The development of finished greases for use in diverse automotive and industrial applications necessitates the act of balancing oxidation, load carrying capacity and wear properties. Factors that impact the performance of the grease include choice of base oil, thickener and specific additives to deliver attributes desired for the targeted application. Furthermore, the severity of the application must be considered from an operating temperature point of view. The ASTM D4950 classification specifies requirements for automotive wheel bearing greases. Of the 12 tests listed in the standard, the ASTM D3527 life test is the most difficult requirement of the classification. Other key tests include ASTM D2266 (four-ball wear), ASTM D2596 (four-ball extreme pressure (EP)), and ASTM D1743 (rust). Each test represents a critical performance characteristic that is required and expected of any high-quality GC automotive grease. The D3527 test is considered a bearing oxidation test for grease. An alternative, non-bearing method of measuring the oxidative stability characteristics of grease is pressure differential scanning calorimetry (PDSC) as measured by the ASTM D5483 test. This paper describes the use of all of the above tests to characterize a new multifunctional, ashless additive capable of delivering robust ASTM D4950 performance characteristics. Additionally, the individual contributions to performance of each additive class in the overall formulation are examined, thus allowing for a more complete understanding of the delicate additive balance required to meet the performance targets. Additional grease life additive testing was made in the high temperature, high speed ASTM D3336 and DIN 51821 tests. The data was compared with industry benchmark greases, demonstrating the multi-functionality of the additive package that was formulated.
展开▼
