Line 02
Reversing Cold Rolling Mills (CRM & TCRM)
Single-stand (CRM) and tandem (TCRM) reversing mills that reach the target gauge through controlled passes, with hydraulic gauge and flatness control.
- Single-stand (CRM) and tandem (TCRM)
- 30,000 – 300,000 t/yr
- Width 600 – 1,550 mm
- Carbon / silicon / stainless / HSLA
The core unit of cold rolling
In a reversing mill the strip passes back and forth through the same stand, so the reduction is built up over several passes instead of across a long train of stands. That is what makes the configuration suitable for medium output, mixed products and specialty grades.
Starting from pickled hot-rolled coil, the mill brings strip down to the target gauge with controlled thickness, flatness and surface — ready for annealing, galvanizing, coating or direct sale.
- Coil entry from the pickling line, 1.5 – 6.0 mm
- Exit gauge 0.15 – 2.5 mm depending on stand design
- Pass schedule matched to grade and final properties
Thickness precision
Hydraulic gauge control holds the pass schedule and corrects deviation while the strip is in the mill.
Flatness control
Bending, tilting and roll shifting act on the shape measured across the strip width.
Product flexibility
Widths, gauges and grades change on the same stand through the pass schedule and roll set.
A lower entry point
For the same product range, a reversing mill needs less capital than a continuous tandem line.
When a reversing mill is the right choice
Reversing mills sit between the small job shop and the continuous tandem line. They suit plants where the product mix moves, the batch size is moderate or the materials need dedicated rolling schedules.
| Scenario | Why it fits |
|---|---|
| Medium-scale cold rolling, 30,000 – 300,000 t/yr | Lower capital outlay than a comparable continuous tandem line |
| Multi-product, short-run output | Quick roll changes and flexible scheduling for frequent grade or width changes |
| Value-added materials | Silicon, stainless and precision strip that need dedicated rolling schedules |
| New plants and developing regions | Proven technology with a moderate capital entry point and straightforward maintenance |
| Complement to a tandem mill | Handles thick gauges, small batches and specialty alloys |
Single-stand and tandem configurations
The single-stand mill performs every reduction in one stand. The tandem reversing mill puts two stands in series, so each traverse applies two reductions and the strip needs fewer passes.
| Single-stand (CRM) | Tandem (TCRM) | |
|---|---|---|
| Configuration | One 4-high or 6-high stand; strip reverses through the stand | Two stands in series; two reductions per traverse |
| Typical passes | 5 – 9 passes | 3 – 5 passes |
| Annual capacity | 30,000 – 150,000 t/yr | 100,000 – 300,000 t/yr |
| Total reduction | 50% – 85% | 60% – 88% |
| Capital cost | Lower | Medium — below a continuous tandem mill |
| Space | Moderate; coilers on both sides of the stand | Larger |
| Best suited for | Small to medium scale, multi-product, compact site | Medium to large scale, stable product mix, higher throughput |
Roll configurations
Roll diameter and stand design follow the gauge range and the material. Four-high is the standard configuration; six-high and twenty-high extend flatness control and thin-gauge capability.
| Mill type | Thickness range | Materials | Characteristics |
|---|---|---|---|
| 4-high reversing mill | 0.3 – 3.0 mm | Carbon and low-alloy steel | Simplest design, lowest cost, most widely used |
| 6-high reversing mill (HC / UC) | 0.15 – 2.5 mm | Carbon, silicon and stainless steel | Better flatness control for wide strip and hard materials |
| 20-high reversing mill | 0.05 – 1.0 mm | Precision strip, silicon and stainless steel | Ultra-thin gauges and extreme precision; higher investment |
| 6-high with intermediate roll shift | 0.15 – 2.5 mm | Wide strip needing advanced flatness control | Flatness capability between standard six-high and twenty-high |
Roll configuration is recommended from the target product mix: grades, gauge range, width and quality requirement.
