AJAX Multiple Screw Feeders
Double, triple and multiple screw feeders may be used to achieve high flow rates with minimal headroom but are more generally used to provide a large inlet area for difficult to handle materials. Feeder inlets must be of a diameter or width that exceeds the critical dimension above which stable arches can be sustained. The critical arching dimension can be determined experimentally with bench scale tests, however, the results of such tests may indicate that a single screw is impractical in terms of headroom requirements or speed of rotation.
To illustrate this consider the situation where powder tests indicate that the inlet diameter required for gravity flow into a screw feeder is three times the diameter of a screw appropriately sized for the throughput. Increasing a screw diameter by a factor of 3 might give the required inlet size but, for a given flow rate, would slow the screw speed down by a factor of 27 whereas adding two parallel screws of the original diameter would achieve the same inlet dimensions but only slow the screw down by a factor of 3 and would not increase the headroom required. .
Multiple screws can also be phased to mitigate the natural pulsing of the screws during feeding. This yields a further benefit of multiple screws over one large screw.
Twin and triple screw feeders are the most common variants of the multi screw feeder, however, four or more screws acting in parallel can be used for materials that resist gravity flow from hoppers and require large outlets to avoid structural arches forming and to accommodate very steep or even divergent wall angles for mass flow (first in, first out) to occur.
Please follow the links below for more information and case studies relating to multi screw feeders.
Twin Screw Feeder for TATA Chemicals
Bradley Pulverizer Hopper and Twin Screw Feeder
Sextuple Screw Feeder for Carbon Fibre
Grain Pellet Handling System for North British Distillery
Quadruple Screw Feeder for Enviropower
Please call AJAX on 44 (0)1204 386723 if you have a screw feeder application or want to know more about our screw feeders.