Bending and annealing Aluminum

[CowboyKell]

I haven't gotten to the aluminum trim on my TD build yet but I have a lot of experience with aluminum both in a past sheet metal profession and in restoring antique aircraft. I have seen very good advice given to questions about bending aluminum trim on the forum but no details on annealing. So, I thought I would share some tips and tricks I have used.

First, as mentioned, aluminum needs to be as soft as possible to make those tight bends that look so good on TD trailers. Anytime you bend a piece of aluminum it will get harder where the bend takes place. This is called "work hardening". A good property of aluminum is that once work hardened it can be re-softened by annealing.

To do a proper annealing takes quite a bit of time and effort. The metal is heated to a precise temperature (usually about 650 deg.) and kept there (soaked) for several hours and then cooled at a slow rate. Well, we usually don't have the time , patience or facilities to do this. So an easier method can be used that gives adequate results. When done properly no change will be made to surface finish.

I try to use a simple plumbers torch, the kind that's a single propane bottle with a nozzle fitted to the top. These give a wider, cooler flame than an oxy-acetylene torch. Heat the metal up fairly slowly and as evenly as you can. On long pieces just the area that needs to be softened is fine. You want the metal to reach 650 degrees for several minutes. Aluminum doesn't change color as it heats like steel. If you get Aluminum too hot you will ruin the finish at best and melt your piece at worst. "How do I know when its 650 degrees?" you ask. The trick I use is a simple 'Sharpie" marker. I make marks all over the area to be annealed. Not colored solid but lots of marks. When heated the marks will change color then "almost" disappear. When the marks disappear (not completely, but you will know) the right temperature has been reached.

This method is not perfect but adequate for the DIYer. Engineers will be abhorred but they would be surprised to see what craftsmen really do when they specify a particular procedure.

[RandyG]

Thanks for the tip. What type of Al do you use this on? Most AC use 2024 or 7075, so do you start with 'O' and end up with something similar to t-3 or t-6?

[michaelrsydney]

Thanks Cowboy

It is a problem that most of the extrusions available here are very stiff. I recently had a lot of trouble bending a J shape as a gutter over a door.

I like the marker pen system... I will give it a try. I did read somewhere of a similar system using soap as a tell-tale. Just rub ordinary hard soap on the job then hit with the gas torch until the soap turns black.. then STOP! I tried this and it worked well. I also experimented with applying a little more heat after the black appeared and it was not long before the aluminium failed dramatically.

I eventually got the arch I wanted using some bending rollers but I think this was the limit without annealing. The roof corner trim on the other hand was nice and soft and was extremely easy.

[Tinbasher]

Good to see another Tinbasher

I was taught that when the aluminium is hot enough to char a sliver of wood or matchstick rubbed on the surface it is at the right temp. Trouble is the best temp is very close to melting point.

Annealing does make a huge difference in workability.

Tinbasher (Tom)

[CarlLaFong]

I have always heard that you coat the aluminum with soot from a candle or a torch, using acetylene only, and then heat it until the soot burns off

[Tinbasher]

In truth is really all about how you hold your toungue

[H.A.]

.

[CarlLaFong]

In truth is really all about how you hold your toungue

That, of course, is of paramount importance, regardless of the job being done

[CowboyKell]

Tempsticks really are the correct way to go. Very precise. You can pick them up at any welding/ gas supply shop.

All the tell tale methods sound reasonable. Might practice on a piece of scrap first.

I don't believe my method ever returns a work hardened area to 0 or full annealed. The temperature reached would need to be more precise and held for a much longer time. But for all practical purposes......


Now for my definition of All practical purposes: If there is a young man on one side of the room and a young lady on the other, and the young man is only allowed to move half the distance to the young lady each time he moves he will never really reach her. But for all practical purposes he will get close enough!

[CowboyKell]

Thanks for the tip. What type of Al do you use this on? Most AC use 2024 or 7075, so do you start with 'O' and end up with something similar to t-3 or t-6?

Truthfully I use it on all alloys (all that I have used, that is). Sheet is almost always 2024, usually used for skin. Structural is usually 6061. Our AI always want the end product T6. How he determines that I don't know. I am not a licensed A&P but help out in my Father-in-law's hanger and do most of the welding and sheetmetal work in his shop.