More on oil-cooled welders and 4 mm rods

Hi all,
Thanks for the advice I received a couple of weeks ago on the subject of oil-cooled welders. This last weekend I burnt a couple of pounds of 4 mm
electrodes, mostly welding fillets on 3 mm and 5 mm steel. I tried both 6011 and 6012 "Weldrite" brand electrodes. I tried to get hold of some of the Murex electrodes that Tim recommended but the welding store didn't have them in stock. I used my Cytringan "Bantam" welder, which is very similar to an Oxford. It provides up to 180 A at 50 V OCV and up to 120 A at 80 V OCV.
The advice I received at the welding store was that some small welders might struggle with 4 mm 6011 electrodes, but that an Oxford-type machine stood a good chance of coping. My machine seemed to cope with running 4 mm 6011 electrodes on 5 mm steel with good penetration. It didn't seem to be struggling either. The 6011 electrodes ran very nicely at 120 A and quite acceptably at 110 A (both at 80 V OCV). My welds looked okay. I still haven't quite mastered the art of a perfect restart and a neater crater fill at the end of a weld, but I guess they're just a matter of practice.
If anything my machine seemed less happy running 4 mm 6012 electrodes, which wasn't what I had expected. Both 4 mm 6011 and 6012 give a recommended current of 120 A to 180 A. The identical current recommendations puzzled me a little as I thought that rutile electrodes needed more current than cellulosics. But 6012 only needs an OCV of 50 V, whereas 6011 needs 70 V, so it gives me the option of running at up to 180 A on my welder. I found that I had to run the 6012s at 165 A to 180 A. Apparently 6012 has a sodium binder rutile coating whereas 6013 has a potassium binder rutile coating. As far as I could tell 6012 welded very much like 6013. I bought them mainly because they were cheap (£8 a box) and I was curious to try them.
I also tried running 4 mm 6012s at 120 A and 80 V OCV. This was useless. There was nowhere near enough power. Obviously 120 A at 80 V OCV doesn't give the same power output as 180 A at 50 V OCV. Presumably the voltage once welding has started sinks to a similar value whether you're using the 50 V terminal or the 80 V terminal. I wish I could find a good explanation of how an Oxford-style AC welder works. Does anyone know where I might find one? Maybe I'll end up taking my welder apart sometime. I still haven't got round to fixing the broken internal battery charger and this would give me an excuse to look inside.
I wasn't sure that my welder was entirely happy running at 180 A and 50 V OCV. I wonder if it is perhaps suffering from the voltage drop across the cable from our house to the shed? It is perhaps 40 m of 2.5 mm2 cable (not laid by me, I would have laid a bigger cable). The supply is single phase. This raises the question of whether the shed power supply would cope with a bigger welder. Last week I saw a couple of Oxford RT300 300 amp machines advertised in excellent condition at prices between £75 and £149. They sound like good deals, but there's not much point in having a welder that's beyond the capabilities of our power supply. I must say that I like the 4 mm rods. They burn down more slowly, allow better control of the welding and fewer restarts. So in a way I am tempted by having the capability to run 5 mm rods, but it does seem that for my intended projects with 6 mm steel my 180 A "Bantam" set will be adequate. If it copes with 5 mm steel in the single pass without struggling, I can't see it failing to cope with 6 mm.
But I wonder if I should get some kind of fume extractor. I can't use more than a couple of electrodes in the shed, even with the door open, before I have to leave to let the smoke disperse. I could do with a centrifugal fan as used in laboratory fume cupboards. Unfortunately I passed on one a few months ago because I didn't realise I'd need it. It always happens, doesn't it? I feel that it ought to be the kind of thing I should be able to scrounge from a demolition site, because there must be hundreds that get tossed every year, and they're pretty expensive new.
Thanks for the advice. Comments and thoughts are welcome!
Best wishes,
Chris
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On Wed, 11 Oct 2006 03:59:11 +0000, Christopher Tidy

Perfect restart? What's that? <G>

I'm no expert on American rod specs, but I don't think there's anything in the 6011,2,3 etc which specifies the type of flux. AFAIK that's a choice made by the manufacturer. please correct me if I'm wrong.

I ran my 180A Oxford for years at the end of 200m of 6 sqmm cable, voltage drop rather than the set was definitely the limiting factor as regards welding current. It's now 16 sqmm cable over the same 200m, there's still a significant voltage drop. Without actually doing the sums, I'd say you would be limited by your cable more than by the present set.

Unfortunately welding fume extractors seem to be silly money for what they are. Welding fumes aren't good for you. As well as trying to disperse the fumes, try a fume mask to reduce the amount you're breathing. There are disposable ones available.
Cheers Tim
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Would the voltage droop mean the 50V terminals are more effective, as there is a bigger ration between input and output?

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html assuming your welder is 50V and 180A -> 9Kw power (might not be correct, but reasonable guess?) then for 40M run you should be using 10mm sq cable, and that would give a 3% voltage drop. With 2.5mm you can probably only pull about 3Kw?

