Crucible SHOCK Using a Electric Furnace

[tgeer2]

Hi Everyone!
Yes I am new at this and I want to thank everyone for all their dedicated time in helping out one another with this forum. I have spent many hours reading these posts and learning before I attempt smelting my scrap gold. I have a electric Jelenko Dental/Jeweler furnace and have successfully melted some gold using a graphite crucible just to make sure the furnace worked, which it did. My question is do I need to purchase a pair of graphite tongs or can I use a different type of tongs so I can remove the gold while still melted without thermal "shocking" the crucible? I eventually want to make gold shot and use the aqua regia method to purify the gold so I can make small bars. Any advice in this process would be much appreciated. Thanks Tom

 

[Harold_V]

You should be able to handle the crucible with steel tongs, although you are at risk of crushing.
Can't you simply pour from the melting furnace? Seems to me they have a built in handle that permits pouring.

I think you'll come to understand that such a furnace is not worth the trouble it takes to run one. You are far better served using a torch and melting dish. You can melt ten ounces of pure gold and have your setup put away before an electric furnace approaches the melting point. Besides, graphite crucibles are very expensive and do not enjoy a long life.

Harold

 

[tgeer2]

Thanks Harold for your advice I appreciate it very much. I just picked this small furnace up for $20.00, thought I could use it for something down the road. The opening is only 6" square, but I know what your saying with torches and I have a set but the wife will get a little upset if I use them in the house, its about 8 degrees outside and wind blowing :lol: This whole thing is a learning thing for me and I have taken everyone's advice and just started reading and trying to absorb information starting with safety then going from there. But now next purchase will be a melting dish so I can use my torches when it warms up, is this just a standard clay melting dish? Thanks again

 

[joem]

Can you just preheat your tongs?

 

[tgeer2]

Yes I can preheat tongs, not quite sure what temperature but I wanted to know if steel tongs would do anything to the graphite crucible (shock) and was told be careful not to crush the crucible, unfortunately this electric furnace does not have a built in handle to pour off the gold you have to reach inside and physically grab the crucible with tongs to retrieve. Thanks Tom

 

[Lou]

Graphite isn't really susceptible to thermal shock nor is SiC. It's anything that's clay bonded that you need to be careful while using.

Lou

 

[goldsilverpro]

Is this the type furnace you have?

http://www.fleamarketstore.com/ca/4-320634256382-12/jelenko_jewelry_kiln_or_dental_inlay_furnace.htm

 

[Harold_V]

Thanks Harold for your advice I appreciate it very much. I just picked this small furnace up for $20.00, thought I could use it for something down the road.
The opening is only 6" square, but I know what your saying with torches and I have a set but the wife will get a little upset if I use them in the house, its about 8 degrees outside and wind blowing :lol:

Well, now that I have my head out of that dark place, you did good. My mind went to a different type of furnace (my fault---your description should have alerted me). While small, that's a nice little furnace and should serve you well. They are used for burning out molds for investment casting, along with other uses. The price was outstanding!

This whole thing is a learning thing for me and I have taken everyone's advice and just started reading and trying to absorb information starting with safety then going from there. But now next purchase will be a melting dish so I can use my torches when it warms up, is this just a standard clay melting dish? Thanks again

Yes, a clay dish is more than adequate. There used to be some light tan colored ones on the market, I think made in Mexico. They were quite unstable and prone to cracking, even when properly seasoned. The white ones on the market, now, do a much better job and can be relied upon for many heats. They can even be cleaned when they get covered with sticky flux, then reused.

Lazersteve offers melting dishes on his web site. They do a fine job----but must be seasoned and covered with a film of borax before being placed in service. There's been a lot posted on that subject, so when you find a little time, do a search.

