Where are Neodymium Magnets Used
Neodymium is a rare earth metal used to create powerful magnets. There are many places where neodymium magnets are used. Neodymium magnets are the strongest type of rare earth magnet, and have many applications.
Neodymium magnets are used as alternatives to AlNiCo and ferrite magnets. They create a strong permanent bond, even in a small package.
Due to their strength and versatility, neodymium magnets have many applications. They are produced for industrial and commercial use. You can find them in everything from jewelry and toys to computers and electric vehicles.
Some of the innovative uses of neodymium magnets are:
- Industry/Manufacturing, and
The transportation industry uses construction magnets and industrial magnets. These magnets help to remove ferrous metal.
Magnetic sweepers may be found in loading areas. These sweepers collect iron scrap from airports, docks, and truck depots that might puncture tires. This helps prevent costly repairs and delays due to down time.
Magnets are frequently used in jewelry and clothing design. Necklace closures can be made magnetic to make fastening and removing jewelry easy. This can be useful for customers with arthritis who may find traditional clasps difficult to manage.
Magnetic backings hold earrings in place without a piercing. Magnets are also commonly used to hold pins or nametags in place. Because they don’t require piercing the fabric, they don’t damage the shirt.
Magnets are increasingly used in fashion as a simple and modern alternative to buttons or zippers. Like magnetic jewelry clasps, these can be invaluable for people with disabilities. Magnetic zippers can help people retain their independence in dressing and undressing.
Magnetic zippers or snaps are also useful when silence is required. They may be added to clothing intended for hunters who want to access a pocket without the sound of a zipper. Magnets can be part of the original design or added later, to replace buttons or snaps. Magnets used to replace snaps or buttons can be sewed into garments, using special sewing magnets.
Hard disk drives have sectors that contain magnetic cells that are charged when data is written to the drive. Typically, there are neodymium magnets in a hard drive, both in the drive and linear head motors.
Microphones, headphones and loudspeakers also contain magnets. Permanent magnets are used in conjunction with coils to carry electrical current. This current converts electricity into mechanical energy. That energy moves the speaker cone to change the pressure of the surrounding air to create sound.
In mobile phones, the vibrating alert may be created by permanent magnet motors.
Amazing Magnets creates sensor magnets used in many engineering and industrial applications. These may include:
- Automobile design,
- Medical devices,
- Space exploration, and
- Industrial measurement tools.
Magnetic sensors detect changes in a magnetic field. By sensing a change to the strength, flux, or direction of the magnetic field, they can detect important changes.
There are many different types of magnetic sensors. Anti-lock brake sensors use neodymium magnets wrapped inside copper coils.
Electric motors contain neodymium magnets. Neodymium magnets are also found in synchronous motors and different types of rotary motors.
In a synchronous motor, a magnet moves the coils of a spinning rotor at the same frequency as the alternative current (AC). This creates a magnetic field that drives the motor.
Rotary motors use a permanent magnet in the rotor. They work by alternating attraction and repulsion between the rotor magnet and the stator electromagnets.
Neodymium magnets power electric motors found all around you. These may be found in:
- Cordless tools,
- Medical equipment,
- Laboratory equipment, and
- Drive motors for electric vehicles.
Magnets are essential components of tools and machines used in the construction. They are used in:
- Chutes, and
- Magnetized pulleys.
Construction magnets are useful for cleaning up construction sites. Magnetic sweepers and tow magnets can help clear a site of ferrous metal debris.
Large construction equipment relies on small magnets that are instrumental to their function. Magnets are used to ensure that formwork installation is safe and accurate. Magnetic shuttering and formwork systems are used for precast concrete production.
Industrial magnets are an integral part of manufacturing and operations.
Some industries use neodymium magnets for manufacturing. These include:
- Glass, and
Other industries use neodymium magnets to help with operations. These include:
- Food manufacturing, and
- Pharmaceutical manufacturing.
Scrap metal and recycling companies use powerful neodymium magnets to help sort recyclables.
