Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
The physical properties of the base oils are given in Table 1.
Discussion Table 1. Physical Properties of Base Oils
The greases were all produced in the same reactor under similar conditions. Each grease was characterized by wt% thickener, unworked penetration, worked penetration (60x and 10,000x strokes), mechanical stability after 10,000 strokes, and US Steel mobility test. In addition, roll stability, oil separation, and dropping point were reported for some of the greases. In order to simplify the formulations, performance additives such as antioxidants, antiwear, and corrosion inhibitors were not included.
Equipment and manufacturing procedure Manufacturing of greases not only depends upon the formulation technology, but is also greatly influenced by the processing parameters and scale up. All these samples were prepared in the laboratory at 1 to 5 gallon batch size. The kettles used for making these samples were Howard-type mixers, and controlled heat was provided through electric heating mantles. The greases based on Li 12-HSA lithium complex, clay base, and aluminum complex greases were prepared with conventional processes and compositions; varying only the base oil component. All efforts were made to keep all processing parameters, composition, and operator consistent to avoid batch-to-batch variation. The Ca sulfonate grease samples in different base oils were made in counter rotating mixers using
Thickener Content The amount of grease of a given consistency that may be made with a specific amount of thickening agent, i.e., grease yield, varies by thickener type and by the solvency of the oils used to prepare the grease. As the grease yield increases, the thickener content decreases, which consequently lowers the cost of the formulation since the thickener system is generally the highest priced component.
Instead of making different types of greases using a standard amount of thickener, this study did the opposite. All the greases were prepared to an NLGI Grade 2 and the amount of thickener was necessarily varied to obtain the same grease consistency. In this way, the properties of the greases could be compared on the same NLGI grade basis.
The data are plotted in Charts 1 – 4. In Chart 1, the oils are aligned in order of increasing required thickener content for the Li 12-HSA greases. This alignment, with one exception, is by type (naphthenic, paraffinic, synthetic) and by decreasing solvency as defined by increasing aniline point. The one exception is with the two ISO VG 150 naphthenics from different suppliers, where the one with the slightly higher aniline point actually requires less thickener.
Thickening efficiency is the opposite of the amount of thickener used to make an NLGI grade 2 grease. It is necessary to use a larger amount of a less efficient thickener to obtain NLGI grade 2 versus a smaller amount of a more efficient thickener. In Chart 1, the thickening efficiency of L1 12-HSA was highest for
LUBE MAGAZINE NO.144 APRIL 2018 35
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proprietary composition and process parameters. After the greases were cooked and brought to desired penetration range, all the samples were milled through the same laboratory scale homogenization mill. The finished grease samples were tested as per ASTM standard test methods.
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