Magnetic couplings transfer motion and torque without direct contact by using strong magnets arranged in concentric rings on either side of a containment shell. When the motor turns the outer ring, magnetic forces cause the inner ring, and the pump it drives, to rotate in sync, enabling a fully sealed, contact-free operation. However, power loss is a common problem that can affect efficiency and performance.
To get the most out of magnetic coupling systems you need to know where the power loss is coming from and how to fix it. In this guide, we’ll cover the main causes of power loss and how to keep your coupling efficient.
What Causes Power Loss in Magnetic Couplings?
To perform at their best, mechanical power transmission systems containing magnetic couplings must be efficient. When these systems are shut down, it can lead to a lot of bad things, including the lack of efficiency, more power and overheating. In applications such as pumps, fans, or conveyors, tiny losses in power transfer can cause increased operating expenses, lower throughput, and system failure without intervention. In the long term, lost power not only reduces component life but increases system reliability. When power is lost in complex machinery or health care equipment, it may damage the torque transmission capability of the coupling, inducing an cascade reaction in all stages.
Understanding the causes of power loss in magnetic couplings is critical to improving their design, reliability, and efficiency. A large part of the power loss of magnetic couplings is caused by the current loop (commonly known as eddy current) generated when the magnetic field passes through the conductor. Eddy currents cause significant magnetic damping and heat during the operation of the magnetic coupling, which in turn affects pump efficiency. Coupling construction materials, air gaps, size, speed, alignment issues, temperature changes, and magnetic field strength all contribute to power loss. These effects, whether built into the coupling design or driven by operation, affect how well torque is transferred between the shafts.
One factor that could reduce power would be torque transmission speed. The amount of torque required to propel a pump varies from application to application. Losses occur when the speed of the torque transmission in a magnetic coupling is less than the load required. Decoupling can occur if torque requirements exceed the coupling, leading to wasted energy transfer and slippage. Make sure the coupling is designed to meet high torque requirements, even during startup, so as not to waste power.
The second reason might be the magnetic discrepancy. The magnetic distance between the inner and outer magnet rings determines the effectiveness of magnetic flux transfer. Less spacing also increases magnetic flux density, which boosts torque transfer, but raises the risk of higher eddy current losses in conductive shells. Conversely, a bigger gap lowers the flux density and therefore transmits less torque. This gap needs to be optimised to maximise torque savings and minimize eddy current losses in order to minimise power losses.
Moreover, magnetic coupling materials can significantly influence loss of power via eddy currents. If the containment shell is metallic (for example), rotating magnetic fields generate eddy currents, leading to drag and power consumption. For this reason, containment shells are usually made from low conductivity or non-conductive composites. Further, material resistivity and thickness influence how far the eddy currents go. These losses can be minimized by selecting high resistance, non-conductive materials.
Both the magnetic and resistive properties of the materials are also affected by variations in operating temperatures. High temperatures can weaken the magnetic field, resulting in a lower transfer of torque and higher potential for decoupling. Higher temperatures also make materials more resistive, increasing eddy currents and power losses. Thermal control (e.g., cooling) is required to avoid heat-related power loss.
This might be caused also by coupling size. The coupling devices – and the magnets in particular – vary in size, which results in the loss of power. Bigger magnetic structures produce larger magnetic fields, which can improve torque transfer but also create bigger eddy currents. The bigger the magnet, the more fluid it must withstand and thus the more frictional drag. Correctly dimensioning components to satisfy torque demands but not oversize magnets can preserve energy savings.
Another reason is the rotation speed. As the coupling turns, magnetic and frictional losses change with speed. At greater speeds, magnetic lines puncture the containment shell more frequently, thereby generating more eddy currents. Accelerating rotation also increases frictional losses from fluid drag, especially when liquids are viscous. It is important to maintain the required torque levels without causing unnecessary eddy current or drag loss at operating speeds.
When it comes to minimizing magnetic coupling loss, it’s all about balance. Engineers can accomplish this by carefully constructing the couplings and optimizing the conditions. Such care in design ensures that couplings transfer torque effectively and safely for the applications they serve. This not only makes energy consumption less, but also provides improved longevity, making magnetic couplings a popular choice for most applications.
Impact of Eddy Currents and Frictional Losses on Magnetic Coupling Efficiency.
