New Build in South Oz

[wotavidone]

Re: New Build in South Oz

My mate has started using the oven without even a chimney. I can assure everyone that it smokes a great deal when there is no chimney and not even the most basic of doors to keep out those pesky afternoon sou'west winds.
He's working on it, like everything else he's searching out a "deal". He's got a nice cast iron plate that may end up being the door since it just happens to be the right size.
Still, the dome goes white regardless of the cold winds blowing in.

He has done the enclosure.
The oven is now enclosed completely in a giant Hebel cube.
6 inches thick all round. Underneath, the sides, and the roof. Cavity filled with loose perlite. He sealed across the heat break gap with perlcrete before he laid the Hebel across the front.

In my opinion, having used both now, perlite makes better insulating concrete than vermiculite. It will be my choice from now on.

He has some super-duper waterproofing render to put over the outside to seal the Hebel.
On Sunday night, he baked some baguettes at about 250C, then put some Hebel off-cuts across the door and left it.

Next day it was 180C according to the thermocouple he put through the dome on the weekend. So he made bacon and eggs for breakfast.
Can't wait to see how hot stays after actually running it white.
Edit: it just occurred to me that he is still cooking out the 2 1/2 inches / 68mm of rain we had as well.

Interesting thing about the thermocouple: the junction (tip) of the thermocouple protrudes into the oven, but it appears to be measuring brick temperature, not air temperature. The rate of rise, even with the flames licking it, suggests it is the bricks. This sort of fits with theory. In theory it is the difference between the hot junction to the cold junction ( the length of the dissimilar metals in the two wires) that develops the voltage differential in a thermocouple, so that six inch probe he has installed through the brick really should be measuring the brick, I guess.

I don't reckon this oven has actually been cold since his missus went back to the Philippines nearly two weeks ago.
Dunno how the little firecracker's gunna react when she gets home and finds out he hasn't actually finished it.
He reckons the best bit about being married to a Filipina is that they never nag.
The rest of us are terrified of her.

[wotavidone]

Re: New Build in South Oz

Only on a snapper drop. Might be something to do with "hurry up and wait"
Had a mate who got a government sponsored trip to Vietnam in 1971.
He called it "hurry up and wait". Hurry and get to your destination, then wait for hours, and then 20 minutes of sheer pandemonium.
My Vietnam touring mate, may he rest in peace, reckoned snapper fishing in South Oz is pretty similar, with the exception that in snapper fishing the quarry never shoots back at you.

You rush home from work, get the boat, rush to launch, rush to get out to your spot before the light goes, rush to get the hooks and berley in the water, then you wait, for hours sometimes, the fish to turn up.
A perfect time for a long leisurely cigarette, if you smoke.

[oasiscdm]

Re: New Build in South Oz

Sorry can't relate I stopped and never once had that feeling of wanting one. All the previous attempts I did have that feeling. Needless to say your mate will be inhaling a lot more smoke unless you have tight fitting blast door. Even then not sure it's doable.

As the oven needs to draw air which requires the door to be vented.

[wotavidone]

Re: New Build in South Oz

Hmmmm. it will work as I said I put a weekend to getting the venting to flow smoothly out of the oven. He wants flat he has got flat. Personally I gave up smoking 12 years ago and don't wish to start again.

28 years ago I gave up the ciggies.

Funny thing is though, when I anchor on my favourite snapper drop on a dark, dead calm winters night, with the berley stream flowing, the hooks baited and the only sound the lapping of the water on the hull and a dog barking in a farmhouse 2 miles away, and all I have to do is wait for the fish to get interested, I still after all this time, feel like a smoke.
I'd get instantly dizzy and fall over the side, but still I feel like a durrie.

[oasiscdm]

Re: New Build in South Oz

Hmmmm. it will work as I said I put a weekend to getting the venting to flow smoothly out of the oven. He wants flat he has got flat. Personally I gave up smoking 12 years ago and don't wish to start again.

