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Recycling aluminium

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alan knight22/02/2012 18:23:31
39 forum posts

Wondering if its worth melting down aluminium cans and casting them into ingots to be kept for use later. As my company probably throws 3 binliners full away a week. Or would the material produced be of little use?

Speedy Builder522/02/2012 18:28:41
1833 forum posts
128 photos

I don't know, but I had the same thoughts about melting down brass taps and fittings etc. Is it worth the gas ?

alan knight22/02/2012 18:36:08
39 forum posts

I was looking at making a 3ph furnace and then do it at work

Michael Cox 122/02/2012 18:40:36
516 forum posts
27 photos

Hi Alan,

I have tried melting aluminium cans. The main problem is that being thin the cans have very high surface area to volume and when melted there is a great deal of dross and a corresponding low recovery of usable aluminium. Recovery is slightly better if you use Lo Salt as a flux.

Cans are also made from pure aluminium. This is very soft and gummy so it does not machine well. Adding a little copper (circa 2-4%) improves the machinability of the metal.

Speeder builder5. I think you would get a good recovery of brass from scrap taps and fittings.

Mike

alan knight22/02/2012 18:53:16
39 forum posts

Thanks Michael, we have about 30kg of old brass hinges really heavy unlacquerd type, I could get an endless supply of brass at the prevailing scrap rate so would that be a more useful path?

Michael Cox 122/02/2012 19:10:56
516 forum posts
27 photos

I find scrap aluminium everywhere. Possible sources are old carpet joining strips, old aluminium furniture, old shower rails, old car wheels, old hard drives etc.

The advantages of aluminium are that it is plentiful, it melts at a relatively low temperature (circa 650 degrees C) and it can be melted in easy to find stainless steel containers. Furnace construction is not critical because the temperatures are fairly low.

Once you move to melting brass then the melting temperatures are much higher (circa 1000 degrees C). The furnace construction is more critical, special clay graphite crucibles (expensive) need to be used and zinc fume (toxic) is troublesome. The potential dangers of the process are large.

I would advise try aluminium melting and casting first and then move to brass once you have some experience.

Mike

wotsit22/02/2012 20:01:42
188 forum posts
1 photos

This thread has some information - http://www.model-engineer.co.uk/forums/postings.asp?th=45889

I have been making my own ally castings for years by various methods. Tins are a total waste of time - they are coated with some kind of plastic which burns off and leaves vast amounts of dross on the metal. I usually go down to the scrapyard and buy an old cylinder head if I have large bits to cast - that way the metal is consistant, and it doesn't matter what condition it is in, so you should only pay scrap prices, not spare parts prices. (I know - scrap price is high enough cheeky). As Michael Cox says, it is not too difficult to find assorted aluminium scrap if you look around - never had much problem.

I have used the trick of dropping in a small piece of copper - the resulting alloy is quite pleasant to machine. Biggest problem I have had is voids in the finished piece - using flux when melting will stop this.

Also a safety issue - in the early days I tried using stainless steel cans for smelting - these will rapidly erode away, and dump hot ally everywhere ('Erode' is the only way I can describe it - it can't be hot enough to melt the stainless - maybe someone with some metallurgy background can explain). The genuine crucibles are expensive (and hard to find where I live).

wheeltapper22/02/2012 20:06:58
avatar
418 forum posts
98 photos

Michael, I'd be wary of old car wheels, they could be magnesium, hence the term 'mag wheels'

should burn well tho.

Roy

MadMike22/02/2012 22:14:50
196 forum posts

Be careful if you are melting aluminium, as the alloys are different for the many uses to which it is put. Best to melt extrusion or plate if you can.

As for car wheels there are few magnesium wheels in general circulation. The majority, possibly 99%, will be aluminium. Mixing the alloys will give you a chunk of aluminium of more than dubious quality. However that may not be an issue to some people.

In particular beware of drinks cans. Carefully check the can walls. these are often plastic these days rather than aluminium. The end caps are still generally aluminium.

HTH rather than confuses.

alan knight22/02/2012 22:51:04
39 forum posts

So your saying stick to a single alloy for a job, eg mabey heads for casting cylinder heads and crank cases or wheels for more general use.

Jon22/02/2012 23:06:28
989 forum posts
46 photos

Been thinking along the lines of something that dont take up much space. Whether it chops it or compresses together not bothered.

Just next weeks alum scrap value alone i could weigh in £72 est which could take 8 weeks to get rid of in wheely bin collections.

Terryd23/02/2012 06:31:00
1926 forum posts
179 photos

Hi,

This guy does a lot of home casting for his engines and his self made videos are well worth watching. This is what he has to say on recycling aluminium for casting (including a simple test for magnesium in alloys):

Best regards
Terry
Ian S C23/02/2012 09:17:14
avatar
7447 forum posts
230 photos

I think the way it should be smelted ,is to start the melt with other scrap, then put the clean dry, and flattened aluminium cans in a paper bag, and plunge it into the molten aluminium.

If you want some cans, I'v got about 50 kg of flattened cans behind my workshop.

Ian S C

Edited By Ian S C on 23/02/2012 09:18:53

Edited By Ian S C on 23/02/2012 09:19:57

peter walton23/02/2012 13:16:08
82 forum posts

I think the video is showing that the larger the surface area of the scrap Ally the less you will get in the actual melt due to the surface oxidising.

