Gearbox stands up to steel production environment

14 August 2013

The harsh environments encountered in the steel industry place huge technical demands on plant and machinery used here. Watt Drive (part of the WEG Group) helical bevel gearboxes are being used in a new straightening unit at steel producer ArcelorMittal’s plant in Belval, Luxembourg.

With annual steel production of 130 million tonnes and around 245,000 employees, ArcelorMittal is one of the world's largest steel producers. At the Belval plant in Luxembourg an electric arc furnace and large continuous casting equipment is used to produce steel products such as light and medium girders and sheet piles. The annual capacity of this plant is approximately one million tonnes of steel.

ArcelorMittal wanted to convert one strand on a six-strand caster to a new casting format. The requirements for this included a new straightening unit in order to be able to cast the different format, which is around 30% larger than the previously biggest format. The new casting format is intended mainly for the production of girders as well as special profiles in the downstream rolling mill.

ArcelorMittal contracted engineering specialist TBR (previously Technisches Büro Rumpler) Casting Technologies to modify the plant. TBR called on Watt Drive to drive the straightening rollers. The decision was made to install the K139 helical bevel gearbox, which can be easily mounted on the plant shaft simply by means of a hollow shaft. Watt Drive delivered five of these models as geared motor units, four of them for use on the straightener and one as a spare.

As steel production is exposed to constant high temperatures, special materials and seals are required on the gearbox to ensure heat resistance. Another challenge in the design was the limited space available – as a result of the larger casting format – together with a strand separation of only 1,400mm. In addition, all straightener frames had to be very stable, easy to maintain and interchangeable within the unit.

Watt Drive customised the standard K139 helical bevel gearbox. The geared motors needed to withstand a high ambient temperature on the new strand, while at the same time delivering a high torque, in a compact housing. In addition to the high ambient temperatures, harsh environment and large control range of the self-ventilated motor, Watt Drive also took into account ArcelorMittal’s requirement for an integrated water cooling system when designing the motor and gearbox.

The drives are designed for a maximum ambient temperature of +100°C without the need for additional oil cooling. A water cooling system was also fitted, providing the gearbox with additional thermal protection. The water cooling system ensures a lowering of the oil temperature by means of internal gear pipework. At these high temperatures, special motor and gearbox seals are also required. Here, Watt Drive used temperature-resistant shaft seal rings (Viton) on hardened running surfaces.

The almost 100mm new, wider format results in extremely cramped conditions between the strands with the strand spacing kept unchanged. Thanks to the especially compact, slim design of the Watt Drive gearboxes, it was possible to implement the new straightener alongside the existing five strands. The gear housing is a uniblock design (‘Multimounting’’) and can be fastened on all sides. The Watt MAS (modular drive system) principle enables the standard gearbox to be quickly customised to application-specific requirements.

Each of the helical bevel geared motors delivers a drive power of 5 kW, a torque of 17,580 Nm and a rotational speed of 2.2 rpm at 50 Hz. The drives are designed for frequency inverter operation, which adjusts the rotational speed of the geared motor, thereby regulating the strand speed – the larger the beam blank formats produced, the slower the speed at which the strand must to be driven. An integrated 100 Nm brake with manual release – also designed for the high ambient temperature – serves to hold the cold strand in a fixed position at the point of entry because at the start of the casting process, a ‘dummy bar’ closes the mould exit outlet. Thanks to the manual release, the brake can be released by hand in an emergency, enabling the strand to be moved.

To improve ease of maintenance, Watt Drive designed the oil level indicator to be more prominent and easier to read. The gearboxes also feature a special expansion tank or oil expansion chamber. The vertical construction requires more oil in the gearboxes, which expands at the high operating temperatures. The expansion tank accommodates the expansion of the oil such that no pressure increase occurs, extending the longevity of the seals.

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