Hi all
Does anyone know if there's a cheaper way of setting up an Oxy/
Acetylene welding/brazing kit, than hiring bottles from BOC.
I have the rest of the kit - burners, goggles, regulators, hoses, anti-
flashback units, etc, etc - from the last time may late Dad and I did
serious gas welding (circa 16 years ago). Back then, the bottles were
circa =A390.00 in hire charges + =A39.00 for each gas refill + delivery
and handling. A little too expensive for the occasional Model
Engineering use I need now. Trouble is, when you need Oxy/Acetylene
nothing else will substitute (I have Propane/Air torches and the "self-
blowing" Sievert kit).
What's really needed is some supply of the Oxy/Acet bottles on the
same basis as Calor Gas bottles - ie Pay a once only charge when
"signing up" and then just for the gas refills after that.
It's a long-shot I guess - BOC do like their Monopoly - but, if anyone
knows, it'll probably be one of the guys in this group.
Regards
Andy
"houstonceng" wrote
I have the rest of the kit - burners, goggles, regulators, hoses, anti-
flashback units, etc, etc - from the last time may late Dad and I did
serious gas welding (circa 16 years ago). Back then, the bottles were
circa £90.00 in hire charges + £9.00 for each gas refill + delivery
and handling.
You'd better sit down and get a stiff drink.
I have a size J acetylene and size T oxygen.
Last refills about 2 months ago were GBP 56 for the acetylene and a mere GBP
15 for the oxygen.
There was a charge of GBP 10 for the transaction (I think this is the same
irrespective the number of cylinders exchanged).
Rental, if I recall from the last invoice, was about GBP 90 per year for the
pair of cylinders.
I don't know whether it's any help, but I use a 5 l/min oxygen
concentrator with MAPP gas for small stuff. Cost £200-odd second-hand
from fleabay, wait around a bit and you may find one at about that price.
Oxy/MAPP is of course not as good as oxy/acetylene, and it won't power
big torches, but it works ok for welding up to 1/8" steel, and with
preheating and an extra air/gas torch it will braze 1/4" + steel. I
don't need to weld bigger stuff, so it was a good solution for me, but ymmv.
The MAPP gas cylinders seem to last a reasonable time, but disposable
oxygen cylinders don't :( and they are very expensive unless you are
doing occasional micro-work.
Disposable oxygen cylinders are however 3 or 4 times better now than
they were some years ago, giving maybe 20 minutes in a nozzle suitable
for brazing 1/8 steel. Only cost-effective if you only do very
occasional work, however you might want to give them a try - they're not
for me though.
I've often thought of building a small compressor to fill bottles from
the concentrator, but high pressure oxygen is BL**DY DANGEROUS (far more
so than liquid oxygen) and I haven't tried.
You can get a professionally made pump for the purpose, but at a price
(ouch!) and you'll probably have to buy a new, expensive model,
concentrator with it..
Another often-mentioned low-capital source of oxygen is water
electrolysis, but a professionally-made outfit will cost mega$$'s, they
are not particularly cheap to run, and they are only really suitable for
very small torches.
I don't know of any cheap small-scale sources of acetylene, much as I'd
like to - while oxy/MAPP welding is quite possible, it's nowhere near as
easy as oxy/acetylene (though oxy/MAPP is fine for brazing).
-- Peter Fairbrother
I have the current price list for BOC as I would like to have oxy/act set up
again, but certainly not at their prices. I used to swap my bottles at work
and just pay for the gas but I haven't worked there for many years.
These prices are for full sized bottles (W = Oxygen, H = Acetylene);
Monthly Rental: Oxy = £ 8.11, Act = £ 10.40
Annual Rental: Oxy = £ 92.47, Act = £ 118.62
If using Annual Rental, a full years rental is due BEFORE initial supply !!
Gas: Oxy = £ 19.96, Act = £ 77.44
If not paying by Direct Debit an Advanced Payment of £ 75 is required.
Delivery = £ 38.19 inc VAT irrespective of number of bottles.
Collection = £ 12.63 inc VAT irrespective of number of bottles.
Soo, try and work that lot out .... no wonder a lot of companies have turn
away from BOC and Oxy/Act. Most scrapyards for example are now using
Oxy/Propane from other suppliers.
I could give you prices of 'portapack' (small bottles of oxy/act) if you
like but they will still be expensive considering all the different charges
that BOC add on.
Hope this is of use to you all.
