Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/136253
COVER STORY metals, resulting in fewer additives available to resist oxidation and lubricant degradation. Abrasives Dirt and other solid contaminants attract additives and can catalytically advance the rate of oxidation. An even bigger problem is associated with the wear debris that is generated from abrasion and its influence as a pro-oxidant. Water Contamination Water contamination leads to oxidation, additive distress, loss of dispersancy and many other lubricant life-related problems. Sludge and Varnish Oil degradation products often contain high concentrations of carboxylic acids, free radicals and hydro peroxides. When oil is drained from a compartment but sludge and varnish remain, the following oil change could be short lived. Makeup Rate Makeup oil refreshes additives and dilutes contaminants. Lube compartments with low makeup rates, while beneficial in one sense, also require more frequent oil changes. Lubricant Quality The quality of base oils and additives can have a marked influence on oil life. Some lubricant suppliers can design lubricants with specific characteristics suited for a high or low ambient temperature environment. High operating temperature accelerates the rate of additive depletion and oxidation. Other Contaminants The ingress of other contaminants can degrade additives and affect the quality of base oils. Any fluid system, reservoir or gearbox that is open or connected to the atmosphere by means of a breather inhales and expels air. By this action, it ingests moisture and collects water. Humid air exposed to temperature variations in a reservoir constantly condenses water into the system, causing hydrolytic action, corrosion, fluid additive breakdown, etc. In certain areas, silica gel dryers can be used with synthetic media hydraulic oil filters to remove dirt and moisture from the air. Hydraulic filters are used as breathers. They filter down to at least a 5-micron absolute level. Establishing Extended Oil Drain Intervals To establish extended oil drain intervals: 12 | May - June 2013 | www.machinerylubrication.com Benefits of a Hydraulic System Redesign The cleanliness of hydraulic oil in the Sishen mine's haul trucks was found to correspond to ISO 21/19, which is extremely poor. The trucks were fitted with three different-sized, high-pressure hydraulic filters for the hoist pump, steering/brake pump and hydraulic blower pump. After installing bypass pressure switches, it was determined that the filters went into bypass after 135 hours, resulting in the poor cleanliness levels. The manufacturer installed high-quality filters in their systems with an expected life of at least 500 hours between service intervals, but the dry, dusty conditions at the mine drastically reduced it. One option was to install return-line filters. However, the cost was prohibitive, so the alternative of resizing the high-pressure filters was chosen instead. The existing blower filter was replaced by the steering/brake filter, while the existing steering/brake filter was replaced by the hoist filter. The existing hoist filter was then replaced by a large hydraulic filter. This step increased the filter area on all the filters. Larger 10-micron absolute air breathers were also installed on the hydraulic tank. The filters used were high-quality depth filters that are very efficient with good dirt-holding capacity. The newly designed system was installed. Previously, the hydraulic filter cost was more than $100,000 per year for 36 haul trucks on 500-hour service intervals, achieving 6,600 hours per year. The new system ran for 1,991 hours at a target cleanliness level of ISO 15/12. At these hours, the filters went into bypass. The direct savings on hydraulic filter costs for the fleet of haul trucks were approximately $121,000 per year. Other benefits were also realized, including: • Less oil usage • Fewer disposal costs • The number of services went down from 475 to 237 per year, resulting in labor savings • For 36 trucks, 2,376 more hours were now available for production. With the trucks moving on average 400 tons per truck per hour, 950,400 tons of additional production per year is possible. • Construct a fleet profile. • Estimate oil drain intervals and potential cost savings associated with the optimum oil drain intervals. • Assess the risk associated with the optimum oil drain intervals. • Develop a testing plan for a small segment of your equipment