Both manufacturers and users of construction equipment agree that grease is cheap insurance against wear and tear on bushings, bearings and any metal components that come in close contact. And while grease manufacturers have fine-tuned their formulas and created a range of general-purpose greases, they also caution against a one-size-fits-all mentality.
“When people say they use one grease for everything, I say, sure you can, but for how long, what is your goal?” says Nick Samman, manager of grease product development for Petro-Canada. “If you’re buying a cheaper grease, in essence you’re using more of it, and it will probably cost you more than if you used a more premium grease.”
A good greasing regimen requires that you select the right grease for the application and environment and apply it properly at the right intervals. Equipment manufacturers give some guidance in the grease specs they list for the equipment they sell, but that’s not everything you need to know. Applications change, temperatures and environments change – and over time most shops and service technicians develop habits that may not be the best possible practice.
Grease is made up of three elements, the base oil, thickeners and additives. To understand how grease protects your machinery, it is helpful to understand how each works.
Base oil content
Up to 95 percent of the content of grease is oil, either mineral, synthetic or biodegradable oils. As with engine oils, there are different viscosities for grease base oils. High-speed components need a low-to-medium viscosity oil. Low speed parts are better served with higher viscosity base oils.
· Mineral oils are the least expensive and most widely used.
· Synthetic oils do a better job of maintaining their consistency and remaining pumpable in environments where you have extreme cold or heat or both.
· Biodegradable oils such as vegetable oils are used on sites with strict environmental controls, such as work over watersheds and wetlands. They’re more commonly used in Europe, but requirements for their use are expected to grow in North America.
Keeping grease in place
Thickeners make grease dense and play a role in lubrication. “Grease is designed for the oil to come out as needed,” says Peter Kane, product line specialist, ChevronTexaco Global Lubricants. “The thickener keeps the grease in place until it does.” Each thickener has different properties and these have a big impact on the performance of the grease.
· Lithium and lithium complex thickeners are the most commonly used, making up about two-thirds of the North American market, says Mark Betner, heavy-duty products manager at Citgo Petroleum. Lithium is the most popular because of its good water resistance and high temperature stability.
· Aluminum complex greases hold up to heat quite well too, and have other advantages. “Aluminum complex greases are thixotropic, meaning they get a little thinner when they’re being worked and harder again when they’re not,” says Jim Girard, lubrication specialist at Lubriplate. “I think you get better protection and shear stability with aluminum complex greases. They’re not as pumpable, but if you’re hand greasing, there’s nothing like them.”
· Polyurea thickeners are used mostly in electric motors and bearings and sometimes in hydraulic system components. Polyurea thickeners are also occasionally used with auto-lube systems because of their pumpability.
· Calcium thickeners are great for corrosion protection and often spec’d where water is frequently present.
There are a variety of other specialty thickeners used in grease but these are found mostly in industrial applications and rarely in construction equipment.
Additives solve specific problems
To help greases meet a variety of specialized needs manufacturers give them additives.
· Extreme-pressure additives are very important in construction. Molybdenum disulfide (moly for short) is the most common, but you’ll also find graphite and zinc oxide EP additives. “These are considered solid lubricants,” says Kane. “Under extreme pressure, even if all of the grease goes away, you still have a layer of dry lubricant sitting there for protection.” Pin-and-bushing assemblies are one place EP additives are a must. Moly greases contain from 0.5 to 5 percent moly, with 3 percent being the most common. Graphite is similar to moly, but less effective.
· Tackifiers make grease sticky. “Tackifiers make sure the product stays where you put it,” Kane says. This is important in open gear applications, trailer fifth wheels or any place where rain and weather would wash off the grease. Greases with tackifiers, however, are not easily pumpable and not as shear stable.
· Rust-inhibiting compounds prevent rust on greased components exposed to air and moisture. Most construction greases contain these.
· Additional additives can include a diverse range of formulations including fragrances to mask smells, dyes to change the color of the grease, borates or sulfur-phosphorous to protect metal and copper flakes to prevent threads from seizing.
The National Lubricating and Grease Institute established a grease classification system that rates greases on their consistency. The chart below shows the grades and what they represent. For hand greasing in most construction applications a Number 2 grease is preferred. If you’re working in cold temperatures or you’re using an auto lube system on your machine, use a Number 1 or even a 0 grade. If you’re worried about adequate protection when using a softer grade of grease in an autolube system, ask your supplier about spec’ing a grease with a higher viscosity base oil if temperatures allow.
Another useful measurement of grease is its dropping point. The dropping point is the temperature at which a grease passes from a semi-solid to a liquid state. The dropping point is stated in degrees, Fahrenheit or Celsius or both. One of the most important differences between “complex” thickeners and non-complex thickeners is that the complex formulations give the grease a higher dropping point.
The viscosity index is a measurement of how much the oil thins out when it’s heated. The higher the VI, the less the oil thins out at high temperatures. Synthetic oils typically have very high VI ratings.
Not all greases agree with each other in a chemical sense. Polyurea-thickened greases are not compatible with lithium- or aluminum-thickened greases. And some synthetic base oils do not mix with mineral oil. It’s usually not a big problem, but something to keep an eye on if you are changing grease types.
“Compatibility is not a disaster,” says Walt Silveira, product-marketing manager, ConocoPhillips. “It might get a little harder or a little more soupy. You can usually tell pretty quickly.” As long as it’s not a closed bearing or something like a wheel bearing where you can’t observe the grease, the solution in most cases is just to pump enough of the new grease into the component to thoroughly flush out the old grease. On critical or high-speed components you may need to disassemble the component and clean out all the old grease with a solvent before applying new grease.
Even the best grease isn’t going to do you any good if it’s incorrectly applied. “Some applications need more grease than others,” Betner says. “You can over-grease anti-friction bearings and cause them to run hot. And in dusty or dirty environments it’s important to keep the dirt purged out of the system.”
“I always preach the cleanliness of the storage or application system,” Silveira says. “Whether it’s a keg, a drum, a cartridge or a grease gun, keep it clean. Keep the lid on. Any water or dirt that gets into your grease is going to get into your equipment, defeating the purpose of the grease.”
Making sure your equipment gets greased is another practice often preached, but sometimes ignored. Operators are normally charged with this task, but on big equipment or big jobs having a lube truck or a dedicated lube technician can help, says Jeff Turner, vice president, Lubrication Engineers. “On a huge paving job with a lot of equipment and a lot going on, it may be unrealistic to expect the operators to keep up with that,” he says.
Care should also be taken not to damage a fitting or component during greasing. “A lot of people don’t realize a good hand grease gun can put out 10,000 psi,” Turner says. “Once you force it to the point where the seal is damaged, you not only lose the grease, but you allow water and dirt to get in,” he says. For that reason it’s important to watch auto-lube systems for clogged lines and to observe the grease exiting the fittings to make sure they aren’t clogged with dirt or hardened grease.