Cheers
Brad
On or around Sat, 30 Aug 2008 10:38:29 -0700 (PDT), houstonceng
enlightened us thusly:
I rent 'em from Air Products. not exactly cheap, still, but a lot less than
BOC
"BRAD" wrote
Interesting. I've never seen a published BOC price list and assumed there
are different pricing structures depending upon the user and annual usage.
I'm relatively lucky in having a good BOC stockist locally, and by taking
the cylinders to the agent I avoid the delivery/collection charges.
There is a published price list that lists the rental charges, along with
the refill charges.
They have started doing the 3 and 5 year rentals again, which saves a good
amount of money on rental charges.
Come to think of it, you could make acetylene from carbide.
3 kg of carbide, producing 1.1 cu m of acetylene, costs £20.75, about
£19 per cubic meter: if a H size cylinder costs £77 to refill, that's
about £10 per cubic meter of useable acetylene,
So acetylene from carbide costs around twice as much as acetylene in a
big cylinder - and no rental, more reasonable delivery fees, no return
fees, and available in small quantities.
The problem then is the generator to produce the acetylene. Small
capacity generators are available at around £40-50, but I do mean small.
Apparently you can get bigger generators for welding for third-world
use, but I don't know where from.
Making your own generator? Could be inexpensive, but I don't advise it
unless you know what you are doing, and thoroughly understand the
dangers (for instance it can explode all by itself, unlike propane etc.,
it has wider flammability limits in air than propane, lower flash point,
and more) of acetylene.
-- Peter Fairbrother
My late Dad and his brother had an original Oxy/Acetylene welding kit
(pre-WWII) which used an "acetylene generator" and compressed Oxygen.
Problem is that you have to have a low pressure torch (not a modern
"Saphire" style) as Acetylene cannot be compressed without exploding.
I don't know what the limiting factor is but, IIRC, the torch used
circa 2 psi.
He kept the torch and oxygen bottle throughout the war - don't know
what happened to the generator. When his brother wanted to set-up a
welding kit again, the torch, hoses and Oxy regulator, etc, went to
him. The Oxy bottle which, as I understand it, was owned by Dad and
Unc was, previously to WWII, swapped for a refilled one at an agent in
Carlisle where they lived at that time (ie, no rental). It proved to
be NBG as it was "round-bottomed" and current bottles are "flat
bottomed" so BOC wouldn't even take it away. The regulator wasn't
suitable for current Oxy-bottle pressures either. To cut a long story
short, my uncle did get the torch working with new regulators and such
like, but it was never easy to use with bottled Acetylene - too touchy
on the regulator.
When my Dad and I wanted to do some serious welding, we invested in a
completely new "BOC Saphire" kit in the '60s. IIRC, we had to upgrade
(by exchange) the "new" regulators when BOC increased the pressure in
bottles a few years before I finally cancelled the contract - after
Dad passed to the great engineerium above (1992).
Chemically speaking the limit is 15 psig at reasonable room
temperatures: but you should use a good safety margin, as acetylene is
seldom pure and the impurities can lower the minimum explosion pressure;
and the explosive limit is absolute, ie 29 psia (15 psi plus the 14 psi
of the atmosphere) - however a non-explosive 7 psig torch supply
*should* be possible.
Unfortunately one of the problems with this idea is that the carbide
container is sometimes replenished, and when that happens air is
admitted when it is opened - ouch. The explosive pressure limit for
acetylene with a little bit of air in it can be much lower - a 2 psi
maximum may also be used to limit the damage from an explosion, with the
generator being perhaps built to withstand it.
I don't know what pressure a Sapphire torch uses, but I have a fairly
ordinary balanced torch which welds okay at 4-5 psi with MAPP gas.
(There are two types of torches, the balanced and injector types. In the
balanced type the fuel and oxygen supply are at about the same pressure
and the gases simply mix in the nozzle - in the injector type the oxygen
(usually) is at a fairly high pressure, maybe 40 psi, and the fuel at a
much lower pressure, maybe 1 psi - the nozzle is built so that the
oxygen flow sucks the fuel gas out. I don't know what type a Sapphire
torch is)
-- Peter Fairbrother
"Peter Fairbrother" wrote
FYI I have a Butbro lightweight torch which can take up to no: 25 nozzles
which will weld up to about 1/4" steel.
I've just check my acetylene regulator and the output pressure gauges has
the green sector as being up to 0.6 bar and the red sector starts at 1.5
bar. I believe acteylene self detonates at about 2 bar. When doing heavy
work with the no:25 nozzle I find that I need to have the pressure at the
top end of the green.
