BLACKSI

wanted to get an idea of what you guys think about back purging ss ? my welding buddy (the best welder ive ever seen) says that for automotive crap especily the thick sch10 everybody is using to make manifolds that its just not somthing that is required nore worthwhile? any thoughts would be nice but i want to hear some educated thoughts not " tony1 on honda tech says its cool so you gotta do it"

Beau

Bone1

Dave @ SMSP has a small writeup on his website about back purging..........



http://sms-products.com/Construction.html

BLACKSI

even that write up is all with the thought of thin "tubing" all the sch 10 and sch40 ---- is considerd pipe i dont belive that on sch 10 with the proper amount of heat very low for stainless that it should penitrate to the inside of the pipe nore for the aplication will stregth be a issue

Beau

LSD Motorsports

Back purging is always beneficial, ive read a few welding books and some different opinions online. Basically, with gas flowing through the runners, you have a much better chance for the whole weld to remain pure and penetrate a little more. It is definately more effective with thinner tubing though. As far as it being necessary for making a manifold, id definately have to say its not, and the manifold can still be quite strong.

SpankedYA!

I have never back purged any of the manifolds I have ever built and I have NEVER had one crack. I am confident enough in my welding that I would pull the engine out of my car by the manifold and it wouldn't break.

hotrex

im with dave, never do i purge, and never have i ever had a problem, sounds like a gross waste of argon to me... i mean, tony1 does it, so i guess we all have too...

RabbitShit

I talked to a guy at Miller about it. He said that if the material is thick enough the surface of the weld isn't 'sugaring' you're pretty good without a back purge. Sugaring is when the weld looks grey and slagy from you giving it too much heat. If you can't give it enough heat to weld without turning the weld grey it's time to back purge.

Although I've seen people make plenty of downpipes out of thinwall without an issue. Just go buy an argon chamber and start making your manifolds out of Ti. :P

myshtern

Just as rabbitshit said, as long as its not sugaring on the inside, then you are fine.
Basically, if you prep the material right, you dont really need to back purge it.

hotrex

i urinate on every mani i make to cool it down, is this normal practice

FooK

if your name is hotrex, yes it is.