melting kilns

[Binraker]

I have been starting to get the kit together to do some casting. To melt my metal I bought a small crucible/kiln kit from ebay, one of these (http://www.technicalsupermarket.com/component/option,com_virtuemart/page,shop.product_details/flypage,shop.flypage/product_id,1635/category_id,386/manufacturer_id,0/Itemid,4/) which works quite nicely. I also bought the "Graphite protector paint" which does protect some of the graphite when it doesn't rub off.

However, after half a dozen uses the graphite is starting to fall apart a bit and is quite obviously of the course grain variety. I was wondering if anyone had any experience of the oxidation of graphite crucibles and whether a fine grain graphite would be less liable to this disintegration. Does anyone own/use one of the 1kg/2kg/3kg melting furnaces (https://www.cousinsuk.com/catalog/5/0/1229/4887.aspx?) (or this (http://www.hswalsh.com/product/crucible-furnace-tf58))that one sees advertised about the place and if so, how long do the crucibles in them last?

My other option is to use a salamander crucible in the little kiln have but that would require some irreversible modification of the fire-brick structure. (Or use my pottery kiln, but that's probably a bit overkill)

[art925]

I would first go back to your supplier and ask them how long they feel the crucible should last. The may be able to suggest something, or replace what you have, it could be substandard in construction.

[Ebo Von Gaz]

It should definitely be lasting you more than half a dozen firings, I melt for casting in a crucible made by a potter friend out of clay and grog, nothing special, and it's done at least a hundred melts.How are you handling and loading the crucible? has it had a knock or been overloaded? sometimes if you wedge in metal, which expands on heating, it can crack crucible. I also use a larger graphite/ceramic crucible for brass casting (2-3 kg) and that's holding up fine after at least half a dozen melts, though you need to temper them before you first use them or the ambient moisture trapped in an unglazed material can expand and damage your crucible, either by cracking or spalling, I think this is also the case for graphite crucibles.

[Binraker]

The company says in their instructions (http://www.technicalsupermarket.com/R-9%20INSTRUCTION%20MANUAL.pdf) that they should last about 10 firings. (although the company are UK based and the thing says "made in UK" on it, I get the feeling there is some translation form a foreign language going on here.) The problem stems from the fact that the crucible is pure graphite and not graphite clay like salamanders crucibles are. However pure graphite comes in a number of grades and one of the grading factors is the size of the grains in the graphite. These seem to be made of a large grain material, which I assume is cheaper and I am wondering if a finer grain material would be more corrosion resistant. Its not craking or spalling, its just slowly disintegrating.

Admittedly this is all a bit academic as I will probably just end up modifying the kiln to take an A5/0 salamander as they last forever with a bit of care.

Ebo, I hadn't thought of standard clay crucible, I have some Raku clay that is naturally high grog and nice and robust so I may try making one with that.

Bottom line, If anyone is looking for a metal melting system, the one I bought probably isn't a very good one. As they say, "If you can't lead by example, at least be a demonstration of how not to do it"

[Ebo Von Gaz]

Crikey 10 firings sounds really shonky!

I can ask my friend the exact makeup of the crucible clay if you like. I do have a feeling it might even have been Raku but I don't have pottery experience.
The crucible its self is only little (holds maybe 2-3 oz silver when melted) but has lasted at least a couple of years of regular (several times a week on average) use.
It has developed a couple of cracks which seem to be holding together with borax glaze more than anything, and I'm very gentle with, it but still i'm very happy with it's performance, especially as she made me three and I'm still on the first one!

Thanks for going there for us all! It sounds like the furnace works fine, but the crucible is a bit of a letdown, and it's a bit of a swizz having to spend good money on an integrated furnace/crucible kit and then have to improvise on the crucible front, or keep buying new ones from the supplier every couple of weeks!

[Binraker]

I have now modified the kiln to take a salamander. you can read all about it here (http://peterblacksart.wordpress.com/2014/03/01/melting-metal/) on my blog should you wish.

[Binraker]

And I have now tested my modified kiln (http://peterblacksart.wordpress.com/2014/03/20/metal-melting-part-2/).

It works!!!

I melted 50g of silver and cast it successfully, twice.

[Tabby66]

Great result!! I bet you're really pleased with the mods and finished piece!!