Magnets often used in the food processing are Seperator Bar Magnets.
Magnets are central to the technologies that medical equipment like MRI machines. Magnets can be used to extract foreign objects from patients, and possibly avoid medical intervention. Tiny magnets are even used to keep dentures securely in place.
Other medical devices that use neodymium magnets include:
- Magnetic switches
- Blood separators, and
- Motors for surgical/dental devices.
Magnetic therapy has been used as an alternative treatment for chronic pain syndromes. Proponents of magnetic therapy claim that it helps reduce pain and inflammation.
Neodymium Magnets are Used Everywhere
Neodymium magnets are a versatile and innovative solution for many problems and challenges that we face in the modern world.
As we find more uses for rare earth magnets, we will continue to enjoy their versatility and unique benefits.
What are Neodymium Magnets?
Neodymium magnets are strong permanent magnets made from an alloy of rare-earth elements. They are a type of rare-earth magnet, and they are the most widely used rare-earth magnet. They’re also the strongest kind of permanent magnet commercially available.
Rare Earth Magnets
Rare earth metals are relatively abundant in the Earth’s crust, but it’s hard to find them in significant concentrations. Though plentiful, they are dispersed very evenly across the Earth. Unlike coal or iron, which forms in seams and lends itself well to mining, rare earth elements are difficult to find in a significant amount in a single place.
Because they’re so inaccessible, and because mining these minerals can be so challenging, the “rare” term refers to their accessibility rather than their abundance. Rare earth magnets are the strongest type of permanent magnets available. They generate stronger magnetic fields than ferrite or ceramic magnets.
Commonly known as Neo magnets, neodymium magnets are produced from an alloy of neodymium (Nd), iron (Fe), and boron (B). A neodymium magnet alloy forms into microscopic crystals. These crystals can be aligned by a powerful magnetic field during manufacturing, which results in all of their magnetic axes pointing in the same direction. Once magnetized, the neodymium magnet is more or less permanent.
The strength of a neodymium magnet is determined by a number of factors, like the tendency of the crystal structure to magnetize along a specific axis. In neodymium magnets, the crystal lattice is very resistant to changing its magnetic direction. This gives the magnet a very high coercivity, which is a way to quantify its resistance to demagnetization.
Once magnetized, neodymium magnets are generally considered permanent magnets. Any magnet can lose its magnetic charge over time, and neodymium magnets can be subject to demagnetization in high temperatures. But neodymium magnets are generally more resistant to demagnetization during regular use than ceramic or ferrite magnets.
How Were Neodymium Magnets Discovered?
Neodymium magnets were invented, not discovered. In 1984, two different companies discovered the formula for neodymium magnets independently. General Motors (GM) and Sumitomo Special Metals both learned how to make neodymium magnets almost simultaneously.
Before neodymium magnets were invented, GM, Sumitomo, and other companies were using samarium cobalt magnets (SmCo5), another variety of rare earth magnets. As the cost of raw materials for samarium cobalt magnets increased, these companies began researching alternatives.
Because neodymium magnets were invented, the process for making them is patented. One of the richest sources of neodymium in the world is China, so Chinese manufacturers control the majority of the world’s neodymium magnet production. Some Chinese factories pay a licensing fee to use the patented formula and technique for neo magnet production, and others attempt to duplicate the technique without paying the licensing fee. This is the difference between “licensed” and “unlicensed” production of neodymium magnets.
Unlicensed neodymium magnets may be cheaper than licensed magnets, but purchasing unlicensed magnets is illegal and can result in lawsuits from the patent holders. Additionally, unlicensed factories sometimes use inferior raw materials or cut corners on the manufacturing process, so you can’t always be certain to receive a high-quality product.
Are There Different Types of Neodymium Magnets?
The performance of a neodymium magnet may differ depending on the magnet’s material, grade, and other factors.
