A grease that is too stiff may not feed into areas requiring lubrication, while a grease that is too fluid may leak out. Grease consistency depends on the type and amount of thickener used and the viscosity of its base oil. A greases consistency is its resistance to deformation by an applied force. The measure of consistency is called penetration. Penetration depends on whether the consistency has been altered by handling or working.
Choosing the right consistency of grease for an application is critical, as a grease that is too soft may migrate away from the area that needs to be lubricated, while a grease that is too stiff may not effectively migrate into the areas that need to be lubricated. The penetration test measures how deep a standard cone falls into a grease sample in the tenths of millimeters. Each NLGI grade corresponds to a specific worked penetration value range. Higher penetration values, such as those over , indicate a lower NLGI grade number. The NLGI scale ranges from semi-fluid to 6 solid block like a cheddar cheese spread.
This video will feature penetration tests. Penetration tests are conducted by Nye technicians in order to determine the stiffness of a grease. They are two of the four required tests performed on every single batch of grease at Nye prior to shipping.
Of course, greases are formulated with oil, thickener and additives. While you may be familiar with the formulation of grease, do you know what grease consistency means and how it should influence your grease selection? Grease is formulated with up to 95 percent base oil.