Hybrid gearboxes deliver high torque from 1.5kW motor

A new filter plant at the BOS plant on the Scunthorpe Corus steelworks is using hybrid gearboxes combining planetary and helical gear technology to open and close the doors on the iron desulphurisation process. The new installation is being used to capture the fumes created during the desulphurisation process and has been built in order to improve the plant's environmental performance. The door drives needed to be compact yet still able to provide high torque output from a low energy input, combined with strength and durability. Brevini PIV was able to address these challenging requirements with its Posiplan BPH shaft-mounted gearbox.

Corus Scunthorpe is one of the largest steel production sites in the UK, producing plates, sections, wire rod and semi-finished steel using the BOS method. As well as reducing dust emissions, the new technology aimed to create a more pleasant working environment for employees and helped to speed up the steelmaking process.

Previously the plant used two wet scrubber systems to remove the fumes generated by the iron preparation and desulphurisation processes; however, these were becoming outdated and inefficient. One new bag filter plant was commissioned to replace the two wet scrubber systems.

The desulphurisation process involves co-injecting lime and magnesium into a ladle of molten iron; the sulphur in the iron reacts with this and rises to the surface as slag. Once the injection treatment has been completed the slag is skimmed off the ladle. The desulphurised iron can then be taken into the BOS vessels to be converted into steel.

It is during the desulphurisation process that the fumes generated need to be extracted and cleaned efficiently. Doors have been designed that close to contain the fumes during the process while the extraction system draws them away. The gearboxes required to drive the doors needed to be compact in order to fit into the available space while providing the strength and torque required to close the heavy doors.

Planetary/helical hybrid gearboxes

The company that was commissioned to build the filter plant turned to Brevini to provide the gearboxes. Brevini was able to design a gearbox that met all the application requirements using its Posiplan range of planetary/helical hybrid gearboxes.

Jon Snaith, General Manager for Sales and Marketing at Brevini UK Ltd, comments: "The Posiplan gearbox offers the best of both worlds, delivering higher capacities from smaller units, which allows for a significant increase in capacity over a more traditional design. Different sized motors are available and selected using motor performance curves to ensure maximum efficiency is realised."

The Posiplan hybrid gearboxes combines the efficiency of low weight and high reduction ratios of planetary gear stages on the input side with the higher capacity, strength and durability of bevel helical gears on the output stage; this is very useful for medium to large industrial applications. The input end employs planetary stages where higher speed and compactness are a major advantage, while the output uses a helical stage as it is slower and has higher torque.

Brevini supplied four Posiplan gearboxes for the filter plant project, each of which has a reduction ratio 2813.5:1 and is fitted with a compact 1.5kW motor. This provides a huge output torque of 22,000Nm and a low speed of 0.5rpm. The gearboxes are shaft-mounted, which makes for a tougher installation than using alternatives such as exposed belts, chains and pulleys.

The gearboxes use the latest labyrinth sealing technology and high-performance bearings, which extends operating life even in harsh environments.