Back Purge Setup - Bicycle Framebuilding

[ToddFarr]

Hey all,
Looking to setup a back purge system. Tried search the forum and there is not too much on the topic.

My first project will be to setup a back purge on my bringheli, can anyone give me the low down on whats desired?

1.) I know you need to VENT somewhere. Looking at the Sputnik and Anvil it looks like they dump from the Top of the Seat Tube, this is probably because Argon is heavier than Air and it will push it down and out but where? Do you want to push down and out to a vent in the BB or out the Chain Stays?

2.) I know I need a Dual Regulator/Flow Meter. Any recommendations?

Thanks in Advance - Todd

[Alistair]

Hey all,
Looking to setup a back purge system. Tried search the forum and there is not too much on the topic.

My first project will be to setup a back purge on my bringheli, can anyone give me the low down on whats desired?

1.) I know you need to VENT somewhere. Looking at the Sputnik and Anvil it looks like they dump from the Top of the Seat Tube, this is probably because Argon is heavier than Air and it will push it down and out but where? Do you want to push down and out to a vent in the BB or out the Chain Stays?

2.) I know I need a Dual Regulator/Flow Meter. Any recommendations?

Thanks in Advance - Todd

Todd,

check out this thread from the Google group,
https://groups.google.com/forum/?fro...s/zEkd_4eBxlEJ

and this one from the MTBR group,
Two tanks or dual out put flow meter for back purging?

The discussions there, and any answers you get from the thread here, should give you a good idea of what your options are.

Alistair.

[VertigoCycles]

Hey all,
Looking to setup a back purge system. Tried search the forum and there is not too much on the topic.

My first project will be to setup a back purge on my bringheli, can anyone give me the low down on whats desired?

1.) I know you need to VENT somewhere. Looking at the Sputnik and Anvil it looks like they dump from the Top of the Seat Tube, this is probably because Argon is heavier than Air and it will push it down and out but where? Do you want to push down and out to a vent in the BB or out the Chain Stays?

2.) I know I need a Dual Regulator/Flow Meter. Any recommendations?

Thanks in Advance - Todd

Be smart about where you put your purge lines. My Anvil fixture has them at the BB, ST and HT...they might not all be necessary there, but I'm sure it speeds up the fill process. Vent holes at each joint so the frame can fill and vent holes at or near the dropouts so air can be pushed out.

FYI - my way is obviously not the only way, but I have a tank dedicated to purging. I start with 12-15 CFH and the frame oriented with the HT facing down (so my stay vents are at the highest point) and after about 10min I back off to about 7 CFH and get to welding.

Any holes not intended to be ventilation need to be plugged. For example, I drill my ST slot relief before building the frame and I have a stainless plug for it. The vent hole for the DT/BB is similarly plugged when I weld the front edge of the ST miter to the BB shell before setting up the entire main frame for tacking.

[ToddFarr]

Thanks for the reply guys! It's really helpful. I started my Back Purge setup for my Jig, now I'm looking to move to the Heat Sinks and Purging on the stand.

I'm debating whether or not to machine my own heatsinks. One in particular is the BB Heatsink, Looking at the one on the Paragon site it would be hard to make that for much less than that already is. 510 Bronze is pretty expensive and not the easiest to machine. Is this a typical material for heat sinks? Also sounds like the paragon will only fit paragon shells?

Here is a picture of the HT and ST cone I made for the Bringheli this weekend. I think I'm going to make a whole new BB Tower. There is not much I can do with the current one.

[Alistair]

I'm debating whether or not to machine my own heatsinks. One in particular is the BB Heatsink, Looking at the one on the Paragon site it would be hard to make that for much less than that already is. 510 Bronze is pretty expensive and not the easiest to machine. Is this a typical material for heat sinks? Also sounds like the paragon will only fit paragon shells?

Todd,

I made my own, mostly because I thought it would be a good exercise in design and fabrication, and a bit of a challenge. It was a somewhat time consuming project, partly because I'm still relatively new to machining and partly because I had to figure it all out from scratch, design and materials wise. I've never gotten a look at anything like this in person before, that would have made it easier to steal some ideas. Anyway, having gotten it all figured out now and made a few, any more that I make will go a lot quicker.

