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Discussion Starter · #1 ·
After using a CR 9080 for a year and seeing what it does, can a 9120 with a single rotor do as much and save as good as two rotors turning faster like the 9080?
 

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I would say the 9120 will not do as much as a 9080 in my conditions. Corn and beans, perhaps, but the twin rotors in small grains seem to be better class for class. Our TR98 ran with a 7010 on a demo. The 7010 has the same rotor size and length (smaller cleaning) as a 9120. The TR has smaller rotors than a 9080.
 

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Discussion Starter · #4 ·
Actually Connor, worms are a great things and serve to improve soil in my understanding. I have a Case dealer close and New Holland dealers about an hour away so the truth is always good if taken the right way. Lots of hearsay happens and I like to see the good of both sides. After a few years with a CR 970, I appreciated the extra support structure on the rotor drive and found the 9080 to be unbelievable in comparison at putting through tough straw, heavy crop and being able to use it's horsepower. It would be good to put that feature on the 9070's and 970's. I found the bigger Iveco it to be very fuel efficient as well. With the same engine in both 9120 and 9080, is there a difference in how one would set the rotors on either one to do the most one could do per hour? I find with the high rotor speed, I am running my rotor concave gap wider than I did on the 970. With higher capacity on the rotors, then one needs to open up the bottom seive and top chaffer more than the default setting says in order to separate the grain at higher flow rates. My losses after watching the land this spring were excellent. The back of the chaffer was always set a bit less than the main chaffer area. It has an identical shoe to my knowledge. Could one speed up rotors on a 9120 and get a similar result.
 

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Discussion Starter · #7 ·
When I first started wheat last year, the cylinder speed default for wheat was about 1050 similar to the 970. I drove there for a while and noticed loss levels as we had hp to go faster-, then went to about 1400 rpm with rotor and losses went totally away in the heavy spots as well as the rest of the field. Rotor clearance used to be set at 20 mm and now I go to 45 mm. At 1400 rotor rpm, we increased machine speed by 2 to 3 miles an hour and had virtually no loss anywhere. At 1050 we were having some rotor loss, in heavy crop area, even if minimal, but still there. At 1400 there was no loss.. and averaged over 1600 + bu per hr with about 60% load and with peaks way over 2000 bu per hr. We found a new level of output with basically the same inner parts to the combine. There is a big difference in power but interesting the original default settings had similar combine speeds. Another improvement was to have hydraulic drive on fan so even under a heavy loaded machine, we now can set shoe different and have no shoe loss and also never plugged return even once. Would 9120's have similar experience vs 8010's?
 

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And remember in the case of the big NH, the 'smaller rotors' are actually only 2 inches smaller than a 40 or 60 (44 or 66) series Axial flow and 95XX series STS Deeres. So they are really not that small!
 

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Well to answer the original question, no the bigger rotor cant do as much as the two smaller faster turning rotors. This is mainly due to the cleaning surface area of the two rotors as compared to the single rotor. The crop enters into only one pinch point in the single rotor, this is where the majority of the seperation happens. Having two slightly smaller rotors will actually increase that surface area and increase your seperation ability.
 

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Also speeding up the 30 inch rotor on a 9120 probably would result in more cracking, than speeding up 2 smaller diameter rotors. Similar RPMS on a smaller rotor vs larger diameter rotor= Larger rotor rasp bar travels at a much high speed (velocity). The propaganda New Holland always said was with smaller rotors at high rpms, they get a gentle threshing (low speed of rasp bar) while very high cetrifugal force for separating due to higher RPMS. They always highlighted that vs Case (and Deere) before the merger.
 

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Just being devils advocate but the bigger rotor should be able to create just as much centrifugal force at a lower rpm therefore not needing a higher rpm and not cracking grain.
 

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I think you need higher speeds on a larger rotor for more centrifugal force (same idea as if you are spinning and pull your arms in you go faster).

A smaller diameter has a tighter 'turn' causing the directional change to be greater and more grain to be thrown out. Since a larger rotor has less tight 'turn', it would require more rotor speed to separate the grain through centrifugal force.

That is how I understand it.
 

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Discussion Starter · #13 ·
Another example of centrifical force would be going around a sharp corner on a road vs a long rounded corner. It's a lot harder to stay in the seat on the sharp corner vs the longer corner. It may sound a bit over the edge complicated but rather than bigger rotors there should be multiple rotors for more capacity.
 

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Another example of centrifical force would be a marry go round, the closer you are to the center the easier it is to hang on for a given speed.
 

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Exactly farminflyboy meaning the further away from the center at any ginen rpm the more force is pulling you off of the marry go round or out of the rotor. Combine 7 Theory is flawed because on a larger rotor the further away you go from the center the faster the speed is. So the bigger corner is being made at a much faster speed at the same rmp. If you stand close to the middle of the marry go round it would have to spin much faster to create the same force pulling you off at a slower speed. imo
 

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Was wondering- What has more centrifical force- The larger roter at a given RPM or two smaller roters at a higher RPM? And, what out trumps the other-centrifical force or grate area? And since it seems to be discussed lots- How does the transverse rotor compare with centifical force since they advertise natural flow?
 

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At a given bar speed (the speed of the rub bars in relation to concaves), a smaller rotor will have More RPM and more centrifugal force. Most engineers agree that there is a specific bar speed that certain crops thresh and separate at, so the difference between rotor diameters is in the rpm needed to attain the bar speed. A larger rotor at the same rpm as a smaller rotor has greater G forces. But that is why twin rotor machines have faster rotor speeds.

http://www.endmemo.com/bio/grpm.php
I have no idea what the site is for. But at 1200 rpm, a 22 inch rotor has about 900g CF, and a 30 incher has 1220. At 1400 rpm for the 22 inch and 1200 for the 30 inch they are equal. And a 17 inch (smaller crs and trs) at their max of 1700 rpm is almost at 1400.

If you could get a 30 inch rotor to spin as fast, then you could have some wild separation until the combine hopped over a cliff or the rotor came through the cab! I don't think there is any difference which way the rotor sits (although I'm sure Gleaner guys will say otherwise)!
 

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Another analogy is if you take a large radius curve at X speed the car will stay on the road. Unless it's icy.

If the car traveling the same X speed on a tight radius curve it will slide off.

Don
 

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All you are explaining with centrifugal force is how much load is being put on the bars and other components that are attached to the rotor, before they physically fly off into the sun set.
The crop that is passing through the combine is not under any centrifugal force as it is not part of the rotor, it is being pulled through the machine by the rotor at a speed determined by the angle of the vanes and actual rotor speed.

The performance of the rotor can also be determined by the moment of Inertia being produced.
For example, consider two rotors, A and B, made of the same material and of equal mass. rotor A is larger in diameter than B. It requires more effort to accelerate rotor A (change its angular velocity) because its mass is distributed farther from its axis of rotation: mass that is farther out from that axis must, for a given angular velocity, move more quickly than mass closer in. So in this case, rotor A has a larger moment of inertia than rotor B but rotor B will do the same job as rotor A but at a slower speed.
 
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