# Steel and aluminum bonding together



## bswartzwelder (Sep 14, 2015)

Hi Gang,

Lately (just for kicks), I have been melting aluminum cans. Even when flattened by backing the car over them, they take up a lot of space for a very little poundage. So, I made an octagon shaped mold from 1/4 inch thick steel and a 1/2 inch thick steel bottom. Welded it together on the outside edges and then noted spaces where one side wall meets the next. To correct that, I ran a weld bead down each joint between the side walls. To make the project neat, I then used an air die grinder and ground the welds down smooth. I ground the bottom edge of all 8 sides down. Now, the bottom edge of the sides is a nice flat surface so I could weld the 1/2 inch thick plate steel to it. It wasn't necessary to weld the bottom to the sides on the inside of the mold.

Well, it worked like a charm. That is until I tried to get the aluminum slug out of the mold. After the aluminum was no longer molten, I removed the mold from the forge and placed it on some bricks. From a distance, I cooled it all down with the garden hose. It made a tremendous amount of steam (expected) and there even appeared to be a slight gap between the sides of the mold and the aluminum slug. But the darn slug just refused to come out. Finally after dropping the entire mold with the slug inside about a dozen times, the aluminum slug finally came out. I have repeated this several times with the same results. The only difference was the number of cans I melted. In the first attempt, I melted about 100 cans. After that, I melted 150 cans and 200 cans respectively. They really don't take up much space anymore and it did have the desired effect of concentrating the aluminum into a more dense package. 

Can anyone tell me why the aluminum is sticking to the steel mold? and is there anything I can apply to the mold to help make releasing the aluminum easier?

Thanks


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## Geo (Sep 14, 2015)

Are the sides at a 90° angle with the bottom? If so, it should be an obtuse at about 130°. The ingot will wedge to one side or the other if the sides and bottom is at right angles from each other.


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## g_axelsson (Sep 14, 2015)

Look at http://goldrefiningforum.com/phpBB3/viewtopic.php?f=67&t=22760 and you will see at least an early version of the mold. :lol: 

Göran


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## goldsilverpro (Sep 14, 2015)

Brush a very thin coating of motor oil on the inside of the mold before pouring - no puddles. Or maybe spray the inside with WD-40. The oil will carbonize with the heat and act as a mold release.


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## FrugalRefiner (Sep 14, 2015)

I was thinking mold release agent too, but if I understand his post he's melting the aluminum in the mold. I would guess any oil would burn off in the process of melting.

I would suggest melting the aluminum in a crucible of some kind, then pouring into a well sooted mold, or one treated with oil or another mold release agent as GSP suggested.

Dave


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## bswartzwelder (Sep 15, 2015)

No, the walls of the mold are angled forming a loose cone shape as pointed out by g_axelssonone. I will look into a crucible for the melting part of the process.

Thank you


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## goldenchild (Sep 15, 2015)

I've used PAM or cooking oil as a mold release with success. Just as a side to anyone that's into firearms, it has recently been discovered that "Fire Clean" is actually just plain old Crisco vegetable oil repackaged at a 10,000% mark up :lol:


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## GotTheBug (Sep 16, 2015)

Correct me if I'm wrong, but it sounds like you melted the aluminum inside your mold, then allowed the whole thing to cool before you tried removing the aluminum. If you did, that's the problem. Crucible (in which you melt) should be a separate "container" than your mold.


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## Harold_V (Sep 17, 2015)

Molten metals are strong solvents of other metals. That's something you should be aware of, especially if you've considered how lead is used in assaying.

Melting in a steel vessel without a refractory wash is not, in my opinion, an acceptable process, for that reason. Under no circumstance would I endorse using the same vessel in which you melt as a mold. It's just not good business. 

If you look closely, you may be able to see points where there's some minor fusing of the aluminum to the steel flask. You are also ruining the properties of the resulting aluminum by dissolving iron. 

