Question about weld shielding.

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Sorry if this is a newb questions, but here it is...   When welding tig or mig, your argon gas (or whatever mix) shields you weld. When welding flux or stick, your flux provides the shield. But when welding O/A welding what shields the molten steel? If anything you are blow oxygen right into the weld! What am I missing? It doesn't make sense.I have only mig (one time), stick, and flux welded so I still don't know very much.______________Clarke 95  Lincoln 135  Lincoln AC 225 ---------I'm an idiot, please talk slowing and simple.
Reply:The oxygen is is completely used up by the burning acetylene.  A flame with too much oxygen produces an oxidized weld.  Too much acetylene and the excess carbon is picked up in the weld pool.
Reply:Originally Posted by lotechmanThe oxygen is is completely used up by the burning acetylene.  A flame with too much oxygen produces an oxidized weld.  Too much acetylene and the excess carbon is picked up in the weld pool.
Reply:actually for brazing (and welding brass) a slightly oxidizing flame should be used. IIRC this encourages the formation of zinc oxide on the surface of the puddle rather than volatizing the zinc which can create porosity
Reply:Originally Posted by hotrodderactually for brazing (and welding brass) a slightly oxidizing flame should be used. IIRC this encourages the formation of zinc oxide on the surface of the puddle rather than volatilizing the zinc which can create porosity
Reply:Here's one brief reference for brazing with a reducing flame.http://silfos.com/htmdocs/product_su...w_to_info.html
Reply:i'll try but i don't completely understand the phenomenon myself- it came up in a discussion about brazing and 'bronze welding' (or fillet brazing). zinc volatization was the justification for using an oxidizing flame it's not a case of the reducing flame, specifically, volatizing the zinc. the boiling point of zinc is just above the melting point of the brazing filler alloy, some of it is going to boil off (how much depends on operator skill, filler alloy etc).nothing on the reasons why but here's one brazing alloy manufacturers guide to technique...   http://www.sifbronze.co.uk/ie/menu/technical.htmwikipedia isn't the best reference but 'section 5' is the relevant bit...   http://en.wikipedia.org/wiki/Oxy-fue...ng_and_cutting
Reply:Thanks for the references, I'll have to keep digging to find out why this would make sense, but I guess there's a reason.
Reply:The 6th edition of A. C. Davies excellent book "The Science And Pratice Of Welding" explains a little about this. It has pictures showing the honeycomb joint made with a neutral flame, the joint made with insufficient excess of oxygen (his words) with some porosity, and joint made with an adequate excess of oxygen which shows a solid joint. He doesn't address why this works. I have done enough brazing to know it does work.