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Lube-Tech


The film formation of greases in rolling/sliding can be influenced by a number of the parameters such as temperature and roughness of material. However, in a tribological context, it is much more complicated than that. The aim of this work was to evaluate the impact of the characteristics of the base oils, thickener type and additive concentration tribologically, by using various SRV®


as four-ball methods. 2. Experimental work


The experimental work that has been carried out in this study can be divided into the following parts: charactertistics of the selected base oils, manufacturing and charactertistics of the lubricating greases as well as tribological evaluation of the lubricating greases.


2.1. The base oils Three hydrotreated naphthenic base oils (BO 150, BO 400 and BO 600) have been chosen for this study. Some of the characteristics of these base oils are illustrated in Table 1.


Table 2: Some of the characteristics of the neat greases Table 1: Typical characteristics of the naphthenic oils


Some comments regarding the selected base oils shown in Table 1;


a) Typically, for the choice of base oils in multipurpose greases, a very important factor is viscosity, with higher viscosity being used for heavy loaded and low speed applications. Hence, theoretically speaking, BO 600 followed by BO 400 should be the most suitable products for this kind of application compared to BO 150.


30 LUBE MAGAZINE NO.165 OCTOBER 2021


A review of Table 2 suggests: a) Low thickener content for all greases, however, BO 600 results in the lowest thickener content followed by BO 400. This can be attributed to a combination of better solvency and the higher kinematic viscosity of BO 600.


b) Dropping point was measured according to IP396. Dropping points for the lithium and lithium complex greases fulfil expectations.


c) The shear stability of the greases after 100,000 strokes has been measured according to ASTM D217 which exhibited good results for both lithium and lithium complex greases despite the low thickener contents that were used. However, it is notable that the repeatability of the worked penetration test is seven unites.


methods as well


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.136 page 2


b) These three naphthenic oils are all wax free and subsequently the viscosity is the dominating parameter that controls the pour point.


2.2. The greases In total, six greases (A, B, C, D, E and F) have been produced in a pilot plant at atmospheric pressure. Grease A, B and C are conventional lithium (Li) and Grease D, E and F are lithium complex greases (Li X).


The acids that have been used are 12-hydroxystearate acid (12-HSA) and azelaic acid. In addition, two additive packages have been used; Package I consists of antioxidant (1 wt.%), anti-wear (0.50 wt.%) and extreme pressure (1.5 wt.%) components and Package II consists of Package I + an extra dosage (2.0 wt. %) of the same extreme pressure agent.


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