Cylindrical screw flights in Hardox steel

Cylindrical screw flights in Hardox steel and similar hardened steel types are a special type of cylindrical screw flights. The processing time is longer compared to standard cylindrical screw flights. BEMA has developed its own pressing tools for these screw flights. We are able to manufacture these types of screw flights without pre-heating. With our method, the steel does not change structure during the forming process.

Cylindrical screw flights in Hardox – how to specify them?

• The outer diameter shall be at least Ø150
• Ensure the pitch is below 70% of the outer diameter – this case is more, but you get a more stable result keeping et below 70% of the outer diameter
• Keep the material thickness as small as possible with respect to your application

Requirements for Manufacturing Screw Flights in Hardox Steel

Producing screw flights in Hardox‑450 or similar hardened steels demands a different engineering approach than standard mild‑steel or stainless‑steel flights. The page you are viewing highlights several of these requirements, and the following sections expand them into a complete technical explanation grounded in the content.

Material Behavior and Forming Forces

Hardox steel/Hardox‑450 is a wear‑resistant, quenched and tempered steel with high hardness and tensile strength. Forming this material into a helical shape requires significantly higher press forces than conventional steels. The material resists deformation, and if the forming process is not controlled precisely, it can crack along the outer edge of the flight. BEMA addresses this by using custom‑developed pressing tools designed specifically for Hardox flights, ensuring the material is shaped without compromising its mechanical properties.

Forming Without Pre‑Heating

A key requirement for Hardox is avoiding excessive heat during forming. Heating the steel softens it temporarily but permanently alters its microstructure, reducing hardness and wear resistance. The page notes that BEMA can manufacture Hardox flights without pre‑heating, which is a significant technical advantage. This ensures the steel retains its original hardness and durability after forming, making the final flight suitable for abrasive applications such as ash, slag, minerals, or heavy bulk materials.

Read more about BEMA screw flights here

Geometric Constraints and Design Requirements

Hardox flights must be designed within specific geometric limits to ensure stable forming and long‑term performance. The page specifies three critical requirements:

• The outer diameter must be at least Ø150 mm, because smaller diameters create too much stress concentration during forming.
• The pitch should remain below 70% of the outer diameter, as larger pitches increase deformation forces and reduce forming stability.
• The material thickness should be kept as small as possible while still meeting the application’s wear and strength requirements, because thicker Hardox becomes exponentially harder to form. These constraints ensure that the flight can be formed accurately without damaging the steel.

Tooling, Processing Time, and Quality Control

Hardox requires longer processing time because each forming step must be executed slowly and with controlled force. BEMA’s specialized tooling allows the steel to deform gradually, preventing micro‑cracks and maintaining uniform pitch. After forming, each flight must be inspected to confirm that the pitch, diameter, and helix angle match the specification. Any deviation can cause assembly issues or operational imbalance in the final screw conveyor. The page notes that processing time is longer for Hardox flights, reflecting the precision and care required.

Structural Integrity and Application Fit

Because Hardox is used in high‑wear environments, the final flight must maintain its hardness and structural integrity throughout the forming process. BEMA’s method ensures that the steel’s structure remains unchanged, preserving the material’s wear resistance. This makes the finished flights suitable for heavy‑duty applications where long service life and resistance to abrasion are essential.

FAQ on Screw Flights Manufactured in Hardox Steel

1. Why is Hardox steel more challenging to form into screw flights?

Hardox‑450 is a quenched and tempered wear‑resistant steel with very high hardness and tensile strength. This makes the material far more resistant to deformation than mild steel or stainless steel. Forming it into a helical shape requires significantly higher press forces, and if the force distribution is not controlled precisely, the material can crack along the outer edge of the flight. BEMA addresses this by using custom‑developed pressing tools designed specifically for Hardox flights, ensuring stable forming without damaging the steel’s mechanical properties.

2. How does BEMA prevent structural changes in Hardox during forming?

Hardox must not be heated during forming, because heat alters the steel’s microstructure and reduces its hardness and wear resistance. BEMA has developed a forming method that allows Hardox flights to be produced without pre‑heating, preserving the steel’s original hardness and durability. This is essential for applications involving abrasive materials such as ash, slag, minerals, or heavy bulk goods.

3. What geometric requirements must be followed when specifying Hardox screw flights?

To ensure stable forming and long‑term performance, Hardox flights must follow three key design rules:

• The outer diameter must be at least Ø150 mm, as smaller diameters create excessive stress during forming.
• The pitch should remain below 70% of the outer diameter, because larger pitches increase deformation forces and reduce forming stability.
• The material thickness should be kept as small as possible while still meeting wear and strength requirements, since thicker Hardox becomes exponentially harder to form. These constraints ensure that the flight can be formed accurately without compromising the steel.

4. Why does manufacturing Hardox flights require longer processing time?

Each forming step must be executed slowly and with controlled force to avoid micro‑cracks and maintain uniform pitch. Hardox’s hardness means the material cannot be rushed through the forming process. After forming, every flight must be inspected to verify pitch, diameter, and helix angle, because even small deviations can cause assembly issues or operational imbalance in the final screw conveyor. This extended processing time reflects the precision and care required to maintain the steel’s structural integrity.