Density temperature profile (DTP)
The oil volume changes with the temperature. If 200 liters of oil are heated by 50°C, the oil expands by about 7 liters. This "additional " oil volume must, of course, be taken into account for the oil level indicators and oil tanks. In order to estimate and calculate by how much the oil volume really changes due to temperature fluctuations, it is necessary to know the density not only at the 15 °C that are usually mentioned. Rather, it is important to know the coefficient of expansion, which can be determined from a density temperature profile, or the density at the required temperatures.
The density at the corresponding temperatures is also necessary for converting the dynamic viscosities measured on the basis of the viscosity temperature profile into kinematic ones.
OELCHECK creates a meaningful density temperature profile and calculates the expansion coefficient on the basis of the density determined at 10 °C and 90 °C, which can be used to calculate the volume per °C by which the oil volume changes with temperature.
The determination of the density temperature profile for lubricants
To determine the density, approximately 3 ml of oil is aspirated into a tempered glass U-tube. After filling, the glass tube is tapped with a small hammer to stimulate vibration.
The change in vibration frequency of an empty and an oil-filled U-tube is proportional to the density. In this way, the density can be determined and calculated at any temperature (see schematic diagram).
The density temperature profile is measured as standard over a temperature range of +10 °C and 90 °C in 10 °C steps. A tabular and graphical representation is provided in the laboratory report. The calculated coefficient of expansion is also listed.
