Share this article

Arc Magnets for Motors

Overview of Arc Magnets

Arc magnets are one of the unique shapes of magnets designed for specialized applications. Due to their special application, they are not as common or popular as the block, ring, and horseshoe magnets. An arc magnet is a magnet that is rectangular in dimension, meaning that the length and breadth are not the same measurements, and the surface is smoothly curved such that it is not parallel to the edges. When several arc magnets of the same dimensions are placed together, they would eventually form a circle.

Arc magnets look like parts of a ring magnet that had been cut apart. You commonly find them in generators and electric motors, functioning as rotors or stators if the motor uses permanent magnets. Manufacturers can make arc magnets with either poles, north and south, to be in the inner or outer radius.

Electric motors are machines designed to convert electrical energy to mechanical energy, while alternators, a type of electric generator, are designed to convert mechanical energy to electrical power. Both electrical motors and alternators are mechanically identical, relying on magnetic fields to function correctly, though their functions are in reverse to one another. In the past, electric motors and generators used electromagnets and field windings, but as technology advanced, scientists found permanent magnets to function more effectively than electromagnets.

Fun fact: an alternator that uses a permanent magnet is called a magneto.

Characteristics of Arc Magnets

Arc magnets are among the most powerful types of magnets out there. They have a very specialized application as they are only used in electric motors and generators. They are designed to have high coercivity ratings and temperature resistance because of the environment where they function.

In terms of shape, arc magnets are curved and possess an inner and outer radius. They can be magnetized both ways depending on their intended use.

Uses of Arc Magnets

Arc magnets have a specialized application, which is their function in aiding the rotation of the rotor in electric motors and generators. Hence, you can find Arc magnets in:

  1. Electric Motors
  2. Electric Generators

Electric motors, as explained, are designed to convert electrical energy to mechanical energy. They make it possible for rotating or mobile assemblies to run on electricity. When electricity flows into the motor, it powers up, and the rotor starts running. The rotor is then directly connected to the mobile object, as seen in fans and blenders, or through a system of gears, as seen in electric vehicles.

Machines that use electric motors include:

  1. Blenders
  2. Ceiling fans
  3. Standing fans
  4. Washing machines
  5. Electric vehicles (EV)
  6. Electric toothbrushes
  7. Vacuum cleaners
  8. Microwave ovens
  9. Refrigerators, and more.

Unlike electric motors, electric generators are designed to convert mechanical energy to electric power. Electric generators are directly connected to the machines that supply the mechanical energy to be converted into electric power. Together, they form a single machine.

Mechanical energy sources for electric generators include steam turbines, water turbines, gas turbines, wind turbines, internal combustion engines, and even hand cranks.

What to Provide When Ordering Arc Magnets for Motors.

When ordering arc magnets for motors, there is some information you must supply to make sure you get exactly what you want for your assembly. An error in the information you provide may significantly affect the outcome of your magnets, making them useless.

To get the best quality magnet that fits your application, you must provide the following information:

Type of Magnet

Different materials are used to manufacture magnets. The material used for your magnet may affect its performance and durability in your machine. Below are the different types of magnets.

  • Neodymium Magnets

Neodymium magnets, also called NIB, NdFeB, or neo magnets, are the most efficient magnets on the market. They are manufactured from an alloy of neodymium, iron, and boron, a discovery made independently by General Motors and Sumimot Special Metals in 1984. Neo magnets can be bonded or sintered depending on the manufacturing process, but both methods produce potent magnets. Due to their high levels of heat resistance, strong magnetic fields, and excellent performance, they have replaced other magnets types in several applications across multiple industries. At ROBO Magnetic, we specialize in manufacturing and supplying neodymium magnets.

  • Alnico Magnets

Alnico magnets are another type of magnet commercially available on a global scale. They are made from an alloy of aluminium, nickel, and cobalt. However, they may sometimes comprise copper, iron, and titanium. Like Neodymium magnets, they are also permanent magnets because they generate magnetic fields without the influence of an external magnetic field. However, they have become redundant in most applications since the development of rare-earth magnets like neodymium magnets.

  • Ferrite Magnets.

Ferrite magnets are made from ferrite–a type of ceramic derived from a mixture of iron(III) oxide (Fe2O3, rust) and little proportions of one or more metallic elements, such as barium, manganese, nickel, strontium, and zinc. There are different types of ferrite magnets: hard, soft, and semi-hard. The significant difference is that they have varying levels of coercivity. Hard ferrite magnets have the highest level, while soft ferrites have the lowest. Unlike neodymium magnets, ferrites cannot conduct electricity. They also do not have as much resistance against demagnetization and cannot generate equally-powerful magnetic fields.

