Magnetic Couplings

No Seals, No Leaks, No Contamination

Magnetic couplings are used to transmit rotational and/or linear motion without direct contact. 

Rotary couplings are principally used to eliminate the use of seals in rotating and reciprocating machines such as seal-less pumps and pistons.  Use of magnetic couplers improves the reliability and safety aspects of such machines because seals are prone to deterioration over time and cause leaks.

Linear and rotary magnetic couplings, and hybrids of the two, also find application in vacuum technology where position or motion must be transmitted across a vacuum barrier.  An added consideration in these applications is stiffness of the coupling; minimizing the lag between driver and follower. 

Rotary magnetic couplers used in these applications are designed in two configurations - co-axial and face-to-face.  In the co-axial configuration, the two halves of the coupler are mounted co-axially with each other and nested one within the other.  The outer member is typically connected to the motor and the inner member to the driven system, for example, the pump in a seal-less pump. A cup-shaped stationary member, mounted to the pump body, resides between the driver and follower and separates the fluids on the pump side from the environment on the motor side.  Materials for the barrier cup and exposed surfaces of the follower are chosen to survive continuous contact with the fluids being pumped.  The thickness of the barrier is designed to withstand any pressure differential without significant deformation.

Face-to-face type couplings are used where axial length is at premium and some misalignment needs to be tolerated.  The two pancake-shaped parts comprising this type of coupler have magnets mounted on the near faces.  The separation barrier in this case can be as simple as a flat wall.  One aspect of face-to-face type couplings is considerable attraction between the two members.

Linear magnetic couplings, following similar principles, allow precise control of robotics inside vacuum systems.  These couplers are used in the semiconductor industry to position objects within a clean chamber. Elimination of seals and reduction of the number of components inside the chamber improves contamination control and enhances system reliability.

In all the above cases, greater torque/force capacity is realized with stronger magnets, increased diameter and reduced radial gap.  An added consideration in these designs is the stiffness of the coupling which results in more precise control.  Devices operating at elevated temperatures (> 120 °C) typically employ Sm-Co magnets while others may use Nd-Fe-B or ceramic magnets.

Other types of magnetic couplings include the hysteresis type and eddy current type.  Hysteresis couplings are typically used where a torque limiting is needed, such as in the bottle capping industry.  Eddy current couplers exhibit torque that increases linearly with increasing revolutions per minute.  They are often employed in clutches and in couplers where extreme misalignment needs to be tolerated.  Hysteresis and eddy current principles may also be used in the design of linear couplers.

Dexter Magnetic Technologies has significant expertise in all of these systems, and can assist you with your magnetic coupler design, and further help you with its integration into your system.

For further inquiries, please e-mail us at info@dextermag.com -or- call us at:  800-345-4082 (In North America) or +44 (0) 1189 602430 (In Europe).