Selecting a screw conveyor requires consideration of several factors, including material properties, conveying capacity, conveying distance, installation angle, screw configuration, and drive system. Different materials have different particle sizes, bulk densities, flow characteristics, and abrasiveness. These differences affect the required screw diameter, flight design, rotational speed, and motor power.
When the conveyor is part of a production line with vibrating screens, hoppers, feeders, or other equipment, its specifications should also match the overall processing capacity and operating sequence of the system. Incorrect selection may result in insufficient conveying capacity, material blockage, motor overload, or premature component wear.
Determine the Required Conveying Capacity
Conveying capacity refers to the amount of material a screw conveyor can handle per unit of time. It is generally expressed as mass flow rate or volumetric flow rate, such as tonnes per hour (t/h) or cubic metres per hour (m³/h).
The first step in equipment selection is to determine the actual throughput required by the production process. The conveyor should not be selected based solely on the motor power or screw diameter of an existing machine.
For a screw conveyor connected to a vibrating screen, such as a rotary vibrating screen, linear vibrating screen, or ultrasonic vibrating screen, the conveyor capacity should be based on the actual feed and discharge rates of the screening equipment. The processing capacities of upstream feeding equipment and downstream receiving equipment must also be considered to prevent excessive or insufficient material flow at any stage.
The following factors should be considered when determining conveying capacity:
Rated conveying capacity: Determine the amount of material that must be conveyed per hour during normal operation.
Peak conveying capacity: If the upstream equipment uses intermittent feeding or discharges large amounts of material over short periods, consider the maximum instantaneous feed rate to prevent blockage during peak loading.
Material bulk density: Mass flow rate and volumetric flow rate are related through bulk density. For materials with significant variations in bulk density, provide data that reflects the actual conveying conditions.
Operating time and duty cycle: Confirm whether the conveyor will operate continuously or intermittently, along with its daily operating hours and startup frequency.
Screw conveyors are primarily designed for bulk materials. They should not normally be selected based on the number of packaged items handled per hour. For bags, cartons, and other unit loads, belt conveyors, roller conveyors, or other unit-load handling equipment are generally more appropriate.
Determine the Conveying Distance and Installation Angle
The conveying distance and installation angle directly affect conveying efficiency, operating resistance, and drive power requirements. The conveyor route should therefore be defined before equipment selection.
Horizontal Conveying
Horizontal screw conveyors are used to move materials along a horizontal path. Common applications include conveying powders and granules between production processes. The screw diameter, rotational speed, and support arrangement should be selected according to the conveying distance, required capacity, and material properties.
For longer screw conveyors, shaft deflection, sectional connections, and intermediate hanger bearing positions must also be considered. These factors help prevent excessive shaft deformation caused by its own weight and the material load.
Inclined Conveying
When a screw conveyor is installed at an angle, gravity tends to move the material backward along the conveyor. This can reduce the actual conveying capacity. As the inclination increases, the screw speed, pitch, and flight configuration may need to be adjusted, and the required drive power must be recalculated.
For inclined applications, a smaller pitch, tubular housing, or other configurations suitable for inclined conveying may be considered, depending on the material properties. The appropriate arrangement must be determined through equipment design and material evaluation. The rated capacity of a horizontal screw conveyor should not be applied directly to an inclined installation.
Vertical Conveying
When material must be lifted vertically, a screw conveyor specifically designed for vertical conveying should be selected. A conventional horizontal screw conveyor should not simply be installed at a steep angle and treated as a vertical conveyor.
Vertical conveying requires the screw to overcome gravity. Material filling, backflow, and discharge conditions also differ significantly from those in horizontal conveying. As a result, vertical screw conveyors have different requirements for flight configuration, rotational speed, and drive capacity.
In addition to the conveying distance and inclination, provide the required lifting height, feed and discharge positions, and available installation space. This information is needed to determine the overall equipment dimensions and mounting arrangement.
Select the Screw Diameter, Pitch, and Configuration
The dimensions of the screw assembly directly affect conveying capacity and operating load. Common design parameters include screw diameter, center shaft or center pipe diameter, pitch, flight thickness, and trough dimensions.
