# casting aluminum?



## gofastman (Jan 23, 2015)

I need to fill a space in my copper flashlight I'm building and I was thinking aluminum would be better than solder or thermal cubes.

I have access to a lot of aluminum, PPE, casting ladles, flux, and oxy/acetylene.

I have cast literally thousands of lead bullets so I'm familiar with the operation. 
I'm just wondering if anyone has some advice they would like to share.


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## gadget_lover (Jan 23, 2015)

It sure sounds interesting. The only thing I can think of is pre-heating the copper so that it does not wick away the heat too fast and cause an irregular fill.

Pictures when you are done? 

Daniel


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## Norm (Jan 23, 2015)

Casting aluminum diy

Norm


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## smokinbasser (Jan 23, 2015)

I worked for a motorcycle fairing manufacturer and we had to make female molds for forming the ABS sheets, the molds were made of aluminum. You would not believe how much heat it takes to liquefy aluminum, we melted down blown up Honda engines and anything made of aluminum like coke cans. I doubt if you will be able to generate enough heat to melt AL down and liquefy it to pour it down a mold. Lead melts down at much lower temps than AL. If there is so much as one drop of water in the mix the aluminum will for lack of a better phrase explode violently. Wear leather aprons and multiple eye protection. Do a google search on casting aluminum. Good luck and be safe!!!!!!


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## gofastman (Jan 23, 2015)

smokinbasser said:


> I worked for a motorcycle fairing manufacturer and we had to make female molds for forming the ABS sheets, the molds were made of aluminum. You would not believe how much heat it takes to liquefy aluminum, we melted down blown up Honda engines and anything made of aluminum like coke cans. I doubt if you will be able to generate enough heat to melt AL down and liquefy it to pour it down a mold. Lead melts down at much lower temps than AL. If there is so much as one drop of water in the mix the aluminum will for lack of a better phrase explode violently. Wear leather aprons and multiple eye protection. Do a google search on casting aluminum. Good luck and be safe!!!!!!



I do know that it takes a LOT of heat, much, much more than lead. I'm confident the combination of oxy/acetylene, a big rosebud tip and a reasonably small amount of aluminum will work ok.

And yes, water (even moisture) and hot liquid metal is a very scary combo! Imagine putting a drop of water in a frying pan full of oil, but instead of grease spatter it's molten metal.


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## gofastman (Jan 23, 2015)

gadget_lover said:


> It sure sounds interesting. The only thing I can think of is pre-heating the copper so that it does not wick away the heat to fast and cause an irregular fill.
> 
> Pictures when you are done?
> 
> Daniel



I was thinking this, I'll probably try to preheat the "mold" to about 600°F

Pictures will be posted


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## idleprocess (Jan 23, 2015)

Making a mini furnace: https://www.youtube.com/watch?v=hHD10DjxM1g
Melting aluminum cans: https://www.youtube.com/watch?v=lSoWxG30rb0

I've got some projects in mind where casting small amounts of aluminum would come in handy. Curious how amenable said castings would be to machining and finishing afterwards to act as flashlight bodies or heatsinks.


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## RedLED (Jan 23, 2015)

Maybe off topic... But in the 7-9th grades in Jr. high and high school we had complete machine shops. Complete with lathes, drill presses, box and pan brakes, gas forge, arc welders and aluminum foundry! Can you imagine kids today allowed to fire up a natural gas foundry or forge. For-get-about-it!

If schools still had these shops, you could just go the local HS and ask some teen to do your castings as a project. How things have changed. I did beautiful sand castings when I was 13, what an experience. Now you learn software. That's right, soft...not a hard machine shop, that is reserved for other countries these days. 

Oh, the castings I mention above, well I gave them to some hot blonde back then, was it worth it? I guess!

Good luck with the project, sounds fun.


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## gofastman (Jan 24, 2015)

New plan:
rather than casting the aluminum, I'm gonna get some aluminum or copper-phosphorus rods and fill it as if I were brazing it.


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## more_vampires (Jan 25, 2015)

Are you filling to add weight or are you filling to shim a space?

If for weight, why not fill the space with #4 lead birdshot in a plastic bag?
If not for weight, delrin plastic would be far easier and safer to fab.

Not saying don't do it. I'm fond of looking for easier workarounds. You'd be set up for aluminum blank casting and recycling.

Pros and cons.


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## gofastman (Jan 25, 2015)

gofastman said:


> New plan:
> rather than casting the aluminum, I'm gonna get some aluminum or copper-phosphorus rods and fill it as if I were brazing it.