A magnet’s grade specifies the quality or purity of the raw material used to construct the magnet. If all other factors are equal, a magnet with a higher grade will have greater strength. The magnet’s grade is listed as it’s “N” number. The most common grades for neodymium magnets are N35, N38, N40, N42, N48, N50, N52, and N55.
The Gauss rating of neodymium magnets determines how fast the magnet works. This may be referred to as magnetic induction or magnetic flux density, and it’s sometimes represented by the symbol G or Gs. The Gauss system of measurement, which is still commonly used in magnetism, has largely been supplanted by the International System of Units (SI), so you may see a Gauss rating expressed in SI rather than Gs. The SI unit for magnetic flux density is the Tesla (T), which equals 10,000 gauss.
In addition to grade and magnetic flux density, a magnet’s performance may be influenced by its shape and thickness. In most cases, with all else being equal, larger magnets tend to produce greater pull strength than smaller magnets.
Environmental temperature and proximity to other magnetic material can also affect the performance of the magnets. High temperature applications and competing magnetic fields can reduce the performance of neodymium magnets or even de-magnetize them, so it’s important to understand how the magnet will be used when selecting the right magnet for the job.
How are Neodymium Magnets Coated?
Because rare-earth magnets are very brittle and prone to corrosion, they are typically coated or plated to protect them from breaking or chipping. Without a coating or plating, the neodymium magnet can flake and chip, leaving sharp pieces behind.
The most common plating process is a two layer process where copper is used as the first (interior) coating and nickel is used as the second (exterior) coating. Three-layer coatings with nickel, then copper, then nickel, can be ideal for high abrasion environments. Other coatings may include zinc, gold, and other epoxies, plastics, metals, or polymers.
The plating of neodymium magnets is an important process. The neodymium substrate can oxidize quickly without a protective layer, leading to significant damage to the magnet.
When magnets are broken or chipped and the inner layer is exposed, it’s important to dispose of the magnet as quickly and safely as possible. Because neodymium magnets are designed with a microcrystalline structure, they produce small and often invisible shards that can become embedded in skin or eyes.
Where are Neodymium Magnets Used?
Neodymium magnets are used in a wide variety of applications and can be found in cellular phones, computer disk drives, speakers and earphones, cordless power tools, and other electronic products.
The increased versatility of neodymium magnets continues to unlock new applications in areas where magnets have not been used before. This enables companies like Amazing Magnets to design, develop, and produce innovative magnetic products that simplify everyday living.
Magnets Bring Family Together
Your home is your sanctuary – a refuge to reconnect with family and friends. At the end of the day, no other place has a stronger attractive power or charm. Here, loved ones come together. Whether gathering with others for a meal or activity, or relaxing alone in a shared space, your home is where it happens.
The allure of a permanent haven, free from the distractions of the world outside, has a deep-rooted resonance. Your home is deeply integral to having a sense of place, and magnets are integral to virtually every space within your home.
You don’t always see them, but magnets all around us. They’re in your phone, your car, your TV, and your electronics. You are even standing (or perhaps sitting) on a giant magnet right now, since the Earth’s core generates a magnetic field.
In your home, your favorite electronics use magnets, from television sets and computer monitors to microphones and laptops. Furniture, children’s toys and hanging art can also use magnets. Magnets are even found in everything from shoes to mattress pads to aid with pain relief.
Outside of the home, magnets can be found when you travel and when you play. Magnets are found in various places in your car. Magnets can launch and stop roller coasters and at the amusement park. Magnets can help keep doors closed and locked at home and on the go.
Magnets in the Kitchen
While magnets have great utility across a wide range of applications, their usefulness in the home is easily overlooked. This is especially true in the kitchen.
Your kitchen is the heart of your home. While the household kitchen was designed primarily for preparing and cooking meals, it has – particularly over the past few decades – evolved into the epicenter of the home.
Used by the entire family, your kitchen sets the tone for the entire house. People invest a great deal into kitchen upgrades because it is the most important room when it comes to the resale value of the home.
