1. Introduction
In cold rolling production, rolls are the most critical consumable components, directly determining strip quality, surface integrity, and production efficiency. However, roll bursting, cracking, and spalling frequently occur in practical operations, especially in single-stand reversible six-high mills.
These failures not only result in unexpected shutdowns and increased operational costs, but also lead to process instability and delivery delays. Therefore, understanding the mechanism of roll failure and implementing targeted preventive measures is essential for modern rolling mills.
2. Roll Bursting Phenomena
2.1 During Rolling Operation
Roll bursting during production is typically characterized by:
- Sudden strip breakage with abnormal noise
- Severe cracking of roll body
- Localized or large-area spalling
In practice, intermediate rolls are the most vulnerable, and their failure often causes secondary damage to work rolls. This leads to strip scrapping and significant material loss.
2.2 After Roll Removal
Roll bursting may also occur:
- During roll changing
- Shortly after removal
Typical features include:
- Audible cracking or explosive sound
- Surface spalling and structural fracture
- In severe cases, fragment ejection (safety risk)
3. Root Cause Analysis
3.1 Stress-Related Factors
(1) Bending Stress
Under normal rolling conditions:
- Rolling force: up to 10 MN
- Roll bending force: 200–300 kN
If roll shifting is performed under high load, it can cause:
- Local stress concentration
- Crack initiation at roll ends
- Progressive spalling
(2) Fatigue Stress
Each roll rotation introduces cyclic stress:
- Alternating tension and compression
- Crack initiation at inclusions
- Crack propagation along stress direction
This is one of the primary causes of roll bursting.
(3) Thermal Shock Fatigue
Rolls continuously experience:
- Heating in deformation zone
- Cooling in spray zone
This results in:
- Repeated thermal stress cycles
- Surface micro-crack formation
- Gradual spalling
3.2 Process Factors
(1) Insufficient Cooling
Field inspection shows:
- Blocked or uneven spray nozzles
- Local roll temperature up to 300°C
Consequences:
- Axial cracks
- Thermal stress concentration
- Accelerated fatigue failure
(2) Slippage Phenomenon
Caused by tension imbalance:
- Friction heat increases rapidly
- Severe vibration occurs
- Roll surface temperature spikes
Result: crack formation and spalling.
3.3 Production Accidents
Strip breakage is closely related to roll bursting:
- Sudden thermal shock damages roll surface
- Steel pile-up causes impact load
- Steel adhesion creates surface indentations
If not removed:
- Defects transfer between rolls
- Micro-cracks propagate
- Final result: large-area spalling
3.4 Roll Quality Issues
(1) Hardness Mismatch
Typical hardness range:
- Work roll: 90–95 HSD
- Intermediate roll: 75–80 HSD
- Backup roll: 60–65 HSD
Deviation or fluctuation leads to:
- Uneven stress distribution
- Local cracking
(2) Incomplete Grinding
If grinding is insufficient:
- Fatigue layer remains
- Micro-cracks are not removed
Under cyclic stress:
- Cracks expand rapidly
- Risk of bursting increases
4. Prevention Measures
4.1 Improve Roll Grinding System
- Ensure adequate grinding allowance
- Remove crack and fatigue layers completely
- Strengthen flaw detection inspection
4.2 Strict Roll Matching
Control parameters:
- Diameter
- Hardness
- Service life
Avoid mixing rolls at different wear stages.
4.3 Optimize Emulsion System
- Maintain proper concentration and cleanliness
- Ensure stable cooling and lubrication
- Prevent oil contamination
4.4 Standardize Roll Change System
- Replace rolls based on condition, not only cycles
- Immediate replacement for defects
4.5 Implement Roll Preheating
- Preheating time: 30–40 minutes
- Pressure: 4–5 MN
- Stable temperature before rolling
4.6 Optimize Rolling Parameters
Adjust dynamically:
- Rolling speed
- Reduction ratio
- Tension
Ensure process stability under varying product conditions.
4.7 Strengthen Process Coordination
- Real-time communication between departments
- Data sharing for roll condition
- Rapid response to abnormalities
5. Conclusion
Roll bursting in cold rolling mills is a systematic issue involving stress, temperature, process control, and maintenance quality.
By combining:
- Scientific roll management
- Stable process control
- Effective maintenance strategies
rolling mills can significantly reduce roll failure rates, improve production efficiency, and ensure product quality stability.
6. FAQ Section (SEO Optimized)
1. What is roll bursting in cold rolling?
It is a sudden failure of rolls caused by stress, fatigue, or thermal effects.
2. What are the main causes of roll spalling?
Fatigue stress, thermal shock, poor cooling, and surface defects.
3. Why do intermediate rolls fail more often?
They experience higher stress concentration and shifting loads.
4. How does cooling affect roll life?
Insufficient cooling leads to thermal cracks and fatigue damage.
5. What is the role of roll grinding?
It removes fatigue layers and prevents crack propagation.
6. Can strip breakage cause roll bursting?
Yes, it creates thermal shock and mechanical impact on rolls.
7. How important is roll hardness matching?
It ensures uniform stress distribution and prevents localized failure.
8. What is process slippage?
Sliding between roll and strip due to tension imbalance.
9. How to reduce roll failure rate?
Optimize process parameters and improve maintenance systems.
10. What is the key to rolling mill stability?
Integrated control of process, equipment, and maintenance.
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