From "The Lubricating Grease Guide".

Where grease is handled in a dispensing system, the grade chosen may be related more to the capabilities of the system than to the requirements of the application. In service, consistency differences are important. Consider, for example, the use of grease in a gear case. The grease should be carried into the meshing gear teeth, which are thus kept covered with lubricant. If the grease is firm, the gear teeth may cut a channel through the grease and run dry, causing damage to the teeth. Unless operating temperature is high, therefore, soft-to- semifluid greases are ordinarily recommended.

In ball or roller bearings, carrying grease to the rolling elements is considered undesirable, because that grease will churn, soften, heat up, and work its way out through the seals. Thus a common recommendation for a ball bearing is to have the bearing space only about one-third full of grease of firm consistency - often NLGI No. 2. If the bearings support a vertical shaft, the grease had best be still firmer - probably NLGI No. 3.

More information about "The Lubricating Grease Guide"

Test your knowledge and prepare for ICML lubrication and oil analysis certification.

QUESTION: An oil that is an ISO 18/16/13 is approximately how much dirtier than an ISO 17/15/12?

Get the answer.

"Which element(s) on an oil analysis report are considered dispersants?"

On your regular routine oil analysis report, the answer would be "none".

A dispersant in oil is defined as: An additive, usually nonmetallic ("ashless"), which keeps fine particles of insoluble materials in a homogeneous solution. Hence, particles are not permitted to settle out and accumulate. The most common chemistry of a dispersant is a polyisobutylene succinimide.

Dispersants, in addition to antioxidants, VI improvers and some antifoam additives are organic molecules. An organic additive molecule contains carbon, hydrogen and possibly oxygen, nitrogen or sulfur, none of which are routinely detected using elemental spectroscopy.

The metallic additives typically monitored via elemental analysis include the following:

Antiwear additives- zinc and phosphorus (ZDDP) Extreme pressure- Phosphorus

Detergents- Calcium, magnesium, barium

It is important to remember that additive depletion cannot necessarily be seen via elemental analysis. A more precise tool for measuring additive depletion is via FTIR spectroscopy. Monitoring the FTIR spectrum will allow for monitoring of dispersants as originally questioned for this piece.

For a more detailed discussion on additives and additive trending, please refer to the article "Molecular Spectroscopy - A Precision Lubrication Tool?".

Matt Spurlock, Noria Corporation

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