Well that was a complete disaster. I'm gonna try again with silicone thermal cubes


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## more_vampires (Jan 25, 2015)

Let me guess, the host body had a lower melt temperature and once the brazing got to speed the host turned to jelly?

No harm, no foul. No trash talk here! Reminds me of trying to powder coat pot metal. It turns to jelly.

Gotta watch out for high heat conduction and low temp melt metals. The whole work piece gets to melt temp before you can weld or braze sucessfully.

Might be better off with a separate process, a cold process if you have to involve the host?


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## gofastman (Jan 25, 2015)

more_vampires said:


> Let me guess, the host body had a lower melt temperature and once the brazing got to speed the host turned to jelly?
> 
> No harm, no foul. No trash talk here! Reminds me of trying to powder coat pot metal. It turns to jelly.
> 
> ...



Yep! 
I gotta say it was a pretty big blow to my ego, I'm pretty competent at oxy/fuel welding steel, even the pretty thin stuff!


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## more_vampires (Jan 25, 2015)

I got a man currently AWOL and owes me money who could weld a sheet of aluminum foil into a tube. Sticking your hands into the tube and pulling to the side, the foil broke before the weld.

Man was an artist. Currently owes my shop $3 grand. YMMV.


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## lunas (Jan 25, 2015)

silver bearing solder since it seems like you are trying to add thermal mass it should bind to clean copper only needs about 600-800F to be like water it would be 40-60% silver heat would conduct better than copper...


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## more_vampires (Jan 25, 2015)

TIG/MIG inert gas welding with a feathery touch on juice settings could do what OP is talking about. We won't go as far as vapor deposition. Argon wire welder should do it with breaks to let a small piece cool.

I'm still thinking a heat interference press fit of a machined piece would be better. Copper, preferrably, if we're talking about wicking away heat.


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## gadget_lover (Jan 25, 2015)

The thread would be a bit more fun if you'd take a minute to tell us more of what you are trying to do. What you've described so far could be almost anything. I imagine you are trying to plug a body so you have a solid heat sink area. Of course, you could be trying to do almost anything.  You could be plugging the hole from a switch that is no longer used, or adding mass so that you can cut some fins. 


I can think of many, many ways to plug a body. One way that I would not try is O/A welding it. The area heated is too imprecise. Even using TIG would be iffy, depending on the material of the body. 

There's a youtube vid of a guy using an arc welder to melt small amounts of aluminum in a carbon crucible. It worked, but I don't know if it's better or worse than other methods.

Dan


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## gofastman (Jan 26, 2015)

It's a 1" copper bar inside a 1" to 1.5" female threaded adapter. Trying to fill the empty space for better thermal conductivity.


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## gofastman (Jan 27, 2015)

So my next question is; what's better, a tight aluminum foil wrap or thermal cubes?
in retrospect, the original idea was overkill, just too dang heavy. Good for heat, bad for carrying


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## more_vampires (Jan 27, 2015)

Copper foil wrap with smear of thermal paste?


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## gofastman (Jan 27, 2015)

more_vampires said:


> Copper foil wrap with smear of thermal paste?



Perhaps, I do have thermal paste. However I don't have copper foil, plenty of aluminum though


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## more_vampires (Jan 27, 2015)

Probably good enough with AL not CU. Are you going for a high heat build? Amps?


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## gofastman (Jan 27, 2015)

10a is the drivers max. thinking probably 7.5a, that's pushing a triple 219B board pretty hard!


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## gadget_lover (Jan 27, 2015)

Since it's a copper bar, solder should work. What is the material for the female threaded adapter? There is a solder paste (flux + solder) that you can coat the copper rod with, then heat it in an oven set at around 400 degrees. That should give you 100% contact as well as a permanent mount. 


Dan


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## gofastman (Jan 27, 2015)

gadget_lover said:


> Since it's a copper bar, solder should work. What is the material for the female threaded adapter? There is a solder paste (flux + solder) that you can coat the copper rod with, then heat it in an oven set at around 400 degrees. That should give you 100% contact as well as a permanent mount.
> 
> 
> Dan



The adapter ia also copper


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## PeterH (Jan 30, 2015)

Filling a void for thermal conductivity I'd expect zinc or tin to do better than thermal paste or packed foil.


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## gofastman (Jan 30, 2015)

PeterH said:


> Filling a void for thermal conductivity I'd expect zinc or tin to do better than thermal paste or packed foil.



Really? Despite their relatively low thermal conductivity?


