Magnetics Business & Technology - Summer 2018 - 25

CASE STUDY
Magnetic Couplings across Industries
Sintex's magnetic couplings are employed in a diverse range
of applications and must be individually tailored based on given
constraints, which can include weight or material requirements
and geometric restrictions. During the design process, engineers
need to be able to interchange shapes and materials of magnets
to meet their customers' requirements without having to build
physical prototypes, as magnetic prototyping is costly and time
consuming. In order to save time, Sintex uses multiphysics simulation to characterize configurations and provide virtual prototypes
of designs. Flemming Buus Bendixen, a senior magnet specialist
at Sintex, has used finite element analysis for twenty years, with
COMSOL Multiphysics® as his primary tool of the last decade.

mount to assuring the reliability of their products. "It is very important to know the temperature that the magnets can withstand,
and I can calculate this quite precisely," Bendixen adds. "If the
magnets get too hot, they can become partially demagnetized."
Bendixen takes further advantage of the flexibility of multiphysics
simulation having imported Sintex's library of magnetic materials,
allowing for a vast array of custom magnetic configurations.
Continued on page 24...

"One of the big advantages of COMSOL from my point of view is
that you can do many kinds of simulations; you can include many
kinds of physics and these physics can interact with each other,"
said Bendixen. His team has a plethora of incredibly thorough and
complex models and because of the intense verification and
validation that the models undergo, the team now places
full trust in them. This not only saves time but also reduces
the price for customers and allows a greater emphasis to be
placed on the finer details.
Eliminating Risk with New Designs
Using multiphysics simulation Bendixen studies the interactions between the drives of a magnetic coupling and calculates the torque transmission from the outer drive to the
inner drive. As the primary purpose of magnetic couplings
is to transmit maximum torque and power along an axis, the
torque transfer is the most defining characteristic; therefore,
it is calculated in multiple ways, including Maxwell's stress
tensor, postprocessing integral methods, and the Arkkio
method. The analysis is verified through experimentation
and has yielded errors as small as 1%, speaking volumes to
the accuracy of the model. During the development process
of a new design, the model can be used to maximize the
torque transferred in a specific configuration.
Since permanent magnets and their fields give rise to
numerous secondary effects, Bendixen makes a substantial
effort to model them. In metals, such as the steel can in
this coupling, eddy currents are generated by the external
magnetic fields, resulting in electrical losses. "The shifting
north and south poles create voltages across the steel; it
conducts electricity and this dissipates energy from the
system," explains Bendixen. These are referred to as can
losses, which are simulated with post-processing tools in
the software, and need to be reduced as much as possible.
The team also recently developed a machine that experimentally tests the can losses of designs and confirms the
accuracy of their model to a few percent.
"We are dedicated to capturing the truly nonlinear nature of
magnetism, and COMSOL allows us to do just that, assuring optimal magnetization of the array," says Bendixen. By
employing highly nonlinear hysteresis curves and utilizing
their own material temperature dependences for magnetic
loading, the simulations (shown above) help prevent the
permanent magnets from reaching their critical temperature
and becoming irreversibly demagnetized, which is para-

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