Extraction and dosing of powder from silos and `big-bag` systems

For a long time, industry has used various systems allowing extraction and dosing of powders.

Vibration systems were traditionally used until the invention of the arch-breaker spindle in the 1980`s. This was soon coupled with a system for dosing the powder, allowing high quality and accuracy of metering.

Arch-Building in a silo

Inside a silo, product flow is generally carried out from the center. This type of flow is described as ideal. Powder is however naturally a clogging agent and when disturbed by the intrusion of moisture, the flow becomes more difficult. Arches are formed typically in a silo due to the geometric layout of the vessel. It is in the cone section of the silo, beneath the vertical-sided tank section, that the arch then will be created. The reduction in diameter and the slope towards the flange can cause blockages and as a result discharge of powder can be affected. The diameter of the vertical-sided tank can reach 4 meters whereas the flanged outlet of the cone-section under the silo typically does not exceed a standard 300 mm diameter, and is usually no more than 200 mm diameter. Therefore due to the reduction in diameter arch-building of powders is not unexpected if not inevitable. There are also various angles for silo cones, the most typical being 60°. Manufacturers use other angles, but 60 ° is the most rational because it reduced pressure on the outlet flange whilst allowing a good flow through the cone.

Generally, the arch is formed very close to the outlet of the silo, just on the top of the flange. As professionals say, beyond one meter of the silo flange, the arch breaks because of the weight of powder.

It is then at this place that the arch is formed: between the outlet flange of the silo and the first meter above this flange.

Principle of the extraction thanks to the arch breaker spindle

The users of vibrating systems know that the vibration can generate important compressing in the silo’s cones; that it can disturb the flow and multiply arch building characteristics This is why, it was necessary to invent another way of extraction. An arch-breaking extractor! The idea is simple: why not insert an arch-breaking spindle inside the cone of the silo? If we insert in the cone an element in perpetual rotation, the arch will never have time to form. The arch breaker spindle is composed of flexible blades, which are fixed by hubs onto a spindle (see picture). The size of the spindle is 1000mm long, therefore designed to suit the arch-building length typically seen.