Magnetic Coupling Assemblies
Magnetism can be used to push or pull other magnets, pull (attract) ferrous objects and even create eddy currents in electrically conductive metals such as aluminium or copper. Magnetism can be used to create forces and torques.
Magnets can be used to make assemblies that, when separated by an air gap (or effective air gap), will interact with each other. Such assemblies are said to be magnetically coupled. As such when you move, turn or rotate one assembly, it causes a movement turn or rotation on the other assembly.
Examples of such magnetic couplings are magnetic pump couplings and hysteresis drives.
Magnetic Pump Couplings tend to be of two design styles pancake and canister.
Pancake magnetic pump couplings comprise one half of the assembly having a disc-shaped plate at the end of a shaft onto which are placed magnets in a -N-S-N-S- arrangement (on a pcd to create a ring shape). The other half of the assembly is either another assembly (mirror-image) or a copper or just an aluminium disc or copper disc at the end of the shaft. The former (mirror-image assemblies) will align such that the North face of one magnet faces a South face on the other assembly) as one assembly is rotated, the other assembly will lag slightly (rotational displacement) creating a torque magnetically (the torque will increase as the lag angle increases until a peak torque is reached called Pull Out torque; the Pull Out torque is a function of the magnetic assembly design). The latter (magnets on a rotating disc facing an aluminium or copper plate) is used to create eddy currents in the aluminium or copper disc which then causes that disc to rotate and follow the rotating magnet disc a hysteresis drive or eddy current drive. The disc holding the magnets is usually ferromagnetic to give extra magnetic performance. The magnets used can be blocks, discs or arc shaped it depends on the design and performance characteristics required.
Canister magnetic pump couplings comprise of a can inside another can (a ring within a ring) the smaller can has magnets around its outer diameter in a N-S-N-S- arrangement; the larger can has magnets around its inner diameter in a N-S-N-S- arrangement. The magnets on the outer and inner cans interact magnetically and line up as you start to rotate one of the cans the two sets of magnets displace by an angle and the magnetic forces create a torque which forces the other can to follow in rotation (by a lag). As with the pancake versions the magnetic design is such that a peak torque exists (Pull-Out torque). The magnets used tend to be blocks or arc segments. The cans tend to be ferromagnetic to carry the magnetism between adjacent magnets to increase magnetic performance and torque production.
So one half of each coupling assembly is a drive (e.g. connected to a motor); the other half is driven. Often the driven half of the assembly is within a hermetically sealed chamber and is often connected to an impeller (fan blade) to push along (pump), stir or agitate the contents surrounding it. A canister can be inserted between each half of the assembly to separate the drive and driven parts. This makes magnetic pumps very useful for pumping along liquids or fluids which are chemically damaging or corrosive the driven part is sealed away within the harsh environment.
The Pull Out torque of the design needs to exceed the torque required to rotate the drive half of the assembly in the given application (e.g. pumping a thicker/viscous fluid would require more torque than pumping a thin fluid).
One factor to note is matching the motor turning the drive to the Pull Out torque. If the motor torque exceeds the Pull Out torque then if the driven assembly gets stuck (e.g. blockage in the fluid) then the motor can still turn (the assembly will cogg) but the motor will not burn out, protecting the motor if such a fault condition were to exist.
Which magnetic material to use and what shape? This depends on the customer application and the environment the magnets will be within. Often such designs as customised to the customer requirements. NdFeB allows higher torques, SmCo allows higher temperatures, ferrite allows lower cost, alnico allows high temperature stability, etc. Use of ferromagnetic materials (mild steel, ferritic stainless) can improve the magnetic circuit. The air gap between each half of the magnetic coupling assembly also impacts on performance (less gap should give more torque). We can work with you to get the most from your design. We have 3D FEA to model such designs. We can also produce your magnets and assemble them for you (giving you sub-assemblies to insert into your systems).
Applications include magnetic stirrers, magnetic pumps, magnetic drives, hysteresis drives, eddy current drives, etc.
If you require assistance with Magnetic Coupling Assemblies, Magnetic Pump Couplings, etc or would like to arrange a visit or would like quotations for the magnets and magnetic assemblies, please get in touch. HSMAG Magnetic can custom produce magnets and magnetic assemblies for you.
