Description

Custom Screw Flight for New and Rebuilt Conveyor Shafts

Screw flight selection begins with the complete shaft geometry, not the outside diameter alone.

The outside diameter determines the running clearance inside the conveyor tube. The inside diameter must fit the shaft or shaft tube. Pitch controls how the helix continues along the shaft, while thickness and flight direction must suit the intended construction and conveying route.

A replacement with the wrong inside diameter, pitch, thickness or helix direction may fit inside the conveyor but still fail to preserve the original screw geometry.

Available supply forms include:

• Continuous screw flighting
• Individual formed flights
• Loose flights for local shaft fabrication
• Replacement flight sections
• Welded screw shaft sections
• Complete internal screw assemblies
• Left-hand and right-hand flights
• Standard and customized dimensions

Screw flights can be produced for cement, fly ash, lime powder, dry mortar, mineral powder, granular materials and other dry bulk handling applications.

Dimensions That Define the Screw Flight

Each flight order should identify the following dimensions clearly:

These dimensions must be considered together.

Increasing the OD reduces the clearance between the flight and conveyor tube. Changing the ID affects the fit around the central shaft. A pitch error repeats through every turn and may prevent a replacement section from aligning with the original helix.

Some continuous flights have a tapered radial section rather than one uniform thickness. In these models, IT identifies the thickness at the inner edge and OT identifies the thickness at the outer edge. Both values must be confirmed when matching an existing flight.

Continuous Flighting and Individual Formed Flights

Continuous Screw Flighting

Continuous flighting is formed as an extended helix and supplied as one section.

It is suitable for:

• Manufacturing new screw shafts
• Replacing several consecutive worn turns
• Rebuilding long areas of an existing shaft
• Producing repeated shaft sections
• Cutting shorter repair lengths in a fabrication workshop

Standard section lengths include:

• 1,000 mm
• 2,000 mm
• 3,000 mm
• Customized lengths

Continuous flighting is available in carbon steel, AISI 304 and AISI 316.

Individual Formed Flights

Individual flights are supplied as single turns or partial helical sections.

They are useful where:

• Wear is limited to a short area
• Only the inlet or discharge-end turns require replacement
• The flight changes near a shaft connection
• A special pitch or thickness is required at one position
• The repair workshop assembles the helix turn by turn

Individual formed flights can be produced in carbon steel, stainless steel and manganese steel for selected abrasive-duty applications.

The joint between adjacent flight sections must maintain the same pitch and helix direction and align at the correct angular position. Correct dimensions alone will not create a continuous helix when the sections are welded out of phase.

Common Continuous Screw Flight Sizes

Dimensions: mm

The table shows commonly supplied combinations rather than the full manufacturing range. OD, ID, pitch, thickness and section length can be produced according to confirmed project dimensions.

The same OD may be combined with different IDs and pitches. For example, a 190 mm flight may use a 60 mm or 76 mm centre opening, while its pitch may be 150 mm or 190 mm.

A description such as “190 mm screw flight” is therefore incomplete for manufacturing.

Restoring the Original Flight Geometry

A worn screw flight should not be copied from its most damaged area.

The outside edge may have become smaller, the leading surface may be thin, and the pitch may appear irregular where the flight has bent or separated from the shaft. Manufacturing a replacement directly from these damaged measurements can reproduce the wear instead of restoring the original geometry.

Before removing the old flight, compare several locations:

• Heavily worn turns
• Less-worn turns
• Inlet and outlet sections
• Flights close to a shaft connection
• Sections that have not contacted the conveyor tube

Useful measurements include:

• Conveyor-tube inside diameter
• Flight OD at several positions
• Shaft or shaft-tube outside diameter
• Flight ID
• Pitch across several consecutive turns
• IT and OT, or uniform thickness
• Number of turns
• Length of the damaged section
• Distance to the nearest coupling or shaft end

Pitch should be measured across several complete turns wherever possible. Divide the total measured distance by the number of turns to reduce the influence of one damaged or distorted section.

The replacement section must also begin at the correct angular position relative to the existing helix. A new section may have the correct OD, ID and pitch but still form a step when its first turn is welded in the wrong rotational position.

A poorly aligned transition can cause:

• Uneven material movement
• Pulsing discharge
• Local material accumulation
• Repeated wear at the joint
• Increased vibration
• Contact between the flight and conveyor tube

The new section should be aligned with the remaining helix before final welding. The completed shaft should then be checked for straightness and free rotation.

Confirming Left-Hand or Right-Hand Direction

Flight direction cannot be confirmed reliably from an unmarked photograph.

