Key words：HSS High Speed Steel roller/work rolls/forged rolls /Infinite Chilled Cast Iron Roller/Adamite alloy Roller
Ⅰ. Causes of Roll Fracture and Failure
1.Mechanical Fatigue and Surface Spalling
（1） Unremoved Crack Sources: This is the main cause of large-area spalling of cold rolling rolls. During rolling, tiny surface cracks (only 0.5mm) are created by foreign objects being pressed in. If these cracks are not detected and removed after rolling, they will expand inward under alternating stress (in a shell-like shape) upon re-rolling, eventually leading to large pieces of metal spalling off.
（2）Contact Fatigue: Long-term contact stress between the support roll and the work roll causes subcutaneous cracks to initiate, ultimately resulting in brittle spalling.
2.Improper Use and Management
(1) Grinding Defects: Improper grinding parameters (mismatched speed and feed rate) will leave "knife marks" or "vibration marks" on the roll surface. These micro-grooves will evolve into cracks during rolling.
(2) Insufficient Stress Release: Grinding immediately after the rolls have come off the mill at a high temperature will not only cause burn cracks but also worsen the stress state. Simultaneously, the residual stress inside the rolls has not been fully released and needs to be allowed to stand for a certain period (e.g., 48 hours after the support rolls have come off the mill) before grinding.
II. Preventive Measures: Standardized Maintenance (Grinding and Flaw Detection)
(1) Post-Mill Standing System: Establish a "Roll Rest Area." Work rolls, intermediate rolls, and support rolls must be allowed to stand for at least 12 hours, 24 hours, and 48 hours respectively after coming off the mill, until the residual stress is fully released before being ground.
(2) Pre-Non-Destructive Testing: Perform flaw detection before grinding to confirm the crack depth; perform flaw detection again after grinding to confirm that the defects have been completely eliminated. For deeper cracks, "point-to-point" grinding is required.
III.Maintenance and Repair Strategies
When defects appear on the rolls, different maintenance solutions should be adopted according to the type:
1.Treatment of Surface Cracks and Peeling
(1) Thorough Removal: For cracks and minor peeling, the defective layer must be completely removed by grinding until flaw detection shows no cracks. If the grinding amount exceeds the safe operating limit (e.g., insufficient remaining working layer thickness), the rolls should be scrapped directly.
(2) Flaw Detection Verification: When it is impossible to determine whether the cracks have been completely removed by visual inspection, dye penetrant testing or magnetic particle testing must be performed for verification.
2.Repair of Roll Surface Vibration Marks and Knife Marks
(1) Parameter Adjustment: If the defect is minor, it can be eliminated by "finish grinding" (i.e., the last cut with an extremely small knife cut).
(2) Grinding Wheel Dressing: If the defect is caused by a dull or sharp grinding wheel, the chamfer on the edge of the grinding wheel needs to be dressed, and the matching relationship between the Z-axis speed and the roll speed needs to be adjusted.
3.Neck Fracture and Severe Failure
For rolls with neck fractures or large-area deep cracks, repair costs are too high and safety hazards exist; they are usually scrapped and used as remelting material.
Ⅳ.Conclusion
Roll management is a systematic project. Fractures often originate from thermal stress or manufacturing defects, while spalling often stems from unremoved fatigue cracks. The optimal maintenance strategy is preventative maintenance: ensuring quality control of rolls before they are put on the mill through rigorous non-destructive testing, releasing roll stress through scientific grinding and resting, and reducing the impact of sudden accidents on the roll surface through optimized rolling processes.