Technical specifications
The range below covers 4-high and 6-high reversing mills. Capacity depends on the pass schedule and the maximum line speed agreed for the product mix.
| Parameter | Range | Notes |
|---|---|---|
| Annual capacity | 30,000 / 50,000 / 80,000 / 100,000 / 150,000 t (CRM); 150,000 – 300,000 t (TCRM) | Depends on passes and speed |
| Entry thickness | 1.5 – 6.0 mm, pickled hot-rolled coil | Thicker entry needs more passes |
| Exit thickness | 0.15 – 2.5 mm | Thinner gauges need additional passes |
| Strip width | 600 – 1,250 mm, up to 1,550 mm | Wider strip needs higher rolling force |
| Max rolling force | 8 – 25 MN (4-high) / 12 – 30 MN (6-high) | Depends on material strength |
| Max rolling speed | 300 / 500 / 800 / 1,000 m/min | Higher speeds need larger motors and more cooling |
| Pass reduction | 15% – 40% per pass | First pass up to 40%, final passes reduced |
| Total reduction | 50% – 88% | Softer materials allow higher total reduction |
| Thickness tolerance | ≤ ± 0.005 – ± 0.010 mm | With AGC in closed loop |
| Flatness tolerance | 5 – 10 I-units | With AFC in closed loop |
| Main motor power | 1,000 – 3,000 kW per stand | TCRM has two motors |
| Work roll diameter | 300 – 500 mm | Set by rolling force requirement |
| Backup roll diameter | 800 – 1,300 mm | Set by rolling force requirement |
| Approx. footprint | 800 – 2,000 m² (CRM) / 1,500 – 3,500 m² (TCRM) | Includes auxiliary equipment |
How the passes work
Reduction is planned as a pass schedule. Each pass takes a share of the total reduction and the coiler alternates sides as the strip reverses through the stand.
Pass schedule example — 3.0 mm to 0.50 mm on a single stand
| Step | Thickness | Coiler |
|---|---|---|
| Entry coil | 3.0 mm | — |
| Pass 1 | 2.4 mm | Left |
| Pass 2 | 1.9 mm | Right |
| Pass 3 | 1.5 mm | Left |
| Pass 4 | 1.2 mm | Right |
| Pass 5 | 0.95 mm | Left |
| Pass 6 | 0.75 mm | Right |
| Pass 7 | 0.60 mm | Left |
| Pass 8 | 0.50 mm | Exit coil |
The schedule is calculated for the grade and entry gauge, and adjusted when thickness or hardness deviates from the model.
Control during rolling
The passes only hold if tension, speed and roll gap stay coordinated. These functions are specified together with the mechanical scope rather than added at commissioning.
| Function | Technology | Purpose |
|---|---|---|
| Pass schedule calculation | Reduction, force, torque and power computed per pass | Stable rolling without slipping or strip breaks |
| Tension control | Entry and exit reelers hold constant unwinding and rolling tension | Keeps the strip centred and supports flatness |
| Speed control | Gradual acceleration and deceleration per pass | Smooth bite-in and tail-out |
| Roll gap setting | Hydraulic preset for the target pass thickness | AGC corrects from there |
| Emulsion cooling | Spray onto the deformation zone | Cools rolls, reduces friction, cleans the surface |
| Flatness measurement | Shape roll measures transverse tension | Feeds tilt, bending and shifting corrections |
Gauge and flatness control
Thickness and flatness are held by two closed loops: AGC acts on the roll gap, AFC acts on the roll profile. Both are tuned against the pass schedule agreed at specification stage.
- Hydraulic gauge control response ≥ 20 Hz
- Displacement transducers with 0.001 mm resolution
- Thickness gauges (X-ray or isotope) accuracy ≤ ± 0.2%
- PLC platform agreed with the plant standard
Gauge control modes
| Mode | Principle | Typical role |
|---|---|---|
| Feed-forward (FF-AGC) | Measures entry deviation and adjusts the gap in advance | Where entry thickness varies |
| Feedback (FB-AGC) | Measures exit deviation and corrects the gap | Primary thickness control |
| Absolute AGC | Targets an absolute value to remove cumulative error | Head and tail sections |
| Monitoring AGC | Closed-loop correction from the exit gauge signal | Final thickness accuracy |
| Tension-thickness decoupling | Holds thickness while tension fluctuates | Acceleration, deceleration and reversal |
Flatness control actuators
| Method | Function | Actuator |
|---|---|---|
| Tilt control | Corrects edge wave by adjusting the gap difference across the stand | Hydraulic cylinder pressure |
| Positive bending | Increases work roll crown to correct centre buckle | Bending cylinders |
| Negative bending | Reduces work roll crown to correct edge wave | Bending cylinders |
| Roll shifting (6-high) | Shapes the gap by moving the intermediate rolls axially | Servo cylinders |
A shapemeter measures transverse tension distribution and closes the loop on all flatness actuators.
