I've just read previous postings related to the extremely high cost of BOC cylinder rental in the UK. I share some of the contributors' frustration.
Does anyone know how to 'decant' a gas like nitrogen, CO2 or oxygen from one of the BOC cylinders into some other vessel? i.e. in order to return their precious cylinder and thereby stem the expense, especially if one only uses a little gas every so often.
Would it be possible to use a cylinder like those used for camping gaz? Can you purchase a valve which will allow gas to flow into the cylinder for recharging? Or can these cylinders be recharged through the existing valve? Pub cylinders might offer another alternative, as could recovery cylinders used for automobile air conditioning work. Any other suggestions?
Before anyone starts registering safety concerns, I'm interested in establishing how it might be done before assessing whether it is feasible or advisable.
The other problem is the transfer process. Simply connecting two cyclinders of equal volume together would presumably result in at least half the gas remaining in the BOC cylinder. It might still be cheaper to throw away half the gas in order to avoid the extortionate cylinder rental charges over a long period of several years. Anyway, perhaps you need a compressor or some other pump in the air line, plus a pressure gauge to ensure the receiving cylinder was only charged up to its safe operating limit.
I am a BOC gas user , I run a small garage in a rural area. As cars are not so rusty as they used to be a bottle of argoshield now lasts me about a year. If I remember correctly I pay about £30 a year for the bottle , and about 40 for a refill. Ok its not cheap , but its not unreasonable. My insurance now costs me ( no I've never claimed in 20 years ) about £2000 odd a year , presumably this is to help pay for new houses for you and your neighbours after you have blown up you entire street. Have you any idea how reactive pure oxygen is? Have you any idea why the bottles are so heavy , it is because the metal is about an inch thick. Bottles are supplied ( depending on product) at about 300 bar, camping gas liquifies at about 10 bar , you are dealing with serious pressure. Please try not to blow or freeze off all your limbs, or you will no longer be able to use a keyboard. A suitable candidate for the Darwin Awards her. steve the grease
Have you tried Calor instead of BOC? I've had CO2 bottles from them & there is no cylinder rental - just turn up & take away a bottle of gas - £13 for a
It is possible, however you are going to need adaptors, high-pressure hoses, valves etc etc. You're dealing with pressures up to 4000psi here, and mistakes are very very dangerous, usually fatal. I have seen (locally) the result of oxy cylinders going bang, and the result is not unlike a bomb exploding.
The bottom line - forget it. Pay the rental and get on with it.
Sounds like £30 per year is cheaper than a funeral?
I use pub cylinders. Get friendly with a local landlord, and he will often just swap the cylinder for as little as a tenner. I also find the half height cylinders so much easier to move around.
Be careful as pub gas is sometimes a mixture of CO2 and Nitrogen as I discovered when my welding suddenly started looking like pigeon poo. I currently buy pure CO2 from a fire protection agent at about 15 quid a bottle. The only catch is he's very careful about checking the date stamps on the cylinders. If I take too long finishing one I can get charged 22 quid to have the cylinder pressure tested and restamped.
I thought the thread was about gas cylinder rental originally
" I've just read previous postings related to the extremely high cost of BOC cylinder rental in the UK. I share some of the contributors' frustration.
Does anyone know how to 'decant' a gas like nitrogen, CO2 or oxygen from one of the BOC cylinders into some other vessel? i.e. in order to"
snip
The bottles I get are pure Co2 although the boc ones are, I believe, often called "argoshield"? and maybe contain someting else pertinant to decent welding?
By definition, you can't MIG with CO2. At the best, you're using dip transfer MAGS, which is a different process. Unless you're using a pulsed supply, you're also unlikely to get a good weld out of it.
It comes down to personal definition of a "good" weld. As I said, some of us are happy with our results even if it may have taken us longer to reach the necessary skill level. I've certainly seen worse "professional" welding. The question is whether the cost saving is justified in relation to the extra effort. Personally, I find that it is, but wouldn't necessarily advise a beginner to struggle along the same route.
The easiest way to avoid rental is to befriend a local garage and get him to swop the cylinders for you whenever you need it....The hardest bit is obtaining the original cylinders.....but that`s not altogether impossible , is it?
This is a shame. If most "amateur" welders swapped their gas, they'd get much better welds.
And an automatic hat, and some deliberate _practice_ would help even more. Get a wheelbarrow full of scrap, in pieces no bigger than 6" square plates. Start welding them together in pairs, and don't stop until the whole thing is solid. Then throw it away. The idea that somehow you can take a rusted-out strut mount and fix it properly with your first-ever weld seems a little odd, when you think about it in isolation - yet it's how so many people start out.
