Aluminum structure modifications for use near a very hot fire

[Jason White]

I'm building an frame out of solid 5/8 inch thick aluminum square bars. this frame will be around a fire temps close to melting points but there will be insulation in make sure it won't melt.

I was thinking about drilling holes in the free space of the aluminum to reduce it's weight and if you increase the surface area, the heat dissipation will be greater. But would these holes going though the thickness, not length (as in hollow), cause the aluminum to be much more likely to bend and distort in shape incase the insulation isn't great enough for the weight the frame has to support?

 

[billy_joule]

Why not hollow section? Why not steel? cheaper, stronger and higher MP

 

[Jason White]

Why not hollow section? Why not steel? cheaper, stronger and higher MP

Well I'm doing homemade foundry so that's why aluminum, its a price issue. Aluminum is just coming from beer cans or pop cans.

 

[billy_joule]

So you will cast the square bar yourself? Casting channel section shouldn't be much harder?
Be aware Creep onset in Al is under 300 deg C

 

[Jason White]

So you will cast the square bar yourself? Casting channel section shouldn't be much harder?
Be aware Creep onset in Al is under 300 deg C

I'm casting multiple bars as a frame, they are of course solid and square in shape. Please explain what Creep onset is?

 

[billy_joule]

http://en.wikipedia.org/wiki/Creep_(deformation)

 

[SteamKing]

Well I'm doing homemade foundry so that's why aluminum, its a price issue. Aluminum is just coming from beer cans or pop cans.

That's a lotta cans.

You should also be aware that most structural aluminum is not just aluminum: it's an aluminum alloy, which is sometimes heat-treated to increase strength.

I couldn't tell you what kind of alloy might be used for a typical beverage can, but it appears that some magnesium is used to add strength:

http://en.wikipedia.org/wiki/Aluminum_can

Magnesium can burn if the temperature gets too high, and a magnesium fire is notoriously difficult to extinguish:

http://en.wikipedia.org/wiki/Magnesium

I would advise saving the beverage cans and then selling them, using the money to buy structural aluminum, which is generally extruded rather than cast.
:

 

[jh0]

I would advise saving the beverage cans and then selling them, using the money to buy structural aluminum, which is generally extruded rather than cast.
:

Even better, buy steel tubing instead, it will be cheaper and will withstand higher temperatures.

 

[Nugatory]

If we knew more about the application, we'd be able to give you better answers. What application is so weight-sensitive that you would consider drilling holes in aluminum members to further lighten them, yet also involves exposure to high heat?

 

[Jason White]

If we knew more about the application, we'd be able to give you better answers. What application is so weight-sensitive that you would consider drilling holes in aluminum members to further lighten them, yet also involves exposure to high heat?

In case somebody wanted to stand on it. picture a cube made of bars and then a cube of similar height but just a but smaller that fits on the inside and then they are connected.

 

[Nugatory]

In case somebody wanted to stand on it. picture a cube made of bars and then a cube of similar height but just a but smaller that fits on the inside and then they are connected.

But why? What is the function of this contraption? Why do you care about the weight, and in what way is it going to be subject to heat?

 

[Jason White]

But why? What is the function of this contraption? Why do you care about the weight, and in what way is it going to be subject to heat?

Honestly i don't see how that information is relevant. The question was specific and you're choosing to deviate from answering it.

 

[berkeman]

Honestly i don't see how that information is relevant. The question was specific and you're choosing to deviate from answering it.

One of the issues is that we have rules against discussing dangerous activities here at the PF. That can include giving advice about support structure fabrication and sizing, when we do not know what it is for.

We frequently get posters asking how they should size beams for structural support of platforms that will be holding up people, for example. We close those discussions and tell the OP to consult a licensed structural engineer. You have been evasive enough in your answers that several of us are concerned about what is said in this thread. If you continue to be evasive, this thread will likely be closed.

 

[billy_joule]

If you can't see how load and environment is relevant to the design of a structure then good luck, you'll need it.

So to answer your initial question - yes, drilling holes in structural elements will reduce their strength.

 

[Jason White]

One of the issues is that we have rules against discussing dangerous activities here at the PF. That can include giving advice about support structure fabrication and sizing, when we do not know what it is for.

We frequently get posters asking how they should size beams for structural support of platforms that will be holding up people, for example. We close those discussions and tell the OP to consult a licensed structural engineer. You have been evasive enough in your answers that several of us are concerned about what is said in this thread. If you continue to be evasive, this thread will likely be closed.

I understand. it is for the frame of an outdoor fire pit.

 

[Jason White]

The new version I'm building consists of this: "The second version will have a ventilation system built into it because we have a dead spot in our yard so like no air gets to the bottom of the flame. There will be modified garden solar light panels to power a light system that interacts with a plug in audio feed for you too hook up your iPhone to, and I'm considering putting in a cooling system, aka a mini fridge sort of into it to have a drink holder/cooler on the corners. The new one will have an aluminum frame insulated by homemade double pane glass, i may use metal (my thermal physics teacher said it would work just fine as long as there is a vacuums for no or little heat transfer to happen, as i suspected) for insulation to protect everything. and i may hollow out the frame and have it water-cooled. not sure yet. Oh yeah, also the mortar between the tiles won't be mortar, it will be light strips and the tiles are going to be magnetically attached for easy access to the inside in so you can remove them to reduce the weight so it's easier to transport."