A relationship between friction plate roughness and the external friction angle of wheat kernels.

The frictional properties of seeds have been extensively studied, but most researchers have identified only the type of tested friction materials (e.g. concrete, steel, wood) without describing their manufacturing characteristics. The aim of this study was to determine the correlations between the external friction angle of wheat kernels vs. the roughness of the friction plate and the basic physical properties of kernels. The experiment was performed on the kernels of winter wheat var. <italic>Jensen</italic> obtained directly from spikes and threshed kernels. The external friction angle of every kernel was measured on six friction plates characterized by different surface geometry. Measurements were performed in five replications with a photosensor device which registered the external friction angle of kernels. The basic dimensions and the mass of every kernel were measured, and the results were used to calculate four shape factors for the analyzed kernels. The correlations between the evaluated attributes were determined by one-way analysis of variance (ANOVA) and linear correlation analysis. The roughness of the friction plate significantly influenced the external friction angle of wheat kernels. The average values of the angle of external friction ranged from around 16° to around 24°. The lowest value of the angle of external friction was noted for surface roughness of <italic>Ra </italic>= 0.93 μm, and the highest value - for surface roughness of <italic>Ra </italic>= 5.86 μm. Higher values of the angle of external friction were observed in kernels obtained directly from spikes than in threshed kernels. [ABSTRACT FROM AUTHOR]