New member, review bar melt process please?

[Yggdrasil]

Thanks for all the help so far, if anyone has the time to address the other quesions I would appreciate any info I can get.


2. Other than glazing the quartz porcelain type crucibles what is the purpose of the borax flux in my situation of melting karat gold. Is it even necessary? I know when I went to a refiner and they melted in front of me they melted in tabletop electric crucible furnace not much different from the cheap ones seen on amazon, and they used what seemed like a ton of borax powder, enough that the resulting brick was coated with about 1/8 to 1/4 inch of molten slag which was easily hammered off. Why would they do this? Is this the right thing to do?

3. I tried to be as detailed without writing 2 novels, What am I doing wrong? what is a safety concern? where might I be losing metals?

4. I have 3 types of crucibles. Small white ceramic quartz dishes, a graphite cylinder crucible about 2 inches tall by 1.5 inches wide, and a larger graphite clay crucible. I have read not to use flux with the graphite clay as it causes oxidation issues. (one of my silver melts I forgot this and added flux which seems to have damaged my crucible, I did not have time to wait for it to cool to properly observe it. Obviously these 3 crucible types have different purposes but I'm not seeing much info on this specific subject, can anyone expound? When would flux be advisable in each of these types of crucible in my specific purpose of melting karat scrap into a bar?

5. I have been placing the crucible directly under the closest flame jet of the forge, is that the wrong place to do it, I suspect this is why I'm getting the oxygen contamination on silver? I may need to learn more about how to properly tune the propane jet flame to reduce oxygen in the forge.

6. Why is everyone so adamant about not melting in graphite? is it because of degradation to the graphite under long high heat situations in an oxygen environment? IE why its ok to use graphite in an electric furnace? If I'm willing toss a graphite mold after 5 or 10 melts as an acceptable loss of consumables, is there some other reason I should be concerned?

I really would prefer not to pour the metal if I can avoid it at this early step, so just loading the graphite mold, and cooking it till melted, stir then turn off forge and allow to cool would be worth the cost of a $10 mold to me assuming there are no potential catastrophic results...

7. with platinum and palladium having such higher melting points I assume any missed PD/PT components (ie diamond heads) will not melt at the metal temps I can achieve, and therefore be recoverable by decanting the molten metal into a mold, or picking them out with tweezers while the gold is still liquid.

Point 7.
This is not how it works.
The Pt/Pd will alloy with the Gold and this will create an alloy with marginally higher melting point than the pure Gold, then what ever Copper and Silver is in the Gold alloy will lower it.

 

[Yggdrasil]

Yah eventually I'll play with ewaste, and I have a 50 gal drum of plates silverware I might melt into anodes, and attempt to concentrate via copper cell.

Re long posts, I read "why can't I ask a simple question and get a simple answer" and since I'm dealing with molten metals and reasonably intimidated by the process and inherent dangers I just posted exactly what my plan was/what I wanted to do and asked for help/tips as was explained in many many posts

Thanks for your answers

Plated Silverware may not have Copper in it, there are many strange alloys used as basis of plated Silver, so check this first.

 

[Mike-ICFGD]

Hi Mike,

I will try to answer question 6 for you, some will agree some won`t.

The purpose of recovery and refining, amongst the joy and happiness that is giving to the hobbyst, is to recover value with lower costs, otherwise it would be more profitable to buy stuff ready made with 1-2% over spot.
That being said, most of us tries to control the flow of input and the gain of output in every process that we use (calculated amounts of acid, amortization of materials, investments, equipment etc.), therefore it is very important that the materials we use can be reused as many times as it is possible, to not raise unnecessary costs, wich will affect the output value.
Using graphite with open flame degrades the graphite faster than using in a homogenous heat environment as electric. Eventually using in electric furnace wiill degrade the crucible, but it will last longer, therefore distributing investment cost over many pours, thus lowering the overall costs with replacement.

Rethink your strategy, make or buy a proper gas operated furnace (as i understand you are thinking 1-2 kg bars) use adequate crucible for melting and graphite mold for pouring. I belive Bigstacked has really good video material on youtube about melting and pouring copper, brass, aluminum and other materials.

What is the point to earn 2-3% on your poured material if you lose 5-6% in investments to make that material?

I might see this wrong, i didn`t run your numbers, but for me, it is always about the parity between the input and the output, and if that parity is negative, it is not worth the time and effort to invest in.

Pete.

Thanks for your input, I totally understand trying to save your equipment for as many uses as possible, especially when working with hobby sized lots. I just wanted to confirm there was no more safety oriented reason not to use graphite in open flame. For the size of my pours, 5 to 10 pours from a $10 mold is an acceptable price to pay significantly smaller than 1%.


