Non-Chemical Best melt technique for small batches

[Shark]

A stand alone mapp tank I am not sure, but would think about the same as a propane tank of similar size. Years ago I used a small mapp tank and an oxygen tank of the same size(like a miniature oxy/acetylene kit). Welding on cast iron or brazing they usually wouldn't last ten minutes together. Back then you could get both tanks for about $14. The cost of those tanks plus the cheap hoses are why I quit using them, they did the job in an emergency, but were not worth it over the long haul. Now days I can have a grill sized propane tank filled for around $12 and my big oxygen tank for $16.

 

[Alabama938]

That is exactly the experience I had… Yellow tank by itself will last quite a while, but the red is crap, right as I got the metal where I wanted it it ran out. My wife is never gonna let me get a huge oxygen tank LOL

 

[butcher]

Tanks come in all sizes, check your local welding shops, harbor freight, tool stores or garage sales, for acetylene/oxygen welding/cutting torch setup (air port size) or small portable tanks and brazing welding set ( gauges hose, back flow check valves or flashback spark arrest er and torch head with tips) can be found fairly cheap.With an addition of different tips for the torch handle you can use a propane tank with this setup (barbecue sized tank if you wished)...
As with most tools, they hold a good resell value, themselves normally being good investments (that can save time or make you money to buy bread) and can be useful for many small repair jobs, these tanks are too small for doing larger welding or metal cutting jobs.

 

[Shark]

They have small sets just for plumbing and HVAC work. They usually run fairly reasonable and need very little space. They are also very portable.

Here one example..

https://www.harborfreight.com/welding/welders/oxygen-acetylene-welders/portable-torch-kit-with-oxygen-and-acetylene-tanks-65818.html

 

[jadedalex]

Alabama, you wrote:

it doesn’t seem like you can overdo it on the borax or sodium carbonate because Au doesn’t dissolve in those liquefied materials.

You most certainly can...Read a thread here about a new refiner who didn't glaze his Graphite crucible and fused his Gold into the crucible. Using filter papers just adds another step to your process. If you gently heat your powders in a flask or beaker before melting, you don't need paper which now requires Borax...just saying.

 

[Alabama938]

Alabama, you wrote:


You most certainly can...Read a thread here about a new refiner who didn't glaze his Graphite crucible and fused his Gold into the crucible. Using filter papers just adds another step to your process. If you gently heat your powders in a flask or beaker before melting, you don't need paper which now requires Borax...just saying.

Oh I was talked about a ceramic melt dish, I haven’t used the graphite, but borax wrecks it I’ve heard, and I’ve certainly learned since then that there is such a thing as too much borax

 

[jadedalex]

Oh I was talked about a ceramic melt dish, I haven’t used the graphite, but borax wrecks it I’ve heard

Borax doesn't wreck Graphite. It is absorbed by the Graphite. Once absorbed, the crucible will work just fine...

 

[shruli]

Hi all. Sorry to add to an old post but I think it is relevant and hope it helps someone out. First, A massive thank you for what I have learned about refining from this site, as it is now a massive part of my life & I love it I am melting regular small amounts of gold, silver & to start I used just propane for melting, which I found okay with the right torch for very small amounts, but was struggling to melt, keep the heat & pour more than a couple of grams. I picked up a cheap oxy propane mini jewellery torch which did the job from 1 to 100grams great, but I was getting through £20 of oxygen in 30 minutes & large oxygen bottles are not really practical for my small workshop. I looked into the cheap eBay oxygen generators but could not find much info anywhere for using them with a small torch. To the point! I spent £100 & took the chance & so glad I did. On the lowest setting of 1l per minute, this machine delivers 92% oxygen, which I find perfect for melting & soldering all precious metal at a fraction of the cost & far safer than industrial oxygen bottles. Any setting above 1L per minute reduces the concentration of oxygen, so would never power cutting & welding torches, but perfect for Smiths little torch or the cheap copies, Oxyturbo 90 & similar. Hope this helps.

 

[orvi]

Hi all. Sorry to add to an old post but I think it is relevant and hope it helps someone out. First, A massive thank you for what I have learned about refining from this site, as it is now a massive part of my life & I love it I am melting regular small amounts of gold, silver & to start I used just propane for melting, which I found okay with the right torch for very small amounts, but was struggling to melt, keep the heat & pour more than a couple of grams. I picked up a cheap oxy propane mini jewellery torch which did the job from 1 to 100grams great, but I was getting through £20 of oxygen in 30 minutes & large oxygen bottles are not really practical for my small workshop. I looked into the cheap eBay oxygen generators but could not find much info anywhere for using them with a small torch. To the point! I spent £100 & took the chance & so glad I did. On the lowest setting of 1l per minute, this machine delivers 92% oxygen, which I find perfect for melting & soldering all precious metal at a fraction of the cost & far safer than industrial oxygen bottles. Any setting above 1L per minute reduces the concentration of oxygen, so would never power cutting & welding torches, but perfect for Smiths little torch or the cheap copies, Oxyturbo 90 & similar. Hope this helps.

Yes, investment to the oxygen concentrator is very good one. If you are going to use it regularly, with small 1-2kW oxy/propane or oxy/acetylene torch it is an awesome combination. Reputable machine will last you many hundreds of hours with high percentage oxygen. After some time, there will probably be a need to replace the cartridge of ?zeolite? inside to come back to good 90+% of oxygen. I will advise machines that can deliver few liters of oxygen/minute, this will give you so much power for melting
I have the experience of using this setup for melting palladium in <10g quantities in magnesia dish wrapped in mineral insulating wool, and it works wonderful. With normal propane/butane gas, no need for acetylene. We could even melt platinum, but it was on the edge of "usability"... For platinum, i couldn´t advise propane/butane as fuel, you will need acetylene.
And a good point here, you will need welding helmet, or your eyes will be pretty well #!&@ed up afterwards

For gold, i use classic quartz dishes from aliexpress (cheap and disposable), sprinkled with borax just to glaze it. I than take an empty iron can, around 3 times as wide as quartz dish, cut the appropriate strip of mineral wool and wrap it around the inside of the can to insulate it - make it somewhat higher than the can itself, as the flame will slowly eat away the exposed edge of the can
Then I poke a hole to the bottom part of a can to create entrance for the burner. Another cut piece of wool just loosely placed to the top of the "furnance" to create a lid. I dont make a hole in the lid, just putting it that way the flame will come out from the sides.
Very important is to insulate the bottom with circular piece of wool too. If the thickness of wool is below one inch, i would advise double it for better insulation.
Also, dont use too large can for small burners and dishes, as the heat will have more places to dissipate out, making the metal nearly impossible to melt.

Pour gold powder to the melting dish and slightly "cake" it on the surface, so putting it into the "furnance" you will not blow out the gold. Then just apply the torch to the bottom hole and heat until the whole thing come up to the temperature and melt. With small batches under 1ozt in the 150g SiO2 dish with propane/butane air torch of 2kW power, it wil take somwhere between 10-20 minutes to properly melt the thing.

Then put out the burner, hold the dish with tongs and heat it directly with the flame of the burner (you just pulled out of furnance) as pouring the gold into the mold. Need some practice to do it right or you can just let it slowly cool inside the dish and then take it out.