A modern kitchen may have magnetic strips to hold kitchen knives securely and magnetic catches on cupboard doors. Some kitchens even have neodymium disc magnets hidden in wooden doors to create invisible closures. Integrated hidden appliances can use magnets to affix a wooden door facade to a metal front.
A magnetic spice rack with neodymium magnets can be useful for clearing valuable counter space and is easy to make as a DIY project. Kitchens may also feature magnetic hooks for utensils to keep them close at hand and free up counter space.
Since electric motors use magnetic fields and electricity and to generate force, nearly any appliance that creates motion with electricity, incorporates magnets. Electric appliances used in the home are typically powered by compact direct current (DC) motors. These motors require small NdFeB magnets to operate. Electric devices, from blenders, lamps and telephones to larger appliances such as dishwashers, refrigerators and washing machines, all use electromagnets to help them function. The permanent magnets in the motors enable the rotors to run synchronously to the alternating (AC) current.
A common countertop appliance such as a blender or mixer may contain an electromagnet with a permanent magnet surrounding it. When activated, electricity flows to the electromagnet. It then reacts with the surrounding permanent magnet, generating motion to spin the blades, or activate another moving component.
The latches used to keep refrigerator doors closed are controlled by magnets. Refrigerators and freezers are sealed with magnetic mechanisms to ensure that they can be easily opened from the inside.
Microwave ovens have changed the way we cook. A magnetron is a vacuum tube containing electrons that circulate inside. A magnet is placed around the tube to provide the magnetic force that causes the electrons to move in a loop. The magnetrons inside of the ovens consist of magnets to generate electromagnetic waves that heat meals by generating intermolecular friction between the molecules of the food.
Magnetic Products can Simplify Everyday Living
Rare earth permanent magnets embody a mature technology, and scientists and engineers use magnets like these to design and develop innovative magnetic products that simplify everyday living. These products can be found throughout the home and are not simply limited to the kitchen.
Magnets can also be found in shower curtain weights, children’s toys, phones, washing machines doorbells, and CRT monitors and television sets.
To prevent corrosion inside your water heater, a magnet is positioned at the intake pipe to catch damaging metallic calcium particles before they can get inside.
The speakers in your audio systems and telephones create sound by converting electricals signal into audio waves. Each speaker contains a wire coil inside a semi-rigid membrane, which vibrates back and forth as it is attracted to and repelled from a permanent stationary magnet.
Data on your computer is stored by magnetism. The storage disks inside computers are coated with magnetic material. When the magnetic orientation of the iron is altered, the designated data is stored within the patterns and can be read by the computer.
Applications involving the use of magnets continue to evolve. Scientists are constantly researching new ideas in magnetics and materials that can help us all live better, simpler, cleaner lives. They’re finding ways to use magnets for sustainable energy, pollution-free refrigeration, and new applications in computing and electronics.
Magnets Help Make Life Better
From the discovery of the first magnetic lodestone over 4000 years ago, to the applications of magnets in everything from science and industry to recreation and everyday living, magnets have enhanced virtually all aspects of modern life.
For more than forty years, neodymium magnets have been used in a wide variety of applications that require powerful, compact, affordable permanent magnets. In magnetic toys, jewelry clasps, mounting fixtures, and modern sporting equipment, these rare earth magnets have improved modern life by enhancing convenience and efficiency, function and form.
Large or small, visible or hidden, fixed or mobile: Magnets help make life better.
Wind Power: Clean Energy with Magnets
Wind energy has developed into one of the most viable clean sources of renewable energy in the world. It reduces air pollution, including sulfur dioxide, nitrogen dioxide, nitric oxide and particulate matter often emitted from other energy production methods.
In the United States, wind energy is one of the fastest growing energy sources in the utility sector. According to a US Department of Energy report, wind energy could generate up to 20% of the nation’s electricity demand by 2030. U.S. wind producers are expected to double existing production capacity from 113 GW in 2020 to 224 GW by 2030.
How do wind turbines work?
