53411

"Hot Dip" or "Electro Galvanizing" - Which will weld better? [India] 

October 21, 2009

I represent a company having a manufacturing facility for EPS (Expandable Polystyrene) Panels used for construction of walls, roofs and floors. Our manufacturing process involves (a) making of EPS Blocks, which are cut to standard thicknesses of 50 mm or 100 mm, (b) fabricating wire mesh having welded joints at several places and (c)sandwiching the cut EPS Blocks with wire mesh panels on both sides by inserting galvanized wire through them and welding both ends.

For this purpose, we have been advised to use Electro Galvanized Wires of 2mm and 2.5mm dia. Currently we are importing this product. Manufacturers of wires located across India use a process called "hot dip". Spot welding is an important process in our manufacturing activity. My question, if I use "hot dip" low carbon steel wire subjected to "hot dip" process, will it result in any welding problem or will it undermine welding joints compared to "electro galvanizing".

I shall be happy to hear from your experts soon.

Thanks,

Mohan Subramanian
Employee - Chennai, Tamil Nadu, India

Hi, Mohan. Either should weld okay. But the fumes from welding zinc coated materials induce Metal Fume Fever, so good ventilation is important.

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Hot Dip will likely cause inclusion and porosity issues with spot welding resulting in a poor quality low-strength joint. With the weldment being small diameter wire, it's doubtful mechanical removal of the zinc at the weld joint is a viable option for a mass-production situation unless it can be done with pneumatic blasting machinery. Electroplated zinc will be less problematic than hot dip because it's thinner but I strongly suggest using higher than normal weld current combined with extended current flow duration so as to displace as much of the zinc as possible from the weld. Welds should be made and tested with increasing current and contact duration until maximum joint strength is achieved. Your description of the process rules out the absolute best method - to complete all fabrication and welding prior to plating so as to eliminate loosing corrosion protection at the welds.

Mark Kisenwether
Fire & Iron Mfg - Webster, Florida, USA