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NewBean
06/12/2019 3:57 PM
Just waiting on my TC4 shipment then it's roasting time

snwcmpr
06/03/2019 11:37 AM
I rarely purchase roasted coffee. I just ordered 4 bags from Mountain Air Roaster.

tm97
05/30/2019 12:34 PM
Hi, I use a wok with a glass lid for roasting. shaking the wok is a good exercise, actually.

NetriX
05/29/2019 9:08 PM
morning

snwcmpr
05/27/2019 1:56 AM
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Info On Centrifugal Roasters???
Dan
Jim, Knowing the theory makes for a good basis of understanding what is going on. I see this as a thought experiment. Of course we both know any roaster that lifts the beans up by rotational velocity only to have them fall back down is going to require a sloped wall. I wasn't suggesting you didn't know this.

I see what you are saying. If spun at 1G, the net force on the bean on a spinning vertical wall is a 45° downward vector, and that leaves plenty of remaining force for the bean to roll down the wall. Hence your call for increased rpms to bring that angular vector up to horizontal.

Now, let's look at the other factors that come into play. Even a hardened steel sphere resting on a hardened steel plate has some friction. As that steel plate is inclined, the sphere will start to roll. So, knowing this angle, we also know that the angular vector mentioned above needs to achieve in order to keep a steel sphere from rolling down a spinning vertical wall. And I agree, it would be very fast.

However, beans aren't ball bearings. I describe them as a bisected ellipsoid. That is, having a minor and major diameter with about a 3:4 ratio and then cut in half longitudinally. Also, they are cellulose, not hardened steel. Combining those factors we see that beans don't roll very well at all. What angle would that steel plate have to be inclined to before the bean rolls down? Actually, I suspect it will never 'roll' at all, but will slide down first. If so, then what we need is that angle to calculate back to the rpm required.

This is more important than you know since adding in the angle of the sloped bucket let's us also calculate the rpm required to get those beans to slide up.

Dan
 
http://www.intactamerica.org
metal
Angle of repose??
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
metal
metal wrote:
Angle of repose??


force X distance = the moment??
Edited by metal on 04/30/2008 2:57 AM
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
farmroast
Just seeing this conversation. Similar theory that I used with my roaster. Jim Schulman mentioned to me when he saw pics of my roaster that it had similarities to an industrial roaster like you pictured but it's nice to see the pics now. Using my bean bats at high enough rpms to elevate the beans and cause increased convection. Depending on bean mass I adjust my rpm from 125-240 to get the right level of lift and pattern. Am now looking at different shaped bats to adjust and splay the pattern of elevated beans. With the CO top the fan shoots the air down the sides directly at the whirling bean mass and then draws up from the center to recirculate. The new Loring roasters use a horizontal fixed drum with paddles that put the beans in motion.
farm
Loring
http://www.smartr...
Edited by farmroast on 04/30/2008 2:57 AM
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills http://coffee-roa...gspot.com/
 
Dan
metal, I believe angle of repose refers to the angle that particulate matter makes when it is dumped in a pile, not when it slides on a flat surface. The angle is slides can be used to calculate the coefficient of friction. I don't have my Machinery's Handbook at home, so can't say more about that.

Ed B., Your roaster uses recirculating heat, which of course these two units do, too. I can understand the savings in production, but do you think there is a cost savings on a 1-5 pound roaster?

Dan

 
http://www.intactamerica.org
dBndbit
Metal, force x distance sounds like a lot of work to me. Were you just waking up out there on the west coast?

Farmroast, nice setup. I can see where the stirring paddles would add some significant air-bean velocity. What shape paddles are you using now? I didn't see the photos on your website except what might have been your original wire stirrer. I guess the difference in these centrifugal machines is that they're trying to keep the entire bean mass in motion all the time, and probably generating a lot more air-bean speed.
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
http://www.ReeferDoor.com
farmroast
Jim: The original rods don't just stir the beans, they bat the beans. The whole bean mass is basically elevated and whirling at all times, fluid bed like. No pictures of new bats yet as I'm still testing different designs. Basically if you think of a golf club a 2 iron creates little loft where a 7 iron creates a lot of loft. Then you need to deal with the centrifugal force factor to bring the splay inward along with elevating. I'm also experimenting with pot shape and am starting one with a wok shape to it but think that the 90 degree sidewall shape may still be the best.
Dan: The efficiency of a mechanically driven fluid bed with modest air circulation is spot on. I have seen one of the Lorings and it is much more efficient per pound than a traditional drum roaster.
I'm working on a design of an approx. 3kg model that could heat with electricity or gas. So many possibilities so little time!
farm
Edited by farmroast on 04/30/2008 5:49 AM
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills http://coffee-roa...gspot.com/
 
dBndbit
Cup_in_hand,

Sorry, I'm only slightly confused. Forget the beach. You said SCAA conference and I somehow thought about Coffee Fest. Not much of a beach in Minneapolis, but a better show. Good luck in any case getting some enlightening Probat-Burns info.