An eddy current is a kind of electric current that zigzags through a conductor in response to a moving magnetic field. The pump experiences eddy currents as the spinning magnetic field moves over electrically charged surfaces. When the magnetic field turns, it creates swirling electric currents (eddy currents) in these materials. These eddy currents repel the magnetic field that generated them, according to Lenz’s law.
This polarization produces power losses as the magnetic field attempts to fight the eddy currents. Most damaged are the containment shell and inner magnet assemblies. When the inner magnets rotate, their magnetic field penetrates the containment shell and creates eddy currents inside. The power lost to counteract these eddy currents is determined by:
- The thickness, material and resistivity of the containment shell. Materials such as metals enable higher eddy currents than non-conductive composites.
- The distance between inner and outer magnet assemblies. The wider the gulf, the lower the density of magnetic flux in the hole.
- Rotation speed. Higher speeds result in more cutting of magnetic lines and eddy currents.
- Magnetic field strength. Stronger magnets produce greater eddy currents than weak ones.
Friction between the inner magnets and surrounding fluid also causes power loss. As the magnets rotate they encounter viscosity drag from the handled liquid. This drag creates a resistive torque that must be overcome. It increases with larger magnet size, higher speeds and when handling thicker fluids versus thinner liquids. In extreme cases, high frictional torque can even cause the inner component to decouple from the outer one.
Decoupling Issues in Magnetic Coupling.
Magnetic couplings work to transmit torque from a rotating shaft to another with minimal effort. That non-contact is one of their main benefits because it cuts out friction, wear, and potential leakage. Yet, for all their advantages, magnetic couplings have their own operational drawbacks, and one such is decoupling. Click here to learn more about the basics of magnetic coupling magnetic fields.
Decoupling occurs when the magnet rings are out of synch and lose their transfer of torque. It generally occurs when the torque exerted on the coupling exceeds its specified performance and the magnetic field weakens or fails to create a bond that will deliver power. As a result, the coupling fails to transfer rotational motion, and may cause operational problems like slipping of the pump shaft or shutting off the pump completely.
Decoupling is most likely to occur in temporary states, like when startup occurs, or when external forces cause unexpected torque loads to spike. At startup, for instance, a motorized system will often suffer from an initial torque surge that exceeds the coupling’s nominal torque capacity. Without accounting for this peak torque during the design and sizing phase, the coupling might fail to engage completely, causing a decoupling phenomenon.
Likewise, load variations, system shock, or operational overloads can suddenly put more pressure on the coupling, increasing the possibility of decoupling. If load exceeds the torque of the magnetic coupling, the system is out of synchrony and power flow stops and it may break down.
In order to avoid decoupling issues, it is important to choose the correct magnetic coupling given the predicted torque bands at constant and peak loads. This means not only taking into account the usual operating torque, but also any sudden spikes that might arise. Effective magnetic coupling under a variety of operating conditions requires appropriate sizing and a comprehensive knowledge of torque characteristics of the system. Furthermore, sophisticated coupling designs (for example, adjustable couplings or couplings with a higher torque rating) can help avoid decoupling in systems that receive high loads. This can be avoided by taking into consideration peak torque conditions while selecting and sizing the coupling and pump.
How to Cool Magnetic Couplings?
Magnetic couplings are crucial for sealing and high-efficiency torque transfer, but there’s one problem with them that we rarely address: heat trapping. When the power is lost via eddy currents and frictional drag (as discussed above), energy turns to heat, particularly in the containment shell and around the inner magnets. Such heat, if not efficiently lost, will create problems ranging from poor efficiency and demagnetisation to, at best, fluid flashing (vaporisation). Overheating can impact the efficiency and life of the magnetic couplings leading to unplanned downtime and high-cost repairs.
The good news is that there are ways of regulating and cooling this heat. Through long-term experience and development precipitation, we can develop flexible cooling solutions during the production process to keep it at the right temperature, minimize power consumption, and maintain the functionality of the magnetic coupling.
- One cooling method is to transfer some of the pumped fluid between the inner magnets and the outer containment shell. In this arrangement, heat is exchanged directly as the moving fluid takes in the heat from the magnets and then passes back to the core without warming up too much. It does this to cool the process fluid at hand, making the system less complex while allowing it to operate safely at room temperature.
