Screw conveyors, also known as auger conveyors, are available in two main configurations: shafted screw conveyors and shaftless screw conveyors. The main difference is whether the spiral flight is supported by a central shaft or shaft pipe. Both types move material along a trough or tube through the rotation of a screw element, but they differ in mechanical structure, material compatibility, drive requirements, and maintenance.
A shafted screw conveyor uses a center shaft or pipe to support the flight and transmit drive torque. It is commonly used for powders, granules, and other materials with relatively good flowability. A shaftless screw conveyor eliminates the central shaft along the conveying section. Instead, it uses a continuous or sectional shaftless spiral flight to move material. This design is better suited to sticky, fibrous, high-moisture, and poorly flowing materials.
Each design has its own application range. A shaftless screw conveyor is not necessarily better than a shafted model in every situation. Selection should take into account material properties, conveying distance, installation angle, and operating conditions.
Structural Differences Between Shafted and Shaftless Screw Conveyors
Shaftless Screw Conveyor Structure
A shaftless screw conveyor generally consists of a drive unit, shaftless spiral flight, conveying trough or tube, wear liner, end supports, and sealing components.
Unlike a conventional screw conveyor, the shaftless design has no central shaft running through the conveying section. The drive unit transmits torque to the spiral flight through a drive-end connection, causing it to rotate inside the trough and move material along the conveying path.
Without a central shaft, more of the internal conveying space is available for material movement. This also reduces the risk of long fibers or strip-shaped materials wrapping around a central shaft.
The shaftless spiral flight is generally manufactured from high-strength steel and must transmit the drive torque while carrying the mechanical loads generated during conveying. During operation, the flight is supported through its contact or interaction with a wear liner inside the trough. The liner material, clearance, and wear resistance therefore affect the operating condition of the conveyor.
Shafted Screw Conveyor Structure
A shafted screw conveyor generally consists of a drive unit, center shaft or pipe, screw flights, conveying trough or tube, bearings, hanger bearings, and sealing components.
The screw flights are mounted on the center shaft or pipe. The electric motor drives the shaft through a gearbox, and the shaft transmits torque to the flights. As the flights rotate, they push material along the conveying direction.
For shorter screw conveyors, the screw shaft is generally supported by bearings at both ends. Longer conveyors may require intermediate hanger bearings to reduce shaft deflection and maintain operating stability, depending on the design and loading conditions.
The center shaft or pipe both transmits torque and supports the screw flights. This arrangement provides a relatively stable mechanical support structure and is suitable for many conventional bulk material conveying applications.
Material Compatibility
Material properties are among the main factors to consider when choosing between a shafted and shaftless screw conveyor. Moisture content, adhesion, particle size, flowability, and fiber length can all affect conveying performance.
Materials Suitable for Shaftless Screw Conveyors
A shaftless screw conveyor has no central shaft along the conveying section. This reduces the areas where material can accumulate or fibers can become entangled. It is therefore suitable for materials that are difficult to handle with conventional shafted screw conveyors.
Common applications include:
High-moisture materials: Such as dewatered sludge, wet sludge, and certain semi-fluid materials.
Sticky materials: Such as wet waste, adhesive residues, and some chemical raw materials.
Fibrous materials: Such as long fibers, municipal solid waste, screenings, and certain textile waste.
Materials with poor flowability or a tendency to bridge: Such as some wet processing residues and mixtures containing fibers.
With these materials, a central shaft can become a surface where material adheres or fibers wrap around the rotating components. Removing the shaft provides more open conveying space and reduces the risk of blockages caused by material buildup around the shaft.
However, a shaftless design does not eliminate blockages. Materials that are highly adhesive, prone to solidification, or contain large foreign objects may still require special attention to trough design, screw speed, feeding arrangements, and cleaning access.
Materials Suitable for Shafted Screw Conveyors
Shafted screw conveyors are generally used for dry powders, granules, and other bulk materials with relatively good flowability.
Common materials include:
Granular materials: Such as grain, plastic pellets, and feed pellets.
Powdered materials: Such as cement, flour, mineral powders, and some chemical powders.
Small lump materials: Such as sand, gravel, and other small bulk solids within the equipment's specified particle size range.
Dry mixtures: Such as certain building material ingredients and industrial processing powders.
The center shaft supports the screw flights and provides a defined torque transmission path. This makes shafted screw conveyors suitable for a wide range of conventional conveying applications.
However, materials with high moisture content, strong adhesion, or long fibers may accumulate around the center shaft, screw flights, and intermediate hanger bearings. This increases the risk of material buildup and entanglement.
A shafted screw conveyor is not limited to dry granular materials. Special flight designs, including ribbon flights, cut flights, and other modified configurations, can also handle certain sticky or adhesive materials. Suitability must be assessed according to the material properties and conveyor design.
Conveying Directions and Installation Angles
Both shafted and shaftless screw conveyors can be designed for horizontal, inclined, or vertical conveying. However, changing the installation angle affects material movement, conveying efficiency, and drive load.
Horizontal Conveying
Horizontal conveying is one of the most common applications for both shafted and shaftless screw conveyors.
A shafted screw conveyor uses a center shaft to support the flights as they rotate, making it suitable for continuously conveying free-flowing powders and granular materials.
A shaftless screw conveyor is more suitable for sludge, wet waste, fibrous materials, and other materials that tend to wrap around a central shaft. The absence of the shaft reduces the risk of buildup around this component.
Inclined Conveying
Both shafted and shaftless screw conveyors can be installed at an incline. However, as the inclination increases, gravity causes more material to move backward, which can reduce conveying efficiency.
For shafted screw conveyors, conveying performance can be adjusted through flight pitch, trough design, conveyor diameter, and rotational speed.