And if you do get to ask some specific questions, I'd be very curious about the physical size of the centrifugal bowl and packed-bed roasters, their RPMs and air velocities or volumes. Numbers, numbers, numbers!

And please pass on our respect for the obvious engineering talent going in to these very creative machines.
Edited by dBndbit on 04/30/2008 6:34 AM
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
http://www.ReeferDoor.com
seedlings
Who will have the first working prototype!?!

Since I can't add any insight, I'll just say GREAT DISCUSSION!!!!

s:2_s:2_s:2_s:2_s:2

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
Dan
I'm not so interested in efficiency. It's OK, but not a big selling point for me. I didn't get into roasting to save on coffee. I got into it to have great tasting beans. I'll go with the roaster that has good profile control and is able to dump the beans NOW when they reach their optimum temperature. Dan
 
http://www.intactamerica.org
dBndbit
Chad,
Don't hesitate to jump in! With all the unknowns on how these things actually work, I figure everybody has as good a chance at getting one to work as anybody else. I know I'm going to be doing a lot of guessing.

I've been trying to decide on how to home-build a big batch roaster, at least 20#, maybe a quarter bag. But I put a lot of limits on this dream machine. Like power efficiency, household AC, low smoke/smell, 200 cable channels... the standard list. After looking hard at all the normal options, I'm liking a modified form of the centrifugal bowl roaster. Only it would be more like a wash tub about 4 feet in diameter.

I'm still thinking (dreaming).
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
http://www.ReeferDoor.com
metal
Dan wrote:
metal, I believe angle of repose refers to the angle that particulate matter makes when it is dumped in a pile, not when it slides on a flat surface. The angle is slides can be used to calculate the coefficient of friction. I don't have my Machinery's Handbook at home, so can't say more about that.

Ed B., Your roaster uses recirculating heat, which of course these two units do, too. I can understand the savings in production, but do you think there is a cost savings on a 1-5 pound roaster?

Dan



Angle of repose also refers the angle of a given surface that gives motion to the subject matter either with declination with gravity or inclination with force applied as with centrifugal force. Either way I think we are dealing with a constant and formula theory that may help. I am confused a bit as I thought we were talking about a bowl of sorts used centrifugally and not a flat surface.

The angle of repose is sometimes used in the design of equipment for the processing of particulate solids. For example, it may be used to design an appropriate hopper or silo to store the material. It can also be used to size a conveyor belt for transporting the material or its design angle of function barring slope collapse.

It can also be used in determining whether or not a slope will likely collapse;
the talus slope is derived from angle of repose and represents the steepest slope a pile of granular material will take. This angle of repose is also crucial in determining the correct calculus of stability in vessels.

I guess I misunderstand the principles of this type of roaster. I digress, as I pay more attention.
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
Dan
metal, I was talking about the angle of the chamber, not the angle of the pile of beans. Those two angles are different because the friction between two or more beans is different than between a bean and the roaster chamber. I'm not sure what the correct nomenclature is for these two terms. Like I said, my handbook isn't home, so can't look it up.

My thinking has been imaging one bean in a spinning chamber (or a bean spinning in a stationary chamber) and not a pile of beans tumbling over one another.

Regarding the bowl versus flat surface: The bean doesnt' know it is in a bowl. All it sees is a sloped surface. Even if that surface is curved, at any given time the bean's movement is predicated on the tangent angle of that curve at the point of contact. So, it might as well be considered flat at that moment in time.

Dan

 
http://www.intactamerica.org
farmroast
Powering the bean in a stationary chamber gives a better chance for evenness in bean speed and evenness of roast. Also less tipping.
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills http://coffee-roa...gspot.com/
 
dBndbit
Metal,

Thanks for the good info on terms! A few months ago I was working on some simulations of air-spout roast chambers but didn't know the terms, so I couldn't look up the necessary equations. Limited to guessing again. Not good. The closest thing I could remember was "slump" used in testing wet concrete, not too useful with coffee beans! I'm just an electronics guy out of my field trying to have fun roasting coffee.

