I have been working on a forge welded billet of roller chain. I had the piece stretched and was unhappy to see the center start to de-laminate.

I opened the section a bit, but in some borax, brought it up to welding heat and gave it a firm blow...firm not hard...and BANG!!! It really did sound like a gun went off and I had hearing protection on!

What did I do? And has this ever happened to any of you?

It ended up welding nicely and I have been able to draw the piece to my desired thickness.

John

Don't sweat it, the flux was partially trapped between the steel. When you hit it it had to escape through a much gap that was being forced closed by the hammer blow. A couple things happen under these circumstances, for the molten flux to escape it has to accelerate considerably and then pass through a very small opening. This typically makes a sound like a gunshot. Using precautions to protect spectators I've been known to cause the big bang for show at demos. It can be good theater.

It's pretty common on large flat welds and so long as the molten flux and dross from the billet doesn't hit anyone or start a fire it's no problem.

The bang can be reduced or even eliminated using a couple tricks. (or should I say techniques?) The trick is to prevent the steel sides of the weld from trapping the flux. One method is to put a little curve lengthwise on the halves so they only contact each other in the center, I like them shallow and long so they touch like laying two pipes together lengthwise. you don't want it to look like pieces of pipe, the curve can be much shallower it just needs to allow the flux out easy. This way when you hit them to start the weld there is lots of room for the flux to escape so there's no bang. Another method is to use a hammer pattern that helps the flux to escape. Start the weld with a ball pein hammer, the first blow falling in the center of the join followed by blows that move towards the edges in a pattern, a spiral for instance. This allows the flux to be driven out of the joint one blow at a time and not become trapped.

I hope that didn't muddy the waters more than it helped.
Frosty the Lucky.

The same thing happened to me.......I was trying to forge weld some strips of a36 (or something) together and had the same thing happen more than a couple times.

The explanation of trapped flux makes a lot of sense to me as I initially thought that it might have been super-heated trapped air/moisture being released by the hammer blow...The same thing has happened while I was working on my anvil while it was a bit damp....Lay a bit of hot steel on a wet anvil, hit it and POW!

Anyways....as Frosty explained-no harm, no foul....In my case I didn't make a successful weld, so I guess I'll have to practice more.

This can also be a side effect of "wet forging" or "water forging" where the face of the anvil and the hammer face are coated with water before each session of forging, commonly used to remove slag from the work. It might be overstating it just a bit but its a hydrothermal explosion of water converting instantly to steam and can give you a large bang or pop I also used a bit of this for theatrical forging at renaissance faire's to bring in a crowd of people heheh

I've wondered if we are getting the flux version of steam explosion as we weld at a temp when borax is fuming off and so hitting it could push a bit of the flux up that little bit from liquid to vapour.

Have to try it with a plain bar of metal someday and see.

I've wondered if we are getting the flux version of steam explosion as we weld at a temp when borax is fuming off and so hitting it could push a bit of the flux up that little bit from liquid to vapour.

Have to try it with a plain bar of metal someday and see.

That sounds plausible Thomas, I don't know the particulars other than how to minimize the chance with scarf shape and hammer pattern. Sometimes you just do NOT want 2,600f liquid borax flying into the audience. Well, okay. . . MOST audiences that is.

The steam bang is a good bit of theatrics as Wesley says and it's unlikely to hurt anyone. Hmmmm, I have a first timer coming over tomorrow to start learning the craft. maybe I should see how high she can jump?

Frosty the Lucky