KRL shear stability

OELCHECK test instrument: The four ball apparatus
Sample quantity: approx. 40 ml
Unit: relative decrease in viscosity at 100 °C in %
Test result: shear stability
Analysis for: multi-grade engine oils, HVLP hydraulic oils, synthetic oils
Brief description:

The VKA apparatus has also been used for this modified method for more than 20 years. In the KRL test, the balls are replaced by a tapered roller bearing filled with the oil under test. Some 40 ml of the oil under test is subjected to the shear stability test at a temperature of 60 °C and a constant load of 5,000 N with the roller bearing rotating at 1,450 min-1 for a time of 4, 8 or 20 hours in the immersion lubrication method.

The speed of rotation, temperature and load remain constant throughout the test. The decline in relative viscosity at 100 °C for a 4-hour test is stated as the test result in the form: KRL/A: 10.2%.

Statement: Multigrade engine and hydraulic oils and some synthetic oils contain a VI improver. Long-chain molecules of this kind can, in part, be badly sheared in operation. The old oil gets consequently much thinner than fresh oil. One method to determine the change in viscosity as a result of the destruction of the VI improvers is the KRL shear stability test.
Underlying test standard: DIN 51350-6