[SteveD]

I have searched all over the internet for the answer to this. It's probably as simple as the nose on my face, but I just can't quite see it .

WHY is it that no one (seems) uses the torch gas output to siphon off enough gas (Argon) to use for backpurging? All the setups I've been able to find on line use a separate line FROM THE ARGON BOTTLE. Some use a simple 'Y' and some use a separate regulator, but ALL have been from the bottle.. which once turned ON, is.. well... ON ->dumping gas constantly to the backpurge line. I have set up mine differently, using a 'controlled Y' (separate KNOBS to 'stiffle' the flow to each/either side of the Y) out of the TORCH OUTPUT from the welder. Then the gas only flows when the button or pedal is depressed. This seems to me to save a literal TON of Argon instead of having the gas flowing freely constantly. I have only a 125 bottle (can't 'OWN' bottles any larger here - have to LEASE them instead) and just can't afford to have the gas flowing constantly to the backpurge line between setup changes. It is TRUE that I've only tried this a couple of times and I'm a PURE AMATEUR at TIG .. well, maybe not 'Amateur'.. something LOWER than that .. like almost BEGINNER NEWBIE, though I've actually done occasional welding for many years as a hobbiest, I've only been fooling with TIG a bit over a year now - and I'm finally up to 'marginally incompetent' .

SO.. am I missing something really important about why the gas has to flow into the backpurge setup at times when I'm moving stuff around and not actually welding anything? I use a long PreFlow and allow a few seconds 'head start' for the BP gas to reach the part - seems to me that it should be enough. As mentioned, I've only tried a couple of parts so far, but they look 'decent' on the inside (well.. as decent as the outside looks anyway) as opposed to NON-BP welding.

Thoughs?
Steve

[LtBadd]

Welcome to the forum
You don't say what it is that you're welding, although for your question it may not be important, still I'm curious to know.

If what you're doing works with your setup then all is good, if I'm welding a part with a back purge then it's typically finished in short order, it could be that to finish I need to reposition the part, but I'll leave the purge on otherwise the purge could be compromised. There are a lot of variables involved, such as the size of the part, material, material thickness and how good of a purge setup I have. Some parts are easier to build a damn for purging then others. Also if you've got a good purge damn then all that is needed is a low CFH flow to keep it (alive), could be as low as 5cfh, really just depends on the part and your purge damn.

Got any photos to post?

[SteveD]

Thanks, Richard. NO.. no pix since I've been working on other things lately. I'm welding (planning to weld) on a stainless exhaust system for my race car (Sports Car Club of America). The collector was damaged in a relatively minor accident at my last race and I've decided to try and repair it myself. I've done a bit of ss welding (also on exhaust parts) before, but nothing as complicated as this. This is an important part of my system and I wanted to study ss welding (mostly on youtube) and learn a good bit more about it before tackling this job. Backpurging, of course, came up (along with a bunch of other things) so I set about to put together the pieces to be able to bp and in looking for ideas, NEVER saw anyone set up a bp system using the torch gas output. I just wanted to make sure I wasn't missing something important that just hadn't occurred to me.

Lots of things are important (more important than mild steel) for ss and I've noted several things that I need to work on - one of the biggest being "don't be too stingy with the argon flow". Still, the cost, frequency and inconvenience of having to refill my 125 bottle is too great to ignore (for me, anyway). I often find myself wasting TONS of time trying to get everything set up just the way I want it and changing things several times. My bottle is not easy to reach from my welding table so I also wanted to minimize the number of times I have to access it to turn the flow off and on. As I was considering how to rearrange for easier access, it dawned on me that I didn't NEED to access it if I used the torch output instead since it was already switched off when I wasn't actually welding on something. I've also learned a lot about HOW to bp various things - some WAY more complicated than others and I'm a KISS kinda guy. I plan to use aluminum foil to plug the ends and just stick a second hose through one of them. After seeing another video this morning, I'm now planning to also 'tighten up' by putting foil over even more of the system as I weld on it instead of just the major openings (3 of them that are the 'ins' and 'out' openings). My tank is also almost empty at the moment so I'll be experimenting some more until I get to zero before making the hour trip to get it exchanged.

Still seemed odd to me that I could find NO ONE that used the 'output' option or even spoke of it.

Steve

[LtBadd]

Still seemed odd to me that I could find NO ONE that used the 'output' option or even spoke of it.

Steve

if you're trying to purge exhaust tube (or any volume) then you'll need flow before you start to weld, you have to flush out the air and that won't happen just when gas is flowing while welding. I thought at first you were purging with the same line that fed the torch (which is ok) but it sounds as if you have the purge line coming after the machine so that your purging only when gas is also flowing to the torch??

