To reduce the risk of electrocuting myself, I made a ceramic box to separate the bare-metal and electrically-live heating coil from the inside of my furnace. Seemed a good idea.
ALERT & UPDATE: Bathroom tiles conduct electricity at 1000C 🙁 See here.
The Problem
Other furnace designs online have the coil in a routed helical channel on the inside face of the furnace’s brick walls. Apart from there being nothing between you and the 240V coil other than STEEL tongs, a STEEL or CARBON crucible and molten metal, it also seems difficult to secure coils in the channel, and over time the coil creeps and sags.
VegOilGuy, the guy I mentioned in the last post, addressed it by putting the coil in a hidden recess. Seemed a lot of work and a pain to replace.
My Solution: The Ceramic Shield
I did a little SketchUp model prior to building and forgot to take a photo of the actual shield before putting it in the furnace.
I have tried to address three things with my ceramic enclosure:
- The “I don’t want to die today” 240V biggie,
- You install the coil in tension around the outside of the shield prior to putting it in the brick enclosure so you can get it pretty tight fit and its held in place between the inner solid ceramic wall and the bricks.
- the terminals both stick out vertically from the base as stainless steel threaded rods, so:
- You can remove the shield as “cassette” without dismantling the whole furnace
- You can keep all the wiring out of the way and safe (and cooler)
How I Made It
The ceramic shield is made from 300sqr white-glazed ceramic bathroom tiles. They are 6mm thick. Porcelain tiles were my preference but they were pretty expensive – I found some basic white ceramic tiles were in a skip. Ceramics, be it plain-Jane clay ceramic or porcelain, are fired at a very high temperature (1000-1250C), and glazed tiles are fired twice, so I reasoned they ought to be pretty stable in my <1000C furnace.
I cut the tiles with a diamond tile cutting wheel on a Stanley battery-powered grinder. Cut like butter.
Bosch Diamond cutting disc. Pretty pricey at 50 bucks. But tiles were free.
I glued it together with Holts Gun Gum car exhaust repair paste. I found that at room (well, garage) temperature this did not set hard so I installed the heating coiling on the still-setting shield and cooked it hard.
A tin of Gun Gum from the local auto shop. I used pretty much the whole tin. Only about 10 bucks.
Gun Gum’s SDS sheet lists Sodium Silicate as the ‘active’ ingredient. Wikipedia says, upon heating, the water is driven off to form silica gel, which a glass-like and hard. So there.
And just to reiterate:
ALERT & UPDATE: Bathroom tiles conduct electricity at 1000C 🙁 See here.