In reversing cold mills the tension reels are placed at both ends of a single- or two-mill-stand arrangement. Due to the reversing rolling passes, production efficiency is lower than that of a tandem mill. However, because the rolling parameters can be quickly changed for each coil, reversing cold mills are especially suitable for small-lot production of various product types. The size of the mill equipment is also smaller, which allows easier access to mill equipment and machinery for maintenance purposes. Due to their simpler design, reversing mills can be more easily stopped and restarted. They are also less expensive to purchase and operate.
Single-stand reversing cold mills
Depending on the product mix, a single-stand cold rolling mill can deliver rolling capacities of 100,000 to 400,000 t/a. Rolling schedules can be carried out with an even or odd number of passes to maximize mill availability and performance. The Universal Crown Control mill (UCM mill) with work roll bending, intermediate roll bending, intermediate roll shifting and all straight roll application ensure enhanced flatness control. Also strip flatness measuring equipment mounted at one or both ends of the mill combined with multi-zone work-roll cooling to meet the highest demands for flatness.
Two-stand reversing cold mills
Primetals Technologies' two stand reversing cold mills combine the flexibility of single-stand reversing mills with the capacity of conventional coil-to-coil tandem mills at substantially reduced investment costs. Steel rolled in two-stand reversing cold mills is suitable for a wide range of applications, offering the best possible performance in terms of quality and productivity. A two-stand reversing cold mill can deliver capacities between 300,000 t/a of thin-gauge products or 1,000,000 t/a and more of thicker-gauge products.
Fig.1- Single stand reversing mill | Fig.2- Two-stand reversing mill
Main benefits of Primetals Technologies' reversing cold mills
- High production capacity and yield
- Flexible, low-cost rolling of a wide range of products, especially for small order lots
- Tight strip thickness and shape tolerances
- Minimum off-gauge length
- High surface quality
- Second stand can serve as a skin pass mill
Fig.3- Limitations of a 4-high mill on strip flatness | Fig.4- Advantages of 6-high Universal Crown Control Mill (UCM) on strip flatness
The HYPER UC-MILL is newly developed to achieve high performance of strip gauge and flatness control for High Strength Steel (HSS) rolling. This technology is also applicable for rolling high grades of non-grain oriented silicon steel and thin products. The technology development is based on the following concepts:
- Optimized roll diameter combination (small work, intermediate and back-up rolls)
- 'Work Roll Driven System' to achieve high flatness controllability
- Development of a high strength small diameter spindle to drive the work roll
Main Feature of HYPER UC-MILL
Optimized Combination of Work, Intermediate and Back-up Rolls
When investigating the selection of roll diameter, there are two major limitations: load limit to maintain good strip flatness and load limit due to the contact stress between the rolls. The graph shows the relationship between these limits. The hatched part is the maximum allowable rolling force. The graph also shows the calculated reduction ratio at the maximum allowable load. The graph shows that the HYPER UC-MILL covers the range of the highest achievable reduction; (Work Roll Diameter)/(Strip Width) = 0.18 - 0.24
Fig.5- Main Feature of HYPER UC-MILL | Fig.6- Comparison of work-roll diameters in a standard UCM and Hyper UCM
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.
Maanshan Iron & Steel, China
Type of Plant:
Reversing Cold Mill
0.35 ~ 0.65 mm
900 mm ~ 1,280 mm