Raw mills are the heartbeat of cement plants, and preventive maintenance—rooted in inspections, wear‑resistant internals, and optimized grinding—pays back fast by slashing downtime, stress, and energy.
Every unplanned stoppage of a raw mill—whether a ball mill or a vertical roller mill (VRM)—burns cash. Industry sources peg a single day of downtime at a 1 MTPA (million tonnes per annum) plant at roughly $300,000 in lost production (UptimeAI).
One Indonesian cement plant study tied raw‑mill availability below 65% OEE (Overall Equipment Effectiveness, a composite index of availability, performance, and quality) to “significant economic losses and very low competitiveness” (MDPI).
The maintenance takeaway is blunt: equipment must not only run, but run well. FLSmidth warns that neglecting routine inspections breeds hidden wear and surprise failures that erode reliability and inflate costs (FLSmidth Cement Hub) (FLSmidth Cement Hub).
Regular inspection and preventive maintenance
A disciplined inspection regime—daily to weekly checks on lubrication, alignment, vibration, and structural integrity—is the first shield against failures. Ball‑mill maintenance guides call for replacing worn oil after the first month and every six months thereafter, monitoring oil level and temperature at every shift, and keeping oil at not more than 55°C (CementEquipment.org).
Any unusual noise, vibration, or leaks—whether from gear teeth, bolts, or bearings—should trigger immediate investigation (CementEquipment.org) (MDPI). Vibration monitoring is especially telling: a severe rise can flag misalignment or failing liners and justify a controlled stop before a breakdown. As one technician quips, “we often find parts that should have been inspected sitting under a pile of dust,” a sign of “productivity at any cost” mindsets (FLSmidth Cement Hub).
Visual and instrumental checks catch wear and damage early. Thorough liner inspections include searching for tramp steel and plating inside the mill, verifying charge volume, and confirming liner bolts show no leaks—since a leak often means the liner has passed its life (Metso). Laser scanning or ultrasonic gauging quantifies wear; a hand‑held laser or 3D scanner can generate a thickness map of all linings (Metso). Best practice schedules planned shuts—monthly or weekly, depending on throughput—to permit these checks, with spares pre‑ordered so repairs bundle into minimal downtime (FLSmidth Cement Hub).
Reactive “run‑to‑failure” maintenance is widely acknowledged to be costlier in time and money than scheduled work (FLSmidth Cement Hub). In Indonesia and elsewhere, preventive programs such as TPM (Total Productive Maintenance) and RCM (Reliability‑Centered Maintenance) are being rolled out to address this. A recent engineering study cited “wear/fatigue” as a top breakdown cause and recommended regular roller/shaft balancing and lubrication checks; the authors conclude that “preventive maintenance ensures the functioning of the machine and extends its service life” (MDPI).
Wear‑resistant materials and component design
Grinding internals—liners, media, tyres, tables, rollers—face severe abrasion and impact. Upgrading these to high‑performance alloys or composites is central to uptime.
In ball mills, high‑manganese or high‑chromium cast liners dominate. High‑manganese steel (e.g., grade Mn13) work‑hardens under impact, forming a 10–20 mm hard skin with elevated surface hardness (upward of 200–300 HB, a Brinell hardness scale) that resists abrasion and avoids spalling under heavy load (Cement Equipment Spares). Added chromium and rare‑earth inoculation further improves hardness and toughness (Cement Equipment Spares).
VRM roller tyres and tables benefit from hardfacing—tungsten‑carbide or high‑Cr overlays—to slow wear. In one 85 tph VRM, hardfaced (re‑welded) liners cut wear rate by ~60% (from 0.30 to 0.12 g of liner per metric ton of cement) (Great Wall Machinery). A Phoenix (US) cement plant that retrofitted VRM liners and monitored 10,000 operating hours reported a 56% drop in wear rate (Great Wall Machinery).