Harold

 

[tgeer2]

Is this the type furnace you have?

http://www.fleamarketstore.com/ca/4-320634256382-12/jelenko_jewelry_kiln_or_dental_inlay_furnace.htm

Yes! This is exactly the type and it really worked well. Thanks for your research.
Tom

 

[tgeer2]

Thanks Harold for your advice I appreciate it very much. I just picked this small furnace up for $20.00, thought I could use it for something down the road.
The opening is only 6" square, but I know what your saying with torches and I have a set but the wife will get a little upset if I use them in the house, its about 8 degrees outside and wind blowing :lol:

Well, now that I have my head out of that dark place, you did good. My mind went to a different type of furnace (my fault---your description should have alerted me). While small, that's a nice little furnace and should serve you well. They are used for burning out molds for investment casting, along with other uses. The price was outstanding!

This whole thing is a learning thing for me and I have taken everyone's advice and just started reading and trying to absorb information starting with safety then going from there. But now next purchase will be a melting dish so I can use my torches when it warms up, is this just a standard clay melting dish? Thanks again

Yes, a clay dish is more than adequate. There used to be some light tan colored ones on the market, I think made in Mexico. They were quite unstable and prone to cracking, even when properly seasoned. The white ones on the market, now, do a much better job and can be relied upon for many heats. They can even be cleaned when they get covered with sticky flux, then reused.

Lazersteve offers melting dishes on his web site. They do a fine job----but must be seasoned and covered with a film of borax before being placed in service. There's been a lot posted on that subject, so when you find a little time, do a search.

Harold

Thanks Harold, I will take your advice and check out lazersteve's web site and season the dish as you mentioned. I'm trying to break the whole process down into steps and research (read) before moving on to the next step. You guys are so wonderful and I greatly appreciate all your wisdom.
Tom

 

[AuMINIMayhem]

kids, don't try this at home..


graphite is really quite good at withstanding thermal shock.. I've run my furnace outside in a snowstorm with temps less than 20 degrees F and then after pouring my melt off, I placed my crucible in a pile of snow (read further.. "placing" = "accidentally dropping").. nothing... it sizzled like crazy,but once it cooled off, I checked it for microscopic cracks, etc.. and found it to be perfectly fine.

This was not a "fool-hardy" experiment.. this was purely by accident, (placing it in the snow = clumsily dropping it in the snow). A few weeks later some discussion at work prompted some experimentation.

We use graphite molds quite a bit in our SiC mirror production, so there were some questions about thermal shock that had never been answered. The topic came up and I told them about how I had dropped my crucible at roughly 1800F into the snow and we decided to run a series of experiments.

It actually turned out to be a handy piece of info to have because some of the things we do with SiC require us to rapidly cool graphite molds. (I had procurred some of the graphite we had to machine out my own crucibles.)

Sometimes those engineers are a little too afraid to try something and they need a clutz like me to come along and show that it can be done. :lol:

That being said...

I DO NOT RECOMMEND ANYONE RAPIDLY COOL ANY CRUCIBLES, MOLDS, ETC BY IMMERSION IN WATER, SNOW, SODA, UNICORN TEARS ETC..

however.. grabbing a hot crucible with room temperature tongs is fine. (provided there are no defects, cracks, etc.) I'd be more worried about deformation/metling/welding of the tongs to the crucible in all honesty.

Also, please remember this is graphite I'm talking about... I have not had this experience with SiC or any other material so I can not speak from experience as to how it reacts to thermal shock.

 

[AuMINIMayhem]

p.s. I know you're asking "why the heck was he doing a melt outside in a snowstorm?"

The short answer is, I have a nice 12' x 12' x 8' high, three walled shop I built originally when I had taken an interest in blacksmithing. It's rather similar to this:
http://www.mofga.org/Publications/M...teerProfileWinter0506/tabid/1127/Default.aspx

I repurposed it when I sarted messing around with the refining stuff. It's nice. I have a little propane heater in there and I'm able to vent fumes out the back and away from the furnace and I have a small fume hood I built for any Nitric work, that way, I'm not out in the open with the "red cloud of death" blowing back in my face. 8) So, I'm able to work in pretty much any kind of weather, short of really high winds or torrential rains without fear of shock or inhaling things I'd rather not inhale..

I may be a clutz, but I'm not carefree and haphazard, I do keep safety in mind. 8) Sometimes though... my hands... they don't like to cooperate.. :mrgreen: