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How Flux Affects Brazing

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How Flux Affects Brazing


 Good & Bad Tips










 Good parts have an even flow to all four corners.  The flow does not go over the sides or down the front. 


How Much Brazing Flux to Use

Black Flux was used in the pictures below.  See our article on brazing flux to see the different types of flux and why using black flux may solve some brazing problems.





Too thick – globs of flux – most of the brazing wire buried under brazing flux so you can’t see the outline 

Flux layer about right – you can see the outline of the brazing wire but the wire is pretty well covered

Too thin you can see the whole brazing wire and see the color of it 


Removing Brazing Flux

Brazing flux can be removed with hot water and a little brushing.  The parts can be tumbled in cold water or sandblasted.  Brazing flux can also be removed by brushing.  Brazing flux that is very hard to brush off while hot can sometimes be removed rather easily once it cools.


If you severely overheat the brazing flux it may be very hard to remove.  In this case you need to add more brazing flux and reheat.  The new flux will mix with the old flux and then you can remove it.


 Anti Flux – braze stops

There are chemical preparations sold that are applied like paint.  They are designed to stop flux flow at a particular line.  They generally work pretty well.  Experiments can be run using Milk of Magnesia from a drugstore.


Crystallized Brazing Flux

This happens rarely but when it does happen it is best not to use the flux.  These are the crystals we found in the flux.  I took the flux and just washed it in warm water to separate the crystals.  This is out of new containers.  These are 50x pictures.  The metal rod is a paper clip (.032” dia.) for scale.  


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