Machinery Lubrication magazine published by Noria Corporation
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44 January - February 2015 | www.machinerylubrication.com Therefore, a sample of the new oil was requested. One sample was taken from the middle of the oil reservoir and another from the foam. The results are shown in Table 5. Elemental analysis revealed the cause of the excessive foaming — the oil was contaminated by another fl uid. The analysis also showed differences in additive elements of the new oil, the foam and the sample from the gearbox's oil reservoir. Case Study #2: New Oil After Filling a Gearbox When new oil was used to fi ll a gearbox and the gearbox was started, the oil showed an increased foaming tendency. The customer believed the cause of the increased foaming tendency was the removal of anti-foaming agents due to bypass fi ltration. To obtain more information, oil samples from the new oil and from the oil in the gearbox were analyzed (Table 6). The results showed the silicon-based anti-foaming agent had been completely removed. There were also small changes in addi- tive content. An infrared spectrum of the gearbox sample in comparison to the fresh oil can be seen in Figure 3. The spectrum revealed cross-contamination by another fl uid. A fresh oil volume was then fi ltered to determine if bypass fi ltration was the only reason for the foaming or if cross-contamination also had an effect. After fi ltration, a sample was taken and analyzed (see Table 7). The analysis showed that the anti-foaming agent was not completely removed. A small amount (2 parts per million) remained. Although the slight changes in the amount of anti-foaming agent are not visible in the infrared spectrum (Figure 4), a good correla- tion of the sample before and after fi ltration is evident. Some fi lter manufacturers have even included the Flender foam test in their testing procedures to avoid problems with removed anti-foam agents. Case Study #3: Main Gearbox of a Wind Turbine A wind turbine's main gearbox was initially fi lled with a mineral oil. After operating for 25,000 hours, the oil was changed, and a switch was made to a synthetic polyalphaolefi n-based oil. The new fi lling started to foam almost immediately. Oil analysis was utilized to determine whether the gearbox was fl ushed properly (see Table 8). Small changes in the element concentrations were visible. The infrared spectrum (Figure 5) shows the contamination more clearly. The brown graph represents the spectrum of the old oil, while the blue graph is the new oil, and the red graph is the oil from the gearbox after the oil change. Case Study #4: Cement Mill Gearboxes During a scheduled downtime, the oil in two industrial gear- 8031962 8021706 Gearbox New Oil Water (Wt.-%) <0.1 <0.1 Silicon (ppm) 0 9 Kin. Viscosity (40°C, mm 2 /s) 330.9 330.8 Kin. Viscosity (100°C, mm 2 /s) 37.4 38.2 Viscosity Index (VI) 162 166 Boron (ppm) 31 33 Phosphorus (ppm) 371 414 Zinc (ppm) 0 0 Barium (ppm) 0 0 Sulfur (ppm) 4,932 5,013 Foam S1 (ml/ml) 110/110 10/0 TABLE 6. Oil analysis results of a sample from a filled gearbox FIGURE 3. An infrared spectrum of an oil sample from a newly filled gearbox 8021708 8021706 Filtered Oil New Oil Water (Wt.-%) <0.1 <0.1 Silicon (ppm) 2 9 Kin. Viscosity (40°C, mm 2 /s) 330.1 330.8 Kin. Viscosity (100°C, mm 2 /s) 38.1 38.2 Viscosity Index (VI) 167 166 Boron (ppm) 31 33 Phosphorus (ppm) 422 414 Zinc (ppm) 0 0 Barium (ppm) 0 0 Sulfur (ppm) 4,938 5,013 Foam S1 (ml/ml) 10/10 10/0 TABLE 7. Oil analysis results for a sample of filtered new oil FIGURE 4. An infrared spectrum for a sample of filtered oil GEAR LUBRICATION