Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/468007
www.machinerylubrication.com | January - February 2015 | 45 ML ML boxes was changed. Due to the positive experiences with the oil, the same oil type was used again. After the oil change in both gear- boxes, increased foaming was observed. The gearboxes were stopped again, and the customer complained to the oil manufac- turer about the "bad oil quality." The oil manufacturer took samples from the foaming oil in both gearboxes and from the new oil that was delivered (see Table 9). The elemental analysis results were not unexpected. Only the viscosity of both gearbox samples was slightly decreased. This decrease was within the limits for ISO VG 220. However, in compar- ison to the fresh oil sample from the same batch, it was noticeable. The infrared-oxidation value was also abnormal and much too high for this limited usage. The infrared spectrum indicated contamina- tion with an ester-containing fl uid (see Figure 6). While discussing the results, the customer revealed that a cleaner had been used. The cleaner contained ester-based compo- nents, and its viscosity was very low. It became obvious that the cleaner was the reason for the increased foaming. In conclusion, the formation of foam or fi nely dispersed air bubbles is one of the most frequently discussed phenomena in the operation of gearboxes. Excessive foaming can lead to serious operational problems as well as safety and environmental hazards. Different standardized test procedures are available to esti- mate the air release and foaming properties of lubricating oils. However, the common test methods for air release (ISO 9120, ASTM D3427-12 and IP 313) and foaming properties (ASTM D892, ISO 6247 and IP 146) do not provide reliable information for industrial gear oils. Therefore, a special test (Flender foam test, ISO 12152) has been developed and standardized. This test delivers much more reliable results and can improve the reliability of gear oils. The examples given in this article demonstrate the application of these test procedures and offer an overview of a variety of foaming problems as well as their causes. 2295772 1504280 2155316 After Oil Change New Oil Old Oil Water (Wt.-%) <0.1 <0.1 <0.1 Silicon (ppm) 16 25 0 Kin. Viscosity (40°C, mm²/s) 332.3 325.1 318.8 Kin. Viscosity (100°C, mm²/s) 36.7 36.5 23.4 Viscosity Index (VI) 157 160 92 Calcium (ppm) 0 0 0 Phosphorus (ppm) 393 432 197 Zinc (ppm) 3 0 22 Barium (ppm) 0 0 0 Sulfur (ppm) 3,992 3,857 10,690 Acid Number (mgKOH/g) 0.94 0.99 0.82 Flender Foam (%) 18 - - TABLE 8. Test results from old and new gear oil FIGURE 5. An infrared spectrum of an oil sample from a wind turbine's main gearbox 1702513 1702514 1702515 Gearbox A Gearbox B New Oil Oil Usage (hours) 500 210 0 Water (Wt.-%) <0.1 <0.1 <0.1 Silicon (ppm) 4 2 3 Kin. Viscosity (40°C, mm 2 /s) 204.3 200.7 216.1 Kin. Viscosity (40°C, mm 2 /s) 18.8 18.6 18.97 Viscosity Index (VI) 101 103 98 IR-Oxidation (A/cm) 7 11 - Calcium (ppm) 15 18 18 Phosphorus (ppm) 175 163 156 Zinc (ppm) 5 6 7 Molybdenum (ppm) 859 861 852 Sulfur (ppm) 10,752 10,768 10,690 Acid Number (mgKOH/g) 0.83 0.79 0.85 TABLE 9. Test results for new and in-service gear oils from cement mill gearboxes FIGURE 6. Part of an infrared spectrum for a contaminated gear oil