Today, though aircraft and associated equipment have become technologically more complex with a service life of 20 years plus, the greases being used could also be 20 to 30 years old. In a modern jet aircraft grease has to work very hard indeed, withstanding extremes of operating conditions: multiple take-offs and landings, long cruises at low temperatures, sudden and extreme temperature changes on landing, frequent wash downs with cleaners and de-icing fluids.
The European Lubricating Grease Institute, which Dicken chairs, established a working group in 1994, at the same time that U.K.s defense agency was attempting to reduce the number of grease specifications for their aircraft. From the results of a survey with the European Airline Committee Materials Technology, the ELGI group decided to rationalize aviation greases and introduce three to four industry specifications.
In 1996 SAE Internationaljoined the effort, forming the AMS-M Committee. Many airline operators in the U.S., said Dicken, were experiencing similar problems as their European counterparts in the plethora of greases specified. The SAE committee holds two meetings each year, alternating between Europe and theU.S., has already issued an industry standard for geared actuators on aircraft.
A host of issues needs attention. Aviation grease formulations have shifted from clay-based products towards lithium complex soap thickeners, water ingress and corrosion protection being major drivers of this change. Work is still needed in the area of compatibility when different greases are mixed together in operational service. With the enormous number of greases specified, misapplication errors can occur. These, Dicken cautioned, may be not too critical if the greases were the same type of chemistry, but now there are both clay and lithium complex products widely available. He felt future specifications would contain not only performance parameters but formulation criteria as well, to ensure that errors will not be catastrophic.
Greases, moreover, are not always stored in their original containers but are packed into components, bearings, valves, etc., which may be stored in conditions that violate the grease manufacturers recommendations. What negative impact could this have? Amsterdam-based ELGI and the U.S.-based National Lubricating Grease Institute have formed a joint working group to examine the effects of such a scenario and the good news, said Dickens, is that they are already forming some recommendations.
The needs of the hour: reduce the number of grease specifications; employ new chemistries and new test methods for formulations; educate users about the effects of mixing different products; reduce product compatibility issues through more detailed specifications.
Happily, tangible progress is discernible as the working groups address these issues, Dickens said.