A Pickling Line and Tandem Cold Mill (PLTCM) is an integrated production line used in steel cold rolling. It combines hot-rolled strip pickling with multi-stand tandem cold rolling to remove surface oxide scale and reduce strip thickness in a continuous process.
Compared with separate pickling and cold rolling lines, a PLTCM reduces intermediate coil handling, storage, and repeated strip threading. This arrangement can improve production efficiency and material yield. Typical products include automotive steel, appliance steel, and other cold-rolled strip products requiring tight dimensional tolerances and good surface quality.
The following sections cover the production process, main equipment, technical features, project examples, and current areas of development.
Production process of a PLTCM
A PLTCM connects the pickling and cold rolling processes. During production, the strip passes through uncoiling, welding, scale removal, pickling, rinsing, edge trimming, and continuous rolling before being wound into a finished coil.
Depending on the line layout, the equipment is commonly divided into five sections: entry, pickling, side trimming, tandem rolling, and exit. Some designs group the side trimming equipment into the pickling process section or the rolling mill entry area.
Entry section: uncoiling, shearing, and welding
The entry section handles hot-rolled coil loading, uncoiling, and strip joining. It prepares the strip for continuous pickling and rolling.
A coil car transfers the hot-rolled coil to the uncoiler. After uncoiling, pinch rolls feed the strip head into a straightening device to correct coil set. A double-cut shear removes irregular head and tail sections. A flash-butt or laser welding machine then joins the tail of the preceding coil to the head of the next coil.
After welding, the strip enters the entry looper. The looper stores a certain length of strip so that the downstream pickling and rolling sections can continue operating while a new coil is being loaded and welded at the entry.
Some lines also use a tension leveler or scale breaker. Mechanical deformation helps crack the oxide scale and improves contact between the pickling solution and the scale.
Pickling section: removing surface oxide scale
Hot-rolled strip develops oxide scale during high-temperature rolling and cooling. The pickling section removes this scale through chemical reactions between the acid solution and the oxides on the strip surface.
Hydrochloric acid is commonly used for continuous pickling of carbon steel strip. Depending on the equipment design, the line may use shallow-tank pickling or turbulent pickling. Acid concentration, temperature, flow conditions, and strip speed are controlled to maintain stable pickling performance.
After pickling, the strip passes through rinsing tanks to remove residual acid. A hot-air dryer then removes water from the strip surface.
Some lines also have an acid regeneration system to recover usable acid components from spent acid, reducing fresh acid consumption and waste acid discharge.
Side trimming section: controlling strip width
After pickling and rinsing, the strip enters the trimming equipment according to the required product width.
Rotary side trimmers remove excess material from both strip edges to achieve the specified width for subsequent rolling and product requirements. The trimmed scrap is usually processed by a scrap chopper for collection and recycling.
Some advanced lines use turret-type rotary side trimmers, which allow online blade changes according to production requirements and reduce downtime associated with blade replacement.
Tandem mill section: multi-stand continuous cold rolling
The trimmed strip enters the tandem mill, where multiple rolling stands progressively reduce its thickness and control its flatness and surface quality.
The number and type of stands depend on the product range and rolling schedule. Four-high, six-high, and other multi-roll configurations can be used. The number of stands is selected according to production capacity, incoming strip thickness, and finished product specifications.
Each stand receives power from its main drive system. The tension control system coordinates the speed relationship between adjacent stands. Hydraulic AGC (Automatic Gauge Control) adjusts the roll gap according to feedback from thickness gauges and rolling force measurements to maintain the required strip thickness.
For products with demanding flatness requirements, the mill may also use work roll bending, intermediate roll bending, and intermediate roll shifting. These actuators work with the AFC (Automatic Flatness Control) system to regulate elongation distribution across the strip width.
An emulsion or rolling oil supply system provides lubrication and cooling to the rolls and strip during rolling.
Exit section: coiling, unloading, and inspection
After the final rolling stand, the strip passes through exit guides and enters the coiler.
The coiler applies the required winding tension according to strip thickness, width, and production conditions, forming a properly wound coil. Some lines use a flying shear and drum-type coiler arrangement to support continuous operation and different coil cutting requirements.
After coiling, a coil car transfers the finished coil to the exit handling equipment for weighing, identification, and quality inspection.
Full-hard coils produced by a PLTCM may enter separate downstream lines according to product requirements. These can include batch annealing, continuous annealing, galvanizing, skin passing, or recoiling and inspection. Such processes are not necessarily part of the PLTCM itself.
