A shaftless screw conveyor is a mechanical conveying system that moves material along a trough through the rotation of a screw flight. Unlike a conventional shafted screw conveyor, it has no central shaft running through the conveying section. Instead, a shaftless spiral flight serves as the main conveying and torque-transmitting component.
Without a central shaft, the conveyor provides a relatively open conveying space and reduces the risk of long fibers wrapping around the shaft. It is commonly used for sludge, screenings, municipal solid waste, wet industrial residues, and other sticky or fibrous materials.
A shaftless screw conveyor generally consists of a drive unit, U-shaped trough, shaftless spiral flight, wear strips, cover plates, feed and discharge openings, and support structures. During operation, the drive unit rotates the spiral flight, which pushes material along the trough toward the discharge end.
Main Components of a Shaftless Screw Conveyor
Drive Assembly
The drive assembly supplies the power required to operate the shaftless screw conveyor. It generally consists of an electric motor, gearbox, drive shaft, and connecting flange.
The motor provides rotational power, while the gearbox reduces the output speed and increases torque according to the equipment requirements. Power is transmitted through the drive shaft and connecting structure to rotate the shaftless spiral flight inside the trough.
Because there is no central shaft running through the conveying section, the spiral flight itself must transmit the drive torque along the conveyor. The motor power, output torque, and mechanical strength of the spiral flight must therefore be properly matched.
The drive assembly is usually installed at one end of the conveyor. Whether the system uses a pushing or pulling arrangement depends on the material properties, conveying direction, and equipment design.
U-Shaped Trough and Support Structure
The U-shaped trough forms the main body of the shaftless screw conveyor. It houses the spiral flight and conveyed material while providing the installation space and support required by the moving components.
The trough is commonly manufactured from formed steel plate or other suitable materials. Carbon steel and stainless steel are typical options, with the final selection depending on the material properties and operating environment.
The support structure secures the trough and carries the loads generated by the equipment and conveyed material. Depending on the conveyor length and installation arrangement, it may include support legs, mounting frames, connecting flanges, and other structural components.
Adjacent trough sections must be properly connected and aligned. Significant misalignment or deformation can affect the clearance around the spiral flight and interfere with its movement.
Shaftless Spiral Flight
The shaftless spiral flight is the main conveying component. It is generally manufactured from high-strength steel and has a continuous helical form.
Unlike a shafted screw conveyor, the shaftless design has no central shaft running through the conveying section. The drive torque is transmitted mainly through the spiral flight itself. As the flight rotates, its outer edge runs against or in contact with the wear strips inside the trough, pushing material toward the discharge end.
The outer diameter, pitch, flight thickness, and material of the spiral flight must be selected according to the required throughput, material bulk density, moisture content, abrasiveness, and conveying distance.
For sticky materials, materials containing long fibers, or highly abrasive materials, the strength of the spiral flight, its wear resistance, and the required drive torque need particular attention.
Wear Strips
Wear strips are installed along the bottom of the U-shaped trough or at other positions where the spiral flight requires support. They are important wear components in a shaftless screw conveyor.
Since the shaftless design has no central shaft to support the flight, the spiral is generally supported by the wear strips inside the trough. The strips support the flight during operation and protect the inner surface of the trough from direct wear.
Common wear strip materials include UHMW-PE and other wear-resistant engineering plastics. The appropriate material depends on the abrasiveness of the conveyed material, operating temperature, and contact conditions.
Wear strips require periodic inspection. If they become excessively thin, damaged, detached, or unevenly worn, they should be replaced. This helps prevent direct contact between the spiral flight and the metal trough.
Cover Plates and Sealing Components
Cover plates are generally installed over the U-shaped trough to form a partially enclosed conveying space.
Their main functions include:
Protection: Reduce the risk of personnel or foreign objects coming into contact with the rotating spiral flight.
Dust containment: Limit the release of powdered material during conveying.
Material containment: Reduce material spillage from the top of the trough.
