Welding Tips and Tricks

last week I welded a Cast Iron Fitting onto a steel Fuel Tank with silicon bronze, worked great, much like the Piggy-bank video. This week same customer asked me to repair a crack in his boat exhaust mufflers. Cast Iron and hallow and about the size of a lunch box. This time however the silicon bronze just wants to stay on top and no wet in. and it seems to be pulling contaminants from the cast iron even though there really isn't any arc wander and I am just on the Puddle. I've tried Pre-heating, but maybe not hot enough, enough to get it to turn purplish hue.

Should i Pre-heat more? Put down what i can and use a rosebud tip to finish the job?

Not sure why i am having such difficulty now.

To Odd Job

Good chance that there is contamination escaping from the inside of the muffler, coming out through the crack.

How have you prepared the crack, have you vee'd it out with a die grinder etc?

It's unlikely that you'll get good wetting of you are trying to weld on the raw cast surface itself.

You probably need to drill a small hole (e.g. 3/16") at the end of the crack if it doesn't continue along the full length. This is to stop the crack line spreading (continuing) later on.

I suspect that you'll need to preheat the entire unit fairly evenly, then the actual weld area will have to be a dull cherry red, and you should wrap the entire item in a fiberglass mat or similar and allow it to cool very slowly afterwards.

Let us know more about your preparation.

Trev

Ground it down and cleaned all old Paint off. took a Carbide burr and V'd out the crack by tracing it. after i ground out the crack a bit i did notice some rust from the inside on the crack. so pre-heating the whole thing seems to be my problem then, I'll have to strip the whole thing. I have Welding glass mats for just such a thing.

Might this be a case where welding on AC may be of benefit for the cleaning action it would provide?
Being an exhaust manifold I imagine you have a lot of carbon contaminates built up on the inside from the exhaust.

That being the case back purging with CO2 or such may also help in keeping the contamination of the puddle down?

DUnno just throwing out some ideas.

yea doing AC 90ish% AC- because its from a boat the main contaminant is Rust. these things are 30 years old.

Probably not what you want to hear - but I would use good old fashioned oxy / acetylene & regular brazing rod with a good flux - on older dirty material such as a manifold all sorts of junk will boil out when hot - this mostly floats to the surface or burns off with oxy - Tig likes clean things - ( but I never really got on with Tig brazing ! )

well the second muffler some one had JB-welded the crack. but after burning it out and the fresh paint job they put on, I found that not only was the crack longer but had also been welded already, probably regular stick as it didn't share the heat with the cast when heated instead it reached kindling temp very quickly and started to recede. so then i used Oxy-Acetylene and regular braze rod. wetted in like a dream but really pulled more crap out of the crack. unfortunately the porous nature of the crappy weld didn't pull this stuff in like i had hoped. I think this is a Wash and the customer will be lucky to get what has no back. If he had told my up front that it had already been welded or that the Paint was still wet when he dropped it off I'd have told him double the time its taken me at least. I got them wrapped in glass blankets atm so I'll have to check em out in the New Year.