Lubricants

Grease Tips for Technicians

Grease. Everybody uses it, but most technicians only know a few things about it. Namely, it's messy, it comes in a bucket or tube, and they want someone else to have to mess with it.

That leaves a lot of grease questions unanswered: Where does it come from? What does it really do? When is the best time to apply it? What's the difference in types? Does color mean anything?

Aviation Maintenance tracked down Walt Silveira, director of industrial and aviation products for ConocoPhillips, to find out just what the scoop is on this slippery subject.

What is grease?

Simply put, grease is oil that's had a solid phase-thickener added to it. Typically grease is 95 percent oil, 5 percent thickener, and has traces of other performance additives. The solid nature of grease is a positive as it acts as a seal to prevent the ingress of water and dirt contaminants.

When applied properly, grease will act as an effective corrosion preventative. When there's grease present, water, dirt, and other contaminants cannot get into critical areas.

"This is very important in aviation applications because of the environment that aircraft are exposed to," Silveira explained. "The overall grease formulation (oil type, additives, and thickeners) is important in the grease's ability to prevent corrosion. Proper and periodic re-greasing is important in order to replenish the grease and flush out any contamination."

Are all greases compatible?

There are several types of thickeners used to make grease today: lithium, calcium, bentonite, and inorganic gels, just to name a few. "Some thickeners are not compatible with each other," Silveira said. "When you mix incompatible types, the consistency of the grease will change and become softer or harder." Either way it means the grease can't do its job, so always check your lubricant supplier before you alter grease types.

What does grease color mean?

Silveira explained that grease comes in all different colors and, he's sorry to say, the grease's color has nothing to do with performance. "Companies add colored dyes just for aesthetic reasons," he said.

But a change in the color of the grease in or around a mechanism can be a warning sign that the material is contaminated by another grease, wear particles, water, and dirt or there may have been some oxidation due to elevated temperatures.

If you find an area where the grease has changed color, it's a good idea to examine the area as closely as possible before cleaning and reapplying the appropriate grease. Then monitor the area periodically for signs of another color change, which would be an indicator of another problem.

Natural versus synthetic grease

In aviation applications synthetic-oil-based greases have become popular because of their improved performance-when compared to mineral oils-at both very low and very high temperatures.

For example, when components are exposed to very cold temperatures for long periods of time the grease can stiffen. Then when the mechanism is put into service, the oil in the grease cannot provide adequate lubrication. Most mineral oil-based greases will not provide proper lubrication in these conditions.

Which grease is the right grease?

The first place to start is in the aircraft's maintenance manual. This is where you'll find definitive guidance on which grease to use and how often to apply it, under normal circumstances. "The number of hours and environmental conditions your aircraft is exposed to will also determine if there needs to be an adjustment to the maintenance service intervals," Silveira said. "I also highly recommend that you speak to your lubrication supplier with any questions you may have."

What about grease build-up around fittings?

Grease build-up on the outside of a fitting is doing its job and keeping contamination out of the area, but that exposed grease is collecting water, dirt, and other contaminants. The exposed grease needs to be carefully removed periodically and the fitting needs to be cleaned before new grease is applied.

Putting a grease gun on a dirty fitting will just force water and dirt into the mechanism. It is important that the fitting and the grease gun itself be properly cleaned before each use. If the tip of the gun is not cleaned you risk taking dirt and water from one fitting and pumping it into another area.

What about pressure washing?

"Any type of moisture on a lubrication point is bad," Silveira said. "This could lead to corrosion, wear, and the ultimate failure of the component. Care should be taken to avoid pressure washing around any bearing, joint, fitting, or actuator. If it must be cleaned, cover the greased area completely."

"In cases where the grease point has been contaminated with water," he continued, "the area should be purged completely with new grease as quickly as possible."

Biggest grease mistakes and misconceptions

• If a little grease is good, more grease is better. "If a bearing is over-greased it can generate more heat due to the insulating effect of the grease," Silveira explained. "Technicians should only re-grease at the proper intervals and follow the proper greasing procedures."
• All greases are the same. "Not true! Aviation greases are formulated for very specific applications," Silveira said. "Care should always be taken to ensure the proper MIL spec grease is being used for the specific application." Grease is no place to cut corners.
• Keep your grease clean. "Keeping new grease sealed and clean and keeping grease-application equipment clean is very important," he added. "You wouldn't add contaminants to your engine oil; why would you purposely add dirt to grease?"