Screw Diameter
The screw diameter should be selected according to the material particle size, required conveying capacity, and available installation space. A larger screw diameter generally provides more space for material conveying, but it also affects the overall equipment dimensions, shaft loading, and required drive torque.
When conveying materials containing large particles or lumps, check whether the maximum lump size is compatible with the clearances between the screw flight, center pipe, and trough.
Screw Pitch and Flight Configuration
The pitch affects the theoretical amount of material moved during each revolution and influences material movement inside the conveyor. Standard-pitch flights are suitable for many conventional conveying applications. Smaller-pitch, variable-pitch, or other special configurations may be used for inclined conveying, controlled feeding, or materials with specific flow characteristics.
Screw flights are available in different configurations, including standard flights, ribbon flights, and specially designed flights with mixing functions. Select the appropriate design according to material adhesiveness, flowability, conveying requirements, and whether mixing is also required.
Shafted and Shaftless Designs
A shafted screw conveyor uses a central shaft to support the screw flights. It is widely used for powders, granules, and many other bulk materials.
A shaftless screw conveyor has no central shaft or pipe running through the conveying section. It can be suitable for some sticky, fibrous, or entangling materials. Its selection must also account for torque capacity, wear liner requirements, and conveying distance.
Trough Configuration
Depending on the conveying distance, sealing requirements, and installation conditions, a U-shaped trough or tubular housing can be selected. For applications requiring dust control, moisture protection, or reduced material leakage, particular attention should be paid to cover plates, flange connections, and shaft-end seals.
Select the Appropriate Screw Speed and Drive Power
The screw speed and drive power must be determined according to conveying capacity, screw dimensions, material properties, and the conveyor route. Conveying capacity is not determined by the motor alone.
Screw Speed
Screw speed affects the amount of material conveyed per unit of time. Under otherwise unchanged conditions, increasing the speed can increase the theoretical conveying capacity. However, actual performance also depends on material flowability, filling ratio, abrasiveness, and conveying angle.
For materials that cause significant wear, have poor flowability, or generate large amounts of dust, excessive speed may increase flight wear, material degradation, and dust generation. The screw speed should therefore be selected according to the material properties rather than simply maximizing conveying speed.
Motor and Gearbox Selection
The motor supplies power, while the gearbox reduces the speed and provides the required output torque. The selection process should include a calculation of the operating power and a check of the torque capacity of the gearbox, coupling, screw shaft, and other drive components.
The following factors require particular attention:
Power required during normal conveying.
Starting resistance and starting torque, including the resistance from material inside the conveyor.
Whether the material is prone to compaction or remains inside the trough after shutdown.
The effects of conveying angle, distance, and operating load on the drive system.
Gearbox output torque and the rated load capacity of the transmission components.
For production lines that require adjustable conveying rates, a variable-frequency motor or a standard motor controlled by a variable frequency drive (VFD) may be used. Speed control must remain within the operating limits of the equipment. It cannot replace proper calculations of screw dimensions and drive power.
Select Materials and Configurations According to Material Properties
Different materials place different requirements on the screw flights, center shaft, trough, and sealing components. Before selecting the equipment, provide information about the material name, particle size, bulk density, moisture content, adhesiveness, abrasiveness, corrosiveness, and operating temperature.
Abrasive Materials
When conveying highly abrasive materials such as sand, mineral powder, and slag, select flight materials with suitable wear resistance. Depending on the wear locations, thicker flights, replaceable wear liners, or surface hardfacing may be required.
Corrosive Materials
For corrosive materials, select the product-contact materials according to the chemical composition, concentration, temperature, and moisture conditions. Stainless steel grades such as 304 or 316L may be considered for suitable applications, along with other corrosion-resistant materials. However, stainless steel suitability cannot be determined by grade alone without considering the actual chemical environment.
High-Temperature Materials
When conveying hot powders, slag, or calcined materials, consider high-temperature material strength, thermal expansion, bearing insulation, and lubrication conditions. For applications with a high thermal load, water-cooled shafts, cooling jackets around the trough, or other dedicated cooling arrangements may be required.
