Magnetic couplings

1. Magnetic couplings

A magnetic coupling is a component which transfers torque from one shaft to another using a magnetic field, rather than a physical mechanical connection.They are also known as magnetic drive couplings, magnetic shaft couplings, or magnetic disc couplings.

Traditional couplings require direct contact between the input and output shafts, and use shaft seals for dynamic sealing.The shaft seals wear out due to friction generated by the operation of the machine, eventually losing their effectiveness.Once the shaft seals fail, the material inside the pump can leak.

The biggest feature of magnetic couplings is that they use a new magnetic coupling principle, breaking the traditional structural form of couplings.This design allows for the transmission of forces and moments between the drive shaft and the driven shaft without direct contact.Therefore, it does not require the use of shaft seals.It also enables the conversion of dynamic seals to static seals, resulting in zero leakage.

2.Magnetic couplings have some notable properties:

①No vibration:Because there is no contact between the active part and the driven part of a magnetic coupling,and there is no rigid connection problem.Sudden changes and vibrations are not directly transferred across the coupling.Therefore, it can avoid the transmission of vibration,resulting in smoother mechanical operation.

②Overload protection:Magnetic couplings offer protection against overload during operation. If the load on the driven component becomes too large, the two parts may slip out of sync and end the transmission of torque. This avoids damage to the system, protecting both the motor from excessive loads and the driven component from deformation.

③Easy maintenance:A magnetic coupling transmission device is relatively simple in structure, and there is a gap between the driving part and the driven part, which is easy to install, disassemble, troubleshoot, and maintain.

④Easy power transmission:Magnetic couplings can transmit power via a linear motion, rotary motion, or helical compound motion (a combination of linear motion and rotary motion). The combination of these transmission methods and different mechanical geometry can realize a wide variety of orderly motion in three-dimensional space.

⑤Safety:Because magnetic couplings do not penetrate the surface they operate across, pumps that use this type of coupling can completely avoid leakage. This is particularly important if the pumped fluid or gas is corrosive, toxic, flammable, explosive, acidic, alkaline, or otherwise harmful. This makes magnetic coupling transmission technology especially applicable in the production of petroleum, chemicals, and pharmaceuticals, and in the industries of offshore oil well operations, non-ferrous metal smelting, wet mineral processing, and food processing.

3.Application of magnetic coupling

① Magnetic pump

Magnetic coupling

The magnetic pump consists of three parts: pump, motor, and magnetic coupling.The magnetic coupling consists of an outer magnetic rotor, an inner magnetic rotor, and a non-magnetic isolation sleeve.When the motor drives the outer magnetic rotor to rotate, the magnetic field can penetrate the air gap and non-magnetic substances, driving the inner magnetic rotor to rotate synchronously, achieving a contactless transmission of power.

Due to the complete sealing of the pump shaft and inner magnetic rotor by the pump body and isolation sleeve, the problem of flammable, explosive, toxic, and harmful substances leaking through the pump seal in the refining and chemical industries is completely solved, ensuring the health and production safety of employees.

Magnetic pumps can prevent liquid or gas leakage inside the pump, as well as prevent contaminants outside the pump from entering the pump.

②magnetic stirrer

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The magnetic stirrer also uses the principle of magnetic coupling to achieve the separation of the power input shaft and the output shaft.It is a laboratory equipment that uses a rotating magnetic field to rapidly rotate a stirring rod immersed in a liquid, thereby stirring the liquid.

The magnetic stirrer consists of a magnetic bar placed inside the liquid, which provides the stirring action.The movement of the stirring bar is driven by another rotating magnet or electromagnet assembly in the stirrer device, which is located below the container containing the liquid.The stirring bar usually has an epoxy resin or glass coating;the coating is chemically inert and will not contaminate or react with the reaction mixture in which they are located.

③ Permanent magnetic drive valve

The application of permanent magnetic couplings in valve design has resulted in an innovative fully enclosed, packing-free permanent magnetic drive valve.This design eliminates the need for the stem to pass through the bonnet, thereby completely eliminating the use of a packing box.Due to the absence of a packing box, the valve can maintain a safe and reliable operating state for a long time, effectively reducing maintenance requirements.At the same time, the friction torque between the stem and the packing is eliminated, making the valve rotation easier.

Especially under negative pressure operating conditions, this design ensures that external gases do not enter the valve interior.Whether it is a globe valve, gate valve, ball valve, or butterfly valve, all industrial valves can be retrofitted in this way to achieve fully enclosed operation.

④ Magnetic reactor

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Reactor is an important equipment widely used in the chemical industry for mixing and reacting various liquids.

Due to the fact that these reactions are usually carried out under pressure, and the reactants may be corrosive, volatile, and at a certain temperature, the sealing of the rotating shaft becomes a major challenge in the design of the reactor.The application of magnetic drive couplings not only achieves absolute sealing effect, prevents medium leakage, but also effectively avoids the oxidation and condensation of the reactants.This technological advancement significantly improves the operational efficiency and safety of the reactor.

4. Development history

The invention and development of magnetic couplings are inseparable from the technological progress of permanent magnet materials.

The first generation magnetic coupling used ferrite material. Ferrite has abundant raw materials and is cheap, but its magnetic performance is very poor, with a maximum magnetic energy product of only 5MGOe. In the same volume as traditional couplings, only a small torque can be transmitted, which limits the development of magnetic couplings.

The emergence of samarium cobalt permanent magnet materials has promoted the secondary development of magnetic couplings. Its magnetic properties have greatly improved compared to ferrite, with a maximum magnetic energy product of up to 32MGOe. Its magnetic properties are greatly increased compared to ferrite materials, allowing the magnetic coupling made of it to transmit a larger torque. However, rare earth elements such as samarium and cobalt, which serve as raw materials, are scarce in reserves and therefore expensive, which restricts the development of magnetic drive couplings.

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Neodymium Magnet

As a third-generation permanent magnet material, the emergence of neodymium iron boron magnets has greatly promoted the development of magnetic couplings. The maximum magnetic energy product of neodymium magnets is 52MGOe, while the maximum magnetic energy product of samarium cobalt magnets is 32MGOe.

This indicates that the magnetic force of neodymium iron boron is much higher than that of the previous generation of samarium cobalt magnets. Not only is it superior in performance, but the raw materials for neodymium magnets are also more abundant. It can use cheap iron (Fe) to replace cobalt and relatively richer neodymium (Nd) to replace samarium, so its price is cheaper and its market competitiveness is stronger.

In addition, neodymium magnets have a high magnetic energy product and require less equipment. Its machinability is also better than that of samarium cobalt magnets, which can be used for cutting and drilling, so using it can reduce the volume of magnetic couplings and improve efficiency.

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