December 18, 2017 01:30:36


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3d Printed Fluid Bed Roaster
Running the numbers it looks like they may have shipped you a 220 volt element which would run at around 480 watts at 120 V.

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Looks like that, Allen. The coil measures about 30 ohms, which is about 1600w at 220-40 rms.

I have a bigger problem though. The shallow roast chamber side may be too shallow - the beans do not slide down towards the heating element. Also, the 120w vacuum may not be powerful enough to push through the ceramic element and much over 100g of beans... Hmm...

Well, I guess it would have been greedy to want this to come together so easily.
Pretty happy with the look / assembly. Just hope I can figure out a perf plate design that will work.
Believe it or not you may want to restrict the airflow coming out of the exit area of the element. By doing so it will create a higher pressure area yet on a smaller area under the beans, causing a spouting of the beans. I encountered the same issue as you when first developing an air roaster (spouting type). What I mention was the solution. So what you would do is cut out a piece of stainless steel in a circle, the diameter of which is the exit circle you now have. Then cut a hole in the middle of it about half the diameter of the original circle. Affix somehow. You may need to do a couple tries with different sizes of holes cut till you get it just right.

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
Hi Len, I'm going to give that a shot. In addition to the top holes, I was considering leaving a small air gap on the edge to inject a blanket of air under the beans as they fall back to the central heating location / get them out of the static coeficient of friction range.

Any reason why I shouldn't use aluminum? Higher heat conductivity might scorch the beans?

Also, any best practices for hole positions?

Thank you for the help! I need all I can get. limb
Edited by Linnaeus on 12-01-2017 05:35
I always use stainless in the roasting chambers; much higher melting point and a tougher metal that does not wear out as fast. I would put the hole directly in the center of the disk you cut out. Interesting thought on the small air gap around the edge. I would say just make sure the area of the gap is less than the area of the hole you cut in the middle of the disk to assure that you will get a good spouting action. Otherwise there may be a negative influence on the spouting action.

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
Several manufacturers have used aluminum for their fluidbed roast chambers and if you ever get your roaster up to the melting point of aluminum you will have much more severe issues to worry about than remaking your roast chamber.

I would suggest reading as much as possible within our fluidbed threads and you'll find many with helpful tips on figuring out RC bottom cone slopes and perf plate holes surface area versus coffee charge weight.

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana

I ran 3 trials with different nozzle designs.

3 large (5mm) / 4 small hole (1mm): Max loft = 120g

1 central hole 9mm: Max loft = 190g

1 slot facing proximal rc wall (60mm^2 opening) = 270g

So, I created a mold for the winning nozzle. I'll try casting with both the refractory, and also rocksett.

There is a compromise in that the more "spouting" of beans, the less contact time the bean mass has with the heated air. I'm going to try to correct for this by adding a cap to the Pyrex tube. The cap will have a metal pipe that travels about 3/4 the way down the opposite wall (from the spouting beans). This will mean that the hot air doesn't travel straight out the top of the RC, but must instead travel back down to the beans for a second pass.
Edited by Linnaeus on 12-04-2017 02:35
So I take it that the nozzle modification did create the spouting you were looking for?

I am envious of your mold making abilities. ThumbsUp

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
Thanks Len - it did. ThumbsUp The compression housing / connection to the roast chamber is leaking the tiniest bit - so unfortunately it's losing head pressure when it needs it most. Still 'spouts' about 250G. I'm on the fence right now because I'm either replacing the heating element with something less restrictive, or adding a second stage to the compression / air intake (in the form of a 24V 20W 45CFM blower I have from another project).

What I'm working on now is a very simple chaff collector / exhaust that will recirculate some of the hot air (not into the intake - but back down into the roast chamber.)

I'll just be using one of these for now (5.5 inches across - $6):

Once I get the rest of the roaster working I'll start focusing on a "micro" cyclonic separator that will be built right into the top of the RC. That way I can install a carbon filter to deal with some of the nasties.
Some trial runs, some results, and a bit of work to do.

So I ran autotuning on 200g of beans and developed a 14 minute programmed ramp up to 200C. Love the PXR4 PID - the menu systems definitely have a learning curve, but once it's dialed in it's really impressive to watch.

I ran a test batch of 200g then 120g through the 14 minute ramp. The bean temp stayed in lock step with the set temp - initially trailing by 5-10C, but completely 1/1 by 140C. The beans hit first crack as predicted around 195-200C.

Unfortunately, the main issue is that one of the roast chamber walls is too shallow, and some beans end up getting stuck. This issue is made worse by the positioning of the temp probe on the shallow wall.

You can see that after the roast was done and the beans were dumped - there were some that did not get roasted at all.

Such a bummer.

Anyway - I've got a few improvements to make:
- Roast chamber needs to be remade with steeper sides
- Roast chamber will be made in two parts: one to hold the heating element, one for the upper chamber / funnel. Two parts will make it easier to replace the element and also to try different funnels without completely rebuilding every time.
- Replace the heating element with an open nichrome element (the ceramic element is super efficient, but increases static pressure too much for my vacuum).

We can rebuild it
Edited by Linnaeus on 12-07-2017 06:58
Keep the faith. I went thru 7 iterations of roast chamber design, getting one I was happy with.
Thanks BT!

I'm taking a short break while I wait for the new heating element to come in. Once in, I'll take measurements and print another chamber.
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