Maintenance access: Some designs use removable covers to allow inspection and cleaning of the internal components.
Sealing components are also required at the drive end, end connections, and trough joints to reduce material leakage, dust release, and the entry of external contaminants.
The cover plate mainly provides protection and containment. Wear between the spiral flight and trough is controlled primarily by the wear strips. These components serve different purposes.
Feed and Discharge Openings
The feed opening allows material to enter the conveying trough. Its position and dimensions are determined by the upstream equipment layout and material discharge direction.
The discharge opening releases material after it has been conveyed along the trough. Depending on the downstream equipment and process layout, it can be located at the end of the trough or at another designated position.
Different applications require different opening sizes, quantities, and mounting arrangements. For example, in wastewater treatment systems, the feed and discharge connections may be designed to match the layout of screens, dewatering equipment, and downstream collection systems.
For systems with multiple feed or discharge points, material distribution, local accumulation, and the flow rate at each discharge point also need to be considered.
Fasteners and Connecting Components
Fasteners connect the trough sections, cover plates, support structures, drive assembly, and other mechanical components.
Common items include bolts, nuts, connecting flanges, support plates, and mounting brackets.
These components must have suitable strength and dimensional accuracy. During long-term operation, inspect the connecting bolts for looseness, check flanges for deformation, and look for abnormal movement in the support structure.
Working Principle of a Shaftless Screw Conveyor
A shaftless screw conveyor moves material by rotating a shaftless spiral flight, which pushes material through the conveying trough in the axial direction.
The Drive Assembly Rotates the Spiral Flight
When the conveyor starts, the electric motor drives the gearbox, which provides the required output speed and torque. Power is then transmitted through the drive shaft and connecting flange to rotate the shaftless spiral flight.
Since the spiral has no central shaft running through the conveying section, the drive connection is generally located at one end of the equipment. During operation, the spiral flight is supported by the wear strips and moves along the inside of the trough.
Material Enters the Conveying Trough
Material enters the U-shaped trough through the feed opening and comes into contact with the rotating spiral flight.
As the flight rotates continuously, it applies a pushing force to the material, moving it along the trough. The actual material movement is also affected by gravity, particle-to-particle friction, friction against the trough, and material flowability.
For sticky materials, sludge, and fibrous materials, the shaftless arrangement reduces the risk of entanglement and buildup around a central shaft or intermediate hanger bearings.
Material Moves Along the Conveying Direction
The shaftless spiral continues to rotate and push material through the U-shaped trough or tubular conveying passage.
Conveying capacity depends on factors such as spiral diameter, pitch, rotational speed, conveying length, and material properties. Increasing the rotational speed does not always improve performance. Excessive speed may increase wear, material disturbance, and drive load.
During equipment design, the spiral dimensions and operating parameters must be selected according to the required throughput and material condition.
Material Discharges Through the Outlet
When the material reaches the discharge point, it leaves the conveyor through the discharge opening and enters downstream conveying equipment, a storage hopper, or another processing unit.
Throughout the process, the drive assembly, shaftless spiral flight, wear strips, and trough work together to move the material. Depending on the material properties and production line layout, the equipment can be designed for horizontal, inclined, or specialized vertical conveying.
Main Features of Shaftless Screw Conveyors
Reduced Risk of Fiber Entanglement
A shaftless screw conveyor has no central shaft running through the conveying section. This reduces the risk of long fibers, strips, and similar materials wrapping around a central shaft.
It is therefore suitable for materials such as municipal solid waste, screenings, sludge, and certain types of textile waste that tend to cause entanglement.
However, the shaftless design does not eliminate blockages. Highly adhesive materials, materials that harden easily, or feed containing large foreign objects can still cause problems. The spiral design and feeding arrangement must be suitable for the material.
More Open Conveying Space
Removing the central shaft increases the space available inside the trough for material movement. It also eliminates the space occupied by the central shaft and intermediate hanger bearings.