- An alternative is to put an outer shell over the containment shell. The jacket spreads heat throughout, preventing hot spots and reducing heat loss to the outside world. This ensures a natural cooling process and, by storing heat within the system, creates a passive cooling effect that keeps temperatures constant without any other components.
- Another strategy to ensure efficient cooling is double shell. When you add a second shell on top of the main containment, there’s a gap through which a separate cooling fluid can flow. The fluid, carefully selected for heat transfer, rotates around the magnets, and thus maintains temperature. This arrangement enables accurate temperature control throughout the entire magnet structure, and hence reduces the risk of excessive heat.
Even the temperature sensors built into the coupling can keep track of the conditions at any given moment. If temperatures begin to increase, these sensors will automatically adjust the operation of the pump so that there is less risk of overheating. Power gauges mounted on the motor will also identify low flow or dry run indicators to help prevent heat buildup, and enable intervention before damage can be done.
Magnetic couplings require cooling. These cooling processes combine to extract heat from the critical components by circulating fluids, wearing jackets and double shells, and monitoring temperature. This keeps the couplings stable and operating properly. This energy-saving thermal control scheme ensures maximum reliability and maximizes the lifetime of the magnetic couplings.
OSENCMAG: Customised Magnetic Coupling Solutions for Your Needs
Every application is different. That’s why at OSENCMAG we offer custom magnetic coupling solutions for you.
- Low or high torque? We’ve got you covered. Our team designs and builds custom solutions for precise torque transfer. And with many sizes to choose from, tested to fit your needs, we have the right one for you.
- Beyond size, we offer high-performance Neodymium (NdFeB) or Samarium Cobalt (SmCo) magnets. Our Neodymium magnets can withstand up to 230°C and samarium Cobalt up to 350°C for extreme environments.
- Customization doesn’t stop there. We offer various housing materials, barrier options and surface treatments to increase durability, corrosion resistance and service life. For our eddy current couplings we use custom conductive materials to optimise torque transfer.
- At OSENCMAG, we are dedicated to delivering the ideal magnetic coupling solution for your unique application. Our attention to detail and commitment to quality ensure your equipment operates at its best, no matter the challenge. So contact us today to get your quote today.
FAQs
Can magnetic coupling be used for quick disconnect?
Magnetic couplings are great for quick disconnects because they are non-contact power transmissions. Since the parts don’t touch, they can be separated when needed without wear or damage.
This makes magnetic couplings perfect for applications where disconnection and reconnection is frequent. And since there is no physical contact they can handle some misalignment and speed variation, making them more versatile in dynamic environments.
How to align a magnetic coupling?
When the system is stationary, make sure both the driver and follower parts are in place. This initial alignment should be checked before operation. Magnetic couplings can handle some axial misalignment but try to minimise significant displacement to get good coupling.
These couplings can handle some radial and angular misalignment as well. The tolerance levels depend on the coupling design and air gap spacing. Larger air gaps can handle more misalignment, but too much can reduce torque transmission. After initial alignment, test the coupling under operating conditions. This will ensure it works and any remaining misalignment won’t affect performance.
What is magnetic coupling used for?
Magnetic couplings are used in linear and rotary applications due to their contactless power transmission properties. For example: drives, pumps, compressors and various assembly systems.
What are the disadvantages of magnetic couplings?
While magnetic couplings have some advantages, they also have some limitations. They can only handle relatively light torque loads compared to ordinary couplings with direct physical connections. Applications that are slow from the drive side or have very low moments of inertia are best suited for magnetic couplings.
What are the failure modes of magnetic coupling?
There are several failure modes of magnetic couplings. The causes are:
- Wrong selection for the application requirements
- Excessive misalignment of the coupled parts
- Insufficient, improper or no lubrication
- Harsh environment or operating conditions
- Exceeding the maximum speed or load
What is the formula of magnetic coupling?
The formula of the coupling is “K = M/√L1+L2”. In this formula of coupling, L1 is the “self-inductance” of the first coil and L2 is the “self-inductance” of the second coil.
What is the principle of magnetic coupling?
The magnetic coupling principle drives the outer magnet by motor and then the outer magnet drives the inner magnet. Inner and outer magnets are in two different spaces so it is force transmission without medium.