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## gadget_lover (Jan 31, 2015)

The problem with a perfectly round plug inside a perfectly round tube is that it really only touches in one line (if parallel) or a couple of spots if it's canted. To get 100 percent of the surface to touch, you need an interference fit... the plug has to be physically larger (by a few 1/1000 inch) than the hole in the tube and it has to be coerced into place. 

Thermal paste is a mixture of small heat conducting particles that hope to be small enough to fit in any gaps between the metals and big enough to bridge that gap. If it's too thick, the heat has to move from particle to particle to particle. A 1/1000 inch thick paste does a much better job than bare metal to metal. A 1/32 inch thick layer is worse than metal to metal.

Using foil is a way to make an interference fit. It deforms as you force it together, conforming to both surfaces. There are still gaps, but not as many.

You can take advantage of copper's malleability to make it conform to a plug that is a close fit. Force a shim between the tube and plug, and the far side will deform to touch at least 50% of the circumference, maybe more.

Just my opinions. 

Daniel


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## more_vampires (Jan 31, 2015)

Ahh, then there is "heat interference fit." It's historically how you take apart certain kinds of engines and drive train components.

Heat the big part, perhaps chill the small part, assemble, allow to equalize. You can't do it at room temperature and as the assembly increases temperature, it does it together and stays together.

Perhaps the thermal paste is like the "smallest shim you can get."


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## idleprocess (Feb 1, 2015)

more_vampires said:


> Ahh, then there is "heat interference fit." It's historically how you take apart certain kinds of engines and drive train components.
> 
> Heat the big part, perhaps chill the small part, assemble, allow to equalize. You can't do it at room temperature and as the assembly increases temperature, it does it together and stays together.
> 
> Perhaps the thermal paste is like the "smallest shim you can get."


I've heard that just freezing the smaller part works wonders - oftentimes without resorting to extremes such as dry ice. A friend that used work on cars said it was a common trick with bushings in hard-to-reach places that would otherwise require nearly-impossible-to-deliver amounts of force to insert.


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## more_vampires (Feb 2, 2015)

Your friend is 100% spot on, IP. I use an oxy-ace with brazing tip for making and breaking heat interference. I normally don't bother to combine chill AND heat. The thing about the heat is that it must be fast, particularly with disassembly.

If the heat isn't fast and you're breaking a heat interference fit, then they'll heat up together. Oxy-ace is what I use on aluminum/magnesium housings. A hot air gun is too slow, IMHO.


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## Lyndon (Feb 6, 2015)

idleprocess said:


> Making a mini furnace: https://www.youtube.com/watch?v=hHD10DjxM1g
> Melting aluminum cans: https://www.youtube.com/watch?v=lSoWxG30rb0
> 
> I've got some projects in mind where casting small amounts of aluminum would come in handy. Curious how amenable said castings would be to machining and finishing afterwards to act as flashlight bodies or heatsinks.



I found that machining isn't the problem, workholding is. A friend asked me to machine a decorative cast brass bottle opener that he made and to square up a cast aluminum ingot. It could be that the castings cooled too quickly and were brittle, but I ended up breaking one of the brass castings clamping it in the vise. The actual machining was quite easy once I figured out how to hold the irregularly shaped objects properly.


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## idleprocess (Feb 6, 2015)

Lyndon said:


> I found that machining isn't the problem, workholding is. A friend asked me to machine a decorative cast brass bottle opener that he made and to square up a cast aluminum ingot. It could be that the castings cooled too quickly and were brittle, but I ended up breaking one of the brass castings clamping it in the vise. The actual machining was quite easy once I figured out how to hold the irregularly shaped objects properly.



Getting moderate precision to do the initial clamping/fixturing would be the challenge, for sure. Need to ensure that it can be clamped in the first place and that you can keep it within your margins so the final shape can be machined.


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## bikedude (Feb 7, 2015)

Castings becoming brittle may be due to sand inclusions or impurities (dross, oxides). Alu and brass don't harden like steel.
Regarding the mini furnace video idleprocess posted, you can add perlite or shredded styrofoam to the mix, it will improve insulation. Some recipes, using firebrick instead of plaster of paris, use up to 8 parts styrofoam, supposedly providing insulation similar to ceramic wool.

That being said plaster is great for molds but a bit dubious as a refractory. Some say it turns to CaO, others say it contains chemicals that could flux the whole furnace, i.e. make it brittle and fall apart. 
Since alu melting happens at fairly low temps (~6-800°C) as far as metal casting goes and since charcoal as a fuel is self-insulating to a degree (only coal exposed to forced air gets seriously hot) I'd expect it to hold out for a while before failing, if it fails at all.


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