[manu de hanoi]

Hello
Have you ever noticed that when you try to weld an object without leaving any opening, it's very difficult ?

It's like the heat from the torch creates pressure inside this object that blows the air out through that last opening we are trying to weld shut ? The air blown prevents good arc formation and also prevent molten metal from closing that hole.

I am specifically trying to weld a float made of SS. The float must be a closed watertight volume with air inside.
Do you have a trick to weld closed volumes ?

[coldman]

Easy as. Weld a screwed socket onto your tank. When you are done seam welding, screw a plug into it with thread seal. Or you can try dipping your tank in water to keep it cool while you complete the last weld.

[Otto Nobedder]

Coldman has a great solution, but if the thread-plug is a "no", try this. Close the weld to a "pinhole" the diameter of your rod. Let it cool a bit, and have an assistant quench the remaining volume, whether with water-spray or wet rags, while you use a "pulse" of current, as for a tack, to close the hole.

Steve S

[Superiorwelding]

Yet another solution is use a heat sink to draw the heat out out the part and then fill the hole like Steve suggested. The key is no or less heat as heat causes the "air" to expand.
-Jonathan

[Arno]

Purging the space with either pure argon or nitrogen also helps a little as moisture in the air inside the container makes it expand a lot more than a completely 'dry' gas.

Bye, Arno.

[manu de hanoi]

thank you guys for the answers, I'll try the wet rags + tack pinhole