壳牌航空润滑脂

 Aeroshell GREASES

ABOUT GREASES

The definition of a grease is "A solid or semi-solid lubricant comprising a dispersion of

a thickening agent in a liquid lubricant to which various additives have been added to

improve particular properties".

So how is a grease made?

All greases consist basically of a base oil, a thickener (essentially a lattice which gives

the stable semi solid consistency) and performance improving additives. Varying

these three basic ingredients leads to different greases suitable for a vast range of

applications. However, in broad terms, a typical grease would consist of about 80% -

90% base oil, 10% - 15% thickener and about 5% - 10% additives.

When they are used as lubricants, greases behave like oils in many ways. They

reduce friction by providing a film which separates moving surfaces and it is actually

oil that carries out this lubrication rather than the grease itself. However, unlike oils,

greases have the advantage that they tend to stay where they are put.

They are less likely than oils to leak out of a machine and less likely to flow away from

the surface that they lubricate under the effect of gravity or centrifugal forces. At the

same time, and this can be significant in many airframe applications, greases can

form an effective seal against moisture and solid contaminants.

Within the aviation industry, there are many grease lubricated applications covering

a very wide range of performance requirements. Those requirements are being

increasingly stretched through new technology developments and extended service

intervals.

Many different grease formulations have been developed to meet specific

requirements. One of Shell's recent objectives, as a major supplier of aviation

greases, has been the development of wide performance range products where a

single grease can cover a multitude of applications.

Greases, depending on the thickening agent, are broadly classified as either soap-

based or non-soap-based. The soap-based greases include, for example, aluminum,

calcium, sodium or lithium soaps; the non-soaps silica gel, clay and substituted urea.

181

The low melting points and water solubility of some soap greases limit their

usefulness. As a result alternative thickening agents have been developed – soap-

complex thickened greases, and non-soap greases with a much higher or no melting

point. These thickening agents were developed for greases needing superior high

temperature performance characteristics. Shell's search for thickeners without the

limitations of the simple soap-type, led to a family of proprietary technologies

including our 'Microgel ® ' and Lithium-Complex systems.

Microgel ® greases rely on an inorganic grease thickening agent, based on hectorite

clay, which has several advantages over simple soap-type thickeners. It provides the

AeroShell greases in which it is used with excellent physical properties, as shown

below. Those properties make them particularly suitable for multi-purpose as well as

specialised applications.

1. No melting point, within any conceivable temperature range for aircraft greases.

2. Very little change in consistency with variation in temperature.

3. Extremely good load carrying ability without the need for extreme pressure

additive.

4. Excellent water resistance due to the use of tenacious waterproofing agents

developed by Shell.

5. Low oil separation or 'bleeding', because of the high gelling efficiency.

During recent years, the number of greases required for aircraft

lubrication/maintenance has been reduced by more extensive use of multi-purpose

greases. However, because of commercial and technological limitations, special

greases are still required. Most aircraft grease requirements are covered by the

products in the AeroShell grease range.

To minimise the number of greases required per aircraft, the most widely used

specification in the aviation industry today is the general purpose grease to MIL-PRF-

23827.

In the early 2000's the Boeing Company introduced a multi-purpose grease

specification (BMS 3-33) to replace many of the different greases previously required

in support of Boeing aircraft. This has led to the development of the accompanying

specification SAE AMS3052. The only grease to meet the most challenging set of

requirements of the initial BMS 3-33A specification has been AeroShell Grease 33.

182

This ground breaking grease, based on a Lithium-Complex thickener system, has a

superior capacity to accommodate a wide range of proprietary performance

additives. This thickener system now forms the basis for future grease developments in

the AeroShell grease family.

Detailed information for each AeroShell grease is given in this section.