Lithium, viscosity, dropping point

Grease is used to lubricate sealed parts and components, components that cannot be lubricated frequently or that require higher viscosity and more resistance than oil in harsh conditions high speed and high load components such as roller bearings.

It is a mixture of 3 types of ingredients:

  • Oil

  • A thickener or soap that provides its semisolid consistency and appearance. Lithium soap is widely used in industrial greases as it provides good adherence to metal, is non-corrosive and may be used under heavy loads and high temperature.

  • Viscosity, durability, or resistance improving additives.

Large, high speed bearing greases should be tested frequently to monitor the depletion of lithium, viscosity and dropping point, which is the temperature at which a grease will degrade from a semisolid to a liquid state.

Wear metal particles and ambient dirt must also be detected. These contaminants can cause bruises, modify the dimension of the rolling elements, reduce bearing efficiency, ending up in critical damage and failure of the equipment.

The Dropping point of a lubricating grease is the temperature at which the grease passes from a semi solid to a liquid state. This grease test establishes and maintains benchmarks for quality control, while identifying the type of grease sampled.
Ferrous Debris Monitor uses magnetometry to measure the wear metal particle contamination of an oil or grease sample and provides trendable parts per million (PPM) results, regardless of the size of the particles. Because its results are provided in PPM, FDM is regarded as an advanced PQ test. The latter indeed only shows them as a unitless index. FDM can be used to measure un-combined ferrous wear metal particle debris in oil or grease in a wide range of types of industrial and marine machinery.
A combination of ICP spectroscopy and Particle Quantifier Index (PQ) will detect wear metal particles and ambient dirt contaminants. Both these tests are complementary: spectroscopy will provide information on the depletion or not of lithium and detect small wear metal particles. PQ will detect wear metal particles regardless of their size, where the concentration, hardness and larger particles may end up causing critical damage.
Lithium soap is the most important thickening additive in industrial greases. ICP spectroscopy will provide information on the depletion or not of lithium and detect small wear metal particles (less than 6 microns).
The particle quantifier index test measures the mass of ferrous wear debris in a sample and displays this as PQ index by Hall Effect regardless the particle size. PQ index is a unitless quantitative number and can be trended with acceptable linearity over a wide range of ferrous debris content and particle sizes. The larger the index the greater the ferrous wear content.
Too much water in grease can reduce its thickness, cause water washout, leading to base oil oxidation and ultimately bearing corrosion. The purpose of this test is to make sure that the percent of water in the grease sample does not exceed the recommendations of the manufacturers.

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