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Roaster construction: wood ignition point
seedlings
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Posted on 07/21/2008 8:57 AM
Which parts of a coffee roaster can safely be constructed from wood? Whichever parts don't get too hot, of course. But, how hot? That depends on who's doing the testing.

I've been considering using wood for the bulk of construction of a roaster, and so I found this --->STUDY<--- which suggests wood can start fire around 250C, or 482F. Safety should be paramount, but it looks to me like wood could be most parts of a roaster, except for those parts immediately near the heat element.

What'd I'd like to ask is if anyone knows how the ignition point would change if the wood is lined with aluminum flashing? Could 500F air pass through a portion of a roaster made of wood (say, pine) with the interior lined with aluminum flashing?

What do you think? I may have to do some sort of testing.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
Dan
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Posted on 07/21/2008 10:35 AM
Chad, I think many parts could be made from wood, too. I not that you missed the obvious wood part: heating fuel!

The ignition point for wood doesn't change becuase it is lined with alumunim. Rather, the aluminum insulates the wood from the heat by reflecting infrared back and from the small air space that would exist.

Your best bet would be to use a liner of aluminum backed with 1/4" ceramic felt insulation. That should do the trick.

I have used 12" aluminum roof flashing as a liner. It is very thin, so you can cut it with shop scissors and bend it with your fingers.

Dan
 
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Alchemist
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Posted on 07/21/2008 11:59 AM
In lieu of ceramic felt, my personal fav would be hardibacker. Then cover in wood.
 
dBndbit
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Posted on 07/21/2008 5:54 PM
Since I'm a worry-wart who has a fire extinguisher by his roaster table, I'll mention a possible problem that shows up on wood stove chimneys. Insulating a metal oven is easy since you're just trying to keep most of the heat in the oven. But in this case any tiny air path through the insulation could be the source for an ignition point. What exacerbates the risk is that the continual heating will make the wood extremely dry.
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
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Alchemist
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Posted on 07/22/2008 7:20 AM
No reason not to be cautious. I keep a fire extinguisher handy also.

The difference though is what is in your wood stove is actively combusting and can well be much hotter than the temperatures you would roast coffee. For my current roaster, I would have no issue covering it in wood. I can lay my hands on the outside of the roaster currently. What I would NOT do is cover the halogen lights with wood. :@
 
seedlings
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Posted on 07/22/2008 8:15 AM
I do have plenty of 1.5" rigid fiberglass insulation (I thought it was Owen's Corning 500 series because it's denser than the 700 series, but I don't see any reference on OC website anymore, maybe it was a Johns Manville product), and had thoughts exactly like yours, Dan, to build the structure with room for the aluminum covered fiberglass lining.

However I do lilke the cement board idea. It would be much heavier, but less work and much less a fire hazard. I've looked at aluminum (or sheet steel) construction, but the expense is too high, plus there would still need to be layers with insulation anyway... which brought me back to wood.

I don't want to build a fire hazard. But the plan is to build an air roaster that recirculates the heat, so the entire structure will be filled with hot air.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
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