I went with the cored bronze (SAE 660) that Enco always seems to have on sale in their monthly flyer thingy. Pretty affordable. Machines nicely, gives a good finish. I ground up some HSS bits with zero back rake which seemed to help a lot, preventing the tool from digging in and being "grabby".

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Here's a link to a Flickr set that gives an idea of the steps involved, complete with some old fashioned 2D AutoCad sectioned drawings ('cause I can't afford SolidWorks...).

That all being said, I don't see how you could go wrong with the offerings from Paragon and Sputnik. Considering the work involved, their prices are very fair I think.

Hope this helps.

Alistair.

[Alistair]

Here's a link to a Flickr set that gives an idea of the steps involved, complete with some old fashioned 2D AutoCad sectioned drawings ('cause I can't afford SolidWorks...).

Oops, forgot the link. Here it is, Purgeable heat sinks. - a set on Flickr

Apologies.

Alistair.

[VertigoCycles]

the nice feature of the Paragon BB tool is that it expands first and then you tighten up the caps...a nice feature when you're capping both sides. all the tools I made are like Alistairs (though not as nicely made) where they expand and load the cap in one operation.

unless you have a lathe and mill with some serious power, super sharp tools and a very rigid setup, avoid the 510. the cored 660 gets the job done and it's cheaper as well as much easier to machine.

[fortyfour]

I have recently been doing research to finalize my own back purge system. While doing key word searches (both via Google and Flickr) I was finding that 44 BIKES was coming up mostly for back purge searches... Me. The one looking for information? So for the sake of this thread, and to return the favor (Sean at Vertigo was kind enough to answer a few questions of my own), I organized all of my back purge set up images into one dedicated Flickr Set. By no means complete nor expert opinion but now it's all in one place, organized and tagged appropriately. More to come as I convert my heat syncs appropriately and make some modifications as well. Thanks to all who have helped with answering questions. Enjoy:

44 Bikes : Back Purge Setup

[Too Tall]

Kristofer Henry, with that last post this thread is going into "The Knowledge" and tag you are it.

[Alistair]

I organized all of my back purge set up images into one dedicated Flickr Set. By no means complete nor expert opinion but now it's all in one place, organized and tagged appropriately. More to come as I convert my heat syncs appropriately and make some modifications as well.

Nicely done Kris. Your Flickr pic's, and some advice I got from Sean via email, were what gave me the inspiration to make my own heat sinks.

I don't think I mentioned that in my above posts, so I'm mentioning it here because I think it's important to acknowledge when builders are kind enough to share information (whether it be in the form of words or pictures) that is helpful to another builder who is trying to solve some issue or other.

Cheers.

Alistair.

[Mark Kelly]

If I may insert my dry and overly technical two cents worth: one issue frequently missed when discussing back purge systems is the importance of minimising mixing between the purge gas and the air it is displacing.

The first factor to consider is density: the purge gas is denser than the air it is replacing, firstly because it's a heavier gas (argon has a density of about 1.7 g.m^-3 at STP, air is about 1.2) but also because it's a bit colder due to expansion; remember, that's how refrigerators work. It is much more efficient for the purge gas to flow upwards from entry to vent as this will allow the lighter air to float on the heavier argon* and be pushed out ahead of it. Flow in the opposite direction will tend to make the argon fall through the air, mixing with it. You only need a few percent of air to contaminate the weld.

The second factor is turbulence: if the argon flow is turbulent it will tend to entrain air at the gas front and mix it into the argon flow. Turbulence is promoted by speed and by speed differences so high flow rates are counterproductive: they use more gas and work less well, a double whammy. Small orifices into large spaces are especially good at promoting turbulence, so think through your gas flow: if it's coming from one section though a vent hole into another section, make sure that hole is a large percentage of the cross sectional area of the second section: remember areas are squares so a 10mm hole leading into a 40mm tube is only 1/16th the area.

