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Thread: roaster drum material

  1. #1
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    roaster drum material

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi,

    Can anyone tell me if stainless steel needs to be used for the drum of a roaster, or is normal steel ok?

    Thanks,

    Damian.

  2. #2
    Senior Member Koffee_Kosmo's Avatar
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    Re: roaster drum material


    Fire and intense heat accelerate the corrosion of most metals.
    Rust is just steel combining with oxygen.

    Stainless steel, is better suited to coffee roasting

    KK

  3. #3
    Mal Dimal's Avatar
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    Re: roaster drum material

    Quote Originally Posted by 4A6E676764645E4A6E726C6E010 link=1234331060/1#1 date=1234334095
    Stainless steel, is better suited to coffee roasting
    Not all s/s is suitable for sustained elevated temperature environments though, but I suspect that most commonly available types would be OK for roasting drums. Heres a link to info on a PDF data-sheet about high temperature resistant s/s alloys... http://tinyurl.com/csstg3

    Cheers,
    Mal.

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    Re: roaster drum material

    thanks.

    Mal - how do you know so much about just about everything!!!

    So it looks like I should go down stainless path. I dropped by a metal cutting/fabrication place today, that I just happened to see while I was driving along. I gave a description of what I wanted, and it didnt sound like it would be too expensive for them to cut and weld for me (which surprised me, I thought it would be expensive). Once I have a design I will ask him about stainless he has available, and its appropriateness for heat application.

    On metal and heat - does stainless expand much under heat - I am trying to figure out how to sit the front of the drum (which wil be open, no end plate, to allow for tryer, probe, filler, emptier) against the front panel. I am wondering if I need allowance for expansion so it doesnt jam? I just wish I could see a pic of commercial roasters to see how they do it, but cant find one. I saw the hottop (which had lots of photos) just pushes against the end from what I could see.

    Damian.


  5. #5
    A_M
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    Re: roaster drum material

    Quote Originally Posted by 3C393531393669580 link=1234331060/3#3 date=1234346207
    thanks.

    Mal - how do you know so much about just about everything!!!

    So it looks like I should go down stainless path. *I dropped by a metal cutting/fabrication place today, that I just happened to see while I was driving along. *I gave a description of what I wanted, and it didnt sound like it would be too expensive for them to cut and weld for me (which surprised me, I thought it would be expensive). *Once I have a design I will ask him about stainless he has available, and its appropriateness for heat application. *

    On metal and heat - does stainless expand much under heat - I am trying to figure out how to sit the front of the drum (which wil be open, no end plate, to allow for tryer, probe, filler, emptier) against the front panel. *I am wondering if I need allowance for expansion so it doesnt jam? *I just wish I could see a pic of commercial roasters to see how they do it, but cant find one. *I saw the hottop (which had lots of photos) just pushes against the end from what I could see.

    Damian.
    If ya from the OLD school of Engineers, then you often had to know lots and in some cases, every one expected you to be a savior and an expert at every thing... Good Engs like reading and often try their hand at many things... Thus over time, gain lots of first hand experience OR know where to get it..

    If you ever spend time with early ships Engs you would know why they are pack rats and can turn their hand to almost every thing... Why, caus in teh old dayswhen at sea you had to do it your self or not make it back..

    Well done and thank you, to Mal; As he also likes to share and pass on knowledge, that many of us may never get the chance to experience..


  6. #6
    Senior Member Dennis's Avatar
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    Re: roaster drum material

    Hi Damian

    I believe the most common materials used for commercial roasters are cast iron, stainless, and high carbon steel, Diedrich using the latter. Some drums are perforated though personally, i dont like that idea.

    The following link might help you regarding the drum.

    http://coffeesnobs.com.au/YaBB.pl?num=1195714810/51

    Whats not shown in the pic is the axle that goes through the centre, and of course the plates mounted at either end. These plates are mounted within a couple of millimetres of the drum, allowing it to rotate, while keeping the beans where they belong.

    Another CSer was toying with the idea of building a 1-2kg roaster and theres a thread somewhere as to where he was at...it fizzled out.

    Im not surprised you cant find pics - roaster manufacturers have invested considerable time and money in the development of their respective equipment.

    What you need to keep in mind is that your drum will need a series of baffles welded in place and configured to stir and lift the beans so that they have the right amount of contact with the drum, and the right amount of time suspended through the air; the baffles also need to constantly cycle the beans from the back to the front - this not only mixes, but its the way the beans are discharged.

    In conjunction with the above, the speed of the drum is critical - too fast and youll turn it into a centrifuge and the beans will be plastered up against the wall. Too slow, and as the drum rotates, the beans will slip down the sides, which is just as bad.

    Cheers!


  7. #7
    Mal Dimal's Avatar
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    Re: roaster drum material

    Quote Originally Posted by 624D4446516E424D4244464E464D57230 link=1234331060/4#4 date=1234347479
    If ya from the OLD school of Engineers, then you often had to know lots and in some cases, every one expected you to be a savior
    That pretty well covers it in a nutshell AM... ;D

    Quote Originally Posted by 4C494541494619280 link=1234331060/3#3 date=1234346207
    So it looks like I should go down stainless path.
    Not necessarily Damian.... There are plenty of decades old roasters around the world that have used the alternatives mentioned by Dennis, especially Cast Iron and more recently, High Carbon Steel. Cast Iron is particularly good as once a patina has been established, little or no further oxidisation will occur. High Carbon Steel is a better thermal conductor compared to Stainless and is also just as long wearing, if not better. For a home-built project, I would opt for the High Carbon Steel and then check out your local steel suppliers to see if any Low Pressure Steam-Pipe or Condensate Return Pipe has been assigned or purchased for any major projects in your region. You just may be able to acquire some of this Pipe of a suitable diameter, which would get you started.

