GREASES


Identifying suitable grease alternatives through rheological analysis


With lithium in short supply, automotive manufacturers are looking to alternative greases for lubrication. Yield stress, viscosity, and thixotropic recovery rate and are amongst the rheological characterisations that will aid manufactures in choosing the most suitable alternative grease for their engines.


The laboratory at The Centre for Industrial Rheology procured four greases with the same base oil but different thickeners, namely Lithium, Calcium Sulphonate, Copper, and Molybdenum Disulphide. Each grease underwent a variety of tests to explore how they behave under different conditions.


Oliver Hurst and Megan Woods, The Centre for Industrial Rheology


Understanding the rheological characteristics of these greases equips machine and engine specialists seeking to substitute their lithium grease with valuable insights about others on the market.


Varying grease viscosities Greases used in automotive engines are certain to have a range of high and low shear rates applied to them, so understanding how their viscosity changes across varying shear conditions is imperative for comparing alternative solutions.


Figure 1: Viscosity of grease samples at low shear. Table 1: Breakdown of the greases and their thickeners.


The lab technicians performed a shear rate sweep at 20°C. All samples displayed similar shear-thinning behaviour and similar viscosities. Looking at the data more closely however, we can see that although initially appearing relatively similar, once the greases are exposed to higher shear rates their viscosities begin to diverge.


Continued on page 14 LUBE MAGAZINE NO.180 APRIL 2024 13


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