If you wish to do as you're doing (I don't recommend it, as there's a lot of loss when melting cans due to the thin material versus the huge amount of surface area), melt the cans in a separate vessel (it can be steel, but should have a refractory wash, to isolate the molten aluminum from the parent metal of the vessel) and pour to your mold, which would have a coating of mold release and is preheated, to prevent formation of steam. Failing to preheat the mold can be the source of a molten aluminum bath.

I would advise you to use a graphite/clay or silicon carbide crucible for your melting. 

Harold


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## bswartzwelder (Sep 17, 2015)

Thank you to all who have responded. While I am well aware of the way some metals react (mercury dissolves gold), I wasn't aware of the fact that aluminum and steel would react. 

Harold_V, your wisdom never ceases to amaze me.


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## jeneje (Sep 17, 2015)

bswartzwelder said:


> While I am well aware of the way some metals react (mercury dissolves gold),


I don't think (Hg) Mercury dissolves gold, I think it is more of a collector of gold, used in black sand cons to bond with micro gold and then removed by way of heat. 

Ken

Edit: I stand corrected-- Mercury will dissolve gold. I always though mercury would collect the gold and when heat was applied using a retort you could collect the mercury back leaving the gold. I would not have figured the mercury could dissolve the gold to a molecule state. Interesting!!

Here is a reference link.... http://silverprospector.com/assaying/au-hg-amalgamation.html


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## jeneje (Sep 17, 2015)

I am not trying to high jack the thread but, if the link I posted is true, "Mercury dissolves gold" how then, can you cold press the Mercury out leaving the gold? Confused somewhat here... 

Ken


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## Anonymous (Sep 17, 2015)

jeneje said:


> I am not trying to high jack the thread but, if the link I posted is true, "Mercury dissolves gold" how then, can you cold press the Mercury out leaving the gold? Confused somewhat here...
> 
> Ken



You use a sealed retort and evaporate the mercury off Ken.


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## justinhcase (Sep 17, 2015)

jeneje said:


> I am not trying to high jack the thread but, if the link I posted is true, "Mercury dissolves gold" how then, can you cold press the Mercury out leaving the gold? Confused somewhat here...
> 
> Ken


If you are talking about when Very poor artisan mine's use mercury to catch fine gold from gravity concentrates and squeezes off the mercury through a fabric gauze. 
This is an amalgam not an alloy,there will be some Au dissolved in the mercury but also very fine particles of Au where only the very surface layer is in a number of transitional states.
This means that the larger particles can be held back by a filter and excess mercury pressed off.
Not some thing that is recommended and a retort is the only practical way to recover the dissolved Au or Ag. 
If I may quote a very interesting lecturer one Keith P Walsh.
Amalgams, including dental amalgams, are not like most other metals in at least one crucial respect; they have a much greater degree of material inhomogeneity. This is true when compared either with pure metals, such as copper, silver, etc., or with true alloys such as brass. The explanation for the difference in the material homogeneities of amalgams and true alloys lies in the difference between the methods by which the two types of material are formed. When a true alloy is formed, the component metals are mixed together at a temperature which is greater than the melting point of all of them. Then, after having been mixed thoroughly in its fully liquid state, the mixture is allowed to solidify by cooling at a controlled rate. By contrast, in an amalgamation process, bits of solid metal, which may themselves be of either pure metal or an alloy, are mixed together with a liquid metal at a temperature which is BELOW THE MELTING POINT of the solid component(s). (And in the case of dental amalgam, where mercury is used as the liquid metal amalgamating agent, this process is normally performed at room temperature.) In the setting process of such an amalgam, the liquid mercury becomes part of the solid material not as a result of any subsequent reduction in temperature, but by joining in solid solution with the outer layer of the solid particles of metal with which it was mixed. But of course, not all of the volume of the solid particles is involved in this process and, as a result, the microstructure of the resulting solid amalgam is as depicted in the schematic diagram at: http://www.bookbootusers.co.uk/setting.htm In this diagram the lumps of "unreacted alloy" (denoted "gamma") are the cores of the original grains of solid silver-tin alloy which have not mixed with any of the mercury during the amalgamation process. At this scale it is not possible to show the spatial relationship between the atoms of silver and the atoms of tin in these alloy "cores". The alloy has too great a degree of homogeneity for this to be done. However, the relative inhomogeneity of the "amalgam" is clearly depicted by the sizes of the unreacted alloy cores. (These being held together by a solid matrix of a dissimilar mixture of metals (denoted "gamma-1") which does have mercury in it, and which may be presumed therefore to have dissimilar physical properties.)


