At Metalnox, we repair fixed-pitch and controllable-pitch propellers, applying straightening, welding, heat treatment, reconstruction and modification processes that restore their original geometry and, when required, enhance their performance. We are equipped with dedicated hydraulic presses to restore the correct profile of deformed blades, along with welding procedures approved by Lloyd’s Register, ensuring safe, controlled interventions in full compliance with industry standards. After welding or straightening, we carry out post-weld heat treatments designed to minimise internal stresses in the material, ensuring the propeller’s structural stability.
Class upgrade and pitch modification
Once its physical integrity has been restored, we can proceed with a class upgrade in accordance with the criteria defined in ISO 484, optimising pitch accuracy and overall geometry to achieve more efficient and balanced operation. It is also possible to modify the pitch of the propeller when operational needs of the vessel have changed, adjusting its performance to new cargo, power or speed conditions.
Dynamic balance
All propellers repaired at Metalnox undergo a high-speed dynamic balancing process, as this method provides greater accuracy and allows the detection of imbalances that cannot be identified using traditional static balancing techniques. This computerised system provides a detailed report on the propeller’s condition before and after balancing, and allows us to accurately identify the weight and exact location where material must be removed or added to achieve optimal performance. Thanks to this procedure we achieve significant improvements in fuel consumption, vibrations reduction and global performance of the drive system. At our facilities, we are capable of dynamically balancing large-diameter propellers of up to 2.5 metres, even when mounted on propeller shafts up to 12 metres in length, with a total assembly weight of up to five tonnes.
Polishing
As a final step, we carry out a uniform polishing of the propeller surfaces, ensuring a clean and smooth finish that helps reduce hydrodynamic resistance, improve propulsion efficiency, and provide greater durability against cavitation and corrosion in the marine environment.
