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SAE ARP6255 2013 Edition, March 1, 2013
Aviation Lubricant Tribology Evaluator (ALTE) Method to Determine the
Lubricating Capability of Gas Turbine Lubricants
Description / Abstract:
Employing ‘ball-on-cylinder' philosophy, a non-rotating steel
ball is held in a vertically mounted chuck and using an applied
load is forced against an axially mounted steel cylinder. The test
cylinder is rotated at a fixed speed while being partially immersed
in a lubricant reservoir. This maintains the cylinder in a wet
condition and continuously transports a lubricating film of test
fluid to the ball and cylinder interface. The diameter of the wear
scar generated on the test ball is used as a measure of the fluid's
lubricating properties.
The apparatus can be used, by adjusting the operating conditions, to reproduce two different wear mechanisms; mild and severe wear, the ALTE therefore has the ability to assess a lubricant's performance in that regard. These mechanisms are described below.
Mild Wear
As the test cylinder rotates, the lubricant is continuously transported to the ball and cylinder interface. At this interface under abrasive wear conditions, there is an elastohydrodynamic/boundary layer of lubricant which only allows contact of the surface asperities of the ball and cylinder. Due to the difference in hardness of these asperities and motion of one surface relative to the other, abrasion and hence mild wear occurs (two body abrasive wear). Hard wear debris carried from the cylinder to the wear scar area can result in three body abrasive wear of the softer surface. Abrasive wear gives a characteristic surface topography consisting of long parallel grooves in the sliding direction.
Severe Wear
At a specific load, a transition from mild to severe wear can be observed, at this transition, a reduction and subsequent breakdown of boundary lubrication and film thickness occurs. This results in full metal-to-metal contact of the sliding surfaces, leading to adhesive wear and a large wear scar. If loading is increased beyond this transition point then localized welding and eventual seizure will occur.
It should be noted that the mild and severe wear mechanisms described above are entirely different tribological phenomena where a transition of lubricating film thickness gives a change in the amount of metal surface contact.
The apparatus can be used, by adjusting the operating conditions, to reproduce two different wear mechanisms; mild and severe wear, the ALTE therefore has the ability to assess a lubricant's performance in that regard. These mechanisms are described below.
Mild Wear
As the test cylinder rotates, the lubricant is continuously transported to the ball and cylinder interface. At this interface under abrasive wear conditions, there is an elastohydrodynamic/boundary layer of lubricant which only allows contact of the surface asperities of the ball and cylinder. Due to the difference in hardness of these asperities and motion of one surface relative to the other, abrasion and hence mild wear occurs (two body abrasive wear). Hard wear debris carried from the cylinder to the wear scar area can result in three body abrasive wear of the softer surface. Abrasive wear gives a characteristic surface topography consisting of long parallel grooves in the sliding direction.
Severe Wear
At a specific load, a transition from mild to severe wear can be observed, at this transition, a reduction and subsequent breakdown of boundary lubrication and film thickness occurs. This results in full metal-to-metal contact of the sliding surfaces, leading to adhesive wear and a large wear scar. If loading is increased beyond this transition point then localized welding and eventual seizure will occur.
It should be noted that the mild and severe wear mechanisms described above are entirely different tribological phenomena where a transition of lubricating film thickness gives a change in the amount of metal surface contact.
SAE ARP6255 2013 Edition, March 1, 2013
Aviation Lubricant Tribology Evaluator (ALTE) Method to Determine the
Lubricating Capability of Gas Turbine Lubricants