Additional tests, the supplement to the all-inclusive analysis kits from OELCHECK

For years we have had our hydraulic oils regularly tested by OELCHECK. Now one of your tribologists has recommended that we also have the relative humidity measured once in addition to the complete all-inclusive analysis. What are the possible reasons for advising further tests that are not included in the scope of an analysis kit?

All-inclusive analysis kits and "additional tests”

We provide all-inclusive analysis kits for every lubricant and machine type as well as for almost every industry. With the test methods contained in them, OELCHECK tribologists can answer almost any question customers may have. But in some cases, our tribologists advise performing one or more additional test methods. In these cases, the additions to an analysis kit allow even more precise statements to be made about the condition of a lubricant. A typical example of this is the determination of relative humidity including the creation of a water saturation curve for your hydraulic oil. The tribologist advised you to do this because you had a question regarding the cloudy appearance of the oil during sampling. Based on the water saturation curve, he can accurately see that the oil is still clear at 70 °C, for example, becomes cloudy at 40 °C, and that corrosive-acting free water will separate out as the temperature drops further below 20 °C.

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This is how precisely OELCHECK detects water

Water is one of the most common contaminants of lubricants and operating fluids and often causes serious operational problems. It can affect not only the lubricating film formation of lubricants, but also hydraulic properties or dielectric strength. Through evaporation processes in the friction point, water can accelerate their aging process and cause corrosion or deposits. For good reason, we therefore devote a considerable amount of attention in the OELCHECK laboratory to any contamination by water.

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Oxidation index – Modern lubricants age differently

Every lubricant ages over the course of its service life. The extent to which an ageing process has progressed is shown in the laboratory report in particular by the "oxidation" data. Among other analytical values, the oxidation value allows conclusions to be drawn about the remaining operating time of the oil. Oxidation is determined by IR spectroscopy in accordance with DIN 51453. This is done by passing infrared light through an oil-filled cell. The decrease in light intensity is measured as absorption. This method has already been defined at times when often simply refined mineral oils were used as base oils. Nowadays, for higher grade Group II or III oils or for partially synthetic or fully synthetic base products, oxidation can often no longer be determined with the relatively simple method, which is only defined for a certain "wave number".

OELCHECK has therefore further developed the method for detecting oxidation. Below the "oxidation" value, which is stated in absorption/cm oil layer thickness (A/cm), modern oils have recently also been given the dimensionless "oxidation index" in the laboratory report. While for oxidation in A/cm at a specific point in the graph, at a "band" at a wave number of 1710 cm-1 , the change in length compared to the base spectrum is calculated in cm, the index is based on an area calculation. In a differential spectrum, the oxidation index therefore not only looks at the change in length of a single peak, but also determines a change in area that can be calculated in a range between two wave numbers in which oxidative changes occur. The number listed in the laboratory report under "Oxidation Index" essentially corresponds to the increase in this oxidation area in cm². OELCHECK tribologists determined the left and right wave numbers and thus the calculation range for the oxidation index, depending on different oils or their intended use. Thanks to the oxidation index defined in this way, in contrast to the pure DIN line calculation in A/cm, the oxidation of modern lubricants can also be detected at a very early stage. The oxidation index thus provides reliable information for an upcoming oil change.

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