Dupont Krytox Properties Lubricants Consistency
Krytox Oil Viscosity
There are two measurements of viscosity: kinematic and dynamic, or absolute viscosity . The viscosity expressed here is kinematic viscosity, the ratio of dynamic or absolute viscosity to density . This is the value usually measured . It can be converted to dynamic viscosity using the following relation:
Kinematic viscosity x density = Dynamic viscosity (Centistokes, cSt x g/cc = Centipoise, cP)
Because of the high density of DuPont Krytox fluids, the dynamic is almost double the kinematic viscosity .
Choosing what viscosity of oil to use depends on the application . Generally, lower viscosity oils flow more readily and are used in operations where high speed is desired. High viscosity oils are preferred for low speeds or heavy loads . Since viscosity drops as temperature increases and rises as temperature decreases, the choice also depends on temperature . Thus, for the same reference temperature, a lower viscosity oil would be preferred for high speed operations and a higher viscosity oil would be preferred for low speeds . This typically applies to choosing a base oil for grease as well .
National Lubricating Grease Institute (“NLGI”) Grease Consistency
Greases are formed by mixing the base oil with a thickener to form a grease . Krytox greases use a special, high-thickening efficiency, low-molecular weight PTFE with very small particle sizes as the thickener . It is one of the most thermally stable thickeners for high temperature, long-term greases . The lower thickener content in the grease maximizes the oil for improved grease life . The stiffness of grease is measured by its NLGI grade . This is determined using the penetration ranges listed in Table 3 . The amount of thickener in the grease determines its stiffness . The more thickener that is added, the stiffer and harder the grease becomes .
|Table 3||NLGI Penetration Ranges|
|NLGI Grade||NLGI Worked Penetration mm/10 at 25 °C (77 °F)||Appearance|
These soft or fluid greases have free-flowing characteristics . They belong to NLGI penetration classes 0-000 and are often used for lubrication of sealed gear drives . Krytox soft or fluid greases can be ordered in all NLGI grades, but NLGI 2 is standard and will be provided if grade is not specified .
Some applications require grease that is stiff and does not fall back easily into the bearing races . These systems often run at higher speeds . Harder NLGI grade 3 Krytox greases are recommended for these applications .
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