15
Screw Flights
Screw flights are the working elements inside screw conveyors that move bulk material through the trough or casing. They can be supplied for new equipment or used to replace worn flighting without replacing the complete conveyor.
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Technical overview
A screw flight is the rotating conveying element of a screw conveyor. As it turns, the flight pushes or carries material along the conveyor while the trough, casing and drive assembly remain stationary.
In many installations, the flight is also the component that experiences the greatest wear. Its edges may gradually become thinner, its profile may deteriorate and conveying capacity can fall over time. Where the remaining conveyor structure is still serviceable, replacing the flighting can restore the conveying element without requiring replacement of the complete conveyor.
Screw flights are available in different diameters, thicknesses, pitches, materials and configurations. Selection depends on the material being conveyed, the conveyor geometry, operating conditions and whether the application requires a shafted or shaftless design.
Screw Flight Types and Dimensions
Three dimensions define the basic geometry of a screw flight: outside diameter (ØD), flight thickness and pitch (P). For shafted designs, the inside diameter (Ød) must also correspond to the shaft or tube on which the flight is mounted.
Pitch determines how far the flight advances during one complete revolution. Fixed-pitch configurations are common, while variable-pitch arrangements can be used where the material flow or feeding requirement changes along the length of the conveyor.
Right-hand and left-hand flights are not interchangeable. The hand of the flight determines the direction in which material travels when the screw rotates. For replacement work, the existing flight direction must therefore be confirmed before manufacturing or selection.
| Type | Outside Diameter | Flight Thickness | Pitch | Typical Material |
|---|---|---|---|---|
| Standard Screw Flight | 50–900 mm | 3–20 mm | Up to 1/2 of ØD | Carbon steel, AISI 304, AISI 316 |
| Heavy-Duty Screw Flight | 100–500 mm | 3–10 mm | Up to 1/2 of ØD | 300 HB wear-resistant steel |
| Small-Diameter Screw Flight | 40–100 mm | 3–8 mm | Fixed or variable | Carbon steel, AISI 304, AISI 316 |
| Shaftless Screw Flight | 150–600 mm | 15–40 mm | Fixed or variable | AISI 304 or Fe 510 |
| Sectional Screw Flight | 30–900 mm | Up to 25 mm | Application dependent | Carbon steel, AISI 304, AISI 316, Hardox® 400 |
| Continuous Flighting | According to requirement | According to requirement | Fixed or variable | Carbon steel, AISI 304, AISI 316 |
| Polymer Screw Flight | Standard sizes | Application dependent | Standard pitches | Wear-resistant polymer |
For shafted flights, the inside diameter is selected to suit the shaft or tube. Small-diameter flights may use inside diameters in the 20–60 mm range, while shaftless configurations may extend through substantially larger centre dimensions depending on the design.
Special geometries may include tapered flights, variable pitch, double-pitch arrangements and other non-standard profiles required by the application.
Selecting the Right Material
Material selection should be based on the actual operating environment rather than simply choosing the material with the highest nominal strength or cost.
Carbon steel is suitable for many dry, non-corrosive and relatively low-abrasion materials. Stainless steels are generally selected where moisture, corrosion, hygiene or chemical exposure are more important. AISI 316 provides greater resistance in applications involving chlorides or more aggressive chemical conditions.
High corrosion resistance does not automatically mean high abrasion resistance. A stainless-steel flight can wear rapidly when handling highly abrasive materials such as sand, clinker or sharp mineral particles. In these conditions, wear-resistant steels such as 300 HB grades or Hardox® 400 may be more appropriate.
