Language
Solutions for Dark & Corroded Nuggets During Projection Welding Nuts on Galvanized Sheets with MF Spot Welders
Jul 21,2026
Projection welding nuts onto galvanized sheets is a standard mass-production process for auto parts and home appliance casings. Dark weld spots ruin appearance, while corrosion breaks anti-rust zinc coating and risks nut loosening, bringing hidden safety hazards.
I Manifestations of Dark & Corroded Welds
1.Dark nuggets: Appear right after welding and darken further after 1–2 days. Weld area and surroundings turn matte black without metallic luster, sometimes covered with peelable oxide scale. Minor darkening only affects appearance; severe cases weaken bonding strength.
2.Corrosion: Occurs days after welding, faster under humid conditions. Reddish rust accumulates around nuggets and gaps between nut & galvanized sheet. Advanced corrosion blocks threads and loosens nuts.
II Root Causes of Discoloration & Corrosion
1.Inadequate pre-cleaning: Oil & dust carbonize under high temperature causing darkening; surface contaminants damage zinc anti-rust layer and induce subsequent rusting.
2.Abnormal electrode condition: Dirty / heavily worn or insufficiently cooled electrodes transfer impurities to welds and create uneven heat, accelerating oxidation & corrosion.
3.Unsuitable welding parameters: Overlarge current & prolonged welding time generate excess heat that burns through galvanized coating and triggers oxidation.
4.Delayed post-weld treatment: Hot nuggets exposed to air oxidize rapidly; unremoved spatter absorbs moisture and speeds up rust formation.
5.Humid & dusty workshop environment accelerates surface oxidation.
6.Low anti-rust performance of nuts themselves spreads corrosion to welds & galvanized panels.
III Preventive Measures
1.Thoroughly degrease and clean galvanized sheets & nuts before welding, process immediately after cleaning.
2.Select corrosion-resistant nuts matching galvanized material; lower current & shorten welding cycle to cut heat accumulation; apply shielding gas if needed to reduce oxidation.
3.Clean & grind electrodes regularly, calibrate machines to stabilize current output.
4.Cool welds rapidly post-weld, clear spatter timely and apply anti-rust treatment based on service environment.
5.Keep workshop dry & ventilated; avoid welding on damp days with moisture-proof measures when necessary.
Related News
Wuxi HAIFEI Intelligent Equipment Co., Ltd.
Wuxi HAIFEI Welding Equipment Co., Ltd.
Add: 28 Shuiyun Road, Yuecheng, Jiangyin, Jiangsu Province, China. (Postal Code: 214404)
Mobile: +86 18915302352
Email: wushijie@jshaifei.com