A theoretical investigation of concave bars for corn ears threshing

Abstract

The values of forces obtained from calculations have been as follows: N1=89.10 N and N12=22.51 N (by given rectangular concave bars), N1=56.08 N and N12=5.50 N (by given rounded concave bars), N1=320.76 N and N12=116.70 N (by given oblique concave bars). The most important constructive parameters by corn ears threshing are design, height, number of concave crossbars and their position in respect of threshing cylinder. There is a lack of research evaluating an impact of concave crossbars design on corn grains detaching from cob, grains damage and separation through the concave. A major hypothesis of the study is that a concave crossbars form has an impact on corn ear threshing efficiency. It is known that the corn ear threshing process depends on effectiveness of first interaction between the cylinder rasp bar and corn ear in threshing apparatus. The theoretical study has been based on investigations of three different forms of concave crossbars: rectangular, rounded and oblique. The force of ear gravity (G); the reaction force (N1) of concave bar on corn ear; the reaction force (N22) of ear cob reaction on grain which is in contact with concave bar; the reaction force (N12) of subsequent grain on grain which is in contact with concave bar; the reaction forces (N2 and N3) of longitudinal rod reaction on ear (based on touch of ear with two grains on longitudinal rod of concave) have been evaluated. Acting frictional forces have been expressed as products of reaction forces and coefficients of friction. Five equilibrium equations with five unknown have been composed. Acting reaction, frictional and gravity forces have been designed to x and y coordinates axes for this reason. Furthermore, moments of acting forces around the chosen points have been fixed. Using the Maple software, numerical values of unknown forces have been found. It has been determined that numerical values of the reaction forces N1 and N12 were the biggest at oblique design of concave bars. Accordingly, it seems possible that then threshing process at the first corn ear contact with the rasp bar will be more effective.