Modern wind turbines are complex pieces of equipment, with many moving parts. In a standard wind turbine, the large fan blades are turned by high winds. Those blades are connected to a central generator that converts the motion into electricity.
Wind turbines and generators require very strong permanent magnets. Rare earth magnets, like neodymium magnets, are used in some of the largest wind turbines in the world. These magnets, made of neodymium, iron and boron, are the strongest type of commercially available permanent magnet.
Neodymium magnets provide efficient electricity generation. They’re used in wind-turbine designs to reduce costs, improve reliability, and lower the need for expensive maintenance.
How have wind turbines changed from earlier models?
In recent years, permanent magnet generator (PMG) systems in wind turbines have eliminated the need for gearboxes. This has led to more cost-efficient, reliable operation. This has also reduced maintenance requirements and enhanced grid compatibility.
Magnets allow mechanical gearboxes to be removable. This helps meet the operational and economic challenges of modern wind turbines.
Large neodymium magnets can produce a magnetic field that does not need an external power source. This eliminates the need for certain parts used in older systems that require additional maintenance.
Newer turbine designs allow the system to capture energy from slower wind speeds, helping to increase efficiency. Smaller batteries or capacitors can be used without reducing the amount of power generated by the turbine.
Where else do you find magnets in wind power?
Magnetic mounting solutions can be used to securely attach ladders and other equipment to the steel tower walls.
The inside of a wind turbine is usually crowded. It’s full of cables, ladders, and other equipment to allow workers access to the turbine housing. This equipment must be secured safely to the wall of the tower. The traditional solution has been to mount the equipment with bolts or welds.
Drilling holes through the tower wall can compromise the overall integrity and safety of the tower. Drilling and welding can hasten metal fatigue and corrosion. Magnetic mounting solutions reduce construction time and costs. They can also protect the tower’s integrity and minimize the risk of metal fatigue or corrosion.
Today, the demand for cleaner energy continues to grow. Wind still plays a relatively small role in overall energy production. Permanent magnets play a crucial role in the conversion of wind power to electricity. They’re an essential component in the design of wind turbine generators.
Whether it’s an offshore wind farm or a high-performance wind farm somewhere along the plains, when it comes to wind power, magnets are an essential component.
How Magnets are Used in the Recycling Industry
Scrap metal is one of the most recycled commodities, and magnets are an important part of metal recycling.
Recycling metal has been a common practice for centuries. The ancient Romans recycled captured bronze statues into armor and weapons. The Vikings smelted and repurposed used or broken weapons. Metal scrapyards become common in the 1920s. Airplane and automotive parts during the 1940s relied heavily on recycled metal.
Magnetic Separation of Metals
Recycling begins with separating different types of metals and alloys. Ferrous metals are metals that include iron, such as tin, steel, iron, cast iron and steel. These alloys are magnetic, so permanent magnets are used to identify these metals.
Since the 1960s, permanent magnets have been used to help separate metals in recycling plants. Magnetic separation is a simple and eco-friendly way to identify and sort metals.
Magnets attract metals containing iron, making them easy to separate. Other metals do not contain iron, so a magnet will not stick to them. Recyclable metals such as aluminum are easy to identify because they aren’t magnetic.
Magnets are also used in recycling to collect fine metallic particles on the recycling line. This helps ensure that other recycled products such as paper are free of metal contamination.
How do Permanent Magnets Work with Different Types of Magnetism?
The atomic structure of certain elements can cause the element to respond differently to a magnetic field.
Ferromagnetic metals – such as iron – are fully magnetic. They are strongly attracted magnets. We can observe this attraction visually and by feeling the pull of the magnet on the metal.
Paramagnetic metals are weakly attracted to magnets. Unlike ferromagnetic metals, they do not remain magnetic when removed from the magnetic field. Paramagnetic metals include platinum, tin, magnesium, and aluminum.
Diamagnetic metals are weakly repelled by both magnetic poles. They’re generally considered to be “non-magnetic”. Gold, silver, copper, carbon, and lead are examples of diamagnetic elements.