Try an old/cheap cooker hood, (possibly with charcoal filters). Not as effective aas a real welding extractor, but certainly an improvement. I use one for OA welding extraction (not as much smoke, but lots of soot...)
Dave
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Tim Leech wrote:
<snip>

Just something you kick yourself over every time you fail to achieve it!
<snip>

I was under the impression that the number does offer a basic description of the flux. I also remember reading that the core wire used in all the 60xx and 70xx electrodes is the same. However, I can't find a full explanation of the AWS numbering system online. The best I can find is this Usenet post by Mike Graham:
http://groups.google.com/group/sci.engr.joining.welding/browse_thread/thread/d49abb7cf6042b96/a7d53dd260054677?lnk=gst&q=aws+numbering&rnum=1#a7d53dd260054677
Perhaps someone more knowledgeable could confirm this?

I think I probably am suffering from the voltage drop to some extent. 40 m of 2.5 mm2 cable won't be as bad as 200 m of 6 mm2, but I think it is affecting the machine at the higher current settings. I measured the welder's OCV: 55.2 V and 83.3 V. This seems okay, but of course it doesn't indicate how large the voltage drop is once welding is in progress. The welder is provided with three input terminals: 240 V, 415 V and 440 V. The presence of both 415 V and 440 V terminals suggests to me that performance is fairly sensitive to the input voltage. This is probably another good reason not to buy a larger welder. Besides, if you can do most of your narrowboat work using an Oxford 180 A set, I should be fine doing some smaller fabrications with 6 mm thick steel.

I saw this machine on eBay recently which didn't sell:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item 0033948957
Any idea if it's suitable for welding fume extraction? Unfortunately it's three phase, but I'm sure I could rig up a circuit that would allow it to work.
Thanks for the advice.
Best wishes,
Chris
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Christopher Tidy wrote:

Rather puzzled why you feel a need to use 4mm rods when welding 3 & 5mm steel, 3.2mm rods would be more than adequate.
Tom
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On 11 Oct 2006 01:52:50 -0700, " snipped-for-privacy@bem.fki-et.com"

It won't be 50V and 180A at the same time, the 50V is open-circuit, the 180A is pretty much short-circuit. It might be as much as 6KW.

Sounds like a good idea.
Tim
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On 11 Oct 2006 01:52:50 -0700, " snipped-for-privacy@bem.fki-et.com"

Just checked for my 200m run, it comes back with 'no suitable cable available' for anything over 3 kW :-(
Tim
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Tim Leech wrote:

What works and what's officially recommendable are often quite different!
Best wishes,
Chris
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Depends on the electrode. Some need scratching, some pressing others pecking. Nasty ones want just a gentle touch.

Two tactics: * continue welding without moving (even a bit back) * interupt welding for a second or so and then restart (see above :-). If you're welding very hot, you might need some restarts to let cool down the puddle.
HTH, Nick
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Nick Mόller wrote:

Thanks Nick. I'll try those.
Best wishes,
Chris
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Tim Leech wrote:

Hmm, yes of course... back to school for me Dave
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wrote:

using
you
as
improvement. I

Arc voltages when welding are remarkably constant at about 20-25 v
AWEM
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On Wed, 11 Oct 2006 16:48:01 +0100, "Andrew Mawson"

A significant point is that the voltage drop between the 50V or 80V open circuit voltage and the 20-25V arc voltage occurs in the separate choke or built in leakage reactance of the welder. so although it might only be pulling 3kW, it could well be pulling 9kVA. transformer Welders have _nasty_ power factors.
Mark Rand RTFM
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On Wed, 11 Oct 2006 17:19:17 +0100, Mark Rand

Power factor correction capacitors used to be available as an option for Oxford style sets, maybe they still are, but I've only ever seen one with them fitted. Presumably inverter type welding sets can have a better power factor, and so in theory would do better on the end of a long cable than a straight transformer type?
Cheers Tim
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On Wed, 11 Oct 2006 17:19:17 +0100, Mark Rand

Just checked the rating plate on my TIG set (transformer type), it gives PF of 0.6, and 10 kVA, at 150A output (TIG or stick)!
Tim
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wrote:

Persakley :-)
Mark Rand RTFM
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Tom wrote:
<snip>

The 3 mm and 5 mm steel just came out of my scrap bin for the test. I want to use 6 mm steel for my next project, and also get decent penetration in a single pass without too many restarts, which was why I tried the 4 mm electrodes.
Best wishes,
Chris
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snipped-for-privacy@bem.fki-et.com wrote:
<snip>

I'm not sure. It seemed to be the other way round: i.e., the 80 V terminal seemed more effective (although I wasn't using the same current setting on both terminals).
<snip>

I'll look out for one.
Best wishes,
Chris
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Tim Leech wrote:

It says 5 kW on the machine. I assume that's its continuous rating. The intermittent rating might be higher.
Best wishes,
Chris
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On Wed, 11 Oct 2006 03:59:11 +0000, Christopher Tidy
(snip)

Chris     Please consider your language when using this public forum. My wife and young children occasionally look over my shoulder and I have enough trouble trying to persuade them that the Viagra ads and penis enhancement spam which floods in is nothing to do with me ...to have to protect them from words like 'shed' is just too much. The proper expression is 'workshop'..........! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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