Thread: Large scale welding of galvanised C section channel

I've recently been mig welding base plates to a few 150 x 65 x 1.5 galvanised channels, I spent a lot of time carefully grinding the gal from the weld area.

Doing this caused me to ponder how the guys that do this for a living - shed makers for instance - cope with gal removal.

Do they have equipment that quickly takes off the gal, maybe a specialised sandblaster, or do they not worry about removal?

Do they leave the gal on and use special mig wire, different welding techniques, and of course PPE to get around the problems that vaporising zinc can cause?

Hi Bob, I weld quite often Duragal, for our sheep ramps and I leave it on, some of the blokes use a 60grit flap disc to take it off, so it's a personal preference and time constraints. Don't grind back too much, probably 10-12mm max. Normal mig wire is used with argon/co2 mix and normal welding process used.
I don't use any PPE apart from the welding mask, some use the paper dust filters to prevent the galv fume/particles.
If you drink milk, it should help prevent the vaporising zinc fumes making you ill, you get used to it after a week or so.
Wire buff the welds and give it a couple of light coats of the cold galv spray, followed by a coat of silver galv paint to blend in the weld area, if you want it to look nice. I find that a small rotary wire brush in a drill, cleans off the fur on the other side of the welds, and compressed air in the corners that the brush won't reach.
HTH
Kryn

A mate of mine had a steel fabrication business that welds large galv items (mining industry stuff etc) on a regular basis usually as repairs, modifications or refurbs. Depending on what the item, they usually remove the welding areas of galv by sandblasting and then have items re-galvanized - at the clients expense. Sometimes they don't remove the galv. For fume control they just use a large fan to blow the ZnO away.

At DIY welding levels (ie a shed frame) the ZnO fumes can't actually kill you although they can make you very ill - like the worst flu you can imagine. The cause is thought to be an auto immune response whereby the body sets of a so called "cytokine storm", not unlike Covld.

RE: Drinking cows milk as a cure - from Wikipedia
The consumption of large quantities of cow's milk, either before or immediately after exposure is a traditional remedy.^[1] However, the United Kingdom Health and Safety Executive challenges this advice, warning, "Don't believe the stories about drinking milk before welding. It does not prevent you getting metal fume fever."^[14]

Hi Bob,
Galvanised coating is way thicker than duragal and outputs more metallic vapours.
If you have any breathing problems at all, avoid welding galvanised.

Even if you have sound wind treat welding it with extreme caution.I worked at Cyclone and made farm gates from gal pipe and have personal experience with metal fume fever.No PPE masks in those days and the milk for me was a joke.

Fifty years later I still suffer from poor breathing and put it down to the gal..

I knew a yank blacksmith who had asthma and died from using galvanised items in his forge. The asthma went to something more serious and he died.The fumes affected the asthma brought on by the fumes from the gal.

If the job has to be done put your breathing zone in a breeze from a fan but obviously not your mig gun and job.

The mig shroud has to be dipped in anti spatter grease and cleaned often.The stuff builds up between shroud and the diffuser contact tip areas and shorts the gun out.

Grahame

One problem is you can easily get used to low levels of ZnO vapours. You might get your breath taken way on the first few breaths but then you might not feel it as much and if you keep getting regularly exposed (ie daily) you might not feel it at all till the weekend when you stop working - then you will feel like you have a flu. If you got a large dose it can be like a really bad flu and you might even have to take time off work. If you go back to work and get exposed again any flu like symptoms may disappear. Something do do with your immune system.

I agree with Grahame that if you have any breathing issues this will only make things worse. Mind you there are lots of things in metal work that do the same thing, grinding dust, welding fumes etc.

Originally Posted by BobL

the ZnO fumes can't actually kill you although they can make you very ill - like the worst flu you can imagine.^]

I can confirm, I had exactly the same symptoms as a bad flu, thankfully it only lasted a day, I was casting brass when it got me, at first I couldn't understand how I caught the flu, I was in my shed alone all weekend, then the realisation hit me, at the time I happen to have some calcium ascorbate powder so I mixed it into juice, I don't know if it helped but it didn't hurt

Originally Posted by bob ward

Do they leave the gal on and use special mig wire, different welding techniques, and of course PPE to get around the problems that vaporising zinc can cause?

I thought fluxcore was recommended for welding Gal ? i've only welded a few Gal things and used fluxcore with no problems, but i do use fluxcore on everything so cannot compare MIG gas welding on Gal.

Milk = myth.
Weld fume = serious business.
I've been in workshops where you can't see the roof thru the gal smoke. Same places where the staff turnover every 3 months- probably in part due to the sickness of a hardcore production environment working thru gal. 10% of the welders were calling in sick each day, and not a fume extractor or adflo helmet in sight. Management oblivious to their obligations under WHS, and workers too scared to talk up.

A Melbourne fella sued and won a case against an employer for weld fume induced lung cancer. Brought on by continued exposure to chromium particulate from stainless welding in a production environment. I don't know about you fellas, but keeping safe and not dead is a pretty high priority for me.

Some of the most spiteful stuff I've worked on was some Angle that was hot dipped, and coated with a thick layer of cold gal paint. no matter how much I ground, it was still fuming like crazy.

If you simply have to weld it-
1) Grind away gal - be generous with the cleaning zone. Abrasive wheel, or 60# 3M cubitron II fibre discs are what I've been leaning to these days.
2) Minimum viable weld fume disposable mask (charcoal ones), ideally adflo helmet or on-gun extraction system. You want to keep the fume away from you, AND others. Don't be selfish.
3) ER70S-6 wire works for GMAW. IDeally bump the CO2 up to 16% or more for better penno and burn-thru.
4) Stick of FCAW are also acceptable, but YMMV, depending on the job.

I have a heap of galv angle that was from the upper part of a power transmission tower that's got a super thick coating of Zn on it Im sure they dipped it about 20 times it looked like the dross skimming spoons on a Zn melting kettle at my work, so far I've made a tank stand and stair/platform entryway for a raised house from it, its mostly 75x8mm.
The only way to remove the super thick coating was to heat it molten with a MAPP torch and wire brush the most of it off then grind it with a flappy disc until could I clearly see sparks flying.(respirator is a must)
Trying to clean it off with only grinding was a lesson in fruitily as it would just melt and smoosh around... could see why these towers were bolted together!

Hello from the old goat. Gal steel can be mig brazed with Silicon Bronze wire. 0.9mm wire keep the amps between 90-115. The local council specs this for gal handrails and pool fenced installed within 1klm of the ocean. It is also great for dissimilar metals. We have welded coupons of gal steel to mild steel to 316L. Use strait argon and keep the torch within 15 deg of vertical, pushing the wire. Very popular in USA, and Wisconsin wire co have lots of info on their web site. Innershield wire does a good job too especially on gal water pipe. You need a long wire stickout and watch the fumes.
Regards
BC

I find Duragal welds reasonably well with no prep and MIG gas, although it is nicer using CO2 gas. The much thicker hot-dipped gal is another matter.