4-Hi 850mm four-high reversible cold rolling mill
1. Equipment Overview
This is a 4-Hi 850mm four-high reversible cold rolling mill, manufactured by Jiangsu Nanbao in 2018 and still in normal operation. This is a professional-grade stainless steel cold rolling mill, specifically designed for high-precision cold rolling of stainless steel strips, suitable for precision rolling of various stainless steel series including SUS 201, SUS 304, and SUS 430. The 850mm width specification places it in the medium category for stainless steel cold rolling, balancing production efficiency and product flexibility.
2. Manufacturer Background
Jiangsu Nanbao is a well-known enterprise in China's metallurgical equipment manufacturing sector, with extensive engineering experience and technical expertise in the R&D and production of stainless steel cold rolling mills, reversible mills, temper mills, and related equipment. The Nanbao brand enjoys high market recognition in the stainless steel processing industry, with products known for high cost-effectiveness and stable operation.
3. Core Highlights — Still in Operation + Recent Manufacturing Year
This equipment was manufactured in 2018 and is still in normal operation, with approximately 8 years of actual service. In cold rolling equipment, 8 years represents the youth phase of the equipment lifecycle, far superior to commonly available second-hand equipment with 15-25 years of service age. This means:
Minimal mechanical wear: Main structures (housings, roll bearing chocks, gearboxes, etc.) have very little wear, approaching new-machine condition;
Virtually no electrical system aging: DC motors, Siemens electrical control system, PLC, etc. remain in their golden phase;
Precision retention close to factory-new levels: Core indicators such as roll gap accuracy, shape control, and thickness tolerances have degraded minimally;
Extremely long remaining service life: Can continue service for 15-20+ years;
Equipment still in operation: Buyers can arrange on-site trial runs with actual materials before dismantling, directly verifying all performance indicators.
4. Main Motor System — Dual Motor High-Power Drive
The mill is equipped with 2 main motors, model Z560-3A, each rated at 750kW, with a speed range of 519/1200 r/min, for a combined total of 1500kW. Dual motor drive is the standard configuration for reversible mills—during the reversing rolling process, the strip passes through the mill in multiple passes, with the coiler and uncoiler swapping roles after each pass, requiring two independent drive systems. The symmetrical configuration of 2 x 750kW motors ensures balanced power delivery in both rolling directions, with 1500kW total power representing an ample configuration for stainless steel rolling, sufficient to handle the high deformation resistance of stainless steel.
5. Recoiler and Uncoiler Systems
The recoiler and uncoiler are equipped with a Z560-5B motor with a power rating of 900kW and a speed range of 450/1200 r/min. The 900kW recoiler/uncoiler motor power exceeds the single main motor power (750kW), reflecting the extremely high tension control requirements of stainless steel rolling—stainless steel rolling requires very high recoiling tension to ensure tight coil shape and stable inter-pass tension. The coiling method adopts a solid drum, offering simple and reliable construction with strong load capacity, suitable for the high-tension coiling requirements of stainless steel strips.
6. Mill Type — 4-Hi Four-High Mill
This equipment is a 4-Hi (four-high) cold rolling mill, consisting of 2 small-diameter work rolls and 2 large-diameter backup rolls. The 4-Hi configuration is the mainstream choice for cold rolling of stainless steel, maintaining excellent shape and thickness accuracy under the high deformation resistance of stainless steel.
7. Roll Systems
Work Roll: Specification Φ165×900mm—roll diameter 165mm, barrel length 900mm. The small-diameter work rolls help reduce rolling force, enable thin-gauge rolling, and ensure strip surface quality;
Backup Roll: Specification Φ730×850mm—the large-diameter backup rolls provide robust support to the work rolls, reducing work roll bending deflection under immense rolling forces, ensuring shape precision and thickness consistency;
Screw-down System: Adopts AGC (Automatic Gauge Control) hydraulic screw-down—featuring fast response and high control precision, capable of real-time roll gap detection and adjustment during high-speed rolling, ensuring that thickness tolerances of finished strips are controlled within extremely tight limits across the entire length.
8. Designed Rolling Parameters
Designed rolling material: SS (Stainless Steel) , covering common stainless steel series including SUS 201, SUS 304, and SUS 430;
Maximum designed input thickness (entry): 3.0mm;
Minimum designed finished thickness (exit): 0.25mm—rolling from 3.0mm to 0.25mm represents a total reduction of 91.7%;
Maximum designed rolling width: 780mm—with work roll barrel length of 900mm, the effective rolling width of 780mm leaves sufficient margin;
Actual maximum rolling width used by the original owner: 780mm—consistent with design;
Actual maximum input thickness used by the original owner: 3.0mm—consistent with design;
Actual minimum finished thickness used by the original owner: 0.2mm—the actual minimum thickness of 0.2mm is superior to the design value of 0.25mm, indicating equipment capability margin;
Maximum rolling speed: 300m/min;
Maximum rolling force: 12000kN (approximately 1200 metric tons of force).
