Magnetic Bearing
Magnetic bearings support moving machinery without physical
contact, for example, they can levitate a rotating shaft and
permit relative motion without friction or wear. Long considered
a promising advancement, they are now moving beyond promise into
actual service in such industrial applications as electric power
generation, petroleum refining, machine tool operation and natural
gas pipelines.
The AVCON magnetic bearing permits motion without friction
or wear.
Among companies producing advanced magnetic bearing systems
for industrial use is AVCON, Inc., Agoura Hills, California.
AVCON offers a unique technological approach that evolved from
the company's work on contracts with Lewis Research Center, and
Marshall Space Flight Center. The technology developed in the
NASA programs contributed to AVCON's ability to overcome the
limitations of early magnetic bearing systems, namely large size
and weight, high power consumption and cost. The company's product
line embraces a family of very compact, lightweight, power efficient,
low cost bearing systems.
Beginning in 1989, AVCON worked with Lewis to explore the
possibilities of a magnetic bearing system for the turbopump
of the Space Shuttle Main Engine. NASA decided to investigate
magnetic bearings, which in theory-at that time-offered multiple
advantages over conventional rolling element bearings.
AVCON worked initially with Lewis on development of a magnetic
bearing system for a Cryogenic Magnetic Bearing Test Facility.
The resulting AVCON development was extensively tested over a
two year span and these tests provided a wealth of data on the
performance of magnetic bearings under severe conditions. In
this program, AVCON developed the basic hybrid magnetic bearing
approach that characterizes its commercial products, an approach
in which both permanent magnets and electromagnets are employed
to suspend a shaft; the permanent magnets provide suspension,
the electromagnets provide control. Analyses of AVCON bearing
tests showed that a hybrid magnetic bearing was typically only
one-third the weight, substantially smaller and dramatically
less power-demanding than previous generations of magnetic bearings.
The bearings were tested in a NASA turbopump unit.
In 1993, Marshall Space Flight Center awarded AVCON a contract
to fabricate a set of magnetic bearings, install them in a fixture
representing a Space Shuttle Main Engine turbopump, and test
them under simulated Shuttle mission conditions. Those tests
are under way.
The technological base afforded by AVCON's NASA work, buttressed
by additional R&D sponsored by the U.S. Air Force and a major
turbine engine manufacturer, enabled AVCON to develop a unique
"homopolar" approach to permanent magnet type bearings
that, the company says, are significantly smaller than prior
designs; additionally, their control electronics are a fraction
of the weight of previous systems and power consumption is much
lower than in all-electromagnetic designs. Among other advantages
cited are virtually zero friction and therefore no lubricant
requirement; no wear, no vibration; longer service life; and
very high reliability because single point failure modes are
eliminated.
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