Main equipment of a PLTCM
A PLTCM integrates several systems for pickling, cold rolling, drive control, and auxiliary operation. The exact equipment configuration varies between production lines.
Pickling equipment
The pickling section removes oxide scale from hot-rolled strip. Its main equipment includes:
Uncoilers and pinch rolls for coil unwinding and strip feeding.
Shears for trimming irregular strip head and tail sections.
Welding machines for joining successive coils.
Tension levelers or scale breakers for improving oxide scale cracking before pickling.
Pickling tanks and circulation systems for supplying acid and controlling temperature, concentration, and flow.
Rinsing equipment for removing residual acid from the strip surface.
Hot-air dryers for removing water after rinsing.
Acid regeneration and exhaust gas treatment equipment for spent acid processing, acid recovery, and environmental control.
Rolling mill equipment
The rolling mill performs thickness reduction and strip flatness control. Its main components include multiple rolling stands, roll assemblies, screwdown mechanisms, and measurement devices.
Depending on the product requirements, four-high or six-high stands can be used. For high-strength steel and precision strip products, the mill may also require roll bending, shifting, and profile control systems designed around the rolling load and flatness requirements.
Main equipment includes:
Work rolls and backup rolls or intermediate rolls.
Roll chocks, bearings, and mill housings.
Hydraulic screwdown systems and AGC.
Work roll and intermediate roll bending systems.
Axial roll shifting mechanisms.
Thickness gauges, tension measuring devices, and flatness inspection equipment.
Emulsion supply and rolling lubrication and cooling systems.
Main drive system
The main drive system supplies the rolling power to each stand. It generally consists of electric motors, variable-frequency drives, reducers, pinion stands, and drive spindles.
Modern PLTCMs commonly use AC variable-frequency drive systems. Motor speed and torque are adjusted according to the requirements of each rolling pass.
The drives of adjacent stands must also maintain coordinated speed and tension control. Poor speed matching can cause strip tension fluctuations, strip breakage, or unstable rolling.
Automation and control system
A PLTCM generally uses a two-level automation architecture consisting of L1 basic automation and L2 process control.
L1 handles equipment sequencing, speed regulation, tension control, looper control, welding sequences, and real-time functions such as AGC.
L2 manages production schedules and material data, calculates rolling schedules, operates pickling process models, sets thickness and flatness targets, optimizes process parameters, and analyzes production quality.
Data exchange between the two levels coordinates the operating speed of the pickling and rolling sections and allows rolling parameters to be adjusted according to material specifications and production requirements.
Auxiliary equipment and utility systems
To maintain continuous production, a PLTCM also requires auxiliary equipment and supporting utility systems, including:
Entry and exit loopers and tension bridles.
Uncoilers, coilers, and coil transfer cars.
Entry and exit flying shears, rotary side trimmers, and scrap choppers.
Hydraulic and lubrication systems.
Emulsion and cooling systems.
Acid circulation and regeneration systems.
Acid fume collection and exhaust treatment systems.
Water supply, drainage, and compressed air systems.
Technical features of a PLTCM
Directly connecting pickling and cold rolling offers advantages in production organization, material handling, and automation control.
Higher production efficiency through reduced intermediate handling
In a conventional arrangement with separate lines, hot-rolled coils are first processed on a pickling line and then transferred to the cold rolling mill for further reduction.
A PLTCM connects the two processes directly, reducing intermediate coil lifting, storage, and repeated threading. By using welding equipment and loopers to manage coil changes at the entry section, the pickling and rolling sections can continue operating during entry-side coil replacement. This improves line availability and production efficiency.
Improved strip surface and dimensional quality
The pickling section removes oxide scale from hot-rolled strip, reducing the risk of residual oxides affecting the rolls and strip surface during cold rolling.
The tandem mill uses AGC, tension control, and flatness control systems to coordinate the rolling stands and regulate strip thickness, transverse thickness distribution, and flatness.
The direct connection between pickling and rolling also reduces the chance of secondary contamination during intermediate coil handling and storage.
Coordinated process control
The pickling and rolling sections exchange production data through the L1 and L2 systems. The line can adjust speed, tension, and rolling schedules according to strip specifications, material properties, and production plans.
For example, when incoming strip thickness, steel grade, or production speed changes, the process control system can coordinate the operating parameters of the pickling and rolling sections to reduce disruptions caused by poor process matching.
