Abstract
The ability of lubricants of the same viscosity to provide adequate lubrication for surfaces in relative motion (lubricity) ,canwidely vary. Under boundary lubrication conditions fluid films of
poor lubricity, can break down giving rise to contact. Contact
results in wear, which under severe conditions, can damage the moving
components beyond repair. The special case of an aircraft, axialpiston, fuel pump has been studied for this project.
The pump consists of steel pistons running in cadmium pleted
aluminium bronze bores lubricated by aviation kerosene of variable
lubricity. Seizure occurs in the pump if the fuel lubricity is poor
but protection is afforded by the inclusion of an additive in the
fuel. The latter is not universally accepted by the operating
companies so the project not only aims to determine the mechanism of
failure of the pump but also the mechanism of protection by the
additive.
Boundary lubricated wear was simulated using a flat-faced pin-on-
disk machine and friction and wear rate measured for bronze sliding
against steel for various fuels. Wear rates of between 10-9 and
10-6mm3 mm-1 were found and, although the additive has an initial
pro-wear effect, very low wear could be obtained when the additive was
present.
The wear pins and disks, samples from a pump simulation rig (the
Lucas two-piston rig) and from 'in service' pumps were analysed. The
physical analytical techniques used, in this part of the work,
included scanning and transmission electron microscopy, X-ray powder
diffraction, electron probe microanalysis and Auger spectroscopy. This analysis has shown that the aluminium content, of the bronze, plays an important role, in the seizure mechanism, by diffusion to the steel surface. The additive prevents seizure by preferential corrosion of aluminium from the bronze, thus preventing its transfer to the steel. Similarities between laboratory, intermediate test rig and 'in service' experience have been found by using this
analytical approach.
Finally a new theory has been instigated to predict wear rates
under conditions of boundary lubrication where oxidation is
occurring.
| Date of Award | Mar 1979 |
|---|---|
| Original language | English |
| Awarding Institution |
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Keywords
- wear
- aluminium bronze
- steel
- aviation kerosene