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    Grease Working and Its Role in Consistency Trending

    Published: 2013

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    The complex nature of grease, as a semi-fluid, dictates the means by which repeatable, meaningful data can be obtained regarding the rheological properties of grease. Because of the non-Newtonian behavior of grease, the measured consistency will change with respect to the amount of shear placed on the grease prior to testing. Because of this, standard methods require grease rheological properties to be taken after a standard shear condition is met, and the grease is considered “worked.” Standard grease working, with a grease worker, provides a standard shear condition so that comparisons can be made between samples from varying batches or locations. In this paper, we compare current methods of grease working to a new approach, using a micro-mixer. The micro-mixer passes the grease through a “cat-eye-” shaped orifice created by the overlapping area of two 0.200-in.-diameter circular holes offset by 0.100 in. Using opposing oscillating mechanical pistons, the grease is worked while passing back and forth through this single orifice. The method requires a much smaller sample size than current methods and supports rheometer and die extrusion testing, allowing greater flexibility for in-service condition monitoring and situations where taking a larger sample is not feasible or desirable. Discussed in this paper are the effects of grease working on measured rheological properties, such as elastic modulus, yield stress, and cone penetration value, as well as the number of strokes required to achieve a comparable worked condition using a standard grease worker and the grease micro-mixer. The results are considered across various grades of a single grease series and do not take into account the variations between thickener types, base oils, or alternate orifice shapes.


    consistency, grease working, in-service fluid, condition monitoring

    Author Information:

    Bupp, Evan
    MRG Laboratories, York, PA

    Wurzbach, Richard
    MRG Laboratories, York, PA

    Committee/Subcommittee: D02.96

    DOI: 10.1520/STP156420120194