1.What are the core points of manual arc welding?
Welding Rod Selection:
Preferably, choose low-hydrogen electrodes (such as E5015-G and E5016) to avoid hydrogen-induced cold cracking. (Q355B contains alloying elements such as Mn and Nb, and has a slightly higher hardening tendency than Q235B. Low-hydrogen electrodes can reduce the hydrogen content in the weld.)
If the zinc coating is thin (≤80μm) and corrosion resistance is not a high requirement, acidic electrodes (such as E5003) can also be used, but the zinc coating in the weld area should be cleaned beforehand to reduce porosity.
Welding Process:
Before welding, grind the zinc coating within 20-30mm on both sides of the weld (exposing the metal matrix) to avoid ZnO inclusions caused by zinc evaporation, which can cause weld embrittlement.
Control the current within the lower limit of the recommended range (e.g., 90-120A for a Φ3.2mm E5016 electrode) to reduce heat input, minimize excessive zinc burnout, and prevent coarsening of the matrix grains. Applicable Scenarios:
On-site steel structure installation (such as streetlight pole docking and bracket welding) and welding of thick plate components (such as equipment bases and steel structure columns).
2.What are the core points of gas shielded welding?
Welding Wire and Shielding Gas:
Choose a low-alloy, high-strength welding wire (such as ER50-6 or ER50-G) that matches the strength of Q355B (weld tensile strength ≥490 MPa, compatible with the base material).
Preferably, use an 80% Ar + 20% CO₂ shielding gas mixture (MAG welding). Ar reduces spatter, while CO₂ improves arc stability, avoiding the excessive spatter caused by pure CO₂. If the galvanized layer is thick, the Ar content can be appropriately increased (e.g., 90% Ar + 10% CO₂) to further reduce zinc vapor interference. Welding Process:
Use short-circuit transfer (suitable for thin plates, current 120-180A, voltage 18-22V) for low heat input and minimal zinc burn-off. Jet transfer can be used for thick plates, but the zinc layer must be polished beforehand.
Control the welding torch angle at 80-90° (perpendicular to the weld seam) to prevent zinc vapor from escaping along the torch and causing pores. Maintain a wire extension length of 10-15mm (too short can easily clog the nozzle, while too long can easily cause pores).
Applicable Applications:
Factory mass production (e.g., continuous welding of photovoltaic brackets and guardrails), and welding of medium-thin plate components (e.g., ventilation duct flanges and equipment casings).
3.What are the core points of submerged arc welding?
Welding Material Selection:
The welding wire and flux combination must match the strength of Q355B. Commonly used are H08MnA welding wire with HJ431 flux (acidic flux, excellent processability) or H08MnMoA welding wire with HJ350 flux (low-hydrogen flux, suitable for low temperatures or heavy loads).
Welding Process:
Before welding, the zinc coating must be thoroughly cleaned (using a grinding wheel or sandblasting). Due to the high heat input of submerged arc welding (current 500-800A, voltage 30-38V), the zinc coating will be burned off significantly, and residual zinc can easily cause slag to separate from the weld.
Use reverse DC connection (with the welding wire connected to the positive terminal) to increase penetration depth. Control the welding speed (30-50cm/min) to avoid rapid cooling of the weld pool and the formation of cold cracks.
Applicable Applications:
Butt welding of heavy steel structures (such as load-bearing beams in factory buildings and bridge components) and large pressure vessel shell sections.
4.What are the core points of tungsten inert gas welding?
Welding Materials and Shielding Gas:
Use ER50-G or ER50-6 welding wire (matching the base material), and pure argon (99.99%) shielding gas to prevent impurities from affecting weld quality.
To improve corrosion resistance, a small amount of silicon (such as ER50Si-1) can be added to the welding wire to reduce ZnO inclusions.
Welding Process:
The galvanized layer in the weld area must be thoroughly ground down to expose the bright metal. Because TIG welding concentrates arc energy, zinc vaporization can easily lead to "pinholes" that cannot be covered by slag.
Use a low current (50-100A), a high argon flow rate (8-12L/min), and a welding gun nozzle diameter of 8-10mm to enhance shielding and prevent air intrusion.
Applicable Applications:
Butt-jointing thin-walled galvanized steel pipes, welding precision equipment components, and transition welding between dissimilar steels (such as Q355B galvanized steel and 304 stainless steel).
5.What are the prohibited/cautious welding methods?
Oxyacetylene welding:
The heat input is dispersed and the temperature is low. A large amount of zinc can easily remain in the weld, resulting in a sharp decrease in weld strength (tensile strength may be below 300 MPa). It is also prone to weld bumps and slag inclusions. Therefore, it is strictly prohibited for welding load-bearing structures.
Resistance spot welding:
The zinc coating has high electrical resistance, which can easily result in "cold welds" (unstable contact resistance). Furthermore, spot welding severely damages the zinc coating in the weld area, resulting in poor corrosion resistance. Therefore, it should only be used for temporary, non-load-bearing connections (such as thin sheet metal splicing and positioning) and should not be used for primary structures.