A, Grease consistency

Consistency is one of the most important property of grease must be considered for selecting of right grease for given application. Grease that is too soft may migrate from the area that needs to be lubricated, while grease that is too stiff may not effectively migrate into the areas that need to be lubricated.

The consistency of grease is controlled by the base oil viscosity, thickener type, and the thickener concentration. Thickener like as "a sponge" to hold base oil (plus additives). Under force pressurizing on the grease, the oil will be released for lubricating, Grease with low consistency will release the oil more readily. Grease with high consistency will release the oil sluggishly.

Consistency, base oil viscosity of grease is critical properties must be appropriate to temperature, speed, and load of machinery it lubricate.

• NLGI grade 000, 00, and 0 (like ketchup, yogurt, and mustard): suitable for enclosed and centralized applications, where grease migration is not an issue, re-grease easily.
• NLGI grade 1, 2, and 3 (like soft butter): are the most commonly used greases, can operate at higher temperature range and at higher speeds than NLGI grades 000-0 group. 
• NLGI grade 4, 5, and 6 (like ice cream, fudge or cheddar cheese): and NLGI grade 4 should be chosen for devices moving at high speeds (greater than 15,000 rotations per minute). For high speed devices, stiff, channeling, churning factor need to be considered, examines carefully. NLGI grade 5 and 6 are not typically used in applications.

Grease's stiffness is measured, indicated by its penetration value (Worked Penetration 60X). The National Lubricating Grease Institute (NLGI) classified the stiff, consistency of grease into NLGI grade from 000 to 6.

B. 5 Categories of penetration

• Undisturbed: Grease that is in its original container
• Unworked: a sample that has received only minimal disturbance in being transferred from the sample can to the test cup.
• Worked: a grease that has been subjected to 60 double strokes in a standard grease worker. NLGI classification is based on worked penetration.
• Prolonged Worked: grease that has been worked the specified number of strokes (more than 60), brought back to 77 degrees F and then subjected to an additional 60 double strokes in the grease worker.
• Block: this is the penetration of a block grease, which is hard enough to hold its shape without a container when testing.

Related artivles:

5 Base oil groups: classification and characteristics

The properties of lubricating oil