36" Mobile Cast Neapolitan

[mefornaio]

Hey Guys. I have a build thread going in the Pompeii section but Im hoping to get some help from those of you that have mounted your ovens on a trailer.
Specifically what I'm wondering about is the insulating material holding up (not compressing or crumbling) under the weight and movement of the oven. I have seen the rigid hi temp board used and vermiculite used on here but no idea how they have held up in use.

My plan is to make a metal pan in the shape of the finished oven for it to sit in, then assemble the oven in there. Starting with an insulation layer then hearth brick.
It would be of great help if I could get some input from you guys?
Thank you.

[david s]

This is a problem. For my mobile oven build I started with a steel cradle made from galv angle which holds 75 mm thick aerated reinforced concrete (Hebel). I chose this option because I thought I could save weight by not having a structural concrete supporting slab, the Hebel being both structural and insulating. The floor, cast in one piece sits on a one inch vermicrete slab between it and the Hebel. My mobile has seen a lot of service and is now around eight years old. Although it still performs ok, both the floor and Hebel supporting slab have cracked. I'm not sure whether this was caused by movement or heat. Driving over corrugated dirt roads and hitting speed bumps forgetting I was towing an oven were probably the cause. I should tear it down and rebuild, but as it still functions ok am loathe to do so. Will not use Hebel again when I do eventually rebuild though.You can make vermicrete as strong or as weak as you like, but adding more cement to make it strong also reduces its insulating capacity. I often use randomly mixed AR fibreglass fibres for strengthening vermicrete.

[mefornaio]

Thanks again David.
I just went to pick up more mix and spoke to the owner. He said the Vesuvius lightweight mix would/should work for the oven too rest on. He said they use it on jobs that have difficult or odd shape areas where using the cal board would be to labor intense. He said the 25/80 mix has the same insulating properties as the board at comparable thickness. Nothing they do is subject to the kind of vibration a trailer would encounter but he seemed confident it would work. I just happen to have 6 bags of it I purchased for the oven before I was told it was wrong.
I'm thinking of using this in the pan. The pan will be 1/4" plate the diamater of the oven including landing.
This will then sit in a angle iron perimeter a mirror of oven pan. The angle will have valve springs around the perimeter and the oven pan will ride on it for a bit of travel up and down. That's the plan any way.. Let's face it anyway u slice it masonry does not like movement in any shape or form.
I guess at this point replacement from trailer use just needs to be factored in. I don't see any of the commercially made trailer mounted ovens with any additional (special) suspension systems for the oven.
I mean one could put airbags on the trailer itself or even incorporate them into the oven mounting. I have thought of the airbags for mine but not sure.
Trial and error I guess.
Hey 8 years is not a bad run all things considered. Do you have a tandem or single axle?

[david s]

Single axle, oven on trolley, rolls on and off trailer. Oven around 180 kg. for your build I'd be worrying about water getting trapped between your supporting slab and the steel plate. Maybe drill plenty of holes in plate so moisture can drain out. Heat+ moisture= corrosion.
I should fit shocks to my trailer, have always intended to but never got around to it.

[mefornaio]

Wow single axle no shocks 8 years is impressive. Clearly leaf springs can be just fine as in your case if they are "springy enough" to allow travel based on weight ratio. Mine are going to take some tweaking to cushion the ride. Maybe a 6" support slab is the easiest solution. lol

I was thinking about the moisture thing the other day and fist though of a shower pan membrane then a roll on one then roll on bed line material. I agree it needs some sort of water/corrosion protection.

My bread oven at home was on a 4" slab insulated on the bottom and the bakery oven sat on a floating 10" hearth slab insulated on the bottom. No thermal couples were installed so have no idea what temps the bottom of the slabs were seeing. Can you speculate on what I might see on this set up as far as heat transfer through that cast insulating material? That's with one layer of fire brick and lets say 3" of cast insulating for now.

Im a bit leary of the cast insulation material transferring a lot of heat to the pan. I really feel like I want to put something semi ridged in there. Perhaps just a layer of blanket. Although it will be compressed by the slab and oven its still a barrier next to the metal. Plus it will give a little cushion for heat moment then again they way these refractory guys talk those material dont really experience much expansion at all from added heat.

Thanks

[david s]

"Can you speculate on what I might see on this set up as far as heat transfer through that cast insulating material?"

No, not without knowing the thermal conductivity of the material you plan to use. You may find this info in the specs of the stuff. They all vary. Generally the stronger the material, the poorer it is as an insulator. As a guide a 4" vermicrete slab (5:1 vermiculite,cement) would see very little heat on the bottom, but it needs to be dry.