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More About the Lufa Bearing
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Self-lubrication, now here’s a touchy subject. You have the homogeneous
(black stuff) injected inside the race that supposedly encapsulates the
ball without creating air pockets. Once cured, the black stuff bonds to
the race but not to the ball. How do they do that? The black stuff
sticks (bonds) to one part but not the other. Must be something magical
applied to the ball’s surface to discourages surface bonding; which, I
would think, introduces surface degradation leading to premature bearing
failure…Or, simply the black stuff de-bonds and falls out. Which
introduces the question of having a race to ball clearance significant
enough (probably .015” to .030” per side) to allow the black stuff to
readily flow inside between the ball and race. How do they keep the ball
centered or from floating around during the cure cycle? Must involve
some complicated fixtures.
PTFE (polytetrafluoroethylene) fabric impregnated self-lubricating liner
systems, the time proven “dry wing” application solution. With all the
advancement in composite materials one might consider them a bit
archaic…but, hey, it’s worked for years. However, you have exactly the
same problems associated with the black stuff. Everyone involved with
self-lubricated spherical bearings has experienced liner de-lamination
and/or liner de-bonding from the race…sometimes before the bearing was
placed in operation. How about moisture absorption? Ever had a bearing
get tight during a humid day while it was just sitting on your desk?
This phenomena is often referenced as wicking (as in a candle wick) the
problem is, once the fabric wicks or absorbs liquid (be it de-icing
fluid, water, oil, etc.) the fabric strand literally release from the
surrounding bonding resin system. Once this occurs, the bearing is
doomed for failure. |
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Wouldn’t it be
advantageous to have the ball element produced from an advanced
composite material? You wouldn’t have liner de-lamination problems,
because the liner system is the actual ball material. You wouldn’t have
any wicking concerns or liner de-bonding issues, because you not dealing
with a .012” to .014” thick resin impregnated woven fabric. |
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The Lufa bearing
offers all of the above stated advantages…Plus more! There are no size
restrictions associated swaged spherical bearings. The Lufa is
completely machined. Material combinations are unlimited. |
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The Lufa design
concept, a two-piece non-swaged spherical bearing, allows the use of
detail components produced from exotic materials previously considered
non-economical to produce. As an example, take a rod end having a
titanium body and a carbon-graphite ball. This particular material
combination has definite advantages when used in specific
applications…the strength of titanium and the self-lubrication and low
coefficient of friction properties of carbon-graphite. However, this
material combination was once considered unthinkable because titanium
doesn’t lend itself to cold forming (swaging) and a carbon-graphite ball
could never be used as a bearing race forming member (it would crush).
Cradin successfully produces this material combination rod end for use
in throttle linkage. |
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The ultimate in
strength, durability, weight savings and non-corrosiveness would be a
100% titanium rod end, but rubbing titanium parts, especially under
load, results in severe galling. Cradin Aerospace has successfully
produced this particular bearing assembly by having the interfacing
titanium component contact surfaces separated by a thin (.0005”) surface
deposition process which also offer self-lubrication. |
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The Lufa design
accommodates any machine capable material in any design configuration or
any size desired by the end users. Cradin produces solid aluminum rod
ends having a fluoropolymer coating applied to the ball surface to gain
lubrication. Want a solid composite ball instead, not a problem. The
advantage of a Lufa rod end is the ball element is easily replaceable.
Meaning, you really don’t have to replace the entire rod end just the
ball. |
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Because the Lufa is
a non-swaged bearing, all established required dimensions are controlled
during the manufacturing processes. Lufa rod ends have zero breakaway
torque and require no break-in to loosen them up. The established
internal tolerances held during manufacture are maintained throughout
the operational life of the rod end. Cradin’s high mis-alignment Lufa
bearings and rod ends do not have the traditional stepped balls. They
have a complete ball sphere which allows for greater mis-alignment
deflection during cyclic actuation movement. |
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Cradin Aerospace
does not employ traditional bearing self-lubrication by incorporating
polytetrafluoroethylene (PTFE) impregnated in a fabric material bonded
to the inside diameter of the bearing race. Our in-house testing
continually demonstrates liner delamination and failure . The PTFE liner
systems are considered, by Cradin Aerospace, to be old technology. With
the rapid and continual advancement of composite materials and surface
treatments, Cradin has elected to offer rod ends having ball elements
produced from solid composite materials demonstrating low coefficient of
friction and elevated temperature operational capabilities. For
metal-to-metal rod end configurations, we apply fluoropolymer coatings
to the ball. It should be note that the Lufa is not and should not be
confused with a Messerschmidt (loader slot) bearing. By design, a loader
slot bearing sacrifices a significant amount of the race material to
gain ball entry, which normally requires the addition of material mass
(weight) added towards compensating for the loss in radial static load
carrying capability. The Lufa is dimensionally the same as “standard”
specified rod ends.
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