Inside Machines: Process models, advanced control support super steel mill

Extensive system integration and custom advanced control software supports one of only four cold mills in the U.S. coupled to a pickle line. The mill automation system supports a continuous process requiring precision control of motor speeds and integration of auxiliary equipment.


The first major greenfield steel facility built in North America in a very long time is in operation in Columbus, MS. Severstal Columbus, a unit of the Russian Severstal Group, developed the facility to manufacture high-quality steels for use by automakers including BMW, Mercedes, and Honda. Phase I of the new mill, commissioned in 2007, employs 450 people to produce 1.5 million tons of hot-rolled, cold-rolled, and coated steel products each year. Phase II, currently under construction, will double the mill’s capacity. (Six additional photos, tables, and graphics - not appearing in the print and digital edition - appear at the bottom in an ONLINE extra, along with relevant links.)

System integrator TMEIC GE, a global joint venture between Toshiba, Mitsubishi-Electric, and General Electric, supplied the new mill with the constant and adjustable speed drives, motors, control and automation systems, and associated electrical equipment. Projects included the continuous galvanizing line with inline skin pass mill, the standalone temper mill, and the unique and impressive continuous pickle line tandem cold mill.

Physics-based computer process models, called Level 2 (in blue), supply references (setpoints) to, and are tightly integrated with, the Level 1 PLC control (in purple). The speed of all the motors is coordinated by the PLCs, which are connected by the control network to the Level 2 computers. Source: TMEIC GE and Control Engineering

An article in the Memphis Business Journal in August 2007 quoted Severstal chief commercial officer Mike Wagner as saying, “Our commitment to invest in only the best available technology can easily be seen in our cold mill. The term state-of-the-art is often overused, but it is an accurate term in this case.”

For this very large system integration project, TMEIC GE responsibilities included writing custom software, conducting the factory system test, and supervising the system installation and commissioning. TMEIC GE is also providing ongoing customer support, and is responsible for these system descriptions and illustrations.

The main challenge of the project was its size, said TMEIC GE project manager, Ron Tessendorf. “This was a huge integration project requiring us to work with a variety of suppliers, and to write a lot of custom software,” he said. “In addition, we decided to use a next-generation PLC with new features. The customer required performance guarantees in terms of product quality and production rate, and we met all of these,” he added.

Continuous operation

The 659,800-sq-ft cold mill is one of only four in the U.S. coupled to a pickle line, and is the only one capable of producing steel coils up to 72 inches wide, according to the company. A pickle line is a series of acid tanks used to clean the metal strip before it enters the cold mill. Large accumulators located under the tanks store long lengths of strip to allow continuous operation of the cold mill while new coils are being added at the input end.

The pickle line tandem cold mill (PLTCM) is a continuous process requiring precision control of motor speeds and supporting sequencing of auxiliary equipment. The strip is moved through the pickle line at the optimum speed for the pickling process and under precise strip tension control. The pickling process never stops, even when the head of a new coil is automatically welded onto the end of the coil being pickled. In the tandem cold mill, precision reductions are made in strip thickness in each of the five reducing stands powered by 5,000 kW motors.

The total length of the PLTCM line is 1,100 ft and its height is 34 ft. Strip delivery speed is an astounding 4,100 ft per minute. In the cold rolling process, precise control of strip tension, speed, and roll force is required to produce a flat strip. To ensure a perfectly shaped (flat) product, the work rolls are bent and moved horizontally by electrohydraulic actuators under control of the PLCs.

The following list of components illustrates the size of the PLTCM control project: 13,582 digital inputs and outputs, 2,893 analog inputs and outputs, 129 ac motors ranging from 2 hp to 6,700 hp, 116 low-voltage variable speed ac drives, 7 high-power medium-voltage variable speed ac drives, and 34 programmable logic controllers (PLCs) and operator interfaces.

Advanced software for control

The tandem cold mill control system is a good example of the advanced software used on this project. TMEIC GE’s hierarchical automation system, developed over 50 years of steel rolling mill experience, provides control based on physics- based computer process models, called Level 2, which supply references (or setpoints) to, and are tightly integrated with, the Level 1 PLC control. The speed of all the motors is coordinated by the PLCs, which are connected by the control network to the Level 2 computers, as shown in the illustration.

