Sunday, February 05, 2006


Progress with cement

I've got a sample of cement curing now, with vermiculite added to improve insulation. I've also bored out another 50mm M6 brass bolt for use as a heater barrel. I'm making a 9 ohm heater element this time so we can reach higher temperatures. I fear we may pop a thermistor, but what the hey.

To insulate the barrel, I'm planning on using BBQ paint. This is a commonly available ceramic-filled paint based on high-temperature polyesters and is good up to 630C. The windings will be held down with plaster and fibreglass. There is a page on the Wiki covering the experimentation:

Concrete and BBQ paint take some time to cure, however, so the results will take a few days to come through.

Vik :v)

Won't the plaster dehydrate and turn to plaster powder again?
Not significantly. Plaster of Paris actually undergoes a curing reaction like cement does. I have used it to mould lead articles, reusing the same mould repeatedly. Friction and rough handling will wear it away but it retains basic integrity. I hope the fibreglass may give more mechanical strength and avoid any cracking caused by thermal expansion of the wire heating element.

Vik :v)
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