When it comes to powder conveying applications, the decision about which type of conveyor to employ sometimes involves a choice between a flexible screw or aeromechanical conveyor. While either type of conveyor can work well for many types of powders, there are some essential differences that may make one equipment type preferred over the other for a given application. In this blog, we highlight some of these differences and offer guidance that should be considered to make the right equipment choice.
Powder handling: flexible screw conveyors
Flexible screw conveyors use a rotating wire auger to “pull” material through the conveyor. While these conveyors work well with many types of powders, there are some factors inherent in their design and operation that should not be overlooked by buyers when considering these equipment types for powder applications. These include the following:
- Type of operation. While flexible screw conveyors can be run continuously, they are best suited for batch or intermittent operation. When running intermittent operations with heavy materials, care should be taken not to start the conveyor under a full load as this may impose severe stresses on the equipment.
- Auger design. Many manufacturers offer various auger designs that are purposed for handling specific types of powders. For example, flat wire augers work best for fine powders while beveled augers are suited for moving powders, such as titanium dioxide, that tend to build up on surfaces. Round wire augers help to move granular materials such as sugar and salt.
- Tube design. Flexible screw conveyor tubes/casings are generally made of UHMWPE plastic. When using these conveyors to move abrasive powders, accelerated wear of the tube can result, necessitating replacement. Nylon and stainless steel casings are also available.
- Flow aids. In some applications, flow aids such as vibrators in the conveyor’s infeed hopper may be required to ensure the successful transfer of powder into the conveyor.
- Equipment mobility. Many manufacturers offer their equipment with optional mobile bases. This feature is especially useful in operations where the conveyor must be moved and relocated within a facility.
Powder handling: aeromechanical conveyors
An aeromechanical conveyor’s design and operating principle allow the conveyor to overcome many of the challenges associated with conveying difficult-to-handle 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, a powdered material “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 conveyor’s tube and housings.
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.
Which is best for powder handling: a flexible screw or aeromechanical conveyor?
The answer to the question of whether a flexible screw or aeromechanical conveyor is best for handling powder is, it depends. Because there are a large number of variables that determine how an equipment type will interact with and affect the material being moved, UniTrak usually recommends that a material test be done to determine how a material will behave once placed into a conveyor. Material testing can help narrow the choice as to whether a flexible screw or aeromechanical conveyor is preferred for a given application.
UniTrak manufactures the UniFlex and Powderflight lines of flexible screw and aeromechanical conveyors respectively. Our application experts will be pleased to review your needs and recommend the optimal equipment solution. For further information on how UniTrak can help with your powder handling needs, please contact our sales team directly.