Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1356397
30 | March - April 2021 | www . machinerylubrication.com 30 | March - April 2021 | www . machinerylubrication.com OIL ANALYSIS an understanding of this stage in which the wear was high and the clearances of the machine had increased. is meant the critical limits of the machinery needed to be recalculated. e question is, how do we achieve new oil analysis limits according to the aging state of machines like this? How do we ensure that these new limits will not have a negative effect on the machinery and will allow it to function as normally as possible without suffering unscheduled downtime? If we analyze the wear data measured as iron (Fe) throughout the service life of the most representative set of these machines, the 3 zones can be clearly observed from an operational point of view. Superimposing the wear graph over the bathtub curve allows us to obtain an esti- mate of the most representative wear values measured as a function of time while also using the failure rate as a background, or what we consider closer to the gearbox poten- tial failure that are part of this analysis. So far we have laid the foundations neces- sary to demonstrate the benefits of oil analysis as a maintenance tool. If an adequate sampling frequency is followed and accompanied by a coherent analytical methodology, maintenance can take great advantage of this technique. In the beginning of this article, we said that increasing the viscosity oil grade is one of the most applied practices if you want to keep equipment in service that has entered the last part of its service life. In the previous graph, the inflection point where this practice is carried out can be seen and the high-risk zone is entered with the equipment still in operation. It is at the beginning of this inflec- tion that it is necessary to rethink the limit values from the wear point of view, taking into account that the previous values are no longer adequate. Although the viscosity of the oil has increased significantly, in some cases the loads and the oil might increase during operation as well. ere are a couple of statistical methods for determining the new critical limits for oil when equipment enters the last zone of the curve. However, to understand these statis- tics it is necessary to apply the knowledge that is obtained over many years of reading oil ana lysis reports, visiting sites and knowing the machine performance and working conditions. Based on this set of variables, it is possible to determine coherent limits that once again allow those maintaining the machine to use oil analysis as a tool to respond with necessary corrective actions. To define the new limits for iron (Fe), the following information is required: ELEMENT NORMAL OPERATION END of LIFE VALUES LIMIT VALUES LIMIT Fe 34 60 76 PQ 7 20 28 Cr 2 4 5 Zn 45 64 51 Cu 3 5 12 Si 12 25 28 P 345 220 318 PC 19/17/15 22/20/18 23/21/20 ELEMENT NORMAL OPERATION END of LIFE VALUES LIMIT VALUES LIMIT Fe 34 60 76 98 PQ 7 20 35 67 Cr 2 4 6 7 Zn 45 64 51 76 Cu 3 8 12 21 Si 12 25 28 41 P 345 220 318 308 PC 19/17/15 22/20/18 23/21/20 24/22/20 Table 1: Oil analysis values of gearboxes Table 2: Limit values for the stage of the aging zone Figure 4: Wear and contamination under the microscope ?