Thin mild steel arc welding

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I am becoming acquainted with the complexity of welding thin mild
steel with a rod/arc welder; the main problem being burn through. I
have read some where that putting an aluminium bar under the joint
helps. Can anyone give me information on the physics/chemistry of this
application? I assume the aluminium would act as a heat sink and if it
works can only assume that the naturally oxide coating on the
aluminium prevents the aluminium from liquefying??!!

Re: Thin mild steel arc welding
The aluminum just supports the molten steel.  If you happen to track the arc
onto the aluminum surface it will create problems, vapourizing the aluminum.
The Zinc in brass bar has the same problem.
  A much better material is copper.  It has a higher melting temp and is
highly conductive like aluminum acting as a heat sink to encourage the
molten steel to freeze against it.
  The big problem is finding some copper bar.  Electricians involved with
high amperage systems sometimes have access to copper buss bar material.

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Re: Thin mild steel arc welding

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Anyone involved in metal-working should find and regularly visit their local
scrap metal yards.  They are a treasure trove of material and neat stuff.
They will buy your small cutoffs and waste (for about .02/lb.) (and used
batteries and old radiators) and sell you much larger industrial cutoffs
(for about .25/lb.)  Take a truck and expect to come away with far more than
you deliver.  Many of these yards keep a section of their yard for the
better or more interesting scrap and is a great place to find small pieces
of thick plate and random lengths of steel wide flange beams.  They will
have bins full of new cutoffs of heavy copper electrical buss material and
surprisingly long pieces of heavy copper cable.  Don't be surprised if you
find long pieces of welding cable that only need small repairs.  The quality
of the scrap is dependant on the local industry and economy.  If you are
near a closing military base you may have a gold mine.

Wear safety boots, glasses and gloves, and a hard hat and high visibility
vest is a good idea.  Bring your own tape measure.  Try to look like you
know what you are doing.  Be extra polite and STAY OUT OF THE WAY of any
forklifts or heavy cranes.  KEEP YOUR EYES OPEN this is a VERY dangerous
environment, be very careful where you step or climb.  A box of donuts for
the crew will be a great investment.

Good luck,

Re: Thin mild steel arc welding
You know, I never thought of that! I bed that would get me some great
service in there - especially when I don't have my rig with me and need a
piece cut in half or help loading something heavy.

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