How do the particle size and composition of the submerged arc welding machine affect the welding quality?

Submerged arc welding machine uses flux to cover the welding area to stabilize the arc, protect the weld and improve the welding quality. The particle size and chemical composition of the flux are crucial to the welding quality, affecting the arc stability, penetration, weld metallographic structure, mechanical properties and the formation of welding defects.

The effect of flux particle size on welding quality

The flux particle size is usually expressed in mesh size, that is, the number of flux particles passing through the screen per unit area. The effects of fluxes of different particle sizes in submerged arc welding are as follows:

Flues with finer particles (80-200 mesh):

Advantages:

Provide a more uniform covering layer and improve arc stability.

It helps with low current welding and is suitable for thin plates and low current applications.

The weld is finer and the weld surface is smoother.

Disadvantages:

It may cause the flux layer to be too dense, affecting gas escape and increasing the risk of pore formation.

Excessively fine particles may sinter into agglomerates at high temperatures, affecting slag fluidity and flux recycling.

Flux with coarse particles (10-60 mesh):
Advantages:
Suitable for high current welding and improve the deposition rate.
Because the flux layer is loose, it is conducive to gas escape and reduce porosity defects.
Suitable for thick plate welding and can provide deeper penetration.
Disadvantages:
It may cause the weld surface to be rough and it is difficult to control the weld bead shape.
Excessive particles will affect the uniform distribution of the flux and reduce welding stability.
Recommendations for particle size selection
Welding of thin plates and small currents: It is recommended to use finer flux (80-200 mesh) to improve the surface quality of the weld.
Welding of thick plates and high currents: It is recommended to use coarser flux (10-60 mesh) to ensure good penetration and reduce porosity problems.
Automated submerged arc welding system: Medium particle size (40-100 mesh) is usually used, taking into account stability and penetration control.
The influence of flux composition on welding quality
The chemical composition of submerged arc welding flux determines its performance, including slag characteristics, deoxidation ability, alloy component supplementation, etc. The main components of flux and their effects are as follows:
Silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃)
Function: Affect the fluidity and covering performance of slag.

Effect:
When the SiO₂ content is high, the slag has good fluidity, which is conducive to weld formation and pore escape.
When the Al₂O₃ content is too high, it may cause the slag to be too sticky, which is not conducive to slag stripping.
Calcium oxide (CaO) and magnesium oxide (MgO)
Function: Affect the basicity and deoxidation ability of slag.
Effect:
Basic flux (high CaO/MgO content) helps to reduce the sulfur and phosphorus content of weld metal and improve welding toughness.
Low basic flux is suitable for ordinary carbon steel welding, while high basic flux is more suitable for high strength steel and low temperature steel welding.
Titanium oxide (TiO₂)
Function: Affect arc stability.
Effect:
TiO₂ helps to stabilize the arc, improve welding operability, and is suitable for automated welding.
Too high TiO₂ may cause the slag to be too hard, affecting the removal of welding slag.
Fluoride (such as CaF₂, calcium fluoride)
Function: Improve deoxidation ability and reduce porosity defects.
Impact:
Increasing the CaF₂ content can improve the crack resistance of the weld, but too high may reduce arc stability.
Suitable for welding high-strength steel, stainless steel and other materials to reduce the tendency of hot cracks.
Manganese (Mn) and silicon (Si)
Function: As a deoxidizer, improve the metal structure of the weld.
Impact:
Appropriate amounts of Mn and Si can improve the strength and toughness of the weld, but too high may lead to hardening tendency and increase the risk of cracks.
Suitable for submerged arc welding of low-alloy steel and high-strength steel to optimize the metallographic structure of the weld.
Optimize the flux particle size and composition to improve welding quality
Choose the right particle size
For automated welding, a moderate (40-100 mesh) flux should be selected to take into account stability and penetration.
For special applications (such as high current welding), coarse-grained flux (10-60 mesh) can be selected to reduce porosity.
Adjust the flux composition to match welding requirements
For high-strength steel, use high-alkalinity flux (high CaO/MgO) to improve weld toughness.
For stainless steel, Si and Mn can be increased to optimize welding strength and crack resistance.
Optimize welding process parameters
Appropriately adjust current, voltage and welding speed to match flux characteristics and avoid welding defects.
In combination with a flux recovery system, ensure that the flux is not damp to maintain stable welding quality.

The flux particle size of the submerged arc welding machine affects the welding penetration, porosity formation and weld bead formation, while the flux composition determines the mechanical properties, arc stability and deoxidation ability of the weld. Reasonable selection of flux particle size and composition can significantly improve welding quality, reduce welding defects, and adapt to the needs of different materials and welding conditions.