Welding galvanized steel
02-08-2010, 10:34 AM
#1
Rennlist Member
Thread Starter
Welding galvanized steel
In the Carbon Fiber Roof Panel threadthe subject of welding galvanized steel came up. Rather than take that thread further OT I started this one with some info I found online as I'm planning to replace my sunroof with non-sunroof welded in place from a no-sunroof roof. (Reminds me of the woodchuck limerick).
Welding Galvanized Steel -- Safely
1) Galvanized steel can be welded using the same arc welding processes that are being used for fabrication today.
2) Galvanized steel can be arc welded safely with little increase in cost or welder discomfort.
3) Corrosion resistance at welds can be effectively restored by application of paint coatings which are high in elemental zinc or by thermal spraying zinc over the weld areas.
4) Galvanizing simple shapes can be controlled better than post-fabrication galvanizing, resulting in smoother surfaces and a more uniform top coating appearance.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900°F and vaporizes at about 1650°F. Since steel melts at approximately 2,750°F and the welding arc temperature is 15,000 to 20,000°F, the zinc that is near the weld does not stand a chance -- it's vaporized! By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
• The vaporized zinc increases the volume of welding smoke and fumes.
• The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.
Zinc Fumes -- A Safety Hazard?
When zinc vapor mixes with the oxygen in the air, it reacts instantly to become zinc oxide. This is the same white powder that you see on some noses at the beach and the slopes. Zinc oxide is non-toxic and non-carcinogenic. Extensive research1 into the effects of zinc oxide fumes has been done, and although breathing those fumes will cause welders to think that they have the flu in a bad way, there are no long-term health effects. Zinc oxide that is inhaled is simply absorbed and eliminated by the body without complications or chronic effects. Current research2 on zinc oxide fumes is concentrated in establishing the mechanism by which zinc oxide causes "metal fume fever," how its effects are self-limiting and why zinc oxide fume effects ameliorate after the first day of exposure even though the welder may continue to be exposed to zinc during subsequent days ("Monday-morning fever"). Other research3 is being done using zinc oxide fumes together with various drugs which results in a synergetic effect for treatment of cancer and AIDS. Another area of research is use of zinc compounds as the active ingredients in throat lozenges that are recognized as significantly effective in reducing the duration and intensity of the common cold.
Typical “metal fume fever” begins about 4 hours after exposure, and full recovery occurs within 48 hours. The symptoms include fever, chills, thirst, headache and nausea. All of these symptoms, pain and suffering, as well as lost work (and play) time, can be avoided entirely by simply not inhaling the zinc oxide fumes. This can easily be done using any of the methods described later.
Attached is the six page article in PDF from which I quoted.
Welding Galvanized Steel -- Safely
1) Galvanized steel can be welded using the same arc welding processes that are being used for fabrication today.
2) Galvanized steel can be arc welded safely with little increase in cost or welder discomfort.
3) Corrosion resistance at welds can be effectively restored by application of paint coatings which are high in elemental zinc or by thermal spraying zinc over the weld areas.
4) Galvanizing simple shapes can be controlled better than post-fabrication galvanizing, resulting in smoother surfaces and a more uniform top coating appearance.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900°F and vaporizes at about 1650°F. Since steel melts at approximately 2,750°F and the welding arc temperature is 15,000 to 20,000°F, the zinc that is near the weld does not stand a chance -- it's vaporized! By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
• The vaporized zinc increases the volume of welding smoke and fumes.
• The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.
Zinc Fumes -- A Safety Hazard?
When zinc vapor mixes with the oxygen in the air, it reacts instantly to become zinc oxide. This is the same white powder that you see on some noses at the beach and the slopes. Zinc oxide is non-toxic and non-carcinogenic. Extensive research1 into the effects of zinc oxide fumes has been done, and although breathing those fumes will cause welders to think that they have the flu in a bad way, there are no long-term health effects. Zinc oxide that is inhaled is simply absorbed and eliminated by the body without complications or chronic effects. Current research2 on zinc oxide fumes is concentrated in establishing the mechanism by which zinc oxide causes "metal fume fever," how its effects are self-limiting and why zinc oxide fume effects ameliorate after the first day of exposure even though the welder may continue to be exposed to zinc during subsequent days ("Monday-morning fever"). Other research3 is being done using zinc oxide fumes together with various drugs which results in a synergetic effect for treatment of cancer and AIDS. Another area of research is use of zinc compounds as the active ingredients in throat lozenges that are recognized as significantly effective in reducing the duration and intensity of the common cold.
Typical “metal fume fever” begins about 4 hours after exposure, and full recovery occurs within 48 hours. The symptoms include fever, chills, thirst, headache and nausea. All of these symptoms, pain and suffering, as well as lost work (and play) time, can be avoided entirely by simply not inhaling the zinc oxide fumes. This can easily be done using any of the methods described later.
Attached is the six page article in PDF from which I quoted.