Each type of magnetism can indicate how long a metal will remain actively magnetic. Using this information can help recycling centers distinguish between different types of metal.
Permanent magnets are a great way to distinguish metals, as they can help distinguish metals without harming the sample. Chemical testing can sometimes require removing or damaging the sample in order to test it.
The tendency of a magnet to attract ferrous metals is still a core principle of metal sorting. Magnetic separator bars can sort metals into ferrous and nonferrous metals. Later sorting processes can go into greater detail.
Valuing Scrap Metal
The value of steel, iron, or other ferrous metals is less than that of nonferrous materials. Nonferrous metals do not contain iron. A magnet does not stick to nonferrous metals.
A permanent magnet is a small, non-destructive way for scrapyards to assess whether a sample is ferrous. This helps the estimator to more accurately assess the value of the metal.
Some common types of nonferrous metals are those made of aluminum. This includes aluminum cans, brass, copper, lead and zinc. Some metals contain both iron and a nonferrous metal. An alloy with ferrous metal will have a lower value than an alloy made entirely of nonferrous material.
The response of a magnet may also help determine whether a metal is suitable for a given application. Copper, for example, being non-ferrous, is commonly used in electrical wiring.
Magnets in Quality Control
When recycling centers begin melting down metals for recycling, it must ensure the metals are pure. Certain mixtures of metals can cause problems with recycling machines.
Magnets are used in a wide range of magnetic separators. They can even separate non-magnetic materials such as aluminum UBC’s (used beverage cans). This enables recycling companies to recover metals or remove metal from a reclaimed material.
The presence of different metals can help discover ferrous contaminants. Using a magnet can determine, for example, if there are steel screws in the aluminum. Should this be the case, the screws must be removed before the aluminum is smelted.
The separation of non-ferrous metals can be simplified by a machine called an Eddy Current Separator. This machine features a multi-pole, strong magnetic rotor that spins at high speed. It induces a current when aluminum enters the field. The current produces a magnetic field in the opposite direction of the rotating field. This results in a force that ejects the aluminum, pushing it away from other materials.
Magnetic Recycling in the Future
Economic and environmental interests will continue to drive an emphasis on reuse and recovery. The global metal recycling market size, which was $217 billion in 2020, is expected to exceed $368 billion by 2030.
Permanent magnets have long been used to identify and recover the ferrous metals. As new technologies continue to develop, rare earth magnets continue to play a role in recycling.
Coercivity of Neodymium Magnets
Permanent magnets radiate magnetic fields and do not require an outside source of magnetism. Their materials will take on the properties of a strong magnetic field when exposed to it. The magnet continues to emit a magnetic field after the initial field is withdrawn.
Resistance to demagnetization is one of the most useful properties for a magnetic material. A high-quality permanent magnet should emit a high magnetic field with a low mass. It should be stable against things that would demagnetize it.
Remanence and coercivity tell how much a material can resist demagnetization. A material that is still very magnetic after the magnetizing field withdraws has high remanence. Coercivity measures how much magnetic intensity is needed to demagnetize a magnet.
Neodymium (NdFeB) magnets are the most powerful permanent magnets available. The coercivity of these magnets will drop notably at higher temperatures. The low Curie point of the NdFeB phase limits their use at high temperatures. Developing high performance magnets requires understanding and managing coercivity.
Coercivity in a magnetic material is a measure of whether it is able to resist an outside magnetic field without losing magnetism. This describes the magnetic properties of a material in a useful way. Another way to understand coercivity is as the resistance of a material to demagnetization.
There are different types of coercivity. The measurement you need will depend on the threshold for demagnetization:
- Normal coercivity, Hcb, is the magnetic field required to reduce the magnetic flux to zero.
- Intrinsic coercivity, Hcj, is the magnetic field required to reduce the magnetization to zero.
