A major advantage of AC over DC motors is that maintenance requirements are much lower. DC motors use carbon brushes that are subject to wear, and the DC roller table motors in POSCO’s hot strip mill required monthly maintenance to clean out carbon dust and replace worn brushes. Maintenance stoppages naturally disrupt the process and increase costs.
Looking for ways to reduce maintenance and increase reliability - a crucial factor in a process where unscheduled downtime has to be minimized - POSCO decided to upgrade to modern AC roller table motors. They selected ABB as the supplier because ABB Roller table and Process performance motors have already proven themselves in other areas of the plant.
“We wanted a robust solution that would reduce our maintenance needs and be easy to manage,” says a POSCO representative. We’ve had very positive experiences with ABB Roller table motors. They provide high reliability and long lifetimes with minimal maintenance in the tough environment of the hot strip mill.”
Customized for specific application
“Roller tables are a very demanding application,” says Young-Ju Ryu, Senior Sales Specialist, of ABB in South Korea. “No two roller tables operate the same way, and the motors have to be customized for their specific application. This takes a lot of domain expertise and experience. For example, the speed and torque characteristics have to be tailored to the process, with very accurate control to ensure optimal performance. The motors have to cope with rapid accelerations and reversals, shock loads and high overloads. They also have to be very rugged, with a strong housing to withstand impacts, and protection against dust and water sprays.”
ABB’s scope of supply included 70 roller table motors. The 8-pole motors are rated at 26 and 36 kW, and built to handle rapid load changes and 250% overload conditions. Encoders provide accurate speed and torque control, and the terminal box is at the non-drive end to keep the connections away from the hot metal on the rollers.
The motors feature IP55 protection and IC410 cooling, which means they are totally enclosed and non-ventilated – a cooling method favored for the harsh rolling mill environment. ABB Roller table motors have vertical cooling ribs to prevent dust from accumulating on the surface, and the motors supplied for POSCO’s roller table upgrade are engineered to run cooler than regular motors.
The roller table motors were bundled in matched packages with ACS880 industrial drives, with 13 single drives and 72 multidrives supplied in total. This drives family is engineered for heavy use in harsh environments and their durable design enhances reliability. They offer seamless integration with automation networks and flexible customization. The drives incorporate Direct Torque Control (DTC), a technology developed by ABB that ensures extremely fast torque response combined with high dynamic speed accuracy. The packages supplied to POSCO were optimized for maximum energy savings and excellent control performance.
ABB Roller table motor 
ABB ACS880 Industrial drives
Over 110 motors in total
In addition to the motors for the roller table upgrade project, ABB supplied a further 44 Process performance motors, comprising 30 kW motors for roll position control and 132 and 160 kW motors for use on another roller table at the plant.
“We built a team to handle this project, including specialists from the ABB IEC Low voltage motors factory,” Young-Ju Ryu adds. “One particular challenge was to optimize the sizing of the motors. AC motors are larger than the equivalent DC motors, which meant there was only limited space available for installation. We paid special attention to the width of the motors, and we used load operation data from the process to choose the optimal motors to meet the size requirements.”
By selecting ABB Roller table and Process performance motors - the same types as were already operating at the plant - POSCO has increased its scope for optimizing the handling and management of spare motors and parts. Work to remove the old DC motors and install the new AC motors began at the end of April and was successfully completed in June 2024. POSCO has confirmed that the new AC motor-drive packages have met all of their expectations for higher reliability and lower maintenance.
POSCO Holdings Inc. is based in Pohang city, South Korea. Its annual capacity of 42 million metric tonnes makes it one of the world's largest steelmakers. POSCO exports a wide range of steel products, including hot rolled sheets, plate, wire rod, cold rolled sheets, galvanized sheets and stainless steel, to more than 50 countries. The company is transitioning to low-carbon manufacturing processes and is committed to achieving carbon neutrality by 2050.