This arrangement is useful for handling wet materials, fibrous materials, and certain bulky mixed wastes. It also reduces the possibility of material accumulating around intermediate support points.
Suitable for Sticky and High-Moisture Materials
Shaftless screw conveyors can handle dewatered sludge, wet industrial residues, screenings, and certain viscous materials.
Without a central shaft, material is less likely to form a continuous buildup around the shaft surface. This can provide an advantage in applications where conventional shafted screw conveyors experience unstable operation.
Actual suitability still depends on material viscosity, moisture content, bulk density, spiral design, and available drive torque. These factors should be checked for the specific application.
Maintenance Focused on Fewer Support Components
The shaftless design eliminates the central shaft running through the conveying section and the conventional intermediate hanger bearings used in many shafted conveyors. This reduces the number of internal support components requiring maintenance.
Routine inspection mainly covers the drive assembly, shaftless spiral flight, wear strips, end supports, and sealing components.
However, the spiral flight itself carries significant torque and remains in contact with the wear strips during operation. Its wear condition, drive connection, and supporting liner therefore require regular inspection.
Enclosed Conveying Structure
A shaftless screw conveyor generally uses a U-shaped trough and removable cover plates to form a partially enclosed conveying space. This helps reduce dust release and material spillage.
Sealed connections can also be designed for applications involving wastewater treatment, chemical waste, and certain types of industrial solid waste.
Overall sealing performance depends on the end seals, inspection covers, feed and discharge connections, and trough joints. The presence of a cover plate alone does not guarantee complete sealing.
Limitations of Shaftless Screw Conveyors
Although shaftless screw conveyors are suitable for many sticky and fibrous materials, their structural design also has limitations.
Higher torque requirements for the spiral flight: Without a central shaft to share the transmission load, the shaftless spiral must transmit torque through its own structure. Its strength and the drive capacity must be checked carefully as conveying length and material resistance increase.
Wear strip replacement: The spiral flight remains in contact with the wear strips during operation. Both components can wear over time. For abrasive materials such as sand and mineral residues, the wear strip material and replacement requirements need particular attention.
Conveying length limitations: As the conveying distance increases, the spiral must transmit more torque. Increasing the trough length alone is not sufficient. Spiral strength, pitch, rotational speed, and drive power must all be considered.
Conveying capacity depends on material properties: Materials with poor flowability, strong adhesion, or a tendency to agglomerate may accumulate inside the trough. Feed continuity and material buildup must be considered to prevent blockages and drive overload.
Selection Considerations for Shaftless Screw Conveyors
The structure and main parameters of a shaftless screw conveyor should be selected according to the material properties and actual conveying requirements.
Material properties: Check moisture content, adhesion, particle size, bulk density, fiber length, and abrasiveness.
Spiral specifications: Select the spiral diameter, pitch, flight thickness, and material according to the required throughput and material condition.
Drive configuration: Determine the motor, gearbox, and output torque according to conveying length, material resistance, and operating conditions.
Conveying route: Confirm whether horizontal, inclined, or vertical conveying is required. Calculate the actual conveying capacity according to the installation angle.
Wear strip material: Select a suitable wear-resistant material according to the contact conditions, material abrasiveness, and operating temperature.
Maintenance access: Provide sufficient space for inspection covers, spiral replacement, wear strip removal, and drive-end maintenance.
For sludge, municipal solid waste, and other materials with variable composition, conduct sample testing before finalizing the equipment specifications. The tests should evaluate conveying continuity, blockage risks, and actual component wear.
Custom Machining for Shaftless Screw Conveyor Components
Although a shaftless screw conveyor has no central shaft running through the conveying section, it still contains various precision mechanical and non-standard metal components. These may include drive shafts, spiral connection flanges, U-shaped trough connectors, wear strip mounting structures, bearing housings, drive mounting bases, and equipment support frames.
The dimensional accuracy, hole positions, connection strength, and assembly fits of these components affect the drive connection, trough installation, and long-term operating 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 shaftless screw conveyors and 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.