Acid recovery and resource management
The pickling process generates spent acid, acid fumes, and rinse wastewater. Acid circulation, spent acid regeneration, multi-stage rinsing, and exhaust treatment help improve acid utilization and reduce acidic waste discharge and pollutant emissions.
The emulsion circulation and oil mist collection systems in the rolling section also help reduce rolling medium consumption and oil mist emissions. Actual resource consumption and environmental performance depend on equipment configuration and operating practices.
PLTCM project examples
Several cold rolling projects in China use integrated pickling and tandem rolling arrangements. Their equipment configurations vary according to product range and production capacity.
Ningxia Jianlong cold rolling project
On June 6, 2023, the PLTCM at the Ningxia Jianlong cold rolling project successfully completed its hot-load commissioning on the first attempt. The first coil met the stated requirements for strip thickness, flatness, and surface quality.
The related cold-rolled product project has an annual production capacity of 800,000 tonnes. Its product range includes galvanized strip measuring 0.5 to 2.5 mm in thickness and 375 to 525 mm in width, as well as zinc-aluminum-magnesium coated strip measuring 1.5 to 4.0 mm in thickness and 375 to 525 mm in width.
These products are intended mainly for pipe manufacturing, cold-formed sections, photovoltaic mounting structures, and other corrosion-resistant structural applications.
Jingye Group 1450 mm PLTCM, Phase II
On May 31, 2023, the 1450 mm PLTCM project for Phase II of Jingye Group's cold rolling facility successfully completed its hot-load commissioning on the first attempt.
The line uses a five-stand six-high tandem cold mill and has a designed annual production capacity of 1.4 million tonnes. The product thickness range is 0.2 to 2.5 mm, with strip widths ranging from 750 to 1300 mm.
The entry speed is 600 m/min, the pickling process speed is 240 m/min, and the mill exit speed is 1500 m/min.
The pickling section uses shallow-tank intensive turbulent pickling and five-stage cascading counter-current rinsing. The line is also equipped with a turret-type rotary side trimmer that allows online blade replacement. A high-speed flying shear and Carrousel coiler are installed at the mill exit to support strip cutting and stable coiling.
MaSteel 1720 pickling tandem mill
The 1720 pickling tandem mill at MaSteel's cold rolling facility uses an integrated pickling and tandem rolling arrangement. Public project documentation lists its designed annual production capacity as 1.55 million tonnes.
Its rolling section uses a four-stand six-high tandem mill. The pickling section adopts a four-stage shallow-tank counter-current pickling arrangement.
The production process includes coil loading, strip welding, looper storage, pickling, rinsing, drying, edge trimming, continuous rolling, and exit coiling.
The line is also equipped with an acid regeneration system to process spent acid and recover reusable acid for the pickling operation.
Technical development of PLTCM systems
As cold-rolled product specifications and quality requirements become more demanding, PLTCM upgrades increasingly focus on process models, automated inspection, and resource utilization.
Process models and automation
Integrating material data, rolling models, pickling parameters, and production status through the L2 process control system allows the mill to optimize interstand tension, rolling speed, roll gap, and pickling conditions. This also reduces the need for manual intervention.
Online inspection and quality tracking
Laser speed meters, thickness gauges, flatness gauges, and surface defect inspection systems collect production and quality data during rolling. Linking inspection results to individual coil production records helps identify defect locations, analyze quality variations, and provide material information for downstream processing.
Energy efficiency and environmental improvements
Acid regeneration, rinse water recycling, rolling oil filtration, and oil mist treatment help reduce resource consumption and pollutant emissions during pickling and rolling. Heat recovery and drive system efficiency improvements are also areas for production line upgrades.
Equipment maintenance and operating optimization
Monitoring the operating condition of motors, gearboxes, roll bearings, hydraulic systems, and lubrication equipment helps identify abnormal vibration, temperature rise, and pressure changes. Maintenance can then be scheduled according to actual equipment conditions, reducing unplanned downtime.
A PLTCM integrates surface treatment and cold rolling within one production line. Its operating performance depends on coordination between pickling quality, rolling accuracy, drive control, and auxiliary systems. Drive connectors, mounting brackets, and other non-standard mechanical components used throughout the line must also meet the required dimensional and assembly specifications. We provide custom precision machining based on customer drawings. Hansheng Automation manufactures custom mechanical components for rolling equipment, non-standard parts for tobacco and packaging machinery and filling equipment, as well as precision structural components for yacht equipment and remote-controlled racing cars.
