1500C Furnace Redesign

As much as I would prefer to only report success we are learning a lot which means of course means making some mistakes along the way.

The first design of our glass melting furnace relied on a 2KW wire heater. After installing the wire we found that it only deliver 1.3KW at best. In addition, burying the metal wire in castable refractory was likely a fatal mistake, because I now suspect that the wire needs to be able contract and expand each operating cycle. Even if it didn’t there is a chance that at operating temperatures the refractory (which is a good insulator at room temperature) could have become conducive at working temps — potentially shorting out the entire heater coil.

In addition, even if the coil had operated at 2KW for any length of time (ignoring the above) it would have taken a long time to heat up and likely struggle to maintain the desired temperatures. In other words, it was vastly underpowered.

The new design is based a 7KW system comprised of Silicon Carbide (SiC) heating elements (ED shape). In addition to heating up rapidly, the new setup will allow us to operate continuously 1500C. This will allow us to print borosilicate (Pyrex®) and possibly interesting things like (fired) ceramics and de-composed granite (that is what the “dirt” we are sitting on top of is mostly comprised of).

XB7A1797 — Sometimes you have to break an egg to make omelet. It was sad to tear apart, but it will be oh-so-much for the better.

XB7A1802 — All stripped done ready for the much improved design. OK tearing it down wasn’t so bad after all.

Screen Shot 2015-10-14 at 1.14.04 PM — Orange is our alumina crucible. The transparent shell represents the lightweight fiber blanket that will be used in place of much heavier (and thus less insulating) refractory used previously. The blue section of each rod is the cold zone of our SiC heater rods, with the hot section shown in red. Electrodes attach to each of the blue ends.

XB7A1792 — Tiny little SiC test coil running 2.0 amps at 41 volts (only 92 watts, we will be running 7,000!). Pretty much melts glass instantaneously. The 2300F rated fiber blanket bonded to it (won’t happen in our actual design).

So while it has been a bit of a misstep, it will only be for the better. Our set of custom SiC rods are currently being fabricated in China and will hopefully ship to us this week. All other aspects our massive printer have been tried and verified to work. More soon.

1500C Furnace Redesign