Influence of knife configuration and tip speed on conveyance in flail forage harvesting

An experimental model of the flail-type forage harvester was fabricated to study the effect of flail tip speed, knife rake angle and bevel angle on conveying of chopped forage sorghum (S. bicolor) through a 90 degrees deflector elbow under laboratory conditions. The exit air velocity from the chute outlet and static pressure head created at the blower outlet were measured. The exit velocity of the chopped forage and the corresponding throw distance were determined considering the aerodynamic properties of the chopped forage material. The knife bevel angle did not have a significant effect on the throw distance of the chopped forage material. The exit air velocity from the chute outlet increased logarithmically as the flail tip speed was increased from 20 to 60 m s(-1) and it decreased linearly as the knife rake angle was increased from 20 to 60 degrees. The static pressure head created by the rotating flails at the blower outlet (chute inlet) increased exponentially as the flail tip speed was increased, and decreased linearly when the knife rake angle was increased. The static pressure head developed by the flail knives was not sufficient to convey the chopped forage through the chute without the influence of acceleration energy imparted to the chopped material during impact cutting by the flail knives. The exit air velocity from the chute outlet was found to be about 50-60% of that observed for the chopped forage material, indicating that the acceleration energy imparted by the flails during impact cutting added energy to the air stream. The throw distance of the chopped forage from the chute outlet increased in the range of 65-95% with the increase in flail tip speed from 20 to 60 m s(-1) and it decreased in the range of 20-40% as the rake angle was increased from 20 to 600. (C) 2001 Silsoe Research Institute.