Let’s say your implement dealer is trying to sell you a rotary combine, but you have always had a conventional. You are hesitant about switching to something you do not understand.
I would like to explain some of the differences in design and what you will face in setting the rotary combine.
I was in the field when the company I worked for introduced the rotary combine so a lot of this information is from experience.
The biggest difference is how the threshed grain is separated from the straw. The old conventional machine used gravity and there wasn’t much a farmer could do to increase its capacity. The designers could have added more walker area, but the farmer could not do that once he bought the machine. He could slow the flow of the material on the walkers but right away the machine’s capacity would be cut.
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The rotary combine uses centrifugal force to drive the grain through the straw. The faster the cylinder spins, the higher the centrifugal force so it’s easy to increase the capacity. The limit to how fast the separation rotor can be turned is controlled by whether the operator is cracking the grain. The separation rotor is also the threshing rotor in most designs.
Another difference is the amount of time the material spends in the threshing area. In a conventional combine, the cylinder had one chance to thresh the material.
In a rotary combine the material passes over the concave two or three times before it leaves the threshing area. Setting the concave to cylinder clearance isn’t nearly as critical.
There is a rumour that rotary combines are not as good in high moisture crops. In my experience, they are a lot noisier than a conventional in high moisture crops. This probably is because the material spends so much time in the cylinder, but that does not make it any less capable of handling the tough stuff.
Also, the way material feeds into the rotor affects the rotor’s ability to handle the high moisture material.
The conventional combine has the material coming into the side of the cylinder and manufacturers have that system pretty well figured out. It works in dry and wet conditions.
Then they tried the rotor. Because it was so long and had to run lengthwise on the machine, the crop was fed against the end of it.
Judging by the wear on the end of the rotor, there is a lot of activity in this area and it seems high moisture material takes a lot of horsepower to jam into the threshing area. It takes some effort and ingenuity to make this setup work.
Another manufacturer, quite successfully I gather, brought up the material from the bottom of the front end of the rotor so it went to the side like a conventional but also around it. Judging by the wear on the front end, this is an easy feed.
The weakness is that the material must be forced to go straight up. An aggressive beater is required to feed that cylinder evenly.
Another design has the rotor sitting sideways in the combine. This solves the feeding problem because it’s like a conventional machine, but there are limits on rotor length because a combine can only be so wide.
A different design splits the rotor in three sections. The section in the centre front sits crossways to feed like a conventional machine. The separation rotors then sit at right angles to this threshing rotor. The people who designed this style spent a lot of time and money to get the material to turn that corner. So every design has its strength and its weaknesses.
Designers are concerned about how the crop feeds into the rotor. A rotary combine is much more sensitive to feeding than the conventional. Producers who have problems such as rumbling in the rotor, losses and cracking of grain should check what’s in front of the rotor.
As for the rest of the combine, the settings are the same on both types. Just remember that for rotor losses you play with the rotor speed. And make sure the components feeding the rotor are doing their job.
So go ahead, get that rotary. You’ll like it.