[SteveD]

After I hit the SUBMIT button, it occurred to me that I DO have some pix of the repairs that need to be made. This is a shot of the damaged collector. You can see the rolled edge right at the center where the input tube is pushed back into the clamshell. The result of that was that the collector output was quite a bit off center and it could not exit probably out of the back of the bodywork. The only solution (other than starting over with a new one) was to cut it apart, straighten out that folded over part and then weld it all back together. Quite the task, but I wanted to also use it as a learning experience.


The first thing was that after I removed the system and turned it over, I found THIS..

The bottom of the calmshell was also torn open almost the entire width (really just made it easier to get started tearing it apart).
There are MANY HOURS between the above shot and the next ones .
The first step was to get it apart and straighten the folded over flange..


then, of course, was to try to get it back together close enough to close all the gaps...


Ultimately, I got it a bit closer that the pic above, but not terribly much.. just a bit.

Anywho... that's where I am now. Trying to gain enough skill to start tacking it so I can paste it back together enough for it to hold for a few events while I wait to have another one professionally built.

I'm open to suggestions
Steve
PS.. Please excuse the MESS in the background and around the work piece(s).. but that's just the way I live

[SteveD]

Richard,
Yes.. I'm purging with the line that goes to the torch from the machine. Splitting the flow at that point from the welder. I am using a long PREflow to give enough time for the argon to get to the work piece. That gives the line some 10 seconds or so to fill the work piece before I strike an arc... and I can 'double clutch' the pedal to increase that time if necessary.

Steve

[cj737]

Steve - 10 seconds of argon won’t fill that system sufficiently. There’s simply too much volume. You need a vent at one end opposite the tin foil to expunge the air the argon is displacing.

You need to really, really clean that material inside and out when you weld it. And you can tack the seam without a purge. Just use a #12 cup and 25CFH over the weld. Use a 1-2 second preflow then about 10-12 seconds postflow. Your tacks will be super clean and strong.

I purge with 3-4cfh only. Lick your finger and place near the vent hole. When you feel cold air, you’re ready to go.

I use Quik Connectors on my purge hose. When I’m ready to weld, I plug it in. Stop welding, disconnect. Gas won’t flow until the connector is connected.

The best part of purging that weld is you can get full penetration and if the flow is high enough, it will help keep the weld from drooping internally.

[SteveD]

...
I use Quik Connectors on my purge hose. When I’m ready to weld, I plug it in. Stop welding, disconnect. Gas won’t flow until the connector is connected.
..

Thanks - I hadn't thought of using quik connects for that line. I'll get some on order.
Steve

[tweake]

you need to have purge gas running well before welding. depending on volume.

the other trick i've seen done is to use an old valved tig torch. you can fit an old gas lens in it. but mainly having the on/off valve helps save a bit of gas if your having to stop and start.

[SteveD]

you need to have purge gas running well before welding. depending on volume.

the other trick i've seen done is to use an old valved tig torch. you can fit an old gas lens in it. but mainly having the on/off valve helps save a bit of gas if your having to stop and start.

OK.. how can I determine when the "bp chamber" is full and it's OK to start welding?

Your idea of the old valved torch reminds me .. I don't have an old torch, but I DO have a couple of small gas ball valves. I could put one inline in my hose and attach it to my table (somehow).

Getting some good ideas here
Thanks to all...
Steve

[LtBadd]

I've used one of these as well, run the line to your bench and have this so you can stop the flow between parts or as needed without getting up

valve.png (144.92 KiB) Viewed 1560 times

[cj737]

OK.. how can I determine when the "bp chamber" is full and it's OK to start welding?
Steve

If you run the purge line into the single inlet, then block the 2 outlets, leaving a small hole for venting, lick your thumb and place it near the vent. When you feel cold air (argon is very chilly) on your thumb, you're good to go.

Orient the piece so that the purge line is as low as possible so it displaces the oxygen (argon is heavier than O2). You can apply some tape around the weld area to help prevent seepage. Just tack everything up 6-8 times around the circumference. That will help seal the weld. You're going to have a challenge due to the gap, so filler will be required.

Use as small diameter of filler as you can to bridge the gap. Stainless welds when purged are very, very strong. I fuse weld my exhausts without filler, but this repair won't due to the damage. 308L wire in 1/16 or 3/32 where large gaps occur is all you need. Run lots of post flow and keep the cup over the weld until the gas shuts off.

Pictures as you go!

[SteveD]

OK.. while we are on the subject of exhaust and ss, I've read about 'cooking your stainless', but nothing was ever said about the result of doing that. I doubt if I will be good enough to NOT "cook my stainless", but wonder if there are long term effects on the base material.. or is it OK (after it cools back down), but of course NOT desirable ? Must cooked stainless be replaced? Any chance my fix is going to survive after being cooked?

