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Is it worth making a Metal Sandwich?

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Is it worth making a Metal Sandwich?

Postby adama » Tue Jun 19, 2012 2:46 am

I have two spun copper pots (about 50L each) that I could join together to make a boiler.
Something a little bigger than what I currently use.
The boiler will be heated with gas.

What about the idea of making the base of the boiler thicker by putting a disc of 5mm aluminium plate on the bottom and then covering that over with a (spare) sheet of copper.

In my case the materials are free – it would just be the job of tacking this “sandwich” together on the bottom of the pot.

Does anyone know if it’s worthwhile doing?

The idea is to spread the heat from the gas flame more evenly, as well as making the (seemingly thin) pot more “robust”.

(Currently I use a keg boiler connected to the VM column.)
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Re: Is it worth making a Metal Sandwich?

Postby myles » Tue Jun 19, 2012 3:10 am

No reason not to laminate the bottom but I am not sure about your choice of materials. As you are just trying to dissipate the heat of the burner a thick copper sheet would be 1 choice - just an expensive one.

How about a spiral of copper tube (left open to atmosphere at both ends for expansion) as the filler between the 2 sheets of copper? Evem heat distribution at not too great a cost.
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Re: Is it worth making a Metal Sandwich?

Postby Harry » Tue Jun 19, 2012 3:24 am

adama wrote:I have two spun copper pots (about 50L each) that I could join together to make a boiler.
Something a little bigger than what I currently use.
The boiler will be heated with gas.

What about the idea of making the base of the boiler thicker by putting a disc of 5mm aluminium plate on the bottom and then covering that over with a (spare) sheet of copper.

In my case the materials are free – it would just be the job of tacking this “sandwich” together on the bottom of the pot.

Does anyone know if it’s worthwhile doing?

The idea is to spread the heat from the gas flame more evenly, as well as making the (seemingly thin) pot more “robust”.

(Currently I use a keg boiler connected to the VM column.)



I wouldn't do it. Because Aluminum expands nearly one third more than copper under changing temperatures (Coefficients of Linear Thermal Expansion). Simpler just to place your Al plate on the burner and put your pot on top. Then it's a diffuser plate setup and won't warp the copper.


HTH


Slainte!
regards Harry
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Re: Is it worth making a Metal Sandwich?

Postby adama » Tue Jun 19, 2012 3:40 am

How about a spiral of copper tube (left open to atmosphere at both ends for expansion) as the filler between the 2 sheets of copper?
Great idea myles and dead-set easy to do.
Simpler just to place your Al plate on the burner and put your pot on top. Then it's a diffuser plate setup and won't warp the copper.
Thanks Harry that too makes a lot of sense.

I guess I was getting "hooked-up" with the design of some pots 'n' pans in the kitchen.
They're s/s; some have a lick of copper on the bottom; others are said to have aluminium between layers of s/s.

Thanks guys ~ you've made it much simpler for me. :)

Regards
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Re: Is it worth making a Metal Sandwich?

Postby zedzedtop » Tue Jun 19, 2012 4:18 am

I wouldn't mess around with it.

http://en.wikipedia.org/wiki/Hume-Rothery_rules

You have the same lattice structure (fcc) but not the lattice spacing, plus there is the need to prevent any bonding with oxygen, which would be a bitch with the Al. Did a whole seminar once on the process that all-clad uses in their cooking pots. It's tricky. You've already got the copper with the high conductivity, so your best bet might be to make the copper thicker. Diffusing the flame would have a similar effect - I'd go that route. If diffusing the thermal gradient is still a concern, go for a mineral oil or glycol bath.
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Re: Is it worth making a Metal Sandwich?

Postby adama » Tue Jun 19, 2012 6:29 pm

Thanks zedzedtop.
For this "relux boiler" I'll just go with a coil of copper pipe on the base and see how I go with, and without an ally diffuser plate on the gas jet.

(the strip boiler however is all about a glycol bath)
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Re: Is it worth making a Metal Sandwich?

Postby Soldat Louis » Wed Jun 20, 2012 3:21 am

Take care that aluminium + copper is a good start for electrolytic corrosion !
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