Influence of tube configuration on seed delivery to a coulter

An investigation has been carried out in order to find how the kinetic energy of seeds sliding and falling down a seed tube was influenced by tube diameter, inclination of the tube and radius of coulter bend in a simulation of a tube and coulter system. The kinetic coefficient of friction found by elevating the tube until the seed velocity was constant was only valid for tube inclinations up to 25 degrees. At higher tube inclinations, the coefficient of kinetic friction had to be replaced with a new apparent coefficient of friction with a higher value. Ideally, the delivery tube leading to the bend should be inclined at 60 degrees to the horizontal plane. Delivery tubes at inclinations of 90 degrees and 45 degrees were tested in the laboratory. The results showed that the seeds lose a considerable kinetic energy when running through a 90 degrees bend. Seeds dropped in a vertical tube or into a bend of small radius, lost almost all their kinetic energy when colliding with the horizontal or low inclination part of the bend. To lower the impact of collisions in the bend, the ratio of the bend radius to the tube diameter should be as large as possible. Tube diameter had no influence on the energy loss when the delivery tube was inclined to 45 degrees. Inclined tubes into the bend were favourable, because collision energy was minimized. The results of this investigation were used in designing a new seed tube and coulter assembly for direct drilling. (C) 1999 Silsoe Research Institute.