1. Definition of Permanent Magnetic Couplings (PMC)
A permanent magnetic coupling (PMC) is a mechanical device installed between driving and driven ends. It flexibly transmits torque and motion via the interaction between permanent magnetic fields and induced magnetic fields.
Basic Working Principle
It follows the fundamental magnetic rule: like poles repel while opposite poles attract, converting magnetic energy into mechanical energy. Based on modern magnetism theories, it leverages magnetic force generated by permanent magnet materials to realize force and torque transmission.
Standard Classification (GB/T 38763-2020)
Per China national standard GB/T 38763-2020, PMCs are divided into six main categories:
- Standard permanent magnetic couplings
- Delay-type permanent magnetic couplings
- Torque-limiting permanent magnetic couplings
- Clutch-type permanent magnetic couplings
- Pulley-type permanent magnetic couplings
- Synchronous permanent magnetic couplings
This article focuses on synchronous permanent magnetic couplings, which are further split into two core types: planar magnetic transmission couplings and coaxial magnetic transmission couplings.
(1) Planar Magnetic Transmission Couplings
Magnets here adopt axial magnetization, with coupled magnetic poles arranged along the axial direction.
When no torque output is required, the N and S poles of driving and driven discs fully align. Once torque is generated, a phase angle forms between the two discs. After displacement, the N pole of the driving disc pushes the aligned N pole of the driven disc, while the adjacent S pole pulls it simultaneously, driving rotary motion.
(2) Coaxial Magnetic Transmission Couplings
Magnets feature radial magnetization with radially arranged coupled poles. The assembly mainly consists of outer magnets, inner magnets and isolation sleeves.
Magnetic poles with alternating polarities are fixed on low-carbon steel rings along the circumferential direction. Rotation is realized through mutual pushing and pulling force between radially arranged N and S poles.
2. Core Design Key Points of Synchronous PMC
2.1 Magnetic Torque Calculation
Magnetic torque is affected by multiple factors: magnet geometry, magnet arrangement, air gap distance between inner & outer magnets, magnetic deflection angle, etc.
The calculation of PMC torque is highly complex, and many design processes still rely on empirical data and formulas. Widely adopted calculation methods include equivalent current method, equivalent magnetic charge method, Maxwell stress method, static magnetic energy torque solving method, air gap numerical method and finite element torque calculation method.
2.2 Permanent Magnet Material Selection
Magnetic steel for couplings must meet three critical criteria:
- High residual magnetic flux density (Br): to generate strong magnetic force and large transmission torque
- High intrinsic coercivity (Hcj): excellent demagnetization resistance
- Stable temperature performance: no demagnetization within designated operating temperature ranges
2.3 Isolation Sleeve Design
The isolation sleeve is the core component to eliminate medium leakage in PMC equipment. Designers must select proper materials to satisfy strength, deformation resistance and anti-corrosion requirements, while minimizing eddy current power loss on metal sleeves.
Common isolation sleeve materials fall into metal and non-metal groups:
- Metal: 0Cr18Ni9Ti, 1Cr18Ni9Ti, Hastelloy-C4, 00Cr17Ni14Mo2, TC4 titanium alloy
- Ceramic & polymer: Zirconia (ZrO₂), Silicon Nitride (Si₃N₄), PTFE, PEEK
3. Main Product Advantages
- High Transmission Efficiency
Magnetic coupling technology delivers power with minimal energy loss during torque transfer.
- No Physical Contact
Rotating parts connect purely via magnetic force without traditional mechanical contact, eliminating mechanical abrasion and corrosion fundamentally.
- Long Service Life & Low Maintenance Cost
Zero physical contact causes negligible wear, extending service lifespan and cutting regular maintenance expenses significantly.
- Strong Environmental Adaptability
Stable operation under extreme working conditions: high temperature, high pressure, strong corrosive media and high vacuum environments.
4. Wide Application Industries
- Chemical Industry
Driving parts for pumps, fans and rotating equipment, especially suitable for corrosive, flammable and explosive working environments.
- Food & Pharmaceutical Industry
Avoid cross-contamination to guarantee hygiene and safety of finished food and medicine products.
- Aerospace
Transmission systems for precision equipment including satellites and spacecraft.
- Semiconductor & Electronics
Ideal for production lines requiring ultra-high vacuum and ultra-clean workshops.
- Medical Devices
Support core transmission structures of precision medical instruments such as MRI and CT scanners.