The Level 1 controls accept I/O signals from the mill stands and generate output signals for motor speed, gap control, roll movement, tension, and a host of other machine functions. Some of the major functions performed include:

  • Gage control. Automatic gage control (AGC) employs mass flow calculation, thickness measurement, feedforward, feedback, tension, and slip compensation.
  • Eccentricity. Eccentricity control dynamically reduces the effect of backup roll irregularities on thickness using Fourier Series Analysis.
  • Flatness. Automatic flatness control uses advanced data filtering, parabolic flatness control, tilt control, segmented coolant spray control, and shape maintenance.
  • Coordination. Coordinated in-coil adjustments use measured and calculated values to maintain targets.
  • Flying gage change. Fast, coordinated, gage control changes minimize strip breaks and mass flow disturbances during rapid changes to products of different thicknesses.
  • Micro-tracking. High-speed data acquisition and tracking allows faster and more accurate control action.

Level 2 controls

TMEIC GE’s Level 2 process models are tightly integrated with the Level 1 PLC controls. Process models are dynamic mathematical models based on the fundamental physics of the rolling process. The models generate the PLC setpoints to ensure production of the highest quality product. Model software runs in the supervisory computer shown in the hierarchical automation diagram.

Some of the process models contained in the system include:

  • Force, torque, and power models showing the effects of tension and friction
  • Deformation resistance models with the material chemistry and work hardening effects on elongation
  • Friction models with compensation for coefficient of friction variations
  • Strain model showing in-coil strain distribution
  • Roll wear model showing the thermal and wear effects on roll diameter profiles
  • Interaction models describing the relationship of tension, forward slip, friction, and speed
  • The coefficient of friction effect of textured rolls
  • Product-dependent transfer functions for Level 1 control
  • Roll bending, roll shifting, and IR bending
  • Generic flatness interface models.

High-quality cold rolling produces strip metal of reduced thickness and with good surface finish. With this mill automation system, the PLTCM is capable of producing high-quality cold rolled steel 24x7, stopping only for scheduled maintenance. Severstal’s hot mill manager, Dan Lambert, is very pleased with the mill’s performance since startup in August 2007. “There have been zero issues with the reliability or performance of the main mill motors at Severstal…. The design of these machines and the ancillary systems lends to minimal maintenance requirements and what appears to be a long service life. Install it and forget it! This was a very nice approach afforded by the TMEIC motors and installation crew during our construction phase, when there were plenty of other issues on which we had to focus our attention.”

Edited by Renee R. Bassett for Control Engineering, rrobbins3000(at)

Inverter technologies

Why Choose Medium-Voltage Drives

Transformerless medium-voltage drives

ONLINE extra (extra images and two tables not appearing in the print and digital editions)

This Severstal Columbus, MS, cold-roll steel mill shows an operator side view of the connected pickle line. Source: TMEIC GE and Control Engineering

Pickle line tandem cold mill steel mill info

PLTCM Process Line


Length, total

    1,100 feet

Height of the PLTCM

    34 feet

Strip delivery speed

    4,100 feet / minute           

Severstal Columbus, MS, cold mill hierarchical automation system uses physics-based computer process models, called level 2, which supply references (setpoints) to, and are tightly integrated with, the level 1 PLC control. Source: TMEIC GE, Control Engine



Hierarchical automation system for the Severstal Columbus, MS, cold-roll steel mill pickle line (Cold Mill not shown); Source: TMEIC GE, Control Engineering


Pickle line and cold mill control system summary

Control system


Digital inputs and outputs, total


Analog inputs and outputs, total


Motors, ac, ranging from 2 hp to 6,700 hp, total


Low voltage variable speed ac drives, total


High-power medium voltage variable speed ac drives, total


Programmable logic controllers (PLC) and operator interfaces



Severstal’s Hot Mill Manager Dan Lambert (right) and engineer Neil Peabody stand in front of 13,000 hp variable speed motor on the hot mill.  Source: TMEIC GE and Control Engineering

Also see ...

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
The true cost of lubrication: Three keys to consider when evaluating oils; Plant Engineering Lubrication Guide; 11 ways to protect bearing assets; Is lubrication part of your KPIs?
Contract maintenance: 5 ways to keep things humming while keeping an eye on costs; Pneumatic systems; Energy monitoring; The sixth 'S' is safety
Transport your data: Supply chain information critical to operational excellence; High-voltage faults; Portable cooling; Safety automation isn't automatic
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Maintaining low data center PUE; Using eco mode in UPS systems; Commissioning electrical and power systems; Exploring dc power distribution alternatives
Synchronizing industrial Ethernet networks; Selecting protocol conversion gateways; Integrating HMIs with PLCs and PACs
Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.