Oxygen Concentrator vs. O2 Bottle?

[Jim G]

This thread details how someone is using a medical oxygen concentrator in place of an O2 bottle for brazing with propane...

http://www.chaski.org/homemachinist/viewtopic.php?f=12&t=87931

Does anyone here have any further experience with such a setup?  What are the pros/cons?  What should one look for in selecting such a unit? 

Thanks!

-Jim G

[Michael Catano]

One of my shopmates is using an oxygen concentrator with his O-A
setup. Aside from being rather noisy, it seems to work fine. I've
not used it myself so I can't really comment on whether or not there's
a noticeable difference when compared to a traditional pair of tanks,
but it seems to get the job done.

Best
Michael

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[Olivier Alonzo]

I have a similar setup. It works fine, brass or silver filler. It has paid for itself over the few years I've had it, vs. renting/buying and refilling a tank. And no need to transport and store an extra hazardous tank.

It's low flow and low pressure, so no cutting or huge heating nozzles. I guess the machine can break down but they are very durable.

Try to get one with low hours, they have a counter.

olivier

[Alex Wetmore]

Try MAPP or Chemtane instead of propane for fillet brazing.  You can test this with a "steak saver" that lets you adapt a plumbing MAPP bottle (1lb) to fit your propane regulator.  If you like how it works and plan on doing a lot of fillets then you can get your local welding gas supplier to fill a normal BBQ cylinder with chemtane instead of propane.  It's not much more expensive.

What pressure can the oxygen generator deliver continuously?  How pure is the oxygen that is generated?  Oxy/propane wants a lot of oxygen to make a hot and sharp flame, and I wonder if your oxygen generator just isn't keeping up and is mixing in normal air.

This is what oxy/propane (not even oxy/chemtane) looks like with an oxygen gas cylinder and normal BBQ propane looking through a didynium lens:

http://alexandchristine.smugmug.com/Bicycles/Racks/Rack-Building-Howto/3575535_F4T3FZ#!i=202963147&k=BDzm4&lb=1&s=XL

That is from a #1 Victor tip.  The cone isn't as sharp as oxy/acetylene or oxy/chemtane, but it does work for building fillets.

alex

---

From: frameb...@googlegroups.com [frameb...@googlegroups.com] on behalf of Legacy Frameworks [le...@legacyframeworks.com]
Sent: Tuesday, October 09, 2012 11:32 AM
To: frameb...@googlegroups.com
Cc: Jim G
Subject: Re: [Frame] Oxygen Concentrator vs. O2 Bottle?

Michael meant to say my O-P setup. I too use a simple barbecue propane tank and craigslist oxygen generator. However I went cheap on the torch as well. Took a gamble and went with a simple $40 Hoke Jewlers torch http://goo.gl/wOZaR and I only use the largest tip. I did get a propane specific regulator, which seems to be not necessary. The gamble payed off and it works great, from silver brazing housing guides to brass brazing and de-brazing 3/16" plate style dropouts in round stays. 

One thing I have not attempted is true fillet brazing, I suspect you could get used to it, but the heat - with my tips at least - is not super concentrated like OA.

Levi 

http://legacyframeworks.com

[ji...@yojimg.net]

Hi Levi,

Really great info -- thanks!  I'd never heard of that brand of torch before. Does your setup put out enough heat for BBs and fork crowns?

Thanks!

-Jim G

On Oct 9, 2012, at 11:32 AM, Legacy Frameworks <le...@legacyframeworks.com> wrote:

Michael meant to say my O-P setup. I too use a simple barbecue propane tank and craigslist oxygen generator. However I went cheap on the torch as well. Took a gamble and went with a simple $40 Hoke Jewlers torch http://goo.gl/wOZaR and I only use the largest tip. I did get a propane specific regulator, which seems to be not necessary. The gamble payed off and it works great, from silver brazing housing guides to brass brazing and de-brazing 3/16" plate style dropouts in round stays. 

One thing I have not attempted is true fillet brazing, I suspect you could get used to it, but the heat - with my tips at least - is not super concentrated like OA.

Levi 

http://legacyframeworks.com

On Monday, October 8, 2012 11:36:49 PM UTC-5, Michael Catano wrote:

[Alistair Spence]

On Tue, Oct 9, 2012 at 1:37 PM, Ji...@yojimg.net <ji...@yojimg.net> wrote:
> Hi Levi,
>
> Really great info -- thanks! I'd never heard of that brand of torch before.
> Does your setup put out enough heat for BBs and fork crowns?
>
> Thanks!
>
> -Jim G
>

Wikipedia has this, http://en.wikipedia.org/wiki/Oxygen_concentrator

which mentions generated flow rates of 5-10 liters per minute. The
Victor website (which I find hard to use and not well designed) links
to this document,

http://victortechnologies.com/IM_Uploads/DocLib_5222_Victor%20Professional%20Welding%20and%20Heating%20Nozzles%20and%20Tips.pdf

at the bottom of the first page in that doc.(page 43) there's a table
that shows nozzle flow rates in SCFH (standard cubic feet per second).