This is why ally turning have so little scrap value, to high an oxidxe content.

peter

Dithering23/02/2012 14:41:17
20 forum posts

Wotsit: The reason for the erosion of your stainless steel containers is that iron actually dissolves in molten aluminium so any iron-based metal crucible will have a short life. On the other hand, Poundland sell stainless steel pots very cheap - I think I bought 4 for £1.

SpeedyBuilder5: Year before last, at the Midland Model Engineering Exhibition, there was a guy melting brass to cast house number plates (I can think of more useful things to cast!). He was largely using old, chromed taps but it took a long time and a lot of gas to melt them. Partly, this was because he was out in the open and it was quite cold but I should think that he wouls have to be in the open because there were a lot of fumes and the flames were roaring about 5 feet high.

Michael Cox 1: I have a collection of old hard drive chassis which I intend to melt down. I'm not sure, though, that they are aluminium. Possibly, they are zinc. Anyone know a test to distinguish between the two.

Regards,

Brian Thompson.

Gordon W23/02/2012 14:53:22
2011 forum posts

What are ready-meal food trays made from? I tried melting a couple (just with a torch) as an experiment, and they just turned to dust. Could it be some coating? A storey on the radio I heard:- Some Aussie is reconned to be the biggest lager drinker/ most for longest time, it was calculated that if he'd kept all the cans the scrap price now would have paid for his beer over all the years.

Michael Cox 123/02/2012 15:15:31
516 forum posts
27 photos

The appearance of some zinc alloys is very similar to aluminium alloys. All the hard drives I have had have been aluminium. There are two ways of distinguishing aluminium and zinc.

The first is based on the density. Zinc is much heavier than aluminium for the same sized piece (zinc has a density of 7.1 g/ml and aluminium 2.7g/ml) Density can be easily determined by weighing dry and then immersed in water.

The second test is based on the fact that zinc will dissolve in dilute acids such as vinegar liberating hydrogen whereas aluminium will not readily dissolve. So just sprinkle a little vinegar on the metal. If it reacts and froths it is probably zinc. Note this test also distinguishes aluminium and magnesium alloys (see the video link in Terryd's response).

In summary, if the metal is light and reacts with vinegar then it is probably magnesium based, if it is heavy and reacts with vinegar then it is probably zinc based, if it is unreactive to vinegar then it is probably aluminium based.

Mike

Swarf, Mostly!23/02/2012 15:22:44
498 forum posts
41 photos

Brian:

If you have a spring balance and a bucket of water, you can determine the specific gravity of the casting. This is an up-to-date version of Archimedes 'eureka' method.

Weigh the casting hanging in air and then weigh it again immersed in water. It will lose the weight of its own volume of water. The specific gravity is equal to the dry weight divided by the difference between the dry & wet weights.

Suppose it weighs 10 kg in air and 8.5 kg immersed in water, then the specific gravity is equal to 10/(10-8.5) ie 10/(1.5) = 6.7 (This example doesn't apply to a real metal - I've just used easy numbers to show the method of calculation.)

Then look up the SG on the internet or in some Tables of Physical Properties. This method will distinguish easily between aluminium and the zinc-based die-casting alloy (aka 'Mazak'. I think pure zinc castings wouldn't often be encountered, Mazak would be more likely.

If you don't have a spring balance, you can use a rod or beam and a counterweight, with bits of string to suspend the beam itself and the casting and counterweight from the beam. You measure the distances from the beam pivot to the casting's string at the balance points dry and in water (keep the counterweight in the same position and move the casting to balance in each case. It's a bit more difficult to explain in a forum like this but by manipulating the two distances, you can calculate the SG.

I hope this helps.

Best regards,

Swarf, Mostly.

Swarf, Mostly!23/02/2012 15:25:27
498 forum posts
41 photos

Mike,

You beat me to it!!!

Best regards,

Swarf, Mostly.

wotsit23/02/2012 17:21:05
188 forum posts
1 photos

Dithering,

Thanks for the input - I mentioned about this happening because there was a suggestion earlier to use stainless steel cans for smelting, - I wanted to point out that this is a dangerous practise. When I first started, I thought stainless cans would be just the thing. I did not know at the time, and would have found it hard to believe that ally at 650 degrees would 'dissolve' or otherwise penettrate stainless steel -The first one lasted for about three smelts, then dumped ally - fortunately inside the furnace, so no harm done. The second one I tried failed at the second attempt, and dumped ally around my feet - I was very glad I had boots on - it also boils the moisture in concrete, which spits violently. The same phenomenon occurs with the chunk of copper suggested in this thread to make the metal easier to work - copper melts at a much higher temperature than ally (my forge certainly won't melt it), yet there is no trace of the lump of copper in the resulting ingots - it dissolves (or otherwise merges) into the ally.

I mention this again, because someone in this thread suggested stainless steel cans for smelting, and the thread seems to have missed that point completely. I use a thick homemade iron can, with a coating of clay inside. Even for 4 cans for a pound, its not worth the risk with stainless.

I have used many old harddrive castings for smelting - so far all of them have been aluminium.

Has anyone reading this forum actually used rubbish metal like drinks cans or picnic trays to produce useful castings with any sort of bulk? - I always had far too much dross, as many people also say in this thread (and on many other threads, over and over again) - IMO, it simply is not worth the time to collect the damn things, then melt them down, then decide what to do with the resulting crap, 'cos it sure isn't useful metal. There is a thread somewhere in this forum (I think) which discussed this long ago, with some interesting details on metal thickness and coatings - the opinion then was forget it.l

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