Magnetic coupling
A magnetic coupling is a component which transfers torque from one shaft to another using a magnetic field, rather than a physical mechanical connection. They are also known as magnetic drive couplings, magnetic shaft couplings, or magnetic disc couplings.
Magnetic couplings allow a physical separation between input and output shafts, precluding the use of shaft seals, which eventually wear out and fail from the sliding of two surfaces against each another. Magnetic couplings are also used for ease of maintenance on systems that require precise alignment, since they allow a greater off-axis error between the motor and driven shaft than physical couplings.
Magnetic couplings are most often used for liquid pumps, propeller systems, mine motors, conveyor belt motors and kiln elevators.
Applications
Some diver propulsion vehicles and remotely operated underwater vehicles use magnetic couplings to transfer torque from the electric motor to the prop. Magnetic gearing is also being explored for use in utility-scale wind turbines as a means of enhancing reliability.The magnetic coupling has several advantages over a traditional stuffing box.
Some aquariums use magnetic drive pumps, which have a magnetic coupling between the motor on the dry side of an aquarium wall and the propeller or impeller in the water on the other side of the wall.
This coupling features two face-to-face magnetized disks: the driving magnet on the dry side, and the driven magnet on the underwater side. Torque is transferred by shear forces between the attracting magnetic disks, but this attraction can also produce an axial load as the disks pull on each other. There are two main designs for the magnetic pattern on each disk. One design minimizes the axial load by counterbalancing a magnetically attractive section with a magnetically repulsive section near the axis.
The other design maximizes torque and resists the consequential axial load with a mechanical thrust bearing.
A magnetic stirrer is another example of magnetic coupling.
Magnetic couplings are often synchronous, meaning the output shaft speed equals input shaft speed.
The first few gears in the geartrain of an Omega Megasonic wristwatch have no teeth; instead, magnetic north and south poles on neighboring gears act like the teeth and trough of spur gears, allowing each gear to drive the next gear in the chain.
Such magnetic gears, like spur gears, always have gear ratios consisting of small integers.
More sophisticated magnetic gearings use pole pieces to modulate the magnetic field. They can be designed to have gear ratios from 1.01:1 to 1000:1.