Vacuum System
Function and Mode of Operation
Auger feed in the roller compactor is critical for mechanical compaction of powder materials.
Highly bulky or fluidizing materials are inadequately fed to the roller feed area through horizontal auger feed.
Alexanderwerk Vacuum Feed is used in such cases.
Feed without vacuum support:
To compact powder products means to vent them.
As the air cannot escape through the roller nip it flows in the direction opposite to the auger feed along the inner housing wall, thus reducing the friction between the worm and housing wall. However, this means that the conveying effect of the auger is reduced, and that not enough product is being fed to the roller nip.
Feeding with vacuum support:
The principle of vacuum feed is based upon the fact that a tubular auger conveyor will function properly only if the friction between the product and the housing inner wall is large and if, at the same time, the friction between the worm and the product is low.
When connecting filter segments to a suction pressure (vacuum), a product layer will build up on the filter segment the thickness of which is determined by the auger outer diameter. Now, this creates an obstacle to the air returning from the roller nip so that this air is forced to flow back along the auger core, which in turn has the positive effect of reducing the friction between the product and the auger resulting in good product handling characteristics.
Important:
The filter segments are not provided to initially vent the powder through the pores. Rather, the vacuum increases the friction between the product and the housing inner wall as powder particles are retained at that point, thus also forming a filter layer which is continuously removed by the rotating auger.
This enhances the conveying and pressure build-up behaviour of the auger for fluidising products resulting in effective powder precompaction being achieved immediately upstream of the roller feed area.
