The magnetic couplings: transmit torque without mechanical contact!

The synchronous magnetic couplings are used to transfer torque between separated members, used for sealless magnetic drive pumps, autoclaves, and agitators.

1. Impeller    2. Inner Rotor   3. Outer Rotor

4. Isolation Shell    5. Motor Shaft

Fig 1) Magnetic drive pump                                     Fig 2) Photo of Magneic couplings  

Principle of magnetic couplings

The magnetic couplings consist of two magnet assemblies. One is the outer rotor (the driver coupling) and the other is the inner rotor (the driven coupling). The outer rotor is connected to a motor and the inner rotor is attached to a pump impeller directly or indirectly.

When the couplings are at rest (no load is applied), the magnet components are aligned with their counterparts of the inner rotor.

When the load is applied to the outer rotor, the inner rotor and outer rotor are magnetically coupled to each other and when the outer rotor rotates it imparts a torque to the inner rotor, causing it to rotate. The inner and outer rotors are locked together by magnetic forces and work as synchronous couplings:

1) The couplings deflect angularly and the magnets create both attraction and repulsion forces simultaneously.

2) The forces are used to transfer torque from the motor to impeller.

3) Under normal working condition, there is no slippage between the inner rotor and outer rotor.

4) If excessive torque is applied, the magnetic force breaks off and the inner rotor and outer rotor will de-couple. They will not re-couple unless the pump is stopped immediately.

The transmitted torque is a function of material properties, number of poles, dimensions, separation distance, and relative angular offset of the magnets.

Transmission Torque of magnetic couplings

I. Torque T as the function of the angle between inner and outer coupling

I. Starting characters of the couplings 

        n: the number of Poles 

       Tmax: Maximun designing torque

       Ts: Maximum staring torque

       Tw: Wotking torque

       Tmax > Ts

                                        Fig 3) Touque per unit length vs rotation angle  

Advantages of Feller magnetic couplings

1) Optimal design, maximum torque per magnet volume, minimum size and best price for a given torque.

2) Working temperature:

     NdFeB <140^oC; SmCo < 280^oC

3) The inertial balance grade for the inner and outer rotor is G6.3.

4) Material: Inner rotor: AISI 304 SS, 316SS, or hastelloy C276 

                         Outer rotor: AISI 304SS or carbon steel

                         Isolation shell: AISI 304SS, 316 SS, TC4, or hastelloy C276

                    or non-conductive material

5) In addition to the pumps, the couplings can be used in autoclaves and agitators.

6) Custom-made is available.

For more info., please click here.

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