Feeding powders can present manufacturers with a range of problems when designing their process.
This is one area where "one size" generally does not fit all!
As explained in our video, powders come with a huge variety flow characteristics and are influenced not just by their own inherent material properties but also by the environment they are being used in, as well as the methods by which they are handled.
Screw Feeders for Powders
The most common type of feeder for powders is the screw feeder. Single or twin screw, volumetric or gravimetric; these choices will depend on your process requirements.
Typically powders that are granular, free or relatively free flowing and simple to handle will work well on a single screw feeder.
If the material is poor flowing or flushes through a single screw then a twin screw device will be better suited.
Additional problems can be caused by a low melting point material. In this case the barrel of the screw feeder may need to be cooled.
Hopper Agitation for Powder Feeders
As your powder feeder empties, a rathole or bridge can form above the rotating screw or screws.
Ratholes are small "tunnels" that reduce the flow whereas a bridge is where the powder creates a void that spans the whole hopper and totally interrupts the powder flow.
This is where your hopper requires agitation which typically takes two forms. Outside paddles and a flexible hopper wall just above the screw trough can prevent a bridge or rathole forming by creating movement in the powder.
Alternatively a fully rotating blade style agitator can sit inside the hopper and rotate together with the screws, constantly stirring the material and again preventing bridging or ratholing.
Refilling your Powder Feeder
Refill systems for powder feeders also require careful consideration. Dropping powders from height can cause flushing or compaction in the hopper below for example.
When refilling a gravimetric feeder, uncontrolled refilling can cause issues with the weighing cycle of the feeder below. A full hopper for example is more likely to have a greater full factor for the screws below than an almost empty hopper. the gravimetric feeder needs to be able to cope with these bulk density changes.
Fortunately, we also offer a wide range of refill devices and can help you in their selection to ensure the whole powder handling system is correctly sized and designed.
Testing your Powder Feeder
We have a fully functional test lab where we can run materials tests on your product so you can witness exactly how the feeder works with your material.
With commonly used powders, we will most likely have tested a similar sample before so can advise you directly on the most effective configuration.
We can of course video trials and provide accuracy data to assist you in your design selection.