On free flowing granular products it is common to use gravimetric pre-weighers for speed improvement fitted with pneumatically operated feed gates that allow for fast and slow feeding of the products. Two types of filling machines are used: equipment where the product is weighed before discharge into the container or bag, and so-called gross weighers where the product is weighed as it is being fed into the bag or container.
When it comes to powders, it is customary to use screw feeders and vibratory feeders and, in some cases, belt feeders for the feeding of the product from the feed bin to the weighing mechanism.
The throughput requirements of the specific installation will determine the design of the filling line. This is normally specified in units/min or in volume (mass) per hour.
Further consideration must also be given to the environment in which the filling machine will operate - is it a hazardous location or a safe area?
Gravimetric vs Volumetric Filling
The advantage of a load cell based or gravimetric filling system over various volumetric filling systems is that the system can compensate automatically for product density changes and maintain high levels of accuracy on a continuous basis without any manual system adjustments.