How difficult is it to learn to gas weld aluminium?

[Bill Edwards]

At work there is a sprayer with aluminium booms. The machine is to be sold but it would probably increase the value if the booms were welded up as they are very badly cracked.
I could do with O/A there anyway for general cutting, heating and thin steel welding but the boss isn't keen on investing in a set.
If I could weld up the spray booms it would probably pay for itself and be very worthwhile, provided it didn't take me too long.

I'm quite experienced at MMA welding (I learned MMA, MIG and gas at college a few years ago) but have never welded ali. I got OK at gas welding - no expert perhaps as my hands are not the steadiest, but perfectly OK - but it has been a couple of years now since I did gas welding.
Will I be able to clean the metal off and more or less jump straight into it without spending hours practicing on the bench first, or is thinking that naive?
The metal is probably around 2, perhaps 3 mill thick and appears to have fatigue cracked. I know I won't be able to do a great job as there is no way to reach the underneath of the weld area to clean it, but provided it doesn't look like a bunch or grapes or be full of holes it'll be OK for this job.

 

[julianthegypsy]

I also learnt to gas weld properly many years ago, but I wouldn't go near aluminium. Amongst the horrors that await you. It doesn't change colour when you heat it, and melts very suddenly. When it melts, because it dissipates heat so well, it won't just be the weldpool that melts unless you're very quick you will have a huge hole where your boom used to be! Others will be along shortly with better input I'm sure, but I wouldn't touch it.

 

[Jan]

If you're talking about fatigue cracks then they will have occurred over a long period of time. As such all sorts of contaminants will have burrowed deep into them. Unless they're cleaned out efficiently the odds are that you'll just be 'papering over the cracks' and the joints will fail catastrophically if/when put under any decent strain. As the seller you would be liable for any injuries or deaths that could occur. Walk away!

 

[hotrodder]

Welding ally, especially with oxy fuel, is often made out to be harder than it is IMO. Personally i'd describe it as different rather than difficult which i suppose is kinda the same deal when new to it as few have it 'click' quickly without a lot of practice or proper tuition.
The flux needed with oxyfuel does a better job than the cathodic cleaning with leccy welding however it's corrosive so the residue needs thoroughly removing afterwoods which'd be complicated if you can't get to the back of the joint. The flux also results in 'sodium glare' so you need proper flux rated lenses to see what you're doing
As said if they're fatigue cracks it might be a waste of time anyway for example dye penning the thing might reveal many many more of them

 

[Bill Edwards]

They have been TIG welded only a few months ago (those welds are fine, these are new cracks) but I know the chap who welded it wasn't happy with it as he couldn't get to both sides.
If the contaminants in the cracks will be a major issue then it would probably be OK to put a strip of ali over each crack instead which would be stronger anyway (something such as http://www.ebay.co.uk/itm/Aluminium...plies_ET&var=450190718284&hash=item232d15b7aa).

I can't seem to find any ali welding goggles on eBay, unless they've a special name? I'm sure a welding shop will have them, but I'd like to get some idea of price.

So, with the correct goggles, flux and perhaps welding flat bar over each crack to avoid welding through the dirt will I get it all done in a few hours, or will I spend the day blowing holes wishing I'd never even considered the idea?

 

[Jan]

A pic or several of the actual item would be of use in determining if that kind of bodge would do the trick. Sadly I doubt it unless the buyer is blind, desperate or careless of his own safety. I still recommend walking away from it - if not running and screaming ...

 

[Bill Edwards]

I'm not that worried about the safety angle as they aren't something that you tend to be under. If they fail then they don't fold up properly as they sag and don't hit the supports/rests very well making it tricky to get together. The other option if they failed in a catastrophic way would result in going over a bump in a field and losing a lump off, probably dragging it behind you by the pipes...

Would welding strips of metal over the cracks really be such a bodge? Think of box section (probably 50mm) with cracks on 3 sides or gone through altogether - a 4 inch strip down each length would surely make it stronger than ever? I'd have thought a potential buyer would pay more for a welded and reinforced boom than one with cracks everywhere.

Of course doing that may be beyond my ability anyway!

 

[hotrodder]

If a bunch of cracks were recently welded and a load of fresh ones appeared afterwoods then it's pretty much a waste of time. Welding gussets over cracks rarely works for a variety of reasons anyway and a strip down each side probably won't stiffen/strengthen it significantly as welding ally anneals it in the HAZ.

As said we need pics to get a proper idea of what we're talking about but it sounds like the booms need replacing

 

[Jan]

If you're talking about box section, then think about the box section (girder) bridges built in the 70's. Particularly the one called the Tinsley Viaduct between Sheffield and Rotherham. It's been taken out of use, braced, uprated, upgraded, repaired, resectioned, etc, etc for decades. Today it's limited to 2 lanes out of 3 and constantly monitored to check for drift, distortion and more on a weekly basis. If it wasn't for the cost and confusion it would cause the whole thing would (should?) have been torn down and rebuilt from scratch.

OK, so we're not talking about anything near the same complexity or load, but the principles are much the same. If it's f*****d then replace rather than repair it.

 

[dannyp]

new clean ali is much easyer to weld than meany people think. with a tig it's a piece of cake and with gas it's not to bad ether.

however when it becomes to repair work the ali is usally FKW grade, as well as being coverd in crud on both side's 1 of whitch you'll neaver reach to clean, the metal will be so deeply contaminated you'll have ground it all away before finding clean metal.

then it ranges from somewhat more intresting to nigh on impossible.

 

[Bill Edwards]

OK, so it looks like it may not be the easiest of tasks. Here are some pictures which may describe it better than I can:





A repaired one, the same as what I'm thinking of doing if possible:



Remember, the machine is to sell - it's an old ('93?) machine built in Britain with several pools of oil under it whenever it is stationary for more than 2 minutes, and with everything just about worn out and dropping to bits. I don't want to do a bodge that'll fall apart, but it doesn't have to be anything special as the rest of the booms (well, entire machine) will be falling apart first. No bodges, but not to the sort of standard you'd normally work to.

 

[Jan]

Personally speaking if it still does what it's supposed to I might be willing to haul it away for my own use (if I had a use for such a machine) and repair it. But there's no way I would bodge it up and sell it on. I may not have much of a reputation, but I treasure and protect what little I do have.

 

[dannyp]

nothing wrong with patching up an old machene to get it working again and selling it on. as long as you sell it as what it is

 

[hotrodder]

To be blunt your chances of fixing that with zero experience of ally are pretty much zero. It's a mute point as knowing that it's been repaired once and just cracked again elsewhere i wouldn't touch it but if i was gonna repair something like that i'd be chopping out sections and letting in fresh metal rather than trying to weld up the cracks and then snotting a gusset over them which creates a new stress riser

 

[Bill Edwards]

Thanks for the advice then, it seems then that it is beyond my ability and may be a bodge.