Hard and Soft Magnetic Materials
Hard magnets have high remanence and high coercivity. Hard magnets resist becoming demagnetized. Their magnetic fields do not dissipate under normal conditions.
For hard magnets, the inherited magnetic field is continuous and will be permanent. It will not get weaker with regular use. A rise in temperature or deliberate demagnetizing of the material can weaken the magnet.
The distinction between normal and intrinsic coercivity is minimal in soft magnetic materials. This distinction may be significant in hard magnets. The strongest rare earth magnets lose very little of the magnetization at Hcb.
Measuring Magnetic Coercivity
Permanent magnets have a high coercivity. These hold on to their magnetic fields most of the time unless they are intentionally demagnetized.
To find the coercivity of a magnetic material, you will need to measure the strength of two magnetic fields. The strength of the magnetic material’s field is denoted as B when fully magnetized. The strength of the opposing field required to reduce B to zero is H.
These magnetic fields are usually measured in Oersted units (Oe), or in amperes/meter (A/m). 1 Oe is equal to 79.57747 A/m.
Coercivity is denoted by HC. It can be measured by empirical measurement or mathematical analysis.
The coercivity of a magnetic material is expressed by the magnetization curve. This may also be called a magnetic hysteresis loop. The hysteresis loop shows how the external magnetizing force and the induced magnetic flux density are related. This gives you data about a material’s response to a magnetic field.
Applications of magnetic coercivity
Magnets are used in many ways, under various constraints and conditions. Hard magnets with strong coercivity are used as permanent magnets.
When a magnet must hold on to its magnetism in the presence of a high magnetic field, it will need high coercivity. Magnets with strong coercive force can resist opposing magnetic fields from cyclic events. This makes them ideal for use in cars and industrial electric motors.
They will also handle harmonic frequencies and noise much better than magnets with lower coercivity. Hard magnets may also be found in hard drives, audio speakers, and electric generators.
Soft magnetic materials have weaker coercivity. This makes them better for things like electric motors and power supply transformers. Soft magnets are best when they need to rapidly reverse polarities. They’re used for things where they must constantly magnetize and demagnetize.
Soft magnets are used in motor laminations like cores of electric motors’ stators and rotors. Here, they will change their polarity in numerous cycles-per-second as they revolve around a magnetic field. The magnetic field is created by an electromagnet or permanent magnet inside the motor.
Coercivity is a key property of permanent magnets. Understanding coercivity helps us to understand the applications and limitations of rare earth magnets. Knowledge of coercivity will enhance technology that benefits the many industries relying on NdFeB magnets.
How are Neodymium Magnets Made?
Neodymium Magnets are strong permanent magnets made from alloys of rare-earth metals.
Neodymium magnets are primarily made with the alloy of neodymium, iron, and boron (NdFeB). They also have small amounts of elements like praseodymium (Pr), dysprosium (Dy), aluminum (Al), and niobium (Nb). These may be added to enhance properties such as strength, temperature tolerance, and resistance to demagnetization and corrosion.
Preparation of the Neodymium alloy begins by melting the metals to a vacuum induction furnace. The melted alloy is cooled by strip casting, a rapid cooling technique, resulting in thin flakes of the material.
These flakes are broken down and placed in a jet mill where they are pulverized into a fine powder.
Sintered neodymium magnets are made by vacuum heating the rare earth metal particles used as raw materials in a furnace. The elements– chiefly neodymium, iron, and boron – are selected to result in a designated grade of magnet. The chemical composition of the of the magnet is adjusted to determine magnetic polarization, Curie point, flux density, and coercivity.
Once melted, the NdFeB (neodymium, iron, boron) mixture is cast into a mold and cooled to form ingots. The ingots are ground into tiny grains and milled, typically in a jet mill. This fine powder is pressed into a shaped mold. Magnetic energy from a wire coil is applied while the powder is heated and melted.>
This forms the neodymium into form dense blocks. The magnetism from the coil is generated when electrical current passes through it.
