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Exploding earring


#1

I am hoping someone can help me understand an incident that occured
yesterday, from a metallurgic point of view.

Having recently remodeled, we are moving into our new “shop,” (ie,
the garage), and I am finding all sorts of pieces and parts to make
things out of. I had this old 24 ga rectangle of marriage of metal -
copper and sterling with a wave down the length, so I decided this
could be cut in two and made into hoop earrings.

I curled up the metal into the hoop shape, then decided it needed sq
wire along the edges to finish it off. So I soldered 18 ga SS wire to
each side edge (long edge of the rectangle), then the first short
edge. As I was soldering to the second short edge, (with easy solder
now) the thing EXPLODED right along the marriage seam. The joints
did not fail, per se, it literally burst apart! Fortunately it did
not hit me (but it did singe my bench top!). It exploded only seconds
after I put the torch on it.

Can anyone help me understand what happened here?

thanks a lot.
Mary Barker


#2
As I was soldering to the second short edge, (with easy solder now)
the thing EXPLODED right along the marriage seam. The joints did
not fail, per se, it literally burst apart! 

While soldering enclosed volumes, you must always leave a small
opening. Otherwise, the trapped air becomes super-heated and explodes
it’s container.

Leonid Surpin
www.studioarete.com


#3
It exploded only seconds after I put the torch on it. 

That would suggest to me that there may have been a little water
trapped inside. It quickly became superheated steam which is very
powerful.


#4

Hi Mary,

The only explanation I can think of is that there is some sort of
cavity in the item that got some water in it.

When quenching, water will be sucked into any cavity if there is the
slightest opening into the cavity. The smaller the opening the more
chance of a steam explosion with the next heating because the steam
cannot get out of the tiny opening fast enough. It only needs the
smallest amount of moisture to create a steam explosion.

If you know or suspect there is a cavity, heat gently to 100*C and
hover there for a few seconds to let the steam escape before going on
to the soldering temperature.

When working with hollow items this problem is often solved by
making a permanent hole somewhere that is big enough to let the water
and steam out. Even then it must be done cautiously to make sure all
the steam is out before heating to the soldering temperature.

Regards, Alastair


#5
While soldering enclosed volumes, you must always leave a small
opening. Otherwise, the trapped air becomes super-heated and
explodes it's container. 

Thanks for the response. The form was not closed; that is what so
confuses me. It was wide open with about a 10 mm gap between the
ends. From the side, it looked like a “C” or a “U”–I was soldering
the square wire perpendicular to the curly sides of the C. I wonder
if I was trying to enclose 2 metals with different coefficients of
expansion, ie, half the piece and its frame were silver, and the
other half was copper?

Thanks again,
Mary Barker


#6
if I was trying to enclose 2 metals with different coefficients of
expansion 

More likely that would have only resulted in distortion, not
explosion. But on a piece as you describe I wouldn’t expect too much
distortion.

Water, or pickle, may have lodged itself in some tiny gap between the
metals after the soldering of the original piece. If indeed it was
pickle (likely, since it goes in pickle first usually), the pickle
may have crystallized during the time it sat in the orphan box and
plugged whatever opening there was. Heat it with no escape
route…POW.

About the only thing I could suggest in the future on questionable
pieces is to steam clean thoroughly after soldering. If no steamer
try warming the piece gently or covering the piece in a sawdust box


#7

I experienced a similar phenomenon while trying to solder a copper
sleeve inside a sterling ring. What I thought was a perfect fit soon
turned into a disaster when I applied heat. The copper ring joined
the silver on one side but due to the different coefficients of
expansion of the two metals, the copper drew significantly away from
the silver on the other side of the ring so that the solder would not
flow. I had to scrap the project and try soldering the two metals
prior to bending them.

We live and learn

John Bowling


#8

Maybe it was put together under tension with a low melt solder like
Sta-Brite and just popped loose when it hit the right temperature.
Blew up as soon as the torch hit it is what makes me think maybe soft
solder.

My first guess would be trapped water somewhere though without
seeing it. Powerful stuff, that.

Dave


#9

Bubble in the solder seam maybe? Was it a thick seam? Did you have it
in locking tweezers or anything else pressing it in interesting ways?

Cheers,
Norah Kerr
www.besmithian.com