[wotavidone]

Re: New Build in South Oz

you talking inside entry or outside entry.

as my inside entry the other day as around 380c

That flue is of concern. Hope he likes lots of smoke in his face as that will happen. Even with the thought I put into my flue gallery I don't get a lot of smoke out front but there is some. With a flat gallery and a flue that wont be straight and travelling reverse direction against the flow of smoke. travel that is a tall ask. Be interested seeing what happens. But you can give people all the great ideas in the world but in the end they just have to see.

Sounds like you are a little frustrated as it appears the collective is out voting you

Outside entry, my inner arch gets hot enough to burn the carbon off too, but the outer arch gets nowhere near that hot.

I'm not [I]particularly[I] frustrated, except by the way this website logs me off before I finish typing.
If, by collective you mean the guys I'm building this oven with, yes on occasion they can be a little testing. But its all part of the fun.

My mate commented the other day that he didn't think this oven would be as much work as it had been.

I pointed out we made the dome in 8 days, and if it wasn't for the client's penchant for departing from the tried and true, we'd be eating pizza by now.

For example his desire to angle the flue back is based on clearing the edge of his shade sail. I'd relocate the bloody sail.

When he expressed a desire for a square entry with no visible steel showing, I said the only way you could do that is with perforated bricks with reo running through it.
I called it a manufactured lintel, and initially I was keen on it.

The client pounced on the idea like a staffy on a pig's ear, and held on as well too.

My mate reads all these posts during his late night bouts of insomnia. Right now he's probably laughing his head off.

His words were "Let's do that, post it on the forum and see how many people say it'll never work."

I reckon the bricks threaded on reo will work fine, though I wish I'd been there to influence the design and execution a bit.

In the unlikely event that it proves structurally unsound the whole entry is free standing and unconnected to the rest of the oven, so it'll take bugger all to remove it and do it different.

The draughting with the flat roof and the angles in the flue is a different story.
But I do have a contingency plan for that.
And I don't think I've yet mentioned his vision for doors. With adjustable vents for combustion air, the controlled admission thereof.

[oasiscdm]

Re: New Build in South Oz

you talking inside entry or outside entry.

as my inside entry the other day as around 380c

That flue is of concern. Hope he likes lots of smoke in his face as that will happen. Even with the thought I put into my flue gallery I don't get a lot of smoke out front but there is some. With a flat gallery and a flue that wont be straight and travelling reverse direction against the flow of smoke. travel that is a tall ask. Be interested seeing what happens. But you can give people all the great ideas in the world but in the end they just have to see.

Sounds like you are a little frustrated as it appears the collective is out voting you

[wotavidone]

Re: New Build in South Oz

I guess if the steel rod is free to move within the holes in the bricks, ie. it's loose and the ends have somewhere to expand to ,then you shouldn't expect problems. I'm interested to hear how it goes.

Actually, he's got a bit of a cunning plan for the exposed ends. I'll have to post a pic when its done.
By the way, the rods are 650mm long.
So if the roof gets to 400 degrees, which is highly unlikely, the difference between the expansion of brick masonry versus steel is 2 mm.
With a thermal expansion of 13 x 10(-6) m/m K, 650 mm of steel should increase in length by 3.4 mm. 650mm of brick (5.5) by 1.4 mm.
So we are debating about bugger all. Especially since the throat won't get that hot. I imagine we'll be able to put our hands on most parts of the entry without a burn.
I reckon the people who have trouble with lintels have them in the oven proper, where they really do get that hot.

If the throat got that hot, then the carbon would burn off, and I've never yet seen an oven with the soot burnt off in that area.
Still got a heatwave here so there'll be no lighting of my oven to check temperatures for a few weeks yet.

BTW, did you note the expansion coefficient for concrete? At 400 degrees, there would be 0.6 mm difference over a metre of length.
I think I see why the Michelevit's brick oven on a shoestring didn't crack despite all the dire predictions to the contrary.

