Machinery Lubrication

Machinery Lubrication July August 2015

Machinery Lubrication magazine published by Noria Corporation

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18 | July - August 2015 | BY DAVE TIFFANY, PIONEER ENGINEERING When the city of Fort Collins, Colorado, purchased new planetary gearboxes for its wastewater sludge dewa- tering centrifuges, it decided to implement a proactive used oil analysis maintenance strategy. This decision resulted in signifi cant cost savings. Unconventional Machinery Two of the machines were installed new in 1998 at a cost of $619,000 each. They replaced existing sludge dewatering belt-fi lter presses. The new machines were complex by comparison, requiring additional research in the proper maintenance to ensure years of cost-effective, reliable service. Appropriate maintenance tasks also had to be developed for this new equipment. The centrifuges are critical to the Water Reclamation and Bio-Solids Division. The belt-fi lter presses have since been decom- missioned, although technically they are on standby as backups. However, for various reasons, startup and re-use of these fi lter presses are not encouraged. Each centrifuge has a bowl assembly that is V-belt driven by a 300-horsepower, AC-induction motor at approximately 1,748 revo- lutions per minute (rpm). The driven bowl speed is roughly 2,800 rpm. A back-driven scroll assembly within this bowl rotates at approximately 3 rpm less than bowl speed. The scroll regulates the rate at which the dewatered solids exit the machine in order to obtain an optimum percentage of dewatered bio-solids. The scroll is powered by a back-drive system that consists of a 100-horse- power DC motor and synchronous belt drive turning the planetary gearbox. The average service duty is approximately six to 10 hours per day, four to fi ve days per week. Loss of one of these centrifuges would mean extended hours of operation for the remaining centri- fuge and more labor hours for the operations staff. A Proactive Maintenance Strategy After the manufacturer's maintenance recommendations and guidelines were reviewed, it was concluded that the proper gear oil level would need to be maintained. The manufacturer's lubrication schedule specifi ed an annual oil drain and replacement of the gear oil. The quantity and type of oil required was 15 quarts of synthetic gear oil. The manufacturer also suggested a gearbox exchange program in which the gearbox would be replaced every two years with a factory-reconditioned gearbox. The exchange cost was esti- mated at $8,000 each, not including labor. The city began exploring ways to extract a representative used oil sample from these gearboxes for oil analysis. If the condition of the gearboxes could be determined through a predictive strategy or a root cause analysis proactive strategy, symptoms of early impending failure could be monitored and detected. The root causes of these detected symptoms could then be identifi ed and eliminated, or at least controlled. Ultimately, oil drains could be extended and the associated maintenance costs reduced with less generation of used oil and less need for new oil replacement. There would also be a greater understanding of the condition of the new gearboxes, increasing reliability and decreasing maintenance costs. Obtaining Representative Oil Samples Due to the planetary design of the gearboxes, it was not possible to obtain a representative oil sample during normal operation, and extracting the samples would not be conventional. A small, rigid brass pipe nipple was fabricated into the gearbox oil plug to provide a means of collecting a sample via gravity into an ultraclean OIL ANALYSIS Gearbox Condition Monitoring Through Used Oil Analysis Sludge dewatering centrifuges

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