Thanks again

 

[Mike-ICFGD]

Point 7.
This is not how it works.
The Pt/Pd will alloy with the Gold and this will create an alloy with marginally higher melting point than the pure Gold, then what ever Copper and Silver is in the Gold alloy will lower it.

Plated Silverware may not have Copper in it, there are many strange alloys used as basis of plated Silver, so check this first.

Thanks will keep that in mind on the silverware when I get to that project. Thats a very good point.

Also thanks regarding the platinum question. I was hoping it would be that easy but Feared it might not . Guess I'll have to stick to visually inspecting for them and setting aside.

 

[Mike-ICFGD]

UPdate: Successfully melted about 7 different lots of various karat gold into buttons, verified lost material, and then melted the whole lot into one bar as planned. Tomorrow it goes to the refiner. will see how bad I did when I analyze the data tomorrow as its very late. I know I saw a few microbeads in my crucible after the final pour, set it aside for later recovery.

 

[Yggdrasil]

Thanks for your input, I totally understand trying to save your equipment for as many uses as possible, especially when working with hobby sized lots. I just wanted to confirm there was no more safety oriented reason not to use graphite in open flame. For the size of my pours, 5 to 10 pours from a $10 mold is an acceptable price to pay significantly smaller than 1%.


Thanks again

If you use Graphite in open flame it will last longer with a reducing flame, which will lower the efficiency.

 

[nickvc]

The flux question is easily answered as you melt karat scrap you will get oxides from from the base metals which makes melting harder, the flux absorbs the oxides plus some gold !
Wonder why your refiner uses so much …
To build a furnace is very simple use your hard fire bricks to create your base then use the soft ones to form an enclosure , only build it to a size that takes your crucible with space to allow the flame to circle it easily or you will waste gas, leave a space to insert your torch at the bottom and create a lid using the soft bricks leaving a space to allow venting , once your gold is molten stir the gold well to ensure it’s homogenous, pour into a preheated mould , once the bar has set pour directly into a cold water tub and most of the flux should shatter off leaving a reasonable surface.

 

[Mike-ICFGD]

The flux question is easily answered as you melt karat scrap you will get oxides from from the base metals which makes melting harder, the flux absorbs the oxides plus some gold !
Wonder why your refiner uses so much …
To build a furnace is very simple use your hard fire bricks to create your base then use the soft ones to form an enclosure , only build it to a size that takes your crucible with space to allow the flame to circle it easily or you will waste gas, leave a space to insert your torch at the bottom and create a lid using the soft bricks leaving a space to allow venting , once your gold is molten stir the gold well to ensure it’s homogenous, pour into a preheated mould , once the bar has set pour directly into a cold water tub and most of the flux should shatter off leaving a reasonable surface.

Thanks, I've already ordered some of the "soft" fire bricks to attempt something like this.
yah I don't know, he was using an electric crucible and he put a good 2 or 3 tablespoon fulls in with about 20 ounces of mixed karat scrap. Oh well he isn't my refiner any more anyway lol.

 

[Mike-ICFGD]

Did the data analysis using the results from my XRF scan and also the refiners pre melt XRF numbers. His came back higher purity than mine amazingly. and upon calculating the numbers I may have more gold than I expected by up to 2%. which is unheard of. taking the worst scans still put me at only 3.36% less than expected "par" gold in there. Considering I spilled the 14k melt and had to clean it up off the counter I consider this extremely good results, probably too good to be true.

Will await final results from the refiner
Thanks to everyone who helped me to get past my fears regarding melting the gold down

 

[Anil]

If you are dealing with 1 kg or 2 kg of refined gold or scrap gold for melting, a small induction melting furnace with a compactly cast graphite crucible will be ideal though the initial cost may be higher. But the operation is neat, clean, noiseless and the output is a homogeneous melted bar.

 

[Martijn]

Point 7.
This is not how it works.
The Pt/Pd will alloy with the Gold and this will create an alloy with marginally higher melting point than the pure Gold, then what ever Copper and Silver is in the Gold alloy will lower it.

I thought an alloy always has a lower melting point that eighter one of the elements in it. So it woud be slightly under the melting point of gold.
PGM's are soluble in lead at even much lower temperatures, correct me if i'm wrong please.

 

[Lou]

I thought an alloy always has a lower melting point that eighter one of the elements in it. So it woud be slightly under the melting point of gold.
PGM's are soluble in lead at even much lower temperatures, correct me if i'm wrong please.

Depends on the phase diagram. There are exceptions to every rule.

 

[Martijn]

Melting Points of Common Materials | Toolbox | AMERICAN ELEMENTS ®
Very usefull chart for melting and alloying.
melting temp's in degr C and F

82

Lead

327.46°C

621.43°F

78

Platinum

1768.3°C

3214.9°F

79

Gold

1064.18°C

1947.52°F

Gold-Lead Alloy

215 °C

419 °F

Lead-Platinum Alloy

290 °C

554 °F

 

[Yggdrasil]

I thought an alloy always has a lower melting point that eighter one of the elements in it. So it woud be slightly under the melting point of gold.
PGM's are soluble in lead at even much lower temperatures, correct me if i'm wrong please.

