Bending aluminium flat bar

[Eric The Viking]

I have just bought some 2" x 1/8" extruded aluminium bar for a project up on the roof. It's a cover for a butt-join between two solar panels, and ideally I need to put a right angle into it, bending one end over, so it covers the ends of the join too.

The metal factor said it was "heat treated" extrusion, so would be hard to bend without fracturing.

Is this likely? I've never heard of it before with aluminium, but my experience is very limited. Admittedly, although I've worked aluminium sheet before, I've never bent anything 1/8" thick. I have enough spare to experiment with, and it doesn't have to be a tight radius either (well, not very). Probably 1-2mm round the inside radius would do it.

Is there anything I can do to ensure I get a good bend , for example heating it (I have propane and MAPP gas)?

Worst case I can simply cut it and use it as two plates at right angles, but sadly I haven't any way of welding it (MIG set but no suitable wire nor shielding gas). I'd rather use it in one piece as it would be more waterproof - important on the roof.

Any thoughts appreciated.

TIA,

E.

 

[chiokli]

You can anneal the aluminium before forming. I put a layer of liquid soap or Fairy Up liquid on the surface so I can see when it has reached temperature from the blowtorch (it'll bubble, go white and dry out). At that point you can quench it with water and it should be more pliable for cold bending. Heating it before bending won't help, it behaves differently to mild steel. 3mm thick is perfectly possible to clamp sturdily (with a piece of square steel on the inside as a right angle die) and bend it with a mallet.

Clamp the short end and bend the long end and you should be fine. If it starts to display signs of cracking or fatigue, you can repeat the annealing process to mitigate it.

 

[Sideways]

First point is to say that I have no experience of this at all, but the recommendation to cool the aluminium in water after heating sounds questionable. I do know that quenching steel in water makes it hard and brittle and this sounds worryingly similar.

Here is a recommendation lifted straight from the web that supports the advice about heating but says that cooling should be done slowly.

The Annealing Process
Above you can see the areas which are to be bent are marked with permanent maker. The trick with annealing Aluminium is NOT to melt the metal. The temperature for annealing is so close to its' melt point that it's easy done.

If you look closely you can see that in some areas the permanent blue marker are beginning to fade due to the heat burning the marker away. Coincidentally, when all of the permanent marker has been burned off, you have reached to correct temperature for annealing this material. Other systems metal workers use as an indicator for annealing Aluminium; to cover the joints with bar soap and burn the soap to brown or applying a smokey carbon surface to the metal with a candle flame or oxy torch and burning all the carbon away.

When you have reached the correct temperature and burned the permanent marker away, let the metal cool slowly. If the Aluminium is quenched the metal will not necessarily regain its' strength, but it will become brittle.

 

[AES]

+1 to both the previous posts.,, but with a couple of additional cautions.

Yes, there is such a thing as heat treated ali (usually done in an induction furnace to toughen it - a very carefully controlled heating and cooling process involving several cycles).

For "home work", using the soap as a temp indicator is a good idea (wait until it turns a chocolaty brown). I don't like the sound of water quenching, IMO that's bound to raise stress cracks, if not during the cooling process then during the bending. I've always allowed heated ali to air cool naturally (takes longer than you may expect).

For the actual bending, try if at all possible NOT to go for a sharp bend - for 3 mm stock a 3mm bend radius (minimum) is good. To get this if bending in the vice, just rig up a piece of 3 mm dia bar in the vice against which you're going to bend (3 handed job, so use a bit of sticky tape or something to get the bar, the job, and the vice jaw nicely aligned).

Also, if at all possible, do NOT use a hammer, but bend by hand, if necessary using a scrap wood block to extend your leverage. Shock blows, especially after annealing ali are NOT a good idea.

If the job is wider than the vice jaws, MUCH better to rig up a pair of temporary bending bars than trying to bend in 2 goes by moving the job along the vice as you go. The jig is just simple 2 straight lengths of hard-ish wood with a nut and bolt at each end. Put a 3 mm radius on the edge you're going to bend against.

If that 3 mm radius is a problem on this job, you COULD think about reducing it, but take it easy.

If you cannot allow any radius on the bend for this job, then sticks of that ali "welding/solder" stuff DO work surprising well and could get you a sharp 90 degree corner. A normal blowlamp of any sort (as you have), a CLEAN Stainless Steel wire brush, the SS "abrader" (thin SS wire) and the above soap trick should get you there. I've done it myself and it does work rather well, but I'd strongly advice practice on similar sized scrap piece first.

HTH, good luck.

 

[chiokli]

Ah, it was my understanding that quenching aluminium had no micro-structure phase change on cooling because it has only one phase, unlike carbon steel which has several. I generally cool aluminium and copper in water after annealing to just speed things along without any noticeable affect. I will say that my experience has mostly been with general aluminium of the 1000 series (1050 I think) and nothing super alloyed. I will always defer to greater experience in the world of work hardening.

I will echo AES's sentiment that sharp bends can invite weakness, though this doesn't sound like a structural application, more cosmetic?

I have brazed aluminium successfully with Sifalumin 15 and Sifbronze aluminium flux using a gas torch tentatively to make a water tight structure. My earlier attempts did result in the material melting at the corner, but worth the practice!

 

[Eric The Viking]

Thanks very much, all of you.

Yes, it's not structural. I'm fitting two pairs of solar (water) panels, where previously they were mounted as four separate ones. This strip replaces a pair of L-section cappings along the adjacent sides, sealing the gap between (probably with a lot of goo underneath it!).