[david s]

Re: New Build in South Oz

I guess if the steel rod is free to move within the holes in the bricks, ie. it's loose and the ends have somewhere to expand to ,then you shouldn't expect problems. I'm interested to hear how it goes.

[wotavidone]

Re: New Build in South Oz

The higher expansion rate of stainless over mild steel explains why it warps so much.
Somewhere else in another thread i took some measurements which showed a stainless sheet in front of the oven mouth considerably hotter than the brickwork around and indeed closer to the fire. This shows that the more conductive material does get hotter and as mild steel is way more conductive than stainless you'd expect the difference to be more marked. I think the fine stainless needles in a castable have a chance to dissipate their heat to the refractory that surrounds them, but a thicker lump of stainless would be more likely to give problems.
I'm not saying it won't work. it'll probably be quite ok, but some members have reported problems when using angle iron as a lintel and without gaps at the ends of the angle iron the expansion creates cracks. I once used a system like yours on a kiln I built years ago, in which i had a lid joined by threaded mild steel rods through holes drilled in firebricks all held together with angle iron and tightened with nuts. worked ok for up to internal stoneware temps.

A stainless sheet in front the fire exposed to the radiant heat isn't a valid comparison to any sort of steel encased in masonry.

It's all a matter of which way the energy is flowing. You keep thinking about high conductivity steel transferring heat to the bricks, but when its encased in the masonry, its more about low conductivity material transferring heat to the steel.

Anyway, no angle iron in this set up, therefore no gap left for it to slide when it expands.
My mate used threaded rod, my only concern being the size of it, and reo bar which I don't have a concern with the size.

(My other concern is appearance, but he's happy with the look so who cares? Beauty is in the eye of the beholder, as they say.)

If it worked up to stoneware temp for you, I suppose it'll work for pizza oven entry temps.

[wotavidone]

Re: New Build in South Oz

Gudday Mick
I did a bit of head scratching about the gravity defying brickwork. Then it hit me, they are house bricks with reo Steel through the holes! Will it attract heat and warp? I don't know. But with angle iron at least its shape stops it from sagging.
One thing you might want to rethink is that 7 in?chimney in the flat 18? in entry. No smoke chamber to collect and direct the smoke up the chimney. Just a flat surface......just pointing it out
Regards dave

Re: the flat roof, I pointed this out too, but I lost the argument.
It'll be even less efficient due to he wants to make a 45 degree bend straight out of the vent and lead the flue back over the oven. Can't see that draughting as well as a nice tall vertical flue.

Fear not, I have a simple improvement plan for when he finds out a smoke chamber is necessary.

Will the lengths of rod let it sag? Dunno, I doubt it, but we'll soon find out.

It'll be easy to replace if it doesn't work.

The client is always right.

[david s]

Re: New Build in South Oz

The higher expansion rate of stainless over mild steel explains why it warps so much.
Somewhere else in another thread i took some measurements which showed a stainless sheet in front of the oven mouth considerably hotter than the brickwork around and indeed closer to the fire. This shows that the more conductive material does get hotter and as mild steel is way more conductive than stainless you'd expect the difference to be more marked. I think the fine stainless needles in a castable have a chance to dissipate their heat to the refractory that surrounds them, but a thicker lump of stainless would be more likely to give problems.
I'm not saying it won't work. it'll probably be quite ok, but some members have reported problems when using angle iron as a lintel and without gaps at the ends of the angle iron the expansion creates cracks. I once used a system like yours on a kiln I built years ago, in which i had a lid joined by threaded mild steel rods through holes drilled in firebricks all held together with angle iron and tightened with nuts. worked ok for up to internal stoneware temps.