And before someone asks, the BOC size J acetylene cylinders are filled to
15.5 bar at 15 degrees C but its disolved in acetone and also I think the
cylinder is packed with asbestos or some other material.
All flamable gases have both a high and lower explosion limit when mixed
with air. Acetylene and Hydrogen are considered the worst, and acetylene in
particular has a very wide band between the LEL and HEL. LELs and HELs are
normally expressed as the percentage of flammable gas in air which will
ignite.
"John" wrote
Just checked the Safety Datasheet for acetylene. The Flammability range is
2.4-88 vol% in air.
By comparison Propane's Flammability Limits are 2% to 11% in air.
It depends on many factors, including the volume and shape of the
container (and the impurity levels). Butbro, and many others, may assume
you only use their equipment and shapes.
The figure I gave of 15 psi is generally regarded as the figure below
which it has never been known to explode.
When doing heavy
That's about 8 psig, still okay.
Yes - and the gas is dissolved in acetone soaked into the porous
contents of the cylinders, rather than being compressed gas.
btw, the porous medium used is "diatomaceous earth" - which
nitroglycerine is also soaked in to make the safer dynamite.
among :)
the worst, and acetylene in
Acetylene has a large explosive air mixture range, as you say later it's
up to 88% acetylene in air, or 12% air - but that's at 0 psig /14psia
(atmospheric pressure): increase the absolute pressure a bit and the
limits change, from 12% air at atmospheric pressure to 0% air at 15 psi.
-- Peter Fairbrother
On or around Sun, 31 Aug 2008 14:25:46 -0000, "John"
enlightened us thusly:
hmmm. tricky. It's all done by direct debit thing, I'd need to find a bit
of paper.
Mind, they recently screwed around with the distribution network. Luckily,
the place not too far away continues to get them as a customer and swaps
them out with their customers, even though they're not a full-blown agent
any more.
Thermodynamic calculations for pure acetylene put it at 274 kPa, or 23.2
psi (= 39.7 psia) for infinite volumes @ 25 C. A Butbro gauge which goes
red at 22 psi is likely taking advantage of small volume factors and
perhaps statistics as well.
I'd still stick by 15 psi for everyday use, with a safety margin.
I do this chemistry stuff in my sleep - not only can I do it, I actually
do do it. I once got 99% in an exam (my chemistry O level), and
furiously demanded my teacher ask the examiners to explain my mistake.
They replied that they had taken off a mark for bad handwriting.
Which was - I don't know exactly what - as I had just recently blown off
several fingers.
When it comes to being infallible, or very nearly always right, as is
required of eg some university professors, things can get weird. For
simple chemistry, for me, it was usually just a question of sanity
checking my replies. No great problem.
But then I became a cryptologist instead of a chemist, and being right
became different. The simple math aspect of cryptology is nice, because
either the math is right or it isn't, forevermore - but the math aspect
isn't everything, and there are scumbags^H^H^H^H^H fellow researchers
who want to find fault in what you do. And who can sometimes even come
up with better math. And of course I try and do it to them^H^H^H^H find
fault with their work too, and am inordinately pleased when I succeed.
And surprisingly often work is just simply wrong, not just insecure, due
to bad math, bad procedures, or bad peer review.
Sometimes you prove someone else's work insecure, and watch them gnaw
their livers - sometimes someone else proves your work is insecure, and
you gnaw your own liver. Which hurts, especially if you have put
yourself on the line.
This is as it should be, as security is about what is actually possible,
not what you, or theory, think is possible.
Nowadays for crypto work, apart from my published papers, I don't try to
be infallible any more in casual talk like usenet.
But for giving practical/engineering chemistry-related advice about a
possibly dangerous situation, I do take care - not that I accept any
legal responsibility, I don't.
But how would I feel if someone followed my advice and lost a few
fingers (been there, done that), or killed himself, or God forbid,
killed some else? Not good. So I try to be accurate, and give safe advice.
-- Peter (beery) Fairbrother
For me, it was the monthly chemistry tests at school. On one of them I got
marked down 4% (one mark). On protest, It appeared that The teacher's
preferred answer to "what is the product of combustion of hydrogen in oxygen?"
was "pure water" instead of the grammatically correct "water" that I had
tendered. I assume that the staff felt the need to knock down the smart alecs
once in a while.
I think it was just the case that O levels were too easy for anyone with an
interest in the way things work. Don't get me started on the modern abortion
of a compromise between CSE and O level. The youngest has just done his :-|
Mark Rand
RTFM
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