When it comes to brazing, choosing the right flux is crucial.
A good flux for brazing should be capable of wetting and remaining on vertical surfaces.
It should also have a residue that can be easily removed.
The flux should be applied as a paste evenly to the joint surfaces.
It must activate and dissolve oxides at a temperature 50°C below the brazing alloy's solidus.
The flux should remain active at least 50°C above the liquidus.
Non-corrosive fluxes like potassium fluoroaluminate are commonly used.
These fluxes melt before the filler metal to dissolve oxide layers and facilitate capillary action.
What is a Good Flux for Brazing? 5 Key Factors to Consider
1. Wetting and Residue Removal
A good flux must wet the surfaces of the joint effectively.
This is especially important on vertical surfaces.
The molten brazing alloy should flow evenly across the joint.
The residue left after brazing should be easily removable.
This is crucial for the final quality and functionality of the joint.
2. Application as a Paste
Applying flux as a paste allows for better control and even distribution.
It is important to apply the paste liberally.
This is particularly at sharp edges where the brazing alloy might not easily reach.
Pre-application of flux to the assembly is preferred.
This ensures thorough coverage and prevents uneven heating effects.
3. Temperature Range and Activation
The flux should activate and start dissolving oxides at a temperature at least 50°C below the solidus temperature of the brazing alloy.
This ensures that the flux is fully active and capable of removing surface oxides before the brazing alloy melts.
It should also remain active at least 50°C above the liquidus of the brazing material.
This ensures continued oxide removal as the alloy solidifies.
4. Non-Corrosive Fluxes
Fluxes like potassium fluoroaluminate are non-corrosive.
They are suitable for use in inert atmospheres.
These fluxes melt at temperatures slightly below the melting point of common brazing alloys (e.g., 565-572°C).
They are effective in dissolving oxide layers.
This facilitates capillary action, which is essential for forming strong brazed joints.
5. Operational Considerations
The quantity of flux applied should be adequate to cover all surfaces effectively.
The brazing time should be minimized to prevent overheating and distortion of the parts.
The brazing temperature should be kept as low as possible to maintain the integrity of the base materials.
Balanced heat input ensures uniform heating across the joint, preventing localized overheating.
Continue Exploring, Consult Our Experts
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