9. Maximum Rolling Force — 12000kN Ultra-Strong Guarantee
The 12000kN (approximately 1200 tons of force) maximum rolling force is one of the most outstanding performance indicators of this equipment. In stainless steel cold rolling equipment, this value represents an extremely high configuration. For comparison, the previously described 980mm stainless steel mill has a maximum rolling force of 1400 tons (approximately 13720kN), but that is designed for wider specifications (900mm) and thicker input material (5.0mm). For the 850mm width and 3.0mm entry thickness specification, the 12000kN (1200 tons) rolling force configuration is more than sufficient, ensuring ample deformation capability when rolling thick stainless steel materials and high-strength grades, maintaining stable thickness accuracy and shape quality over the long term.
10. Recoiler/Uncoiler Motor Power — 900kW Advantage
The 900kW recoiler/uncoiler motor power stands out particularly against the main motor power (750kW×2=1500kW). This configuration of"relatively higher recoiling power"has special significance in stainless steel reversible mills:
Stainless steel rolling requires extremely high tension between passes to ensure shape and prevent strip deviation;
The 900kW recoiling power ensures stable recoiler operation under high-tension, high-speed rolling conditions;
High-power recoiling also means the equipment can handle heavier mother coils, reducing coil change frequency and improving production efficiency.
11. Electrical Control System — Siemens Brand Guarantee
The mill's electrical control system is supplied by Siemens, a globally leading brand in industrial automation and drive control, with world-class technology in stainless steel cold rolling control. According to the technical data sheet, the electrical control system is in good condition (Yes) with no missing components—meaning the mill's automation control system, drive control system, AGC, PLC, sensors, and associated equipment are all complete and functional.
12. Spare Parts — Exceptionally Ample Inventory
The extensive spare parts included with this equipment represent the single greatest added-value highlight of this procurement. For second-hand buyers, this means virtually no additional spare parts procurement for years after commissioning:
| Spare Part | Quantity | Value Analysis |
|---|---|---|
| Work Rolls (WR) | 108 pcs (with 2 pairs of chocks) | Work rolls are the most consumable spare part in cold rolling mills. An inventory of 108 work rolls is astonishing—under normal production consumption, this can meet 5-8 years of demand, significantly reducing initial spare parts procurement costs, with 2 pairs of chocks further reducing maintenance costs. |
| Backup Rolls (BUR) | 2 pcs (with 4 chocks) | Backup rolls have high individual value and long manufacturing lead times (typically 6-12 months). 2 spare backup rolls can substantially reduce long downtime caused by backup roll regrinding or unexpected damage. |
| New Bearings | 8 sets | Brand new bearings can be used directly for roll changes or equipment maintenance, ensuring long-term stable operation. |
| Solid Drums | 30 pcs | The drum is a core wear part of the coiler. An inventory of 30 solid drums is sufficient to support 5+ years of stable production, greatly reducing downtime for drum replacement due to wear. |
By market estimation, the value of these spare parts alone could exceed one million RMB. For the buyer, this is essentially"buy the equipment, get the spare parts warehouse for free"—not only significantly reducing total cost of ownership but also eliminating post-commissioning concerns about parts shortages.
13. Special Requirements for Stainless Steel Rolling
Stainless steel cold rolling differs significantly from carbon steel cold rolling, and this equipment has been specifically designed to address these differences:
High deformation resistance: Stainless steel has far higher yield strength and work-hardening rate than carbon steel, requiring greater rolling force and higher equipment rigidity (12000kN rolling force);
Extremely high surface quality requirements: Stainless steel is extremely sensitive to surface defects, requiring high work roll surface finish and stable rolling processes;
High tension control precision: Stainless steel rolling is sensitive to tension fluctuations (900kW high-power recoiler/uncoiler motors + Siemens electrical control);
High roll consumption: Stainless steel rolling accelerates work roll wear (108 work roll spares provide ample support).
14. Equipment Status and Services
The technical data sheet clearly records:
Equipment still in operation—on-site trial runs available for performance verification;
Electrical control system intact (Siemens), no missing components;
Spare parts list provided (108 WR + 2 BUR + 8 sets bearings + 30 solid drums);
Disassembly services available (Yes);
Equipment refurbishment and maintenance services available (Yes).
