Machinery Lubrication

ML_September-October_2020

Machinery Lubrication magazine published by Noria Corporation

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ML www . machinerylubrication.com | September - October 2020 | 17 ML Since the spectrophotometers recom- mended in this standard are not designed to address the specific needs of the test, a significant portion of the varnish sub-mi- cron particles trapped inside the membrane volume are not visible and are often missed during measurement. As you see in Figure 1, the intensity of the color when the membrane is lit from the back leads to different results when compared to the way it looks when lit from the front. In 2015, Professor Sasaki developed a new colorimetric patch analyzer (CPA) which can measure the color of contami- nants on the patch surface using reflected light and the color inside the patch by using transmitted light. One of the most common concerns when using a solvent to dilute in a lab test is that the solvent may dissolve part of what is to be measured and distort the test results. In 2014, Andy Sitton presented a new index in order to address this concern in Machinery Lubrication magazine. In Sitton's method, the volume of oil sample is passed through membranes in accordance with ASTM D7843, but no solvent is used. Although the proposed method can take considerable time because of the need to pass thick oil through the membrane, it will eliminate the possible effects of the solvent. e varnish potential is obtained by using a solvent in the ASTM D7843. Sitton's new index is also measured by a spectro- photometer and is called iMPC. e final index will be the number obtained from the division of iMPC into MPC. e closer the index is to the unit, the more likely it is to deposit varnish on the interior surfaces of the turbine and the greater risk it poses to its safe operation. Soluble and insoluble varnish contaminant: e results from the ASTM D7843 standard do provide a useful index, but do not provide distinct estimates of the probable volumes of soluble and insoluble varnishes. Because of the 72 hour oil reten- tion time required by the ASTM D7843 and the agglomeration phenomenon, soluble varnish particles are instead added to the volume of insoluble varnish in the Figure 1. Comparison of reflecting light and transmitting light Surface View by reflecting light Back View by transmitting light

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