Precision dosing of powders by vibratory and screw feeders: an experimental study

Abstract

The addition of small amounts of very precisely dosed powdery ingredients into bulk powders and/or liquid mixtures is important in such industrial operations as mixing, granulation and crystallization. The general practice is to use a screw, vibration or belt feeder combined with a loss by weight device and an appropriate controller. The present work concentrates on two vibratory feeders, one with and the other without vibration control, and a screw feeder which were used to feed a wide variety of powders. The main goal of the present work was to quantify the goodness of feeding, i. e. constant rate of powder flow as a function of time, using different powders with vastly different characteristics. It was found that both vibration feeders are generally well suited for precision feeding operations, yielding a more or less linear relationship between flow rate and vibration amplitude, especially for the larger sized materials. The feeder with vibration control proved to be somewhat more reliable, ensuring a much wider range of feed rate with a smaller variation in time. Both feeders exhibited somewhat larger variation in feed rate when used with the fine, more cohesive materials such as zeolite and cement powders. From the work with the screw feeder it was found that the presence of the vibrator on the hopper had a significant role in improving both the overall flow as well as the precision of feeding.