Brazing Tips

Problem

The braze alloy balls up and fails to wet the surface or run into the joint.

Possible solutions

• 1. Improve cleaning methods to insure removal of contaminants.
• 2. Clean and roughen the surface by grit blasting.
• 3. Grind or machine off surfaces of cold-drawn and coldrolled bar stock.
• 4. Improve protective atmosphere quality.
• 5. Change position of the part to encourage the braze alloy to run into the joints.

Problem

Capillary action doesn't occur even though the braze alloy melts and forms a fillet.

Possible solutions

• 1. Increase time at heat.
• 2. Loosen or tighten the joint fit-up.
• 3. Increase braze temperature.
• 4. Clean mating parts more thoroughly.
• 5. Check for improper or insufficient cleaning.
• 6. Check for contamination in the joint from cements or gels used to apply the filler metal. 
• 7. Check for voids in the fillet.
• 8. Check for bad fit-up of mating parts during assembly. 

Problem
The braze alloy flows away from the joint rather than into it.

Possible solutions

• 1. Check base metal properties for elements that oxidize and inhibit braze flow.
• 2. Check cleaning process.
• 3. Compare actual size of the joint gap to the size recommended for the braze alloy being used.
• 4. Remove any burrs at the edge of the joints or any other obstacles which stop the flow of the alloy. 
• 5. Try providing a reservoir for better placement of the alloy at the joint. 
• 6. Try using a stop-off to retard the flow of the alloy away from the joint area. 
• 7. Try changing the alloy form to pre-place the braze alloy into the joint area.

Problem

There is indication the alloy melted but there was no flow.

Possible solutions

• 1. Look for surface contaminants left from poor cleaning.
• 2. If possible, clean the filler metal (wipe clean wires, rod and foil forms of alloy).
• 3. Increase braze temperature or time at heat.
• 4. Check the atmosphere quality and improve it, if necessary.
• 5. Check if braze gap is too large or too small.

Problem
A tight fitting joint opens up during brazing.

Possible solutions

• 1. Check for high coefficient of expansion.
• 2. Check for incompatible expansion between dissimilar metals.
• 3. Check for release of base metal stresses during heat cycle.
• 4. Check for poor support of the components.
• 5. Check for a press fit that is too tight and stretches the outer component beyond its elastic limit.
• 6. Check for fixturing that constrains the part too much.
• 7. Try adjusting the heating and cooling rates to allow for differences in expansion.
• 8. Try lighter weight fixtures that support well but do not constrain the components.

Problem
Braze splatters appear around the braze joint.

Possible solutions

• 1. Try slowing the heating rate between 150 – 540 °C (300 – 1000 °F) and use stabilizing holds to help remove liquids from binders used to apply the filler metals.
• 2. Try changing the form of the alloy, if possible.
• 3. Try to control cooling from 35 – 95 °C (100 – 200 °F) from the braze temperature before quenching the parts.

Problem
The joint appears starved or lacking alloy in areas.

Possible solutions

• 1. Check the braze alloy deposit to be sure there is sufficient material to fill the joint. 
• 2. Make sure the alloy is securely attached to the part right up to the melting temperature.
• 3. Be sure the filler metal has not been blown off by quench gas while it is still liquid from the brazing temperature.
• 4. Check if the braze gap is too large.
• 5. Check the vapor pressure chart to see if a component in the braze alloy was vaporized, leaving the alloy unable to melt or flow.