fillet is uneven)

1.Poor fitting components

2.Uneven heating

3.Poor joint ventilation

4.Bad fluxing

5.Overheating Liquation

1.Check that capillary gaps are consistent throughout the joint area

2.Make sure that whole joint area is brought up to brazing temperature simultaneously

3.Make sure gases generated have escape route

4.Check grade of flux and increase amount used

5.Reduce brazing temperature to 50°C above liquidus
Increase heating rate or change to SBA with narrower melting range
Voids (obvious gaps) Variable or excessive joint clearances; uneven or insufficient heating; poor venting; inadequate fluxing Correct the applicable faults.
Blowholes (localised holes with rounded and shiny interiors) Hydrogen pickup by brazing alloy Adjust burners to give neutral to slightly oxidising flame, check that organic contaminants like oil, grease and paint are not present; check that joint is vented. Pinholes can also be caused by overheating resulting in zinc or cadmium vapourizing.
Porosity (shrinkage observed externally in the joint) Excessive local tolerance, unbalanced heat pattern, overheating, use of alloy with too wide a melting range Correct the applicable fault.
Cracking of filler metal Thermal stress set up by differential contraction Redesign joint with higher coefficient of expansion material on outside of joint
Cracking adjacent to one of the parent metals 1.Contamination of the surface concerned

2.Formation of embrittling intermetallic layer.
1.Upgrade preparation techniques

2.Identify possible contaminations, consider trifoil.



Johnson Matthey 
Matthey corporate site: www.matthey.com  SilBRAZE Johnson Matthey (Aust.) Ltd. brand.
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