Unfortunately, I have only a very few pieces of exhaust that have been USED in combat to test with and I don't want to mess this one up if I can avoid it.
- thanks again for the tips -

Steve

[cj737]

Cooking stainless damages the base metal. You pull all the chromium up and out and change the composition. You would do well to pick up some flat pieces of equal thickness (guessing your exhaust is 0.065 wall). Experiment with amperage settings and filler dabbing rates.

It is always better to use too low of amperage on stainless than too high. It is a tricky material to weld. I almost always use pulse when I weld it, especially when the fit-up is good. That tubing I showed was welded autogenously, with pulse (82 amps, 45% on time, 15% background, 1.2PPS). Purge was 7CFH, preflow was 2 sec, post flow 14 sec. Almost an imperceptible weld and silver-straw color.

What machine are you using?

[SteveD]

I have a Miller Dialarc HF, now some 30 years old (and about as HEAVY as my race car). It works just fine, but has a water cooled torch that is also HEAVY. I don't like the weight and hassle of trying to get it (the torch) into (and KEEP IT THERE) the right position. The Miller is also missing a lot of the features available in today's transformerless units.. SO.. I just received TODAY a brand new PrimeWeld 225A, along with a new cart to hold it off the floor . I opened the box, but it's a bit heavy (probably 75 lbs or so) to extract from the box with one hand, so am waiting until I can get some help tomorrow to get it out and onto the cart safely (this wouldn't ordinarily be a problem for me, but I hurt my back (again) some 3 weeks ago and am trying to be very careful with it during what I HOPE is the 'healing process'. I'm too old to need ANOTHER back surgery!)

At any rate, I should have it up and operating tomorrow .. and THIS TIME, I'll have pulse options and freq options and an AIR COOLED torch (with SUPERFLEX hose) and who knows what other kinds of cool things might suddenly become available to me .

I also ordered (from Amazon) a couple of pieces of 304 SS sheet that are similar to my exhaust parts (although not USED), which are not quite as 'substantial' as you thought - about 0.038 on the clamshell and 0.050 on the flange that I have to weld it to. BTW.. that GAP is not nearly as bad as it is in the pic. That is a relaxed shot (I wasn't HOLDING IT). I believe I can get the gap down to < 1/16", probably even ZERO for the majority of it as I 'tack and go'. However, considering all the issues I have, I'm going to WAIT until I get my new sheets to practice on before tackling the collector itself.

OH.. and I DO have some 1/16 filler and should have some .045 by the time I'm ready to try the collector. Also have 1/8, 3/32, and 1/16 tungstens (all in 2% Lanthanated). I was playing around with 1/16 tungstens, but my new torch (with the welder) is set for 3/32, so I'll try that first. Also have a Furick 12 cup, but haven't tried it yet since I'm so low on Argon.

When I get to the real collector, I'll TRY to remember to take some intermediate pics as I progress (hopefully) through the repair.
Steve

[SteveD]

Well... it's been a WHILE and I've learned a LOT - but unfortunately not been able to convert what I've learned into very much SKILL at welding

I did get the job done. Just completed a few hours ago and I think it was "successful".. at least from a construction standpoint - with absolutely NO REGARD for beauty.

A few pics to brighten your day - drop by my website if you dare
Glad I don't have to answer to anyone else (like a CLIENT) on this job....

http://www.wedgeracing.com/exhaust/20AtlantaConcreteT7/

The WELDING part starts about 2/3 of the way down the page.

BTW.. I did go ahead and use the torch gas feed for the backpurge - just upped the CFH and played a bit with my 'y fitting adjusters' till I had what I think I needed. I kept the collector full by 'pre-tapping' the pedal while changing setups. The biggest challenge (other than the welding) was trying to CLAMP the part in some manner so I could access the angles I needed. This part is not BUILT the way I had to weld it, so most places were really tough to access .. and the collector is a really ODD shape and doesn't even lay down on a table well, much less stand up to do end welds. The backpurging seems to have worked reasonably well, although I did start getting some darker color near the end. I upped the CFH and it didn't seem to help.. I finally figured it out when I was DONE.. the AL foil in the output tube where I put the argon in, had torn and was letting most of the BP argon drip out onto the floor. However, I looked into the pipe afterward and saw only a darker color than I would have liked. No sugaring or really ugly mountains of crap - thankfully.

I can also say with assurity that the end result was substantially better as a result of all the info I have received over the internet these last 2 weeks - both the forums and youtube. Without all that, I most likely would have ended up with a pile of burning rubble. Thanks for all the suggestions and help.

Steve

[Oscar]

Got it done, nice. Sometimes you just gotta do it and learn one way or another. We all get better with practice.