The Hidden Factor: Why Flux Grain Size (Mesh) Matters

 Why Flux Particle Size (Mesh Number) Matters

When selecting submerged arc welding (SAW) fluxes, most engineers immediately focus on the basicity index or alloy content. However, the physical particle size (mesh number) of the flux plays a surprisingly crucial role in the welding process.

Jinan Gujin Welding Materials Co., Ltd. offers fluxes in various mesh ranges (typically 10-60 mesh or 8-40 mesh). But why do we provide fluxes of different sizes? Which one is suitable for your project?

1. Understanding Mesh Number

Mesh number refers to the number of holes per linear inch in a sieve.

• Coarse flux (e.g., 8-40 mesh): has larger particles.
• Fine flux (e.g., 14-60 mesh): a mixture of smaller, dust-like particles and medium-sized particles.

2. Impact on "Gas Permeability" (Key to Eliminating Pitting)

• This is the most critical factor. During welding, the flux melts to form slag, and the electric arc generates gases. These gases need to escape through the layer of unmelted flux above.
• The gaps between coarse particles are larger, facilitating gas escape. This is very suitable for heavy-duty welding or dirty plates with high gas generation.
• Fine particles pack tightly. If the flux is too fine and the current is high, gases will be trapped and forced to escape through the molten slag, which often causes "pitting" (shallow gas depressions) on the weld surface.

Recommendation: For thick plates and high current parameters (>600A), use a coarser mesh to ensure better degassing.

3. Impact on Weld Bead Appearance

• Although coarse particles have better gas permeability, fine particles provide better support for the molten pool.
• Fine flux usually produces a smoother, flatter weld bead with better edge fusion (transition). It is ideal for high-speed fillet welding or thin plate welding with high appearance requirements and low gas generation.

4. Flux Consumption Rate

• Surprisingly, particle size can affect cost.
• Fine flux has a higher bulk density. Generally speaking, compared with extremely coarse flux, using finer flux results in a slightly lower consumption ratio (kilograms of flux per kilogram of welding wire) because the "flux pile" above the arc is denser and has higher melting efficiency.

Conclusion: One Size Does Not Fit All

• At Jinan Gujin, our standard product (10-60 mesh) is optimized to balance gas permeability and weld bead appearance, suitable for 80% of applications. However, for special needs:
• For deep grooves and multi-pass welding, choose a coarser flux (8-40 mesh) to avoid pitting.
• For high-speed automated production lines requiring a smooth surface finish, choose a finer flux (14-60 mesh).

Experiencing pitting or arc instability?

It may be related to the flux particle size you are using. Please visit www.gjflux.com to contact our technical team for consultation.