05-09-2014, 03:49 PM
Friction optimization on hydraulic piston rod seals
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ABSTRACT
Everywhere, where high forces have to be transmitted
and linear movements have to be performed, the use of
hydraulic cylinders is a common praxis. In this case the
so called “characteristics of convenience” are getting
more and more important for the operators of modern
hydraulic systems. In first line the friction performance of
rod and piston seals has to be stated. High friction forces
will cause a higher use of energy connected with a
worse degree of efficiency. High friction can create also
a higher wear on the used seals and this will result into a
significant reduction in life time of the hydraulic system
INTRODUCTION
Friction and wear of rod seals and rod sealing systems
have a significant influence on efficiency and life time of
a hydraulic cylinder or hydraulic system. As long as
sufficiently high hydraulic power of the pump is available,
the influence of seal friction will be of minor importance
regarding the effectiveness of the hydraulic system. In
this case, the primary task of the seals and scrapers
installed in a hydraulic cylinder is to prevent leakage and
the prevention of intrusion of dirt into the hydraulic
cylinder system.
In many applications, though, this type of functional
performance is no longer sufficient. Particularly with
regard to positioning accuracy in cylinder applications or
defined control behavior with small hysteresis, the
friction behavior of a hydraulic rod seal can be of crucial
importance. In this case, not only the absolute friction
level is of interest but also the sealing behavior in terms
of stick-slip, with the total friction band width depending
on such conditions as pressure, velocity, temperature
and mating rod surface. A too high sticking friction and
also a too high sliding friction will have a negative impact
on the wear behavior of the used seals within a hydraulic
cylinder and can result into stick-slip effects or into
undesirable too high break-off friction after longer still
stand periods, for example over a longer weekend. This
effect is also known as so called “Monday morning
effect”. Inappropriate friction characteristics are
DEVELOPMENT OF ROD SEAL DESIGN HL
The target of this development was to develop a seal
design, which fulfills under all applied conditions the
demands regarding low friction in static but also in
dynamic modus. This should result into less stick-slip for
the seal and also in a significant reduction of the
“Monday morning effects”. The seal should have equal
or even better behavior compared to standard U-cups
regard leakage, wear and extrusion. Additional the seals
CONCLUSIONS
The new rod seal design type HL supports all hydraulic
end user in their demands for use of low friction
applications. The new active principle of the incremental
pressure activation of the sealing edges generates a
very low friction under nearly all thinkable performance
conditions. Especially under very low piston rod speeds
stick-slip behavior is almost excluded. High break-off
friction after longer periods of still stand can be
dramatically reduced. Additional with the decrease in
friction advantages regarding wear behavior and energy
saving can be received. Together with the friction
optimized function this will give the Customer a suitable
aid in reducing his operating expenses.