Picking the right magnetic coupling can be a real headache, especially when it comes to torque. But don’t worry, it’s not as complicated as some people make it sound.
Here’s the deal, torque is just about how much turning power you need. Think about it like this, if you’ve ever tried to open a stuck jar, you know exactly what torque is. It’s that twisting force you use to get the job done.
I’ve seen plenty of people mess up their machines by getting this wrong. Trust me, you don’t want to be the person who has to explain to your boss why the equipment isn’t working right. So let’s cut through all the technical mumbo-jumbo and talk about what really matters when choosing a magnetic coupling.
What is the Maximum Torque of Magnetic Coupling?
Maximum torque is the maximum amount of rotational force that can be transmitted by a magnetic coupling before slippage occurs between the driving and driven magnets. The maximum torque of a magnetic coupling can vary depending on the type of coupling, but it can be as high as 1000 N.m. For instance, for high-performance applications that require frictionless power exchange, magnetic couplings can provide torques ranging from a few Newton metres (Nm) for precision machinery to greater than 500 Nm for high-efficiency machines. Maximum torque depends on several factors including the magnet materials and their strength (rare-earth magnets like neodymium, for example, provide high torque), the number and shape of poles, and the distance of air between magnets. Optimised, sophisticated magnetic couplings deliver torques as high as 1,000 Nm for demanding applications in aerospace, automotive and renewable energy. It is this great versatility that makes magnetic coupling a powerful choice for applications requiring mechanical stability and high-power transmission.
What are the Factors that Determine the Maximum Torque of Magnetic Coupling?
There are some important concepts you need to understand before calculating the maximum torque of a magnetic coupler. The understanding of the conditions that impact the maximum torque of a magnetic coupling plays a key role in choosing the correct coupling for a particular application and its performance. As a manufacturer of magnetic couplings, we understand the importance of the factors that impact the maximum torque of our products. This knowledge plays a crucial role in designing and recommending the right coupling for our customer’s specific applications, ensuring optimal performance. Now let’s find out the principal considerations that determine the maximum torque of a magnetic coupling.
The quality and type of magnetic material in the magnetic couplings play an important role in the determination of torque. It is not uncommon to employ powerful magnets such as Neodymium-Iron-Boron (NdFeB) or Samarium-Cobalt (SmCo) that possess powerful magnetic fields. NdFeB magnets come in grades from N35 to N52, with N – “neodymium iron boron,” where the number represents the magnet’s grade and magnetic strength; the greater the number, the stronger the magnet. By selecting the right NdFeB quality, engineers can produce the most torque in almost all applications. Yet in extremely high-temperature environments, Samarium-Cobalt magnets are preferred due to their better thermal conductivity (though pure NdFeB is much more magnetic). This balance between magnetism and thermal resistance allows for high torque under many different conditions. Temperature has a big effect on both the magnetic content of the material and the total torque capacity of magnetic couplings. In the case of neodymium magnets, there are variations with different resistance at different temperatures in each grade.
In most magnetic couplings, high-temperature-resistant neodymium alloys are selected for their excellent magnetic characteristics in conjunction with thermal resistance. When extreme temperature stability is desired, but the need for magnetic strength is moderate, Samarium-Cobalt (SmCo) is selected because it is highly resistant to high temperatures. This method makes sure that the magnetic coupling works perfectly even under extreme temperatures.
The structural tuning of magnetic coupling systems also requires optimisation to ensure maximum torque and efficiency. Important measurements include the number of magnetic poles, yoke iron thickness, and the thickness of the permanent magnets. Adding more poles tends to boost storage efficiency by increasing magnetostatic energy, which is converted to kinetic energy as it works. But too many poles can cause flux leakage, which reduces air gap flux density and torque. Larger effective radii (or wider air gaps) systems need fewer poles, while smaller radii systems need more poles to preserve energy density in small spaces.
It is also related to the thickness of the yoke iron and the thickness of the magnet. The yoke iron protects the system from external fields and maintains a magnetic field. If it is too narrow, the yoke will experience magnetic saturation, producing more resistance and less torque. The same is true with increasing the permanent magnet thickness – this increases the flux density and torque of the air gap, but only to a certain point; any thickness over this threshold yields less than the original value due to magnetic resistance and flux leakage. With the balance of these parameters correct, magnetic coupling provides the best torque performance possible for the given application.
