Introduction
Short-stress-line mill bearing burn-out is one of the most common and harmful equipment failures in modern bar and wire rod rolling workshops. Les lignes de laminage finition du N°1, N°2, Les laminoirs à barres n°3 et la deuxième ligne de laminage de barres à grande vitesse adoptent tous des laminoirs à ligne de contrainte courte. These mills use four-row cylindrical roller bearings as main load-bearing components and different types of thrust bearings for axial positioning. In actual continuous production, short-stress-line mill bearing burn-out often causes unexpected shutdowns, roll replacement and component scrapping. Vertical rolling mills show higher failure rates than horizontal mills. To solve this problem and stabilize production efficiency, this article systematically analyzes the root causes of short-stress-line mill bearing burn-out and provides practical improvement measures for field application.
1. Lubrication-Related Root Causes of Short-Stress-Line Mill Bearing Burn-out
Disassembly inspection of failed bearings shows obvious abnormal conditions inside the bearing chamber. Cooling water and iron oxide impurities easily invade the internal structure, which severely emulsifies lubricating grease. Burnt bearing surfaces appear rough and overheated, and some grease becomes dry or carbonized under high temperature. Multiple unreasonable structural and operational factors lead to repeated bearing burn-out failures.
1.1 Defective Bearing Sealing Structure
The original single labyrinth sealing structure cannot block external water and dust effectively. When the roll rotates at high speed, centrifugal force thins internal grease and creates internal and external pressure differences. Poor sealing allows air, cooling water and oxide scale to enter the bearing cavity continuously. This common defect directly causes grease emulsification, lubrication failure and eventual bearing overheating.
1.2 Incorrect Sealing Installation Standards
Workshops previously adopted unified sealing installation methods for both horizontal and vertical mills without targeted adjustment. Vertical mills require upward V-ring installation to block cooling water splash. Non-standard assembly greatly reduces sealing performance and accelerates early bearing damage.
1.3 Internal Friction Heat Accumulation
Unreasonable labyrinth clearance causes contact friction between static and moving sealing parts. Impurities inside the bearing also increase operational resistance and generate extra heat. Continuous heat accumulation raises grease temperature rapidly, reduces viscosity and leads to grease loss and dry friction.
1.4 Extended Service Cycle and Lack of Automatic Lubrication
Laser-strengthened roll passes greatly increase rolling tonnage and extend bearing online working time. Cependant, most production lines do not support automatic online greasing. Long-term operation without effective grease renewal significantly increases the risk of bearing burn-out.
2. Technical Improvements for Short-Stress-Line Mill Bearing Burn-out Prevention
2.1 Composite Sealing Structure Optimization
Replace the single labyrinth structure with a combined sealing system of labyrinth passages and special V-shaped sealing rings. Install vertical mill V-rings with openings facing upward to prevent cooling water infiltration. Adjust labyrinth outlets toward the outer side and expand clearance from 1 mm à 1.5 mm to avoid friction deformation. Add water-blocking shoulders and anti-dust grooves to strengthen anti-invasion performance. Fix rotating labyrinth components by spot welding to eliminate friction heat between roll end faces.
2.2 Scientific and Standardized Grease Management
Select high-performance composite calcium sulfonate grease as the official lubricant. This material features excellent water resistance, stable mechanical performance and extreme-pressure anti-wear properties. It forms a protective iron sulfide film under high temperature to avoid metal sintering. Control greasing volume strictly to fill bearing gaps moderately without excess or shortage. Clean all bearings and labyrinth components thoroughly with kerosene before assembly to remove old grease and impurities.
Adopt seasonal grease grading strategies. Use No.2 grease in low-temperature winter conditions and No.3 grease in high-temperature summer environments. Supplement grease regularly for offline standby mills to maintain stable lubrication performance.
3. Optimize Assembly Process to Reduce Mill Bearing Burn-out Risk
Unstandard assembly operations are critical hidden causes of bearing failure. Strict assembly specifications effectively reduce short-stress-line mill bearing burn-out frequency.
Keep the assembly environment clean and isolate unpacked bearings from ground contamination. Control bearing inner ring heating temperature steadily between 80℃ and 100℃ to ensure precise interference fitting without grease deterioration. Use copper rods for symmetrical tapping during bearing installation to avoid impact damage. Inspect bearing cages, rolling elements and inner sleeves carefully before formal assembly.
Test roll flexibility after installation to eliminate abnormal axial play. Weld anti-loosening bolts on vertical mill base nuts to prevent mill vibration and unstable operation during rolling.
4. Thrust Bearing Selection to Avoid Short-Stress-Line Mill Bearing Burn-out
Field comparison shows that iron-cage thrust bearings easily crack under high-speed alternating load, causing roller jamming and bearing burn-out. En revanche, copper-cage thrust bearings deliver better toughness, stability and fatigue resistance. Fully replace iron-cage bearings with copper-cage thrust bearings for all intermediate and finishing mills. This measure effectively reduces sudden bearing failure rates during long-term operation.
5. Online Automatic Greasing System Transformation
Install automatic bearing greasing systems on main production lines. The system supplements fresh grease every 3 à 4 hours during continuous rolling to renew lubricating oil films. For lines without automatic equipment, arrange manual grease supplementation during routine maintenance and product switching. Promote full-line lubrication system upgrading to achieve long-term stable bearing protection.
Conclusion
Structural sealing improvement, standardized grease selection, precise assembly technology and optimized bearing selection significantly alleviate short-stress-line mill bearing burn-out problems. These measures effectively reduce unplanned shutdowns and equipment scrap losses. Cependant, minor water and impurity invasion still occurs under complex working conditions. Long-term online operation still causes mixed aging grease and reduces lubrication stability. Further technical optimization and intelligent maintenance strategies will continuously improve the service life and operational reliability of short-stress-line mill bearings in bar rolling production.
