Hydraulic breakout forces that can exceed hundreds of thousands of pounds... Dirty, wet and muddy work environments that are home to damaging contaminants... It's no wonder that articulation joints, pins and bushings can seize and lock up if not given the appropriate care.

To keep moving parts functioning properly for a long and productive life, it's essential to maintain regular greasing intervals using the appropriate grease formulation.

"When you grease a bearing, a universal joint, connecting rod, etc., it's important to re-grease it at the proper intervals to pump out the old grease that is contaminated with water, dirt or even metal from any wear that may have happened during the application," says Walt Silveira, U.S. technical services manager, Shell Lubricants. "Selecting the right grease will help extend service life. It's about reliability and longevity of the equipment to keep it from wearing prematurely."

Thick or thin?
There are several things to consider when selecting a grease. One of the first you will want to evaluate is pumpability.

Greases are classified according to National Lubricating Grease Institute (NLGI) grades, which rate a grease's thickness or fluidity. Essentially, the difference between grades boils down to how much soap, or thickener, is added to the base oil - the higher the grade number, the greater the amount of soap used, and the greater the tendency for the grease to stay put in heavily loaded components.

The most fluid grease, Grade 000, has a consistency similar to molasses or heavy gear oil, while a Grade 6 resembles a bar of soap. The grades used most often in the construction industry fall into the 0 to 2 range.

Grade 0 grease is commonly used in auto lube systems where the grease has to be fluid enough to circulate through several feet of hose. Grade 1 is thicker and can be a good choice for cold climates in winter, because they maintain sufficient pumpability when temperatures plummet. Grade 2 is typically used in the summer in colder climates and in warmer climates year round. It provides a balance between pumpability and clingability.

The type of soap used in a particular grease is also a determining factor in selection. It is essentially a holding agent that traps droplets of oil. When force is applied to the grease, the soap releases the oil to lubricate the metal surfaces. "The thickener acts like a spider's web," says Mark Betner, heavy-duty lubricant manager, Citgo. "It interlaces and locks in the oil until you need it to be released."

Be aware of the type of thickener being used, because they don't all get along. "There's a lot of family fueding between thickening agents," Betner notes. "Lithium greases are like type O blood; they get along with everyone. Other thickeners, such as aluminum complex-type greases, can offer advantages in performance, but they don't like other thickeners.

"If you put two greases that are chemically incompatible with each other, they start to fight, and one of them leaves," he continues. "That's why we tell owners if you're changing brands or types of greases, be aware of the chemical compatibility. You may have to lubricate the fitting more often to remove the old grease as fast as possible."

Which additives do you need?
Once you've selected a grade, it's time to evaluate properties of the base oil - such as viscosity - and additives that can enhance performance for a given application.

Oil viscosity plays a role in determining a grease's load carrying ability and how well it will perform under extreme pressure. Load carrying ability ratings are reported on data sheets as the four-ball weld load and the Timken "OK" load. "The higher the numbers, the greater the load carrying capacity, and the greater the grease's ability to withstand heavy loads without breaking down," says Corey Taylor, grease technology manager, BP Lubricants.