Sticky and Entangling Materials
For sludge, wet cohesive powders, fibers, and elongated materials, particular attention should be paid to shafted or shaftless construction, flight configuration, trough liners, and cleaning arrangements. These factors help reduce material buildup, entanglement, and blockage during operation.
Consider the Feeding Method, Discharge Position, and Connected Equipment
Screw conveyors are often integrated with hoppers, bins, feeders, vibrating screens, and other production equipment. The connection arrangement between upstream and downstream equipment affects the feeding conditions and actual conveying capacity.
Before selecting the conveyor, confirm the following:
Feeding method: Determine whether material enters continuously, intermittently, or directly from a hopper.
Feed rate control: If a stable metered feed rate is required, consider a dedicated screw feeder rather than using a conventional conveying screw as a metering device.
Discharge position: Specify the number and orientation of discharge outlets and their connection dimensions to downstream equipment.
Feed and discharge elevations: Confirm the required interface heights and compatibility with the site layout and connected equipment.
Interconnected control: If the conveyor operates with a screening machine, crusher, or another conveyor, define the startup and shutdown sequence, capacity matching, and fault interlock requirements.
It is also important to distinguish between a screw conveyor and a screw feeder. A screw conveyor is primarily used to transport material, while a screw feeder also controls the discharge rate from a hopper or bin. Screw feeders generally require specific designs for the inlet section, filling conditions, and starting torque.
Consider Installation Conditions and Future Maintenance
Site conditions also affect screw conveyor selection. For production lines with limited space, confirm the overall conveyor length, width, height, maintenance clearance, and drive assembly position in advance.
Other factors to consider include:
Bearings and support arrangement: Determine the end bearings and intermediate hanger bearing configuration according to screw shaft length and loading.
Maintenance access: Check whether covers, inspection openings, and bearing locations allow convenient cleaning and component replacement.
Sealing requirements: For dusty, damp, or enclosed conveying applications, select suitable shaft-end seals and trough sealing arrangements.
Maintenance intervals: Establish inspection schedules for flights, liners, bearings, and seals according to material abrasiveness, operating hours, and equipment load.
Safety protection: Depending on the site environment and material hazards, consider protective guards, electrical protection, grounding, and appropriate dust hazard controls.
Before placing an order, provide the equipment layout drawing, conveying route, material data, and interface information for connected equipment. This helps avoid changes to the installation arrangement after the conveyor has been manufactured.
What Information Is Required for Screw Conveyor Selection?
To help the equipment supplier determine the correct screw conveyor specifications, provide the following information during selection or quotation.
| Parameter category | Information required |
|---|---|
| Material information | Material name, composition, particle size, maximum lump size, and bulk density |
| Material condition | Moisture content, adhesiveness, abrasiveness, corrosiveness, and operating temperature |
| Conveying capacity | Normal and maximum throughput, expressed as mass or volumetric flow rate |
| Conveying route | Horizontal or inclined conveying, conveying length, lifting height, and inclination angle |
| Screw configuration | Shafted or shaftless design, screw diameter, pitch, and flight type |
| Feed and discharge conditions | Feeding method, inlet dimensions, number and position of discharge outlets |
| Drive requirements | Motor power, gearbox configuration, and speed control requirements |
| Installation conditions | Available space, installation height, foundation, and maintenance clearance |
| Special requirements | Dust control, corrosion resistance, wear resistance, high-temperature operation, food contact, or explosion protection |
Conclusion
Screw conveyor selection should not be based only on conveying distance or required hourly throughput. Material properties, screw configuration, conveying angle, operating speed, drive torque, and site installation conditions must all be considered.
For ordinary powders and granules, the basic specifications can be determined from the required throughput and bulk density. For sticky, abrasive, corrosive, or high-temperature materials, the flight configuration, shaft construction, contact materials, and protective features may require further adjustments.
Providing complete material data and site layout information before purchasing helps suppliers calculate conveying capacity, drive power, and transmission component specifications more accurately. This reduces the risk of blockage, overload, and premature wear after the equipment enters service.
Hansheng Automation provides CNC precision machining of non-standard metal components according to customer-supplied engineering drawings. Our machining work covers components for yacht equipment, RC racing cars, tobacco and packaging machinery, and filling machinery.
