Welding flux particle size distribution
The grain fraction of a welding flux determines how quickly it expands during combustion and what gas emissions occur. Too large a grain size can lead to uneven combustion, while too small a grain size can cause rapid cooling and excessive gas pressure.
Physical-Chemical Mechanism
The grain size of a welding flux affects burn rate and gas generation. Small grains burn faster and make more gas, while large grains burn slower and make less gas.
Metallurgical Relevance & Welding Risks
Too large a grain size can lead to uneven burning, which causes porosity and loss of strength. Too small a grain size can cause fast cooling and too much gas pressure, which can lead to hot cracking and wreck the weld structure.
Workshop Practice & Procedures
For most jobs, pick flux with a grain size between 20 and 45 µm. Check grain size regularly with a microscope and adjust the flux as needed. Avoid flux that's too coarse or too fine to get proper burning and a safe weld.