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  #771  
Old 12-20-2013, 10:16 PM
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Default Re: new build in werribee

Gudday
There's another factor at play here that should be mention is that most of the heat in the entranceway is heat radiating from the fire through the air rather than through the brick.
My oven has no heartbreak. In summer particularly, by the time you have burnt a fire in the dome for a couple of hours the entranceway is roasting hot. It makes it a bit uncomfortable to operate the oven. I have taken to placing just my insulated door in front of the chimney. Not as a blast door as the air is free to flow past the sides unregulated but as a heat shield for the entrance. Never taken any reading of the difference but the entrance I'd definitly cooler. Heat radiates faster though the air than through brick. I recon most of the heat bypasses the heat break through the air.
Heat radiating through the air does some funny things too. I'm ex navy and constantly got to play at the fire ground with some pretty realistic fires. Inside a steel compartment with even a small fire going it gets pretty hot very fast. The heat radiates from the walls making things pretty hot just like inside a WFO .You wear flameproof overalls, boots, elbow length flameproof gloves and a flameproof hood. Everything is covered bar a slit for eyes. It can get so hot the heat will burn your eyelashes off from behind the mask of your breathing equipment. If your silly enought to wear jewelry next to you skin it will attract the radiant heat through you clothes and burn the skin. The girls are in there too, so no underwire bra or metal clips. Underwear and sock elastic doesn't fare to well also, and losses its spring.
The human body, the flameproof overalls and gloves all have an insulating value metal has none. Once those metal atoms start to vibrate it then starts to radiate the heat back by itself. A plastic pen in the pen slot in the from of your overalls will not be at melting point before the metal end has heated up and boiled the ink in it .
Same things happening with the s/steel on the heartbreak its absorbing the radiant heat and once it gets to saturation point it throws the heat back rather than absorbing more like the brick on either side.
Sorry this is not highly scientific but its my practical experience with heat.
Regards dave
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  #772  
Old 12-20-2013, 11:26 PM
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Default Re: new build in werribee

Agree.... the radiant heat made it very difficult working the oven. The best figures re heat break were had with no active fire.

The stainless was always [heat wise] in the middle of temp range but closer to hearth with an active fire.

It's interesting I guess I will learn more as I use it more.

Must get to the temp door though. Like you Dave hebel and some scrap wood
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  #773  
Old 12-21-2013, 01:32 AM
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Default Re: new build in werribee

Gudday Colin
http://www.fornobravo.com/forum/f51/...html#post99622 (oven door construction)

The Hebel door is not my idea, I got it from this bloke, he warned me as well that even if you call it a temporary door it works and you never get around to building better.

Regards Dave
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  #774  
Old 12-21-2013, 02:51 AM
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Default Re: new build in werribee

Some one else recently did a door from hebel and wood. Cannot remember who any ideas.
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  #775  
Old 12-21-2013, 04:24 AM
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Default Re: new build in werribee

Colin, how strong and abrasion resistant is shiralite?

I am rethinking doors, and the issues with SS and other metals.

If a door was cast with shiralite and perhaps coverd with SS only on the internal face, and external face with wood. Would it work?

Note, if the external strength is good enough, the core could be a better insulator encapsulated in shiralite

also is shiralite safe? carcinogen etc.

Steve.

Last edited by brissie; 12-21-2013 at 04:38 AM.
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  #776  
Old 12-21-2013, 05:51 AM
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Default Re: new build in werribee

Quote:
Originally Posted by brissie View Post
Colin, how strong and abrasion resistant is shiralite?

I am rethinking doors, and the issues with SS and other metals.

If a door was cast with shiralite and perhaps coverd with SS only on the internal face, and external face with wood. Would it work?

Note, if the external strength is good enough, the core could be a better insulator encapsulated in shiralite

also is shiralite safe? carcinogen etc.

Steve.
That could work, although if the Shiralite were fully contained by the stainless you may as well use loose perlite which would be both better insulating and cheaper.

The problem of using stainless at the hot face is that stainless is a pretty good conductor and therefore not a good insulator. If it is thin and it needs to be so that it won't sap too much heat, it is likely to give you sealing problems as stainless has a propensity to warp with heat.
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  #777  
Old 12-21-2013, 06:38 AM
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Default Re: new build in werribee

Quote:
Originally Posted by david s View Post
That could work, although if the Shiralite were fully contained by the stainless you may as well use loose perlite which would be both better insulating and cheaper.

The problem of using stainless at the hot face is that stainless is a pretty good conductor and therefore not a good insulator. If it is thin and it needs to be so that it won't sap too much heat, it is likely to give you sealing problems as stainless has a propensity to warp with heat.
Okay leave SS out of it. almost any commodity metal will do.

If the Shiralite product can withstand the workload
it could be:
wood -- Shiralite -- metal
or
wood -- Shiralite

Can Shiralite handle this? The metal is only for protection and may be disregarded if Shiralite is tough.

For a door it may outlast hebel, and be easy to make. Hebel breaks down with heat, but Shiralite may not at WFO temperatures.

Last edited by brissie; 12-21-2013 at 06:52 AM.
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  #778  
Old 12-21-2013, 12:35 PM
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Default Re: new build in werribee

I tried a 25 mm Hebel panel attached via stainless bolts to a wooden door. It only lasted about four firings before cracking. I know Dave's Hebel door has lasted well, but I think his is much thicker. So far I've found no matter what you use, if you try to make it robust enough it is not insulating enough and the reverse also applies.

Glass slumpers often use Hebel as moulds for their work, but they only last about four firings (generally around 900 C)
I have been experimenting with the use of expanded clay, perlite and foam in varying ratios in conjunction with clay to make suitable panels (fired to 1000C) the main problem is getting the shrinkage rate right and the tendency for clay tiles to warp on drying and firing.

I'd be interested to hear how your Shiralite would perform.
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  #779  
Old 12-21-2013, 02:26 PM
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Default Re: new build in werribee

The shiralite would work but would need to be contained directly against heat and reinforced. I have enough shiralite left over to try this later as a filler between something. I will construct my door in 2 front half and back: half. I am looking at then containing ceramic tape locked into the 2 halves as a sealer around the door that seals against the entry arch side walls. I have noticed that out will end up blackened by soot. If that makes sense. The shiitake would need reinforcing in this type of set up I think.

Aren't blast doors metal?

The insulation I can try is hebel, calsil, shiralite, a combination is also possible.

Looking at SS front, 4" of insulation. Back half SS or ?????? Well isolate the SS from the brick at the front. 2 halves joined by 3 to 4 studs with a sour temp thermometre in the middle.
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Last edited by oasiscdm; 12-21-2013 at 03:17 PM.
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  #780  
Old 12-21-2013, 02:30 PM
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Default Re: new build in werribee

Quote:
Originally Posted by oasiscdm View Post
The shiralite would work but would need to be contained. Directly against heat I have enough shiralite left over to try this later as a filler between something. I will construct my door in 2 front half and back: half. I am looking at then containing ceramic tape locked into the 2 halves as a sealer around the door. If that makes sense. The shiitake would need reinforcing in that set up I think.
Shiitake?? Are we cooking mushrooms now?

There are a number of different Shiralite products with varying densities, strength and insulating properties. You may be lucky enough to have the one that is suitable for this application. Try it and see. It's strength can also be enhanced without altering its insulating properties if it is sintered ( fired to around 1000 C)

Last edited by david s; 12-21-2013 at 02:39 PM.
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