Thermal expansion concern

[nissanneill]

Hi all,
I was wondering whether anyone has experienced problems of different thermal expansion (and the inherent results) of their firebricks when built around a mild steel angle iron door frame?
I am about to manufacture a substantial door frame for my Pompeii oven whick will be checked into the oven entrance on which I plan to swing some cast iron custom doors. First things first before I make the casting patterns but I have a concern that the frame, although only 300mm high, will expand at a greater degree than the fire bricks and cause movement and maybe cracking.
I could secure the frame from/at the lintel and allow for expansion of the frame within the oven hearth. Width wise maybe is a little different. Being around 500mm, I could allow the angle of the upright to slip within the checked out groove in the bricks.
Any ideas?
Neill

[Les]

Re: Thermal expansion concern

I understand your concern and that would be a difficult one to call. Some have used metal to support their flu and I haven't heard of that as causing a problem. Instead of using a frame, you could insert some "L" pins into the side brick. Then your doors would be floating on the pins. I don't see how the thermals would be a factor if you were to do that.

Les...

[nissanneill]

Re: Thermal expansion concern

Hi Les.
I would prefer not to use pins as they may come loose in time. Also I intended to use the angle edge of the frame on the sides and the lintel across the top for the rope seal to contact when closed, thus keeping in the heat and extending the usefull cooking time.
I plan on making hinges that will drop the door approx 3-5mm when they are almost closed in order to seal the bottom. I realise that it will not be air tight but better than a "door" or panel propped up against the oven entrance.

[Xabia Jim]

Re: Thermal expansion concern

Neill

My oven has angle iron around the door entrance....sides and top. The flat door mates to the angle iron.

It has not seemed to be a problem.....I think it is shielded from direct heat by the reveal of the firebrick, it's basically on the outside so it's cooler as well. On many of these pizza ovens there is a tunnel entrance so that would further set you back from where it's really hot.

I think if you could shield the angle iron from the direct fire using some firebrick, that might help.

Maybe someone has actual calculations for steel vs firebrick....

[johnrbek]

Re: Thermal expansion concern

It seems like every commercial Neapolitan oven I've seen has a steel arch to set the opening. It looks to be a pretty standard thing.. With that said, I don't know what kind of steel they're using and what impact any variation may have on the expansion characteristics... There is an italian web site that even sell iron oven doors on the web... Here's a link: ACUNTO - Napoli

Russell Jeavons also discusses the manufacture and use of a steel arch insert.. He seems to have included one in at least some of his ovens as shown in his pictures in his book. He's down in Australia.. You might also give him a call for some input. I've heard he provides training classes on working with ovens, so I suspect he may be accessible for a question like this..

Good luck.

JB

[nissanneill]

Re: Thermal expansion concern

Thanks for your input Jim.
I could cut the bricks to keep the steel in the 'shadow' of the heat but it is reassuring to hear that similar constructed ovens are not overly cause for concern.

Neill

[nissanneill]

Re: Thermal expansion concern

Thanks John,
I feel a little more satisfied with the idea now since Xabia Jim replied. I will protect the frame from doing damage through cracking the brittle fire bricks by allowing room for free expansion without binding on the lintel or dome.
This very time next week, I will be seated at Russell's restaurant enjoying his meals, checking out his ovens and enrolling in 2 of his courses that he conducts. You need to book around 4 to 6 weeks to get into his place as it is very popular and some of the courses he runs is preparing food for the night's guests, some rather exotic topics and in fact anything you want if you can fill a class. A sample of his current courses include:
"Smoking" -burning sawdust, rice, tea and sugar, , sit down to succulent oysters, salmon, and quail....
'In the raw' - delicous foods not cooked in the traditional way, but rather cured, pickled or just dressed
"Risoto" - A few simple techniques that lead to a myriad of flavours using scallops, duck, chorizo and mushrooms
"Northern Italy" - no pasta or tomatoes here. Rather Polenta & Pancetta, artichokes & Tapenade with a great italian wine
"Baking bread in Russell's brick oven" This one speaks for itself
"Japanese delights" - Okonoyaki, teriyaki, cgawan mushi, goma ae and miso soup and soul food
Middle East spices" -Saffron to make chemoula and harissa to cook with poultry, mixed with olives or dates, quinces or almonds and then salt some limes to take home
"Baking with russell in his brick oven" - he prepares for another saturday night and you learn all about wood fired ovens, firewood, hot spots etc.
All of his courses include a baked lunch and vary in price from Aust $65 to $90 for 3 to 5 hours. They sound good, especially with a lunch and often some take home goodies.

Neill

[dmun]

Re: Thermal expansion concern

If I understand, you are going to use your cast iron door frame to support the course of oven bricks above it, like the angle iron in the original pompeii plans. Might I suggest putting something compressable, like door seal rope or a layer of insulation pad between the door and the first course of bricks? That way if the door expands more than the brick it will compress the soft stuff rather than crack the dome.

[nissanneill]

Re: Thermal expansion concern

Hi dmun,
Thanks for your input.
I planned to use a refactory rope as a seal which is compressible as used in a kiln or industrial oven door serals. It is for this reason that I don't have a problem with the doors expanding at a different rate to the fire bricks, only the frame and lintel that may cause the problem. I think I have the problem solved with the frame checked into the wall and "floating" so that it can move slightly up and down and side to side without cause for concern.

Neill

[enz]

Re: Thermal expansion concern

A quick trip to the engineering handbook tells me that you guys are right on track. Brick has a thermal coefficient of expansion of .000003 in/in deg F, while the steel has a Cte of .000006. So, the delta expansion is .000003 in/in deg F. In an 11 in high door thats .015", assuming the steel hits 500F. Probably not enough to worry about. At the top of the door, where the combustion gases exit, you will see much higher temperatures. Let's assume 1000F, since the gases wrap around the steel angle on their way up the flu. Then, a 19" wide door will have an expansion delta of .054". This is significant but only if you are worried about leakage, as the brick will always move away from the steel. I think the refractory rope is a great idea.

Enz

[Balty Knowles]

Re: Thermal expansion concern

It's been a long long time since my college days but I remember a lab test where we stopped a steel bar from expanding & when it cooled it actually reduced in dimension. I would think the brick work would have more than enough strength to prevent the expansion in a 12 " long angle iron without cracking. It would be more likely to loosen up a little bit when it contracts again. Fix it from he side to prevent this & leave a little longtitudinal tolerance in the bolt holes.

Rgds

Balty

[nissanneill]

Re: Thermal expansion concern

Hi Enz and Balty,
the frame has been set into a groove cut 50mm into the adjoining soldier course of bricks and can bove a little without causing any ill effects to the oven. The 53 thousands of an inch expansion can be more than catered for in the design and I am quite confident that no problems will eventuate.
I have a motto that I tend to live by, (and I encourage my students to do the same) and that is "Prevention is better than cure". I tend to anticipate any potential problems and try to design around them.