1.How can we block it at its source?
Degreasing: Carefully wipe the bevel and an area at least 20-30mm on both sides using acetone, a specialized cleaner (such as propanol), or a high-efficiency carburetor cleaner. Do not use gasoline, laundry detergent, or other cleaning agents that may leave residue.
Rust/Oxide Removal: Although cold-rolled coils do not have thick rust, they may have a slight oxide film. Use a stainless steel wire brush or sandpaper (specifically for stainless steel or this material; avoid contamination with carbon steel) to polish until a metallic luster is exposed.
Drying: After cleaning, wipe with a dry, clean cloth, ensuring the area is completely dry before welding. If possible, lightly heat with a flame torch (be mindful of temperature to avoid affecting material properties).
2.How to control the welding process?
Shielding gas is crucial:
Purity: Ensure the use of high-purity (≥99.99%) argon or a mixed gas (e.g., Ar+CO₂). Inferior gas cylinders are a common cause of porosity.
Flow rate and pressure: Adjust according to nozzle diameter and welding current. Typically, the flow rate for MAG welding is 15-25 L/min. Insufficient flow rate provides inadequate protection, while excessive flow rate can create turbulence and draw in air.
Gas path check: Inspect the gas cylinder, pressure reducing valve, gas tubing, and welding torch for leaks and blockages. Ensure the welding torch nozzle is clean and free of spatter.
Welding Parameter Matching:
Current and Voltage: Use appropriate welding parameters. Excessive voltage leads to a wide but shallow molten pool, making it difficult for gas to rise; insufficient voltage results in inadequate penetration.
Welding Speed: Too high a speed causes rapid solidification of the molten pool, preventing gas from escaping; too low a speed results in excessive heat input, a large molten pool area, and increased gas absorption. A balance must be found.
Wire Extension Length: Maintain a stable and appropriate extension length (typically 10-15 times the wire diameter). Excessive length can cause wire pre-melting, reducing the protective effect.
Welding Operation Techniques:
Maintain a stable arc: Avoid excessive arc length or excessive arc oscillation to prevent damage to the protective gas layer and air entrapment.
Pay attention to the welding torch angle: A forward tilt angle (pull welding) is generally recommended, as it facilitates gas protection and observation of the molten pool.
Wind protection: Even indoors, avoid drafts from fans, doors, and windows, as these can disperse the protective gas. Use windbreaks if necessary.
3.How can materials and the environment be controlled?
Welding Consumables Management:
Use high-quality welding wire compatible with the base metal.
Ensure the welding wire is clean, rust-free, and oil-free. Once opened, the welding wire should be stored in a dry oven to prevent moisture absorption. Moist welding wire is a direct source of hydrogen porosity.
Environmental Control:
Ambient Humidity: High humidity air introduces hydrogen into the arc. For critical welding, it is recommended that the relative humidity be below 60%.
Base Metal Temperature: Avoid direct welding on damp, cold steel surfaces. Preheating (50-100°C) if necessary helps to remove moisture and delay the cooling of the molten pool.
4.What are some special tips for common welding methods?
MAG/MIG welding (most common): Focus on checking the gas system and wire cleanliness. Appropriately increasing the argon proportion in the gas mixture can improve molten pool flow and facilitate gas escape.
TIG welding: Requires extremely high cleanliness. In addition to clean base metal, the welding wire must also be extremely clean. Ensure argon purity and proper pre-/post-gas delivery.
5.What is a quick diagnostic and screening checklist?
Immediately check: Is the protective gas depleted? Is the flow rate correct? Is the gas hose kinked or bent?
Clean and re-inspect: Use a new grinding wheel and acetone to thoroughly clean the test plate before re-welding. If the porosity disappears, the original cleaning was inadequate.
Replace materials: Replace with a new gas cylinder and try again with a newly opened bundle of welding wire. If the problem improves, it was a gas or welding consumable issue.
Check equipment: Check for wear on the contact tip, stability of the wire feed, and fluctuations in the mains voltage.