I have always been under the impression that it will lower the temperature under the highest melting point.
I do not think an alloy of Lead and Gold will melt under, say 330C but it will be lower than 1064C.
If it does it will not make sense to me, but then again I have been wrong before.

 

[Yggdrasil]

Melting Points of Common Materials | Toolbox | AMERICAN ELEMENTS ®
Very usefull chart for melting and alloying.
melting temp's in degr C and F

82

Lead

327.46°C

621.43°F

78

Platinum

1768.3°C

3214.9°F

79

Gold

1064.18°C

1947.52°F

Gold-Lead Alloy

215 °C

419 °F

Lead-Platinum Alloy

290 °C

554 °F

Hmm, nice.
I learned something new today
But I guess the amount will come into play as well.

 

[Martijn]

Yes the ratio determines where on the graph you end up.
like this one:

that's why platinum with lead is only at 290 degrees C, I guess that's a 50/50 ratio.

 

[Mike-ICFGD]

If you are dealing with 1 kg or 2 kg of refined gold or scrap gold for melting, a small induction melting furnace with a compactly cast graphite crucible will be ideal though the initial cost may be higher. But the operation is neat, clean, noiseless and the output is a homogeneous melted bar.

thanks, I had considered them but I see so many reviews of them crapping out quickly. at least the ones on amazon. Perhaps I should be looking at higher end models. I wouldn't mind a tabletop cupelling furnace either, but I'm easing into this.


and of course once I get pin samples I'll need a rolling mill as well

Then someday I'll break down and want to do some refining work and will ahve to buy lab glass and a vaccum pump and a fume hood and ... lol ya it doesn't end.

 

[nickvc]

To be honest once you find out how easy you can build a furnace to just about any size , almost anywhere , very cheaply and if you add blown air to your torch it’s also very fast why buy a fixed expensive furnace unless you are melting all day every day.
If you have an outside area you can put a sheet metal roof up and melt there, once done and everything is cold , dismantle put away until needed again .

 

[Mike-ICFGD]

To be honest once you find out how easy you can build a furnace to just about any size , almost anywhere , very cheaply and if you add blown air to your torch it’s also very fast why buy a fixed expensive furnace unless you are melting all day every day.
If you have an outside area you can put a sheet metal roof up and melt there, once done and everything is cold , dismantle put away until needed again .

First off as with everyone else thanks for your input.


My "soft" fire brick just arrived today, so I'll be able to play with that soon, but since I don't have any melt needs at the moment it will probably wait a few days. I'm excited to see if I can get my hose type propane torch to convince a melt with these new bricks. Also have a small amount of kaowool arriving Wednesday so I can work with that as well.

**How would you suggest adding blown air to the torch? IE aim it as a 2nd air stream into the flame to mix inside the melt dish? or into the back of the nozzle or something else I haven't thought of? What's the most efficient way to add blown air to a torch that's originally made for ambient air only.



The reason to buy a pre made propane furnace imho is just to get the gas plumbing prefabricated vs creating myself. Looks like with an estimated $50 to 75 in parts I can create my own burner/hose setup, or for $175 I can buy a prefab unit with 2 burners and the needed plumbing... Then if I decide the furnace isn't to my liking I can use the plumbing to create my own bigger furnace using my bricks and kaowool.


Then the digital cupelling furnace is specifically for fire assay, and I'm really not aware of any way to accomplish that task affordably and accurately without it.



I tried a little of this when using the hard brick the only time I accomplished a melt outside of my brothers forge was with a weed burner and a pinhole air blower pointed directly into the back of the burner nozzle where the air/fuel mixes pointed into an enclosure of the "hard" fire bricks. I don't think I wan to go back to using the weed burner though, (its my sous vide blowtorch ) I'll buy an acetylene torch before I go back there, just too much wasted heat/gas on that weed burner due to so much of the flame enveloping/missing the melt dish. Feels like I'm using a trebuchet to hit an ant...

 

[Mike-ICFGD]

Yes the ratio determines where on the graph you end up.
like this one:
View attachment 59482
that's why platinum with lead is only at 290 degrees C, I guess that's a 50/50 ratio.

So yeah this had me thinking on a total tangent... If you can melt noble metals in lead at stovetop temps, wouldn't a significantly easier way to refine by inquarting with lead, and then using HCL boils to remove the lead? Similar to the basic nitric process ?


I guess this wouldn't do anything about the copper and silver impurities....


So it would only be a way to take pure gold and dilute it with lead then get your pure gold back. Seems there would not many practical uses for mixed gold from ewaste, gold filled scrap, or karat scrap in that case?