At the top of the pair of panels, I want to turn the strip over the edge, so that it also covers the thickness of the panel boxes. It's for waterproofing mostly (also helps them to stay neatly together).

I think a 3mm radius should be fine - it's only really to help shed water in the heaviest of rainstorms.

The panels are 2m tall (boxes are around 2060mm). I have 2.5m lengths so plenty to experiment with. I only have to make two bends altogether, identical pieces "L" shaped with the bend around 75mm from the end.

I can't work outside at the back right now, because the washing is out (back garden is full of scaffolding and piles of stuff off the roof, and all the flowerpots displaced from where the scaffolding is presently).

I'll be allowed out again in a couple of hours so I'll see what I can achieve simply by heating (+ washing-up liquid), cooling and bending gently with vice plus rounded hardwood jaws.

Before anyone suggests it, it's more'n'my life's worth to take the washing in myself, as it definitely "won't be dry". You know how these things work...

Thanks again - I'll report back

E.

 

[AES]

Ah chiokli, I do NOT pretend to be any sort of specialist when it comes to metallurgical grain structures, just basic practical experience (hobby mainly) and what I learnt as an apprentice (aircraft engineering).

There are 2 variables here, as you suggest - first whatever actual alloy it was that the manufacturer "cooked up" to meet the required spec; and secondly, whatever the specific heat treatment actually ended up producing in terms of material properties (again to meet a specific requirement).

As you clearly appreciate, referring to aluminium ("ali") as just ali is about as informative as talking about "a piece of wood". But it's what we hobbyists are all forced into doing 99% of the time (especially if like me, you go looking in allsorts of skips &things)

.But assuming the OP bought it over the counter somewhere, it's fairly safe to assume that it although wasn't too exotic an alloy, even though it was then extruded, it WAS apparently heat treated afterwards for some purpose (AFAIK, ali can only be heat treated AFTER extruding, but stand to be corrected).

Anyway, I believe that when dealing with "any ali", it's best to treat it with a certain amount of caution, especially if A) heating (which is probably necessary here to get his 90 degree bend), and/or B) bending.

BUT a common factor to just about any type of ali is that it will work harden and become (generally speaking), more "brittle", both after heating and after bending. Hence my caution about no water quenching - it MAY well be OK, but just as/more likely, not OK.

And again the reason for my caution about bending around a radius at least equal to the stock thickness.

As you say, I too got the impression from EtV's OP that this job is more cosmetic than structural, but as it's for a solar panel (so presumably high up, like on a roof) I wanted to give the OP the best chance of not having to go up there to fix it because it's broken loose in a gale or something.

 

[Eric The Viking]

Absolutely - this is a fix for a failed original mounting system, and it's quite expensive enough already. I could almost install a new solar system for what it's costing (we're doing other stuff at the same time on the scaff though).

[aside] It's infuriating that truly green water heating, rather than electricity generating, doesn't get adequate subsidy in the UK. My system went up before there were proper subsidies, and the manufacturer went bust as soon as the electrickery scam started, as everybody wanted "free" electricity. The actual energy collection system has performed very well indeed for 15 years, and I'm putting it back as there's pretty much nothing to fail - extremely reliable.[/]

 

[chiokli]

Admittedly, most of what I know on this subject is through study and personal development. Though it can't be said that what works for one person will work for another. I have numerous coat hooks and the like around made from 25x3mm aluminium flat bar that I just clamped into my metal vice and bent over with shear force of will. I will say that this method only allows you one try (due to the work hardening). 50mm wide in Eric's case is a much larger beast.

I think you're set up for a successful run and wish you the best!

 

[hawkeyefxr]

Do not pull a tight bend with Ali it will crack. Pull it around say a 25mm bar or dowel, you need to make a radius of the bend. By all means heat it and let it cool naturally till cold.
As for steel you cannot harden mild steel, it needs carbon in it to make the metal hard. You can 'case harden' it but this is a bit of a tricky process, the steel has to be quite hot, way hotter than cherry red. It's then put into the casenite ( which smells like cats piddle at this stage.
You then need to heat it up again to a near white heat, it's then plunged into cold CLEAN water. It should make a loud crack as it's dropped into the water.
Did quite a bit of this in my apprenticeship. We also had HSS steel which we made press tools with, when they were all assembled we would break them down and harden the HSS steel to either a cutting edge of a forming tool for bending smallish sheet metal parts.
Showing my age now lol.

 

[Eric The Viking]

I did have some success actually.

I tried yesterday, first heating using MAPP gas, played over a couple of inches of the bar either side of where I wanted the bend, using washing up liquid as a telltale*. I didn't quench, but I did let it thoroughly cool in its own time (an hour or so to be sure).

I clamped it tightly between two steel blocks, the lower one having a slightly rolled edge, and used a third steel block/plate to start the bend, mainly because I needed mass.

I managed a slow bend with about 1-2mm radius, which will do fine. I had difficulty getting the right-angle I need, so after consideration resorted to a Thor rawhide mallet, which let me tidy up the bend and set it as tight as I possibly could (bend beyond 90 then pull back to square it up).

It'll serve nicely.

Thanks to all.

E.

(*I didn't realise you could actually set fire to washing up liquid!)

 

[AES]

Glad it worked OK re the bend EtV.

Just FYI, I didn't know washing up liquid burns either! I collect the nearly useless/nearly gone bars of soap from the bathroom and after wetting a piece I use that as my tell tale! Useful when driving in screws too.

 

[Eric The Viking]

Fascinating actually: you boil off the water, then you get a smoky yellow flame that persists when you remove the heat. It leaves a sooty patch on the surface too. Asda's finest Fairy liquid copy...