I don't know if it matters much, as the manufactures of every mill spec their own out individually, but what should the typical speed of the rollers be on an average mill? We were thinking in the 250 RPM range? Is this way off or in the realm?
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http://probrewer.com/vbulletin/showthread.php?t=13818&highlight=mill+crush
http://probrewer.com/vbulletin/showt...ght=mill+crush

Thanks
That helps for when we get it going, but right now we are looking at sheaves tying to figure out our ratio. This is for the Micro Brewery Mill that BC Entr. makes. Anyone else with an idea of an acceptable speed? We are a small brewery looking at 120200# of grain.
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we are looking at sheaves tying to figure out our ratio.
For my toy mill I used a Bodine gear motor and run the mill at 94 RPM, 3 lbs a minute with 11/2" rollers.
The Barley Crusher mill design might limit your speed to below 500 RPM.
Call BC and ask for specs.
Cheers,
ClaudiusBMy setup:http://photobucket.com/ClaudiusB
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I believe the one your talking about is the home brew version. I have that one from times past. We are looking at the Micro series that BC makes. I was hoping for the neighborhood of 1020# a min. I think a smaller complete mill from Apollo or Robix might be a better choice for us.
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Gabe, your answer is in the link that BigMuddy sent you. RPM is NOT the deciding factor, periphery speed is.
"Rolls should run at 2.5  4.0 m/s on the periphery. "
I'd be wary of tiny rolls, too. They produce an inferior crush. A few percentage points on yeild will add up over a few years. Good luck!Phillip KelmPalau Brewing Company Manager
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Originally posted by gitchegumeeGabe, your answer is in the link that BigMuddy sent you. RPM is NOT the deciding factor, periphery speed is.
"Rolls should run at 2.5  4.0 m/s on the periphery. "
I'd be wary of tiny rolls, too. They produce an inferior crush. A few percentage points on yeild will add up over a few years. Good luck!
v = 2.5m/s = rw = 0.0254(m) x w(rev/s)
w = 98.4 rev/s = 5905 rpm
For a 6 in roller...
2.5m/s = rw = 0.0762(m) x w (rev/s)
w = 32.8 rev/s = 1968.5 rpm
I guarantee no brewery is running their mill at 6000rpm or 2000rpm. You would shred the grains. Unless I am making a bad assumption, that rule doesn't work. RPM would be a better data point to look at or those speeds are wrong. Are you sure it wasn't 2.5  4 in/s? That works better.
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Roller Speed
Originally posted by BFCbc View PostI am assuming you mean 2.5m/s is the tangential velocity on the roller. For a smaller mill with 2" rollers like many micros have you would need an RPM of 6000 to achieve that at the roller not at the motor.
v = 2.5m/s = rw = 0.0254(m) x w(rev/s)
w = 98.4 rev/s = 5905 rpm
For a 6 in roller...
2.5m/s = rw = 0.0762(m) x w (rev/s)
w = 32.8 rev/s = 1968.5 rpm
I guarantee no brewery is running their mill at 6000rpm or 2000rpm. You would shred the grains. Unless I am making a bad assumption, that rule doesn't work. RPM would be a better data point to look at or those speeds are wrong. Are you sure it wasn't 2.5  4 in/s? That works better.
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But the grain DOES know the difference
Small rollers don't work well. The reason large rollers are used is at least twofold: the periphery speed is lower for equal throughput, AND the nip angle on the machine is much less. This is essential for good crush. From A TEXTBOOK OF BREWING, DeClerk; "The diameter of the rolls should be at least 250mm otherwise the feed will fall on to the rolls at an obtuse angle, and will not be snatched up by the rolls. The crushing time would also be too short with rolls of any smaller than 250mm." My experience bears this out.
There is also a very good discussion of roller radius, roll gap, forces & energy required for milling in MALTING AND BREWING SCIENCE, Briggs, Hough, Stevens, Young. There is a derivation of optimum roll nip angle of 16 degrees. Also backs up sound brewing science.Phillip KelmPalau Brewing Company Manager
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Originally posted by gitchegumee View PostSmall rollers don't work well. The reason large rollers are used is at least twofold: the periphery speed is lower for equal throughput, AND the nip angle on the machine is much less. This is essential for good crush. From A TEXTBOOK OF BREWING, DeClerk; "The diameter of the rolls should be at least 250mm otherwise the feed will fall on to the rolls at an obtuse angle, and will not be snatched up by the rolls. The crushing time would also be too short with rolls of any smaller than 250mm." My experience bears this out.
There is also a very good discussion of roller radius, roll gap, forces & energy required for milling in MALTING AND BREWING SCIENCE, Briggs, Hough, Stevens, Young. There is a derivation of optimum roll nip angle of 16 degrees. Also backs up sound brewing science.
We're on the same page about the contact length being gentler with the larger roller, like I said, although it's not as much as some might think. Going from a 2" to a 10" roller, you're only doubling the distance that the grain is in contact with the roller. For this size, the grain is in contact with the mill for about 8mm until it hits the smallest gap and maintains contact with the mill for about .0026 seconds to hit that point. The 2 inch mill would be about 4mm and .0013 seconds at the same peripheral speed. To put a visualization to this, it takes a person more than 100 times longer to blink than the amount of time the grain spends getting crushed, even with a 10" roller.
I'm also just keeping this in context of the scale that was being asked in this thread. He's only crushing 120200 lbs of grain, so he probably doesn't need to buy a grain mill that can do 5,000 lbs per hour and is more than double the cost of the rest of his brewery equipment combined, lol.
Don't get me wrong, if money wasn't an object definitely go for the larger mill.
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