Mill stand components
Housing stiffness and roll assembly accuracy set the ceiling for what the control system can hold, so both are part of the mechanical specification.
| Component | Function | Detail |
|---|---|---|
| Mill housing | Carries the rolling force | Closed housing, monoblock cast or welded; stiffness ≥ 5,000 kN/mm |
| Work rolls | Contact the strip and impose the reduction | Forged steel, high-chromium cast iron or high-speed steel |
| Backup rolls | Support the work rolls and distribute force | Forged or alloy cast steel |
| Screw-down | Adjusts the roll gap | Hydraulic servo for fast response with electric coarse adjustment |
| Roll bending | Adjusts work roll crown | Positive and negative bending cylinders |
| Roll shifting (6-high) | Moves intermediate rolls axially | Servo controlled, position accuracy ± 0.1 mm |
| Main drive | Provides rolling torque | DC or AC variable-frequency motor with gearbox |
Automation hierarchy
Automation is split into three levels so that equipment control, process models and operator supervision stay separable during commissioning and later upgrades.
| Level | Function | Content |
|---|---|---|
| L1 — basic automation | Equipment-level control | Speed, tension, position and sequence control with safety interlocks |
| L2 — process control | Process optimisation | Rolling schedule models, adaptive learning and pass optimisation |
| HMI — operator interface | Monitoring and operation | Graphical interface, trends, alarm logging and production reports |
What changes the result
Two mills with the same tonnage can produce different strip. The difference usually sits in these six areas, and each is a choice made at specification stage.
| Aspect | Basic configuration | Enhanced configuration |
|---|---|---|
| Gauge control | Electric screw-down with manual correction | Hydraulic AGC in closed loop |
| Flatness | Operator-adjusted bending | Shapemeter with automatic AFC |
| Pass scheduling | Operator experience | L2 model-based schedule with adaptive learning |
| Emulsion | Single flow | Zone spray with flow control |
| Roll change | Manual, several hours | Roll change cart, under 30 minutes |
| Automation | Dispersed controls | Centralised HMI with an automatic rolling sequence |
Materials and applications
Silicon and stainless grades need different schedules and roll sets from carbon steel, so the material list is reviewed before the stand configuration is fixed.
Suitable materials
| Material | Representative grades | Entry | Exit | Difficulty |
|---|---|---|---|---|
| Carbon steel | ASTM A1008 / EN DC01 / JIS SPCC | 2.0 – 4.0 mm | 0.2 – 2.0 mm | Low |
| Quality carbon steel | ASTM A1011 / EN C45 / JIS S50C | 2.0 – 4.0 mm | 0.3 – 2.0 mm | Medium |
| HSLA steel | ASTM A572 / EN S420 / JIS SPA-H | 2.0 – 4.0 mm | 0.4 – 2.0 mm | Medium to high |
| Silicon steel | Non-oriented / grain-oriented | 2.0 – 2.5 mm | 0.15 – 0.65 mm | High — brittle |
| Stainless steel | ASTM 304 / 430 / 201 | 2.0 – 4.0 mm | 0.2 – 2.0 mm | High — work hardening |
| Deep-drawing steel | EN DC04 / DC06 / IF steel | 2.0 – 3.5 mm | 0.4 – 1.5 mm | Medium |
| Precision strip | High-tolerance cold-rolled strip | 1.5 – 2.5 mm | 0.05 – 0.5 mm | Very high |
End-product applications
| Industry | Applications |
|---|---|
| Appliances | Refrigerator panels, washing machine shells, air conditioner housings, microwave cavities |
| Automotive | Underbody panels, wheel housings, interior components, fuel tank shields, seat rails |
| Construction | Light-gauge framing, C and Z purlins, galvanizing and colour coating substrate |
| Metal packaging | Drums, containers, can body sheet |
| Hardware | Shelving, tool chests, electrical cabinets, cable trays |
| Precision industry | Motor laminations, precision stamping parts |
Standard scope of supply
The line is supplied as one sequence from entry to exit, with instrumentation and the emulsion system included rather than left to site supply.
