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Lubricating Bearings and Other Machine Elements
Published in Heinz P. Bloch, Kenneth E. Bannister, Practical Lubrication for Industrial Facilities, 2020
Heinz P. Bloch, Kenneth E. Bannister
The temperature range over which a grease can be used depends largely on the type of base oil and thickener as well as the additives. The lower temperature limit, i.e., the lowest temperature at which the grease will allow the bearing to be started up without difficulty, is largely determined by the type of base oil and its viscosity. The upper temperature limit is governed by the type of thickener and indicates the maximum temperature at which the grease will provide lubrication for a bearing. It should be remembered that a grease will age and oxidize with increasing rapidity as the temperature increases and that the oxidation products have a detrimental effect on lubrication. The upper temperature limit should not be confused with the “dropping point” which is quoted by lubricant manufacturers. The dropping point only indicates the temperature at which the grease loses its consistency and becomes fluid.
Lubricating Greases
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
The dropping point of a grease is the temperature at which a drop of material falls from the orifice of a test cup under prescribed test conditions (Figure 4.5). Two procedures are used (ASTM D566 and ASTM D2265) that differ in the type of heating units and, therefore, the upper temperature limits. An oil bath is used for ASTM D566 with a measurable dropping point limit of 500°F (260°C); ASTM D2265 uses an aluminum block oven with a dropping point limit of 625°F (330°C). Organo-clay soap thickened greases do not have a true melting point but have a melting range during which they become progressively softer. Some other types of greases may, without change in state, separate oil. In either case, only an arbitrary, controlled test procedure can provide a temperature that can be established as a characteristic of the grease.
Additives for Grease Applications
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Robert Silverstein, Leslie R. Rudnick
The hardness of grease is a function of temperature. Greases act as thickened lubricants only to a point, and then at some temperature they become fluid. A standard measure of the resistance of a grease to flow as temperature is increased is the dropping point (ASTM D2265) [15]. In essence, the dropping point is the measure of the heat resistance of the grease. In the dropping point test, a grease sample is packed into a standard test cup with a small opening. The sample is heated by introducing the sample into a preheated aluminum block. The sample temperature plus one-third of the difference between that temperature and the block temperature when the first drop of fluid leaves the cup is defined as the dropping point. Guidelines for the maximum usable service temperature and ranges for dropping points of greases made with various thickeners are summarized in Table 24.3 [16,17]. The self-diffusion of oil in lubricating greases has been studied using nuclear magnetic resonance spectroscopy at temperatures between 23°C and 90°C. Greases based on naphthenic mineral oils and PAO synthetic oils were measured. It was shown in this temperature range (40°C–90°C) that, using the same base fluid, the concentration of the thickener affected diffusion [18].
Tribological and rheological properties of calcium grease with hybrid nano additives
Published in Journal of Dispersion Science and Technology, 2022
Bahaa M. Kamel, Alaa Mohamed, M. S. Gad
The dropping point is the temperature at which the first substance drop leaves the cup or the moment at which grease transition from semi-solid to liquid form. A sample of the lubricating nano grease contained in a cup suspended in a test tube heated in oil is the basic working component of the dropping point. According to ASTM standard D-566,[42] the temperature at which the first drop of grease leaks from the cup is sometimes referred to as the grease dropping point. The thermal properties of the nano grease should be taken into account most carefully while analyzing its thermo-physical features. The thermal conductivity and thermal resistance of the created nano grease were measured using the KD2 thermal properties analyzer. The transient hot-wires approach provides the foundation for the operation of the KD2 thermal properties analyzer.[43] In earlier papers,[44] the experimental setup, testing, and temperature control were described in detail.
Tribological and rheological properties of the ultrafine CaCO3 blended nano grease
Published in Journal of Dispersion Science and Technology, 2022
Khalida Akhtar, Saniya Yousafzai
The dropping point establishes the maximum useable temperature of the grease. For the dropping point, ASTM D-566 test procedure was used. During the test, the grease cup with a small hole in the bottom was coated with the sample grease and is supported in a test tube placed in an aluminum block oven at a preset constant temperature. The thermometer was inserted in the cup without coming in contact with the grease. A drop of grease fell from the cup to the bottom of the test tube with a rise in temperature. The reading on the thermometer was noted as the observed dropping point (Table 1).