Magnetic couplings can also be set as intermittent or combined, depending on how they affect the maximum torque:
Consists of magnets separated by intervals that form a periodic magnetic field. The torque in an intermittent coupling is not as steady because it changes with the magnet position, leading to torque pulses. This may reduce overall torque capacity but may work for applications where you don’t need constant torque.
This design means that there are several discrete magnets situated extremely close together without a gap between them and/or one magnet placed on top of the other forming a continuous and even field. Combinations create more peak torque because the unbroken magnetic field creates torque that is smoother without the fluctuations of intermittent setups.
Another important aspect is the magnetic gap or air gap. The magnetic gap is the distance between the inside and outside magnet rings. A smaller gap increases magnetic flux density, which raises magnetic force and torque. But even a tiny lapse can increase losses of eddy currents, and so generate power and heat. Having a larger distance, however, weakens the magnetic field, thereby lowering the effective torque. This optimal gap size permits as much transmission of torque as possible while allowing low eddy current losses.
In addition, adding more magnet pairs on each coupling element boosts magnetic flux and torque capacity. The more pairs of magnets, the greater force exerted upon the coupling, which increases the transmission of torque. However additional magnet pairs can make the setup heavier and more complex, affecting rotation speed and efficiency.
Notice how the coupling reacts to rotation. You always find a sweet spot, where you get the most torque, but go beyond it and you slip. This is particularly true for intermittent-type couplings.
Trust me, I’ve seen some people discount a couple of these things and scratch their heads when they see that their system is not working. This is not about having these elements figured out theoretically, but how they work together in practice. So when it comes to choosing a magnetic coupling, remembering all these things will allow you to make a sound choice that suits your requirements.
Torque Calculation Formula: How To Calculate
Not that it should be hard to calculate magnetic coupling torque. There’s some maths involved but the principles are simple. You can calculate magnetic coupling torque by employing formulas that take different values of the angular velocity, magnetic pole pairs and magnetic flux density into account. Here’s the formula, and the components:
The Basic Formula:
At its core, torque comes down to two things: force and distance. The formula is:
T=k⋅B⋅A⋅sin(θ)
Where:
- T = Torque
- k = A constant that depends on the system design
- B = Air-gap magnetic flux density (measured in Tesla)
- A = Area of the magnetic coupling (measured in square metres)
- θ= Angle between the magnetic field and the normal area
The angular velocity can be calculated using the formula:
wp= 60/ 2πpn
Where:
- p = Number of pairs of magnetic poles
- n = Slip or rotational speed in revolutions per minute (RPM).
It is important to calculate how strong the magnetic field must be to withstand the torque from the motor shaft. This usually involves simulations or experimental measurements to identify the required magnetic strength for a given application. In higher-end applications, especially permanent magnet couplings, torque density can be computed to figure out the coupling design’s limit of performance.
If you incorporate all these variables, you’ll have a much clearer idea of your coupling’s real-world performance. Keep in mind that theoretical calculations are only the beginning, experience and sensitivity to operating environments will ensure that your magnetic coupling works consistently in real life. Keep in mind that the amount of torque a magnetic coupling will transmit is dependent on many variables: the strength of the magnets, the shape of the magnetic structure, and the distance, or air gap, between magnets. A larger magnetic field induces more transfer of torque; close, well-aligned magnets maximise this.
How to Choose the Right Magnetic Coupling & Coupler?
The right type of magnetic coupling will ensure good, reliable performance in any environment. If the right magnetic coupler is chosen, this allows contactless, seamless torque transmission, minimises mechanical component wear, and preserves operation under a wide range of operating conditions thereby increasing the system’s life and performance. Conversely, the wrong coupler may result in poor torque capacity, overheating, magnetic degradation, or even system failure, increasing the expense of maintenance and time lost during operation. To stay out of these situations, it is vital to carefully consider the following factors when selecting a magnetic coupling: torque requirements, operating temperature, magnetic material, environment, and size limitations. With every aspect taken into account, you’ll optimise performance, avoid costly mistakes, and ensure that the magnetic coupling meets all your system requirements. These are the guidelines you need to follow when choosing a magnetic coupling.
- Maximum Torque Requirements
Figure out how much torque the coupling must accommodate at full load. This is a basic criterion, as the magnetism needs to be strong enough to transfer the desired torque without slippage. Identifying your torque needs will determine the correct magnetic strength and coupling size.