| Module | Included equipment | Engineering detail |
|---|---|---|
| Entry section | Double-cone uncoiler, pinch leveler, crop shear; entry looper on TCRM | Stable unwinding tension for heavy coils |
| Mill stand | Closed housing, work and backup rolls, bearing chocks | Precision-machined housing and roll assembly |
| Screw-down | Hydraulic cylinders with servo valves, electric worm gear | Fast response and accurate positioning |
| Bending and shifting | Positive and negative bending cylinders, shifting servos | Wide flatness adjustment range |
| Main drive | Main motor, gearbox, universal spindles | Gearbox supplier agreed with the plant |
| Reeling system | Left and right reelers, bridle rolls | High-tension coiling with constant tension control |
| Auxiliary equipment | Entry and exit thickness gauges, shapemeter, tensiometers, encoders | High-precision instrumentation |
| Emulsion system | Circulation tank, filtration, cooling, spray headers | Multi-stage filtration |
| Hydraulic system | Pumps, valves, accumulators | Stable pressure, contamination resistant |
| Electrical and automation | PLC, HMI, AC drives, field panels | Platform per plant standard |
| Quick roll change | Roll change cart, rails, auxiliary hydraulics | Complete roll change under 30 minutes |
Optional add-on systems
| System | Function | Benefit |
|---|---|---|
| Roll grinding machine | On-line or off-line grinding of work and backup rolls | Maintains roll surface and extends roll life |
| Magnetic emulsion filtration | Removes iron fines from the emulsion | Better cooling and cleaner strip surface |
| On-line roughness measurement | Measures strip surface roughness | Controls surface quality in production |
| Roll thermal spray | Sprays cooling water onto the work rolls | Limits thermal expansion and supports flatness |
Support after handover
Spare parts, retrofit work and remote diagnostics continue after the warranty period. Common requests are listed below.
- Rolling force, tension, thickness and flatness data uploaded in real time
- Roll wear prediction and roll change scheduling
- Equipment health monitoring with vibration and temperature trends
- Remote parameter optimisation and rolling schedule sync
- Mobile dashboard with alerts and production reporting
Typical spare parts
| Part | Application | Detail |
|---|---|---|
| Work rolls | Mill stand | Ground to the roll specification |
| Backup rolls | Mill stand | Ground to the roll specification |
| Roll bearings | Work and backup rolls | Four-row or oil-film type |
| Universal spindles | Main drive | Cross-pin type, various sizes |
| Hydraulic cylinder seals | Screw-down and bending | Full sets |
| Emulsion nozzles | Cooling system | Various spray angles |
| Filter elements | Hydraulic and emulsion systems | 3 – 5 μm and 10 – 20 μm ratings |
| Gauge parts | Thickness gauges | Ion chambers or X-ray tubes matched to the gauge |
| Load cells | Tension measurement | Matched to the existing system |
Retrofit options
| Retrofit | Scope | Typical driver |
|---|---|---|
| AGC upgrade | Electric or manual screw-down to hydraulic AGC | Thickness tolerance not met |
| L2 process control | Model-based scheduling with adaptive learning | Product consistency depends on the operator |
| Main motor upgrade | Higher power motor with drive upgrade | Capacity increase |
| Quick roll change | Roll change cart and rails | Long roll change times |
| Emulsion upgrade | Magnetic and precision filtration with temperature control | Surface quality and roll wear |
| Remote monitoring | Data acquisition, cloud platform and mobile app | Remote site with limited technical staff |
Configuration inputs
What we need to specify this line
- 01Strip grades and target mechanical properties
- 02Entry and exit thickness
- 03Width and coil weight
- 04Output target and the CRM or TCRM choice
Questions
Questions we hear on this line
When is a tandem reversing mill worth the extra investment?
When the product mix is stable and output sits above roughly 150,000 t/yr. Two stands cut the number of passes and raise throughput, at the cost of a larger footprint and a higher capital outlay.
Can gauge control be added to an existing mill?
Often yes, provided the stand, screw-down and drive condition are checked first. A hydraulic AGC retrofit is usually combined with roll and emulsion changes so the new control has something to work with.
How is flatness verified?
Shape is measured across the strip during commissioning and compared with the agreed I-unit target. The measurement points and acceptance method are written into the configuration document.
Related terms
What engineers search for on this line
- reversing mill
- cold rolling mill
- single-stand reversing mill
- tandem reversing mill
- CRM
- TCRM
- cold rolling equipment
- reversing cold mill
- automatic gauge control
Other lines
Sections planned in the same scope
Pickling Lines (PPL & CPL)
Turnkey push-pull and continuous pickling lines for hot-rolled strip, covering scale breaking, acid pickling, rinsing, fume treatment and acid regeneration.
Continuous Hot-Dip Galvanizing Line
Turnkey continuous hot-dip galvanizing lines for GI, 55% Al-Zn and Al-Zn-Mg coatings, from cleaning and annealing through the zinc pot, skin-pass and chemical treatment.
Continuous Color Coating Line (CCL)
Turnkey colour coating lines for prepainted steel: 2C2B and 3C3B configurations, PE to PVDF coating systems and RTO fume treatment in one scope.
Planning a new line or an upgrade?
Send the product mix and target capacity, and we will review the configuration.