Lastly, consider how you know your backside is adequately purged: if it's blind, you won't know for sure unless it fails, by then it's too late. You could test your purge exit using a canary or a candle (don't laugh, both have been done) or you could use a gas monitor. There are monitors made for this purpose, routinely used where weld quality is really critical.

Caveat and declaration: I'm not a welder but have lots of experience in process engineering for beverage, food and pharmaceutical manufacturing. I understand clean welds.

*Argon's not the heaviest gas, sulphur hexaflouride is so much heavier than air that you can float a very lighweight boat on it: google "sulphur hexafluoride boat"

[Mark Kelly]

That's 1.7 kg.m^-3. Can one of the mods edit for me and then remove this?

[ToddFarr]

Hopefully getting back to converting my Bringheli soon. However, the UPS guy dropped this off today.

Where ya hose at?


Purge Tubing...Why? Well mostly because with my OEM discount print is free... by Todd Danger Farr, on Flickr

[afwalker]

Hope it's ok to ask this purge related question here, ow please move.
I would like to hook my anvil frame jig up for purging and want to put a quick-connect 1/4 male fitting on. What size is the fitting on the bottom of the intake switch box? My screw checker is coming up with like 7/16 24 tpi, but it's not the best fit, and I want to be sure I get the correct adapter. Thanks in advance
andy walker

[EnginCycles]

Hope it's ok to ask this purge related question here, ow please move.
I would like to hook my anvil frame jig up for purging and want to put a quick-connect 1/4 male fitting on. What size is the fitting on the bottom of the intake switch box? My screw checker is coming up with like 7/16 24 tpi, but it's not the best fit, and I want to be sure I get the correct adapter. Thanks in advance
andy walker

Just about all things that involve air or liquid are never standard threads (they are tapered). That is a 1/8" NPT which stands for National Pipe Thread. The 1/8" refers to the inner diameter of the gas pipe that is sold as this fitting. You can get a 1/8" NPT quick connect from McMaster Carr or the like.

[Meriwether]

I saw someone else do this but i used air compressor fittings work really well as quick-connects and also shut off the flow when disconnected. One line goes to the fixture and one goes to the BB heatsink when i'm welding in the Park stand.
airpurge-BB.jpgairpurge-jig.jpg

[afwalker]

Whit that's how I'm ending up doing it thanks. Had I read Drew's post a little more closely I could have used this:
Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies
An 1/8" NPT to male quick connect and saved a few adapters.
And I'm thinking that push to connect adapter is an 1/4" NPT male to an 1/4 OD like this:
Grainger Industrial Supply - MRO Supplies, MRO Equipment, Tools & Solutions
cheers
andy walker

[PJN]

This thread and the thread on MTBR have been very helpful in getting a backpurge set up rolling. I've purchased the parts-list zank cooked up in this MTBR forum:
Two tanks or dual out put flow meter for back purging?- Mtbr.com

I do have some questions though - what are the pros/cons of purging all the heat sings at once or only purging the joint that you are currently welding on.

It looks like Tyler @ Firefly only purges the joint he's working on:


I believe quite a few of you hook all of the heatsinks up and fill the entire bike up.

Any downsides to purging one joint at a time?

Thanks,
James (PJ) Nelson

[EnginCycles]

There are things to consider here about purging and your goals. Steel purging is very simple as you are not really doing anything other than a basic step to help prevent hardened penetration on the inside of the weld. It takes almost no argon to achieve this and having oxygen present along with the argon is still fine. Titanium is another story and you need to be very concerned with the argon presence and turbulence. I look at each joint as having three points of entry. I tend to run argon in two of the ports (the lower two) and allow the third port to exhaust the dirty air. The chain stays and seat stays are much trickier since your argon is entering the tube from the seat tube or the BB and you are trying to allow for exhaust from the same tube you are filling with argon. The breather hole needs to be large enough to prevent pressure build up inside the tube.

You would never want to have all the points of entry getting argon. How does the dirty air escape if you pump stuff in from all points of entry?

Not sure if that helps or answers your question.