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Post by satamax on Mar 6, 2014 22:43:22 GMT -8
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Post by Deleted on Mar 7, 2014 3:23:18 GMT -8
Operating temperature: up to 400 ° C
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Post by satamax on Mar 7, 2014 3:59:40 GMT -8
Operating temperature: up to 400 ° C Yep Karl, they all say the same. Even the Landini ones are rated for that. But i know first hand that they can cope with a batch rocket. They sure do crack, once or twice. But that's it. Well, looking at the price anyway, doesn't make it affordable. I'll stick to flue liners myself. |
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Post by smarty on Mar 30, 2014 0:16:42 GMT -8
www.jerrybennett.net/paperclay.htmlthis is a link to a bit about paper clay. I think that the thing about heat risers is that they don't really need to be gas-tight. Gas tightness and resistance to thermal shock don't really go together. Generally the more porous clay is the more resistant to thermal shock - also the more insulating it will be. I've made heat risers out of clay slip mixed with glass fibre strands and they do seem to hold up. So long as the firing temp of the clay is around the operating temp of the riser they seem fine. you hear lots of micro cracking and pinging as they cool from red heat at room temp but that's just the internal stress being let of piecemeal rather than in one whopping great crack. I haven't tried it yet but I don't see any reason why you couldn't make an inner liner wrap it in ceramic wool and then add an outer liner made of the clay fibreglass mix. Being so porous however the actually are really quite insulating in their own right and I would be inclined to use them built up in layers, and bisque fired in between, to 1" thick and leave it at that. The paper clay link above is another possibility if you don't fancy the fibreglass. It is more resistant to thermal shock than straight clay, in fact I read somewhere about its use as a ceramic cook plate if made as a flat tile. It can be used to make wafer-thin ceramics which is another way of helping with thermal shock, it will stick to itself either after drying or even after bisque firing. I have never fired the stuff but I think that the more paper in it the better for thermal shock resistance - although there is a trade off with workability and shrinkage. If formed over a rigid waxed cardboard former it could be preshrunk by playing a propane flame over wafer thin layers and built up slowly to required thickness. this will result in cracking of course but each layer should crack in a different place. once the liner is burned out in a bisque firing you could make good any draggy cracks on the inner surface of the riser with fresh paper clay then fire to full strength. I don't know much about water glass but others have mentioned it, perhaps this could be added to the clay somehow either before or after firing to increase durability?
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Post by photoman290 on Apr 21, 2014 12:45:11 GMT -8
another way to make up a riser using paper clay would be to rotate the cardboard tube on a mandrel slowly painting it with the clay mix as you go and dry it with a row of halogen flood lights. i have used this method to insulate large tesla coil secondaries with potting epoxy quite successfully.
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