Maintain Mix Integrity with Flexible Screw Conveyors

by James Podevyn

A flexible screw conveyor (FSC) is ideal to preserve the homogeneity of a mixture even where particle size or density vary widely between the components. This is essential when transferring from a mixer to further process or packaging machinery.

How It Works

A flexible screw conveyor works by having a rotating helical screw inside an ultra-low friction polymer tube running at speeds normally in the 500-960 rpm range. The flight of a traditional rigid screw sweeps the whole area of its conveying tube. With an FSC it only impacts a modest percentage of the whole tube cross-section. An FSC conveyor works by using the internal friction within a powder or bulk solid to transfer the forward motion of the powder in contact with the spiral to the whole tube contents.  With an angled system, a dynamic equilibrium is set up with the spiral action moving some particles upwards. Gravity can cause other particles to fall back down the center of the tube and this is why the spiral needs to be run at a fast speed.

The Benefits

The completion between conveying and fall back means that a flexible screw conveyor constantly mixes the product while it is conveyed.  If you want to convey a formulation which tends to segregate then an FSC is an excellent choice. The re-mixing ensures that your mixture exits the conveyor as well, if not better, mixed than at the conveyor inlet.  Many over-the-counter health products are mixtures of very fine active components mixed with a coarse grade of sugar. To ensure every sachet is the same, many packing lines use FSCs as the final conveying technology so every packet contains the same formulation.

Be aware, however, that not just any FSC supplier could achieve this effect.  Careful design of the discharge chute and integration into the next stage of the process is essential to minimize any material separation due to free fall or rolling/sifting segregation as the material forms a heap in the receiver.

It is also possible to take two pure components and, by correctly configuring two flexible screw conveyors, produce a continuous mixer to prepare and convey a blend with a total equipment length only a little longer than the two feed hoppers for the raw materials.

Finally, the dynamic flow balance also means that the output rate of a flexible screw conveyor does not exhibit the pulsing effect of a rigid screw making them ideal as metering systems, either volumetric or gravimetric, with accuracies of +/- 0.05% readily achieved.

Get in Touch

Spiroflow has been a global leader in the field of powder handling and dry bulk solids processing for more than 45 years. To learn more visit spiroflow.com, email sales@spiroflow.com or call +44 (0) 1200 422525 in the UK or (1) 704 246 0900 in the US.