[Superiorwelding]

On Jody's video on the tap removal, he mentioned upcoming videos on back purges and how to build them. I thought I would get a thread started in anticipation of those videos. I made this 1/2" copper tubing back purge for a one time custom application. I used Silicon Bronze to braze the brass inert gas fitting to the copper and this back purge worked very well.
Lets see your back purge set ups or purge chambers. I am actually waiting on parts for a purge chamber and will share the pics and progress when I start building it. I also have some 316L that I am planning on using for a back purge set up. I cant wait to see Jody's set up.
I once talked to some friends about back purges and the price gouging involved in units sold (my opinion). I mentioned the idea of marketing some purges at reasonable prices but the drawback is those who would use a purge can make one as easily as I.
-Jonathan

[Superiorwelding]

I also have this CK Worldwide TS300 trailing shield that I have not had the opportunity to use. Thought I would throw it out there for those who would need one, as this is very reasonably priced.
-Jonathan

[Otto Nobedder]

I saw some interesting creations, akin to torture devices from the Inquisition, used to back-purge sanitary pipe for Hershey Foods, Inc. I'd think the microbrewers would use the same quality. These items were custom-made to fit behind a pipe joint, and were fed some distance up the pipe to accomplish the goal.

Steve S

[Greg From K/W]

Why not just back the weld up with a piece of copper or something? The copper traps the gas behind the weld that way purging the whole thing isn't needed. It works good for stainless steel.

[Superiorwelding]

Why not just back the weld up with a piece of copper or something? The copper traps the gas behind the weld that way purging the whole thing isn't needed. It works good for stainless steel.

I actually did use some copper and alum foil to back up for 1/8" SS plate, this was used for 18 ga SS. I honestly just wanted to try something different to see if it would work.
-Jonathan

[Wes917]

Why not just back the weld up with a piece of copper or something? The copper traps the gas behind the weld that way purging the whole thing isn't needed. It works good for stainless steel.

Sometimes that's enough, in some environments it's not. For common repairs we had our machinists make use copper back ups for heat sinks and gas distribution. We would also make "one off" back ups out of stainless and put screens and steel wool in them. Lots of ways to do it, a lot depends on the job/environment.

[Superiorwelding]

Wes917,
Do you have pictures of some of those copper back ups?
-Jonathan

[Wes917]

Wes917,
Do you have pictures of some of those copper back ups?
-Jonathan

Nope, no electronic devices allowed on shop floor

[Greg From K/W]

I used a spring clamp and a a chunk of copper wool to tig some stainless steel. I actually used even a small chunk of 1/2" copper water pipe one time. It worked well. Of course spring clamps are a welders best friend too.

[Bill Beauregard]

At G.H. Grimm a manufacturer of Maple syrup equipment all stainless equipment used to be soldered. Now with the controversy over lead, they've been forced to take up TIG welding. These people learn fast! For every joint they have a machined fixture to exactly fit the back of each joint and distribute the shielding gas. These leave minimal space for gas, and fit tight to the backside to draw away excess heat. Their machine choice: two big Lincoln hogs probably stand 4.5' tall. No need for AC. They probably work as well as inverters on stainless.

[Bill Beauregard]

Might there be a material like plaster of Paris one could squash up against the back side of a weld, that would handle the heat. One could grind away enough material after it sets to allow room for the gas, drill some holes for gas line, and have a good fit. In my case I never have occasion to purge a flat surface. It's always irregular.

[Braehill]

Bill,
You could use Solar Flux B on those occasions and skip the purge all together. Just another option, if you can get to the back side to form plaster, you can apply the flux.

Len

[Bill Beauregard]

I'm going to try the Solar Flux B.
A new tangent; I've heard that any purge gas will work, steel mix, argon, helium, even nitrogen. Is this true?

[Braehill]

I personally wouldn't use a mix like 75/25 but any of the others will work, Nitrogen being the least favorable but way cheaper than the others. Some of the mixes meant for stainless would be fine but at an added expense for the gas. We always have Nitrogen available at work and we still choose to use Argon whenever possible.

On piping that can be removed we use Argon in most cases because it offers the most benefit for the least amount of money. In some of the process piping where we can't remove a section of piping to make your final welds, or in the case of a repair we use Nitrogen as a last resort because of availability and price. It would take a truckload of Argon cylinders to purge hundreds of feet of 4" pipe and a purge dam can't be removed after the final welds are in place. We have a 20,000 gallon Nitrogen tank on site that we use for purging compressor seals and explosive proof cabinets as well as the process lines in the event of a shutdown. Sometimes we're lucky enough to be able to double block and bleed a smaller area and then we'll use Argon off a cylinder.

