Mobile Oven Dome in MIchigan

[szv9n5]

So, I made my sand form for my dome today. I started to cast the dome but I only got about half done. Meaning....the finished dome is planned to be 2 1/2” thick and I only got about an inch covering the whole dome. I’m assuming it is best to do the entire dome cast at one time. But how bad is it to do it over two days? I did scratch the surface so that the next layer will have something to bite into....

[david s]

Here’s the recommended schedule for that product.
Typical dryout schedule for a single layer, 9” thick or less:

• Ambient to 250F at 75F per hour. Hold at 250F 1/2 hour per inch thickness.
• 250F to 500F at 75F per hour. Hold at 500F 1/2 hour per inch thickness.
• 500F to 1000F at 75F per hour. Hold at 1000F 1/2 hour per inch thickness
• 1000F to use temperature 75F per hour

It doesn’t matter if the castable is a CAC based one or homebrew, it is the slow elimination of mechanical water (steam) that is imperative. Suddenly expanding water will cause steam spalling splitting the walls of your casting neatly from the centre of the walls.Typically this will occur at around 250-300 C. The presence of water will also hold the temperature down in that area so it is important to try to dry the oven out evenly, otherwise uneven temperature will create uneven expansion which leads to stress.This is practically impossible with the crown drying off first so try not to allow flame impingement on the dome for the first few fires. CAC requires only 24 hrs to reach its full strength (give it two to be safe) so damp curing as would be done with anything contains Portland cement is unnecessary. Allowing the oven to cool off each day returns the whole structure back to an even temperature again.Further techemical and physical changes take place north of 600 C but as you won’t get the oven that hot it’s not necessary, although the ingredients in the castable allow the material to reach double that temperature. The above firing schedule refers to a more controllable heat source like gas. For a WFO the 7 fires in 7 days, getting progressively bigger is a better approach.

[szv9n5]

The cure/dry out schedule for this product appears to be :
24 hours at 72 degrees
then increase temp 100 degrees per hour until 1,200 degrees is reached
hold 1,200 degrees for 1 hour for each inch of thickness (2.5 hours in my case).
then cool at a rate of -100 degrees per hour until room temp.

i have Understood a slow cure is better...keep it damp for 10 days. Then several fires starting very small and growing in temp over another 10 days. Is the slow cure only needed with the home brew because of the portland? Should I trust the product data sheet and cure and dry it in two days. It goes against most of what I have read....

[david s]

That's good stuff. Most castable refractories already have the burn out fibres in the mix. To make sure they have take a sieve and sieve out the finer particles and you should see some very fine fibres left behind. It is important that these fibres are dispersed in the mix well, so mix it more than you would think necessary, but not for too long as the stuff goes off very quickly. If it's hot weather use chilled water it is very temperature dependent. so do not mix more than half a 25 kg bag in one batch and be sure to wash out your barrow and tools after each batch, otherwise it will accelerate the next batch. Stainless needles (not absolutely necessary) should be added min 2% by weight of dry material. They are not called needles for nothing so if you add them just handle the mix gently to avoid stick injuries.

[szv9n5]

Can I add the stainless needles and burnout fibers to this?

[szv9n5]

Ok... cast it is.

after reading many posts on the topic of home brew vs proprietary.....I decided to buy this castable from Harrison Walker. Heck of a time to ask as I have already purchased it but any thoughts on this stuff? Anyone use it before. Data sheet attached....

[david s]

I’ve heard reports of brick ovens rattling to bits and it doesn’t surprise me. Mine takes a pounding if I go off the bitumen. My first mobile oven was a one piece dome, but when I rebuilt it I made the dome castings in three pieces. It’s standing up pretty well. Some manufacturers offer cast ovens in one piece specifically for mobiles

[Karangi Dude]

szv9n5 welcome to the forum

To me it was a matter of weight and heat up time, cast ovens weigh a lot less and also heat up much faster than solid brick ovens

See my trailer build https://community.fornobravo.com/for...-s-mobile-oven

Cheers Doug

[szv9n5]

Let me first start by thanking the contributing members of this board....you guys are an unbelievable resource for so many. You just don’t see that on many boards these days. Thanks for all the help.

i am starting work on my second oven. The first was a brick dome build on cinder block frame on my patio. Now, I want to build an oven on a trailer so I can take it to events like tailgating. I have read many posts on this site and gathered tons of info but still have a couple I need help with....

Question 1: I assume because this is being built on pull behind trailer a cast dome would be better than a brick dome? I auromatically assumed the brinks would rattle loose .....do you guys agree?