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  #31  
Old 03-03-2012, 05:24 PM
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OZWELDER OZWELDER is offline
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Just some points about oxy acetylene fusion cast iron welding that may need clarification. There can be more to the process than meets the eye, so to speak.I did part of my apprenticeship on this welding process for cracked pre combustion chambers on Cat D4 cylinder Heads.

Because of its cooling contraction rate and carbon % content -up to 9% carbon content it CAN be a pita to weld successfully.

The following is what I was taught as an apprentice and has earned me good money over 40 years or so.


Using a strictly neutral flame is real important.
Should you permit the flame adjustment to drift into a carburising flame condition the resultant carbon% of your deposited cast iron can be too high and therefore get too hard to allow machining.I mean hard enough to damage the stones when a head was being machine surfaced.The extra carbon in the unbalanced flame migrates to the molten cast iron and serves to increase the carbon content - big time!


Size and shape of item welded
Pre heating and post cooling on the item to be welded certainly needs to be considered - the dominant factor being the shape of the part to be welded .

Cast iron should be heated and cooled evenly to prevent differential cooling - a thin section returning to room temperature quicker than the thick section.Believe me the sound you least want to heat is a clink! A sound signifying a new crack.Evenly distributed cooling is essential on shapes like wheels or spoked pulleys with the thin spokes likely to cool first and crack.Even having a breeze blowing over the cooling job can cause a crack.

Torch may need a water jacket if in a confined area.
The oxy acetylene torch may need mods too as if it is to be welding in a hole - eg-a pre combustion chamber- the welding nozzle should be water jacketed to avoid backfires-very nasty -an explosion in a small confined space with shooting molten cast iron about.

Manipulation and technique.
Cast iron welds differently( moves ) from other metals. Its like pushing treacle about and can have a puddle of 1/2" to 3/4". It is often necessary to work the molten puddle with pressure from the point of the flame to release impurities and gas pockets.

Flux your filler rod often
Cast sucks up contamination not well removed just by surface cleaning.When the fluxed rod is dipped in the molten pool and the flame point is used to move the pool about this floats to the surface and is picked up by the flux which floats on the top of the molted pool.

Most of the above points don't seem to be written in any text I have seen.

I hope this helps you.

Grahame
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Last edited by OZWELDER; 03-03-2012 at 05:47 PM.
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  #32  
Old 03-03-2012, 10:26 PM
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Paychk Paychk is offline
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Thanks for taking the time to post these tips
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