Advanced ceramic‑composite linings, such as alumina tiles, reach surface hardness up to Rockwell A90 (a Rockwell hardness scale) and “far exceed” steel’s wear resistance; 95%‑alumina composite liners have achieved 5+ years of service in cement mill barrels (KingCera). Rubber‑metal hybrid liners are also in service, offering a wear life roughly 2–3× that of plain steel (Metso). Even feed/discharge chutes, cyclone walls, and ducts take wear linings to shield high‑velocity flow paths—extending campaigns and cutting liner change‑outs.
Grinding process optimization and aids
Reducing internal forces and circulating load lowers abrasion on liners and media. Chemical grinding aids—typically amine‑ or glycol‑based molecules—modify particle surface forces so fines don’t re‑agglomerate on balls or liners. In effect, the powder is “lubricated,” reducing ball coating and dust packing on mill surfaces. A lab study found additives significantly decreased agglomeration and led to “less ball coating and mill lining coating,” confirming higher powder flowability (ResearchGate).
Field trials back this up. Sika reports a VRM grinding aid that reduced mill vibration by 72% while boosting throughput by 14% (Sika). Adding just 0.05% of a specialty aid cut specific energy use by 8–10% and increased output by 9–11% (Sika), with proportional vibration drops of 8–24% using the same aids (Sika). Accurate chemical dosing supports the low addition rates described (e.g., 0.05%) and stable operation (dosing pump). Operators also report smoother “material bed” behavior on VRM tables and ball beds; Sika’s process chart highlights that with optimal aids, vertical mills show higher internal friction but much more compacted, deaerated beds—with “reduced vibration, less wear” (Sika).
Beyond additives, process discipline matters: maintain proper feed rate and moisture; watch VRM bed pressure (ΔP, the pressure drop across the grinding bed) and vibration in real time; if ΔP spikes, stop feeding or adjust water to avoid bridging; keep separators tuned to limit coarse recirculation that gouges table liners; and use advanced controls to adjust mill speed or throw‑forward to keep the process in its sweet spot (Sika).
Outcomes: productivity, energy, and life‑cycle gains
In the Phoenix case, a wear‑rate drop of 56% translated into longer campaigns between rebuilds; halving wear turns months into years of service for a liner set (Great Wall Machinery). Fewer liner change‑outs mean higher grinding availability.
Grinding aids improve profitability twofold: more tons per day and lower energy per ton. While 90% uptime was once a benchmark, new analytics suggest top plants now push beyond this with predictive maintenance (UptimeAI). Reducing downtime even by 10% at a 1 MTPA plant (from 90% to 99% uptime) could yield dozens of thousands of extra tons annually—worth millions of dollars. That business case is why upgrades that cut mill vibration 50–70% (and energy use ~10%) on a 5 MW mill easily pay back in months.
Maintenance guide summary
A practical guide centers on: systematic inspections (visual and measured) at weekly minor and monthly major shutdown intervals; aggressive lubrication and alignment checks; targeted replacement of wear parts (liners, media) before failure; and retrofits to advanced alloy or ceramic components wherever feasible. In parallel, optimizing grinding via additives and controls can reduce internal forces by tens of percent, directly lowering wear. Together, these measures have been shown to increase raw‑mill availability and lifetime throughput while reducing energy per ton (Sika) (Great Wall Machinery) (Sika).
Sources and references: UptimeAI; FLSmidth Cement Hub and FLSmidth Cement Hub; Metso and Metso; MDPI and MDPI; CementEquipment.org and CementEquipment.org; Great Wall Machinery; Cement Equipment Spares; KingCera; ResearchGate; Sika, Sika, and Sika. Reference details: Gil (2023); Bouvette (2024); UptimeAI (2024); Nugroho et al. (2024); CementEquipment.org (n.d.); Great Wall Machinery (2017); Dietrich (2018); Hashim (2018); AGICO Cement (n.d.); KingCera (n.d.).
