A number of features are available to improve the flow of powders with poor flowability and to ensure fragile powders are not damaged.
(1) Double-paddle feeder:
The double-paddle rotary feeder is, at present, the most used feeder type, because the time the die travels under the feeder is longer than with other feeder types. This enables faster tablet output speeds. The first paddle of the feeder is located above the overfill cam, while the second paddle is situated above the dosing cam recycling the powder back to the first paddle.
Advantages of the GEA double-paddle feeder:
- Independent drive for each paddle, with individual speed setting
- Light weight
- No sprockets or belts for transmission between paddles
- Easy to remove, open and clean
- Exchangeable paddle shapes for different powder characteristics
- Available with slide-in wear plate, allowing the feeder to make contact with the turret surface. This minimizes the quantity of powder outside the feeder, increasing yield.
(2) Single-paddle powder feeder:
Improves filling compared to a gravity feeder, with a minimum of energy input.
(3) Vibra-fluid feeder:
A vibratory device improves the flow of difficult powders.
(4) Gravity feeder:
For fragile powders, the gravity feeder can be the best option.
(5) Small-dosage feeder:
To avoid feeder jamming, a very precise measurement of the powder level in the feeder triggers the powder in-feed.
(6) Powder dosing valve or PDV:
Presses are often fed from IBCs or silos. As these run empty, the powder pressure in the press feeder and hence the die varies, resulting in tablet weight variations. The tablet weight control system on the press or the operator can adjust the die fill, but the PDV is a much easier way to keep the feeder pressure constant. A sensor detects the powder level in a transparent tube and controls the motor of the powder scraper. When the scraper does not rotate the powder flow stops. In addition to keeping the powder pressure constant, the PDV prevents powder segregation. Another advantage is that the PDV can be used with abrasive powders.
(7) Powder agitator:
The agitator is designed especially for powders with a tendency for bridging. A central rod with side bars rotates gently in the powder, breaking bridges.