Feedrate deviations caused by hopper refill of loss-in-weight feeders

Continuous powder processing requires accurate and consistent feed streams of the raw materials which makes loss-in-weight feeders invaluable. Periodic hopper refill of the feeders, which is needed for continuous operation, can lead to inconsistent and poor feeding performance. This paper presents both a method for measuring the feeding performance during hopper refill as well as several methods for quantifying the resultant deviations from feedrate setpoint caused by refill. The main results show that hopper fill level is the most significant factor that can be used in mitigating the deviations effects during refill. The use of discharge screens also showed a small improvement in feeding accuracy. Another potentially useful method of reducing deviations during refill is to use refilling systems that have a lower more controlled rate of refill that gently replenishes the feed hopper rather than the high rate refill of some refilling systems.