Steelmaking arguably poses one of the most challenging operating environments for motor and drive technologies. Vibration, heat and contamination are among the forces working against the reliable and efficient operation of motion control products. Indeed, maintenance-free motors and drives are an increasingly important requirement for steelwork engineers under pressure to minimise both scheduled and unscheduled downtime to achieve demanding productivity levels to meet delivery schedules.
Among the trends, particularly for those producing popular steel products such as spiral welded pipe and tubes, is the move from DC motors to the latest induction motors. Due to the cost of maintaining and running some DC motors, many plant engineers in the steelmaking sector are seeking alternative, more cost-effective solutions, which is where variable frequency induction motors and inverter drives, preferably from a single source, come into play.
In such a scenario, a key factor is identifying induction motors that can be easily exchanged for DC technology without any loss of performance. As a point of note, check the rated torque and speed for work at constant power. The latest induction motors for variable frequency will provide rated torque up to circa 3000 Nm, and 0 to 10,000 rpm speed. Steelmakers that choose accordingly will benefit from an economic solution which provides lower maintenance costs and a competitively priced motor and drive assembly.
Motor performance
Always opt for a drive that facilitates class-leading induction motor performance. The drive should also offer flexible speed and a positional feedback interface that supports a wide range of feedback technologies, from robust resolvers to high-resolution encoders. Here, the latest AC variable speed drives used in closed-loop control can deliver the same performance as DC regulators.
This type of inverter drive is proving popular for example, at steelmakers producing tracks for the railway industry. Here, cut-to-length production lines, which are paramount in meeting growing throughput demands, process rails that can measure from 30 to 120m in length. Today, longer rails are preferred as they not only reduce the number of joins but significantly improve safety in railway transport.
The latest inverter drives and gearbox technologies offer combined solutions for two types of principal mechanisms on cut-to-length lines: chain conveyors and roller tables. Again, a single source is preferable as this strategy can provide a performance level way beyond that attainable from separate suppliers. Most solutions of this ilk are also extremely easy to install and decommission, which is important from a maintenance perspective if a roller bearing or encoder needs to be replaced, for example.
Equipment
Of course, much steel today is produced in a coil, which in turn demands the manufacture of efficient coil-processing equipment featuring correctly specified drive and motor technologies that are able to maximise reliability, productivity and precision. Typical equipment here includes steel winders/unwinders, stacking machines, rolling machines, longitudinal and transversal slitters, turning machines, packaging machines and cutting systems. With regard to the latter, a rotary knife device for high thickness coil is often expected to work at speeds of 100m/min, while a flying shear system for higher yield stress materials works at 50m/min. Despite these elevated speeds, precision in the coil-processing sector is typically within ±0.2 mm.
Variable speed drives must provide the necessary speed and response, which in turn allow high dynamic applications control with repeatable precision. The latest drive technologies feature intelligent modules that permit users to manage comprehensive programs requiring motion in several axes and profiles, synchronised with high precision. This involves fast and accurate movements that serve to minimise reject rates and maximise production uptime, all without inducing stress on the mechanical parts.
Solutions
A typical solution for a transversal cutting line featuring an uncoiler, levellers, flying shear, conveyors and stackers, for example, would comprise a control cabinet housing circa 20 AC drives, often in a DC bus configuration that ensures good stability and optimised energy consumption. Networking configurations will of course vary, but it is commonplace to see Profinet connect the PLC with drives, encoders and remote I/O, while Ethernet allows the checking and changing of system parameters via a remote PC, including the parameters of the drives. This capability makes for easy fault-finding and element replacement.
Variable frequency drives can also boost the uptime of finishing mill operations at aluminium manufacturing facilities. Such mills offer acceleration and deceleration in the region of 1.5 seconds per 1000 rpm. Furthermore, many of these mills have to run in closed-loop configuration and stop and start in 1 to 1.5 seconds. Casting houses around the world which produce aluminium wire-rod coil and billets for the global automotive and consumer goods markets demand high levels of reliability that often require AC VFD standby drives systems working with liquid-cooled induction motors, which are particularly suited to variable-speed operation. Such solutions are used increasingly to help eradicate downtime on production mills.
Again, the latest smart modules can be used to provide high-speed drive access, global connectivity and integration with IT technologies such as wireless networking.