building home made firedome for trailer oven

[kirshner]

Hi ,
I need some good advice on how to create my own inner dome/firewall,igloo shaped for mobile oven,dont want to use bricks as heard they more likely to loosen with trailer vibrations.am a mold maker so doing the form is no problem.
I have already built one ,the mix was 2 part aluminate cement,2 p river sand,3 p river gravel and half p hydrating lime.dome is 2 inches thick.got some feedback from forum saying it would explode on first firing but no reason why,is shell too thick, wrong aggregate? anyway am at stage where i need to decide if I should start again or go with what I have
cheers to you all!!

[Tscarborough]

Re: building home made firedome for trailer oven

You heard wrong. With unitized construction all cracks are pre-engineered, with a cast oven cracks are random and can be fatal to the performance of the dome, especially when the aggregate is prone to spalling.

If yours was the (since disappeared) post that stated that you used river pebbles, that type of aggregate is unsuitable for refractory concrete, unless your river happens to be bedded with a highly silicious limestone which won't normally wear to pebbles.

[Tscarborough]

Re: building home made firedome for trailer oven

If you want to build a cast oven, use a commercial mix for castable refractory or make your own. 1p Al cement, 2 parts graded sand, and 1-2 parts graded grog plus stainless steel needles at the manufacturer's recommended loading.

[kirshner]

Re: building home made firedome for trailer oven

ok , sounds good,
I,m a beginner so
what is graded grog and graded sand,and what thickness should the dome be,Yes I dont know how my post disapeared but thanks I really appreciate it.
i will post pics as i go

[david s]

Re: building home made firedome for trailer oven

You probably want the oven to be as light as you dare because you have to haul it around. I wouldn't go thinner that 50 mm grog is crushed fired clay. You are better off getting a proprietary castable refractory which has the correct blend, will produce a workable mix, has the appropriate fibres, but is expensive.

[kirshner]

Re: building home made firedome for trailer oven

thanks david
am considering the premix option,worth the money in the long run,so if the shell is that thin would you suggest a 3 or 4 part shell?

[david s]

Re: building home made firedome for trailer oven

That is a really hard question. When I built my mobile I was conscious of others experiences with brick ovens for mobiles which had disintegrated from road bumps and vibrations, so I decided to do my dome cast in one piece, also the floor cast in one piece. After about 5 years and lots of use, travel and hire (wow this mobile oven is great, let's see how hot we can get it, the owner's not here), the dome has developed one vertical crack in the rear right opposite the door. The floor has cracked basically into four pieces, roughly evenly quartered. These cracks may look a little unsightly, but have no adverse problems with the oven performance. If you engineer joins to avoid this then you are also inviting the pieces to separate from vibration. I did not use stainless steel needles in the refractory castable for this oven, but now I always do, I have no idea how much stronger they make the end product, but presumably it is better with them added. This probably does not definitively answer your question, but I hope is is of some use.

[kirshner]

Re: building home made firedome for trailer oven

sounds good
faster to make it as one piece anyway,will use that castable refractable after all.
have a bag of illuminate cement left over so might use it for the base,wont need stainless needles for that i expect,
just released my first dome from mold,shame to waste it,our river (where pebbles came from)is extremely high in limestone,will find out more,so maybe it could be used occationally as my neighbor is interested in taking it

[david s]

Re: building home made firedome for trailer oven

If you are planning on casting the floor then if anything the floor needs the stainless steel needle reinforcing more than the dome.

[Ken524]

Re: building home made firedome for trailer oven

If yours was the (since disappeared) post that stated that you used river pebbles, that type of aggregate is unsuitable for refractory concrete, unless your river happens to be bedded with a highly silicious limestone which won't normally wear to pebbles.

His post (and your reply) are still there. No disappearing posts.
http://www.fornobravo.com/forum/6/ad...tml#post140069

[kirshner]

Re: building home made firedome for trailer oven

thanks...
better order the needles then, i was wondering for the base,could I put the middle perlite insulation layer on top of a 3 inch slab of hard wood or does that first bottom layer have to be concrete,it will be attached to a steel frame.
and any ideas on how to attach the frame to the trailer,I have a few ideas but wouldnt mind some feedback on suspension

[ironpony]

Re: building home made firedome for trailer oven

I cast mine in 4 pieces with Z shape construction joints at each seam.
I feel this will help control the cracking by allowing some movement, stress relief.
I worked with a refractory manufacturers, engineer to come to this.
Mine is very similiar to Fornos design, there is a thread on here with some pics.
also used a lightweight castable refractory for the insulation layer in the same way, over the dome and under the cast base. mine is 2.5 inch thick dome and 3inch thick base.
I was a model maker at an aircraft manufacturer and also made my own mold. good luck with everything and post some pics of your mold. as far as trailer mounting have some ideas but the most important would be rigidity which I would avoid wood. steel frame with steel plate on top. or reinforced concrete which will get heavy.

[kirshner]

Re: building home made firedome for trailer oven

thanks ironpony,
i feel pretty confident now,hopefully one last question,whats a good mortar mix for between construction joints especially for joining dome to base

[ironpony]

Re: building home made firedome for trailer oven

from what I have learned, no mortar on joints, so everything can expand / contract some
especially dome to base
if you mortar them they will crack there anyway-weakest spot
not sure what will happen on a trailer driving around
my insulating dome is one piece castable refractory which holds everything together
look on here at thier dome directions/specs

[kirshner]

Re: building home made firedome for trailer oven

ok,
could i make mix insulating dome 1 to 5 of cement to perlite then another final stronger mix on top of that to finish it of,hold it down? leaving out the insulation blanket.
or what is your insulating dome mix recipe...