The physical characteristics of particles (seeds and fertilisers) can strongly influence their movements both in seeding and spreading machines and in the air. It is therefore essential to study these particles when constructing such machines. In this respect the size, shape, coefficient of friction and aerodynamic resistance of particles are o...f great importance.
Due to their irregular shape, determining the size of particles is a troublesome process. A precise description of particles has to include several sizes and can be obtained from their screen size. Many physical properties of particles are relevant during movement in the air, but the aerodynamic resistance coefficient is the most important (Hofstee et al., 1990). Two types of wheat and four types of fertiliser particles were investigated (supported by the National Scientific Foundation OTKA, T-026482). An elutriator was designed and constructed (Csizmazia et al., 2000), in which an airflow is supplied by a centrifugal fan. Air velocity was measured with a thermal sensor. Particle sizes, mass and terminal air velocity were measured. The influence of the aerodynamic resistance coefficient on the particles’ motion is also discussed.
The knowledge of the physical characteristics of fertiliser particles is essential for the constructors and operators of fertiliser distributors. Among physical characteristics, the most important are the frictional and aerodynamic properties for the description of particle movement. Adjustable angled slopes, shearing boxes and various rotating... disks are used to identify frictional properties. We have developed a high precision shearing box with digital force measuring cells and a distance signaller (incremental transducer) that we use for slide tests efficiently. We measured the frictional characteristics of 6 different fertilisers: the inner coefficient of friction and the coefficient of friction on ten test surfaces most commonly used in machinery, and we specified the relationship between displacement, loading and the coefficient of friction. We can conclude that the material of the frictional surface significantly influences the force of friction.
However, our experience tells us that the shearing box is not suitable for the measurement of the inner friction, since the examined particles slide on the metal surface of the shearing box in a growing extent in the course of displacement, so it does not measure the real inner friction. Therefore, in our experiment we have developed rotating shearing equipment with a constant shearing surface to identify the inner friction. We tested the equipment with fertilisers and we identified the inner frictional characteristics of 6 different fertilisers. With the developed rotating shearing apparatus we could measure the real inner friction of the particles.
To identify the aerodynamic characteristics of granules, wind tunnels and free-fall tests are used. An elutriator have been developed for our investigation. We have used fertilisers for testing the measuring equipment and we have identified the aerodynamic characteristics of 6 different fertilisers.