For a number 2 tip (a middle of the road tip size for bike fab.) it
lists flow acetylene flow at 5-10 SCFH. A footnote says that O2 flow
is 1.1 times C2H2 flow, under neutral flame conditions. That puts the
upper bound for O2 flow at 11 SCFH , for a no. 2 tip.

My back of the envelope chicken scratch conversion tells me that 11
SCFH = 5.2 liters per minute, which, referring to the number from the
Wikipedia page, suggests that the O2 generator would be able to keep
up.

I don't think this quick and dirty calculation definitively answers
your question Jim, but I think it does seem to suggest that there are
possibilities here.

Alistair.

[Olivier Alonzo]

I use up to a no. 4 Victor tip with the concentrator and propane. Most concentrators max out around 5 lpm, and that seems to be fine for the large tip. The purity goes down as flow goes up. It's apparently 93% pure O2 at 5 lpm. Pressure is about 7 psi.

It's fine for a BB shell and brass filler. For a heavy crown (& brass) I like to surround it by some firebricks, it speeds things up a bit.

Fillet brazing is also okay. See pics. Far from a "no-file" but I lack experience. That was a no.3 tip at 3 lpm.

I have even less experience with acet. but filleting seems to work better with the sharp inner cone of O/A.

Olivier

[Alex Wetmore]

From: Alistair Spence [alspe...@gmail.com]

> For a number 2 tip (a middle of the road tip size for bike fab.) it
> lists flow acetylene flow at 5-10 SCFH. A footnote says that O2 flow
> is 1.1 times C2H2 flow, under neutral flame conditions. That puts the
> upper bound for O2 flow at 11 SCFH , for a no. 2 tip.
>
> My back of the envelope chicken scratch conversion tells me that 11
> SCFH = 5.2 liters per minute, which, referring to the number from the
> Wikipedia page, suggests that the O2 generator would be able to keep
> up.

The oxy/propane ratio for a neutral flame requires about twice the oxygen compared to the oxy/acetylene ratio for a neutral flame. According to http://mewelding.com/oxyfuel-flame-adjustment-and-flame-type/ a neutral flame for oxy/acetylene is about 1:1 or 1:1.1 as Alistair found. For oxy/MAPP (similar to propane) it is 1:2.3 to 1:2.5. That pushes you from 5 liters per minute up to 12 or 13, doesn't it?

I bring this up because an oxygen concentrator really only makes sense to me if you are brazing with oxy/propane instead of oxy/acetylene. If you can easily acquire acetylene then you can easily acquire oxygen.

This table is really interesting and comes from the same webpage:
http://mewelding.com/images/tab11-3.gif

It shows why oxy/propane (and even oxy/propelene) isn't as good as oxy/acetylene for fillet brazing. Look at the outer cone to inner cone heat ratio for the different gasses. Acetylene gives a much hotter flame on the inner cone than the outer, where the LP gasses don't have as big of a break. The oxy/propane flame is also cooler, but most of the other LP gasses (like MAPP) are nearly as hot at acetylene. Oxy/MAPP is still making a much hotter outer cone though, which could make precise control of the fillet more difficult. I haven't seen this table or anything like it before, but it explains some of what I'm observed in my brazing with oxy/chemtane (which I think behaves most like MAPP of the options listed).

alex

[Jim G]

I finally got my torch rig + oxygen concentrator set up and attempted some brazing with it. First, some photos:

Everything: http://www.flickr.com/photos/jimg/9864332385/
Torch: http://www.flickr.com/photos/jimg/9864691305/
First braze attempt: http://www.flickr.com/photos/jimg/9888893413/

Taking a tip from Levi, I went with a simple Hoke jeweler's torch. I'm planning to mostly build racks, so I figured this would be a good entry-level torch -- and if not, it's no big loss since it's only $40. The Hoke comes with 4 tips: 1A, 2A, 3A, and 5A. In the lit-torch photo above, that's a 3A tip. In the first-braze attempt photo, I used the 2A and 5A tips. I had about 5psi on the propane, and the oxy-con was set at 3lpm for the 2A tip and 5lpm for the 5A tip.

The oxy-con makes more than enough O2 for the smaller tips -- if I open up the oxy torch knob too much, I can blow the flame out. With the largest tip, I cannot blow the flame out even if I open up the torch knob all the way. The machine has an internal regulator, and I haven't yet tried to adjust it to gain more pressure -- should I?

Coming off using a simple MAPP/air torch, this is a whole new ball game -- there are lots of parameters to adjust, and the resulting torch flame is very different. I'd welcome any basic advice from anyone who has experience using an oxygen concentrator and propane!

Thanks!
-Jim G