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Tandem Cold Mill

Tandem Cold Mill

Tandem cold-mill solutions from Primetals Technologies stand for high product yields combined with flexible production, low operational costs and simplified maintenance work.

Depending on the product mix, the production capacity of continuous tandem mills from Primetals Technologies can exceed 1.2 million tons per year. The goal is to provide solutions that offer maximum added value for customers. Advanced mill stand actuators contribute to improved yield, user-friendly mill operation, and high-quality strip that lies within the specified tolerance values. Both 6-high and 4-high mill stands with their specific features and benefits are supplied on the basis of detailed analyses of product and customer requirements.

 Technology

Benefits

By joining coils prior to entering the mill, a continuous tandem cold mill results, provides additional benefits such as:

  • Highest production rates
  • Optimized yield
  • Reduced roll consumption
  • Flexible production
  • Tight tolerances for strip thickness, shape, and high surface quality
  • Low costs for operation, maintenance, and minimum down times
  • Fewer operators
  • Reduction in off-gauge material
  • Elimination of strip threading problems

Fig.1- Six-high cold mill stand  |  Fig.2- Five stand continuous cold tandem mill  |  Fig.3- Carrousel tension reel

Features

The Tandem mill consists of three to six mill stands arranged in series to progressively reduce the thickness of the strip in a single pass. A continuous tandem mill has a welder and accumulator looper at the entry end to join successive coils of pickled hot rolled material. This provides a large-scale mill that is capable of full automation to deliver the most advanced levels of quality and operating stability. It provides high production efficiency, and is used in the production of a broad range of steel types, from general construction materials to high-grade materials for automobile panels and other purposes.

Increasingly, for automotive steels, high-tensile materials at thinner gauges are being demanded to save vehicle weight and hence improve fuel consumption. As a result, higher performance is being demanded of the rolling mills. To meet this need, a continuous 5-stand tandem mill directly connected to the pickling line and using 6Hi UCM-Mill (Universal Crown Control mills) for all stands has become the standard. The UCM-Mill features:

  • Work roll bending
  • Intermediate roll bending
  • Intermediate roll shifting
  • Super heavy reduction
  • High strip shape control
  • Stable operation
  • Roll inventory reduction
  • Yield increase (by decreasing edge drop of the strip)

To cope with the high speed of delivery of the rolled strip a carrousel tension reel coils the strip on exiting the mill. This has two mandrels enabling the strip to be cropped on completion of a coil allowing the second mandrel to accept the oncoming strip without stopping the mill. 

 

Fig.4- Advantages of 6-high Universal Crown Control Mill (UCM) on strip flatness

 Automation

Complete process control at every level

Technological controls and process models form the core of any sophisticated automation solution that aims to maximize utilization of the mechanical, hydraulic, and other positioning elements. The value of the Primetals Technologies solution for cold mills can be seen in the rolled strip: considerably improved gauge tolerances, less off-gauge material, and perfect flatness. Our solutions for cold rolling mill automation cover the complete range of requirements, from "fit-for-use" single-stand cold mills to linked pickling and tandem cold rolling mill complexes. Highest performance levels are achieved by combining extensive process knowledge and using the most advanced automation solutions which feature artificial intelligence with neural networks, optimized scheduling to minimize costs, and multi-variable auto-adaptive control.The Primetals Technologies automatic gauge and tension control satisfy even the most challenging demands, such as those for flying gauge changes. The model-based flatness-control system, which incorporates multi-variable functions, allows the tightest flatness tolerances to be met. On the basis of its modular design, all available roll-gap profile actuators can be used.

Contactless flatness measurement system - Look, but don’t touch

Most systems still measure flatness through contact-based radial force measurements. This technique suffers from several shortcomings. As an alternative, non-contact flatness measurement is based on periodic excitation of the strip and measurement of the excitation amplitude across the strip width. Excitation force is applied by creating a low pressure between the strip and the sensor plate below the pass line of the mill stand. The resulting strip excitation is measured by non-contact eddy current sensors and converted to flatness distribution.

Speed Optimization System

Speed optimization achieves smooth running production, i.e. a good production rate at a high quality level, by avoiding any stoppages in each of the individual aggregates of the line. Just as a concert of musicians of great talent are nothing without a good conductor, all the individual aggregates of a pickling line and tandem cold mill (PLTCM) must be coordinated together in order to get the most out of them. The purpose of the Speed Optimization System is to run each part of the plant as fast as possible to increase throughput, but only as fast as necessary while keeping the speed of each part as constant as reasonable for quality reasons. The result is a process that is more homogeneous in operation and products are of higher quality, as well as line throughput is maximized.

