Lube-Tech Table 2: The measured characteristics of the greases.
A review of Table 2 suggests: a) Thickener content was low for all greases; however, less thickener was needed to make greases with BO2 than BO1. The reductions were about 9 percent for lithium grease, 12 percent for lithium complex grease and 22 percent for bentonite grease.
b) Dropping point was measured according to IP396. Excellent dropping points for the lithium and lithium complex greases were measured. It is well known that bentonite clay based grease is a gel and doesn’t have a dropping point.
c) The shear stability of the greases after 100,000 strokes was measured according to ASTM D217, and results were good for the lithium and lithium complex greases despite their low thickener contents. However, slightly better stability was noted for the lithium complex grease based on BO1 compared with the lithium complex grease based on BO2, which may be explained by the higher thickener content (about 13.5 wt.% higher).
d) Bentonite clay based grease is known to have poor in shear stability compared with, e.g., lithium grease, due to the nature of the thickener system. However, it has been documented that the use of high viscosity naphthenic oil with relatively high polarity has offset and reduced this weakness. Hence, the measured consistency after 100,000 strokes should be regarded as good for this type of grease.
e) The results for the degree of oil separation, measured according to IP 121 (40 °C/168 hrs.), for these greases are quite interesting. The higher soap content is expected to correspond to lower oil
34 LUBE MAGAZINE NO.154 DECEMBER 2019
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.125 page 3
separation, of course if the manufacturing process is kept constant. However, BO2 based greases showed less oil separation despite having lower thickener content, which can be explained by the viscosity differences between BO1 and BO2 at 40 °C.
f) Pumpability of the lubricating greases can be simulated by different methods, e.g., measurement of the flow pressure according to DIN 51805. Parameters such as consistency of the grease, polymer content, kinematic viscosity of the oil and pour point, as well as the degree of the wax content in the base oil, are the main parameters that can affect the mobility of the greases. In this study, wax content and polymers were eliminated, and the low temperature mobility of the greases depended on the thickener content, the viscosity and the pour points of the oils. Good low temperature mobility for all greases at -20 °C was noted. Nevertheless, higher pressure was needed for the BO2 based greases because of the significantly higher viscosity of BO2 and its higher pour point.
g) Water wash out was measured according to ASTM D1264. The outcome was good to excellent for all greases. Better resistance to water for lithium complex greases was expected due to the significantly higher thickener content of those greases. If Grease A and Grease B (lithium greases based on BO1 and BO2, respectively) are compared, much better resistance to water can be noted for Grease B despite having lower thickener content. Most probably, this is because of the significantly higher viscosity of BO2.
h) Four ball tests were conducted according to ASTM D2266, with 40 kg load for 60 min., which is a severe test for a neat grease. In Table 2, the average wear scar diameter for each grease is shown. All the greases showed the same degree of wear, with the exception for Grease B which showed a significantly smaller wear scar.
Oxidation stability tests were conducted by using a small-scale oxidation test (RSSOT). By using this
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