These are just a few conditions that I have to deal with personally, and some of the ways we deal with them. We also back purge our carbon steel welds if we can to keep the weld reinforcement as smooth as possible.

Len

[Otto Nobedder]

I agree with Len.

You must consider the effect of the backing gas on the molten steel. In the example of 75/25, CO2 is an active gas, and when heated to plasma state will disassociate, and can deposit carbon in the weld, and form oxides in the steel. Most mixes will have some active component, the reason for the mix, and, as stated, most are costlier than 100% argon. Nitrogen is not a big issue for mild steel (though argon makes a smoother root), but can cause "nitrogen embrittlement" in Austinitic stainless steels like the 300 series.

I will use nitrogen on SS in two cases. Vent piping that sees no pressure and would require a lot of argon to purge, and the outer vessel of a large vacuum-jacket vessel. In the first case, it's strictly economy. In the second it's both economy (due to the huge amount of argon it would take), and simplicity, as I break the vacuum with nitrogen, and therefore don't have to wait for atmosphere to be displaced by the purge gas.

I've made backpurge containment from aluminum foil and tape, with the tape two inches from the weld, when tape residue from the heat isn't an issue (It's a bitch to get "oxygen clean" when that's required).

Steve S

[nathan]

We have two at work, one is made from 4x4" aluminum angle with a bent piece welded to form a square gas chamber. The corner of the angle is milled off and holes are spaced about 1.25" apart. Our other is a piece of aluminum, bent on a 1/8" radius with another bent piece welded on the other side, this chamber is filled with stainless shavings for a gas-lense effect. The holes are drilled on the radius every inch on the second one. The aluminum soaks up a lot of the heat, but I also use two pieces of 3/4"x3" along the weld seam, positioned about .025" off the weld. These heat sink blocks soak up most of the heat and allow me to walk the cup on the outside corner joint, making something truly beautiful. I take the blocks off right after welding and the joint is almost color-free on both sides and it's cool enough to touch. This probably wouldn't work so well in tight quarters, but I imagine you could use some copper wire or copper weave stuff (like on the inside of ground clamp jaws) to sink some heat on pipe.

[redacres]

Nathan, Could you post a few pics please?

[nathan]

Nathan, Could you post a few pics please?

I'll try to remember to get a couple good ones this week. I have one but it's a pretty bad picture.

[Superiorwelding]

I decided to try my hand at making a trailing shield for my jumbo pyrex gas lens. This is all just scrap SS I have laying around and all hand cut and you can tell. I am waiting on SS wool to come in and have to go get the barb fitting. This is set up for 8" pipe. I do wonder if it would be worth my time to try to market something like this.
-Jonathan

[Superiorwelding]

This is what I am getting for the SS wool, anyone out there use this before and will it work ok?
http://www.ebay.com/itm/Stainless-Steel ... 4840a25c24
-Jonathan

[Wes917]

I decided to try my hand at making a trailing shield for my jumbo pyrex gas lens. This is all just scrap SS I have laying around and all hand cut and you can tell. I am waiting on SS wool to come in and have to go get the barb fitting. This is set up for 8" pipe. I do wonder if it would be worth my time to try to market something like this.
-Jonathan

Jonathan,

These look a lot like some of the ones we would make that didn't need heat sinks and used them for backups. We also had some for cups too, that we'd use for titanium sometimes. Nice work

[GreinTime]

Jonathan,

By saying it's setup for 8" pipe, are you implying that the radius of the 'C', if you will, is the same as the outside radius of an 8" pipe?

[Superiorwelding]

Jonathan,

By saying it's setup for 8" pipe, are you implying that the radius of the 'C', if you will, is the same as the outside radius of an 8" pipe?

GreinTime,
Yes it is in fact a 4" radius. I will still have to angle the back side to allow my torch to angle back. Still a work in progress.
-Jonathan

[GreinTime]

How do you plan on attaching it?

Sent from my DROID RAZR using Tapatalk

[Superiorwelding]

A continuous strap with a small bolt to tighten it up.
Or I could try brazing the SS to the Pyrex
-Jonathan