After the crushed magnetic powder is put into the mold, an external magnetic field is applied for orientation. The directional orientation of the magnetism is fixed as the mixture is being pressed. The powder is fully compacted after the orientation.
The resulting magnet is said to be anisotropic, i.e., the direction of the magnetism aligns with the particle structure. By maximizing the magnetic orientation in the direction of the magnet’s poles, the strength is enhanced.
There are three distinct methods used to press sintered NdFeB magnets, each yielding a slightly different end product. The common methods are axial, transverse, and isostatic pressing. Each represents a particular relationship between the pressing axis and the magnetic alignment axis.
With axial pressing, the pressing and alignment axes are the same. Transverse pressing indicates that the pressing axis is perpendicular to the alignment axis. Finally, applying pressure equally from all directions is known as isostatic pressing. When pressing magnets isostatically, the magnetism is aligned before the magnets are pressed.
After the magnetic direction is locked, magnetized material is demagnetized. Because the material is too brittle for practical use, it must now be sintered. Sintering heats it in an oxygen free environment to near its melting point so that the magnetic particles fuse together.
After sintering, the magnet is quenched. The heated material is rapidly cooled, imbuing the material with greater strength and hardness. After the sintered magnet is quenched, a tempering treatment is performed to cool the magnetic powder.
Once it reaches the designated temperature it is reheated. The rapid cooling enhances the performance of the magnet by reducing the areas of poor magnetism.
The magnets can now be machined into their appropriate, useful shapes. Diamond plated cutting tools are used, due to the magnets’ hardness. The machining methods include grinding and slicing, laser processing, and electrical discharge machining (EDM).
Bonded NdFeB magnets are rare earth magnets made from NdFeB magnetic powder and a binder. The powder is prepared by grinding the NdFeB alloy into a powder and combining it with a polymer. Bonded magnets are not only extremely useful as finished magnets, they are also used as components in many other products. Compared to other types, these magnets often contain less neodymium and more iron.
Bonded magnets may be made by injection molding, extrusion, calendering, or compression bonding.
With injection molding, a melted thermoplastic compound is injected into a mold. There, it cools and solidifies into the right shape. For neodymium magnets, NdFeB is used as the magnetic powder in this mixture. Magnets can be shaped and formed by this process, which works well with assembles and over molding manufacturing techniques.
The extrusion process pushes the mixture through a heated barrel with a large screw. The mixture is pressed through a heated die, and that material is cut to the right length.
Calendering is a way to make continuous magnet sheets. This is often used for flexible magnets. A powdered compound of iron powder and elastomer is pushed through a set of hot rollers. These rollers stretch and smooth the strip, creating a uniform sheet.
In compression bonding, NdFeB is processed through a powder refinement process, blended with a plastic material and compression molded. Compression bonded neodymium magnets can be magnetized in any direction and with multiple poles. They are typically used in small motors, mobile phones, electronics, automobiles, etc. Other applications include brushless motors, speakers, buzzers and toys etc.
Because neodymium magnets are brittle, they are prone to chipping and breaking. The NdFeB substrate can also oxidize quickly without a protective layer. To prevent this, they are coated, cleaned, and plated to protect the magnet against corrosion.>
Before the material is re-magnetized, a protective coating is applied to extend the lifespan of the magnet. This is usually an electroplated coating of three layers consisting of nickel, copper, and nickel.
Any coating or plating must be applied to a sintered magnet before the it is saturated (charged). High heat can demagnetize the magnet, and the magnetic field can disrupt the electroplating process. The most common plating is a nickel-copper-nickel mixture, but other metals or PTFE polymers can also be applied.
Bonded Neodymium magnets are also typically coated prior to use, usually with an Electrophoresis Coating (“E-coating”) or Spray Coating process. Alternative coatings and methods can be used for magnets used in extreme temperature applications or corrosive environments. E-coating is widely used because it is suitable for different applications and has a uniform thickness. Spray coating is more suitable for smaller magnets and not recommended for corrosive environments.