[cobblerdave]

Re: New Build in South Oz

Gudday Mick
I did a bit of head scratching about the gravity defying brickwork. Then it hit me, they are house bricks with reo Steel through the holes! Will it attract heat and warp? I don't know. But with angle iron at least its shape stops it from sagging.
One thing you might want to rethink is that 7 in?chimney in the flat 18? in entry. No smoke chamber to collect and direct the smoke up the chimney. Just a flat surface......just pointing it out
Regards dave

[wotavidone]

Re: New Build in South Oz

A more thermally conductive material will get hotter than the material that surrounds it. A couple of examples of this are 1. On my first oven iset in a dense rock with the word PEACE on it above the arch. We found that this rock got so hot that you could not hold your hand on it when the oven was ready for pizza, yet the outer shell around the rock was still cool enough to hold your hand on it.
2. The steel rails underneath the Hebel supporting slab on my mobile get hotter than the Hebel that sits on top of them.

The hotter a material gets the more it expands.

There are many different stainless steels, but they all seem to have less thermal conductivity than mild steel.

The preferred reinforcement for refractory is stainless needles presumably because they perform better than mild steel. Not saying your mild steel won't work, just use what does work.

The tables you referenced do show a big difference between the thermal expansion of brick and mild steel though.

1) Can't quite get my head around your reasoning. We aren't talking about a kilo of brick and a kilo of steel sitting side by side in a kiln with the steel absorbing energy quicker than the brick due to different conductivity.
Even then they can only reach the temperature the kiln is set to.
A piece of steel fully encased in masonry can only absorb heat at the rate the masonry conducts it to the steel. And surely, since I presume we are not talking about any phase changes in the steel or the masonry, the steel can only get to the same temperature as the surrounding masonry.

Thermal dynamics wasn't my major at school, but I can't see how masonry that gets to say, 300 degrees, can raise the temperature of any steel encased in it any higher than that.

Especially since the steel runs the full length, one would think that, if anything it would assist in transferring heat from the hottest part of the masonry to the coldest part, thus evening things out a little.

2) Don't forget, if two materials are the same temperature which is hotter than your hand, the one with the highest conductivity will feel hotter as it more easily transfers the energy to your hand.
If they are cooler than your hand, the one with the least conductivity will then feel hotter as it retards the loss of body heat from your hand. All depending on which way the heat is flowing.The only way to really tell which is actually hotter is to measure each with a contact thermometer.
So, did you actually measure the temperature of your steel rails vs your hebel, or just feel it with your hand? Ditto the hot rock v the cooler rock? How much hotter did the rock feel? Possibly just a much better conductor than the other rock?

3)The tables I referenced show an even bigger difference between the thermal expansion of masonry and every stainless steel mentioned except one.
The one with the slightly lower expansion rate is 410 grade. Its a hardened steel with lesser temperature and corrosion resistance that is unlikely to be the one they supply for your application.
In fact my research has turned up fibres for refractory made from 304 and 310 grade stainless, both of which have higher expansion rate than steel.

I reckon the only reason they use stainless fibres rather than steel to reinforce refractory is superior corrosion resistance.
In the unlikely event that my mates reinforcing corrodes (since it isn't inside the oven getting really belted, we only have to protect it from water infiltration), we'll be able to replace it easily.

[david s]

Re: New Build in South Oz

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.

Coefficients of Linear Thermal Expansion
Thermal Conductivity of Metals

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.

A more thermally conductive material will get hotter than the material that surrounds it. A couple of examples of this are 1. On my first oven iset in a dense rock with the word PEACE on it above the arch. We found that this rock got so hot that you could not hold your hand on it when the oven was ready for pizza, yet the outer shell around the rock was still cool enough to hold your hand on it.
2. The steel rails underneath the Hebel supporting slab on my mobile get hotter than the Hebel that sits on top of them.

The hotter a material gets the more it expands.

There are many different stainless steels, but they all seem to have less thermal conductivity than mild steel.

The preferred reinforcement for refractory is stainless needles presumably because they perform better than mild steel. Not saying your mild steel won't work, just use what does work.

The tables you referenced do show a big difference between the thermal expansion of brick and mild steel though. This could create a problem for you. Did you leave a little gap at the ends of the steel so it can expand without forcing the bricks apart?

It also shows quite a difference between the thermal expansion of concrete and brick that I was not aware of, I thought they were much the same.