Tests reveal that a new lithium-soap-thickened, synthetic grease may help mission-critical aerospace components keep rolling under extreme loads and corrosive environments. For example, the force exerted on the C-5's landing gear makes its gears mission-critical components. The AFRL began testing a synthetic grease called Rheolube 374A to meet MIL-PRF 32014 grease specifications. Rheolube 374A is a lithium-soap-thickened, PAO (polyalphaolefin) grease with anti-wear and anticorrosion additives. It has an operating range of -54 to 175 degrees C. PAO is a synthetic hydrocarbon fluid widely used as a lubricant. The molecular structure of a PAO is simple and resilient, providing reduced friction, wear protection, and low-temperature serviceability. The previously specified grease on the C-5, MIL-PRF-81322, is also PAO-based, but is thickened with organic clay rather than lithium soap. Tested roller bearings had little to no corrosion and were also considered serviceable. Despite the washout of the grease during the test, the remaining film of grease was still able to provide good corrosion resistance. Tested roller bearings had little to no corrosion and were also considered serviceable. Navair also conducted other tests to ensure the new grease would function mechanically as the original MIL-PRF 81322. Grease chemistry can also affect machine torque, particularly at low temperatures. A cold-soak-bearing test showed the two greases have comparable cold performance. Lithium soaps are not water soluble or hydroscopic. Therefore lithium-soap-thickened grease can create a better barrier against environmental intrusion than a thickening substance that absorbs water. Though the overall resistance to washout might be lower in lithium-soap grease, the remaining lubricant film provides an elemental barrier sufficient to prevent corrosion. A grease can be as much of an engineered material as the parts it's lubricating. It is a design element that can be used to improve the overall per-formance of a mission-critical application like the landing gear in a 380-ton airplane. Grease should be a carefully considered component of any mechanical design.


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    Title :

    Good grease, good landing


    Contributors:

    Published in:

    Machine Design ; 77 , 21 ; 88-94


    Publication date :

    2005


    Size :

    4 Seiten, 8 Bilder



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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