Back to the Basics II: Fundamental Building Blocks of Grease Formulation – The Next Chapter Joseph P. Kaperick Afton Chemical Corporation Richmond, VA, USA
Abstract Earlier work by the author focused on the evaluation of common additives and additive systems in a simple lithium base grease. Some routine and several less common performance tests were used to compare different types of additives and packages and look at the impact of additive combinations. The focus was on antiwear (AW), extreme pressure (EP), antioxidant (AO) and borate components along with performance packages containing different component combinations. This study explores the different responses observed in these performance tests when using the above components in a base grease formulated with a lithium complex thickener. Background Work Previous work by this author investigated the performance of three types of zinc dithiophosphate, two sulfur sources, a combination of antioxidant and boron components aimed at high temperature performance and additive packages formulated to meet various performance targets. The different components were all evaluated in a simple lithium 12-hydroxy stearate grease using a variety of bench tests. The tests ranged from common bench tests included in many specifications to less common evaluations of performance aimed at differentiating characteristics of the additives employed [1]. Much work has been done to evaluate different additive components using a variety of grease bench and rig tests. Some of this work has been published on this subject. Many authors used the Four-Ball Weld test to measure the effectiveness of novel EP agents or in studies of synergies or tribochemical interactions that improve boundary lubrication protection [2-10]. Pressurized Scanning Differential Calorimetry (PDSC) was used by Reyes-Gavilan [11] to evaluate different antioxidants in polyurea- and lithium-thickened greases by a standard test method (ASTM D5483). Senthivel et al. [12] looked at PDSC as well as a variety of other techniques including spectroscopic analysis and thermal aging to investigate the high temperature behavior of greases. Samman [13] discussed relative characteristics of different components in greases and their relationship to high temperature performance, and he utilized case studies of greases in high temperature applications. Rheological techniques have become more commonly used in evaluating the performance of high temperature greases in recent years. Nolan and Sivik [14,15] used rheology to compare the high temperature performance of a variety of different thickeners and compared those results to data obtained with a dropping point apparatus. Coe [16] looked at high temperature applications of grease formulations and examined their performance in dropping point as well as a number of other high
- 10 NLGI Spokesman | VOLUME 85, NUMBER 3 | July/August 2021
