Subject: repairing pot metal and cast iron

From: [email-masked] (David Erickson)
Date: Tue, 20 Jul 1993 18:08:51 GMT

What is the best way to repair cracks in pot metal (zinc)?  I've tried normal 
flux-core solder and gas welding without success.  Are there special solders
or fluxes that work?  Would an arc welder (or mig, tig) work for this
application?

Same question for cast iron.  Brazing is one method of repair, but if I want 
to make an invisible repair, what is the best solution?

-Dave Erickson

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From: [email-masked] (David Jenkins)
Date: 22 Jul 1993 07:32:39 GMT

In article <[email-masked]>, [email-masked]
(David Erickson) writes:
|> What is the best way to repair cracks in pot metal (zinc)?  I've
|> tried normal 
|> flux-core solder and gas welding without success.  Are there special
|> solders
|> or fluxes that work?  Would an arc welder (or mig, tig) work for
|> this
|> application?
|> 

I would be _very_ reluctant to use welding gear (oxy-acetylene/propane
or electric) on anything containing zinc - the fumes are unpleasant 
and probably poisonous.

Welding galvanised sheet is horrible enough.

|> 
|> Same question for cast iron.  Brazing is one method of repair, but if
|> I want 
|> to make an invisible repair, what is the best solution?
|> 
|> -Dave Erickson
|> 

Some forms of cast iron can be welded (I can't remember which) but it
usually involves heating everything up to dull red heat (using
propane) before welding, followed by prolonged cooling, all to prevent
stress cracking.

You'd have to look in a welding textbook for the exact methods (in
other words, my book's at home :-)

You should be able to silver-solder or braze cast iron, with careful
attention to cleanliness etc. but it won't be invisible.

-- 

David Jenkins

* All incorrect spelling and faulty grammar is intentional.   *  
* Corrections are superfluous and will be ignored.  So there. *         
*

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From: [email-masked] (Mark Williams)
Date: Thu, 22 Jul 1993 19:02:08 GMT

Welding cast iron is tough.  It cracks after you weld it unless
you heat the whole piece.  That is how it is done by the blacksmiths
and tool repair guys (Dave Bradstreet at Castico).  

Heat the whole piece in a forge if you can.  Use a flux for cast iron
(borax) and cast iron rod.  The rod is hard to find but some welding suppluy
places to carry it.  Cool gradually, and hope for no cracks.

(One source says use a nitride rod)

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From: [email-masked] (David Erickson)
Date: Fri, 23 Jul 1993 21:16:40 GMT

Thanks for all the information I've received.  The piece that I need to repair
is fairly large (it is the head casting for a Delta/Walker Turner heavy
duty radial drillpress), and it is broken clean through (the web between
the quill and the idler pulley/motor mount is broken, about 8-10" of
fracture.  I'll probably go ahead and braze it and hope for the best.

-Dave Erickson

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From: [email-masked] (James W. Swonger)
Date: Mon, 26 Jul 1993 12:58:34 GMT

You might oughtta be sure this piece isn't cast aluminun, not pot metal.
A friend of mine had good results using a MIG on a piece of big machine
shop equipment which was cast Al. Pot metal is cheesy stuff and I don't
think it's the material any reputable manufacturer of heavy duty 
equipment would use. Maybe somebody here has a good simple test for
telling one from the other?
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