how to anneal aluminium gates after welding

[s410man]

Have a job to do making a load of 6 foot by 4 foot alu gates

They have to remain flexible after welding so I'm going to have to anneal them somehow

As there will be loads is there any places about with a big oven as i don't really want to heat every weld with oxy acet!!

If it can be done for a reasonable cost will be repeated every few months approx 100 gates at a time

I know they've got to be heated until soap turns black but struggling to remember how hot that is!!-380 degrees is in the back of my head somewhere? ?

Gates are apprix 8 kgs each don't mind travelling

Cheers

 

[bigegg]

Powder coating place?

 

[Chris Stevens]

Have a job to do making a load of 6 foot by 4 foot alu gates

They have to remain flexible after welding so I'm going to have to anneal them somehow

As there will be loads is there any places about with a big oven as i don't really want to heat every weld with oxy acet!!

If it can be done for a reasonable cost will be repeated every few months approx 100 gates at a time

I know they've got to be heated until soap turns black but struggling to remember how hot that is!!-380 degrees is in the back of my head somewhere? ?

Gates are apprix 8 kgs each don't mind travelling

Cheers

What cost have you added to the job to cover the annealing process? I would guess getting the job done properly is going to be fairly expensive, and I be very careful about providing any sort of price quotes without figuring in heat treatment costs. Might be less costly to alter the design, so heat treatment isnt needed?

 

[TechnicAl]

Annealing will soften it. That doesnt mean its flexible it means it bends very easily
Are they sure they want them annealed?
Ive never heard of gates being annealed

What grade Aluminium is it?

 

[hotrodder]

Welding aluminium locally softens it. Depending on the flavour of ally the welds & HAZ are already gonna be partially to fully annealed

If the gates were made from extrusions (box, tube etc) then they'll almost certainly be a 6xxx-T6 (either 6063 or 6082), annealing temp is 413°C and while simply heating them to/beyond that temp softens them noticably to really anneal them they need soaking for an hour or 3 and controlled cooling down to ~200 - 250°. Simpler/non heatable flavours just need heating through, temp is either 413 again or 340ish depending on flavour. The soap (or soot, or permanent marker) trick is close enough when you just want to soften the part so it can be worked more without cracking

Like Al i can't understand why anyone would want to anneal some gates... have they had problems with them cracking in the past?

 

[s410man]

They are for handling sheep so will constantly be being pushed and nudged

The commercial ones are annealed so I'm guessing they do it for a reason

 

[TechnicAl]

They are for handling sheep so will constantly be being pushed and nudged

The commercial ones are annealed so I'm guessing they do it for a reason

Sorry but I had to laugh

 

[Sarto]

@TechnicAl
Could you explain a little in more depth?
This thing is interesting. And sound strange to me too.

 

[TechnicAl]

@TechnicAl
Could you explain a little in more depth?
This thing is interesting. And sound strange to me too.

To be honest Hotrodder is the man for Aluminium

 

[hotrodder]

I didn't look very hard but can't find any reference to annealed sheep hurdles/gates. This example mentions the exact opposite http://www.rappamobileyards.co.uk/

All aluminium is of a high grade and a heat treatment added to give further strength and durability

which suggests they're either using common 6xxx extrusions (dirt cheap but more complicated/expensive to heat treat properly) or something like 7020 which is typically unobtanium as tube unless you pay for several tonnes to be extruded but doesn't need a solution heat treatment to 'repair' the damage caused by welding. It age hardens reasonably well by itself or for better results just needs a precipitation heat treatment to artificially age it [/gross generalisation]

Basically heat treatable aluminiums are supersaturated solid solutions. Just like you can dissolve more salt or sugar in hot water than you can in cold the solubility of the alloying elements and the intermetallic compounds* they form varies with temperature. As with the water + salt thing if you let the aluminium cool naturally the excess alloying elements come out of solution in an uncontrolled manner and don't do anything particularly useful. If you heat the lump of metal up then at some point above the solvus temperature (and sometimes fairly close to the solidus temp, above which it starts to melt) and hold it there for a few hours all of the alloying elements dissolve. If you then quench it they don't have time to precipitate out resulting in a supersaturated solution at room temp. The excess still wants to escape but it's now a lot more difficult so they precipitate out as tiny, miniscule grains which fill in voids in the crystal structure making the metal harder/stronger

Depending on the flavour of ally this precipitation (aging) can happen fairly quickly producing a stable alloy in a few days or it can take a loooong time. In the later case things can be sped up by increasing the temp a bit which is what artifical aging / precipitation heat treatments are about... something that takes months or even years to age naturally can be done in say 8 hours at gas mark 4
As an aside some flavours some flavours age so quickly there properties can be taken advantage of another way. 2017 or 2024 icebox rivets are a good example, they're stored in a soft condition at low temps to stall the aging process until they've been bucked

If you still want soft gates then i'd try and find a supplier that can sort you out with some 5083-O tube/pipe as it's already annealed. Your average stockholder usually only carries 5083 as shate and plate and in either case it's usually offered as 5083-O or 5083-H111 which means it was lightly rolled or whatever after annealing which resulted in a little strain/work hardening
Mechanical properties wise probably fairly similar/not much softer than 'as welded' 6xxx series