The same helix may appear left-handed or right-handed when viewed from opposite ends. Correct identification requires three details:

• Which end of the shaft is facing the viewer
• Normal shaft rotation
• Required direction of material travel

Photos or drawings should clearly mark:

• Drive end
• Discharge end
• Direction of shaft rotation
• Direction of material movement

For a complete shaft section, the helix direction must also agree with the end connections and installation orientation. A correctly manufactured flight installed in the opposite direction will move material away from the intended outlet.

Loose Flighting or a Complete Screw Shaft Section

The condition of the existing shaft determines the most suitable supply form.

Loose Screw Flighting

Loose flighting is suitable when:

• The shaft tube remains straight
• Existing shaft ends and couplings are reusable
• Only part of the flight is worn
• The repair workshop can control pitch and alignment
• Suitable welding and positioning fixtures are available

The formed flight is supplied for welding onto an existing or newly fabricated shaft.

Welded Screw Shaft Section

A completed shaft section is more suitable when:

• Several consecutive turns are worn
• The shaft tube is bent or damaged
• The flight has separated from the shaft
• Shaft couplings also require replacement
• Finished shaft length must be controlled accurately
• Suitable local fabrication equipment is unavailable

The section can be supplied with the shaft tube, screw flight and confirmed end connections already assembled.

Complete Internal Screw Assembly

For a larger conveyor rebuild, the internal assembly can include:

• Multiple screw shaft sections
• XA shaft couplings
• Drive-end connection
• End-bearing connection
• Hanger-bearing joints
• Planned gaps between adjacent flight sections

The flights on adjacent shaft sections must leave a clear gap at each hanger-bearing position. This space is required for the internal bearing housing, shaft connection and maintenance access.

Information Needed for Production

Loose Screw Flighting

Please provide:

• OD
• ID
• Pitch
• IT and OT, or uniform thickness
• Left-hand or right-hand direction
• Required section length
• Material
• Quantity

Replacement Flight Section

Also provide:

• Conveyor-tube inside diameter
• Shaft outside diameter
• Number of turns to be replaced
• Distance to the nearest shaft end
• Position of any coupling or hanger bearing
• Photos of worn and less-worn turns
• Normal shaft rotation
• Required material direction

Complete Screw Shaft Section

Please include:

• Finished shaft length
• Flight starting and ending positions
• Shaft-tube dimensions
• Coupling type at each end
• Hanger-bearing locations
• Required flight gaps
• Drive-end and discharge-end identification

A marked drawing or clear hand sketch can be used when every dimension has a fixed reference point.

Frequently Asked Questions

The old screw flight is worn unevenly. Which diameter should we use for production?

Do not select the replacement OD from the smallest worn section.

Compare several locations along the shaft and measure the conveyor-tube inside diameter, the less-worn flight sections and the intended running clearance. An original drawing or an undamaged turn near a shaft connection is usually a better reference than the most heavily worn edge.

Can we replace only the first two or three damaged turns?

Yes, when the remaining flights, shaft tube and welded joints are still in usable condition.

The new turns must continue the existing pitch and angular position. The repair area also needs enough sound shaft surface for welding. When damage extends into several adjoining turns or the shaft tube, replacing a longer section may provide a more stable repair.

Our replacement section has the correct OD and ID, but it will not align with the remaining helix. What else should we check?

Check the pitch and the rotational starting position of the new section.

OD and ID define only the outside and inside diameters. The replacement must also begin at the correct angular position and continue the original pitch. Even a small phase difference at the first joint can create a visible step between the old and new flights.

Can you make the replacement flight thicker so it lasts longer?

Possibly, but thickness should not be increased without reviewing the complete shaft assembly.

A thicker flight changes the formed profile, rotating mass and welding conditions. It may also affect clearance around the shaft, the load on the shaft connections and the power required to rotate the assembly.

The material, wear pattern and drive requirements should be considered before changing from the original thickness.

We only have photos of the old screw shaft. Can you confirm whether the flight is left-hand or right-hand?

Only when the viewing direction and operating direction are clearly identified.

The photos should mark the drive end, discharge end, normal shaft rotation and material-travel direction. Without those references, a photograph taken from the opposite end can make the same flight appear to have the opposite hand.

Is it better to order loose flighting or a complete screw shaft section?

Loose flighting is practical when the shaft remains straight and the workshop can accurately control pitch, welding and alignment.

A complete shaft section is usually more suitable when the shaft is bent, several turns are worn, the couplings also require replacement or the finished assembly cannot be rebuilt accurately at the installation site.