Operating Parameters: Excessive grinding pressure, low coal feed (leading to metal-on-metal contact), and inconsistent feed distribution accelerate wear.
Maintenance Practices: Proper roll alignment and maintaining the correct roll-to-ring clearance (or spring pressure) are crucial. Misalignment causes uneven wear and premature failure.
Typical Lifecycle: Under average conditions, a set of rolls and rings may last between 6,000 to 15,000 operating hours. Monitoring is done through:
Output and Fineness Trends: A gradual drop in capacity at constant power, or a coarsening of product at constant classifier setting, indicates wear.
Mill Motor Power: Worn profiles reduce grinding efficiency, often requiring more power for the same output.
Vibration Analysis: Increasing vibration can signal uneven wear or component failure.
Overhaul (Major Inspection) Strategy:
A proactive, scheduled overhaul is preferred over a reactive breakdown. A typical major overhaul includes:
Planning & Isolation: Secure the mill (electrical, mechanical), purge with inert gas, and assemble necessary tools, cranes, and spare parts (rolls, rings, seals, bolts).
Disassembly: Remove the classifier, top housing, and internal separators to access the grinding zone. Extract the roll assemblies from their pivots or yoke.
