A: Andy Forrester, Spiroflow
When selecting a mechanical conveyor for cohesive materials, there are many factors to consider, but one of the most critical is the amount of shear force that will be imparted on the conveyed material. Mechanical conveyors that push or pull the material through a housing, such as a screw or drag conveyor, generate high shear forces between the material and conveyor surfaces, which can cause excessive smearing or material buildup. These forces may also cause significant undesirable material degradation. Belt-type conveyors can be a good solution to minimize shear forces, but they may not offer other features required in many applications, such as a totally enclosed conveying environment or ease of conveyor cleaning.
An aeromechanical conveyor minimizes shear forces, encloses the material, and allows for easy conveyor cleaning. At first glance, this conveyor type can be mistaken for a tubular drag conveyor, as it consists of a cable and discs that are pulled through a tube; however, this conveying method is very different.
In an aeromechanical conveyor, the discs move through the tube at speeds around 1,000 fpm, which creates pockets of air between each pair of discs. A low-pressure area is generated behind each leading disc and the material is drawn along in the slipstream that’s created, with the particles being suspended in the air pocket and having minimal contact with the conveyor surfaces. The resulting shear forces imparted on the material are extremely low, minimizing material buildup and degradation. This conveyor style also offers a totally enclosed, dust-free environment and is energy efficient, with high transfer rates possible at very low power consumption.
To view more tips on this topic and read the entire article that appears in the July issue of Powder and Bulk Engineering magazine click here.
Spiroflow, Monroe, NC, supplies standard and custom powder handling equipment.