melting metal

In attempt to do some silver casting I decided to buy a small electric melting kiln. I bought a new one off ebay of this verity along with a spare crucible and the protector paint.

It worked.

However, the crucibles show quite severe corrosion and start to fall apart after half a dozen melts. It should be noted that this is what the supplier suggested might happen but the extent to which it occurred was slightly alarming. The graphite that the crucibles are made from is a course grain variety and I wonder if this is a cheap material and in fact if they were made of fine grain graphite this would not be so much of a problem. The reason I am thinking this is that the disintegration seems to be arising from the material between the grains disappearing and the grains then falling off. Not wanting to spend the rest of my life buying these crucibles, I decided to modify the kiln to take an A5/0 salamander crucible.

Salamander crucibles are graphite/clay and this makes them far more oxidation resistant. They will last many years if cared for properly and should perform hundreds of melts before they need replaced and what’s more, they are cheaper than the disintegrating pure graphite ones!! The only problem with graphite/clay is it is porous to gas at high temperatures so careful degassing is normally required when using them with a flame (especially and oxygen rich flame as copper allows tend to absorb oxygen when molten and then release it when they cool leaving bubbles in the casting.) With an electric heating apparatus, this is of course not a problem!

To perform the modification three things were needed.

1. A larger orifice to get the crucible and tongs in and out.
2. new tongs
3. a new lid.

This is how the top of the kiln looked when I started. The disintegrating crucibles sit on their top flange dangling their body into the kiln proper.

After a little cutting with a coping saw blade (the brick is very soft so easy to cut.)

Now we have a big enough hole to things in and out. A pair of tongs…

These were made with a length of 2.5mm TIG welding filler rod. I made 2 “C” forms by heating a length of rod up and forming it round my ring triblet, then cutting them off and attaching them to a folded length of rod with my home made Pulse Arc Welder.

Finally the new lid for the kiln is simply half a thermal brick that I had left over from some work on my pottery kiln with 2 holes and another bit of welding rod as handle.

I am now just waiting on my shiny new investment casting flasks and then I’ll fire it up. I will post what success if any I have.