Unworked penetration is determined by bringing a grease lubricant sample to a temperature of 25°C (77°F) and transferring it to a standard cup. The grease surface is then smoothed, and the penetrometer assembly, consisting of a cone and its movable parts weighing 150 grams (0.33 lbs.), is positioned so that the cone’s tip barely touches the grease surface.
After placing the assembly on top of the grease for precisely five seconds, the distance the cone drops and penetrates the grease is measured and recorded as the unworked penetration level.
The NLGI stands for the National Lubricating Grease Institute, an organisation founded in the United States in . The NLGI is a non-profit trade association that sets standards, provides technical support, and promotes research on lubricating greases.
One of the most widely used and recognised standards established by the NLGI is the NLGI Classification, which categorises greases based on their consistency or hardness. The NLGI Classification uses a scale from 000 to 6 to define different grades of grease. The classification is based on penetrating a standard cone into the grease lubricant under specific conditions.
The NLGI Classification grades are as follows:
NLGI 000 – Very fluid, almost liquid-like consistency.
NLGI 00 – Soft, semi-fluid consistency.
NLGI 0 – Soft, butter-like consistency.
NLGI 1 – Semi-soft consistency.
NLGI 2 – Normal consistency, also known as “multipurpose” or “general purpose” grease.
NLGI 3 – Firm consistency.
NLGI 4 – Very firm consistency.
NLGI 5 – Hard consistency.
NLGI 6 – Very hard consistency.
The NLGI Classification is crucial because it helps users and manufacturers select the appropriate grease lubricant for specific applications based on the required consistency and performance characteristics. For example, greases with lower NLGI numbers (000 to 2) are often used in centralised lubrication systems or in applications where low friction is essential. In comparison, greases with higher NLGI numbers (3 to 6) are used in applications requiring high stability and mechanical stability.
It’s worth noting that the NLGI Classification is just one aspect of grease specifications, and other factors such as base oil type, thickener type, additives, and performance properties also play a significant role in determining the suitability of grease for a particular application.
The SKF EMCOR test helps manufacturers and engineers select the right grease for specific applications where corrosion protection is critical. Corrosion can significantly affect the performance and lifespan of machinery and equipment, leading to costly maintenance and repairs. Greases that perform well in this test are preferred for use in marine environments, outdoor equipment, and any other application where exposure to moisture is a concern.
It’s important to note that while the SKF EMCOR test is a valuable tool for assessing a grease’s corrosion resistance, it is just one of many tests and factors considered in selecting the most suitable grease for a particular application. Other properties such as load-carrying capacity, temperature resistance, and shear stability also play important roles in determining the overall performance of grease in various applications.
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