Dynamic Rolling Program

Dynamic Rolling achieves smooth and safe production during transitions by controlling target gauge changes on the fly (within the same strip or at weld seam). Cold rolling on continuous tandem cold mills requires methods to optimize production and minimize yield losses on the transition between individual strips. Maximum flexibility of the rolling schedule can be retained as an additional requirement. Smooth operations can be achieved to reduce the danger of roll surface damage or strip breaks. The purpose of the Dynamic Rolling Program is to supply your continuous cold mill with the ability to automatically roll transitions whatever they are: transitions between strips, transitions within the same strip for purposes of load redistribution, or target thickness change under extreme transitions.

Drive Train Package

Primetals Technologies offers modernization and upgrading for drive train system of your cold rolling mills. This package comprises all electrical and automation components of the whole drive train for mill stands or coilers. It consists of medium voltage power supply and harmonic filters, the drive transformer, the drive system and contactors, synchronous motors and asynchronous motors, sensors and brakes, reducer or pinion gear, couplings, spindles and torque limiters (e.g. shear pins).

Safety System - For a maximum risk reduction of your lines

Safety requirements are getting stricter to protect personnel from harm through industrial injuries. Our Safety System is designed according to European or International standards ensuring the state of the art in terms of risk reduction. Based on the defined risk reduction measures of the risk assessment and failsafe automation system, the Safety System includes the following safety functions: emergency stop, safe stop for access to a mill area, controlling and monitoring of the access facilities to the safety areas, operation or if necessary stopping of movements inside a safety area, safely reduced speed monitoring. The Safety System also comprises safety stop solutions for drives and hydraulic equipment.

Roll Eccentricity Compensation

The Roll Eccentricity Compensator improves strip quality by eliminating thickness deviations caused by roll eccentricities. Getting strip thickness within narrow tolerances is particularly important to ensure a good strip quality. Thickness variations at mill exit come not only from the incoming strip gauge variations or from the forward slip effect from changes in strip tension, but also from eccentricity of rolls. For various reasons such as non-uniform thermal expansion of the rolls, grinding inaccuracy, or asymmetrical adjustment of the bearing rolls shell via drive keys, each roll creates oscillations with an eccentricity frequency that has to be compensated to produce a strip with uniform thickness. Based on its long experience in rolling technology, Primetals Technologies improved its REC system using, depending on rolling conditions, the measured exit thickness, the roll force, or the entry tension deviation for evaluating the eccentricity.

Equipment Performance Analyzer

The Equipment Performance Analyzer is designed to monitor and improve the effectiveness of the rolling process and the metallurgical equipment (rolling mills, processing line, …) The key issue today is to identify the right improvement measures as investment budgets are very restricted. The purpose of the package is to optimize operation, in other words, produce more and better without new investment in production. Most industries already monitor what is coming out of their metallurgical equipment. The Equipment Performance Analyzer package goes deeper and monitors what could have come out versus what has been really produced. In another way, it provides excellent gauges for measuring where the losses are and how the situation can be improved according to the following three improvement axis: non-stop production, top speed production, zero defect production.

Off-Gauge Optimizer - Optimized productivity due to a major reduction in off-gauges.

The need for product quality and productivity are continually growing in terms of dimensional accuracy, thickness, flatness, mechanical properties, surface quality, and yield. Scrap resulting from off-gauge lengths leads to additional processing costs that decrease overall yield. Primetals Technologies proposes a solution involving low investment costs and fast return of capital investment (typically 1 year) derived from the so-called “hidden potentials” of your mill equipment. Based on the perfect combination of technology, process control, and instrumentation, the Off-Gauge Optimizer features the smart implementation of the control algorithm of a tandem cold mill based on the mass flow principle.

SIAS - Automated Surface Inspection System.

SIAS, the solution for automatic surface inspection from Primetals Technologies is designed for surface quality monitoring for billets and flat products. Composed of an on-line sensor (light source and cameras) coupled with image processing hardware and software, the goal of the system is to replace partial and random surface inspection with constant, repeatable, and systematic inspection of 100% of the production. SIAS exclusive and patented classification method “Coulomb Hyperspheres” enables the system to detect and classify the most critical defect after generally two weeks of operation. Fully integrated to the system, the coil grading application is an additional functionality that aids decision-making by automatically computing a global quality level based on final customer surface quality requirement and the product surface evaluation through SIAS.


 Integrated Plants & Solutions

Integrated Plants & Solutions for tandem cold mill - Experience that Matters

Please follow the corresponding links to learn more about our competences:

Reference Story

TCM for Thin Gauge and High Speed Rolling

Customer:
POSCO-Vietnam PL-TCM (TCM Section) / Phu My, Vietnam

Main Specification:
Material: Low Carbon Steel, High Strength Steel
Strip Thickness: Entry 1.8 to 5.0 mm, Delivery 0.15 to 1.6 mm (For Construction)
Strip Width: 700 to 1,570 mm
Coil Weight: Max. 35,000 kg
Rolling Speed: Max. 1,700 m/min
Mill Type: 6Hi UCM-Mill (No.1 to 5 Stand)

 

 

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