Shaftless conveyors also place different structural demands on the flight because the spiral itself must transmit torque without the support of a centre shaft.
| Material | Suitable Conditions | Typical Applications |
|---|---|---|
| Carbon Steel | Dry, non-corrosive and relatively low-abrasion service | Grain, flour, bran and similar dry bulk materials |
| AISI 304 Stainless Steel | Moist environments, corrosion risk and hygienic processes | Wastewater, sludge and food-processing applications |
| AISI 316 Stainless Steel | Chlorides and more aggressive chemical exposure | Chemical processes, textile wastewater and applications exposed to saline conditions |
| 300 HB Wear-Resistant Steel | Continuous abrasive duty | Sand, slag, minerals and clinker |
| Hardox® 400 | Severe abrasive duty involving hard or sharp particles | Mining, aggregates and recycling |
| Fe 510 | High-strength shaftless configurations | Dewatered sludge and screening waste |
| Wear-Resistant Polymer | Applications where lightweight operation or reduced metal contact is required | Selected food dosing and powder-additive applications |
Replacing Worn Screw Flights
A worn screw conveyor does not always require replacement of the complete machine. If the trough, drive, shaft, bearings and supporting structure remain in serviceable condition, the conveying flight may be renewed separately.
The correct approach depends on how and where the flight has worn. Uniform wear along the full length generally points to complete flight replacement. Localised wear at an inlet, discharge point or other heavily loaded section may instead allow only the affected flight section to be replaced.
Material changes can also alter wear behaviour. A conveyor originally designed for one bulk material may experience much faster deterioration when a more abrasive product is introduced. In that situation, changing the flight material may be more effective than simply reproducing the original component.
| Condition | Possible Approach | Reason |
|---|---|---|
| Flight edges are worn and capacity has fallen | Replace the complete flighting | Wear is distributed along the conveyor length |
| Wear is concentrated near the inlet or discharge | Replace the affected section | Only the heavily loaded area needs renewal |
| Flight is bent and rubbing against the trough | Replace or repair with alignment and balance checks | Misalignment can increase vibration and bearing loads |
| The conveyed material has changed and wear has accelerated | Review the flight material | A more wear-resistant material may be required |
| Existing conveying capacity is insufficient | Review pitch or flight geometry | Geometry influences material throughput |
Replacing Only the Worn Section
Sectional screw flights can be useful where wear is limited to a particular area. Instead of replacing the complete spiral, individual flight sections can be fitted to the damaged region where the conveyor design allows this type of repair.
Build-up welding may also be used as a temporary repair in some applications, but it should not automatically be treated as a permanent solution. Welding can change the geometry and balance of the flight and may introduce additional stresses. The material, operating speed, wear pattern and condition of the remaining flight should therefore be considered before deciding between repair and replacement.
Defining a Replacement Without a Drawing
Older conveyors do not always have an available technical drawing. A replacement can still be specified by measuring the existing flight or an available sample.
The key information is the outside diameter, inside diameter where applicable, flight thickness, pitch, total length and flight direction. Photographs of the existing screw and its installation can also help confirm the configuration and identify details that may not be obvious from dimensions alone.
Special Configurations and Surface Treatments
Depending on the operating conditions, screw flighting may require additional manufacturing or finishing operations. Typical options include:
- Wear-resistant coatings for abrasive service
- Balancing for rotating assemblies operating at higher speeds
- Tapered flighting for variable-section troughs or controlled feeding
- Electropolishing for stainless-steel surfaces used in hygienic environments
- Glass bead blasting for a uniform stainless-steel finish
- Blasting and painting for corrosion protection on carbon-steel components
- MIG or TIG welding according to the material and fabrication requirement
- Couplings and intermediate bearings for longer shafted conveyor assemblies
The suitability of any treatment or special configuration depends on the material being conveyed, operating speed, environment and conveyor construction.
Shafted or Shaftless Screw Flights?
Shafted and shaftless screw conveyors solve different conveying problems.
In a shafted design, the flighting is attached to a central pipe or shaft. The shaft supports the spiral and allows intermediate bearings to be used on longer conveyor runs.
