Lubricating greases are a mixture of a base oil, additives and a thickening agent. These three components all contribute to a grease’s viscosity but, regardless of the composition, low temperatures will have a stiffening effect on grease. Lubricants tend to stiffen near their lower temperature limits, which has a deleterious impact on their lubricity. However, unless the grease is aged, the lubricant will typically return to full performance when the temperature is raised.
It’s essential for grease manufacturers to accurately determine their products’ behaviour at a range of temperatures, as too-viscous lubricants can cause severe mechanical issues. These can include local overheating, local lubricant starvation and wear debris scoring. As a result, grease analysis, including low temperature mobility testing, is a vital consideration for meeting grease production regulations.
The Low Temperature Flow Tester, or K95300, from Koehler is a new grease mobility testing instrument with a host of advantages over its competition. A fully automatic test system, the K95300 can achieve an impressive temperature range down to -50 °C without external cooling devices.
The K95300 uses a guided touch user interface, setting it apart from the cursor-based text interface employed by similar machines. It offers standard USB storage capacity and even boasts a mobile app for remote monitoring purposes, neither of which are available in other instruments.
The Koehler K95300 employs the Kesternich method and adheres to DIN 51805. For this test, the user fills the test nozzle with the grease sample, typically by repeatedly pressing the nozzle against the sample until a sufficient amount is inside. After the device has been cooled to the selected temperature, pressure is applied to the grease sample and increased every 30 seconds until the grease sample has been forced out of the nozzle.
The instrument uses a cascaded Peltier system to cool the test sleeve down to the desired temperature. When the system recognises a rapid pressure decrease, the system will store the maximum pressure value as the test result. This pressure value can be converted to reflect the viscosity of the grease sample at the desired temperature.
The Kesternich test, employed by the Low Temperature Flow Tester, only requires a sample size of approximately 2 g. By contrast, the current low temperature grease testing standards, such as ASTM D1092, the US Steel Mobility and the Lincoln Ventmeter tests all require at least 220 g of sample to conduct the test. This brings obvious cost benefits, as less sample is consumed to obtain the information.
The maximum pressure values produced by the Kesternich method are highly repeatable, with a range of no more than 50 mbar and a maximum standard deviation of 2%. The 25 measurements for each run, displayed in Fig. 1, were collected at -20°C, 25 mbar steps and 30 second increase time.
Figure 1 – Maximum pressure values from a range of grease samples tested using K95300
To find out more about the Low Temperature Flow Tester (K95300) click the button below. Alternatively, to speak to one of SciMed’s team about how you can use the Low Temperature Flow Tester (K95300) to demonstrate the mobility of your lubricant samples under controlled conditions