Metal rolling mill operators can get consistently high quality and better control with digitally-enabled ABB drives

Rolling mill operations in metals plants are among the most demanding industrial processes that exist, creating difficult challenges for operators. Better control of the rolling mill with ABB’s new digitally connected ACS6080 drive can improve quality, reliability and productivity, while lowering waste and emissions, to help meet both sustainability and profitability targets.

The bottom-line objective for any rolling mill operation in metals processing is to make consistently high quality while using the lowest energy and raw materials input, and with minimal scrap and waste production. When those criteria are achieved, metals producers have the best conditions for generating consistently high profitability. Thus, high productivity and profitability, based on efficient raw material usage, go 100% hand-in-hand with reduced environmental impact.

A key tool that can help metals manufacturers accomplish the combined aims of consistently high quality production and high energy efficiency, with the lowest reject rate, is ABB’s new ACS6080 medium voltage drive. This drive is specifically tailored to manage the toughest requirements in terms of power and torque, such as those needed in rolling mills. The ACS6080 is built on the proven technology of its predecessor, the ACS6000 that has been successfully used for more than 23 years in demanding rolling mill applications.

As metal plant operators know very well, rolling mills are extremely dynamic processes involving wide ranges of acceleration and deceleration rates and huge variations in power demand, which is much more challenging than the nominal power demands in any other motor-drive application.So the drive must be extremely flexible to meet this broad range of power demands and overloads. Anything that gives the operator better control of the mill with tighter precision and response can deliver very sizable benefits in both production quality and sustainability. The new ACS6080 drive does this through a number of key design advances and options, which are explained in the following paragraphs.

Braking energy regeneration for lower CO2 and energy impact

New regulations being enacted by many international organizations are aimed at lowering the carbon footprint of the metals industry. An obvious way to do this is through improved energy efficiency and for this the ACS6080 medium voltage drive is perfectly suited. The drive comes with a four-quadrant operation variant that efficiently manages cyclical or continuous braking by means of an active rectifier unit (ARU). This supports regenerative braking in both motor rotation directions, across the entire power range, and reduces the overall energy consumption in many applications.

In addition, the drive offers minimal reactive power consumption, which means that reactive power demand can be neglected due to use of the ARU, which controls the power factor to unity across the whole operating range. Additionally, the ARU can compensate reactive power generated by other loads that are connected to the same network.

Multi-motor drive topology means fewer parts and better energy use

Further energy gains are made easy with the multi-motor drive topology. The significance of multi-motor configuration is that with a single lineup you can control more than one motor, with the ACS6080 managing up to 8 motors. The energy, CAPEX and harmonics benefits are considerable, and the space footprint can be reduced up to 50% compared to a single drive configuration. Reliability is also greatly increased, due to having fewer components that may possibly fail.  

Redundant configurations are also possible with the ACS6080 multi-motor topology because, even if one module fails, the mill can still roll out the material at reduced speed if needed.

With the ACS6080 topology, braking energy generated in one motor can be transferred to another directly via the DC link, without the need to feed the required power from the network (i.e. the rectifier). This means lower energy consumption since, in case of excessive power or full braking, green energy can be fed into the network. While a common DC bus is now an established method for low voltage drives, ABB was the first to introduce the multi-motor configuration for medium voltage drives with such flexibility. And today ABB continues to be the market leader in terms of successful references in rolling mills applications with multidrive topology.

  • Example of a multidrive master-follower for cold rolling mill
  • Cold rolling mill application

Reliable for high quality and superior productivity

The drive can be thought of as the muscle of the rolling mill since it must transfer the control request physically to the motor and ultimately to the rolls of the mill. Thus, the drive is extremely important in achieving the highest quality and reliability, by managing demand swings and minimizing downtime on the line – while consistently meeting the buyer’s quality specs.

The ACS6080 design includes a range of features to give this superior reliability. One is the low parts count, due to numerous design refinements like the IGCTs (Integrated Gate Commutated Thyristors) which are based on well-proven GTO (Gate Turn-Off Thyristor) technology and have been used successfully in medium voltage drives for more than 23 years. IGCTs are power semiconductors which are ideal switches for high-powered medium voltage applications.

In addition, the multi-motor capability in the ACS6080 also contributes to the reduced parts count, adding further to the reliability. Other key long-life design features include self-healing oil-filled capacitors that have a substantially longer lifetime than electrolytic capacitors.

Other design advantages include the fast switching capability of the IGCT which allows snubberless circuit topologies, meaning fewer power components and improved operational reliability. Also, a fuseless design means that the power semiconductors used for short-circuit protection act extremely rapidly in case of a fault, thus limiting potential electrical fault energy surges into the drive. 

Concerning the very important issue of safety, the drive supports the highest level of protection for both people and assets, based on the arc-resistant design, using ABB's patented IGCT fuseless fire-through technology, made to provide fast arc-fault elimination. ACS6080 drives are as default IAC Certified according to IEC62271-200 Class IV.

Digitally connected diagnostics, services and fault prediction for remote analysis

Among the biggest advances in the new ACS6080 drive technology concern the wide range of digital connectivity tools to get better, more consistent quality and mill operations. This includes various machine diagnostics, digital services and fault prediction functions, as well as remote condition monitoring under the ABB Ability™ platform and a Bluetooth enabled control panel that interfaces with smart devices without needing to connect to a Service PC.

The built in self-diagnostic monitoring system generates concise error messages with information about error type and location. This enables quick and precise localization of disturbances and reduces time spent on fault finding.

The simplicity of the power circuit and modular design mean both high availability as well as easy maintenance and repair, with minimum outage times. For example, replacing a complete phase module takes less than 15 minutes thanks to the special mechanical design with fast disconnectors on the back.

And for longer term maintenance needs, remote condition monitoring of many key components on the rolling mill allow spotting of potential problems, long before they become surprising, and very expensive, breakdowns. Condition monitoring also helps make planned maintenance shutdowns much more time and cost efficient.

Upgrade of existing drive is possible

Although the ACS6080 is primarily intended to be installed as a new drive, the modular ACS6000 Modernization Service allows upgrading of an existing ACS6000 asset on site to obtain the ACS6080's absolute latest technology for implementing digitalization tools in metal plants.

This gives operators and operations managers a broad variety of new solutions that can bring them better productivity, quality, reliability and safety, for faster maintenance, less downtime and overall better plant performance and profit potential.

Summary – Digital services for tough rolling mill applications

By using the advanced digital connectivity functions like remote monitoring and performance enhancement algorithms and services that are built into the ACS6080 drive, rolling mill operators can reach much higher levels of control and productivity on demanding metals manufacturing lines.

In addition, the improved reliability and flexibility resulting from the unique combination of multi-motor topology, arc resistant design and historical metals industry references from cold to hot rolling mills means that users of the ACS6080 will be well positioned for superior operation – both for today and for a very long time into the future.

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