Webinar: Grinding technology - best practices for operation and maintenance

The upper seal of the separator plays a vital role in maintaining grinding efficiency. When this seal becomes worn, damaged, or broken, coarse material that should be rejected for further grinding instead bypasses into the product stream. This reduces product fineness and overall grinding efficiency. We recommend inspecting the seal condition every 2-3 months and performing Tromp curve analysis periodically to monitor separator efficiency. When gaps increase in the seal, you lose the sealing effect and experience more bypass of oversized particles in your finished product.

When a roller stops turning in an OK mill, FRM, or similar equipment, the most common cause is bearing failure. This typically results from either complete lubrication loss over time or contamination. Lubrication issues may stem from the lubrication system itself or seal failure allowing oil leakage. Contamination often occurs when cement dust or raw material enters the bearings through damaged seals, causing accelerated wear or complete lockup. If you encounter a locked roller, immediate action is required—remove it and install a spare unit or begin rebuilding the affected roller promptly.

The optimal airspeed varies by mill type and material being processed: - For OK mills in cement grinding: 35-45 meters per second, targeting 5-10% reject from production - For raw mills: 35-50 meters per second, with typical reject rates of 15-25% of feed inputs - For coal mills: 60-70 meters per second, aiming for minimal reject (approximately 1 kg/hour)

Implement systematic wear tracking at regular intervals. When installing new segments on the table and roller, measure their thickness/position to establish a baseline "zero level." After operating for approximately six months, document production volume and power consumption, then measure the wear rate on roller segments and table (in grams per ton or grams per kilowatt). Each segment has an expected lifetime (typically around 6,000 hours) depending on material quality. The OK mill offers the advantage of segment reversibility to extend service life. When wear reaches critical limits, either perform hard-facing (which can be repeated multiple times on the same segments) or replace segments entirely.

For most vertical mills, the optimal location for grinding aid and water injection is directly on the table, just before the feed passes beneath the tire (between the tire and table liner). Some configurations use lances through the mill housing that spray immediately before this point. In newer designs, grinding aid may be delivered through the feed chute with water injection positioned just before the rollers. The primary objective is controlling the material bed on the table for optimal grinding performance.

For ball mill operations, we recommend maintaining higher mill outlet temperatures (around 110°C) to ensure complete gypsum dehydration within the mill, preventing further dehydration in the silo. This differs from vertical mills, where two strategies are viable: either very high temperatures for complete dehydration or significantly lower temperatures (around 75°C) to minimize silo temperature. The 90°C outlet temperature referenced in your question is likely insufficient for complete gypsum dehydration in a ball mill configuration, potentially contributing to lump formation during storage.

We offer several packages for online condition monitoring services with varying scopes. While specific pricing requires consultation with our sales team to align with your particular requirements, these services consistently deliver strong return on investment by identifying potential issues in early stages—before they escalate to critical situations requiring unplanned downtime or costly emergency repairs. Our OCMS has proven particularly valuable in preventing hydraulic system failures, bearing issues, and other conditions that could otherwise result in significant production losses.

The OK mill delivers exceptional operational flexibility by functioning effectively with a reduced number of rollers. For example, a four-roller mill can maintain approximately 60-70% of normal production capacity while operating with just two rollers. This capability allows continued production during maintenance of specific rollers, significantly minimizing downtime. Additionally, the OK mill demonstrates remarkable product flexibility, capable of grinding nearly every type of cement worldwide—from OPC and general-use cement to pozzolanic and slag-based products—with minimal adjustments required between different cement specifications.

The OK mill demonstrates significant energy advantages compared to alternative grinding solutions. When grinding OPC cement to 3800 Blaine, the OK mill consumes approximately 29 kWh/ton, representing a 40% reduction compared to standalone ball mills (40.8 kWh/ton) and a 29% improvement over roller press/ball mill combinations (37.4 kWh/ton). This enhanced efficiency directly translates to reduced operational costs and improved profitability, particularly important considering that grinding processes typically consume about two-thirds of a cement plant's total electrical power.

Upgrading to our latest ROKSH or RARM separators typically delivers multiple operational advantages: reduced power consumption by 1-1.5 kWh/ton, increased production capacity by up to 10%, enhanced product quality meeting diverse cement specifications, and reduced maintenance costs. These improvements result from optimized physical dimensions that ensure lower air velocity, reduced component wear, lower differential pressure, improved system stability, and reduced energy demand. Installation can be completed with minimal downtime, as assembly work can be performed before scheduled shutdowns with the new separator installed in a single lift.

We recommend two primary strategies for vertical roller mill operation to prevent silo lumps. The first approach maintains lower mill outlet temperatures (around 75°C) to reduce silo temperature and prevent gypsum dehydration, effectively preventing lump formation. Alternatively, a high-temperature approach (above 120°C) provides positive strength properties and gypsum activation but requires careful moisture management to prevent dehydration issues during extended storage. Importantly, never mix cement from different mill types (ball mills and vertical mills) in the same silo, even for identical cement types, as varying gypsum dehydration levels between products can lead to lump formation.