8-Hi 850mm eight-high reversible cold rolling mill

1. Equipment Overview
This is an 8-Hi 850mm eight-high reversible cold rolling mill,manufactured by Jiangsu Nanbao in 2018 and still in normal operation. This is a high-end stainless steel ultra-thin strip cold rolling mill, specifically designed for ultra-precision, ultra-thin gauge cold rolling of stainless steel strips. The 8-Hi (eight-high) configuration represents an advanced design in cold rolling mills—compared to 4-Hi and 6-Hi mills, the 8-Hi mill achieves smaller work roll diameters and stronger shape control capability through the combination of more roll sets, enabling stable rolling of ultra-thin gauge stainless steel strips.

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, multi-roll mills, reversible 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 + Very 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 Z500-4A, each rated at 710kW, with a speed of 305 r/min, for a combined total of 1420kW. 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 710kW motors ensures balanced power delivery in both rolling directions, with 1420kW total power representing an ample configuration for stainless steel rolling in an 8-Hi mill.

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 425/1200 r/min. The 900kW recoiler/uncoiler motor power exceeds the single main motor power (710kW), reflecting the extremely high tension control requirements of ultra-thin gauge stainless steel rolling—rolling of ultra-thin strips requires very high recoiling tension to ensure tight coil shape, stable inter-pass tension, and to prevent strip breakage. 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 — 8-Hi Advanced Configuration
This equipment is an 8-Hi (eight-high) cold rolling mill, consisting of 2 work rolls, 4 intermediate rolls (or side support rolls), and 2 backup rolls. The 8-Hi configuration represents an advanced design for stainless steel ultra-thin strip cold rolling, offering the following significant advantages over 4-Hi and 6-Hi mills:

• Smaller work roll diameter: The work roll diameter is only Φ110/120mm, far smaller than the Φ165mm of 4-Hi mills—the smaller diameter significantly reduces rolling force, making stable rolling of ultra-thin gauges (0.12mm) possible;

• Superior shape control: Multiple intermediate rolls and side support rolls provide stronger roll system stability, effectively compensating for bending deformation caused by rolling force;

• Higher rolling precision: Minimal roll system deformation enables more precise thickness tolerance control;

• Thinner finished gauges: The 8-Hi structure is the ideal choice for rolling ultra-thin stainless steel strips below 0.15mm.

7. Roll Systems

• Work Roll: Specification Φ110/120×900mm—new roll diameter 120mm, replaced when worn to 110mm, barrel length 900mm. The extremely small diameter significantly reduces rolling force, serving as the core technical guarantee for achieving 0.12mm ultra-thin gauge rolling;

• Intermediate Roll: Specification Φ100×900mm—roll diameter 100mm, barrel length 900mm. Intermediate rolls are the key actuators for shape control in the 8-Hi mill;

• Backup Roll: Specification Φ630/650×850mm—new roll diameter 650mm, replaced when worn to 630mm, barrel length 850mm. The large-diameter backup rolls provide robust rigid support to the entire roll system, ensuring minimal roll system deformation under high rolling forces;

• 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. For the 0.12mm ultra-thin gauge, AGC precision is particularly critical.

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): 0.12mm—rolling from 3.0mm to 0.12mm represents a total reduction of 96%, demonstrating the powerful ultra-thin gauge rolling capability of the 8-Hi mill;

• 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: 0.12mm—consistent with design;

• Maximum rolling speed: 320m/min;

• Maximum rolling force: 9000kN (approximately 900 metric tons of force).

9. Minimum Finished Thickness — 0.12mm Ultra-Thin Capability
The 0.12mm minimum finished thickness is the core performance indicator of this equipment. In stainless steel cold rolling, 0.12mm represents the ultra-thin gauge category, typically used for high-end precision applications:

• This thickness is approximately equivalent to the thickness of two standard A4 sheets of paper, reflecting extremely high rolling precision;

• The 8-Hi structure significantly reduces rolling force through small-diameter work rolls, making stable rolling of ultra-thin gauges possible;

• 0.12mm stainless steel thin strip imposes extreme requirements on equipment rigidity, roll system stability, tension control, and AGC precision—the ability to stably produce this gauge indicates that the equipment is at a high technical level.

10. Maximum Rolling Force — 9000kN Full Guarantee
The 9000kN (approximately 900 tons of force) maximum rolling force, while lower than the 12000kN of the 4-Hi 850mm mill, represents a reasonable and sufficient configuration for the 8-Hi structure. The 8-Hi mill effectively reduces rolling force demand through small-diameter work rolls—9000kN rolling force is fully sufficient for stainless steel rolling with 3.0mm entry thickness and 0.12mm exit thickness. The smaller work roll diameter enables the same deformation to be achieved at lower rolling forces, while also reducing roll system deformation, ensuring ultra-thin gauge shape and thickness accuracy.

11. Thickness Advantages of the 8-Hi Structure
The 8-Hi mill offers incomparable advantages over 4-Hi and 6-Hi mills in ultra-thin gauge rolling:

• Significantly reduced rolling force: The smaller the work roll diameter, the shorter the contact arc length and the lower the rolling force, making ultra-thin gauges easier to achieve;

• Superior shape control: Intermediate rolls and side support rolls provide multi-dimensional roll system adjustment capability;

• Better thermal stability: Smaller diameter work rolls dissipate heat faster during high-speed rolling, reducing thermal expansion effects on thickness accuracy;

• Higher surface quality: Small-diameter work rolls combined with precision roll systems produce smoother strip surfaces.

12. Recoiler/Uncoiler Motor Power — 900kW Full Guarantee
The 900kW recoiler/uncoiler motor power has special significance in 8-Hi ultra-thin strip mills:

• Ultra-thin gauge rolling requires extremely high tension to ensure strip stability in the roll gap, preventing wrinkling and strip breakage;

• The 900kW recoiling power ensures stable recoiler operation under high-tension conditions;

• High-power recoiling also means the equipment can handle heavier mother coils, reducing coil change frequency and improving production efficiency.

13. 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 ultra-thin strip cold rolling control. According to the technical data sheet, the electrical control system is in good condition (Yes) with no missing components. For 0.12mm ultra-thin gauge rolling, the response speed and control precision of the electrical control system are critical—the Siemens system ensures precise coordination of speed control, tension control, and thickness control.

14. Spare Parts — Exceptionally Ample Inventory
The extensive spare parts included with this equipment represent a significant added value in this procurement:

This spare parts inventory not only significantly reduces post-commissioning parts procurement costs but also eliminates concerns about parts shortages.