Rudimentary tilting furnace.

[Amol Gupta]

So I came across a sreertips video of melting silver.



I like the idea of wrapping the ceramic wool around the crucible, makes for a very good candidate for tilting furnace.

A few things I'd like to do differently, firstly I'd like to use an electrical source for heating(kanthal wire most probably) instead of a torch flame, wrapped around with ceramic wool this way the heat source will be consistent during the melt even at the time of pouring, leaving no residue on the crucible which is often the case if the charge is not hot enough.

A set up like this will be easy to mount and pour from, making it a one man job.

Something I cannot figure out is the material for the crucible. I am looking for something that is thermally conductive but electrically insulated. My first choice was using a graphite crucible it has very good thermal properties but it is also electrically conductive which makes it dangerous for handling.
I was thinking of coating the crucible with some material as is shown in this video.



But I guess I'm better of using a suitable material, I have seen furnaces where the heating element is coated with some sort of ceramic being extensively used but I'm not sure of the material.

Any input on the same would be highly appreciated.

Thanks.

 

[4metals]

The issue with a tilting furnace is the crucible tends to want to fall out of the furnace so it has to be secured in place. There are 2 ways I have seen this done. One method uses what are called T crucibles. They have a pour spout built into the crucible. The entire crucible sits in the furnace and a lid secures it in place. These furnaces are heated by heat coils and the entire furnace tilts to pour. One manufacturer of these furnaces is Vcella kilns HERE. The smallest one has a number 16T crucible and they go all the way up to a #400 crucible. Heat up is longer and the max temp is 2300ºF but the crucibles change out quickly. Plus they are a fraction of the cost of an induction furnace of comparable size.

Another route used with induction furnaces is to actually cast the crucible into the furnace and using a moldable refractory make a pour spout to allow the molten metal to pour when titled. There are 2 types of refractory used to set the crucibles one to set the crucible into the furnace which I believe is called grog, and the second to mold the pour spout which which is called shamrock. The down side to this is the maintenance required to cast the crucible in and the set up time as well as the time to change out a crucible.

The video of the gentleman coating his graphite crucibles is interesting. He uses pure graphite crucibles which break down when exposed to oxygen. The coating effectively keeps the oxygen from reacting with the graphite.

 

[snoman701]

The video of the gentleman coating his graphite crucibles is interesting. He uses pure graphite crucibles which break down when exposed to oxygen. The coating effectively keeps the oxygen from reacting with the graphite.

Yes, I was especially interested in that. I figured it was one of the ITC products. I use little graphite cup crucibles for gold in my induction heater, but the lifespan isn't great. Even doubling the lifespan would be pretty amazing.

 

[Amol Gupta]

The issue with a tilting furnace is the crucible tends to want to fall out of the furnace so it has to be secured in place. There are 2 ways I have seen this done. One method uses what are called T crucibles. They have a pour spout built into the crucible. The entire crucible sits in the furnace and a lid secures it in place. These furnaces are heated by heat coils and the entire furnace tilts to pour. One manufacturer of these furnaces is Vcella kilns HERE. The smallest one has a number 16T crucible and they go all the way up to a #400 crucible. Heat up is longer and the max temp is 2300ºF but the crucibles change out quickly. Plus they are a fraction of the cost of an induction furnace of comparable size.

Another route used with induction furnaces is to actually cast the crucible into the furnace and using a moldable refractory make a pour spout to allow the molten metal to pour when titled. There are 2 types of refractory used to set the crucibles one to set the crucible into the furnace which I believe is called grog, and the second to mold the pour spout which which is called shamrock. The down side to this is the maintenance required to cast the crucible in and the set up time as well as the time to change out a crucible.

The video of the gentleman coating his graphite crucibles is interesting. He uses pure graphite crucibles which break down when exposed to oxygen. The coating effectively keeps the oxygen from reacting with the graphite.


View attachment 67283

I do get you point of the crucible tipping over and handling the same seems trivial(atleast for the small size furnaces I will be dealing with).

Here is the primary issue I'm facing, in the rudimentary design I am proposing the kanthal wire I will be using for heating will be touching the crucible that will be holding the charge. I want the crucicle to effectively transfer the heat onto the charge(low heat resistance). Secondly, now if the crucible is not electrically insulated(i.e does not have a very high resistance), it affect the calculation for the wire resistance as the crucible which is now in contact with the wire creates a parallel electrical connection reducing the total resistance throwing off the resistance calculations. Also this is a safety hazard as if anyone now touches the crucible it can be a source of electrical shock.

So for these reasons the material of the crucible or some coating material I'm looking for should have low thermal resistance but high electrical resistance.

I'm not exactly sure of what grog is and if it is readily available.

 

[Amol Gupta]

The white crucible as seen in sreetips videos seems like a good candidate with respect to thermal conductivity as I can see the gap between the ceramic wool and the crucible is red hot i.e passing on the heat through the material only if it has high electrical resistance I will have something I can work with.
Does anybody has an idea what material it is....?

 

[4metals]

The crucible looks like a fire assay fusion crucible. This is what AI has to say about the different materials these crucibles are made from.

AI speaking :

Fire assay fusion crucibles can be made from cordierite, fire clay, or other refractory materials. The crucibles are designed to withstand high temperatures and resist thermal shock, erosion, cracking, and flux attack.

Materials
Cordierite: Can withstand the temperatures required for assaying

Fire clay: Mixed with other refractory materials to create crucibles that can withstand high temperatures

Boron nitride: A synthetic ceramic material with high thermal conductivity and thermal shock resistance

Alumina, zirconia, and magnesia: Ceramics that can tolerate high temperatures
Silica: A heat-resistant and chemically inert material that can withstand high temperatures

Crucible design
Fire assay crucibles are available in a wide range of shapes and sizes
Their design and composition give them excellent resistance against flux attack, erosion, cracking, and thermal shock

Back to me, human speaking.

Typically these crucibles are used once and are not re-used. While they can likely withstand a few firings re use for assaying is not wise.

So you want to wrap a crucible with the heating element wire and cover it in an insulating blanket and heat it up? Interesting approach, I would like to hear how you make out.