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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Relative humidity at defined temperature and water saturation curve

OELCHECK now determines the relative humidity of oils at defined temperatures and also creates water saturation curves! This provides additional valuable information for proactive maintenance. Appropriate oil maintenance measures or oil changes can now be carried out even earlier and, above all, large hydraulic systems and circulation systems can be protected against malfunctions caused by free water.

Oils used for lubrication, pressure transmission or insulation should contain as little water as possible. But fresh oils always contain a small proportion of water. This water is dissolved in the oil. The proportion depends mainly on the base oil type and the additive. The relative humidity percentage indicates the concentration of water dissolved in the oil. Depending on the temperature, the oil cannot "carry" any more water if the concentration is above 100% relative humidity or if the water saturation point is reached. At this point, fine water droplets usually form and the oil becomes cloudy. If the proportion of these droplets is too high, free water settles in the form of a clearly visible phase separation, particularly during the cooling process. At a relative humidity of over 100 %, abrasive wear can occur at moving friction points. Where water is deposited instead of oil, the extremities of the surfaces are no longer lubricated. Water can cause massive corrosion and rust formation. OELCHECK uses the Karl Fischer method to measure all the water present in the oil, i.e. dissolved and free amounts, in ppm. This absolute water content does not indicate the relative humidity and thus not how much water is dissolved in the oil or how much water the oil could absorb before it separates. But knowing the relative humidity relative to the total water present in ppm is particularly important for oil fills in large hydraulic systems, in transformers or in circulation systems where water poses a risk, such as the paper industry or cold rolling mills, but also in systems with condensation.

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Alternative fuels: Types and their characteristics

It will be a long time before we are all travelling in electric cars or under hydrogen power. If Germany is to reach its ambitious goal of climate neutrality by 2050, alternative fuels will play an important role at least until then. Some of them are already widely used today in their pure form or as a mixture with fossil diesel and petrol fuels. Since 2007 the German Biofuel Quota Act (BioKraftQuG) has even stipulated a minimum share of biofuels as a percentage of total fuel sales in Germany.

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