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Grease sampling Hesitation around the proper method to collect an in-service grease sample may hinder the thought of sampling greased components. With the new ASTM methods, a standardisation for sampling and testing in-service grease should provide insight for proper sampling and testing to be applied.
ASTM D7718 provides a practice to obtain a trendable in-service lubricating grease sample from most in-service and failed grease components. The method provides standardisation for sample containers, sampling procedures and handling taking the guess work out of how to pull proper sample for testing. Only 2.5 grams of grease is required for in-service grease testing.
The life of a machine has three obvious wear regions: 1) Running-in period of new equipment, 2) machine life wear during normal operation and 3) end of life wear indicating failure. The fdM+ test will provide a total ppm of magnetic ferrous content in the sample with no limitation on the size of wear particles like elemental analysis has. The difference in fdM+ and elemental analysis is identifying possible wear size and concentration.
FTIR compares an in-service grease to a baseline grease. Differences can indicate mixing, contamination and base oil degradation.
Figure 1: FTIR Spectra in red is indicative of an obstructed beam path, possibly due to wear metals and/or dust and debris.
Figure 2: FTIR Spectra in black shows oxidation of base oil.
Colour testing compares an in-service grease to baseline grease. Colour change itself does not dictate an unacceptable change in performance but may be a warning parameter for further investigation. Differences may indicate mixing, degradation and or accumulation of debris (wear contaminants) in grease.
Example 1: Grease sampler with grease sample.
Maintenance in-service testing ASTM D7918 is a standard test method for measurement of flow properties and evaluation of wear contaminates, oxidative properties of lubricating grease by die extrusion and preparation. Testing includes, but is not limited to, fdM (Ferrous Debris Monitor), colour, FTIR (Fourier Transform Infrared Spectroscopy), die extrusion, ruler, microbial (ATP), elemental analysis and/or water to provide recommendation and identify concerns.
Example 2: Colour Test.
Ruler testing provides an indication of useful life of the base oil of the grease by comparing the in-service grease to the baseline grease amines. Changes or loss of amines in the in-service grease or loss of antioxidants indicates oxidation.
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