With annual steel production of 130 million tonnes and around 245,000 employees, ArcelorMittal is one of the world's largest steel producers. At its plant in Belval, Luxembourg, the industrial giant uses an electric arc furnace and large continuous casting equipment to produce steel products such as light and medium girders and sheet piles. The annual capacity of the 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 Beam Blank 4 (BB4). The requirements for this strand included a new straightening unit in order to be able to cast the BB4 format, which is around 30 percent larger than the previously biggest format, which will continue to be produced on the other five strands (BB3).
The new casting format is intended mainly for the production of girders as well as special profiles in the downstream rolling mill. The annual production of the BB4 strand is planned to be around 100,000 tonnes of steel.
ArcelorMittal contracted engineering specialist TBR (previously Technisches Büro Rumpler) Casting Technologies to modify the plant. TBR took care of the engineering, planning and delivery of components such as the segment comprising the secondary cooling and straightening unit, but called in Watt Drive for help with the straightening roller drives.
The decision was taken to install Watt Drive’s K139 helical bevel gearboxes, which are easily mounted thanks to their hollow shaft arrangement. Watt Drive delivered five of these models as geared motor units, four of them for use on the straightener and one as a spare.
With steel production comes high temperatures, so special materials and seals were required for these gearboxes to ensure their reliable operation. Another challenge was the limited space available because of the larger casting format and a strand separation of only 1,400mm. In addition, all the straightener frames had to be very stable, easy to maintain and interchangeable within the unit.
Watt Drive customised its standard K139 helical bevel gearbox to meet this demanding specification, as well as taking into account ArcelorMittal’s requirement for an integrated water cooling system when designing the motor and gearbox combination.
The drives were designed for a maximum ambient temperature of 100°C without additional oil cooling. At the client's wish, they were also fitted with a water cooling system (which acts to lower the temperature of the gearbox lubricating oil), providing additional thermal protection. Further precautions included the use of temperature-resistant Viton shaft seal rings on hardened running surfaces.
The wider BB4 format (an increase of nearly 100mm on the previous arrangement) results in somewhat cramped conditions between the strands whose spacing remained unchanged. Thanks to the compact, slim design of the Watt Drive gearboxes, it was possible to implement the new straightener alongside the existing five strands.
The novel ‘uniblock’ gearbox housing design enables mounting on all sides, while Watt Drive’s modular drive system principle enables the standard gearbox to be quickly customised to application-specific requirements.
Each of the K139 helical bevel geared motors delivers a drive power of 5kW, a torque of 17,580Nm and a rotational speed of 2.2 rpm at 50 Hz. The drives are designed for frequency inverter operation, which enables the strand speed to be regulated according to the size of the beam blank formats being produced.
An integrated 100Nm brake with manual release – also designed for high ambient temperature operation – serves to hold the cold strand in a fixed position at the point of entry; this is because, at the start of the casting process, a ‘dummy bar’ closes the mould exit outlet. The manual release facilitates brake operation by hand in an emergency, enabling the strand to be moved.
The vertical construction of the gearbox has one drawback in that it requires a greater quantity of oil, which is subject to expansion at the high operating temperatures. To combat this, the gearboxes also feature an additional chamber to accommodate this expansion and ensure that no pressure increase occurs, thus extending the longevity of the seals and contributing to greater operational reliability.
According to TBR Casting Technologies’ engineering manager, Leonhard Paar, the comparatively slim design of the K139 gearbox was a fundamental prerequisite for creating a reliable and easy-to-maintain straightener. “Thanks to its particular compactness and robustness, the larger BB4 format at the modified plant can be cast to the required quality, while at the same time reducing the servicing overhead,” he adds.
A gearbox for all occasions
The steel industry demands high performance as well as special robustness and temperature resistance. With its application-specific, customised helical bevel gearboxes for the driving rollers in ArcelorMittal's new straightening unit, Watt Drive has demonstrated that its gearboxes are a suitable choice for any demanding application.
And the partnership with TBR Casting Technologies could soon be repeated as it is anticipated that a further strand at ArcelorMittal Belval will shortly be converted.