Using Magnetic Coupling for transmitting torque.

We, in India, are very much familiar with various Mechanical drives in our Industrial application. Depending on the type of its use and the magnitude of torque, we use Flange coupling, Fluid Coupling etc. in our Power, Cement, Coal, Fertilizer Plants and various Mining sites for transmitting Torque in any Mechanical Drive.

In all the above application, we mechanically connect the coupling between the driving and the driven ends. For low value torque transmission – for very low and low kw-rating motors, we recommend Flange coupling (Direct drive) but for Medium, High and Very high kw-rating motor (where the magnitude of Torque to be transmitted is very high), and where jerk load necessarily be totally eliminated or not desired ,we always recommend Fluid coupling. In fluid coupling, the jerk load is taken by the Fluid stored inside the coupling. Like fluid coupling, there is no other coupling which could absorb huge jerk load and does not transmit the jerk atall to the driven side of the Drive. This is basically the reason of Fluid coupling being so popular in different types of Industrial application in India.

In the recent past, apart from the above, there is another type of Innovative Coupling – named "Magnetic coupling" has come for use . This coupling has got two parts – one is mounted onto the Driving side (Prime Mover) and the other part is mounted onto the driven shaft of the equipment (like Centrifugal Pump) . These two parts of the coupling are held together, keeping a small gap (say 1.5mm) between the two parts. Either part of the coupling has got in-built strong& very powerful permanent Magnet, installed inside. When driving part of the coupling connected with drive starts rotating, the driven part of the coupling, due to its having strong magnetism, starts also rotating.

Since there is a gap between the two parts, the jerk load is fully being prevented and not being transmitted to the driven side. This helps the driven equipment to get a "SOFT START" and thereby totally eliminating any chance of getting damaged due to JERK START during starting. Again, in a Fluid Coupling, due to internal churning of fluid(oil), there always will be some internal loses of power. But in Magnetic Coupling, there would be absolutely Zero Power loss in transmitting Torque. Since there is always a gap kept between the two parts of the coupling, any misalignment between the driving and driven shaft (upto1.5 Degree) also it can take care, which no other coupling can accommodate.

In Fluid coupling ,due to overloading or any jamming in the driven equipment , the fluid inside coupling is highly heated-up and finally blows the fuse plug. This creates spilling of hot oil all around . In Magnetic coupling ,in similar incident occurs, the driving side of the coupling part only rotates without creating any hazardous situation like Fluid coupling. Instead ,the electrical signalling mechanism connected to the system gives instant signal to stop the prime mover.

Magnetic coupling does not have any consumable component which calls for replacement. Hence it could be considered to be a totally maintenance-free item and could be considered to a Lifetime Guaranteed Item. Since no spare-part is required to be kept for regular maintenance purpose, No spare-parts inventory is required to be maintained for this.

The magnetism of the coupling will not at all deteriorate unless it is exposed to direct flame or fire. Hence manufacturers of such couplings are willingly to give Guarantee for life not less than 30 years.

After learning its very highly economical & successful application in various plants and industries in many countries (except India) a no of present users have retrofitted this coupling and thereby saving considerable revenue. Presently the Magnetic couplings are available for transmitting Torque corresponding to 4500KW Drive Motor.

Torque corresponding to 30 KW (minimum) also could be transmitted through such Magnetic Coupling.

For clear conceptualisation of such coupling, a photo of a handy model coupling is being attached. Also attached herewith ‘Working principle of Magnetic Coupling and its application (with its advantages)’ for better understanding.

Author: U.K.Mullick, a Mechanical Engineer by education, Diploma in Export Management from IIEP, Chennai . Worked with L&T, Wirtgen India, Tata Motors, AMW Motors (ESSAR Group), Mahindra & Mahindra etc.