Virtually unweldable steel

[mowersman]

Today I have been welding up an auxiliary fuel tank for my Land Rover, as part of the vegetable oil conversion. I knew when I started that It wasn't going to be the easiest thing to make, as I am making it out of an old steel drill carry case. However, trying weld it is almost impossible, the splatter coming off the weld has to be seen to be believed, the weld pool will often almost "explode" for want of a better word. I have managed to weld it, though I won't be putting any pictures on here, as the welds are poor.
Anyone come across anything this bad before?
Andrew

 

[jonjoe]

is the steel cleaned back to shiny metal

 

[mowersman]

Not exactly shiny, I suspect it is zintec, which I have read is fine to weld onto. Would it cause this much problem?
Andrew

 

[madkayaker]

It could be plated in any number of nasty hard to weld things getting the weld area clean is the only way forward

 

[Tino]

Yes coatings on steel can be nasty to weld. Lots of spatter and the odd explosive ejection. Grind both sides where you will be welding. Mig likes clean.

 

[Hitch]

Its probably remarkably thin, which never helps matters, once any coating has been ground off, its even thinner.

You don't want a leaking tank...

 

[Lawnmowerboy]

I'll show you up tomorrow, Andrew. Only joking mate But make sure the metal is actually clean. It will really help remember the trouble with those zintec footwells on your landie. Lots of white marshmallow stuff!

 

[mowersman]

Its probably remarkably thin, which never helps matters, once any coating has been ground off, its even thinner.

You don't want a leaking tank...

Its not too thin actually, about 1.2mm.
Hopefully it won't leak, as after a lot of perseverance the welds have worked alright, though they aren't anything special aesthetically.
Andrew

 

[pob30]

1.2mm...ive welded steel as thin as 0.5 mm...not easy i must admit.im no expert although i class myself as a very good mig welder(others debatable)..the only thing that comes to mind is the coating...some have a tendency to eat into the steel so no matter how much you clean them certain properties of the coating remain in the steel.

 

[Engineer1964]

Not exactly shiny, I suspect it is zintec, which I have read is fine to weld onto. Would it cause this much problem?
Andrew

You can spot weld zintic which is idea but you cannot weld it, You need to sand the zinc off and then the metal will be far too thin to get a decent weld without blowing holes.

making an extra fuel tank i would use just 2.5mm steel sheet, I used to make tanks for power packs and found that 2.5mm steel is the best choice for tanks in general. Forget the Zintec idea if you don't want long term issues with your fuel tank

 

[hairymel]

You can spot weld zintic which is idea but you cannot weld it, You need to sand the zinc off and then the metal will be far too thin to get a decent weld without blowing holes.

i use light grey matt finish zintec sheet all the time for car body repairs and never need to grind it back.

afaik 'zintec' has a very thin layer of zinc for corrosion protection which is designed to be welded through/on.

sure you arent thinking of zinc galvanised coating shiny often frosted looking finish? this welds very badly

 

[nickk]

the other consideration is to grind back way beyond the weld area as there is something called the 'heat affected zone'[HAZ] as when you start the welding process conduction pulls the contaminant into the weld pool & pollutes it.