What a great group on this website! Thanks, everybody. Keep this up!
Edited by dBndbit on 05/01/2008 1:39 AM
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
http://www.ReeferDoor.com
Dan
OK, I checked at wikipedia. The angle of repose refers to the angle particulate material makes when poured onto a flat surface forming a cone-shaped pile.

There is no name that I can find for the angle at which an object begins to slide down a flat surface as it is tilted.

Did some more checking and found that high-velocity hot-air roasting might not be the end-all-be-all of roasting.

United States Patent 4169164. A coffee roasting process for forming roasted coffee in which the green coffee beans are dry roasted by passage in a fluidized bed through a two-stage roaster. In the first stage, the beans are heated by a roasting gas for partial roasting and expansion of their cellular structure. Then, in the second zone, the beans are contacted with an independent roasting gas stream at a temperature of 515° F.- 545° F. to stabilize the open structure of the beans and to provide the desired dark brown color without burning. The second gas is supplied at a lower velocity and higher temperature than the first gas. The roasted coffee bean product is of low density while providing high yield of soluble solids.

Edited by Dan on 05/01/2008 3:39 AM
 
http://www.intactamerica.org
metal
Dan wrote:
OK, I checked at wikipedia. The angle of repose refers to the angle particulate material makes when poured onto a flat surface forming a cone-shaped pile.

There is no name that I can find for the angle at which an object begins to slide down a flat surface as it is tilted.

Did some more checking and found that high-velocity hot-air roasting might not be the end-all-be-all of roasting.

United States Patent 4169164. A coffee roasting process for forming roasted coffee in which the green coffee beans are dry roasted by passage in a fluidized bed through a two-stage roaster. In the first stage, the beans are heated by a roasting gas for partial roasting and expansion of their cellular structure. Then, in the second zone, the beans are contacted with an independent roasting gas stream at a temperature of 515° F.- 545° F. to stabilize the open structure of the beans and to provide the desired dark brown color without burning. The second gas is supplied at a lower velocity and higher temperature than the first gas. The roasted coffee bean product is of low density while providing high yield of soluble solids.


If you read farther on wikipedia you will see my second paragraph of my last post came directly from that site.
What do you suppose they mean by stating it is used in the design of equipment?

I don't want get into a contest here, as it is possible that my college professor was an idiot. He probably had no clue that
Wikipedia had the full spectrum on this theory. He probably had no clue that he was only allowed to use the angle of repose to measure "the angle particulate material makes when poured onto a flat surface forming a cone-shaped pile". Now that you brought this to my attention, I think I will petition my old college to remove this useless term from their teaching, being worthless in the field of engineering and all.
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
metal
Angle of Repose
Also:
The lowest slope angle at which a granular material will begin to slide, or the steepest incline at which it will not slide.

http://www.avalan...repose.php

They must get their information from wikipedia? Or OSU?

It's good we caught this abuse of terminolgy. Good folks could have been led astray...
Edited by seedlings on 05/02/2008 2:02 PM
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
metal
http://www.columb...asting.htm

These people should be talking in terms of piles only... Another abuse! Don't trust these universities!
Edited by seedlings on 05/02/2008 2:02 PM
i44.photobucket.com/albums/f10/metalcrafter/coffeebloomfeathertransparent.jpg
 
Dan
I brought my Machinery's Handbook home and it has solved the nomenclature mystery FOR ME. The term angle of repose is used both for the included angle in a pile of particulate matter as well as the angle of a flat plate as an object on it is "just barely able to remain stationary." Both are the same name. However, they might not be the same angle.

What is useful for is is this: the tangent of the plate's angle is the coefficient of friction between those two materials under those conditions.

Friction is not a material property, it is an environmental property, and the coefficient will change in the presence of a lubricant, temperature changes, velocity, etc.

Friction = coeficient of friction x weight (as applied perdendicularly to the plate)

A greater force is required to start an object sliding and to keep it sliding because the friction at rest is greater than the friction in motion. Something to keep in mind designing a roaster.
Edited by Dan on 05/03/2008 5:35 AM
 
http://www.intactamerica.org
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