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  #21  
Old 01-05-2014, 04:01 AM
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Default Re: New Build in South Oz

Colin,
Do your floor bricks lay straight on the hebel like Cobblerdaves?
I think the layer of bricks protect the hebel from the direct fire, and ensure the hebel heats slowly and evenly.
With all respect to my mate, I do hope to win the debate about the thermal mass/reinforcement. An inch of render will result in 4 inches of thermal mass. According to the Forno Bravo plans that's "high but acceptable" for a domestic oven.
I also will try to convince him on taking the chimney straight up from the entry.
The plan with the rest of the insulation is to make the enclosure from the rest of the hebel blocks he has, then pour perlite into the voids. Rectangular "house", round oven, gotta be some voids, right?

Perlite, because there just might be a supplier here in town.
Right now, I'm expecting we will end up with an oven with 3 inch floor, 4 inch dome, and very well insulated. My hope is this will allow reasonable heat up times and good ability to roast meats in the oven.
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  #22  
Old 01-05-2014, 02:59 PM
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Default Re: New Build in South Oz

Photos. First flame.
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New Build in South Oz-2014-01-05-16.17.04.jpg   New Build in South Oz-2014-01-05-16.15.59.jpg   New Build in South Oz-2014-01-05-16.14.52.jpg  

Last edited by wotavidone; 01-05-2014 at 05:43 PM.
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  #23  
Old 01-06-2014, 06:11 AM
UtahBeehiver's Avatar
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Default Re: New Build in South Oz

nice brick work closing the dome tight and symetrical.
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  #24  
Old 01-06-2014, 12:12 PM
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Default Re: New Build in South Oz

Quote:
Originally Posted by UtahBeehiver View Post
nice brick work closing the dome tight and symetrical.
Thanks Russell. I do subscribe to the theory that the tighter the bricks fit the less critical the mortar is.
Speaking of management by committee, there was a couple of strong opinions on how the last brick should be cut. Two guys competed to make the keystone.
One by cutting bricks with an angle grinder, one by boring a brick with his concrete borer.
The winner was the angle grinder, the other guy isn't happy with me for not using his perfectly round plug. Unfortunately it was about 20mm too small in diameter.
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  #25  
Old 01-06-2014, 12:42 PM
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Default Re: New Build in South Oz

Quote:
Originally Posted by wotavidone View Post
Colin,
Do your floor bricks lay straight on the hebel like Cobblerdaves?
I think the layer of bricks protect the hebel from the direct fire, and ensure the hebel heats slowly and evenly.
With all respect to my mate, I do hope to win the debate about the thermal mass/reinforcement.
No bricks sit on calsil board 2" thick then hebel.
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  #26  
Old 01-20-2014, 08:31 PM
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Default Re: New Build in South Oz

Progress report.
Managed to score some 65 mm pavers. These were just what we needed to get around a particular issue.
i.e. with the three inch/75mm bricks sitting on the floor, we had an issue with mortaring the floor bricks under the outer entry. We wanted to do this to retain the floor bricks inside the oven in place, but then the mortared bricks would be higher than the floor bricks. With the 65 mm bricks there was room for a 10 mm mortar layer. So there is now an apron of bricks in front of the oven.

Next problem:
The client who, as supplier of the materials and beer, is always right, wants a rectangular entry, one and a half bricks deep, with a flat top. i.e. not even a shallow arch to stop the roof bricks falling in.

Hmmm. Steel lintels, maybe?

He didn't like the look of that, , and I figured there would be all sorts of movement cracking everything.

However, three Southwark stubbies later, new idea.
We will obtain some house bricks, the ones with the holes through them. We will fabricate the roof of the outer arch in one piece, consisting of bricks mortared together with reo rod running through the holes. Sort of hidden lintels. I reckon, with the reo inside the bricks , it can't get hot quicker than the bricks, so the expansion rates get closer together.

Taper everything to a 7 inch by 7 inch chimney hole in the middle.

Why 7 inches by 7 inches? Because we have discovered that all the old fire extinguishers he has are not aluminium as first thought, but some sort of non-magnetic steel, presumably stainless.

So, we will be having a flue fabricated from 7 inch diameter stainless steel that is about 2 mm thick. Beautiful.

Remember the committee of self employed contractors supervising this job?
It would appear one of them knows a man who has welding equipment capabilities the home handyman can only dream of.

My only concern is whether we can shape everything for good air flow.
Like everything else we've done, we'll cut some bricks and try a few things.

I reckon the old drop saw I bought at a garage sale is going to be fit for scrap by the time we finish. The bearings are getting noisy and it tends to run off course a bit. Still 2 ovens for a $25 investment is pretty good.
When we've finished I'll pull it apart and see if the bearings are replaceable.
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  #27  
Old 01-20-2014, 10:09 PM
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Default Re: New Build in South Oz

I've found a list of expansion coefficients that says steel expands at around 16 x 10-6 metres per metre per K.
At least, that's what I think it says.
Anyway, if I work this out right, increasing the temperature by 400C gives a 6.4 mm increase in length per 1 metre length of steel.
Anyone reckon that sounds about right?
I'm thinking that expansion over about 600mm is not going to be an issue, since I sincerely doubt the bricks of the outer entry tunnel are going to get anywhere near 400C.
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  #28  
Old 01-21-2014, 12:30 AM
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Default Re: New Build in South Oz

I think the main problem of steel reinforcing in the refractory is the greater thermal conductivity of the steel compared to the refractory. It means the heat rushes to it and expands it more than the refractory that surrounds it. I think this is why stainless needles are used. Stainless so they won't corrode as easily in the hot and moist environment and needles so they can dissipate their heat more easily to the refractory that surrounds them. Steel and concrete in the normal situation have almost identical expansion rates and that's why they are so good for reinforced concrete in bridges and buildings etc, but any heat increase from the weather is slow enough for both materials to equalize their temperature and therefore their expansion easily, not so when heating an oven at 400C/hr. Also presuming brick, or castable have similar expansion rates to concrete.

Last edited by david s; 01-27-2014 at 03:05 AM.
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  #29  
Old 01-21-2014, 12:42 AM
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Default Re: New Build in South Oz

Quote:
Originally Posted by david s View Post
I think the main problem of steel reinforcing in the refractory is the greater thermal conductivity of the steel compared to the refractory. It means the heat rushes to it and expands it more than the refractory that surrounds it.
The steel will be encased in the brick. If the brick has a lower conductivity than the steel, how will the heat rush to it?

BTW, many stainless steels have a higher thermal expansion and the same thermal conductivity.

http://www.engineeringtoolbox.com/li...ents-d_95.html
http://www.engineeringtoolbox.com/th...als-d_858.html

It really depends on what steels you are comparing, but I reckon the only real reason to use stainless is the corrosion resistance, if you need it.

Last edited by wotavidone; 01-21-2014 at 01:56 AM.
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  #30  
Old 01-21-2014, 01:21 AM
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Default Re: New Build in South Oz

Gudday Mick

New Build in South Oz-image.jpg

Outer arch added later. But flat brick entrance supported by angle iron. No cracks as this is possible cooler than the entrance. Oven entrance is also angle iron and also supports the rear wall of the chimney which is 5 bricks high. This has 2 cracks which cannot be photographed cold probably due to the soot if anything. Hot they can be seen a mm or two wide. They don't appear at the top of the chimney or outside. It think I expected a least some cracking. So they don't bother me and I don't bother them.
Regards dave
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