Download Grease Thief Analyzer

1. Introduction
The Grease Thief Analyzer (GTA) measures the consistency of in-service lubricating grease
and compares it to the values obtained from a reference sample. A linear actuator is used to
push a load cell which pushes the handle of a Grease Thief (GT). A second actuator moves a
table holding a substrate. This substrate is moved at a speed proportional to the grease thief
movement so the extruded grease is captured as a thin-film along the length of the substrate.
The die extrusion process is currently under review by ASTM CS96 subcommittee for integrated
testers for development of a standard practice. This practice will also address the additional
tests that can be performed with the full grease thief, and with the thin-film substrate, including:

Ferrous Density

RULER/Linear Sweep Voltametry

Optical Spectroscopy/Grease Colorimetry

Elemental Spectroscopy

FT-IR
The force required is measured as the grease is extruded through the indexing die, which is
threaded onto the other end of the GT. The test cycle includes 3 speeds and rapid transitions in
grease pressure to provide insight into shear and non-Newtonian rheology, and the force data is
averaged for each speed to calculate the “Grease Thief Index” or GTI. The GTI is the ratio of the
used grease load to the reference load, reported as a percent.
Appendix III shows a list of terms used within this document. You can reference that list as
needed throughout the analysis process.
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