Pls explain process of Tig brazing

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Can someone please outline the procedure for Tigging cast iron with Silicon bronze?Actually, I'm not even sure that this would be a recommended process as I only seem to see Si Bronze and Tig in the same sentence when it's referring to mild steel or copper/brass/bronze "welding".Any advantages over O/A brazing?  No flux I guess, but anything in the way of preheat, post weld controlled cooling etc?Do you need to bring the cast up to a red temp and tin the surface?Totally ignorant on this (and much else)TIA.
Reply:What is the CI part for repair? New?Old, cracked, burnt-out and degraded CI exhaust manifold?TIG DC (I've also used AC-HF for part or all of the welding, depending on 'how' the SI-Bronze is wetting).Any advantages over O/A brazing?Yes--O/A brazing requires lots of heat input into the casting, before brazing. TIG needs NADA.When heating cast, if it's not heated uniformly and preferably in a oven--one runsthe risk of cracking.I normally do not pre or post heat any CI--prefer to use 'cold welding'--for a wholebunch of reasons---keeping interpass temperature to 200 degrees F, or less.  No flux I guess, but anything in the way of preheat, post weld controlled cooling etc?.....see aboveDo you need to bring the cast up to a red temp and tin the surface? No preheat, no tinning (that's actually a soldering term). What helps significantly in anycast welding is to very lightly (extremely low amps--like 5), go over the prepared castarea (the ground bevels, cracks) playing the HF arc to de-carbonize, de-gas, and doan extreme cleaning job. (In really decent cast--this can create conditions where thecast can fuse back to itself--without filler (not reccomended). A pic of this is posted below.http://weldingweb.com/attachment.php...1&d=1260414597     [The above, HF pre-cleaning has never been tried, or acknowledged by mostof the 'pros/experts' in cast....so, therefore--the above must be internet trash.]I normally do not pre or post heat any CI--prefer to use 'cold welding'--for a wholebunch of reasons.*****If the repair part is to be machined/drilled, etc.---be aware that depending on the parent cast material, it may become ungodly hard. I've had this occur-once withSI-BRNZ. It can also occur with SS, nickel or steel fillers--not so much a dealwith O/A brazing. Attached ImagesBlackbird
Reply:Dave,The item I'm currently working towards getting up the courage to weld is the following: http://weldingweb.com/vbb/showthread.php?t=35731I've been practising my O/A brazing and am probably going to do it that way, but was wondering why Si Bronze isn't used more often to achieve the same thing. It sounds from what you are saying that there might be real advantages to doing it with Tig rather than O/A.There has to be a downside though, or every one would do it that way right?I can't imagine you need an un-Godly amount of current, so what are the downsides?Thanks!
Reply:Originally Posted by kenc184Dave,The item I'm currently working towards getting up the courage to weld is the following: http://weldingweb.com/vbb/showthread.php?t=35731I've been practising my O/A brazing and am probably going to do it that way, but was wondering why Si Bronze isn't used more often to achieve the same thing. It sounds from what you are saying that there might be real advantages to doing it with Tig rather than O/A.There has to be a downside though, or every one would do it that way right?I can't imagine you need an un-Godly amount of current, so what are the downsides?Thanks!