Although a rotary combine uses a rotor instead of a cylinder and even if the concaves do look a bit different, the concaves on conventional and rotary combines both have to perform the same two functions–threshing and separating.
To allow for threshing and separation in different crops you can use wide wire or narrow wire concaves or any combination. Round bar concaves are also available.
HARVEST Concaves are precision bored so they fit better and are easier to properly adjust. The wire holes are drilled with state of the art, computer controlled, multiple head drills. This ensures the precision alignment of holes, and a snug wire fit. With a HARVEST precision built Concave there’s no wire-to-hole gap to trap straw.
Rotary combines are achieving very high capacity figures. Along with higher capacities, rotary combines tend to have higher wear factors. To help control maintenance costs HARVEST wire concaves are manufactured using 1045 steel and have more steel bar over the wire. They are more aggressive and last longer. Side frames, hooks and wire diameters are also heavier so they last longer and keep their shape.
HARVEST manufactures a round bar concave for popcorn, high moisture corn and specialty crops. Rather than wires the concave has 1018 ¾” steel bars. Since the round bar is less aggressive than the square bar of the wire concave, the kernel is treated gentler.
Most people believe it is the impact of the cylinder bars on grain that does the threshing. The truth is that it is material rubbing on material that does the threshing. You know this if you have ever run a combine as slow as it would go or by cleaning up a corner when straight cutting. You will have cracks, unthreshed heads and whitecaps all at the same time. Then, when you increase the travel speed, all the problems disappear. The only thing that changed was the amount of material coming into the combine.
The rotor simply drives the heads through of the concave before they are threshed. This leads to unthreshed heads. They will overload the return, end up in the tank as dirty sample or become loss out the back of the combine.
You simply have to have something at the front of the concave to hold the heads in place long enough for the rub bars to thresh the seeds out of the head.