    Quote Originally Posted by 4C494541494619280 link=1234331060/3#3 date=1234346207
    On metal and heat - does stainless expand much under heat - I am trying to figure out how to sit the front of the drum (which wil be open, no end plate, to allow for tryer, probe, filler, emptier) against the front panel.
    Yes mate, most materials have what is termed a "Coefficient of Thermal Expansion" meaning that as they increase in temperature, they will expand proportionally with respect to dimensions of the structure. As a result, you need to take this into consideration when designing the drum support system.

    Commercial Roasters are nearly all of fully enclosed design so as to enable the control of Air Flow, and Thermal Transfer Rate within the Rotating Drum. This requires that each end of the Drum needs to be supported on a Pillar/Flange or Trunnion Bearing system using bearing material(s) that are little affected by extended operation at high temperatures, yet still be able to function satisfactorily at ambient temperatures. This narrows down the material suitability quite severely and will probably have to be a Graphite based bearing, such as these here... http://www.graphalloy.com/html/pillow_block_.html, or here perhaps... http://www.graphalloy.com/html/flange_block.html

    As you can see, there is quite a lot to take into account if you want to build a miniature commercial roaster yourself, at home. And we havent even touched on the internal drum dynamics that you will need to experiment with otherwise, as Dennis has pointed out above, you wont be able to achieve the ideal mix of conduction versus air heat-exchange to roast the beans properly. Youll have to be prepared for significant trial and error until you find something that works properly.

    Then again, you could aim to keep things very simple and just expand upon the BBQ Roaster design. Personally, I think it would be far easier to design and build an effective "Fluid Bed" roaster of the capacity range you have mentioned. This produces a different style of roast result to that of a Drum Roaster but not deficient by comparison. A couple of CSrs have knocked together satisfactorily working designs and a search through the forum may turn up where discussions about these have taken place.

    Hope some of this is of help to you Damian.... Not an insignificant project by any measure so all the best with what you decide :)

    Mal.

  8. #8
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    Re: roaster drum material

    Hi,

    Thanks for all the info Dennis and Mal. A lot of terms and info for me to look up, and work with. I suppose I should say, I realise there is a lot of r&d goes into these commercial roasters, and I in no way expect my roaster to compare at all. What I want is something larger quatity, which is easy to load and empty without delay. this is the aspect that I want from teh commercial roasters (and of course I want everything else hidden away in there, but I wont get it!). I see it like a BBQ roaster, but without hassles of dealing with the heat and drum each roast. I am personally very happy with the turbo oven roast results (but some control issues I would like to improve), so I would be more than happy it I achieved similar results, but with larger quantity, and more convenince.

    No going back now - I have already started buying up my bits and pieces!

  9. #9
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    Re: roaster drum material

    Quote Originally Posted by 604D494548240 link=1234331060/6#6 date=1234364204
    This requires that each end of the Drum needs to be supported on a Pillar/Flange or Trunnion Bearing system using bearing material(s) that are little affected by extended operation at high temperatures, yet still be able to function satisfactorily at ambient temperatures. This narrows down the material suitability quite severely and will probably have to be a Graphite based bearing, such as these here... http://www.graphalloy.com/html/pillow_block_.html, or here perhaps... http://www.graphalloy.com/html/flange_block.html
    Mal, there is an industrial machinery scrapyard closeby where there are many items that look to be very similar to the pillow blocks you mention. I can see a couple of these would be very useful. Are all high temp rated, or do I need to be specific with what I get?

    They also have nice looking gearboxes, cogs, chains, pulleys, 1m big motors, and monster size machinery I have no idea what does! The only problem is finding things that arent 10X the size you want.

  10. #10
    Senior Member Dennis's Avatar
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    Re: roaster drum material

    Quote Originally Posted by 6065696D656A35040 link=1234331060/8#8 date=1234408516
    The only problem is finding things that arent 10X the size you want.
    Aaw Damian, wheres your sense of adventure - just build a bigger roaster! ;D

    BTW, if you have any welding done, make sure they use the same material in the rods as what is being welded - this will reduce the likelihood of hot/cool spots around that area.

    Cheers!


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    Re: roaster drum material

    ok, dont know anything about welding, but i will ask about it. Im guessing if I get too specific it may go from a reasonably cheap project, to quite expensive - I may just have to live with a few deficiencies.

    They have some machine there that looks like it turns a big drum - probably fit 15 of me inside - that could do a bit of coffee!!!

    thanks for linking the pics of the roaster drum. Intersting to see. Im thinking of going a perforated drum - im concerned that if I go solid, and dont get the agitation/rotation right I will do a bit too much scorching of the beans.

    I also found this link fun. You get to drop the beans in the roaster one by one!

    http://www.whydontwehavethisguy.com/_WDWHTG/portfolio/Detail.asp?id=PROBAT

  12. #12
    Mal Dimal's Avatar
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    Re: roaster drum material

    Just on something that Dennis mentioned above... 8-)

    Since your project roaster isnt going to be all that huge, you would quite easily get away with a central axle that both supports the Drum and provides a means to fit appropriate bearings. Would be a much simpler setup than having to fit flange or pillow block units. Would be easy to accommodate a thrust load bearing too with an axle design.

    Will be a very interesting project mate.... Keep us up to date wont you ;)

    Mal.

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    Behmor Coffee Roaster
    Old but very informative discussion
    Thanks very much
    Dimal likes this.



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