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## jeneje (Sep 17, 2015)

Thanks everybody for explaining the differences. I was associating the dissolution to AR, therefore I was getting confused. Thank you!!

Ken


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## Geo (Sep 17, 2015)

Mercury bonds bits of metal together like cement bonds gravel together when making concrete. After the amalgamate is allowed to sit for a moment, it solidifies just like concrete. Once the mercury and silver is mixed in the dental office, it must be used quickly or it will harden.


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## justinhcase (Sep 17, 2015)

Geo said:


> Mercury bonds bits of metal together like cement bonds gravel together when making concrete. After the amalgamate is allowed to sit for a moment, it solidifies just like concrete. Once the mercury and silver is mixed in the dental office, it must be used quickly or it will harden.


I may be incorrect,but it look's to me like the relevant concentration's liquid and solid metal's affect the nature of the Amalgam.
50/50 mix's like dental amalgam set very quickly where as weaker mix's 95/5 such as you get when using mercury for recovery stay reasonably fluid for a good time.(well long enough for our poor artisan miner to separate by pressing.) 
But having never tried squeezing liquid mercury through a flannel this is just theoretical speculation.


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## FrugalRefiner (Sep 17, 2015)

I just happened to be reading Rose's _The Precious Metals Comprising Gold, Silver and Platinum_, and thought the following excerpt might be of interest:



T Kirke Rose said:


> GOLD AND MERCURY.
> These alloys are known as amalgams, and
> are formed, although with difficulty, by the direct union of the two metals
> at the ordinary temperature. According to Kasentsof, 1
> ...


Dave


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## Deano (Sep 18, 2015)

Gold has solubility in mercury which is dependent on temperature, the hotter the mercury the more gold is dissolved.

listings of solubilities vs temperatures are available in internet articles and are similar to the values given by others in this forum.

If 10 to 20g of pure gold is placed in 50ml of clean mercury in a small beaker and kept at 80C for a week or so then clusters of beautiful crystals of gold mercury compounds will form.

Depending on exactly what ratio of gold to mercury is used and what temperature is maintained the crystals will be 5 to 25mm in length and 1 to 5mm in diameter.

These crystals have formulas ranging from AuHg2 to Au8Hg.

WARNING

Enough mercury will be volatilised during the extended heating process to be a major safety hazard, this should only be attempted in a properly fitted out lab.

The crystals will have some free mercury associated with them, even if cleaned up in dilute nitric acid the crystals are only safely stored in a sealed glass vessel.

If it is thought that the above may be an incentive for untrained people to have a try at crystal making in unsafe conditions I am happy to have the post deleted.


Deano


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## Harold_V (Sep 23, 2015)

Deano said:


> If it is thought that the above may be an incentive for untrained people to have a try at crystal making in unsafe conditions I am happy to have the post deleted.


It is my opinion that informative posts that are not intended to mislead readers, in particular when cautionary notes are included (this one being a good example), they should remain, as the knowledge gained can be useful. 

Harold


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## rickbb (Sep 24, 2015)

Harold_V said:


> Molten metals are strong solvents of other metals.




Now I know why my cast iron pot I use as a mold for my molten aluminum gets all rusted after a pour. I need to use more release agent coating.


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## bswartzwelder (Sep 27, 2015)

Rickbb - You're a genius. I have a cast iron pot sitting here that will never be used for food processing. It would make a great mold for the aluminum.


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