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The Pfister Wear Index for DRW weighfeeders

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World Cement,

Machine life is rough in a cement plant. Unpredictable wear may cause expensive downtime when unscheduled maintenance becomes necessary. Sturdy materials and a smart predictive maintenance strategy is the key to uninterrupted production and highest customer satisfaction.

The new Pfister® Wear Index provides system operators with comprehensive information about the current status of wear parts and are issued a predicted time to maintenance. The result: increased machine life and lower service and operational cost.

Analysing wear in a Pfister DRW weighfeeder

The rotor weighfeeder Pfister DRW is designed for dosing pulverised fuels such as petcoke, lignite, or coal dust to the kiln in the cement-making process. It is a compact system that integrates material extraction, weighing, dosing and material transfer into the pneumatic conveying line. Additionally, due to its dosing strategy ProsCon®, it allows for high short- and long-term accuracy, as well as dosing stability.

To ensure runtime just as reliable as proper dosing, FLSmidth Pfister has developed several mechanisms to predict wear effects and to decrease them where wear is unavoidable. As part of its predictive maintenance strategy, Pfister further deep-dived into analysing the root causes for wear of the Pfister DRW by taking a tribosystem perspective and consequently developing the Pfister Wear Index.

Several factors contribute to wear: the intensity of usage, pneumatic conditions, and the individual friction factor have to be taken in consideration. To clearly understand and analyse the reciprocity of effects, a scientific approach was needed. Tribology, or the science of interacting surfaces in relative motion, proved to be the key to develop a maintenance pre-warning system. Mini portions of pulverised fuel residues act as wear agents between parts moving relative to each other. Additionally, the pneumatic extraction of the pulverised fuel out of the rotor chambers causes abrasion. Combined, this leads to two major wear symptoms: surface alteration and metal loss.

Developing a standardised model of wear

Analysing wear drivers and their impact patters led FLSmidth Pfister head of R&D Dr.-Ing. Daniel Kasperek to the development of model-based condition surveillance. In a standardised model, the typical phases of wear in correlation to operation time have been identified. Based on the typical curve of wear, the control system indicates the current condition of a running system and supports the customer in proper maintenance planning, thus reducing the risk of wear-triggered downtime.

Each cement plant is different, so the wear index is customised to individual field conditions. After each visual inspection of wear parts during maintenance, the wear index’s prediction quality is rated in three steps: wear index too high, correct, or too low. Each time, the result automatically re-calibrates the index, making individual prediction quality better and better over time.

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