The Effect of Hammermill Screen Hole Diameter and Hammer Tip Speed on Particle Size and Flow Ability of Ground Corn

The most common method of altering particle size with hammermills involves exchanging the size of screens for smaller or larger hole diameters. Screen changes, however, lead to increased down time and loss of production within a facility. Alternatively, a variable frequency drive can be installed on the motor of the hammermill to adjust motor speed and ultimately hammer tip speed. This enables particle size adjustments to be made externally without requiring screens to be changed, therefore reducing idle time. The objective of this study was to determine the effect of screen hole diameter and tip speed on geometric mean diameter (d_gw), geometric standard deviation (S_gw), and angle of repose (AoR) of ground corn. Treatments were arranged as a 3×3 factorial in a completely randomized design using three screen hole diameters and three hammer tip speeds. Each treatment replicate (n=3) was manufactured as a separate grinding queue with individual queue samples as the experimental unit. Whole corn was ground using three common screen hole diameters (2, 4, and 6 mm.) at varying hammer tip speeds (3124, 4686, and 6248 m/min). Results indicated a marginally significant linear interaction (P<0.077, SEM=52.3) between screen hole diameter and tip speed for d_gw, and S_gw. For d_gw, when tip speed increased from 3124 to 6248 m/min the rate of decrease in d_gw was greater as screen hole diameter increased from 2 to 6 mm. Therefore, when tip speed was increased from 3124 to 6248 m/min, d_gw was reduced by 233, 258, and 305 μm for corn ground using the 2, 4, and 6 mm. screen hole diameter, respectively. For S_gw, when tip speed increased from 3124 to 6248 m/min the rate of decrease in S_gw was smaller as screen hole diameter increased (P=0.067, SEM=0.055). Therefore, when tip speed increased from 3124 to 6248 m/min, S_gw was reduced by 0.31, 0.24, and 0.13 for corn ground using the 2, 4, and 6 mm. screen hole diameter, respectively. There was no observed interaction between screen hole diameter and tip speed on AoR. Increasing hammer tip speed increased (linear, P<0.001, SEM=0.80) AoR. Increasing screen hole diameter decreased (linear, P<0.001, SEM=0.80) AoR. In summary, the particle size range for a specified hammermill screen size can be adjusted through manipulation of the hammer tip speed, which is made possible using motor variable frequency drives. This enables operators to quickly change the particle size output, while reducing idle time in the mill.