Comprehensive analysis of magnetic coupling
Magnetic coupling is a transmission device that uses the magnetic force of permanent magnets or electromagnets to achieve non-contact torque transmission, and can complete power transmission without mechanical connection. The following is a comprehensive analysis of it:
1. Core Principle
- Magnetic coupling
The torque transmission between the active end and the driven end is achieved through the interaction of the magnetic field generated by permanent magnets (such as NdFeB, SmCo) or electromagnets.
- Non-contact transmission
There is a physical gap (air gap) between the two components to avoid mechanical friction. The typical gap is 0.1~10mm, depending on the design.
2. Main Types
- Synchronous magnetic coupling
Structure: The inner and outer rotors are inlaid with permanent magnets, and the N-S poles are arranged alternately.
Features: Torque is synchronized with speed, but may lose step (slip) when overloaded.
Application: Scenarios that require precise transmission such as pumps and fans.
- Eddy current magnetic coupling (asynchronous type)
Structure: The conductor disk (copper/aluminum) rotates in the magnetic field to generate eddy currents and form torque.
Features: With soft start and overload protection capabilities, but there is slip (speed difference).
Application: High-power speed regulation or buffer start equipment.
- Axial and radial magnetic circuit design
Axial: The magnets are arranged along the axial direction, suitable for small torque and high speed.
Radial: The magnets are arranged along the radial direction, with greater torque but complex structure.
3. Key Advantages
Zero leakage: The sealing field (such as chemical pumps) eliminates medium leakage.
Maintenance-free: No wear parts, long life.
Vibration reduction and noise reduction: Isolate vibration and reduce system noise.
Overload protection: Automatically slip when the torque exceeds the limit to protect the equipment.
Adapt to harsh environments: Corrosion resistance, high temperature (Samarium Cobalt magnets can reach 350℃).
4. Performance Parameters
| Parameter | Typical Range / Description |
|---|---|
| Torque | 0.1 Nm ~ 50 kNm (Customizable for high torque) |
| Efficiency | Synchronous type > 95%, Eddy-current type 80%~90% |
| Maximum Speed | Up to 50,000 rpm (Requires high-precision balancing) |
| Temperature Limit | -50°C ~ +300°C (Depends on magnet material) |
5. Selection Points
Torque requirements: Start torque, working torque and peak torque need to be calculated.
Air gap requirements: The larger the air gap, the more significant the decrease in torque transmission capacity (inversely proportional to the square of the distance).
Environmental factors: Corrosive media need to be encapsulated in stainless steel; samarium cobalt magnets are used in high temperature environments.
Out-of-step torque: Select a rated value 20%~30% higher than the working torque to prevent slippage.
6. Typical Application Scenarios
Chemical/pharmaceutical: magnetic pump, reactor stirring (leakage prevention).
Vacuum system: semiconductor equipment transmission (pollution-free).
Food machinery: avoid lubricant contamination.
New energy: fuel cell circulation pump, wind power generation variable pitch system.
7. Limitations
High cost: Permanent magnetic materials (especially rare earth magnets) are expensive.
Axial force problem: The influence of axial attraction between magnets on bearings needs to be considered at high power.
Torque limitation: Super large equipment requires multi-magnetic circuit parallel design.
8. Future Trends
High temperature superconducting magnets: Improve torque density and reduce magnet volume.
Intelligent control: Combine sensors to achieve real-time torque monitoring and adjustment.
Composite materials: Lightweight and corrosion resistance optimization.