02-08-2010, 10:46 AM
#2
Three Wheelin'
So Rick...... if a sunroof roof could woof, how much less woof would a sunroof-less roof woof? Interesting reading BTW. Hope things are going good for you in that state that honors a hairy nut that has no value! (the Buckeye)
Paul Barrera '91 $$$$4
Paul Barrera '91 $$$$4
02-08-2010, 10:57 AM
#3
Rennlist Member
Thread Starter
Hi Paul,
I was going to do the no sunroof conversion this winter (I have a non-sunroof roof in a crate), but an opportunity to buy a SharkTuner came up and I'm doing that instead. Are you going to make it to SITM or only SIH?
I was going to do the no sunroof conversion this winter (I have a non-sunroof roof in a crate), but an opportunity to buy a SharkTuner came up and I'm doing that instead. Are you going to make it to SITM or only SIH?
02-08-2010, 11:03 AM
#4
Three Wheelin'
Hi Rick. Sharks in Hell for sure, SITM......probably not, unless I find an extra $10K to complete the previous $10K I have already put in my $12K 928. I know you know what I mean. But you still didn't answer the question: If a sunroof could .........oh, never mind.
Paul Barrera '91 $$$$4
Paul Barrera '91 $$$$4
02-08-2010, 11:13 AM
#5
Man of many SIGs
Rennlist Member
Rennlist Member
Anytime you weld galvanized steel you will need to drink a big glass of milk first. It coats your throat and stomach and help to keep you from getting sick. Trust me, you don't want to skip this step.
02-08-2010, 11:41 AM
#6
Burning Brakes
Hi, as a galvanized boat trailer manufacture ,we some times have our welders weld galv. material . Rick is right on . As well as fabio . The best plan is to grind the galv. off in the area +1" to be welded , if there is galv. in the weld it will cause inclusions in the weld ( ugly/ weak) as for the fumes just set up a fan to keep a air flow AWAY from your face and to a open door . The underside of the material will smoke like mad if it still has its galv. coating . Terry
02-08-2010, 12:43 PM
#7
Shameful Thread Killer
Rennlist Member
Rennlist Member
Not complicated, grind back Zinc from weld joint, weld immediately, then grind/chip clean and recoat. Don't forget the back side of the joint is also usually coated.
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02-08-2010, 06:02 PM
#8
Drifting
I've had the "metal fume fever" a few times and for me, it's little more then bad congestion. I've got a Millermatic DVI gas Mig welder. I don't know if the shielding gas has any bearing on the fumes produced. I always assumed that most of what was causing me to feel congested was more related to breathing the particles that come off the grinding disc when cleaning up the welded area.
I don't worry about the zinc that's on the panel. Most of that will go away when you prep the area for welding. The more important thing is to make sure the metal is cleaned of anything else that could contaminate the area. Contaminants on metal are like water in bacon. When bacon grease pops and goes everywhere, the water in the bacon is what does it as it boils off. When welding sometimes there are pops and spatter. It's usually caused by contaminants in the weld that are burning off, or a lack of shielding gas (for Mig.)
3M makes a zinc primer that theoretically is to be applied on seams to be welded. I tried using it. After a few minutes, I got fed up, and ground off all the primer I had put on because it just made a mess and was causing pops and spatters everywhere.
The biggest problem with welding anything is getting access to the backside to treat the metal to prevent rust. In some cases there's not a lot you can do, and most people don't worry about it since they usually sell the car within a year or two of having something on it welded. Part of the floor on my 928 needed to be replaced. On those seams, I could access both sides. What I did was mix up some chromated epoxy primer. I added a little reducer to make it flow out. And then I brushed the primer onto/into all of the seams. After it flashed, I used some 1K seam sealer and thinned it down with some more reducer, put on some gloves, and smeared it over the welded areas. In 2 1/2 years and 50K miles, it's all very intact and holding.
I don't worry about the zinc that's on the panel. Most of that will go away when you prep the area for welding. The more important thing is to make sure the metal is cleaned of anything else that could contaminate the area. Contaminants on metal are like water in bacon. When bacon grease pops and goes everywhere, the water in the bacon is what does it as it boils off. When welding sometimes there are pops and spatter. It's usually caused by contaminants in the weld that are burning off, or a lack of shielding gas (for Mig.)
3M makes a zinc primer that theoretically is to be applied on seams to be welded. I tried using it. After a few minutes, I got fed up, and ground off all the primer I had put on because it just made a mess and was causing pops and spatters everywhere.
The biggest problem with welding anything is getting access to the backside to treat the metal to prevent rust. In some cases there's not a lot you can do, and most people don't worry about it since they usually sell the car within a year or two of having something on it welded. Part of the floor on my 928 needed to be replaced. On those seams, I could access both sides. What I did was mix up some chromated epoxy primer. I added a little reducer to make it flow out. And then I brushed the primer onto/into all of the seams. After it flashed, I used some 1K seam sealer and thinned it down with some more reducer, put on some gloves, and smeared it over the welded areas. In 2 1/2 years and 50K miles, it's all very intact and holding.
