Many powdered materials have properties and characteristics that make them difficult-to-handle and convey. A question we are often asked is, which conveyor type is best suited for handling these hard to move materials? While no one conveyor type can successfully move all difficult-to-handle powders, aeromechanical conveyors are a proven equipment solution for transferring many of these materials. In this blog we look at how handling difficult powders with aeromechanical conveyors is made possible by the unique design and operating principle of this type of conveyor.
About difficult-to-handle powders
Powders are dry bulk solids consisting of very fine particles that may or may not flow freely. Powders that are free-flowing maintain their movement and velocity once set in motion. Difficult-to-handle powders, in contrast, tend to be poor-flowing and are thus much more challenging to convey and move. In bulk powder processing applications, maintaining a free-flowing behavior is important for reducing downtime and preserving product quality and homogeneity.
The ability of a powder to flow freely is a function of many factors, including:
- Material bulk density
- Material form
- Particle size and shape
- Moisture/humidity levels
- Particle cohesive strength
- Electrostatic charge
- Equipment used for handling, transportation and storage
As a general rule, as a powder’s particles become progressively smaller, the powder becomes more cohesive, making it more difficult to handle. In addition, because fine powders tend to be more compactable and therefore possess a higher wall friction, they are often more difficult to feed into, move through, and discharge from, conveyors. Although there are numerous powders that have poor flow properties, some well-known examples of difficult powders include: titanium dioxide: tin oxide; carbon black; calcium carbonate; and cement powder.
Handling difficult powders with aeromechanical conveyors: conveyor design and operating principle
An aeromechanical conveyor’s design and operating principle allow the conveyor to overcome many of the challenges associated with conveying difficult powders. Sometimes known as “rope and disk” conveyors, aeromechanical units consist of a fully enclosed tube in which a series of disks attached to a continuous wire rope travels at high speed, creating a high-velocity airstream. This airstream draws material into and through the conveyor, allowing the conveyor to closely mimic pneumatic conveyors with this mode of operation.
Because the high-speed airstream fluidizes the material as it moves through the conveyor, an aeromechanical unit avoids many of the problems associated with conveying difficult powders. The powder “rides” through the aeromechanical’s conveying tube quickly, making little contact with the tube wall and discharging completely during operation. This greatly reduces the likelihood of the powder caking, packing, or smearing, and prevents deposits or buildup of material inside the conveying tube and housings.
Handling difficult powders with aeromechanical conveyors: the need for controlled feeding
To ensure proper operation, controlled feeding of an aeromechanical conveyor is required – material must be fed into the conveyor at a regulated rate. When conveying difficult powders, it is important to ensure controlled feeding by avoiding widely fluctuating material flows that may arise from the poor flow properties of the material. For example, when conveying powders that tend to cake or pack, it will be necessary to feed the aeromechanical conveyor from an infeed hopper of steep-wall design that encourages material flow along the hopper walls and prevents bridging and ratholing of the material. Vibratory flow-aid devices can also be installed on the infeed hopper to promote a regulated flow of material into the conveyor.
In summary, aeromechanical conveyors offer a proven and economical equipment solution for conveying difficult powders. Experienced equipment vendors will be able to provide buyers with details on how well their aeromechanical conveyors will handle a particular powder in a given application. Where there is uncertainty about the suitability of an aeromechanical conveyor for handling a particular powder, a material test should be undertaken to determine how effectively the conveyor can handle the material.
If you are considering handling difficult powders with aeromechanical conveyors in your facility, UniTrak can help. Our Powderflight aeromechanical units are proven in use in facilities the world over and we have over 50 years’ experience in helping our customers solve their bulk solid materials conveying challenges. To find how Powderflight aeromechanicals from UniTrak can service your difficult powder applications, please contact our sales team directly.