  • Samarium Cobalt (SmCo) Magnets

Samarium Cobalt magnets are another rare-earth magnet made from Samarium (a rare earth metal) and cobalt. Smco magnets have about the holding strength rating as neodymium magnets. However, they are much more expensive and generate much weaker magnetic fields. Samarium-cobalt magnets were developed in the 1960s by Strnat and Ray. Their process was based on the work done by Karl Strnat at Wright-Patterson Air Force Base and Alden Ray at the University of Dayton. Neo magnets have replaced SmCo magnets in many applications because of their affordability and powerful magnetic fields, which are required in several specialist machines such as the MRI scanner.

Arc Magnets for Motors


We require customers to provide a drawing of the motor arc magnets they want. The diagram must also include the dimensions for every measured area and surface, such as the length, breadth, height, thickness, curvature, and countersink. Consider the image below.

  • Dimensions

The dimensions will determine the size of the magnet. They must be included in the image sent to us to ensure an exact match. The customer must also double-check to ensure they’ve entered the correct figure because an error in the dimensional measurement will affect the magnet’s size.

  • Grade

There are different grades of neodymium magnets. Each grade has a unique magnetic field strength, holding power, temperature rating, and coercivity value. When placing an order, customers are required to provide the grade of neodymium magnet they want. Choosing the correct magnet grade will ensure that it functions correctly in your application and that its field does not affect other parts of the machine.

  • Temperature

Customers should also pay attention to the temperature rating when ordering neodymium magnets for motors. Motors and electric generators tend to generate much heat. So it is essential to determine your machine’s heat range and communicate it with us. Then we can determine the heat resistance your magnet should have.

  • Tolerance

The tolerance refers to the geometrical and dimensional difference between the provided measurement and the finished product. Since magnets have to go through a process of casting, cutting, and shaping, there may be differences in the dimensions supplied by the customer and the actual size of the finished product. Customers are required to provide the limit of these differences.

  • Chamfering

Arc magnets meant for use in motos don’t usually have chamfers. However, if your assembly requires that your magnet possess a chamfer, please provide the chamfer dimensions, position on the magnet, and a diagram depicting the chamfer. Be sure to supply the chamfer’s acceptable tolerance to ensure compliance.

  • Coating

Neodymium magnets are highly prone to corrosion as they contain iron. Exposure to the atmosphere and moisture will cause them to rust quickly, affecting their performance. Hence, they must be coated with an external rust-resistant layer to protect the actual magnet from moisture and other substances.

Typically, our neodymium magnets are coated in 3 layers: nickel + copper + nickel. However, customers can refer to our neodymium magnets coating page to see other options.

  • Magnetizing Direction

Magnetizing direction refers to the position of the north and south poles, which affect the direction in which a magnet can attach to other magnets. Arc magnets for motors can have their magnetizing direction in the inside or outside diameter. Nothing can change a neodymium magnet’s magnetization direction after its production is complete. So it is essential to specify your desired magnetizing direction beforehand. For full details, reference our magnetizing direction page.


At ROBO Magnetics, we ship our neodymium magnets using an iron sheet magnetic isolation packaging. Our style introduces two to three magnetic shield packaging. Customers who desire special packaging should provide their choice of materials and dimension requirements.


A spacer refers to the material we use to separate neodymium magnets inside the packing box to dampen their magnetic fields and the force of attraction between them during storage or shipment. The spacer will make it easier to detach them from one another. The rule of thumb is that stronger magnets get thicker spacers than weaker ones.

We use different materials for magnet spacers, including heavy cardboard or plastic. However, customers who want unique spacer materials should provide material requirements.

Where to Get Quality Arc Magnets for Motors

ROBO Magnetic is the ideal supplier if you are looking to procure large quantities of arc neodymium magnets for use in electric motors and generators. For almost 20 years, we have led the permanent magnet industry by producing high-quality neodymium magnets and supplying them to Asia, Europe, and America. Using our state-of-the-art technology and a process approved by international bodies, our engineers manufacture neodymium magnets that match international standards. All our products are ISO 9001:2015 certified, and our staff give the best customer experience. Contact us with your requirements to get started.


Article by

ROBO Magnetic Product Team

We are the manufacturer with 16 years of experience in custom neodymium magnets.

Need A Quote? Get in touch with us directly.

Share this article

Leave A Comment