I had one of those "Doh!" moments this morning...

Last weekend I had to bend some aluminium channel (windscreen frame) and had quite a bit of bovver getting it annealled correctly. Tried rubbing soap on it - it disappeared before turning black. Tried rubbing the safe end of a match on it until the woodstarted to char and leave a black mark - sort-of worked.

Now I remember that I have a Maplins remote IR thermometer... Doh! It's accurate to a few degrees and, apart from having to make an adjustment for the metal's shiny surface (it's calibrated for a dark surface) very easy to use.

So, the question is, what's the annealing temperature for aluminium alloy? Oh - and what's the melting point, just in case?!

I don't know the answer to your question, but....

The shinny thing is one problem, and the fact that these IR things only go to 200deg C is another.

I had some issues with this on my exhaust headers/manifold.

To solve the shinny problem I painted with VHT paint first (just a little square).


Matt

The way i was tought to do it for 3mm sheet was to dust it over with just the acetalyne turned on which leaves a layer of soot. Then turn the oxy on and when the soot burns off the plate has got hot enough. No idea what the actual temp was though.

Hi

A general rule of thumb is to cover the area being warmed with a block of soap.

When the soap turs brown & starts to blister. The alloy has reached the correct tem and is ready for bending.

By that, i do mean, smear the area with a soap block
Don't heat up the block of soap

[Edited on 21/7/09 by bonzoronnie]

An extract from Azom.com.

Annealing is carried out in the range 300-410°C depending on the alloy. Heating times at temperature vary from 0.5 to 3 hours, conditional on the size of the load and the alloy type. Generally, the time need not be longer than that required to stabilise the load at temperature. Rate of cooling after annealing is not critical.

Mike

[Edited on 21-7-2009 by miikae]

Hi David. This looks a good article.

Hi,
Use a black marker pen on the panel, then warm it up until it disappears!

bonzoronnie method is the way I was taught, any hotter and the alloy melts.

Hmm - as said above - I tried soap and it disappeared before turning black.

Good point about the IR thermometer's upper limit...

The oxy-acetylene would be good - if I had it in my workshop!

Ah well - another good idea flushed down the WC pan of life...

Hi David,

Anneal 350 - 400C

MP 659C (pure)

I use the soap method.
Always mark the underside so you don't play the flame onto the soap mark,
or mark either side of where you heat and let the heat creep along the bar to the marks.

In saying all that I've just done mine, no need to anneal, just bent it, but then again I am a big strong boy.

Cheers
Paul G

p.s. A useful book to have is A C Davies, The Science and Practice of Welding.
Look it up on Amazon
Rescued attachment windscreen-frame-s.jpg

when back in school we used to put washing up liquid on it.

IIRC it went black when at the right temperature.

If you wanted to borrow my jigs David you are more than welcome.


Cheers
Paul G
Rescued attachment WS-jigs-s.jpg

Thanks Paul, but mine are all done now.

Hi ,all the tips the guys gave will work however it will remain in the temper state you heated to ,
At work i have to make some complex shapes in alu there are different temper rates of alu and different alu mixes dependant on if you want sheer or tensional .but for your screen frame you should go for some 2024T0 and the thinnest gauge you can get away with ,at temper rate of 0 the alu will be soft to work with shape to your screen frame this will then have to be heat treated to your desired temper rate 6 would be fine for your frame these treatment times are on the net .good luck vin

I used a red marking pen (Sharpie) and heated with a hand held propane torch till area marks disappeared and Voila! easy bend.
regards