Ah, but those who have mastered welding rust to rust with the wrong gas end up as highly skilled welders!
Or in layman's terms, a Morris Marina.
Well yes, but only after driving it around for a year or two.
True, but the MOT tester is there to see that it's all good and solid. My point is, that many people get all their practice on old bangers that really don't matter, before graduating to proper restoration of classics that do. Or at least, that's how it was in my day...
Being a vaguely competent wire-feed welder requires you to understand the process. It's simple stuff, but if you don't know what it's meant to do, you'll never know what's going wrong when it does.
There are four ways to get metal from the gun to the workpiece; spray transfer, dip, globular and pulsed transfer.
Spray transfer is the best. Droplets are melted on the tip of the wire, "pinched off" by the magnetic field and fly freely across the gap. The noise is a quiet hissing, because many droplets are in flight simultaneously. You can only obtain spray transfer by using a high voltage and (importantly) a high wire speed. This is why you need to learn on thicker material, with the dials turned right up. Spray transfer is a hot process, so it's hard to use if you're working vertically (the pool runs away), but you can usually manage on aluminium or thick steel, because of the heatsinking effect. Small machines may not have the power to get into the spray transfer regime at all. Using CO2 as a shield gas, especially at low voltages, may also prevent it working.
Dip transfer is used for thin steel, where the heat of spray transfer would be excessive. The wire feeds, contacts the workpiece and the tip melts off, breaking the circuit. Repeat. The noise is more staccato than spray transfer, as you can hear the rapid cycling process. Penetration isn't as good as spray transfer, so be careful using it for structural fabrication in vertical runs.
Globular transfer is the most popular process for small amateur welders, but it's WRONG ! If (especially with CO2) spray transfer never quite gets going, or dip transfer is cycling too slowly, then the droplets hang on the end of the wire to form a large blob (bigger than the wire), then fly off together. This half-cooled blob hits the workpiece and sticks, but there's inadequate heat in the workpiece and no penetration. Welds are ugly "pigeon crap" and have no strength.
Pulsed transfer is a solution to globular transfer, without the high heat of spray, but you need a welder than can pulse the current rapidly to force droplet formation. These are only found at the high end.
To weld thin steel well, you need to use dip or pulsed transfer. If you're welding moderately thin steel (clean 18 gauge) then even a cheap set ought to run dip with CO2 quite happily. To weld really thin steel, then you _need_ pulsed transfer.
The tricky bit is where the steel is "a bit on the thin side". Although you could use CO2, you can equally well use Argoshield. The margin of error with CO2, where your good dip welds turn into bad globular welds is that much narrower. A good welder probably slows down, but a less skilled welder starts to make poor welds.
If you're welding heavy gauges, then you can't use CO2. Full stop. If you try it, you'll get poor transfer, poor penetration and weak welds.
CO2 makes a fine welding gas for thin metal, where you're competent to do it. You can't say that CO2 is simply _wrong_, as if they'd supplied a cylinder of nitrogen. It's also cheap.
But CO2 is harder to use than argon or tri-mixes, and it's inflexible as you can't use it for heavy stuff. Why make things harder for yourself ?
So how do you know they're good welds ? It's a basic technique to do nick-break tests from time to time, to check that your welds really are that good.
Welding up rusty old sills isn't rocket science. The stresses are low (that's the joy of monocoques) and the holes tend to appear in the least stressed corners. But try repairing a wishbone, or replacing a chassis leg, and you're into a whole different ballgame.
Thanks for that, now I know what you meant. I was in fact taught welding as a factory apprentice, but it didn't run to MIG (well it was 20 years ago!), so I do know something of the theory & techniques, just not MIG. I do now! I was taught by guys who weld pressure vessels!
For heavy stuff I drag out the old faithful stick welder!
Maybe it's just what I'm used to, but when I ran out on a Sunday and my wife bought one of those little bottles of argoshield I found it more difficult.
By reference to the times when I've had to undo my welds. They _are_ strong!
I did the chassis sections on my old LandCruiser (sitting under the jacked-up back end). That was too heavy for my little MIG to cope and I stick-welded it. I have a "soapbox" that won competitions for three years, all welded up out of 25mm and 20mm box sections. A downhill course in a field puts huge stresses on the structure. Nothing ever broke - well not the welds anyway. I bent the back wheels and ended up fitting caravan wheels to a welded-up axle.
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