Inclined shaftless screw conveyors also require careful consideration of spiral strength, support arrangements, liner design, and material flow characteristics.
There is no universal maximum inclination of 20 degrees for all shaftless screw conveyors. The allowable angle and conveying capacity depend on the specific equipment design and material properties.
Vertical Conveying
Vertical conveying generally requires a specially designed vertical screw conveyor. The screw, casing, and feeding arrangement must work together to overcome the weight of the material and move it continuously upward.
Shafted screw conveyors can be used for vertical lifting, but shaft support, transmission stability, and material movement inside the conveyor must be considered.
Some manufacturers also offer shaftless vertical screw conveyor designs for specific materials such as dewatered sludge. Vertical conveying is therefore not exclusive to shafted screw conveyors. However, these systems normally require a design developed for the material and required lifting height. A conventional horizontal model should not simply be installed vertically without checking its suitability.
Advantages and Limitations of Shafted and Shaftless Screw Conveyors
Advantages and Limitations of Shaftless Screw Conveyors
Main advantages:
Reduced risk of entanglement: The absence of a central shaft along the conveying section makes the design suitable for long fibers, strips, and other materials that tend to wrap around rotating components.
More open conveying space: No central shaft occupies the internal conveying area, making it easier to handle certain sticky, wet, and bulky materials.
Fewer intermediate support components: Shaftless designs generally do not require the traditional intermediate hanger bearings used in long shafted conveyors. This reduces potential material buildup around these support points.
Suitable for difficult materials: They are widely used in applications involving sludge, municipal solid waste, and certain industrial residues.
Main limitations:
High torque requirements: Without a central shaft to carry and share the mechanical load, the shaftless spiral itself must transmit the torque along the conveying section. Its material, cross-section, and drive configuration must therefore be designed carefully.
Wear at the liner: The spiral flight remains in contact with the wear liner during operation. Both components can wear, so their condition needs to be inspected regularly.
Conveying length limitations: As the conveyor length increases, the shaftless spiral must transmit greater torque. The maximum conveying length must be checked against spiral strength and drive capacity.
More demanding design requirements: Spiral diameter, flight construction, rotational speed, and liner material should be selected according to the material and operating conditions.
Advantages and Limitations of Shafted Screw Conveyors
Main advantages:
Good mechanical support: The center shaft supports the screw flights and provides a suitable structure for many conventional bulk material applications.
Established design: Shafted screw conveyors use mature transmission and support arrangements, making standard designs and manufacturing processes widely available.
Wide range of applications: Different flight designs can be selected for powders, granules, and certain sticky materials.
Flexible conveying arrangements: With suitable engineering, shafted screw conveyors can be used for horizontal, inclined, and specialized vertical conveying.
Main limitations:
Risk of material entanglement: Long fibers, strips, and similar materials may wrap around the center shaft, affecting conveying efficiency.
Material buildup around intermediate supports: Long conveyors fitted with hanger bearings may experience accumulation of material around these support points.
Reduced internal conveying space: The center shaft occupies part of the conveying area, leaving less space around the shaft for material movement.
Additional maintenance points: The center shaft, screw flights, bearings, and intermediate hanger bearings require inspection and maintenance.
How to Choose Between Shafted and Shaftless Screw Conveyors
The choice should not be based on equipment structure alone. Material properties, conveying distance, installation angle, and maintenance conditions all need to be considered.
When to choose a shaftless screw conveyor
A shaftless design is worth considering when the material has high moisture content, strong adhesion, or contains long fibers, strips, or other components that tend to wrap around a shaft.
Examples include dewatered sludge from wastewater treatment plants, screenings, and municipal solid waste. These materials often require a conveying arrangement that reduces the risk of entanglement and buildup around the central shaft.
When to choose a shafted screw conveyor
A shafted design is generally suitable for free-flowing powders and granules such as grain, plastic pellets, cement, and mineral powders. It is also an established option for longer conveying sections where intermediate support is required and can be incorporated into the design.
Other Selection Parameters
Material properties: Check moisture content, adhesion, particle size, bulk density, fiber length, and abrasiveness.
Conveying capacity: Determine the required throughput and use the feeding arrangement and material fill ratio to select the screw diameter, pitch, and rotational speed.
Conveying distance: Evaluate the torque capacity of the spiral, shaft support arrangement, and required drive power.
Installation angle: Confirm whether the application requires horizontal, inclined, or vertical conveying. Evaluate how the angle affects conveying efficiency and drive load.
Wear and corrosion requirements: Select the spiral material, trough material, and liner according to the material characteristics.
Maintenance access: Consider how the flights, liners, bearings, and seals can be inspected and replaced.
For materials with strong adhesion, variable composition, or a tendency to cause entanglement, conduct material testing before finalizing the conveyor design. The test should assess conveying continuity, blockage risks, and component wear.
Custom Machining for Screw Conveyor Components
Both shafted and shaftless screw conveyors contain various mechanical structures and non-standard metal components.
Common machined parts for shafted designs include screw shafts, shaft-end connectors, bearing housings, drive mounting bases, flanges, and support structures. Shaftless designs may require components such as spiral flight end connections, drive connection flanges, trough connectors, liner mounting structures, and support brackets.
The dimensional accuracy, concentricity, hole positions, thread quality, and assembly fits of these components affect drive connections, screw operation, and long-term equipment stability.
Hansheng Automation provides CNC precision machining of non-standard metal components according to customer-supplied engineering drawings. These services support structural and transmission parts used in shafted and shaftless screw conveyors, as well as other industrial conveying equipment.
In addition to conveying equipment components, we also undertake custom machining of precision yacht parts, RC racing car parts, tobacco packaging machinery components, and filling machinery parts.
