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5 Lb Roaster Perf Plate Design Help!


PhilH wrote:

Sorry Im very late on this thread
Im with Tamarian on trying the steeper angle on the ramp

My Roaster is similar and maybe some comparisons could be helpful
I have a 5kg FB using 6? cylindrical RC and Burner with 45deg ramp and flat perf plate
I measure ET about 1cm below perf plate and ET is often measuring around 150C(270F) above BT
I measure BT about 50% of the bean mass height and about 5cm from the ramp and well out of the main spouting airflow.

Its notoriously difficult to understand with certainty the fluid/thermodynamics of a specific FB roaster geometry (esp wrg to Temp measurement). I measure peak ET about 350C(662F) which would seem to theoretically break ?the rules?. However I know there is a very significant temp drop as soon as the heated airflow crosses the perf plate which is difficult to measure accurately. I am comfortable this likely puts me back inside ?the rules?. Tasting (as Tamarian points out) is a great way to assess/confirm whether changes result in improvement or deterioration of roasted beans.

I use 2x cheap VC blowers ? one was not enough) and use a long burner chamber approx 750mm (30") from burner to perf plate (probably overkill) with a baffle plate to promote turbulence / mixing of heated air prior to reaching perf plate. Leaks prior to the perf plate (even small ones) are easy to miss and will mess up bean movement and lose a lot of heat.

Sounds like you have got it largely sorted now.

Well where the heck were you! Haha. Just kidding. (Sort of) Glad to have your input! I actually looked at your thread while trying to sort out my issues and gleaned a little bit of useful info there.

The steeper angle was definitely key, I think because of the square roast chamber.

My ET was definitely causing me major issues. While I wasn't positive I needed to place a lot of emphasis on adhering to the rules, it was limiting my thinking and ultimately figuring out how to get that down was the key to my success. I've roasted some excellent coffee the lay few batches and the roaster is very controllable more. That is something I could not have said before the furnace baffling. What does your furnace baffle look like, and where is it located/how much area for flow did you leave around it? I saw a huge drop in temp across my perf plate without beans so o4 moved my ET probe to above the perf plate. But I noticed that with the roaster loaded, the temp drop was no where near as great. I was also seeing roast defects caused by high heat though. That's why we finally added the baffle. It is directly under the perf plate so air has to flow across the furnace chamber twice before going through the perf. It extends out to about 2" from the back wall.
I put the baffle plate ahead of the burner. The air comes in the bottom of the burner thru the rectangular hole and has to go around the outside of the circular baffle plate there is a gap of approx 1cm between the baffle plate and the 150mm outside pipe

pics attached - I hope they come thru ok
PhilH attached the following image:

Edited by PhilH on 12/19/2019 12:14 PM
Dalla Corte Mini, Compak K10F, 1.2kg FB LPG/PID FB, 5kg FB LPG/PID
That's exactly how i used to have mine set up. If you can, I'd recommend trying a baffle above the flame. I'd bet money your ET will look better. Thats precisely what did it for me.

I attached a drawing of how mine is set up now.

I'm going add one in my little 1 lber too. The roaster was a lot more controllable after adding that baffle as well
pisanoal attached the following image:
I'll try it and report back. A bit busy at the minute so wont be for a few weeks.
Dalla Corte Mini, Compak K10F, 1.2kg FB LPG/PID FB, 5kg FB LPG/PID
Found today this roaster... maybe the picture with lateral section help you, if still in trouble...


Scroll down to the bottom of page
Thanks for sharing Renatoa - good find! I've never seen a curved "return" like that for the bean mass. It makes a ton of sense in reducing friction and encouraging better flow I would imagine. I wonder if production is that much more difficulty proving to be a challenge in most FB designs
If you noticed, your beans are falling in the middle of the column. it should be blown to the left end so it will smoothly slide on the 45 degree plate. If you can add curved plate in the top as a trial similar to the attached design.

Edit, Oops you already have the photo.
Husamka attached the following image:


Husamka wrote:

If you noticed, your beans are falling in the middle of the column. it should be blown to the left end so it will smoothly slide on the 45 degree plate. If you can add curved plate in the top as a trial similar to the attached design.

Edit, Oops you already have the photo.

Are you referring to the OP roaster design or the attached image Husamka?
Regarding the beans are falling in the middle, this is refer to "pisanoal" video. the curve in the photo is to correct that.
Thanks for the link renatoa. I actually saw that roaster or something similar in my search for answers during the build. I really liked the idea, unfortunately the RC was already built and the way the beans were being loaded, there was no good way to add a curved deflection plate. This is something that RoasterRob made reference to trying as well.

CharcoalRoaster - It definitely increases the difficulty of fabrication, but not too bad. If designed right, you could use a section of SS pipe, or get a piece of SS sheet bent to your desired radius. Still more complexity then flat sides. For large volumes of coffee, definitely makes sense. Also would be extremely useful for shortening the RC height.

Husamka - Thank you for taking the time to look at the thread and provide suggestions. I have actually already successfully completed the project. The design is capable of roasting upwards of at least 8 pounds of coffee in very reasonable amounts of time (drop times under 15 minutes), with good ETs (below 525F). The roaster has produced some really great coffee. The problem with adding an angled plate would have been loading the roaster. I would have had to add two angled plates stacked like a curved version of "<". The beans load from the top and would have hung on the curved plate. Ultimately, the beans falling in the middle of the pile only happened very early on in the roast. The key changes that made this successful were:
1. Increasing the angle of the angled plate (square RC requires steeper plate angle for good agitation, something around 60 degrees)
2. Baffling the furnace above the flame to ensure good air mixing and even heat distribution.
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