A shaftless screw has an open centre. The spiral itself transmits the drive torque and normally runs against a replaceable liner in the trough. The absence of a centre shaft can make this arrangement better suited to materials that are sticky, fibrous or prone to wrapping around a conventional shaft.
| Material or Operating Condition | Typical Configuration | Reason |
|---|---|---|
| Fibrous or stringy materials | Shaftless | No centre shaft for material to wrap around |
| Sticky and wet sludge | Shaftless | Reduces accumulation around a central shaft |
| Dewatered sludge cake | Shaftless | Suitable for high-fill applications and difficult material |
| Dry, free-flowing powders and granules | Shafted | Well suited to conventional higher-speed conveying |
| Abrasive minerals, sand and clinker | Shafted | Allows the flight and trough arrangement to be selected specifically for abrasive duty |
| Long conveyor runs | Shafted | Intermediate bearings can be used to control shaft deflection |
What Affects Screw Flight Cost?
Screw flight cost cannot be determined from diameter alone. Two flights with the same outside diameter may require very different materials, thicknesses, manufacturing methods and finishing operations.
The main cost factors are:
- Material grade — carbon steel, stainless steel and wear-resistant grades have different material and processing costs.
- Flight thickness — thicker material increases both weight and forming requirements.
- Outside diameter and pitch — larger diameters and tighter pitches affect the amount of material and forming work required.
- Standard or special geometry — non-standard dimensions and custom profiles require additional manufacturing work.
- Surface treatment — painting, wear-resistant coatings, electropolishing and balancing add separate operations.
- Total length and quantity — production quantity affects the unit manufacturing cost.
Information Required for Selection and Quotation
The following information is normally sufficient to define a screw flight requirement:
- Outside diameter (ØD) and inside diameter (Ød), where applicable
- Flight thickness
- Pitch (P) and total length
- Right-hand or left-hand flight direction
- Conveyed material, including particle size, moisture and operating temperature
- Shafted or shaftless configuration and the relevant drive connection
Where all dimensions are not available, photographs and measurements from the existing conveyor can be used to help identify the required geometry.
Typical Applications
Screw flights are used across a wide range of bulk-material and process applications.
In flour mills, they can be used for the transfer of flour, bran and milling by-products. Feed mills use screw conveying for raw materials and finished feed products. Cement and ready-mix plants use screw systems for cement and additive handling.
In municipal and industrial wastewater treatment, screw conveyors can transport screenings, sludge and other process residues. Stainless-steel configurations are also used in food-processing and wastewater applications where corrosion resistance and hygiene are important.
Frequently Asked Questions
Can only the screw flight be replaced?
Yes. Where the remaining conveyor is in serviceable condition, the flighting can be replaced separately from the trough, drive and other components. If wear is confined to a limited area, sectional flighting may also allow only the affected portion to be renewed.
What information is needed if no technical drawing is available?
A technical drawing is not always necessary. The main dimensions are the outside diameter, inside diameter where applicable, flight thickness, pitch and total length. The flight direction must also be identified. Photographs of the existing screw can provide useful additional information.
Are sectional screw flights and continuous flighting the same?
They perform the same basic conveying function but are produced differently. Sectional flights are formed as individual sections that can be joined together or used for local repairs. Continuous flighting is formed as a continuous spiral and is suited to longer, consistent flight sections.
What diameters and thicknesses are available?
The technical ranges covered on this page extend from 30 mm to 900 mm in outside diameter, depending on the flight type. Flight thicknesses range from 3 mm up to 40 mm for the heavier shaftless configurations. The available range depends on material, diameter, flight type and geometry.
Does stainless steel always provide longer service life?
No. Stainless steel is primarily selected for corrosion resistance, hygiene or chemical exposure. It is not automatically the best material for abrasive duty. Sand, clinker, minerals and other highly abrasive products may require a dedicated wear-resistant steel instead.
What determines manufacturing lead time?
Lead time depends on the required dimensions, material grade, flight configuration, quantity and any additional finishing or fabrication processes. Special geometries and surface treatments generally require additional manufacturing operations.
Is build-up welding a permanent repair for worn flighting?
Not necessarily. Build-up welding can be useful as a temporary repair in some conditions, but it may alter the flight geometry and balance. Where wear is significant, replacing the affected section or renewing the complete flighting may provide a more controlled solution.
