One raw mill logged 137.76 hours of breakdowns in a single month and ran at roughly 57% overall equipment effectiveness. Data from industry and academia point to three fixes: disciplined inspections, wear‑resistant internals, and optimized grinding with aids.
At one Indonesian plant, the raw mill’s month included 137.76 h of breakdowns and an overall equipment effectiveness, or OEE (aggregate score of availability, performance, and quality), of about 57% (www.mdpi.com). The same study flags that OEE should exceed 65% to avoid “significant economic losses.” Root causes were prosaic but punishing: wear/fatigue and misalignments (www.mdpi.com).
The fix is less about heroics and more about habits. Weekly visual checks, smarter wear materials, and grinding aids that calm the process cut stress on internals and extend the intervals between rebuilds. The data trail is clear across sources from engineering journals to supplier case studies (www.mdpi.com; www.zkg.de; gbr.sika.com; www.nbmcw.com).
Routine inspections and condition monitoring
Frequent condition checks—weekly visual inspections of rollers, bearings, linings, lubrication, and alignment—are critical in raw milling. Catching liner erosion, bearing play, or cracks early prevents sudden failures and lost hours (www.mdpi.com).
Plants that use inspection data alongside vibration, temperature, and oil analysis (predictive “condition monitoring”) can schedule replacements before failures. The cited OEE study explicitly recommends replacing rollers and realigning idlers at set intervals and lubricating bearings—practical steps that quickly restore performance (www.mdpi.com). Industry experience shows regular maintenance drastically raises MTBF (mean time between failures) and lowers MTTR (mean time to repair) (www.mdpi.com).
The bottom line: routine inspections and predictive maintenance—whether via sensors or manual TPM rounds—are data‑driven investments that minimize breakdown hours (as illustrated by the 57% OEE case) and maintain throughput and energy efficiency (www.mdpi.com).
Wear‑resistant grinding components
Vertical roller mills (VRMs) in raw milling face extreme abrasive wear. Choosing high‑performance materials for liners, rollers, grinding balls, and tables can multiply service life. Alloyed cast‑iron or composite liners “minimize loss of material on friction surfaces,” extending component life (www.researchgate.net).
Modern metal‑matrix composite (MMC) rollers—ceramic‑granular particles bonded in high‑chrome steel—have shown 3–5× longer wear life than mono‑metal high‑chrome parts in the field (www.zkg.de). In one cement mill, conventional high‑chrome rollers wore out (≈30 mm wear) in ≈5,000 operating hours; replacing them with MMC “Xwin®” rollers yielded ≈20 mm wear after ≈15,000 h—roughly a 3.7× lifetime gain (www.zkg.de). A similar composite “neoX®” showed 40% lower wear under the same conditions (www.zkg.de).
Even simpler measures pay. Hardfacing liners can cut the wear rate roughly in half—e.g., from ≈0.30 g/t to ≈0.12 g/t of throughput (www.serem-industrie.fr). Coatings matter too: composite ceramic faces on VRM rollers have achieved lifetimes up to ≈8,000 h (www.researchgate.net).
Design details—liner geometry and material hardness—reduce impact stresses. Using harder, tougher alloys (e.g., Ni‑hard for presses and rollers (www.intechopen.com), or high‑chrome steel in air classifiers and ball mills) significantly slows wear. The ZKG analysis concludes that state‑of‑the‑art composites’ extreme durability extends grinding campaigns, “reducing overall cost” even when a piece costs 2–3× more (www.zkg.de; www.zkg.de).
Grinding aids and process stabilization
Optimizing the process reduces stress on the mill internals. Using cement grinding aids—chemicals added to the raw mix (accurate chemical dosing)—can dramatically improve efficiency. These additives adsorb on particle surfaces, reduce interparticle friction, and prevent fines from agglomerating, so internal circulation drops and the grinding bed stabilizes (gbr.sika.com; www.nbmcw.com).
In one Loesche mill study, a tailored grinding aid formulation boosted mill output by ≈14% at the same fineness, while cement Blaine fineness (surface area index) rose ≈12% (gbr.sika.com). Crucially, mill vibration—a proxy for stress cycles—fell by ≈72% (gbr.sika.com). Another source notes that grinding aids “reduce agglomeration of particles on the balls & liners,” easing abrasive loads (www.nbmcw.com).
Stabilized powder flow allows a higher differential pressure (mill load) without bed collapse, yielding higher throughput and smoother operation (gbr.sika.com; www.nbmcw.com).
Quantified outcomes and energy savings
Optimized grinding reduces the wear rate and saves energy: additives often cut specific power (kWh/t) by several percent while maintaining output, indirectly lowering heat and stress on bearings and drives (www.nbmcw.com). One review notes ≈40% of a cement plant’s power goes to grinding (www.nbmcw.com).
Wise process tuning—avoiding overloaded conditions or excessive recirculation—minimizes “sliding” of the material bed that spikes wear. Combined with routine inspections, the measures above yield quantifiable outcomes: higher net throughput (+10–20% typical), lower kWh/t, and fewer unplanned stops (gbr.sika.com; www.nbmcw.com).
Budget planning and reliability gains
The evidence base—from the 57% OEE case study to MMC and ceramic wear trials—points in one direction. Regular inspections that track wear, bearing health, and alignment keep OEE high (vs 57% in the cited plant: www.mdpi.com). Advanced wear‑resistant components can triple or quadruple part life (www.zkg.de; www.researchgate.net). And process optimization—right classifier settings and grinding aids—boosts capacity, slashes vibration, and smooths operation (gbr.sika.com; www.nbmcw.com).
The combined effect shows up where it matters: longer campaigns between outages, concrete cost savings on parts and energy, and more reliable production throughput—vital information when planning maintenance budgets or technical upgrades (www.zkg.de; www.mdpi.com).
