Materials The base greases used were a NLGI Grade 2 clay grease containing 8.5% clay filler in ISO 460 paraffinic bright stock base oil with 0.5% antioxidant and no additional additives and a NLGI Grade 2+ fumed silica grease containing 9.2% silica. The base oil viscosity was 117 cSt at 40°C, and is a 600 Neutral Group 1 base stock.
Polymers were incorporated into the base grease by mixing in a Hobart mixer at 80°C. The polymer additives used in this study were in solutions of mineral oil and are shown above in Figure 3. Polymers were added and mixed for 3 hours to ensure complete solubilization of the polymer.
Experimental Methods Cone Penetration The NLGI consistency grade of each of the unworked samples used in this study was determined using one-quarter scale cone penetration following ASTM D1403. Water Spray-off The water spray-off was determined by ASTM D4049. Water Washout The water washout was determined at 79°C (175°F) following ASTM D1264 by an outside laboratory.
US Steel Mobility Test The U.S. Steel mobility test determines the resistance of lubricating grease to flow at a given temperature and pressure. Mobility is determined by the flow rate of the grease through a pressure viscometer.14 Typically the pressure viscometer is constructed of stainless steel and is fitted with a No. 1 (40:1 ratio) capillary. With the sample at the test temperature, the flow of grease is started under the selected pressure using a nitrogen tank and regulator. Typical test pressure is 150 psi and temperatures of ambient, 32°F, 20°F, 10°F, and 0°F. Flow rate, usually measured in grams per second, is determined by collecting the grease for a specified period. The samples used in this testing were run at 150 psi and 32°F. Lower temperatures were not evaluated due to the pervasiveness of inorganic greases in high temperature applications.
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