Combine harvesters are well known farm machines that have been used for many years. An integral part of the device is the threshing concave or concave guide, that separates and guides the crop as it is carried by the cylinder. The grain is rubbed and beaten thereon by the cylinder to separate the grain from the straw stalks. The grain then passes from the concave into a cleaning mechanism in which the chaff is separated and discarded.
The normal course of the incoming straw, as a result of the action of the auger and straw conveyor, is to move the straw to the centre of the concave and overload the centre of the concave as well as the centre of the feeder house, the sieve and straw walker. The overloading of the centre causes the rasp bars of the threshing cylinder to wear out more quickly near the centre. The disproportion of load also causes a plugging of the sieve and walker components as well thus reducing the capacity of the combine.
Some attention has been given in the prior art to modifications to the design of the concave for various purposes. For example:
U.S. Pat. No. 1,643,683 describes a concave with grooves thereon, rather than ribs, arranged to converge as the straw is moved rearwardly so that the straw is turned as it moves over the concave.
U.S. Pat. No. 923,324 describes a device with a number of fingers that extend outwardly from the rear of the concave, after the grain emerges from the concave. It is stated that this is to move the material outwardly so that it is more evenly spread over the grate and straw rack.