I still don't get the need for either PWHT or annealing gates... whoever is responsible for carting the things about, erecting them, packing them up etc would no doubt prefer PWHT as for a given strength they can be lighter. 'As welded' is probably a chunk more attractive to whoever is paying for them. If farmers and/or sheep regularly break the things i'd wager it's welding and/or design flaws most of the time if this is fairly typical

hardened, annealed or as welded it's not gonna take much repeated abuse to damage/break that... hardened will probably crack without bending much, annealed will probably get mangled and as welded somewhere in the middle; say lightly mangled and then cracks when someone tries to straighten it


* for example magnesium silicide (Mg2Si) for the 6xxx series alloys

 

[s410man]

@hotrodder bloody brilliant info there mate some a bit over my head but i can't help being a bit thick !lol

There is a video online somewhere of one of them mobile yards where they pull about 10 gates out in a line and secure each end

Then then push in the middle until it is lay down flat on the floor and telease and it springs back perfectly straight to demonstrate how flexible they can be without breaking

So would you recommend i just make a few and see how they age over a few months??

And start with a 6... grade??

 

[Welderpaul]

Are you working to a specification written by some lunatic?

It's a 'walk-away' job.

 

[gaz_moose]

sounds like they should be made out of rubber.

I agree with Paul on it being a thanks but no thanks situation.

 

[hotrodder]

There is a video online somewhere of one of them mobile yards where they pull about 10 gates out in a line and secure each end

Then then push in the middle until it is lay down flat on the floor and telease and it springs back perfectly straight to demonstrate how flexible they can be without breaking

So would you recommend i just make a few and see how they age over a few months??

And start with a 6... grade??

Cheers. The vid sounds as much like a good bit of marketing as anything to me if i'm picturing it right? With each end secured there's 60 odd feet free to move when you push in one spot? Grab a 5m length of tube and it's pretty easy to flex it a fair distance elastically, a 0.5m offcut of the same material is either impossible to bend by hand or won't move very far before taking a permanent set. Metals behave both elastically and plastically, they bend (or stretch etc) elastically until the yield strength is exceeded and if you carry on bending them past this point they deform plastically and stay bent. The small amount of springback that occurs when bending sheet or tube is a result of the elastic behaviour
Annealing lowers the strength so it's easier to exceed the elastic region and bend things permantly. Hardening/strengthening does the opposite so it takes more force to permantly bend

Like Paul and Gaz i'd be inclined to run away, obviously we haven't got the full story but it's sounding like the client is hard work/may have unreallistic expectations?
For a sample/test panel it's gonna be relatively difficult and/or expensive to find any round or square tube in anything other than 6082-T6 and 6063-T6 as that's all most stockholders carry with a much wider range of sizes in the former. If there's a choice in the size you're after then 6063 is a bit more formable but depending on bend radius/tube size vs wall thickness may still need locally annealing to bend cleanly. Obviously at the moment we don't know if you're bending round tube or cutting up and welding square tube etc

 

[Kent]

Sheep hurdles! Have you seen what they actually cost!! need to talk money upfront on this job mate - I bet it goes away real fast

The whole annealing thing will have come from some stupid Chinese sales BS. Sometimes with their capacity for deceit and their lack of English.....

 

[rikrobson]

why are they not galvanized steel? Do they need to be light?

 

[mr migwire]

£14 quid each from ebay for galvy hurdles....

 

[norlander]

Sheep hurdles! Have you seen what they actually cost!! need to talk money upfront on this job mate - I bet it goes away real fast

The whole annealing thing will have come from some stupid Chinese sales BS. Sometimes with their capacity for deceit and their lack of English.....

You lost me there. He is in Wales. Is he exporting sheep hurdles to China?? Or is he making sheep hurdles in Wales for a Chinese company??
Or, is he making hurdles for imported martial arts trained Chinese sheep?

Whatever, I'd check somebody has not confused annealing with anodising

and their lack of English.....

Way things are going, lack of the Chinese Language might be a problem for some

I would not be suprised if the spec for the gates had not come from MOD though

 

[Screwdriver]

Haha, I think it's an English company exporting gates to Wales when they have some Chinese sheeps. They are delicious but after you've eaten one you still want another.

Agree, I guess the client really wants these gates anodised!

S.

 

[s410man]

Yes they have to be aluminium for weight as the idea is you geab hold of one which is linked to approx 10 more and your able to walk backwards and pull the whole lot out into a line something which would be impossible with steel gates

Going back to facts not myths now....

When queried i have now been told they are "heat treated " for strength and to resist cracking

Different to what i was initially told but that's customers for you eh

Nothing off the shelf is available to this exact design so it will be a well paid job so not worried about cost to a degree...

Any idea what this heat treatment could be? ?

Is anealing likely to be a part of it or??

Thanks for all the help so far I've learnt a lot even if the job doesn't come off for any reason! !

@hotrodder