Understanding Magnetic Safety and Assemblies
Permanent magnets are a fundamental part of motion control. For motors, couplings, stators and more, magnetic assemblies deliver torque and motion in small packages – they’re at the heart of the motion control function.
There are a lot of upsides to permanent magnet assemblies, however, they can also be dangerous when they degrade or break, so it’s important to take every precaution possible to maintain the integrity of permanent magnets.
Permanent Magnet Assemblies in Motion Control
Permanent magnets used in motion control are typically fully sintered rare earth magnets. Motion control applications leverage Neodymium – Iron – Boron (NdFeB) or Samarium Cobalt (SmCo) permanent magnets for their high energy density. It’s also common to see bonded or injection molded magnets in motion control, however, they only have about 20% of the energy density of fully sintered versions.
Permanent magnets are dynamic – they never turn off. They generate a staggering amount of force – especially large magnetic assemblies – where extreme caution is called for. These properties require constant safety considerations, but they also make permanent magnets extremely practical. In couplings, for example, when a pump and motor are working in tandem, there’s more tolerance for parallel and angular misalignment between components because of the strength of the magnets, making the system more durable.
With proper safety precautions, permanent magnets have significant performance advantages over other types of magnets.
Permanent Magnet Safety Precautions
Many permanent magnets, particularly NdFeB magnets, require nickel coating for corrosion resistance. While there are dozens of safety considerations surrounding permanent magnets, this is one of the most important. When the process of nickel plating is done incorrectly it can lead to major safety concerns.
If break provisions are not provided, “dog boning” can happen where an excess of current builds up along the corners of a magnetic assembly – sometimes several times larger than the plating itself – which poses a threat to the magnet’s integrity.
Further, NdFeB magnets are highly susceptible to degradation from hydrogen – a process called hydrogen decrepitation. This is why they’re coated in the first place. But too often in the assembly process, a caustic washing process is used before corrosion resistance is applied and a microscopic layer of hydrogen becomes trapped under the nickel plating. This causes hydrogen decrepitation over time and poses a threat to any NdFeB magnet.
There are plenty of other safety considerations for permanent magnets, but correctly applying nickel plating is extremely important. Permanent magnets are used because of the massive amount of force they can generate – any miscalculation or mistake can quickly become a safety concern.
Once safety considerations are appropriately accounted for though, permanent magnets present many advantages over other types of magnets. Magnets are a fundamental part of motion control applications – proper deployment ensures reaping their full benefits.
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