adiel
Junior Member
Posts: 119
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Post by adiel on Jul 14, 2015 12:23:44 GMT -8
does anyone know if this is a must when making a pvdb bb from an insulating refractory from gouda cast 3 cm thick?
up to what temperature?
thanks...
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Post by peterberg on Jul 14, 2015 13:40:44 GMT -8
I honestly don't know, never did it myself. Dragon Heaters in Texas did, but I am quite sure they used a different castable. What I do know is that it's better for the quality of the product to drive out the water completely before raising the temperature to the specified working level. After that, the resistance to cracks is much higher.
Educated quess- 6 hours by a temp of 150 C should do the trick...
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adiel
Junior Member
Posts: 119
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Post by adiel on Jul 14, 2015 23:53:49 GMT -8
It is strange that the manufacturer recommends 40 hours of kiln dried and up to 900 c
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Post by peterberg on Jul 15, 2015 1:00:22 GMT -8
Yes, that isn't drying only but also bringing up to spec temperature. By doing this, the product will also get the maximum shrinkage, all over. The risk of developing cracks should be brought back to an absolute minimum this way. But this is a very costly process, is it that much worth?
I've never done this, the best I did was let it dry for a month, assemble the heater and bring this up to temperature very slowly in the course of two weeks. Once, building the first cast batchbox core, the time difference between the two halves was a month. The latter one was released from the mold and exposed to the first test run the same day, wet and all. In the short video of the first double vortex featured this core. This latter one developed cracks all over and ended up much more brittle than the properly air dried other half.
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terry
Junior Member
Posts: 128 
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Post by terry on Jul 29, 2015 14:00:38 GMT -8
I asked the supplier of my castable refractory the best method to 'fire' my casting. That is, to cure/fire/treat the casting as a WHOLE rather than rely on a fire within the burn tunnel and expecting it to sure outwards nicely. If that made sense.
He reckoned on 48 hrs air dry, then (best within a suitable container, maybe a 44 gal drum??) grab a couple of bags of heat beads, the type used on charcoal BBQs, pack them around the casting and burn the heat beads (no forced air. If they are red burning then not over 300 degrees I think he said) and let the beads burn for a few hours. That will slowly raise the temp of the entire casting, rather than a very hot burn tunnel etc inside a cold uncured casting.
Hope that helps.
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Post by AlexHarpin on Jul 30, 2015 4:43:25 GMT -8
I cooked mine in a raku kiln. work pretty good.  |
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Post by AlexHarpin on Jul 30, 2015 5:00:49 GMT -8
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terry
Junior Member
Posts: 128
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Post by terry on Jul 30, 2015 16:03:21 GMT -8
cool video
I know what my next heat riser will be made out of. Make a tube of that ceramic blanket.
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