Torque - Transmission Speed (RPM)
The rotation speed at which torque will be transferred (in RPM) is also important. At greater speeds, you may need tighter tolerances and better alignment on couplings to ensure stability and efficiency. Some couplings are tuned to certain speeds, so make sure they work with your actual RPM. - Air Gap Distance
As mentioned earlier, the distance of the magnets (or the “air gap”) directly affects torque transmission performance. The narrower the spacing, the more torque can be transmitted (although in practice this distance will depend on both heat and mechanical tolerances). Select a coupler that can keep an air gap stable for the required operational conditions. - Operating Temperature
Magnetic couplings are similarly susceptible to temperature because magnetic strength is eroded at higher temperatures, reducing torque capacity. Test the temperature of the workspace (both ambient and machine heat). When working in very high temperatures, look at couplings that are made from materials that resist heat stress. - Material and Corrosion Resistance
If you’re looking for something that’s going to be used in harsh or corrosive conditions like in a chemical-, water- or salt-water-resistant application, make sure to choose corrosion-resistant materials. Couplings made of stainless steel or coated with special coatings can provide the protection required in this application. - High-Temperature Resistance
If the use case calls for high temperatures, ensure that the coupling materials will resist high temperatures without cracking or weakening. Special magnetic materials and housings are made available for high-temperature use. - Physical Size and Space Constraints
Lastly, the physical dimensions of the coupling should not exceed the space available in your equipment configuration. Think about the coupler’s diameter as well as any housing or mounting needs. A smaller coupling might be your best option if you don’t have room, but make sure it still meets all of your needs. In some cases, you might even be plugging a magnetic coupling into an existing power supply. For this, the magnetic coupling’s aperture and disc size match the power device’s shaft size in order to transfer torque. Add any housing or mounting requirements, which may affect the alignment of the coupling within the machine. Even if a small coupling is best suited for small spaces, make sure that the coupling fulfils all performance and dimension requirements for safe use.
When you consider all these considerations carefully, you can select a magnetic coupling that will naturally meet your application’s needs and provide reliable, smooth performance across complex operating systems. A suitable magnetic coupling not only meets technical requirements, it also increases overall performance, reduces the number of parts required, and provides superior stability over time.
Partner with OSENCMAG to Drive Your Project Forward
Finding the right magnetic coupling is just the start. To truly optimise your system’s performance, you need a partner who can provide tailored solutions and streamline your supply chain. At OSENCMAG, we specialise in delivering top-quality custom neodymium magnets and magnetic assemblies tailored to your precise needs.
Low or high torque? We’ve got you covered. Our team designs and builds custom solutions for precise torque transfer. As specialists in custom neodymium magnets and magnetic assemblies, we’re here to do more than just deliver high-quality products. Our mission is to become an extension of your team, leveraging our extensive experience and trusted manufacturing network to enhance the efficiency and effectiveness of your project.
Whether you need guidance on magnetic product development or support securing the best factory resources, OSENCMAG offers the flexibility, expertise, and exceptional outcomes your project demands. We’ll minimise your time and communication costs, helping you navigate the complexities of sourcing and manufacturing with ease. So contact us today to discuss your business needs.
FAQs
Why does orbital coupling increase magnetic moments?
Orbital coupling increases magnetic moments because it enhances the alignment of an electron’s magnetic dipole with an external magnetic field. In atoms or molecules, orbital and spin magnetic moments interact through spin-orbit coupling, which combines the effects of an electron’s spin and its orbital motion around the nucleus. When the orbital coupling is strong, it magnifies the overall magnetic moment, as the electron’s orbital and spin angular momenta tend to align more favourably with the external magnetic field. This alignment creates a larger effective magnetic moment by amplifying the contributions from both spin and orbital components, especially in heavier atoms where spin-orbit coupling is more pronounced due to relativistic effects.
What is the difference between orbital magnetic moment and spin magnetic moment?
In an atom, the magnetic field results from the combined spin and orbital magnetic moments associated with electron motion. The spin magnetic moment arises from the electrons spinning around their own axes, while the orbital magnetic moment is due to the electrons moving around the nucleus.
What causes magnetic moments?
In magnetic materials, magnetic moments originate from the spin and orbital angular momentum of electrons. This effect varies depending on whether atoms in one area align with atoms in another.
