Piston-Ring Vibration and Breakage Page: 4 of 26
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NACA A R No. E5006
of a bakelite-bnded, wire-wound construction especially designed
for these tests. Connecting wires to the gages were small and
flexible to avoid interferene with vibrations. The strain signals
after being mplified werere recorded on a 12-channel oscillograph.
Equipment for Observing Piston-Ring Motion
Ring fluctuations were observed through the polished Lucite
cylinder with a stroboscope and the motions that might cause break-
age were photographed with a high-speed motion-picture camera. The
camera was a oontinuous-film, rotating-priam type capable of taking
pictures at the rate of 2500 frames per second. The light necessary
for high-speed photography was supplied by an 8000-watt carbon aro
light supplemented with flood lamps. Same of the high-speed pictures
were taken with the cylinder and the exciter assembly mounted on a
pivot, which rotated the assembly past the stationary camera to
permit a 3600 view of the ring.
Equipment for Simulating Engine Canditions
Air pressure above the piston was manually controlled at
values varying from 0 to 15 pounds per square inch gage pressure.
The power output obtainable from the exciter and the strength of
the cylinder limited the amount of pressure that could be used.
The Lucite cylinder was machined to give a piston side clearance
of 0.015 inch between the piston lands and the cylinder wall,which
corresponds to the estimated hot clearance of an actual engine in
operation. Blow-by measurements were made with a gas meter in the
air-supply line. Air pressure was used to force a thin oil into
the cylinder for lubrication.
DISCUSSION AND ECBIES
The type of piston-ring failure that would cause breakage of
the rings at approximately 1 inch from the end or gap location was
investigated. Similar breakage has often been thought to be the
result of ring vibration,
Preliminary Tests
In order to have a basis for comparison, rings were broken by
statically loading them at various points. Breaks were made by
clamping the ring and by applying conorntrated loads at the free
end either perpendioular or parallel to the auis of the ring.3
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Nettles, J. C. & Meyer, André J., Jr. Piston-Ring Vibration and Breakage, report, August 1945; (https://digital.library.unt.edu/ark:/67531/metadc62005/m1/4/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.