There is a trend, perhaps it’s only local to our area, for farmers to set the sieves on their combines too wide. This can create problems, especially when harvesting high-moisture corn early in the season.
Several years ago Dan Renaud with Case told me,"It’s very common for guys to use the lower sieve to try and correct problems elsewhere in the machine. That lower sieve really shouldn’t be doing anything except a final separation, putting very little material back into the return elevator. If you do a kill-stall and see a lot of material on the lower sieve or in the return elevator, you need to reset your concave or rotor or fan speed so that the lower sieve isn’t doing so much work.”
The trend among combine operators seems to be to run the upper sieve nearly wide open to ensure no grain escapes, then tighten the lower sieve to clean up what goes to the grain tank. This overloads and overworks the lower sieve, causes more grain damage because of the amount of grain being re-threshed via the return elevator, and ultimately decreases the performance of the combine.
The best way to optimize combine performance is to start with the settings recommended by the manufacturer for a specific crop, then make small adjustments. Keep specific goals in mind:
-minimize the amount of trash taken into the combine at the cornhead by adjusting ground speed and deck plate width.
-adjust concave clearance to produce half- or whole-length cobs. Any split cobs suggest concave settings are too tight.
-increase rotor speed until grain damage is evident, then back it down till damage is acceptable.
-set upper sieves only slightly wider than lower sieves. If an upper sieve is open twice as wide as the lower sieve, it would be good to re-think things.
-run cleaning fans nearly wide open unless harvesting chaffy, drought-damaged or flood-damaged corn. Upper and lower sieves work best when there’s enough air blasting through them to “float” crop material across them, allowing grain to filter down through the residue.f
Don’t be afraid to experiment with various settings, but you’ll often be surprised to find that the optimum settings are somewhere in the ranges suggested by the combine manufacturer in the owner’s manual.
